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Recovering the seismic history of multiple segments within a fault system provides a spatiotemporal framework for the fault activity across the system. This kind of data is essential for improving our understanding of how faults interact during earthquake cycles and how they are distributed within a fault system. Bedrock fault scarps, reaching up to 10‐m height, are abundant across the Bet Kerem fault system, Galilee, northern Israel. Using the 36Cl exposure dating method, we recovered the last 30 ka scarp exhumation history of three fault segments from the Bet Kerem fault system. Results indicate that the three faults were active simultaneously in at least three distinguished activity periods, during which a minimum of 1.2 m of surface rupturing occurred in each period. The synchronized activity and total surface rupture at each activity period suggest that the three dated segments were ruptured simultaneously by the same earthquake. That is, a multi‐segment rupture earthquake and that each activity period included a cluster of at least two large multi‐segment earthquakes. The results also indicate a recurrence interval between clusters of 3.5–4.5 ka and the existence of a seismic super cycle with a recurrence interval of about 13 ka. Plain Language Summary: Surface rupture occurs when a large earthquake caused by movement along a fault, breaks through the Earth's surface. The 36Cl cosmogenic dating is used to recover past earthquakes that generate surface rupture. Using this method to constrain the fault activity over multiple earthquake cycles and across fault systems provides essential data to understand how earthquakes behave along fault systems and how faults interact during the earthquakes. We recovered the last 30 ka surface rupture history of three fault segments, each approximately 5 km in length, from the Bet Kerem fault system, northern Israel, using the 36Cl exposure dating method. Results indicate that the three segments were active in at least three distinguished periods, in each of which a minimum of 1.2 m of surface rupturing occurred at each fault segment. The amount of surface rupture observed at each of the segments is too large to be generated by one single earthquake that only ruptures the fault segment. However, when all segments are considered together their total length corresponds well with the amount of offset. We, therefore, suggest that the large surface rupture observed at each activity period is caused by large earthquakes that ruptured the three dated segments at once. Key Points: The earthquake history of three normal fault segments is reconstructed with 36Cl exposure datingOver the last 30 ka, the three fault segments ruptured the earth's surface simultaneously in at least three distinguished periodsDuring each activity period, at least two earthquakes occurred very closely in time, each resulting in a rupture of the three segments [ABSTRACT FROM AUTHOR]

The Golan Heights plateau in northern Israel is underlaid by volcanic rocks ranging in age from ~5.5 to 0.1 Ma. Throughout the Golan Heights, these rocks are covered by shallow soils that rarely exceed 0.5 m in depth. The soils are generally assumed to form a chronosequence, in which their ages correspond to those of the basalts they cover. Such age correspondence would imply that the soils have been slowly accumulating over hundreds of thousands to a few million years, suggesting a generally stable system. The ages of these soils and their temporal correlation to the basalts, however, have never been determined or tested. Here, we present age constraints for the soils of the Golan Heights. Soils were surveyed and sampled with their corresponding basalt bedrock. Mass balance calculations based on conservative immobile elements, coupled with 36Cl-based basalt denudation rates, suggest that the soil ages are decoupled from the ages of the underlying basalts, and represent up to a few thousand years of soil production, at most. This time frame is orders of magnitude shorter than the basalt age, challenging the prevalent assumption that the soils form a chronosequence. Our findings strongly suggest that erosion is a significant factor controlling soil formation and accumulation on the plateau, despite the generally flat morphology of the Golan Heights. The erosion is associated with tectonic activity along the Dead Sea transform, with the development of the Kinarot and Hula valleys, and with the consequential development of drainage systems of various sizes on the plateau. Throughout the Golan Heights, the timing of volcanic activity in relation to the development of the valleys and drainage systems also appears to strongly affect soil development and accumulation. [ABSTRACT FROM AUTHOR]

The impact of climate on topography, which is a theme in landscape evolution studies, has been demonstrated, mostly, at mountain range scales and across climate zones. However, in drylands, spatiotemporal discontinuities of rainfall and the crucial role of extreme rainstorms raise questions and challenges in identifying climate properties that govern surface processes. Here, we combine methods to examine hyperarid escarpment sensitivity to storm‐scale forcing. Using a high‐resolution DEM and field measurements, we analyzed the topography of a 40‐km‐long escarpment in the Negev desert (Israel). We also used rainfall intensity data from a convection‐permitting numerical weather model for storm‐scale statistical analysis. We conducted hydrological simulations of synthetic rainstorms, revealing the frequency of sediment mobilization along the sub‐cliff slopes. Results show that cliff gradients along the hyperarid escarpment increase systematically from the wetter (90 mm yr−1) southwestern to the drier (45 mm yr−1) northeastern sides. Also, sub‐cliff slopes at the southwestern study site are longer and associated with milder gradients and coarser sediments. Storm‐scale statistical analysis reveals a trend of increasing extreme (>10 years return‐period) intensities toward the northeast site, opposite to the trend in mean annual rainfall. Hydrological simulations based on these statistics indicate a higher frequency of sediment mobilization in the northeast, which can explain the pronounced topographic differences between the sites. The variations in landscape and rainstorm properties across a relatively short distance highlight the sensitivity of arid landforms to extreme events. Plain Language Summary: Identifying the link between climatic properties and topography helps to elucidate key controlling processes affecting Earth's landscape evolution. In drylands, however, it is harder to associate topography with average climate as surface processes are significantly affected by spatially disconnected, discrete and short‐duration rainstorms. In this study, we investigate whether variations in rainstorm properties can account for topographic differences along a 40‐km‐long hyperarid escarpment. Results indicate that in the drier parts of the escarpment, cliffs are steeper, and slopes are covered by finer sediment. Rainstorm statistical analysis indicates that the drier part of the escarpment is associated with extreme rainstorms characterized by higher rainfall intensities. We demonstrate that these storms mobilize sediment more frequently in the drier part of the escarpment, which can explain the pronounced topographic differences along the escarpment. This study presents a rarely‐recognized link between small‐scale variations in arid rainstorm properties and topography and highlights the susceptibility of arid landscapes to extreme rainstorms. Key Points: The morphology of cliffs and sub‐cliff slopes varies significantly with rainfall along a 40‐km hyperarid escarpmentThe observed morphologic variability is triggered primarily by differences in sediment mobilization frequencies on sub‐cliff slopesRainstorm properties in arid landscapes could change over relatively short distances and leave a significant geomorphic imprint [ABSTRACT FROM AUTHOR]

The progress of miniaturization in integrated electronics has led to atomic and nanometer‐sized dopant devices in silicon. Such structures can be fabricated routinely by hydrogen resist lithography, using various dopants such as P and As. However, the ability to non‐destructively obtain atomic‐species‐specific images of the final structure, which would be an indispensable tool for building more complex nano‐scale devices, such as quantum co‐processors, remains an unresolved challenge. Here, X‐ray fluorescence is exploited to create an element‐specific image of As dopants in Si, with dopant densities in absolute units and a resolution limited by the beam focal size (here ≈1 µm), without affecting the device's low temperature electronic properties. The As densities provided by the X‐ray data are compared to those derived from Hall effect measurements as well as the standard non‐repeatable, scanning tunneling microscopy and secondary ion mass spectroscopy, techniques. Before and after the X‐ray experiments, we also measured the magneto‐conductance, which is dominated by weak localization, a quantum interference effect extremely sensitive to sample dimensions and disorder. Notwithstanding the 1.5 × 1010 Sv (1.5 × 1016 Rad cm−2) exposure of the device to X‐rays, all transport data are unchanged to within experimental errors, corresponding to upper bounds of 0.2 Angstroms for the radiation‐induced motion of the typical As atom and 3% for the loss of activated, carrier‐contributing dopants. With next generation synchrotron radiation sources and more advanced optics, the authors foresee that it will be possible to obtain X‐ray images of single dopant atoms within resolved radii of 5 nm. [ABSTRACT FROM AUTHOR]

Evaluating the impact and implications of eolian repositories that mark large-scale climatic transitions requires knowledge about the timing of their emplacement and the mechanisms responsible for their production, which remain highly uncertain. Here we apply numerical modeling of cosmogenic nuclide data, measured in the largest continuous terrestrial body of sand on Earth, to determine settings under which the sand was generated, by constraining the timing of sand introduction into the interior of southern Africa. Our findings reveal that major events of sand formation and accumulation in the Kalahari Basin occurred between ~2.2 and 1 Myr ago. The establishment of the Kalahari sand field corresponds to regional, continental, and global scale morphotectonic and climatic changes that contributed to the mass production and widespread dispersion of sand. These changes substantially altered existing habitats, thus constituting a crucial milestone for flora, fauna, and hominins in southern Africa during the Pleistocene. Modeling cosmogenic nuclides concentrations from Kalahari Desert Sand reveals the time of sand introduction into the landscape. This coincides with morphotectonic and climatic changes that could have triggered sand production and its impact on the environment. [ABSTRACT FROM AUTHOR]

The weathering of continental surfaces and the transport of sediments via rivers into the oceans is an integral part of the dynamic processes that shape the Earth's surface. To understand how tectonic and climatic forcings control regional rates of weathering, we must be able to identify their effects on sedimentary archives over geologic timescales. Cosmogenic nuclides are a valuable tool to study rates of surface processes and have long been applied in fluvial systems to quantify basin‐wide erosion rates. However, in large rivers, continual processes of erosion and deposition during sediment transport make it difficult to constrain how long sediments spend within the fluvial system. In this study, we examine the role of rivers in buffering erosional signals by constraining the timescales of fluvial transport in large rivers across the world. We apply a stochastic numerical model based on measurements of cosmogenic nuclides concentrations and calculate sediment residence times of 104–105 years in large rivers. These timescales are equal to or longer than climatic cycles, implying that changes to rates of erosion brought on by climatic variations are buffered during transport in large rivers and may not be recognizable in the sedimentary record. Plain Language Summary: Large rivers are the most effective agent for transporting sediment from the weathering continents into the oceans, with the world's biggest rivers draining nearly half of the continental surface. In this work, we calculate the time sediment spends in large rivers between weathering and deposition in four large rivers across the world. We do this by simulating the processes of sediment erosion and deposition in rivers and applying this model to new and existing data. The results of this model show that the time it takes for sand to be eroded from the source rock and transported down the river is tens to hundreds of thousands of years. These extended timescales mean that sediment transport in large rivers buffers the effect of climatic fluctuations on weathering rates. This finding can explain how seemingly contradictory evidence of climatic variations impact erosion rates, while products of erosion measured at the oceans show no significant changes during these times. Key Points: We constructed a numerical model simulating sediment transport dynamics in large‐scale fluvial systems constrained by cosmogenic nuclidesExamining data from four large rivers across the world, we constrain sediment residence time in large riversEstimated residence times of sediments in four large rivers across the world range 104–105 yr [ABSTRACT FROM AUTHOR]

To understand the timing of deglaciation of the northernmost marine-terminating glaciers of the Cordilleran Ice Sheet (CIS), we obtained 26 10Be surface-exposure ages from glacially scoured bedrock surfaces in Prince William Sound (PWS), Alaska. We sampled six elevation transects between sea level and 620 m and spanning a distance of 14 to 70 km along ice flow paths. Most transect age–elevation patterns could not be explained by a simple model of thinning ice; the patterns provide evidence for lingering ice cover and possible inheritance. A reliable set of 20 ages ranges between 17.4 ± 2.0 and 11.6 ± 2.8 ka and indicates ice receded from northwestern PWS around 14.3 ± 1.6 ka, thinned at a rate of ~120–160 m/ka, and retreated from sea-level sites at 12.9 ± 1.1 ka at a rate of 20 m/yr. The retreat rate likely slowed as glaciers retreated into northern PWS. These results are consistent with the growing body of reported deglacial constraints on collapse of ice sheets along the Alaska margin indicating collapse of the CIS soon after 17 ka. These data are consistent with paleotemperature data indicating that a warming North Pacific Ocean caused catastrophic collapse of this part of the CIS. [ABSTRACT FROM AUTHOR]

The structural depression that occupies the Okavango Basin in southern Africa comprises a depo-centre within the intracratonic Kalahari Basin where sediments of the Cenozoic Kalahari Group have accumulated. The Okavango Basin has been formed due to stretching and subsidence at an area of diffused deformation, southwestwards to the main East African Rift System (EARS). Sediments from two full Kalahari Group sequences, located on opposite sides of the Gumare Fault that forms a major fault within the Okavango Basin, were studied to determine their provenance and chronology. Terrestrial Cosmogenic Nuclide (TCN) 26Al/10Be burial dating was used to constrain a chronostratigraphical framework, and Pb, Sr, and Nd isotopic ratios combined with geochemical and sedimentological analyses were applied to track the source areas of the sediments. Results indicate the following sequence of basin filling: (a) Accumulation between ca. 4-3 Ma during which the currently downthrown (southern) block received a mixture of sediments mostly from the Choma-Kalomo, Ghanzi-Chobe, and Damara terranes, and possibly from the Lufilian Belt and/or Karoo basalts during earlier stages of deposition. Simultaneously, the upthrown (northern) block received sediments from more distant Archean sources in the Zimbabwe and/or Kasai cratons, (b) Hiatus in sedimentation occurred at both sites between ca. 3-2 Ma, (c) Sediments on both sides of the Gumare Fault share a similar source (Angolan Shield) with minor distinct contributions to the downthrown block from the Kasai Craton and local sources input to the upthrown block, and (d) Regional distribution of aeolian sand since at least 1 Ma. The change in source areas is attributed to rearrangements of the drainage systems that were probably linked to vertical crustal movements on the margins of the Okavango Basin. The tectonically induced morphodynamics controlled the landscape evolution of the endorheic basin where vast lakes, wetlands and salt pans have developed through time. [ABSTRACT FROM AUTHOR]

Featured Application: Knowledge of temperature dependence of refractive indices of Ge and Si at THz frequencies is required in many applications where these materials are used for THz devices and optical components. Refractive indices of high resistivity Si and Ge were measured at temperatures between 4–296 K and at frequencies between 4.2–7.7 THz using a Fourier-transform spectrometer (FTS) in transmission mode. A phenomenological model of the temperature dependence of the refractive index is proposed. [ABSTRACT FROM AUTHOR]

In this work, we utilize a novel application of cosmogenic 21Ne measurements in chert to compare exposure times measured in eroding surfaces in the central Jordanian Plateau with exposure times from chert pebbles transported by the Miocene Hazeva River. The Miocene Hazeva River was a large fluvial system (estimated catchment size > 100 000 km 2) that drained the Arabian Plateau and Sinai Peninsula into the Mediterranean Sea during the early-to-mid Miocene. It was established after the rifting of the Red Sea uplifted the Arabian Plateau during the Oligocene. Following late-Miocene-to-early-Pliocene subsidence along the Dead Sea rift, the Hazeva drainage system was abandoned and dissected, resulting in new drainage divides on either side of the rift. We find modern erosion rates derived from cosmogenic 21Ne , 26Al , and 10Be in exposed in situ chert nodules to be extremely slow (between 2–4 mm kyr -1). Comparison between modern and paleo-erosion rates, measured in chert pebbles, is not straightforward, as cosmogenic 21Ne was acquired partly during bedrock erosion and partly during transport of these pebbles in the Hazeva River. However, 21Ne exposure times calculated in Miocene cherts are generally shorter (ranging between 0-0+59 and 242±113 kyr) compared to exposure times calculated in the currently eroding chert nodules presented here (269±49 and 378±76 kyr) and other chert surfaces currently eroding in hyperarid environments. Miocene exposure times are shorter even when considering that they account for bedrock erosion in addition to maintained transport along this large river. Shorter exposure times in Miocene cherts correspond to faster paleo-erosion rates, which we attribute to a combination of continuous surface uplift and significantly wetter climatic conditions during the early-to-mid Miocene. [ABSTRACT FROM AUTHOR]

Optically stimulated luminescence (OSL) of quartz is an established technique for dating late Pleistocene to late Holocene sediments. Unfortunately, this method is often limited to up to 100 ka (thousands of years). Recent developments in new extended-range luminescence techniques show great potential for dating older sediments of middle and even early Pleistocene age. These methods include thermally transferred OSL (TT-OSL) and violet stimulated luminescence (VSL) for quartz and post-infrared infrared stimulated luminescence (pIRIR) for feldspar. Here we investigate the luminescence behaviour of the TT-OSL, VSL, and pIRIR signals of quartz and feldspar minerals of aeolian sediments of Nilotic origin from the eastern Mediterranean. We sampled a 15m thick sequence (Kerem Shalom) comprising sandy calcic palaeosols, which is part of a sand sheet that covers an extensive region in south-western Israel. Dose recovery and bleaching experiments under natural conditions indicated that the pIRIR250 signal is the most suitable for dating the Nilotic feldspar. Luminescence intensity profiles revealed natural saturation of the three signals at the same depth of ~6 m, indicating that ages of samples below that depth are minimum ages. Using TT-OSL and pIRIR250, a minimum age of 715 ka for the base of the section was obtained, suggesting aeolian sand accumulation along the eastern Mediterranean coastal plain already since the early Pleistocene. Our results indicate that both TT-OSL and pIRIR250 can accurately date aeolian sediments of Nilotic origin up to 200 ka and that minimum ages can be provided for older samples up to the early Pleistocene. [ABSTRACT FROM AUTHOR]

Quantum cascade lasers (QCLs) are compact sources that have demonstrated high output powers at terahertz (THz) frequencies. To date, all THz QCLs have been realized in III-V materials. Results are presented from Si1-xGex quantum cascade superlattice designs emitting at around 3 THz which have been grown in two different chemical vapor deposition systems. The key to achieving successful electroluminescence at THz frequencies in a p-type system has been to strain the light-hole states to energies well above the radiative subband states. To accurately model the emission wavelengths, a 6-band k·p tool which includes the effects of nonabrupt heterointerfaces has been used to predict the characteristics of the emitters. X-ray diffraction and transmission electron microscopy have been used along with Fourier transform infrared spectroscopy to fully characterize the samples. A number of methods to improve the gain from the designs are suggested. [ABSTRACT FROM AUTHOR]

A multidisciplinary study was conducted in a newly discovered Paleolithic locality, named 'Evron Landfill. This locality is a part of the Lower Paleolithic complex of 'Evron located at the western Galilee, Israel. Examination of artifacts has enabled the cultural attribution of 'Evron Landfill to the Early Acheulian, while detailed paleomagnetic stratigraphy places the hominin occupations near the Brunhes–Matuyama transition ~0.77 Ma. This age is constrained by cosmogenic isotope burial dating of the sediments overlying the Paleolithic finds, providing a minimum age of ~0.66±0.11 Ma for hominin activity at the site. These results are further supported by the biochronological information derived from the faunal assemblage. Comparative analyses of faunal remains and lithic artifacts from 'Evron Landfill demonstrate similarities to the assemblages from the Early Acheulian site of Evron Quarry, located ~300 m to the south. Pedo-sedimentological analyses indicate that hominin activity took place in a marsh environment in proximity to the Mediterranean coast, which probably fluctuated in both space and time with a fluvial environment. In addition, this study provides important data about ancient coastal activity during the early to middle Pleistocene. [ABSTRACT FROM AUTHOR]

The Dead Sea Transform (DST) accounts for ~105 km of left-lateral slip between the Arabian plate and the Sinai subplate since the Miocene. Paleoseismic studies along the Arava Valley segment of the DST suggest that late Quaternary deformation has been primarily concentrated along the axis of the transform valley. Here, we examine late Quaternary changes in drainage system characteristics and attribute them to recent tectonic deformation in this region. Field-based geomorphic mapping, topographic cross sections, and optically stimulated luminescence (OSL) dating of fluvial deposits were used to map and date recent changes in the fluvial characteristics of catchments along the western margin of the southern Arava. Our results reveal coeval migration of channels, consistent with tectonically induced surface tilting caused by north–south compressional deformation along the western margin of the transform valley. OSL dating indicates this tilting was initiated in the late Pleistocene and continued at least into the mid-Holocene. The late Quaternary tectonic deformation along the southern Arava segment of the DST is distributed across a wider zone than previously considered and extends out to the margins of the transform valley. We associate the inferred wider deformation zone to possible changes in the geometry of motion along the DST. [ABSTRACT FROM AUTHOR]

Kalahari Group sediments accumulated in the Kalahari basin, which started forming during the breakup of Gondwana in the early Cretaceous. These sediments cover an extensive part of southern Africa and form a low-relief landscape. Current models assume that the Kalahari Group accumulated throughout the entire Cenozoic. However, chronology has been restricted to early–middle Cenozoic biostratigraphic correlations and to OSL dating of only the past ~ 300 ka. We present a new chronological framework that reveals a dynamic nature of sedimentation in the southern Kalahari. Cosmogenic burial ages obtained from a 55 m section of Kalahari Group sediments from the Mamatwan Mine, southern Kalahari, indicate that the majority of deposition at this location occurred rapidly at 1–1.2 Ma. This Pleistocene sequence overlies the Archaean basement, forming a significant hiatus that permits the possibility of many Phanerozoic cycles of deposition and erosion no longer preserved in the sedimentary record. Our data also establish the existence of a shallow early–middle Pleistocene water body that persisted for > 450 ka prior to this rapid period of deposition. Evidence from neighboring archeological excavations in southern Africa suggests an association of high-density hominin occupation with this water body. [ABSTRACT FROM AUTHOR]

Most research focuses on varying the resonator and dielectric spacer to configure the absorption and resonant frequency of terahertz (THz) metamaterial absorbers (MAs), where a metal ground plane is used as a perfect reflector of incident THz waves. In this paper, we modulate the MAs absorption by varying the conductivity of the ground plane. Two THz MAs were fabricated by replacing the gold ground planes with cobalt silicide films, and the measured absorptivity decreases by 4% for the electric resonance and increases by 44% for the dipole resonance. Our quantitative analysis reveals that when the conductivity of the ground plane decreases from 1.8 x 107S/m to 3.0 x 105S/m, the absorptivity of the electric resonance decreases by 23%, while that of the dipole resonance increases by 62%. Our approach also provides a practical method to measure the electric conductivity of conductive films in the THz regime. [ABSTRACT FROM AUTHOR]

ABSTRACT: Mesas are ubiquitous landforms in arid and semiarid regions and are often characterized by horizontal stratified erodible rocks capped by more resistant strata. The accepted conceptual model for mesa evolution and degradation considers reduction in the width of the mesa flat‐top plateau due to cliff retreat but ignores possible denudation of the mesa flat‐top and the rates and mechanism of erosion. In this study we examine mesas in the northeastern hyperarid Negev Desert where they appear in various sizes and morphologies and represent different stages of mesa evolution. The variety of mesas within a single climatic zone allows examination of the process of mesa evolution through time. Two of the four sites examined are characterized by a relatively wide (200–230 m) flat‐top and a thick caprock whereas the other two are characterized by a much narrower remnant flat‐top (several meters) and thinner caprock. We use the concentration of the cosmogenic nuclide 10Be for: (a) determining the chronology of the various geomorphic features associated with the mesa; and (b) understanding geomorphic processes forming the mesa. The 10Be data, combined with field observations, suggest a correlation between the width of flat‐top mesa and the denudation and cliff retreat rates. Our results demonstrate that: (a) cliff retreat rates decrease with decreasing width of the flat‐top mesa; (b) vertical denudation rates increase with decreasing width of the flat‐top mesa below a critical value (~60 m, for the Negev Desert); (c) the reduction in the width of the flat‐top mesa is driven mainly by cliff retreat accompanied by extremely slow vertical denudation rate which can persist for a very long time (>106 Ma); and (d) when the width of the mesa decreases below a certain threshold, its rate of denudation increases dramatically and mesa degradation is completed in a short time. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

We report the characteristics of a simple complementary metal-oxide-semiconductor compatible terahertz detector device with low response time (nanoseconds) determined using a short-pulse, high intensity free-electron laser. The noise equivalent power was 1×10-11 W Hz-1/2. The detector has an enhanced response over narrow bands, most notably at 9.5 THz, with a continuum response at higher frequencies. Using such a device, the dynamics of donors in silicon can be explored, a system which has great potential for quantum information processing. [ABSTRACT FROM AUTHOR]

The Dead Sea fault (DSF) is one of the most active plate boundaries in the world. Understanding the Quaternary history and sediments of the DSF requires investigation into the Neogene development of this plate boundary. DSF lateral motion preceded significant extension and rift morphology by ~10Ma. Sediments of the Sedom Formation, dated here between 5.0±0.5Ma and 6.2-2.1+infMa, yielded extremely low 10Be concentrations and 26Al is absent. These reflect the antiquity of the sediments, deposited in the Sedom Lagoon, which evolved in a subdued landscape and was connected to the Mediterranean Sea. The base of the overlying Amora Formation, deposited in the terminal Amora Lake which developed under increasing relief that promoted escarpment incision, was dated at 3.3-0.8+0.9Ma. Burial ages of fluvial sediments within caves (3.4±0.2Ma and 3.6±0.4Ma) represent the timing of initial incision. Initial DSF topography coincides with the earliest Red Sea MORB's and the East Anatolian fault initiation. These suggest a change in the relative Arabian-African plate motion. This change introduced the rifting component to the DSF followed by a significant subsidence, margin uplift, and a reorganization of relief and drainage pattern in the region resulting in the topographic framework observed today. [ABSTRACT FROM AUTHOR]

Rockfall ages in tectonically active regions provide information regarding frequency and magnitude of earthquakes. In the hyper-arid environment of the Dead Sea fault (DSF), southern Israel, rockfalls are most probably triggered by earthquakes. We dated rockfalls along the western margin of the DSF using terrestrial cosmogenic nuclides (TCN). At each rockfall site, samples were collected from simultaneously exposed conjugate boulders and cliff surfaces. Such conjugate samples initially had identical pre-fall (“inherited”) TCN concentrations. After boulder detachment, these surfaces were dosed by different production rates due to differences in post-fall shielding and geometry. However, in our study area, pre-rockfall inheritance and post-rockfall production rates of TCN cannot be evaluated. Therefore, we developed a numerical approach and demonstrated a way to overcome the above-mentioned problems. This approach can be applied in other settings where rockfalls cannot be dated by simple exposure dating. Results suggest rockfall ages between 3.6±0.8 and 4.7±0.7ka. OSL ages of sediment accumulated behind the boulders range between 0.6±0.1 and 3.4±1.4ka and support the TCN results. Our ages agree with dated earthquakes determined in paleoseismic studies along the entire length of the DSF and support the observation of intensive earthquake activity around 4–5ka. [ABSTRACT FROM AUTHOR]

ABSTRACT Calcrete-coated remnants of landslide debris and alluvial deposits are exposed along the presently stable hillslopes of the Soreq drainage, Judea Hills, Israel. These remnants indicate that a transition from landslide-dominated terrain to dissolution-controlled hillslope erosion had occurred. This transition possibly occurred due to the significant decrease in tectonic uplift during the late Cenozoic. The study area is characterized by sub-humid Mediterranean climate. The drainage hillslopes are typically mantled by thick calcrete crusts overlying Upper Cretaceous marine carbonate rocks. Using TT-OSL dating of aeolian quartz grains incorporated in the calcrete which cements an ancient landslide deposit, we conclude that incision of ~100 m occurred from 1056 ± 262 to 688 ± 86 ka due to ~0·3° westward tilt of the region; such incision invoked high frequency of landslide activity in the drainage. The ages of a younger landslide remnant, alluvial terrace, and alluvial fan, all situated only a few meters above the present level of the active streambed, range between 688 ± 86 ka and 244 ± 25 ka and indicate that since 688 ± 86 the Soreq base level had stabilized and that landslide activity decreased significantly by the middle Pleistocene. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: Colluvial sediments of talus relicts (“talus flatirons”) around mesas preserve a record that sheds light on slope-forming processes at temporal scales >103 yr. The sedimentology and soil stratigraphy of two groups of talus flatirons in the northeastern hyperarid Negev desert reveal four deposition events in the younger talus and at least two in the older one. Numerical modeling of high-resolution 10Be depth profiles suggests that these taluses were deposited during the middle Pleistocene; the younger talus group first depositional event occurred at 551 −142 +80 ka and its abandonment occurred at 270 −38 +17 ka. The abandonment of the older talus group and stabilization of its surface occurred at 497 −114 +176 ka. These ages indicate that the development of the studied talus sequence is not specifically associated with Pleistocene glacial–interglacial cycles. The 10Be modeled concentrations indicate significant differences in the average inheritance of talus flatirons of different groups. These differences can be attributed to variability in the transport distance and duration of gravel exposure during transport but could also reflect some temporal variability in cliff retreat. Our results also demonstrate that talus slopes in hyperarid areas, despite their steepness, can store sediment for long periods (~500ka) and thus constitute a valuable archive. [Copyright &y& Elsevier]

The current detailed chronostratigraphic framework of the last 1 Ma of an eastern Mediterranean sequence (Haifa Bay, Israel) aims to examine the relative roles of sea-level changes, climate and tectonics. Seven continuous marine cores, up to ∼120 m long, were recovered from shallow water depths. The cores were dated by optically stimulated luminescence, 14C, magnetostratigraphy, 230Th/234U, 26Al/10Be, occurrence of index fossils and correlated to the global sea-level curve and Marine Isotope Stages (MIS). The sedimentary sequence accumulated during the last ca. 1.0 Ma consists of 21 transgression-regression units with hiatuses between them. Five marine/terrestrial cycles, which occur in the lower part of the sequence, are attributed to the Jaramillo subchron and the Brunhes-Matuyama boundary, and correspond to MIS 29-21. The top ∼50 m includes three sedimentary cycles deposited in the last ca. 400 ka. The regressive phases during this interval correspond to Glacial MIS 8, 6 and 2, while the transgressions correspond to Interglacial MIS 11, 7, 5 and 1. Thus, for the first time, this study documents the longest Quaternary succession dated so far in a key area of the Levant, sensitive to global history of sea-level changes and glacial/interglacial fluctuations. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

A cased and sealed borehole in the Northern Barbados accretionary complex was the site of the first attempts to measure permeability in situ along a plate boundary décollement. Three separate efforts at Hole 949C yielded permeability estimates for the décollement spanning four orders of magnitude. An analysis of problems encountered during installation of the casing and seals provides insights into how the borehole conditions may have led to the wide range of results. During the installation, sediments from the surrounding formation repeatedly intruded into the borehole and casing. Stress analysis shows that the weak sediments were deforming plastically and the radial and tangential stresses around the borehole were significantly lower than lithostatic. This perturbed stress state may explain why the test pressure records showed indications of hydrofracture at pressures below lithostatic, and permeabilities rose rapidly as the estimated effective stress dropped below 0.8 MPa. Even after the borehole was sealed, the plastic deformation of the formation and relatively large gap of the wire wrapped screen allowed sediment to flow into the casing. Force equilibrium calculations predict sediment would have filled the borehole to 10 cm above the top of the screen by the time slug tests were conducted 1.5 years after the borehole was sealed. Reanalysis of the slug test results with these conditions yields several orders of magnitude higher permeability estimates than the original analysis which assumed an open casing. Overall the results based on only the tests with no sign of hydrofracture yield a permeability range of 10-10 m and a rate of increase in permeability with decreasing effective stress consistent with laboratory tests on samples from the décollement zone. [ABSTRACT FROM AUTHOR]

Abstract: We present 10Be exposure ages from moraines in the Delta River Valley, a reference locality for Pleistocene glaciation in the northern Alaska Range. The ages are from material deposited during the Delta and Donnelly glaciations, which have been correlated with MIS 6 and 2, respectively. 10Be chronology indicates that at least part of the Delta moraine stabilized during MIS 4/3, and that the Donnelly moraine stabilized ∼17ka. These ages correlate with other dates from the Alaska Range and other regions in Alaska, suggesting synchronicity across Beringia during pulses of late Pleistocene glaciation. Several sample types were collected: boulders, single clasts, and gravel samples (amalgamated small clasts) from around boulders as well as from surfaces devoid of boulders. Comparing 10Be ages of these sample types reveals the influence of pre/post-depositional processes, including boulder erosion, boulder exhumation, and moraine surface lowering. These processes occur continuously but seem to accelerate during and immediately after successive glacial episodes. The result is a multi-peak age distribution indicating that once a moraine persists through subsequent glaciations the chronological significance of cosmogenic ages derived from samples collected on that moraine diminishes significantly. The absence of Holocene ages implies relatively minor exhumation and/or weathering since 12ka. [Copyright &y& Elsevier]

We investigate a kilometer-scale steep relay ramp structure in the Galilee, northern Israel. The data indicate an asymmetric fold above the buried tip of the southern boundary fault as well as at the lower part of the ramp. Structural analysis suggests that the buried tip of the bounding fault is only a few hundred meters below the surface. A sequence of colluvial wedges, exposed at the base of the southern flank of the relay ramp over the blind tip of the boundary fault, presents successively decreasing angles from 67° at the bottom to 30° at the top. The lower three wedges rest at angles greater than the angle of repose, suggesting tilting during and after deposition. We suggest that the increasing angle of the wedges is the result of the development of the monocline over the buried tip of the boundary fault, which in turn reflects the development of the entire relay ramp structure. Paleomagnetic measurements test this hypothesis. Samples from three of the four lower wedges and the carbonate fill in the fractured bedrock yield northerly declination and positive inclination. Inclination anomalies are 19.4° ± 3.3° and 11.3° ± 1.8° for the fractured bedrock and the wedges, respectively. These anomalies reflect part of the tilt. Paleomagnetic measurements and optically stimulated luminescence (OSL) constrain the time of initial deformation of the monocline above the southern boundary fault between 780 ka and 461 ± 75 ka (OSL age of wedge 1) and the termination of deformation to 176 ± 22 ka (OSL age of wedge 5). These bounding ages suggest tilting rates that range between 1°/16 kyr and 1°/8 kyr. Termination of tilting along the southern flank of the relay ramp and the fact that the tip of the buried normal fault is only a few hundreds of meters below the surface suggest that the relay ramp may be close to being breached by a connecting fault. [ABSTRACT FROM AUTHOR]

Producing an electrically pumped silicon-based laser at terahertz frequencies is gaining increased attention these days. This paper reviews the recent advances in the search for a silicon-based terahertz laser. Topics covered include resonant tunneling in p-type Si/SiGe, terahertz intersubband electroluminescence from quantum cascade structures, intersubband lifetime measurements in Si/SiGe quantum wells, enhanced optical guiding using buried silicide layers, and the potential for exploiting common impurity dopants in silicon such as boron and phosphorus to realize a terahertz laser. [ABSTRACT FROM PUBLISHER]

Abstract: Cosmogenic nuclide concentrations measured on abandoned fan surfaces along the Mojave section of the San Andreas Fault suggest that sediment is generated, transported, and removed from the fans on the order of 30–40 kyr. We measured in situ produced cosmogenic 10Be, and in some cases 26Al, in boulders (n = 15), surface sediment (n = 15), and one depth profile (n = 9). Nuclide concentrations in surface sediments and boulders underestimate fan ages, suggesting that 10Be accumulation is largely controlled by the geomorphic processes that operate on the surfaces of the fans and not by their ages. Field observations, grain-size distribution, and cosmogenic nuclide data suggest that over time, boulders weather into grus and the bar sediments diffuse into the adjacent swales. As fans grow older the relief between bars and swales decreases, the sediment transport rate from bars to swales decreases, and the surface processes that erode the fan become uniform over the entire fan surface. The nuclide data therefore suggest that, over time, the difference in 10Be concentration between bars and swales increases to a maximum until the topographic relief between bars and swales is minimized, resulting in a common surface lowering rate and common 10Be concentrations across the fan. During this phase, the entire fan is lowered homogeneously at a rate of 10–15 mm kyr−1. [Copyright &y& Elsevier]

Activities of 26Al and 10Be in five chert clasts sampled from two beach ridges of late Pleistocene Lake Lisan, precursor of the Dead Sea in southern Israel, indicate low rates of chert bedrock erosion and complex exposure, burial, and by inference, transport histories. The chert clasts were derived from the Senonian Mishash Formation, a chert-bearing chalk, which is widely exposed in the Nahal Zin drainage basin, the drainage system that supplied most of the material to the beach ridges. Simple exposure ages, assuming only exposure at the beach ridge sampling sites, range from 35 to 354 ky; using the ratio 26Al/10Be, total clast histories range from 0·46 to 4·3 My, unrelated to the clasts'' current position and exposure period on the late Pleistocene beach ridges, 160–177 m below sea level. Optically stimulated luminescence dating of fine sediments from the same and nearby beach ridges yielded ages of 20·0 ± 1·4 ka and 36·1 ± 3·3 ka. These ages are supported by the degree of soil development on the beach ridges and correspond well with previously determined ages of Lake Lisan, which suggest that the lake reached its highest stand around 27 000 cal. years BP. If the clasts were exposed only once and than buried beyond the range of significant cosmogenic nuclide production, then the minimum initial exposure and the total burial times before delivery to the beach ridge are in the ranges 50–1300 ky and 390–3130 ky respectively. Alternatively, the initial cosmogenic dosing could have occurred during steady erosion of the source bedrock. Back calculating such rates of rock erosion suggests values between 0·4 and 12 m My−1. The relatively long burial periods indicate extended sediment storage as colluvium on slopes and/or as alluvial deposits in river terraces. Some clasts may have been stored for long periods in abandoned Pliocene and early Pleistocene routes of Nahal Zin to the Mediterranean before being transported again back into the Nahal Zin drainage system and washed on to the shores of Lake Lisan during the late Pleistocene. Copyright © 2003 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

There has been considerable interest in using impurity dopants in silicon, such as boron and phosphorus, since it was demonstrated that such materials can show emission in the THz region of the electromagnetic spectrum. The measured temperature dependence of these transitions in this letter shows that the most optimistic maximum operating temperature of such an impurity-based laser is 90 K. In a real device with current flowing and associated Joule heating, the actual operating range is likely to be much narrower and it is therefore unlikely that such a device would have a maximum operating temperature above 40 K. [ABSTRACT FROM AUTHOR]

The selective amplification of DNA in the polymerase chain reaction is used to exponentially increase the signal in molecular diagnostics for nucleic acids, but there are no analogous techniques for signal enhancement in clinical tests for proteins or cells. Instead, the signal from affinity-based measurements of these biomolecules depends linearly on the probe concentration. Substituting antibody-based probes tagged for fluorescent quantification with lasing detection probes would create a new platform for biomarker quantification based on optical rather than enzymatic amplification. Here, we construct a virus laser which bridges synthetic biology and laser physics, and demonstrate virus-lasing probes for biosensing. Our virus-lasing probes display an unprecedented > 10,000 times increase in signal from only a 50% increase in probe concentration, using fluorimeter-compatible optics, and can detect biomolecules at sub-100 fmol mL−1 concentrations. Many ligand-binding assays still rely on signals that scale linearly with probe concentration. The authors present lasing detection probes with a dye-labelled virus as the gain medium to optically amplify the signal, which could enable much higher signals than for fluorescent quantification. [ABSTRACT FROM AUTHOR]