December 4, 2003

David E. Steitz 
Headquarters, Washington
(Phone: 202/358-1730)

Alan Buis 
Jet Propulsion Laboratory, Pasadena, Calif.
(Phone: 818/354-0474) 

RELEASE: 03-390

PROGRESS, PROMISE IN SPACE-BASED EARTHQUAKE RESEARCH

Nearly 10 years after Los Angeles was shaken by the devastating, 
magnitude 6.7 Northridge earthquake, scientists at NASA and other 
institutions say maturing space-based technologies, new ground-based 
techniques and more complex computer models are rapidly advancing our 
understanding of earthquakes and earthquake processes. 

Dr. Andrea Donnellan, a geophysicist at NASA's Jet Propulsion 
Laboratory, Pasadena, Calif., says the past decade has seen 
substantial progress in space-based earthquake research. "We've 
confirmed through space observation the Earth's surface is constantly 
moving, periodically resulting in earthquakes, and we can measure 
both the seismically quiet motions before and after earthquakes, as 
well as the earthquakes themselves," she explains. "These 
technologies are allowing us to pursue lines of data and research we 
didn't know existed only a few years ago." 

Two months before the Northridge earthquake, Donnellan and university 
colleagues published a paper in the journal Nature on ground 
deformation north of Los Angeles' San Fernando Valley. Six years of 
Global Positioning System (GPS) data showed the area's faults were 
active and building up strain, and indicated the size and style of a 
potential earthquake there. Following the earthquake, the data made 
it possible to rapidly determine where the fault ruptured and to 
measure how the earthquake had deformed the Earth's surface.

Space-based instruments can image Earth movements to within fractions 
of an inch, measuring the slow buildup of deformation along faults, 
and mapping ground deformation after an earthquake. Two primary tools 
are the space-based GPS navigation system and Interferometric 
Synthetic Aperture Radar (InSAR). The latter compares satellite radar 
images of Earth taken at different times to detect ground movement. 

InSAR complements surface measurements because it lets us look at 
whole regions in a spatial context. An InSAR mission is also a key 
component of EarthScope, a jointly led initiative by the National 
Science Foundation (NSF), NASA and the U.S. Geological Survey (USGS).

EarthScope studies the North American continent's structure and 
evolution, and the physical processes that control earthquakes and 
volcanic eruptions, according to Dr. James Whitcomb, section head for 
Special Projects, Earth Sciences Division, National Science 
Foundation, Arlington, Va.

Precise Earth surface-movement data measure strain, and provide a 
first approximation of where earthquakes are likely to occur, notes 
Dr. Brad Hager, a Massachusetts Institute of Technology (MIT) 
professor and co-author of the 1993 Nature paper. "In California, 
patterns of ground deformation are complicated by the complex 
interactions between fault systems," he says. "Interpreting this data 
requires computer models that can estimate how much deformation has 
accumulated and identify regions where strain should be released, but 
hasn't been."

University of California, Davis, researcher Dr. John Rundle says the 
complexity of earthquakes requires we study them as part of the full 
Earth system. "Most natural events result from interrelated Earth 
processes over various lengths and times," he adds. "These processes 
have variables that can't be readily observed, so understanding them 
requires computers."

NASA's QuakeSim project is developing a similar forecasting 
methodology. Its tools simulate earthquake processes, and manage and 
model the increasing quantities of data available. "We're focusing on 
observing and understanding earthquakes in space and time, and 
developing methods that use patterns of small earthquakes to forecast 
larger ones," Rundle explains. "New simulations of earthquakes on 
California's active faults are providing considerable insight, 
showing earthquakes tend to "cluster" in space and time due to their 
interactions: that is, an earthquake on one fault section can turn on 
or off earthquake activity on nearby fault sections, depending on the 
relative orientation of the faults. Simulations have led researchers 
to conclude that fault system geometry determines earthquake activity 
patterns."

A NASA/Department of Energy-funded research team reports promising 
results from an experiment to forecast earthquakes in 
southern/central California from 2000 to 2010. It uses mathematical 
methods to forecast likely locations of earthquakes above magnitude 5 
by processing data on earthquakes of about magnitude 3 from the past 
decade. The high-risk regions identified in the forecast are refined 
from those already identified by the government as susceptible to 
large earthquakes. Five earthquakes greater than magnitude 5 have 
occurred since the research was completed, all in those high-risk 
regions. 

Dr. Wayne Thatcher, a senior research geophysicist at the USGS, Menlo 
Park, Calif., says as these technologies are validated they will be 
transferred to end users. "Such data and models improve understanding 
of earthquake and volcanic processes, substantially refining seismic 
hazard maps and resulting in more appropriate, earthquake-resistant 
construction codes and more targeted retrofitting strategies," he 
says.

Points of contact for other organizations cited in this release are: 
Andy Fell, University of California, Davis, 530/752-4533; Stephanie 
Hannah, USGS, 206/220-4573; Deborah Halber, MIT, 617/258-9276; Cheryl 
Dybas, NSF, 703/292-7734.

For images and captions related to this Earthquake research visit: 

http://www.jpl.nasa.gov/releases/2003/esu-2.cfm 

	
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