Aftershocks – Jing Ci Neo

Aftershocks

Aftershock Area of Earthquakes

**Figure from Neo et al 2020**: Early (1-day) aftershock ratios [defined by aftershock zone area/mainshock rupture area] for 12 large earthquakes in California. Aftershock zone areas are calculated using earthquakes from the ANSS Catalog, and mainshock rupture areas are calculated using multiple slip inversion models for each mainshock. Aftershock ratios evaluated using the entire aftershock duration are shown in the background (light grey).

The aftershock area of an earthquake is the area delineated by the aftershocks. It is thought to represent the area where stress is accumulated and released during the mainshock, and is often used to approximate rupture area. My research asks: Is the aftershock area a good proxy for the mainshock rupture area? How does the aftershock area change with time? How does it vary with aftershock triggering mechanisms like static stress change? Does it differ for the various earthquakes mechanisms in different tectonic regions?

However, to date there is no clear scientific consensus on a space-time windowing algorithm to determine which earthquakes are aftershocks. In other words, up to how long after a mainshock and how far away would you consider an earthquake to be an aftershock? How should the aftershock area be calculated? Should we draw a convex boundary, fit an ellipse, define energy contours or something else? All these problems are further compounded in places with high background seismicity. Hence, I developed a consistent method to delineate the aftershock zone area using the Beta statistic to address some my research questions.

My paper on aftershock zones in California has been published in the Bulletin of Seismological Society of America! Check it out here