HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text (PDF) References Citation Map Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by TOTH, T. Articles by KISSLINGER, C. Search for Related Content GeoRef GeoRef Citation

Revised focal depths and velocity model for local earthquakes in the Adak Seismic zone

COOPERATIVE INSTITUTE FOR RESEARCH IN ENVIRONMENTAL SCIENCES AND DEPARTMENT OF GEOLOGICAL SCIENCES UNIVERSITY OF COLORADO AT BOULDER, BOULDER, COLORADO 80309

Abstract

A technique suggested by Hales et al. (1981) for determining hypocentral depths that are relatively independent of the velocity model originally used to locate the earthquakes is applied to a carefully selected set of earthquakes located with the Adak Seismic Network. The origin times are taken from the Wadati diagram for each event and the epicentral distances from the standard hypocenter solution are assumed to be correct. A straight-ray interpretation, based on the use of a single average velocity from the hypocenter to the surface, is then used to determine the average velocity and the depth from the slope and intercept of the linear X² – T² plot.

From the Adak catalog for August 1974 to May 1983, 8046 located events, 579 earthquakes with good P-data and 347 with good S-data were selected on the basis of excellent time picks, good quality solutions, and reliable Wadati and X² – T² plots. The revised depths show that the sharp cutoff of the shallower main thrust zone activity at 26 km seen in the Adak data set is an artifact of the routine location procedure. Routine depths are found to be systematically too shallow by a mean amount of 4.35 km, with origin times 0.20 sec too early.

The velocities derived in this study agree with those in the standard model for depths below 80 km, but are higher than the standard values at shallower depths. The two models can be reconciled by invoking small gradients of velocity in the uppermost three layers, but this result is not unique. The results indicate local variations of the shallower velocities within the Adak seismic zone, one of which, low velocities beneath the volcanic arc, has been found in an earlier, independent study.

This article has been cited by other articles:

				E. R. ENGDAHL and S. BILLINGTON Focal depth determination of central Aleutian earthquakes Bulletin of the Seismological Society of America, February 1, 1986; 76(1): 77 - 93. [Abstract] [PDF]

				A. SILLIMAN and S. BILLINGTON Seismicity associated with a recent earthquake of mb 5.8 beneath Adak Canyon, central Aleutian islands Bulletin of the Seismological Society of America, December 1, 1985; 75(6): 1853 - 1858. [PDF]

				C. NICHOLSON and D. W. SIMPSON Changes in Vp/Vs with depth: Implications for appropriate velocity models, improved earthquake locations, and material properties of the upper crust Bulletin of the Seismological Society of America, August 1, 1985; 75(4): 1105 - 1123. [Abstract] [PDF]

				F. SCHERBAUM and C. KISSLINGER Variations of apparent stresses and stress drops prior to the earthquake of 6 May 1984 (mb = 5.8) in the Adak Seismic Zone Bulletin of the Seismological Society of America, December 1, 1984; 74(6): 2577 - 2592. [Abstract] [PDF]

				J. MORI and K. SHIMAZAKI High stress drops of short-period subevents from the 1968 Tokachi-Oki earthquake as observed on strong-motion records Bulletin of the Seismological Society of America, October 1, 1984; 74(5): 1529 - 1544. [Abstract] [PDF]