variations in spatial patterns of soil vegetation properties over subsidence related ground fissures at an arid ecotone in northeastern iran this study examines variations in the spatial patterns of soil vegetation properties in the vicinity of subsidence related ground fissures caused by groundwater over pumping over an arid ecotone situated in northeastern iran it was assumed that subsidence related fissures have a possible effect on the soil vegetation structures vegetation metrics mean canopy area mean volume vegetation cover percentage and soil properties ec ph caco3 particle size distribution were measured for locations with differing spatial expanses of ground fissures including surface ground fissures deeper ground fissures as well as those exhibiting no signs of ground fissure statistical analyses indicated significant differences p 0 05 in the spatial patterns of vegetation and soil properties for locations with different expanses of ground fissures greater degradation of soil vegetation presenting as mortality of plants and the formation of impermeable layers on the soil surface was observed around deep fissures linked to groundwater over pumping in comparison with other locations these findings confirm the relationship between heterogeneities in patterns of vegetation and soil properties and variations in structure and extent of ground fissures as well as indicating that the expansion of groundwater over pumping induced surface ground fissures can promote soil vegetation degradation over time leading ultimately to barren soils

tilts strains and ground water levels near an earth fissure in the mimbres basin new mexico vertical deflection profiles derived from microradian sensitivity tiltmeter data collected over a 1 yr period suggest that an earth fissure in the subsiding mimbres basin is located near the inflection point of an evolving surficial fold of infinitesimal amplitude water levels beneath the study site also fell steadily during the period of observation calculated curvature profiles which reflect the sign and relative magnitude of fiber strain along the ground surface further imply that the fissure was within a zone of contraction throughout the study period observed fissure perpendicular tilts and the location of the fissure at an inflection point rather than along an anticlinal crest are consistent with a mode ii fracture shearing mode crack or fault rather than a mode i fracture opening mode crack or joint tilting parallel to the fissure further suggests a component of mode iii tearing mode crack displacement during the study period thus the three dimensional displacement strain and stress fields around the fissure were considerably more complicated than those suggested by previous fissure monitoring studies and suggest that the fissure may have been formed in compression as a shear crack rather than in tension as an extensional crack on the basis of the occurrence of right steps in the trace of the fissure we speculate that our data may reflect contraction across one of the steps as a consequence of left lateral slip along the fissure

genesis and evolution of the fumaroles of vulcano aeolian islands italy a geochemical model a geochemical model explaining the presence of fumaroles having different gas composition and temperature at the top of the crater and along the northeastern coast of vulcano island is proposed a pressurized biphase liquid vapor reservoir at the depth of about 2 km is hypothesized energy and mass balance sheets controlp t conditions in the system p t must vary along a boiling curve of brine as liquid is present the co2 content in the steam is governed by the thermodynamic properties of the fluids in the h2 nacl co2 system on the assumption that oxygen fugacity in the system is between the hm fmq oxygen buffers observed so2 h2s co2 co co ch4 ratios in the fumarolic gases at the fossa crater appear in equilibrium with a temperature higher than that observed such as may exist at depth the more reduced gas phases present on the sea side may result from re equilibrium processes in shallower aquifers the suggested model would help in monitoring changes in volcanic activity by analyzing fumarolic gases

a new method for sampling and analyzing volcanic sublimates application to merapi volcano java abstract a new method for the sampling of sublimates from high temperature volcanic gases has been used at merapi volcano java in 1978 the sublimates were collected on the inner walls of silica tubes introduced into fumarolic vents volcanic gases were allowed to move freely through the tubes and as they cooled a fraction of the volatile components condensed on the inner walls of the tubes along the temperature gradient the sublimates were then analyzed by a combination of light microscopy scanning electron microscopy electron microprobe and x ray diffraction six successive zones of different compositions and mineralogical associations have been identified along the covered range of temperatures 900 to around 400 c from the high to the low temperatures these zones are composed of 1 cristobalite magnetite hercynite 2 molybdenite 3 acmite 4 halite sylvite 5 sphalerite pyrite and 6 galena equilibrium calculations show that these crystalline phases are stable for ps 2 pc 1 and po 2 values typical of magma buffered gases that have not been contaminated by atmospheric oxygen the deposits observed in the tubes may be useful in aiding the understanding of the mechanisms acting during the cooling of the gaseous phase on its way to the surface and before its emission into the atmosphere

trace elements in the thermal groundwaters of vulcano island sicily abstract the chemical concentrations of many trace elements that have never before been examined in vulcano island groundwaters are reported chemical data indicate that rock composition is not the only factor determining the metal content in the aqueous system the observed concentrations depend mainly on 1 the chemical composition of the host rocks 2 the chemical physical conditions of the weathering solution temperature acidity redox conditions 3 input of magmatic gases 4 adsorption of metal ions on oxide particles formation of soluble complexes and or precipitation of solid phases chloride complexes in solution are of minimal significance for all elements with the exception of cd whereas carbonate complexes are important for pb uo 2 zn and ni temperature and trace element distribution maps are also presented

land subsidence and earth fissures due to groundwater withdrawal in the southern yangtse delta china excessive extraction of groundwater has caused severe land subsidence and earth fissures in the southern yangtse delta china based on field data the temporal and spatial distribution of land subsidence is investigated and the causes for earth fissures are analyzed the areal distribution of the land subsidence is closely related to the cones of depression in the main exploited aquifers the compaction of a hydrostratigraphic unit depends on its mechanical behavior thickness compressibility and the piezometric level changing the primary subsidence layers in shanghai have been the first aquitard before 1990 and the third confined aquifer since then but the second aquitard unit was the primary subsidence layer in changzhou earth fissures trending in several directions occurred in the husu tectonic zone they were mainly caused by differential subsidence and horizontal displacement that resulted from tensile stress and shear stress in units the majority of fissures in the study area are tensile

formation and evolution of strike slip faults rifts and basins during the india asia collision an experimental approach the processes which have governed the formation and evolution of large tertiary strike slip faults during the penetration of india into eastern asia are investigated by means of plane strain indentation experiments on layered plasticine models the steady state deformation of plasticine obeys a power creep flow law e c t n the stress exponent n is between 6 and 9 at 25 c uniaxial plane strain tests on cubic specimens show that the growth of faults in layered plasticine results from strain softening a process observed for strain rates ranging from 3 5 10 5 to 3 6 10 3 s 1 fault or shear zones form after only 7 10 bulk strain subsequent deformation is controlled by the geometry of the fault pattern rather than the physical properties of the plasticine a series of nine plane strain indentation experiments shows the influence of boundary conditions as well as that of the internal structure of the plasticine model on the faulting sequence the ubiquity of strain softening in experimental deformation of a variety of rocks as well as the widespread occurrence of shear zones in nature suggest that long term deformation of the continental lithosphere may also be primarily influenced by the geometry of large faults which rapidly develop with increasing strain the deformation and faulting sequence observed in the plasticine indentation experiments may thus be compared to collision induced strikeslip faulting in asia particularly to total offsets and rates of movements on the faults the experiments simulate the evolution of the western ends of the strike slip faults which have probably been analogous to trench fault fault triple junctions the experiments also illustrate mechanisms for the formation of extensional basins such as the south china sea north china basin and andaman sea near active continental margins the basins which appear to absorb terminal offsets along major strike slip faults near such margins may result from mismatch between the sharply angular shape of the deformed continental edge and the more regularly curved trench along which the smoothly flexed oceanic lithosphere subducts the existence of distinct phases of strike slip extrusion corroborates the idea that the discontinuities in time which typify intracontinental tectonics and orogenic cycles may often result from strain localization and the ensuing discontinuous non steady state deformation of the continental lithosphere

origin of the fumarolic fluids of vulcano island italy and implications for volcanic surveillance variations in d and 18o values with h2o contents and outlet temperatures indicate that the fumaroles of la fossa crater have discharged mixtures of magmatic water and marine hydrothermal water since 1979 the contribution of meteoric water was low in the period 1979 1982 and very low afterwards the 18o values of the marine hydrothermal component of 5 to 7 2 are due to isotopic exchange with the 18o rich silicates of the rocks under high temperature and low permeability conditions the 18o value of the magmatic end member is generally 3 5 to 4 3 although values as high as 5 5 to 6 5 were reached in the summer of 1988 when magma degassing appears to have extended into the core of the magma body the d values of the end member were close to 20 typical of andesitic waters both the isotopic values and chemical data strongly support a dry model consisting of a central magmatic gas column and a surrounding hydrothermal envelope in which marine hydrothermal brines move along limited fracture zones to undergo total evaporation on approaching the conduits of magmatic fluids the vents at the eastern and western boundaries of the fumarolic field are fed by fluids whose pressure is governed by the coexistence of vapor liquid and halite giving rise to a high risk of phreato magmatic explosions should magma penetrate into these wet environments most la fossa eruptions were triggered by an initial hydrothermal blast and continued with a series of phreatomagmatic explosions the fluids discharged by the forgia vecchia fumaroles are mixed with meteoric water which is largely evaporated although subordinate loss of condensed steam may be responsible for scrubbing most of the acidic gas species the temperatures and pressures and the risk of a sudden pressure increase are low a boiling hydrothermal aquifer at 230 c is present underneath the baia di levante beach this area has a minor risk of hydrothermal explosions

chemical features and isotopic composition of gaseous manifestations on vulcano island aeolian islands italy an interpretative model of fluid circulation abstract between 1987 and 1995 gases were sampled from various manifestations on vulcano island including various fumaroles at la fossa crater and baia di levante and diffuse soil gas emissions in several areas which are characterized by high c02 fluxes since the end of 1987 volcanic activity has increased considerably showing a marked rise in temperature 300 c in 1987 to 670 c in december 1992 and in output of steam from crater fumaroles in addition variations have been observed in the chemical and isotopic compositions of gases and thermal waters which can be attributed to an increased inflow of deeper fluids the isotopic composition of fumarolec steam seems to be the result of mixing processes between a positive endmember of deep origin d 10 15 18o 6 8 and two endmembers of meteoric origin with different oxygen shifts variations observed in the c02 isotopic composition suggest that all sampled manifestations are fed by a single deep source which may be magmatic such a source would be characterized by the 613cco2 values of high temperature fumaroles 13cco2 0 these values are noticeably more positive than those generally attributed to magmatic gases 13cco2 5 8 implying crustal contamination processes of the magma the observed decrease in 18oco2 values of the crater fumaroles from 20 in 1978 to between 12 and 15 in 1993 1994 was probably caused by two different processes the first is a reduction of the enrichment factor between c02 and h2o which is related to the increased temperature of the gases and the second is a mixing with more negative waters of meteoric origin finally c02 addition or removal processes caused by interactions between deep gases and shallow hydrothermal waters are likely to be responsible for the different chemical and isotopic compositions of gaseous emissions in the vulcano porto area and the crater fumaroles

laboratory investigation of pore pressure dissipation in clay around permeable piles excess pore water pressures induced by pile driving could have a detrimental effect on a project especially on the construction sequence and ground settlement measures that can effectively accele

isotopic variation of the hydrothermal system on vulcano island italy the isotopic and chemical composition of thermal waters and the isotopic composition of high temperature fumarolic steam at vulcano island indicate an evolution of the hydrothermal system from its magmatic origin through interaction with rocks and mixing with meteoric water seawater is not a component in this system the isotopic values of the fumaroles indicate a local magmatic composition of 7 to 8 18o and 5 to 15 d the high d values of this vapor may reflect contamination of the magma by connate water the isotopic and chemical composition of water from well w2 indicates the existence of geothermal fluid formed by mixing of hcl and so2 bearing condensates of volcanic origin with groundwater with subsequent evolution via water rock interaction the estimated isotopic composition of the geothermal water is 18o 1 and d 5 local shallow seismic events result in a temporary increase in fracture permeability enabling the mixing of magmatic vapor with groundwater or geothermal water tectonic activity associated with deep structures appears to increase the contribution of magmatic vapor to the fumaroles

radioactive isotopes and trace elements in gaseous emissions from white island new zealand abstract measurements of the radioactivity of gases released by white island volcano show variations in 210 po concentrations with temperature in fumarolic gases and this is interpreted to be due to dilution of magmatic gases with vapours derived from an envelope of acid brines surrounding the vent system the degassing model derived for mount etna emissions is tested on white island magmatic gases the results are a short degassing time 2 days small degassing magma volume 5 10 6 m 3 and the following estimations of emanation coefficients pb 1 bi 2 7 cd 0 05 and cu 0 07 the initial content of s in the magma is estimated to be within the range 300 600 mg kg fluxes of trace metals kg day emitted by the volcano are estimated to be pb 125 bi 6 cu 300 and cd 9

distribution and mechanism of the ground fissures in wei river basin the origin of the silk road wei river basin wrb is the origin of the ancient and new silk road and it is located in southern fen wei graben system china since 1950s hundreds of ground fissures have formed in this affluent basin and these ground fissures have become the main geohazard in wrb this paper used a series of geological investigations such as site investigation trench excavation geological drilling and geophysical survey to understand the distribution and mechanism of formation of the ground fissures in wrb the results are 1 212 ground fissures in wrb were located in xi an xianyang weinan city and they have clear orientations mainly distributed from nee to sww nw to se and e to w moreover the ground fissures are accompanied by active faults along the same directions 2 ground fissures in wrb can be divided into two types some ground fissures display obvious horizontal and vertical separations on the earth surface whereas others only display obvious horizontal separations on the earth surface 3 ground fissures in wrb are triggered by four factors viz basin structure active fault human activities and loess erosion 4 the mechanism for the formation of ground fissures has also been proposed tectonic faulting is the fundamental cause of ground fissures in the wei river basin and imbalances in the man land caused by human actives accelerated the ground fissures activities 5 many effective measures have also been proposed to mitigate the hazards of ground fissures in wrb such as planning engineering measures controlling the exploitation of groundwater and monitoring this research will be helpful in safeguarding the sustainable development of the silk road economic belt

the mobility of zirconium and other immobile elements during hydrothermal alteration abstract development of zircon and other zr phases in hydrothermal deposits indicates that zr can be highly mobile in these systems mobility is most common in but not restricted to f rich hydrothermal systems related to alkalic f rich igneous suites these suites can range from peralkaline through metaluminous to peraluminous a few examples are neither alkalic nor f rich three locations in the trans pecos magmatic province texas u s a demonstrate this hydrothermal zr mobility all three igneous systems are alkalic and f rich but vary in alkali al ratios peralkaline rhyolites and trachytes in the christmas mountains contain as much as 2100 ppm zr mostly in aegirine or arfvedsonite zircon is rare or absent fluorspar replacement deposits in limestone at contacts with the rhyolites contain as much as 38 000 ppm zr occurring as small disseminated zircons the deposits also are enriched in a variety of incompatible elements including be rare earth elements ree y nb mo hf pb th and u the sierra blanca intrusions a series of mildly peraluminous f rich rhyolite laccoliths contain as much as 1000 ppm zr mostly as zircon hydrothermal zircon occurs as overgrowths on magmatic grains as veinlets connected to overgrowths and in fluorspar replacement bodies in adjacent limestone the highest zr concentrations in fluorspar are 200 ppm metaluminous quartz monzonite from the infiernito caldera contains 400 600 ppm zr mostly as zircon euhedral zircon in quartz fluorite veins in the quartz monzonite indicates mobility of zr zirconium concentrations in the veins are unknown but the paucity of zircon suggests little zr enrichment relative to the host zircon and more rarely zirconolite occur in skarn in the ertsberg district of irian jaya indonesia unlike in texas related igneous rocks are metaluminous and the hydrothermal system was f poor worldwide hydrothermal zircon other zr phases and ti and al bearing phases occur in skarn epithermal precious metal veins volcanogenic massive sulfide deposits and mylonites we propose that differences in zr mineralogy of igneous source rocks is an important factor in determining the availability of zr to hydrothermal fluids although zr concentrations in the sierra blanca and christmas mountains rhyolites are similar zr enrichment in fluorspar was much greater in the christmas mountains we suggest that hydrothermal solutions could easily break down aegirine and arfvedsonite to release zr but that zircon was only moderately attacked therefore far more zr was available for transport and subsequent deposition in the christmas mountains than at sierra blanca availability of other trace elements probably is also governed by their mineral host although zr mobility is most common in f rich hydrothermal systems related to alkalic and f rich igneous systems mobility at ertsberg may have been promoted by sulfate complexing

the behaviour of so called immobile elements in hydrothermally altered rocks associated with volcanogenic submarine exhalative ore deposits evidence is available that some elements notably zr tio2 y sc ce and nb are largely immobile during the alteration of volcanic rocks owing to metamorphism hydrothermal events and weathering e g floyd and winchester 1978 however it is shown by reference to analyses of rocks from the environment of five volcanogenic massive sulphide bodies that while zr tio2 and ce are mostly immobile even during intense hydrothermal alteration y and particularly sc and nb may be extremely mobile when elements are removed by solution in a hydrothermal fluid it seems that reaction rates are such that these elements are almost totally removed from the rock therefore of the so called immobile trace elements only zr and tio2 may be used with any reliability to identify the degree of magmatic differentiation in an hydrothermally altered rock however if an element has been mobile it is usually readily identified as having moved

evolution and origin of the ground fissures in xian china large scale extraction of ground water in xian has resulted in significant drawdown of the phreatic surface and in land subsidence across this ancient capital of china it has also triggered the rejuvenation of the normal faults in the upper portions of the quaternary deposits underlying the city leading to surface rupturing and the development of ground fissure zones across the city these ground fissure zones are structurally controlled in the sense that they are directly linked to the normal faults in the quaternary deposits all trending in an east northeasterly direction in essence they are the surface expressions of the deeper faults under current drawdown conditions the ground fissures have resulted in extensive property damage along their paths of propagation this paper describes their occurrence their possible causative mechanism and the resultant damage of necessity xian will still be dependent on ground water supply to a large extent in the years ahead however ground water extraction will have to be managed in an environmentally sustainable manner in order to minimize the geological hazards associated with the ground fissures

the origin and impact of the shizhuang ground fissure yingxian area datong basin china abstract the datong basin is part of the regionally extensive fenwei graben system a major tectonic zone impacted by active tectonics and the resulting damage to life and infrastructure the basin also contains the shizhuang ground fissure system in this study the likely origin surface extent and fissure subsurface characteristics are explored by traditional methods surveying mapping trenching drilling and seismic exploration the shizhuang ground fissure is located at the intersection of the xiaoshikou fault and the southern liuleng margin fault in yingxian county it has a length of 2 1 km excellent continuity and semi elliptical surface morphology the dislocation of strata induced by the fissure increases significantly as the depth increases the strata bend downward and form typical traction structures near the fissure plane indicating that the fissure has prominent synsedimentary fault characteristics the fissure causes serious damage to houses farmlands roads and public facilities featuring large tensile cracks and vertical dislocations the resulting data and interpretations indicate that 1 the ground fissures connect to two major subsurface active faults which lay the tectonic foundation for the fissure 2 accelerated groundwater extraction has reactivated the underlying faults and exacerbated fissure development and 3 mitigation is best achieved by cessation of excessive groundwater pumping appropriate engineering design and local avoidance for placement of critical structures this paper provides a heretofore generally unknown example promotes research on the mechanisms of fissures and has guiding significance for disaster prevention and reduction in this area

volatilization transport and sublimation of metallic and non metallic elements in high temperature gases at merapi volcano indonesia abstract condensates silica tube sublimates and incrustations were sampled from 500 800 c fumaroles and lava samples were collected at merapi volcano indonesia in jan feb 1984 with respect to the magma merapi gases are enriched by factors greater than 105 in se re bi and cd 104 105 in au br in pb and w 103 104 in mo cl cs s sn and ag 102 103 in as zn f and rb and 1 102 in cu k na sb ni ga v fe mn and li the fumaroles are transporting more than 106 grams day g d of s cl and f 104 106 g d of al br zn fe k and mg 103 104 g d of pb as mo mn v w and sr and less than 103 g d of ni cu cr ga sb bi cd li co and u with decreasing temperature 800 500 c there were five sublimate zones found in silica tubes 1 cristobalite and magnetite first deposition of si fe and al 2 k ca sulfate acmite halite sylvite and pyrite maximum deposition of cl na k si s fe mo br al rb cs mn w p ca re ag au and co 3 aphthitalite k na sulfate sphalerite galena and cs k sulfate maximum deposition of zn bi cd se and in higher deposition of pb and sn 4 pb k chloride and na k fe sulfate maximum deposition of pb sn and cu and 5 zn cu and k pb sulfates maximum deposition of pb sn ti as and sb the incrustations surrounding the fumaroles are also chemically zoned bi cd pb w mo zn cu k na v fe and mn are concentrated most in or very close to the vent as expected with cooling atmospheric contamination and dispersion the highly volatile elements br cl as and sb are transported primarily away from high temperature vents ba si p al ca and cr are derived from wall rock reactions incomplete degassing of shallow magma at 915 c is the origin of most of the elements in the merapi volcanic gas although it is partly contaminated by particles or wall rock reactions the metals are transported predominantly as chloride species as the gas cools in the fumarolic environment it becomes saturated with sublimate phases that fractionate from the gas in the order of their equilibrium saturation temperatures devolatilization of a cooling batholith could transport enough acids and metals to a hydrothermal system to play a significant role in forming an ore deposit however sublimation from a high temperature high velocity carrier gas is not efficient enough to form a large ore deposit re se cd and bi could be used as supporting evidence for magmatic fluid transport in an ore deposit

overview of ground fissure research in china ground fissures in china have garnered increasing international attention in recent years due to their areal extensiveness large scale and high hazard potential these fissures especially those in the fen wei basin and north china plain severely restrict planning and construction in big cities threaten the operation of underground and above ground railways and cause serious economic loss recent research shows that ground fissures in china occur mainly in sedimentary basins and develop along active faults and at the edges of groundwater cones of depression most of these fissures are caused by the combined action of tectonic stress and hydrodynamic force effective ground fissure disaster reduction technologies are developed and they include pumping control reasonable avoidance adaption to deformation and local strengthening this paper provides an overview on ground fissure studies in china and demonstrates how research results can serve economic development and geohazard mitigation

characteristics of land subsidence earth fissures and related disaster chain effects with respect to urban hazards in xi an china the ancient capital of xi an is a typical city in china with a shortage of water resources with an urban population of 7 million its domestic and industrial use of water depends almost entirely on groundwater large scale long term extraction of groundwater has caused severe land subsidence and triggered the reactivation of active normal faults in the quaternary under consolidated sediments underlying the city this has further led to ground ruptures that have gradually evolved into earth fissure zones during this process there has been a close spatiotemporal relationship between land subsidence and the formation of earth fissures from field monitoring data the subsidence bowls are typically located in loess depressions between earth fissure zones within structural blocks of sediment cut by active quaternary faults and preexisting fault planes the subsidence bowls are generally elliptical in shape with the long axes consistent with the preferred orientation of the earth fissures the underlying quaternary active faults and preexisting fault planes predispose the intervening sediment blocks to formation of earth fissures and intense groundwater extraction has led to accelerated subsidence and earth fissuring during the past 50 years mining groundwater land subsidence and earth fissures occur in a sequence and constitute a disaster chain with respect to urban hazards in xi an thus it is important to understand the relationships between these events this paper summarizes the characteristics of land subsidence and earth fissures in xi an and discusses the chain of relationships that connects them

a nonlinear modeling and forecasting system of earth fractures based on coupling of artificial neural network and geographical information system exemplified by earth fractures in yuci city shanxi china earth fracturing or fissuring is a natural phenomenon and a major geohazard in many countries the factors that cause the earth to fracture were analyzed in yuci city in shanxi province of china using the geographical information system gis a nonlinear simulation and assessment model of earth fracturing was established using the artificial neural network ann technology to simulate the structure and function of the neural network nn of the human brain with engineering technology the developed nonlinear modeling and forecasting system was used to assess and forecast the earth fracture hazard in yuci city the results of this study provided useful and essential information for scientific policy making in the areas of city planning environmental protection and land development

characteristics and mechanisms for origin of earth fissures in fenwei basin china abstract the most serious earth fissure disasters in china occur in the fenwei basin since the late 1950s earth fissure disasters have widely occurred in the weihe yuncheng linfen taiyuan and datong sub basins in the fenwei basin and such disaster has increased progressively in recent years the current paper summarizes the characteristics of earth fissures in the fenwei basin earth fissures usually occur in an extensional faulted basin along an active fault zone and within an area of land subsidence earth fissures often have a similar trend with many branches that intermittently appear along their strike the main and secondary earth fissures at a shallow depth form rupture belts of different widths but they merge into a single shear belt and stay connected with the underlying active fault the throw of two blocks increases with depth along a sedimentary fault earth fissures usually show the characteristic of three dimensional movement vertical dislocation is the primary aspect of earth fissure movement the horizontal tension is smaller and the horizontal twist is the smallest which is consistent with the movement pattern of underlying active faults earth fissures have exhibited activity three or four times since the late pleistocene in the past half century earth fissures formed during four or five periods of peak activity were influenced strongly by groundwater fluctuation our research also indicates that cluster formation of earth fissures is polygenetic and results from a combination of tectonic and human activities earth fissures are driven by deep tectonic motions beneath the basin and are controlled by the local tectonic stress of the local fault zones one of the most important factors contributing to earth fissure formation is groundwater overexploitation this paper provides a scientific basis for proposed administrative means mitigation measures and engineering solutions in the field of engineering geology

land subsidence and ground fissures in xi an china 2005 2012 revealed by multi band insar time series analysis abstract xi an china has been undergoing significant land subsidence along with ground fissure development these geohazards have brought about severe damages to buildings bridges and other facilities in order to warn of and mitigate disasters it is urgently necessary to obtain the latest rate extent and temporal evolution of land subsidence in xi an with multiple sar datasets as well as leveling gps and ground water level of aquifers we study and map the spatial and temporal evolution of land subsidence and ground fissures over xi an first 62 synthetic aperture radar sar images acquired by envisat alos and terrsar x during 2005 2012 are used to form three independent interferometric stacks to unveil the spatial and temporal variations of land subsidence and ground fissures by using the time series interferometric synthetic aperture radar insar technique gps and leveling measurements are applied to calibrate the insar results precision of our insar annual subsidence results is less than 9 mm we derive the east west and vertical components of the observed land deformation in 2009 using descending and ascending insar observations finding out that the horizontal component of land deformation cannot be ignored if the deformation is large or ground fissures are active second four main land subsidence zones are detected in xi an with an average subsidence rate of 50 mm a during 2005 2012 time series insar results indicate that land subsidence rates in xi an increased by 200 from 2005 2007 to 2008 2010 extending existing ground fissures third insar derived land subsidence correlates with the change in ground water level and seasonal variations in subsidence correlate with changes in ground water pumping last the consistency on the spatial temporal distribution variation between ground fissures and land subsidence could be drawn from the time series results and profile analysis shapes of subsiding zones follow the general trends of mapped ground fissures and main faults in an ene direction changes in the subsidence gradient are also observed over most of the ground fissures and faults subsidence triggered fissures can cause localized surface displacements aggravate localized subsidence discontinue the integrity of ground water flow and limit the horizontal spread of subsidence funnels with continuing mass construction projects in xi an monitoring ground deformation with satellite insar therefore can provide efficient means to image land subsidence movements of fissures and faults and the associated geohazards

distribution and generative mechanisms of ground fissures in china abstract in this study 5002 ground fissures in more than 1500 localities across 22 provinces in china are investigated and mapped to reveal their spatial distribution the distribution of these ground fissures in china exhibits six regular patterns assemblages in north china syngenesis in extensional basins clustering along fault zones distributing along geomorphic boundaries developed on the edge of subsidence areas and clustering in large and medium sized cities combined with regional gps numerical simulations physical model test and in sar monitoring the generative processes of ground fissures are analyzed and discussed in relationship to four mechanisms 1 deep dynamic tectonism controls on the location of ground fissures 2 intracontinental dynamic tectonism resulting in ground fissure assemblages 3 fault stress inducing formation of ground fissures and 4 groundwater overmining resulting in the reactivation and expansion of ground fissures the geological environment is thus responsible for the establishment and appearance of ground fissure more importantly ground fissure propagation in china is the result of the synergistic effects of internal geological dynamic including in deep tectonism intracontinental tectoniim and fault movement coupled with anthropomorphic stress this genetic model can be summarized as one that is tectonically controlled stress driven and affected by regional hydrodynamic

modern ground failure in the garlock fault zone fremont valley california modern ground failures ranging from renewed displacement on 2 5 km long fault scarps to 1 km long tension cracks occur in fremont valley california most of the failures formed along pre existing holocene fault scarps that are part of the tectonically active garlock fault system the failures began to form in the 1960s and currently affect an area of 17 km 2 that is coincident with ground water level decline induced by pumping for crop irrigation several observations indicate that these failures were caused by water level decline rather than natural tectonism first modern ground failure began after water level started to decline and was restricted to the area affected by decline land subsidence was associated with this decline and appears to be caused by aquifer compaction second geodetic monitoring from 1977 to 1982 of faults near the center of the cone of depression demonstrated that fault creep occurred during periods of seasonal water level decline and stopped during periods of seasonal water level recovery by contrast faults near the margin of the cone of depression where water levels declined at a constant rate moved at a steady rate third surface strain fields near failures suggest that subsurface fault associated deformation was restricted to aquifer level depths and fourth seasonal rebound of the land surface across one fault was caused by elastic expansion of the aquifer system that was induced by large seasonal water level recovery

development characteristics and mechanisms of the taigu qixian earth fissure group in the taiyuan basin china since the 1980s increasing human activity and continuing over exploitation of groundwater resources have caused the earth fissures in the rift basin in shanxi china to enter an active phase buildings along these earth fissures have been seriously damaged four massive earth fissures that developed in the taigu and qixian areas of the eastern taiyuan basin endanger the operational safety of the high speed railway that passes through this region using field observations measurements and exploration we determined that the four earth fissures are parallel to each other have a northeast trend and are separated by approximately equal distances the rupture zones of these earth fissures are generally 10 50 m wide and are formed by the main fissures and secondary fissures the width of the zone affected by the earth fissures is 20 50 m based on deformation and the damage done to buildings these fissures formed on the earth s surface their hanging walls are lower than their foot walls forming normal faults and the ground surface around the fissures exhibits ridges and depressions the fissures are connected to deep hidden faults the fault displacement increases with increasing depth which is characteristic of syn sedimentary faults these earth fissures are characterized by vertical displacement and their average annual activity rate is 1 3 cm we believe that the formation of this large scale fissure group may be related to the tectonic structure of the hidden faults in the basin and may also be affected by the continuous regional extensional stress of the basin the current increased level of activity could be caused by the over exploitation of groundwater in the area

characteristics and mechanism of sanyuan ground fissures in the weihe basin china abstract shuanghuaishu ground fissures in sanyuan county ones of over 200 ground fissures developed in the weihe basin are well known for their sudden occurrence which often cause severe damage to the infrastructures after heavy rainfall in order to reveal the origin of their formation the geological background developmental characteristics and genetic mode of the shuanghuaishu ground fissures were investigated in details by surveying mapping trenching geological drilling geophysical prospecting and field water immersion the fissures are almost parallel with a ne50 ne65 strike and the obvious linear length is 800 m these characteristics are well consistent with the secondary faults of the liquan pucheng heyang fault the fissures cause damage to buildings and farmlands in the form of a horizontal tensile crack and subsidence the deeper the stratum is the bigger fault displacement of the stratum it will be so these fissures possess the characteristics of synsedimentary faults regarding their genesis the fissures were generated under the coupling action of multiple factors the regional extension caused secondary faults of the liquan pucheng heyang fault to slip resulting in a fracture system in the surface strata during the period of heavy rainfall large volumes of water seeped into these hidden fissures causing a strong erosion and washout effect on the soil filled in the fissures this process promoted the formation of the current ground fissures

ground cracks in ethiopian rift valley facts and uncertainties abstract no accurate relationship has been obtained in this study between ground cracks in ethiopian rift valley and the most common causes of earth fissures such as aquifer system compaction and increased horizontal seepage stresses this is due to the fact that the level of groundwater withdrawal responsible for these processes is still negligible in ethiopia if aquifer system compaction and increased horizontal seepage stresses have a certain role then it should be through the long term effect of groundwater flow from basins to neighboring lakes the ground cracks appeared also not to have a direct link with active faulting or distant earthquakes structurally the ethiopian rift valley is dominated by ne sw trending tensional faults but no evidence is obtained in this study to associate the process of surface cracking with major tectonics however an aseismic elastic strain which originates at depth and propagates upward through sediments without the formation of bedrock faults could result in conditions conducive to the development of cracks then fissures might ultimately be created after heavy rainfalls by near surface processes such as piping and hydrocompaction along water line sources

analysis and comparison of two types of ground fissures in dali county in the weihe basin china dali county is located in the eastern weihe basin where frequent ground fissure disasters occur dali ground fissures are macroscopically part of the ground fissure group in the weihe basin and have caused serious damage to infrastructure and agricultural production in this area in this paper 25 ground fissures in dali county are identified through investigation and two typical ground fissures in fengcun and weizhuang are selected for research through field investigation trench excavation geophysical exploration soil water content tests and collapsibility coefficient tests the basic features shallow structural characteristics deep structural characteristics and genetic mechanisms of the two ground fissures are revealed the strike of the fengcun ground fissure is 45 almost parallel to the shuangquan linyi fault the length is 2 km and the profile is ladder like and extends deep with synsedimentary characteristics the weizhuang ground fissures are circular in plan view with a length of 315 m and trumpet shaped in profile they disappear in the paleosol layer the mechanism of the fengcun ground fissure is related to basin extension and fault activity the ground fissures are the surface reflections of deep faults the mechanism of the weizhuang ground fissures is related to loess collapsibility and seepage the malan loess has differential settlement in collapsible and noncollapsible areas and ground fissures are the boundary line for differential settlement of loess finally based on the genetic mechanisms of ground fissures dali ground fissures can be divided into two types tectonic and nontectonic

diffuse emission of co2 from the fossa crater vulcano island italy numerous measurements of co2 degassing from the soil carried out with the accumulation chamber method indicate that in the period april july 1995 the upper part of the fossa cone released a total output of 200 t d 1 of co2 which corresponds to approximately 1000 t d 1 of steam these large amounts of fluids are of the same order of magnitude as those released by the high temperature fumarolic field located inside the crater the spatial distribution of soil gas fluxes shows that the main structures releasing co2 are the inner slopes of the crater and a nw se line located ne of the crater rim which correspond to the main direction of vulcano island active faults the comparison of the co2 maps with the soil temperature distribution derived from both direct measurements and airborne infrared images indicates the occurrence of extensive condensation of fumarolic steam within the upper part of the fossa cone whose total amount is comparable to the rainfall budget part of the condensate which originates from this process contributes to the recharge of the phreatic aquifer of porto plain modifying the chemical and isotopic composition of the groundwater

characteristics and mechanism of the longyao ground fissure on north china plain china abstract among more than 1000 ground fissures developed over the past 30 years having induced severe geohazards in the north china plain the longyao ground fissure in hebei province is famous for its longest length and causing the worst damage and widest influence in this region in order to reveal the origin of its formation the geological background developmental characteristics and genetic mode of the longyao ground fissure were investigated in detail by geological surveys measurements trenching drilling and seismic exploration this fissure has a total length of 39 km and is characterized by normal fault extension left lateral slip and dominant along polyline distribution these characteristics are well consistent with its underlying fault the nei jv fault the fissure causes the damage to buildings structures along a polyline and in the form of a horizontal tensile crack subsidence and shear failure according to the trenching drilling and shallow seismic profiling this fissure possesses the characteristics of synsedimentary faults reflecting the historical stages of fissure activities regarding its genesis this fissure was generated under the coupling action of multiple factors which took shape after the earthquake and was enlarged under the action of groundwater pumping the regional extension first caused a fracture system in the surface strata and then the action of seismic activities started to control the fracture and finally the pumping action of excessive groundwater and other influential factors promoted the formation of the current ground fissure

geochemical and geo electrical study of mud pools at the mutnovsky volcano south kamchatka russia behavior of elements structures of feeding channels and a model of origin this study presents data on the geochemical composition of boiling mud pools at the mutnovsky volcano the physicochemical characteristics of the pools and the concentrations of major minor and trace elements in pool solutions vary widely a comparison of the geochemical compositions of host rocks and solutions indicates that leaching from rocks is not the only source of chemicals in thermal solutions geophysical studies reveal the inner structure of thermal fields which reflect the shapes of the underground reservoirs and feed channels using geophysical methods electrical resistivity tomography and frequency domain investigations it was shown that the vertical structure and complex geochemical zonation of the feed channels leads to a high contrast in the compositions of the mud solutions these findings answer questions about the origin and composition of surface manifestations to elucidate the mechanisms of solution formation an attempt was made to describe the magmatic fluid evolution and the resulting mixing of waters by physical and mathematical models the model illustrates fluid migration from a magma chamber to the surface it is shown that the formation of brines corresponding to the mud pool composition is possible during secondary boiling

a study of the symbiotic relationship between tectonic fissures and faults in the fenwei graben system china the fenwei graben system is an important extensional fault depression zone which is the tectonic boundary between the ordos block and the south china block and the north china block the graben system presents an s shape with a total length of 1200 km and a width of 30 60 km and an overall strike of nne due to complex tectonic background and active faults nearly 612 ground fissures develop in these basins and more than 90 of these ground fissures are tectonic fissures which are closely associated with fault activities to reveal the plane symbiotic phenomena profile symbiotic modes and symbiotic mechanism between tectonic fissures and faults in the fenwei graben system the developmental characteristics were investigated in detail by surveying mapping trenching and drilling in the study area the main conclusions are as follows 1 the tectonic fissures of the fenwei graben system are mainly distributed along the margin faults of basins the boundary faults between blocks and the hidden faults within blocks causing serious damages to farmlands houses and roads the symbiosis between these fissures and faults is obvious on the surface 2 the profile symbiotic morphology includes vertical extension type syncline and anticline y type and stepped type 3 the symbiotic mechanisms include vertical growth lateral rupture and clustery derivation 4 the activities of underlying faults give impetus to the formation and expansion of tectonic fissures the exposure of the fissures makes underlying faults continue to develop in the form of surface fractures

isotope composition of rain water well water and fumarole steam on the island of vulcano and their implications for volcanic surveillance abstract water samples from eight wells in the vulcano porto area and fumarole steam from the crater of vulcano southern italy were collected at monthly intervals over a two year period from february 1987 to january 1989 samples of bulk precipitation were also collected in three points at vulcano porto and vulcano piano island of vulcano and castroreale tyrrhenian coast of sicily again at monthly intervals the weighted mean isotopic composition of rain water on vulcano is d 32 and d 18 o 6 4 results for well waters tend to support the existence of at least two water bodies one of purely meteoric water and the other of brackish thermal water an intermediate water body probably the result of mixing of the other two was also recognized the isotope composition of fumarolic steam from the crater suggests the mixed contribution of both sea and rain waters although mixing is not the only process occurring the existence of a deep marine brine body is inferred characterized by d and 18o values more positive than those of mediterranean sea water a close relationship indicating common source effects is shown by temporal isotopic variations at some wells and the fumarolic steam wich may be used for volcano survey at distance from the active crater

a novel approach to model earth fissure caused by extensive aquifer exploitation and its application to the wuxi case china initially observed in the semi arid basins of southwestern usa earth fissures due to aquifer over exploitation are presently threatening a large number of subsiding basins in various countries worldwide different mechanics have been proposed to explain this process such as differential compaction horizontal movements and fault reactivation numerical modeling and prediction of this major geo hazard caused by overuse of groundwater resources are challenging because of two main requirements shifting from the classical continuous to discontinuous geomechanics and incorporating 2 dimensional features the earth fissures into large 3 dimensional 3d modeling domain the subsiding basin in this work we proposed a novel modeling approach to simulate earth fissure generation and propagation in 3d complex geological settings a nested two scale approach associated with an original non linear elasto plastic finite element interface element simulator allows modeling the mechanics of earth discontinuities in terms of both sliding and opening the model is applied on a case study in wuxi china where groundwater pumping between 1985 and 2004 has caused land subsidence larger than 2 m the model outcomes highlight that the presence of a shallow 80 m deep bedrock ridge crossing the yangtze river delta is the key factor triggering the earth fissure development in this area bending of the alluvial deposits around the ridge tip and shear stress due to the uneven piezometric change and asymmetrical shape of the bedrock have caused the earth fissure to onset at the land surface and propagate downward to a maximum depth of about 20 30 m maximum sliding and opening are computed in the range of 10 to 40 cm in agreement with the order of magnitude estimated in the field

geochemistry of metallic trace elements in fumarolic condensates from nicaraguan and costa rican volcanoes metallic trace element composition of volcanic gas from cerro negro momotombo san cristobal telica and masaya volcanoes in nicaragua and poas volcano in costa rica is indicated by analyses of fumarolic condensates for alkalis alkaline earths transition elements precious metals halogens and sulphate the temperatures of the fumaroles varied from 85 to 852 c element concentrations range from 104 to 10 3 ppm statistical tests indicate that the trace element constituents of the condensates are log normally distributed although there are variations in element concentrations in individual condensates the general order of decreasing elemental abundances in nicaraguan and costa rican fumarolic gas is cl so4 certain igneous rock forming elements si al fe ti f and alkalis li na k alkaline earths mg ca ba br and transition elements cr mn co ni cu zn other ore forming elements mo cd sn pb semi metals as sb sc hg and precious metals au ag li mn cr and pb were found to be near or below detection limits in many of the condensates analyzed so4 ti al k na zn sn cr and br all tend to decrease in abundance as mean fumarolic temperature between volcanoes decreases the remaining elements remain constant in abundance or behave erratically the metallic trace element composition of the nicaraguan and costa rican fumarolic condensates is very similar to condensates from subduction zone volcanoes around the pacific margin and the mediterranean metals in volcanic gas are postulated to have been transported as halogen sulphate and oxide compounds chloride and fluoride compounds are considered to be the primary transporters of metals in volcanic gas correlations between metal and halogen content vary considerably between volcanoes statistically significant correlations between metal content and both chlorine and bromine are found in the cerro negro and between metal content and bromine and fluorine in the momotombo condensates metal bearing compounds in volcanic gas are postulated from correlation matrices bromine though seldom reported in condensates is a minor but important constituent of volcanic gas with concentrations similar to those of fluorine metal bromide compounds have higher volatilities than fluoride compounds and volatilities similar to chloride compounds significant correlations between bromine content and metal concentration suggests that bromide compounds play a role in the transportation of metals in volcanic gas

lead isotope composition of the sublimates from the fumaroles of vulcano aeolian islands italy inferences on the deep fluid circulation the fumarolic fluids of vulcano aeolian islands italy consist of a mixture of both deep and shallow components the final products the fumarolic gases and the sublimates associated with them provide information on the complex interactions that occur at depth as radiogenic isotopes do not undergo fractionation after they are incorporated in a fumarolic gas they can be used directly to characterize the components that mixed lead isotopes are particularly suitable because seawater which plays an important part in the formation of the fumarolic fluids of vulcano contains only negligible amounts of it 10 12 g g therefore the lead present in the fumarolic gases and sublimates is derived from the magmatic component and a water rock interaction process the lead isotope compositions of the lead sulfosalt sublimates collected from the fossa crater of vulcano in 1924 and between 1989 and 1993 are given the lead isotope ratios of most of the samples are the same within the range of analytical error regardless of their collection date the only samples that display slight variations are those collected in 1993 on the whole the compositional trend of the lead isotopes of the sublimates coincides with that of the latitic rhyolitic activity of fossa and differs substantially from that of the pre fossa trachy basaltic activity the lead composition of the sublimates is very different from that of the calabrian basement rocks the data presented here show that the magma presently degassing at vulcano has the same lead isotopic composition as the products of the recent activity of fossa whereas the fumarolic fluid circulation of vulcano has not involved basement rocks similar to the calabrian metasediments

mechanism of fuping ground fissure in the weihe basin of northwest china fault and rainfall the special geological conditions of the weihe basin located in the southern fenwei graben system are the cause of many of the ground fissures developing in this area the tingzi ground fissure in fuping county is one of the typical and particular ground fissures found in the weihe basin the ground fissure is famous for its sudden appearance after heavy rainfall to explore the characteristics and mechanism of the fissure some geological methods were carried out in the study area for this study such as surveying mapping trenching drilling and seismic exploration the main conclusions are as follows 1 the fissure is located on the hanging side of the secondary fault of the liquan pucheng heyang fault with a ne40 ne75 strike and a length of 2 7 km 2 the fissure is steeply inclined and presents a funnel shape in the shallow strata there are many secondary cracks near the main fissure 3 the fissure is connected with underlying fault and possesses the characteristics of synsedimentary faults reflecting the historical stages of fissure activities 4 the fissure destroys farmlands and houses along the fissure and mainly causes tensile damage 5 the fissure was controlled by regional extension and fault and it was promoted and enlarged by rainfall and other influential factors

variability of alkali and heavy metal fluxes released by mt etna volcano sicily between 1991 and 1995 abstract we regularly collected volcanic gases and aerosols at mt etna volcano over a long period 1991 1995 and measured their chemical composition by icp ms based on these data we present new evidence on the high volatility of both alkali and some heavy metals in contrast both lanthanides and actinides are not produced as significant gaseous compounds at magmatic temperatures and can be used as tracers of spattered materials all metals of each chemical family maintained systematic trends during the study period at both summit craters and effusive vents located in the valle del bove during the 1991 1993 eruption during the eruption we observed high metal enrichments at effusive vents these enrichments seem to be characteristic of the secondary degassing of a magma previously degassed under the summit area lower metal enrichments are recorded in aerosols sampled in summit crater plumes according to the primary degassing type occurring at these vents while a primary degassing type still occurs at both bocca nuova and voragine during the post eruptive period sud est crater exhibits a transition from primary to secondary type according to the variations of the volcanic activity level we confirm that the alkali metals fractionate systematically within their family as they cross the melt vapour interface the heavier members being always more enriched than the lighter ones in aerosols we also show that this fractionation is not related to the volcanic activity and the degassing type but seems to be a significant feature of the alkali family itself estimation of new emanation coefficients for rubidium caesium tin and thallium 0 07 0 15 0 50 and 21 respectively yields annual outputs around 1000 t yr 60 t yr 240 t yr and 1600 t yr respectively mount etna is a very important source of metals injected into the atmosphere contributing to the global volcanic budget about 16 for heavy metals and 19 for alkali metals in eruptive periods and only 2 and 4 respectively in quiet periods

trace element geochemistry of volcanic gases and particles from 1983 1984 eruptive episodes of kilauea volcano compositional data have been obtained for volcanic gases and particles collected from fume emitted at the pu u o o vent on the east rift zone of kilauea volcano the samples were collected by pumping fume through a filter pack system consisting of a front stage particulate filter followed by four base treated filters 7lioh particles and condensed phases are trapped on the particulate filter and acidic gases are collected on the treated filters the filters are analyzed for 30 elements by instrumental neutron activation analysis fume samples were collected from the pu u o o vent for two eruptive episodes 1 7 days after episode 11 cooling vent samples and 2 the waning stage of episode 13 active vent samples additional samples were collected by aircraft from the gas plume released during the lava fountaining phase of episode 17 aircraft samples element concentrations in the vent gases were 104 g m 3 for s cl and f enrichment factors efs for the volcanic fume versus the source magma were calculated using the volatile element br as the reference element for normalization and the u s geological survey standard bhvo 1 as the magma standard this removes the ash dilution effect obtained by using an ash constituent al sc or mg as the reference element bromine normalized efs 105 range from 101 to 102 for na k and cu 102 to 105 for zn w sb in ir ag f and as and 105 for au cd re cl se and s the highest enrichment factors are for aircraft samples collected during the most gas rich phase of an eruption cycle metal and volatile element data form two groups 1 elements showing little or no variation in abundance ratios with sample type group 1 cl br and re and 2 elements that show significant variation in abundance ratios by sample type group 2 zn w sb in ir au and cd bivariate plots of elements of the first group versus elements of the second group separate by sample type the separation corresponds to samples collected during eruptive activity versus samples collected during repose periods monitoring trace metal ratios in volcanic fume could provide an additional tool for predicting volcanic eruptions the f cl ratio of cooling vent samples is higher than those of active vent or aircraft samples and the ratio is inversely correlated with efs for most volatile metals

airborne aerosol measurements in the quiescent plume of mount st helens september 1980 atmospheric particulate matter and condensed volatile species were collected in the quiescent plume of mount st helens volcano in sept 1980 using air filter systems mounted aboard a nasa turbo prop p 3 aircraft concentrations of 27 elements were determined by instrumental neutron activation analysis and ion chromotagraphy the volatile elements cl br f zn w in s cd se sb hg as and au were enriched relative to bulk ash emitted during the earlier eruptions by factors of 50 to 20 000 particulate s concentrations were approx 3 mu g m sup 3 and accounted for 6 of the total plume sulfur gas phase hg concentrations were 2 5 to 16 ng m sup 3 fluxes of elements were estimated by normalizing elemental concentrations to the concurrently measured total sulfur flux emission rates vary from 3500 kg day for particulate cl to 3 kg day for au with substantial quantities of the enriched elements zn as hg sb se and cd also being released estimated global fluxes of these elements from volcanoes to the atmosphere are in reasonable agreement with other literature estimates

origin of ground fissures in the shanxi graben system northern china abstract since the 1950s hundreds of ground fissures have occurred in the shanxi graben system in northern china the fissures and related subsidence and differential settlement have caused and are causing substantial damage to homes agricultural land roads canals and other infrastructure although generally similar in appearance the fissures have different origins 1 some fissures coincide with northeast trending faults trenching shows that the fissures extend into the near surface faults increasing vertical offset clay beds and other stratigraphic markers at depth and therefore are probably the surface expression of fault movements 2 some fissures are demonstrably related to accelerated groundwater withdrawal this is particularly apparent in xi an city where groundwater levels have declined by about 15 m within 4 years 3 other fissures owe their origin to the well known process of soil collapse this is particularly common in the silty loessial sediments that occur within most of the valleys that comprise the shanxi graben system