HR: 16:45h
AN: S32E-04    [PDF]
TI: News from MIDSEA Seismograms on the Upper Mantle of the Eurasia-Africa Plate Boundary Region
AU: * van der Lee, S
EM: suzan@earth.northwestern.edu
AF: Dept. of Geological Sciences, Northwestern University 1850 Campus Dr., Evanston, IL 60208
AU: van der Meijde, M
EM: mark@tomo.ig.erdw.ethz.ch
AF: Inst. of Geophysics, ETH Honggerberg, Zurich, CH-8093 Switzerland
AU: Giardini, D
EM: giardini@seismo.ifg.ethz.ch
AF: Inst. of Geophysics, ETH Honggerberg, Zurich, CH-8093 Switzerland
AU: Marone, F
EM: federica@seismo.berkeley.edu
AF: Berkeley Seismological Laboratory, University of California 215 McCone Hall, Berkeley, CA 94720
AU: Schmid, C
EM: schmid@tomo.ig.erdw.ethz.ch
AF: Inst. of Geophysics, ETH Honggerberg, Zurich, CH-8093 Switzerland
AB: From an extensive study of {\it P} to {\it S} converted waves, surface waves, and literature data on crustal thickness in this region, we first mapped the depth to the Moho. Our Moho map extends from relatively well-known southern Europe into northern Africa to the south and the Atlantic ocean to the west. We interpret the western Mediterranean to have considerably extended continental crust, the central Mediterranean to have oceanic crust in the north and standard continental crust in the south, the eastern Mediterranean to have continental crust underlying a thick pile of sediments, and the Atlantic Ocean to have an anomalously thick crust and/or a very low sub-Moho {\it S} velocity. Mapping this highly heterogeneous crust has helped us to obtain cleaner tomographic images of upper mantle {\it S}-velocity structure than possible without our Moho map. In addition to well-known high-velocity subducting lithosphere, these images reveal a widespread shallow low-velocity layer beneath the Mediterranean basin that strongly varies spatially. The images also show widespread high-velocity anomalies in the transition zone beneath the Mediterranean region, which we interpret as fragments of subdcuted lithosphere. One such fragment is beneath NE Spain and possibly related to early Cenozoic subduction there. We also investigated mantle discontinuities below the Mediterranean region and find that {\it P} to {\it S} converted waves from the 660 km discontinuity are consistent with a sharp discontinuity while those for the 410 km discontinuity indicate that this discontinuity can be 20 to 30 km thick. Our preferred explanation for this anomalously thick 410 km discontinuity is that it was thickened by olivine being hydrated by about 0.05 wt %.
UR: http://www.sg.geophys.ethz.ch/midsea/
DE: 7205 Continental crust (1242)
DE: 7218 Lithosphere and upper mantle
DE: 8180 Tomography
DE: 9305 Africa
DE: 9335 Europe
SC: Seismology [S]
MN: 2003 Fall Meeting