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A large normal-fault earthquake at the junction of the Tonga trench and the Louisville ridge

Eissler, Holly and Kanamori, Hiroo (1982) A large normal-fault earthquake at the junction of the Tonga trench and the Louisville ridge. Physics of the Earth and Planetary Interiors, 29 (2). pp. 161-172. ISSN 0031-9201. doi:10.1016/0031-9201(82)90070-X.

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The source mechanism of a large (M_s = 7.2) earthquake that occurred in the oceanic plate at the junction of the Tonga—Kermadec trench systems with the aseismic Louisville ridge is found by inverting long-period vertical-component Rayleigh waves recorded by the IDA network. The solution is an almost-pure normal fault, on a plane striking roughly parallel to the trench axis, with seismic moment of 1.7 × 10^(27) dyn cm, and thus is among the ten largest documented shallow normal-fault earthquakes. A point-source depth of 20 km for the event is resolved by modeling teleseismic body waves; the actual rupture may have extended deeper, to 30 or 40 km. The earthquake was a multiple event, consisting of two sources separated by 16 s. A rupture velocity of 3.5 km s−1 is inferred. The earthquake can be interpreted as tensional failure in the shallow portion of the downgoing plate caused by the gravitational pull of the slab. The Louisville ridge may be creating a local degree of decoupling of the oceanic plate from the overriding plate, and/or a zone of extension within the slab, which could enhance the effect of the gravitational forces in the shallower part of the downgoing plate. In particular, the earthquake could be associated with the break-up of the leading seamount of the ridge, which is currently right at the trench. Alternatively, the earthquake may have been caused by stresses associated with the bending of the plate prior to subduction.

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Kanamori, Hiroo0000-0001-8219-9428
Additional Information:© 1982 Elsevier Scientific Publishing Company. Received February 26, 1982; accepted for publication March 25, 1982. The IDA data used in this study was made available by courtesy of the IDA project team at the Institute of Geophysics and Planetary Physics, University of California, San Diego. Seiya Uyeda and Kazuo Kobayashi kindly sent us material on the Kashima seamount. We thank Larry Ruff for helpful discussions during various phases of the project, and for critically reading the manuscript. Laszlo Lenches drafted the figures. This research was supported by the Division of Earth Sciences, National Science Foundation NSF Grant EAR78- 11973, the National Aeronautics and Space Administration Contract No. NSG-710 and the U.S. Geological Survey Grant No. 14-08-001-19265. Contribution No. 3749, Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125.
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Official Citation:Holly Eissler, Hiroo Kanamori, A large normal-fault earthquake at the junction of the Tonga trench and the Louisville ridge, Physics of the Earth and Planetary Interiors, Volume 29, Issue 2, August 1982, Pages 161-172, ISSN 0031-9201, (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:51245
Deposited By: Tony Diaz
Deposited On:04 Nov 2014 22:22
Last Modified:10 Nov 2021 19:08

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