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Seismic hazard: Faults discovered near Lake Tahoe could generate earthquakes ranging from 6.3 to 6.9

Date:
May 24, 2012
Source:
Geological Society of America
Summary:
Results of a new US Geological Survey study conclude that faults west of Lake Tahoe, Calif., referred to as the Tahoe-Sierra frontal fault zone, pose a substantial increase in the seismic hazard assessment for the Lake Tahoe region of California and Nevada, and could potentially generate earthquakes with magnitudes ranging from 6.3 to 6.9.

Lake Tahoe Faults, Shaded Relief Map. Shaded relief map of western part of the Lake Tahoe basin, California. Faults lines are dashed where approximately located, dotted where concealed, bar and ball on downthrown side. Heavier line weight shows principal range-front fault strands of the Tahoe-Sierra frontal fault zone (TSFFZ). Opaque white boxes indicate approximate segment boundaries and right steps in range front separating principal fault strands. EB— Emerald Bay; ELP—Ellis Peak; EP—Echo Peak; MT—Mt. Tallac; RP—Rubicon Peak; TW—Twin Peaks
Credit: James Howle , U.S. Geological Survey

Results of a new U.S. Geological Survey study conclude that faults west of Lake Tahoe, Calif., referred to as the Tahoe-Sierra frontal fault zone, pose a substantial increase in the seismic hazard assessment for the Lake Tahoe region of California and Nevada, and could potentially generate earthquakes with magnitudes ranging from 6.3 to 6.9. A close association of landslide deposits and active faults also suggests that there is an earthquake-induced landslide hazard along the steep fault-formed range front west of Lake Tahoe.

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Using a new high-resolution imaging technology, known as bare-earth airborne LiDAR (Light Detection And Ranging), combined with field observations and modern geochronology, USGS scientists, and their colleagues from the University of Nevada, Reno; the University of California, Berkeley; and the U.S. Army Corps of Engineers, have confirmed the existence of previously suspected faults. LiDAR imagery allows scientists to "see" through dense forest cover and recognize earthquake faults that are not detectable with conventional aerial photography.

"This study is yet one more stunning example of how the availability of LiDAR information to precisely and accurately map the shape of the solid Earth surface beneath vegetation is revolutionizing the geosciences," said USGS Director Marcia McNutt. "From investigations of geologic hazards to calculations of carbon stored in the forest canopy to simply making the most accurate maps possible, LiDAR returns its investment many times over."

Motion on the faults has offset linear moraines (the boulders, cobbles, gravel, and sand deposited by an advancing glacier) providing a record of tectonic deformation since the moraines were deposited. The authors developed new three-dimensional techniques to measure the amount of tectonic displacement of moraine crests caused by repeated earthquakes. Dating of the moraines from the last two glaciations in the Tahoe basin, around 21 thousand and 70 thousand years ago, allowed the study authors to calculate the rates of tectonic displacement.

"Although the Tahoe-Sierra frontal fault zone has long been recognized as forming the tectonic boundary between the Sierra Nevada to the west, and the Basin and Range Province to the east, its level of activity and hence seismic hazard was not fully recognized because dense vegetation obscured the surface expressions of the faults," said USGS scientist and lead author, James Howle. "Using the new LiDAR technology has improved and clarified previous field mapping, has provided visualization of the surface expressions of the faults, and has allowed for accurate measurement of the amount of motion that has occurred on the faults. The results of the study demonstrate that the Tahoe-Sierra frontal fault zone is an important seismic source for the region."


Story Source:

The above story is based on materials provided by Geological Society of America. Note: Materials may be edited for content and length.


Journal Reference:

  1. J. F. Howle, G. W. Bawden, R. A. Schweickert, R. C. Finkel, L. E. Hunter, R. S. Rose, B. von Twistern. Airborne LiDAR analysis and geochronology of faulted glacial moraines in the Tahoe-Sierra frontal fault zone reveal substantial seismic hazards in the Lake Tahoe region, California-Nevada USA. Geological Society of America Bulletin, 2012; DOI: 10.1130/B30598.1

Cite This Page:

Geological Society of America. "Seismic hazard: Faults discovered near Lake Tahoe could generate earthquakes ranging from 6.3 to 6.9." ScienceDaily. ScienceDaily, 24 May 2012. <www.sciencedaily.com/releases/2012/05/120524123236.htm>.
Geological Society of America. (2012, May 24). Seismic hazard: Faults discovered near Lake Tahoe could generate earthquakes ranging from 6.3 to 6.9. ScienceDaily. Retrieved October 31, 2014 from www.sciencedaily.com/releases/2012/05/120524123236.htm
Geological Society of America. "Seismic hazard: Faults discovered near Lake Tahoe could generate earthquakes ranging from 6.3 to 6.9." ScienceDaily. www.sciencedaily.com/releases/2012/05/120524123236.htm (accessed October 31, 2014).

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