Pseudo-Prospective Testing of UCERF3-ETAS Aftershock Forecasts During the 2019 Ridgecrest, California Earthquake Sequence

Session: Observations From the 2019 Ridgecrest Earthquake Sequence [Poster]
Type: Poster
Date: 4/28/2020
Time: 08:00 AM
Room: Ballroom
Description: 

The Ridgecrest sequence began with a M_w 6.4 earthquake on July 4, 2019, that was followed 36 hours later by a M_w 7.1 earthquake. This sequence included the largest earthquake in California since the 1999 M_w 7.1 Hector Mine event and is the first significant California earthquake since the USGS rolled out a national operational aftershock forecasting program with updated methods. Forecasts from the Uniform California Earthquake Rupture Forecast Version 3 – Epidemic Type Aftershock Sequence (UCERF3-ETAS) were computed within hours of the initial M_w 6.4 event. In contrast to traditional ETAS models, UCERF3-ETAS also provides probabilities of triggering earthquakes on specified nearby faults. The Ridgecrest sequence provides an opportunity to evaluate these forecasts in a pseudo-prospective sense and to assess the quality of real-time data products. We evaluate the forecasts with new metrics developed within the Collaboratory for the Study of Earthquake Predictability (CSEP). The metrics consider the synthetic catalogs (stochastic event sets) generated by UCERF3-ETAS rather than simplified synoptic probability maps. This testing approach uses Turing-style tests where metrics from the stochastic event sets are compared directly against observations. In this way, we can directly compare the full distribution for a given metric as provided by the forecast against observations. We find that UCERF3-ETAS overpredicts the rates of earthquakes in the vicinity of the fault zone. The magnitude-number distribution and spatial distributions of observed seismicity fall within the variability of the forecasts. The spatial distribution of seismicity tends to be more diffuse spatially than the observed catalog, while the observed interevent time distribution is largely consistent with the simulations. The evaluations indicate no significant differences between forecasts produced by UCERF3-ETAS and a more traditional ETAS model that does not consider faults during the Ridgecrest Sequence.

Presenting Author: William Savran

Authors