HR: 1340h
AN: T33C-0573    [Abstracts]
TI: Seismicity in the Calabrian Forearc: Is it Consistent with Ongoing Subduction?
AU: * Kim, W
EM: wykim@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory, 61 Rt. 9W, Palisades, NY 10964 United States
AU: Guerra, I
EM: guerra@unical.it
AF: University of Calabria, dipartimento di fisica, Rende, CS CS Italy
AU: Armbruster, J G
EM: armb@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory, 61 Rt. 9W, Palisades, NY 10964 United States
AU: Gervasi, A
EM: a.gervasi@unical.it
AF: University of Calabria, dipartimento di fisica, Rende, CS CS Italy
AU: Seeber, L
EM: nano@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory, 61 Rt. 9W, Palisades, NY 10964 United States
AU: Harabaglia, P
EM: hphppz@yahoo.com
AF: University of Calabria, dipartimento di fisica, Rende, CS CS Italy
AB: Regional seismicity and published focal mechanisms are consistent with the upper plate of the Calabrian forearc moving east relative to the southern Apennines and eastern Maghrebides. E-W zones of left and right-lateral nodal planes mark the northern and southern boundaries of the arc, respectively. In contrast, lower plate seismicity below the southern Apennines is characterized by approximately E-W right-lateral nodal planes, which may stem from slab pull increasing toward the Calabrian arc. Upper plate seismicity within the forearc is consistent with Pleistocene faults and basins indicating extension both normal and parallel to the forearc. This multi-directional stretching of the upper plate is therefore correlative with regional uplift of the forearc as shown by flight of late Pleistocene terraces. This unusual correlation suggests a deeper cause for the uplift. We examine two earthquake sequences along the boundary zone between Apennine arc-continent collision and Calabrian subduction using CAT/SCAN and other data. In the Mercure Basin, slightly north of the surface boundary between Apennine carbonate rocks and Calabrian crystalline rocks, over a 100 hypocenters from a complex and long-lasting sequence delineate composite faulting including normal with NE-SW strike and right-lateral with E-W strike. Hypocenters are as deep as 30 km and may reach into the lower plate. An Mw 4.4 mainshock on 04/23/2005 on the north flank of the Sila massif was followed by many aftershocks. The moment tensor inversion requires a depth of about 20+/-2 km, in the range of the plate interface as imaged by receiver functions, and shows fault kinematics consistent with subduction. S waves are more attenuated when traveling through the upper plate (to the west) than in the lower plate (to the east), as expected in a subduction system.
DE: 7205 Continental crust (1219)
DE: 7215 Earthquake source observations (1240)
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
SC: Tectonophysics [T]
MN: Fall Meeting 2005