Contacts: Mario Aguilera
On Oct. 16, 1999,
approximately 37 miles from Palm Springs, Calif., a magnitude 7.1 earthquake
ripped through 28 miles of faults in the Mojave Desert. Because of the
area’s sparse population and development, the massive quake caused
virtually no major measurable injuries or destruction.
Yet the “Hector Mine” event, named after a long-abandoned mine in the area, has produced a treasure of information about earthquakes, faults, and ruptures for scientists at Scripps Institution of Oceanography at the University of California, San Diego.
Scripps’s Yuri Fialko, the lead author of the study, says the implications of the study include providing a new way to identify potentially active faults, helping to track when the last earthquake occurred in a fault zone, and perhaps better understanding the earthquake process.
Fialko calls the Hector Mine event the “perfect” earthquake for the satellite and radar technologies that he and his colleagues used.
It is the first event comprehensively imaged using interferometric synthetic aperture radar (InSAR), as Fialko and coauthors demonstrated in an earlier study published in Geophysical Research Letters. InSAR uses a series of satellite recordings to detect changes in Earth’s surface.
According to Science study coauthor David Sandwell, the fresh data gave researchers an uncommon and immediate window into earthquake processes in fault areas that are only typically imaged after being altered by natural forces such as rainstorms and unnatural forces such as off-road vehicle disruption.
and coauthors Duncan Agnew, Peter Shearer, and Bernard Minster of Scripps,
and Mark Simons of Caltech, studied the information to find unusual
signatures of fault displacements caused by Hector Mine in the Eastern
California Shear Zone (ECSZ) in an area thought to be relatively inactive.
The study argues that the backward motion on the faults is caused by the dissimilar material within the faults, rather than the frictional failure.
“We used an analysis model that effectively says that material within the faults is mechanically distinct from the material surrounding the faults,” said Fialko, of the Cecil H. and Ida M. Green Institute of Geophysics and Planetary Physics at Scripps. “The rocks within the faults appear to be softer.”
He says the fault
zones become strained during periods of stress, acting like a soft,
sponge-like material. The soft area thus becomes squeezed during periods
of energy release.
attributes these detailed results to the “breakthrough”
offered by InSAR technology.
“We hope that
NASA will launch the U.S. InSAR satellites to monitor surface changes
in California and elsewhere,” Fialko said. “This will dramatically
improve our ability to study earthquakes as well as other potentially
hazardous phenomena, such as volcanic activity and man-made deformation.”