Grevemeyer, Ingo

Matias, L.

English

OceanRep

Geophysical Research AbstractsVol. 15, EGU2013-5799, 2013EGU General Assembly 2013© Author(s) 2013. CC Attribution 3.0 License.Seismotectonics of the Gulf of Cadiz and Horseshoe Abyssal Plain – activefaulting in continental and oceanic mantleIngo Grevemeyer (1) and Luis Matias (2)(1) GEOMAR | Helmholtz Centre of Ocean Research, Marine Geodynamics, Kiel, Germany (igrevemeyer@geomar.de), (2)Centro de Geofisica, Universidade de Lisboa, Lisboa, PortugalIn the area to the west of the Gibraltar Arc the plate boundary between Africa and Iberia is poorly defined. Thedeformation in the area is forced by the slow NW-SE convergence of 4 mm/yr between the oceanic domains ofIberia/Eurasia and Africa and is accommodated over a 200 km broad tectonically-active deformation zone. Theregion, however, is also characterized by large earthquakes and tsunamis, such as the 1969 Mw=7.9 HorseshoeAbyssal Plain earthquake and the November 1, 1755 Great Lisbon earthquake with an estimated magnitude ofMw∼8.5. The exact location of the source of the 1755 Lisbon earthquake is still unknown. Recent work, however,may suggest that the event occurred in the vicinity of the Horseshoe fault, an oblique thrust fault. Further, thearea is marked by the presence of compressive structures with a roughly NE-SW orientation and E-W trending,segmented, crustal-scale, strike slip faults that extend from the Gorringe Bank to the Gibraltar arc in the easternGulf of Cadiz, which were called “South West Iberian Margin” or SWIM faults. The fault system may mark adeveloping Eurasia-Africa plate boundary. Two local seismic networks were operated in the area. First, within theframework of TOPOE-EUROPE, a network of 24 ocean bottom seismometers (OBS) monitored the seismicitybetween January and July 2010 in the northern Gulf of Cadiz to the north of 36◦N between 9◦30’W and ∼7◦W. The second network operated between April and October 2012 14OBS in the vicinity of the Horseshoe faultbetween 10◦W to 11◦W, and 35◦50’N to 36◦10’N. Recordings from the both deployments were supplementedby land stations operated in Portugal and the Gibraltar Arc. The networks provided in the order of 100 localeearthquakes occurring with the networks. In the Gulf of Cadiz, the two largest events of Mw∼3.6 where thrustfaulting events occurring in the vicinity of the Portimao Bank. With a depth of 40-50 km these events, amongothers, occurred within the continental mantle. Earthquakes in the Horseshoe occurred at even greater depth, at40-60 km, either in oceanic or unroofed continental mantle. The large source depth observed in the HorseshoeAbyssal plain supports the interpretation that large catastrophic earthquakes, like the Great Lisbon earthquake of1755, may indeed occur in the area.

Seismotectonics of the Gulf of Cadiz and Horseshoe Abyssal Plain - active faulting in continental and oceanic mantle

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