HR: 14:40h
AN: S32C-05    [PDF]
TI: Analysis of teleseismic {\it P}, {\it S}, and {\it SKS} waves recorded in the Mediterranean region
AU: * Schmid, C
EM: schmid@tomo.ig.erdw.ethz.ch
AF: Inst. of Geophysics, ETH Honggerberg, Zurich, CH-8093 Switzerland
AU: van der Lee, S
EM: suzan@earth.northwestern.edu
AF: Dept. of Geological Sciences, 1850 Campus Dr. Northwestern University, Evanston, IL 60208
AU: Giardini, D
EM: giardini@seismo.ifg.ethz.ch
AF: Inst. of Geophysics, ETH Honggerberg, Zurich, CH-8093 Switzerland
AB: The Mediterranean region comprises a large and highly complex part of the Africa-Eurasia plate boundary. The plate boundary deformation in this region has been dominated by compression accommodated by several zones of subduction. Other zones are characterized by extension. Consequently 3-D Mediterranean upper mantle structure is heterogeneous. We determined azimuthal anisotropy in the Mediterranean region by measuring splitting of SKS waves. The distribution of the fast axis is laterally consistent, and correlates with plate motion at many stations. We observe E-W alignment in the Western part of the Mediterranean, while N-S directions are observed farther east. The transition between these domains occurs over Italy, with the strongest anomalies over the Calabrian subduction zone. Here the largest splitting times in the Mediterranean are observed with values up to 2s. In contrast, stations associated with the Hellenic subduction show small splitting times with a fast axis that is not well defined. We have also measured delay times of teleseismic {\it P} and {\it S} waves from seismograms recorded by the MIDSEA and permanent seismic arrays in the region. The vertical and transverse components of recordings from about 90 events with a distance range from 30$\deg$ to 100$\deg$ were analyzed to derive delay times for {\it P} and {\it S} waves. We derived relative delay times by cross-correlating the recordings from different stations. The pattern of mean station delays for {\it P} resembles that for {\it S} and {\it S} delay times are about 3 times larger than those for {\it P}. As expected, most prominent early arrivals are observed around subduction zones such as the Hellenic one. Latest arrivals are observed near the Dead Sea Transform. Furthermore we determined the azimuthal dependence of the {\it P} delay times and compared the results with those from the splitting analysis, with the goal of determing the relative importance of anisotropy compared to lateral heterogeneity. We find that the influence of heterogeneity is several times that of anisotropy. From an observed slight dependence of the measured delay times on wave frequency, we estimate that heterogeneity on length scales of over 100 km is primarily responsible for the observed delay times.
UR: http://www.sg.geophys.ethz.ch/midsea
DE: 7203 Body wave propagation
DE: 7218 Lithosphere and upper mantle
DE: 8150 Plate boundary--general (3040)
DE: 9305 Africa
DE: 9335 Europe
SC: Seismology [S]
MN: 2003 Fall Meeting