Comments on physical simulator models David D. Jackson, UCLA

Forecast capabilities Statistical distributions of earthquakes on prespecified faults Magnitude frequency Temporal (recurrence) for initiation, participation, and combinations Spatial Paleoseismic rate, sigma, slip rate, displacement distribution

Off-fault earthquakes Not defined in phys sim models Contribute to stress, and presumably to earthquake probability, on faults Are counted in actual earthquake statistics (magnitude, temporal, spatial) but not in phys sim models Participate in clustering models as sources and receivers, but not in phys sim models

UCERF2 Assignment of historic earthquakes to faults

UCERF2 Assignment of instrumental earthquakes to faults

Summary, UCERF2 Earthquakes on faults total M>7 After 1931 Yes 15 7 11 no 8 2 1 maybe 23 6 Total 46 19

Limits to forecasting power Phys sim models are explicitly time-dependent (conditional on history), but history can’t be input or matched in simulations Can’t be tested because they could forecast only on-fault quakes, which are not defined. Paleoseis record is presumably recording on-fault quakes, but is not complete. ?Clustering studies show that small earthquakes are important in triggering, but phys sim models can include them only with massive calculations?. Models depend on Coulomb stress, which hasn’t yet demonstrated clear forecasting ability. But simulators could help make the case by setting up initial conditions.

Conditional Stopping Probability in 10km segment boundary according to WGCEP2008

Smoothed seismicity and faults

Stochastic earthquake simulation, 100 m=6.5+ events