HR: 15:10h
AN: S33C-07    [Abstracts]
TI: Retrieval of Earthquake Source Parameters in Anisotropic Media - Application to Swarm Events in W-Bohemia, Central Europe
AU: * Rößler, D
EM: diroess@rz.uni-potsdam.de
AF: University of Potsdam, K.-Liebknecht-Str. 24, Golm, 14476 Germany
AU: Krüger, F
EM: kruegerf@geo.uni-potsdam.de
AF: University of Potsdam, K.-Liebknecht-Str. 24, Golm, 14476 Germany
AU: Rümpker, G
EM: rumpker@geophysik.uni-frankfurt.de
AF: University of Frankfurt/Main, Feldbergstr. 47, Frankfurt/Main, 60323 Germany
AU: Pšenčík, I
EM: ip@ig.cas.cz
AF: Academy of Sciences of the Czech Republic, Bocni II 1401, Praha 4, 141 31 Czech Republic
AB: Anisotropic material properties may significantly influence characteristic features of moment tensors. Moment tensors of shear sources in anisotropic media may comprise double-couple and apparent non-double-couple components. On the other hand real non-double-couple source components of earthquakes may not be visible in moment tensors. As a result moment tensors of sources in anisotropic rocks may be difficult to interpret in terms of volumetric changes, i.e. opening or closing of a crack, that may occur during faulting. Although commonly observed in many regions of the earth, seismic anisotropy is usually neglected during the inversion process of source parameters of earthquakes. We propose an inversion algorithm for the determination of properties of seismic point sources in inhomogeneous anisotropic media based on ray-theory computations. Hereby, we directly invert for the geometry of the seismic source, i.e. we retrieve the dyadic product of the slip vector and the fault normal, as well as for the strength of the earthquake. From the source geometry we derive the angle between the slip direction and the fault normal to describe volumetric source changes. We apply the proposed algorithm to the events from W-Bohemia, Central Europe that occurred during the last intense swarm episode from August until December, 2000. During this time a dense network of permanent and temporary seismic stations was installed and up to 10000 events M_L ≤ 3.3 were recorded. Here, we study focal mechanisms of the largest events (M_L≥q1.7). During inversion, we use different inhomogeneous anisotropic / isotropic models and investigate the relevance of anisotropy for the interpretation of the results. The obtained fault orientations dominantly show strike-slip faulting on a North-South trending fault. For many events we observe small opening of the fault plane indicating volume increase connected to the faulting process. The volumetric source components vary with time and focal depth. Using our new algorithm we may constrain observations of other authors suggesting fluid-controlled event triggering.
DE: 7209 Earthquake dynamics (1242)
DE: 7215 Earthquake source observations (1240)
DE: 7223 Earthquake interaction, forecasting, and prediction (1217, 1242)
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
DE: 7290 Computational seismology
SC: Seismology [S]
MN: Fall Meeting 2005