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This study provides a temporal analysis of the seismicity occurring before three significant energetic earthquakes recorded in the Al Hoceima, Morocco, area: earthquakes in 1994 (Mw 6.0), 2004 (Mw 6.4), and 2016 (Mw 6.3). The analysis is based on the multifractal seismicity characteristics in the Trans-Alboran shear zone. For the computation of the multifractal spectrum f(α)-α , two measurements were considered, the temporal distribution of earthquakes and the temporal distribution of energy released by the earthquakes. In addition, the quantities D 1 (entropy), D +∞ (dimension of the large measurements), R (α 0 -α max) and L (α min -α 0), from the multifractal spectrum, were also defined. The obtained results prove that maximum values in the fractal dimensions D 1 and D +∞ appear just before the occurrence of the largest earthquakes in the multifractal spectrum computed from the earthquake-released energy. This particular trend, which is connected to the maximum values, is also noticeable before the occurrence of seismicity, which is less energetic for earthquakes with magnitudes above Mw 4.5, and may be evidence that the dynamic and geometrical properties of seismicity are associated. • The multifractal dynamics reflecting the complex seismotectonic context. • Maximum values in the fractal dimensions appear before of the largest earthquakes. • The evolution of the fractal dimensions might help us determine the evolution seismic. [ABSTRACT FROM AUTHOR]

This study presents a probabilistic seismic hazard assessment for the central part of northern Algeria using two complementary seismic models: a fault-based model and a gridded seismicity model. Two ground-motion attenuation equations were chosen using the Pacific Earthquake Engineering Research Center Next-Generation models, as well as local and regional ones. The ranking method was used to assess their ability to gather accurate data. To account for epistemic uncertainty in both components of the assessment, the seismic hazard was computed using a logic tree approach. Expert judgment and data testing were used to evaluate the weights assigned to individual ground-motion prediction equations. The seismic hazard maps depicted the obtained results in terms of spectral accelerations at oscillation periods of 0.0, 0.2, and 1.0 s, with 10% and 5% probabilities of exceedance in 50 years, and for soil types B, B/C, C, and C/D, as defined by the National Earthquake Hazards Reduction Program. From the analysis, the uncertainty is expressed as both a 95% confidence band and the coefficient of variation (COV). Annual frequencies of exceedance and hazard curves were estimated for the selected cities, as well as uniform hazard spectra for the previously quoted probabilities of exceedance and the soil types considered. Peak ground acceleration values of 0.44 ± 0.17 g and 0.38 ± 0.06 g were reported for the B/C soil type in the cities of Algiers and Blida, respectively, for a return period of 475 years. Seismic maps for the selected return periods depicting the classification of the estimated values are also displayed in terms of very high, high, medium, low and very low degrees of reliability. Furthermore, a seismic hazard disaggregation analysis in terms of magnitude, distance, and azimuth was carried out. The primary goal of such analyses is to determine the relative contribution of different seismic foci and sources to seismic hazard at specific locations. Thus, for each studied city, for the considered return periods and for the soil type B/C, the so-called control or modal earthquake was estimated. At Algiers, events with magnitudes Mw 5.0–5.5 and distances of less than 10 km contribute the most to the mean seismic hazard over a 475-year period. However, for the same return period, those events with Mw 7.0–7.5 and located between 10 and 20 km away contribute the most to the seismic hazard at Tipaza. [ABSTRACT FROM AUTHOR]

The main topic of this study is to characterize the seismic activity in the studied region by performing qualitative and quantitative analyses of several selected seismic sequences (seismic swarms and aftershock sequences). Clustering analysis of the selected seismic sequences, located in recent years in the Ibero-Maghrebian region, has been performed using the concept of fractal dimension. Analyses of the temporal variation of the fractal dimensions D - 2 (T) , D 0 (T) and D 2 (T) , as well as the spectral slope, have been also performed in order to characterize each analyzed sequence. The variation of the b-value parameter of the Gutenberg-Richter relationship with time has been derived using the windowing method, and a comparative analysis of the variation in time and space of the D 2 -value is assessed. Taking into account that b-value variations are often used in seismic hazard and earthquake forecasting studies, this type of work highlights the importance of fractal dimension research in seismic sequences. From our dataset, a positive correlation between b-value and the fractal dimension D 2 has been obtained, as shown in the following relations D 2 = 1.36 ± 0.27 b + 0.59 (± 0.26) and b = 0.74 ± 0.13 D 2 - 0.44 (± 0.24). [ABSTRACT FROM AUTHOR]

The aftershock sequence of the 2010 Beni-Ilmane (MW 5.5) earthquake is studied in depth to analyze the spatial and temporal variability of seismicity parameters of the relationships modeling the sequence. The b value of the frequency-magnitude distribution is examined rigorously. A threshold magnitude of completeness equal to 2.1, using the maximum curvature procedure or the changing point algorithm, and a b value equal to 0.96 ± 0.03 have been obtained for the entire sequence. Two clusters have been identified and characterized by their faulting type, exhibiting b values equal to 0.99 ± 0.05 and 1.04 ± 0.05. Additionally, the temporal decay of the aftershock sequence was examined using a stochastic point process. The analysis was done through the restricted epidemic-type aftershock sequence (RETAS) stochastic model, which allows the possibility to recognize the prevailing clustering pattern of the relaxation process in the examined area. The analysis selected the epidemic-type aftershock sequence (ETAS) model to offer the most appropriate description of the temporal distribution, which presumes that all events in the sequence can cause secondary aftershocks. Finally, the fractal dimensions are estimated using the integral correlation. The obtained D2 values are 2.15 ± 0.01, 2.23 ± 0.01 and 2.17 ± 0.02 for the entire sequence, and for the first and second cluster, respectively. An analysis of the temporal evolution of the fractal dimensions D−2, D0, D2 and the spectral slope has been also performed to derive and characterize the different clusters included in the sequence. [ABSTRACT FROM AUTHOR]

This study analyses the temporal clustering, spatial clustering, and statistics of the 2012–2013 Torreperogil-Sabiote (southern Spain) seismic swarm. During the swarm, more than 2200 events were located, mostly at depths of 2–5 km, with magnitude event up to m bLg 3.9 ( M w 3.7). On the basis of daily activity rate, three main temporal phases are identified and analysed. The analysis combines different seismological relationships to improve our understanding of the physical processes related to the swarm's occurrence. Each temporal phase is characterized by its cumulative seismic moment. Using several different approaches, we estimate a catalog completeness magnitude of m c ≅ 1.5. The maximum likelihood b -value estimates for each swarm phase are 1.11 ± 0.09, 1.04 ± 0.04, and 0.90 ± 0.04, respectively. To test the hypothesis that a b -value decrease is a precursor to a large event, we study temporal variations in b -value using overlapping moving windows. A relationship can be inferred between change in b -value and the regime style of the rupture. b -values are indicators of the stress regime, and influence the size of ruptures. The fractal dimension D 2 is used to perform spatial analysis. Cumulative gamma and beta functions are used to analyse the behaviour of inter-event distances during the earthquake sequence. [ABSTRACT FROM AUTHOR]

Highlights: [•] Probabilistic modeling is used to analyze the spatio-temporal behavior of aftershocks. [•] Gutenberg-Richter relationship for aftershock sequences. The Omori–Utsu law. [•] The modified Bath’s law is used to analyze in details the energy partitioning. [•] The fractal dimension D 2 and the correlation integral. [•] Analysis of the Aki’s relation D =3b/c. [Copyright &y& Elsevier]

This study examines distinctive features of ground motion parameters in northern Algeria. An initial computation of seismic hazard in terms of horizontal peak ground acceleration (PGA) and spectral acceleration (SA) at different periods, damped at 5%, is carried out for three different types of soils (rock, stiff soils and soft soils) for return periods of 100 and 475 years. In addition, uniform hazard spectra (UHS) are computed for these two return periods at several locations in the region. Then, the UHS computed for different soil types are proposed as a starting point to define elastic design spectra for building-code purposes. We have used the well-known Newmark-Hall approach. As proposed in the most recent International Building Codes, the SA (0.2 s) value is used to establish the spectral region for lower periods (region controlled by acceleration), whereas the SA (1.0 s) value is used to establish the spectral region for intermediate periods (region controlled by velocity). We also obtained important relations, dependent on site condition, between SA (0.2 s), SA (1.0 s) or SA values, and the PGA, for both return periods of 100 and 475 years. Other relationships between PGA or SA values have also been derived for return periods of 100 and 475 years, in this case independent of site condition. [ABSTRACT FROM AUTHOR]

Seismic hazard in terms of spectral acceleration ( SA) has been estimated for the first time in northern Algeria. For this purpose, we have used the spatially-smoothed seismicity approach. The present paper is intended to be a continuation of previous work in which we have evaluated the seismic hazard in terms of peak ground acceleration ( PGA) using the same methodology. To perform these evaluations, four complete and Poissonian seismic models have been used. One of them considers earthquakes with magnitudes above M S 6.5 in the last 300 years, that is, the most energetic seismicity in the region. Firstly, seismic hazard maps in terms of SA, at periods of 0.1, 0.2, 0.3, 0.4, 0.5, 1.0, 1.5 and 2.0 sec, with 39.3% and 10% probability of exceedance in 50 years, have been obtained. Therefore, uniform hazard spectra ( UHS) are computed and examined in detail for twelve of the most industrial and populated cities in northern Algeria. All the reported results in this study are for rock soil and 5% of damping. It is noteworthy that, in the seismic hazard maps as well as in the UHS plots, we observe maximum SA values in the central area of the Tell. The higher values are reached in the Chleff region (previously El Asnam), specifically around the location of the destructive earthquakes of September 9, 1954 ( M S 6.8), and October 10, 1980 ( M S 7.3). These maximum values, 0.4 g and 1.0 g, are associated with periods of about 0.2 and 0.3 sec for return periods of 100 and 475 years, respectively. [ABSTRACT FROM AUTHOR]

The occurrence of the Algiers earthquake ( M 6.8) of May 21, 2003, has motivated the necessity to reassess the probabilistic seismic hazard of northern Algeria. The fact that this destructive earthquake took place in an area where there was no evidence of previous significant earthquakes, neither instrumental nor historical, strongly encourages us to review the seismic hazard map of this region. Recently, the probabilistic seismic hazard of northern Algeria was computed using the spatially smoothed seismicity methodology. The catalog used in the previous computation was updated for this review, and not only includes information until June 2003, but also considers a recent re-evaluation of several historical earthquakes. In this paper, the same methodology and seismicity models are utilized in an effort to compare this methodology against an improved and updated seismic catalog. The largest mean peak ground acceleration (PGA) values are obtained in northernmost Algeria, specifically in the central area of the Tell Atlas. These values are of the order of 0.48 g for a return period of 475 years. In the City of Algiers, the capital of Algeria, and approximately 50 km from the reported epicenter of this latest destructive earthquake, a new mean PGA value of 0.23 g is obtained for the same return period. This value is 0.07 g greater than that obtained in the previous computation. In general, we receive greater seismic hazard results in the surrounding area of Algiers, especially to the southwest. The main reason is not this recent earthquake by itself, but the significant increase in the mmax magnitude in the seismic source where the city and the epicenter are included. [ABSTRACT FROM AUTHOR]