HR: 0800h
AN: G51A-0059    [Abstracts]
TI: Non-Double-Couple Source Models of Volcanic Seismicity
AU: * Minson, S E
EM: minson@gps.caltech.edu
AF: California Institute of Technology, Seismological Laboratory, 1200 E. California Blvd. MC 252-21, Pasadena, CA 91125 United States
AU: Dreger, D S
EM: dreger@seismo.berkeley.edu
AF: University of California, Berkeley, 301 McCone Hall, Berkeley, CA 94720 United States
AU: B\"{u}rgmann, R
EM: burgmann@seismo.berkeley.edu
AF: University of California, Berkeley, 301 McCone Hall, Berkeley, CA 94720 United States
AU: Kanamori, H
EM: hiroo@gps.caltech.edu
AF: California Institute of Technology, Seismological Laboratory, 1200 E. California Blvd. MC 252-21, Pasadena, CA 91125 United States
AB: The source mechanisms of many earthquakes from the 2000 Miyakejima, Japan, eruption sequence are unusual in that the seismic data clearly indicate the existence of non-double-couple components. The period of volcanic unrest was marked by substantial crustal deformation as well as an earthquake swarm which included many magnitude five and larger earthquakes. These earthquakes were well observed by local and regional seismic and GPS networks. Thus the Miyakejima eruption provides an excellent opportunity to study non-double-couple earthquake source processes. Earthquakes related to volcanic unrest may be expected to have non-double-couple mechanisms or to have mechanisms which include significant volume changes. These types of earthquake source mechanisms have been successfully determined through moment tensor inversions. However, unconstrained moment tensor inversions can produce moment tensors which are indicative of non-physical event parameters or which contain multiple compensating volume changes. Also, the additional model parameters in an unconstrained moment tensor inversion can lead to instabilities. By imposing certain constraints on the seismic source, we can develop models which are physically realistic, such as source models related to extension and tensile faulting. We will present a new moment tensor decomposition to describe the faulting mechanics of non-double-couple earthquakes. In this moment tensor decomposition, non-deviatoric moment tensors are described as the sum of a double-couple mechanism and a tensile component. GPS-measured coseismic surface displacements will be used to provide additional constraints on the event kinematics. Such a source model is both mechanically realistic and well constrained. This model will be compared to other possible models for the source mechanisms of these volcanic earthquakes, including both conventional models and more exotic non-double-couple models. We will then use these mechanisms to infer the volcanic processes which led to this seismicity.
DE: 7280 Volcano seismology (8419)
DE: 7209 Earthquake dynamics and mechanics
DE: 7215 Earthquake parameters
SC: Geodesy [G]
MN: 2004 AGU Fall Meeting