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Assessment of tectonic activity in a seismically locked segment ofHimachal HimalayaMoulishree Joshi a; Girish Ch. Kothyari a

a Department of Geology, Durham House, Kumaun University, Nainital, Uttaranchal, India

Online publication date: 23 February 2010

To cite this Article Joshi, Moulishree and Kothyari, Girish Ch.(2010) 'Assessment of tectonic activity in a seismicallylocked segment of Himachal Himalaya', International Journal of Remote Sensing, 31: 3, 681 — 689To link to this Article: DOI: 10.1080/01431160902894509URL: http://dx.doi.org/10.1080/01431160902894509

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Assessment of tectonic activity in a seismically locked segmentof Himachal Himalaya

MOULISHREE JOSHI* and GIRISH CH. KOTHYARI

Department of Geology, Durham House, Kumaun University,

Nainital-263002, Uttaranchal, India

(Recieved 4 November 2008; in final form 4 December 2008)

Bilaspur (31� 230 5860 0 N; 76� 450 17800 E) lies in the south-west Himachal close to

the Main Boundary Thrust (MBT). Neotectonic studies carried out in this region

have revealed that the area is traversed by several faults, many of which may be

active. GPS studies carried out in the entire Himalayan region indicate crustal

shortening leading to strain accumulation. This is manifest in enhanced tectonic

activity in the form of major and minor earthquakes. However, there are certain

areas where stress release has not been witnessed and these areas can fail in large

magnitude earthquakes in the future. Bilaspur lies in the zone of strain accumula-

tion. This zone is building up a slip deficit at the rate of 14 � 1 mm year-1. In the

light of these revelations and the fact that Bilaspur houses one of the biggest water

reservoirs of the country an attempt has been made to assess the implications of

these observations.

1. Introduction

Progressive northward movement of the Indian plate and its collision with the

Eurasian plate has led to the formation of various geological structures and recent

seismicity (Molnar and Tapponier 1975, Bilham and Gaur 2000, Bilham 2004). The

convergence is accommodated by active thrusts and faults and is expressed in asso-ciated geomorphic features. After the collision of the Indian and the Tibetan land-

masses resulting in the development of the Himalaya, tectonic activity has been

witnessed in the form of intracontinental deformation along major faults and thrusts

(Nakata 1986, Nakata et al. 1990, Valdiya 1986, 2001). This activity is evident from

geomorphic features such as triangular facets, waterfalls, terraces and landslides, and

also from the continuous uplift of the Himalayan terrain which is being recorded even

today (Bilham et al. 1997, Bilham 2001, Bilham et al. 2001). The formation of paired

or unpaired terraces and their uplifted nature are considered to be evidence ofneotectonism (Nakata 1972, 1975, Valdiya 1981, 1986, Valdiya et al. 1984, Merritts

and Vincent 1989, Bhargava 1990, Sah 1991, 1994). Geomorphic features such as

triangular facets and cones, fault breccias, deep gorges, meandering rivers and offset

Quaternary sediments are very important indicators of neotectonic activity in a region

(Winter and Lavenu 1989, Briais et al. 1990, Sah 1994).

GPS studies carried out in the north-western Himalayan region reveal that crustal

shortening has been taking place about 100 km north of the Siwalik foothills and the

Main Frontal Thrust (MFT) (Powers et al. 1998, Wesnousky et al. 1999, Kumar et al.

*Corresponding author. Email: moulishreej@yahoo.com

International Journal of Remote SensingISSN 0143-1161 print/ISSN 1366-5901 online # 2010 Taylor & Francis

http://www.tandf.co.uk/journalsDOI: 10.1080/01431160902894509

International Journal of Remote Sensing

Vol. 31, No. 3, 10 February 2010, 681–689

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2001). This zone is estimated to build up slip deficit at the rate of 14� 1mm year-1 and

can fail in a high magnitude earthquake (Banerjee and Burgmann 2002). There is little

deformation across the Siwalik foothills and the surface trace of the MFT, which

shows that the faults that apparently accommodate most of the Quaternary

Himalayan shortening did not slip appreciably during the observation period(Powers et al. 1998, Larson et al. 1999, Lave and Avouac 2000).

2. Geological setting

Bilaspur in Himachal Pradesh is a part of the Proterozoic-Tertiary sequence in the

Lesser Himalayan zone. The oldest exposed Proterozoic sediments exposed in

Bilaspur are whitish grey, cherty dolomitic limestone. The Tertiary sediments rest

unconformably on the Pre-Tertiaries. Rocks of Subathu Formation are exposed

between Palampur Thrust and the Main Boundary Thrust (MBT). This formation

is made up of orthoquartzite, carbonaceous shale and fossiliferrous limestone. Rocksof the Dharamsala Group overlie the Subathus (Das et al. 2001). The Siwalik Group

has a gradational contact with the underlying Dharamsala Formation and is made up

of a thick succession of terriginous clastic deposits consisting of sandstone and

claystone with minor siltstone. Towards the upper part, conglomeratic bands are

very conspicuous (Das et al. 2001).

Bilaspur lies in the vicinity of the MBT and related thrusts (figure 1). The region is

drained by the Satluj, which is the third most important river in India next to the Indus

and Brahmaputra, as it cuts through the entire Himalaya terrain. The entireHimalayan foothills have been divided into three tectonic units, (a) outer tectonic

belt, (b) median tectonic belt and (c) inner tectonic belt. Bilaspur falls within the inner

tectonic belt. The main structural elements of the inner tectonic belt are Gambhar,

Jwalamukhi, Barsar back thrust, Galma and Bilaspur thrusts formed during the Late

Miocene (Das et al. 2001) (figure 1(b)). A Google Earth image of Bilaspur showing the

position of various faults in the region is given in figure 2.

This paper presents the tectonic turmoil of the region by studying the impact of

active tectonics over the landscape with the help of a digital elevation model andgeomorphic field evidence.

3. Methodology

In order to carry out the present investigation, a digital elevation model was prepared

with the help of a toposheet (1:50 000 scale). The data were generated using Surfer 8

software. Satellite imagery was downloaded from Google Earth to get an overview of

the area. Intensive fieldwork was carried out to identify and delineate the tectonic

features which were identified with the help of the satellite data and the DEM.

4. Tectonics

Neotectonic investigations were carried out in Bilaspur along river Satluj and its tribu-

tary Ali Khad. Geomorphic features observed in the area which point at tectonic

rejuvenation include unpaired terraces, offsetting of the Quaternary sequence, triangular

facets, shifting of the river channel by more than 100 m, fault breccia and presence of

gorges and springs (figure 3). Drainage anomalies such as beheaded streams, abandoned

channels, knickpoints in the longitudinal profiles, high values of morphometric para-

meters such as Gradient Index (GI) and Topographic Sinuosity Index (TSI) all point

682 M. Joshi and G. Ch. Kothyari

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Figure 2. Satellite image of the study area, showing the location of faults.

(a)

(b)

Figure 1. (a) Location and (b) tectonic maps of Bilaspur (after Das et al. 2001).

Tectonic activity in Himachal Himalaya 683

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towards the active tectonics of the region (Joshi et al. 2007). Springs and landslide cones

were observed in the vicinity of the faults. The detailed morphotectonic analyses of

Bilaspur and adjacent area have established the existence of a ,10 km long, NNW–SSE

trending Ali Khad fault (Joshi et al. 2007). Moreover, there are other faults such as the

Hirambadevi fault and other NW–SE and NNW–SSE trending faults that have dis-

sected the region which have led to anomalous drainage patterns (figure 2). River Satluj

has shifted by 100 m towards the north-east due to the tectonic movement in the area.

This is evident from the presence of abandoned channel deposits in the area (figure 3).

5. Discussion

Bilaspur assumes geological importance owing to its proximity to the MBT and

several other related thrusts. In the entire NW Himalayan region GPS studies have

revealed that the zone of crustal shortening roughly coincides with the belt of activemicroseismicity (Banerjee and Burgmann 2002).

Figure 4 is a fault and seismicity map of the study area (shown within the rectangle),

taken from Banerjee and Burgmann (2002). It is evident from the figure that there

have been very few earthquakes in the study area compared to the adjoining area,

where stress has been released in the form of minor earthquakes from time to time.

Bilaspur lies in the zone of maximum crustal shortening in SW Himachal Himalaya.

However, in the Bilaspur region, no major earthquakes have been reported in the recent

Figure 3. Digital elevation model of Bilaspur, showing the tectonically evolved terrain.

684 M. Joshi and G. Ch. Kothyari

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past and very few minor earthquakes have been reported from the region (figure 4).

Nevertheless, the area provides ample evidences of active tectonics. The area is dissected

by several faults and thrusts as discussed above. It seems that the stresses generated bycrustal shortening are being accommodated by these faults and thrusts.

The Himalayan region is undergoing continuous crustal adjustments due to the

convergence of the Indian and the Eurasian plate. This is evident from a variety of

geological and geomorphological features that suggest morphotectonic evolution.

GPS studies carried out by Banerjee and Burgmann (2002) suggest that the study

area lies in the zone of accumulating stresses which are likely to be released in the form

of major seismic activity.

Figure 4. Fault and seismicity map of the study area with observed (solid black arrows tippedwith 95% confidence ellipses) and modelled (white open arrows) GPS site velocities relative tostation WIH 2 (indicated by the white square) in Dehradun. Earthquakes of M . 4 from 1970to 2001 (from CNSS catalogue) are shown in small circles. KR: Kangra Reentrant; NH: NahanSalient; DDR: Dehradun Reentrant; KF: Karakoram Fault; MBT: Main Boundary Thrust;MFT: Main Frontal Thrust. Reproduced from Banerjee and Burgmann (2002). Shaded rec-tangle is the area of present study.

Tectonic activity in Himachal Himalaya 685

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Figure 5 shows earthquake magnitude distribution in the Himalayan region. Blackdots represent the microseismic activity reported from the Himalayan region. The

area of present investigation lies within the square. As can be seen in the figure,

Bilaspur has no record of microseismic activity. However the region seems to be

accumulating stresses, as the area shown in various shades of red is likely to experience

an earthquake of magnitude .6 according to the data (data source: Paul et al. 2004).

The presence of faults such as the Ali Khad fault throws light on the tectonic

turmoil of the region. It seems likely that such faults are accumulating the stresses that

are being generated in the region. Such faults and thrust can eventually fail in futurelarge earthquakes and we should expect major tectonic activity in this segment of

MBT in future.

In order to prevent a seismic catastrophe, observations for detecting earthquake

precursory phenomena should start in the region. Electrotelluric stations could be

installed in order to detect precursory electrical variations. Transient variations in the

Earth’s electric field, called seismic electric signals (SES), are detectable before the

occurrence of an earthquake (Varotsos and Alexopoulos 1984a, Varotsos and

Lazaridou 1991, Varotsos et al. 2003, Varotsos et al. 2005). These signals are gener-ated due to aliovalent impurities existing in the rocks (Varotsos et al. 1982). The

electric field measurements are carried out by means of electric dipoles (Varotsos and

Alexopoulos 1980a, 1981). When the stress increases before an earthquake, the

relaxation time of these dipoles may gradually decrease (Varotsos and Alexopoulos

1980b), giving rise to the emission of a precursory signal. The time lag between SES

Figure 5. Hyposeismal contour map showing intensity of earthquake magnitude. Datasource: Paul et al. (2004).

686 M. Joshi and G. Ch. Kothyari

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and earthquakes varies from half a minute to several hours (Varotsos and

Alexopoulos 1987). Areas which have been quiescent for a long time produce SES

with a time lag of the order of a few days or more (Varotsos and Lazaridou 1991).

Several earthquake predictions based on SES have been made using accurate

interpretations of SES in Greece (Varotsos and Alexopoulos 1984a, 1984b,Varotsos et al. 1986, Varotsos and Alexopoulos 1987, Varotsos et al. 1988).

Continuous monitoring of the electrotelluric field can be carried out using an array

of measuring stations at various sites in the study area in order to predict the epicentre

and magnitude of an impending earthquake.

Acknowledgements

Financial assistance provided by CSIR, Delhi in the form of Research Associateship

(No. 9/428 (57) 2004-EMR-I) to the first author is gratefully acknowledged. Head,

Department of Geology, Kumaun University, Nainital is acknowledged for providing

necessary facilities.

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