The recent (upper Miocene to Quaternary) and present tectonic stress distributions in the Iberian...

TECTONICS, VOL. 19, NO. 4, PAGES 762-786 AUGUST 2000

The recent (upper Miocene to Quaternary) and present tectonicstress distributions in the Iberian Peninsula

M. Herraiz,1 G. De Vicente,2 R. Lindo-Naupari,1 J. Giner,3 J. L. Simon,4

J. M. Gonzalez-Casado,3 O. Vadillo,1 M. A. Rodriguez-Pascua,2 J. I. Cicuendez,1

A. Casas,4 L. Cabanas,1 P. Rincon,2 A. L. Cortes,4 M. Ramirez,5 and M. Lucini6

Abstract. A general synthesis of the recent and present stresssituation and evolution in the Iberian Peninsula was obtainedfrom microstructural and seismological analysis. The stressevolution was deduced from (1) fault population analysis (FPA)from 409 sites distributed throughout the Iberian Peninsula, (2)paleostress indicators given by 324 stations taken from thebibliography, and (3) seismic data corresponding to 161 focalmechanisms evenly spread in the studied region. The applicationof FPA together with the determination of stress tensors and focalmechanisms for the whole Iberian microplate has provided twomain results: (1) the Iberian Peninsula is undergoing a NW-SEoriented compression, except for the northeastern part (Pyrenees,Ebro Basin, and Iberian Chain), where it is N-S to NE-SW, andthe Gulf of Cadiz, where it seems to be E-W, and (2) the maintrends of the stress field have remained almost constant since theupper Miocene. The analysis performed by zones suggests thepresence of local heterogeneities in the stress field.

1. Introduction

Since the beginning in 1986 of the World Stress Map Project(WSM), increased efforts have been made in order to collect andinterpret data about the orientation and magnitude of the presentstress field in different tectonic environments all over the world[Zoback, 1992]. In the case of Europe the studies have allowed aprogressive understanding of the acting stresses on the frame ofthe continent [Muller et al, 1992] and on some particular zones:central Europe [Grunthal and Stromeyer, 1992], theMediterranean area [Jackson and McKenzie, 1988; Rebai et al,1992], Fennoscandia [Gregersen, 1992], France [Delouis et al,1993], Portugal [Ribeiro et al, 1996], western Europe [Muller etal, 1997], etc. In this context, the general trend of the maximumhorizontal stress SHmaK is NW-SE to NNW-SSE, but this

1 Departamento de Geofisica y Meteorologia, Facultad de Ciencias Fisicas,Universidad Complutense de Madrid, Spain.2 Departamento de Geodinamica, Facultad de Ciencias Geologicas, UniversidadComplutense de Madrid, Spain.3 Departamento de Quimica Agricola, Geologia y Geoquimica, UniversidadAutonoma de Madrid, Spain.4 Departamento de Geologia, Universidad de Zaragoza, Zaragoza, Spain.5 Consejo de Seguridad Nuclear, Madrid, Spain.6 Empresa Nacional de Residues Radiactivos, Sociedad Anonima, Madrid, Spain.

Copyright 2000 by the American Geophysical Union.

Paper number 2000TC900006.0278-7407/00/2000TC900006$ 12.00

orientation is locally deflected by major geological structures[Muller etal, 1992].

In the case of the Spanish peninsular territory the availableinformation of WSM in 1995 was very scarce. Some data werealready found by Mezcua et al. [1984], Vidal [1986], Udias andBuforn [1991], Philip et al [1991], Olivera et al. [1992], theseismotectonic map of the Iberian Peninsula, the Baleares andCanary Islands [Instituto Geogrdfico Nacional (IGN), 1992],Grellet et al [1993a,b], and Galindo-Zaldivar et al [1993, 1999].In this context, in November 1995 the Sigma Project waslaunched with the primary aim of assessing the recent (upperMiocene-Quaternary) and current stress states in the IberianPeninsula [Herraiz et al, 1998]. The study ended in April 1998and, according to previous works [De Vicente et al, 1996;Herraiz et al, 1996], adopted a methodology that used both faultpopulation and focal mechanisms analysis. The application to alarge sample of seismic and geological data has allowed us toestimate the stress field acting from the upper Miocene.

In this paper we describe the methodology and the mainresults of the Sigma Project concerning the recent and presentregional stress distributions for continental Spain. The regionalstress state is defined as the "dominant" state at the scale ofhundreds of kilometers. To extend the evaluation to the wholeIberian Peninsula, the results obtained by Ribeiro et al [ 1996] forPortugal have been also incorporated in the analysis.

2. DataSeveral different techniques can be used to obtain the tectonic

stress state in an area. Among them, those founded on thesimultaneous application of fault population analysis and faultplane solutions analysis are particularly useful when the datasamples are large. These methods are complementary becausethey allow a direct checking of the results from geological andgeophysical analysis.

In this study, the geological information collected to draw therecent stress map was based on 733 stations: 409 stations are siteswhere the tectonic mesostructures and microstructures weremeasured and analyzed in order to obtain the stress tensor, and324 stations reflect tectonic information from the bibliography.The main structures analyzed were faults and slip striations. Thefieldwork has provided a total number of 8770 fault/striae pairs,and 8165 from them have been used to calculate 474 stresstensors. The geological stations have a heterogeneous spatialdistribution because the Cenozoic rocks are also irregularlyspread throughout the Spanish territory of the Iberian Peninsula.The data cover nearly 75% of the area of interest. Their maincharacteristics are summarized in Tables 1 and 2. The dataquality has been evaluated introducing a parameter Q defined as:

762

HERRAIZ ET AL.: TECTONIC STRESSES IN THE IBERIAN PENINSULA 763

Table 1. Results of Fault Population Analysis With the Reches MethodLat,deg

43.5343.6843.6843.4543.1443.1043.0743.0543.0342.8542.8742.8642.8642.8442.8342.8342.7342.7342.7642.5642.5342.6442.5842.5242.5242.5242.5142.4442.4442.4242.4542.4642.4342.4242.4842.4842.2942.0142.0742.1342.0541.8541.8641.8541.9341.9441.9543.6043.3943.3943.3943.3940.2740.2640.2840.2840.24

Lon,deg

-8.12-7.46-7.46-7.88-8.30-8.26-8.21-8.21-8.15-7.37-7.37-7.16-7.16-7.18-7.22-7.22-6.58-6.58-6.62-7.49-7.49-6.56-6.56-6.63-6.63-6.63-6.54-7.04-7.02-6.93-6.97-6.94-6.98-6.82-6.79-6.79-7.59-7.89-7.68-7.75-6.64-7.39-7.43-7.44-7.50-7.50-7.45-5.93-6.33-5.58-5.58-5.58-3.53-3.53-3.38-3.38-3.35

N DA

16 PUM10 M15 M31 PUM38 M7 M14 M21 PUM26 PUM19 PUM13 M7 PUM15 PUM11 PUM14 PUM12 PUM15 PUM7 PUM

21 PUM15 M22 PUM7 PUM7 M18 PUM20 PUM18 PUM22 PUM14 M15 M17 M34 M20 PUM12 PUM11 M6 M

20 M15 M19 M22 M20 M28 M7 M13 M19 M30 M33 M17 M8 M11 PUM18 M7 M10 PUM16 Q5 Q

20 PUM20 PUM10 PUM

CTl CT2 63 R S/ftnax

65/131 23/311 06/041 0.43 13765/206 18/022 15/113 0.02 6379/220 03/129 09/038 0.22 12685/220 01/310 04/040 0.07 13285/139 02/319 04/049 0.12 14146/195 36/292 19/080 0.10 14783/240 03/058 05/148 0.27 5789/140 00/307 00/037 0.18 12882/194 04/104 05/023 0.13 10182/23605/14605/0500.11 15181/229 02/323 08/054 0.14 14769/068 20/243 01/333 0.37 6436/240 52/156 05/060 0.28 14683/195 04/007 04/092 0.75 848/304 41/126 00/032 0.40 12536/240 53/069 04/334 0.95 7033/156 10/065 54/330 0.19 16502/125 37/217 52/040 0.18 12674/34009/077 11/1690.25 8605/067 00/156 86/248 0.79 6702/319 05/049 83/138 0.89 13707/295 18/200 70/020 0.18 11682/263 02/176 07/085 0.96 17672/028 16/203 04/294 0.30 2378/048 00/150 11/240 0.86 15012/319 67/052 18/225 0.84 13627/159 50/250 26/054 0.62 15166/171 23/355 01/265 0.09 17377/192 10/023 07/291 0.09 1070/178 18/016 05/284 0.70 1476/085 05/276 11/184 0.05 9679/076 10/256 00/346 0.17 7778/150 08/320 07/051 0.32 14419/11870/29900/2080.59 11916/084 70/269 10/177 0.29 8504/337 84/67 02/247 0.63 15787/117 02/313 00/223 0.26 13401/081 84/345 05/171 0.87 8187/259 02/075 01/165 0.37 7685/227 03/049 01/319 0.72 4974/095 12/279 08/187 0.07 8763/19604/29625/0290.06 11659/231 28/072 08/337 0.68 6675/343 13/170 04/079 0.28 16878/238 11/054 00/144 0.21 5586/07903/16900/2590.11 17081/245 08/063 02/153 0.54 6411/159 15/066 69/253 0.12 16013/134 06/042 74/234 0.36 13305/235 64/335 25/143 0.36 5502/160 07/251 81/075 0.13 16172/210 16/033 04/302 0.32 3078/124 03/230 10/321 0.05 5376/198 11/024 06/293 0.28 2018/061 71/235 04/329 0.66 6000/140 82/232 07/049 0.39 14003/244 83/130 05/334 0.60 65

T

EEEEE

SSEEEEEESSE

SSSSccECccEEE

SSSSEEEEEESSSSSSESSEEEEEEEEECCSScEEE

SSSSSS

Q222322232221212121234212121222242112222220212221221231321

Lat,deg

39.9843.3943.3943.3943.3943.9543.9543.3843.3843.3843.3643.3743.3743.3943.3943.2043.2443.1543.0643.0642.8842.9942.9942.8942.8942.8842.8042.7942.7942.8042.8042.5340.7540.7540.5840.5840.6040.6040.5540.5540.5140.6440.4240.4540.4540.3840.4140.4240.4240.4740.4740.4740.4738.7238.7238.7438.74

Lon,deg

-6.53-4.57-4.38-4.33-4.33-4.41-4.41-4.51-4.44-4.44-4.42-4.48-4.484.394.39-5.33-5.38-5.27-5.14-5.14-5.45-5.00-5.00-4.75-4.75-4.70-5.65-5.74-5.74-5.67-5.67-5.98-3.03-3.03-3.08-3.08-2.72-2.72-2.75-2.75-2.77-2.50-3.57-3.12-3.12-3.11-3.05-2.91-2.91-2.95-2.95-2.78-2.78-0.45-0.47-0.47-0.47

N DA

5 M15 M10 M6 UM9 UM

28 M40 M20 M13 M22 M10 M7 M7 M

20 M16 M5 M18 M29 M15 M10 M20 M14 M15 M22 M13 M15 M7 M8 M7 M6 M6 M9 Q

30 PUM28 PUM21 PUM22 PUM13 Q8 Q9 PUM7 PUM11 PUM22 PUM30 UM50 PUM29 PUM39 UM16 PUM10 PUM15 PUM20 PUM8 PUM

40 Q31 Q10 Q14 PUM9 PUM14 PUM

CTl CT2

81/376 02/10600/316 16/04631/362 47/18268/060 17/23105/330 76/06279/177 00/08509/178 57/08586/359 00/26875/267 14/08703/202 44/10909/115 35/02302/251 41/34026/342 17/07102/128 17/21968/221 07/12458/301 31/12281/296 01/02932/046 57/22224/128 59/30804/252 85/05085/179 02/27873/211 02/30106/196 74/28986/342 00/07163/145 25/31983/316 06/13684/168 03/07863/323 02/05326/017 13/28775/280 12/08407/163 72/25889/240 00/06085/318 00/22309/332 76/15982/051 06/24084/330 04/14618/077 70/24943/312 45/12800/312 76/04277/232 11/05278/198 11/01715/327 72/14586/131 02/04186/236 03/05643/144 45/32481/172 04/27120/209 05/30184/055 02/14686/029 03/20982/057 02/32744/219 44/03986/312 02/22279/154 10/33486/173 03/35787/054 00/14471/049 11/31804/139 75/048

a3 R

07/196 0.2473/226 0.2524/088 0.1611/325 0.4011/2390.1610/352 0.1830/274 0.1703/178 0.2502/357 0.3944/285 0.3752/208 0.6848/159 0.0356/248 0.2372/030 0.0620/031 0.1001/031 0.1908/119 0.1402/315 0.6815/219 0.8401/162 0.4003/008 0.1516/032 0.6913/105 0.2703/161 0.6006/050 0.5602/046 0.5704/348 0.0426/145 0.1660/195 0.7908/175 0.2115/071 0.4500/150 0.0704/133 0.0110/064 0.4504/149 0.8602/236 0.6105/347 0.7205/220 0.4813/222 0.2805/321 0.0701/107 0.4806/236 0.5802/311 0.0800/146 0.2308/055 0.2006/002 0.1069/041 0.3404/237 0.8602/119 0.4607/237 0.4303/125 0.5702/132 0.2302/064 0.2000/267 0.1401/234 0.7914/228 0.2013/230 0.61

S//max T Q

108 E 1136 C 2139 SS 160 E 2150 SS 185 E 2179 SS 288 E 287 E 223 SS 3121 C 272 SS 1159 C 1129 C 3128 E 3120 E 032 E 346 SS 2129 SS 173 SS 2100 E 2123 E 217 SS 271 E 3142 E 2136 E 271 E 249 E 120 C 192 E 1163 SS 160 E 442 E 2153 SS 259 E 2147 E 276 SS 3137 SS 2133 SS 241 E 218 E 2

147 SS 241 E 357 E 2151 SS 297 E 328 C 2147 E 229 E 2147 E 237 SS 142 E 2156 E 3177 E 2144 E 2127 E 1140 SS 1

764 HERRAIZ ET AL.: TECTONIC STRESSES IN THE IBERIAN PENINSULA

Table 1.Lat,deg

40.2340.2340.2340.1840.1840.1940.2440.2440.2840.2840.2940.2940.1340.0540.0740.1340.1740.1740.1240.1240.1839.8739.3038.9338.9738.9738.9838.8938.8938.9138.9138.8438.8438.8438.8438.8438.8138.8138.8338.8338.7738.7739.2539.2539.2839.0038.7238.4938.4838.4838.4638.4638.4638.4538.4538.4238.4738.47

(continued)Lon,deg

-3.46-3.41-3.46-3.04-3.04-3.03-2.84-2.84-2.84-2.84-2.84-2.84-3.84-3.77-3.73-2.91-3.09-3.09-2.56-2.56-2.69-3.03-1.34-4.04-3.99-3.99-4.05-3.65-3.65-3.70-3.70-3.67-3.67-3.673.613.61-4.11-4.11-3.75-3.75-3.78-3.78-0.55-0.55-0.57-0.29-0.46-2.32-2.18-2.18-2.14-2.05-2.05-2.07-2.07-2.03-2.17-2.17

N DA

16 PUM16 PUM20 PUM10 Q14 Q13 Q12 UM7 UM30 PUM8 PUM

20 PUM8 PUM

27 UM20 UM21 UM10 Q9 Q

20 Q20 PUM11 PUM6 Q16 PUM19 PUM12 Q20 PUM11 PUM39 Q45 PUM32 PUM30 PUM23 PUM50 PUM20 PUM25 PUM30 PUM22 PUM34 PUM30 PUM39 PUM39 PUM60 PUM30 PUM8 PUM8 PUM

32 Q15 Q9 PUM15 M6 PUM15 PUM36 PUM16 M15 M18 M8 M

22 M23 PUM20 PUM

CTi CT2 CJ3 R S/Anax

37/235 52/051 02/144 0.92 5486/220 03/045 00/315 0.09 4587/047 01/137 02/227 0.12 13886/132 01/243 03/334 0.07 6315/196 02/105 74/016 0.87 2086/032 03/237 01/147 0.11 5779/137 08/047 05/316 0.30 4517/326 19/062 63/152 0.77 13112/335 75/129 06/243 0.95 15481/100 05/210 06/301 0.43 3278/050 06/141 09/233 0.70 14447/227 38/020 16/118 0.42 3687/132 01/041 02/311 0.04 4083/055 05/230 03/320 0.11 5380/168 09/345 02/075 0.02 17084/344 04/074 04/165 0.07 7932/228 56/040 08/136 0.56 4986/144 03/324 01/054 0.35 14507/239 43/340 45/149 0.15 5878/260 10/054 05/145 0.24 5880/119 08/291 04/022 0.17 11585/132 00/225 03/315 0.14 4601/321 67/229 22/052 0.27 14280/013 09/193 00/103 0.79 1460/060 28/243 03/152 0.65 6303/333 86/150 00/243 0.80 15324/147 63/339 08/241 0.46 15080/222 09/048 00/318 0.60 4879/146 10/324 01/055 0.76 14522/046 67/220 03/314 0.76 4817/332 72/153 02/063 0.95 15483/220 06/032 02/123 0.31 3206/042 36/137 52/309 0.03 4335/333 53/156 05/067 0.88 15379/128 10/307 01/037 0.47 12888/049 01/231 00/141 0.35 5267/039 20/211 06/303 0.41 3781/178 07/269 01/005 0.62 9084/247 04/043 02/133 0.65 4405/320 84/143 01/230 0.72 14079/232 05/052 08/142 0.72 5387/318 02/136 00/226 0.82 13774/143 13/327 07/235 0.33 14237/053 52/222 05/319 0.39 5175/168 14/341 01/072 0.60 16284/313 00/044 05/134 0.21 4570/089 18/265 05/356 0.43 8981/153 05/333 06/242 0.59 15224/085 12/349 61/179 0.09 8607/325 33/233 54/060 0.59 14909/29080/11201/0200.39 11116/202 69/292 11/111 0.34 2411/30578/14403/0350.04 12511/143 70/050 14/236 0.45 14319/222 70/049 02/313 0.47 4518/200 18/293 63/025 0.18 1201/207 86/297 02/117 0.52 2786/069 02/247 01/337 0.15 67

T

SSEEECEECSSEESSEEEE

SSECEEE

SSE

SSCSSEESSSSECSSEEEEE

SSEE

SSSSEEEECCSSSSSSSSSSCSSE

Q2I22222 •I222I3222212212221222323212132342231123111222222122

Lat,deg

38.0938.7438.7438.7338.7238.7738.7538.7538.7038.7438.8338.6438.6438.6638.6238.6238.5538.5838.5938.5938.6338.6338.5238.5938.5938.6038.6038.6038.6038.6038.5738.5738.5538.5538.5538.5638.7338.5038.5338.4738.4738.4538.4538.4838.4838.4838.4838.4937.5437.5437.2137.2637.2737.0637.0337.0337.0337.14

Lon,deg

-0.49-0.45-0.46-0.45-0.48-0.47-0.45-0.45-0.34-0.270.00-2.44-2.44-2.41-2.49-2.49-2.38-2.40-2.44-2.44-2.30-2.30-2.51-2.17-2.17-2.14-2.14-2.14-2.12-2.12-2.07-2.07-2.08-2.08-2.11-2.01-2.01-1.66-0.08-2.54-2.54-2.69-2.69-2.45-2.45-2.42-2.42-2.32-3.11-3.11-4.29-4.31-4.38-5.81-4.53-4.57-4.60-4.72

N DA

14 PUM20 M18 PUM12 PUM7 PUM30 PUM20 PUM8 PUM

21 PUM10 Q20 Q16 Q15 Q28 Q9 PUM

20 PUM25 M28 M12 M12 M14 M8 M

23 M14 M12 M13 M20 M9 M16 M8 M10 M14 M14 M12 M26 M17 PUM19 Q10 Q13 PUM12 M17 M20 M21 M17 M15 M16 M10 M18 M20 Q16 Q11 PUM36 PUM13 PUM24 Q16 M17 PUM21 PUM11 PUM

<TI d286/137 03/31771/309 13/12982/336 00/24583/069 06/25188/198 00/01875/146 14/32676/045 08/31642/294 34/16581/129 03/30829/251 53/15176/193 02/10402/325 24/23475/125 13/03523/156 55/06500/276 86/00709/343 45/07380/120 01/21001/124 19/21526/067 08/15823/302 66/12214/046 63/13810/111 77/20256/038 06/12704/122 84/30384/053 04/23382/224 06/13406/096 83/27682/215 01/12507/263 52/17410/151 39/06018/320 38/05086/205 03/02564/326 23/14576/125 11/03543/024 45/20278/265 09/08280/324 09/14305/221 81/26280/217 06/30780/326 08/14540/238 48/04421/142 67/32274/310 11/22086/291 03/09383/107 001/0072/208 17/%3871/160 16/31365/317 24/13406/232 03/14203/152 83/06230/162 59/34172/113 15/29365/174 23/01104/302 76/03275/046 03/30608/187 49/27701/183 22/09380/214 09/033

d3 R

00/227 0.0211/219 0.2607/159 0.1401/161 0.1400/108 0.6300/236 0.1610/226 0.0928/053 0.8107/038 0.0619/342 0.5213/014 0.0565/055 0.4306/305 0.1924/247 0.1003/185 0.0942/253 0.2909/300 0.3470/034 0.2161/248 0.6103/032 0.5621/316 0.4306/020 0.1833/232 0.1202/212 0.4402/143 0.4602/044 0.2400/186 0.0807/034 0.1136/353 0.3149/241 0.1545/226 0.1501/295 0.4408/055 0.5607/305 0.3408/293 0.6506/352 0.2504/234 0.0906/040 0.4306/037 0.2104/236 0.6706/142 0.5004/052 0.5510/130 0.3601/183 0.4906/270 0.4402/307 0.3407/045 0.6201/224 0.3282/023 0.1105/243 0.4201/071 0.2802/023 0.2406/278 0.6612/211 0.3313/215 0.0438/097 0.3267/273 0.1902/124 0.27

<$//max T Q

137 E 2141 E 269 E 270 E 218 E 2146 E 4121 E 2140 SS 1139 E 378 SS 2100 E 2146 C 231 E 2158 SS 296 SS 2153 SS 231 E 2124 C 352 C 2122 SS 245 SS 2112 SS 0120 E 1123 SS 253 E 2134 E 296 SS 3123 E 183 SS 2160 C 3140 C 125 E 1143 E 231 E 232 SS 382 E 2143 E 241 SS 1131 E 1145 SS 245 SS 2144 SS 237 E 193 E 21 E 2

36 E 2137 E 1135 E 253 C 2153 SS 2162 SS 2119 E 28 E 1

122 SS 2126 E 26 SS 24 C 235 E 2


Table 1. (continued)Lat,deg

38.4638.4638.4738.4238.4638.4238.4138.4238.4838.4838.3838.3838.3438.3438.3738.3738.3538.3538.2638.2638.2838.2838.1838.1838.2238.2438.2438.1638.1638.0137.9337.9637.9637.8637.8437.9637.9737.7937.5737.5737.5837.1337.0937.0937.0737.0737.1636.9436.9136.9936.8536.9536.9437.0037.0036.8736.8736.87

Lon,deg

-1.94-1.94-1.99-2.00-1.94-2.00-2.00-2.03-1.79-1.79-1.76-1.80-1.65-1.65-1.67-1.67-1.70-1.70-2.78-2.78-2.76-2.76-2.80-2.80-1.59-1.72-1.72-2.99-2.99-3.04-2.98-2.95-2.95-3.04-1.42-1.38-1.30-3.05-2.95-2.95-3.11-1.83-1.85-1.85-1.85-1.85-1.83-3.02-3.02-2.46-2.29-2.20-1.91-1.90-1.90-2.16-2.15-2.15

N DA

29 PUM7 PUM17 PUM15 PUM7 PUM13 PUM25 PUM17 PUM21 PUM50 PUM33 PUM46 PUM21 PUM10 PUM46 PUM60 PUM4 Q12 Q11 M15 M20 M21 M20 M20 M14 Q14 PUM9 PUM

20 M11 M15 M31 M15 M19 M28 M11 PUM11 PUM11 M42 M15 M14 M25 M6 PUM

20 PUM7 PUM15 M18 M40 PUM27 Q16 Q17 PUM7 PUM5 Q

40 PUM26 Q20 Q10 PUM36 Q30 Q

<J, CT2

83/066 05/24514/039 13/30681/230 08/04801/059 76/15003/162 15/07150/293 40/11884/320 05/14273/120 04/30010/231 26/14071/284 13/19405/053 00/14366/242 23/06503/342 03/07283/269 04/08903/149 24/05771/140 14/04914/156 33/05976/009 6/27017/298 70/11003/034 86/12401/202 74/29554/279 34/10504/260 75/35519/179 69/35786/349 03/17180/061 09/33187/225 00/13108/242 59/13822/134 64/32053/138 36/30844/202 44/02334/144 55/32263/048 24/23087/311 01/13150/027 37/20475/116 14/29780/090 5/17979/195 08/01230/130 59/31629/271 60/08855/299 33/11273/100 16/20102/302 81/03552/050 36/22932/131 56/31066/095 22/28331/150 58/33254/345 33/17079/173 03/26372/308 17/12486/339 03/15878/119 10/31080/319 02/22410/159 69/06521/209 66/02376/278 08/18403/319 81/05084/050 04/230

d3 R

03/336 0.3169/129 0.0902/138 0.0412/328 0.0373/269 0.4805/028 0.3900/052 0.4009/030 0.0561/328 0.0112/101 0.1084/236 0.6102/334 0.6084/252 0.4704/180 0.3465/242 0.2412/316 0.2052/246 0.1711/179 0.0608/206 0.1801/304 0.2415/112 0.2605/011 0.4113/162 0.3805/087 0.6500/081 0.0501/241 0.7902/041 0.0929/337 0.1712/229 0.2804/011 0.2708/114 0.0900/053 0.5409/139 0.4001/221 0.8410/295 0.3700/206 0.2008/270 0.2705/102 0.7904/223 0.2104/178 0.9509/208 0.2701/292 0.5608/212 0.2007/320 0.9408/041 0.6406/190 0.1603/243 0.8309/078 0.1109/353 0.1001/214 0.3001/249 0.1205/219 0.6608/134 0.0517/250 0.2810/115 0.8309/093 0.0907/228 0.5903/320 0.31

s//max6540545916312014212051171546416289150361588011835229980174171151131631361303114445132311173131

8912423122511339415315991126159129401612817013951

T

ECE

SSCSSEECECECECECE

SSSSSSE

SSSSEEESSSSESSSSEEEEEE

SSSSEE

SSESSESSEEEEEESSSSESSE

Q2033122222322333020223222221222224221312211222232211222222

Lat,deg

37.1536.8936.8736.9936.8636.8636.8636.7236.7536.4636.3436.4836.2536.2536.2036.2537.7037.7037.7137.7137.7137.7137.7137.8337.7337.3837.1937.3037.0837.0837.0737.0637.0637.0537.0537.1037.0537.0537.0337.1437.1437.1340.8440.9241.0340.5140.6140.3640.2940.2440.2540.1940.3040.3040.0641.8541.8441.84

Lon,deg

-4.52-5.59-5.81-5.58-6.04-5.19-5.19-6.03-5.81-5.93-5.82-5.77-5.95-5.93-5.98-5.97-1.65-1.64-1.64-1.64-1.63-1.62-1.61-1.79-1.81-1.62-1.82-1.80-2.07-2.07-2.05-2.02-2.02-2.04-2.04-2.12-1.88-1.88-1.93-1.85-1.85-1.831.90-1.27-1.280.240.20-1.08-0.730.060.010.040.190.19-1.31-1.23-1.24-1.25

N DA (J, CJ2 CJ3 R SWmax

6 PUM 05/343 83/125 04/253 0.43 1638 Q 84/148 03/058 03/328 0.07 55

34 PUM 50/149 20/333 32/239 0.12 15215 Q 77/250 05/340 10/071 0.09 16027 Q 81/142 02/052 08/322 0.10 4810 PUM 59/060 02/149 30/240 0.08 1498 PUM 89/180 00/091 000/01 0.17 90

22 PUM 76/104 02/014 13/284 0.12 107 PUM 57/095 31/274 06/004 0.34 98

21 Q 60/20808/11522/0250.30 10416 M 23/136 53/226 25/044 0.14 13514 M 80/178 08/019 04/289 0.17 158 Q 14/146 01/236 75/327 0.54 1467 PUM 75/262 13/082 02/172 0.22 807 Q 12/126 72/035 12/216 0.17 12715 Q 13/20104/11075/0200.37 2223 Q 08/355 04/086 80/265 0.14 17525 Q 09/353 44/083 44/264 0.24 17220 Q 11/337 51/067 35/247 0.30 14624 Q 66/233 22/053 04/323 0.59 6424 Q 01/172 02/262 87/082 0.16 17221 Q 10/355 37/085 50/265 0.32 1738 Q 05/015 06/285 81/195 0.69 16

38 M 82/16306/34302/0730.11 16510 PUM 86/371 02/191 12/1000.21 117 PUM 58/041 27/311 14/2220.87 1238 Q 84/243 05/063 01/333 0.19 6217 PUM 70/163 03/253 19/344 0.03 7318 PUM 80/277 03/097 09/187 0.11 9215 PUM 08/312 74/133 12/042 0.93 13413 PUM 75/234 14/054 00/324 0.12 536 PUM 50/150 39/330 00/240 0.77 150

20 PUM 71/137 12/047 13/317 0.03 477 UM 05/127 50/040 38/217 0.13 12820 UM 25/082 55/352 21/173 0.77 886 Q 39/151 43/261 20/061 0.28 14517 UM 00/144 82/234 07/054 0.88 14523 UM 77/052 10/232 05/141 0.27 4912 Pli 84/078 05/258 01/348 0.36 787 PUM 15/328 51/238 34/058 0.12 1497 PUM 79/163 08/343 06/073 0.18 1636 PUM 69/139 24/319 00/229 0.40 13910 PUM 89/260 00/350 00/080 0.01 1715 Q 74/248 12/068 08/338 0.06 505 Q 68/253 13/163 16/073 0.08 15818 M 78/088 02/268-11/178 0.11 8135 M 81/042 07/222 03/312 0.47 4311 PUM 83/070 04/160 04/251 0.07 16623 Q 85/20502/29503/0250.08 11733 M 82/129 06/219 04/309 0.04 4025 M 84/138 01/228 05/318 0.09 5035 M 77/287 05/197 10/106 0.24 1313 M 06/269 34/179 58/359 0.35 9118 M 88/325 01/145 00/055 0.08 1457 PUM 86/186 00/276 03/006 0.04 9811 PUM 81/08908/26901/1790.02 8627 PUM 80/339 09/158 00/248 0.04 15911 PUM 82/071 01/16007/2500.03 160

T Q

SS 0E 2E 4E 3E 2E 2E 2E 2E 0E 2SS 2E 2C 2E 1

SS 1C 2C 3SS 2SS 2E 2C 2C 2C 1E 2E 2E 1E 1E 1E 2

SS 2E 2E 1E 2

SS 1SS 2SS 1SS 1E 2E 1

SS 1SS 1E 1E 2E 1E 1E 2E 2E 2E 2E 3E 3E 1C 1E 3E 2E 2E 2E 3


Table 1. (continued)Lat,deg Lon,deg N DA cr2 R S//max T Q Lat,deg Lon,deg N DA R T Q

36.88 -2.04 10 PUM 80/09708/27603/0070.11 10136.88 -2.04 15 PUM 79/033 10/213 02/303 0.30 3437.00 -1.90 13 Q 77/175 12/001 01/270 0.57 136.79 -2.96 23 Q 84/216 03/126 02/036 0.06 12436.82 -2.25 15 Q 83/224 06/044 00/314 0.20 4436.77 -2.09 20 PUM 76/121 09/031 09/220 0.05 3038.08 -3.99 10 M 67/336 20/151 08/244 0.40 15836.82 -2.25 13 Q 32/338 38/132 35/222 0.10 15638.08 -3.99 20 M 73/198 15/023 04/292 0.78 2238.11 -3.94 20 M 79/20510/02402/1150.43 2638.11 -3.94 14 M 73/31916/14001/0490.7014038.08 -4.17 8 Q 79/030 07/208 07/299 0.02 6138.17 -3.78 15 M 81/065 02/160 07/250 0.56 16138.17 -3.78 16 M 44/23739/05618/1470.11 7438.11 -3.77 7 PUM 79/06803/15909/2490.55 16038.11 -3.77 6 PUM 36/237 07/141 52/051 0.20 6038.09 -3.84 42 M 76/012 06/279 12/188 0.25 9437.38 -6.73 7 Q 86/231 03/051 00/141 0.18 5237.47 -5.64 17 PUM 32/222 57/042 04/133 0.28 5137.30 -7.32 14 Q 78/04400/13711/2270.1613837.25 -7.22 34 PUM 83/306 05/126 02/036 0.03 12137.23 -7.23 24 PUM 82/300 02/032 07/123 0.05 3037.23 -7.20 24 PUM 64/153 10/243 22/338 0.05 6037.24 -7.22 17 PUM 89/131 00/311 00/041 0.21 13237.24 -7.22 33 PUM 81/321 08/143 00/053 0.06 14337.24 -7.21 36 PUM 87/309 02/128 00/218 0.03 12937.24 -7.23 18 PUM 89/309 00/147 00/237 0.03 14737.24 -7.23 6 PUM 86/348 02/168 02/078 0.06 16737.28 -7.21 9 PUM 83/29004/20004/1100.08 1637.23 -7.20 15 Q 47/30242/11903/2120.0812741.54 -1.52 31 PUM 76/209 07/030 10/122 0.58 3341.61 -1.60 38 PUM 78/20504/29511/0260.03 11541.15 -1.39 31 PUM 01/215 88/036 00/125 0.24 3541.16 -0.85 11 PUM 76/151 12/33305/2410.06 15141.16 -0.85 25 PUM 85/142 03/232 03/322 0.08 5541.58 -3.22 40 PUM 03/142 85/322 02/232 0.87 14242.63 -3.46 20 PUM 87/29900/20901/1190.13 2942.63 -3.46 17 PUM 00/061 86/152 03/331 0.76 6241.63 -3.39 20 PUM 01/15482/24403/0640.30 15541.51 -3.30 15 PUM 59/154 29/338 06/244 0.69 15441.51 -3.30 17 PUM 64/194 25/012 00/102 0.68 1341.54 -2.95 18 Q 48/050 36/229 17/320 0.30 7041.60 -2.44 6 PUM 13/231 76/054 04/322 0.55 5341.45 -2.70 12 Q 88/285 01/106 00/016 0.05 10641.46 -2.80 10 M 00/319 72/049 17/229 0.04 13941.50 -2.36 6 PUM 86/237 02/055 02/146 0.45 5641.35 -2.47 10 Q 81/338 02/248 07/157 0.05 5941.29 -2.23 24 PUM 85/359 04/186 01/096 0.09 641.24 -1.93 5 Q 79/19507/28407/0150.1711041.25 -3.71 18 M 83/228 01/135 05/045 0.17 13541.06 -4.41 21 M 06/149 07/240 80/059 0.13 14941.12 -4.01 17 M 79/335 08/152 04/243 0.03 16041.14 -4.00 16 M 11/14324/04863/2360.11 14441.14 -3.88 7 M 22/139 30/035 50/231 0.07 14140.96 -3.21 20 M 04/136 62/037 26/229 0.07 13740.79 -3.67 12 M 33/156 28/046 43/246 0.08 15940.83 -3.57 19 Q 01/314 82/224 07/044 0.55 13440.58 -4.73 6 PUM 07/356 59/085 29/265 0.30 175

EEEEEEE 2SS 1EEEEE 2SS 2E 1C 2E 2E 1SS 2EEEEEEEEEE

SSEESSEESSESSSSEEESS 1E 2SS 2E 2E 2E 2E 1E 2C 2E 3C 3C 1SS 2C 2SS 2SS 1

41.86 -1.20 18 PUM 82/136 06/316 03/046 0.06 14341.86 -1.23 9 PUM 75/262 04/172 13/081 0.10 16539.94 -1.38 12 PUM 71/118 18/297 02/028 0.24 12039.94 -1.38 10 PUM 73/261 13/081 09/351 0.02 8039.73 -1.48 8 PUM 63/086 22/266 12/356 0.19 8639.73 -1.48 5 PUM 78/046 11/226 00/316 0.38 4639.75 -1.47 6 PUM 76/268 12/089 01/358 0.06 8539.72 -1.45 24 PUM 74/150 15/329 03/059 0.87 15039.55 -1.08 33 M 68/063 20/244 04/153 0.53 6239.51 -1.08 17 PUM 74/241 05/331 14/061 0.12 15139.51 -1.08 10 PUM 78/308 05/218 10/127 0.19 3839.67 -0.60 30 PUM 85/336 04/156 00/246 0.62 15139.67 -0.60 39 PUM 67/177 19/357 09/087 0.10 1639.51 0.05 7 PUM 61/191 27/011 07/101 0.81 1239.51 0.05 6 PUM 39/320 42/161 21/050 0.33 12939.54 -0.44 15 PUM 75/335 14/155 00/065 0.23 15539.59 -0.42 12 PUM 67/239 21/059 03/329 0.72 5839.61 -0.53 6 PUM 73/316 15/136 04/226 0.67 13839.47 -1.71 15 PUM 06/144 82/054 04/234 0.42 14539.47 -1.71 16 PUM 85/231 04/051 01/321 0.20 5139.56 -1.05 18 PUM 13/188 59/278 26/098 0.09 18539.56 -1.05 28 PUM 10/095 71/005 15/185 0.18 9639.41 -0.73 43 PUM 05/033 82/214 05/124 0.60 3439.44 -0.77 6 PUM 82/141 05/321 04/051 0.12 14942.45 -3.69 11 M 87/331 01/151 00/061 0.06 15142.30 -3.62 11 Q 85/18302/27303/0030.02 10141.91 -3.73 7 PUM 87/244 00/136 02/046 0.10 13741.91 -3.73 10 PUM 85/300 03/120 02/210 0.32 12141.86 -3.58 12 Pli 79/286 07/106 07/015 0.04 10941.97 -3.80 7 PUM 77/194 10/284 07/015 0.31 10441.79 -3.53 8 PUM 86/223 02/313 02/044 0.04 13741.80 -3.53 12 PUM 79/083 10/262 00/352 0.03 8341.78 -3.36 15 Pli 85/284 03/194 03/104 0.05 1441.70 -3.40 6 PUM 73/017 16/198 01/107 0.19 1641.51 -3.70 12 M 55/347 34/147 03/237 0.64 15041.51 -3.70 10 M 55/335 34/147 03/245 0.64 15139.95 -6.51 17 M 25/145 64/325 04/055 0.63 14439.76 -6.44 10 M 83/068 01/158 06/249 0.15 16042.83 -3.34 10 PUM 60/297 28/117 03/027 0.08 11342.86 -3.33 41 PUM 88/173 00/353 01/262 0.55 17242.77 -3.01 9 M 18/065 71/245 00/335 0.65 6642.65 -2.98 42 PUM 87/002 00/094 02/184 0.02 9542.66 -2.13 14 PUM 80/140 06/230 07/321 0.12 5742.35 1.74 14 Q 11/16861/25826/0770.0916842.37 1.72 15 Q 17/00702/09872/1960.45 742.20 2.77 10 Q 23/19063/01111/2810.64 1442.19 2.80 14 Q 85/274 04/085 00/175 0.02 8742.22 2.67 7 Q 12/052 03/322 77/232 0.52 5442.17 2.74 12 Q 86/172 02/262 02/352 0.13 8442.21 2.78 6 Q 84/177 05/357 05/267 0.08 17541.97 0.61 24 Q 13/027 03/296 75/206 0.39 2839.52 -6.67 18 M 75/19411/28407/0150.0610439.21 -7.00 18 M 78/345 06/075 09/166 0.08 7039.29 -5.10 15 Q 64/342 23/159 07/249 0.51 17539.17 -6.98 16 M 22/176 66/356 04/266 0.57 17838.99 -6.11 12 Q 34/272 53/90 10/0020.55 9738.58 -4.70 37 M 62/151 22/061 14/331 0.42 4938.53 -4.11 23 PUM 79/142 08/323 04/232 0.30 141

E 2E 1E 2E 2E 0E 1

1E 2E 2E 1E 2E 3E 2E 1SS 0E 2E 2E 0SS 2E 2SS 3SS 2SS 2E 0E 2E 3E 2E 2E 2E 3E 1E 2E 2E 1E 2E 2SS 2E 1E 1E 2SS 2E 3E 2SS 2C 2SS 1E 2C 1E 4E 2C 2E 1E 2SS 2SS 1SS 2E 2E 2


Table 1. (continued)Lat,deg

40.0940.0540.0040.0140.02

Lon,deg

-6.67-6.42-6.10-6.10-6.10

N DA

6 M6 M6 PUM18 M10 M

CTl O2

83/272 06/09683/118 06/29686/181 03/00032/132 47/32080/282 09/096

03 R '

02/006 0.3300/026 0.7400/090 0.2024/229 0.1602/187 0.30

$//,nax

96117

113598

T Q

E IE 1E 1SS 2E 2

Lat,deg

38.6638.2238.2241.8241.80

Lon,deg

-4.11-3.60-3.600.781.80

N DA

18 PUM14 M10 M9 Q9 Q

dl CT2

87/036 01/30670/154 13/06401/000 69/27008/008 28/09813/128 44/038

O~3 R

02/216 0.5613/334 0.0520/090 0.7359/278 0.2342/238 0.32

Sftma*

1276017

131

T Q

E 2E 2

SS 2C 2SS 1

Lat, latitude (north); Lon, longitude (Greenwich meridian); N, number of faults; DA, deformation age (M, Miocene; UM = upper Miocene; PUM,post upper Miocene; Pli, Pliocene; Q, Quaternary). Values al, 02, and 03 are the orientation of the principal axes (dip / dip direction). R= (02 - <J3) /(0r 03). SWmax is the maximum horizontal stress direction. T is the stress regimen (E, extensional; C, compressional; SS, strike slip). Q is the data qualityfrom 5 (high quality) to 0 (low quality).

fi= -where a stands for the average angle between theoretical andcalculated fault striae, t represents the number of explained faultsby the calculated stress tensor, and n is the number of faultsunexplained by any tensor [Herraiz et al., 1998], Q values rankfrom 0 (lowest quality) which corresponds to 2=0, to 4 (highestquality), which corresponds to Q > 0.7. Intermediate values are 1for 0< Q < 0.1, 2 for 0.1 < Q < 0.4, and 3 for 0.4 < Q < 0.7. As itcan be noticed, this parameter considers criteria similar to thoseadopted by Reba'i et al [1992], and it is easy to establish anequivalence of qualities 1-4 from both classifications. Therelationship with the Zoback's [1992] criteria is not as easy, butthe results rated with 4, 3, and 2 indicate very good to fairly goodin quality and can be assimilated to qualities A and B fromZoback's classification. Quality 1 represents poor quality, and 0indicates that the corresponding result has been discarded.

The seismological information compiled to estimate thepresent stress state consisted of 156 earthquakes located on theIberian Peninsula and surrounding areas and selected from thedata file of the Institute Geografico Nacional (IGN) for the periodJanuary 1, 1980, to December 31, 1995. The reason for havingchosen this starting date was that from that time on the SpanishSeismic Network has fulfilled the necessary quality requirements.

The selection from the data file was accomplished in differentsteps. The first choice was a sample of 1981 earthquakes withmagnitudes greater than or equal to 3.0 and focal depths less thanor equal to 30 km. Their corresponding hypocenters had beencalculated with a number of observations greater than or equal to7 and solutions having the root-mean-square travel time residual(RMS) less than or equal to 1 s and the vertical and horizontalerrors (ERZ and ERH, respectively) less than or equal to 5 km.This initial set was carefully analyzed in such a way that all thephases were read again and the first arrival P wave polaritieswere checked. The hypocenters were recalculated using theHYPOINVERSE program [Klein, 1978] and the crustal modeladopted by the IGN for the whole Iberian Peninsula [Mezcua andRueda, 1993]. This process required reading 10728 P phases and8566 S phases. A new selection was made keeping the conditionsalready mentioned for RMS, ERZ, ERH, and focal depth andchoosing only the events with at least 7 polarities, 10observations (first P and/or S arrival time readings), 1 S phasewith weight greater than or equal to 0.1, and condition numberlower than 100. No maximum gap selection criterion was used.The new data bank of 128 earthquakes included 3 events with

magnitude lower than 3.0 that had occurred in an interesting areafrom the tectonic point of view (Guadalquivir Basin) and fromwhich very precise information obtained with a localmicroseismic survey was available [Herraiz et al., 1996]. Thissample was increased with the other 28 events chosen from thebibliography because of their magnitude, location, and accuracy[Vidal, 1986; Delouis et al. 1993; Buforn et al, 1995; Goula etal, 1999]. The polarities of the earthquakes that occurred inCatalonia and the eastern Pyrenees were obtained from the datafile of the Institut Cartografic de Catalunya. Three of the addedevents, Lorca (June 6, 1977, M= 4.2), Alcocer (June 30, 1979, M= 4.1), and the Pyrenees (February 12, 1996, M= 5.3), took placeout of the 1980-1995 period but were considered in the seriesbecause of their location and magnitude.

The total sample (156 events) includes 2372 P wave polarities(Pn or Pg phases). The histograms of the magnitudes and thenumber of polarities corresponding to these earthquakes areplotted in Figure 1. Finally, five more events with five or sixpolarities have been added to the last set only when the techniquedeveloped by Giner [1996] was applied. The main focalparameters of the 161 events are listed in Table 3.

3. Methodology

3.1. Recent Stress Tensor

Three techniques of fault population analysis weresuccessively applied: the slip model [Reches, 1983; De Vicente,1988], the right dihedra method [Angelier and Mechler, 1977],and the stress inversion method [Carey and Brunier, 1974;Carey, 1979; Reches, 1987; Reches et al, 1992]. The slip modelwas used to establish fault groups compatible with the samehorizontal shortening direction. This model was applied afterchecking that the main assumptions concerning the data taken inthe field were satisfied [Capote et al, 1991] and that their angularerrors were lower than 5°. When a generalized data misfit wasobserved, attention was paid to check the presence of later tiltingor folding. In these cases, and when it was possible to do so, thestructures were restored to their original position.

The right dihedra method was applied to both the whole dataset of each station and the subpopulations obtained through theslip model. Next, the stress inversion method [Reches et al,1992] was applied to the whole population to establish, ifpossible, several fracturation episodes. These results werecompared to those obtained previously, and if similar, the faultgroups made in the first step were considered correct. In every


Table 2. Maximum Horizontal Shortening Directions Taken From Bibliographical InformationLat,deg

37.3737.3737.3237.3237.3237.3737.3737.3737.4137.4137.4337.4337.5137.5137.5837.5837.5837.5937.5937.6137.6137.6637.6637.7837.7838.0438.0438.0938.0938.1738.1738.5438.5538.3338.5938.5638.5638.5438.5238.5238.5338.5839.1138.9938.7738.7141.5341.4641.4637.0537.0537.0537.0537.0637.0737.0637.0537.0537.0337.0337.0337.0437.0237.0037.0036.9036.89

Lon,deg

-2.98-2.98-3.56-3.56-3.56-3.73-3.73-3.73-3.66-3.66-3.66-3.66-3.72-3.72-3.69-3.69-3.69-3.65-3.65-3.85-3.85-3.67-3.67-3.84-3.84-2.89-2.89-2.84-2.84-2.81-2.81-0.48-0.50-0.69-0.78-0.48-0.26-0.51-0.40-0.50-0.53-0.26-0.68-0.180.06-0.04-2.26-2.61-2.68-2.08-2.05-2.05

. -2.03-2.02-2.02-2.01-2.00-1.99-2.08-2.06-1.99-1.97-1.85-1.86-1.92-2.00-1.97

DefAge

MMMMMMMMMMMMMMMMMMMMMMMMMMMMMMM

MM-UMMM-UMMM-UMMM-UMMM-UMMM-UMMM-UMMM-UMMM-UMMM-UMMM-UM

UMUMUMUMPliUMUMUMUMUMUMUMUMUMUMUMUMUMUMUMUMUMUMUMUM

SH^.

261398

17616447341206290176126205314411312

171139941193413042541529823140141129141129134138421311148010310794111154117155504570128127121145149133141127141145128125130113125145140125

Ref

1111111111111111111111111111111222222222222222888444444444444466666

Lat,deg

36.9237.0937.0937.2137.2137.2537.2537.2937.1736.2736.7436.2136.2336.2837.1137.1137.1137.0937.0937.0737.0837.0837.0537.0437.0537.0337.0437.0437.1137.1137.1037.0937.0737.0837.0537.0637.0737.0537.0437.0537.1237.1237.1137.0837.0937.0941.9541.8841.9741.4241.3741.3641.2841.2441.2441.2542.1242.1240.9641.4541.5641.6341.5241.2541.2241.2641.25

Lon,deg

-3.66-3.53-3.53-3.47-3.47-3.38-3.38-3.30-3.53-5.50-5.02-5.49-5.48-5.48-2.11-2.08-2.01-2.06-2.01-2.06-2.04-2.02-2.04-2.09-2.08-2.08-2.05-1.97-2.08-2.09-2.07-2.01-2.07-2.04-2.05-2.04-2.02-2.08-2.06-2.07-2.01-1.98-2.01-2.06-2.00-2.01-0.27-0.20-0.51-2.79-2.71-2.47-2.44-2.29-2.29-1.94-1.76-1.76-0.45-1.11-0.21-0.33-0.51-0.90-0.93-0.96-0.93

DefAge

MMMMMMMMMQQQQQQQQQQQQQQQQQQQ

UMUMUMUMUMUMUMUMUMUMUMUMUMUMUMUMUMUMMMM

UMPliPliPliPliPliPli

UMUMUMUMUMUMUMLMLMLMLM

s*n«1361241124015274137974

15016010

1701622715610415310211

154114601036

10713010817917817516416117115416116017017816211912911113912313716512410740202464304

1405551544267

12246134130141

Ref

111111111333334444444444444444444444444444444411111188121012128131381111111111111111

Lat,deg

38.7538.6338.7338.5638.5338.7238.5236.8736.7136.7136.4936.2936.1837.1136.6036.3136.1936.1037.3337.2237.2337.1937.0637.1437.1437.0637.0637.0237.0236.9236.9236.9536.9536.9236.8536.8537.1637.0642.5242.5742.5442.4642.4141.6741.5441.6041.6441.4542.0641.9741.9641.8541.7941.8341.8241.7341.6941.7841.7741.7441.7141.6941.6941.6741.7141.7041.72

Lon,deg

-0.02-0.01-0.35-0.48-0.53-0.46-0.40-5.97-6.12-5.85-6.18-6.15-5.99-4.98-6.26-6.21-6.01-5.73-3.67-4.15-3.90-3.80-3.88-3.41-3.41-3.47-3.47-3.49-3.49-3.45-3.45-3.26-3.26-3.66-2.00-1.98-3.47-3.46-3.89-3.90-3.79-3.83-3.61-3.02-2.77-2.442.341.62

-1.15-0.48-0.41-0.28-0.46-0.39-0.24-0.25-0.21-0.36-0.36-0.44-0.28-0.27-0.230.09-0.030.100.12

DefAge

UMUMUMUMUMUMUMQQQQQQQQQQQQQQQQMMMMMMMMMMMQQQQ

UMUMUMUMUMQ

MMUMQQ

MMMMMMMMMMMMMMMMMMMM

SWmax

141

172181391323832130135155177160145173623

1551650

160170801601691051726912013572086841061651701751609510580142851752517560451501391451392022214016798119108101921030

1029574

Ref

222222233333333333555551

66557777788815159111111111111111111111111111111111111


Table 2. (continued)Lat,deg Lon,deg DefAge S/Anw

36.8836.8936.9036.8836.9037.0237.0237.0137.0036.8936.8936.8936.8936.8936.8936.90

.94 UM

.94 UM

.93 UM

.92 UM

.87 UM

.85 Q

.84 Q

.95 Q

.86 Q

.89 Q

.91 Q

.93 Q

.93 Q

.95 Q

.96 Q

.97 Q40.11 -0.53 UM41.94 -0.71 UM40.08 -0.56 UM40.05 -1.53 UM39.34 1.39 Pli42.12 -0.80 M42.11 -0.71 M42.13 -0.76 M41.95 -0.22 M41.91 -0.22 M41.91 -0.26 M41.92 -0.27 M42.72 -2.28 Q41.97 -i37.69 -j37.52 -537.35 -j

$.65 Q$.57 Q$.69 Q$.83 Q

39.83 -7.35 Q38.17 -7.65 Q38.17 -7.75 Q41.27 -7.07 Q40.31 -7.86 Q38.07 -i$.75 Q40.99 -1.10 M40.66 -1.37 Pli40.66 -1.37 Pli40.66 -1.37 Pli40.66 -1.37 Pli40.45 -1.25 UM40.44 -1.13 Q40.24 -1.13 MM40.39 -1.23 Pli

15515513014015317016716417031791701701681751781751356718010139130112176129134117851181911514914717317014012010331146221221306933

Ref666666666666666698108101111111111111117181818181818181818181910101010208910

Lat,deg41.2141.5341.6341.5041.3541.8341.8241.4041.4641.5841.5541.5641.9241.9741.6041.6041.6041.6041.6041.8540.7440.8141.0341.4040.9641.0541.0941.2340.2740.2740.2740.2740.2740.1840.1741.2341.2741.3041.6541.5741.6241.3841.3841.8341.7041.7541.83

Lon,deg-0.99-0.93-0.98-0.30-0.35-0.52-0.53-0.75-0.80-1.17-0.08-0.08-0.93-0.96-1.09-1.09-1.09-1.09-1.09-1.860.490.520.561.980.800.850.921.12-1.22-1.22-1.19-1.19-1.19-0.83-0.550.300.330.380.160.380.40-0.43-0.21-0.52-0.35-0.41-0.53

DefAgeLMMMMMUMUMUMUMLMLMUMUMUMUMUMUMUMUMUMUMQQQQQQQQQUMUMUMUMUMUMUMMMMMMMMMMMMM

•SWmax

4112483149146128871411466113813996102151143158144100140135145170130901801254073239170104145125180166147171370041661

Ref1111111111111111111111111111111111111114151515151515151510101010101414111111111111111111111111

Lat,deg41.8141.7741.7641.7541.8241.8041.7941.5541.5841.6241.6541.6141.5541.4941.4341.3741.3741.2741.8541.8441.6642.5442.8142.8542.7243.5642.6142.6142.2642.2542.0441.6641.5641.6642.0242.0241.4941.4541.6541.6741.5941.9241.6941.6841.9841.9441.85

Lon,deg DefAge-0.03-0.06-0.04-0.17-0.16-0.14-0.06-0.37-0.22-0.21-0.21-0.250.12-1.15-0.39-0.50-0.430.14-2.04-1.98-2.042.722.853.051.88-1.98-2.24-1.62-0.55-0.13-0.56-0.37-0.21-0.24-0.98-0.940.450.200.130.05-0.05-1.02-0.000.06-0.65-0.59-0.53

MMMMMMMMMMMMMMMMMMPliMPliQQQQPliPliPliMMMMMMMMMMMMMMMMMMM

«$Mnax

1281011041231201261361111281084811512583140131116123254525501601801709080401802310423105131721772041721117403

Ref1111111111111111111111111111111111111414141616161614141411111111111111111111111111111111111111

Lat, latitude (north); Lon, longitude (Greenwich meridian); Def Age, deformation age (M, Miocene; LM, lower Miocene; MM, middle Miocene;UM, upper Miocene; Pli, Pliocene; Q, Quaternary). SHmsai is the maximum horizontal stress direction. Ref, reference (1, Galindo-Zaldivar et al. [1993];2, De Ruig [1992]; 3, Benkhelil [1976]; 4, Stapel et al, [1996]; 5, Sanz de Galdeano [1985]; 6, Huibregtse et al. [1998]; 7, J.L. Simon (unpublisheddata, 1990a); 8, Cortes and Maestro [1997]; 9, Paricio and Simon [1986]; 10, Simon [1989]; ll,Arlegui [1996]; 12, Maestro [1994]; 13, Casas [1990];14, Cortes and Simon [1997]; 15, Massana [1995]; 16, Goula et al. [1996]; 17, J.L. Simon (unpublished data, 1990a); 18, Ribeiro et al. [1996]; 19,Colomer [1987]; 20, Simon and Soriano [1993].

case the angular confidence margins of the main stress axes havebeen estimated using the bootstrapping technique [Stuart, 1984].The three methods used in the fault analysis (slip model, rightdihedra, and Reches et al.'s [1992] method) show analogousresults although the last one gives the most complete solution.Then, in order to simplify the presentation of the fault dataresults, only those obtained with Reches et al/s method havebeen shown. More detailed information can be found in the workof Herraiz et al. [1998].

Fault population analysis provided 824 orientations of themaximum horizontal stress S//max, from which 474 were obtainedfrom field data and 350 were obtained from bibliographicalinformation. SHmax trends and geologic site locations are plottedin Figure 2. Histograms of these orientations and the stresstensors deduced for each trend appear in Figure 3. In some sitesthe analytical procedure has yielded two or more stress tensors,but their chronological sequence has been established only in afew cases.

770 HERRAIZ ET AL.: TECTONIC STRESSES IN THE IBERIAN PENINSULA.

(a)

0)CS3ortOS0)M-oL.0)

I

20-

8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46Number of polarities per earthquake

(b)

CDJ*CS3O"

<D

CDJQE3

18 2.0 2.2 2.4 2.6 2.8 3.0 3.2 3.4 3.6 3.8 4.0 4.2 4.4 4.6 4.8 5.0 5.2 5.4 5.6 5.8

MagnitudeFigure 1. (a) Histogram of number of polarities per earthquake used in the simultaneous inversion of the stresstensor and the individual focal mechanisms [Rivera and Cisternas, 1990] considering the main database (156events; see also Table 3). (b) Histogram of the earthquake magnitudes for the same set of earthquakes.

3.2. Present-Day Stress Tensor

The study of the present-day stress field has been made usingtwo different procedures. The first one was the application ofRivera and Cisternas's [1990] method to obtain the stress tensorinversion using the data set of 156 earthquakes and 2372 P wavepolarities described in section 2. This method assumes Soft's[1959] hypothesis and the homogeneity of the stress field in theregion of interest. The main feature is that polarities are the input

data instead of previously calculated fault plane solutions. Thealgorithm seeks the maximum of a likelihood function thatdepends on the radiation pattern function and on the probabilityof obtaining either a compressive or a dilatational polarity. Thealgorithm calculates the shape and orientation of the stress tensorin the studied area and the individual fault plane solutionsconsistent with it. The shape of the tensor is usually given by thestress ratio R, defined as R = (a2 - cj3)/(cji - 03), where CTI, cj2, and03 are the maximum, the intermediate, and the minimum


Table 3. Hypocentral Parameters of the Earthquakes Chosen to Study the Present Stress StateEven!

123456789101112131415161718192021222324252627282930313233

3435363738394041424344454647484950515253545556575859606162636465666768

Date

March 5, 1981Sept. 14,1985April 26, 1986May 30, 1985July 5, 1986March 11, 1987June 7, 1989March 29, 1990Aug. 14, 1991Aug. 20, 1992Nov. 11,1993Nov. 11,1993Dec. 5, 1993Dec. 11,1993Jan. 20, 1994March 5, 1994March 23, 1994June 7, 1994Aug. 4, 1994Aug. 10, 1994Sept 6, 1994Sept. 23, 1994Oct.7, 1994Nov. 28, 1994Jan. 25, 1995June 6, 1995July 1,1995July 11,1995Oct. 4, 1995Nov. 26, 1995Nov. 26, 1995Dec. 6, 1995Dec. 18, 1995

June 6, 1977June 24, 1984Sept 13, 1984Sept. 16, 1985.Aug. 16, 1986March 20, 1988May 2, 1988Aug. 20, 1988Dec. 6, 1988Dec. 22, 1993Dec 23, 1993Jan. 3, 1994Jan. 4, 1994Jan. 4, 1994Jan. 8, 1994Jan. 9, 1994Jan. 16, 1994Jan. 16, 1994Jan. 17, 1994Jan. 26, 1994Feb. 2, 1994Feb. 2, 1994March 11, 1994March 29, 1994March 29, 1994March 30, 1994AprilS, 1994AprilS, 1994April 19, 1994April 20, 1994April 23, 1994June 12, 1994July 13, 1994July 24, 1994Nov. 8, 1994

Hour

1401116003103271426151536

202151272014318256103

1014422181910166

2018188

22161517516618211422234423211761000

Minute

212512223536121032385

331551322610104350

41513013582927639251347

4930342510445142911003

47481

553501633

422942601352235331124517

Second

5211

265

4148219566024429

407

313642163025172111508347

406

3115

1251119

4047175216388715288

3641027456

40382

21445330385946312235

Lat,deg

38.4937.3837.2237.0938.7737.7337.1538.2938.7538.2638.3138.1838.4838.0537.2636.9637.8338.938.1837.2036.8137.0736.2338.5137.8537.2537.4537.4538.8038.0038.0238.0037.46

37.6536.8436.9837.0237.0737.1437.1837.1937.0337.0136.7536.7936.5636.6037.0736.6136.5636.6437.2836.6536.6736.4937.3336.6236.6737.0637.3737.3537.3437.3537.3636.9336.5236.9936.98

Lon,degExternal Betics

0.21-3.65-3.72-4.26-0.24-3.40-4.530.16-0.96-0.88-0.910.00-1.26-0.65-4.23-4.37-4.14-0.39-1.06-4.35-5.40-4.32-6.10-1.25-4.07-4.19-3.80-3.820.32-1.23-1.26-1.27-3.76

Internal Betics-1.73-3.74-2.34-3.82-3.22-2.10-3.61-3.74-3.85-3.94-2.99-2.97-2.83-2.84-3.91-2.86-2.86-2.85-3.16-2.83-2.81-2.80-1.81-2.80-3.36-2.51-2.01-2.04-2.00-2.04-2.02-2.04-3.82-2.51-2.35

3epth, km

1755116684164839678163265178521420621724

959591

1124127692136573101146432271252113

RMS,s

1.00.60.60.80.50.90.30.60.90.50.70.70.70.30.90.40.60.50.70.90.80.60.60.70.60.60.70.50.60.60.70.60.5

0.80.70.90.60.30.30.20.40.40.80.90.60.60.50.50.30.80.90.30.60.60.70.80.80.70.50.60.60.50.50.60.50.60.40.9

Erh, km

321222

1111111111111111111111

324211111111111211111111

Erz, km

421222122221212111221112132121211

112421111121121111212121111111111212

M *

4.93.54.03.73.44.33.43.64.13.03.23.73.23.43.33.23.43.03.33.13.73.13.03.43.23.13.43.63.84.13.73.63.3

4.25.05.03.03.03.13.03.43.13.63.83.74.93.53.63.13.43.53.23.73.43.73.23.53.73.13.93.13.73.23.23.13.33.34.0

$ Polarities

381621157

291581988

23158151717891522131212167711131811710

2245281197813142326323417281718151923213318143322401526131713182436


Table 3. (continued)Event Date Hour Minute Second Lat,deg Lon,deg Depth, km RMS,s Erh, km Erz, km M N Polarities

Internal Betics (continued)697Q71"*")7374757677787980

8182838485

86878889909192939495*96979899100

101102103104105106107108109

110111112113114115116117118119120121122123124125126127128129130

Dec. 3. 1994Dec. 25 1994Feb. 25. 1995March 17, 1995March 18, 1995April 29, 1995May 18, 1995May 29, 1995June 7, 1995Sept. 18, 1995Nov. 9, 1995Nov. 18. 1995

Aug. 13, 1994Aug. 28, 1994Sept. 26, 1994Dec. 26, 1994March 5, 1995

May 14,1986Oct. 28, 1986July 6, 1987Aug. 24, 1987May 19, 1988Dec. 28, 1988Sept. 24, 1989Dec. 15, 1991Dec. 21, 1991Jan. 24, 1992May 25, 1993Aug. 15,1993Oct. 25, 1993Sept. 26, 1994May 15, 1995

Dec. 12, 1988Dec. 30, 1988June 10, 1989Aug. 30, 1989Nov. 22, 1990April 15, 1994Nov. 29, 1995Nov. 30, 1995Dec. 24, 1995

Feb. 29, 1980July 19, 1981Sept. 28, 1981June 22, 1982Aug. 25, 1982Feb. 25, 1984Sept. 30, 1985April 19, 1986May 26, 1987June 26, 1987Nov. 7, 1987Nov. 11,1987Nov. 12,1987Dec. 15, 1987Jan. 6, 1989Feb. 28, 1990April 1,1 990June 19, 1990July 26, 1990Aug. 5, 1990March 19, 1992

18121914137

2316165190

1613201723

236418216

2011597

220515

121671141323215

20191

192022916171171719131921162118

4242444037132120142024

25432

4846

55483243162116508

497

32163837

144115433326562049

41584150593

281

3213715333533231348293253

4428251434416

2736415348

1812172223

371025

31154

253213256

40398

261419293443.

23

19

52

13

43341234

37.2936.0737.3137.1637.0936.7336.8536.8736.9236.9436.4036.97

36.4636.7236.7636.4936.10

39.9039.8440.9540.9339.5439.4041.2040.9839.4240.8639.4340.2940.5941.4140.80

42.1642.1542.1642.1142.2843.5642.8342.8242.82

43.1743.0943.1742.8643.0743.2143.0343.0943.1343.0843.0443.0743.1743.4342.9942.9143.1542.7942.5042.2742.23

-2.98-3.09-2.64-3.79-2.16-2.83-3.00-3.86-2.17-4.07-2.72-2.53

Guadalquivir Basin-7.24-7.79-7.77-7.79-7.48

Iberian Range-1.40-1.30-1.001.57

-1.04-0.29-1.152.06-0.79-2.39-0.80-1.09-1.582.551.52

Northwest-7.76-7.75-7.78-7.52-7.61-7.36-7.32-7.31-7.17

Pyrenees-Ebro Basin-0.390.07-0.03-1.81-0.28-1.12-0.44-0.51-0.38-0.41-3.70-0.18-0.17-0.610.17-1.04-1.43-1.66-1.151.092.06

912616168163

2524272814

9558217612212321015

5311141729101016

66131811610431681

111110133112

0.50.80.50.60.40.70.40.60.60.50.60.3

0.50.90.60.70.7

0.80.50.6

0.50.60.8

0.90.62.30.50.5

0.20.20.30.50.50.70.60.20.1

0.7

0.5

0.5

0.4

0.70.40.60.7

111111111111

12212

222

213

13122

1111111

1

2

1

2

1

2112

122112311221

22122

233

222

23132

111122321

2

2

2

1

2114

3.53.33.23.93.93.13.13.04.03.03.44.0

3.53.33.03.63.7

3.33.23.44.23.23.43.34.23.33.43.33.43.24.24.6

3.23.23.23.83.64.24.63.83.7

5.74.64.34.44.34.83.83.93.83.93.94.13.63.94.43.63.43.43.63.74.2

201017193014911177718

2320109

25

1991310137131576131611914

778108

2425178

3281071016710997871116158109918


Table 3. (continued)Event Date Hour Minute Second Lat,deg Lon,deg Depth, km RMS, s Erh, km Erz, km M N Polarities

131 Oct. 8, 1993 22 9132 Feb. 18,1996 1 45

133 July?, 1990 23 30134 Nov. 17, 1995 15 11

135 April 13, 1994 3 33

136137138139140141*142143*144145146147148149150*151*

June 30, 1979Feb. 23, 1982May 13,1986May 13, 1986Oct. 19, 1987Sept. 28, 1988Oct. 4, 1988Oct. 11,1988Oct. 24, 1988Feb. 20, 1989Nov. 30, 1990May 30, 1991April 20, 1992Feb. 6, 1994Feb. 14, 1994March 29 1995

117182012121314432120251216

44593824544351538255210827310

152153154155156157158159160

May 26, 1985May8, 1986Dec. 20, 1989March 10, 1991Aug. 22, 1991May 19,1992July 4,1994March 30, 1995April 11, 1995

161 Feb. 20, 1989

182341191913156

20

51015174223385442

52

1848

361544194351112952371239260507

10375673

474220

28

Pyrenees-Ebro Basin (continued)42.43 2.13 342.80 2.53 8

40.7340.57

41.55

Central System-3.54-4.00

Duero Basin-3.10

412

12

40.6640.6439.2339.2340.2640.1040.0840.0740.0738.9039.2139.2339.5239.5040.4539.62

Tajo Basin - Mancha Plain-2.52-2.75-2.73-2.67-3.24-3.54-3.56-3.58-3.24-3.09-2.83-2.31-2.54-3.33-2.62-2.79

107555222982486161

Toledo - Sierra Morena Mountains37.7938.1037.2737.7538.2637.5737.6338.1038.43

43.08

-4.64-4.40-7.37-5.49-5.04-6.02-6.92-6.53-2.88

55171561023117

Cantabrian Range-5.11 5

0.80.4

0.3

1.41.30.70.70.40.30.30.40.40.50.60.50.40.60.30.6

0.60.70.40.10.10.10.50.60.6

0.5 1

11

3.35.2

3.33.3

3.4

5.13.25.02.01.92.44.33.83.5

3.7

1322

209

11

7533143322222622

4.14.13.63.03.23.03.13.13.43.63.03.53.43.52.83.1

981912768614237149755

321420777

301712

Date, hour, minute, and second columns show the origin time parameters. Lat, long, and depth columns show the hypocentral coordinates. RMS,root-mean-square residual. Erh is the horizontal error. Erz is the vertical error. Mis the magnitude. N Polarities is the number of polarities used for thefocal mechanism determination.

* Events have been used only with Giner's [1996] technique.

principal stresses, respectively. The orientation is evaluated byEuler's angles that result in the transformation of thegeographical system of reference into the one defined by theprincipal axes (a\, 02> cr3). The mathematical quality of thesolution is evaluated by the likelihood function normalized to theunity and the score. This last parameter is defined as the ratiobetween the number of polarities consistent with the tensor andthe total number of polarities. Rivera and Cisternas's method isone of the most used procedures to estimate the stress tensor froma population of focal mechanisms [Dorbath et al, 1991; Delouiset al., 1993; Undo, 1993; De Vicente et a/., 1996; Fuenzalida etal, 1996; Herraiz et al, 1996; Goula et a/., 1999]. In this study,more than 7000 trial sets, obtained with increments of 10° forEuler's angles and different solutions for the focal mechanisms,were used in each case to diminish the dependence of thesolutions on the trial conditions.

The second method was a technique developed by Giner[1996] applying FPA methods to earthquake focal mechanisms.

In our work, these fault population methods were the same asthose used to analyze the recent fault data, in particular, the stressinversion method [Reches, 1987] and the slip model [Capote eta/., 1991]. This implies that mechanical restrictions to focalmechanisms should be imposed. It is worth noting that thismethod deduces which mechanical parameters better match thesample, instead of attributing values selected a priori. Reches[1987] proved that the methods that do not take into account thecohesion factor during the slip on the fault, according toCoulomb's law, assume that this parameter is null; that is, theyimpose a determined mechanical condition. At present, theconsideration of the cohesion factor in the stress inversion is inprogress, and the results will be improved when new physicaldata about rock friction are available.

Giner's [1996] technique begins with the application of agraphical-interactive program developed by Cabanas et al[1996]. This program uses P polarities and azimuth and incidenceangles to yield all the possible individual focal mechanisms that


Figure 2. ^^orientations obtained from geologic sites using the stress inversion method [Reches et aL, 1992].

satisfy a previously chosen score value. The discrimination ofwhich one of the nodal planes corresponds to the fault has beendone following the procedure developed by De Vicente [1988]and Capote et al [1991] that uses the slip model [Reches, 1983].In this way, a new population of possible fault planes for all theearthquakes is created. The resulting sample is analyzed with thefault population techniques in order to get one stress tensor andthe directions of maximum horizontal compression that fit thesample. Then, these results are used to select only one focalmechanism for each seismic event, according to the angular errorbetween the ey directions and the Kr values (K'= ey/ez). After that,the whole procedure is repeated to obtain one stress tensor andthe ey directions that fit the new focal mechanism population.Once the best stress tensor has been deduced and the mechanicalcharacteristics and the individual incompatible mechanisms havebeen determined, all the focal mechanisms are plotted with theusual stereographical projection. The study ends with the

application of the Lissage program [Lee and Angelier, 1994] todraw the trajectories of SHmax.

The whole methodology has been applied in two steps. Firstly,the Spanish peninsular territory has been divided into 12 zones.All of them, bar the Iberian Massif, are mainly based on thetectonic criteria ofJulivert et al. [1972]. The Iberian Massif hasbeen subdivided into four subzones (Northwest, CantabrianRange, Central System, and Toledo and Sierra MorenaMountains) according to the tectonic units resulting from thealpine deformation (Figure 4). Geological and seismological datacorresponding to each zone have been studied separately.Secondly, attention has been paid to a single set of data made outof the whole information corresponding to Spain and the resultsobtained for Portugal by Ribeiro et al [1996]. This procedureallows us to obtain detailed knowledge in each zone as well as anoverview of the stress distribution for the whole IberianPeninsula. In addition, the comparison of the results for the upper

( A )

hx?| EXTENSIONAL

BB STRIKE-SLIPHI COMPRESSIONAL

| | UNKNOWN TENSOR

( B )

0-10 20-30 40-50 60-70 80-90 100-110 120-130 140-150 160-170trends

(C)

0-10 20-30 40-50 60-70 80-90 100-110 120-130 140-150 160-170SHMAX trends

Figure 3. Type of stress tensor and histograms of the SHmui trends displayed in Figure 2. (a) All data, (b) Fielddata, (c) Bibliographic data.

40°-

Betic CordillerasIberian Range

i i i Pyreneesl l Tertiary Basins

Iberian Massifo°

Figure 4. Distribution of areas with common tectonic characteristics selected to perform the analysis of regionalstress tensors. BEX, External Units of the Betic Cordilleras; BIN, Internal Units of the Betic Cordilleras; CAN,Cantabrian Range; DUE, Duero Basin; EBR, Ebro Basin; GUA, Guadalquivir Basin; IBE, Iberian Range; NW,northwest Iberian Massif; FOR, Portugal; PYR, Pyrenees; TAJ-MAN, Tajo Basin and La Mancha Plain; TOL-MOR, Toledo and Sierra Morena Mountains; SCE, Central System.


Table 4. Number of Geological Stations and Data Corresponding to the Areas With Similar Structural Characteristics

Zone

BEXBINNWTAJ-MANQUADUECANTOL-MORFORIBEPYREBRSCE

Total

Number ofStations

110424844192629130

4116219

409

Field DataNumber of

Data

248789388914534313505293780

87324318

226

8770

Bibliographic DataNumber ofey Trends

14358546924323716056172

23

531

Number ofS//max Trends

135514768202835100

4613219

474

Number ofStations

55860001700101188300

324

Number ofS/Max Trends

69950001800101198

310

350

Table 4 includes the number of orientations of the maximum shortening axis, %, and the maximum horizontal stress, 5//max, obtained with theslip model [De Vicente, 1988] and the stress inversion method [Reches et aL, 1992], respectively. Zone abbreviations correspond to: BEX, ExternalUnits of the Betic Cordilleras; BIN, Internal Units of the Betic Cordilleras; CAN, Cantabrian Range; DUE, Duero Basin; EBR, Ebro Basin; QUA,Guadalquivir Basin; IBE, Iberian Range; NW, northwest Iberian Massif; POR, Portugal; PYR, Pyrenees; TAJ-MAN, Tajo Basin and La ManchaPlain; TOL-MOR, Toledo and Sierra Morena Mountains; SCE, central System. For locations, see Figure 4.

Miocene and Pliocene-Quaternary periods to the present-daystress field, allows us to sketch its temporal evolution. A detailedexplanation of both data and methodology can be found in thework ofHerraiz et aL [1998].

4. Regional and Dominant Stress Tensorsin the Iberian Peninsula

The results of the World Stress Map [Zoback, 1992] haveemphasized that the S//max orientations can be uniform within theplates over distances up to 5000 km. These "regional" fields areusually accompanied by local modifications in the stresscharacteristics that can show a large variety of scales andmagnitudes. Nevertheless, as Rebai et al [1992] pointed out, thechanges of stress directions on a particular scale are consistentwith the kinematics of the faults on the same scale. WesternEurope, where both regional [Muller et al, 1992] and local[Rebai et al, 1992] patterns of SHmwi can be found, is a clearexample of the existence of local variations in the frame of abroader uniform stress distribution. The results of our study seemto confirm this fact. In sections 4.1 and 4.2 we describe the recentand present-day stress tensors obtained both for the zonessketched in Figure 4 in which there were enough data to performthe analysis and for the whole Spanish mainland. These lasttensors will be called "recent dominant tensor" and "presentdominant tensor." Geological sites located within each zone andthe number of S//max trends obtained in each case are summarizedin Table 4.

4.1. Recent Stress Tensors

In order to study the regional distribution of recent stresstensors, fault data of each zone have been analyzed using thestress inversion method [Reches et al, 1992] and the bootstrapsampling technique. The obtained results are displayed in Figure5. Tensors corresponding to Cantabrian Range and Ebro Basin

zones are not included, because they were considered not wellconstrained. The solution for Duero Basin only represents itseasternmost part (Almazan Basin), because the appropriateoutcrops were found only in this area. The quality of the resultslogically depends on the number of data (Tables 1, 2, and 4), butwhen this is high, the S//max can be considered accuratelyestablished. The results indicate a clear predominance ofextensional stress tensors.

With the aim of deducing the dominant recent stress tensor forthe whole Spanish mainland, the structural data were grouped inonly one set and analyzed as a unique sample. The results aredisplayed in Figure 3 a where a well-defined mode for S//maxtrending 120°N-160°E can be noted. This mode can be alsoobserved when field and bibliographic data are plotted in aseparated way (Figures 3b and 3c, respectively). A clearpredominance of extensional tensors (dj = az) and a much lowernumber of compressional stress tensors are noticeable in Figures3a-3c. Trajectories obtained using Lee and Angelier's [1994]technique to interpolate the data that follow the predominantNW-SE orientation are displayed in Figure 6.

4.2. Present-Day Stress TensorsRivera and Cisternas's [1990] method and Giner's [1996]

technique have been tried in each zone although the lowseismicity of some of the zones has limited their simultaneousapplication to seven areas: Northwest, Pyrenees, Iberian Range,Tajo Basin and La Mancha Plain, Toledo and Sierra MorenaMountains, External Betics, and Internal Betics. The results arelisted in Table 5 and appear in Figures 7-9. Figures 7 and 8describe the tensors and the focal mechanisms, respectively,given by Rivera and Cisternas's method, whereas Figure 9 showsthe tensors obtained with Giner's procedure. In some cases, morethan one stress tensor per region was estimated with this lasttechnique.

Directions for the maximum horizontal stress SHmax obtainedwith both techniques are systematically coincident. Concerning


SHMAX TRENDSTRENDS

Figure 5. Recent regional stress tensors corresponding to some of the zones indicated in Figure 4. The tensorshave been obtained using the stress inversion method [Reches et a/., 1992].

the stress tensors, both the slip model and the inversion stressmethod, which are the basis of Giner's [1996] technique, assumemechanical requirements. These conditions constrained thepossible solutions in a different way from that of Rivera andCisternas's [1990] method, whose aim is to find mean tensors.These two points of view are complementary to each other andlook for different objectives. The aim of Rivera and Cisternas'smethod is to determine the stress tensor capable of explainingevery focal mechanism of the earthquakes that have taken placein a zone assumed technically homogeneous. This method doesnot try to find focal mechanisms with the greatest score butlooks for the tensor parameters and the focal mechanisms thatmaximize the probability that the polarities are placed correctlyaccording to the radiation pattern of each fault plane solution.

Therefore the objective is to optimize the likelihood function,not the score. On the contrary, the fault population methods onwhich Giner's technique is based, are oriented to find one orseveral tensors mechanically different. With this approach thepossible individual focal solutions are stressed. If there exists afault that is not mechanically compatible with the averagesolution, the method keeps high scores but indicates theexistence of a heterogeneity between the deformation conditionsof this mechanism and those corresponding to the others. As aconsequence, Rivera and Cisternas's method is prone to chooseonly one solution of those deduced by Giner's procedure or, as ithappens in our study for the Pyrenees and the External Betics,finds an intermediate solution. It has already been observed thatwhen deformation is heterogeneous, two or three tensors may be


Figure 6. SHmax trajectories drawn applying the Lee andAngelier [1994] interpolation program to data that followthe NW-SE predominant orientation which appears in Figure 3.

separated for microseismic activity of aftershock sequences.These tensors are coaxial in the range of uncertainties, and oneof them is in agreement with the regional state of stress [Mercierand Carey-Gailhardis, 1989; Carey-Gailhardis and Mercier,1992].

With these approaches the results given by Rivera andCisternas's [1990] method for the different zones (Figure 7) arestrike-slip stress tensors except for the Internal Betics and theIberian Range, where triaxial extensions are present. Giner's[1996] technique (Figure 9) indicates compression close to theuniaxial type in Sierra Morena and External Betics; extension inthe Iberian Range and the eastern Pyrenees, and a strike-slipregime in the Northwestern sector and the Tajo Basin-LaMancha Plain. All the zones except the Pyrenees and the InternalBetics show a NW-SE compression that dominates in bothrecent and present stress states. The western Pyrenees and the

External and Internal Betics show two stress tensors that aremechanically incompatible.

The joint application of Rivera and Cisternas's [1990]method to the sample of 156 events indicates a maximumcompressional axis oriented NW-SE and a strike-slip regimewith a shape factor R equal to 0.51 (Figure 10). The score is0.77, and the likelihood is 0.85. This low value reflects theheterogeneity of the sample.

Application of Giner's [1996] technique to the same sampleextended to 161 events reveals the presence of an absolutemaximum of SHmax oriented N135°E and a relative maximumtrending N30°E (Figure 11). As it can be observed in thehistogram of fault types and S//max orientations (Figure 12), bothmaxima show a large variety of associated faults, those ofreverse type being the most numerous. This fact represents adisagreement with the geological results obtained from field sites


Table 5. Shape Factors, R= (<j2-<*3y(<Sr<J3), and Maximum Horizontal Stress Directions, SHmax, Obtained in the Areas Plotted inFigure 4 in Which There Were Enough Data to Analyze the Regional Stress Tensor

Giner [1996] MethodZone

PYR

NW

TAJ-MAN

TOL-MOR

IBE

BEX

BIN

R0.04 (SS)0.63 (E)0.24 (E)

0.67 (SS)

0.21 (SS)

0.27 (C)

0.58 (E)

0.05 (SS)

0.10(E)0.17(C)0.06 (E)

S/Anax

14(1)

15(2)111(2)

140(1)

143 (1)

115(1)

163(2)

136(1)

121 (2)11(1)

166(2)

Score0.960.940.98

0.82

0.85

0.89

0.86

0.90

0.910.830.87

Quality

A

A

B

A

A

A

A

R

0.47 (SS)

0.86 (SS)

0.36 (SS)

0.70 (C)

0.60 (E)

0.37 (SS)

0.49 (E)

Rivera-Cisternas [1990] Method<$Fftnax

5(1)

155(1)

130(1)

157(1)

160(2)

130(1)

160(2)

Score

0.86

0.77

0.75

0.83

0.86

0.80

0.78

Quality

A

A

A

A

A

A

A

Letters associated with R values indicate the tensor characteristics: E, extensional; SS, strike slip; and C, compressional. Numbers inparenthesis indicate the axis defining the corresponding direction. Quality ranking follows Zoback's [1992] criterium.

Figure 7. Present-day regional stress tensors obtained with the technique developed by Rivera and Cisternas[1990]. The shape factor (R=(G2-G^/(G{-Gjj) for each region is also shown.


-5°

;f> x5 4 3

Fault plane solutions fromRibeiro etal. (1996)

Figure 8. Focal mechanisms of the 156 individual events computed using the method of Rivera and Cisternas[1990] (see the corresponding tensors in Figure 1). The six mechanisms taken from Ribeiro et al. [1996] are alsoplotted and distinguished with a star. The fault plane solutions are shown in a lower hemisphere Schmidtprojection, and numbers close to each representation indicate the event date.

that showed a clear predominance of normal faults. A possibleexplanation will be discussed in section. 5.

Focal mechanisms obtained with Giner's [1996] methodtogether with the SHmax trajectories of the dominant NW-SEstress field are displayed in Figure 13. Figure 13 also includesthe six mechanisms obtained by Ribeiro et al. [1996], whichhave been used to draw stress trajectories in Portugal. The stressmethod [Reches et al, 1992] applied to the whole population ofmechanisms yields two tensor types with a common orientationfor SHmax (Figure 14). The first one (Figure 14a) corresponds toan extensional regime (0! = az) and explains 80 mechanisms.The shape factor R is 0.07, pointing to a triaxial, close to radialextension. The second tensor (Figure 14b) explains 58mechanisms and corresponds to a strike-slip regime (cj2 vertical);the stress ratio R = 0.14 indicates high reverse components. Thescores of these solutions are 0.87 and 0.88, respectively.

5. Discussion and Conclusions

The application of fault population analysis together withfocal mechanism determination makes it possible to obtain abroader and complete picture of the recent and present-day stressfields but requires a large number of data and a good spatialdistribution. In our case this problem has been important becauseof the low seismicity of several zones in the Iberian Peninsulaand the uneven geographical distribution of the outcrops ofrecent rocks. Nevertheless, the amount of geological andseismological data used in the study allows us to consider ourresults well founded, especially when they have been obtainedwith different techniques. It is necessary to consider that datataken in the measurement sites only represent the fracturecharacteristic near the surface, whereas the information obtainedfrom earthquake analysis casts some light on the stresses acting


45'

TOL-MOR4

R = 0.27 \v^ _•• (Ji,

I I I I

"* «. S^ TRENDS

*" c* s^ TRENDS

Figure 9. Present-day regional stress tensors deduced by means ofGiner's [1996] method for some areas of Figure 4.

on the crust, down to 30 km deep. This fact can explain thedifferent stress regime obtained from geological and seismicdata, but this argument must be verified in the future byimproving the hypocentral locations and increasing the numberof seismic data. Microseismicity studies carried out in specificareas can be a useful tool to achieve this purpose [see, e.g.,Herraiz et a/., 1996]. A change of the stress tensor in time cannot be totally ruled out either, although the results obtained indifferent zones indicate the continuity of the stress distributionfrom late Miocene to present time.

The comparison of the results obtained for the whole IberianPeninsula to those corresponding to individual zones makes clearthe existence of (1) a primary pattern for the stress fieldcharacterized by the constancy of the *S//max NW^SE directionand (2) the possibility of some regional stress fields associated tospecific tectonic or geologic features. These fields can beassimilated to "first-," and "second-," order patternsrespectively, according to the terminology proposed by Zoback

[1992]. The primary pattern seems to reflect the stressesgenerated by the convergence between African and Eurasianplates and the W-E ridge push originated in the middle Atlanticrift. N-S to NE-SW orientations of SHmax in NE Spain (see Figure2) are not consistent with the western European mean direction,suggesting the occurrence of tectonic forces coming from thePyrenean zone [Cortes and Maestro, 1998]. Secondary stressfields in the Pyrenees and Betics (Figure 9) can be related totopographic highs and upper crust structures.

The results obtained for the Pyrenees are complex. For thewhole chain, Rivera and Cisternas's [1990] method defines awrench regime with the shape factor R=QA7 and SHmax in N-Sdirection. For the western part, Giner's [1996] technique givestwo coaxial stress tensors. The predominant one points out astrike-slip regime with a horizontal compression (00 at N14°Eand R = 0.04. This solution is analogous to that given by Riveraand Cisternas's method. The second tensor is extensional andpresents SHmaai oriented N15°E. The shape factor is 0.63. In the


Shape Factor: R=0.51Orientation : a, :azimuth = 150° dip= 41°

<j2 :azimuth = 330° dip= 49°a3 :azimuth = 60° dip= 0°

Quality: Likeiihood=0.85Score=0.77

Figure 10. Mean stress tensor representation obtained by thejoint inversion of the whole main set of earthquakes (156 eventslisted in Table 3) using the technique developed by River a andCistemas [1990].

eastern Pyrenees the same procedure indicates an extensionalregime with a SHmax in the Nl 11°E direction, but in this case thelow number of events analyzed (only four) diminishes thereliability of the result. Recently, Goula et al [1999] have founda strike-slip or compressional stress tensor with 5//niax i*1 the N-S

330° 30°

60°

270*

120°

210 150°180°

Figure 11. SHtmK rose diagram from the enlarged population ofseisms with calculated focal mechanism (161 events). The modalvalue of S/fmax orientation is N135°E.

IxX] EXTENSIONAL

Jill STRIKE-SLIP|H COMPRESSIONAL

Figure 12. Stress tensor types and histogram of SHmaxorientations deduced from the total population of seisms (161events) with calculated focal mechanism.

direction for a zone that includes the NE of Spain and the southof France. This solution was obtained considering 21 geologicalsites and 18 earthquakes. Although this variety of results showsthat the stress state in the Pyrenees is not well understood yet,the existence of an acting N-S compression can be consideredwell established.

A situation similar to that in the western Pyrenees can befound in the External Betics, where 33 events have beenanalyzed. Giner's [1996] technique gives two different solutions:one compressive (R=0.05) and another extensive (/?=(). 10). Bothhave a very similar orientation for SHmax. Rivera and Cisternas's[1990] method indicates a strike-slip stress tensor and a majorityof normal focal mechanisms even though several clearly definedreverse solutions have been already found (Figure 8).

In the Internal Betics the application of Giner's [1996]method to a sample of 47 earthquakes also provides twosolutions that are not mechanically compatible. The predominantsolution shows a compressive stress tensor with R = 0.17. The GIcomponent is located Nl 1°E. The nodal planes are interpreted asreverse faults, and they do not show a defined trend. The secondsolution corresponds to an extensional stress tensor close toradial (^=0.06), although in this case the interpretation of thenodal planes suggests the existence of normal faults with NW-SE orientation, As has been already commented on in section4.2, in this zone Rivera and Cisternas's [1990] method givesonly one solution which is analogous to the extensional stresstensor deduced by means of Giner's procedure. Thesimultaneous presence of normal and reverse faults can beexplained as a topographic effect: the creation of an importantrelief generated by compression may induce extensional stresses.

For the other zones where the joint application of bothmethodologies has been possible (Northwest, Iberian Range, andToledo and Sierra Morena Mountains), Giner's [1996] techniqueobtains only one tensor (Figure 9). In each case the orientation ofSnmax agrees well with that given by Rivera and Cisternas's[1990] method.

The temporal evolution of stress fields in the IberianPeninsula has been locally studied considering the sites where it


Sfcm« trajectoriesFocal mechanism (SHMAX NW-SEJ"Focal mechanism (S^^ NE-SW)

Figure 13. Focal mechanisms obtained using Giner's [1996] method or taken from Ribeiro et al [1996] (starredmechanisms). Fault plane solutions are shown in a lower hemisphere Schmidt projection. SHrmx trajectories havebeen drawn interpolating local stress information deduced from focal mechanism fault planes and using the Lee andAngelier's [1994] program. Shaded mechanisms represent solutions with SHmax located NE-SW. Solid focalmechanisms indicate solutions with SHmsai oriented NW-SE.

R=0.07n=80

B

was possible to find fractures that affect both upper Miocene andPliocene-Quaternary materials. In these cases the fault samplehas been divided into two groups according with the deformationage. The results obtained after applying the stress inversionmethod to these populations show stress tensors that are similarfor both ages (see the two examples in Figure 15). Nevertheless,the NNW-SSE compression in the Tajo Basin-La Mancha Plain

Figure 14. Stereographic plot of mean stress tensors obtainedapplying the stress inversion method [Reches et al,9 1992] to thepopulation of 161 focal mechanisms, (a) Extensional regimeexplaining 80 focal mechanisms, (b) Strike-slip solution thatexplains 58 focal mechanisms.

784DEFORMATION AGE

MIOCENEDEFORMATION AGE

PLIOCENE-QUATERNARY

Axesorientations01 88/349CF2 01/15203 00/242

Confidenceradiusdi 202 4603 46

Axesorientations01 80/20802 03/32003 08/050

Confidenceradius

01 202 1703 17

N=227


Confidenceradius0! 3

02 1503 15

N=374


Confidenceradius

C* 102 1803 18

N=156

Figure 15. Results obtained applying the stress inversion method [Reches et a/., 1992] to faults of the (top)Northwest area and (bottom) Toledo-Sierra Morena area. Results are grouped according to the deformation age.The orientation of the main axes (cr^ <J2, cr3) and the corresponding confidence radius are indicated. N represents thenumber of data. Temporal continuity of the stress orientation can be easily noticed.

DEFORMATION AGEMIOCENE

DEFORMATION AGEPLIOCENE-QUATERNARY

Axesorientations0! 87/12202 01/24403 02/334

Confidenceradius

01 302 18Oa 18


Confidenceradius

01 302 4603 46

N=136

Axesorientations0! 89/30302 00/17203 00/082

N=1218


Confidenceradiusdi 1<J2 7<*3 7

N=275

Figure 16. Results obtained applying the stress inversion method [Reches et a/., 1992] to faults of the (top) TajoBasin-La Mancha Plain area and (bottom) Guadalquivir Basin area. Results are grouped according to thedeformation age. The orientation of the main axes (cj1? a2} 03) and the corresponding confidence radius areindicated. N represents the number of data. The results for the Pliocene-Quaternary data show a better definition ofthe NNW-SSE compression.


and Guadalquivir Basin zones is more defined for the Pliocene-Quaternary period (Figure 16). The last one involves switchingof the a2 and a3 axes, a phenomenon recognized as well in theCantabrian and Pirenean zones. On the other hand,compressional tensors registered in Pliocene-Quaternarydeposits are very scarce. At the same time, in sites wherecompressional and extensional tensors are found together,extensional tensors are usually younger. This suggests a generaltrend from compressional to extensional regime for the wholeIberian Peninsula (except for the Betic Chain) during theMiocene-Quaternary times. Finally, a broader picture referred tothe whole Spanish mainland can be reached comparing thepresent-day SHmaK trajectories displayed in Figure 13 with thosecorresponding to the main S//max trend for the dominant recentstress tensor (Figure 6). In both cases the trajectories have beendrawn following Lee and Angelier's [1994] technique and usinglarge interpolation radii due to the unequal data distribution. Asthese large values tend to smooth the curves, changes in SHmaxorientations can be steeper. In any case, the comparison of bothmaps indicates that the main trends of the stress field in theIberian Peninsula have remained almost invariable at least sincethe upper Miocene.

Summarizing the results, we can conclude that the IberianPeninsula is undergoing a NW-SE compression except for thenortheastern part (Pyrenees, Ebro Basin, and Iberian Chain),where it is mainly N-S to NE-SW, and the Gulf of Cadiz, where

the direction seems to be E-W. Rivera and Cisternas's [1990]method allows us to obtain a dominant stress regime of strike-slip type. Results of Giner's [1996] procedure indicate the sameregime for the intraplate zones of the Iberian Peninsula, whereasit shows the presence of two stress tensors in the areas closest tothe Iberian plate borders: one of compressional character andother of extensional. The recent (since upper Miocene) stresstensor points to a dominant compression oriented 120°N-140°E,similar to the present-day field, together with another stresstensor of 30°N-60°E direction. The predominant type of faults isnormal. When the number of geological sites is sufficient, theorientation of the maximum horizontal compression is welldefined and agrees with that deduced from seismicity data.

Acknowledgments. We are very grateful to the followinginstitutions, which have facilitated data and information: InstituteGeografico Nacional, Institute Andaluz de Geofisica y Prevencion deDesastres Sismicos, Real Instituto y Observatorio de la Armada, InstitutCartografic de Catalunya, Instituto de Meteorologia (Lisbon, Portugal),and Institut de Physique du Globe (Strasbourg, France). We also want toexpress our gratitude to Armando Cisternas and Luis Rivera for theircontinuous advice during the Sigma project. E. Buforn and F. Vidalkindly provided us with information on focal mechanisms. The helpfrom Ramon Vegas, Diego Cordoba, Alfonso Munoz-Martin, NoemiCasero, and Raul Perez has been very efficient at different steps of thework. This research has been supported by the Consejo de SeguridadNuclear and the Empresa Nacional de Residuos Radioactivos S.A.

References

Angelier, J., and P. Mechler, Sur une methodegraphique de recherche des contraintes principalsegalement utilisable en tectonique et sismologie:La methode des diedres droits, Bull. Soc. Geol.Fr., 19(6), 1309-1318, 1977.

Arlegui, L. E., Diaclasas, fallas y campo de esfuerzosen el sector central de la Cuenca del Ebro:Relacion con el campo de esfuerzos neogenos,tesis doctoral, Univ. de Zaragoza, Zaragoza,Spain, 1996.

Benkhelil, J., Etude tectonique de la terminaisonoccidental des Cordilleres Betiques [Espagne],these de doctoral, Univ. de Nice, Nice, France,1976.

Bott, M. H. P., The mechanism of oblique-slipfaulting, Geol. Mag., 96, 109-117, 1959.

Buforn, E., C. Sanz de Galdeano, and A. Udias,Seismotectonics of the Ibero-Maghrebian region,Tectonophysics, 248, 247-261, 1995.

Cabanas, L., R. Undo, and M. Herraiz, MF96: Unprograma interactivo para la determinacion graficade mecanismos focales, Geogaceta, 20(6), 1377-1379, 1996.

Capote, R., G. De Vicente, and J. M. Gonzalez-Casado, An application of the slip model of brittledeformations to focal mechanism analysis in threedifferent plate tectonics situations,Tectonophysics, 191, 399-409, 1991.

Carey, E., Recherche des directions principales decontraintes associees au jeu d'une population defailles, Rev. Geol Dyn. Geogr. Phys., 21, 57-66,1979.

Carey, E., and M. B. Brunier, Analyse theorique etnumerique d'un modele mecanique elementaireapplique a 1'etude d'une population de failles,C.R. Acad. Sci. Ser. D, 279, 891-894, 1974.

Carey-Gailhardis, E., and J. L Mercier, Regional stateof stress, fault kinematics and adjustments ofblocks in a fractural body of rock: Application tothe microseismicity of the Rhine graben, J. Struct,Geol, 14(8/9), 1007-1017, 1992.

Casas, A. M., El frente norte de las Sierras deCameros: Estructuras cabalgantes y campo deesfuerzos, tesis doctoral, Univ. de Zaragoza,Zaragoza, Spain, 1990.

Colomer, M., Estudi geologic de la vora sud-oest de lafosa de Calataiud-Daroca, entre Villafeliche iCalamocha, tesis de licenciatura, Univ. deBarcelona, Barcelona, Spain, 1987.

Cortes, A. L., and A. Maestro, Analisis de los estadosde esfuerzos recientes en la Cuenca de Almazan,Rev. Soc. Geol. Esp., 10(1-2), 183-196, 1997.

Cortes, A. L., and A. Maestro, Recent intraplate stressfield in the eastern Duero Basin (N Spain), TerraNova, 10, 287-294, 1998.

Cortes, A. L., and J. L. Simon, Campos de esfuerzorecientes en la fosa de Alfambra-Teruel-Mira, inAportaciones al Conocimiento del TerciarioIberico, edited by J.P. Calvo and J. Morales,pp.65-68, Univ. Complutense de Madrid andMuseo Nacional de Ciencias Naturales, Madrid,1997.

Delouis, B., H. Haessler, A. Cisternas, and L. Rivera,Stress tensor determination in France andneighbouring regions, Tectonophysics, 221, 413-417, 1993.

De Ruig, D., Tectono-sedimentary evolution of thePrebetic fold belt of Alicante (SE Spain), Ph.Dthesis, Vrije Univ., Amsterdam, 1992.

De Vicente, G., Analisis Poblacional de Fallas: Elsector de enlace Sistema Central-CordilleraIberica, tesis doctoral, Univ. Complutense deMadrid, Madrid, 1988.

De Vicente, G., J. L. Giner, A. Munoz-Martin, J. M.Gonzalez-Casado, and R. Lindo, Determination ofpresent-day stress tensor and neotectonic intervalin the Spanish Central System and Madrid Basin,central Spain, Tectonophysics, 266, 405-424,1996.

Dorbath, L., C. Dorbath, E. Jimenez, and L. Rivera,Seismicity and tectonic deformation in the easterncordillera and the sub-Andean zone of the centralPeru, J. S. A. Earth Sci., 4, 13-24, 1991.

Fuenzalida, H., L. Dorbath, A. Cisternas, H.Eyidogan, A. Barka, L. Rivera, H. Haessler, H.Philip, and N. Lyberis, Mechanism of the 1992Erzincan earthquake and its aftershocks, tectonicsof the Erzincan Basin and decoupling on the NorthAnatolian Fault, Geophys. J. Int., 129, 1-28, 1996.

Galindo-Zaldivar, J., F. Gonzalez-Lodeiro, and A.Jabaloy, Stress and palaeostress in the Betic-Rifcordilleras (Miocene to the present),Tectonophysics, 227, 105-126, 1993.

Galindo-Zaldivar, J., A. Jabaloy, I. Serrano, J.Morales, F. Gonzalez-Lodeiro, and F. Torcal,Recent and present-day stresses in the GranadaBasin (Betic Cordilleras): Example of a lateMiocene-present-day extensional basin in aconvergent plate boundary, Tectonics, 18, 686-702, 1999.

Giner, J. L., Analisis Neotectonico y Sismotectonicoen el Sector Centro-Oriental de la Cuenca delTajo, tesis doctoral, Univ. Complutense deMadrid, Madrid, 1996.

Goula, X., L. Talaya, A. Termens, I. Colomina, J.Fleta, B. Grellet, and T. Granier, Evaluacio de lapotencialitat sismica del Pirineu Oriental, Terra,28(11), 41-58, 1996.

Goula, X., C. Olivera, J. Fleta, B. Grellet, R. Lindo,L.A. Rivera, A. Cisternas, and D. Carbon, Presentand recent stress regime in the eastern part of thePyrenees, Tectonophysics, 308, 487-502, 1999.

Gregersen, S., Crustal stress regime in Fennoscandiafrom focal mechanisms, J, Geophys. Res., 97,11,821-11,827, 1992.

Grellet, B., P. Combes, T. Granier and H. Philip,Sismotectonique de la France Metropolitaine,Mem. Soc. Geol. Fr., vol.1, 76 pp., Mem. de laSoc. Geol.de Fr., Paris, 1993a.

Grellet, B., P. Combes, T. Granier and H. Philip,Sismotectonique de la France Metropolitaine,Mem. Soc. Geol. Fr., vol.2, 24 maps, Mem. de laSoc. Geol.de Fr., Paris, 1993b.

Grunthal, G., and D. Stromeyer, The recent stressfield in central Europe: Trajectories and finite


element modeling, J. Geophys. Res., 97, 11,805-11,820, 1992.

Herraiz, M., G. De Vicente, R. Lindo, and J, G.Sanchez- Cabanero, Seismotectonics of the SierraAlbarrana area (southern Spain): Constraints for aregional model of the Sierra Morena-GuadalquivirBasin limit, Tectonophysics, 266, 425-442, 1996.

Herraiz, M. et al, Proyecto Sigma: Analisis del Estadode Esfuerzos Tectonicos, Reciente y Actual en laPeninsula Iberica, 240 pp., 2 maps, Cons, deSeguridadNucl, Madrid, 1998.

Huibregtse, P.W., J. M. Van Alebeek, M. E. A. Zaal,and C. Biermann, Paleostress analysis of theNorthern Nijar and Southern Vera basins:Constraints for the Neogene displacement historyof mayor strike-slip faults in the Betic Cordilleras,SE Spain, Tectonophysics, 300, 79-101, 1998.

Institute Geografico Nacional (IGN), AnalisisSismotectonico de la Peninsula Iberica, Baleares yCanarias, Pub. Tec. 26, Madrid, 1992.

Jackson, J. A., and D. P. McKenzie, The relationshipbetween plate motions and seismic momenttensor, and the rate of active deformation in theMediterranean and Middle East, Geophys. J., 93,45-73, 1988.

Julivert, M., J. M. Fontbote, A. Ribeiro, and L. E.Nabais Conde, Mapa Tectonico de la PeninsulaIberica y Baleares, map, scale 1:1,000,000, Inst.Geol. Miner. Esp., Madrid, 1972.

Klein, A., Hypocenter location programHYPOINVERSE; part I; Users guide to versions1,2,3, and 4, U.S. Geol. Surv., Open File Rep., 78-694, pp. 65, 1978.

Lee, J. C., and J. Angelier, Paleostress trajectory mapsbased on the results of local determinations: The"lissage" program, Comput. Geosci. 20(2), 161-191, 1994.

Lindo, R., Sismotectonique des Andes du PerouCentral: Apport des donnees sismologiques dehaute precision, these de doctoral, Univ. Louis-Pasteur, Strasbourg, France, 1993.

Maestro, A., Las deformaciones alpinas en la Cuencade Almazan (provincias de Soria y Zaragoza),tesis de licenciatura, Univ. de Zaragoza, Zaragoza,Spain, 1994.

Massana, E., L'activitat neotectonica a les CadenesCostaneras Catalanes, tesis doctoral, Univ. deBarcelona, Barcelona, Spain, 1995.

Mercier, J. L., and E. Carey-Gailhardis, Regional stateof stress and characteristic fault kinematicsinstabilities shown by aftershock sequences of the1978 Thessaloniki (Greece) and 1980 Campania-Lucania earthquakes as examples, Earth. Planet.Sci. Lett., 92, 247-264, 1989.

Mezcua, J., and J. Rueda, Location of earthquakes

under Iberia: Consequences of the ILIHA-DSSAdata, Monogr. 10, pp. 251-262, Inst. Geogr. Nac.,Madrid, 1993.

Mezcua, J., M. Herraiz, and E. Buforn, Study of the 6June 1977 Lorca (Spain) earthquake and itsaftershock sequence, Bull. Seismol. Soc. Am., 74,167-180, 1984.

Mttller, B., M. L. Zoback, K. Fuchs, L. Mastin, S.Gregersen, N. Pavoni, O. Stephansson, and C.Ljunggren, Regional patterns of tectonic stress inEurope, J. Geophys. Res., 97, 11,783-11,803,1992.

Miiller, B., V. Wehrle, H. Zeyen, and K. Fuchs, Short-scale variations of tectonic regimes in the westernEuropean stress province north of the Alps andPyrenees, Tectonophysics, 275, 199-219, 1997.

Olivera, C., T. Susagna, A. Roca, and X. Goula,Seismicity of the Valencia Trough andsurrounding areas, Tectonophysics, 203, 99-109,1992.

Paricio, J., and J. L. Simon, Aportaciones alconocimiento de la compresion tardia en laCordillera Iberica Centro-Oriental: La cuencaneogena inferior del Mijares (Teruel-Castellon),Estud. Geol., 42, 302-319, 1986.

Philip, H., J. C. Bousquet, J. Escuer, J. Fleta, X.Goula, and B. Grellet, Presence de failles inversesd'age quaternaire dans 1'Est des Pyrenees:Implications sismotectoniques, C. R. Acad. Sci.Ser. II, 314, 1239-1245, 1991.

RebaT, S., H. Philip, and A. Taboada, Modern tectonicstress field in the Mediterranean region: Evidencefor variation in stress directions at different scales,Geophys. J. Int., 110, 106-140, 1992.

Reches, Z., Faulting of rocks in three-dimensionalstrain fields, II, Theoretical analysis,Tectonophysics, 95, 133-156, 1983.

Reches, Z., Determination of the tectonic stress tensorfrom slip along faults that obey the Coulomb yieldcondition, Tectonics, 6, 849-861, 1987.

Reches, Z., G. Baer, and Y. Hatzor, Constraints on thestrength of the upper crust from stress inversion offault slip data, J. Geophys. Res., 97, 12,481-12,493, 1992.

Ribeiro, A., J. Cabral, R. Baptista, and L. Matias,Stress pattern in Portugal mainland and theadjacent Atlantic region, West Iberia, Tectonics,15, 641-659, 1996.

Rivera, L. A., and A. Cisternas, Stress tensor and faultplane solutions for a population of earthquakes,Bull. Seismol. Soc. Am., 80, 600-614, 1990.

Sanz de Galdeano, C., La fracturacion del borde surde la Depresion de Granada (discusion acerca delescenario del terremoto del 25-XII-1884), Estud.Geol, 41, 59-68, 1985.

Simon, J. L., Late Cenozoic stress field and fracturingin the Iberian Chain and Ebro Basin (Spain), J.Struct. Geol, 11(3), 285-294, 1989.

Simon, J. L., and A. Soriano, La falla de Concud(Teruel): Actividad cuatemaria y regimen deesfuerzos asociado, in El Cuaternario en Espana,Vol. U, edited by T. Aleixandre and A. Perez, pp.,729-737, Inst. Geol. Miner. Esp., Madrid, 1993.

Stapel, G., R. Moeys, and C. Biermann, Neogeneevolution of the Storbas Basin (SE Spain)determined by paleostress analysis,Tectonophysics, 255, 291-305, 1996.

Stuart, A., The Ideas of Sampling, Charles Griffin,London, 1984

Udias, A., and E. Buforn, Regional stresses along theEurasia-Africa plate boundary derived from focalmechanisms of large earthquakes, in SourceMechanism and Seismotectonics, edited by A.Udias and E. Buforn, pp. 433-448, BirkhauserBoston, Cambridge, Mass., 1991.

Vidal, F., Sismotectonica de la region de las Beticas-Mar de Alboran, tesis doctoral, Univ. de Granada,Granada, Spain, 1986.

Zoback, M. L., First- and second-order patterns ofstress in the lithosphere: The World Stress Mapproject, J. Geophys. Res., 97, 11,703-11,728,1992.

L. Cabanas, J. I. Cicuendez, M. Herraiz, R. Lindo-Naupari, and O. Vadillo, Dpto. de Geofisica yMeteorologia, F. CC. Fisicas, UniversidadComplutense de Madrid, 28040 Madrid, Spain.(mherraiz@eucmax. sim. ucm.es)

G. de Vicente, P. Rincon, and M. A. Rodriguez-Pascua, Dpto. de Geodinamica, F. CC. Geologicas,Universidad Complutense de Madrid, 28040 Madrid,Spain, ([email protected])

J. Giner and J. M. Gonzalez-Casado, Dpto. deQuimica Agricola, Geologia y Geoquimica,Universidad Autonoma de Madrid, 28049 Madrid,Spain, ([email protected])

A. Casas, A. L Cortes, and J. L. Simon, Dpto. deGeologia, Universidad de Zaragoza, Plaza de SanFrancisco s/n, 50009 Zaragoza, Spain.(acortes@posta. unizar. es)

M. Ramirez, Consejo de Seguridad Nuclear,c/Justo Dorado, 11, 28040 Madrid, Spain.

M. Lucini, Empresa Nacional de ResiduesRadiactivos, S.A., c/Emilio Vargas, 7, 28043 Madrid,Spain.

(Received July 23, 1999;revised January 5, 2000;accepted January 11, 2000.)

The recent (upper Miocene to Quaternary) and present tectonic stress distributions in the Iberian...

Documents

Transcript of The recent (upper Miocene to Quaternary) and present tectonic stress distributions in the Iberian...