A Comprehensive Method for the Risk Assessment of Ground Fissures:Case Study of the Eastern Weihe Basin

Ground fissures are influenced by the coupling of geological factors and human activi-ties.They threaten the safety of infrastructure and restrict town planning in many areas in China.One of the area most severely affected by ground fissures is the Weihe Basin in North China,which has the most extensive distribution of ground fissures and all the elements that control their occurrence,pro-viding an ideal study area for the study of ground fissures.In this study,we took the eastern Weihe Ba-sin as the study area and determined the distribution and hazard characteristics of ground fissures via field investigation.Based on the analytic hierarchy process,we propose a multi-level,comprehensive method for evaluating the hazards of ground fissures.This method considers the geological back-ground,development status,and triggering factors of ground fissures,including all nine currently known assessment indices of ground fissures.We used judgment matrices to rank the constructed ground fissure assessment index system at the single and total levels and quantified the nine assessment indices of ground fissures according to the field survey data.Finally,we plotted the ground fissure risk zoning map and evaluated the ground fissure risk at the study area.Our findings indicated that the proposed method could facilitate ground fissure hazard assessment and prediction and provide support for hazard prevention and urban/rural planning.

Geological Factors for the Formation of Xi＇an Ground Fractures

Xi＇an ground fractures are the most typical ground fractures in China. Fourteen fractures have nearly divided the historical city into several distinct sections. These fractures are parallel and dis- tributed in NEE direction at the same interval, with all features exhibiting a down dropping southerly block which extends to connect with the underlying fault. The activities of fractures are primarily ex- pressed as normal faults. The faulted strata are well defined and dislocation displacement increases with depth. Thus, fractures have the characteristics of syn-sedimentary faults, which constitute the hanging wall of the Lintong-Chang＇an fault branch system. Crustal thinning caused by the uplifting of upper man- tle provides a power source for extension and stretching along the fracture surface of the upper crust, which results in a series of extensional faults and the suitable conditions for forming massive ground frac- tures. The movement of tectonic blocks influences the normal dip-slipping tension of Lintong-Chang＇an fault branches, and produces a series of secondary tectonic fractures adjacent to surface, which constitute the prototype of ground fractures. The recent regional tensile stress produced by modern mainland de- formation, also profoundly influences the current activity of Xi＇an ground fractures.

Formation Mechanism of Ground Fissures Originated from the Hanging Wall of Normal Fault:A Case in Fen-Wei Basin,China

This paper takes Fen-Wei Basin(FWB)as a case to study the ground fissures controlled by normal fault.Based on the field investigation,geophysical exploration,drilling,GNSS data and numerical calculation,the characteristics and mechanism of ground fissures originated from the hanging wall of normal faults are revealed.The results show that the distribution of ground fissures in the hanging wall and heading wall of the active faults is not uniform.Ground fissures are mostly distributed in the hanging wall of active faults and show a linear distribution on the surface,their strike is consistent with the fault,mainly characterized by vertical offset and horizontal tension.Ground fissures destroy the farmland and building foundation through which they pass and cause the rupture or displacement.In profile section,the ground fissure shows the characteristics of normal faults and dislocates the strata,and is connected with the underlying faults.Numerical analysis shows that the vertical displacement of normal fault activity in hanging wall is much larger than that in heading wall,which is the reason that tectonic ground fissures mainly originate from hanging wall.The range of dangerous area of ground fissures is controlled by the depth of fault,the strength of the ground fissures disaster is mainly controlled by the activity of fault.The formation of the ground fissures originated from the hanging wall of the fault experienced three stages:the main fault activity stage,the secondary fault activity stage and the fissure formation stage.

Development characteristics and formation analysis of the Liangjia Village earth fissure in the Weihe Basin,China

Liangjia Village earth fissure,one of the 79 earth fissures along the Kouzhen-Guanshan fault located in the northern Weihe Basin,causes severe damage to buildings and farmlands.Since the late 1950s,40 earth fissures have occurred in a similar east-west(EW)direction parallel to the Kouzhen-Guanshan fault,and a further 39 earth fissures have occurred with north-west,east-north,or north-east orientations intersecting the fault.In this study,a case study of Liangjia Village earth fissure was conducted to investigate the mechanisms of fissure generation in detail.Geotechnical and geophysical methods including measurements,trenching,drilling,and seismic exploration were used to reveal the basic characteristics,geological background,and origin model of the Liangjia Village earth fissure.This earth fissure,with a total length of 800 m in 2014,runs EW parallel to the Kouzhen-Guanshan fault,and it has damaged buildings and farmlands by forming sinkholes,gullies,subsidence,and a scarp.The trenching results indicated that this fissure underwent multi-phase activity.Analysis of geological drilling and shallow seismic profiling results showed that the fissure also possessed characteristics of a synsedimentary fault.Regarding its genesis,the fissure was formed through the combined actions of three factors:an earthquake created the fissure,the Kouzhen-Guanshan fault controlled its development,and loess erosion and groundwater runoff subsequently enlarged the fissure.Regional extension first generated many buried faults along the hanging wall of the Kouzhen-Guanshan fault before seismic activity caused the buried faults to propagate to the surface,where loess erosion and ground-water runoff promoted the formation of the current earth fissure.