this week’s issue of the journal Science, a team of scientists from the
United States, Mexico and China reports the most comprehensive
before-and-after picture yet of an earthquake zone, using data from the
magnitude 7.2 event that struck near Mexicali, Mexico, in April 2010.
can learn so much about how earthquakes work by studying fresh fault
ruptures,” said Michael Oskin, a geologist at the University of
California, Davis, and lead author of the paper.
team, working with the National Center for Airborne Laser Mapping
(NCALM), flew over the area with LiDAR (light detection and ranging),
which bounces a stream of laser pulses off the ground.
airborne LiDAR equipment can measure surface features to within a few
inches. The researchers were able to make a detailed scan over about 140
square miles in less than three days, Oskin said.
Oskin said that they knew the area had been mapped with LiDAR in 2006 by the Mexican government.
the earthquake occurred, Oskin and Ramon Arrowsmith at Arizona State
University received rapid-response funding from the National Science
Foundation (NSF) to carry out an immediate aerial survey to compare the
co-authors John Fletcher and Orlando Teran from Mexico’s Ensenada
Center for Scientific Research and Higher Education (CICESE) carried out
a traditional ground survey of the fault rupture, which helped guide
planning of the aerial LiDAR survey and interpretation of the results.
study is an excellent demonstration of an emerging tool for Earth
science,” said Greg Anderson, NSF program director for EarthScope, which
funded the research.
scientists conduct research using data from instruments that measure
motions of the Earth’s surface, record seismic waves, and recover rock
samples from the depths at which earthquakes originate.
models of fault rupture and off-fault deformation from large
earthquakes can provide new insights into fault behavior,” said
Anderson, “with implications for estimating seismic hazards.”
the ground, features like the five-foot escarpment created when part of
a hillside abruptly moved up and sideways are readily visible.
the LiDAR survey further reveals warping of the ground surface adjacent
to faults that previously could not easily be detected, Oskin said.
example, it reveals folding above the Indiviso Fault running beneath
agricultural fields in the floodplain of the Colorado River.
“That would be very hard to see in the field,” Oskin said.
survey also revealed deformation around a system of small faults that
caused the earthquake and allowed measurements that provide clues to
understanding how multi-fault earthquakes occur.
members used the “virtual reality” facility at UC Davis’s W. M. Keck
Center for Active Visualization in Earth Sciences to handle and view the
data from the survey.
By comparing pre- and post-earthquake surveys, they could see exactly where the ground moved and by how much.
2010 Mexicali earthquake did not occur on a major fault, like the San
Andreas, but ran through a series of smaller faults in the Earth’s
minor faults are common around major faults but are “underappreciated,”
Oskin said. “This sort of earthquake happens out of the blue.”
The new LiDAR survey shows that seven of these small faults came together to cause a major earthquake, Oskin said.
Hudnut, a geophysicist with the U.S. Geological Survey and co-author of
the paper, made the first use of airborne LiDAR about ten years ago to
document surface faulting from the Hector Mine earthquake.
“pre-earthquake” data were lacking. Since then, NCALM has carried out
LiDAR scans of the San Andreas system and other active faults in the
Western United States (a component of EarthScope), thereby setting a
trap for future earthquakes.
this case, fortunately, our CICESE colleagues had set such a trap and
this earthquake fell right into it and became the first ever to be
imaged by ‘before’ and ‘after’ LiDAR,” said Hudnut.
The post-event dataset collected by the team is publicly available on the Open Topography website.
co-authors of the paper are: Austin Elliott and Peter Gold, UC Davis;
J. Ramon Arrowsmith, Arizona State University; Alejandro Hinojosa Corona
and J. Javier Gonzalez Garcia, CICESE, Mexico; Eric Fielding, NASA Jet
Propulsion Laboratory; and Jing Liu-Zeng, Chinese Academy of Sciences.
The work was also supported by the U.S. Geological Survey, Mexico’s National Council of Science and Technology and NASA.
Please see EarthScope for more information.