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Seismicity and Seismic Hazard in Morocco 1901-2010
Abstract and Figures
The seismic activity in Morocco is not as important as in other world areas such as Japan, California, Greece, Turkey, etc. Nevertheless, background seismicity in Morocco is not negligible and has produced a few historical and instrumental earthquakes with local magnitudes above 6. The Agadir earthquake 1960, for instance, destroyed this city with several villages and caused 12,000 deaths. Later, other remarkable earthquakes occurred: in Al Hoceima in 2004 in the North of Morocco, caused 629 deaths. The mechanisms governing the spatial distribution of these earthquakes and their frequency remain poorly understood. Most probably the seismicity of northern Morocco and Atlas mountain reflects primarily deformation induced by the ongoing collision between Africa and Europe (the convergence rate being of the order of 5mm/yr at most). In this work, we presented an earthquake catalogue covering the period 1901- 2010, comprising about 25,000 events for the region lying between 0°W-20°w and 21°N-38°N. It results from raw data of Morocco, Spain, Portugal and Algeria seismic networks, enabling an input consisting of origin time H, geographical coordinates (longitude λ and latitude φ) and at least one of the following parameters: surface wave magnitude Ms, body wave magnitude Mb, epicentral intensities Io. A first application of this catalogue allows the drawing up of an updated Seismicity and maximum observed intensities map of Morocco. This map is obtained by using about 1,700 values of MSK intensity observed in 670 localities. This document may be useful in mapping the seismic hazard in Morocco. There is a similarity between this map and the seismic hazard map from the SESAME project.
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... However, we suggest that even more approach work is needed regarding the seismic risk for the Al Hoceima region and its surroundings, located in zone 5 of the seismic zoning map, which is considered the highest level of risk in seismic zoning in acceleration for probabilities of 10% in 50 years in Morocco 2011 (Acceleration %g) [20]. A zone where the risk is the highest. ...
... Sustainable urban development prioritizes economic growth while minimizing environmental impacts [3]. Urban planning guided by seismic hazard assessment ensures infrastructure resilience [20]. Sustainable development underscores the protection of natural resources and ecosystems. ...
... Sustainable development underscores the protection of natural resources and ecosystems. Integrating disaster resilience into urban planning enhances community readiness and recovery [18,20]. Considering seismic risk enables cities to promote longterm sustainability. ...
This article presents an analysis of the earthquake in Al Hoceima City through the combination of land use and seismic hazards. This study is based on a probabilistic analysis of the seismic hazard performed following an attenuation to predict the maximum ground acceleration at each square kilometer. The land use of the area was estimated using GIS tools with the Gaussian maximum likelihood integrated supervised analysis method on remote sensing data processed from Landsat images 8, and the distribution of the values of PGA (Peak Ground Acceleration) in Al Hoceima. The numerical values ranging from this latter are around between 0.268g and 0.275g within the city, The maximum values indicate that the acceleration towards the north is approaching the seismic source of the Alboran Sea, which is regarded as a principal source generating several seismic events. The main global objective of this paper is to assess seismic hazard risk by combining seismic hazards (PGA) and land use maps, is to identify the most susceptible areas, especially those that have had expanding populations.
... In Morocco, the offshore seismicity is mostly found in the Atlantic along the Azores-Gibraltar shear region and in the Mediterranean basin in the Alboran Sea (Cherkaoui and El Hassani 2012). While the Atlas and Rif structural domains represent the two major seismic provinces where inland seismicity may be categorized. ...
... Reported historical and instrumental earthquakes felt in and around Morocco(Cherkaoui and El Hassani 2012; USGS). The star denotes historical events ...
The North Africa region extends from the Red Sea and Gulf of Aqaba in the East to the Atlantic Ocean in the West, including five countries: Egypt, Libya, Tunisia, Algeria, and Morocco. The earthquake record demonstrates that this region suffers from earthquakes with considerable level of hazard due to the complex convergent plate boundary along the African continental plate near to the comparative movements of tectonic microplates from the Mediterranean Sea in the North and the Red Sea in the East. Additionally, the inland tectonic activities induce local seismic sources inside the African plate in its North African segment. Furthermore, local site effects, vulnerability of the built environment, and the dramatic increase of concentration of population within hazardous areas, alongside the nature of the sociocultural in North Africa in respect to natural disasters, all these factors can significantly increase the damage posed by earthquakes in this region. Several researchers studied the seismicity of North Africa and gained valuable results; however, their studies commonly focused on a particular region or subject. Therefore, the authors of this article are hopeful to introduce a piece of simple and informative material to the reader about the region of North Africa by compiling earthquake data from several sources and by a systematic literature review. In this chapter, the reader can find information about location, seismotectonic setting, seismic sources, and historical and instrumental earthquakes with a brief description of the devastating events, earthquake recording history, and seismic networks of each country in North Africa.
... Along the Atlantic coast of Morocco, the seismicity rate is significantly elevated because of the subduction process associated with the convergence of the African and Eurasian Plates (Cherkaoui and El Hassani, 2012). In contrast to these subductionzone earthquakes, shallow intraplate earthquakes on the Morocco arc, located far from the trench, are rare, especially for events with a moment magnitude (M w ) above 5.0 ( Figure 1). ...
... However, according to the USGS catalog, earthquakes in this area exhibit a wide range of depths. Most earthquakes are confined to depths within 30 km, but some extend beyond 40 km (Cherkaoui and El Hassani, 2012). Gosset (2004) indicated a Moho depth of approximately 30-35 km in this region. ...
The Mw 6.8 Adassil earthquake that occurred in the High Atlas on September 8, 2023, was a catastrophic event that provided a rare opportunity to study the mechanics of deep crustal seismicity. This research aimed to decipher the rupture characteristics of the Adassil earthquake by analyzing teleseismic waveform data in conjunction with interferometric synthetic aperture radar (InSAR) observations from both ascending and descending orbits. Our analysis revealed a reverse fault mechanism with a centroid depth of approximately 28 km, exceeding the typical range for crustal earthquakes. This result suggests the presence of cooler temperatures in the lower crust, which facilitates the accumulation of tectonic stress. The earthquake exhibited a steep reverse mechanism, dipping at 70°, accompanied by minor strike-slip motion. Within the geotectonic framework of the High Atlas, known for its volcanic legacy and resulting thermal irregularities, we investigated the potential contributions of these factors to the initiation of the Adassil earthquake. Deep seismicity within the lower crust, away from plate boundaries, calls for extensive research to elucidate its implications for regional seismic hazard assessment. Our findings highlight the critical importance of studying and preparing for significant seismic events in similar geological settings, which would provide valuable insights into regional seismic hazard assessments and geodynamic paradigms.
... Along the Atlantic coast of Morocco, the seismicity rate is significantly elevated because of the subduction process associated with the convergence of the African and Eurasian Plates (Cherkaoui and El Hassani, 2012). In contrast to these subductionzone earthquakes, shallow intraplate earthquakes on the Morocco arc, located far from the trench, are rare, especially for events with a moment magnitude (M w ) above 5.0 ( Figure 1). ...
... However, according to the USGS catalog, earthquakes in this area exhibit a wide range of depths. Most earthquakes are confined to depths within 30 km, but some extend beyond 40 km (Cherkaoui and El Hassani, 2012). Gosset (2004) indicated a Moho depth of approximately 30-35 km in this region. ...
The Mw 6.8 Adassil earthquake that occurred in the High Atlas on September 8, 2023, was a catastrophic event that provided a rare opportunity to study the mechanics of deep crustal seismicity. This research aimed to decipher the rupture characteristics of the Adassil earthquake by analyzing teleseismic waveform data in conjunction with interferometric synthetic aperture radar (InSAR) observations from both ascending and descending orbits. Our analysis revealed a reverse fault mechanism with a centroid depth of approximately 28 km, exceeding the typical range for crustal earthquakes. This result suggests the presence of cooler temperatures in the lower crust, which facilitates the accumulation of tectonic stress. The earthquake exhibited a steep reverse mechanism, dipping at 70°, accompanied by minor strike-slip motion. Within the geotectonic framework of the High Atlas, known for its volcanic legacy and resulting thermal irregularities, we investigated the potential contributions of these factors to the initiation of the Adassil earthquake. Deep seismicity within the lower crust, away from plate boundaries, calls for extensive research to elucidate its implications for regional seismic hazard assessment. Our findings highlight the critical importance of studying and preparing for significant seismic events in similar geological settings, which would provide valuable insights into regional seismic hazard assessments and geodynamic paradigms
... The regional tectonics underlying Morocco's seismicity is framed by the boundary of the Eurasian and African plates and is governed by the convergence of both tectonic plates. This boundary is broadly defined between the Azores and west of the Gibraltar Strait, where large earthquakes have occurred, Mw > 6, with epicenters aligned along the contact of the two plates, such as the Lisbon earthquake of 1755 (Mw ≈ 8.5), and other more recent earthquakes in 1915 (Mw = 6.2), 1941 (Ms = 8.4), 1964 (Ms = 6.4), 1969 (Mw = 7.8), and 2007 (Mw = 6.1) [3]. However, to the east of the Strait of Gibraltar, seismicity is more diffuse and of lower magnitude, characteristic of collision zones between continental plates with a wide deformation band. ...
... However, sparse and diffuse seismic activity are still observed in the Atlas chain region over the three distinct Atlas blocks (Middle, High and Anti-Atlas) ( Figure 2). To the south, in the Sahara region, no seismic activity is generally observed and the seismicity decreases along the eastern High Atlas [3]. According to the worldwide teleseismic catalogues, this Atlas seismicity corresponds mostly to Mw < 5 events, and only two Mw > 5.5 events were recorded over the last 40 years on the eastern Anti-Atlas zone. ...
This research investigates the post-earthquake performances of structures in four rural villages in the Moroccan Atlas, emphasizing common construction system characteristics and design flaws that render buildings susceptible to seismic events. Village selection was based on a prior multispectral satellite-image study, proving effective for planning high-impact, post-earthquake field campaigns. The significance of this research resides in on-site data collection, facilitating the physical assessment of earthquake-induced damage and identification of inherent vulnerabilities in construction systems. The constructions in the study area exhibited structural design deficiencies, inadequate construction techniques, and urban modifiers, leading to damage extensively documented in the literature, as well as less-documented unique damage. Predominant seismic-design shortcomings in the study area included subpar material quality, insufficient earthquake-resistant design, and unskilled labor. In situ data were complemented by a global geospatial approach using differential synthetic aperture radar interferometry with Copernicus Sentinel 1 data. Once calibrated the proposed methodology with field data, the analysis of remote sensing processing results, allow assessing the damages in other earthquake-affected areas, including those not visited in the field but also impacted by the seismic event.
... Seismologists study historical earthquakes to better understand the frequency, magnitude, and location of seismic activity in the region. This information can be used to improve building codes and construction practices in areas prone to earthquakes [16]. ...
... The Impact of Bracing Type on Seismic Response of the Structure on Soft SoilFigure 1. Seismicity map of Morocco[16] ...
Building in civil engineering usually involves a lot of expertise and knowledge, especially when working with soft soil, which is infamous for being cohesive due to its low shear strength and consequently unstable under its geotechnical conditions. This is why extra care must be taken while researching how a building constructed on soft ground will behave during an earthquake. In these situations, the bracing system, which is well-known for its beneficial effects for resistance against seismic loads, must be thoroughly investigated and its selection must be reasonable and wise. In this perspective, we studied several models by changing the two most used types of bracing (columns and shear walls) while modifying the height of the buildings (3-6-9 and 12-story) using Etabs software. We then optimized the buildings in order to choose the optimal option for each case. Global displacements, inter-story displacements and structural mass were checked and compared. Following model validation and outcome analysis, we came to the conclusion that shear wall bracing would be advantageous for buildings taller than eight stories; otherwise, column bracing would be the better option. The outcomes of this study can be used to strengthen regulations, and as a guide for designers.
... More recently, on Monday, January 26, 2016, an earthquake measuring 6.3 in magnitude occurred roughly 50 kilometers off the coast of Al Hoceima, causing significant material damage. Particularly, the central Rif region has experienced a number of recent seismic occurrences, highlighting the prevalence of earthquakes in this region [46][47][48]. Numerous studies have been conducted on this matter, delving into seismology, seismic risk assessment, and vulnerability to earthquakes [49,50]. ...
Due to its geographical location, Morocco is situated on the northwest edge of the African plate, which is continuously moving towards and colliding with the Eurasian plate. This movement makes Morocco a country with moderate seismic activity, occasionally resulting in destructive earthquakes reaching a magnitude close to 6.5 (2004 Al Hoceima earthquake). The application of seismic building codes to new constructions has been mandatory in Morocco since 2002 for nearly all buildings located in areas other than Zone 0. However, there is no obligation for preventive strengthening concerning existing buildings. Yet, the seismic vulnerability of these structures can be quite high, and in the most exposed areas, significant loss of human life could be caused by high-intensity earthquakes. Seismic prevention must naturally be complemented by methods to determine the damage to a structure and, consequently, its vulnerability. Therefore, the objective of this contribution is to study the seismic performance and identify the levels of damage in reinforced concrete structures in the city of Al Hoceima, taking into account the nonlinear behavior of the structures and considering soil-structure interaction.
... The 1755 Lisbon earthquake, which affected the Atlantic coastlines of Europe and Africa, caused widespread destruction in most Moroccan coastal cities, particularly Agadir (Silva et al., 2021). The 1960 Agadir earthquake (Mw = 5.9) resulted in the loss of more than 12,000 lives and the destruction of over 75% of the city (Cherkaoui and Hassani, 2012). More recently, the 2023 Al Haouz earthquake, representing the most powerful seismic event (Mw 6.8) to hit Morocco, led to 2901 fatalities and the destruction of most buildings within a 60 km radius of the epicenter. ...
Ghabt Admin, located in western Morocco, is prone to seismic activity and site effects due to its position within an alluvial basin situated between two faulted mountain belts. The region has experienced several devastating earthquakes, including the 1960 Agadir earthquake that resulted in the loss of 12,000 lives and the destruction of over 75% of the city. Moreover, the area has recently undergone rapid urbanization, necessitating the implementation of seismic studies to make informed decisions regarding land use. This study aims to conduct the first seismic microzonation and site characterization studies by using HVSR, 1D-MASW, and geotechnical investigations. The datasets consist of 80 microtremors, 15 1D-MASW profiles, detailed geological observations, boreholes, and soil/rock identification tests. Due to challenges related to anthropogenic sources and soil heterogeneities, only 31 H/V measurements met the SESAME criteria. The HVSR results indicate the following: (i) the predominant peak frequency (f0) ranges from 1.4 to 15.7 Hz, with lower values (1.4–3 Hz) observed in the Oued Issen alluvial fans and the sand dune area, while moderate to high values (4–15.7 Hz) are found in the lacustrine limestone and Tagragra’s dome. (ii) The amplitude peak frequency (A0) ranges from 2 to 7.7, with higher values observed in the southwestern zone and certain parts of the glacis-fans zone, particularly in the Oued Issen zone. (iii) The seismic vulnerability index (Kg) ranges from 0.28 to 39.5. The Oued Issen area, which is composed of recent unconsolidated deposits and affected by the Oued Issen fault, exhibits high Kg values. Analysis of HVSR curve typology reveals complex geology. The VS30 map shows VS values ranging from 179 m/s to 830 m/s, classifying the study area into soil classes A, B, and C according to Eurocode 8. Furthermore, the 1D-MASW results are compatible with the HVSR results and the distribution of the geological units.
... One of the most significant earthquakes in Morocco's history occurred in 1960, with a magnitude of 5.7 on the Richter scale. The earthquake caused significant damage to buildings and infrastructure in the city of Agadir, resulting in more than 15,000 deaths [12]. Since then, the Moroccan government has implemented several measures to improve earthquake preparedness, such as stricter building codes and improved emergency response plans [13]. ...
The design of earthquake-resistant buildings has always been a critical aspect of structural engineering, especially in regions prone to seismic activity. The use of reinforced concrete (RC) structures as a seismic-resistant system has been widely adopted due to their strength, stiffness, and ductility. One of the critical components in RC buildings is the bracing system, which plays a vital role in resisting the lateral loads generated during an earthquake. In this article, we will discuss the importance of using different types of bracing in RC buildings, their response to seismic loads, and the limitations imposed by building codes and standards. We will also present a study, in which we modeled various RC building structures with different types of bracing using finite element software. Our objective was to evaluate the best bracing option for a given structure based on the seismic zone and the number of stories. We analyzed and compared the global displacements of the stories and the additional mass of materials required to stabilize the structure for buildings with 3, 6, 9, and 12 stories. After a detailed analysis, we concluded that RC buildings using a shear wall bracing system are more suitable for structures taller than 21 meters. On the other hand, buildings using a moment-resisting frame bracing system are more effective for structures with no more than six stories. The detailed results presented in this article can facilitate the work of architects and designers who must perform complex calculations to arrive at the right bracing system, saving them valuable time. Moreover, our study may influence building codes and standards to evolve and include more tailored guidelines for bracing types based on the seismic zone and building height.
The missing link in the plate boundary between Eurasia and Africa in the central Atlantic is presented and discussed. A set of almost linear and sub parallel dextral strike–slip faults, the SWIM1 Faults, that form a narrow band of deformation over a length of 600 km coincident with a small circle centred on the pole of rotation of Africa with respect to Eurasia, was mapped using a new swath bathymetry compilation available in the area offshore SW Portugal. These faults connect the Gloria Fault to the Rif–Tell Fault Zone, two segments of the plate boundary between Africa and Eurasia. The SWIM faults cut across the Gulf of Cadiz, in the Atlantic Ocean, where the 1755 Great Lisbon earthquake, M ~ 8.5–8.7, and tsunami were generated, providing a new insight on its source location.
L'objectif que nous avons essayé d'atteindre dans le cadre de cette thèse est l 'évaluation de l'aléa sismique au Maroc par l'application de différentes étapes. La première partie de ce travail consiste en l'élaboration d'un fichier informatisé (chapitre 1) de la sismicité de la région comprise entre 21°N-38°N et O°W-20°W à partir du début de ce siècle. Un peu plus de quatre mille six cent événements ont été recensés faisant l objet d'une révision complète, 34% des événements ont été relocalisés. Nous avons effectué un nouveau dépouillement des archivés au D.P.G., ce qui nous a permis de traçer une cartes macrosismiques des séismes largement ressentis. Nous avons essayé d'utiliser ce fichier pour calculer l'aléa sismique à l'aide du programme de calcul EQRISK développé par McGuire (première partie: chapitre 2). Les résultats obtenus sont donnés sous forme de cartes des valeurs d'intensités susceptibles d'être ressenties pour les deux valeurs de probabilité annuelle: 0.01 et 0.005. Dans le premier chapitre de la deuxième partie de cette tIhèse, nous avons procédé à une révision complète des données macrosismiques et instrumentales du séisme d'Agadir, ce qui nous a permis de dresser une nouvelle carte macrosismique et de mieux préciser le mécanisme au foyer. Une étude de l'effet de site a été effectuée pour mettre en évidence l'influence des couches sédimentaires, sous la ville d'Agadir, sur les constructions pendant le tremblement de terre. Au dernier chapitre, de la deuxième partie, une étude sismotectonique détaillée a été réalisée dans la province d'Al Hoceima dans le cadre de l'Action Inteqrée 359/80. Cette région est l'une des plus sismiques au Maroc, de nombreuses secousses y sont ressenties chaque année . Une compagne de microsismicité a été effectuée à proximité de l'accident de Nekor. Un réseau, composé de 16 stations sismiques portables et de 9 stations numériques à 3 composantes télécommandées, a été installé pour une durée de cinq semaines . L'objectif de cette expérience était de localiser précisément la sismicité, de calculer des mécanismes à la source, d'entreprendre une étude du mouvement du sol en réponse à une sollicitation sismique ..
L’activité sismique dans le Nord du Maroc est due en grande partie à une intense activité tectonique Plio-Quaternaire et Actuel engendrée par le rapprochement des deux plaques lithosphériques Afrique-Eurasie dont la vitesse de rapprochement est de l'ordre de 0.5 cm/an au niveau du détroit de Gibraltar. La direction générale de convergence est NNW-SSE à N-S.
Dans ce travail, nous avons tenté d’évaluer les intensités qu’on aurait observées dans le Nord du Maroc, engendrées par trois importants séismes historiques en utilisant des lois d’atténuation établies pour le Maroc, et de tracer une esquisse des intensités maximales observées. Les résultats obtenus montrent l’importance de la sismicité historique pour l’évaluation du risque sismique.
The Lisbon Earthquake of November 1, 1755, one of the most catastrophic events that has ever occurred in Portugal, Spain, or Morocco, caused severe damage and many casualties. The tsunami generated by this earthquake is well documented in historical accounts, it was reported throughout the North Atlantic Ocean, as it reached not only Portugal, Spain, and Morocco, but also the Madeira and Azores Archipelagos, England, Ireland, and the Caribbean. In spite of the importance of this event, the source of the tsunami remains unknown. In this paper, the authors reevaluate some of the historical tsunami travel times obtained by previous authors. Based on these times, wave ray analysis is used to determine the location of the tsunami source area. These results, combined with turbidites obtained by previous authors at the Tagus and Horseshoe Abyssal Plains, lead to the conclusion that the source of the 1755 Lisbon Tsunami could be located in the area of the Gorringe Bank. Then, a hydrodynamic simulation is carried out with this area presupposed as the source. The numerical model results provide good agreement when compared with both historical and sedimental records. However, in the past, the Gorringe Bank has been dismissed as the source of this tsunami for several reasons. Therefore, these issues are discussed and discredited. As a consequence of all these facts, it can be concluded that the origin of the 1755 Lisbon Earthquake and Tsunami could be located in the area of the Gorringe Bank.
We study the Tell and Rif neotectonic structures and the geodynamics of the Africa-Eurasia plate boundary in the western Mediterranean. Pliocene and Quaternary deformations west of the Gibraltar strait show NE-SW fault-related folds related to a N-S to NW-SE compressional movements. Neogene and Quaternary basins which are elongated in a E-W direction and reflect a N-S shortening direction, are superimposed on the inherited Alpine geological structures. Based on geological and geophysical data (seismicity and magnetic anomalies) in the Alboran sea, the E-W dextral transcurrent Yussuf fault appears to control the distribution of the NE-SW trending Quaternary folds associated with thrust faults, blind or sometimes emergent, similar to that of El Asnam, and extends inland across the Cheliff basin. Recent folding in the Rif is parallel to the main frontal thrust but is also associated to the main left-lateral reverse faults of Jebha and N'kor. The recent tectonics of the Tell and Rif continental domain and surrounding areas (Alboran sea and Atlantic) are interpreted as a transpressive system which results from right lateral movements along the Azores-Gibraltar transform zone and the convergence of Africa toward Iberia (Eurasia). The active tectonics in agreement with the main seismicity support the existing deforming zone (called GALTEL) of 50 km to 100 km wide, extending from Gorringe, across the southern Alboran sea to the Tell Atlas. A kinematic model explains the interaction between dextral transcurrent faults and left lateral faults with block rotations, no lateral extension (pinned model) and lateral displacement in the Rif mountains. Shortening and lateral movement rates during the Quaternary are estimated to be 2.0-2.5 mm/year, and block rotation rate of 2.5-3.9 °/Ma, then the plate boundary seems to correspond to a transpression zone with active thrusts controlled by dextral transcurrent faults, the deformation being widely distributed due to preexisting Alpine structures.
