...) . Bulletinofthe SeismologicalSocietyofAmerica,Vol.73,No.2,pp. 449-457,April1983 PLAYA AZUL, MICHOACAN, MEXICO, EARTHQUAKE OF 25 OCTOBER 1981 (Ms = 7.3) BY J. HAVSKOV, S. K. SINGH, E. NAVA, T. DOMINGUEZ, AND M. RODRIGUEZ ABSTRACT The Playa Azul earthquake broke the central part of the Michoacan gap along...

... during this period can be characterized by a sequential failure of five distinct asperities. Before 1981, the Michoacan gap had not experienced a large earthquake since 1911 when an M S = 7.8 earthquake occurred. The recent sequence started in October 1981 with the Playa Azul earthquake which broke...

... asperities located southeast of the Michoacan segment were ruptured first by the 1979 Petatlan event. The 1981 Playa Azul event ruptured two asperities in the central zone with a stress drop higher than 80 bars. The largest 1985 Michoacan earthquake resulted from the rupture of two large-size, strong...

... further downdip at depths between 27 km and 39 km. Aftershock activity following the earthquake was associated mainly with the two shallow sources. These two sources are separated by the aftershock zone of the 1981 Playa Azul earthquake. Bulletinofthe SeismologicalSocietyofAmerica,Vol.79,No.3,pp. 655-669...

... 1979 Petatlan (Me = 7.6), 25 October 1981 Playa Azul (Ms = 7.3), and 21 September 1985 Michoac~n (M~ = 7.6) earthquakes. These earthquakes occurred in the northwest portion of the Middle America trench (Fig. 1) and ruptured the interface between the North American plate and the subducting Cocos plate...

... J. Buchanan and P. J. Jackson Dominguez, T., J. Havskov, S. Slngh, F. Nava, and M. Rodriquez--Playa Azul, Mmhoacan, Mexico Earthquake of 25 October 1981 (Ms = 7.3) Doornbos, D. J., S. Mykkeltvelt, K. Astebol, and E. S. Husebye--Seismic Array Configuration Optimization Doser, Diane and Robert Smith...

.... Domínguez T. Rodríguez M. (1983) . Playa Azul, Michoacan, Mexico earthquake of 25 October, 1981 ( M S = 7.3) , Bull. Seism. Soc. Am. 73 , 449 - 458 . Kanamori H...

.... Nava E. Dominguez T. Rodriguez M. (1983) . Playa Azul, Michoacan, Mexico, earthquake of 25 October 1981 ( M s = 7.3) , Bull. Seism. Soc. Am. 73 , 449...

.... Domínguez T. Rodríguez M. (1983) . Playa Azul, Michoacán, México earthquake of 25 October 1981 ( M s = 7.3) , Bull. Seism. Soc. Am. 73 , 449 - 457 . Kelleher J...

... T. Rodriguez M. (1983) . Playa Azul, Michoacan, Mexico earthquake of 25 October 1981 ( M s = 7.3) , Bull. Seism. Soc. Am. 73 , 449 - 457 . Kanamori H...

... of Earthquake Date (yyyy/mm/dd) Number of Asperity Depth (km) Stress Drop (MPa) 1 Petatlán 1979/03/14 1 11.685 0.558 2 29.830 0.504 2 Playa Azul 1981/10/25 1 16.330 3.049 3 Michoacán 1985/09/19 1 15.247 1.577 2 18.610 1.442 4 Zihuatanejo 1985/09/21 1 20.005...

... previously in 1899-1911. Alternatively, the central Guerrero region could rupture in a single great earthquake of about M w 8.0, similar to the 19 September 1985 Michoacan earthquake. Note that the 1985 shock was preceded by a smaller shock in 1981 (Playa Azul, Ms 7.3, Havskov et al., 1983). Hence...

... horizons. The base of the lowermost, the Peñas Azules Formation, is constrained by a tuff dated by zircon fission track at 10.7 ± 1.7 Ma ( Strecker, 1987 ). A tuff within lacustrine sediments in the middle Playa del Zorro Formation constrains deposition to 5.7 ± 0.4 Ma ( Bossi et al., 2000 ). The Playa...

... T. Rodríguez M. (1983) . Playa Azul, Michoacán, México earthquake of 25 October, 1981 ( M s = 7.3) , Bull. Seism. Soc. Am. 73 , 449 - 458 . Heaton T. H...

.... Nava, T. Dominguez, and M. Rodriguez along the coast of Oaxaca, Mexico, Seism. Res. Lett. 67, 33-39. (1983). Playa Azul, Michoacan, Mexico earthquake of 25 October 1981 (Ms = 7.3), Bull. Seism. Soc. Am. 73, 449-457. Pacheco, J., S. K. Singh, G. Reyes, J. Dominguez, A. Hurtado, C. Ramirez, Houston, H...

... that of the Mexican earthquakes (Table 1).The spectra of the Costa Rica earthquake of 1983 (event 12) and the Playa Azul earthquake of 1981 (event 5) both with M~ = 7.4, are comparable, and the number of aftershocks is within a factor of 4. These results suggest that the number of aftershocks may correlate...

... Caleta de Campos. The slip occurred on a fault patch bounded by the previously broken zones of the 1981 Playa Azul earthquake in the south and 1973 Colima earthquake in the north. We assume that the rupture initiated at 17 km depth, 20 km northeast from the station as indicated by hypocentral locations...

... of the fault which is interpreted as having a low moment release is found to coincide with an inner region of this rectangular fault which slipped in the Playa Azul earthquake in 1981. It is conjectured that this inner regio~ accumulated little or no stress since 1981, and since it had preslipped, little...

... Shock 12. D. Harvey* and M. Wyss: A Detailed Source Model for the Multiple 1975 Hawaii Rupture, M = 7.2 MINUTES OF THE ANNUAL MEETING OF SSA $401 13. J. Havskov*, S. K. Singh, E. Nava, T. Dominguez, and M. Rodrignez: Playa Azul, Michoacan, Mexico Earthquake of 25 October 1981 (Ms = 7.3) 14. E. Fehler...

... of strong-motion to teleseismic source spectra (recomputed with t* = 1 sec if required) estimated from the studies mentioned earlier. Note that the strong- motion spectra are from hard sites, except for the earthquake of Playa Azul, Mexico, whose data are shown by square brackets. With the exception...