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Authors: Geissler, W. H.*
Matias, L.*
Stich, D.*
Carrilho, F.*
Jokat, W.*
Monna, S.*
IbenBrahim, A.*
Mancilla, F.*
Gutscher, M.-A.*
Sallarès, V.*
Zitellini, N.*
Title: Focal mechanisms for sub‐crustal earthquakes in the Gulf of Cadiz from a dense OBS deployment
Title of journal: Geophysical Research Letters
Series/Report no.: / 37 (2010)
Publisher: American Geophysical Union
Issue Date: 30-Sep-2010
DOI: 10.1029/2010GL044289
Keywords: oceanic lithospheric mantle
focal mechanisms
stress tensor inversion
Gulf of Cadiz
ocean bottom seismometer
1755 Lisbon earthquake
Abstract: An eleven‐month deployment of 25 ocean bottom seismometers provides an unprecedented opportunity to study low‐magnitude local earthquakes in the complex transpressive plate boundary setting of the Gulf of Cadiz, known for the 1755 Lisbon earthquake and tsunami. 36 relocated earthquakes (ML 2.2 to 4.8) concentrate at 40– 60 km depth, near the base of the seismogenic layer in ∼140 Ma old oceanic mantle lithosphere, and roughly align along two perpendicular, NNE‐SSW and WNWESE striking structures. First motion focal mechanisms indicate compressive stress for the cluster close to the northern Horseshoe fault termination which trends perpendicular to plate convergence. Focal mechanisms for the second cluster near the southern termination of the Horseshoe fault indicate a strike‐slip regime, providing evidence for present‐day activity of a dextral shear zone proposed to represent the Eurasia‐Africa plate contact. We hypothesize that regional tectonics is characterized by slip partitioning.
Description: An edited version of this paper was published by AGU. Copyright (2010) American Geophysical Union.
Appears in Collections:04.07.04. Plate boundaries, motion, and tectonics
04.07.05. Stress
04.06.10. Instruments and techniques
04.06.03. Earthquake source and dynamics
Papers Published / Papers in press

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