Post-Seismic to Co-Seismic Moment Ratios for the 2016 Moderate Earthquakes Along Chaman Fault

Postseismic-to-coseismic moment ratios (PCMR) for strong (M > 6) earthquakes typically do not exceed similar to 0.3, but there have been limited estimates for moderate-to-small earthquakes. Three M5-class earthquakes and one M4.7 earthquake occurred along the Chaman fault, Pakistan, on May 13 and July 10, 2016. Using Sentinel-1A InSAR time-series from October 2014 to August 2018, we estimate spatial-temporal evolution of the co- and post-seismic fault slip and its velocity. Because of the long-lasting (>1 year) afterslip, the estimated PCMRs of the M5-class events and M4.7 event were 0.7 +/- 0.2 and 8.3 +/- 2.2, respectively, which are both larger than those of M > 6 earthquakes but consistent with previous events that occurred on the Chaman Fault System. Unlike in case of large earthquakes, geodetic inversions are not able to resolve spatial relationships between coseismic slip and afterslip. In case of a non-complementary slip distribution, one explanation might be heterogeneity of friction properties on the fault surface, while other interpretations are possible.