A Nonextensive Statistical Physics Analysis of the 1995 Kobe, Japan Earthquake

This paper presents an analysis of the distribution of earthquake magnitudes for the period 1990–1998 in a broad area surrounding the epicenter of the 1995 Kobe earthquake. The frequency–magnitude distribution analysis is performed in a nonextensive statistical physics context. The nonextensive parameter q M , which is related to the frequency-magnitude distribution, reflects the existence of long-range correlations and is used as an index of the physical state of the studied area. Examination of the possible variations of q M values is performed during the period 1990–1998. A significant increase of q M occurs some months before the strong earthquake on April 9, 1994 indicating the start of a preparation phase prior to the Kobe earthquake. It should be noted that this increase coincides with the occurrence of six seismic events. Each of these events had a magnitude M = 4.1. The evolution of seismicity along with the increase of q M indicate the system’s transition away from equilibrium and its preparation for energy release. It seems that the variations of q M values reflect rather well the physical evolution towards the 1995 Kobe earthquake

Temperature and pore pressure effects on the shear strength of granite in the brittle-plastic transition regime

Currently published lithospheric strength profiles lack constraints from experimental data for shear failure of typical crustal materials in the brittle-plastic transition regime in wet environments. Conventional triaxial shear fracture experiments were conducted to determine temperature and pore pressure effects on shear fracture strength of wet and dry Tsukuba granite. Experimental conditions were 70MPa < P-C < 480MPa, 10MPa < P-p < 300MPa, 25 A degreesC < T < 480 degreesC, at a constant strain rate of 10(-5)s(-1). An empirical relation is proposed which can predict the shear strength of Tsukuba granite, within the range of experimental conditions. Mechanical pore pressure effects are incorporated in the effective stress law. Chemical effects are enhanced at temperatures above 300 degreesC. Below 300 degreesC wet and dry granite strengths are temperature insensitive and wholly within the brittle regime. Above 400 degreesC, semi-brittle effects and ductility are observed

Memory in sea ice friction

Friction between sea ice floes is a control on rafting, ridging, and in-plane sliding, and is therefore relevant to a range of engineering problems. Understanding sea ice friction is complicated, because the contact surfaces abrade and melt as sliding occurs. Currently most representations of sea ice friction (for example in discrete element modelling) use Amontons’ law for friction, with a wide uncertainty over μ. In this paper we discuss recent work on incorporating memory into an empirical model of sea ice friction. We present a simple model with rate and state dependence derived from laboratory results, and show how this model predicts varying friction on a sliding surface under varying slip rate. We then use this model within a discrete element model to investigate the importance of friction modelling to the modelling of sea ice behaviour as aggregated across many floes

Climate change driven disaster risks in Bangladesh and its journey towards resilience

Globally, disasters from natural and anthropogenic hazards or humanitarian crises can reverse development gains and weaken resilience. In recent years, some countries have made significant progress towards building resilience to disaster risks, including those driven by the climate crisis. Bangladesh is a leading example as it is well-known as one of the most vulnerable countries for its multifaceted hazard risks projected to intensity under climate change. Today, the scale of loss of human life from both rapid and slow-onset disasters (e.g. cyclone, flood and drought) is significantly lower than in the 1970s. This remarkable achievement was made possible by independence and the government’s proactive investment in development and societal changes through education, technologies and reduction in poverty and inequalities. However, the climate crisis is threatening these development and disaster risk reduction gains. In addition, disaster displacement is a major challenge. The COVID-19 pandemic has unveiled both strengths and weaknesses in our societies. The article argues that disaster management plans need to adapt to the climate crisis and human displacement and reduce migrants’ vulnerability while responding to infectious disease transmission

Flash flood susceptibility assessment using the parameters of drainage basin morphometry in SE Bangladesh

Predicting the occurrence and spatial patterns of rainfall induced flash floods is still a challenge. Instant genesis and typically smaller areal coverage of the flash floods are the major impediments to their forecasting. Analysis of the morphometric parameters provides useful insight on hydrological response of the drainage basins to high intensity rainfall events. This information is valuable for understanding the flash flood potential of the drainage basins and for evading the destructions caused by the hazard. Here, we use eighteen morphometric parameters that influence the runoff volume, flow velocity, and inundation depth scenario of a flash flood. The analysis has been carried out for simulating the relative flash flood susceptibility of thirteen watersheds (B1 to B13) of variable sizes in southeastern Bangladesh. The morphometric parameters were derived from Digital Elevation Model (DEM) using Geographic Information System (GIS). The evaluated basin parameters include: area (A), perimeter (P), length (Lb), stream order (Su), stream number (Nu), stream length (Lu), stream frequency (Fs), drainage density (Dd), texture ratio (Rt), bifurcation ratio (Rb), basin relief (Hr), relief ratio (Rr), ruggedness number (Rn), time of concentration (Tc), infiltration number (If), and form factor (F). Two relative flash flood susceptibility scenarios were generated: (i) general watershed level, and (ii) more precise pixel level status. The watershed level comparison reveals that B4 and B6 watersheds constituting 72.61% of the total area are ‘very high’ susceptible, whereas the susceptibility of the other watersheds has been found as ‘high’ [B5 (6.95%)], ‘moderate’ [B8 and B13 (8.63%)], ‘low’ [B2, B10, B11 (4.64%)], and ‘very low’ [B1, B3, B7, B9, and B12 (7.18%)]. The derived watershed susceptibility map was subsequently integrated with two spatial analysis algorithms i.e., topographic wetness index (TWI) and topographic position index (TPI) through overlay analysis. The integration helped to understand the combined role of the general watershed morphometry and the in situ topography for determining flash flood susceptibility of each spot (30  m × 30  m) within all the selected watersheds. The quantitative analysis and characterization of the watersheds from the perspective of flash flood hazard in this investigation is expected to be useful for implementing the site-specific mitigation measures and alleviating the effects of the hydrological hazard in the study area

The performance of fiber reinforcement in completely decomposed granite

Adding discrete fibers to soils can improve their strength; however, fiber reinforcement remains scarce in practice. Previous studies on the performance of soils reinforced with discrete fibers consist mainly of laboratory studies with either clay or, most often, uniform sand as the host soil, so there is a lack of data on other types of soils such as weathered soils, which tend to be well graded. Unlike uniform soils, which are generally dilative, well-graded soils usually show a contractive behavior. This study examines the effect of adding fibers to a completely decomposed granite (CDG) typical of many residual soils, which has the characteristics to be sensitive to material and sample preparation and also to be compressive during shearing. It is found that adding discrete fibers to the CDG homogenizes it because the reinforced soil is not sensitive to the method of material or sample preparation. It is also found that, despite its compressive nature, fibers mobilize extra strength compared with the unreinforced soil, and this effect does not reduce at large confining stresses. Adding discrete fibers to soils can improve their strength; however, fiber reinforcement remains scarce in practice. Previous studies on the performance of soils reinforced with discrete fibers consist mainly of laboratory studies with either clay or, most often, uniform sand as the host soil, so there is a lack of data on other types of soils such as weathered soils, which tend to be well graded. Unlike uniform soils, which are generally dilative, well-graded soils usually show a contractive behavior. This study examines the effect of adding fibers to a completely decomposed granite (CDG) typical of many residual soils, which has the characteristics to be sensitive to material and sample preparation and also to be compressive during shearing. It is found that adding discrete fibers to the CDG homogenizes it because the reinforced soil is not sensitive to the method of material or sample preparation. It is also found that, despite its compressive nature, fibers mobilize extra strength compared with the unreinforced soil, and this effect does not reduce at large confining stresses

Cyclone risk assessment of the Cox’s Bazar district and Rohingya refugee camps in southeast Bangladesh

Bangladesh has a long history of devastating tropical cyclones. In view of the effects of the storms on the country, risk assessment is essential for devising the mitigation strategies at various levels. By way of bringing the conceptual structure of general risk model in practice, this work aims to examine the spatial patterns of cyclone risk in the Cox’s Bazar district (I) and Rohingya refugee camps (II) located on the southeastern coast of Bangladesh. We use 14 parameters representing the hazard, exposure, and vulnerability as the components of risk. The selected parameters were analyzed and integrated though the complementary use of Analytic Hierarchy Process (AHP) and Geographic Information System (GIS) for depicting the cyclone risk situation comprehensively at both the spatial scales. The status of the cyclone risk was identified and quantified as very high (6.84%, 3.43%), high (45.78%, 27.82%), moderate (5.97%, 39.42%), low (40.62%, 28.70%), and very low (0.81%, 0.61%) for the spatial scale I and II respectively. In general, northwestern and southern peripheral areas exhibited higher risk than the central and northeastern parts of the Cox’s Bazar district; and in the refugee settlements, camp number 1E, 1W, 7, and 13 revealed relatively higher levels of the risk. The results of the assessment (I) were correlated with experiential damage from the 1991 cyclone; a reasonable consistency was noticed between the simulated scenario and the observed impacts. We assume that the deliverables of this spatial analysis could be useful to stakeholders while formulating the cyclone risk mitigation policies for the region. Furthermore, this work demonstrates that the applied method would deliver reliable results if tested in other coastal environments

The effect of ice rubble on ice-ice sliding

Ice deformation processes in the Arctic can generate ice rubble. Many situations arise where ice fragments of varying size separate sea ice floes. While the shear forces between sea ice floes in direct contact with each other are controlled by ice-ice friction, what is not known is how the slip of the floes is affected by the presence of rubble between the sliding surfaces. We present the result of field experiments undertaken on sea ice in the Barents Sea. A doubledirect-shear experiment was done on floating sea ice in the field, with the addition of rubble ice between the sliding surfaces. This was achieved by pulling a floating ice block through a cut channel of open water 3m long, where broken ice filled the gap between the block and the channel sides. The displacement of the block and the force needed to move the block were measured. The time that the block was held motionless to allow the rubble to consolidate was recorded - this ranged from seconds to several hours. We found that the 'hold time' controls the maximum force needed to move the block. The relation between hold time and force is highly non-linear from which we deduce thermal consolidation is the controlling mechanism

Continuum sea ice rheology determined from subcontinuum mechanics

[1] A method is presented to calculate the continuum-scale sea ice stress as an imposed, continuum-scale strain-rate is varied. The continuum-scale stress is calculated as the area-average of the stresses within the floes and leads in a region (the continuum element). The continuum-scale stress depends upon: the imposed strain rate; the subcontinuum scale, material rheology of sea ice; the chosen configuration of sea ice floes and leads; and a prescribed rule for determining the motion of the floes in response to the continuum-scale strain-rate. We calculated plastic yield curves and flow rules associated with subcontinuum scale, material sea ice rheologies with elliptic, linear and modified Coulombic elliptic plastic yield curves, and with square, diamond and irregular, convex polygon-shaped floes. For the case of a tiling of square floes, only for particular orientations of the leads have the principal axes of strain rate and calculated continuum-scale sea ice stress aligned, and these have been investigated analytically. The ensemble average of calculated sea ice stress for square floes with uniform orientation with respect to the principal axes of strain rate yielded alignment of average stress and strain-rate principal axes and an isotropic, continuum-scale sea ice rheology. We present a lemon-shaped yield curve with normal flow rule, derived from ensemble averages of sea ice stress, suitable for direct inclusion into the current generation of sea ice models. This continuum-scale sea ice rheology directly relates the size (strength) of the continuum-scale yield curve to the material compressive strength

Geological and soil engineering properties of shallow landslides occurring in the Kutupalong Rohingya Camp in Cox's Bazar, Bangladesh

The Forcibly Displaced Myanmar Nationals (FDMN), historically known as ‘Rohingya’ who fled the 2017 ethnic atrocities and genocide in the Northern Rakhine State of Myanmar, took shelter in Cox’s Bazar District of Bangladesh. The camp network, known as Kutupalong Rohingya Camp (KRC), is situated in the tectonically active tertiary hilly terrain. The KRC has been experiencing hydrometeorological hazards, where landslides are frequent. This study investigated the slopes’ geological condition, engineering properties and human interventions, which influence the landslides. The exposed slopes were relatively high (> 10 m) and steep ranging from 40° to 60° that have numerous polygonal tension cracks and fissures. From the geological and geotechnical aspects, there are three successive units of slope materials: (1) residual soils of sandy silt with clay, (2) highly weathered silty sandstones and (3) shale/clay with silt and fine sand intercalations at the bottom of the slopes. Field observations revealed that most slope failures occurred in the residual soil and weathered silty sandstone units. The residual soils have a bulk density of 1.49–1.97 g/cm3, a liquid limit of 25–48%, a plasticity index of 5–16% and an undrained shear strength of 23–46 kPa. The silty sandstones have a bulk density of 1.44–1.94 g/cm3, an internal friction angle of 34°–40° and a cohesion of 0.5–13 kPa. The mineralogical composition determined by the X-ray diffraction shows low clay mineral content, which does not affect landslides. However, the slope geometry, low shear strength with strain softening properties and torrential rainfall accompanied by anthropogenic factors cause numerous landslides every year. This study will help take proper mitigation and preparedness measures for slope protection in the KRC area and surroundings