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The Lake Tahoe Report
UNR Scientists Study Earthquake Faults at
Tahoe
By John Cobourn, Water Resource Specialist and
Heather Segale, Education and Outreach Coordinator
Date: July 15, 2005
Article # 126
The June 26 earthquake centered
about 3 miles east of Truckee reminded us
that we live in a seismically active part of
North America. It measured 4.8 to 5.0 and
was the third earthquake of similar magnitude
in the past six years in the Truckee area. Although the faults there are not well-mapped,
geologists recognize that it is a region of
earthquake hazard.
In fact, this California-Nevada boundary area is second only to the California coast
in earthquake activity in the states of California and Nevada. One of the largest fault systems in this region is the Carson Range fault
system, which runs for 60 miles along the
east face of the Carson Range from Reno to
Markleeville. One of the more active faults in
this system is the Genoa Fault.
UNR scientists have discovered that
the Tahoe area has many active faults and
are busy mapping them.
Richard Schweickert, Ph.D., of the
UNR Geology Department, has been studying the faults here since the mid-1990s with
colleagues and graduate students in his department, the UNR Seismological Lab, and
the United States Geological Survey (USGS).
Although Lake Tahoe has not had a large
earthquake recently, Schweickert and his colleagues have mapped several previously undiscovered faults here and believe there are
many others yet to be found. They have undertaken detailed structural mapping, trenching, drilling, soil gas profiling, and geophysical
studies. They are developing a new digital
geologic map of the Lake Tahoe Basin, in cooperation with the Reno Field Office of the
USGS.
These scientists have uncovered evidence that Tahoe Basin faults have had prehistoric earthquakes of a magnitude of 7
within the past 10,000 years. However,
Schweickert says, “More trenching and other
detailed examination of the faults is needed in
order to determine more precisely when
these local earthquakes occurred.” From extensive study of other Great Basin fault
zones, scientists believe that large quakes
are “rare events” in the basin, meaning
quakes of magnitude 6.5 or greater occur on
individual faults about every 3,000 to 4,000
years.
There are at least three major fault
zones the Lake Tahoe Basin. All three appear
to be “normal faults,” which means a block of
crust rises on one side of the fault and slips
down on the other side. The North TahoeIncline Village fault zone runs from the deepest parts of the lake in a northeast direction
through Incline Village and north Stateline,
over the Mount Rose Highway summit and
down toward southwest Reno.
The West Tahoe-Dollar Point fault
zone is partially submerged under the lake. It
runs from approximately Emerald Bay to Carnelian Bay, and continues north toward
(Continued on page 2)
The Lake Tahoe Report airs each week on KOLO-TV News Channel 8 Tuesdays at 5 p.m. The Lake Tahoe Report weekly television segments and
newspaper articles are a collaborative effort between the University of Nevada Cooperative Extension and the UC Davis, Tahoe Environmental Research
Center. Funding was provided by the California State Water Resources Control Board and U.S. Forest Service, Lake Tahoe Basin Management Unit.
Coauthor John Cobourn is a water resource specialist with University of Nevada Cooperative Extension. Coauthor Heather Segale is the education and
outreach coordinator for the UC Davis, Tahoe Environmental Research Center. For more information, contact Heather Segale, (530) 583-3279, or logon
to www.lteec.org, www.tahoe.unr.edu, or terc.ucdavis.edu.
The Lake Tahoe Report
(Continued from page 1)
Truckee.
The Tahoe-Sierra frontal fault zone
extends from Donner Pass to the southeast
through the mountains on the west shore of
Lake Tahoe, to the area near Echo Summit
on Highway 50. This fault zone is believed to
form the boundary between the Sierra and
Great Basin geologic provinces.
Schweickert and his colleagues have
also found evidence of landslides and tsunamis in the Lake Tahoe Basin. Computer modeling shows that magnitude 7 earthquakes on
submerged faults could generate tsunamis. “It
is also possible that ground shaking from prehistoric earthquakes along any of these faults
may have triggered landslides within the
lake,” Schweickert says. “Evidence suggests
that some of the larger underwater landslides
may also have caused tsunamis. Many of the
features in the lake and along the shore are
youthful, meaning 10,000 years old or
younger, and our group and others are trying
to determine when they occurred.”
In next week’s article, we will describe
some new findings of underwater geologic
mapping in Lake Tahoe by Schweickert and
his colleagues.
Watch for the “Lake Tahoe Report” in
the North Lake Tahoe Bonanza each Friday,
and tune in to KOLO-TV News Channel 8
Tuesdays at 5 p.m. to learn more. The “Lake
Tahoe Report” is a collaborative effort of the
Lake Tahoe Environmental Education Coalition, University of Nevada Cooperative Extension, UC Davis Tahoe Environmental Research Center and the California State Water
Resource Control Board. For more information, contact Heather Segale, UC Davis Tahoe Environmental Research Center, (530)
583-3279, or logon to www.lteec.org or
www.tahoe.unr.edu.
The Lake Tahoe Report airs each week on KOLO-TV News Channel 8 Tuesdays at 5 p.m. The Lake Tahoe Report weekly television segments and
newspaper articles are a collaborative effort between the University of Nevada Cooperative Extension and the UC Davis, Tahoe Environmental Research
Center. Funding was provided by the California State Water Resources Control Board and U.S. Forest Service, Lake Tahoe Basin Management Unit.
Coauthor John Cobourn is a water resource specialist with University of Nevada Cooperative Extension. Coauthor Heather Segale is the education and
outreach coordinator for the UC Davis, Tahoe Environmental Research Center. For more information, contact Heather Segale, (530) 583-3279, or logon
to www.lteec.org, www.tahoe.unr.edu, or terc.ucdavis.edu.