thumbnail

The 25 March 1993 Scotts Mills, Oregon, earthquake and aftershock sequence: Spatial distribution, focal mechanisms, and the mount angel fault

Bulletin of the Seismological Society of America

By:
, , , and

Links

  • The Publications Warehouse does not have links to digital versions of this publication at this time
  • Download citation as: RIS

Abstract

The 25 March 1993 ML = 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 after-shocks with quality locations. Hypocenters of these aftershocks lie on a northwesttrending 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.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
The 25 March 1993 Scotts Mills, Oregon, earthquake and aftershock sequence: Spatial distribution, focal mechanisms, and the mount angel fault
Series title:
Bulletin of the Seismological Society of America
Volume
86
Issue:
4
Year Published:
1996
Language:
English
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Bulletin of the Seismological Society of America
First page:
925
Last page:
935