1983 Borah Peak, Idaho earthquake: a review of seismicity, surface faulting and regional tectonics
The October 28, 1983 Borah Peak, Idaho earthquake (M/sub s/ = 7.3) occurred in an area of low historic seismicity within east-central Idaho along a segment of the Lost River fault active during the Holocene. A dense network of portable short period seismographs (up to 45 stations, station spacings of 2 to 10 km) was installed beginning several hours after the main shock and operated for 22 days. In addition to records from the portable instrumentation, data from permanent seismograph stations operating in Idaho, Utah, Montana, Oregon, Washington, and Wyoming, provide a good regional data base. No foreshock activity above magnitude 2.0 (M/sub L/) was detected for the two month period preceding the main shock. The distribution of 421 aftershocks of M/sub L/ > 2 defines an epicentral pattern, 75 km x 15 km, trending north-northwest parallel to the surface rupture but displaced laterally southwest by 5 to 10 km. The epicenter of the main shock is approximately 14 km south-southwest of the end of surface faulting. This relationship suggests unilateral rupture propagating to the northwest. Aftershocks extend to depths of approximately 16 km and in the southeastern portion of the aftershock pattern define a zone, dipping approximately 45/sup 0/ SW, that intersects the surface near the fault scarp. The entire aftershock zone as observed during the first 3.5 weeks was active shortly after the main shock occurred. Fault plane solutions indicate predominantly normal faulting with varying components of strike slip. 17 refs., 8 figs. 1 tab.
- Research Organization:
- EG and G Idaho, Inc., Idaho Falls (USA)
- DOE Contract Number:
- AC07-76ID01570
- OSTI ID:
- 5376508
- Report Number(s):
- EGG-M-09985; CONF-8510118-4; ON: DE85017474
- Country of Publication:
- United States
- Language:
- English
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