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AuthorsGeissler, W. H.*
Matias, L.*
Stich, D.*
Carrilho, F.*
Jokat, W.*
Monna, S.* 
IbenBrahim, A.*
Mancilla, F.*
Gutscher, M.-A.*
Sallarès, V.*
Zitellini, N.*
TitleFocal mechanisms for sub‐crustal earthquakes in the Gulf of Cadiz from a dense OBS deployment
Issue Date30-Sep-2010
Series/Report no./ 37 (2010)
Keywordsoceanic lithospheric mantle
focal mechanisms
stress tensor inversion
Gulf of Cadiz
ocean bottom seismometer
1755 Lisbon earthquake
Subject Classification04. Solid Earth::04.06. Seismology::04.06.03. Earthquake source and dynamics 
04. Solid Earth::04.06. Seismology::04.06.10. Instruments and techniques 
04. Solid Earth::04.07. Tectonophysics::04.07.04. Plate boundaries, motion, and tectonics 
04. Solid Earth::04.07. Tectonophysics::04.07.05. Stress 
AbstractAn 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.
DescriptionAn edited version of this paper was published by AGU. Copyright (2010) American Geophysical Union.
Appears in Collections:Papers Published / Papers in press

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