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Structure of the Benioff Zone beneath the Shumagin Islands, Alaska: Relocation of local earthquakes using three-dimensional ray tracing

Hauksson, Egill (1985) Structure of the Benioff Zone beneath the Shumagin Islands, Alaska: Relocation of local earthquakes using three-dimensional ray tracing. Journal of Geophysical Research B, 90 (B1). pp. 635-649. ISSN 0148-0227. doi:10.1029/JB090iB01p00635.

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Seismic rays are traced through a prescribed three-dimensional inhomogeneity that simulates the subducted slab below the Shumagin Islands region to calculate local station delays for a given hypocenter and a slab model. Hypocenters determined by the Shumagin seismic network are then relocated using the station delays, a flat-layered velocity structure and a standard earthquake location computer program. Station delays are calculated for 12 hypocenters with respect to six different slab models to identify the slab model that is most consistent with the available arrival time and waveform data. A set of path corrections that is calculated for each grid point-station pair on a preliminary grid of 36 points in the depth range from 60 to 300 km is used to recalculate the hypocenters for all of the 1982 earthquakes with depths greater than 50 km. Application of this method to data from 1982 for the digitally recording Shumagin seismic network shows the following results: (1) a previously observed apparent increase in dip of the subducted slab at depths of ≈ 100 km disappears, (2) the subducted slab can be modeled as a dipping structure that dips at a constant angle of 45° toward north-northwest at depths between 80 and 250–300 km and has a 7% higher velocity than the surrounding mantle, (3) hypocenters determined from Shumagin network data are located only 10–20 km south of high-quality hypocenters determined from teleseismic data alone, (4) qualitative comparison of digitally recorded seismograms with calculated ray paths shows enrichment of high-frequency coda, possible converted phases, and low amplitudes of first P arrivals for rays that travel mostly along the slab. Conversely, for rays that travel almost vertically through the upper plate the seismograms show a high amplitude of first P arrivals that are followed by an insignificant coda and low-amplitude S waves.

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Hauksson, Egill0000-0002-6834-5051
Additional Information:© 1985 by the American Geophysical Union. Received November 21, 1983; revised July 13, 1984; accepted August 1, 1984. The manuscript was read critically by L. Jones, K. Jacob, C. Nicholson, and G. Suarez. Valuable comments were provided by R. Cockerham and W. A. Prothero, Jr. The author would like to thank K. Jacob for giving helpful suggestions and encouragement and for making the three-dimensional ray-tracing programs available. Thanks are due to S. Rosen and M. Luckman, who located the 550 earthquakes recorded during 1982. D. Johnson and L. Skinta provided the technical effort that was needed to keep nearly all of the Shumagin network stations operating during 1982. L. Niebur and S. Turnbow typed the manuscript, and K. Nagao and M. Luckman drafted the figures. This work was supported by the U.S. Department of Energy (contracts DE-AC02-76ERO-3134 and DE-FG-02-84-ER13221). Lamont-Doherty Geological Observatory contribution 3707.
Group:Seismological Laboratory, Division of Geological and Planetary Sciences
Funding AgencyGrant Number
Department of Energy (DOE)DE-AC02-76ERO-3134
Department of Energy (DOE)DE-FG-02-84-ER13221
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Lamont-Doherty Geological Observatory3707
Issue or Number:B1
Record Number:CaltechAUTHORS:20130508-084252162
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Official Citation:Hauksson, E. (1985), Structure of the Benioff Zone beneath the Shumagin Islands, Alaska: Relocation of local earthquakes using three-dimensional ray tracing, J. Geophys. Res., 90(B1), 635–649, doi:10.1029/JB090iB01p00635
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:38343
Deposited By: Ruth Sustaita
Deposited On:08 May 2013 15:59
Last Modified:09 Nov 2021 23:36

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