A local magnitude scale (ML) for Northern Algeria

• Published in: Tectonophysics 2024-09, Vol.886, p.230435, Article 230435
• Main Authors: Roubeche, Khaled, Semmane, Fethi, Abacha, Issam, Boulahia, Oualid, Rahmani, Sofiane Taki-Eddine, Tikhamarine, El-Mahdi
• Format: Article
• Language: English
• Subjects: Algerian Digital Seismic Network; Local Magnitude Scale; Northern Algeria; Station Correction; Trilinear Regression
• ISSN: 0040-1951
• DOI: 10.1016/j.tecto.2024.230435

This study presents a local magnitude scale (ML) based on the original Richter definition and designed for use within the Algerian Digital Seismic Network (ADSN). The magnitude scale is derived from the analysis of 17,377 zero-peak maximum amplitude traces extracted from the vertical component, simulated as Wood-Anderson seismograms. These traces are taken from a dataset of 1901 earthquakes recorded between January 1, 2010, and June 1, 2022, at a minimum of five stations in the ADSN network. To better account for the attenuation of direct and refracted waves in northern Algeria, amplitude decay analysis reveals the presence of two transition distances at 90 and 190 km, resulting in three segments. A distance correction term, −log10(A0), is introduced and described by the following trilinear function:−logA0=0.6747∗log10R+0.0002∗R+1.6306R≤901.7736∗log10R+0.0002∗R−0.516990190 R represents the hypocentral distance in kilometers. The derived distance correction formula provides a well-constrained ML relationship for northern Algeria that is valid over a distance range of 5 to 600 km. Compared to other local magnitude relationships, the methodology proposed in this study consistently gives ML values slightly higher than those calculated by the Southern California relationship over all distances, with an average difference of 0.2 units. We computed corrections for 72 stations by minimizing the ML residuals. These corrections range from −0.50 to 0.54, highlighting the influence of local site effects on the amplitude of the seismic signal. The magnitude residuals using our magnitude relationship and incorporating the station corrections, show that the standard deviation has improved significantly, from 0.34 to 0.24. An ML relationship specific to the northern Algerian region provides a valuable tool for seismic monitoring, hazard assessment, and earthquake research in the region. •The first local magnitude scale has been developed in Northern Algeria.•This new scale will aid in creating a more accurate and homogenized earthquake catalog for Algeria.•Station corrections have been determined for 72 different geological sites.•The new scale will significantly improve seismic hazard studies in Northern Algeria