HR: 09:00h
AN: S41C-05    [Abstracts]
TI: New evidence for and against a retreating subduction zone model for Northern Apennines.
AU: Agostinetti, N P
EM: piana@ingv.it
AF: INGV, Via Vigna Murata 605, Rome, 00143, Italy
AU: * Levin, V
EM: vlevin@rci.rutgers.edu
AF: Rutgers University, Dept. of Geological Sciences, Piscataway, NJ 08854, United States
AU: Park, J
EM: jeffrey.park@yale.edu
AF: Yale University, Dept. of Geology and Geophysics, New Haven, CT 06520, United States
AU: Salimbeni, S
EM: salimbeni@bo.ingv.it
AF: INGV, Via D. Creti 12, Bologna, 40128, Italy
AB: We investigate crustal structure of the northern Apennines using broadband seismic data from a dense linear transect. Receiver functions reveal significant differences between the responses of the Tyrrhenian and Adriatic sides of the Apennines, and determine the spatial location of a change in this response, just west of the high crest of the mountains. We find a clear signature of the crust-mantle transition on the eastern Tyrrhenian side, and no obvious signature on the western Adriatic side. We also use relative timing of likely direct and multiply-reflected P-S converted waves in the crust to develop estimates of crustal thickness and Vp/Vs ratio within it. A nearly-uniform thickness of about 25 km is seen between the island of Elba and the crest of the Apennines, while further east crustal thickness increases to 35+ km over 10-30 km lateral distance. Crustal thickness is much less certain east of the Apennines due to complex structure or the interference of near-surface reverberations. Within the Po plain P-SV response of the crust is dominated by the resonance in the sediments, which limits our ability to determine crustal parameters. The abrupt change in crustal properties coincides with a major change in SKS birefringence, with areas south-west and northeast of the Apennines' crest showing distinct patterns. Shear-wave birefringence integrates seismic anisotropy along the wave's path, and likely documents a change in the upper mantle texture, rather than the crust. The spatially coincident change in the crustal structure and the upper mantle texture is expected for the subduction zone retreat model. However, the nature of the upper mantle deformation suggested by anisotropy observations presents a challenge for this interpretation, as we infer flow (extension) along the Apennines beneath the thin crust of the Tyrrhenian coast, i.e. in the back-arc area, not beneath the retreating slab. We speculate that crustal structure in northern Apennines is a relict of the subduction zone retreat that has (nearly or completely) ceased here, while upper mantle texture reflects an ongoing 3-dimensional deformation of the region.
UR: http://earth.geology.yale.edu/RETREAT/
DE: 1213 Earth's interior: dynamics (1507, 7207, 7208, 8115, 8120)
DE: 1219 Gravity anomalies and Earth structure (0920, 7205, 7240)
DE: 3040 Plate tectonics (8150, 8155, 8157, 8158)
DE: 7203 Body waves
SC: Seismology [S]
MN: 2007 Fall Meeting