Risques géologiques et activité sismique dans la région d'Al Hoceima (Maroc) : Approche de la quantification des facteurs responsables du déclenchement des instabilités de terrain Geological hazards and seismic activity within the area of Al Hoceima (Morocco): Approach of quantifying factors responsible for the triggering of the ground instabilities

International audienceCe travail présente une étude des risques géologiques liés à l'activité sismique de la région d'Al Hoceima, Maroc. Cette étude a nécessité l'identification des modifications récentes enregistrées dans les formations géologiques, conséquentes de la crise sismique qu'a connue la région en 1994. L'analyse de ces phénomènes a permis de mettre en évidence les liens entre la sismicité et les instabilités de terrain. Un essai de quantification des facteurs responsables du déclenchement de ces instabilités a conduit à suggérer que la pente ainsi que la sismicité constituent les facteurs capitaux dans l'occurrence des mouvements de terrain. This work presents a study of the geological hazards caused by seismic activity within Al Hoceima region, Morocco. This study required the identification of recent geological modifications caused by the seismic crisis of 1994. The analysis undertaken revealed the existence of a good correlation between seismicity and the geological field data. Furthermore, an attempt of quantifying the triggering factors of land instabilities caused us to suggest that the slope and seismicity are the main factors in the studied area

On the moroccan tsunami catalogue

A primary tool for regional tsunami hazard assessment is a reliable historical and instrumental catalogue of events. Morocco by its geographical situation, with two marine sides, stretching along the Atlantic coast to the west and along the Mediterranean coast to the north, is the country of Western Africa most exposed to the risk of tsunamis. Previous information on tsunami events affecting Morocco are included in the Iberian and/or the Mediterranean lists of tsunami events, as it is the case of the European GITEC Tsunami Catalogue, but there is a need to organize this information in a dataset and to assess the likelihood of claimed historical tsunamis in Morocco. Due to the fact that Moroccan sources are scarce, this compilation rely on historical documentation from neighbouring countries (Portugal and Spain) and so the compatibility between the new tsunami catalogue presented here and those that correspond to the same source areas is also discussed

Body waves tomography from OBS-recorded earthquakes in the Gulf of Cadiz

The gulf of Cadiz is a region considered as a complex seismic area, where strong earthquakes occur and where the plate boundary between the African and Eurasian plates is not exactly known. In this paper, we use high resolution seismic data recorded by a network of OBS stations deployed for one year in the Gulf of Cadiz as well as eight permanent Portugal land seismic stations. The OBS network was deployed within an experiment of the NEAREST project. Nearly 600 seismic events are extracted from the recorded data set and their analysis revealed that most of them occur at 20 to 80 km depths, with clusters of seismicity that occur mainly at the Gorringe Bank, within the SW segment of the Horseshoe fault and the Marques de Pombal Plateau and the S. Vicente Fault. A new NW-SE trend of seismicity has been revealed with depths that extend from 35 to 80 km. This seismicity trend is close and nearly parallel to the SWIM (South West Iberian Margin) faults lineament. We further present in this paper, the first regional-scale high resolution P- and S-velocity distributions across the Gulf of Cadiz region. These velocity models are obtained using three-dimensional seismic tomography to invert the OBS data-set. The results show that the patterns of anomalies in the Gulf of Cadiz are in general, oriented in NE-SW and NW-SE directions. They also show the presence of a low velocity zone (LVZ) to the SE of our study area. At shallow depth, this LVZ is interpreted as due to a large accumulation of sediments within the accretionary wedge, while at a greater crustal depth, it may reflect a continental crustal composition rather than an oceanic crust. Moreover, seismic velocity profiles show that under this region of the Cadiz Gulf, the Moho averages a 30-km depth. The Gorringe Bank and the Marquise de Pombal plateau are found to be deeply rooted and represent expressions of mantle uplifting. The association of these deep anomalies with active seismicity that occurs at their levels, indicates that the uplifting of these ridges is still an ongoing process. Furthermore, a NW-SE zone of high velocity is found to the SW of our study area. This zone occurs along and parallel to the SWIM faults zone (SFZ) and appears to support the hypothesis that the SFZ represents the boundary between the Nubia and the Eurasia plates at the Gulf of Cadiz level as previously suggested [1]

Probabilistic TSUnami Hazard MAPS for the NEAM Region The TSUMAPS NEAM Project

As global awareness of tsunami hazard and risk grows, the North-East Atlantic, the Mediterranean, and connected Seas (NEAM) region still lacks a thorough probabilistic tsunami hazard assessment. The TSUMAPS-NEAM project aims to fill this gap in the NEAM region by 1) producing the first region-wide long-term homogenous Probabilistic Tsunami Hazard Assessment (PTHA) from earthquake sources, and by 2) triggering a common tsunami risk management strategy. The specific objectives of the project are tackled by the following four consecutive actions: 1) Conduct a state-of-the-art, standardized, and updatable PTHA with full uncertainty treatment; 2) Review the entire process with international experts; 3) Produce the PTHA database, with documentation of the entire hazard assessment process; and 4) Publicize the results through an awareness raising and education phase, and a capacity building phase. This presentation will illustrate the project layout, summarize its current status of advancement including the firs preliminary release of the assessment, and outline its connections with similar initiatives in the international context