Coda wave attenuation tomography in Northern Morocco

In this study we focused on seismic attenuation (1/ Q) tomography in Northern Morocco. For this purpose, two different models are employed: The Single Backscattering model hypothesis of Aki and Chouet (1975) to calculate values of Coda Q (Q) and the Back-projection technique of Xie and Mitchell (1990) to estimate lateral variation in Q via a tomographic inversion. For this investigation, the Coda Q method is applied to a number of 94 local earthquakes with a magnitude between Ml=0.7 and Ml=4. The digital seismograms of these earthquakes were recorded during the year 2008 by both local temporary and permanent broadband seismic station network deployed in Northern of Morocco. The Q quality factor values have been computed at central frequencies 0.75, 1.5, 3, 6 and 12 Hz. The lapse time windows are restricted to 30s in order to sample the earth's crust only. The Q results indicate that strong frequency dependence follow a power law for the entire area. The preliminary results of seismic Coda Q attenuation tomography shows a dependence at each frequency band, between seismic attenuation and the geology structure units in the study area, especially in the region of Al Hoceima and the eastern part of the Rif which are characterized by high attenuation values due to active faults area, while low attenuation values are seen in the west and the south of the Rif in high frequencies.Peer Reviewe

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

15 pages, 12 figures, 5 tables, supplementary data https://doi.org/10.1016/j.jafrearsci.2020.103815The 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 zoneThis study was supported by the Scientific Institute, Rabat, MoroccoWith the funding support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S), of the Spanish Research Agency (AEI

A Correlation between P-wave velocity and thermal conductivity of heterogeneous porous materials Corrélation entre la vitesse d'onde P et la conductivité thermique des matériaux hétérogènes et poreux

International audienceIn the present study, the petrophysical properties of five different rocks have been measured and analyzed. This is the thermal conductivity, P-wave velocity and porosity. The methodology to estimate the thermal conductivity is to impose heat flux unidirectional on a sample and measure the temperature difference across the sample. The ultrasonic testing is based on the measurement of propagation time of a P-wave in the longitudinal direction. The porosity is measured by the mercury porosimetry technique, based on the measurement of the volume of mercury intruded into the rock under different pressures (mercury intrusion). The results have been shown a direct effect of porosity on thermal conductivity and P-wave velocity. We have found good relationship between the petrophysical properties such as P-wave velocities versus porosity and P-wave velocities versus thermal conductivity coefficient .The experimental results have been then compared with theoretical models available in the literature. These results, consistent with theory, show the possibility of estimating the thermal conductivity from the P-wave velocity and the use of non-destructive methods. Résumé. Dans ce travail, des propriétés pétrophysiques de cinq roches différentes ont été mesurées et analysées. Il s'agit de la conductivité thermique, la vitesse de propagation d'onde P et la porosité. En ce qui concerne la conductivité thermique, on impose à un échantillon un flux de chaleur unidirectionnel et on mesure la différence de température aux bornes de l'échantillon. Le test ultrasonique est basé sur la mesure du temps de propagation d'une onde P dans le sens longitudinal. La porosité est mesurée par la technique de porosimétrie au mercure, basée sur la mesure de la quantité de mercure insérée dans les pores d'une roche sous différentes pressions (intrusion de mercure). Les résultats obtenus montrent un effet direct de la porosité sur La Web of Conference

Estimation of Coda Wave Attenuation in Northern Morocco

We studied the attenuation of coda waves and its frequency and lapse-time dependence in northern Morocco. We analysed coda waves of 66 earthquakes recorded in this region during 2008 for four lapse time windows of length 30, 40, 50, and 60 s, and at five frequency bands with central frequency in the range of 0.75–12 Hz. We determined the frequency dependent Q relation for the horizontal (NS and EW) and vertical (Z) component seismograms. We analyzed three-component broadband seismograms of 66 local earthquakes for determining coda-Q based on the single back-scattering model. The Q values show strong frequency dependence in 1.5–12 Hz that is related to high degree of heterogeneity of the medium. The lapse time dependence of Q shows that Q (Q at 1 Hz) significantly increases with lapse time that is related to the depth dependence of attenuation and hence of the level of heterogeneity of the medium. The average frequency-dependent Q(f) values are Q= (143.75 ± 1.09) f, Q= (149.12 ± 1.08) f and Q= (140.42 ± 1.81) f for the vertical, north–south and east–west components of motion, respectively. The frequency-dependent Q(f) relations are useful for evaluating source parameters (Singh et al. 2001), which are the key inputs for seismic hazard assessment of the region.Peer Reviewe