InSAR Constrained Downdip and Updip Afterslip Following the 2015 Nepal Earthquake: New Insights into Moment Budget of the Main Himalayan Thrust

We use ALOS-2 and Sentinel-1 data spanning 2015-2020 to obtain the post-seismic deformation of the 2015 Mw 7.8 Nepal earthquake. ALOS-2 observations reveal that the post-seismic deformation was mainly distributed in four areas. A large-scale uplift deformation occurred in the northern subsidence area of the co-seismic deformation field, with a maximum uplift of ~80mm within 4.5 yr after the mainshock. While in the southern coseismic uplift area, the direction of the post-seismic deformation is generally opposite to the co-seismic deformation. Additionally, two notable deformation areas are located in the region around 29°N, and near the MFT, respectively. Sentinel-1 observations reveal post-seismic uplift deformation on the north side of the co-seismic deformation field with an average rate of ~20 mm/yr in line-of-stght. The kinematic afterslip constrained by InSAR data shows that the frictional slip is distributed in both updip and downdip areas. The maximum cumulative afterslip is 0.35 m in downdip areas, and 0.2 m in the updip areas, constrained by the ALOS measurements. The stress-driven afterslip model shows that the afterslip is distributed in the downdip area with a maximum slip of 0.3m during the first year after the earthquake. Within the 4.5 years after the mainshock, the estimated moment released by afterslip is ~1.5174 × 1020 Nm,about 21.2% of that released by the main earthquake.

Atmospheric phase delay correction of PS-InSAR to Monitor Land Subsidence in Surabaya

Atmospheric phase delay is one of the most significant errors limiting the accuracy of Interferometric Synthetic Aperture Radar (InSAR) results. In this research, we used the Generic Atmospheric Correction Online Service for InSAR (GACOS) data to correct the tropospheric delay modeling from the persistent scatterers’ InSAR monitoring. Eighty-one (81) Sentinel-1A images and tropospheric delay maps from GACOS monitored land subsidence in Surabaya city between 2017 and 2019. InSAR processing was carried out using the GMTSAR software, continued with StaMPS and TRAIN, which were used to correct the tropospheric delay of PSInSAR-derived deformation measurements. The results before and after the atmospheric phase delay correction using GACOS were confirmed and analyzed in the main subsidence area. The findings of the experiments reveal that the atmospheric phase affects the mean LOS velocity results to some extent. The average difference between PS-InSAR before and after tropospheric correction is 1.734 mm/year with a standard deviation of 0.550 mm/year. The significance test of the two variables, 95%, showed that the tropospheric correction with GACOS data could affect the PS-InSAR results. Furthermore, GACOS correction may increase the error at some points, which could be due to its turbulence data’s low accuracy.

Study on The Influence of Direct Ground Liquid CO2 Injection on Soil Chemical Properties in Subsidence Areas under Shallow Buried Geological Conditions

In order to reveal the impact of a high concentration of CO2 on the soil in the coal mining subsidence area, the surface above the goaf before CO2 injection is regarded as a subsidence area model. Based on the actual vertical depth of 70∼80 m shallow buried coal seam geological conditions, CO2 diffusion in the goaf is regarded as a short-term high-concentration CO2 leakage model. The surface soil samples before and after 60 tons of direct injection of liquid CO2 in the goaf of Huojitujing in the Daliuta Coal Mine could be collected to conduct the experimental observation. By measuring the changes in the five indicators of soil air-dried and fresh sample including pH, available nitrogen, available potassium, water-soluble salt, and total organic carbon, the changes of pH and mineral content in the soil could be analyzed quantitatively and qualitatively at different time periods before and after CO2 injection. This proves that the injection of CO2 into the goaf has an impact on the chemical properties of the surrounding soil.

Spatial Variability of Soil Moisture in Mining Subsidence Area of Northwest China

The current research only investigates the impact of coal mining on deep soil moisture from the perspective of the absolute value of soil moisture. This study applied the combined method of classical statistics and multi-dimensional geo-statistics to analyze the temporal and spatial changes of soil moisture from 0-10m in the mining face of Nalin River No.2 Mine in Northwest China from the perspective of spatial variability. The results of the study showed that in time distribution, on the whole, the soil moisture in the partial areas of the 1-year and the 2-year subsidence area was lower than that in the control area, and the variability increased, but as the subsidence entered a stable period, the degree of variability decreased; vertically observed, in space distribution, the 0-10m soil moisture in the control area had obvious distribution rules with low spatial variability. However, the spatial variability of soil moisture in the 1-year subsidence area and the 2-year subsidence area increased, and the variability showed a trend of increasing continuously with the increase of depth. During the principal component analysis, it was found that the change of soil texture caused by coal mining subsidence, the change of soil pores microstructure caused by geotechnical deformation, as well as the preferential flow caused by changes in groundwater level were the main reasons for the increasing spatial variability of soil moisture. This study revealed the principles of spatial variability of soil moisture in coal mining subsidence areas in Northwest China, which can provide a scientific basis for the restoration of mining areas.

Spatial Variability of Soil Moisture in Mining Subsidence Area of Northwest China

The current research only investigate the impact of coal mining on deep soil moisture from the perspective of the absolute value of soil moisture. This study applied the combined method of classical statistics and multi-dimensional geo-statistics to analyze the changes of soil moisture of time and space from 0-10m in the mining face of Nalin River No.2 Mine in Northwest China from the perspective of spatial variability. The results of the study showed that in time distribution, on the whole, the soil moisture in the partial areas of the 1-year and the 2-year subsidence area was lower than that in the control area, and the variability increased, but as the subsidence entered a stable period, the degree of variability decreased; vertically observed, in space distribution, the 0-10m soil moisture in the control area had obvious distribution rules with low spatial variability. However, the spatial variability of soil moisture in the 1-year subsidence area and the 2-year subsidence area increased, and the variability showed a trend of increasing continuously with the increase of depth. During the principal component analysis, it was found that the change of soil texture caused by coal mining subsidence, the change of microstructure of soil pores caused by geotechnical deformation, as well as the preferential flow caused by changes in groundwater level were the main reasons for the increasing spatial variability of soil moisture. This study revealed the principals of spatial variability of soil moisture in coal mining subsidence areas in Northwest China, which can provide a scientific basis for the restoration of mining areas.