HR: 09:45h
AN: S41E-08    [Abstracts]
TI: Simultaneous Inversion for 3D Crustal and Anisotopic Lithospheric Structure and Regional Hypocenters Beneath Germany
AU: * Koch, M
EM: kochm@uni-kassel.de
AF: Department of Geotechnology and Geohydraulics, University of Kassel Kurt-Wolters Str. 3, Kassel, 34119 Germany
AU: Muench, T W
EM: tmuench@uni-kassel.de
AF: Department of Geotechnology and Geohydraulics, University of Kassel Kurt-Wolters Str. 3, Kassel, 34119 Germany
AU: Schlittenhardt, J
EM: J.Schlittenhardt@bgr.de
AF: Federal Institute of Geosciences, Stilleweg 2, Hannover, 30655 Germany
AB: There is now ample evidence from both refraction seismic studies, done already a quarter century ago and from more recent local earthquake travel analysis of some of the authors above that large sections of the upper mantle underneath Europe and Germany, in particular, are anisotropic. More exactly, the investigations of Song et al. [2001] and Song et al. [2004] by means of a 1D time-term analysis and a full 2D Pn anisotropic inversion of regional travel time data, respectively, indicate that an anisotropic velocity ellipse with the fast axis pointing ~N250E and an anisotropy level of ~3.5% explains best the data and, additionally, show that geologically meaningful Pn-velocities (>8 km/sec) are only obtained if the large-scale anisotropy is included in the inversion. Employing a modified version of the method of simultaneous inversion for structure and hypocenters (SSH) of the frst author, including a priori known upper mantle anisotropy, the studies above are extended here to a full 3D SSH-inversion underneath Germany. Regional travel times from local events occurring between 1975-2003 are used which, after application of several selection criteria, results in ~1300 events with a total of ~30000 P- and S-phases for the SSH inversion. Because many of the recorded events appear to suffer from relatively poor hypocentral depth locations a full SSH analysis becomes an intricate undertaking. To alleviate the problem the SSH procedure is carried out in several incremental steps of increasing complexity. First of all improved vertically inhomogeneous velocity (1D) models are derived assuming an isotropic as well as an anisotropic upper mantle. In addition of a slightly better model fit for the anisotropic than for the isotropic model, the latter gives also a somewhat too low Pn-velocity of ~7.90 km/s, compared with ~8.0 km/s for the former. This indicates that inclusion of upper mantle anisotropy into the model is required to obtain physically reasonable Pn-velocities. The results for the P-velocity in the lower crustal layer of the model are less clear, as there appears to be some trade-off in the velocity of that layer and that of the upper mantle. Significant improvements for both the isotropic and anisotropic upper mantle cases are obtained for the full 3D SSH inversion models. Similar to the 1D Pn-velocity models there are remarkable differences in the lateral Pn-velocities, depending whether the lithosphere is corrected for anisotropy or not. Namely, for an anisotropic upper mantle the median ellipse velocities are generally higher, laterally smoother and behave also more stably throughout the inversion than those obtained assuming an isotropic upper mantle. Checkerboard resolution tests are performed indicating a rather well-resolved upper crust und upper mantle and a less-resolved lower crust. As for the geological and tectonical interpretation of the seismo-tomographic crustal velocities obtained, there appears to be congruence of the latter, namely, in some portions of the upper crust, with some of the important features and lineaments defined by the central European Variscides.
DE: 7205 Continental crust (1219)
DE: 7215 Earthquake source observations (1240)
DE: 7218 Lithosphere (1236)
DE: 7270 Tomography (6982, 8180)
SC: Seismology [S]
MN: Fall Meeting 2005