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

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

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

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.

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

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