Deterministic model of earthquake clustering shows reduced stress drops for nearby aftershocks

• Published in: Geophysical research letters Vol. 42; no. 21; pp. 9231 - 9238
• Main Authors: Shaw, Bruce E., Richards-Dinger, Keith, Dieterich, James H.
• Format: Journal Article
• Language: English
• Published: Washington Blackwell Publishing Ltd 16.11.2015; John Wiley & Sons, Inc
• Subjects: Aftershocks; Area; Clustering; earthquake clustering; Earthquakes; Faults; Geophysics; Ground motion; Productivity; rate and state friction; Reproduction; Rupture; Rupturing; Seismic activity; spatial dependence; Stress concentration; stress drops; Stresses
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1002/2015GL066082

While a number of viable physical mechanisms have been offered to explain the temporal clustering of aftershocks, the spatial clustering of aftershocks, in particular the concentrated productivity of aftershocks very near the mainshock rupture area, has been difficult to reproduce with physical models. Here we present a new deterministic physical model capable of reproducing both the spatial and temporal clustering. We apply this new model to a longstanding puzzling question raised by ground motion observations, which suggest that nearby aftershocks show reduced ground motions relative to similar magnitude mainshocks. In the model, the physical basis for these observations is reduced stress drops for nearby aftershocks compared to similar magnitude mainshocks. These reduced stress drops are due to nearby aftershocks rerupturing incompletely healed parts of the fault which ruptured in the mainshock. Key Points Development of new model which reproduces spatial dependence of aftershocks Aftershocks show reduced stress drops explaining puzzling GMPE observations Lower stress drops arise from rerupturing incompletely healed fault