Tomographic three-dimensional seismic velocity structure of the SW Ibero-Maghrebian region

The present tomographic study focuses on SW Ibero-Maghrebian region. To locate the seismic events and find the local velocity structure of epicentral area, the P and S arrivals at 42 stations located at north of Morocco, south of Portugal and Spain are used. The arrival times data used, in this study, were obtained by the “Instituto de Meteorologia” (IM, Lisbon, Portugal), the National Institute of Geophysics (CNRST, Rabat, Morocco) and the “Instituto Geografico Nacional” (IGN, Madrid, Spain) (between 12/1988 and 30/2008). The preliminary estimate of origin times and hypocentral coordinates are determined by the hypocenter 3.2 program. In this study we use a linearized inversion procedure comprising two steps: 1) finding the minimal 1-D model and simultaneous reloca- tion of hypocenters and 2) determination of local velocity structure assuming a continuous velocity field. The earth structure is represented in three dimensions by velocity at discrete points, and velocity at any intervening point is determined by linear interpolation among the surrounding eight grid points. The resolutions tests results indicate that the calculated images give near true structure for the studied region at 15, 30, 45 and 60 km depth. At 5km depth it gives near true structure in the continental region of Portugal, Spain, and Morocco. This study shows that the total crustal thickness varies from 30 to 35 km and contains low-velocity anomalies. A prominent low velocity anomaly that shows a maximum decrease in P-wave velocity of approximately 6 per cent in the Gibraltar region is observed extending down to a depth of approximately 30 km. This low velocity demarcates a small bloc located between Iberia and Nubia plates. The resulting tomographic image has a prominent high velocity anomaly that shows a maximum increase in P-wave velocity of approximately 6 per cent between 45 to 60 km depth beneath South of Portugal and the Golf of Cadiz. High-velocity anomalies could be associated with the location of deep active faults in the uplift and upper crust of South of Portugal. In the Golf of Cadiz, these anomalies could be associated with the seismogenic zone and probably more at the south with the Iberia-Nubia plate boundary

Tomography and geodynamics structure of the Ibero- Maghrebian region

The present study has two main goals: 1) use the most actual seismological data from recent earthquakes in the extended Alboran region to develop a geodynamic-structural model for the region through the application of seismic local tomography techniques; 2) modelling seismogenic sources using specific applications of analysis. The structural scheme detailed in depth will allows us to define possible structural blocks in region between north of Morocco and Alboran sea. Currently the GPS studies show local movements in northern morocco independently of the general movement of the African plate. The present tomographic study focuses on SW Ibero-Maghrebian region. The P and S arrival times at 52 stations located at north of Morocco (National Institute of Geophysics, CNRST, Rabat), south of Portugal (Instituto de Meteorologia, Lisbon) and Spain (Instituto Geografico National, Madrid) are used for the period between 12/1988 and 30/2008. We use a linearized inversion procedure to find a 3D velocity model for the studied region. The resolution tests indicate that the calculated images give near true structure for the Tanger peninsula, the Alhoceima region and southern Spain at 5km depth. At 15, 30, 45 km depth we observe a near true structure in northern Morocco, and southern Spain. At 60 and 100 km, the southern Spain and SW of Alboran Sea gives a near true structure. The resulting tomographic image shows that the total crustal thickness varies between 25 and 35 km and contains low-velocity anomalies. Is defined clearly a prominent negative P- wave velocity anomaly with a maximum decrease of approximately 6 per cent, at 15 km depth, in the northern Morocco. This low velocity demarcates a small bloc located between Iberia and African plate. This bloc is presented by a prominent high velocity anomaly that shows a maximum increase in P-wave velocity of approximately 6 per cent. The area with high velocity values could represent brittle and competent parts of the crust and lithosphere which sustain seismogenic stress where asperities along the faults could exist and probably more with the Iberia-Africa plate boundary. Strong ground motions from major earthquakes depend strongly upon the 3D seismic velocity structure of the crust. Moreover the 3D velocity model is crucial for a better comprehension of structures behavior and has important practical applications toward understanding earthquake hazard in the Ibero-Maghrebian region. In particular, we hope to contribute, with this model, for seismic risk mitigation in north of Morocco

To the question about foreign students’ social adaptation in relation to human typological aspects

The article touches the questions on UMSA foreign students various adaptation to study and influencing factors: managing the foreign languages, education type (remote and nonremote), human individual peculiarities (dependently on belonging to typologies in part country, gender, interhemispherical asymmetry individual profile, temperament type), psychological atmosphere in the academic group, health condition. The authors emphasize the necessity tocreate optimal conditions for educating maximal individualization that is impossible without typological aspects taking into account. There are some recommendations on such an education individualization creating on the base of own experience in the article

The Al Hoceima Mw 6.4 earthquake of 24 February 2004 and its aftershocks sequence

The Al Hoceima Mw 6.4 earthquake of 24 February 2004 that occurred in the eastern Rif region of Morocco already hit by a large event in May 1994 (Mw 5.9) has been followed by numerous aftershocks in the months following the event. The aftershock sequence has been monitored by a temporary network of 17 autonomous seismic stations during 15 days (28 March-10 April) in addition to 5 permanent stations of the Moroccan seismic network (CNRST, SPG, Rabat). This network allowed locating accurately about 650 aftershocks that are aligned in two directions, about N10-20E and N110-120E, in rough agreement with the two nodal planes of the focal mechanism (Harvard). The aftershock alignments are long enough, about 20 km or more, to correspond both to the main rupture plane. To further constrain the source of the earthquake main shock and aftershocks (mb > 3.5) have been relocated thanks to regional seismic data from Morocco and Spain. While the main shock is located at the intersection of the aftershock clouds, most of the aftershocks are aligned along the N10-20E direction. This direction together with normal sinistral slip implied by the focal mechanism is similar with the direction and mechanisms of active faults in the region, particularly the N10E Trougout oblique normal fault. Indeed, the Al Hoceima region is dominated by an approximate ENE-SSW direction of extension, with oblique normal faults. Three major 10-30 km-long faults, oriented NNE-SSW to NW-SE are particularly clear in the morphology, the Ajdir and Trougout faults, west and east of the Al Hoceima basin, respectively, and the NS Rouadi fault 20 km to the west. These faults show clear evidence of recent vertical displacements during the late Quaternary such as uplifted alluvial terraces along Oued Rihs, offset fan surfaces by the Rouadi fault and also uplifted and tilted abandoned marine terraces on both sides of the Al Hoceima bay. However, the N20E direction is in contrast with seismic sources identified from geodetic inversions, which favour but not exclusively the N110-120E rupture directions, suggesting that the 1994 and 2004 events occurred on conjugate faults. In any event, the recent seismicity is thus concentrated on sinistral N10-20E or N110-120E dextral strike-slip faults, which surface expressions remain hidden below the 3-5 km-thick Rif nappes, as shown by the tomographic images build from the aftershock sequence and the concentration of the seismicity below 3 km. These observations may suggest that strain decoupling between the thrusted cover and the underlying bedrock and highlights the difficulty to determine the source properties of moderate events with blind faults even in the case of good quality recorded data