Great Basin and Sierra Nevada
The Lake Tahoe basin lies within one of the most active parts of the Sierra Nevada-Great Basin boundary zone. New geologic mapping and new geophysical data show that numerous active faults and landslides occur within the Lake Tahoe basin. Active faults define a northeast-southwest-trending zone, the North Tahoe-Incline Village fault zone, a north-south-trending zone, the West Tahoe-Dollar Point fault zone, and a northwest-trending zone, the Tahoe-Sierra frontal fault zone. These zones include faults on land and on the lake bottom, where scarps are well preserved. Other faults in many other areas around the basin may be active, but data are presently insufficient to characterize most of them. The October 30, 1998, M4.9 earthquake occurred near the North Tahoe-Incline Village fault zone, and other historic earthquakes may have occurred along both fault zones as well.
Active faults are spatially associated with landslides along the sides and bottom of the lake, suggesting that at least some of the landslides have been triggered by large earthquakes. Evidence also exists for seiches or tsunamis that may have been generated by past earthquakes and landslides.
Currently available data indicate that Lake Tahoe lies within a tectonically active, asymmetric half-graben. Large (M7) earthquakes can be expected along active faults in the basin in the future, and emergency planning scenarios should include provisions for strong ground-shaking, landslides, and seiches. Additional research, both on land and within the lake, is underway to quantify the seismic hazard within the basin.
Figures & Tables
Great Basin and Sierra Nevada, the second volume of the Geological Society of America Field Guide Series, focuses on the dynamic and spectacular geology of this region, providing the inspiring backdrop for the 2000 GSA Annual Meeting in Reno. This volume gives complete coverage of field trips held in conjunction with that meeting, and contains 20 chapters organized into three sections. The first section consists of 16 chapters arranged in geochronological order, beginning with the active tectonics of Lake Tahoe and the historical surface faulting and paleoseismicity of the central Nevada seismic belt, and ending with the Neoproterozoic glacial record of Death Valley. In between are chapters dealing with Basin and Range extension, Eocene magmatism, Mesozoic plutonism in the Sierra Nevada, Paleozoic subduction, and Ordovician stratigraphy, to name a few. The second section covers the geology of the Nevada Test Site and the nuclear-waste repository at Yucca Mountain. The last section is an invited field guide from the 1999 GSA Cordilleran Section meeting that covers the wines and geology of Napa Valley, California. Overall, Great Basin and Sierra Nevada is a comprehensive compilation of new and exciting research on this amazingly diverse region, with well-crafted guides to field localities of special interest. Full-color plates in some chapters make this guide an especially appealing and useful volume.