HR: 0800h
AN: V11C-0756    [Abstracts]
TI: The Influence of Near Surface Velocity Structures on Long-Period (LP) Volcano-Seismic Signals: Examples Using Simulations from Mt Etna.
AU: * Lokmer, I
EM: ivan.lokmer@ucd.ie
AF: Seismology and Computational Rock Physics Lab, School of Geological Sciences, University College Dublin, Belfield, Dublin, 4, Ireland
AU: Bean, C J
EM: chris.bean@ucd.ie
AF: Seismology and Computational Rock Physics Lab, School of Geological Sciences, University College Dublin, Belfield, Dublin, 4, Ireland
AU: O'Brien, G S
EM: gareth.obrien@ucd.ie
AF: Seismology and Computational Rock Physics Lab, School of Geological Sciences, University College Dublin, Belfield, Dublin, 4, Ireland
AB: Long Period (LP) signals with dominant periods in the range 0.2-2 Hz have received particular attention on volcanoes, as they are thought to be directly associated with moving fluids or resonating fluid-filled conduits. Consequently, in an effort to better understand fluid-driven processes, inverting for LP source mechanisms is becoming increasingly common. As the majority of LP events occur at shallow depths & have short path lengths and km-long wavelengths, the role of edifice heterogeneity is usually ignored. We use 3D full wavefield simulations in heterogeneous Mt Etna models with topography to generate a wavefield radiated from a synthetic LP source. Greens functions are calculated for a homogeneous model with topography. Moment Tensor plus single force inversions of these synthetics demonstrate the extreme sensitivity of the solution for LP source forces to near-surface volcano structure. In particular, spurious forces and incorrect source orientation are obtained if the top 400 m is poorly constrained. Sensitivity kernels help to elucidate the details of the propagation effects which lead to poor source characterization and allow us to suggest an improved protocol for the inversion of real LP signals. We conclude that the effect of poorly resolved velocity structure can be minimized by using a priori information about the source geometry and inverting signals for as few free model parameters as possible.
DE: 7280 Volcano seismology (8419)
DE: 7290 Computational seismology
DE: 8400 VOLCANOLOGY
DE: 8419 Volcano monitoring (7280)
DE: 8494 Instruments and techniques
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting