Seminario de Tierra Sólida | Understanding the Marianas' 2006-2007 Volcanic Earthquake Swarm: A Perspective From Fundamental Mechanical Quantities

Expositor:
Felipe Orellana Rovirosa
Profesor Asistente de Investigación
Southern University of Science and Technology, Shenzhen, China

Abstract:
An earthquake swarm occurred in the Pacific-Marianas' subduction zone during the years 2006-2007, with events manifesting from depths of 300+km in asthenosphere, lithosphere and crust, up to the surface active volcanoes; spanning about 50 km in horizontal diameter and with its largest event being Mw5.5. Using scaling-theory approximations on continuum-mechanics' equations we estimate characteristic magnitudes of mechanical variables (forces per unit area, forces per unit volume and associated energies) in the swarm region, for its inertial-kinetic, viscous and elastic behaviors; in interseismic (local background) and coseismic frameworks/regimes; and independently using approximations for the classic visco-elastic models of Maxwell (interseismic) and Kelvin-Voigt (coseismic) for a secondary alternative assessment. For comparison, we also carry out assessments for Japan's Mt. Yake (1998) volcanic earthquake swarm, and for a common tectonic crustal system (continental environment). Regarding forces and energies, our volcanic systems are quasi-indistinguishable from each other, but significantly different from the tectonic. Non-dimensional ratios of Coseismic-to-Interseismic energies (for same behaviors), reveal that our volcanic systems have coseismic-regime expected energy-density-rates >1000x the interseismic ones. The tectonic system's larger ratios (≤10^12) suggest a larger energy-flux regime contrast with a more quiescent interseismic. Thermo-mechanical energy conservation (buoyancy to dissipation) for the Marianas' inter-seismic-background suggests melt-filled porosity values roughly of about 29% (asthenospheric) or 24%(crustal) for (in trade-off with) a ~22 km-diameter (~45% of seismicity's) buoyant region. Co-seismic energy estimates align with first-order energy conservation, with coseismic change in elastic shear-potential-energy in source-and-vicinity, roughly equating released energy (wave-radiated plus viscous-dissipated), within a factor 11.7 in highest-uncertainty case.