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When a big landside occurs, source material can change into loose deposit during its runout, causing the increase of the total landslide volume to some extent. Such changes can influence the quantification of seismic landslides. The objective of this paper was to study the volume expansion rate of landslides based on the data of 1417 co-seismic landslides triggered by the 2008 Wenchuan, China Mw 7.9 earthquake. We also analyzed the correlations between this rate and landslide geometric parameters (volume, height (H), length-width ratio (L/W), length-height ratio (L/H)), and environmental factors (peak ground acceleration (PGA), lithology, slope angle and aspect). The results show that the total source volume of the 1417 landslides is 1248 million m3, while the total volume of the deposit is 1501 million m3, which means the total volume expanding rate (Et) is 20.3% with the average volume expansion rate (Ea) 22.6%. The analysis indicates that volume expansion rate generally decreases with the increasing volume and height of landslides, while becoming larger with increasing L/H and L/W. Besides, the volume expansion rate is closely related to the landslide type and the volume scale of landslides. This study analyses volume change of co-seismic landslides deeply, permitting to help the correct quantification of the source volume and deposit volume of seismic landslide and a useful reference for the correct quantification of landslide volume. [ABSTRACT FROM AUTHOR]

The Yushu Ms 7.1 earthquake occurred on April 14, 2010 in Qinghai Province, China. It induced a mass of secondary geological disasters, such as collapses, landslides, and debris flows. Risk assessment maps are important for geological disaster prevention and mitigation, and also can serve as a guide for post-earthquake reconstruction. Firstly, a hazard assessment index system of secondary geological disasters in the earthquake region was built in this paper, which was based on detailed analysis of environmental and triggering factors closely related to geological disasters in the study area. GIS technology was utilized to extract and analyze the assessment index. Hazard assessment maps of secondary geological disasters were obtained by spatial modeling and overlaying analysis. Secondly, an analysis of the vulnerability of hazard bearing bodies in the area was conducted, important information, such as, population density, percentage of arable land, industrial and agricultural outputs per unit area were regarded as assessment indices to evaluate socioeconomic vulnerability. Thirdly, the risk level of secondary geological disasters of the area was obtained by the formula: Risk=Hazard × Vulnerability. Risk assessment maps were categorized into four levels, including 'low', 'moderate', 'high' and 'very high'. These results show that some urban areas are at very high risk, including Jiegu, Chengwen, Xiaxiula and Sahuteng towns. This research can provide some references and suggestions to improve decision-making support for emergency relief and post-earthquake reconstruction in the study area. [ABSTRACT FROM AUTHOR]

Debris flows can be extremely destructive because they can increase in magnitude via progressive entrainment. In this paper, a total of 18 landslide-type debris flows and 268 channelized debris flows in Wenchuan earthquake and Taiwan region, as well as other regions were collected to analyze the entrainment rate of debris flows in each triggering condition. Results show that there is a power relationship between volume of initial triggered mass and final deposited debris for landslide type debris flow. The debris flows during 2008 and 2013 in Wenchuan earthquake-region have smaller entrainment rate than that from 2001 t0 2009 in Taiwan. The entrainment rate of debris flow events from 2001 to 2009 in Taiwan shows a decaying tendency as elapsed time. Comparison of the entrainment rate in the two earthquake-hit regions with other regions proves that entrainment rate has a close relation with major sediment availability and secondary rainstorm conditions. [ABSTRACT FROM AUTHOR]

The Loess Plateau is an earthquake prone region of China, where the effects of loess deposit on ground motion were discovered during the 2008 Wenchuan earthquake (Ms8.0) and the 2013 Minxian-Zhangxian earthquake (Ms6.6). The field investigations, observations, and analyses indicated that large number of casualties and tremendous economic losses were caused not only by collapse and damage of houses with poor seismic performance, landslides, but also amplification effects of site conditions, topography and thickness of loess deposit, on ground motion. In this paper, we chose Dazhai Village and Majiagou Village as the typical loess site affected by the two earthquakes for intensity evaluation, borehole exploration, temporary strong motion array, micro tremor survey, and numerical analysis. The aim is to explore the relations between amplification factors and site conditions in terms of topography and thickness of loess deposit. We also developed site amplification factors of ground motion for engineering design consideration at loess sites. The results showed that the amplification effects are more predominant with increase in thickness of loess deposit and slope height. The amplification may increase seismic intensity by 1 degree, PGA and predominant period by 2 times, respectively. [ABSTRACT FROM AUTHOR]

Emergency road networks (ERNs), an important part of local disaster prevention systems, can provide security to residents and their property. Exploring the ERNs structure is of great significance in terms of promoting disaster prevention and establishing road safety in dangerous mountainous areas. This study considered the ERNs of the Kangding section of the Dadu River Basin as the area for a case study. Complex Network Analysis was used to examine the relationship between the four characteristic indicators of mountain roads and the degree of earthquake impacts under the Lushan, Wenchuan, and Kangding Earthquake scenarios. Based on the analysis results, the southwest mountain road network was evaluated; then, computer simulations were used to evaluate the structural changes in the road network after index changes. The network was optimized, and the corresponding emergency avoidance network was proposed to provide a reference for the establishment of the mountainous ERN. The results show that the overall completeness of the mountainous ERNs in Southwest China is poor and prone to traffic accidents. Moreover, the local stability is poor, and the network is susceptible to natural hazards. The overall structure of the road network is balanced, but that of certain road sections is not. Road sections with different attributes present a "gathering-scattering" spatial distribution, i.e, some sections are clustered together while others are far apart. Accordingly, a planning optimization strategy is proposed to better understand the complexity and systematic nature of the mountainous ERN as a whole and to provide a reference for disaster prevention and mitigation planning in mountainous regions in Southwest China. [ABSTRACT FROM AUTHOR]

Coseismic landslides and subsequent mobilization of sediment greatly aggravated the landscape evolution and river sedimentation after the Wenchuan earthquake. The debris-flow alluvial fan and river morphological index was combined to describe quantitatively the effects of debris-flow sediment on the river characteristics in Longmen Mountains. The section of the Min River from the urban area of the Wenchuan county to the epicenter, the Yingxiu town in this county, was selected as the study area. We identified 27 river-blocking debris-flows (5 partial-, 7 semi-, 7 over semi-, and 5 fully-blocking degrees) in the study area via remote sensing interpretation and field survey. Based on this, the response of river longitudinal profile and curvature to debris-flow sediment was qualitatively and quantitatively analyzed. The results show that the channel gradient has decreased due to debris-flow aggradation, while two marked peaks in the river steepness index (ksn, represents the relative steepness degree of the channel) changed from 585 m0.9 to 732 m0.9 in zone 1, from 362 m0.9 to 513 m0.9 in zone 2. Moreover, the main channel has undergone substantial lateral migration with channel width decreased and river curvature increased. The temporal and spatial variation between river morphological characteristics and debris-flow sediments in short-term provides insights into the internal dynamic role of mass wasting processes in river morphology, which could be served as useful information for natural hazards management to prevent the river from being blocked by episodically debris flows after the earthquake. [ABSTRACT FROM AUTHOR]

Jiuzhaigou is a world-heritage site located in the plateau area of Northwest Sichuan Province, China. Serious slope failures in the epicentral area were triggered by the Ms7.0 Jiuzhaigou earthquake occurred on August 8, 2017. The source areas of the hazards are usually concentrated near ridge crests, revealing the possible occurrence of ground motion amplification phenomena. To explore the role of the amplification of ground motions in the formation of earthquake-triggered slope failures, two seismometers were installed, on the next day after the main shock, at the bottom of the slope of Jubao Mountain near the seismogenic fault. The two monitoring sites are located at elevations of 1414 m (J1) and 1551 m (J2, the top of the mountain). Five aftershocks were recorded by the monitoring instruments. We compared the mean levels of the peak ground acceleration (PGA) observed at different locations, and investigated the directional variations in the shaking energy by analyzing the polar diagrams of the Arias intensity (Ia). Then, in order to identify the directional resonance phenomenon and their frequencies and amplification coefficients, we examined the horizontal-to-vertical spectral ratio (HVSR) and the standard spectral ratio (SSR). Polar diagrams of the Arias intensity (Ia) indicated that the site response of Jubao Mountain showed a pronounced directivity (in the EW direction) with shaking maxima near the hill top oriented orthogonally to the elongation of the relief. We observed an obvious resonance phenomenon at site J2 at relatively low frequencies (2.5–9 Hz) and very weak spectral amplifications at site J1 at high frequencies (5–15 Hz), which suggested that the predominant frequency of monitoring site J2 was obviously attenuated and that the difference in the spectra was related to the influences of the local-scale site conditions of the whole mountain. The results of spectral ratio analyses (HVSR and SSR) showed that the direction of resonance was concentrated around an EW orientation, and the amplification factors near the hill top were larger than 2. It suggests that geologic factors also play a significant role in the anisotropic amplifications affecting the tops of slopes besides the topographic effects. [ABSTRACT FROM AUTHOR]

Peak discharge of flood in small mountainous watershed is usually calculated using the "Rainstorm-runoff calculation method in small watersheds in Sichuan Province" (RRM). This study evaluated the RRM calculation using real-time monitored rainfall and hydrologic data from a small watershed in the Wenchuan Earthquake area of Sichuan Province, China. The results indicated that the discharge values given by the RRM are commonly overestimating the measured discharge. The overestimation rate was discussed and empirical equations were proposed for improving RRM estimations, based on the relationship between calculated and measured discharge values at different watershed scales (2, 30, and 40 km2), under different rainfall probabilities (0.97-0.5, 0.5-0.2, and 0.2-0.002), and for different rainfall durations (0-6, 6-24, and >24 h). The results of this study help contribute to the understanding of water floods formation and help provide more accurate estimations of peak flow discharge in small watersheds in the Wenchuan Earthquake area. [ABSTRACT FROM AUTHOR]

On August 8, 2017, a Ms 7.0 earthquake occurred 5 km to the west of Jiuzhaigou National Park, causing 25 deaths and injuring 525. The objective of this study was to explore the seismogenic fault of the earthquake and tectonic dynamics of the source rupture. Field investigations, radon activity tests, remote sensing interpretations, and geophysical data analyses were carried out immediately after the earthquake. The Jiuzhaigou earthquake occurred at the intersection of the northern margin of the Minshan uplift belt and the south part of the Wenxian-Maqin fault in the south margin of the West Qinling geosyncline. There are two surface rupture zones trending northwest (NW), which are ground coseismic ruptures caused by concealed earthquake faults. The rupture on the southwest is the structure triggering the earthquake, along the Jiuzhaitiantang-Epicenter-Wuhuahai. The other one on the northeast (Shangsizhai-Zhongcha-Bimang) is a reactivation and extension of the secondary fault trending NW. The source rupture of this earthquake is a strike-slip shear fracture associated with the fault plane trending NW 331° and steeply dipping 75°, which is continuously expanding at both ends. The tectonic dynamics process of the source rupture is that the “Jiuzhaigou protrusion” is left-lateral sheared along the seismogenic fault in the NW direction. Finally, the Maqin fault and the arc fault system at the top of the “Wenxian protrusion” will be gradually broken through sometime in far future, as well as earthquaketriggered landslides will be further occurred along the narrow corridor between the seismogenic faults. The research results revealed the basic geological data and tectonic dynamic mechanism in this earthquake. [ABSTRACT FROM AUTHOR]

Quaternary silt is widely distributed in China and easily liquefies during earthquakes. To identify the influence of the dry density on the liquefaction behaviour of Quaternary silt, 40 cyclic triaxial liquefaction tests were performed on loose silt (dry density ρd=1.460 g/cm3) and dense silt (ρd=1.586 g/cm3) under different cyclic stress ratios (CSRs) to obtain liquefaction assessment criteria, determine the liquefaction resistance, improve the excess pore water pressure (EPWP) growth model and clarify the relationship between the shear modulus and damping ratio. The results indicate that the initial liquefaction assessment criteria for the loose and dense silts are a double-amplitude axial strain of 5% and an EPWP ratio of 1. The increase in the anti-liquefaction ability for the dense silt is more significant under lower confining pressures. The CSR of loose silt falls well within the results of the sandy silt and Fraser River silt, and the dense silt exhibits a higher liquefaction resistance than the sand-silt mixture. The relationships between the CSR and loading cycles were obtained at a failure strain of 1%. The EPWP development in the dense and loose silts complies with the “fast-stable” and “fast-gentle-sharp” growth modes, respectively. The power function model can effectively describe the EPWP growth characteristics of the dense silt. Finally, based on the liquefaction behaviour of silt, a suggestion for reinforcing silt slopes or foundations is proposed. [ABSTRACT FROM AUTHOR]

On August 8th, 2017, an Ms 7.0 magnitude earthquake occurred in Jiuzhaigou County, northern Sichuan Province, China. The Jiuzhaigou Valley World National Park was the most affected area due to the epicentre being located in the scenic area of the park. Understanding the distribution characteristics of landslides triggered by earthquakes to help protect the natural heritage sites in Jiuzhaigou Valley remains a scientific challenge. In this study, a relatively complete inventory of the coseismic landslides triggered by the earthquake was compiled through the interpretation of high-resolution images combined with a field investigation. The results indicate that coseismic landslides not only are concentrated in Rize Gulley, Danzu Gully and Zezhawa Gully in the study area but also occur in the front part of Shuzheng Gully along the road network (from the entrance of Jiuzhaigou Valley to Heye Village). The landslides predominantly occur on the east- and southeast-facing slopes in the study area, which is a result of the integrated action of the valley direction and fault movement direction. The back-slope effect and the slope structure caused the difference in coseismic landslide distribution within the three gullies (Danzu Gully, Rize Gully, and Zezhawa Gully) near the inferred fault. In addition, the topographic position index was used to analyse the impact of microlandforms on earthquake-triggered landslides by considering the effect of the slope angle. The study results reveal a higher concentration of landslides in the slope position class of the middle slope (30°-50°) in Jiuzhaigou Valley. These findings can provide scientific guidance for the protection of natural heritage sites and post-disaster reconstruction in Jiuzhaigou Valley. [ABSTRACT FROM AUTHOR]

The Lamuajue landslide is located in Lamuajue village on the right bank of the Meigu River, Sichuan Province, China. This landslide is an ancient landslide with an extremely wide distribution area, covering an area of 19 km with a maximum width of 5.5 km and an estimated residual volume of 3×10 m. The objectives of this study were to identify the characteristics and failure mechanism of this landslide. In this study, based on field investigations, aerial photography, and profile surveys, the boundary, lithology, structure of the strata, and characteristics of the landslide deposits were determined. A gently angled weak interlayer consisting of shale was the main factor contributing to the occurrence of the Lamuajue landslide. The deposition area can be divided into three zones: zone A is an avalanche deposition area mainly composed of blocks, fragments, and debris with diameters ranging from 0.1 m to 3 m; zone B is a residual integrated rock mass deposition area with large blocks, boulders and 'fake bedrock'; and zone C is a deposition zone of limestone blocks and fragments. Three types of failure mechanism were analyzed and combined to explain the Lamuajue landslide based on the features of the accumulation area. First, a shattering-sliding mechanism caused by earthquakes in zone A. Second, a sliding mechanism along the weak intercalation caused by gravity and water in zone B. Third, a shattering-ejection mechanism generated by earthquakes in zone C. The results provide a distinctive case for the study of gigantic landslides induced by earthquakes, which is very important for understanding and assessing ancient earthquakeinduced landslides. [ABSTRACT FROM AUTHOR]

In order to investigate the role of the amplification of peak ground acceleration (PGA) in seismic landslide formation mechanisms and study how earthquake waves interact with rock structures, a few strong-motion seismometers are installed at various locations on both sides of the Lengzhuguan gully. Five strong-motion seismometers were triggered at different depths in a tunnel at the same altitude during the Kangding Ms 5.8 earthquake on November 25th, 2014. The data reveal that the horizontal peak acceleration (PGA) at each site decreased with increasing site depths. The PGAH at the deepest monitoring site (99 m from the tunnel entrance) was approximately half that of the outermost site. The amplitude of the acceleration response spectrum was also attenuated from the entrance inwards, the dynamic magnification factor (β) of the standard acceleration spectrum was less than 3.5, and rate of change was the same as that for the amplitude acceleration response. The Fourier spectra of each monitoring site also decreased from the outside inwards, and the components of the Fourier spectra were more complex at the surface. [ABSTRACT FROM AUTHOR]

The upper Yangtze River region is one of the most frequent debris flow areas in China. The study area contains a cascade of six large hydropower stations located along the river with total capacity of more than 70 million kilowatts. The purpose of the study was to determine potential and dynamic differences in debris flow susceptibility and intensity with regard to seasonal monsoon events. We analyzed this region's debris flow history by examining the effective peak acceleration of antecedent earthquakes, the impacts of antecedent droughts, the combined effects of earthquakes and droughts, with regard to topography, precipitation, and loose solid material conditions. Based on these factors, we developed a debris flow susceptibility map. Results indicate that the entire debris flow susceptibility area is 167,500 km, of which 26,800 km falls within the high susceptibility area, with 60,900 km in medium and 79,800 km are in low susceptibility areas. Three of the six large hydropower stations are located within the areas with high risk of debris flows. The synthetic zonation map of debris flow susceptibility for the study area corresponds with both the investigation data and actual distribution of debris flows. The results of debris flow susceptibility provide base-line data for mitigating, assessing, controlling and monitoring of debris flows hazards. [ABSTRACT FROM AUTHOR]

In the Wenchuan Earthquake area, many co-seismic landslides formed blocking-dams in debris flow channels. This blocking and bursting of landslide dams amplifies the debris flow scale and results in severe catastrophes. The catastrophic debris flow that occurred in Qipan gully (Wenchuan, Southwest China) on July 11, 2013 was caused by intense rainfall and upstream cascading bursting of landslide dams. To gain an understanding of the processes of dam bursting and subsequent debris flow scale amplification effect, we attempted to estimate the bursting debris flow peak discharges along the main gully and analyzed the scale amplification process. The results showed that the antecedent and triggering rainfalls for 11 July debris flow event were 88.0 mm and 21.6 mm, respectively. The event highlights the fact that lower rainfall intensity can trigger debris flows after the earthquake. Calculations of the debris flow peak discharge showed that the peak discharges after the dams-bursting were 1.17-1.69 times greater than the upstream peak discharge. The peak discharge at the gully outlet reached 2553 m/s which was amplified by 4.76 times in comparison with the initial peak discharge in the upstream. To mitigate debris flow disasters, a new drainage channel with a trapezoidal V-shaped cross section was proposed. The characteristic lengths (h1 and h2) under optimal hydraulic conditions were calculated as 4.50 m and 0.90 m, respectively. [ABSTRACT FROM AUTHOR]

To study the characteristics of long period microtremor and applicability of microtremor survey, we have made microtremor observations using long period seismometers of the China's mainland from coastal cities like Shanghai and Tianjin through Beijing, Xi'an, to the far inland cities of Lanzhou and Tianshui. The observation shows that the level of power spectrum of long period microtremors reduced rapidly from the coast to the inland area. However, the energy of long period microtremors in Beijing, Xi'an, Lanzhou and Tianshui area are only approximately ten-thousandth to thousandth of that in Shanghai. Aiming at the complexity of the underground structure in the far inland, a series of underground structure models with different distributions were assessed using three-dimensional, dynamic finite element method (FEM) analyses. The results were used to evaluate microtremor survey methods and their limitations with regard to aggregate variability and thickness determinations. Multiple-wave reflections between layers with the change of underground structure distribution occurred, which have significant effect on the performance of the different field approaches. Information over a broad spectrum from which velocity-depth profiles were produced via inversion approaches. Neither the thickness nor the shear wave Velocity V of the subsurface layer inversion results appeared over a large evaluation with increasing slope angle. In particular, when the angle of the model reached 45°, it could not be accurately evaluated using one-dimensional inversion methods. Finally, the array microtremor survey (AMS) was carried out in Shanghai City, China. Although AMS techniques do not have the layer sensitivity or accuracy (velocity and layer thickness) of borehole techniques, the obtained shear wave velocity structure is especially useful for earthquake disaster prevention and seismic analysis. [ABSTRACT FROM AUTHOR]

The Longmenshan fault is a thrust fault which runs along the base of the Longmen Mountains in Sichuan province, southwestern China. The southern segment of the fault had two distinct responses to the Ms 8 Wenchuan and Ms 7 Lushan earthquakes. This study determines characteristics of the structural geology of the Longmenshan fault to evaluate how it influenced the two aforementioned earthquakes. This research was done within a Geo-information Technologies (GiT) environment based on multi-source remote sensing and crustal movement data extracted from the Global Positioning System (GPS). The spatial distribution of the southern segment of the Longmenshan fault zone was comprehensively analyzed to study both earthquakes. The study revealed that the Wenchuan and Lushan earthquakes occurred on two relatively independent faults. In addition, there was a nearly constant-velocity crustal movement zone between the two epicenters that probably had a compressive stress with slow motion. Furthermore, the central fault and a mountain back fault gradually merged from north to south. The Lushan earthquake was not an aftershock of the Wenchuan earthquake. The research showed that fault zones within 30-50 km of State Highway 318 are intensive and complex. In addition, crustal movement velocity decreased rapidly, with a strong multi-directional shear zone. Thus, activity in that zone was likely stronger than in the northern part over the medium to long term. [ABSTRACT FROM AUTHOR]