摘要:

Moment tensor inversion of low frequency teleseismic data for the September 19, 1985 Michoacan, Mexico earthquake gave an average strike 298°, slip 268°, and seismic moment 10.3×1027dyne‐cm. Low frequency body waves clearly show the complex nature of this event. Cross‐correlation of the September 19 P‐wave with that of the smaller, and colocated October 25, 1981 Playa Azul earthquake, show that the Michoacan earthquake consisted of two subevents separated in time by 25 s, and located approximately 30 km northwest and 40 km southeast respectively, of the Playa Azul epicenter. Body wave inversion of the first subevent gave strike 298°, slip 266°, and seismic moment 3.0×1027dyne‐cm. The second subevent had a comparable seismic moment. The cumulative moment for large earthquakes occurring along the Michoacan‐northwest Guerrero coast indicate that seismic displacement along this segment of the Mexican subduction zone is similar to that occurring on other portions, indicating that the "former" Michoacan gap was not anoma

ISSN:0094-8276    

DOI:10.1029/GL013i006p00601

年代:1986

数据来源: WILEY

摘要:

Long‐period seismograms from the GDSN, RSTN, and IDA network are used in a centroid‐moment tensor analysis of the September 19, 1985 Michoacan, Mexico, earthquake (Ms=8.1). The long‐period data are also used together with broad band displacement P‐waveforms in a joint very broad band inversion for the moment tensor and the moment rate distribution in time and space. Results are that the earthquake had a total scalar moment of 1.1×1028dyne‐cm and that the moment release occurred mainly in two subevents, the second of which was located approximately 70 km southeast of the first. Observations of Earth's normal modes at ultra long periods (600 to 2000 sec) are shown to be consistent with the obtained scalar moment and source

ISSN:0094-8276    

DOI:10.1029/GL013i006p00605

年代:1986

数据来源: WILEY

摘要:

IDA records of the 19 Sept 85 Michoacan earthquake and its large aftershock of 21 Sept 85 have been used to estimate source‐mechanism spectra and total‐moment spectraMT(ω) in 1‐mHz bands over the frequency interval 1‐11 mHz. Source mechanisms, obtained by the phase‐equalization method of Riedesel and Jordan, show no significant frequency dependence and no significant non‐double‐couple components. The best average double‐couple solution has a strike, dip and rake of 289° ± 4°, 19° ± 15° and 76° ± 5° for the main event, and 293° ± 3°, 24° ± 12° and 73° ± 4° for the aftershock. Total‐moment spectra, obtained by the power‐spectral method of Silver and Jordan, are parametrized by a total integrated momentMT0and a characteristic timeτc. For the main event, we obtainMT0= (10.7 ± 2.0) × 1020N−m andτc= 49 ± 7 s; the corresponding parameters for the aftersnock areMT0= (2.6 ± 0.6) × 1020N−m andτc= 30 ± 11 s. Both events are relatively slow; in particular, the aftershock has a larger characteristic time than either the fast‐rupturing 29 Nov 78 Oaxaca or the 14 Mar 79 Petalan earthquakes, although the static moments are about the same. Our results support the model of the main shock as a multiple‐rupture event with moment re

ISSN:0094-8276    

DOI:10.1029/GL013i006p00609

年代:1986

数据来源: WILEY