H. M. Hussein

Neo-deterministic seismic hazard assessment in North Africa

North Africa is one of the most earthquake-prone areas of the Mediterranean. Many devastating earthquakes, some of them tsunami-triggering, inflicted heavy loss of life and considerable economic damage to the region. In order to mitigate the destructive impact of the earthquakes, the regional seismic hazard in North Africa is assessed using the neo-deterministic, multi-scenario methodology (NDSHA) based on the computation of synthetic seismograms, using the modal summation technique, at a regular grid of 0.2 × 0.2°. This is the first study aimed at producing NDSHA maps of North Africa including five countries: Morocco, Algeria, Tunisia, Libya, and Egypt. The key input data for the NDSHA algorithm are earthquake sources, seismotectonic zonation, and structural models. In the preparation of the input data, it has been really important to go beyond the national borders and to adopt a coherent strategy all over the area. Thanks to the collaborative efforts of the teams involved, it has been possible to properly merge the earthquake catalogues available for each country to define with homogeneous criteria the seismogenic zones, the characteristic focal mechanism associated with each of them, and the structural models used to model wave propagation from the sources to the sites. As a result, reliable seismic hazard maps are produced in terms of maximum displacement (Dmax), maximum velocity (Vmax), and design ground acceleration.

Preface to the special issue “Seismotectonics and Seismic hazards in North Africa”

North Africa region from Egypt to Morocco experienced several damaging earthquakes in the past, and the largest recorded seismic event reached Mw 7.3 in 1980 at El Asnam (now Chlef) in the Tell Atlas of Algeria. This reality is linked with the regional situation along the Africa–Eurasia plate boundary, or in proximity of the Hellenic Arc plate boundary, or near the midRed Sea spreading floor. This special issue in seismotectonics and relationships with the seismic hazards includes different contributions in seismotectonics, seismology, active faulting, and seismic hazard and risk assessment in North Africa. Specifically, nine articles address the earthquake activity and its effect at the crustal level, Earth surface, and building design. The issue begins with the article of Bezzeghoud et al. that describe the earthquake distribution along the Africa–Eurasia plate boundary and gives the characteristics and seismic strain rate of the tectonically active regions from the Gloria transform fault to NW Africa. Using the tomographic investigations, Timoulali and coauthors explore the crustal structure of the Rif Mountains (Morocco), Alboran Sea, and surrounding areas. A fairly exhaustive account of the earthquake distribution and related active tectonic structures by Bahrouni and coauthors reveals the potential for large earthquakes in Tunisia. Badawy and coauthors describe the seismic activity of east North Africa using relocation procedure and source mechanisms of main continental earthquakes in Egypt. The volume switches into the study of historical earthquakes in Algeria by Ferdi and Harbi using epigraphic documents. Benhamouche and coauthors investigate the surface effects and liquefaction features of past earthquakes in the coastal region of Jijel (east Algeria) that experienced the damaging 1856 earthquakes with tsunami (Io IX, EMS). The evaluation of earthquake hazards and risks represents a natural continuation of previous studies on the seismotectonics of North Africa. The comprehensive analysis of the seismic hazards using an updated deterministic approach provides new results and emphasizes the need for the integration of geological and seismological data along the whole North Africa (Mourabit et al.). Gherboudj et al. present a probabilistic seismic hazard assessment as applied to the Algiers city. Finally, the vulnerability of building design to destructive seismic events is explored through conceptual frameworks and application in Algeria by Mebarki et al. J Seismol (2014) 18:203–204 DOI 10.1007/s10950-014-9424-5

Infrasound detection of meteors

Abstract Meteorites that penetrate the atmosphere generate infrasound waves of very low frequency content. These waves can be detected even at large distances. In this study, we analyzed the infrasound waves produced by three meteors. The October 7, 2008 TC3 meteor fell over the north Sudan Nubian Desert, the February 15, 2013 Russian fireball, and the February 6, 2016 Atlantic meteor near to the Brazil coast. The signals of these three meteors were detected by the infrasound sensors of the International Monitoring System (IMS) of the Comprehensive Test Ban Treaty Organization (CTBTO). The progressive Multi Channel Technique is applied to the signals in order to locate these infrasound sources. Correlation of the recorded signals in the collocated elements of each array enables to calculate the delays at the different array element relative to a reference one as a way to estimate the azimuth and velocity of the coming infrasound signals. The meteorite infrasound signals show a sudden change in pressure with azimuth due to its track variation at different heights in the atmosphere. Due to movement of the source, a change in azimuth with time occurs. Our deduced locations correlate well with those obtained from the catalogues of the IDC of the CTBTO.

Mapping b-values beneath Abu Dabbab from June to August 2004 earthquake swarm

Abstract Abu Dabbab area is considered as one of the most active earthquake sources in Egypt. It is defined by its swarm type activity, and complicated stress pattern. This study was conducted to evaluate the two and three dimensional spatial distribution of b-value at Abu Dabbab area (Margin of the northern Red Sea Rift, Egypt). The gridding technique of Wiemer and Wyss (1997) was used to compute b-value using ZMAP software. The b-value is calculated from a catalog consisting of 850 well-located earthquakes, which were recorded from 1st June to August 2004, using the maximum likelihood method. These earthquakes were recorded by temporary digital seismic network, with magnitudes ranging from −1 to 3.4 ML. It is important to mention that the variations of b-value with time cannot be easily detected for a short period. Hence, this study has been carried out to examine the variations of b-value in space. The computed b-value in the Abu Dabbab area does not follow a uniform distribution. A small volume of anomalously high b-value (b > 1.8) exists in the central part of the area at a depth between 6 and 9 km. This seems to agree with the reported low velocity value derived from previous P-wave travel time tomography studies (Hosny et al., 2009) and the low Q value (Abdel-Fattah et al., 2008). The existence of an anomalously high b-value region may be attributed to the presence of a magma reservoir or dyke zone beneath the northern Red Sea Rift that causes an intensively heterogeneous fractured crust or unusually high pore pressure.