Evaluation of simulation results: Aftershocks in space Karen Felzer USGS Pasadena Subject to change! The ETAS simulations assign aftershock density with distance, r, from the mainshock as: Aftershock density = 1/(r+dmin) -distDecay dmin (km) distDecay Trial parameter combinations: Which simulation parameters recreate real data the best? Trial Cases Landers earthquake Northridge earthquake Before we start: Wheres the fault? The parameter r must be measured to the mainshock fault plane, but where exactly is the real rupture surface? Faults can be very complex Detail of El Mayor- Cucapah rupture, (Rymer et al. in preparation, courtesy of Katherine Kendrick) Quick and dirty aftershock-based fault- tracing approach Place aftershocks into 5x5x5 km bins Sort the bins by aftershock density Calculate Nbin = min((Fault area)/10,(Total number of populated bins)/4) Place fault points at the median aftershock location in the Nbin most populated bins The distance r is measured from aftershock hypocenters to the nearest fault point. Fault points for the Landers earthquake M 3+ aftershocks Fault points for a simulated Landers earthquake with minDist = 0.3 km and distDecay = 1.7 M 2.5+ aftershocks Fault points for the Northridge earthquake M 2.0+ aftershocks Fault points for a simulated Northridge earthquake with minDist = 0.3 km and distDecay = 1.7 M 2.5+ aftershocks Data and simulation comparison: Landers earthquake Aftershock density decays more quickly in the near field, and more slowly in the far field, than any of the simulations Suggests we need dmin