Time-dependent and spatio-temporal statistical analysis of seismicity: application on the complete data set of the 2010 Beni–Ilmane earthquake sequence

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Abstract
The Beni-Ilmane (BI) seismic sequence, situated in the north-central region of Algeria, began on May 14, 2010 with a mainshock of ML 5.4 followed by 2 other shocks on the 16th and 23rd May of ML 5.3 for both. Using the complete dataset from the 14th of May to the 31st of August and the Epidemic Type Aftershock sequences (ETAS) model to separate background from aftershocks contribution gave a first insight around the uncertainty that surrounds the causes and mechanisms of the seismicity. According to our findings, two phases have been determined, the first one, beginning from May 14th, shows low b and p values with most of the seismicity being self-triggered. In contrast, the second phase, beginning from May 23rd, demonstrates an increase of both the b and p values with a high number of background events. In the second phase, the background contribution involves 53% of all seismic activity after May 23rd’s peak which is high compared to typical mainshock-aftershocks sequences. A possible explanation is that the mainshocks began or assisted aseismic processes in addition to causing aftershocks. A sealed source at depth may have been broken by the third mainshock, opening the way for the following incursion of highly pressurized fluids (hydrocarbures) confirmed by a high Vp/Vs ratios.

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