IASPEI - Picture Gallery

IUGG XXIV General Assembly July 2-13, 2007 Perugia, Italy
(S) - IASPEI - International Association of Seismology and Physics of the Earth's
Interior
JSS014 Oral Presentation 2270
Significant lateral crustal elasticity contrast across the East Kunlun Fault in
northern Tibet, inferred from co-seismic INSAR measurements of the 2001
MW 7.8 Kokoxili earthquake
Dr. Wei Tao
Institute of Geology China Earthquake Administrat IASPEI
Zhengkang Shen, Yongge Wan, Xinjian Shan, Chao Ma
We use co-seismic deformation data of the 2001 Mw 7.8 Kokoxili earthquake obtained from InSAR
measurements to study crustal elasticity contrast across the East Kunlun fault. Co-seismic deformation
field of the earthquake documented by InSAR studies indicated that the displacements on the south side
were 20-30% higher than that on the north side of the fault. We develop an elastic finite element model
and invert InSAR data from two deformation profiles to estimate two parameters: the Youngs modulus
contrast across the fault and the fault rupture depth. The starting lithospheric structural model is
adopted from a seismic reflection study on the north side of the East Kunlun fault. Our result places
optimal estimates of the earthquake rupture depth as 20-22 km and the crustal Youngs modulus
contrast between the south and north side as 81-92%. Such a result, obtained from study of crustal
deformation, suggests a softer crust south than north of the fault, which is consistent with previous
tomographic and magnetotelluric studies of a low-velocity and high-conductivity layer existed in lower
crust of the Kokoxili-qiangtang block south of the Kunlun Fault. The cause of the contrast must be
related to the uplift and evolution process of the plateau. The rising of the Kunlun mountains may have
been resulted from the southward thrusting of the material in the Qaidam basin, producing relatively
cold and strong mountain roots. On the other hand, south of the East Kunlun fault, the northeastward
indentation of the India plate into Tibet has led to crustal thickening for the Kokoxili-Qiangtang block up
to ~70 km, resulting in temperature increase in the crust and development of the slow-velocity and
high-conductivity layers in the lithosphere. All of these should have reduced the strength of the crust on
the south side of the fault, and led to the results we presented above.
Keywords: coseismic deformation, elasticity contrast, tibet