The 2008 Uniform California Earthquake Rupture Forecast, Version 2, or UCERF2, is one of a series of earthquake forecasts prepared for the state California by the Working Group on California Earthquake Probabilities (WGCEP), collaboration of the United States Geological Survey, the California Geological Survey, and the Southern California Earthquake Center, with funding from the California Earthquake Authority. UCERF2 was superseded by UCERF3 in 2015.
Of the hundreds of seismogenic (earthquake causing) geologic faults in California,See USGS QFFDB. UCERF classifies only six faults as Type A sources, meaning there is sufficient information to both estimate and model the probability of a Magnitude (M) 6.7 or greater earthquake within 30 years.. These six faults (summarized in Table A, below) are the: (1) San Andreas (split into northern and southern sections, (2) San Jacinto, (3) Elsinore, (4) Garlock, (5) Calaveras, and (6) Hayward-Rodgers Creek., and Table 12 Faults which are known to be slipping (and therefore seismogenic) but lack sufficient information to fully model how close they might be to rupture are classified as Type B. About twenty of these faults (see Table B) are estimated to have a 5% or greater chance of an M ≥ 6.7 earthquake within 30 years., p. 74. An additional six areas where strain is accumulating but where knowledge is insufficient to apportion slip onto specific faults are classified as Type C sources..
There is additional chance of earthquakes on faults that were not modeled, and of lesser earthquakes. Northern California has an estimated 12% chance over the same 30 years of an M ≥ 8 megathrust earthquake on the Cascadia subduction zone., p.75. UCERF has also prepared "participation probability maps", p. 79. of the chance that any area will experience an earthquake above a certain magnitude from any source in the next 30 years (see figure).
Methodology UCERF probabilities of an earthquake on a given fault are based on four layers of modeling:UCERF, pp. 12–13, and fig. 3. A fault model of the fault's physical geometry. A deformation model of slip rates and related factors for each fault section. An earthquake rate model of the region. A probability model for estimating probability of an earthquake during a specified interval.
These are used to produce both time-independent and time-dependent forecasts of earthquake probabilities. The former are based on "stress-renewal" models of seismic stress being released by an earthquake, then renewing (or rebounding; see Elastic-rebound theory) until it triggers another earthquake. In time-dependent models the probability of a fault rupturing thus depends on how long stress has been accumulating since the last rupture. However, the details of how this happens are not adequately known, so time-dependent methods estimate the periodicity and currently accumulated strain based on observed seismicity. Out of this a time-independent earthquake rate model (ERM) is produced, from which the time-dependent probability model (UCERF) is derived.UCERF, p. 12. (For more information see "Can earthquakes be predicted?" in the External links.)
The concept of stress-renewal has been criticized, and may even be invalid,See Kagan, 1997, esp. §3.3.3.
Table A These are the six geologic faults in California with sufficient data to use a stress-renewal model for estimating the probability of an M ≥ 6.7 earthquake within the next 30 years. The Hayward fault zone and Rodgers Creek fault are treated as a single fault; the San Andreas fault is treated as two sections. A complete listing of known Quaternary faults can be found at the U.S. Geological Survey's Quaternary Fault and Fold Database (QFFDB). Earthquake probabilities and other details from The Uniform California Earthquake Rupture Forecast, Version 2 (UCERF 2).
NameQFFDB fault#1Maps1Length2Strike3TypeSlip rate (mm/yr)4Notable Earthquakes30 yr. prob.5Hayward/ Rodgers Creek Fault Zone55a 55b 55c 32S. Fran. S. Jose S. Rosa150 km93 milesN39°W9.01868 Hayward earthquake31%San Andreas Fault north1a 1b 1c 1d 1eUkiah S. Rosa S. Fran. Monterey472 km293 milesN12-36°WDextral strike-slip17.0–24.01906 San Francisco earthquake21% San Andreas Fault south1f 1g 1h 1i 1jSLO LA S. Bern. S. Ana546 km339 milesN67°WDextral strike-slip10.0–34.01857 Fort Tejon earthquake59% San Jacinto Fault Zone125a 125b 125c 125d 125e 125f 125gS. Ana El Centro309 km192 milesN58°W4.0–14.81918 San Jacinto earthquake31%Elsinore Fault Zone126a 126b 126c 126d 126e 126f 126gS. Ana S. Diego El Centro249 km217 milesN51°W2.5–5.01910 Elsinore earthquake11% Calaveras Fault 54a 54b 54c 54dS. Fran. S. Jose. Monterey123 km76 milesN31°WDextral strike-slip6.0–15.0 7% Garlock Fault69a 69b 69cLA Bakersfd Trona254 km158 milesN68°E3.0–7.05%
Notes for Table A. 1. Fault numbers and maps from USGS Quaternary Fault and Fold Database. 2. Lengths from UCERF-2, Table 4; may vary from QFFDB values. 3. Strikes (orientation) from QDFFB. 4. Slip rates from UCERF-2 Table 4; range reflects different sections. 5. Estimated probability of a M≥6.7 event in 30 years. From UCERF-2 Table 12.
Table B
Approximately twenty geologic faults in California are of "Type B" status, where the probability of an earthquake of M ≥ 6.7 in the next 30 years is estimated to be greater than 5%, but the data is insufficient for stress-renewal modeling. (Not to be confused with the USGS QFFDB class B category of faults of unknown or minor seismicity.)
NameQFFDB fault#2Maps2LengthStrikeTypeSlip rate (mm/yr)4Notable Earthquakes30 yr. prob.5 Imperial132El Centro 1940 El Centro earthquake, 1979 Imperial Valley earthquake 27% Maacama- Garberville30a 30bUkiah S. Rosa 13% Bartlett Springs29a 29b 29cUkiah 9% Hunting Creek- Berryessa35a 35b 35cS. Rosa 9% Little Salmon (Onshore)15Eureka 8% San Cayetano95Los Ang. 8% Death Valley (N)49d 141a 141b 141cGoldfield Death V. 7% Death Valley (N. of Cucamongo)49a 49b 49c 49dMariposa Goldfield 7% San Gregorio Connected60a 60bS. Fran. Monterey 7% Black Mtns Frontal (Death Valley)142a 142b 142c 142dDeath V. Trona 6% Laguna Salada126gEl Centro 1892 Laguna Salada earthquake 6% Oak Ridge (Onshore)94Los Ang. 5% Santa Susana (Sierra Madre)105aLos Ang. 5% Anacapa-Dume100Long Beach 5% Death Valley (S)143a 143bTrona 5% Oak Ridge Connected94Los Ang. 5% Palos Verdes128a 128b 128cLong Beach 5% Coronado Bank131a 131bS. Ana S. Diego 5%
Notes for Table B. 1. List of faults from UCERF-2, Table 13. Unless otherwise noted other details are from Appendix A, Table 1. 2. Fault numbers and maps from USGS Quaternary Fault and Fold Database. Some faults lack a QFFDB entry. 5. Estimated probability of a M≥6.7 event in 30 years. From UCERF-2 Table 13.
See also California Earthquake Prediction Evaluation Council Cascadia subduction zone Earthquake prediction Elastic-rebound theory San Andreas Fault Southern California faults Walker Lane
Notes
References . . . . . . Also published as California Geological Survey Special Report 203 .
External links Forecasting California's Earthquakes—What Can We Expect in the Next 30 Years? Explains UCERF. Working Group on California Earthquake Probabilities (WGCEP) U.S. Geological Survey California Geological Survey Southern California Earthquake Center Earthquake Frequently Asked Questions (USGS) Can you predict earthquakes (USGS FAQ) Can earthquakes be predicted? A good explanation. Recent earthquakes in California and elsewhere (SCEC) Recent earthquakes in the U.S. and the world (USGS) Fault Activity Map (CGS) National Seismic Hazard Maps and related resources (USGS)