Quick Search:    advanced search

GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help

This Article Full Text (PDF) References Alert me when this article is cited Alert me if a correction is posted 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 Thomas, G. C. Articles by Yelin, T. S. Search for Related Content GeoRef GeoRef Citation

The 25 March 1993 Scotts Mills, Oregon, earthquake and aftershock sequence: Spatial distribution, focal mechanisms, and the Mount Angel Fault

University of Washington Geophysics, Box 351650, Seattle, Washington 98195-1650
U.S. Geological Survey, Box 25046, Federal Center, Denver, Colorado 80225-0046
U.S. Geological Survey University of Washington Geophysics, Box 351650, Seattle, Washington 98195-1650

Abstract

The 25 March 1993 M_L = 5.7 crustal earthquake near Scotts Mills, Oregon, was the largest earthquake to occur in the Pacific Northwest in over a decade. The mainshock was located at 45.033°N, 122.586°W and at a depth of about 15.1 km, based on arrival time data from the short-period Pacific Northwest Seismograph Network. Beginning about 12 h after the mainshock, investigators from the U.S. Geological Survey deployed 22 digital seismographs to record aftershocks. Using data from the temporary and permanent stations, we analyzed a subset of 50 aftershocks with quality locations. Hypocenters of these aftershocks lie on a northwest-trending steeply dipping plane (strike 290 ± 10°, dipping 60 ± 5° to the north-northeast), in agreement with the preferred slip plane of the mainshock focal mechanism solution (strike 294°, dipping 58° to the north-northeast). The planar structure defined by the aftershock locations may be a southeast continuation of the Mount Angel Fault, a reverse fault identified from both surface and subsurface evidence. The mapped southeast extent of the Mount Angel Fault is located less than 10 km west of the Scotts Mills epicentral region. In addition, the mainshock focal mechanism solution, with a combination of reverse motion and right-lateral strike slip, has a geometry and sense of motion consistent with the Mount Angel Fault. While aftershock focal mechanisms are varied, P axes are consistently oriented in a subhorizontal north-south direction. This earthquake sequence, together with the geological and geophysical evidence for the Mount Angel Fault, suggests a significant crustal earthquake hazard for this region of northwest Oregon.

This article has been cited by other articles:

				Late Pleistocene and Holocene Tectonics of the Portland Basin, Oregon and Washington, from High-Resolution Seismic Profiling Bulletin of the Seismological Society of America, August 1, 2001; 91(4): 637 - 650.

				R. J. Blakely, R. J. Blakely, R. E. Wells, T. L. Tolan, M. H. Beeson, A. M. Trehu, and L. M. Liberty New aeromagnetic data reveal large strike-slip (?) faults in the northern Willamette Valley, Oregon Geological Society of America Bulletin, August 1, 2000; 112(8): 1225 - 1233. [Abstract] [Full Text] [PDF]

				L. M. Liberty, A. M. Trehu, R. J. Blakely, and M. E. Dougherty Integration of high-resolution seismic and aeromagnetic data for earthquake hazards evaluations: An example from the Willamette Valley, Oregon Bulletin of the Seismological Society of America, December 1, 1999; 89(6): 1473 - 1483. [Abstract] [PDF]

				J. Bhattacharyya, S. Gross, J. Lees, and M. Hastings Recent earthquake sequences at Coso: Evidence for conjugate faulting and stress loading near a geothermal field Bulletin of the Seismological Society of America, June 1, 1999; 89(3): 785 - 795. [Abstract] [PDF]

				S. R. Dewberry and R. S. Crosson The MD 5.0 earthquake of 29 January 1995 in the Puget Lowland of western Washington: An event on the Seattle fault? Bulletin of the Seismological Society of America, August 1, 1996; 86(4): 1167 - 1172. [Abstract] [PDF]