Coda wave attenuation parallel and perpendicular to the Mexican Pacific coast |
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| Institution: | 1. Instituto de Investigaciones en Ciencias de la Tierra, Universidad Michoacana de San Nicolás Hidalgo, Ciudad Universitaria, Morelia, Michoacán, México;2. Instituto de Geofísica, Universidad Nacional Autónoma de México, Campus Morelia-UNAM, Antigua carretera a Pátzcuaro 8701, 58190 Morelia, Michoacán, México;3. Geophysical Institute, University of Alaska Fairbanks, Fairbanks AK 99775, USA;1. Department of Geology & Geophysics, King Saud University, Riyadh 11451, Saudi Arabia;2. National Research Institute of Astronomy and Geophysics, 11421 Helwan, Cairo, Egypt;3. Princess Nourah bint Abdulrahman University, Riyadh, Saudi Arabia |
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| Abstract: | We calculated the quality factor, Qc, at frequencies from 6 to 24 Hz using coda waves of 97 aftershocks of the Petatlan, Mexico, earthquake (March 14, 1979; MS=7.6). The data were recorded parallel (between Acapulco and Playa Azul) and perpendicular (between Petatlan and Mexico City) to the coast. The results are the following: at 12 and 24 Hz there is no significant difference in the attenuation (Qc?1) along the two paths; at 6 Hz, Qc?1 has a large scatter in both directions. This observation indicates strong site effects at this frequency; average Qc?1 is slightly higher between Petatlan–Acapulco (toward SE) than between Petatlan–Playa Azul (toward NW); and at high frequencies, Qc?1 remains essentially constant perpendicular to the coast. These results show that the large seismic wave amplifications in Mexico City are caused by shallow site effects. |
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