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Variable rupture mode of the subduction zone along the Ecuador-Colombia coast

Kanamori, Hiroo and McNally, Karen C. (1982) Variable rupture mode of the subduction zone along the Ecuador-Colombia coast. Bulletin of the Seismological Society of America, 72 (4). pp. 1241-1253. ISSN 0037-1106.

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Three large earthquakes occurred within the rupture zone of the 1906 Colombia-Ecuador earthquake (M_W = 8.8): in 1942 (M_S = 7.9); 1958 (MS = 7.8); and 1979 (M_S = 7.7). We compared the size and mechanism of these earthquakes by using long-period surface waves, tsunami data, and macroseismic data. The 1979 event is a thrust event with a seismic moment of 2.9 × 10^(28) dyne-cm, and represents subduction of the Nazca plate beneath South America. The rupture length and direction are 230 km and N40°E, respectively. Examination of old seismograms indicates that the 1906 event is also a thrust event which ruptured in the northeast direction. The seismic moment estimated from the tsunami data and the size of the rupture zone is 2 × 10^(29) dyne-cm. The 1942 and 1958 events are much smaller (about 1/5 to 1/10 of the 1979 event in the seismic moment) than the 1979 event. We conclude that the sum of the seismic moments of the 1942, 1958, and 1979 events is only Formula of that of the 1906 event despite the fact that the sequence of the 1942, 1958, and 1979 events ruptured approximately the same segment as the 1906 event. This difference could be explained by an asperity model in which the fault zone is held by a discrete distribution of asperities with weak zones in between. The weak zone normally behaves aseismically, but slips abruptly only when it is driven by failure of the asperities. A small earthquake represents failure of one asperity, and the rupture zone is pinned at both ends by adjacent asperities so that the effective width and the amount of slip are relatively small. A great earthquake represents failure of more than one asperity, and consequently involves much larger width and slip.

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Kanamori, Hiroo0000-0001-8219-9428
Additional Information:© 1982 Seismological Society of America. Manuscript received 6 November 1981. We thank John Kelleher for providing us with valuable comments and information on the 1906 events. Jim Brune suggested that we should examine the possibility that the 1906 event is a normal-fault event similar to the 1933 Sanriku earthquake. We thank the directors of seismographic stations at Göttingen, Germany, and Uppsala, Sweden, for kindly sending us the records of the 1906 Colombia earthquake. Katsuyuki Abe, Tokutaro Hatori, Harold Loomis, and Jack Fancher provided us with valuable information on the tsunami height of the 1906 and 1979 events. George Purcaru and Ines Cifuentes sent us useful information on the 1979 and 1906 events, respectively. Fumiko Tajima translated for us some key sentences in Rudolph and Szirtes (1911). This research was supported by the U.S. Geological Survey Contracts 14-08-0001-19265 and 14-08-0001-19755 and also by the National Science Foundation Grant EAR78-05352.
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Caltech Division of Geological and Planetary Sciences3603
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Official Citation:Kanamori, H., & McNally, K. C. (1982). Variable rupture mode of the subduction zone along the Ecuador-Colombia coast. Bulletin of the Seismological Society of America, 72(4), 1241-1253.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:48542
Deposited On:14 Aug 2014 20:41
Last Modified:09 Mar 2020 13:18

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