This 3D airborne light detection and ranging (lidar) oblique view of the Borrego Fault, taken from the post-earthquake topographic survey. NASA said the colours in the landscape represent elevation changes during the earthquake. Image by UC Davis
Geologists have come up with a new 3D tool that studies how earthquakes change landscapes, paving the way for scientists to have more insight into how earthquakes behave. The research team studied the earthquake that struck near Mexicali, northern Mexico, on 4 April 2010.
They believe they have reported the most comprehensive before-and-after picture yet of an earthquake zone.
The 2010 earthquake itself measured 7.2 on the moment magnitude scale and supposedly lasted for about a minute and a half. It started 26 kilometres south of Guadalupe Victoria, Baja, California, in Mexico.
The geologists have used data from the earthquake and their findings have recently been published in Science. The team comprised scientists from the US, Mexico and China, including geophysicist Eric Fielding of NASA’s Jet Propulsion Laboratory (JPL), which is based in Pasadena, California.
Michael Oskin, geology professor at the University of California, Davis, was the lead author of the study, which was funded by the National Science Foundation, the U.S. Geological Survey, Consejo Nacional de Ciencia y Tecnología (Mexico) and NASA.
Oskin said the researchers were able to make a detailed scan after the earthquake over about 363 sq kilometres in less than three days.
Fault zones and earthquakes
The scientists believe they have reported the most comprehensive before-and-after picture yet of an earthquake zone.
Fielding said the study provides new information on how rocks in and around fault zones are deformed during earthquakes.
“It helps scientists understand past events and assess the likelihood of future earthquakes in other complex systems of faults,” he said.
Light detection and ranging
So how did they carry out the 3D mapping? The team of geologists worked with the National Center for Airborne Laser Mapping. They flew over the earthquake area near Mexicali with lidar (light detection and ranging). Such technology works by bouncing laser pulses off the ground and measures their reflection to determine the height of the surface.
NASA said today that new airborne lidar equipment can measure features in the surface height to within a few inches.
It was back in 2006 that the Mexican government mapped the area with lidar. When the earthquake occurred in 2010, Oskin and Ramon Arrowsmith at Arizona State University applied for and received funding from the National Science Foundation to carry out an immediate aerial survey of the previously mapped area.
By comparing pre- and post-earthquake surveys, the team said they could see exactly where the ground moved and by how much.
This 1.5 meter-high surface rupture, called a scarp, formed in just seconds along the Borrego fault during the magnitude 7.2 El Mayor Cucapah earthquake in northern Baja, California, on 4 April 2010. NASA says topographic surveys of the surrounding landscape reveal the complexity of earthquake deformation, including how this fault interacted with adjacent faults. Image by Centro de Investigacion Cientifica y de Educacion Superior de Ensenada (CICESE)
Out of the blue
The 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 crust, they said.
“This sort of earthquake happens out of the blue,” explained Oskin.
He pointed to how the new lidar survey shows how seven of these small faults came together to cause a major earthquake.
NASA vehicles
NASA’s JPL has been flying its airborne uninhabited aerial vehicle synthetic aperture radar (UAVSAR) over the California border region to measure ground deformation in the area since 2009. UAVSAR, which flies on a NASA Gulfstream III aircraft, uses a different technique – interferometric synthetic aperture radar – to measure ground deformation over large areas, according to the space agency.
Apparently, UAVSAR flew repeat GPS-guided passes over the California side of the border region twice in 2009 and six times since the Baja quake, imaging it and its continuing deformation since.
Fielding said NASA recently secured approvals from the Mexican government and began flying UAVSAR south of the California border over the Baja, California, earthquake zone in February 2012.
He said these flights will be conducted every three months to monitor fault movements.
