Identifying drivers of urban landuse changes in the Wenchuan earthquake- affected area by using night-time light data

To learn the process of urban land evolution before and after an earthquake is vital to formulate the urban reconstruction control policies and recovery measures in the earthquake-stricken areas.However,spatiotemporal evolution and its driving factors of urban land in earthquake-prone areas remains limited due to the scarcity of ground observation data.This research,leveraging night-time light remote sensing imagery and land cover data,conducted a comprehensive analysis of the long-term evolution characteristics of urban land in earthquake-prone areas.It introduced methodologies for assessing the socio-economic impact and the primary natural environmental factors driving urban land evolution in these regions.To validate the proposed methods,the 2008 Wenchuan earthquake-affected area in China was selected as a representative study area.The results indicated that the average Digital Number(DN)values in socio-economically impacted areas showed a trend of rising,falling,and then rising again after the earthquake.DN values in three types of damaged areas including Type Ⅱ,Type Ⅲ,and Type Ⅳ exceeded pre-earthquake levels.The analysis of determinative factors influencing urban land evolution revealed that slope and elevation were key elements in controlling urban land expansion before the earthquake,whereas factors such as slope,elevation,lithology,and faults had a stronger influence on urban land expansion after the earthquake.It can be seen that,in view of the differences in the natural conditions of regions for post-disaster reconstruction,the local government need to actively adjust and adapt to urban spatial planning,so as to leverage the scale effect of large-scale inputs of funds,facilities,human resources and other factors after the disaster,thus enhancing resilience and recovery efficiency in response to disaster impacts.

Airblast evolution initiated by Wangjiayan landslides in the M_(s)8.0 Wenchuan earthquake and its destructive capacity analysis

Airblasts,as one common phenomenon accompanied by rapid movements of landslides or rock/snow avalanches,commonly result in catastrophic damages and are attracting more and more scientific attention.To quantitatively analyze the intensity of airblast initiated by landslides,the Wangjiayan landslide,occurred in the Wenchuan earthquake,is selected here with the landslide propagation and airblast evolution being studied using FLUENT by introducing the Voellmy rheological law.The results reveal that:(1)For the Wangjiayan landslide,its whole travelling duration is only 12 s with its maximum velocity reaching 36 m/s at t=10 s;(2)corresponding to the landslide propagation,the maximum velocity,28 m/s,of the airblast initiated by the landslide also appears at t=10 s with its maximum pressure reaching594.8 Pa,which is equivalent to violent storm;(3)under the attack of airblast,the load suffered by buildings in the airblast zone increases to 1300 Pa at t=9.4 s and sharply decreased to-7000 Pa as the rapid decrease of the velocity of the sliding mass at t=10 s,which is seriously unfavorable for buildings and might be the key reason for the destructive collapse of buildings in the airblast zone of the Wangjiayan landslide.

Analysis of debris flow control effect and hazard assessment in Xinqiao Gully,Wenchuan M_(s)8.0 earthquake area based on numerical simulation

Xinqiao Gully is located in the area of the 2008 Wenchuan M_(s)8.0 earthquake in Sichuan province,China.Based on the investigation of the 2023"6-26"Xinqiao Gully debris flow event,this study assessed the effectiveness of the debris flow control project and evaluated the debris flow hazards.Through field investigation and numerical simulation methods,the indicators of flow intensity reduction rate and storage capacity fullness were proposed to quantify the effectiveness of the engineering measures in the debris flow event.The simulation results show that the debris flow control project reduced the flow intensity by41.05%to 64.61%.The storage capacity of the dam decreases gradually from upstream to the mouth of the gully,thus effectively intercepting and controlling the debris flow.By evaluating the debris flow of different recurrence intervals,further measures are recommended for managing debris flow events.

Rapid repair techniques for severely earthquake-damaged circular bridge piers with flexural failure mode

In this study, three rapid repair techniques are proposed to retrofit circular bridge piers that are severely damaged by the flexural failure mode in major earthquakes. The quasi-static tests on three 1：2.5 scaled circular pier specimens are conducted to evaluate the efficiency of the proposed repair techniques. For the purpose of rapid repair, the repair procedure for all the specimens is conducted within four days, and the behavior of the repaired specimens is evaluated and compared with the original ones. A finite element model is developed to predict the cyclic behavior of the repaired specimens and the numerical results are compared with the test data. It is found that all the repaired specimens exhibit similar or larger lateral strength and deformation capacity than the original ones. The initial lateral stiffness of all the repaired specimens is lower than that of the original ones, while they show a higher lateral stiffness at the later stage of the test. No noticeable difference is observed for the energy dissipation capacity between the original and repaired pier specimens. It is suggested that the repair technique using the early-strength concrete jacket confined by carbon fiber reinforced polymer （CFRP） sheets can be an optimal method for the rapid repair of severely earthquake-damaged circular bridge piers with flexural failure mode.

A comparative study of the main factors controlling geohazards induced by 10 strong earthquakes in Western China since the Wenchuan earthquake in 2008

Determining the main controlling factors of earthquake-triggered geohazards is a prerequisite for studying earthquake geohazards and post-disaster emergency response.By studying these factors,the geomorphic and geological factors controlling the nature,condition,and distribution of earthquake-induced geohazards can be analyzed.Such insights facilitate earthquake disaster prediction and emergency response planning.The authors combined field investigations and spatial data analysis to examine geohazards induced by seismic events,examining ten earthquakes including the Wenchuan,Yushu,Lushan events,to elucidate the main control factors of seismic geohazard.The authors observed that seismic geohazard occurrence is usually affected by many factors,among which active nature of the seismogenic fault,seismic peak ground acceleration(PGA),topographic slope and geomorphic height differences,and distance from the fault zone and river system are the most important.Compared with strike-slip earthquakes,thrust earthquakes induce more high-altitude and high-speed remote landslides,which can cause great harm.Slopes of 0°–40°are prone to secondary seismic geohazards,which are mainly concentrated 0–6 km from the river system.Secondary geohazards are not only related to seismogenic fault but also influenced by the associated faults in the earthquake area.The maximum seismic PGA and secondary seismic geohazard number are positively correlated,and the horizontal and vertical ground motions play leading and promoting roles in secondary geohazard formation,respectively.Through the research,the spatial distribution of seismic geohazards is predicted,providing a basis for the formulation of emergency response plans following disasters.

Transient postseismic slip and aftershock triggering:A case study of the 2008 M_W7.9 Wenchuan Earthquake,China

In this study,we investigate how a stress variation generated by a fault that experiences transient postseismic slip(TPS)affects the rate of aftershocks.First,we show that the postseismic slip from Rubin-Ampuero model is a TPS that can occur on the main fault with a velocity-weakening frictional motion,that the resultant slip function is similar to the generalized Jeffreys-Lomnitz creep law,and that the TPS can be explained by a continuous creep process undergoing reloading.Second,we obtain an approximate solution based on the Helmstetter-Shaw seismicity model relating the rate of aftershocks to such TPS.For the Wenchuan sequence,we perform a numerical fitting of the cumulative number of aftershocks using the Modified Omori Law(MOL),the Dieterich model,and the specific TPS model.The fitting curves indicate that the data can be better explained by the TPS model with a B/A ratio of approximately 1.12,where A and B are the parameters in the rate-and state-dependent friction law respectively.Moreover,the p and c that appear in the MOL can be interpreted by the B/A and the critical slip distance,respectively.Because the B/A ratio in the current model is always larger than 1,the model could become a possible candidate to explain aftershock rate commonly decay as a power law with a p-value larger than 1.Finally,the influence of the background seismicity rate r on parameters is studied;the results show that except for the apparent aftershock duration,other parameters are insensitive to r.

区域产业结构对灾后恢复韧性的影响——以汶川县和北川县为例

灾后恢复是评价地震恢复韧性的重要指标。不同的区域经济产业所提供的就业数量存在差异,将对灾后恢复韧性产生极大影响。该文基于5.12汶川地震中受灾最严重的汶川县和北川县共736户受灾家庭的灾后恢复调查,研究了区域产业结构对恢复韧性的影响。研究表明:北川的家庭生活恢复滞后汶川近2年,主要是由于北川的外地务工家庭比例(49.60%)高于汶川(5.79%),这些受灾家庭恢复重建的主要资金来源是外地务工,但家庭成员长期外出不能参与恢复重建,造成其灾后恢复缓慢。外地务工家庭比例高的原因是北川第一产业占比高达27.20%,汶川仅为8.40%,第一产业所提供的本地就业数量远低于第二产业。因此,农业产业为主地区是灾后恢复最缺乏韧性的地区,需要大力提高防灾减灾能力,也可以通过产业结构调整,提高韧性。

汶川震区山洪灾害场次洪水最大携沙量预测模型

汶川地震后,震区产生了大量松散堆积体,受强降水影响产生了破坏性更强的山洪灾害,加剧了灾害的危险性,增加了灾害防治的困难度,研究震区山洪灾害可为评估灾害的风险性及后续的管理提供依据。本研究以66处历史山洪灾害作为样本数据,进行可量算影响因子的相关性分析,揭示山洪灾害的携沙量影响机制,确定流域面积、主沟长度、相对高差、物源量四个影响因子作为主控因子,基于SPSS进行非线性回归分析,建立了基于场次洪水最大携沙量及最大携沙距离的估算模型,并选取了汶川县和都江堰市的共23处山洪水沙灾害数据进行了模型的验证且与其他模型对比。结果表明,本研究建立的模型可靠性好,精度更高。研究成果有助于预测汶川震区潜在的山洪水沙灾害区域,为山洪水沙灾害的风险评估提供依据。

课程思政视角下地球物理学专业认识实习教学实践

在地球物理学专业认识实习课程中提炼和挖掘课程思政元素,把专业教育和思想品德教育有机地结合起来,特别是在汶川地震遗址现场讲解专业知识的同时,挖掘抗震救灾过程中涌现的可歌可泣的故事,使学生树立“万众一心、众志成城,不畏艰险、百折不挠,以人为本、尊重科学”的抗震救灾精神,使学生认识到学好地球物理学不仅是专业人才培养目标的需求,更是社会使命的需要,从而激发学生热爱专业、学好专业。实现专业课程思政与思政教育同向同行的立德树人协同目标。

预滑活动可能是地震前兆异常远程关联的物理机理

关注地震前兆异常的远程关联现象,有助于准确预测未来震中位置。2008年汶川M_(W)7.9地震发生前,大约在2008年3月20日前后,华北地块区及次级地块准同步发生了预滑活动。临震前1天,在冀鲁和鲁东黄海地块上,有10个地震台的水位仪、形变仪、地面和井下气压计记录到低频震颤震相Tp,且在地域和时间上与华北地块的预滑活动及此次汶川M_(W)7.9地震的发生相关性较好。推测认为,可能是华北地块区及次级地块在地幔热物质对流力的驱动下发生的震前预滑活动,地下气体逸出激发低频震颤,形成此次汶川M_(W)7.9地震前兆异常的远程关联现象。在数千千米尺度上的预滑活动,可能是地震前兆远程关联的物理机理,厘清异常位置(震中附近或远程关联),对作好未来震中预测具有重要作用。

Characteristics and Prevention of Secondary Geological Disasters of Wenchuan Earthquake

In the research, secondary geological disasters of Wenchuan earthquake were defined and the consequences were illustrated based on geological disasters, such as collapse, landslide and debris flow, and threats of barrier lakes. In addition, the characteristics of secondary disasters were analyzed, as follows： Rupture of geological faults lays foundation in terms of geological structure; loose solids provide resources of an earthquake; abundant rainfall and large runoffs are driving forces of an earthquake; rainstorm, flood, and long-term high temperature are major inducing factors. Furthermore, suggestions on prevention of secondary disasters were proposed in terms of prevention before, at and after an earthquake. Finally, the scientific and practical significances of secondary disasters were illustrated.

岷江上游汶川地震前后泥石流易发性评价

科学准确地绘制泥石流易发性区划图以及确定主控因子及其贡献率,是区域泥石流预警预报和风险管理的重要基础。文章以岷江上游为研究区,以小流域为评价单元,分别采用了5种机器学习模型构建了泥石流易发性评价模型,对汶川大地震前、后岷江上游泥石流易发性和评价因子贡献率进行了定量分析。结果表明:(1)集成机器学习模型的预测精度及受试者工作特征曲线下面积值均高于浅层机器学习模型,其中随机森林模型在地震前、后泥石流易发性评价中表现最优;(2)震前、震后泥石流发生率均随易发性等级的提高逐渐增大,且等级越高增量越大,各等级震后泥石流发生率均高于震前;(3)地震前、后侵蚀传递系数的贡献率均显著高于其他因子,与汶川大地震地震烈度空间分布特征叠加,加大了震后干流和支流泥石流由下游向上游发育程度逐渐降低的空间分布规律。

汶川县降雨时空分布特征及设计暴雨频率分析

为减少降雨及设计暴雨时空异质性对汶川县造成的损失,揭示汶川县降雨时空分布特征与设计暴雨特征,基于2001~2020年的GPM卫星降雨数据,采用Mann-Kendall等方法,从年、月、汛期、日等时间尺度和不同量级尺度,对汶川县降雨时空变化进行分析,并采用随机暴雨移置法(Stochastic Storm Transposition, SST)进行设计暴雨频率分析。结果表明:(1)汶川县年总降雨量呈显著增长趋势,主要受汛期降雨变化影响。(2)降雨空间分布不均匀,小雨主要分布在汶川县西南部,中到暴雨主要分布在汶川县东部。(3)基于随机暴雨移置法得到的设计降雨结果具有可靠性;随着降雨历时的增长,设计暴雨中心有从汶川县西南部向中东部移动的趋势;小重现期时,设计暴雨的空间分布不均匀性更为显著。研究成果可为汶川县暴雨洪涝防治提供参考。

青川刨地里地震滑坡发育特征及其成因机制探讨

以“5·12”汶川地震诱发的青川县刨地里滑坡为例,现场调查了滑坡的地质特征,并基于离散元软件(UDEC)分析了1号滑坡动力响应及变形破坏过程,探讨了滑坡的成因机制。现场调查表明,刨地里1号滑坡具有近水平“上硬下软”的地层结构,其中石坎断层穿过了滑坡后缘;滑坡堆积体的岩性分带特征表明,刨地里1号滑坡下部千枚岩先于上部硅质岩被破坏,且破坏时间早于2号和3号滑坡;数值模拟研究揭示,峰值加速度放大效应在断层带附近的千枚岩内最强,其放大系数达6.79,导致下层千枚岩首先沿陡倾面产生拉裂破坏,随后上层硅质岩体产生拉裂破坏,结果与现场调查堆积物特征较吻合;断层和上硬下软的地层结构对刨地里滑坡动力响应、变形及破坏起到了控制作用。该研究可为上硬下软且含断层的地震滑坡的评价提供参考。

基于遥感解译的典型强震区泥石流物源发育及演化--以四川都汶高速沿线为例

四川都汶高速位于2008年汶川地震强震区内,震后泥石流灾害异常活跃,对人类财产造成严重损失、人居安全构成重大威胁。为了查清山体斜坡物源空间分布规律,探讨汶川震区泥石流物源成因,选择区内震前DEM、震后Landsat TM多波段融合数据及典型泥石流沟2期全色波段遥感数据,进行泥石流物源发育特征及演化分析。结果表明:①汶川地震强震区物源发育受地形坡向、坡度、高程及水系的共同控制。在坡向上具有背坡面放大效应和逆冲(错动)方向放大效应,高程和坡度选择与山体斜坡发育的动力过程相关;②地震能量释放是物源发育基础,建立了强震区物源发育密度与地震烈度的指数关系模型,并认为研究区断层的存在可能促进了泥石流物源的进一步发育;③物源演化具有面积缩小、大型物源解体为多个小型物源、小型物源汇聚而致规模增大、物源迁移、出现新物源等特征。

2008年M_(W)7.9汶川地震早期余震频度衰减速率空间分布特征分析

深入认识余震频度衰减及其影响因素对理解余震触发机理和震后应急救援具有重要意义.然而,由于强震后余震数量庞大,波形相互叠加导致了目录中余震缺失,进而影响了余震频度衰减速率的估计.本研究采用模板匹配技术对2008年M_(W)7.9汶川地震后约50天内连续数据进行扫描,检测余震数量约为模板地震数量的5倍,完备震级由M3.0降低到M2.3.根据余震沿映秀—北川断裂走向优势深度分布的变化,以映秀、汶川、茂县、北川、南坝为界,余震活动大致可分为6个区域.本研究利用最大似然法分别计算了各个区域的余震频度衰减速率,结果显示:以茂县、青川为界,余震频度衰减速率表现出映秀—北川断裂西南段较快、中间段居中、东北段较慢的特征.将余震频度衰减速率和余震空间分布、断裂类型、震后形变、同震形变等进行对比分析,本研究得到以下结论:1、余震频度衰减速率分区与断裂类型分区吻合.其中,映秀—北川断裂西南段余震频度较快衰减速率区域断裂以逆冲为主,中间段为经过各种震源机制类型交替出现的过渡带,映秀—北川断裂东北段余震频度较慢衰减速率区域断裂以右旋走滑为主;2、余震频度衰减速率西南段较快、东北段较慢的空间分布特征与震后形变特征相一致;3、余震频度衰减速率与同震形变相关性不强.结合本研究观测到的同震滑移量较大区域余震分布较少、部分区域余震数目和震后形变空间分布一致性等特征,我们推测汶川地震早期余震可能主要与震后余滑相关,余震频度衰减速率的空间分布差异主要与不同类型断裂震间滑移速率不同相关,震间滑移速率较快的区域余震频度衰减速率较快及震后形变较大.

联合无人机光学与机载LiDAR在高位滑坡要素识别中的应用:以川西汶川龙溪沟滑坡为例

高位和高隐蔽性滑坡调查人力难至、效率低下且安全风险大,利用无人机光学和机载LiDAR等航空遥感技术进行调查识别能够有效克服该问题,已成为当前研究应用的热点。目前多数研究与应用以宏观调查和解译为主,针对滑坡拉裂缝、滑坡壁等发育要素的精细化识别和量测研究较少。为进一步细化无人机光学和机载LiDAR识别的滑坡要素解译特征,提高该技术的综合应用效果,本文选取川西地震活跃区的汶川龙溪沟高位滑坡为示范,采用无人机摄影测量、机载LiDAR、解译对比与空间测量以及实地调查复核等方法,提取了28条拉张裂缝、2条剪切裂缝、8处下挫陡坎、2条滑坡壁、5条前缘边界、5个次级变形体,基于滑坡要素排列组合划分了2个次级滑体、4个变形区。野外验证结果与室内解译高度吻合,证明了该方法的可靠性和准确性。研究成果总结对比滑坡要素在不同数据上的色调、纹理、光谱差异,探索联合无人机光学与机载LiDAR的滑坡要素“色调-纹理-图谱”协同对比提取方法,阐述了高位滑坡“先解译要素再分区组合”的精细识别过程。研究成果可为其他高危高位滑坡的精细化识别研究及防治应用提供技术参考,具有应用推广价值。

Seismic-induced surficial failure of cohesive slopes using three-dimensional limit analysis:A case study of the Wangjiayan landslide in Beichuan, China

A seismic-induced landslide is a common geological catastrophe that occurs in nature.The Wangjiayan landslide,which was triggered by the Wenchuan earthquake,is a typical case in point.The Wanjiayan landslide caused many casualties and resulted in enormous property loss.This study constructs a simple surficial failure model based on the upper bound approach of three-dimensional(3D)limit analysis to evaluate the slope stability of the Wangjiayan case,while a traditional two-dimensional(2D)analysis is also conducted as a reference for comparison with the results of the 3D analysis.A quasi-static calculation is used to study the effect of the earthquake in terms of horizontal ground acceleration,while a parametric study is conducted to evaluate the critical cohesion of slopes.Rather than employing a 3D analysis,using the 2D analysis yields an underestimation regarding the safety factor.In the Wangjiayan landslide,the difference in the factors of safety between the 3D and 2D analyses can reach 20%.The sliding surface morphology as determined by the 3D method is similar to actual morphology,and the parameters of both are also compared to analyze the reliability of the proposed 3D method.

基于非线性回归的暴雨泥石流堵河预测

堵河型泥石流灾害在汶川震区较为常见,其链式灾害效应严重威胁到了区域内人民的生命财产安全。故准确预测泥石流堵河程度,并采取相应的防治措施是至关重要的。以四川省绵竹市清平镇于2010年8月13日暴发的群发性泥石流为研究对象,通过分析因子权重,利用非线性回归建立了泥石流堵河程度的预测模型,并与已有模型进行了对比,论证了所建立模型的可用性,其后对不同降雨频率下的泥石流堵河程度进行预测。结果表明:流量比和流域面积是最佳的建模因子,所建立的模型绝对平均误差为0.049;与不同模型对比发现本文模型对于清平镇泥石流堵河预测具有很好的适用性;在极端降雨下,部分沟道堵河预测程度为1,会造成绵远河堵断。研究成果可为该地区泥石流灾害的防治和治理提供参考。

A modified stochastic finite-fault method for estimating strong ground motion:Validation and application

We developed a modified stochastic finite-fault method for estimating strong ground motions.An adjustment to the dynamic corner frequency was introduced,which accounted for the effect of the location of the subfault relative to the hypocenter and rupture propagation direction,to account for the influence of the rupture propagation direction on the subfault dynamic corner frequency.By comparing the peak ground acceleration(PGA),pseudo-absolute response spectra acceleration(PSA,damping ratio of 5%),and duration,the results of the modified and existing methods were compared,demonstrating that our proposed adjustment to the dynamic corner frequency can accurately reflect the rupture directivity effect.We applied our modified method to simulate near-field strong motions within 150 km of the 2008 MW7.9 Wenchuan earthquake rupture.Our modified method performed well over a broad period range,particularly at 0.04-4 s.The total deviations of the stochastic finite-fault method(EXSIM)and the modified EXSIM were 0.1676 and 0.1494,respectively.The modified method can effectively account for the influence of the rupture propagation direction and provide more realistic ground motion estimations for earthquake disaster mitigation.