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Department of Geology and Geophysics, Yale University, New Haven, Connecticut, USA
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- PublicationRestrictedAbrupt change in mantle fabric across northern Apennines detected using seismic anisotropy(2007-04-14)
; ; ; ; ; ; ;Salimbeni, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia ;Pondrelli, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia ;Margheriti, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia ;Levin, V.; Department of Geological Sciences, Rutgers University, Piscataway, NJ, USA ;Jeffrey, P.; Department of Geology and Geophysics, Yale University, New Haven, Connecticut, USA ;Jaroslava, P.; Geophysical Institute, Czech Academy of Science, Prague, Czech Rep.; ; ; ; ; We estimated SKS splitting parameters for 18 earthquakes observed over 2 years on a dense linear seismometer array crossing the Apennines orogen (Northern Italy). An abrupt (within 30 km) change in fast polarization occurs near the crest of the Apennines. Southwest of the crest, fast polarization parallels the Apennines strike (WNW–ESE), rotating to EW orientation near the Tyrrhenian Sea. Northeast of the crest, toward the Po Plain, fast polarization is NNE–SSW, roughly normal to the orogen’s strike. Delay times (0.6–2.9s) do not show a remarkable pattern. Splitting parameters beneath the Apennines argue against anisotropy restricted to the crust, and suggest that the mantle region deformed by Apennines slab rollback is spatially limited. We hypothesize that the rollback process has been uneven, evolving to a contortion of the northern edge of the Apennines slab, and perhaps incipient detachment. Lithospheric anisotropy beneath the Po-Plain may also be significant.194 23 - PublicationRestrictedEnd of subduction in northern Apennines confirmed by observations of quasi-Love waves from the great 2004 Sumatra-Andaman earthquake(2007-02-21)
; ; ; ; ; ;Levin, V.; Department of Geological Sciences, Rutgers University, Piscataway,NJ,USA ;Jeffrey, P.; Department of Geology and Geophysics, Yale University, New Haven, Connecticut, USA ;Lucente, F. P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia ;Margheriti, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia ;Pondrelli, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; ; ; ; Surface waves from the great Sumatra-Andaman earthquakes of 2004 and 2005 that cross Italy south of 44 N display Love-to-Rayleigh scattered waves (quasi- Love phases) diagnostic of sharp lateral gradients in the anisotropic properties of Earth’s upper mantle. Surface waves that traverse Italy further north lack this distinctive phase, documenting a change in the upper mantle fabric that is corroborated by a shift in the fast polarization of shear wave birefringence. These observations suggest that orogen-parallel asthenospheric extension behind the retreating Apennines slab has limited geographical expression. We hypothesize that subduction rollback currently terminates at 44 N, while the upper mantle flow pattern further to the north has been recently rearranged.208 33