Wenchuan Ms Research Articles

Background and clustering characteristics of recent seismicity in Southwestern China

SUMMARY This study analysed seismicity in southwestern China (1 January 2008 to 30 June 2021) using the earthquake catalogue compiled by the China Earthquake Network Center and four different space–time Epidemic-Type Aftershock Sequence models: the 2-D point-source (PS) model, the 2-D finite-source (FS) model, the 3-D PS model and the 3-D FS model. Our objective was to understand the features of the background seismicity and the patterns of earthquake clusters to better evaluate the regional seismic hazard. We carefully investigated the aftershock sequences that followed 7 of the 10 MS ≥ 6.0 earthquakes that have struck this region since the occurrence of the 2008 Wenchuan MS 8.0 earthquake [i.e. the Panzhihua (31 August 2008; MS 6.0), Yaoan (9 July 2009; MS 6.0), Lushan (20 April 2013; MS 7.0), Ludian (3 August 2014; MS 6.5), Jinggu (7 October 2014; MS 6.6), Kangding (11 November 2014; MS 6.3) and Yangbi (21 May 2021; MS 6.4) earthquakes]. Our results revealed the following. (1) The background seismicity level for natural earthquakes is usually stable but can experience sudden change due to major events, such as the 2014 Ludian MS 6.5, and the 2014 Jinggu MS 6.6 events. Such changes in the background rate can reach 50 per cent. (2) Reservoir-induced earthquakes substantially increase the level of regional seismicity, indicating that they cannot be ignored when analysing natural seismicity and evaluating regional earthquake hazards. (3) Events triggered directly by the main shock occur mostly in regions adjacent to areas with large coseismic slip, showing a pattern complementary to the main shock ruptures.

Reactive Transport Process of Earthquake‐induced Hydro‐chemical Changes in Guanding Thermal Spring, Western Sichuan, China

AbstractEarthquake‐related hydrochemical changes in thermal springs have been widely observed; however, quantitative modeling of the reactive transport process is absent. In the present study, we apply reactive transport simulation to capture the hydrochemical responses in a thermal spring following the Wenchuan Ms 8.0 and Lushan Ms 7.0 earthquakes. We first constrain deep reservoir geothermal fluid compositions and temperature by multicomponent geothermometry, and then a reactive geochemical transport model is constructed to reproduce the hydrochemical evolution process. The results show that the recharge from the shallow aquifer increases gradually until it reaches a peak because of the permeability enhancement caused by the Lushan earthquake, which may be the mechanism to explain the earthquake‐related hydrochemical responses. In contrast to the postseismic effect of the Wenchuan earthquake, the chemical evolution can be considered as hydrochemical anomalies related to the Lushan earthquake. This study proves that the efficient simulation of reactive transport processes is useful for investigating earthquake‐related signals in hydrochemical time series.

The analysis of seismic induced progressive instability and failure mechanisms: A case study

The 2008 Wenchuan Ms8.0 earthquake triggered a catastrophic landslide, i.e., the Daguangbao (DGB) landslide (1.2 ✕ 109 m3). Its shear failure occurred within a deep-seated (average depth of 400 m) saturated carbonate bedding fault in the Paleozoic Formation. The frequent seismic events in the tectonic belt make the landslide initiation mechanism more complex. Shake table tests were conducted on the DGB landslide to understand the coupling effect of multiple earthquakes, geology and hydrology. The results showed that the multiple earthquakes weakened the friction coefficient as the Boltzmann function on the sliding surface of the landslide. The friction law of the basal surface related to seismic energy was established and incorporated into the Newmark analysis. And the seismic energy consumed in the steep scarp surface release of landslide during an earthquake is also considered. It found that the traditional Newmark model overestimates the time for earthquake-induced landslides due to ignoring the steep scarp surface release stage. It proposed that evaluating pre-earthquake induced slope damage, and critical seismic energy for triggering co-seismic landslides are important for predicting post-seismic landslides.

Comparative experimental study on shaking table test of small radius curved bridge considering different connection types between pier and beam

During the Great Wenchuan Ms 8.0 earthquake, many small-radius curved bridges suffered varying degrees of damage, including Baihua Bridge, Huilan Overpass, and Xiaohuangou Bridge. To understand the damage mechanism, shaking table tests were conducted on two scaled bridge models with different middle pier connection types. In one model, the middle pier and beam were cast monolithically together (CM bridge), while the other had a fixed support installed at the pier-beam connection (FS bridge). Both bridges were subjected to two earthquake ground motions. Visually, damage differed considerably between the bridges. The CM bridge exhibited many horizontal and circumferential cracks at the top and bottom. Meanwhile, the FS bridge concrete was crushed at the top of the middle pier, which must be paid attention to. Amplification factors, maximum drift ratios, residual drift, planar rotation angles, and bearing slip were analyzed for both bridges. For both structures, amplification factors in the X and Y directions decreased with stronger ground motions, while those in the Z direction showed an opposite trend; meanwhile, maximum drift ratios, residual drift, rotation angles, and bearing slip all increased with stronger motions. The acceleration amplification factors of the CM bridge increased with greater ground motion, rising rapidly. The CM bridge saw a maximum drift ratio of 7.07 versus 3.16 for the FS bridge. The trend for the CM bridge was a gradual increase, while the FS bridge had a sudden increase after the maximum drift ratio reached 1.61%. The CM bridge planar rotation angle rose gradually to 0.23°, while the FS bridge angle increased much faster, reaching 0.54° or 2.35 times that of the CM bridge. The FS bridge concrete splitting failure demonstrated vulnerability to seismic events exceeding the design level and the structural measures in this region should be enhanced in the design.

An MDT-based rapid assessment method for the spatial distribution of trafficable sections of roads hit by earthquake-induced landslides

In mountainous areas, roads are often damaged by earthquake-induced landslides (EL). The degree of road damage and the existing functional state will have a very important impact on the whole earthquake relief work. However, this question has long been plaguing scientists engaged in the risk assessment. Now, an MDT-based rapid assessment method for the spatial distribution of trafficable sections of roads (TSR) hit by EL is proposed. The method mainly consists of three procedures: 1) Demarcate the road sections in the evaluated region; 2) Create the data for earthquake-induced landslide sensitivity level for the evaluated region; 3) Use the sample data to devise the MDT model for the TSR hit by EL and calculate the trafficability of road sections. This method was applied in the study of the 2008 Wenchuan Ms 8.0, the 2014 Ludian Ms 6.5, the 2012 Yiliang Ms 5.6 and Ms 5.7 earthquake-stricken regions. The case of Wenchuan earthquake was adopted to establish the method. The cares of Ludian and Yiliang were used to evaluate whether the method could be transplanted into similar regions. The p-value and the kappa coefficient were used to test and evaluate the significance and the consistence of the actual situation. Our results suggest: ⅰ) The Wenchuan evaluated region had the p-value 2.52 × 10−203 and the kappa coefficient 0.91. Less than 1% of the road sections that were inferred to be trafficable with the established method were actually interrupted by EL. The interruptions in the road sections that were inferred to be un-trafficable were 12 times of those in the other road sections. ⅱ) The Ludian and Yiliang earthquake-stricken regions had the p-value 9.7 × 10−107 and the kappa coefficient 0.81. Only 1.31% of the road sections that were trafficable according to the calculation results of the model had been actually interrupted by EL. The interruptions caused by EL in the un-trafficable road sections according to the calculation results were 5.2 times of those in the trafficable road sections. This method could be applied in other similar regions when a certain error was permitted.

Characteristics of the present crustal deformation in the Tibetan Plateau and its relationship with strong earthquakes

AbstractTo study the characteristics of the present crustal movement in the Tibetan Plateau and explore its relationship between strong earthquakes with magnitudes of 8 and above, the velocity field size was analyzed based on the global position system (GPS) campaign observations and the time series of site north-ward displacement and long baseline were discussed using the GPS continuous observations. The results show that the velocity field size in the Tibetan Plateau decreases from southwest to north, northeast, and southeast, and the value of the velocity in the west is significantly greater than that in the east in the same dimension. The maximum value is located in the southwest and the minimum value is located in the east. The Wenchuan earthquake is located in the mutation region, where the rate and the direction of the crustal movement are quite different. The crustal deformation extent is large in the region close to the seismic source before the earthquake, reflecting that the regional stress accumulation is fast and its required time is relatively short. However, the crustal deformation extent is relatively small in the region away from the seismic source before the earthquake, reflecting that the regional stress accumulation is slow and its required time is relatively long. The N-ward movement became significantly strong after NepalMS8.1 earthquake; the occurrence of this earthquake may have caused the unlocking of large-scale faults near the seismic source, which further intensified the NE-ward subduction and collision of the Indian Plate. The compression of the Indian Plate to the Tibetan Plateau slowed down after the 2008 WenchuanMS8.0 earthquake, and increased significantly after 2015, which boosted strain accumulation in the Tibetan Plateau, and attention needs to be paid continuously to strong earthquake risk in this region.

The comprehensive risk assessment of the Tangjiashan landslide dam incident, China.

Risk assessment for landslide dams is very important to avoid unanticipated landslide failure and calamity. Recognition of the risk of landslide dams associated with changing influencing factors is to identify the risk grade and provide early warning of oncoming failure, while quantitative risk analysis of landslide dams due to many influencing factors changing in spatiotemporal domain is currently lacking. We applied the model to analyze the risk level of the Tangjiashan landslide dam caused by the Wenchuan Ms 8.0 earthquake. The risk evaluation, obtained according to the analysis of the influencing factors located in the risk assessment grade criteria, clearly shows that the risk reaches a higher level at that moment. Our analysis shows that the risk level of landslide dams can be quantitatively analyzed with our assessment method. Our results suggest that the risk assessment system can be an effective measure to dynamically predict the risk level and provide a sufficient early warning of the oncoming hazard by analyzing the variables of influencing factors at different times.

Progress and prospect of the time-varying gravity in earthquake prediction in the Chinese Mainland

This paper mainly introduces the application and progress of the time-varying gravity in earthquake research in the Chinese Mainland. Since the Xingtai earthquake in 1966, China has begun mobile gravity monitoring, trying to explore the relationship between gravity changes and seismic activities. The gravity changes before and after the Haicheng MS7.3 earthquake in 1975 and the Tangshan MS7.8 earthquake in 1976 were observed. In 1981, a high-precision metal spring gravimeter was introduced to carry out high-precision mobile gravity observation in the key earthquake monitoring areas in western Yunnan. The gravity anomaly changes near the epicenters of the Lijiang MS7.0 earthquakes in 1996 were observed. In 1998, a high-precision absolute gravity survey was introduced to carry out the overall scale gravity field monitoring in the Chinese Mainland, and the large-scale gravity change information before Wenchuan MS8.0 and Yutian MS7.3 earthquakes in 2008 was obtained, and the effective prediction opinions were given. After the Wenchuan MS8.0 earthquake in 2008, the integration of the national network and the regional network accelerated, forming the whole gravity observation network in the Chinese Mainland, which made a relatively successful medium-term prediction for a series of earthquakes with MS6.0 or above (such as Lushan MS7.0, Menyuan MS6.4, and Jiuzhaigou MS7.0) in recent years and played an important role in the study of the earthquake mechanism and earthquake prediction level in China. Finally, the existing problems in time-varying gravity monitoring in China are pointed out, and the prospect of earthquake research using time-varying gravity monitoring data is put forward.

Earthquake-Induced Stress Amplification and Rock Fragmentation within a Deep-Seated Bedding Fault: Case Study of the Daguangbao Landslide Triggered by the 2008 Wenchuan Earthquake (Ms=8.0)

Abstract The 2008 Wenchuan Ms 8.0 earthquake triggered the Daguangbao (DGB) landslide, of which the shear surface belongs to a thrust bedding fault 400 m below the carbonate slope. After the landslide, a 1.8 km-long inclined sliding face (0.3 km2) was exposed in the south source area. By using shaking table test, the contributions of the fault to the landslide sliding have been studied in this paper. The bedding fault in the test model is simplified as a weak layer with small elasticity and the carbonate layers as a hard layer with high elastic modulus, which is 296 times the weak one. The test records larger displacement amplitude in the upper hard layer than that in the lower one and larger pressure amplitude in the weak layer than that in the hard ones. We ascribed the stress amplification in the weak layer to time delay of shaking wave as wave velocity in the weak layer is only 1/15 of that in the hard layers. Such time delay gives rise to phase differences between the hard layers during shaking. The compressive stress amplification occurs in the weak layer when the upper hard layer moves downwards relative to the lower one; otherwise, tensile stress amplification occurs. It is suggested that this kind of stress amplification triggered an extensive fragmentation of the bedding fault rock mass during the Wenchuan earthquake, which can be verified by a good deal of gentle-dip and steep-dip cracks observed on site. It is proposed that stress amplification had caused a fast dropping of shear strength in the bedding fault to enhance the suddenness of DGB landslide initiation.

Remote Sensing Land Use Evolution in Earthquake-Stricken Regions of Wenchuan County, China

Earthquakes and their secondary geological disasters have a certain impact on the land cover, which leads to the degradation of the ecological environment and the stability of the ecosystem. At present, there are few studies on the spatial–temporal evolution characteristics of land-use change in earthquake-stricken regions, especially the lack of quantitative evaluation of the impact of earthquakes on land use at the micro-scale. The “5·12” Wenchuan ms8.0 earthquake caused serious damage to the surface resources in the disaster area. The study on the spatial–temporal evolution characteristics of land-use change in the disaster area can provide a reference for the remote sensing dynamic monitoring of the ecological environment. Therefore, based on geographical big data, this paper used a land-use comprehensive degree index, land-use transfer matrix, and landscape ecological index to explore and analyze the spatial–temporal evolution characteristics of land use in Wenchuan County before and after the earthquake. The results showed that the types of cropland, forest, built-up, and bare land changed greatly before and after the earthquake. During the earthquake recovery period, the comprehensive index of land use in the study area basically showed an increasing trend. Under the effect of artificial measures and natural restoration, land use was continuously improved, and vegetation was restored well. After 2008, the Patch Density (PD) and Landscape Shape Index (LSI) values of most landscape types decreased, and the Aggregation Index (AI) values increased, indicating that the ecological environment of the whole region showed a benign development in the post-earthquake period. The results not only contribute to the establishment of scientific ecological environment management in earthquake-stricken regions but also contribute to the formulation of long-term ecological environment monitoring and ecological restoration planning according to the law of land-use change.

The Doppler effect induced by earthquakes: A case study of the Wenchuan MS8.0 earthquake

Seismologists have found that the first arrival frequencies of P waves at different seismic stations have different widths, that is, different periods or frequencies, and they think that this phenomenon can be used to identify whether a Doppler effect is induced by earthquakes. However, the fault rupture process of a real earthquake is so complex that it is difficult to identify a frequency shift similar to the Doppler effect. A method to identify whether a Doppler effect is induced by an earthquake is proposed here. If a seismic station is in the direction of fault rupture propagation, this station could observe a Doppler effect induced by the earthquake. The Doppler effect causes the frequency of the seismic wave to shift from low frequency to high frequency, and the high frequency amplitudes become mutually superimposed. Under the combined influences of the absorption effect, geometric spreading effect and Doppler effect, the high frequency amplitude of the seismic wave will gradually become higher than the low frequency amplitude with increasing epicentral distance. If we find that the high frequency amplitude is higher than the low frequency amplitude with increasing epicentral distance in the direction of fault rupture propagation, then there is a Doppler effect. The fault that generated the Wenchuan earthquake is a reverse fault, and its horizontal rupture propagation velocity was low. To link fault rupture propagation velocity with the Doppler effect and identify the Doppler effect more easily, we decompose three-component records into two directions: the direction of fault rupture propagation and the direction perpendicular to the fault rupture propagation along the fault plane. The initial components of the two directions are processed by wavelet transform. Several seismic stations in the direction of fault rupture propagation of the Wenchuan earthquake were selected, and it was found that with increasing epicentral distance, the high frequency amplitudes of the wavelet spectra become obviously higher than the low frequency amplitudes. It can be concluded that due to the existence of the Doppler effect, high frequency amplitudes can overcome the influences of the absorption and geometric spreading effects on seismic waves in the fault rupture propagation process.

Hydrogeochemical Characteristic of Geothermal Water and Precursory Anomalies along the Xianshuihe Fault Zone, Southwestern China

Hydrogeochemical changes in association with earthquakes are considered as a potential means of identifying earthquake precursors. The Xianshuihe fault zone (XSHF) is considered one of the most active seismic fault zones in China; 43 hot springs were sampled and analysed in the laboratory for major elements, silica, stable isotopes (δD and δ18O) and strontium isotopes were investigated from 2008 to 2021. The meteoric water acted as the primary water source of the hot spring in the XSHF, and recharged elevations ranged from 1.9 to 4.8 km. The geothermometers method was used to estimate the region of thermal storage temperature and its temperature between 8 and 142 °C. And the circulation depth ranged from 0.1 to 6.9 km. Most of the hot spring water was immature water with a weak degree of water-rock reaction. However, the degree of water-rock reaction and the depth of hot spring water circulation were high in part of the Kangding and Daufu segments, which also had the highest reservoir temperature and the most frequent strong earthquakes. Temporal variations of hydrogeochemical showed that Na+, Cl− and SO42− decreased obviously following the 12 May 2008 Wenchuan Ms8.0 and existed abnormal value fluctuations from the 20 April 2013 Lushan Ms7.0 to 22 November 2014 Kangding Ms6.3 occurred and after 20 July 2017 returned to the normal levels. And the ion concentrations in hot springs increased by 5% to 35% three months before 22 November 2014 Kangding Ms6.3 with the obvious precursor anomaly. Hydrogeochemical anomalies could be useful for predicting an earthquake in the study area.

The response law of far-field seismic ground motion of the Wenchuan earthquake and its damaging mechanism in the Loess Plateau

A series of housing collapses and other serious damage was caused by the 2008 Wenchuan MS 8.0 earthquake in the seismic intensity Ⅵ areas of the Loess Plateau, which is hundreds of kilometers away from the epicenter, and which showed a remarkable seismic intensity anomaly. The seismic disasters are closely related to the seismic response characteristics of the site, therefore, the systematic study of the far-field seismic response law of the Wenchuan earthquake in the Loess Plateau is of great significance to prevent the far-field disaster of great earthquake. In this paper, the seismic acceleration records of several bedrock stations and loess stations from the seismogenic fault of the Wenchuan earthquake to the Loess Plateau were collected, and the attenuation law of ground motion along the propagation path and the characteristics of seismic response on the loess site are studied, and the mechanism of amplification effect of ground motion is analyzed based on the dynamic feature parameters of the loess site obtained through the HVSR method. Taking a typical loess site of thick deposit as the prototype, a series of shaking table tests of dynamic response of loess site models with different thicknesses were carried out. Amplification effect, spectral characteristics of acceleration in model sites were analyzed under the action of a far-field seismic wave of the Wenchuan earthquake. The results show that seismic attenuation on the propagation path along the NE strike of the seismogenic fault to the Loess Plateau is slower than that in other directions, and the predominant period range of ground motion on bedrock site of the Loess Plateau presents broadband characteristics. Because the natural periods of loess sites with thick deposits are within the predominant period range of bedrock input wave, loess sites appear significant amplification effect of ground motion, the horizontal acceleration of ground motion exceeds 0.1 ​g, the seismic intensity reaches 7°. The thicker the loess deposit is, the more significant the change of spectral characteristics of ground motion on loess sites, and the narrower the predominant period range of ground motion becomes, and the closer it is to the natural period of loess sites. Therefore, for some old houses on thick loess sites, the poor seismic performance and strong seismic response eventually led to their collapses and damages because their natural periods are very close to the predominant period of ground motion of the Wenchuan earthquake on thick loess sites; For these damaged high-rise buildings, the resonance effect might be the main reason for their damages because their natural periods are included in the predominant period range of ground motion of the Wenchuan earthquake on thick loess sites.These research results would provide a basis for seismic disasters prediction and evaluation and seismic design of construction engineering in the Loess Plateau.

Can We Reduce Carbon Emissions While Improving Disaster Resilience? An Empirical Analysis from 5.12 Wenchuan Ms 8.0 Earthquake Stricken Area on 2008 in China

Can We Reduce Carbon Emissions While Improving Disaster Resilience? An Empirical Analysis from 5.12 Wenchuan Ms 8.0 Earthquake Stricken Area on 2008 in China

Contemporary background stress field in the eastern Tibetan Plateau: Insights from 3D geomechanical modeling

Knowledge of the crustal stress state is important for understanding tectonic processes and seismic hazard assessment as well as for various practical applications. In this study, we present a model describing the contemporary 3D crustal background stress field of the eastern Tibetan Plateau. The model incorporates a complex fault system and an appropriate initial stress state that matches both model-independent stress observations and kinematic data well. Our results show that the modeled maximum horizontal stress SH is generally oriented in NW-SE direction. The Bayan Har Block and the Chuan-Dian Block are dominated by a strike-slip faulting stress regime. However, in some local areas, the crust is governed by a normal faulting regime. We infer that the local normal faulting stress regime in the Bamei-Kangding area is caused by the clockwise rotation of the strike of the Xianshuihe fault at Kangding. This normal faulting stress regime would promote the ascent of intrusions and provide the space necessary for the emplacement of the Zheduoshan granite. The stress state on the Longmen Shan fault zone is rather inhomogeneous. For the Yingxiu-Beichuan fault, the northeastern segment has a lower normal stress but a higher shear stress than the southwestern segment. This inhomogeneous stress state on the Yingxiu-Beichuan fault could provide an explanation for the northeastward propagation of the ultra-long unilateral rupture in the Wenchuan Ms8.0 earthquake. According to the stress state on the Xianshuihe fault, we conclude that the Kangding-Shimian segment has a high potential to produce a strong earthquake due to its high normal stress and a fast slip rate and should be carefully monitored. On the Bamei-Kangding segment, which is governed by a normal faulting stress regime and may be lubricated by fluids, slip seems to be facilitated favoring more frequent small to moderate magnitude earthquakes to occur on this segment.

Spatial distribution of landslides triggered by the Wenchuan Ms 8.0 earthquake near the epicenter

The 2008 Wenchuan earthquake (Ms = 8.0) occurred in Sichuan, China, and triggered many landslides that were more concentrated near the epicenter. A watershed of Min River of length 80 km and an area of approximately 2100 km2 was chosen in this study to assess the spatial distribution of the co-seismic landslides. Both the widely used indexes, including co-seismic landslides number (LN) and landslide concentration (LC), and two new indexes, slope pixel percentages (SPP) and landslide pixel percentages (LPP), are used to make correlation analysis with topographical factors. The SPP is defined as the pixel percentage of topographic factors related to the entire study area on pre-earthquake digital elevation model. The difference between the SPP and LPP is that the latter is only considered in the area where co-seismic landslides occur. The main results of this study are: (1) The distance from surface rupture (rf) leads to a better correlation with LC; (2) greater than one twice of the landslides that occur on the west side of the Min River line; (3) the distribution of the landslides in our study area shows a larger average distance to fault rupture comparing to the average value in the total Wenchuan earthquake; (4) the most remarkable correlation found is with the topographic aspects and the fault thrusting direction.

Excess Pore Water Pressure within a Deep-seated Bedding Fault: Understanding of Earthquake Induced Large Landslide Initiation

The 2008 Wenchuan Ms8.0 earthquake triggered a landslide (i.e., Daguangbao landslide) with a volume of near 1.2 billion m3. This landslide involved the Paleozoic carbonate strata and the geological background of the sliding zone is a pre-existing bedding fault with a maximum thickness of 5 m and depth of 400 m in the slope. The bedding fault was the groundwater channel in the slope with saturated rock mass, according to the latest survey. To reveal the initiation mechanism of Daguangbao landslide (hereinafter short for DGB landslide) related to groundwater, a kind of simplified model of hard carbonate rock-cut slope with weak layer has been proposed to generalize bedding fault to weak layer in hard carbonate rock layer. And response characteristics of the model have been simulated by fluid-solid coupling algorithm in the FLAC3D program. The results showed that the hard carbonate rocks above and below the weak layer were different in deformation during strong earthquake, which led to the dynamic behavior of vibratory stamping-tension to the weak layer. And then, the discordant deformation of the two layers resulted in the excess pore water pressure featured with instant amplification and cumulative growth in the saturated water weak layer. So it was inferred that the rapid drop of inside effective stress caused by excess pore water pressure in the weak layer during strong earthquake would give rise to the sudden shearing of stress in the front locked segment of the slope after rapid stress concentration, and consequently trigger the DGB landslide.

Seismic response analysis of loess site under far-field bedrock ground motion of the Wenchuan earthquake.

In this paper, considering the far-field seismic input, an accelerogram recorded in the bedrock at Wuquan Mountain in Lanzhou city during the 2008 Wenchuan Ms8.0 earthquake was selected, and numerical dynamic analyses were conducted. The one-dimensional equivalent linear method was implemented to estimate the ground motion effects in the loess regions. Thereafter, slope topographic effects on ground motion were studied by applying the dynamic finite-element method. The results revealed the relationship between the PGA amplification coefficients and the soil layer thickness, which confirmed that the dynamic response of the sites had obvious nonlinear characteristics. The results also showed that there was an obvious difference in the dynamic magnification factor between the short-period and long-period structures. Moreover, it was found that the amplification coefficient of the observation point at the free surface was greater than the point inside the soil at the same depth, which mainly occurred in the upper slope. Through this study, the quantitative assessment of ground motion effects in loess regions can be approximately estimated, and the amplification mechanism of the far-field ground motion mechanism can be further explained. In addition to the refraction and reflection theory of seismic waves, the resonance phenomenon may help explain the slope topographic effect through spectrum analysis.

What Promotes Post-Earthquake Economic Recovery: The Role of Counterpart Assistance Policy After the Wenchuan Ms 8.0 Earthquake, China

Despite the economic statistics from recent years indicating outstanding economic recovery in disaster-affected areas after the Wenchuan Ms 8.0 Earthquake, the causes of these macro-economic changes remain ambiguous. The Chinese Government set up the counterpart assistance policy to aid post-disaster reconstruction after the Wenchuan Ms 8.0 Earthquake in 2008; however, whether the changes seen in the economic statistics can be attributed to this policy remains unclear. This article uses the difference-in-differences model to evaluate the effects of counterpart assistance on economic development in disaster areas. Thirty-nine severely affected counties were chosen as research objects and divided into a treatment group (18 recipient counties) and a control group (non-recipient counties). Empirical results indicate the counterpart assistance policy helped to significantly improve the real GDP and GDP growth rate per capita in the treatment group. Counterpart assistance influenced the real GDP principally by increasing investment in fixed assets, employment, urbanization level, and fiscal expenditure. The findings of this study deepen our understanding of counterpart assistance within the Chinese context.

Study on Seismic Precursory Anomaly Signals Based on Critical Slowing Phenomena

This paper applied the principle of critical slowing down to the processing of radon concentartions observation data, calculated the autocorrelation coefficient and variance which can characterize critical slowing down by taking Wenchuan Ms8.0 earthquake on May 12, 2008, Lushan Ms7.0 earthquake on April 20, 2013, Minxian-Zhangxian Ms6.6 earthquake on July 22, 2013, Jiuzhaigou Ms7.0 earthquake on August 8, 2017 as examples. The result indicated that the water radon concentration at several stations has obvious critical slowing phenomenon before server earthquakes. The formation mechanism of radon concentration anomalies in seismic underground fluids was discussed in the context of the focal mechanism solution of several earthquakes. It is considered that the phenomenon of critical slowing down before server earthquakes is related to the earthquakes occurrenced combined with the hydrodynamic mechanism of radon anomaly and the structure of the abnormal points.