May 19th 05, 06:42 PM
MEDIA RELATIONS OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIF. 91109 TELEPHONE (818) 354-5011
http://www.jpl.nasa.gov
Alan Buis (818) 354-0474
Jet Propulsion Laboratory, Pasadena, Calif.
Erica Hupp/Dolores Beasley (202) 358-1237/1753
NASA Headquarters, Washington, D.C.
News Release: 2005-079 May 19, 2005
LA's 'Big Squeeze' Continues, Straining Earthquake Faults
New NASA research confirms that northern metropolitan Los
Angeles is being squeezed at a rate of 5 millimeters (0.2
inches) a year, straining an area between two earthquake
faults that serve as geologic bookends north and south of
the affected region.
The compression of the Los Angeles landscape is being
monitored by a network of more than 250 precision global
positioning system receivers known as the Southern
California Integrated Global Positioning System Network, as
well as by measurements from interferometric synthetic aperture
radar (InSAR) satellites operated by the European Space Agency.
Information from these two sources of precision ground
deformation measurements is accumulating and enhancing our
knowledge of the forces shaping the land surface in the Los
Angeles region. These forces include motion along faults due
to motions of the North American and Pacific tectonic plates
and ground movement caused by human activities, such as oil
drilling and pumping water into and out of local aquifers.
A team led by Dr. Donald Argus of NASA's Jet Propulsion
Laboratory, Pasadena, Calif., that includes scientists from the
University of California at Los Angeles, set out to distinguish
between motions induced by human activity and those generated
by movements of Earth's tectonic plates.
Their results, recently published in the Journal of Geophysical
Research, indicate the human-caused motions are very slow and
could not account for the significant ground shift observed in
northern Los Angeles.
The new study used space-based navigation to determine the
exact position of hundreds of points around the metropolitan
area to measure the strain building up across faults.
Scientists believe the strain will ultimately be released in
earthquakes much like the 1994 Northridge temblor. The study
also suggests which faults might be most likely to rupture.
"These findings remove uncertainty about the rate at which
strain is building up in northern metropolitan Los Angeles,"
Argus said. "In addition, by taking into account the effects
of humans and observations from the many new global
positioning system sites established in the past few years,
we can identify the areas where strain is building the fastest."
He cautioned, however, that more studies are needed, since
scientists do not yet fully understand the consequences and
risks of this stress accumulation. "Nevertheless, these data
have important implications for hazard management and
retrofitting strategies," Argus said.
The study finds strain is rapidly accumulating within an area
12 to 25 kilometers (7.5 to 15.5 miles) south of the San Gabriel
Mountains, primarily in the San Gabriel and San Fernando Valleys
and nearby hills. The region is located between the Puente
Hills fault, which begins south of downtown Los Angeles and
extends east, and the Sierra Madre fault, which runs along the
base of the San Gabriel Mountains.
The new analysis indicates the crust above the Los Angeles
segment of the Puente Hills Fault is being squeezed the most.
The finding suggests that the Puente Hills Fault and nearby
faults in the area, such as the upper Elysian Park Fault, may
be more likely to break than those elsewhere in metropolitan
Los Angeles. Previous studies have estimated the Puente Hills
Fault might generate an earthquake of magnitude 6.6 to 7.5.
The researchers constructed models of the accumulating strain,
varying which faults "creep" (move continuously without producing
earthquakes), how fast they creep, and the depths at which the faults
go from being "locked" in place (and building strain) to creeping.
The model that best fit their actual global positioning system
observations is one where a thrust fault (a fault where one block of
Earth shifts up or down relative to the other) is locked above 6
kilometers (3.7 miles) deep and creeps at about 9 millimeters (0.4
inches) a year beneath that depth. From that model, they inferred
that the deep part of the Los Angeles segment of the Puente Hills
Fault is creeping, as is a deep unknown buried fault east of downtown
that lies north of the Whittier Fault and south of the Sierra Madre
Fault. The model does not allow scientists to infer which fault
segments are locked, however.
Argus said a significant discrepancy exists between the relatively
shallow locking depth of their model and the historical record
showing that earthquakes that struck the region in 1971 and 1994
were much deeper. Scientists speculate the discrepancy may be due
to the presence of sediments filling parts of the Los Angeles basin.
Further studies are planned to examine how these sediments
may be affecting fault strain in the region.
The study used InSAR data collected from 1992 to 2000 from the
European Space Agency's European Remote Sensing satellites to
estimate vertical ground motion. Horizontal strain buildup
measurements were made from Southern California Integrated Global
Positioning System Network observations from 1994 to 2004.
JPL is managed for NASA by the California Institute of Technology in
Pasadena.
-end-
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIF. 91109 TELEPHONE (818) 354-5011
http://www.jpl.nasa.gov
Alan Buis (818) 354-0474
Jet Propulsion Laboratory, Pasadena, Calif.
Erica Hupp/Dolores Beasley (202) 358-1237/1753
NASA Headquarters, Washington, D.C.
News Release: 2005-079 May 19, 2005
LA's 'Big Squeeze' Continues, Straining Earthquake Faults
New NASA research confirms that northern metropolitan Los
Angeles is being squeezed at a rate of 5 millimeters (0.2
inches) a year, straining an area between two earthquake
faults that serve as geologic bookends north and south of
the affected region.
The compression of the Los Angeles landscape is being
monitored by a network of more than 250 precision global
positioning system receivers known as the Southern
California Integrated Global Positioning System Network, as
well as by measurements from interferometric synthetic aperture
radar (InSAR) satellites operated by the European Space Agency.
Information from these two sources of precision ground
deformation measurements is accumulating and enhancing our
knowledge of the forces shaping the land surface in the Los
Angeles region. These forces include motion along faults due
to motions of the North American and Pacific tectonic plates
and ground movement caused by human activities, such as oil
drilling and pumping water into and out of local aquifers.
A team led by Dr. Donald Argus of NASA's Jet Propulsion
Laboratory, Pasadena, Calif., that includes scientists from the
University of California at Los Angeles, set out to distinguish
between motions induced by human activity and those generated
by movements of Earth's tectonic plates.
Their results, recently published in the Journal of Geophysical
Research, indicate the human-caused motions are very slow and
could not account for the significant ground shift observed in
northern Los Angeles.
The new study used space-based navigation to determine the
exact position of hundreds of points around the metropolitan
area to measure the strain building up across faults.
Scientists believe the strain will ultimately be released in
earthquakes much like the 1994 Northridge temblor. The study
also suggests which faults might be most likely to rupture.
"These findings remove uncertainty about the rate at which
strain is building up in northern metropolitan Los Angeles,"
Argus said. "In addition, by taking into account the effects
of humans and observations from the many new global
positioning system sites established in the past few years,
we can identify the areas where strain is building the fastest."
He cautioned, however, that more studies are needed, since
scientists do not yet fully understand the consequences and
risks of this stress accumulation. "Nevertheless, these data
have important implications for hazard management and
retrofitting strategies," Argus said.
The study finds strain is rapidly accumulating within an area
12 to 25 kilometers (7.5 to 15.5 miles) south of the San Gabriel
Mountains, primarily in the San Gabriel and San Fernando Valleys
and nearby hills. The region is located between the Puente
Hills fault, which begins south of downtown Los Angeles and
extends east, and the Sierra Madre fault, which runs along the
base of the San Gabriel Mountains.
The new analysis indicates the crust above the Los Angeles
segment of the Puente Hills Fault is being squeezed the most.
The finding suggests that the Puente Hills Fault and nearby
faults in the area, such as the upper Elysian Park Fault, may
be more likely to break than those elsewhere in metropolitan
Los Angeles. Previous studies have estimated the Puente Hills
Fault might generate an earthquake of magnitude 6.6 to 7.5.
The researchers constructed models of the accumulating strain,
varying which faults "creep" (move continuously without producing
earthquakes), how fast they creep, and the depths at which the faults
go from being "locked" in place (and building strain) to creeping.
The model that best fit their actual global positioning system
observations is one where a thrust fault (a fault where one block of
Earth shifts up or down relative to the other) is locked above 6
kilometers (3.7 miles) deep and creeps at about 9 millimeters (0.4
inches) a year beneath that depth. From that model, they inferred
that the deep part of the Los Angeles segment of the Puente Hills
Fault is creeping, as is a deep unknown buried fault east of downtown
that lies north of the Whittier Fault and south of the Sierra Madre
Fault. The model does not allow scientists to infer which fault
segments are locked, however.
Argus said a significant discrepancy exists between the relatively
shallow locking depth of their model and the historical record
showing that earthquakes that struck the region in 1971 and 1994
were much deeper. Scientists speculate the discrepancy may be due
to the presence of sediments filling parts of the Los Angeles basin.
Further studies are planned to examine how these sediments
may be affecting fault strain in the region.
The study used InSAR data collected from 1992 to 2000 from the
European Space Agency's European Remote Sensing satellites to
estimate vertical ground motion. Horizontal strain buildup
measurements were made from Southern California Integrated Global
Positioning System Network observations from 1994 to 2004.
JPL is managed for NASA by the California Institute of Technology in
Pasadena.
-end-