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The October 1980 earthquake sequence near the New Hebrides

Vidale, John E. and Kanamori, Hiroo (1982) The October 1980 earthquake sequence near the New Hebrides. Geophysical Research Letters, 10 (12). pp. 1137-1140. ISSN 0094-8276. doi:10.1029/GL010i012p01137.

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Four large earthquakes occurred in 1980 in a seismic gap near the Loyalty Islands in the New Hebrides. At 3:25 UT on October 24 an event with M_s = 6.7 initiated the sequence. Three events, M_s = 6.7, 7.2, and 6.5, followed on the next day. We investigated this sequence by using the seismicity, first-motion, and waveform data and long-period surface waves. The first-motion data constrain one of each pair of nodal planes. With this constraint, inversion of Rayleigh- and Love-wave spectra at 256 seconds determines the other nodal plane. The mechanisms of all four events are almost pure thrust on a plane dipping about 20 degrees east and striking parallel to the local strike of the New Hebrides trench. The first-day aftershocks indicate an initial rupture zone of about 2,000 km², which is consistent with the estimated seismic moment of 3 × 10^(27) dyne-cm. During the next two days, the aftershock activity expanded to an area of 10,000 to 20,000 km² in the directions both along and perpendicular to the trench. Within 5 hours after the third and largest event, the initial rupture zone had become mostly quiescent. Modeling of waveforms suggests a body-wave moment of between 0.5 and 1.0 × 10^(27) dyne-cm and a source process time of 11 seconds. This pattern suggests that the initial rupture zone represents a zone of increased strength (i.e. an asperity), and the stress change due to failure of this asperity subsequently migrated outward. During the two-year period before the main event, seismicity in the initial rupture zone was very low except near the point where the first mainshock initiated. A very tight clustering of activity occurred there. This pattern indicates gradual stress concentration near the asperity which finally failed during the mainshock sequence.

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Kanamori, Hiroo0000-0001-8219-9428
Additional Information:© 1983 American Geophysical Union. Received June 28, 1983; accepted July 19, 1983. This work was partly supported by USGS contract No. 14-08-0001-21223. We thank Jeff Given for providing us with computer programs. William McCann generously supplied a preprint of his paper, some of his data, and permission to use a figure from his paper. Larry Ruff, Thorne Lay, and Jim Pechmann provided valuable advice. The figures were drafted skillfully by Laszlo Lenches. J.E.V. was supported by a Gutenberg Fellowship and an NSF Fellowship. The IDA data were provided by the IDA Project team at the University of California, San Diego, and the SRO and ASRO data were provided by the U.S. Geological Survey. Contribution 3856 of the Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125.
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Deposited On:05 Nov 2014 23:59
Last Modified:10 Nov 2021 19:09

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