The Quaternary Tahoe-Medicine Lake trough: The western margin of the Basin and Range transition, NE California
- Pacific Gas and Electric Co., San Francisco, CA (United States). Geoscience Dept.
- Woodward-Cycle Federal Services, Oakland, CA (United States)
The Tahoe-Medicine Lake trough is a series of small right-stepping, en echelon tectonic depressions that extend 400 km NNW from Lake Tahoe to near the Oregon border. The trough developed since the Miocene, and forms the eastern edge of the Sierra Nevada and southern Cascade Mountains, and the western boundary of the Plumas province and Modoc Plateau, which are transitional to the Basin and Range. The geomorphic expression of the trough indicates late Pleistocene and Holocene fault activity along its length. The continuity of the structure, however, has been masked in places by volcanic deposits that have filled or partly filled the tectonic lows. Moderate historical earthquakes (M5-6) have occurred only along the southern trough. Microearthquakes prominently follow the trough from Lake Tahoe north [omega] Lake Almanor. From there northward, seismicity patterns are predominantly shallow (<5 km) volcanic-related clusters at Mt. Lassen, Medicine Lake, and Tennent and Stephens passes. Geologic and seismicity data indicate that the NW-trending south-central section has a significant component of right-slip, which appears to be related to the Walker Lane shear zone. To the south, the trough is the NNW-striking, 10- to 20-km-wide Tahoe depression, which extends from Lake Tahoe to the Sierra Valley and is partly filled with Quaternary volcanic deposits near Truckee. The escarpment and probable displaced moraines along this section indicate late Pleistocene and possibly Holocene activity. Seismicity is diffuse except in the vicinity of the 1966 Truckee earthquake (M6.0). Northward, from Sierra Valley to American Valley, the trough changes trend to the NW, and is the 6-km-wide Plumas trench, which down-faults the Mehrten Fm. (Miocene to early Pliocene) about 1,000 m.
- OSTI ID:
- 5024451
- Report Number(s):
- CONF-9305259-; CODEN: GAAPBC
- Journal Information:
- Geological Society of America, Abstracts with Programs; (United States), Vol. 25:5; Conference: 89. annual meeting of the Cordilleran Section and the 46th annual meeting of the Rocky Mountain Section of the Geological Society of America (GSA), Reno, NV (United States), 19-21 May 1993; ISSN 0016-7592
- Country of Publication:
- United States
- Language:
- English
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