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Earthquake doublets in the Solomon Islands

Lay, Thorne and Kanamori, Hiroo (1980) Earthquake doublets in the Solomon Islands. Physics of the Earth and Planetary Interiors, 21 (4). pp. 283-304. ISSN 0031-9201. doi:10.1016/0031-9201(80)90134-X.

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Large, shallow, thrust earthquakes in the Solomon Islands region tend to occur in closely related pairs. Two recent sequences are July 14, 1971 (M_S = 7.9) and July 26, 1971 (M_S = 7.9) and 14^h37^m, July 20, 1975 (M_S = 7.9) and 19^h54^m, July 20, 1975 (M_S = 7.7). The mechanism of these seismic doublets has important bearing on the triggering mechanism of earthquakes in subduction zones. Detailed analysis of the seismic body waves and surface waves were performed on the 1971, 1974, and 1975 doublets, providing a better understanding of: (1) the mechanics of seismic triggering, (2) the state of stress on the fault plane, and (3) the nature of subduction between the Pacific and Indian plates. The results indicate that although the geometry of the subduction zone in the Solomon Islands is complicated by the presence of several sub-plates, the slip direction of the Indian plate with respect to the Pacific plate is relatively uniform over the entire region. The large seismic moments of the 1971 sequence (1.2 · 10^28 and 1.8 · 10^28 dyne cm) indicate that these events directly represent the underthrusting of the Indian and Solomon plates beneath the Pacific plate. The body waves from these doublets, recorded on the WWSSN long-period seismograms, are remarkably impulsive and simple compared with those from events of comparable seismic moment in other subduction zones. In addition, the source dimensions of the body waves are 30–70 km in length, substantially smaller than the overall rupture surfaces radiating the surface waves which are 100–300 km in length. These facts suggest the existence of relatively large, isolated high-stress zones on the fault plane. This type of stress distribution is distinct from other regions which have more heterogeneous stress distribution on the fault plane, and this is proposed as the principal characteristic of this region responsible for the occurrence of the doublets and for the apparent efficiency of triggering in the Solomon trench. Prior to the 1971 sequence, similar sequences have occurred in the same area in 1919–1920 and 1945–1946. From the amount of slip (1.3 m) determined for the 1971 sequence and the apparent recurrence interval of 25 years, a seismic slip rate of 5 cm yr^−1 is determined. This value is a significant portion of the convergence rate between the Indian and Pacific plates indicating that the plate motion here is taken up largely by seismic slip.

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Lay, Thorne0000-0003-2360-4213
Kanamori, Hiroo0000-0001-8219-9428
Additional Information:© 1980 Published by Elsevier B.V. Received May 4, 1979; revised and accepted July 5, 1979. We would like to thank Gordon S. Stewart for helpful discussions and use of his equalization programs, and G. Pascal for providing a preprint. We also thank Gordon S. Stewart and John E. Ebel for critically reading the manuscript. This research was supported by a grant from the National Science Foundation (EAR78-11973) and by U.S. Geological Survey Contract (14-08-0001-17631). One of the authors, Thorne Lay, was supported by a National Science Foundation Graduate Fellowship. Contribution No. 3163, Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California, 91125.
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Caltech Division of Geological and Planetary Sciences3163
Issue or Number:4
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Official Citation:Lay, T., & Kanamori, H. (1980). Earthquake doublets in the Solomon Islands. Physics of the Earth and Planetary Interiors, 21(4), 283-304. doi:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:54558
Deposited On:09 Feb 2015 23:20
Last Modified:10 Nov 2021 20:35

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