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Seismic tomography of the area of the 2010 Beni-Ilmane earthquake sequence, north-central Algeria.

Abacha I, Koulakov I, Semmane F, Yelles-Chaouche AK - Springerplus (2014)

Bottom Line: This sequence, which lasted several months, was triggered by conjugate E-W reverse and N-S dextral faulting.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.

View Article: PubMed Central - PubMed

Affiliation: Centre de Recherche en Astronomie, Astrophysique et Geophysique, BP. 63, Bouzareah, Alger, 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.

No MeSH data available.


Related in: MedlinePlus

Example of seismic record of several aftershocks by 3 portable stations with indications of the P and S arrivals is presented.
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Fig2: Example of seismic record of several aftershocks by 3 portable stations with indications of the P and S arrivals is presented.

Mentions: The data for the study were recorded by a temporary seismic network consisting of 11 three-component short-period portable stations deployed for about five months in the epicentral area of the 2010 Beni-Ilmane sequence, in addition to the permanent stations of the Algerian seismic network (Figure 1b). Three stations of the permanent network are located at distances of less than 50 km from the epicentral area. For a description of the type and technical characteristics of these stations, see Yelles et al. (2013). The arrival times of P- and S waves from local events were manually picked using the Antelope software of Kinemetrics. Figure 2 shows an example of a seismic record of several aftershocks from three portable stations with indications of the P- and S-wave arrivals. To select the data, we used events with no less than 8 picks having the residuals of smaller than 0.8 s. A total of 1406 events were initially selected for the study, corresponding to 12,380 P-wave and 2604 S-wave picks for the interval between 14 and 31 May 2010 (the period of maximum aftershock activity).Figure 2


Seismic tomography of the area of the 2010 Beni-Ilmane earthquake sequence, north-central Algeria.

Abacha I, Koulakov I, Semmane F, Yelles-Chaouche AK - Springerplus (2014)

Example of seismic record of several aftershocks by 3 portable stations with indications of the P and S arrivals is presented.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4230316&req=5

Fig2: Example of seismic record of several aftershocks by 3 portable stations with indications of the P and S arrivals is presented.
Mentions: The data for the study were recorded by a temporary seismic network consisting of 11 three-component short-period portable stations deployed for about five months in the epicentral area of the 2010 Beni-Ilmane sequence, in addition to the permanent stations of the Algerian seismic network (Figure 1b). Three stations of the permanent network are located at distances of less than 50 km from the epicentral area. For a description of the type and technical characteristics of these stations, see Yelles et al. (2013). The arrival times of P- and S waves from local events were manually picked using the Antelope software of Kinemetrics. Figure 2 shows an example of a seismic record of several aftershocks from three portable stations with indications of the P- and S-wave arrivals. To select the data, we used events with no less than 8 picks having the residuals of smaller than 0.8 s. A total of 1406 events were initially selected for the study, corresponding to 12,380 P-wave and 2604 S-wave picks for the interval between 14 and 31 May 2010 (the period of maximum aftershock activity).Figure 2

Bottom Line: This sequence, which lasted several months, was triggered by conjugate E-W reverse and N-S dextral faulting.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.

View Article: PubMed Central - PubMed

Affiliation: Centre de Recherche en Astronomie, Astrophysique et Geophysique, BP. 63, Bouzareah, Alger, 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.

No MeSH data available.


Related in: MedlinePlus