Testing ETAS Catalogs from UCERF3

Morgan T. Page, Nicholas J. van der Elst, Edward H. Field, & Kevin R. Milner

Submitted August 15, 2016, SCEC Contribution #6962, 2016 SCEC Annual Meeting Poster #299

Epidemic-Type Aftershock Sequence (ETAS) catalogs generated from the 3rd Uniform California Earthquake Rupture Forecast (UCERF3) model are unique in that they represent a marriage between two types of earthquake forecast models that have never previously been formally combined. UCERF3 is a complex fault-based model with geologic, paleoseismic, and geodetic constraints as well as elastic rebound effects. The ETAS model adds short-term spatio-temporal clustering from aftershock triggering. Significant challenges in the construction of the UCERF3-ETAS model were encountered, particularly with respect to the magnitude-frequency distributions in the UCERF3 model and the application of elastic rebound.

Given the challenges present in its construction, to what extent do UCERF3-ETAS catalogs reproduce the observed statistics in real earthquake catalogs? We present Turing-style tests of the temporal and spatial statistics of synthetic and real catalogs. We find that UCERF3-ETAS is more spatially diffuse than the observed historic catalog in California. This discrepancy is due to the diffusivity of the background seismicity, which is based on a model that has been quite successful in short-term tests – the adaptive smoothed seismicity model of Helmstetter et al. (2007). We also find that UCERF3-ETAS is lacking quiet periods that are present in the real catalog. This is caused by the steady background hum of the stationary events in the ETAS model, which constitute 1/3 of all modeled earthquakes.

Key Words
UCERF3, ETAS, Seismic Hazard, Earthquake Forecasting

Page, M. T., van der Elst, N. J., Field, E. H., & Milner, K. R. (2016, 08). Testing ETAS Catalogs from UCERF3. Poster Presentation at 2016 SCEC Annual Meeting.

Related Projects & Working Groups
Working Group on California Earthquake Probabilities (WGCEP)