HR: 1340h
AN: S53A-0190    [Abstracts]
TI: Small Aperture Array Resolution Capabilities for Use in Locating Deep Tremor
AU: * La Rocca, M
EM: mlarocca@ov.ingv.it
AF: Osservatorio Vesuviano - INGV, Via Diocleziano 328, Napoli, 80124 Italy
AU: Malone, S
EM: steve@ess.washington.edu
AF: Earth & Space Sciences, University of Washington, 310 Condon Hall, Seattle, WA 98195 United States
AU: Saccorotti, G
EM: gilberto@ov.ingv.it
AF: Osservatorio Vesuviano - INGV, Via Diocleziano 328, Napoli, 80124 Italy
AU: McCausland, W
EM: wendy@ess.washington.edu
AF: Earth & Space Sciences, University of Washington, 310 Condon Hall, Seattle, WA 98195 United States
AU: Galluzzo, D
EM: galluzzo@ov.ingv.it
AF: Osservatorio Vesuviano - INGV, Via Diocleziano 328, Napoli, 80124 Italy
AU: Del Pezzo, E
EM: delpezzo@ov.ingv.it
AF: Osservatorio Vesuviano - INGV, Via Diocleziano 328, Napoli, 80124 Italy
AB: Three small aperture seismic arrays (diameter ~600m) were operated in Northern Washington during spring and summer, 2004 to monitor an expected episode of Deep Tremor which occurred in July. Each array was composed of six 3-component, short-period seismometers. Besides recording two weeks of strong, deep tremor many earthquakes with a range of magnitudes, distances and azimuths were also recorded. Earthquake signals have been used to test the resolving ability of the arrays for subsequent analysis of the deep tremor signals. Analysis techniques tested were "Zero Lag Cross-Correlation" and classical "Beam Forming" array techniques in time domain, and "High Resolution" array methods in the frequency domain. Calculated backazimuth and slowness values of P and S direct phases were compared with those calculated based on the hypocenters determined by the regional network and the regional velocity structure to give an estimate of the error associated with array techniques. The time domain analysis results show good agreement with the real earthquake locations. The resolution capability associated with the Zero Lag Cross-Correlation method is between 0.01 and 0.02 s/km for slowness and 5-10 degrees in back azimuth, depending mostly on the signal to noise ratio. On the contrary, the results of spectral techniques are less reliable and generally differ more than expected from the true values. This is probably due to the small number of stations composing the arrays which affects the spectral techniques more than the time domain techniques. As a further test, synthetic waveforms were calculated for a variety of parameters including backazimuth, slowness, array geometry and noise level (injected synthetic noise). The synthetic tests results are comparable with those obtained by the analysis of earthquakes. These results will be used for estimating location errors of deep tremor signals as recorded simultaneously on all three arrays.
DE: 7230 Seismicity and seismotectonics
DE: 7294 Instruments and techniques
DE: 7203 Body wave propagation
DE: 7209 Earthquake dynamics and mechanics
DE: 7218 Lithosphere and upper mantle
SC: Seismology [S]
MN: 2004 AGU Fall Meeting