Is the Aftershock Zone Area a Good Proxy for the Mainshock Rupture Area? [post]

Jing Ci Neo, Yihe Huang, Dongdong Yao, Shengji Wei
2020 unpublished
Large earthquakes are usually followed by sequences of small earthquakes, exhibiting a mainshock-aftershock pattern. The locations of aftershocks are often observed to be on the same fault plane as the mainshock and used as proxies for its rupture area. However, there has been limited research on how well aftershock location actually approximates mainshock rupture area. Furthermore, recent developments in earthquake relocation techniques have led to great improvements in the accuracy of
more » ... ke locations. Hence, we investigate this assumption using slip distributions and relocated aftershocks of 12 Mw≥5.4 mainshocks in California. We calculate the area enclosed by the aftershocks, normalized by the mainshock rupture area derived from slip contours. We find that overall, the ratios of aftershock zone area to mainshock rupture area, hereinafter referred to as "aftershock ratio", lie within a range of 0.5 to 5.5, with most values larger than 1. Using different slip inversion models for the same earthquake can have a large impact on the results, but the ratios estimated from both the relocated catalogs and Advanced National Seismic System (ANSS) catalog have similar patterns. The ratios for earthquakes in Southern California fall between 0.5 and 3, while earthquakes in Northern California exhibit a wider range of ratios from 1 to 5.5. We also measure aftershock ratios for the early aftershock window (within 1 day) and find a similar range but smaller values than using the entire aftershock duration, suggesting that continuing afterslip could contribute to the expanding aftershock zone area of several mainshocks. Our results show that areas with positive Coulomb stress change scale with aftershock zone areas, indicating that aftershock distribution generally outlines the mainshock rupture area.
doi:10.31223/osf.io/cp9vn fatcat:gdfihhs2frdltl3sb2zdqj5tiu