[1] 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 WNW-ESE 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. Citation: Geissler, W. H., et al. (2010), Focal mechanisms for sub-crustal earthquakes in the Gulf of Cadiz from a dense OBS deployment, Geophys.

International audienceA systematic multi-parameter and multi-platform approach to study the slow process of earthquake preparation is fundamental to gain some insights on this complex phenomenon. In particular, an important contribution is the integrated analysis between ground geophysical data and satellite data. In this paper we review some of the more recent results and suggest the next directions of this kind of research. Our intention is not to detect a particular precursor but to understand the physics underlying the various observations and to establish a reliable physical model of the preparation phase before an impending earthquake. In this way, future investigation will search for suitable fore-patterns, which the physical model of multi-layers coupling predicts and characterizes by quasi-synchronism in time and geo-consistency in space. We also present alternative explanations for some anomalies which are not actually related to earthquakes, rather to other natural or anthropic processes

In this study, we present a three‐dimensional P wave upper‐mantle tomography model of the southwest Iberian margin and Alboran Sea based on teleseismic arrival times recorded by Iberian and Moroccan land stations and by a seafloor network deployed for 1 year in the Gulf of Cadiz area during the European Commission Integrated observations from NEAR shore sourcES of Tsunamis: towards an early warning system (EC NEAREST) project. The three‐dimensional model was computed down to 600 km depth. The tomographic images exhibit significant velocity contrasts, as large as 3%, confirming the complex evolution of this plate boundary region. Prominent high‐velocity anomalies are found beneath Betics‐Alboran Sea, off‐shore southwest Portugal, and north Portugal, at sublithospheric depths. The transition zones between high‐ and low‐velocity anomalies in southwest and south Iberia are associated to the contact of oceanic and continental lithosphere. The fast structure below the Alboran Sea‐Granada area depicts an L‐shaped body steeply dipping from the uppermost mantle to the transition zone where it becomes less curved. This anomaly is consistent with the results of previous tomographic investigations and recent geophysical data such as stress distribution, GPS measurements of plate motion, and anisotropy patterns. In the Atlantic domain, under the Horseshoe Abyssal Plain, the main feature is a high‐velocity zone found at uppermost mantle depths. This feature appears laterally separated from the positive anomaly recovered in the Alboran domain by the interposition of low‐velocity zones which characterize the lithosphere beneath the southwest Iberian peninsula margin, suggesting that there is no continuity between the high‐velocity anomalies of the two domains west and east of the Gibraltar Strait.

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The NEutrinoMediterranean Observatory-Submarine Network 1 (NEMO-SN1) seafloor observatory is located in the central Mediterranean Sea, Western Ionian Sea, off Eastern Sicily (Southern Italy) at 2100-m water depth, 25 km from the harbor of the city of Catania. It is a prototype of a cabled deep-sea multiparameter observatory and the first one operating with real-time data transmission in Europe since 2005. NEMO-SN1 is also the first-established node of the European Multidisciplinary Seafloor Observatory (EMSO), one of the incoming European large-scale research infrastructures included in the Roadmap of the European Strategy Forum on Research Infrastructures (ESFRI) since 2006. EMSO will specifically address long-term monitoring of environmental processes related to marine ecosystems, climate change, and geohazards. NEMO-SN1 has been deployed and developed over the last decade thanks to Italian funding and to the European Commission (EC) project European Seas Observatory NETwork-Network of Excellence (ESONET-NoE, 2007-2011) that funded the Listening to the Deep Ocean-Demonstration Mission (LIDO-DM) and a technological interoperability test (http://www.esonet-emso.org). NEMO-SN1 is performing geophysical and environmental long-term monitoring by acquiring seismological, geomagnetic, gravimetric, accelerometric, physico-oceanographic, hydroacoustic, and bioacoustic measurements. Scientific objectives include studying seismic signals, tsunami generation and warnings, its hydroacoustic precursors, and ambient noise characterization in terms of marine mammal sounds, environmental and anthropogenic sources. NEMO-SN1 is also an important test site for the construction of the Kilometre-Cube Underwater Neutrino Telescope (KM3NeT), another large-scale research infrastructure included in the ESFRI Roadmap based on a large volume neutrino telescope. The description of the observatory and its most recent implementations is presented. On June 9, 2012, NEMO-SN1 was successfully deployed and is working in real time