HR: 1340h
AN: T53B-0484    [Abstracts]
TI: Investigation of the Influence of Different Velocity Models on the Focal Mechanism Solutions Derived from Inversion of Regional Broadband Waveforms for Earthquakes in Greece
AU: * Konstantinou, K
EM: kostas@earth.sinica.edu.tw
AF: Institute of Earth Sciences Academia Sinica, POB 1-55 Nankang, Taipei, 115 Taiwan
AU: * Konstantinou, K
EM: kostas@earth.sinica.edu.tw
AF: Institute of Geodynamics National Observatory of Athens, POB 20048, Athens, 118 10 Greece
AU: Sokos, E
EM: esokos@gein.noa.gr
AF: Institute of Geodynamics National Observatory of Athens, POB 20048, Athens, 118 10 Greece
AU: Melis, N
EM: nmelis@gein.noa.gr
AF: Institute of Geodynamics National Observatory of Athens, POB 20048, Athens, 118 10 Greece
AU: Stavrakakis, G
EM: g.stavr@gein.noa.gr
AF: Institute of Geodynamics National Observatory of Athens, POB 20048, Athens, 118 10 Greece
AU: Boukouras, K
EM: kbouk@admin.gein.noa.gr
AF: Institute of Geodynamics National Observatory of Athens, POB 20048, Athens, 118 10 Greece
AB: The routine use of regional broadband data for the determination of moment tensors for even very small (Mw $\sim$ 3.5) events, has considerably enhanced our understanding of tectonic processes in many active regions around the world. However, this advance comes at the expense of having to know an adequate regional one-dimensional model that can successfully predict the source-to-receiver path effects, thus minimizing the differences between observed and synthetic data during the source inversion process. This is especially true for the data recorded by the Greek national network, due to the limited bandwidth of its stations that record periods of up to 20 s, increasing the dependency of the source inversions on the velocity model used. The network is operated by the Institute of Geodynamics of the National Observatory of Athens and consists of 22 digital, three-component seismometers that cover most parts of the country. In order to investigate this dependency, we selected five moderate to large (Mw $\sim$ 5.0-6.4) earthquakes based on the following two criteria: (1) the available moment tensor solutions for these events reported by the Harvard CMT group, the USGS and/or the Swiss Seismological Service showed good agreement with each other, (2) the events should occur in geographically different parts of the Greek region. As a first step before the inversion we gathered all the published velocity models for the Greek region resulting from teleseismic/local earthquake/surface-wave tomography, created average one-dimensional models and did forward modelling of the waveforms of each event. If the calculated misfit of the forward-synthetic and observed waveform was small, then this velocity model was further used in the source inversion in the frequency band 0.05-0.08 Hz. The results from the inversions showed that in all five cases the focal mechanism was exhibiting only minor differences when compared to the other available solutions. However, the amount of CLVD was high ($\sim$ 70%) for events in the central and northern Aegean Sea, while the misfit versus depth curve showed no clear minimum for a range of depth values. The situation was better for events occuring in western and southern Greece with lower CLVD values ($\sim$ 2-34%) and clear minima in the corresponding misfit versus depth curves. These observations suggest that most published models for the Greek region are probably insufficient for matching all path effects for the frequency bandwidth used in our inversions, but at the same time seem adequate for the recovery of a reliable focal mechanism. The results of this study have great importance in view of future efforts to routinely invert regional waveforms for the determination of focal mechanism solutions for earthquakes in Greece.
DE: 7230 Seismicity and seismotectonics
DE: 8123 Dynamics, seismotectonics
DE: 7209 Earthquake dynamics and mechanics
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting