Attenuation of seismic coda waves in the Rif area, northern Morocco

Abstract

The northern morocco, precisely the Rif region has known moderate tectonic activities in the last years (Al Houceima earthquakes 1994, 2004 and 2016). The aim of this work is to investigate the variety of tectonic activity by using the attenuation scattering of coda waves and its dependency with the frequency. The illustrated case in this work implies 70 seismic events focusing on the Rif Mountains with recorded seismic data during all 2014 period. These recordings have been used with a magnitude (Ml) less than 5. In this work we utilized 15 broadband stations deployed in a surface area defined by longitudes 34°N to 35.50°N and latitude 5.3°W and 3.20°W. The quality factor is inversely proportional to the seismic attenuation which is defined by the backscattering model (Aki and Chouet, 1975). The quality factor estimated values were computed at different central band frequencies that start from 1.5 till 18 Hz for five lapse time windows 20, 30, 40, 50 and 60 s. For 20s window lapse time, the quality factor average for the whole study area gives estimation of about 83.55 ± 10.84 at 1.5 Hz and 491.66 ± 150.07 at 18 Hz, as well as the estimation for 60s window lapse time is about 157.49 ± 15.61 at 1.5 Hz and 1787.65 ± 807.88 at 18 Hz central band frequencies. We find that the quality factor rise when both frequency and lapse time window increase; which reveals a clear dependency between the quality factor and frequency and reflects heterogeneities within the underlying crust and the complexity of geological/geophysical pattern in this zone.