The Crustal and Mantle Velocity Structure in Central Asia from 3D Travel Time Tomography

• Main Authors: Martin, Randolph J, Gulen, Levent, Sun, Youshun, Toksoz, M N
• Format: Report
• Language: English
• Subjects: CENTRAL ASIA; EARTH CRUST; Geology, Geochemistry and Mineralogy; SEISMIC VELOCITY; SEISMIC WAVES; Seismology; THREE DIMENSIONAL; TOMOGRAPHY; TRAVEL TIME

The lithospheric structure in Central Asia features large blocks such as the Indian plate, the Afghan block, the Turan plate, and the Tarim block. This geologically and tectonically complicated area is also one of the most seismically active regions in the world. We developed P- and S-wave velocity structures of Central Asia in the crust using the travel-time data from Kyrgyzstan, Tajikistan, Kazakhstan, and Uzbek Republic. We chose the events and stations between 32N65E and 45N85E and focused on the areas of Pamir and western Tianshan. In this data set, there are more than 6000 P and S arrivals received at 80 stations from about 300 events. Double difference tomography is applied to relocate events and to determine seismic velocities simultaneously. Our results provide an improved earthquake location and high resolution crustal structure in this region. To extend the model deeper into the mantle through the upper mantle transition zone, ISC/EHB data for P and PP phases are combined with the ABCE data. To counteract the smearing effect, the crust and upper mantle velocity structure, derived from regional travel-times, is used. An adaptive grid method based on ray density is used in the inversion. Regional teleseismic tomography provides a high-resolution, 3-D P-wave velocity model for the crust upper mantle, and the transition zone. The crustal models correlate well with geologic and tectonic features. The upper mantle tomograms show the images of Tian Shan. The slab geometry is quite complex, reflecting the history of the changes in the plate motions. Published in Proceedings of the 2010 Monitoring Research Review - Ground-Based Nuclear Explosion Monitoring Technologies, 21-23 September 2010, Orlando, FL. Volume I. Sponsored by the Air Force Research Laboratory (AFRL) and the National Nuclear Security Administration (NNSA). U.S. Government or Federal Rights License