Understanding the Marianas’ 2007 volcanic earthquake swarm: A perspective from fundamental quantities

Abstract

In this project I am trying to understand the mechanics of the 2007 Marianas earthquake-swarm region and surrounding vicinity; located in the asthenosphere and lithosphere of the Marianas microplate above the subducting Pacific plate. The earthquake swarm exhibited seismicity for almost 2 years, with events occurring from depths of 300 km and up to the surface, right underneath the Marianas arc currently-active basaltic volcanoes.My approach is to estimate the magnitudes of mechanical variables (forces per unit area, forces per unit volume) that control the evolution of this system. These forces are evaluated for the swarm region, where the ambient rock is heavily fractured and intruded by migrating magmas, thus altered and weakened. From continuum-mechanics momentum equation, the specific terms under consideration are the elastic, viscous and inertial forces. These are evaluated as characteristic magnitudes, following approximated scaling forms of their analytical expressions. Additionally and alternatively, I am carrying out separate assessments of the viscous and elastic forces using visco-elastic (VE) theory (Kelvin-Voigt and Maxwell VE models).For comparison, I am also carrying out the corresponding estimates for Japan’s Mt. Yake (1998) volcanic earthquake swarm, and also, for a typical continental crustal seismogenic environment.  Importantly, the deformation of the system is very different when-and-where earthquakes are occurring, than at other times and locations. For this reason, my assessment distinguishes  two regimes: (i) short length-scales and short duration Co-Seismic, and (ii) long-length-scale and long duration A-/Inter-Seismic background. It is for these two time frames that I estimate the stress-strain and forces per unit volume. Additionally, associated energies and energy density-rates are also estimated, and finally the energy budget of the co-seismic and inter-seismic frameworks are studied.