Intraplate seismicity and releated mantle hydration at the Nicaraguan trench outer rise.

Lefeldt, Marten, Grevemeyer, Ingo , Goßler, J. and Bialas, Jörg (2009) Intraplate seismicity and releated mantle hydration at the Nicaraguan trench outer rise. Open Access Geophysical Journal International, 178 (2). pp. 742-752. DOI 10.1111/j.1365-246X.2009.04167.x.

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We examine micro-earthquake records from a dense temporary array of ocean bottom seismometers (OBS) and hydrophones that has been installed from September to November 2005 at the trench outer rise offshore Nicaragua. Approximately 1.5 locatable earthquakes per day within the array of 110 × 120 km show the high seismic activity in this region. Seismicity is restricted to the upper ∼15 km of the mantle and hence where temperatures reach 350–400 °C, which is smaller than values observed for large mantle intraplate events (650 °C). Determination of moment tensor solutions suggest a change of the stress region from tensional in the upper layers of the oceanic plate to compressional beneath. The neutral plane between both regimes is located at ∼6–9 km beneath Moho and thus very shallow. Fluids, which are thought to travel through the tensional fault system into the upper mantle, may not be able to penetrate any deeper.

The earthquake catalogue, which seems to be complete for magnitudes above Mw = 1.6–1.8, suggests a strong change of the lithospheric rheology when approaching the trench. And b-factors, that is the ratio between small and large earthquakes increase significantly in the closest 20 km to the trench axis, implying that the crust and upper mantle is massively weakened and hence ruptures more frequently but under less release of stress. We explain this with a partly serpentinized upper mantle.

Document Type: Article
Keywords: Seismicity and tectonics; Seismic tomography; Subduction zone processes; Intra-plate processes; Lithospheric flexure; Rheology: mantle
Research affiliation: OceanRep > The Future Ocean - Cluster of Excellence
OceanRep > SFB 574 > A1
OceanRep > SFB 574 > A5
OceanRep > SFB 574
OceanRep > GEOMAR > Applied R&D > Energy and CO₂ Sequestration Projects
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.2009.04167.x
ISSN: 0956-540X
Projects: Future Ocean, SFB574
Contribution Number:
SFB 574114
Date Deposited: 17 Jul 2009 12:03
Last Modified: 23 Sep 2019 18:42

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