Astronomy and Astrophysics – Astronomy
Scientific paper
Feb 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007geoji.168..797k&link_type=abstract
Geophysical Journal International, Volume 168, Issue 2, pp. 797-808.
Astronomy and Astrophysics
Astronomy
3
Aftershocks, Creep, Earthquake-Source Mechanism, Fault Slip, Seismicity
Scientific paper
It is known that the aftershock areas of large earthquakes often expand over time. This expansion indicates that the stress-increase associated with a main shock gradually propagates outward from the main shock rupture area. It is likely that this propagating stress-increase is caused by the propagation of post-seismic sliding, which has been detected for many large earthquakes from geodetic observations, mainly global positioning system (GPS). In the present study, I perform a numerical simulation of the expansion of the aftershock area caused by the propagation of post-seismic sliding. The model fault exists within an infinite elastic medium and is loaded at a constant displacement rate. The frictional stress on the fault obeys a laboratory-derived rate- and state-dependent friction law. Non-uniformity of the frictional constitutive parameters is introduced to the model fault plane to represent a large asperity for a large earthquake (main shock) and many possible nucleus sites for aftershocks around the main shock asperity. Negative values of A - B are assigned to areas of seismic slip for the main shock and aftershocks, while positive values of A - B are assigned to regions where aseismic sliding occurs. Here, A - B is defined by dτss/d lnV that describes the velocity (V) dependence of steady-state friction stress τss. Seismic slip may be nucleated for negative A - B, and aseismic slip occurs for positive A - B. Slip histories on the model fault plane are simulated through numerical integration of the friction law under the condition of uniform shear loading of a constant velocity. The simulation can reproduce aftershocks triggered by stress-increases related to post-seismic sliding and expansion of the aftershock area. The rate of expansion of the aftershock area decreases with increasing distance from the main shock asperity or increasing value of A - B in the velocity-strengthening region. This finding suggests that the A - B value for a plate interface can be estimated from aftershock data. The simulation indicates that the 7-day and 30-day aftershock areas are 14-22 and 24-39 per cent larger, respectively, than the 1-day aftershock area. These numbers are approximately consistent with observations from large earthquakes at subduction zones.
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