Ambiguous Source Radiation in Anisotropic Media and Consequences for the Interpretation of Earthquakes Mechanisms

HR: 1330h
AN: S42E-0205 [PDF]
TI: Ambiguous Source Radiation in Anisotropic Media and Consequences for the Interpretation of Earthquakes Mechanisms
AU: * Roessler, D
EM: diroess@rz.uni-potsdam.de
AF: University of Potsdam, K.-Liebknecht-Str. 24/H25, Golm, 14476 Germany
AU: R\, G
EM: rumpker@gfz-potsdam.de
AF: GeoForschungsZentrum Potsdam, Telegrafenberg, Potsdam, 14473 Germany
AU: Krueger, F
EM: kruegerf@geo.uni-potsdam.de
AF: University of Potsdam, K.-Liebknecht-Str. 24/H25, Golm, 14476 Germany
AB: Anisotropic material properties are usually neglected during inversions for earthquake source parameters using conventional methods. Here we investigate the effects of homogeneous and heterogeneous anisotropy within the source region on the radiated wavefield. Based on formulations for the moment tensor and the Green's function in anisotropic media, we find that anisotropy can greatly influence the radiation pattern. For example, apparent non-double-couple components can be produced for pure shear sources when the axes of anisotropic symmetry are oriented arbitrarily with respect to the fault plane. The direction of slip on the fault may affect the total seismic moment, which is in contrast to the isotropic case. Furthermore, similar moment tensors can be created by either pure shear or tensile faulting in anisotropic host media, if the fault plane is generally oriented. When anisotropy in the source region is not accounted for, erroneous conclusions regarding the source mechanisms may be drawn. We find that the source mechanisms infered from synthetic radiation patterns for pure shear sources in anisotropic media may show characteristics which are similar to those deduced in recent studies on microearthquakes. However, the latter have been interpreted to show evidence of tensile faulting under the assumption of an isotropic host medium.
DE: 7200 SEISMOLOGY
DE: 7203 Body wave propagation
DE: 7209 Earthquake dynamics and mechanics
DE: 7215 Earthquake parameters
DE: 7260 Theory and modeling
SC: Seismology [S]
MN: 2003 Fall Meeting