| Freeway overpass collapse in the 1994 magnitude
6.7, Northridge, California earthquake.
Recent earthquakes around the world outline the boundaries
of Earth's tectonic plates.
| Recent earthquakes in the continental United
| Interferometric synthetic aperture radar (InSAR)
uses a satellite’s radar picture of the Earth’s surface. When
that satellite takes the same picture at some time interval
later, the two images are compared for differences in a computer
to produce a picture of the ground’s movement during the interval.
This picture of ground movement is represented as fringes,
or contours of the movement. Each fringe, or contour, represents
an additional increment of movement that can be summed to give
the total picture of ground distortion at a point.
| This U.S. Geological Survey National Seismic
Hazard Map depicts earthquake hazard by showing, by contour
values, the earthquake ground motions (as a percent of the
force of gravity) that have a common given probability of being
exceeded in 50 years.
| EarthScope is an integrated, multi-agency program
led by the National Science Foundation, U.S. Geological Survey
and NASA that applies modern observational, analytical, and
telecommunications technologies to investigate the structure
and evolution of the North American continent and the physical
processes controlling earthquakes and volcanic eruptions. A
dedicated InSAR satellite is a vital component of EarthScope.
| Aerial view of the Northridge earthquake region
in the Los Angeles area. The Santa Susanna Mountains are shown
in the foreground and are north of the San Fernando Valley.
These mountains grew 38 centimeters (15 inches) in the 1994
Northridge earthquake and continued to grow quietly for two
years following the earthquake. The projection of the fault
is shown as the oblique rectangle. The fault dips at a 45 degree
angle. The top of the fault underlies the Santa Susanna Mountains
at a depth of 4.8 kilometers (3 miles). The bottom of the fault
is under the central San Fernando Valley, in Reseda, and is
at a depth of about 19.3 kilometers (12 miles). The region
above the fault moved upwards and to the north along the fault.
Computer generated simulation of the 1994 Northridge earthquake.
The flyover animation shows the topography of the region, including
the San Fernando Valley, the mountains to the North and the
ocean to the South. The yellow line shows the projection of
the fault onto the surface. The fringes show Simulated Synthetic
Aperture Radar data. Each fringe is similar to a contour on
a map and represents approximately 6.35 centimeters (2.5 inches)
of motion. Overall the mountains grew 38.1 centimeters (15
inches) as a result of the earthquake. Following the earthquake,
the mountains continued to grow another 12.7 centimeters (5
inches) for two years following the earthquake. 90 percent
of that continued growth was quiet and was not a result of
aftershocks. Space-based observations of surface deformation
make it possible to measure the quiet strain build up and release
associated with earthquakes. The models help us study the entire
earthquake cycle, which takes place over hundreds to thousands
This animation was developed by Dr. Wayne Thatcher’s group
at the United States Geological Survey as part of their work
explaining the 1999 earthquake in Izmit, Turkey. Imagine that
a square grid of streets had been laid out in the area following
the previous earthquake, almost 300 years ago. The grid would
have been deformed, slowly but surely, leading up to the earthquake,
when the fault broke and the elastic energy stored in the deformed
crust was released, with stress being transferred to adjacent
| This map shows the slow crustal deformation
measured in the decade before the Izmit Earthquake by Rob Reilinger
of the Massachusetts Institute of Technology and a group of
international collaborators. The arrows show the direction
and speed of motions of the Earth’s surface measured using
the global positioning system. The highest velocities are about
25 millimeters (9.8 inches) a year, which is about the speed
at which your fingernails grow.
| This figure is a satellite radar image that
shows the deformation of the surface that occurred as a result
of the Izmit earthquake. The more closely spaced the fringes,
the larger the deformation. The red line represents the fault
that ruptured. Displacements of more than a meter occurred
close to the fault.
| The arrows show the direction and speed of
the motion of the crust of California observed over about the
last 10 years using the global positioning system. The gray
lines represent faults. The pattern is more complicated than
in Turkey because of the interaction of the many faults in
the Southern California fault system. The velocities show a
deformation pattern with an "eddy" near San Bernardino and
the crust deflecting westward through Los Angeles.
| This map shows the accumulation of deformation
in southern California since 1800 estimated using the MIT computer
model. The warmer colors show regions of higher accumulation
of deformation. The hottest area represents the trace of the
San Andreas Fault; there has also been substantial deformation
accumulated in the Mojave Desert.
| This map repeats on the left the accumulation
of deformation in southern California since 1800 estimated
using the MIT computer model. On the right is the deformation
released by earthquakes during the same time. The warmer colors
show regions of higher accumulation and release of deformation.
The northern section of the San Andreas Fault has had substantial
release of deformation, mostly during the 1857 and 1952 earthquakes.
Much less deformation has been released on the southern segment
of the San Andreas.
| The map on the right shows the deficit in release
of deformation since 1800 from the MIT computer model. It is
obtained by subtracting the deformation release from the deformation
accumulation in the preceding figures. The map on the left
shows the estimate obtained previously, by only considering
geological estimates of fault activity, without the information
obtained from space geodesy. The newer estimate (right) shows
more deficit in the Los Angeles region and northern Mojave,
and less deficit in the San Bernardino region, than the older
This animation depicts simulated earthquakes on the active
geological fault systems of California over a time period of
1,000 years. The colors represent data corresponding to movements
of the ground surface that would be seen by a radar satellite.
The "fringes" are due to the radar wavelength of 5.7 centimeters
(2.2 inches). One can determine the ground motion in the direction
of the line of sight to the spacecraft by counting the number
of complete fringes (color cycle) and multiplying by 5.7.
We can gain considerable understanding and insight by looking
at simulations such as this. For example, you can see that
the earthquakes, some of which are quite large, tend to "cluster" in
space and time. There will be a period of time during which
there are no earthquakes, then there will be a sudden "cluster" of
events in one area. Analysis of these simulations indicates
that this clustering pattern is due to the fact that the
earthquakes "interact" with each other. This means that an
earthquake on one section of fault may either advance or
retard the occurrence of earthquakes on other nearby fault
sections. Whether one event advances or retards another depends
primarily on the relative orientation of the fault segments.
So simulations have led us to conclude that the patterns
of earthquake activity we see are a direct result of the
geometry of the entire fault system.
When the fault system is very complex, as it is in California,
these activity patterns can become very complex and difficult
to interpret from observations alone. For that reason, computer
simulations are beginning to play a critical role in the
analysis and interpretation of earthquake data.
| This"scorecard" is a newly developed method
that is becoming useful for earthquake forecasting. The color
spots, or"anomalies," are locations where the potential for
larger earthquakes, with a magnitude of 5 or greater, may occur
within the next decade or so. The intensity of the color is
related to the likelihood of an earthquake occurring near that
spot. Our research indicates not that large earthquakes will
necessarily occur in these regions, but rather that the large
earthquakes that do occur are likely to be located near those
regions. We should emphasize that all the regions shown in
the figure represent a small subset of the regions that government
agencies such as the United States Geological Survey have already
identified as being susceptible to large earthquakes.
The color anomalies are computed by calculating the change
in potential for large earthquakes over the years 1990-2000.
The inverted triangles represent the larger earthquakes that
actually did occur during that time period, 1990-2000, located
in the picture for reference. The circles represent the five
larger earthquakes that have occurred in the region since
January 1, 2000, which is the period of applicability of
the forecast. It is important to point out that three of
these five large earthquakes have occurred after the paper
containing the figure was published in the Proceedings of
the National Academy of Sciences on February 19, 2002. These
three events therefore represent"unbiased" or"honest" successes
of the method, in the sense that the forecast was not changed
while the test events were being observed.
| This interferogram (map) depicts ground displacement
near the November 2003 magnitude 7.9 Denali earthquake in Alaska.
Each color cycle corresponds to 28 millimeters or about an
inch of ground displacement. Stars show epicenters (locations)
of the magnitude 7.9 main shock and the magnitude 6.9 foreshock
that occurred two weeks prior. The red line is the part of
the Denali fault that slipped in the main shock. The figure
shows how space geodetic imaging can now provide maps of earthquake
ground displacement in remote and largely inaccessible areas
like central Alaska on a routine basis.
| Photograph of Three Sisters Volcano, Oregon,
with old lava flow in the foreground and two of the three Sisters
on the skyline (the shy sister is hiding behind her larger
sibling). The volcano has been dormant (non eruptive) for the
last 1,500 years, but ground uplift suddenly resumed in about
| Interferogram for the period from 1995 to 2001,
draped over topography, looking east over the 3 Sisters volcano.
Total ground uplift during this time is about 13 centimeters
(5 inches). White tacks locate two continuous global positional
system sites that have operated since 2001 and show that uplift
at a rate of about 4 centimeters or 1.5 inches per year is
continuing to the present. This unusual uplift implies that
hot, fluid rock (‘magma’) is being pumped into the crust about
8 kilometers (5 miles) beneath the volcano, raising the possibility
of a future eruption. 3 Sisters is therefore being carefully
watched using space geodetic methods and seismic recording
networks to continually assess the hazard it poses to surrounding
areas, including the nearby community of Bend, Oregon.
| This photo shows an example of the unusual
thermal activity in the Norris Geyser Basin of Yellowstone
National Park that began in the spring of 2003. This activity
includes the occurrence of boiling water at the ground surface,
increase ground surface temperatures and unusual geyser activity
like that pictured here for Steamboat geyser. For example,
Steamboat normally erupts only every 10 years or so but has
erupted three times since 2000, including twice in March 2003.
| Interferogram for the period from 1996 to 2000
showing unusual ground uplift centered near Norris Geyser Basin
in Yellowstone National Park. This uplift, which occurred during
1998-2000, was probably due to injection of hot, fluid rock
about 18 kilometers (10 miles) deep beneath Yellowstone. This
injection at depth stretched the top several miles of the Earth’s
crust under Norris Geyser Basin, opening cracks in the rock
and permitting hot, gas saturated waters to seep towards the
Earth’s surface. They reached the surface in early 2003, producing
the thermal unrest that is still ongoing in the Norris area.
The dashed line shows an outline of Yellowstone. Yellow lines
are roads in the park.
| This map of Greece and Turkey shows the relative
seismic hazard of the region, with browner colors indicating
higher hazard. It was obtained using the relatively short (about
100 year) history of large earthquakes and the locations of
earthquake faults in the region and making assumptions about
how frequently earthquakes repeat in the same place. Note that
most of the map is brown, suggesting the hazard is quite high
| This map is the same as the previous one, but
also shows, with the black lines, where global positioning
system measurements made during the past 10 years indicate
the Earth’s surface is being strained (stretched or compressed).
The places that are being strained will eventually release
those built-up strains through large earthquakes. In fact,
nearly all future earthquakes will occur near these lines,
so the seismic hazard is actually only high in these locations
and is much lower everywhere else. Updated seismic hazard maps
are now being constructed that take into account the new GPS
Animation depicting an artist's concept for a dedicated Interferometric
Synthetic Aperture Radar (InSAR) mission. A primary tool of
space geodesy, InSAR works by comparing satellite radar images
of Earth taken at different times to detect ground movement.
A 2002 NASA study called a dedicated InSAR satellite to continuously
monitor surface deformation the solid Earth science community's