Lushan M S7.0 earthquake: A blind reserve-fault event

Identification and deformation analysis of potential landslides after the Jiuzhaigou earthquake by SBAS-InSAR

A World Natural Heritage Site, Jiuzhaigou, is the first nature reserve in China whose primary purpose is to protect natural scenery. On August 8, 2017, a M_s 7.0 earthquake caused many unstable slopes in Jiuzhaigou, Sichuan Province, China. In the extreme storm conditions that follow, the unstable slopes tend to develop into potential landslides, which can cause many casualties and property losses in scenic areas. Sentinel-1A ascending orbit data were obtained in this paper to establish a SAR database. The large-scale deformation rate map of the study area was obtained using a small baseline set InSAR technology. The potential landslides in the deformation area are preliminarily confirmed with remote sensing interpretation. The field verification is further carried out by studying the deformation information of the characteristic points on the potential landslides. The results show that 13 deformation zones were preliminarily identified, and three typical deformation zones were selected for coupling verification and identified as potential landslides. At the same time, further analysis shows that the four potential landslides have been in continuous linear deformation for a long time since the earthquake, posing a severe threat to the safety of local people's lives and property. The research results provide a reference for the early identification and warning of potential landslides in earthquake-prone regions.

Two multi-temporal datasets to track debris flow after the 2008 Wenchuan earthquake

We provide two datasets for tracking the debris flow induced by the 2008 Wenchuan Mw 7.9 earthquake on a section of the Longmen mountains on the eastern side of the Tibetan plateau (Sichuan, China). The database was obtained through a literature review and field survey reports in the epicenter area, combined with high-resolution remote sensing image and extensive data collection and processing. The first dataset covers an area of 892 km², including debris flows from 2008 to 2020 (an updated version). 186 debris flows affecting 79 watersheds were identified. 89 rainfall stations were collected to determine the rainfall events for the post-earthquake debris flow outbreak. The second database is a list of mitigation measures for post-earthquake debris flows, including catchment name, check dam number, coordinates, construction time, and successful mitigation date. The datasets can aid different applications, including the early warning and engineering prevention of post-earthquake debris flow, as well as provide valuable data support for research in related disciplines.

Gender differences in trajectories of mental health symptoms among Chinese earthquake survivors

BACKGROUND

Posttraumatic stress symptoms and depressive symptoms are prevalent after natural disasters. However, in a Chinese trauma context, little research examined the long-term trajectories of these two symptoms with a gender perspective.

METHODS

Data came from an 8-year longitudinal survey of 3522 Wenchuan earthquake adult survivors. We used multilevel growth-curve models to investigate the trajectories of PTSS and depressive symptoms; adopted conditional growth-curve models to explore the gender differences in trajectories together with gendered factors associated with mental health symptoms; conducted Chow tests to examine the significance of gender differences. Standardized coefficients, P values, and effect sizes were reported.

RESULTS

With covariates controlled, both linear (β = -1.33, p < 0.001, Cohen's d = 0.79) and quadratic effects (β = 1.03, p < 0.001, Cohen's d = 0.59) of time were significant in PTSS trajectory, whereas quadratic effect (β = 0.27, p < 0.001, Cohen's d = 0.14) in the declining depressive trajectory was clinically nonsignificant. Compared with men, women are at higher risk of PTSS (β = 0.12, p < 0.001, Cohen's d = 0.21) and depressive symptoms (β = 0.10, p < 0.001, Cohen's d = 0.20), but also with a faster-declining rate in PTSS within first five years after the disaster. No gender difference was found regarding depressive trajectory. Additionally, poor education and income associate with more PTSS in women, while sickness predicts severer depression in women and more PTSS in men.

CONCLUSIONS

This study proposes a gendered U-shape trajectory for PTSS and a declining depressive trajectory without gender difference. The findings of this study shed light on mental health intervention in future natural disasters.

A possible precursor prior to the Lushan earthquake from GPS observations in the southern Longmenshan

Global Positioning System (GPS) stations installed in and around the epicenter of the Lushan earthquake (Mw 6.7), which occurred almost 5 years after the 2008 Wenchuan earthquake, recorded preseismic deformation corresponding to the Lushan earthquake within the southern Longmenshan thrust belt. A half-space dislocation model is used to simulate the theoretical values of the postseismic displacements caused by the 2008 Wenchuan earthquake, and after transforming the reference frame and filtering the GPS displacement time series, the theoretical and observed GPS values are compared to identify the geodetic anomaly preceding the Lushan earthquake. The abnormal extent of this geodetic anomaly decreases with increasing epicentral distance for each GPS site. This geodetic signal reflects preslip along a locked section of the 2013 seismogenic fault, which caused the accumulation of elastic strain energy until the faulting strength was overcome, thereby generating the Lushan earthquake. Hence, this anomaly might be used as an observable and identifiable precursor to forecast an impending earthquake within a period of less than two and half years before its occurrence.

Multi-Parametric Climatological Analysis Reveals the Involvement of Fluids in the Preparation Phase of the 2008 Ms 8.0 Wenchuan and 2013 Ms 7.0 Lushan Earthquakes

A multi-parametric approach was applied to climatological data before the Ms 8.0 2008 Wenchuan and Ms 7.0 2013 Lushan earthquakes (EQs) in order to detect anomalous changes associated to the preparing phase of those large seismic events. A climatological analysis for seismic Precursor Identification (CAPRI) algorithm was used for the detection of anomalies in the time series of four parameters (aerosol optical depth, AOD; skin temperature, SKT; surface latent heat flux, SLHF and total column water vapour, TCWV). Our results show a chain of processes occurred within two months before the EQs: AOD anomalous response is the earliest, followed by SKT, TCWV and SLHF in the EQs. A close spatial relation between the seismogenic Longmenshan fault (LMSF) zone and the extent of the detected anomalies indicates that some changes occurred within the faults before the EQs. The similarity of time sequence of the anomalies between the four parameters may be related to the same process: we interpret the observed anomalies as the consequence of the upraising of gases from a fluid-rich middle/upper crust along pre-existing seismogenic faults, and of their release into the atmosphere. Our multi-parametric analytical approach is able to capture phenomena related to the preparation phase of strong EQs.

Joint Inversion of GPS, Leveling, and InSAR Data for The 2013 Lushan (China) Earthquake and Its Seismic Hazard Implications

On 20 April 2013, a moment magnitude (Mw) 6.6 earthquake occurred in the Lushan region of southwestern China and caused more than 190 fatalities. In this study, we use geodetic data from nearly 30 continuously operating global positioning system (GPS) stations, two periods of leveling data, and interferometric synthetic aperture radar (InSAR) observations to image the coseismic deformation of the Lushan earthquake. By using the Helmert variance component estimation method, a joint inversion is performed to estimate source parameters by using these GPS, leveling, and InSAR data sets. The results indicate that the 2013 Lushan earthquake occurred on a blind thrust fault. The event was dominated by thrust faulting with a minor left-lateral strike–slip component. The dip angle of the seismogenic fault was approximately 45.0°, and the fault strike was 208°, which is similar to the strike of the southern Longmenshan fault. Our finite fault model reveals that the peak slip of 0.71 m occurred at a depth of ~12 km, with substantial slip at depths of 6–20 km. The estimated magnitude was approximately Mw 6.6, consistent with seismological results. Furthermore, the calculated static Coulomb stress changes indicate that the 2013 Lushan earthquake may have been statically triggered by the 2008 Wenchuan earthquake.

Effects of Seismogenic Faults on the Predictive Mapping of Probability to Earthquake-Triggered Landslides

The seismogenic fault is crucial for spatial prediction of co-seismic landslides, e.g., in logistic regression (LR) analysis considering influence factors. On one hand, earthquake-induced landslides are usually densely distributed along the seismogenic fault; on the other hand, different sections of the seismogenic fault may have distinct landslide-triggering capabilities due to their different mechanical properties. However how the feature of a fault influence mapping of landslide occurrence probability remains unclear. Relying on the landslide data of the 2013 Lushan, China Mw 6.6 earthquake, this study attempted to further address this issue. We quantified the seismogenic fault effects on landslides into three modes: the distance effect, the different part effects, and the combined effects of the two. Four possible cases were taken into consideration: zoning the study area vertical and parallel to the fault (case 1), zoning the study area only vertical to the fault (case 2), zoning the study area only parallel to the fault (case 3), and without such study-area zonations (case 4). Using the LR model, predictive landslide probability maps were prepared on these four cases. The model also fully considered other influencing factors of earthquake landslides, including elevation, slope, aspect, topographic wetness index (TWI), peak ground acceleration (PGA), lithology, rainfall, distance from the epicenter, distance from the road, and distance from the river. Then, cross-comparisons and validations were conducted on these maps. For training datasets, results show that the success rates of earthquake-triggered landslides for the former three scenarios were 85.1%, 84.2%, and 84.7%, respectively, while that of the model for case 4 was only 84%. For testing datasets, the prediction rates of the four LRs were 84.45%, 83.46%, 84.22%, and 83.61%, respectively, as indicated by comparing the test dataset and the landslide probability map. This means that the effects of the seismogenic fault, which are represented by study-area zonations vertical and parallel to the fault proper, are significant to the predictive mapping of earthquake-induced landslides.

Ductile gap between the Wenchuan and Lushan earthquakes revealed from the two-dimensional Pg seismic tomography

A high-resolution two-dimensional Pg-wave velocity model is obtained for the upper crust around the epicenters of the April 20, 2013 Ms7.0 Lushan earthquake and the May 12, 2008 Ms8.0 Wenchuan earthquake, China. The tomographic inversion uses 47235 Pg arrival times from 6812 aftershocks recorded by 61 stations around the Lushan and Wenchuan earthquakes. Across the front Longmenshan fault near the Lushan earthquake, there exists a strong velocity contrast with higher velocities to the west and lower velocities to the east. Along the Longmenshan fault system, there exist two high velocity patches showing an “X” shape with an obtuse angle along the near northwest-southeast (NW-SE) direction. They correspond to the Precambrian Pengguan and Baoxing complexes on the surface but with a ~20 km shift, respectively. The aftershock gap of the 2008 Wenchuan and the 2013 Lushan earthquakes is associated with lower velocities. Based on the theory of maximum effective moment criterion, this suggests that the aftershock gap is weak and the ductile deformation is more likely to occur in the upper crust within the gap under the near NW-SE compression. Therefore our results suggest that the large earthquake may be hard to happen within the gap.