Are earthquake probabilities or forecasts the same as prediction?
No. Probabilities and forecasts are rather like climate probabilities and weather forecasts, while predictions are more like statements of when, where, and how large, which is not yet possible for earthquakes.
Probabilities describe the long-term chances that an earthquake of a certain magnitude will happen during a time window. Most earthquake probabilities are determined from the average rate of historical events. Assuming the annual rate is constant, one can make a probability statement about the likelihood of such an event in the next so-many years. These probabilities might range from 1-in-30 to 1-in-300.
For some faults, historical occurrences are not available, but rate of slip along the fault can be estimated. Assuming a particular magnitude, one can estimate the number of years it would take to accumulate the required amount of slip. This estimate can be used to give an annual rate and used in the same manner as historical rates. These probabilities might range from 1-in-300 to 1–in-3000.
Forecasts are like probabilities but for shorter time windows, and we generally apply this term to aftershocks. After a large earthquake, there are aftershocks that are typically less frequent and smaller over time. Most aftershock sequences follow the same pattern, so the probability of an aftershock in a time window following an earthquake can be determined. These probabilities might be larger than 1-in-30.
For information on Predictions, see the FAQ under Earthquake Myths – Can you predict earthquakes?
(contributed by Dave Perkins, edited and modified by Lisa Wald, Jan 2017)
What is the probability that an earthquake will occur in the Los Angeles Area? In the San Francisco Bay area?
What is the likelihood of a large earthquake at location X? Is it safe to go to X since they've been having a lot of earthquakes lately?
What is seismic hazard? What is a seismic hazard map? How are they made? How are they used? Why are there different maps, and which one should I use?
Why was an earthquake in Virginia felt at more than twice the distance than a similar-sized earthquake in California? The answer is one that many people may not realize. Earthquakes east of the Rocky Mountains can cause noticeable ground shaking at much farther distances than comparably-sized earthquakes in the West.
USGS collaborates with key academic, state, local, and industry partners to provide a new look at what could happen during a major earthquake in the San Francisco Bay Area.
New seismic hazard and risk assessments can help at-risk communities prepare for future earthquake disasters
New Audiences, New Products for the National Seismic Hazard Maps
Twenty years after the Loma Prieta earthquake caused loss of life and widespread property damage, advances in science, technology and engineering have the San Francisco Bay Area better prepared for the next big earthquake. When the Loma Prieta quake hit just after 5 p.m. October 17, 1989 – 20 years ago Saturday – the digital age was in its infancy.
What if you knew that a magnitude 7.8 earthquake would happen in less than three weeks? In a new video interview, USGS earthquake scientist Dr. Lucy Jones explains that millions of Southern Californians will be preparing as if they do know, thanks to the Great Southern California ShakeOut.
Friday's magnitude-5.2 earthquake in southern Illinois is a reminder that earthquakes are a national hazard.
Title: The 150th Anniversary of the Damaging 1868 Hayward Earthquake: Why It Matters and How We Can Prepare for Its Repeat
- The Hayward Fault in the heart of the Bay Area is one of the most urbanized faults in the US.
- Studies of the fault reveal that it has produced 12 large earthquakes in the past 2000 years spaced 100-220 years apart.
Title: ShakeAlert: The Path to West Coast Earthquake Early Warning ... how a few seconds can save lives and property
- The ShakeAlert earthquake early warning system will begin limited operations this year.
- Alerts could save lives and properties but several challenges remain.
- With millions at risk, why isn't full public alerting happening yet?
Three-dimensional perspective view of the likelihood that each region of California will experience a magnitude 6.7 or larger earthquake in the next 30 years (6.7 matches the magnitude of the 1994 Northridge earthquake, and 30 years is the typical duration of a homeowner mortgage).
by Morgan Page, USGS Research Geophysicist
- Scientists cannot currently predict the precise time, location, and size of future damaging earthquakes.
- Historical records of earthquakes in California date back over 150 years.
- Geologists have dug trenches to extend the known history on some faults back to around 1,000 years before
--updating earthquake prediction--fact vs. fiction
by Susan Hough, USGS Seismologist
- Although scientists were optimistic about earthquake prediction in the 1970s, reliable short-term prediction has remained an elusive goal
- What have seismologists learned from recent earthquakes in Haiti, Chile, and Japan?
This map depicts the difference in USGS estimates of earthquake hazards across the nation in 2002 and 2014. The new FEMA earthquake loss report includes the 2014 data, while the previous 2008 report includes the 2002 data. The negative values represent a decrease in estimated hazard since 2002 and the positive values represent an increase.
ESC Seminar: HayWired Scenario Progress Discussion
Map of known active geologic faults in the San Francisco Bay region, California, including the Hayward Fault. The 72 percent probability of a magnitude (M) 6.7 or greater earthquake in the region includes well-known major plate-boundary faults, lesser-known faults, and unknown faults. The percentage shown within each colored circle is the probability that a M 6.7 or...