HR: 1340h
AN: T13B-1330    [Abstracts]
TI: Investigation of seismic anisotropy in the area of the German Regional Seismic Network (GRSN) using P-to-S converted phases.
AU: * Eckhardt, C
EM: ceckpost@gmx.net
AF: University of Kiel, Otto-Hahn-Platz 1, Kiel, SH 24118, Germany
AU: Rabbel, W
EM: rabbel@geophysik.uni-kiel.de
AF: University of Kiel, Otto-Hahn-Platz 1, Kiel, SH 24118, Germany
AB: Based on SKS and Pn-residual analysis several studies have shown evidence that the crust and/or the upper mantle are seismically anisotropic beneath the area of the German Regional Seismic Network (GRSN). The aim of our study is to estimate the crustal and mantle shares of seismic anisotropy by analyzing the polarization of P-to-S converted waves (receiver functions) generated at the Moho Pms and at the upper mantle discontinuities P410s, P660s. Seismic anisotropy finds its expression in a directional dependence of seismic velocities and in the travel time delay between orthogonally polarized S-waves (S-wave splitting). For the estimation of S-wave splitting we used the energy minimization technique and an azimuthal stacking approach. The P-to-SV converted wave fields generated at the Moho show a frequency variation with azimuth, broading of amplitude peaks and an azimuth periodicity in amplitude strength. These are indications of both a thickness variation of a transition zone and existence of anisotropy. On the SH-component converted energy is observed, too. Its amplitude and polarity periodicity is 360° for most of the GRSN stations. Some stations show less than 360° or unclear periodicity. The greatest change in fast direction of the 3 discontinuities exist between crust and upper mantle. More than a half of the stations show equal directions for the crust Pms compared to SKS/SKKS studies. High delay times δt>0.5s are observed for crustal structures versus small changes in time to deeper strutures. Since about 16 years the GRSN provides continuous seismological data records for most of its stations. Based on an analysis of back azimuth and incidence rotated ray component L we determined an average signal/noise ratio from 4.5 to 22 for these data. Because of the long observation time the azimuth coverage of incidence angles is sufficient for the major part of station (18/25). The data basis for an analysis seismic anisotropy is well established. For the analysis of P-to-S converted waves we selected 2455 events of magnitude mb>5.5 and epicentral distances of 0°-100°. To process the receiver functions - rf, of this data volume we set up an automatic process including the computation of various quality criteria. The processing steps included in the procedure are: (1) rf calculation based on real and theoretical polarization angles, (2) rf selection based of signal-to-noise ratio, (3) rf weighting based on the quality of polarization. The rate of data reduction during this process is approximately between 50 and 70 percent.
DE: 8120 Dynamics of lithosphere and mantle: general (1213)
DE: 8138 Lithospheric flexure
DE: 8160 Rheology: general (1236, 8032)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting