The constant plate tectonic motions between the Pacific and North American plates guarantees that the crust in the western US is continually building up stress.
Crustal deformation refers to the changing earth’s surface caused by tectonic forces that are accumulated in the crust and then cause earthquakes.
Tracking Stress Buildup
The constant plate tectonic motions between the Pacific and North American plates guarantees that the crust in the western US is continually building up stress. The image of crustal velocities provided by extensive GPS coverage reveals where these velocities change rapidly over short distances, demanding that the intervening crustal rock stretch and build up stress over time. Such a map of the stress reveals two main lines where stress is concentrated: The San Andreas fault zone and the Eastern California Shear Zone. These zones have experienced numerous earthquakes over the century and a half that earthquakes have been historically observed.
The mechanism of stress buildup within these fault zones is uncertain. One hypothesis is that the hot rocks below the upper 15-km-thick layer (the upper crust that has the vast majority of continental earthquakes) flows continually in response to periodic earthquakes, forcing the upper crust to bend with this flow. Another hypothesis is that slip of the deeper continuation of faults, steady slip that doesn’t produce earthquakes but still involves motions across the fault, forces the upper crust around the faults to bend and thus concentrate stress. Both hypotheses are the subject of active research. But the fact remains that high stressing rates observed on the surface likely translate to high stressing rates at the depths (~10 km) where earthquakes typically nucleate, so these stressing rates are a guide to the seismic hazard.
Crustal Deformation
Crustal deformation refers to the changing earth’s surface caused by tectonic forces that are accumulated in the crust and then cause earthquakes. So understanding the details of deformation and its effects on faults is important for figuring out which faults are most likely to produce the next earthquake. There are several hypotheses about how this works, but more data is needed to determine which one is the best.
Crustal deformation is a heavily data driven field. To measure the motions of earth’s surface, the USGS employs a variety of methods, including LIDAR, the Global Positioning System (GPS), Interferometric Synthetic Aperture Radar (InSAR), creepmeters, and alinement arrays. In parts of the U.S. with few or no historically-recorded major earthquakes or where background seismicity is sparse, geodetic data may provide the only insight into present-day seismic hazard.
The constant plate tectonic motions between the Pacific and North American plates guarantees that the crust in the western US is continually building up stress.
Crustal deformation refers to the changing earth’s surface caused by tectonic forces that are accumulated in the crust and then cause earthquakes.
Tracking Stress Buildup
The constant plate tectonic motions between the Pacific and North American plates guarantees that the crust in the western US is continually building up stress. The image of crustal velocities provided by extensive GPS coverage reveals where these velocities change rapidly over short distances, demanding that the intervening crustal rock stretch and build up stress over time. Such a map of the stress reveals two main lines where stress is concentrated: The San Andreas fault zone and the Eastern California Shear Zone. These zones have experienced numerous earthquakes over the century and a half that earthquakes have been historically observed.
The mechanism of stress buildup within these fault zones is uncertain. One hypothesis is that the hot rocks below the upper 15-km-thick layer (the upper crust that has the vast majority of continental earthquakes) flows continually in response to periodic earthquakes, forcing the upper crust to bend with this flow. Another hypothesis is that slip of the deeper continuation of faults, steady slip that doesn’t produce earthquakes but still involves motions across the fault, forces the upper crust around the faults to bend and thus concentrate stress. Both hypotheses are the subject of active research. But the fact remains that high stressing rates observed on the surface likely translate to high stressing rates at the depths (~10 km) where earthquakes typically nucleate, so these stressing rates are a guide to the seismic hazard.
Crustal Deformation
Crustal deformation refers to the changing earth’s surface caused by tectonic forces that are accumulated in the crust and then cause earthquakes. So understanding the details of deformation and its effects on faults is important for figuring out which faults are most likely to produce the next earthquake. There are several hypotheses about how this works, but more data is needed to determine which one is the best.
Crustal deformation is a heavily data driven field. To measure the motions of earth’s surface, the USGS employs a variety of methods, including LIDAR, the Global Positioning System (GPS), Interferometric Synthetic Aperture Radar (InSAR), creepmeters, and alinement arrays. In parts of the U.S. with few or no historically-recorded major earthquakes or where background seismicity is sparse, geodetic data may provide the only insight into present-day seismic hazard.