HR: 1340h
AN: T23B-1421    [Abstracts]
TI: Hypocenter depths and focal mechanisms of trench-outer rise earthquakes from a local seismic network
AU: * Lefeldt, M
EM: mlefeldt@ifm-geomar.de
AF: SFB 574, Wischhofstr. 1-3, Kiel, 24148, Germany
AU: Grevemeyer, I
EM: igrevemeyer@ifm-geomar.de
AF: SFB 574, Wischhofstr. 1-3, Kiel, 24148, Germany
AU: Grevemeyer, I
EM: igrevemeyer@ifm-geomar.de
AF: IFM-GEOMAR, Wischhoftsr. 1-3, Kiel, 24148, Germany
AU: Ivandic, M
EM: mivandic@ifm-geomar.de
AF: SFB 574, Wischhofstr. 1-3, Kiel, 24148, Germany
AU: Gossler, J
EM: jgossler@ifm-geomar.de
AF: SFB 574, Wischhofstr. 1-3, Kiel, 24148, Germany
AU: Gossler, J
EM: jgossler@ifm-geomar.de
AF: IFM-GEOMAR, Wischhoftsr. 1-3, Kiel, 24148, Germany
AU: Bialas, J
EM: jbialas@ifm-geomar.de
AF: SFB 574, Wischhofstr. 1-3, Kiel, 24148, Germany
AU: Bialas, J
EM: jbialas@ifm-geomar.de
AF: IFM-GEOMAR, Wischhoftsr. 1-3, Kiel, 24148, Germany
AB: At subduction zones, the bending of the incoming oceanic plate leads to a reactivation or creation of normal faults that have been inferred to cut deep enough into the mantle to provide a pathway for seawater to penetrate into the lithosphere, changing "dry" peridotites into "wet" serpentinites. Such a mechanism would present an efficient system to transport fluids into the slab and therefore would influence a wealth of subduction zone processes as dehydration at depths of 50-300 km can trigger intermediate-depth earthquakes and promote the melt generation under volcanic arcs. Supported is the idea perhaps by seismic wide-angle and refraction lines that show unusually low P-wave velocities in the crust and upper mantle seawards of the trench axis, which are best explained by a fractured and serpentinized lithosphere. Yet the extent and the importance of this process remain under debate, since bending-related faults might cut much deeper into the mantle than tomographic inversions could resolve so far. We present implications for a unique data set obtained from a dense, local seismic monitoring network. A combination of local earthquakes within or nearby the network and well-located earthquakes in distances of 200- 700km allow us to constrain a velocity model that reflects almost the entire lithosphere. We document a relation between bending-related faults and trench-outer rise seismicity, but state that micro-seismicity reaches much deeper than velocity anomalies and therewith possible serpentinization. We explain the latter with a change of the stress regime from tensional at the top of the incoming lithosphere to compressional beneath, as we infer from the determination of focal mechanism for a number of events. Seawater might not be able to penetrate into an area governed by compressional stresses.
DE: 3060 Subduction zone processes (1031, 3613, 8170, 8413)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting