Spatio‐Temporal Complexity of Aftershocks in the Apennines Controlled by Permeability Dynamics and Decarbonization
Thanushika Gunatilake, Stephen A. Miller
Abstract
Abstract In 2016, a series of large normal faulting earthquakes in the Apennines filled the seismic gap between the 1997 Colfiorito and 2009 L’Aquila earthquakes. These earthquakes, known as the Amatrice‐Visso‐Norcia (AVN) sequence, spawned hundreds of thousand of aftershocks in the first year, extending about 60 km along strike. The Colfiorito and L’Aquila aftershocks showed a significant high fluid‐pressure component in their aftershock genesis, and here we show evidence that the AVN aftershocks also include a significant high pressure CO 2 component. This CO 2 is both deeply‐derived, and internally generated by thermal decomposition. Using a simple model of non‐linear diffusion with a source term, we compare model results with the observed cumulative number of aftershocks, and also spatial comparisons between the calculated fluid pressure and the hypocenters of about 35,000 well‐located events. The good comparisons between model and observations provide evidence that the AVN sequence includes a contribution (additional fluid source) from co‐seismic decarbonization. Our results suggest that internal fluid generation through devolitization or decarbonization is responsible for non‐Omori type aftershock behavior such as observed for the AVN sequence and for the 2011 M w 9.1 Tohoku (Japan) and the 2014 Iquique (Chile) M w 8.2 megathrust subduction zone earthquakes.