What methods are currently used for earthquake forecasting?
The United States Geological Survey, through its Working Groups on California Earthquake Probabilities, has been developing long term earthquake forecasts for regions in California since 1988. These forecasts are based on data describing historic averages of major earthquakes as well as paleoseismic geologic data, obtained from trenching studies on active fault traces, and instrumental data. The result of these studies are 30 year probabilities for major earthquakes, typically having magnitudes M > 6.7, on major earthquake faults in California. The process by which these probabilities are computed is an extensive consultation and collaboration among over 100 scientists lasting several years. Expert opinion plays a significant role as well. An analysis of these forecasts was recently published in the scientific journal Nature ("Shaking Up Earthquake Theory, Nature, volume 46, pp. 870-872, 15 October, 2009).
Other forecasts include the Accelerated Moment Release (AMR) method, pioneered by scientists in the United States and Europe; the Epidemic Type Aftershock Sequence (ETAS) method developed by scientists in Japan, the United States and Europe; M8 and the Reverse Tracing of Precursors (RTP) method developed by scientists in Russia; the Psi method developed by scientists in New Zealand; the USGS STEP method for computing 24 hour probabilities of ground shaking due to aftershocks of major earthquakes; and a variety of methods based on earth strain and ground deformation measures.
The OH forecasts use methods that are based on ideas that have been in the peer reviewed literature for the past decade or more. These methods are data driven, using the ANSS catalog of earthquakes from online sources, together with well known observational laws including the Gutenberg-Richter relation and the Omori-Utsu aftershock frequency law. When the parameters in these laws are fit to the past observations, future probabilities can be computed. An example of a method of this type is the USGS STEP method, which is used to compute 24 hour aftershock probabilities. The advantage of the OH method is that it can be applied in a uniform way world-wide, and does not require local knowledge of the geology. Methods similar to this have been repeatedly tested over the past years, and continue to be tested by a variety of statistical techniques. The resulting forecasts may differ from the official forecasts as developed by the US Geological Survey, which uses the method as described above.
OH forecasts are fully time- and space-dependent, so calculated earthquake risk will change both as a result of changing earthquake probabilities, as well as changing human exposure. Even without the occurrence of a large earthquake and its aftershocks, earthquake probabilities can increase or decrease by as much as several per cent per month in active areas.
- OH Community
- Web Apps
- About Us