Seismicity and seismic hazard mapping of northern Algeria: Map of maximum calculated intensities (MCI)

Abstract

An earthquake catalogue covering the period 1716-2000, comprising 2430 events, has been compiled for the region lying between 3°W-9°E and 31°N-38°N. It results from raw data of IGN, ISC, USGS and Algerian sources, enabling an input consisting of origin time H, geographical coordinates (longitude λ and latitude ψ) and at least one of the following parameters: surface wave magnitude Ms, body wave magnitude Mb, epicentral intensities Io. Empirical relations permit transformations of Mb and Ms into Io. The output consists of H, λ, ψ, Ms, Mb, Io, and focal depth h which is fixed to 10 km. The number of events falls to 1458 characterised by Ms ≥ 3.3 and Mb ≥ 3.6, or Io ≥ III. The fixed depth is suggested by the best documented Algerian macroseismic maps that also lead to an empirical intensity attenuation law. A first application of this catalogue allows the drawing up of an updated Seismicity and a Maximal Calculated Intensities (MCI) Map of Algeria. The MCI map is obtained by using the empirical attenuation law: the intensities inferred by the whole events constituting the catalogue are computed at nodes of a 5×5-km grid covering the area of study. The corresponding maximum value is assigned to each node. The MCI map produced that way gives precise spatial information in comparison with Maximum Observed Intensities (MOI) maps obtained in previous macroseismic studies. This document may be useful in mapping the seismic hazard in Northern Algeria, without attaching probabilities to ground-motion parameters.