Prehistoric movement along the 1915 Pleasant Valley fault zone and implications for the central Nevada seismic belt

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

OSTI ID:5126566

Machette, M N; Haller, K M ^[1]; Berryman, K R ^[2]

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1. Geological Survey, Denver, CO (United States)
2. New Zealand Crown Inst. for Geological and Nuclear Sciences, Ltd., Lower Hutt (New Zealand)

The 1915 Pleasant Valley earthquake formed 60-km of en echelon scarps at the northern end of the Central Nevada Seismic Belt (CNSB), which is defined by 11 surface-rupturing earthquakes in the past 140 yrs. This pattern of earthquake clustering implies a high strain rate for the CNSB; one would expect that the associated faults would have average recurrence intervals (RI) of several thousands of years, rather than tens of thousands of years as evidenced by geologic data. Mapping by R.E. Wallace and the author's team shows that the central part of the Pleasant Valley fault zone is characterized by (1) historic single-event scarps (commonly < 4 m high) on Holocene and latest Pleistocene (10--20 ka ) alluvial and colluvial deposits, or (2) composite scarps (8--13 m high) on older alluvial deposits. These relations suggest that RIs for 1915-like earthquakes are at least 10--20 k.y. Last summer, the authors excavated four trenches across the Tobin and Pearce scarps to investigate the timing of prehistoric movement along the fault zone. Results of TL and [sup 14]C dating, tephrochronology, and quantitative soil studies could provide further evidence for long RIs. Colluvial wedges in the trenches record three or four faulting events at each site. In the Sheep Creek trench, three faulting events occurred after deposition of a mafic ash. One possibility is that this ash may be correlative to the Wadsworth ash bed which is found in the upper part of the Eetza Alloformation about 150 km southwest of Pleasant Valley. The studies suggest that the average RI of M[ge]7 earthquakes on the Pleasant Valley fault zone is measured in tens of thousands of years. Careful dating of paleoseismic events elsewhere in the CNSB will be required to document whether or not there were ancient episodes of temporal or spatial clustering and whether long RIs are typical of the CNSB.

• OSTI ID: 5126566
• 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

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
CENOZOIC ERA
DEVELOPED COUNTRIES
EARTHQUAKES
GEOLOGIC AGES
GEOLOGIC FAULTS
GEOLOGIC FRACTURES
GEOLOGIC HISTORY
GEOLOGIC STRUCTURES
NEVADA
NORTH AMERICA
QUATERNARY PERIOD
SEISMIC EVENTS
SEISMICITY
STRATA MOVEMENT
USA