A computer model showing stress changes near a fault immediately after an earthquake. The red areas have more stress, and the blue areas have less stress, than before the earthquake. Image by Ross Stein, USGS.
The overarching theme of this research is for scientists to discover as much as they can about earthquakes and faulting from field and laboratory observations, and to combine this with geophysical, geological, geochemical, and mathematical (including computational) modeling of earthquake sources and fault zones so as to best improve USGS earthquake hazard assessments. The USGS issues long-term probabilistic hazard assessments in the form of shaking hazard maps and 30-year earthquake probability reports, and updates these estimates with foreshock and aftershock probabilities in the days and weeks following large and moderate earthquakes. Societal uses of these products ranges from the development of building codes, siting critical facilities, retrofit plans, and the reoccupation of partially damaged buildings during aftershock sequences.
Samples of granite used in laboratory studies of earthquakes. The rock in the foreground was fractured under high pressure, creating an irregular "fault surface."
The high level of earthquake activity and the complexity of the fault systems throughout California area provides a unique natural laboratory for the study of the physics of earthquakes. Scientists are studying fault interaction by comparing the seismic behavior in California to analogous areas in the world with large strike-slip faults, to provide insight into possible past and future earthquakes in the region.
In addition, earthquakes are generated in the laboratory under controlled conditions to learn how they start and what indications there might be that they are about to happen. Also, fault zone materials are carefully tested to learn about the physical and chemical processes that control earthquakes.
This research strives to increase the quality and impact of these products, and to reduce their uncertainties, through multidisciplinary research aimed at better understanding the earthquake process. The project works in close collaboration with regionally focused projects and with the National Seismic Hazard Mapping (NSHM) project in order to support those efforts at issuing earthquake hazard products.
Some of the key scientific questions scientists seek to answer
- How is stress loaded onto faults as a function of space and time by both plate motions and other geological processes?
- How do the stresses redistributed by one earthquake affect the probability of future events?
- Do identifiable earthquakes recur with some average repeat time and definable variation or is each earthquake unique?
- How does the structure of faults control the nucleation of small earthquakes and their growth into larger ones and what does this predict about the distribution of sizes of earthquakes we can expect in a region or along a fault?