HR: 0800h
AN: S41A-0256    [Abstracts]
TI: Surface-Wave Amplitude Tomography from Worldwide Magnitude Measurements
AU: * Hearn, T M
EM: thearn@nmsu.edu
AF: Physics Department, New Mexico State University, Las Cruces, NM 88003, United States
AB: Surface-wave amplitudes are routinely collected by the International Seismological Centre to determine earthquake magnitudes. These form a large database for amplitude tomography studies. I selected data from vertical instruments with data averaging around 20 seconds. These waves have their primary sensitivity in the crust and cover most of the globe. Average amplitude decay rates indicate an average global surface wave Q near 380 with cylindrical spreading on a spherical earth. The tomographic inversion estimates station corrections, event size corrections, and regional variations in surface-wave Q. Both site corrections and event size corrections have rms values of 0.2 magnitude units; although some events have corrections exceeding a full magnitude unit. Q values range from less than 100 to over 1000 with resolution as good as several degrees in densely covered areas. Regional variations show low Q values in tectonic and sedimentary regions, such as the western United States, the Middle East, and basins of the North China Block. Cratons show high Q in Canada, north Asia, and Europe.
DE: 7207 Core (1212, 1213, 8124)
DE: 7218 Lithosphere (1236)
DE: 7219 Seismic monitoring and test-ban treaty verification
DE: 7270 Tomography (6982, 8180)
DE: 8110 Continental tectonics: general (0905)
SC: Seismology [S]
MN: 2007 Fall Meeting