Earth Fissures Research Articles

Characterization of earth fissures in South Jiangsu, China

Abstract. The Suzhou-Wuxi-Changzhou (known as "Su-Xi-Chang") area, located in the southern part of Jiangsu Province, China, experienced serious land subsidence caused by overly exploitation of groundwater. The largest cumulative land subsidence has reached 3 m. With the rapid progress of land subsidence since the late 1980s, more than 20 earth fissures developed in Su-Xi-Chang area, although no pre-existing faults have been detected in the surroundings. The mechanisms of earth fissure generation associated with excessive groundwater pumping are: (i) differential land subsidence, (ii) differences in the thickness of the aquifer system, and (iii) bedrock ridges and cliffs at relatively shallow depths. In this study, the Guangming Village Earth Fissures in Wuxi area are selected as a case study to discuss in details the mechanisms of fissure generation. Aquifer exploitation resulted in a drop of groundwater head at a rate of 5–6 m yr−1 in the 1990s, with a cumulative drawdown of 40 m. The first earth fissure at Guangming Village was observed in 1998. The earth fissures, which developed in a zone characterized by a cumulative land subsidence of approximately 800 mm, are located at the flank of a main subsidence bowl with differential subsidence ranging from 0 to 1600 mm in 2001. The maximum differential subsidence rate amounts to 5 mm yr−1 between the two sides of the fissures. The fissure openings range from 30 to 80 mm, with a cumulative length of 1000 m. Depth of bed rock changes from 60 to 140 m across the earth fissure. The causes of earth fissure generation at Guangming Village includes a decrease in groundwater levels, differences in the thickness of aquifer system, shallow depths of bedrock ridges and cliffs, and subsequent differential land subsidence.

Modeling of earth fissures caused by land subsidence due to groundwater withdrawal

Abstract. Land subsidence and earth fissures are phenomena related to groundwater withdrawal in a sedimentary basin. If the rock basement or basin lithology is irregular, both vertical and horizontal displacements can be induced due to differential settlement and tensile stresses appearing in the soil mass. If the differential settlement is of sufficient magnitude, earth fissuring can occur within tensile zones. The magnitudes of compaction and fissure geometry are closely related to the thickness and skeletal compressibility of fine-grained sediments within the aquifer system. Land subsidence and earth fissuring were modeled by employing a two-dimensional (2-D) coupled seepage and stress-strain finite element analysis. The basin bedrock geometry, lithological variation, measurements of surface displacements, and changes in hydraulic head were the critical input parameter for the subsidence modeling. Simulation results indicate that strain had exceeded the approximate threshold for fissure formation of 0.02 to 0.06 % in the area of the identified fissures. The numerical model was used to predict future subsidence and potential earth fissures for flood control structures within the metro Phoenix area.

Visualization of three dimensional earth fissures in geological structure

Abstract. This paper proposes a new method for visualizing the earth fissures of geological structure in three dimensional (3-D) domains on the basis of the seismic data and features information of earth fissures. The seismic data were interpreted for obtaining the stratagraphic data with various lithological information and the depth of the earth fissures. The spatial distribution of the ground fissures including the dip, strike and width were digitalized on an ArcGIS platform. Firstly, the 3-D geological structure was rebuilt using the Generalized Tri-Prism (GTP) method which is a real solid method for displaying geological structures. The GTP method can reflect the inner material of the strata and can simulate complicated geological structures such as faults and stratagraphic pinch outs. The upper and lower surfaces of each stratum consist of Triangle Irregular Networks (TIN). The inner solid between the two surfaces are a series of triangular prisms. Secondly, since the width of the ground fissure gradually decreases with depth, multiple edge lines of the earth fissures on the bottom stratum surface are deduced on the basis of the fissure characteristics. Then, the model of the earth fissures consisting of a series of triangular pyramids can be constructed using these points and the edge lines. A cutting operation was carried out on the 3-D geological structure using this ground fissures model. If the surfaces of the ground fissures model intersects with the GTPs in the geological structure model, new GTPs were generated within the local regions. During this process, the topological relations between TIN, triangular prism and lines were reconstructed so that the visualization of ground fissures in the geological structure model is realized. This method can facilitate the mechanism for studying fissures and avoid the gaps between the fissure solid and the geological structure to accurately reflect their 3-D characteristics.

Continuous monitoring of an earth fissure in Chino, California, USA – a management tool

Abstract. Continuous measurements of deformation have been made in Chino, California across an earth fissure and nearby unfissured soil since 2011 in two buried, horizontal, 150 mm pipes, 51 m long, which are connected by sealed boxes enclosing vertical posts at mostly 6 m intervals. Horizontal displacements and normal strain are measured in one line using nine end-to-end quartz tubes that are attached to posts and span fissured or unfissured soil. The free ends of the tubes are supported by slings and move relative to the attachment post of the next quartz tube. Linear variable differential transformer (LVDT) sensors measure the relative movements. Five biaxial tilt sensors were also attached to selected posts in that line. Relative vertical movement was measured at nine locations along the line in the second pipe using low-level differential pressure sensors. The second pipe is half full of water giving a free water surface along its length. Data are recorded on a Campbell CR10 using multiplexers. The quartz-tube horizontal extensometers have exhibited more than 3 mm of predominantly elastic opening and closing in response to about 32 m of seasonal drawdown and recovery, respectively, in an observation well 0.8 km to the south. The nearest production well is 1.6 km to the west. The horizontal strain was 5.9 × 10−5 or 30 % of the lowest estimate of strain-at-failure for alluvium. Maximum relative vertical movement was 4.8 mm. Maximum tilt in the fissure zone was 0.09 arcdeg while tilt at a separate sensor 100 m to the east was 0.86 arcdeg, indicating a wider zone of deformation than is spanned by the instrumentation. High correlation of horizontal displacements during drawdown, and especially recovery, with change in effective stress supports differential compaction as the mechanism for earth-fissure movement. The continuous measurements of horizontal strain coupled with water-level fluctuations and vertical borehole extensometry can provide a real-time adaptive management tool for restricting pumping if strain approaches the lower limit of strain-at-failure or a stress-strain curve deviates from the previous mostly elastic regimen.

Modelling ground rupture due to groundwater withdrawal: applications to test cases in China and Mexico

Abstract. The stress variation induced by aquifer overdraft in sedimentary basins with shallow bedrock may cause rupture in the form of pre-existing fault activation or earth fissure generation. The process is causing major detrimental effects on a many areas in China and Mexico. Ruptures yield discontinuity in both displacement and stress field that classic continuous finite element (FE) models cannot address. Interface finite elements (IE), typically used in contact mechanics, may be of great help and are implemented herein to simulate the fault geomechanical behaviour. Two main approaches, i.e. Penalty and Lagrangian, are developed to enforce the contact condition on the element interface. The incorporation of IE incorporation into a three-dimensional (3-D) FE geomechanical simulator shows that the Lagrangian approach is numerically more robust and stable than the Penalty, thus providing more reliable solutions. Furthermore, the use of a Newton-Raphson scheme to deal with the non-linear elasto-plastic fault behaviour allows for quadratic convergence. The FE – IE model is applied to investigate the likely ground rupture in realistic 3-D geologic settings. The case studies are representative of the City of Wuxi in the Jiangsu Province (China), and of the City of Queretaro, Mexico, where significant land subsidence has been accompanied by the generation of several earth fissures jeopardizing the stability and integrity of the overland structures and infrastructure.

Numerical simulation of earth fissures due to groundwater withdrawal

Abstract. Excessive groundwater withdrawal can cause land subsidence and earth fissures. The initiation and propagation of earth fissures are related to tensile failure and crack propagation in soils. Based on fracture mechanics, the crack band model (CBM), one of the smear crack models which is relatively easy to construct and convenient to be integrated into standard finite element codes is used in this paper. The calculated results of CBM are less dependent on the sizes of finite elements. The model was applied to simulate the formation and propagation of earth fissures in the hydrostratigraphic units with a bedrock ridge. The simulated positions and patterns of earth fissures coincide with field observations, suggesting that the modeling approach is adept to simulate the initiation and propagation of earth fissures due to groundwater withdrawal.

Land subsidence and earth fissures in south-central and southern Arizona, USA

Land subsidence due to groundwater overdraft has been an ongoing problem in south-central and southern Arizona (USA) since the 1940s. The first earth fissure attributed to excessive groundwater withdrawal was discovered in the early 1950s near Picacho. In some areas of the state, groundwater-level declines of more than 150 m have resulted in extensive land subsidence and earth fissuring. Land subsidence in excess of 5.7 m has been documented in both western metropolitan Phoenix and Eloy. The Arizona Department of Water Resources (ADWR) has been monitoring land subsidence since 2002 using interferometric synthetic aperture radar (InSAR) and since 1998 using a global navigation satellite system (GNSS). The ADWR InSAR program has identified more than 25 individual land subsidence features that cover an area of more than 7,300 km2. Using InSAR data in conjunction with groundwater-level datasets, ADWR is able to monitor land subsidence areas as well as identify areas that may require additional monitoring. One area of particular concern is the Willcox groundwater basin in southeastern Arizona, which is the focus of this paper. The area is experiencing rapid groundwater declines, as much as 32.1 m during 2005–2014 (the largest land subsidence rate in Arizona State—up to 12 cm/year), and a large number of earth fissures. The declining groundwater levels in Arizona are a challenge for both future groundwater availability and mitigating land subsidence associated with these declines. ADWR’s InSAR program will continue to be a critical tool for monitoring land subsidence due to excessive groundwater withdrawal.

ANALYSIS FOR MECHANISM OF GUOCHANG EARTH FISSURES IN LINFEN BASIN

Earth fissures are one of the geohazards in Linfen Basin. They firstly occurred here in 1970s.86 earth fissures were found in Linfen Basin in August, 2012. This paper examines the Guochang earth fissure. It expounds in detail the geological environment of Linfen Basin. The geological investigation, measurement, trenching, drilling and geophysical exploration are used to study the characteristics of earth fissure. They include the planes, damages, shallow sectional structure, deep features. It then summarizes the activity of earth fissure. Finally, this paper discovers the main characteristics of Guochang earth fissure. It has planar long extend, fat width, stability of trend, and severe damages. The shallow section is wide at the top and narrow at the bottom, which look likestrumpet.The deep features show the extractive activity existed in the lower part of earth fissure. The activity of ground fissure is controlled by rainfall. The effects of different factors on Guochang earth fissure are analyzed. The factors include tectonic activity, excessive extraction of groundwater and heavy rains. The formation of Guochang earth fissure is divided into the three steps of inoculation, formation and expansion. At last, the formation mechanism of Guochang earth fissure is acquired. The mechanism includes that (1)tectonic activity inoculates the fissure, (2)pumping groundwater triggers the fissure and (3)heavy rainfalls extend the fissure.

Mechanisms for earth fissure formation due to groundwater extraction in the Su-Xi-Chang area, China

Excessive groundwater withdrawal has caused many earth fissures in the cities of Suzhou, Wuxi, and Changzhou (i.e., the Su-Xi-Chang area or “SXC area”) in Jiangsu Province, China. The appearance of these fissures is closely associated with groundwater withdrawal both temporally and spatially. Based on field investigations, three models of the earth fissures in the SXC area were conceptualized. The changes in and distributions of normal and shear stress in hydrostratigraphic units due to groundwater extraction were analyzed numerically for each conceptualized model. Results from these numerical simulations indicated that geological conditions play a crucial role in the occurrence and distribution of earth fissures. Earth fissures are much more likely to initiate in areas where the depth of the bedrock below the ground surface is small, the thickness of the exploited aquifer unit changes abruptly, and the surface of the bedrock undulates dramatically. Earth fissures are also likely to occur in the vicinity of a distant restricted boundary. In addition, very stiff topsoil is more prone to cracking, and the locations of discharge wells also influence the occurrence of earth fissures.

Methane Fuels Deep-Sea, Rock-Hosted Ecosystem

Far beneath the ocean surface, vast quantities of methane percolate through the Earth's crust, following fractures and fissures into the shallow subsurface and frequently into the depths of the sea. These features are marine methane seeps, important components of the planet's climate regulation system. Methane moving through these seeps derives from the breakdown of larger organic molecules nestled within the crust and from closer-range biological production.

Occurrence assessment of earth fissure based on genetic algorithms and artificial neural networks in Su-Xi-Chang land subsidence area, China

Earth fissures in Su-Xi-Chang land subsidence area have induced massive damages to the area. The non-linear characteristic associated with the process of earth fissure formation requires non-linear method for evaluating the occurrence of the hazard. Based on quantification of influence factors on breeding the hazard, GA-ANN method, which integrates artificial neural networks (ANN) with genetic algorithms (GA), is developed for evaluating the occurrence of earth fissure hazard. Six indicators, that include the depth of bedrock burial (DBB), the degree of bedrock relief (DBR), water level (WL) (the II confined aquifer), the gradient of land subsidence (GLS), transmissivity (T) (the II confined aquifer) and the thickness of clay soil (TCS), are selected as the input patterns of the integrated approach, and danger index (DI) as the output pattern. A multilayer back-propagation neural network is trained with 30 sets of data samples including 15 sets of earth fissure samples and 15 sets of safety samples for defining the architecture of ANN. Subsequently, GA is employed by optimizing the initial weights of trained ANN by minimizing the deviation of output. The efficacy of the integrated approach is demonstrated by comparing the deviation of output from ANN and GA-ANN for 5 testing samples and the result shows that the GA-ANN method is more accurate than ANN in identifying the occurrence of earth fissure. The integrated method is applied to the assessment of earth fissure hazard in typical regions of earth fissure. According to the classification of DI, the regions are divided into four zones — danger zone, sub-danger zone, sub-safe zone and safe zone.

Mining-induced geo-hazards with environmental protection measures in Yunnan, China: an overview

There are abundant mineral resources in Yunnan Province, which is located in the southwestern part of China, due to its unique geological conditions. The distribution of minerals is related to geological formations and past tectonic movements. The mineral resources extracted in Yunnan Province constitute 83 % of total mineral production in China. The local environment around the mines in Yunnan Province has been destroyed due to harmful mining methods. Yunnan is a province with complicated and serious mining-induced environmental problems. Mining-induced geo-hazards found here include collapse, landslide, debris flow, sinkhole collapse, earth fissure, and water flowing into mine pits. To protect and control the geological environments in mining areas, countermeasures such as monitoring, and engineering rehabilitation and recovery, need to be adopted. Monitoring measurement combined with a digital mine information system can be used to forecast mine induced geo-hazards effectively. Moreover, appropriate engineering rehabilitation technology should be chosen according to the type of mining-induced geo-hazards.

Earth Fissures in Wadi Najran, Kingdom of Saudi Arabia

The formation of earth fissures due to groundwater depletion has been reported in many places in North America, Europe, and Asia. Najran Basin is in the southern part of the Kingdom of Saudi Arabia, and agricultural activities and other groundwater uses have caused significant groundwater depletion there. The basin recently experienced a sudden appearance of numerous earth fissures. An interdisciplinary study consisting of an evaluation of land-use changes, and hydrological, hydrogeological, and geophysical investigations was conducted to determine the reason for the formation of the earth fissures. The hydrological analysis strongly revealed that the groundwater level is decreasing with time. Groundwater depletion would lead to the accumulation of subsurface stress, causing soil hydro-consolidation which creates the ideal condition for the formation of earth fissures. Electrical resistivity, data indicated that there are anomalies in the profiles, which are most probably due to the presence of subsurface topography, another key factor for the formation of the earth fissures.

Earth fissure formation from groundwater pumping and the influence of a stiff upper cemented layer

Typical soil profiles in arid and semi-arid regions where groundwater is pumped consist of geological materials that vary from uncemented soils to rock. A finite-element analysis using a 20 m thick stiff cemented top layer over a 400 m thick aquifer is used to study how the cemented layer affects earth fissure initiation. This paper presents the results of this study on the key parameters influencing earth fissure formation in a soil profile with a top cemented layer. Three scenarios, each representing three cementation strength parameters, are investigated. A method based on the gradient of the slope of the subsidence bowl is proposed to determine earth fissure initiation. It is shown that earth fissures will not form for gradients below 8 × 10 −5 . The gradient at which an earth fissure would form depends on the cementation strength and tensile strength of the upper cemented alluvium layer. A highly cemented upper alluvium layer is more prone to earth fissure formation than an uncemented one. However, if the top layer is stiff enough to be classified as a ‘rock’, it will be less prone to earth fissure initiation when the cementation increases.

Fault-controlled deformation and stress from pumping-induced groundwater flow

Four two-dimensional numerical model scenarios are developed to gain a better understanding of how earth fissures form under pumping induced stress. The simulated aquifer–aquitard system contains a low compressibility sub-vertical 100 m wide fault zone that transects the hydrostratigraphic system that includes a 100 m thick vadose zone. Two scenarios represent constant and cyclical pumping over a 5-year period and two scenarios are used to evaluate the difference between using purely elastic aquitards versus elasto-plastic aquitards. The model provides for the analysis of the spatial distribution of deformation, and normal and shear stress that potentially lead to the formation of earth fissures. Results indicate that this fault-zone largely controls the deformation and stress regime of the system during pumping. Patterns of deformation and stress are similar for all scenarios with only the magnitudes being affected. Simulation results show that pumping induces a counterclockwise rotation of the fault plane on the footwall. The distribution of deformation through the fault is damped and the deformation patterns are more subdued on the hanging wall but all deformation is directed toward the pumping well. These deformation patterns result in two areas of stress accumulation that may lead to fissure formation: (a) near the land surface in the fault zone, and (b) near the saturated–unsaturated interface on the hanging wall adjacent to the fault zone. These results reveal the importance of both the fault and vadose zones in fissure genesis.

Controls on initiation and propagation of pumping-induced earth fissures: insights from numerical simulations

Pumping-induced earth fissuring occurs in many localities and represents an important economic problem associated with damage to infrastructures. In this work, a descriptive analysis of the natural conditions of selected localities undergoing fissuring is first performed. Then, numerical simulations are developed using the finite-element code ABAQUS to analyze the evolution of stress induced by pumping that can favor the initiation and propagation of fissures. The scenario used in the numerical simulations is based on the observed features from the descriptive analysis. These natural conditions include a complex stratigraphy, a buried fault scarp and a fault zone cutting the entire sedimentary sequence. Both fault zones and buried fault scarps influence the accumulation of stresses at different times. The fault zone has more influence on the patterns of tension/compression, while the buried fault scarp has more influence on the patterns of shear stress. Results show that a tensile-induced fissure is initiated close to the fault zone in the hanging wall. This fissure originates near the surface and migrates downward, terminating near the saturated–unsaturated interface. Factors involved in the propagation path of the fissure are the occurrence of a fault zone, the location of pumping, and the hydromechanical properties of the vadose zone.

Earth Fissure Formation from the Mechanics of Groundwater Pumping

This paper presents the formulation of the mechanics governing the changes in stress state from groundwater pumping. A 2-layer alluvium consisting of a cemented alluvium layer on top of an unconfined aquifer alluvium layer is considered. It is shown that the stress state in the aquifer alluvium consists of compression, simple shear, and couple stresses. The shear stresses on the vertical planes and horizontal planes are not equal. Consequently, a Cosserat rather than the conventionally used Cauchy continuum better simulates the stresses in the aquifer alluvium. Land subsidence from groundwater level decline consists of vertical compression (consolidation), shear displacement, and macrorotation. The latter occurs when conditions are favorable for the microrotation imposed by asymmetric stresses to become macrorotation. Earth fissures are formed in aquifer alluvium from groundwater pumping by simple shear on vertical planes and rotation and not by tension as commonly suggested. Earth fissures are formed in the upper cemented alluvium by simple shear strains and rotations. Highly cemented alluviums are more prone to earth fissure formation than weakly cemented alluviums. It is shown that there is a critical characteristic length of √2 times the aquifer alluvium thickness below which earth fissures would, theoretically, not develop. The distances from the well face at which earth fissures will form depend not on the total drop in groundwater level but on the gradient of the groundwater profile. The slope of the subsidence bowl, which consists of simple shear strain and rotation, is established as an indicator for the initiation of earth fissures.

Large differential land subsidence and earth fissures in Jiangyin, China

Jiangyin County is in the infamous Su–Xi–Chang land subsidence area caused by excessive groundwater withdrawal in Jiangsu province, China. The maximum accumulated land subsidence reached 1,310 mm near the centre of the subsiding trough in 2006 in southern Jiangyin, and earth fissures of significant vertical offsets have been observed at Changjing, Hetang and Wenlin which form an arc towards the subsidence trough. An ancient Yangtze River course is found underlying and passing through the depression in southern Jiangyin, forming a local basin surrounded by outcropped bedrock ridges in the north and south. The Quaternary stratigraphy demonstrates significant heterogeneities in the basin; the second confined aquifer is much thicker and deeper and encapsulated inside the basin and absent above the ridges. The development of earth fissures along the Changjing–Hetang–Wenlin arc might be a combination of an inward rotation of sediments due to a large differential subsidence, an inward movement driven by seepage force and a steeper slope along the south-eastern shoulder of the basin that facilitates the development of horizontal tensile strain and/or shear strain necessary for fissuring. The land subsidence has slowed down and no new earth fissure zone has occurred in the area after the banning of deep groundwater extraction was enacted in 2001.

The formation of floor-fractured craters in Xanthe Terra

Floor-fractured craters (FFC) are a peculiar form of degradation of impact craters defined by the presence of crevice networks and mesas affecting crater floors. They are preferentially distributed near chaotic terrains and outflow channels. The scope of this paper is to present a detailed systematic analysis of FFC at Xanthe Terra. FFC morphologies in this region are classified into five types making a picture of different stages of the same degradation process. FFC are geographically intermixed with un-fractured normal craters (non-FFC). Young craters are less prone to show this type of degradation, as suggested by fresh ejecta layer with preserved crater floor. Size distributions of FFC and non-FFC indicate that larger craters are preferentially fractured. Careful examinations of the crater floor elevations reveal that the crevices often extend deeper than the original crater cavity. Furthermore, an onset depth for the formation of FFC is evidenced from the difference of spatial distributions between FFC and non-FFC. Roof-collapsed depressions observed in the same region have been also documented and their characteristics suggest the removal of subsurface material at depth from about 1200 to 4000 m. These observations taken together suggest a subsurface zone of volume deficit at depth from 1 to 2 km down to several kilometers responsible for FFC formation. Then a scenario of FFC formations is presented in the context of groundwater discharge events at the late Hesperian. This scenario involves two key processes, Earth fissuring and piping erosion, known to occur with rapid groundwater migrations on Earth.

Surface Deformation in the Chengdu Plain Area Produced by the Wenchuan Ms8.0 Earthquake of 12 May 2008, Sichuan, China

AbstractThe 12 May 2008 Wenchuan MS8.0 (Mw7.9) earthquake occurred on the Longmen Shan (Mountains) thrust‐nappe structure zone in the eastern margin of the Tibetan plateau. It has produced 240 km long and 72 km long rupture zones on the surface along the Yingxiu–Beichuan fault and Guanxian–Jiangyou fault, respectively, which are branches of the Longmen Shan fault system. Besides, our field investigation found that this shock has also caused a weak rupture zone on the ground nearby the Shigu town, Shifang city that lies in the western Chengdu plain east to the epicenter. This rupture zone and the other two ruptures in the Longmen Shan mountainous area aforementioned constitute a northwest‐dipping imbricate structure. It is about 7.5 km long, trends in 30‐, and is manifested by a series of deformation phenomena such as damages of buildings, channel dislocations, ground folds, erupted sand and earth fissures on the surface. Observations in the exploratory trenches indicate that there is a fold uplift of 0.2 m in the youngest strata (including the surface) produced by the Wenchuan MS8.0 event, and a fold uplift of 0.4 m in the clay bottom in the trench, presumably resulted from a paleoearthquake of similar size to the Wenchuan shock in 2008. Seismic exploration of shallow subsurface demonstrates that in the place of seismic rupture zone in the Chengdu plain exist active faults of the late Pleistocene as well as active folds of the Quaternary.