Km In Length Research Articles

Water Quality Simulation in the Bois River, Goiás, Central Brazil

The Cerrado is a hotspot for biodiversity conservation and holds the headwater springs that are major Brazilian river basins. The development of industry, agriculture, and mining causes water quality deterioration. Mathematical models appear as a management tool to simulate water quality parameters and the dispersion of pollutants in water bodies. Thus, this study aimed to evaluate the behavior of dissolved oxygen (DO) and other parameters through the QUAL2Kw (Stream Water Quality Model) model in a river in the Brazilian Cerrado. Complementary data were obtained in four experimental measurement campaigns. The calibration results showed a good fit, especially for the DO. The most critical situation occurred in October, where DO remained below 5 mg/L for a long stretch, and the ammoniacal nitrogen (NH4) and biochemical oxygen demand (BOD) presented non-compliance concerning the legal Brazilian requirements. In all campaigns, BOD remained above 5 mg/L for at least 5 km in length, disagreeing with the legislation for exceeding the distance from the mixing zone. The uncertainty analysis for the DO confirmed the critical scenario of October, and the sensitivity analysis by the Monte Carlo Simulation showed the significance of the reaeration coefficient for DO. Thus, it is concluded that the QUAL2Kw model proved dependable for the simulation of point launches in the Bois River, supplying a good fit in the calibration act. Because BOD does not meet the legal requirements in all samplings, the water use of the downstream population may be impaired by the activities found in the basin. Activities such as sand extraction, tanneries, and other food industries increase the organic burden of waterbodies and, therefore, require greater environmental inspections.

Dependence of ocean surface filaments on wind speed: An observational study of North Atlantic right whale habitat

Coherent filaments at the ocean surface often appear to be transient watermass boundaries, where currents converge, surfactants accumulate, and frontal structure at depth can possibly delineate enhanced biological activity in the upper water column. Spaceborne synthetic aperture radar (SAR) permits filaments to be observed at O[1-km] resolution, but extensive coherent structures are more apparent in weaker winds. A wind speed adjustment is proposed for filaments (i.e., contiguous SAR contrasts) of at least 10 km in length. Measures of dependence (distance correlation and the linear and nonlinear components of Pearson correlation) are examined to identify a broad peak in the relationship between filament contrast and weak or moderate values of surface wind speed, where a variable wind speed exponent is employed to maximize these measures.Three locations of recent North Atlantic right whale (Eubalaena glacialis) sightings in the Gulf of St. Lawrence are sampled between 2008 and 2020 by 324 Radarsat-2 SAR scenes and 10-m wind speed from the ERA5 reanalysis. The inverse relationship between SAR contrast magnitude and wind speed is quantified, and a reduced correlation is obtained for all three domains when SAR contrast is weighted by wind speed to the power of 0.8. A more uniform emphasis on ocean surface structure within a SAR scene, or across multiple scenes, can thus be considered in the search for prey aggregations of the North Atlantic right whale.

Seasonal and Interannual Variability of the Subtropical South Indian Ocean Sea Surface Salinity Maximum

AbstractThe sea surface salinity (SSS) maximum of the South Indian Ocean (the SISSS‐max) is a high‐salinity feature centered at 30°S, 90°E, near the center of the South Indian subtropical gyre. It is located poleward of a region of strong evaporation and weak precipitation. Using several different satellites and in situ data sets, we track changes in this feature since the early 2000s. The centroid of the SISSS‐max moves seasonally north and south, furthest north in late winter and farthest south in late summer. Interannually, the SISSS‐max has moved on a northeast‐southwest path about 1,500 km in length. The size and maximum SSS of the feature vary in tandem with this motion. It gets larger (smaller) and saltier (fresher) as it moves to the northeast (southwest) closer to (further from) the area of strongest surface freshwater flux. The area of the SISSS‐max almost doubles from its smallest to largest extent. It was maximum in area in 2006, decreased steadily until it reached a minimum in 2013, and then increased again. The seasonal variability of the SISSS‐max is controlled by the changes that occur on its poleward, or southern, side, whereas interannual variability is controlled by changes on its equatorward side. The variations in the SISSS‐max are a complex dance between changes in evaporation, precipitation, wind forcing, gyre‐scale ocean circulation, and downward Ekman pumping. Its motion correlated with SSS changes throughout the South Indian Ocean and may be an indicator of changes in the basin's subtropical circulation.

Unravelling the impact of geological heterogeneities in the reservoir management. An integrated study of the deep-water Akpo field (Niger delta)

Geological and seismic data have been integrated to describe the impact of structural and sedimentological heterogeneities on fluid dynamics for one of the reservoirs (Reservoir X) of the Akpo field (deep offshore of Niger Delta). Akpo is a sinuous 4-way anticline formed because of strong deformation occurring within the over pressurized shales of the Akata Formation. Weak deformation may have started since 9 Ma; however, most of the strain associated with shortening was accumulated between ca 7 Ma and ca 3 Ma. The cumulative shortening has been estimated in the order of 4% (ca 400 m). From 3 Ma (during the latest stages of growth of the Akpo anticline) up to Present-day, the residual strain was taken up by oblique (right lateral strike-slip component) extensional faults, between 2 km and ca 15 km in length, organized into two main trends: N-dipping, ENE-WSW to NE-SW striking faults, and NNW-SSE striking faults mainly dipping to the east. These faults are segmented and have a maximum throw in the order of 70 m. Based on the architectural elements identified in this work, the Reservoir X of the Akpo field has been subdivided into three main intervals: a basal lobe (Interval 1a) and a related channel (Interval 1 b); two intermediate generations of meandering channels (Interval 2a and 2 b); and an upper and strongly erosional constructive channel (Interval 3). The 4D signal has been integrated to better understand the complex fluid flow within Reservoir X in time and space. The extensional faults play a role in baffling mainly in the central part of the field, where across-fault flow is likely to occur in correspondence with the spill points. Facies distribution and the nature of the contact between various reservoir intervals are also important because vertical and lateral communication between sand bodies can be complex. Levees or mud barriers can inhibit flow, impacting both efficiency of support between injectors and producers. On the other hand, sand-to-sand communication due to the strong erosional character of the contacts enhances dynamic connectivity between sands belonging to different reservoir intervals. As an example, even if sands belonging to Interval 3 totally erode (i.e. dynamically isolate) those of Interval 2 in the southern part of the field, in the northern sector the two reservoir intervals are in (vertical) communication as suggested by the 4D signal. A key result of this integrated work is that of documenting in detail the modes in which faults and sedimentary features impact fluid flow within and across reservoir intervals in a deep-water environment.

Builder's Competency Improvement About Simple Earthquake Resistant Houses in Blang Pulo Village, Lhokseumawe City

The Indonesian region has a very high seismic intensity. Its geographic location is on three active tectonic plates, namely Indo Australia, Eurasia and the Pacific and is part of the circum Pacific belt, a series of volcanoes (ring of fire) that reaches 40,000 km in length, causing Indonesia to be frequently hit by tectonic earthquakes and volcanic eruptions. . Incident after incident seemed to alternately hit various regions in Indonesia. An earthquake with a magnitude of 9.1 on the Richter scale followed by a tsunami wave devastated the Aceh region in 2004. Another major earthquake occurred in Jokjakarta in 2006, which was followed by dozens of earthquakes in various regions in Indonesia. The most recent event was an earthquake with a magnitude of 6, 6 on the Richter scale in Banten on January 14 2022 which is reported to have damaged more than 3000 buildings. Simple houses are the group of buildings that most often experience collapse, heavy damage and minor damage.
 This community service activity will try to improve the ability of builders in five villages around the Malikussaleh University campus on simple earthquake-resistant housing technology. Efforts to increase these competencies will be carried out through theoretical explanations using examples and drawings, which will then be followed up with direct practice of making key components that have a major influence on the ability of buildings to withstand earthquake loads.

Assessments and Historical Changes the Water Quality of Sawa Lake, Southern Iraq for the Period 1977-2020

This investigation pertains to the evaluation of water quality in SAWA Lake, located in the Al-Muthanna province of Southern Iraq, from 1977 to 2020. Understanding the water quality and assessments of this Lake is of great importance. The Lake is home to small, transparent, blind fish measuring approximately 10 cm and is often referred to as the "wonderful" or "strange" Lake due to its many unique features. The study focuses on several elements to represent water quality, including total dissolved solids (TDS), electrical conductivity (EC), pH, and temperature (T), which were measured directly in the field. Additionally, scientific concepts such as K+, Ca2+, Cl-, HCO3, and KSO4 were used in each sample. Scientists have analyzed the density and salinity of the lake water and found that its water density exceeds that of seawater, and its salinity exceeds that of the Gulf of Arabia by about 1.5 times. The water is salty, surrounded by natural lime, and is automatically renewed by nature when it is broken. Its hardness also characterizes it, and its water volume fluctuates depending on the wet and dry seasons. The Lake is roughly 4.74 km in length, and all the elements under study showed an increase in concentration during the periods of 1977, 1983, and 2003 with NaSO4, which later changed to MgCl between 2007 and 2011. The study found that Sawa Lake water was unsuitable for drinking or irrigation purposes between 2016 and 2020 due to the increased concentration of certain elements. This increase in concentration is attributed to the Lake's location, nutrition, and the lack of rain, which means it relies solely on groundwater.

Observations on the utilisation of a restored wildlife corridor by echo‐locating microbats in North Queensland's Wet Tropics

SummaryMicrobat studies are uncommon in the Wet Tropics of north‐east Queensland, despite the group comprising 20% of the bioregion's mammal fauna. The significance of fragmentation and habitat connectivity to the echolocating insectivore group is unknown. Over a 12‐month period in 2021–2022, microbat presence was recorded in a 25‐year‐old restored wildlife corridor 1.2 km in length. We deployed Anabat detectors in the restored corridor, in adjacent open paddocks and in mature rainforest at either end of the corridor. Species in reference forest and corridor vegetation were consistently ‘clutter‐adapted’ bats, with low aspect ratio wings; there was little overlap with high aspect ratio species of the open pasture. Low aspect ratio microbats appear to respond to the similarity in structure between restored and adjacent natural vegetation. Re‐establishing structural and functional connectivity may improve the local persistence of ‘clutter‐adapted’ microbats.

High-precision comparison of time scales over fiber optic lines using satellite modems with additional tone modulation

The use of a new type of modems with pseudonoise coding and additional tone modulation designed to compare reference time scales over telecommunication geostationary satellites is considered. Experimental studies were carried out on the possibility of comparing time scales of hydrogen keepers from the State primary standard of unit of time, frequency and national time scale using these modems via an optical link. A fiber-optical lines of various lengths were used for a two-way signal transmission. The output radio-frequency signals of the modems connected to the optical transmitters at the ends of the fiber-optical lines were transmitted towards each other on an optical carrier with a wavelength of 1.55 μm. Demodulation of optical signals into the radio frequency range was carried out using optical receivers at the ends of fiber lines. The results of experimental evaluation of type A uncertainty by comparing time scales using fiber-optical lines with 50, 100, and 200 km of length are presented. For the 200 km line, the type A measurement uncertainty does not exceed 3 ps for one day of averaging interval. For the first time, it has been experimentally shown that the implementation of the method of time scales comparison using modems with pseudo-noise coding and additional tone modulation over 200 km of fiber line is possible without the intermediate optical amplifiers. The result opens up the prospect of creating cascaded systems for comparing time scales of remote standards via fiber-optic communication lines with a smaller number of intermediate optical amplifiers.

РАЗРАБОТКА НАБЛЮДАТЕЛЯ ЛЮЕНБЕРГЕРА ПОЛНОГО ПОРЯДКА ВЕКТОРА ПЕРЕМЕННЫХ СОСТОЯНИЯ УЧАСТКА КАБЕЛЬНОЙ ЛИНИИ С ПОВЫШЕННОЙ ПАРАМЕТРИЧЕСКОЙ РОБАСТНОСТЬЮ

In addition, in the Russian Federation, 75 % of oil-producing wells in operation at old fields are low- to medium-flow rate wells. One way to increase the profitability of oil production from low- to medium-flow rate wells using ESPs is to reduce the power consumption of the Submersible Electric Motor (SEM) by switching the ESP from a scalar open-loop control system to a sensorless vector control system. To implement the vector control system for ESPs, it is necessary to develop a methodology for identifying the parameters of the electrical equipment in the power channel of the ESP, as well as to implement a full-order observer of the SEM vector state variables to create a feedback channel for angular speed. One of the electrical components in the ESP power channel that affects the accuracy of the SEM vector state variable estimation is the power cable, which can reach up to 5 km in length. Such a long cable length results in the output voltage at the cable end being significantly different in amplitude and frequency from the measured input voltage, and the cable parameters themselves change as the temperature of the well varies depending on the depth. Failure to estimate the output voltage of the cable will result in incorrect estimation of the torque and angular speed of the SEM, which, in turn, may cause the angular speed of the SEM to oscillate and the ESP to trip at the bottom of the well. Due to the above factor, the development of a full-order observer for the vector state variables of the cable line with increased parametric robustness is a relevant and timely task

Petrogenetic insights on tephritic magmatism from Davis Bank (South Atlantic Ocean - Vitória-Trindade Ridge (VTR), Brazil): The role of a CO2-enriched mantle source

Davis Bank is one of the largest physiographic features in the Vitória-Trindade Ridge (VTR), which is located offshore of the Eastern Brazilian margin, midway between the coastline and the South Atlantic mid-ocean ridge. The VTR is related to a linear volcanic track of ca. 1200 km in length, composed of several volcanic seamounts that are lithologically characterized by nephelinitic/tephritic alkaline rocks. The Davis Bank lies between the parallels 20°29′ and 20°32′ S and the meridians 29°17′ and 29°21′ W, and is located southeast of the Abrolhos Volcanic Complex (AVC), at the middle of the volcanic ridge, far from the Brazilian coast. This work focuses on the 40Ar/39Ar age determination of the rocks recovered from the seamount and characterization of Sr–Nd isotopes, mineral chemistry and whole-rock composition, aiming to access information about physical properties of magmas, source composition, magmatic evolution of the volcanic ridge, and the regional tectonic interpretation in the context of other seamounts along the Vitória-Trindade Ridge (VTR). Davis Bank presents 40Ar/39Ar age of ca. 21 Ma and is in an oceanic lithosphere of ca. 100 km thickness, which represents a recharging area in the oceanic lithospheric mantle for CO2-metasomatism enrichment. It is associated with mantle anomalies caused by a hotspot or mantle plume that was influenced by the E-W direction of leaking transform fracture zones in the South Atlantic Ocean. Age constraints indicate decreasing ages eastward of the AVC, favoring the hotspot hypothesis for the generation of magmatic rocks in the Vitória-Trindade Ridge.

Toward a theory of ‘stepped-leaders’ in lightning

An unresolved issue in the physics of lightning is an explanation for lightning proceeding to the ground by successive luminous steps separated by ‘dark’ times of many microseconds. There is also no explanation of the structure of the dark column connecting the streamer step with the cloud that can be km in length, is electrically conducting, yet has a very low sustaining electric field. It is proposed that these two processes can be explained by the accumulation of singlet delta metastable oxygen molecules excited in the corona pulses of lightning. The step time is necessary for the excitation of large metastable densities to produce significant metastable detachment of electrons from negative ions. The detached electrons form a highly conducting step, initially luminous, that causes a redistribution of electric fields and an increase in the potential and electric fields at the end of the step to make possible a further step by ionization. These features are supported by calculations of densities of electrons, positive ions, negative ions and singlet delta metastable oxygen molecules for the first 7 μs of a discharge chosen to be initiated by a 50 cm sphere of charged hail particles. The calculated corona streamers produce metastable densities of 1017 cm−3 near the corona source. These metastables, by electron detachment, produce a conducting cylinder 10 m long with a radius of 1 cm and an electron density ∼1012 cm−3 that is attributed to being the first step and a lightning ‘leader’. These conducting regions develop within them very low electric fields. Successive steps are likely to combine to form the long conductive columns of lightning that exist before the return stroke. Electron densities in the leader and the column are an equilibrium between electron production by metastable detachment and electron loss by attachment to neutral oxygen molecules, requiring no electric field.

Winds at the Mars 2020 Landing Site. 2. Wind Variability and Turbulence.

Wind speeds measured by the Mars 2020 Perseverance rover in Jezero crater were fitted as a Weibull distribution. InSight wind data acquired in Elysium Planitia were also used to contextualize observations. Jezero winds were found to be much calmer on average than in previous landing sites, despite the intense aeolian activity observed. However, a great influence of turbulence and wave activity was observed in the wind speed variations, thus driving the probability of reaching the highest wind speeds at Jezero, instead of sustained winds driven by local, regional, or large-scale circulation. The power spectral density of wind speed fluctuations follows a power-law, whose slope deviates depending on the time of day from that predicted considering homogeneous and isotropic turbulence. Daytime wave activity is related to convection cells and smaller eddies in the boundary layer, advected over the crater. The signature of convection cells was also found during dust storm conditions, when prevailing winds were consistent with a tidal drive. Nighttime fluctuations were also intense, suggesting strong mechanical turbulence. Convective vortices were usually involved in rapid wind fluctuations and extreme winds, with variations peaking at 9.2 times the background winds. Transient high wind events by vortex-passages, turbulence, and wave activity could be driving aeolian activity at Jezero. We report the detection of a strong dust cloud of 0.75-1.5km in length passing over the rover. The observed aeolian activity had major implications for instrumentation, with the wind sensor suffering damage throughout the mission, probably due to flying debris advected by winds.

Kuwari Lake: Potentially Dangerous for Landslide Lake Outburst Flood (LLOF)

Abstract Here a report of a lake of about one km in length that resulted from damming of a river by landslide near Kuwari village at the altitude of 1733 m asl and located between N 30o 5' 16"- 30o 5' 16" and E 79o 48' 30" - 79o 48' 29". On the basis of Google Earth images, it has been observed that a huge landslide took place from 16th to 17th June, 2013 and also in 2019 (as per the local sources) that blocked the Shambhu Gad (Baura Gad) in Bageshwar district and formed a huge lake, which covered ~15666 m2 area. It was also observed that an old landslide was reactivated due to cloud burst or toe erosion and affected an area ~862913 m2 between 2664 and 1761 m asl. The area affected by the landslide is ~4 km, the maximum width is about 650 m. In the vicinity of Kuwari village the impact of this Kuwari landslide also observed in the Jhaliya village (district Chamoli) established over south facing slope in the right bank of Pinder river. Both the villages are separated by E-W trending ridge (3700 m asl).

The Ar-Hötöl surface rupture along the Khovd fault (Mongolian Altay)

ABSTRACT We present a 1:200,000 scale map of the Ar-Hötöl surface rupture along the Khovd fault (Mongolian Altay), presumed to be the expression of the 1761 CE Mw ∼ 7.8 Great Mongol earthquake. The detailed mapping combines airborne and terrestrial imaging and topographic techniques (Sentinel-2, Pleiades, TanDEM-X, UAV and TLS) to quantify right-lateral and vertical offsets ranging from ∼ 1 m to ∼ 4 km over a length of 238 km. The smaller offsets document the deformation associated with the last surface-rupturing earthquake that affects several Bronze to Iron Age burial mounds. Their analysis yields a robust segmentation model comprising 6 segments of 20 to 51 km in length, a maximum co-seismic slip value of 4.8 m ± 0.5 m located near the center of the rupture. Our observations precise the varying kinematics along strike, bring new evidence of repeated faulting and confirm a Mw of 7.8 ± 0.3.

Variations in Avian Species and Functional Diversity in Different Habitat Types in a Vulnerable Savannah Ecosystem in Ghana

Most research on avian functional diversity in the tropics is focused on forest and agroecosystems, leaving a gap in knowledge about the effects of habitat types on functional diversity in savannah landscapes. Savanna ecosystems are fragile and are under threat of anthropogenic destruction, particularly in developing Sub-Saharan Africa and could be eliminated in the face of the ever-increasing human population exacerbated by the changing climate. This study investigated the influence of the three major habitat types (grassland, riparian forest, woodland) on bird species and functional diversity in the Mole National Park (MNP) in Ghana. We used the line transect method to survey birds along 39 transects, each 1 km in length, and collected data on environmental variables along the same transects. Data from these surveys was used to estimate species and functional diversity indicators. We found significant variations in species and functional diversity measures between the three habitat types in the MNP. These variations were significantly influenced by species abundance and environmental covariates. Diversity measures were particularly higher in the riparian forest habitats compared to the woodland and grassland, with the latter being the least diverse habitat both functionally and species wise. The results of this study suggest that the avifauna assemblages in MNP are largely influenced by the riparian forest and are important for ecosystem function and stability. We recommend management efforts to intensify the protection of such vital habitats of the Mole National Park from illegal human activities, especially the rising removal and export of rosewoods (Dalbergia nigra) around the park. Further research on the avian community composition and structure in the MNP is recommended.

CHS priority planning tool - A GIS to prioritize data gaps

Spanning close to 250,000 km in length, the Canadian coastline is the longest in the world. Collecting and managing data that is required by the Canadian Hydrographic Service (CHS) to produce navigational products for such a vast area can be challenging. Despite CHS products covering the full extent of Canadian waters, gaps in the data persist. To prioritize these gaps, CHS has developed a Geographic Information Systems (GIS) tool, the CHS Priority Planning Tool (CPPT). The derived output of the CPPT helps prioritize the areas that pose the highest risk to navigation.

Morphometric Analysis of the Rawandoz River Basin, Erbil, Kurdistan Region, Iraq

In this research detailed morphometric investigation of the Rawanduz river basin in the northeastern part of Erbil, Iraq has been made. The study area covers an approximately 977.68 km2. Digital Elevation Model data (DEM 12.5 m), Remote sensing and GIS methods were used for studying basin morphometric parameter such as linear, aerial, and relief aspects, as well as to delineate lineaments in the study area.The results reveal that there is an opposite correlation between stream order, stream number, and length of streams in the research region basin by R2 values (R2 = 0.77 and 0.73) which is good value depending on statistical analysis. Streams were also ordered, with a total of 6376 streams totaling 2376.4 km in length. The basin's elongation ratio (0.54), circulation ratio (0.45), and form factor (0.23) data suggested that it was semi-elongated to elongated in nature, with poor permeability material, high relief, steep slopes, and main drainage pattern types affected by lineaments and fracture traces. In the research region, the stream frequency value is 5.6 km2 which is a high value suggesting impermeable lithology and enhanced surface runoff in the basin area. The drainage density in the investigated area is 2.43 km-1. The Rawanduz river basin's high drainage density value (2.43 km-1) reveals a fine drainage texture value (38.77 km-3). This study will help decision-makers and local residents to benefit from the resources for the sustainable development of the basin area.

Effects of frequent debris flows on barrier lake formation, sedimentation and vegetation disturbance, Palongzangbo River, Tibetan Plateau

In incised mountain valleys, debris flows often cause damage to vegetation, especially when debris flows form fans or block receiving rivers. In such contexts, riparian trees may be partially buried in aggrading fans or temporary lakes. The Guxiang gully is the largest debris flow system along the Palongzangbo River on the Tibetan Plateau and at least 13 debris flows (volume > 104 m3) have occurred since 1953. Four of these debris flows (in 1953, 1965, 1975 and 2005) dammed the river forming a barrier lake which is now more than 25 km in length. The repeated damming by debris flows has increased the dam height and thereby affected the sedimentation rates in the barrier lake. The frequent debris flow activity has prevented vegetation recovery on the fan, while sedimentation in the barrier lake has allowed vegetation to colonize the deltas. This study investigated the effects of frequent debris flow damming on sedimentation rates as well as on revegetation and tree disturbance along the river. We documented the landscape evolution and measured the sedimentation thickness and grain size of deposited material at different locations of the barrier lake using cores. We also collected and analyzed growth-ring records from disturbed trees on the fan and the deltas of the barrier lake. We found that frequent debris flows had created a stepped river morphology and greatly increased sedimentation rates in the lake, affecting vegetation on the fan and behind the dam.

Airborne LiDAR-Based Mapping of Surface Ruptures and Coseismic Slip of the 1955 Zheduotang Earthquake on the Xianshuihe Fault, East Tibet

ABSTRACTSurface ruptures and coseismic slip distributions of large earthquakes are the keys to understanding earthquake rupture processes, analyzing rupture history of associated faults, and assessing earthquake hazards. Detailed mapping of surface ruptures of large historical earthquakes is needed but is difficult in remote regions. The 1955 Ms 7.5 Zheduotang earthquake occurred in a prominent restraining bend of the central sinistral Xianshuihe fault and within a high-relief and densely vegetated mountain range. This study characterizes the 1955 earthquake surface rupture via 50 cm resolution airborne light detection and ranging (LiDAR) data, combined with field investigations. Our mapping of geomorphic features showed that relatively fresh mole tracks and fault scarps are still preserved beneath the dense vegetation cover. The 1955 earthquake ruptured at least 30 km in length, which consisted of four sections separated by stepovers or changes in the strike. Overall, the multistranded rupture was more complex than that of other historical earthquakes to the northwest along the Xianshuihe fault but consistent with its local structural setting. We collected 47 LiDAR-derived and 48 field-based left-lateral (with minor vertical) measurements. The clustering of the smallest offsets suggests that the average sinistral coseismic displacement of the 1955 earthquake was ∼2.1 m based on LiDAR-derived data and ∼1.5 m based on field measurements. This difference highlights the ambiguity and difficulties associated with surface rupture investigations of historical earthquakes decades after the event. The rupture length (∼30 km) and average sinistral displacement (1.5–2.1 m) suggest a moment magnitude of 6.6–7.4 based on empirical relationships of strike-slip earthquakes worldwide. The magnitude is smaller than the widely accepted Ms 7.5 in the catalog, suggesting that the previously reported magnitude was possibly overestimated. Our data have implications for the seismic hazard evaluation of the Sichuan–Tibet railway, which passes through the northern part of the ruptured fault.

Airborne data processing and 3D modeling of magnetic structures between Nador region and the Chaffarine Islands: Geological significances

The Cap of Trois Fourches-Nador-Chaffarine Islands zone (CTF-N-CI) located in the Moroccan Oriental Rif is recognized by Neogene-Quaternary volcanic outcrops. Those later formed volcanic cones and are considered the main source of the huge Nador magnetic anomaly. This study aims to enhance the magnetic context using geophysical techniques and identify the geometry of magnetic sources by performing 3D modeling using Talwani method. We have achieved the following findings: (1) The elaborated residual magnetic map (Rs) that shows three aligned magnetic anomalies. They are oriented W-E and register a maximum intensity of 380 nT. Applying reduction to the pole to (RTP) the Rs map makes the anomalies on the top of their body sources. Thus, we have found that those anomalies have resulted essentially from the Gourougou volcano and Chaffarine Islands volcanoes outcropping in the study area. Except for the middle Pm anomaly, which is related to volcanic rocks of the Kariate Arekmane drillhole. (2) Performing horizontal derivative (HD) technique leads to establishing the edges of the source bodies. Hence, the inversed map of the magnetization distribution proves that the three bodies are homogeneous and probably splintered from a unique mass. (3) The downward up continuation (DC) to different heights (from 500 to 2000 m) indicates the source's depth. Thus, we have demonstrated that the common source could reach 0.6 km of altitude. (4) Finally, we have constructed a 3D Talwani model of the volcanic edifices. The released 3D model demonstrates that the anomalies are related to a very extensive mass of 80 km in length, 20 km in width, 1.3 km in thickness. This model supports that the Neogene-Quaternary volcanism of the study area was fissural and related to the W-E fracture zone of up to 80 km in length. This volcanism was also affected by the sinistral Nekor fault, which probably made the Trois Fourches Cap body isolated from the other volcanic edifices.Previously mentioned elements probably prove the simultaneous establishment of this large magnetic structure. Moreover, they emphasize the crucial role of the magmatic phenomena which occurred in Northeastern Morocco at the beginning of the Messinian.