Fan Surface Research Articles

SfM-Based Method to Assess Gorgonian Forests (Paramuricea clavata (Cnidaria, Octocorallia))

Animal forests promote marine habitats morphological complexity and functioning. The red gorgonian, Paramuricea clavata, is a key structuring species of the Mediterranean coralligenous habitat and an indicator species of climate effects on habitat functioning. P. clavata metrics such as population structure, morphology and biomass inform on the overall health of coralligenous habitats, but the estimation of these metrics is time and cost consuming, and often requires destructive sampling. As a consequence, the implementation of long-term and wide-area monitoring programmes is limited. This study proposes a novel and transferable Structure from Motion (SfM) based method for the estimation of gorgonian population structure (i.e., maximal height, density, abundance), morphometries (i.e., maximal width, fan surface) and biomass (i.e., coenenchymal Dry Weight, Ash Free Dried Weight). The method includes the estimation of a novel metric (3D canopy surface) describing the gorgonian forest as a mosaic of planes generated by fitting multiple 5 cm × 5 cm facets to a SfM generated point cloud. The performance of the method is assessed for two different cameras (GoPro Hero4 and Sony NEX7). Results showed that for highly dense populations (17 colonies/m2), the SfM-method had lower accuracies in estimating the gorgonians density for both cameras (60% to 89%) than for medium to low density populations (14 and 7 colonies/m2) (71% to 100%). Results for the validation of the method showed that the correlation between ground truth and SfM estimates for maximal height, maximal width and fan surface were between R2 = 0.63 and R2 = 0.9, and R2 = 0.99 for coenenchymal surface estimation. The methodological approach was used to estimate the biomass of the gorgonian population within the study area and across the coralligenous habitat between −25 to −40 m depth in the Portofino Marine Protected Area. For that purpose, the coenenchymal surface of sampled colonies was obtained and used for the calculations. Results showed biomass values of dry weight and ash free dry weight of 220 g and 32 g for the studied area and to 365 kg and 55 Kg for the coralligenous habitat in the Marine Protected Area. This study highlighted the feasibility of the methodology for the quantification of P. clavata metrics as well as the potential of the SfM-method to improve current predictions of the status of the coralligenous habitat in the Mediterranean sea and overall management of threatened ecosystems.

Alluvial fan surface ages recorded by Landsat-8 imagery in Owens Valley, California

Alluvial fans are important depositional landforms that offer valuable records of terrestrial sedimentation history if their surfaces can be mapped and dated accurately. Unfortunately, as this often depends on detailed field mapping and intensive absolute dating techniques, it can be a challenging, expensive and time-consuming exercise. In this study, we demonstrate that quantitative information about the ages of alluvial fan surfaces in Owens Valley, California, is recorded by Landsat-8 multispectral satellite imagery. We show that systematic changes in the wavelength-dependent brightness of fan surfaces occur gradually over a timescale of ~100 kyr in this semi-arid setting, and are highly correlated with known deposit ages. Using spectro-radiometry and X-ray diffraction analysis of sediment samples collected in the field, we interpret that surface reflectance evolves primarily in response to the in-situ production of secondary illite and iron oxide by weathering in this landscape. Furthermore, we demonstrate that first-order predictions of absolute fan surface age can be derived from multispectral imagery when an initial age calibration is available. These findings suggest that multispectral imagery, such as Landsat data, can be used (i) for preliminary mapping of alluvial fans prior to detailed field work and before choosing sampling sites for conventional dating techniques, and (ii) to extend age models to un-dated neighbouring surfaces with equivalent physical properties, once an age-brightness calibration has been established.

Late Quaternary slip rates for the southern Elsinore fault in the Coyote Mountains, southern California from analysis of alluvial fan landforms and clast provenance, soils, and U-series ages of pedogenic carbonate

Offset alluvial fans along the Elsinore fault in the south-central Coyote Mountains were studied to resolve an average late Quaternary slip rate for this major western strand of the San Andreas fault system in southern California. Alluvial fans and their offsets were mapped using high-resolution DEMs combined with field observations of fan-surface morphology and the character of the soils developed in each fan remnant. Clast assemblage data was used to determine the source of each alluvial fan upstream of the fault, and U-series dating of pedogenic carbonate was used to estimate minimum ages of the alluvial fan surfaces. Forty U-Th dates on pedogenic carbonate confirm the utility of the technique for dating late Pleistocene alluvium in arid regions and suggest that age variation among late Pleistocene fans grouped on the basis of soils and geomorphic criteria may be significant. Based on these data, the southernmost segment of the Elsinore fault has sustained a slip rate of 2.4 ± 0.4 mm/y for the past 60–70 ka and probably for the past 150 ka. Because displacement in the most recent surface rupture increases northwest of our slip rate sites, this rate is likely a minimum for the southern Elsinore fault, with the actual rate more likely close to 3 mm/y in the central part of the range. These new data confirm that slip gradients along individual fault segments must be considered when estimating pre-Holocene slip rates for seismic hazard estimates. These new results show that the southern Elsinore fault accounts for about 6% of the total relative motion between North America and the Pacific lithospheric plates in southernmost California. Assessment of previous estimates of slip in the most recent event suggests earthquakes of about Mw 6.8 and, when combined with the slip rate data, a recurrence of such events about every thousand years.

Variable character and diverse origin of hybrid event beds in a sandy submarine fan system, Pennsylvanian Ross Sandstone Formation, western Ireland

AbstractHybrid event beds comprising both clean and mud‐rich sandstone are important components of many deep‐water systems and reflect the passage of turbulent sediment gravity flows with zones of clay‐damped or suppressed turbulence. ‘Behind‐outcrop’ cores from the Pennsylvanian deep‐water Ross Sandstone Formation reveal hybrid event beds with a wide range of expression in terms of relative abundance, character and inferred origin. Muddy hybrid event beds first appear in the underlying Clare Shale Formation where they are interpreted as the distal run‐out of the wakes to flows which deposited most of their sand up‐dip before transforming to fluid mud. These are overlain by unusually thick (up to 4·4 m), coarse sandy hybrid event beds (89% of the lowermost Ross Formation by thickness) that record deposition from outsized flows in which transformations were driven by both substrate entrainment in the body of the flow and clay fractionation in the wake. A switch to dominantly fine‐grained sand was accompanied initially by the arrest of turbulence‐damped, mud‐rich flows with evidence for transitional flow conditions and thick fluid mud caps. The mid and upper Ross Formation contain metre‐scale bed sets of hybrid event beds (21 to 14%, respectively) in (i) upward‐sandying bed set associations immediately beneath amalgamated sheet or channel elements; (ii) stacked thick‐bedded and thin‐bedded hybrid event bed‐dominated bed sets; (iii) associations of hybrid event bed‐dominated bed sets alternating with conventional turbidites; and (iv) rare outsized hybrid event beds. Hybrid event bed dominance in the lower Ross Formation may reflect significant initial disequilibrium, a bias towards large‐volume flows in distal sectors of the basin, extensive mud‐draped slopes and greater drop heights promoting erosion. Higher in the formation, hybrid event beds record local perturbations related to channel switching, lobe relocations and extension of channels across the fan surface. The Ross Sandstone Formation confirms that hybrid event beds can form in a variety of ways, even in the same system, and that different flow transformation mechanisms may operate even during the passage of a single flow.

Link between concentrations of sediment flux and deep crustal processes beneath the European Alps

Large sediment fluxes from mountain belts have the potential to cause megafans to prograde into the neighbouring sedimentary basins. These mechanisms have been documented based from numerical modelling and stratigraphic records. However, little attention has been focused on inferring temporal changes in the concentrations of supplied sediment from coarse-grained deposits. Here, we extract changes of this variable in the field from a Late Oligocene, c. 4 km-thick suite of fluvial conglomerates situated in the North Alpine foreland basin, which evolved in response to the tectonic and erosional history of the Alps. We measure a decrease in channel depths from >2 m to <1 m and an increase in the largest grain sizes from <15 cm to >20 cm from the base to the top of the suite. These constraints are used to calculate an increase in fan surface slopes from <0.3° to >1.0° based on the Shields criteria for sediment entrainment. We combine slope and bulk grain size data with the Bagnold equation for sediment transport to infer higher concentrations of the supplied sediment. We use these shifts to propose a change towards faster erosion and a steeper landscape in the Alpine hinterland, driven by mantle-scale processes beneath the Alps.

A calculation method of the optimal distance of the long-drawn short-pressure type localfan in minebased on the principle of the jet and Suction volume

In order to dilute the harmful smoke and dust of the working surface in the production of the roadway in the mine shaft, the combination of mine local ventilation is often considered when conditions permitting. However there is no definite method to determine the distance between fan and working surface. Considering the concentration of smoke, the size of working face, the ventilation time, the wind speed of the working face and the principle of suction volume, this paper analyzes the long - drawn short - pressure type of the ventilation scheme, and presents an optimal algorithm for the distance between the exhaust ventilator and the working face: Then this paperpresentsa reference distance for different wind speed requirements of a project.

Formation Ages of Terraced Fan Surfaces Constituting Alluvial Fans along the Eastern Foot of Mt. Ikeda, Central Japan

Formation Ages of Terraced Fan Surfaces Constituting Alluvial Fans along the Eastern Foot of Mt. Ikeda, Central Japan

The Influence of Surface Roughness on the Flow Fields Generated by an Oscillating Cantilever

With the current trend of miniaturisation of electronic devices, piezoelectric fans have attracted increasing interest as a means of inducing forced convection cooling, instead of traditional rotary solutions. Although there exists an abundance of research on various piezo-actuated flapping fans in the literature, the geometries of these fans all consist of a smooth rectangular cross section with thicknesses typically of the order of 100 μm. The focus of these studies has primarily been on variables such as frequency, amplitude and, in some cases, resonance mode. It is generally noted that the induced flow dynamics are a direct consequence of the pressure differential at the fan tip as well as the pressure driven ‘over the top’ vortices generated at the upper and lower edges of the fan. Rough surfaces such as golf ball dimples or vortex generators on an aircraft wing have proven to be beneficial by tripping the boundary layer and energising the adjacent airflow. This paper aims to examine the influence of surface roughness on the airflow generation of a flapping fan, and to determine if the induced wake can be manipulated or enhanced by energising the airflow around the fan tip. Particle-Image Velocimetry (PIV) is carried out on mechanically oscillated rigid fans with surfaces consisting of protruding pillars and dimples. A smooth rigid fan surface is also investigated as a control. No significant difference was noted between the smooth and roughened fans through observation of the induced flow fields. Both fans produced results that were largely consistent with the existing literature on oscillating cantilevers. The results of this paper may be used to inform the design of piezoelectric fans and to aid in understanding the complex aerodynamics inherent in flapping wing flight.

Monogenetic origin of Ubehebe Crater maar volcano, Death Valley, California: Paleomagnetic and stratigraphic evidence

Paleomagnetic data for samples collected from outcrops of basaltic spatter at the Ubehebe Crater cluster, Death Valley National Park, California, record a single direction of remanent magnetization indicating that these materials were emplaced during a short duration, monogenetic eruption sequence ~2100years ago. This conclusion is supported by geochemical data encompassing a narrow range of oxide variation, by detailed stratigraphic studies of conformable phreatomagmatic tephra deposits showing no evidence of erosion between layers, by draping of sharp rimmed craters by later tephra falls, and by oxidation of later tephra layers by the remaining heat of earlier spatter.This model is also supported through a reinterpretation and recalculation of the published 10Be age results (Sasnett et al., 2012) from an innovative and bold exposure-age study on very young materials. Their conclusion of multiple and protracted eruptions at Ubehebe Crater cluster is here modified through the understanding that some of their quartz-bearing clasts inherited 10Be from previous exposure on the fan surface (too old), and that other clasts were only exposed at the surface by wind and/or water erosion centuries after their eruption (too young).Ubehebe Crater cluster is a well preserved example of young monogenetic maar type volcanism protected within a National Park, and it represents neither a protracted eruption sequence as previously thought, nor a continuing volcanic hazard near its location.

Tributary effects on fluvial terrace development since the last interglacial in the upper Tama River valley, central Japan

To understand the sediment routing system from mountains to lowlands in the Quaternary Period, it is necessary to evaluate the interactions of fluvial processes and their response to climate changes. We reconstructed the development of fluvial landforms along the upper Tama River valley of central Japan since the last interglacial, focusing on distinguishing toe-cut terraces (remnants of tributary fans) from trunk-river terraces by combining analyses of the sediments and geomorphology of terrace deposits with age dating of tephra and organic matter in these deposits. Our results show that late in MIS 5, the tributaries supplied sediment to the trunk valley that, together with sediment in the trunk river, elevated the bed of the trunk river. In MIS 4 and 3, tributary deposits built small fan surfaces around the tributary junctions, while trunk river sediment was transported downstream and did not contribute to filling of the trunk valley. After the last glacial maximum, lateral erosion by the Tama River transformed the tributary fans into toe-cut terraces, and the reworked tributary deposits contributed to the formation of fill-cut terraces while helping the trunk river maintain an equilibrium state. In the Tama River basin, the contribution of tributaries to the sediment routing system systematically increased upstream, where steeper tributaries, with catchment basins of higher relief, join the trunk valley more frequently. Our findings suggest that cutting and filling of tributary sediment around stream junctions contributed buffering effects that have stabilized the bed of the Tama River against Quaternary climatic changes.

Aeroacoustic Analysis of Low-Speed Axial Fans With Different Rotational Speeds in the Design Point

One of the main design decisions in the development of low-speed axial fans is the right choice of the blade loading versus rotational speed, since a target pressure rise could either be achieved with a slow spinning fan and high blade loading or a fast spinning fan with less flow turning in the blade passages. Both the blade loading and the fan speed have an influence on the fan performance and the fan acoustics, and there is a need to find the optimum choice in order to maximize efficiency while minimizing noise emissions. This paper addresses this problem by investigating five different fans with the same pressure rise but different rotational speeds in the design point (DP). In the first part of the numerical study, the fan design is described and steady-state Reynolds-averaged Navier–Stokes (RANS) simulations are conducted in order to identify the performance of the fans in the DP and in off-design conditions. The investigations show the existence of an optimum in rotational speed regarding fan efficiency and identify a flow separation on the hub causing a deflection of the outflow in radial direction as the main loss source for slow spinning fans with high blade loadings. Subsequently, large eddy simulations (LES) along with the acoustic analogy of Ffowcs Williams and Hawkings (FW–H) are performed in the DP to identify the main noise sources and to determine the far-field acoustics. The identification of the noise sources within the fans in the near-field is performed with the help of the power spectral density (PSD) of the pressure. In the far-field, the sound power level (SWL) is computed using different parts of the fan surface as FW–H sources. Both methods show the same trends regarding noise emissions and allow for a localization of the noise sources. The flow separation on the hub is one of the main noise sources along with the tip vortex with an increase in its strength toward lower rotational speeds and higher loading. Furthermore, a horseshoe vortex detaching from the rotor leading edge and impinging on the pressure side as well as the turbulent boundary layer on the suction side represent significant noise sources. In the present investigation, the maximum in efficiency coincides with the minimum in noise emissions.

Late Quaternary fluvial dynamics and landscape evolution at the lower Shulaveris Ghele River (southern Caucasus)

AbstractThe southern Caucasus was intensively settled through the Neolithic period to present. Studies of late Quaternary fluvial dynamics and landscape development at the lower Shulaveris Ghele River in southeastern Georgia aid understanding of the Quaternary history of this region. Our studies show that following river aggradation to form a fan-shaped alluvial surface during the late Pleistocene, fluvial sedimentation shifted west, leaving a fan surface subject only to local fluvial and colluvial processes as well as late Neolithic settlement. At about 6 ka, the river avulsed to the east and eroded some late Neolithic settlements occupying the eastern portion of the fan. The avulsion was followed by 3 distinct episodes of aggradation at about 6 ka, 3–2 ka, and since 1.0 ka. No such aggradation is evident in the early Holocene. Regional Holocene fluvial activity in this area was apparently influenced by vegetation dynamics, possibly controlled by regional climatic and/or anthropogenic factors, and significantly differs from the eastern Mediterranean region. All late Neolithic settlements were originally built far from an active river, possibly indicating late Neolithic water management systems.

Late Quaternary strike-slip along the Taohuala Shan-Ayouqi fault zone and its tectonic implications in the Hexi Corridor and the southern Gobi Alashan, China

The Hexi Corridor and the southern Gobi Alashan are composed of discontinuous a set of active faults with various strikes and slip motions that are located to the north of the northern Tibetan Plateau. Despite growing understanding of the geometry and kinematics of these active faults, the late Quaternary deformation pattern in the Hexi Corridor and the southern Gobi Alashan remains controversial. The active E-W trending Taohuala Shan-Ayouqi fault zone is located in the southern Gobi Alashan. Study of the geometry and nature of slip along this fault zone holds crucial value for better understanding the regional deformation pattern. Field investigations combined with high-resolution imagery show that the Taohuala Shan fault and the E-W trending faults within the Ayouqi fault zone (F2 and F5) are left-lateral strike-slip faults, whereas the NW or WNW-trending faults within the Ayouqi fault zone (F1 and F3) are reverse faults. We collected Optically Stimulated Luminescence (OSL) and cosmogenic exposure age dating samples from offset alluvial fan surfaces, and estimated a vertical slip rate of 0.1–0.3mm/yr, and a strike-slip rate of 0.14–0.93mm/yr for the Taohuala Shan fault. Strata revealed in a trench excavated across the major fault (F5) in the Ayouqi fault zone and OSL dating results indicate that the most recent earthquake occurred between ca. 11.05±0.52ka and ca. 4.06±0.29ka. The geometry and kinematics of the Taohuala Shan-Ayouqi fault zone enable us to build a deformation pattern for the entire Hexi Corridor and the southern Gobi Alashan, which suggest that this region experiences northeastward oblique extrusion of the northern Tibetan Plateau. These left-lateral strike-slip faults in the region are driven by oblique compression but not associated with the northeastward extension of the Altyn Tagh fault.

The shallow structure of a surface-rupturing fault in unconsolidated deposits from multi-scale electrical resistivity data: The 30 October 2016 Mw 6.5 central Italy earthquake case study

We report the results of a shallow electrical resistivity investigation performed across a normal fault that ruptured the surface displacing with average ~0.05m vertical offset alluvial fan deposits (<23kyr old) within an intermontane fault-bounded basin following the 30 October 2016 Mw 6.5 earthquake in central Italy. We adopted a multi-scale geophysical approach, by acquiring three 2-D electrical resistivity tomography (ERT) profiles centred on the coseismic ruptures, and characterized by different spatial resolution and investigation depth. Below the fault scarp, the ERT models show a narrow (~10m wide) and steeply-dipping moderately-resistive region (100–150Ωm), which we interpret as the electrical response of the fault zone displacing layers of relatively high-resistivity (300–700Ωm) values. We explain the electrical signature of the retrieved fault zone as due to an increment of permeability caused by coseismic fracturing, and to the subsequent water migration from adjacent shallow aquifers squeezed by compaction induced by seismic waves. By using a statistically-based classification of electrical units, we estimate that the shallowest alluvial fan layer is affected by 2.7±0.9m vertical offset, which is consistent with the measured 2.3–2.8m morphologic offset of the top fan surface, and suggesting a post-12 kyr throw-rate of 0.23±0.08mm/yr. Similarly, we evaluate a post-23 kyr throw of 5.1±1.7m, indicating a Late Pleistocene throw-rate of 0.22±0.07mm/yr, in accordance with available paleoseismic data. We further hypothesize a minimal total fault throw >30m, which likely accrued since the Middle Pleistocene (possibly in the last 350–500kyr). The investigated fault structure is therefore an important splay characterized by a thick and highly permeable damage zone in unconsolidated deposits, and which ruptured the surface during several tens of strong (M>6) earthquakes.

The Effect of A Pre-Deposited Mobile Substrate On Terminal-Fan Evolution and Channel Organization: Tank Experiments

Abstract: Depositional processes interact with mobile substrates in nearly all passive-margin settings throughout the world. The interplay between sedimentation and a mobile substrate (e.g., salt layer) results in a complex stratigraphic record, making it difficult to reconstruct basin-fill history. Herein we investigate the dynamic feedback between sediment loading and substrate deformation to understand morphologic change and stratigraphic development. We used simplified tank experiments of a linked fan and terminal-channel system evolving over a deformable substrate. A series of experiments were conducted with controlling variables including mobile substrate thickness, sediment supply rate, and basin slope. Experimental results indicate: (1) an increase in substrate thickness resulted in increased subsidence around the fan that limited sediment transport to its terminal channels, (2) a higher sediment discharge rate on a substrate resulted in faster fan progradation coupled with relatively less subsidence and more sediment transport to terminal channels, and (3) a higher-slope experiment caused the largest amount of sediment transport downstream, while a decrease in basin slope resulted in a larger number of established channels along with a wider fan surface. An analysis of surface processes is also used to determine the expected stratigraphy between a linked fan and terminal-channel system as it interacted with the mobile substrate. We apply the experimental findings to understand the fluvial-dump–wind-redistribute system deposited on top of the Louann Salt layer in the eastern part of the Late Jurassic Gulf of Mexico basin.

Glacial-interglacial climate changes recorded by debris flow fan deposits, Owens Valley, California

It is hotly debated whether and how climate changes are recorded by terrestrial stratigraphy. Basin sediments produced by catchment-alluvial fan systems may record past climate over a variety of timescales, and could offer unique information about how climate controls sedimentation. Unfortunately, there are fundamental uncertainties about how climatic variables such as rainfall and temperature translate into sedimentological signals. Here, we examine 35 debris flow fan surfaces in Owens Valley, California, that record deposition throughout the past 125,000 years, during which climate has varied significantly. We show that the last full glacial-interglacial cycle is recorded with high fidelity by the grain size distributions of the debris flow deposits. These flows transported finer sediment during the cooler glacial climate, and became systematically coarser-grained as the climate warmed and dried. We explore the physical mechanisms that might explain this signal, and rule out changes in sediment supply through time. Instead, we propose that grain size records past changes in storm intensity, which is responsible for debris flow initiation in this area and is decoupled from average rainfall rates. This is supported by an exponential Clausius-Clapeyron-style scaling between grain size and temperature, and also reconciles with climate dynamics and the initiation of debris flows. The fact that these alluvial fans exhibit a strong, sustained sensitivity to orbital climate changes sheds new light on how eroding landscapes and their sedimentary products respond to climatic forcing. Finally, our findings highlight the importance of threshold-controlled events, such as storms and debris flows, in driving erosion and sedimentation at the Earth's surface in response to climate change.

Simulated evolution of three-dimensional magnetic nulls leading to generation of cylindrically-shaped current sheets

The performed magnetohydrodynamic simulation examines the importance of magnetofluid evolution, which naturally leads to current sheets in the presence of three-dimensional (3D) magnetic nulls. The initial magnetic field is constructed by superposing a 3D force-free field on a constant axial magnetic field. The initial field supports 3D magnetic nulls having the classical spine axis and the dome-shaped fan surface and exerts non-zero Lorentz force on the magnetofluid. Importantly, the simulation identifies the development of current sheets near the 3D magnetic nulls. The morphology of the current sheets is similar to a cylindrical surface where the surface encloses the spine axis. The development is because of favorable deformation of magnetic field lines constituting the dome-shaped fan surface. The deformation of field lines is found to be caused by the flow generated by magnetic reconnections at current sheets which are located away from the cylindrically shaped current sheets.

Quaternary deformation in the Gorubathan recess: Insights on the structural and landscape evolution in the frontal Darjiling Himalaya

The Gorubathan recess in the Darjiling frontal Himalaya is an unusual and unique region in the Himalaya as the Ramgarh thrust (RT) rather than the MFT defines the mountain front and the width of the Himalayan arc or the N-S aerial distance between the foreland (27.0947°N, 88.8744°E) and the Tibet Plateau (27.6781°N, 89.1175°E) is merely ∼70 km here. South of the mountain front, blind faults have deformed several Quaternary alluvial fans and formed scarps over a ∼35 km N-S zone. We first used field observations and fold-thrust belt concepts to re-interpret thrust nomenclature and geometry in the recess by correlating structures and lithology with the adjacent Dharan salient across the salient-recess separating Gish Transverse fault (GTF) and renamed the locally recognized faults to their regional equivalents. We then used Real Time Kinematic Global Navigation Satellite Systems (RTKGNSS) corrected SRTM 30 m C-Band data to compute geomorphic indices along with their uncertainties. Our results indicated that neotectonic deformation has generated an active but mature landscape in the Gorubathan recess. Quantitative topographic profiles based on RTKGNSS measurements reveal neotectonic warping and formation of geomorphic scarps on the fan surfaces. Geomorphic scarps form due to motion along thrusts but are not actual fault scarps. These profiles were used to model topographic growth and perturbation of fan slopes by active thrusting and fault-propagation folding by Boundary Element Method based dislocation modelling. Results indicate activity through much of the Quaternary on the Ramgarh thrust, a hanging wall imbricate and a rejoining splay in its footwall as well as the Main Boundary thrust. Comparison of modelled and measured topographic profiles in the recess points to erosion of the fault-related scarp-tops in the deformed alluvial fans on the windward side of the SW monsoon in both the Gorubathan and the Samsing-Matiali fans. Our integrated methodology improves the understanding of coupled fault-generated deformation and topographic growth and may be applied across the entire Himalayan front.

Self-similar growth of a bimodal laboratory fan

Abstract. Using laboratory experiments, we investigate the growth of an alluvial fan fed with two distinct granular materials. Throughout the growth of the fan, its surface maintains a radial segregation, with the less mobile sediment concentrated near the apex. Scanning the fan surface with a laser, we find that the transition between the proximal and distal deposits coincides with a distinct slope break. A radial cross section reveals that the stratigraphy records the signal of this segregation. To interpret these observations, we conceptualize the fan as a radially symmetric structure that maintains its geometry as it grows. When combined with slope measurements, this model proves consistent with the sediment mass balance and successfully predicts the slope of the proximal–distal transition as preserved in the fan stratigraphy. While the threshold-channel theory provides an order-of-magnitude estimate of the fan slopes, driven by the relatively high sediment discharge in our experimental system, the actual observed slopes are 3–5 times higher than those predicted by this theory.

Active fault topography along Kangra Valley Fault in the epicentral zone of 1905 Mw7.8 earthquake NW Himalaya, India

The 1905 CE Kangra earthquake (Mw7.8) was one of the most damaging earthquakes in Himalaya. Malik et al (2015) suggested that the Kangra Valley Fault (KVF) from the epicentral zone was the source of the 1905 Kangra earthquake. In this article we discuss the active fault topography along KVF marked by distinct right lateral strike-slip movement, extends for about 60 km between Patka Village in NW and Tanda Village in SE. The prominent offset of streams ranging from 10 m to 340 m have been identified along the fault trace; the lateral offset of 10 m may be indicative of displacement during a single event. Lateral as well as the vertical offset of alluvial fan surfaces and fluvial terraces, resulted in formation of the north as well as south facing fault scarps ranging in height from 1.2 to 14 m. KVF between two major thrust systems i.e., Main Boundary Thrust (MBT) and Jawalamukhi Thrust (JMT), suggest that slip-partitioning is taking place between the thrust and strike-slip faults and is a net result of oblique convergence in NW Himalaya. The end points of the fault traces exhibit typical “Y” shape because of stepping and branching out of rupture from the main fault. Considering the pre-stress axis from the GPS velocity vectors from Banerjee and Bürgman, (2002), the branching scenario we obtained for KVF, is not consistent with the simulated models by Kame et al., (2003) and Poliakov et al., (2002) for other faults. This could be attributed to the ongoing oblique convergence in NW Himalaya. Based on the “Y” shape pattern, and the upthrown and downthrown sides mapped along the fault trace, we suggest two possibilities for surface rupture, (1) the fault rupture initiated from Pathiyar-Malan side and propagated unilaterally towards west, (2) taking into account the “Y” shape on both the end sections of the fault trace, it can be inferred that the rupture during most recent event probably started in the center at Miniana and propagates bilaterally in E-W.