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Evaluation of simulation results: Aftershocks in space

Evaluation of simulation results: Aftershocks in space. Karen Felzer USGS Pasadena. Preliminary Work!!. Subject to change!. The ETAS simulations assign aftershock density with distance, r , from the mainshock as:. Aftershock density = 1/(r+ dmin) - distDecay.

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Evaluation of simulation results: Aftershocks in space

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  1. Evaluation of simulation results: Aftershocks in space Karen Felzer USGS Pasadena

  2. Preliminary Work!! Subject to change!

  3. The ETAS simulations assign aftershock density with distance, r, from the mainshock as: Aftershock density = 1/(r+dmin)-distDecay Trial parameter combinations: Which simulation parameters recreate real data the best?

  4. Trial Cases Northridge earthquake Landers earthquake

  5. Before we start: Where’s the fault? • The parameter r must be measured to the mainshock fault plane, but where exactly is the real rupture surface?

  6. Faults can be very complex Detail of El Mayor-Cucapah rupture, (Rymer et al. in preparation, courtesy of Katherine Kendrick)

  7. 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.

  8. Fault points for the Landers earthquake M 3+ aftershocks

  9. Fault points for a simulated Landers earthquake with minDist = 0.3 km and distDecay = 1.7 M 2.5+ aftershocks

  10. Fault points for the Northridge earthquake M 2.0+ aftershocks

  11. Fault points for a simulated Northridge earthquake with minDist = 0.3 km and distDecay = 1.7 M 2.5+ aftershocks

  12. 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<0.3 km, distDecay<1.7 Real data

  13. Data and simulation comparison: Northridge earthquake • Aftershock density decay rate is similar to the distDecay=2.0 and distDecay=2.5 simulations in the near field • Far field decay is closest to the distDecay=2.5 simulation. • Different results than for Landers!! Real data

  14. How similar is the aftershock decay for different real earthquakes? • I compare aftershock density vs. distance for Landers, Hector Mine, Northridge, and Joshua Tree. • Each earthquake is different, but Hector Mine and Joshua Tree are closer to Northridge-type than Landers-type behavior: supports distDecay=2.0-2.5. • Big Bear aftershock may be an issue?

  15. Future work • Refine method for finding fault points. • Do aftershock measurements for many more large to moderate mainshocks. • Do measurements with relocated aftershocks. • Test sensitivity of results to minimum magnitude and duration of aftershocks used. • Look for systematic variation of aftershock behavior with mainshock characteristics. • Decide whether sequence-specific parameters will be necessary.

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