Physics – Geophysics
Scientific paper
Nov 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001aps..4cf.cc003h&link_type=abstract
American Physical Society, Four Corners Annual Meeting November 2 - 3, 2001 New Mexico State University; Las Cruces, New Mexico
Physics
Geophysics
Scientific paper
Seismic tomography revolutionized geophysics over fifteen years ago by allowing us to image the Earth's interior and see the effects of plate tectonics on the planet's interior. I will review some of the basic aspects of seismic tomography and show how it is yielding new insights into the tectonic development of China and Tibet. Seismic tomography uses the travel times from earthquake epicenters to seismic stations to deduce the velocity variations within the Earth. The tomographic "inverse problem" relies on large amounts of data to find an even larger number of unknown velocity variations. As such, tomography constitutes an "ill-posed" inverse problem that is inherently non-unique. Data sets are from the Annual Bulletin of Chinese Earthquakes and from the INDEPTH-III Tibet seismology expedition. The Bulletin of Chinese Earthquakes reports the travel-time data used to locate earthquakes in China. These data are used to tomographically image the top of the Earth's mantle beneath China at a depth of about 40 km. The tomography shows clear differences between the accreted terrains of eastern China and older cratonic terrains of western China. Also revealed is the thicker crust of western China and Tibet. For Tibet, data collected from the INDEPTH-III seismology experiment were used. This experiment deployed 50 seismometers in a north-south profile in central Tibet. Tomography using these data shows that northern Tibet has a significantly slower mantle than in the south but similar crustal thicknesses. This indicates a hotter mantle beneath northern Tibet, but the lack of crustal thickness variation suggests such hot, low-density mantle may be only at the top of the mantle.
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