Physics
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufm.s23a1871w&link_type=abstract
American Geophysical Union, Fall Meeting 2008, abstract #S23A-1871
Physics
7240 Subduction Zones (1207, 1219, 1240), 7255 Surface Waves And Free Oscillations, 7270 Tomography (6982, 8180), 7280 Volcano Seismology (8419)
Scientific paper
How a subduction system evolves to a transform system is a fundamental question in plate tectonics and is still not well understood. It is believed that fragmentation of both the subducting and overriding plates is one of the key steps of the evolution. Such a process is occurring in the Rivera subduction zone of the western Mexico. In this region, the Rivera plate detached from the Cocos plate a few million years ago and is presently subducting beneath the Jalisco block, which is separating from the North American plate along the Colima graben and Tepic-Zacoalco Rift to the east and north, respectively. Seismic imaging of the velocity structure and boundaries of the Rivera-Cocos-Jalisco microplate system is thus essential to understanding the regional tectonics as well as the broad question of subduction-to-transform transition. Fifty broadband seismic stations were temporarily deployed between January 2006 and June 2007 to explore the geodynamic processes of this plate boundary region under the MARS (MApping the Rivera Subduction zone) project. Here we present preliminary results on the crustal and upper mantle structure of the Jalisco block based on the analysis of surface waves recorded by the seismic array. Phase velocities at periods from 5 to 35 s were measured by cross correlating continuous records of two-station pairs. High SNR (signal-to-noise ratio) Green's functions were obtained along 474 ray paths and were inverted to generate the phase velocity map of the region. There is a good agreement between the phase velocity maps and the regional tectonic structure. The strongest low velocity anomaly is located beneath the Colima volcano system and is shown in all period bands. The NS trending Colima graben and the NW trending Tepic-Zacoalco Rift are also featured by distinct low velocity lineaments. We also analyzed the fundamental mode Rayleigh waves of 116 teleseismic Mw>6 events in the 20-100s period bands using the two-plane wave method. The resulting phase velocity maps were combined with those derived from ambient noise data to yield dispersion curves covering a period range of 5 to 100 s. These dispersion measurements will be used to estimate the S-wave velocity structure of the crust and upper mantle to ~200 km depth beneath the Jalisco block.
Grand Stephen
Ni Jian
Niu Feng
Wang Xinhua
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