HR: 13:55h
AN: S22C-02    [PDF]
TI: Earthquake Focal Depths and Crustal Structure of Northern India: Implications for Crustal Rheology
AU: * Priestley, K
EM: keith@esc.cam.ac.uk
AF: Bullard Laboratories, Madingley Rise, Madingley Road, Cambridge, CB30EZ United Kingdom
AU: Mitra, S
EM: mitra@esc.cam.ac.uk
AF: Bullard Laboratories, Madingley Rise, Madingley Road, Cambridge, CB30EZ United Kingdom
AU: Jackson, J
EM: jackson@esc.cam.ac.uk
AF: Bullard Laboratories, Madingley Rise, Madingley Road, Cambridge, CB30EZ United Kingdom
AU: Rai, S S
EM: ssrai_ngri@rediffmal.com
AF: NGRI, Uppal Road, Hyderabad, 500 007 India
AU: Gaur, V K
EM: gaur@cmmacs.ernet.in
AF: CMMACS, NAL Belur Campus, Bangalore, 560 037 India
AB: Most intraplate continental earthquakes occur in the upper $\sim$15 km of the crust but occasionally earthquakes occur at deeper levels beneath the continents in some regions. This observation coupled with laboratory measurements of rock properties as a function of temperature and pressure, led to a model for the continental crust consisting of a brittle upper layer and a weak lower layer, overlying a brittle uppermost mantle. Key observations leading to this model came from earthquake foci and crustal structure in northern India. We re-examine these observations. We use receiver function and published refraction/reflection results to determine the variation in crustal structure of India. We find that the crust beneath the south Indian shield is relatively uniform with a thickness of $\sim 36 \pm 2$ km, but the north Indian crust thickens to about $\sim$50 km as a result of the down-bending of the Indian plate as it thrust beneath the Himalaya and southern Tibet. The Moho of the Indian crust beneath southern Tibet is at $\sim$85 km depth. We redetermine focal depths for earthquakes in northern India using this crustal model. For recent events we determine focal depths using waveform modelling or from the timing of depth phases on broadband waveforms. We correct the foci of published event hypocenters using our crustal velocity model. Earthquakes occur to $\sim$35 km depth in central India, $\sim$50 km depth beneath the Himalaya, and $\sim$80 km depth below southern Tibet. All major earthquakes across northern India and southern Tibet occur in the crust and there is no evidence for significant sub-Moho seismicity beneath northern India and southern Tibet.
DE: 1236 Rheology of the lithosphere and mantle (8160)
DE: 5120 Plasticity, diffusion, and creep
DE: 7218 Lithosphere and upper mantle
DE: 8164 Stresses--crust and lithosphere
SC: Seismology [S]
MN: 2003 Fall Meeting