Source spectra and RMS acceleration of Mexican subduction zone earthquakes
Por:
Singh S.K., Mena E., Anderson J.G., Quaas R., Lermo J.
Publicada:
1 ene 1990
Resumen:
Strong motion (SM) data of six Mexican subduction zone earthquakes (6.4?MS?8.1) recorded near the epicentral zone are analyzed to estimate their far-field source acceleration spectra at higher frequencies (f?0.3 Hz). Apart from the usual corrections such as geometrical spreading (1/R), average radiation pattern (0.6), free surface amplification (a factor of 2), and equal partitioning of the energy into two orthogonal horizontal components (a factor of 1/ {Mathematical expression}), the observed spectra are corrected for a frequency dependent Q(Q=100 f), a site dependent filter (e-?kf), and amplification of S waves near the surface (a factor of about 2 at f?2Hz). We take R as the average distance from the rupture area to the site. If we model the high frequency plateau (f?1 Hz) of the source spectra, by a point source ?-2-model, and interpret them in terms of Brune's model we obtain ?? between 50 and 100 bars for all earthquakes. The low-frequency broadband teleseismic P wave spectra, corrected with t*=1.0 s, agrees within a factor of two with SM source spectra near 1 Hz. The ?-2-model is inadequate to explain the observed source spectra in a broad frequency range; these resemble spectra given by Gusev (1983) with some differences. SM source acceleration spectra require significant corrections to explain observed spectra and RMS acceleration (arms) (a) at farther coastal sites for extended sources due to directivity effect and (b) at inland sites (100?R?200 km) because of unaccounted path and site amplification and/or invalidity of body-wave approximation. The observed spectra and arms at these sites are significantly greater than the predicted values from the estimated source spectra. © 1990 Birkhäuser Verlag.
Filiaciones:
Singh S.K.:
Instituto de Geofisica, U.N.A.M., C.U., México, 04510, D.F., Mexico
Instituto de Ingeniería, U.N.A.M., C.U., México, 04510, D.F., Mexico
Mena E.:
Instituto de Ingeniería, U.N.A.M., C.U., México, 04510, D.F., Mexico
Anderson J.G.:
Seismological Laboratory, Mackay School of Mines, University of Nevada-Reno, Reno, 89557, Nevada, United States
Quaas R.:
Instituto de Ingeniería, U.N.A.M., C.U., México, 04510, D.F., Mexico
Lermo J.:
Instituto de Ingeniería, U.N.A.M., C.U., México, 04510, D.F., Mexico
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