HR: 1340h
AN: T33C-0567    [Abstracts]
TI: 2004-2005: The Winter of quasi-Love in Tuscany
AU: * Levin, V
EM: vlevin@rci.rutgers.edu
AF: Department of Geological Sciences, Rutgers University, Piscataway, NJ 08854 United States
AU: Park, J
EM: jeffrey.park@yale.edu
AF: Department of Geology and Geophysics, Yale University, New Haven, CT 06520 United States
AB: Seismic wave speed in the upper mantle is commonly found to be direction-dependent. This anisotropy, especially beneath the lithosphere, is generally thought to reflect the coherent deformation of olivine-rich mantle rocks. We detect anisotropy by the Love-to-Rayleigh converted surface wave, ( quasi-Love wave), which originates most readily from lateral gradients in seismic anisotropy structure. Observations of this wave are most commonly done at relatively long (50 - 200 s) periods where the effects of isotropic perturbations are easier to discount. In this presentation we document a number of observations of quasi- Love waves obtained by the temporary seismic array deployed in Northern Italy in the framework of the RETREAT project. The most spectacular observation comes from the Sumatra-Andaman earthquake of 12/26/04. We also observe quasi-Love phases in the records of the M=8.1 Macquarie Island earthquake that occurred only three days prior to it, and in the records of 03/28/05 M=8.7 Northern Sumatra earthquake. For the Sumatra-Andaman earthquake record sections constructed across the Apennines show clear distortions of the Love wavefield. A coeval vertically polarized phase (a diagnostic of quasi-Love phase) appears on records from all sites in Tuscany, west of the Apennines, but not at sites east of them. We interpret the raypaths' geometry and distribution of quasi-Love observations as suggestive of an anisotropic gradient associated with the descent of the Adriatic lithosphere beneath the Apennines. The isotropic fast velocities of the Apennines slab, as obtained from previous tomographic studies, are far too modest to generate the observed Love-to-Rayleigh conversion. Using a combination of raypath geometries from a number of earthquakes we will evaluate the location of anisotropic gradients responsible for the quasi-Love observations. Frequency dependence may put first-order constraints on the depth extent of anisotropic gradients. We will discuss implications of the findings in terms of scenarios for the Northern Apennines geodynamics.
UR: http://earth.geology.yale.edu/RETREAT/
DE: 7255 Surface waves and free oscillations
DE: 8120 Dynamics of lithosphere and mantle: general (1213)
DE: 8124 Earth's interior: composition and state (1212, 7207, 7208, 8105)
SC: Tectonophysics [T]
MN: Fall Meeting 2005