Karim Keddadouche

Bio: Karim Keddadouche is an academic researcher from Aix-Marseille University. The author has contributed to research in topics: Glacier & Glacial period. The author has an hindex of 17, co-authored 66 publications receiving 952 citations. Previous affiliations of Karim Keddadouche include Aster.

Earthquake synchrony and clustering on Fucino faults (Central Italy) as revealed from in situ Cl-36 exposure dating

Abstract: We recover the Holocene earthquake history of seven seismogenic normal faults in the Fucino system, central Italy. We collected 800 samples from the well-preserved limestone scarps of the faults and modeled their 36Cl concentrations to derive their seismic exhumation history. We found that > 30 large earthquakes broke the faults in synchrony over the last 12 ka. The seven faults released strain at the same periods of time, 12-9 ka, 5-3 ka, and 1.5-1 ka. On all faults, the strain accumulation and release occurred in 3-6 ka supercycles, each included a 3-5 ka phase of slow (≤ 0.5-2 mm/yr) strain accumulation in relative quiescence, followed by a cluster of three to four large earthquakes or earthquake sequences that released most of the strain in < 1-2 ka. The large earthquakes repeated every 0.5 ± 0.3 ka during the paroxysmal phases and every 4.3 ± 0.9 ka between those phases. Earthquakes on the northern faults produced twice larger surface slips (~ 2 m) and had larger magnitudes (Mw 6.2-6.7) than those on the southern faults. On most faults, the relative strain level was found to control the amount of slip and the time of occurrence of the next large earthquake. Faults entered a phase of clustered activity once they had reached a specific relative strain threshold. The Tre Monti fault is identified as the most prone to break over the next century. Our data document earthquake synchrony and clustering at a broader space and time scale than has been reported to date.

Preparation of \ASTER\ in-house 10Be/9Be standard solutions

Abstract: Since its commissioning in 2006, the commercially available certificated National Institute of Standards and Technology standard reference material NIST SRM 4325 is used at the French national facility ASTER (CEREGE, Aix-en-Provence) to normalize 10Be measurements. This standard solution being no longer disposable, we thus decided to produce in-house standards. As a first attempt, a STD-12 standard (10Be/9Be = (4.939 ± 0.053) × 10−12) has been prepared from 2.5 kg of marine sediments with an adapted chemical protocol. Then, a 10Be enriched solution of known concentration being available, a STD-11 standard (10Be/9Be = (1.191 ± 0.013) × 10−11) that will be used at ASTER in the near future to calibrate 10Be measurements and its dilution to the 10−14 level (STD-14 (10Be/9Be = (5.468 ± 0.064) × 10−14)) have been prepared from it.

Determination of muon attenuation lengths in depth profiles from in situ produced cosmogenic nuclides

Abstract: Cosmogenic nuclides are important tools to understand and quantify the processes that control the development and evolution of landscapes during the quaternary. Among all published studies, few are related to the accurate and precise determination of the physical parameters governing their production in the Earth’s crust surface (in situ produced cosmogenic nuclides) and its evolution as a function of depth below the Earth’s surface. Currently, it is nearly impossible to advocate global parameters that could be used worldwide. Indeed, at each sampling site, not only the geometry and the mineralogy will differ but also their evolution as a function of depth. In this paper, a new approach based on the measurement of the evolution of cosmogenic nuclide concentrations along depth profiles to determine the muon attenuation lengths is proposed. Contrarily to previous studies that used to describe both slow and fast muons, only one type of muons will be considered in this paper and nuclide accumulation at depth will be described by a single exponential. The determined attenuation length integrates the potential effect of the chemical composition of the overlying matrix and takes into account the entire energy range of the incident particles. Additionally, when denudational steady state is reached, muon contributions can be determined. When scaled to sea level, these contributions appear to be comparable for a given nuclide whatever the site where they have been determined. The average weighted muon contributions are 0.028 ± 0.004 atoms g−1 a−1 for 10Be, 0.233 ± 0.045 atoms g−1 a−1 for 26Al and 1.063 ± 0.329 atoms g−1 a−1 for 36Cl and are valid within the depth range 0–6500 g cm−2.

Steady erosion rates in the Himalayas through late Cenozoic climatic changes

Abstract: Sediment accumulation rates and thermal trackers suggest a substantial and global increase in erosion rates over the past few million years. That increase is commonly associated with the impact of the Northern Hemisphere glaciation, but methodological biases have led researchers to debate this hypothesis. Here, we test whether Himalayan erosion rates increased by measuring beryllium-10 (10Be) in the sediment of the Bengal Bay seabed. Sediment originated from rocks that produced 10Be under the impact of cosmic rays during erosion near surface. Thus, the 10Be concentrations indicate erosion rates. The 10Be concentration of the Bengal Bay sediment depends on the contributions of the Ganga and Brahmaputra rivers. Their sediments have distinct 10Be concentrations because of distinct elevations and erosion in their drainage basins. Variable contributions could thus complicate erosion-rate calculation. We traced these contributions by a provenance study using the strontium (Sr) and neodymium (Nd) isotopic sediment compositions. Within uncertainties of ±30%, our reconstructed past erosion rates show no long-term increase for the past six million years. This stability suggests that climatic changes during the late Cenozoic have an undetectable impact on the erosion patterns in the Himalayas, at least on the ten thousand to million year timescales accounted for by our dataset. Long-term Himalayan erosion rates remained stable through the global climatic changes of the past six million years, according to the cosmogenic nuclide composition of terrestrial sediments recovered from the Bay of Bengal.

Crustal-scale duplexing beneath the Yarlung Zangbo suture in the western Himalaya

Abstract: The fate of the Indian plate during continental collision with Asian terranes, and the proportion of the Indian crust that is underthrust or subducted beneath Tibet as opposed to transferred to the upper (Himalayan) plate, are much debated. The active geometry of low-angle underthrusting or subduction of the Indian plate beneath the Lesser and Greater Himalayan thrust sheets is well known from seismic imaging. Previously, only lower-resolution images of the Main Himalayan Thrust have been obtained beneath the Yarlung Zangbo suture that separates Indian and Asian rocks at the surface. It remains controversial whether the orogenic wedge between the Main Himalayan Thrust and the Yarlung Zangbo suture, formed of Indian crust transferred to the upper plate, is evolving by thrust-faulting in a critical-taper wedge or by southward extrusion of a ductile channel flow. Here we present a seismic reflection profile across the western Himalaya at 81.5° E, and show that the Main Himalayan Thrust dips ∼20° to ∼60 km depth beneath the Yarlung Zangbo suture, approaching a continuous Moho reflection at ∼70–75 km depth. The Indian crust being transported northwards beyond the Yarlung Zangbo suture is no more than ∼15 km thick, reduced from its original ∼40 km thickness by transfer of material from the lower plate to the upper plate through crustal-scale duplexing. The fate of the Indian plate during collision with Asia is debated. Seismic images of the western Himalaya reveal large-scale thrust faults that transfer Indian crust upwards, into the overriding Asian plate.

Glacier melt, air temperature and energy balance in different climates: the Bolivian Tropics, the French Alps and northern Sweden

Abstract: [1] This study investigates the physical basis of temperature-index models for three glaciers in contrasting climates: Zongo (16°S, 5050 m, Bolivian Tropics), St Sorlin (45°N, 2760 m, French Alps), and Storglaciaren (67°N, 1370 m, northern Sweden). The daily energy fluxes were computed during melt seasons and correlated with each other and with air temperature on and outside the glacier. The relative contribution of each flux to the correlations between temperature and melt energy was assessed. At Zongo, net short-wave radiation controls the variability of the energy balance and is poorly correlated to temperature. On tropical glaciers, temperature remains low and varies little, melt energy is poorly correlated to temperature, and degree-day models are not appropriate to simulate daily melting. At the yearly scale, the temperature is better correlated to the mass balance because it integrates the ablation and the accumulation processes over a long time period. At Sorlin, the turbulent sensible heat flux is greater because of higher temperatures, but melt variability is still controlled by short-wave radiation. Temperature correlates well with melt energy mainly through short-wave radiation, probably because of diurnal advection of warm air from the valley. At Storglaciaren, high correlations between temperature and melt energy result from substantial variability of the sensible and latent heat fluxes (which both supply energy to the glacier), and their good correlations with temperature. In the three climates, long-wave irradiance is the main source of energy, but its variability is small and poorly correlated to the temperature mainly because cloud emissions dominate its variability.

Fault Segmentation as Constraint to the Occurrence of the Main Shocks of the 2016 Central Italy Seismic Sequence

Abstract: We perform the finite-extent fault inversion of the three main events of the 2016 Central Italy seismic sequence using near-source strong-motion records. We demonstrate that both earthquakes nucleation and rupture propagation were controlled by segmentation of the (N)NW–(S)SE-trending Quaternary normal faults. The first shock of the sequence (August 24th, Mw 6.0) ruptured at the relay zone between the Laga Mts (LF) and the Cordone del Vettore (CVF) normal faults. The second shock (October 26th, Mw 5.9) nucleated at a minor relay zone within the Mt. Vettore–Mt. Bove fault (VBF), while the third and largest one (October 30th, Mw 6.5) initiated at the relay zone between the VBF and CVF, triggering the multiple rupture of the VBF, CVF and probably LF. We show that this latter relay zone corresponds to the deeper, high-angle, fault-zone of the Sibillini Mts cross-structure, a thrust-ramp inherited from the Miocene-Pliocene contractional phase of the Apennines. This structure acted as a barrier to rupture propagation of the first two events thus defining an area of large stress concentration until it acted as the initiator of the rupture originating the largest Mw 6.5 event that crossed the barrier itself. We suggest that the “young” CVF have started to cut through the barrier acting as a soft-linkage between the two long-lived LF and VBF. The evidence that coseismic cumulative slip shows a maximum at the CVF, provided by both slip inversion and original surface rupture data, suggests that the CVF is growing faster than the adjacent faults.