The global aftershock zone (Invited)
Abstract
There is little doubt that the whole planet becomes the aftershock zone of large (M≥7) earthquakes. Surface waves distort fault zones and volcanic centers as they pass through the crust, leading to seismic failures. From a hazard perspective we are obviously concerned that this dynamic process might encourage high magnitude earthquakes. Great strides have been made in operational earthquake forecasting near mainshocks in time and space, but we are far less certain how to assess the hazard posed at global distances. Results from global compilations demonstrate significant rate increases during, and immediately after (~45 minutes) M>7.0 mainshocks in all tectonic settings and ranges. However, it is difficult to find strong evidence for M>5 rate increases during the passage of surface waves in combined global catalogs. On the other hand, studies of individual large mainshocks correlate M>5 triggering at global range that is delayed by hours to days after surface wave arrivals. These examples tend to lie in the noise when the global catalogs are examined simultaneously, which implies that they are relatively rare events. However, if large triggered earthquakes can occur in the global aftershock zone, then we must be concerned about how to calculate and convey the hazard they pose. Results from comparative responses of individual regions to hundreds of global M>7 mainshocks give us some preliminary insights into the likelihood of damaging global aftershocks. About 50% of the catalogs we studied showed possible (delayed) remote triggering, and ~20% showed probable (instantaneous) remote triggering. However, in any given region, at most only about 2-3% of global mainshocks cause significant local earthquake rate increases. We note that surface wave amplitude, mainshock magnitude, and relative proximity are not important factors in determining which mainshocks cause remote triggering. Instead, azimuth, and polarization of surface waves with respect to receiver faults appear to be more important factors.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2013
- Bibcode:
- 2013AGUFM.S44B..04P
- Keywords:
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- 7223 SEISMOLOGY Earthquake interaction;
- forecasting;
- and prediction;
- 7230 SEISMOLOGY Seismicity and tectonics;
- 7255 SEISMOLOGY Surface waves and free oscillations;
- 8118 TECTONOPHYSICS Dynamics and mechanics of faulting