The 2015 Mw7.8 Gorkha earthquake in Nepal resulted in 9,084 fatalities, the collapse of thousands of buildings, and a large number of landslides. Field investigations revealed the poor seismic performance of structures in the affected area, which can be categorized as self-built reinforced concrete frame structures, brick and concrete structures, brick and timber structures, and rubble structures. Interpretation of earthquake-induced landslides was conducted based on high-resolution satellite imagery. The landslides triggered by the Mw7.8 Gorkha earthquake were primarily distributed in the boundary area between the High Himalaya and the Low Himalaya, and basically spread along the Main Central Thrust (MCT). The distribution of landslides was consistent with the characteristics of topography, seismic intensity, and aftershocks. The intensity map of the Mw7.8 Gorkha earthquake was revised based on the investigation of building damage and secondary hazards. The overall intensity circle featuring two macro-seismic epicenters, appeared elliptical with a NWW orientation on the long axis, and a highest intensity reaching Ⅸ.
The comprehensive positioning and seismic hazard assessment of fault zones are significant challenges faced by many countries worldwide. The author employs SBAS-InSAR technology to conduct spaceborne interferometry radar timeseries dynamic monitoring of the Handan area, with a focus on the Handong fault as the main subject of investigation. The monitoring period spans from the beginning of 2017 to 2021, comprising a total of 48 monitoring phases. The comprehensive deformation velocity fields and monthly cumulative deformation data were obtained and primarily used to analyze the Handong fault in conjunction with multiple data sources. The results indicate that the Handong fault is the primary structural feature in this area, acting as the demarcation line between regional uplift and subsidence deformations. On the western side of the Handong fault, there is evidence of uplift, while the eastern side experiences subsidence. The average uplift rate on the western side is approximately 0.51 mm/a, which is generally consistent with the overall uplift rate of the Taihang Mountain. On the eastern side, the average subsidence rate is -29.8 mm/a, which is mainly attributed to the over-extraction of groundwater, with a relatively lower likelihood of being influenced by tectonic activity.
The author collected, organized, and analyzed data from 2,525 representative boreholes in the Handan region, conducted lithological stratification and established a database. Via the software platforms Petrel and ArcGIS, a 3D stratigraphic sequence-structural framework model was developed based on the typical borehole database and stratigraphic sequence-structural framework. The model provides valuable insights into the structural evolution in the Handan region, presenting structural maps, thickness maps, and Quaternary structural profile maps since the Late Quaternary. Through a detailed analysis of the deformation within the Qp 2 , Qp 3 , and Qh stratum groups, this study unveils the distribution patterns and activity characteristics of concealed faults, including the Taihang Mountain piedmont fault (F1), the Handan concealed fault (F2), and the Lianfanglu fault (F3).
Most major earthquakes worldwide occur within subduction zones, but there is a death of studies on earthquake induced landslides in subduction zones. the Mw7.8 earthquake that jolted Nepal on April 25, 2015, the first strong earthquake in the Himalayan Subduction Zone in nearly 70 years, triggered a large landslide event, and the area served as a good venue for conducting research on earthquake-triggered landslides in Himalayan Subduction Zones. Based on remote sensing interpretation and field investigation, 2,072 sets of earthquake-triggered landslide information were obtained, revealing that the Nepalese earthquake-triggered landslides are distributed between 1,000-3,000 m above sea level, in the transition area between the High Himalaya and the Low Himalaya, basically along the Main Central Thrust, with a large topographic drop; The dominant distribution range of landslide slope values is 35-40°; the dominant distribution range of aspect values is 120-200°, which is closely related to the horizontal deformation field. The basic characteristics of earthquake-triggered landslides in the Himalayan Subduction Zone are initially discussed: The landslide points are clearly distributed in a faceted pattern and are closely associated with deep, low-dip fault rupture surfaces; the landslides are all located in the upper plate, and are easily induced by the inertia of seismic motion on slopes with slopes that are oriented in the same direction as the reverse thrust of the upper plate.
The author collected, organized, and analyzed typical borehole data in Nantong City and established a database for borehole lithological stratification and stratigraphic sequence. With the help of typical borehole database and under the stratigraphic sequence-structural framework, a 3D model of the Quaternary stratigraphic sequence-structural framework of Nantong City is constructed via MVS and ArcGIS. The model includes layered contour maps and typical lithostratigraphic profiles, enabling 3D geological modeling and visualization of Nantong City. The modeling results are analyzed in conjunction with the findings of shallow seismic exploration, revealing the spatial distribution of major stratigraphic interfaces and the spatial correspondence between the undulating morphology of the bottom interface and the location of target faults.
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