Centroid depth and mechanism of trench-outer rise.

Lefeldt, Marten and Grevemeyer, Ingo (2008) Centroid depth and mechanism of trench-outer rise. Open Access Geophysical Journal International, 172 . pp. 240-251. DOI 10.1111/j.1365-246X.2007.03616.x.

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Abstract

Trench-outer rise earthquakes occur by reactivation or creation of normal faults caused as the oceanic lithosphere approaches a subduction zone and bends into the deep-sea trench. These faults may cut deep enough into the mantle to allow sea water to penetrate into the lithosphere, causing serpentinization. The amount of water carried into the mantle is linked to the maximum depth that the tensional faults cut into the lithosphere, which in turn is directly linked to the maximum focal depths of outer rise normal faulting earthquakes.

We analysed teleseismic P and S waves of seven earthquakes from the trench-outer rise offshore of Central America using teleseismic waveform inversion of broad-band data. For the computation of Green's functions for waveform inversion, probabilistic earthquake locations were calculated. To study the rupture process, earthquake centroid depths and focal mechanisms for a sequence of subevents were calculated. Both, hypocentral depths from the relocation process and the estimated centroid depths from the waveform inversion show that all events occur at shallow depths (<30 km). Furthermore, the locations of the subevents relative to each other suggest that fault planes for Mw∼ 6 are in the order of 50 km in length and only 5–10 km in width. Rupture generally propagates downdip and the focal mechanisms change for most events from normal faulting to strike-slip or oblique thrusting with time. The depth at which this mechanism change is observed may represent the depth of the nodal plane between tensional and compressional regions in the incoming plate.

Document Type: Article
Keywords: Earthquake source observations; Body waves; Subduction zone processes; Dynamics and mechanics of faulting; Dynamics of lithosphere and mantle; Pacific Ocean
Research affiliation: OceanRep > SFB 574 > A5
OceanRep > SFB 574
OceanRep > GEOMAR > FB4 Dynamics of the Ocean Floor > FB4-GDY Marine Geodynamics
Refereed: Yes
Open Access Journal?: No
DOI etc.: 10.1111/j.1365-246X.2007.03616.x
ISSN: 0956-540X
Projects: Future Ocean
Contribution Number:
ProjectNumber
SFB 574113
Date Deposited: 16 Jan 2009 12:08
Last Modified: 13 Jul 2018 12:21
URI: http://oceanrep.geomar.de/id/eprint/2782

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