California earthquake forecast

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UCERF participation probability map. Mean probability that a given location will be involved in an M ≥ 5 rupture of any source during the next 30 years. The most prominent red line is the San Andreas fault (overall probability of rupture ~70%). The red zone at the northwest corner is the southern end of the Cascadia subduction zone, that on the California-Nevada state line is Walker Lane. Modified from UCERF-2 figure 35.

A California earthquake forecast, the 2008 Uniform California Earthquake Rupture Forecast, Version 2 (UCERF 2), has been prepared by the Working Group on California Earthquake Probabilities (WGCEP).[1] Of the hundreds of seismogenic (earthquake causing) geologic faults in California[2] 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.[3] 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.[4] 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.[5] 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.[6]

There is additional chance of earthquakes on faults that were not modeled, and of lesser earthquakes. Northern California has an estimated 12% chance of an M ≥ 8 megathrust earthquake on the Cascadia subduction zone.[7] UCERF has also prepared "participation probability maps" [8] 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[edit]

UCERF probabilities of an earthquake on a given fault are based on four layers of modeling:[9]

  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 (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.[10] (For more information see "Can earthquakes be predicted?" in the External links.)

It should be noted that the concept of stress-renewal has been criticized, and may even be invalid,[11]

Table A[edit]

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).

Name QFFDB fault#1 Maps1 Length2 Strike3 Type Slip rate (mm/yr)4 Notable Earthquakes 30 yr. prob.5
Hayward/ Rodgers Creek Fault Zone

55a
55b
55c
32

S. Fran.
S. Jose
S. Rosa

150 km
93 miles
N39°W 9.0 1868 Hayward earthquake 31%
San Andreas Fault north

1a
1b
1c
1d
1e

Ukiah
S. Rosa
S. Fran.
Monterey

472 km
293 miles
N12-36°W Dextral strike-slip 17.0—24.0 1906 San Francisco earthquake 21%
San Andreas Fault south

1f
1g
1h
1i
1j

SLO
LA
S. Bern.
S. Ana

546 km
339 miles
N67°W Dextral strike-slip 10.0—34.0 1857 Fort Tejon earthquake 59%
San Jacinto Fault Zone

125a
125b
125c
125d
125e
125f
125g

S. Ana
El Centro

309 km
192 miles
N58°W 4.0—14.8 1918 San Jacinto earthquake 31%
Elsinore Fault Zone

126a
126b
126c
126d
126e
126f
126g

S. Ana
S. Diego
El Centro

249 km
217 miles
N51°W 2.5—5.0 1910 Elsinore earthquake 11%
Calaveras Fault

54a
54b
54c
54d

S. Fran.
S. Jose.
Monterey

123 km
76 miles
N31°W Dextral strike-slip 6.0—15.0 1911 Calaveras earthquake [12]
1979 Coyote Lake earthquake [13]
1984 Morgan Hill earthquake [14]
2007 Alum Rock earthquake [15]
7%
Garlock Fault

69a
69b
69c

LA
Bakersfd
Trona

254 km
158 miles
N68°E 3.0—7.0 5%

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[edit]

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.)

Name QFFDB fault#2 Maps2 Length Strike Type Slip rate (mm/yr)4 Notable Earthquakes 30 yr. prob.5
Imperial 132
El Centro
1940 El Centro earthquake, 1979 Imperial Valley earthquake 27%
Maacama- Garberville 30a

30b

Ukiah

S. Rosa

13%
Bartlett Springs 29a

29b
29c

Ukiah
9%
Hunting Creek- Berryessa 35a

35b
35c

S. Rosa
9%
Little Salmon (Onshore) 15
Eureka
8%
San Cayetano 95
Los Ang.
8%
Death Valley (N) 49d

141a
141b
141c

Goldfield

Death V.

7%
Death Valley (N. of Cucamongo) 49a

49b
49c
49d

Mariposa

Goldfield

7%
San Gregorio Connected 60a

60b

S. Fran.

Monterey

7%
Black Mtns Frontal (Death Valley) 142a

142b
142c
142d

Death V.

Trona

6%
Laguna Salada 126g
El Centro
1892 Laguna Salada earthquake 6%
Oak Ridge (Onshore) 94
Los Ang.
5%
Santa Susana (Sierra Madre) 105a
Los Ang.
5%
Anacapa-Dume 100
Long Beach
5%
Death Valley (S) 143a

143b

Trona
5%
Oak Ridge Connected 94
Los Ang.
5%
Palos Verdes 128a

128b
128c

Long Beach
5%
Coronado Bank 131a

131b

S. 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.

Notes[edit]

  1. ^ WGCEP is a collaboration of the U.S. Geological Survey, the California Geological Survey, and the Southern California Earthquake Center).
  2. ^ See USGS QFFDB.
  3. ^ UCERF 2008, p. 33.
  4. ^ UCERF 2008, p. 33, and Table 12
  5. ^ UCERF 2008, Table 13, p. 74.
  6. ^ UCERF 2008, p. 34.
  7. ^ UCERF 2008, Fig. 32, p.75.
  8. ^ UCERF 2008, Fig. 35, p. 79.
  9. ^ UCERF, pp. 12-13, and fig. 3.
  10. ^ UCERF, p. 12.
  11. ^ See Kagan, 1997, esp. §3.3.3.
  12. ^ Dozer et al. 2009, pp. 1746–1759
  13. ^ Yeats 2012, p. 92
  14. ^ Hartzell & Heaton 1986, p. 649
  15. ^ Oppenheimer et al. 2010

See also[edit]

References[edit]

External links[edit]