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.

Experimental study on the effect of concrete strength and corrosion level on bond between steel bar and concrete

Corrosion of the steel reinforcement bars reduces the area of the steel bar and the bond stress between the steel bars and around concrete that decreases the capacity of concrete structures. In this study, the bond stress between steel bar with a diameter of 12mm and concrete was examined with the effect of different corrosion levels and different concrete grades. A steel bar was inserted in a concrete block with a size of 20×20×20cm. The compressive strength of concrete was 25.6MPa, 35.1MPa, and 44.1MPa. These specimens were soaked into solution NaCl 3.5% to accelerate the corrosion process with different corrosion levels in the length of 60mm. The pull-out test was conducted. Results showed that the bond strength of the corroded steel bar was higher than that predicted from CEB-FIP. Slip displacement and the range of slip displacement at the bond strength were reduced when the concrete compressive strength was increased. The rate of bond stress degradation occurred faster with the increment of the corrosion level when the concrete compressive strength was increased.

Geological structures beneath the River Thames in London: findings from the Thames Tideway Tunnel investigations

The Thames Tideway Tunnel is 25 km long and extends west – east through central London, beneath the River Thames for most of its route. A detailed preconstruction ground model has been assembled, using data from borehole and river-borne seismic reflection survey investigations. The two data sets have together delineated several significant geological structures along the route.The investigations have led to an improved understanding of the morphology of some structures, such as the Greenwich Fault, London Bridge Fault Zone, Millwall Anticline and Greenwich-Plaistow Syncline, which were only generally indicated during preliminary desk studies. Other structures, such as the Putney-Hammersmith Fault Zone, Chelsea Embankment Fault Zone and Lambeth Anticline, are entirely new discoveries.Most of the structures described here have characteristics compatible with strike-slip displacement and, although this has been previously widely suspected, this paper presents new evidence towards this. When intersected by the tunnel during its construction phase, they have imposed significant changes in geological strata, leading to changes in the performance of tunnelling plant or creating adverse ground conditions. Their early identification by the ground model has assisted engineering design and planning, for the benefit of construction cost efficiency and, importantly, Health and Safety of underground personnel.Thematic collection: This article is part of the Geology of London and its implications for ground engineering collection available at: https://www.lyellcollection.org/cc/london-basin

A Three-Section-Settlement Calculation Method for Composite Foundation Reinforced by Geogrid-Encased Stone Columns

The analysis of the bearing characteristics and deformation mechanism of composite foundation reinforced with geogrid-encased stone columns is presented in order to obtain its settlement calculation method. The settlement of composite foundation is divided into three sections which are the reinforced section, unreinforced section, and underlying stratum. Based on Hooke’s law of space problem and the thoughts of the layer-wise summation method, the relative slip displacement between pile and soil of reinforced section without plastic zone is analyzed. The settlement of reinforced section is calculated by the layered iteration method based on the pile element model. The compatibility of vertical and radial deformations of unreinforced section is analyzed based on the pile-soil element model. The settlement of underlying stratum is still calculated by the layer-wise summation method. Finally, two engineering examples are analyzed and the results show that the settlement calculated by the presented method is close to the measured one. The method overcomes the defect that the calculated results by the other existing methods are more dangerous and it is more feasible and can be applied in engineering practice.

Supplemental Material: ‘Taters versus Sliders: Evidence for a Long-Lived History of Strike-Slip Displacement along the Canadian Arctic Transform System (CATS)

Probability plots, Shepard plot, and sources of U/Pb data in Figure 2A.

Supplemental Material: ‘Taters versus Sliders: Evidence for a Long-Lived History of Strike-Slip Displacement along the Canadian Arctic Transform System (CATS)

Probability plots, Shepard plot, and sources of U/Pb data in Figure 2A.

Development and Performance Evaluation of a Bevameter for Measuring Soil Strength

The driving performance of an off-road vehicle is closely related to soil strength. A bevameter is used to measure the soil strength, and it usually consists of two independent devices: a pressure–sinkage test device and a shear test device. However, its development and measurement processes have not been standardized; thus, researchers apply it in various fields according to their own discretion. In this study, a new bevameter was developed, and experiments were conducted to clarify the factors that affect the measurement performance of the bevameter. The pressure–sinkage test device was tested with circular plates of different sizes, and the results confirmed that the pressure–sinkage parameters decreased with the plate size. For the shear-test device, normal pressure was applied using a dead load to prevent normal-pressure variation due to displacement and speed. In addition, a spline was installed on top of the shaft connected to the shear ring to measure slip sinkage during the shear test. The results showed that the slip sinkage increased in proportion to the normal pressure and slip displacement, but the increase gradually decreased and converged to a certain point.

Establishing primary surface rupture evidence and magnitude of the 1697 CE Sadiya earthquake at the Eastern Himalayan Frontal thrust, India

Historical archives refer to often recurring earthquakes along the Eastern Himalaya for which geological evidence is lacking, raising the question of whether these events ruptured the surface or remained blind, and how do they contribute to the seismic budget of the region, which is home to millions of inhabitants. We report a first mega trench excavation at Himebasti village, Arunachal Pradesh, India, and analyze it with modern geological techniques. The study includes twenty-one radiocarbon dates to limit the timing of displacement after 1445 CE, suggesting that the area was devastated in the 1697 CE event, known as Sadiya Earthquake, with a dip-slip displacement of 15.3 ± 4.6 m. Intensity prediction equations and scaling laws for earthquake rupture size allow us to constraints a magnitude of Mw 7.7–8.1 and a minimum rupture length of ~ 100 km for the 1697 CE earthquake.