Paleoseismicity of the Intermountain Seismic Belt from Late Quaternary faulting and parameter scaling of normal faulting earthquakes

Conference · Thu Apr 01 04:00:00 EST 1993 · Geological Society of America, Abstracts with Programs; (United States)

OSTI ID:5023614

Mason, D B; Smith, R B ^[1]

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1. Univ. of Utah, Salt Lake City, UT (United States). Dept. of Geology and Geophysics

The eastern Basin-Range, 1,300 km-long Intermountain Seismic Belt (ISB) is reflected by a [approximately]100 km-wide zone of scattered earthquakes that in general do not correlate with the mapped Quaternary faults. Yet this region has experienced two of the largest historic earthquakes in the western US, the M[sub S] = 7.3, Borah Peak, Idaho, and the M[sub S] = 7.5, Hebgen Lake, Montana, events, which occurred in areas that had previously low historical seismicity. These observations indicate the lack of spatial and temporal uniformity between the historical and Holocene seismic record. The authors have studied this problem by first investigating fault-magnitude scaling relationships using a global set of 16 large normal- to oblique-slip earthquakes, then applying the scaling laws to data from a compilation of well studied Late Quaternary faults of the ISB. Several regression models were evaluated but the authors found that magnitudes predicted by displacement alone were consistently 20% larger than those determined from lengths. They suggest that the best estimator is given by: M[sub S] = 0.47 log (d[sub sM]L[sub s]) + 6.1. These results revealed at least 24 large multiple-segment, paleoearthquakes, 6.3 [le] M[sub s] [le] 7.3, that were associated with faults within the dual-branched seismicity belt which surrounds the aseismic Snake River Plain in the central ISB. They believe this unusual bow-wave pattern of seismicity and faulting is related to plume-plate interaction associated with the Yellowstone hotspot with an additional component of concomitant Basin-Range extension. In the southern ISB, the 370 km-long Wasatch fault, Utah, experienced at least 7 multiple-segment paleoearthquakes, 7.1 [le] M[sub s] [le] 7.3, and contrasts with a historic record of seismic quiescence. Intraplate crustal extension is though to be the primary mode of regional strain release for this region of the ISB.

• OSTI ID: 5023614
• Report Number(s): CONF-9305259--
• Conference Information: Journal Name: Geological Society of America, Abstracts with Programs; (United States) Journal Volume: 25:5
• Country of Publication: United States
• Language: English

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58 GEOSCIENCES
580000* -- Geosciences
CENOZOIC ERA
COMPILED DATA
DATA
DATA ANALYSIS
DEVELOPED COUNTRIES
EARTHQUAKE FOCI
EARTHQUAKE MAGNITUDE
GEOLOGIC AGES
GEOLOGIC FAULTS
GEOLOGIC FRACTURES
GEOLOGIC HISTORY
GEOLOGIC STRUCTURES
IDAHO
INFORMATION
MONTANA
NORTH AMERICA
NUMERICAL DATA
QUATERNARY PERIOD
SEISMICITY
USA