Evidence for mid-Holocene surface rupture on the Oquirrh fault zone, Utah

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

OSTI ID:5023022

Olig, S S; Lund, W R; Black, B D ^[1]

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1. Utah Geological Survey, Salt Lake City, UT (United States)

The Oquirrh fault zone (OFZ) bounds the east side of Tooele Valley, extending along the western base of the northern Oquirrh Mountains in the Basin and Range Province. This fault has long been recognized as a potential source for large earthquakes that would affect the city of Tooele, Tooele Army Depot, and the populous central Wasatch Front, including Salt Lake City, Utah. Scarps of the OFZ offset the Provo shoreline of Lake Bonneville and previous studies of scarp morphology suggested that the most recent surface-rupturing earthquake (MRE) occurred between 9 and 13 kya. The authors results from trenches excavated across scarps near the mouth of Big Canyon indicates that the MRE is actually much younger and occurred within the last 7,000 years. At the Big Canyon site, a wide graben (50 to 140 m) is formed by a west-facing main fault scarps as high as 18 m, and an east-facing antithetic fault scarp as high as 1.5 m. They excavated two trenches across the main scarp, one of which extended across the graben and antithetic fault scarp. The trenches exposed similar stratigraphy with a prominent main fault zone and colluvial wedge. An organic-rich debris-flow deposit overlies Lake Bonneville transgressive beach and deep-water sediments on the downthrown side of the fault, whereas a thick sequence of pre-Bonneville alluvial-fan deposits was exposed on the upthrown side of the fault. Although very different styles of deformation were exposed in each trench, colluvial-wedge deposits overlie the debris flow on the downthrown block in both trenches. Samples collected from the debris-flow deposit, directly under the colluvial wedge, yielded radiocarbon ages of 6,840 [+-] 100 yr B.P. (north trench) and 7,650 [+-] 90 yr B.P. (south trench).

• OSTI ID: 5023022
• 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
AGE ESTIMATION
CENOZOIC ERA
DEVELOPED COUNTRIES
EARTHQUAKES
GEOLOGIC AGES
GEOLOGIC FAULTS
GEOLOGIC FRACTURES
GEOLOGIC HISTORY
GEOLOGIC STRUCTURES
GEOLOGY
NORTH AMERICA
QUATERNARY PERIOD
SEISMIC EFFECTS
SEISMIC EVENTS
USA
UTAH