One of the main experimental components of TOPOIBERIA, a multidisciplinary large scale research p... more One of the main experimental components of TOPOIBERIA, a multidisciplinary large scale research project aiming to study the links between the deep and superficial processes in the Iberian Peninsula, is the deployment of the IBERARRAY seismic network. A dense array (60x60 km) of new generation data-loggers equipped with broad-band seismometers will cover Iberia and North Morocco in three successive deployments, each lasting for about 18 months. The first leg, deployed in 2007, covers the southern part of Iberia (35 stations) and northern Morocco (20 stations). A standard procedure has been established to recover and process the data; field teams collect the recorded hard disk on the field and send data and metadata to a central processing center, where raw data is collected and stored and a quality control checking is performed. This include a systematic inspection of the experimental parameters (batteries charge, thermal insulation, time adjustments, geophone leveling etc), the visual verification of the seismic waveforms and the analysis, using power density spectra (PSD), of the noise level of each station. All this information is disseminated between the research teams involved in the project using a dedicated website and the continuous seismic data is made accessible through FTP and CWQ servers. Some of the nodes of the theoretical network are covered by permanent stations of the national broad-band network (IGN) or other networks operating in the region (IAG-UGR, ROA). Data from those stations will also be integrated to the Iberarray database. This Iberarray network will provide a large database of both waveform and catalogued events, with an unprecedented resolution. Earthquake data at local, regional and teleseismic scales will be analyzed using different methodologies. The first result would be an increase in the accuracy of the location of regional seismicity and the determination of focal mechanisms. A special emphasis will be attributed to seismic tomographic techniques using travel times and waveforms of P and S arrivals at different scales as well as surface waves, using dispersion measurements as well as studies dealing with background/ environmental noise. In addition, receiver function analysis for seismic imaging of deep lithospheric features and splitting analysis of shear-wave arrivals will also be developedPeer Reviewe
ABSTRACT During the TopoIberia experiment, a total of 26 seismic broadband stations were recordin... more ABSTRACT During the TopoIberia experiment, a total of 26 seismic broadband stations were recording in northern Morocco, providing for the first time extended regional coverage for investigating structure and seismotectonics of the southern branch of the Betic-Rif arc, its foreland and the Atlas domain. Here, we analyze P-to-S converted waves in teleseismic receiver functions to infer gross crustal properties as thickness and Vp/Vs ratio. Strong lateral variations of the crustal thickness are observed throughout the region. Crustal thicknesses vary between 22 km and 44 km and display a simple geographic pattern that divides the study area into three domains: entire northwestern Morocco underlain by a thickened crust with crustal thicknesses between 35 km and 44 km; northeastern Morocco affected by significant crustal thinning, with crustal thicknesses ranging from 22 km to 30 km, with the shallowest Moho along the Mediterranean coast; and an extended domain of 27-34 km thick crust, further south which includes the Atlas domain and its foreland regions. Vp/Vs ratios show normal values of ~ 1.75 for most stations except for the Atlas domain, where several stations give low Vp/Vs ratios around 1.71. The very sharp transition from thick crust in northwestern Morocco to thin crust in northeastern Morocco is attributed to regional geodynamics possibly the realm of present-day subcrustal dynamics in the final stage of western Mediterranean subduction. Crustal thicknesses just slightly above 30km in the southern domain are intriguing, showing that high topography in this region is not isostatically compensated at crustal level.
The purpose of this investigation is to compute the seismic vulnerability in the Rif area in orde... more The purpose of this investigation is to compute the seismic vulnerability in the Rif area in order to estimate the occurrence susceptibility to liquefaction sites. In addition to that, evaluating the liquefaction potential is one of the most useful investigations for risk mitigation and seismic hazard zonation and assessment. The parameter of the seismic vulnerability can be quantified and expressed by Kg index which is derived from the well-known ambient noise horizontal-to-vertical spectral ratio (HVSR) method of Nakamura. In this paper, the depicted analysis involves 15 broadband stations extended across the Rif region. The HVSR method was conducted on the whole micro-tremor data of 2014. By extracting the fundamental frequency F0 and the amplification factor A0 from the micro-tremor data, the Kg index was calculated, and the liquefaction potential was evaluated. The lowest estimated Kg value was about 0.19 (34.97° N–3.32° W), while the highest value reached 11.93 (35.33° N–4.96°...
This article has been accepted for publication and undergone full peer review but has not been th... more This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process which may lead to differences between this version and the Version of Record. Please cite this article as
l-mixing collisions Li(n/sup 2/D)+X..-->..Li(n/sup 2/L,L>2)+X induced in Rydberg states of ... more l-mixing collisions Li(n/sup 2/D)+X..-->..Li(n/sup 2/L,L>2)+X induced in Rydberg states of lithium (n = 4,5,...,13) by rare-gas atoms or Li ground-state atoms are studied in a heat-pipe arrangement. The l-mixing cross sections deduced from the time analysis of the n/sup 2/D laser-induced fluorescence agree with experimental values obtained with the heavier alkali-metal atoms and with different theoretical models developed for quasielastic Rydberg-electron--target collisions. Quenching of the n/sup 2/D fluorescence at higher rare-gas pressures is interpreted as inelastic collisional transfer of the L> or =1 mixed states to the nonhydrogenic S sublevel. Finally the radiative lifetimes of the n/sup 2/D states and n/sup 2/L mixed states with L> or =1 are deduced, respectively, from the low-pressure limit and intermediate-pressure study of the n/sup 2/D fluorescence relaxation rate.
In the present study, the petrophysical properties of five different rocks have been measured and... more In 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 Conferences
Controversial evolutionary models have been proposed for the Gibraltar Arc system, a complex inte... more Controversial evolutionary models have been proposed for the Gibraltar Arc system, a complex interaction zone between the Eurasia and African plates. Here we derive new mantle anisotropic constraints from SKS splitting measurements on a dense network of about 90 broad-band stations deployed over South Iberia and North Morocco. The inferred fast polarization directions (FPD) clearly show a spectacular rotation along the arc following the curvature of the Rif-Betic chain, while stations located at the South and SouthEast edges show distinct patterns. These results support geodynamical processes invoking a fast retreating slab rather than convective-removal and delamination models. The FPD variations along the Gibraltar arc can be explained by fossil anisotropy acquired during the Western Mediterranean Eocene subduction, while changes to the South and SouthEast of the Rif-Betic chain could be the imprint of a flow episode around an Alboran high velocity slab during its Miocene fragmentation from the Algerian slab.
We present a 3-D shear wave velocity model for the crust and upper mantle of the western Mediterr... more We present a 3-D shear wave velocity model for the crust and upper mantle of the western Mediterranean from Rayleigh wave tomography. We analyzed the fundamental mode in the 20-167 s period band (6.0-50.0 mHz) from earthquakes recorded by a number of temporary and permanent seismograph arrays. Using the two-plane wave method, we obtained phase velocity dispersion curves that were inverted for an isotropic Vs model that extends from the southern Iberian Massif, across the Gibraltar Arc and the Atlas mountains to the Saharan Craton. The area of the western Mediterranean that we have studied has been the site of complex subduction, slab rollback, and simultaneous compression and extension during African-European convergence since the Oligocene. The shear velocity model shows high velocities beneath the Rif from 65 km depth and beneath the Granada Basin from 70 km depth that extend beneath the Alboran Domain to more than 250 km depth, which we interpret as a near-vertical slab dangling from beneath the western Alboran Sea. The slab appears to be attached to the crust beneath the Rif and possibly beneath the Granada Basin and Sierra Nevada where low shear velocities (3.8 km/s) are mapped to >55 km depth. The attached slab is pulling down the Gibraltar Arc crust, thickening it, and removing the continental margin lithospheric mantle beneath both Iberia and Morocco as it descends into the deeper mantle. Thin lithosphere is indicated by very low upper mantle velocities beneath the Alboran Sea, above and east of the dangling slab and beneath the Cenozoic volcanics.
... Chafik NAKHCHA Faculté des Sciences-Rabat - Géologue Aziz KHIYARI ... 8 Op. Cit. 9 El Alami S... more ... Chafik NAKHCHA Faculté des Sciences-Rabat - Géologue Aziz KHIYARI ... 8 Op. Cit. 9 El Alami SO, Tadili B.-A., Cherkaoui T.-E., Medina F., Ramdani M., Aït Brahim L. & Harnafi M. 1998 - The Al Hoceima earthquake of May 26, 1994 and its aftershocks: a seismotectonic study. ...
Pulsed CO2 laser‐induced ablation of solid lithium is studied in the low‐energy‐density regime wh... more Pulsed CO2 laser‐induced ablation of solid lithium is studied in the low‐energy‐density regime where no plasma forms on the surface. Li atoms emitted from the surface are characterized using laser‐induced fluorescence and absorption spectroscopy. Atom densities measured as a function of time for different distances from the surface are well described by a full‐range Maxwellian in a center‐of‐mass coordinate system. For 0.9 J/cm2 incident energy density (a fraction being absorbed), the beam velocity and the characteristic temperature are 3×105 cm/s and 8500–10 000 K, respectively. Under these conditions, the number of ablated atoms is about 5×1011 per laser shot. The determined effective beam temperature is much higher than the boiling point of pure lithium. This could be explained considering that a film of oxide with greater vaporization temperature is always present on the surface even in relatively good vacuum conditions.
One of the main experimental components of TOPOIBERIA, a multidisciplinary large scale research p... more One of the main experimental components of TOPOIBERIA, a multidisciplinary large scale research project aiming to study the links between the deep and superficial processes in the Iberian Peninsula, is the deployment of the IBERARRAY seismic network. A dense array (60x60 km) of new generation data-loggers equipped with broad-band seismometers will cover Iberia and North Morocco in three successive deployments, each lasting for about 18 months. The first leg, deployed in 2007, covers the southern part of Iberia (35 stations) and northern Morocco (20 stations). A standard procedure has been established to recover and process the data; field teams collect the recorded hard disk on the field and send data and metadata to a central processing center, where raw data is collected and stored and a quality control checking is performed. This include a systematic inspection of the experimental parameters (batteries charge, thermal insulation, time adjustments, geophone leveling etc), the visual verification of the seismic waveforms and the analysis, using power density spectra (PSD), of the noise level of each station. All this information is disseminated between the research teams involved in the project using a dedicated website and the continuous seismic data is made accessible through FTP and CWQ servers. Some of the nodes of the theoretical network are covered by permanent stations of the national broad-band network (IGN) or other networks operating in the region (IAG-UGR, ROA). Data from those stations will also be integrated to the Iberarray database. This Iberarray network will provide a large database of both waveform and catalogued events, with an unprecedented resolution. Earthquake data at local, regional and teleseismic scales will be analyzed using different methodologies. The first result would be an increase in the accuracy of the location of regional seismicity and the determination of focal mechanisms. A special emphasis will be attributed to seismic tomographic techniques using travel times and waveforms of P and S arrivals at different scales as well as surface waves, using dispersion measurements as well as studies dealing with background/ environmental noise. In addition, receiver function analysis for seismic imaging of deep lithospheric features and splitting analysis of shear-wave arrivals will also be developedPeer Reviewe
ABSTRACT During the TopoIberia experiment, a total of 26 seismic broadband stations were recordin... more ABSTRACT During the TopoIberia experiment, a total of 26 seismic broadband stations were recording in northern Morocco, providing for the first time extended regional coverage for investigating structure and seismotectonics of the southern branch of the Betic-Rif arc, its foreland and the Atlas domain. Here, we analyze P-to-S converted waves in teleseismic receiver functions to infer gross crustal properties as thickness and Vp/Vs ratio. Strong lateral variations of the crustal thickness are observed throughout the region. Crustal thicknesses vary between 22 km and 44 km and display a simple geographic pattern that divides the study area into three domains: entire northwestern Morocco underlain by a thickened crust with crustal thicknesses between 35 km and 44 km; northeastern Morocco affected by significant crustal thinning, with crustal thicknesses ranging from 22 km to 30 km, with the shallowest Moho along the Mediterranean coast; and an extended domain of 27-34 km thick crust, further south which includes the Atlas domain and its foreland regions. Vp/Vs ratios show normal values of ~ 1.75 for most stations except for the Atlas domain, where several stations give low Vp/Vs ratios around 1.71. The very sharp transition from thick crust in northwestern Morocco to thin crust in northeastern Morocco is attributed to regional geodynamics possibly the realm of present-day subcrustal dynamics in the final stage of western Mediterranean subduction. Crustal thicknesses just slightly above 30km in the southern domain are intriguing, showing that high topography in this region is not isostatically compensated at crustal level.
The purpose of this investigation is to compute the seismic vulnerability in the Rif area in orde... more The purpose of this investigation is to compute the seismic vulnerability in the Rif area in order to estimate the occurrence susceptibility to liquefaction sites. In addition to that, evaluating the liquefaction potential is one of the most useful investigations for risk mitigation and seismic hazard zonation and assessment. The parameter of the seismic vulnerability can be quantified and expressed by Kg index which is derived from the well-known ambient noise horizontal-to-vertical spectral ratio (HVSR) method of Nakamura. In this paper, the depicted analysis involves 15 broadband stations extended across the Rif region. The HVSR method was conducted on the whole micro-tremor data of 2014. By extracting the fundamental frequency F0 and the amplification factor A0 from the micro-tremor data, the Kg index was calculated, and the liquefaction potential was evaluated. The lowest estimated Kg value was about 0.19 (34.97° N–3.32° W), while the highest value reached 11.93 (35.33° N–4.96°...
This article has been accepted for publication and undergone full peer review but has not been th... more This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process which may lead to differences between this version and the Version of Record. Please cite this article as
l-mixing collisions Li(n/sup 2/D)+X..-->..Li(n/sup 2/L,L>2)+X induced in Rydberg states of ... more l-mixing collisions Li(n/sup 2/D)+X..-->..Li(n/sup 2/L,L>2)+X induced in Rydberg states of lithium (n = 4,5,...,13) by rare-gas atoms or Li ground-state atoms are studied in a heat-pipe arrangement. The l-mixing cross sections deduced from the time analysis of the n/sup 2/D laser-induced fluorescence agree with experimental values obtained with the heavier alkali-metal atoms and with different theoretical models developed for quasielastic Rydberg-electron--target collisions. Quenching of the n/sup 2/D fluorescence at higher rare-gas pressures is interpreted as inelastic collisional transfer of the L> or =1 mixed states to the nonhydrogenic S sublevel. Finally the radiative lifetimes of the n/sup 2/D states and n/sup 2/L mixed states with L> or =1 are deduced, respectively, from the low-pressure limit and intermediate-pressure study of the n/sup 2/D fluorescence relaxation rate.
In the present study, the petrophysical properties of five different rocks have been measured and... more In 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 Conferences
Controversial evolutionary models have been proposed for the Gibraltar Arc system, a complex inte... more Controversial evolutionary models have been proposed for the Gibraltar Arc system, a complex interaction zone between the Eurasia and African plates. Here we derive new mantle anisotropic constraints from SKS splitting measurements on a dense network of about 90 broad-band stations deployed over South Iberia and North Morocco. The inferred fast polarization directions (FPD) clearly show a spectacular rotation along the arc following the curvature of the Rif-Betic chain, while stations located at the South and SouthEast edges show distinct patterns. These results support geodynamical processes invoking a fast retreating slab rather than convective-removal and delamination models. The FPD variations along the Gibraltar arc can be explained by fossil anisotropy acquired during the Western Mediterranean Eocene subduction, while changes to the South and SouthEast of the Rif-Betic chain could be the imprint of a flow episode around an Alboran high velocity slab during its Miocene fragmentation from the Algerian slab.
We present a 3-D shear wave velocity model for the crust and upper mantle of the western Mediterr... more We present a 3-D shear wave velocity model for the crust and upper mantle of the western Mediterranean from Rayleigh wave tomography. We analyzed the fundamental mode in the 20-167 s period band (6.0-50.0 mHz) from earthquakes recorded by a number of temporary and permanent seismograph arrays. Using the two-plane wave method, we obtained phase velocity dispersion curves that were inverted for an isotropic Vs model that extends from the southern Iberian Massif, across the Gibraltar Arc and the Atlas mountains to the Saharan Craton. The area of the western Mediterranean that we have studied has been the site of complex subduction, slab rollback, and simultaneous compression and extension during African-European convergence since the Oligocene. The shear velocity model shows high velocities beneath the Rif from 65 km depth and beneath the Granada Basin from 70 km depth that extend beneath the Alboran Domain to more than 250 km depth, which we interpret as a near-vertical slab dangling from beneath the western Alboran Sea. The slab appears to be attached to the crust beneath the Rif and possibly beneath the Granada Basin and Sierra Nevada where low shear velocities (3.8 km/s) are mapped to >55 km depth. The attached slab is pulling down the Gibraltar Arc crust, thickening it, and removing the continental margin lithospheric mantle beneath both Iberia and Morocco as it descends into the deeper mantle. Thin lithosphere is indicated by very low upper mantle velocities beneath the Alboran Sea, above and east of the dangling slab and beneath the Cenozoic volcanics.
... Chafik NAKHCHA Faculté des Sciences-Rabat - Géologue Aziz KHIYARI ... 8 Op. Cit. 9 El Alami S... more ... Chafik NAKHCHA Faculté des Sciences-Rabat - Géologue Aziz KHIYARI ... 8 Op. Cit. 9 El Alami SO, Tadili B.-A., Cherkaoui T.-E., Medina F., Ramdani M., Aït Brahim L. & Harnafi M. 1998 - The Al Hoceima earthquake of May 26, 1994 and its aftershocks: a seismotectonic study. ...
Pulsed CO2 laser‐induced ablation of solid lithium is studied in the low‐energy‐density regime wh... more Pulsed CO2 laser‐induced ablation of solid lithium is studied in the low‐energy‐density regime where no plasma forms on the surface. Li atoms emitted from the surface are characterized using laser‐induced fluorescence and absorption spectroscopy. Atom densities measured as a function of time for different distances from the surface are well described by a full‐range Maxwellian in a center‐of‐mass coordinate system. For 0.9 J/cm2 incident energy density (a fraction being absorbed), the beam velocity and the characteristic temperature are 3×105 cm/s and 8500–10 000 K, respectively. Under these conditions, the number of ablated atoms is about 5×1011 per laser shot. The determined effective beam temperature is much higher than the boiling point of pure lithium. This could be explained considering that a film of oxide with greater vaporization temperature is always present on the surface even in relatively good vacuum conditions.
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