Imaging the Alpine Mantle Transition Zone using Receiver Functions

Imaging the Alpine Mantle Transition Zone

using Receiver Functions

Lombardi D.1, Braunmiller J.2, Kissling E.1 and Giardini D.1

EGU 2008 Vienna 15.04.2008

1: 2: [email protected]

EUROPEAN CONTINENT

ADRIATIC BLOCK

N

S

A L P S

BEST STUDIED OROGEN !

European lower-crust Adriatic lower-crust

(Schmid et al. 2004)

CR

US

T

N

S N S

Dipping Moho

Lower-crust indentation


Subduction of lithospheres


UP

PE

RM

OS

T M

AN

TLE

CR

US

T

N

S N S

Dipping Moho

Lower-crust indentation


UP

PE

RM

OS

T M

AN

TLE



Dipping Moho

Lower-crust indentation CR

US

T M

AN

TLE

TR

AN

SIT

ION

ZON

E (M

TZ)

Bijwaard and Spakman 2000

Velocity anomaly within the MTZ

N

S N S

Remnants of the Alpine Tethys Ocean

ADRIATIC BLOCK


N S U

PP

ER

MO

ST

MA

NTL

E



Dipping Moho

Lower-crust indentation CR

US

T M

AN

TLE

TR

AN

SIT

ION

ZON

E (M

TZ)


Velocity anomaly within the MTZ

Remnants from Alpine Tethys Ocean

Do Receiver Functions image

the remnants of Alpine Tethys ?

NETWORK

DATA

RECEIVER

FUNCTIONS

MTZ

CONCLUSIONS

STATION NETWORK

DATA

RECEIVER FUNCTION IMAGING

MANTLE TRANSITION ZONE

CONCLUSIONS

OUTLINE

STATION NETWORK

ACCESSIBILITY: . SED database . AutoDRM1/NetDC2 . web interface3

STATION NETWORK:

. 14 Networks (for 7 countries)

. 87 BB + 5 SP

1: http://www.seismo.ethz.ch/autodrm 2: http://www.iris.edu/manuals/netdc 3: http://www.dipteris.unige.it/geofisica

NETWORK

DATA

RECEIVER

FUNCTIONS

MTZ

CONCLUSIONS

DATA

NETWORK

DATA

RECEIVER

FUNCTIONS

MTZ

CONCLUSIONS

. Epicentral distance D  = 30° - 100°

. Magnitude Mmax > 6.0

(Mmax > 5.5 for back-az.=90°-270° (i.e. South))

DATASET COMPOSED OF STRONG TELESEISMIC EARTHQUAKES:

DATA

. Time period

1999-2007

complete 8 years for 25 stations

. Receiver function dataset ~ 6500 useful RF for 92 stations (~ 60 RF/station)

DATASET COMPOSED OF STRONG TELESEISMIC EARTHQUAKES:

NETWORK

DATA

RECEIVER

FUNCTIONS

MTZ

CONCLUSIONS

0 10 20 30 TIME (sec)

PsMoho multiplesMoho


(P-to-S) Receiver Function: time series for which P-to-S conversions are enhanced by deconvolution of vertical from radial seismograms

NETWORK

DATA

RECEIVER

FUNCTIONS

MTZ

CONCLUSIONS

0 10 20 30 TIME (sec)

station surface Moho

depth

PsMoho multiplesMoho NETWORK

DATA

RECEIVER

FUNCTIONS

MTZ

CONCLUSIONS


0 10 20 30 40 50 60 70 TIME (sec)

PsMoho P410s P660s multiplesMoho NETWORK

DATA

RECEIVER

FUNCTIONS

MTZ

CONCLUSIONS


0 10 20 30 40 50 60 70 TIME (sec)

surface Moho

410 km

660 km

depth

station

PsMoho P410s P660s multiplesMoho

P410s

P660s P-wave leg S-wave leg

NETWORK

DATA

RECEIVER

FUNCTIONS

MTZ

CONCLUSIONS


surface Moho

410 km

660 km

depth

0 10 20 30 40 50 60 70 TIME (sec)

station


DATA

RECEIVER

FUNCTIONS

MTZ

CONCLUSIONS


surface Moho

410 km

660 km

depth

station

0 10 20 30 40 50 60 70 TIME (sec)

station B


DATA

RECEIVER

FUNCTIONS

MTZ

CONCLUSIONS


surface Moho

410 km

660 km

depth

station

0 10 20 30 40 50 60 70 TIME (sec)

station B

PsMoho P410s P660s multiplesMoho

amplitude stacking

amplitude stacking

NETWORK

DATA

RECEIVER

FUNCTIONS

MTZ

CONCLUSIONS


station

410

660

NETWORK

DATA

RECEIVER

FUNCTIONS

MTZ

CONCLUSIONS


station

410

660

. dense sampling covering the entire chain at 410 km and 660 km

NETWORK

DATA

RECEIVER

FUNCTIONS

MTZ

CONCLUSIONS



IN THE ALPS

NETWORK

DATA

RECEIVER

FUNCTIONS

MTZ

CONCLUSIONS

CROSS-SECTIONS

NETWORK

DATA

RECEIVER

FUNCTIONS

MTZ

CONCLUSIONS

CROSS-SECTIONS

Cell dimension: 10x10x5 km Velocity model: IASP91

~140 km for P410s ~180 km for P660s

Fresnel 1st radius:

NETWORK

DATA

RECEIVER

FUNCTIONS

MTZ

CONCLUSIONS

WEST Rhine Graben Molasse EAST

MOHO

MOHO MULTIPLES

East-West profile in the Alpine Foreland

. Significant amplitude at ‘410’ and ‘660’

. No particular topography

CROSS-SECTIONS

NETWORK

DATA

RECEIVER

FUNCTIONS

MTZ

CONCLUSIONS

North-South profile across the Central Alps

NORTH Swabian Jura Central Alps North. Apennines SOUTH

MOHO

MOHO MULTIPLES

CROSS-SECTIONS


NETWORK

DATA

RECEIVER

FUNCTIONS

MTZ

CONCLUSIONS


MOHO

MOHO MULTIPLES


. ~40 km depression of the ‘660’ over 300 km


CROSS-SECTIONS

NETWORK

DATA

RECEIVER

FUNCTIONS

MTZ

CONCLUSIONS

man

tlepl

umes

.org

MOHO

MOHO MULTIPLES


. ~40 km depression of the ‘660’ over 300 km

CROSS-SECTIONS



NETWORK

DATA

RECEIVER

FUNCTIONS

MTZ

CONCLUSIONS


thicker MTZ

‘normal’ MTZ

thinner MTZ

. SW-NE 1000 km long anomaly

. ~ 40 km thicker min. ~ 400° C colder MTZ

NETWORK

DATA

RECEIVER

FUNCTIONS

MTZ

CONCLUSIONS


Spakman and Wortel 2004

? A

MAP VIEW

-1.5%

1.5%

NETWORK

DATA

RECEIVER

FUNCTIONS

MTZ

CONCLUSIONS



MOHO

MOHO MULTIPLES

Alpine Tethys remnant

X-SECTION

51 49 47 45 43


51 48.5 46 43.5

Piromallo and Morelli 2003

NETWORK

DATA

RECEIVER

FUNCTIONS

MTZ

CONCLUSIONS

80 Ma after Piromallo and Faccenna 2004


MOHO

MOHO MULTIPLES

Alpine Tethys remnant

X-SECTION


30 Ma

Present

NETWORK

DATA

RECEIVER

FUNCTIONS

MTZ

CONCLUSIONS

CONCLUSIONS

RF do detect 410- & 660-km discontinuities . large and high-quality dataset

410- & 660-km discontinuities

. continuous features

. significant amplitude

Mantle Transition Zone . normal MTZ in the Alpine forelands

. anomalously ~40 km thicker (400°C colder) MTZ south of the Alps and Western Alps

. evidence for the presence of the Alpine Tethys ocean stalling at 660 km

MOHO

MOHO MULTIPLES

PsMoho P410s P660s

OUTLOOK:

Connection to the South (Ligur.+Apenn.) and to the East (previous talk by W. Geissler)

Absolute depth (3D velocity model)

Properties of the 410 and 660-km discontinuities (waveform amplitude)

ACKNOWLEDGMENTS:

GEOSCOPE, GIS-RAP, GRSN, IGCAS, INGV, LGIT-Observatoire de Grenoble, LRGB Freiburg, MedNet, Rosalp, RSNI, SNRS, SDS-Net, TGRS and ZAMG

CONCLUSIONS

Imaging the Alpine Mantle Transition Zone using Receiver Functions

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