The Scotts Mills, Oregon, earthquake of March 25, 1993; intensities, strong-motion data, and teleseismic data

Dewey, James W.; Reagor, B.G.; Johnson, Dennis A.; Choy, George L.; Baldwin, F.W.

doi:10.3133/ofr94163

Cited by 2 publications

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“…The estimated stress drop of 40 bar for the mainshock is average on a world-wide basis, supporting the view that the rather large damage was caused primarily by poor construction of the pre-1950 structures [Bonneville et al, 1993;Dewey et al, 1994], and not by exceptional properties of the source.…”

Section: Summary and Discussionmentioning

confidence: 55%

Moment‐tensor analysis using regional data: Application to the 25 March, 1993, Scotts Mills, Oregon, Earthquake

Nábělek¹,

Xia²

1995

Geophysical Research Letters

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In this paper we outline a procedure we use for routine moment‐tensor analysis of regional data from broadband seismic stations in northwestern North America and apply it to the moment magnitude 5.5, March, 1993, Scotts Mills, Oregon, earthquake. The results compare favorably with those obtained from teleseismic data. We found that the earthquake occurred at a depth of 13–15 km and had a mechanism with approximately equal amounts of reverse and right‐lateral strike‐slip components. The estimated stress drop of 40 bar is average on a world‐wide basis, supporting the view that the rather large damage was caused primarily by poor construction and not by exceptional properties of the source. The Scotts Mills earthquake is most likely related to the Mt. Angel Fault. This fault is a part of the Gales Creek‐Mt. Angel structural lineament (GCMAL) extending about 150 km across the Willamette Valley. At present data are not sufficient to estimate the likelihood of an earthquake involving the entire GCMAL, but given its length an earthquake of magnitude 7 is conceivable. The results of this study, together with investigations of other earthquakes, suggest that sparse broadband networks can be used efficiently for determining source parameters of earthquakes of magnitude greater than 4.0 in regions with infrequent seismicity.

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Section: Summary and Discussionmentioning

confidence: 55%

Moment‐tensor analysis using regional data: Application to the 25 March, 1993, Scotts Mills, Oregon, Earthquake

Nábělek¹,

Xia²

1995

Geophysical Research Letters

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

Thomas

Crosson

Yelin

1996

Bulletin of the Seismological Society of America

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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 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.

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The Scotts Mills, Oregon, earthquake of March 25, 1993; intensities, strong-motion data, and teleseismic data

Cited by 2 publications

References 0 publications

Moment‐tensor analysis using regional data: Application to the 25 March, 1993, Scotts Mills, Oregon, Earthquake

Moment‐tensor analysis using regional data: Application to the 25 March, 1993, Scotts Mills, Oregon, Earthquake

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

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