UCERF2


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, collaboration of the U.S. 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 UCERF2 was superseded by UCERF3 in 2015.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 geologic faults in California, UCERF classifies only six faults as Type A sources, meaning there is sufficient information to both estimate and model the probability of a Magnitude 6.7 or greater earthquake within 30 years. These six faults are the: San Andreas San Jacinto, Elsinore, Garlock, Calaveras, and Hayward-Rodgers Creek. Faults which are known to be slipping but lack sufficient information to fully model how close they might be to rupture are classified as Type B. About twenty of these faults are estimated to have a 5% or greater chance of an M ≥ 6.7 earthquake within 30 years. 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. UCERF has also prepared "participation probability maps" of the chance that any area will experience an earthquake above a certain magnitude from any source in the next 30 years.

Methodology

UCERF probabilities of an earthquake on a given fault are based on four layers of modeling:
  1. A fault model of the fault's physical geometry.
  2. A deformation model of slip rates and related factors for each fault section.
  3. An earthquake rate model of the region.
  4. 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 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 is produced, from which the time-dependent probability model is derived.
The concept of stress-renewal has been criticized, and may even be invalid,

[|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 . Earthquake probabilities and other details from .
NameQFFDB fault#[|1]Maps1Length2Strike3TypeSlip rate [|4]Notable Earthquakes30 yr. prob.5-
Hayward/ Rodgers Creek Fault Zone

150 km
93 miles		N39°W9.01868 Hayward earthquake31%-
San Andreas Fault north

472 km
293 miles		N12-36°WDextral strike-slip17.0–24.01906 San Francisco earthquake21%-
San Andreas Fault south

546 km
339 miles		N67°WDextral strike-slip10.0–34.01857 Fort Tejon earthquake59%-
San Jacinto Fault Zone

309 km
192 miles		N58°W4.0–14.81918 San Jacinto earthquake31%-
Elsinore Fault Zone

249 km
217 miles		N51°W2.5–5.01910 Elsinore earthquake11%-
Calaveras Fault

123 km
76 miles		N31°WDextral strike-slip6.0–15.0


7%-
Garlock Fault

254 km
158 miles		N68°E3.0–7.05%-

Notes for Table A.
1. Fault numbers and maps from USGS .
2. Lengths from UCERF-2, Table 4; may vary from QFFDB values.
3. Strikes 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.
NameQFFDB fault#2Maps2LengthStrikeTypeSlip rate 4Notable Earthquakes30 yr. prob.5
Imperial

1940 El Centro earthquake, 1979 Imperial Valley earthquake27%-
Maacama- Garberville

13%-
Bartlett Springs

9%-
Hunting Creek- Berryessa

9%-
Little Salmon

8%-
San Cayetano95

8%-
Death Valley

7%-
Death Valley

7%-
San Gregorio Connected

7%-
Black Mtns Frontal

6%-
Laguna Salada

1892 Laguna Salada earthquake6%-
Oak Ridge 94

5%-
Santa Susana

5%-
Anacapa-Dume100

5%-
Death Valley

5%-
Oak Ridge Connected94

5%-
Palos Verdes128a

5%-
Coronado Bank131a
131b

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 . Some faults lack a QFFDB entry.
5. Estimated probability of a M≥6.7 event in 30 years. From UCERF-2 Table 13.