Abstract
Lg-waves propagate over long distances in the northern part of Africa and are recorded on the seismic station located close to Abeche (Chad). We have applied the well-known coda analysis method developed by Aki and Chouet [1] to study the Lg-wave anelastic attenuation in this area. We found a frequency dependence: Q( f ) = (650±34) f (0.77±0.2). This result shows an average value of Q0 (Q0 ≈ 650) for earthquakes occurred in tectonic areas as the East African Rift system, Turkey, Greece and Red Sea. The higher value of Q0 (Q0 ≈ 800) is obtained for the event occurred in the middle of the stable plate close to the Tamanrasset (TAM) station in Algeria.
Highlights
Attenuation of regional seismic waves has been studied for years from various points of view including theoretical researches and numerous applied researches in various geophysical environments
The recorded data show a very nice record of this event, as shown by the bottom part of Figure 3. This record exhibits a well developed coda ranging at least 600 s, very fruitful for coda-Q measurement
As described in the introduction, we have used the original model of coda decay, proposed by [4] in which the amplitude is represented by a function of frequency and time as follows: ( ) = A( f,t ) C ( f )t−γ exp −2πft (2Qc ( f ))
Summary
Attenuation of regional seismic waves has been studied for years from various points of view including theoretical researches and numerous applied researches in various geophysical environments. Nubia is going away of Arabia at roughly 20 mm/year [16] and the divergence velocity through the East African Rift ranges from 6 to 3 mm/year from North to South [15] [17] This situation explains that the events recorded by the ABC (Abeche) seismic station are mainly located far from the station, more precisely at distances greater than 1700 km (Table 1, Figure 1). The special case of the event located in south Algeria, close to the city of Tamanrasset, is of major interest This mb 4.2 event clearly occurs in a very stable area; it is well recorded in the ABC station as shown by Figure 3. Exhibits a well developed coda ranging at least 600 s, very fruitful for coda-Q measurement
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