The October 13, 2020, deadly rapid landslide triggered by heavy rainfall in Phong Dien,Thua Thien Hue,Vietnam

Landslides - At about 12:00 a.m., on October 13, 2020, a rapid rotational landslide induced by rainfall swept over Ranger Station-7 in Phong Xuan commune, Phong Dien district, Thua Thien Hue...     

Geodetic measurement of horizontal strain across the Red River fault near Thac Ba, Vietnam, 1963–1994

Geodetic measurements from 1963 through 1994 are used to estimate horizontal strain rates across the Red River fault near Thac Ba, Vietnam. Whether or not this fault system is currently active is a subject of some debate. By combining: (1) triangulation from 1963, (2) triangulation in 1983, and (3) Global Positioning System (GPS) observations in 1994, horizontal shear strain rates are estimated without imposing any prior information on fixed stations. The estimated rates of shear strain in ten triangular subnetworks surrounding the fault trace are not significantly different from zero at 95% confidence. The maximum rate of dextral shear is less than 0.3 μrad/year in all but one of the triangles. The estimates help bound the slip rate in a simple elastic dislocation model for a locked, vertical strike-slip fault. By assuming a locking depth of 5–20 km, the most likely values for the deep slip rate are between 1 and 5 mm/year of right-lateral motion. These values delimit the 23% confidence interval. At 95% confidence, the slip rate estimate falls between 7 mm/year of left-lateral motion and 15 mm/year of right-lateral motion. Received: 18 November 1997 / Accepted: 28 January 1999     

Propagation of Pc 1 pulsations in off-meridian directions

Experimental investigations on the horizontal propagation of Pc 1 pulsations in directions out of the geomagnetic meridian have been carried out using data recorded over a three-year period at four widely-separated middle and low latitude stations. The results obtained show that Pc 1 signals propagate in off-meridian directions, and that horizontal propagation characteristics in the early morning hours have small directional changes.     

Quaternary sediments in the Dien Bien Phu fault zone, NW Vietnam: a record of young tectonic processes in the light of OSL-SAR dating results

The Dien Bien Phu fault zone (DBP), orientated NNE to N, is one of the most seismically active zones in Indochina. In NW Vietnam, this zone is 160 km long and 6–10 km wide, cutting sedimentary and metamorphic rocks of the Late Proterozoic, Palaeozoic and Mesozoic age, as well as Palaeozoic and Late Triassic granitoids. Along the DBP relatively small, narrow pull-apart basins occur, the three largest of which (Chan Nua, Lai Chau and Dien Bien Phu) have been studied in detail. All of them are bounded by sinistral and sinistral-normal faults, responsible for offset and deflected drainage, presence of numerous shutter ridges and displaced terraces and alluvial fans. The normal component of motion is testified to by well-preserved triangular facets on fault scarps, highly elevated straths in river watergaps, overhanging tributary valleys, as well as high and uneven river-bed gradients.Our observations indicate a minimum recent sinistral offset ranging from 6–8 to 150 m for Holocene valleys to 1.2–9.75 km for middle–late Pleistocene valleys in different fault segments. The thickness of Quaternary sediments varies from 5–25 m in the Lai Chau area to some 130 m in the Dien Bien Phu Basin. In the Lai Chau Basin, the middle terrace (23 m) alluvia of Nam Na River at Muong Te bridge have been optically stimulated luminescence/single aliquot regenerative dose technique (OSL-SAR) dated at 23–40 to 13 ka. These sediments were normal-faulted by some 11 m after 13 ka, and mantled by vari-coloured slope loams, 8–12 m thick, containing colluvial wedges composed of angular debris. These wedges were probably formed due to at least three palaeoseismic events postdating 6 ka. In the Dien Bien Phu Basin, in turn, alluvium of the upper Holocene terraces has been OSL-SAR dated to 6.5–7 and 1.7–1.0 ka, whereas the younger (sub-recent) terrace sediments give ages of 0.5–0.2 ka.Displaced terraces and alluvial fans allow us to suppose that the sinistral and sinistral-normal faults bounding narrow pull-apart basins in the southern portion of the DBP fault reveal minimum rates of left-lateral strike-slip ranging from 0.6 to 2 mm/year in Holocene and 0.5–3.8 mm/year in Pleistocene times, whereas rates of Holocene uplift tend to attain 1 mm/year north of Lai Chau and 0.4–0.6 mm/year west of Dien Bien Phu. More precise estimations, however, are difficult to obtain due to poor age control of the displaced drainage. Rates of Quaternary strike-slip are comparable with those of the Red River fault; the sense of movement being, however, opposite. Taking into account the presence of two phases of Late Cenozoic strike-slip of contrasting sense of motion, as well as the geometry of the two fault zones, we hypothesize that the Red River and Dien Bien Phu faults are conjugate faults capable of generating relatively strong earthquakes in the future.     

Spatial prediction of landslide susceptibility in western Serbia using hybrid support vector regression (SVR) with GWO,BAT and COA algorithms

In this study, we developed multiple hybrid machine-learning models to address parameter optimization limitations and enhance the spatial prediction of landslide susceptibility models. We created a geographic information system database, and our analysis results were used to prepare a landslide inventory map containing 359 landslide events identified from Google Earth, aerial photographs, and other validated sources. A support vector regression (SVR) machine-learning model was used to divide the landslide inventory into training (70%) and testing (30%) datasets. The landslide susceptibility map was produced using 14 causative factors. We applied the established gray wolf optimization (GWO) algorithm, bat algorithm (BA), and cuckoo optimization algorithm (COA) to fine-tune the parameters of the SVR model to improve its predictive accuracy. The resultant hybrid models, SVR-GWO, SVR-BA, and SVR-COA, were validated in terms of the area under curve (AUC) and root mean square error (RMSE). The AUC values for the SVR-GWO (0.733), SVR-BA (0.724), and SVR-COA (0.738) models indicate their good prediction rates for landslide susceptibility modeling. SVR-COA had the greatest accuracy, with an RMSE of 0.21687, and SVR-BA had the least accuracy, with an RMSE of 0.23046. The three optimized hybrid models outperformed the SVR model (AUC = 0.704, RMSE = 0.26689), confirming the ability of metaheuristic algorithms to improve model performance.     

Change in carbon flux (1960–2015) of the Red River (Vietnam)

Global riverine carbon concentrations and fluxes have been impacted by climate and human-induced changes for many decades. This paper aims to reconstruct the longterm carbon concentrations and carbon fluxes of the Red River, a system under the coupled pressures of environmental change and human activity. Based on (1) the relationships between particulate and dissolved organic carbon (POC, DOC) or dissolved inorganic carbon (DIC), and suspended sediments (TSS) or river water discharge and on (2) the available detailed historical records of river discharge and TSS concentration, the variations of the Red River carbon concentration and flux were estimated for the period 1960–2015. The results show that total carbon flux of the Red River averaged 2555?±?639 kton C year^?1. DIC fluxes dominated total carbon fluxes, representing 64% of total, reflecting a strong weathering process from carbonate rocks in the upstream basin. Total carbon fluxes significantly decreased from 2816 kton C year^?1 during the 1960s to 1372 kton C year^?1 during the 2010s and showed clear seasonal and spatial variations. Organic carbon flux decreased in both quantity and proportion of the total carbon flux from 40.9% in 1960s to 14.9% in 2010s, reflecting the important impact of dam impoundment. DIC flux was also reduced over this period potentially as a consequence of carbonate precipitation in the irrigated, agricultural land and the reduction of the Red River water discharge toward the sea. These decreases in TSS and carbon fluxes are probably partially responsible for different negatives impacts observed in the coastal zone.     

On the importance of river hydrodynamics in simulating groundwater levels and baseflows

Research to date affirmed the key role of stream–aquifer interactions in integrated water resources management. The importance of river hydrodynamics on the spatial and temporal behaviour of groundwater was, however, not yet fully investigated. In contrast to the common approach where topography-based estimates of riverbed elevation may lead to inappropriate discretization and constant river stages, this study couples a fully hydrodynamic and one-dimensional river model to a two-dimensional catchment hydrological model. The surface and subsurface runoff, groundwater, and river components are integrated into a single modelling framework. The coupled model was applied to a medium sized catchment in Belgium with three model setups, in which the level of detail of representation of river hydrodynamics varies. Further model iterations were carried out for the most exhaustive setup to assess the importance of the bi-directional interactions between model components. Results show that higher details of river hydrodynamics help to improve the simulation of time-averaged groundwater levels. However, the impacts were not that clear for the time-varying groundwater levels. Moreover, visual and statistical model performance evaluation indicates a strong enhancement of the coupled models compared to the output from the hydrological model with respect to river discharge observations at catchment outlet and at internal stations. It also reveals the impact of river hydrodynamics on groundwater discharges when the most detailed setting delivered the highest performance among the three coupled models.     

Propagation characteristics of hydromagnetic waves in various layers of the ionosphere

This paper derives the basic propagation characteristics of hydromagnetic waves in various layers of the ionosphere. It is shown that propagation in the upper ionosphere and the F₂ layer is largely isotropic. In the lower region of the ionosphere there are two possible modes of propagation, both being anisotropic. Propagation characteristics of waves in this lower region, however, are relatively independent of the direction of horizontal propagation. Calculations of intrinsic wave attenuation show that ducted propagation of Pc 1 signals over appreciable horizontal distances may only take place in the upper layers of the ionosphere.