Coseismic Deformation Mechanisms of the 2021 Ms 6.4 Yangbi Earthquake, Yunnan Province, Using InSAR Observations

At 21:48 on 21 May 2021, an Ms 6.4 earthquake occurred in Yangbi County, Dali Prefecture, Yunnan Province. At present, uncertainty remains regarding the source parameters and deformation mechanism of the Yangbi earthquake. In this study, we determine fault geometry and slip distribution of the earthquake by InSAR analysis. Then, the Coulomb stress loading caused by the Yangbi earthquake is further analyzed. The results show that the moment magnitude of the Yangbi earthquake was Mw 6.14. The slip mainly occurred at depths of 3–13 km, with a maximum slip of approximately 61 cm at a depth of 6.98 km. The Yangbi earthquake was triggered by a blind fault in the NW-SE in the west parallel to the Weixi-Weishan Fault and its seismogenic fault exhibits strike-slip displacement. A large number of aftershocks were distributed along the fault rupture surface where the Coulomb stress increases. As the depth of the crust increases, the area where the Coulomb stress increases in the Yangbi earthquake, decreases. The occurrence of this earthquake also caused a significant increase in the Coulomb stress in the southeastern section of the Weixi-Weishan Faul. We should pay more attention to its seismic hazards.

Numerical Investigation on the Triaxial Compression Behavior of Large-Scale Jointed Coal

Accurate estimation of the triaxial compression behavior of coal mass is essential for coal mining. In this study, a numerical synthetic rock mass method was used to study the triaxial compression behavior of coal mass. The jointed-coal specimens were constructed based on in-situ joint measurements and microparameter calibration against laboratory tested data. A series of triaxial compression tests on jointed-coal specimens with different loading orientations and confining pressures were performed to obtain joint and confining-pressure effects and to reveal the related failure mechanism. The results suggest that jointed coal has a strong joint effect and confining-pressure effect. Joints weaken the strength and elastic modulus, reduce the lateral deformation, and affect the geometries of the shear-rupture surface. With increase in the confining pressure, the peak strength and residual strength increase but the elastic modulus remains stable; the lateral strain decreases, especially at low confining pressure; the mechanical behavior transitions from brittleness to ductility; the failure mode transitions from shear-rupture surface to plastic flow; and the joint effect diminishes and even disappears. The shear-rupture surface is formed by the combined effect of shear stress and joints at low confining pressure, and the contribution of joints decreases with increase in confining pressure.

Regional-scale susceptibility modelling of shallow landslides involving the weathered and fractured sub-surface bedrock

<p>Landsliding is a complex phenomenon and its modelling aimed at predicting where the processes are most likely to occur is a tricky issue to be performed. Apart the chosen modelling approach, for both data-driven and physically-based models, paying adequate attention to the predisposing and triggering factors, as well as the input parameters is no less important. Generally, shallow landslides mobilize relatively small volumes of material sliding along a nearly planar rupture surface which is assumed to be roughly parallel to the ground surface. In the literature it is also widely accepted that shallow landslides involve only unconsolidated slope deposits (i.e., the colluvium), then the rupture surface corresponds to the discontinuity between the bedrock and the overlying loose soil. In this work, based on systematic field observations, we highlight that shallow landslides often involve also portions of the sub-surface bedrock showing different levels of weathering and fracturing. Then, we show that the engineering geological properties of slope deposits, as well as those related to the underlying bedrock, must be considered to obtain more reliable shallow landslides susceptibility assessment. As a first task, a multi-temporal shallow landslide inventory was built by photointerpretation of aerial orthoimages. Then, a new fieldwork-based method is proposed and implemented to acquire, process and spatialize the engineering geological properties of both slope deposits and bedrock. To support the regional scale approach, field observations were collected within, in the neighbour and far from the shallow landslide areas. Finally, both physically-based and data-driven methods were implemented to assess and compare shallow landslide susceptibility at regional scale, as well as to analyse the role of spatial distribution of rock mass quality for shallow slope failure development. The results highlight that, according to geology, structural setting and morphometric conditions, bedrock properties spatially change, defining clusters influencing both the distribution and characters of shallow landslides. As a consequence, the physically-based modelling provides better prediction accuracy when two possible rupture surfaces are analysed, the shallower one located at the slope deposit / bedrock discontinuity, and the deeper one located at the bottom of the fractured and weathered bedrock horizon. Even though the physically-based and data-driven models provide similar results in terms of ROC curves, the resulting susceptibility maps highlight quite substantial differences.</p>

Residual Stresses of Round Steel Rod at Elastoplastic Twisting

In the elastoplastic twisting of a rod under the action of an external torque, the cross-section of the rod is divided into two zones: the inner elastic zone and the outer plastic zone. After removing the external loads, we observe the residual deformations and the residual stresses inside the rod that significantly affect on the subsequent mechanical processes at manufacturing the products from the round rod. Under too much twisting, the longitudinal surface fibers of the rod begin to tear, the outer surface of the rod ceases to be cylindrical, and the rod’s cross-section ceases to be flat (the Bernoulli’s hypothesis about the flat sections is violated). Next a rupture of the rod is followed. For the plastic materials, the destruction is caused by the pure shear, and the rupture surface is perpendicular to the axis of the rod. For the brittle materials, the destruction occurs, due to the rupture along the screw surface inclined to the axis of the round rod at the angle of 45. In this paper, the residual stresses of the round rod at twisting are obtained for an elastoplastic medium with linear hardening in depending on the rod’s diameter, the shear modulus, the hardening modulus in shear and the yield strength in shear of the rod’s material.

A Pseudodynamic Approach of Seismic Active Pressure on Retaining Walls Based on a Curved Rupture Surface

Reasonable determination of the magnitude and distribution of dynamic earth pressure is one of the major challenges in the seismic design of retaining walls. Based on the principles of pseudodynamic method, the present study assumed that the critical rupture surface of backfill soil was a composite curved surface which was in combination with a logarithmic spiral and straight line. The equations for the calculation of seismic total active thrusts on retaining walls were derived using limit equilibrium theory, and earth pressure distribution was obtained by differentiating total active thrusts. The effects of initial phase, amplification factor, and soil friction angle on the distribution of seismic active earth pressure have also been discussed. Compared to pseudostatic and pseudodynamic methods for the determination of planar failure surface forms, the proposed method receives a bit lower value of seismic active earth pressures.

English-Ukrainian landslide terminology

The interaction between scientific schools in different countries should begin with revision of terminology in the specified science branch and correlation of interpretation, meaning of terms, such as, in Ukrainian and in English. The causes of difficulties of English-Ukrainian landslide terminology are considered in the article, in particular, the different traditions of defining a landslide as a phenomenon, the different degrees of detailing if we talk about the morphological elements and mechanisms of their movement, and the different approaches to criteria of landslides and other hillslope processes classification in regulatory documents (in Ukraine there are ДБН DBN – The State Norms of Construction, and ДСТУ DSTU – The State [Technical] Standards of Ukraine), especially the restricted quantity of suggested terms among them. However, the authors should use the broader terminology to adequately reflection of the Ukrainian researches results in English. For this purpose, a short glossary about six dozen of English terms divided into five thematic blocks (material, movement, surfaces, parts of a landslide, and other structures and smaller forms) is compiled. Several neologisms have been proposed: боковина [bokovyna] – a flank (as a flank of landslide according to D. M. Cruden’s definition (1993): the undisplaced material next to the sides of the rupture surface), маргінальна межа [marhinalʹna mezha] – a toe (by D. M. Cruden’s definition (1993), the lower, usually curved margin of the displaced material of a landslide). It is also suggested using the word верхів’я [verkhivya] as a term, and it means the crown – the practically undisplaced material still in place and adjacent to the highest parts of the main scarp of the landslide. We did not find any English matching to some elements of the landslide, such as брівка головного уступу [brivka holovnoho ustupu] – the contact line between the crown surface and the main scarp surface; зсувні тераси [zsuvni terasy] – terrace-like upper surfaces of the slump blocks; підошва зсуву [pidoshva zsuvu] – the undisturbed or slightly disturbed areas adjacent to the toe of the landslide; ложе зсуву [lozhe zsuvu] – the surface of undisturbed soils and rocks (although there are different meanings of this term). Sometimes a right or left side of the rupture surface is included to the meaning of flank, but in Ukrainian tradition, the term борт зсуву [bort zsuvu] does not contain the undisplaced material adjacent to the sides of the rupture surface. In general, many questions remain, first, a correlation between the landslide classification in the Ukrainian and foreign traditions, so we invite you to continue the discussion about terminology and difference in the meaning or interpretation of terms. Key words: landslides, terminology, Ukrainian, English.