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Freeway overpass collapse
Freeway overpass collapse in the 1994 magnitude 6.7, Northridge, California earthquake.
Earth's tectonic plates.
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Recent earthquakes around the world outline the boundaries of Earth's tectonic plates.
image of Western continental United States
Recent earthquakes in the continental United States.
ground movement represented as fringes, or contours of the movement.
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.
U.S. Geological Survey National Seismic Hazard Map
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.
words "EarthScope"
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
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
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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 of years.
image depicting stress being transferred to adjacent fault segments
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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 fault segments.
This map shows the slow crustal deformation measured in the decade before the Izmit Earthquake
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
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 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.
map shows the accumulation of deformation in southern California since 1800
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
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.
This map on the right shows the deficit in release of deformation since 1800
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 estimate.
image from animation that depicts simulated earthquakes
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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.

map with spots, or"anomalies," indicating locations where the potential for larger earthquakes
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
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 road sign pointing to Three Sisters Volcano, Oregon
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 1998.
Interferogram for the period from 1995 to 2001, draped over topography, looking east over the 3 Sisters volcano
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.
thermal activity in the Norris Geyser Basin of Yellowstone National Park
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
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.
map of Greece and Turkey shows the relative seismic hazard of the region
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 almost everywhere.
map of Greece and Turkey shows the relative seismic hazard of the region
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 results.
still from Zareh Gorjian
Animation depicting an artist's concept for a dedicated Interferometric Synthetic Aperture Radar (InSAR) mission
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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 highest priority.