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#           STEPS: Slip time earthquake path simulations applied to the San Andreas and Toe Jam Hill Faults to redefine geologic slip rate uncertainty      

      October 6, 2021    

Geologic slip rates are a time-averaged measurement of fault displacement calculated over hundreds to million-year time scales and are a primary input for probabilistic seismic hazard analyses, which forecast expected ground shaking in future earthquakes. Despite their utility for seismic hazard calculations, longer-term geologic slip rates represent a time-averaged measure of the tempo of strain release and do not measure variability across earthquake cycles. We have developed a numerical approach called STEPS (Slip Time Earthquake Path Simulations), which is built upon field-based observations and explicitly incorporates realistic variations in displacement per event and variability in the recurrence interval between earthquakes. The STEPS approach, which simulates strain release through time, relies on representing earthquake cycles as stairsteps, rather than straight-line paths, connecting per earthquake time-displacement coordinates. We simulate earthquake histories based on these input constraints using two examples: the Carrizo section of the San Andreas fault and the Toe Jam Hill fault of the Seattle fault zone. We find that modeled slip rate distributions agree with slip rates reported for the sites of interest by the original investigators, while providing a slip rate distribution that reflects the variability of earthquake frequency and displacement. The STEPS approach provides an estimate of fault slip rate uncertainty based on a synthetic suite of plausible time-displacement paths resulting from individual earthquakes, rather than measurement uncertainties associated with offset features. When considering this simulated earthquake behavior between measurements, the uncertainty associated with earthquake paths is greater than that calculated by the long-term rate.

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October 1, 2021

####                 STEPS: Slip Time Earthquake Path Simulations applied to the San Andreas and Toe Jam Hill faults to redefine geologic slip rate uncertainty (Matlab code)              

Natural Hazards Mission Area, Earthquake Hazards Program, Geologic Hazards Science Center

#### Alexandra (Alex) Hatem

##### Research Geologist

Earthquake Hazards Program

ahatem@usgs.gov

303-273-8474

#### Ryan D Gold, Ph.D.

##### Director, Geologic Hazards Science Center

Geologic Hazards Science Center

rgold@usgs.gov

303-273-8633

#### Rich Briggs

##### Research Geologist

Earthquake Hazards Program

rbriggs@usgs.gov

303-273-8465

#### Katherine (Kate) Scharer

##### Research Geologist

Earthquake Hazards Program

kscharer@usgs.gov

626-583-7240

#### Ned Field

##### Research Geophysicist

Earthquake Hazards Program

field@usgs.gov

303-273-8469

## Related Content

October 1, 2021

####                 STEPS: Slip Time Earthquake Path Simulations applied to the San Andreas and Toe Jam Hill faults to redefine geologic slip rate uncertainty (Matlab code)              

Natural Hazards Mission Area, Earthquake Hazards Program, Geologic Hazards Science Center

#### Alexandra (Alex) Hatem

##### Research Geologist

Earthquake Hazards Program

ahatem@usgs.gov

303-273-8474

#### Ryan D Gold, Ph.D.

##### Director, Geologic Hazards Science Center

Geologic Hazards Science Center

rgold@usgs.gov

303-273-8633

#### Rich Briggs

##### Research Geologist

Earthquake Hazards Program

rbriggs@usgs.gov

303-273-8465

#### Katherine (Kate) Scharer

##### Research Geologist

Earthquake Hazards Program

kscharer@usgs.gov

626-583-7240

#### Ned Field

##### Research Geophysicist

Earthquake Hazards Program

field@usgs.gov

303-273-8469

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####               Earthquake Science Center          

350 N. Akron RoadMoffett Field, CA94035United States

#### Geologic Hazards Science Center

1711 Illinois St.Golden, CO80401United States

303-273-8500

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