## Breadcrumb

-  Publications 
-  Articles 

#           Long‐term time‐dependent probabilities for the third Uniform California Earthquake Rupture Forecast (UCERF3)      

      March 1, 2015    

The 2014 Working Group on California Earthquake Probabilities (WGCEP 2014) presents time-dependent earthquake probabilities for the third Uniform California Earthquake Rupture Forecast (UCERF3). Building on the UCERF3 time-independent model, published previously, renewal models are utilized to represent elastic-rebound-implied probabilities. A new methodology has been developed that solves applicability issues in the previous approach for un-segmented models. The new methodology also supports magnitude-dependent aperiodicity and accounts for the historic open interval on faults that lack a date-of-last-event constraint. Epistemic uncertainties are represented with a logic tree, producing 5,760 different forecasts. Results for a variety of evaluation metrics are presented, including logic-tree sensitivity analyses and comparisons to the previous model (UCERF2). For 30-year M≥6.7 probabilities, the most significant changes from UCERF2 are a threefold increase on the Calaveras fault and a threefold decrease on the San Jacinto fault. Such changes are due mostly to differences in the time-independent models (e.g., fault slip rates), with relaxation of segmentation and inclusion of multi-fault ruptures being particularly influential. In fact, some UCERF2 faults were simply too long to produce M 6.7 sized events given the segmentation assumptions in that study. Probability model differences are also influential, with the implied gains (relative to a Poisson model) being generally higher in UCERF3. Accounting for the historic open interval is one reason. Another is an effective 27% increase in the total elastic-rebound-model weight. The exact factors influencing differences between UCERF2 and UCERF3, as well as the relative importance of logic-tree branches, vary throughout the region, and depend on the evaluation metric of interest. For example, M≥6.7 probabilities may not be a good proxy for other hazard or loss measures. This sensitivity, coupled with the approximate nature of the model and known limitations, means the applicability of UCERF3 should be evaluated on a case-by-case basis.

## Citation Information

## Related Content

                  -              Connect           

#### Ned Field

##### Research Geophysicist

Earthquake Hazards Program

field@usgs.gov

303-273-8469

#### Andrew Michael

##### Research Geophysicist

Earthquake Hazards Program

ajmichael@usgs.gov

650-439-2777

#### Morgan T Page

##### Research Geophysicist

Earthquake Hazards Program

mpage@usgs.gov

626-583-6804

#### Tom Parsons

##### Research Geophysicist

Pacific Coastal and Marine Science Center

tparsons@usgs.gov

650-439-2374

## Related Content

#### Ned Field

##### Research Geophysicist

Earthquake Hazards Program

field@usgs.gov

303-273-8469

#### Andrew Michael

##### Research Geophysicist

Earthquake Hazards Program

ajmichael@usgs.gov

650-439-2777

#### Morgan T Page

##### Research Geophysicist

Earthquake Hazards Program

mpage@usgs.gov

626-583-6804

#### Tom Parsons

##### Research Geophysicist

Pacific Coastal and Marine Science Center

tparsons@usgs.gov

650-439-2374

### Contact

#### Geologic Hazards Science Center

1711 Illinois St.Golden, CO80401United States

303-273-8500

### Explore Search

                  - Natural Hazards

View All **