HR: 0800h
AN: S11B-1013    [Abstracts]
TI: Regional Moment Tensor Parameter Resolution Tests
AU: * Lloyd, S M
EM: simon@earth.northwestern.edu
AF: Department of Geological Sciences, Northwestern University, 1850 Campus Drive, Evanston, IL 60208-2150 United States
AU: Braunmiller, J
EM: jochen@seismo.ifg.ethz.ch
AF: Institute of Geophysics, ETH Hoenggerberg, Zurich, 8093 Switzerland
AB: With the establishment of dense broadband seismic networks in many regions worldwide, regional moment tensor (RMT) inversion is becoming a routine tool for source parameter determination of weak ($M \geq 4$) earthquakes. We invert complete three-component regional waveforms to systematically investigate the influence of station distribution, crustal model, inversion frequency band, and assumed depth on source parameter (magnitude, depth, moment tensor) resolution. Synthetic tests involve pure strike-slip and dip-slip sources similar to the real data, the $M_W = 6.6$ July 26, 2001 Skyros, Aegean Sea earthquake and two $M_W = 4.5$ and 5.0 aftershocks. We define seven networks with average event-station distances from 420 to 1500 km and azimuthal gaps between $95-350\deg$. The networks are based on Skyros events and mimic typical configurations in the Mediterranean. We invert for all networks, 4 crustal models, 6 frequency bands (15-40 s to 50-100 s) and 12 source depths (4 to 36 km). Solutions close to the correct (synthetic) or an independent reference (observed) are selected. We find a complex interplay of inversion parameters, event size and type on source parameter resolution. Generally, more strike-slip than dip-slip solutions are selected, but depth is better resolved for dip-slip solutions; magnitude is well constrained. For dip-slip events, selected solutions depend strongly on the model. For strike-slip events, we obtain solutions for all models and good azimuthal coverage for larger events. For small events with few traces above noise level only a combination of close stations, good coverage and short-period analysis provides selected solutions. Generally, the true structure is unknown, therefore the best possible coverage and close-by stations should be used for RMT analysis. Phase mismatch at short-periods and long paths requires a careful selection of frequency bands considering crustal model knowledge and event-station distances. Preliminary tests with path-dependent models derived from a recent regional 3-D model do not show a significant resolution improvement over simple average 1-D models.
DE: 7215 Earthquake parameters
SC: Seismology [S]
MN: 2004 AGU Fall Meeting