Search

The establishment of a unified earthquake catalog is a basic requirement for attaining a detailed seismological analysis and an improved seismic hazard assessment. Accordingly, the current research paper aims to present a reliable instrumental unified earthquake catalog for the northern part of Algeria. This unified catalog is compiled using regional empirical relationships derived from converting different magnitude scales to an advanced physical-based moment magnitude scale suggested in the recent literature and denoted by Mwg. The regression methodology used in this study is called the New General Orthogonal Regression approach (N.GOR), which was selected since it is the most trustworthy procedure for scaling the magnitudes to Mwg. To highlight the significance of using the N.GOR, the obtained outcomes of the scaling relations were compared with those issued from the conventional general orthogonal regression (GOR) method, which is deemed to be the most dependable methodology used worldwide for magnitude conversion problems. The unified earthquake catalog was assembled from 1954 to 2022. Reliably converting the original magnitudes into homogenized moment magnitude leads to a complete and consistent unified earthquake catalog. Indeed, the unified moment magnitude catalog presented in this paper could provide reliable data for studying earthquakes distribution and the assessment of seismic hazards in the north of Algeria. [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]