Aftershock Patterns of Ms>7 Earthquakes in the India-Asia Collision Belt: Anomalous Results from the Muzaffarabad Earthquake Sequence, Kashmir, 2005

Abstract

The seismicity rate triggered by the Muzaffarabad, Kashmir, 2005 M w 7.6, M s 7.7 earthquake is above the average when analyzing the aftershock rate of the 18 M s≥7.0 events in the India–Asia collision belt between 1973 and 2008. All 17 M s≥7.0 events occurred within 10° latitude and 20° longitude distance from the 2005 Muzaffarabad earthquake epicenter. We determined the huge aftershock productivity for this earthquake is not driven by a specific Omori law parameter. This anomaly in aftershock rate value corresponds to a relatively higher rate decay (as measured by the p ‐value), and a larger density value in a higher background seismicity rate setting (prestress conditions) than the other 17 sequences, respectively. After normalizing by the mainshock size and by the magnitude range of observation, we resolved the anomalies, with a 95% confidence level for five aftershock sequences, for either the duration, the productivity, the density, or the background seismicity rate. When we did not include the local processes that drive these specific anomalies, two other global results emerged for the averaged data from the 18 M s>7.0 aftershock sequences. First, for all sequences, background seismicity and duration are anticorrelated (![Graphic][1] ). Within the framework of rate‐and‐state friction law, this result supports the assertion that the observed background seismicity rate can be used as a proxy for the stressing rate (Dieterich, 1994). Second, we robustly resolve the dependence of aftershock productivity on the mainshock faulting styles; for example, the aftershock productivity for strike‐slip mainshocks is on average four times smaller than the productivity of thrust faulting mainshocks. [1]: /embed/inline-graphic-1.gif