アメリカ合衆国西部,シェラネバダ山脈内タホ湖底の活断層

Lake Tahoe sits astride the crest of the Sierra Nevada and is cut by the border between California and Nevada. Physiographic evidence has now long been the basis to interpret that Lake Tahoe occupies a fault graben. The steep and straight range fronts and scarps that bound the east, west, and northern edges of the basin have been referred to as the East, West and North Tahoe faults, respectively. Yet little is known about the rate and recency of faulting along the faults. Therefore we conducted the seismic reflection survey in this lake.<BR>Survey of the area offshore of Sugar Pine Point provided evidenc e of a north-striking zone of faults that cut sediments of the lake bottom. The section displays a broad fault graben with near -surface sediments sharply truncated by faults. Nonetheless, the fault displacement of shallow sediments argues for relatively young displacements.<BR>The faulting of young sediments is al so indicated in the profiles collected within Crystal Bay. The profiling delineated a distinct northwest striking scarp in sediments that corresponds approximately with the offshore projection of the Incline Village Fault. The warping and faulting of the lake bottom sediments is consistent with a late Pleistocene to Holocene recency of movement.<BR>Logistics limited the opportunity to conduct seismic reflection within Lake Ta hoe to 2 days. The available time did not allow an accompanying effort to obtain sample cores from the sites to aid in directly determining the age of the sediments involved in the faulting and warping. Nonetheless, the profiles do preliminary but arguable evidence for very young faulting in. Lake Tahoe. The results provided here should, at minimum, provide a springboard for future efforts.