The new Algerian Digital Seismic Network (ADSN): towards an earthquake early-warning system

Seismic monitoring in Algeria has seen great changes since the Boumerdes earthquake of 21 May 2003. Indeed, the installation of a new digital seismic network has resulted in a significant upgrade of the previous analog telemetry network. <br><br> During the last four years, the number of stations in operation has increased substantially from 25 to 69, and 20 of these are broadband, 2 are very broadband, 47 are short period. 21 are equipped with accelerometers. They are all managed by Antelope software from Kinemetrics (US Cie), and they are all connected in real time and use various modes of transmission (e.g., satellite, internet, mobile phone). The spatial repartition of the stations now cover most of northern Algeria. In addition, 70 GPS stations have recently been added to this seismological network, most of them collocated with the seismological stations. <br><br> Since the installation of the network, the records of local or distant events have improved significantly. The automatic processing of the data in a few minutes allows alert messages to be distributed to Civil Defense and other national authorities to react promptly to any emergency. The current strategy is to improve the data quality, to increase the density of the network by adding about 50 new stations, to reduce the processing time, and to reduce the time needed to send out an alert message. The result should be greatly improved network performance, which will lead to an effective early-warning system

The August 1st, 2014 (Mw 5.3) Moderate Earthquake: Evidence for an Active Thrust Fault in the Bay of Algiers (Algeria)

On August 1st, 2014, a moderate-sized earthquake struck the capital city of Algiers at 05:11:17.6 (GMT+1). The earthquake caused the death of six peoples and injured 420, mainly following a panic movement among the population. Following the main shock, we surveyed the aftershock activity using a portable seismological network (short period), installed from August 2nd, 2014 to August 21st, 2015. In this work, first, we determined the main shock epicenter using the accelerograms recorded by the Algerian accelerograph network (under the coordination of the National Center of Applied Research in Earthquake Engineering–CGS). We calculated the focal mechanism of the main shock, using the inversion of the accelerograph waveforms in displacement that provides a reverse fault with a slight right-lateral component of slip and a compression axis striking NNW–SSE. The obtained scalar seismic moment (M o = 1.25 × 1017 Nm) corresponds to a moment magnitude of M w = 5.3. Second, the analysis of the obtained aftershock swarm, of the survey, suggests an offshore ENE–WSW, trending and NNW dipping, causative active fault in the bay of Algiers, which may likely correspond to an offshore unknown segment of the Sahel active fault