title: Seismic tomography of the area of the 2010 Beni-Ilmane earthquake sequence, north-central Algeria.
abstract: The region of Beni-Ilmane (District of M'sila, north-central Algeria) was the site of an earthquake sequence that started on 14 May 2010. This sequence, which lasted several months, was triggered by conjugate E-W reverse and N-S dextral faulting. To image the crustal structure of these active faults, we used a set of 1406 well located aftershocks events and applied the local tomography software (LOTOS) algorithm, which includes absolute source location, optimization of the initial 1D velocity model, and iterative tomographic inversion for 3D seismic P- and S-wave velocities (and the Vp/Vs ratio), and source parameters. The patterns of P-wave low-velocity anomalies correspond to the alignments of faults determined from geological evidence, and the P-wave high-velocity anomalies may represent rigid blocks of the upper crust that are not deformed by regional stresses. The S-wave low-velocity anomalies coincide with the aftershock area, where relatively high values of Vp/Vs ratio (1.78) are observed compared with values in the surrounding areas (1.62-1.66). These high values may indicate high fluid contents in the aftershock area. These fluids could have been released from deeper levels by fault movements during earthquakes and migrated rapidly upwards. This hypothesis is supported by vertical sections across the study area show that the major Vp/Vs anomalies are located above the seismicity clusters.
authors.affiliation: Centre de Recherche en Astronomie, Astrophysique et Geophysique, BP. 63, Bouzareah, Alger, Algeria.
authors.forename: Issam
authors.initials: I
authors.lastname: Abacha
authors.affiliation: Trofimuk Institute of Petroleum Geology and Geophysics, SB RAS, Prospekt Koptyuga, 3, Novosibirsk, 630090 Russia ; Novosibirsk State University, Novosibirsk, Russia.
authors.forename: Ivan
authors.initials: I
authors.lastname: Koulakov
authors.affiliation: Centre de Recherche en Astronomie, Astrophysique et Geophysique, BP. 63, Bouzareah, Alger, Algeria.
authors.forename: Fethi
authors.initials: F
authors.lastname: Semmane
authors.affiliation: Centre de Recherche en Astronomie, Astrophysique et Geophysique, BP. 63, Bouzareah, Alger, Algeria.
authors.forename: Abd Karim
authors.initials: AK
authors.lastname: Yelles-Chaouche
keywords: Aftershocks; Beni-Ilmane earthquake; Fluids; Seismic tomography; Tellian chain