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IUGG XXIV General Assembly July 2-13, 2007 Perugia, Italy (S) - IASPEI - International Association of Seismology and Physics of the Earth's Interior JSS015 Oral Presentation 2335 Project INDEPTH and the Deep Structure of the Tibetan Plateau Prof. Larry Brown Institute for the Study of the Continents Cornell University IASPEI Wenjin Zhao Project INDEPTH is a multinational, multidisciplinary initiative that has now collected an extensive suite of geophysical data extending from the high Himalayas to the central portion of the Tibetan plateau. INDEPTH I detailed the geometry of the Main Himalayan detachment beneath which Indian continental crust is subducting beneath the deforming leading edge of Asia, providing an important new constraint on the amount of plate convergence that could be attributed to crustal shortening in the Himalaya. INDEPTH II seismic and magnetotelluric indications of partial melt in southern have lent support to tectonic models involving warm, weak crust and attendant material flow at depth. INDEPTH III results that are consistent with such flow beneath the central plateau include a highly conductive crust, restriction of local seismicity to the uppermost crust, reflective lamination in the lower crust, and coherent crustal anisotropy. Mantle tomography of INDEPTH III teleseismic recordings indicate a steeply dipping zone of anomalously fast (cold) material in the mantle beneath central Tibet that likely marks subducted Indian lithosphere, an interpretation consistent with the gravity field over Tibet. Receiver functions computed beneath INDEPTH stations indicate a segmentation of the Moho that may reflect post-collisional reactivation of older accreted terranes. INDEPTH IV is now poised to complete its megatransect with new surveys across the northeast boundary of the Tibet Plateau as represented by theKunlunMountainsandQaidamBasins. INDEPTH IV will begin in the Spring of 2007 toaddress outstanding crustal issues such as the role of Moho faults, the extent of lower crustal flow, andpossible subduction of Asian lithosphere beneath the northern plateau. Keywords: tibet, lithosphere, orogeny

IUGG XXIV General Assembly July 2-13, 2007 Perugia, Italy (S) - IASPEI - International Association of Seismology and Physics of the Earth's Interior JSS015 Poster presentation 2336 Geophysical investigations of the Eastern Alpine crust and upper mantle Dr. Michael Behm Institute of Geodesy and Geophysics Vienna University of Technology IASPEI Ewald Brckl, Franz Kohlbeck, Ulrike Mitterbauer, Laszlo Szarka, Alpass Working Group, Hungarian Mt Team Currently the deep structure of the Eastern Alps and their surroundings is intensively studied by several large-scale geophysical investigations. We present latest results and ongoing projects. The 3D seismic refraction experiments CELEBRATION 2000 and ALP 2002 delivered much new insight into the P-wave velocity distribution of the crust and the structure of the complex Moho boundary in the area. In both experiments, seismic waves generated by 55 and 39 blasts, respectively, were recorded each with approximately 900 recorders. The results are a 3D velocity model of the crust, a new Moho depth map and 2D interpretations along selected profiles. The most important outcome is the determination of a pronounced fragmentation of the crust, including the new interpretation of the crustal block Pannonia which may be related to Miocene-to-date extrusion tectonics. Based on these results, the ALPASS experiment was launched to investigate the structure of the upper mantle down to the 660 km discontinuity. 110 permanent and 79 temporarily deployed stations recorded earthquake waveforms in the time from May 2005 to April 2006. These data provide the input for surface wave inversion, receiver functions, and teleseismic tomography. Seismic recodings from 144 earthquakes have been selected for a teleseismic tomographic inversion. A preliminary first model of the P-wave velocity structure of the upper mantle will be presented. Of particular interest is the direction of subduction below the Eastern Alps , since previous investigations yield contradicting results. Magnetotelluric soundings targeting the crust have been performed in the frame of the DIMS project. Ten test measurements with different instruments were carried out along the Hungarian-Austrian border. Another 33 measurements followed a seismic profile from the Hungarian border toward NW. Preliminary results indicate low resistivity of sediments in the Graz Basin in the SE part of the profile, as opposed to the highly resistive Eastern Alps in the NW. Large-scale tectonic fractures appear as conductive dikes. The long period soundings along the Hungarian-Austrian border might delineate the asthenosphere. We conclude that all three projects deliver much new insight into the deep structure of the investigated area. The joint interpretation of the existing and forthcoming models will contribute to a better understanding of the complex geodynamic processes that took place in the Eastern Alps . Keywords: eastern alps, seismic, magnetotelluric

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