Mexico Quake Studies Uncover Surprises for California

MEDIA RELATIONS OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
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PASADENA, CALIF. 91109 TELEPHONE 818-354-5011
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Alan Buis 818-354-0474
Jet Propulsion Laboratory, Pasadena, Calif.
Alan.buis@jpl.nasa.gov

News release: 2010-421 Dec. 16, 2010

Mexico Quake Studies Uncover Surprises for California

The full version of this story with accompanying images is at:
http://www.jpl.nasa.gov/news/news.cfm?release=2010-421&cid=release_2010-421

PASADENA, Calif. -- New technologies developed by NASA and other agencies are revealing
surprising insights into a major earthquake that rocked parts of the American Southwest and Mexico
in April, including increased potential for more large earthquakes in Southern California.

At the fall meeting of the American Geophysical Union in San Francisco, scientists from NASA and
other agencies presented the latest research on the magnitude 7.2 El Mayor-Cucapah earthquake, that
region's largest in nearly 120 years. Scientists have studied the earthquake's effects in unprecedented
detail using data from GPS, advanced simulation tools and new remote sensing and image analysis
techniques, including airborne light detection and ranging (LiDAR), satellite synthetic aperture radar
and NASA's airborne Uninhabited Aerial Vehicle Synthetic Aperture Radar (UAVSAR).

Among their findings:

-- The earthquake is among the most complex ever documented along the Pacific/North American
tectonic plate boundary. The main shock activated segments of at least six faults, some unnamed
or previously unrecognized. It triggered slip along faults north of the border as far as 165
kilometers (about 100 miles) away, including the San Andreas, San Jacinto, Imperial and
Superstition Hills Faults, and many faults in California's Yuha Desert, some not previously
mapped. Some of this slip was quiet, without detectable earthquakes. Activity was observed on
several northwest-trending faults due for potentially large earthquakes.
-- The rupture's northern end in Southern California resembles the frayed end of a rope. The
complex, 32-kilometer (20-mile) network of faults that slipped there during and after the
earthquake-- many unnamed or previously unrecognized--reveals how the earthquake distributed
strain.
-- Satellite radar, UAVSAR and GPS station data show additional slip along some of the Yuha
Desert faults in the months after the main earthquake. Recent data from UAVSAR and satellite
radar show this slip slowed and probably stopped in late summer or early fall.
-- Mexico's Sierra Cucapah mountains were, surprisingly, lowered, not raised, by the earthquake.
-- The main rupture jumped an 11-kilometer (7-mile) fault gap—more than twice that ever observed
before.
-- UAVSAR and satellite radar reveal deep faulting that may be a buried continuation of Mexico's
Laguna Salada Fault that largely fills the gap to California's Elsinore Fault. This could mean the
fault system is capable of larger earthquakes. A connection had only been inferred before.
-- Analyses show a northward advance of strain after the main shock, including a pattern of
triggered fault slip and increased seismicity. The July 7, 2010 magnitude 5.4 Collins Valley
earthquake on the San Jacinto Fault may have been triggered by the main earthquake.
-- Forecasting methods in development suggest earthquakes triggered by the main shock changed
hazard patterns, while experimental virtual reality scenarios show a substantial chance of a
damaging earthquake north of Baja within three to 30 years of a Baja quake like the one in April.

"This earthquake is changing our understanding of earthquake processes along the Pacific/North
American plate boundary, including earthquake physics, forecast modeling and regional faulting
processes," said Professor John Fletcher of the Center for Scientific Research and Higher Education
at Ensenada (CICESE), Baja Calif., Mexico. Fletcher led a multi-agency Mexico fault mapping effort
that included the U.S. Geological Survey and California Geological Survey, among others.

UAVSAR, developed by NASA's Jet Propulsion Laboratory, Pasadena, Calif., uses a technique
called interferometric synthetic aperture radar to measure ground deformation over large areas to a
precision of 0.1 to 0.5 centimeters (0.04 to 0.2 inches). A NASA Gulfstream III aircraft carrying the
radar flew repeat GPS-guided passes over the California border region twice in 2009 and four times
since the April earthquake, imaging it and continuing deformation since. Field mapping since April
has demonstrated its ability to show remarkable surface rupture detail.

"UAVSAR is blanketing California's seismic danger zones about every six months to detect changes
such as earthquakes or creeping faults," said JPL Geophysicist Eric Fielding. "The major earthquake
in Baja last April is providing direct evidence that time-critical monitoring of hazardous faults is
possible through NASA-funded technology."

"The accurate and detailed imagery derived from synthetic aperture radar, and in particular
UAVSAR, produced a more complete picture of fault patterns, precisely guiding field geologists to
remote areas of fault rupture and saving significant mapping time," said geologist Jerry Treiman of the
California Geological Survey, Los Angeles.

JPL geophysicist Jay Parker said UAVSAR's precise images are adding realism to NASA's
QuakeSim crustal models and forecasts. "Once we have these precise measurements of the changing
landscape, we use them to deduce changes in stress that accelerate or delay the next major
earthquakes, with the help of structural models and forecasting tools," he said.

For more on UAVSAR, see: http://uavsar.jpl.nasa.gov/ . For more on QuakeSim, see:
http://quakesim.jpl.nasa.gov/ .

Additional media contacts: Ed Wilson, California Geological Survey, 916-323-1886,
Ed.Wilson@conservation.ca.gov ; Leslie Gordon, USGS, 650-329-4006, lgordon@usgs.gov ; Norma
Herrera, CICESE, 646-175-05-00, ext. 22164/22168, nherrera@cicese.mx .

JPL is managed for NASA by the California Institute of Technology in Pasadena.

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