a newly recognized type of slickenside striation abstract this note summarizes current views on the origin of slickenside striations and points to the existence of a type of striation not readily explained by established genetic ideas such striations have been seen on fault surfaces in naturally deformed shale and in experimentally deformed paraffin wax they are defined by arrays of shallow slip parallel ridges and grooves of millimetric width and below on any given slip surface the ridges are as common as the grooves and display similar dimensions and profile shapes across any pair of slip surfaces in contact at the end of faulting ridges protruding from one surface fit into or nest with grooves on the other surface the origin of these features is not yet understood

investigations of changjing earth fissures jiangyin jiangsu china fissuring of the earth began at changjing jiangyin city jiangsu province in 1995 the earth fissure zone consists of a main fissure with a number of secondary fissures on both sides which range from 20 to 60 m wide the main fissure is about 500 m long trends 15 to 30 and has a scarp 100 200 mm high extensive field investigations including shallow seismic surveys and geological drilling have been conducted over 20 years deposits of a quaternary paleoriver at 150 160 m depth curve around a bedrock spur which is situated beneath and lies parallel to the fissure at about 90 m a regional trough has formed due to land subsidence over the paleoriver channel with changjing at its eastern edge the fissures resulted from differential subsidence of the quaternary deposits as a result of extended over exploitation of groundwater groundwater extraction facilitates compaction of the quaternary aquifers and aquitards from the increase of the effective in situ stresses which leads to subsidence positive relief of the subsurface bedrock defines the location and formation of the earth fissures on one hand differential subsidence causes the quaternary sediments to rotate over the ridge leading to tensional cracking on the other hand temporal differential in subsiding aggravates the vertical shearing or faulting of the fissure forming a scarp

regional variation in exhumation and strain rate of the high pressure sambagawa metamorphic rocks in central shikoku south west japan regional variation in the p t path of the sambagawa metamorphic rocks central shikoku japan has been inferred from compositional zoning of metamorphic amphibole rocks constituting the northern part saruta river area exhibit a hairpin type p t path where winchite actinolite grew at the prograde stage the peak metamorphism was recorded by the growth of barroisite to hornblende and sodic amphibole to winchite actinolite grew at the retrograde stage in the southern part asemi river area rocks exhibit a clockwise type p t path where barroisite to hornblende core is rimmed by winchite to actinolite the difference in p t path could suggest a faster exhumation rate i e more rapid decompression in the southern than in the northern part on the other hand physical conditions of deformation during the exhumation stage have been independently inferred from microstructures in deformed quartz recrystallized quartz grains in rocks from the low grade chlorite and garnet zones are much more stretched in the southern part aspect ratio 4 0 than in the northern part aspect ratio 4 0 indicating a higher strain rate in the former than in the latter these facts may indicate that the exhumation and strain rates are correlated i e the exhumation rate increases with increasing the strain rate the difference in the exhumation rate inferred from amphibole zoning between the northern and southern parts could be explained by an extensional model involving normal faulting where the lower plate can be exhumed faster than the upper plate due to the displacement along the fault furthermore the model may explain the positive correlation between the exhumation and strain rates because the lower plate tended to support more stress than the upper plate

k ar age and chemistry of phengite from the sanbagawa schists in the kanto mountains central japan and their implication for exhumation tectonics abstract epma analyses and k ar age determinations were carried out on phengite in pelitic schist from the sanbagawa metamorphic belt of the kanto mountains central japan phengite from the sanbagawa pelitic schist in the kanto mountains generally occurs as aggregates of fine grained crystals it is extremely fine grained in domains adjacent to relatively rigid garnet and albite porphyroblasts this suggests that deformation induced grain size reduction took place in phengite during the ductile deformation accompanying the exhumation of the host schists epma analysis shows that phengite is chemically heterogeneous at the thin section scale suggesting that it formed during retrograde metamorphism in restricted equilibrium domains the retrograde chemical reaction was promoted by the ductile deformation k ar ages of phengite get younger from the southern unit 82 ma to the northern unit 58 ma in the kanto mountains the age range is similar to that in central shikoku the older schists occur in the higher metamorphic grade zone in central shikoku and in the lower grade zone in the kanto mountains the thermal structures in central shikoku are inverted so that the highest grade zone occurs in the upper or middle parts of the apparent stratigraphic succession in contrast the kanto mountains have a normal thermal structure the higher grade zone is in the lower part of the apparent stratigraphic succession the different tectonic features in exhumation produced the two contrasting age temperature structure relations at the western side of sanbagawa belt in central shikoku and the eastern end of the sanbagawa belt in the kanto mountains that are 800 km distant from each other namely the western sanbagawa belt in central shikoku underwent longer ductile deformation during the exhumation than the eastern sanbagawa belt in the kanto mountains

subsidence and liquefaction analysis in mexicali mexico during the cucapa earthquake april 4 2010 using envisat asar and spot images an earthquake 7 2 moment magnitude occurred on april 4 2010 its epicenter was located in southern cucapa range northern baja california peninsula mexico in the confluence of a set of active tectonic faults two additional hazards after the earthquake affected population subsidence and liquefaction farmer communities and agriculture lands located in southern mexicali city were flooded due to the liquefaction phenomenon great volumes of fine sediments and water sprouted in different points flooding agricultural lands and some small communities the fault displacement during the earthquake damaged roads and buildings land subsidence was observed in some areas more than 35 000 inhabitants and 60 000 ha of agricultural lands were affected to analyze the consequences of such an earthquake two multi spectral and two panchromatic spot images before and after the earthquake were acquired by means of the national commission of water the mexican government water agency in addition to these optical images three interferometric pairs from envisat asar radar sensor were acquired on the grounds of the project c1p6926 with the european space agency esa a red green blue rgb false color composite of the multi spectral images before and after the earthquake shows the inundated areas caused by the liquefaction phenomenon the two panchromatic images form a stereoscopic pair these images were integrated into multi spectral images to derive the texture relief caused by the liquefaction phenomenon an interferometric analysis was applied to the three interferometric pairs the coherence images and the digital elevation model dem were calculated as well the interferometry the amplitude and the dem were overlaid this overlay shows subsidence occurrence in the area of study due to the earthquake from results and field data it was possible to identify subsidence affected areas as well as flooded areas due to the liquefaction phenomenon

earthquake induced ground failures in italy abstract the national catalog of ground failures induced by strong earthquakes in italy cedit is described the catalog holds data on ground failures triggered by the earthquakes that occurred in italy in the last millennium and which had a nominal epicentral intensity equal to or greater than viii in the mercalli cancani sieberg mcs intensity scale the ground effects reported in the catalog are the following landslides fractures liquefaction surface faulting and topographic changes of the ground level subsidence settlements tilting and so on each effect is described in terms of seismological parameters of the triggering earthquake site coordinates and administrative code lithology and kinematic type of the ground failure the catalog represents a tool to assess the susceptibility of geologic materials to ground shaking and to validate predictive models of seismically induced ground displacements scenarios of earthquake induced geologic risks in the context of this study a simple statistical analysis of the database yielded useful relations between the parameters of the triggering earthquakes and the related effects

the late holocene history of prairie brush prairie and jack pine pinus banksiana forest on outwash plains north central minnesota usa pollen diagrams from six sites on outwash plains of north central minnesota are interpreted as records of similar extralocal vegetation changes since c 5000 bp all of the study sites have undergone a shift from prairie to an aspen oak community followed by the jack pine dominated vegetation that now occupies the sites all of the species capable of directly invading prairie aspen bur oak willow and some entomophilous shrubs were probably established on the surrounding moraines prior to their invasion of the adjacent prairie occupied outwash plains only short distances 20 km were involved in these local invasions and the chronology of their establishment does not indicate a regional westward migration of these taxa in the late holocene because climate varies little over the short distances separating the study sites the asynchroneity of the dates for the establishment of aspen brush zone 3 zone 4 boundary and the following establishment of jack pine zone 2 zone 3 boundary indicates that locally varying conditions determined where and when these vegetational shifts occurred sloughs and wet swales are apparently prerequisite for aspen to invade prairie and they probably appeared on the outwash plains at different times because locally varying hydrologic conditions determined the absolute increase in precipitation required for the water table to rise and flood depressions the rate at which afforestation proceeded culminating with the establishment of jack pine appears to be related to local variability in the distribution of wet depressions as they serve as firebreaks where peat filled channels and chains of lakes occur afforestation occurred first and was relatively rapid where lakes and peatlands are scattered afforestation occurred later and required more time where wet depressions are rare some patches of prairie have persisted since the mid holocene

a review of the western part of the altaids a key to understanding the architecture of accretionary orogens abstract the altaids is one of the largest accretionary collages in the world and the tectonic styles of the accretionary processes have been interpreted in several ways including as an amalgamation of multiple terranes as a result of oroclinal bending of a long single arc or as a caledonian continental collision based on recent tectonostratigraphic analyses together with paleomagnetic data the tectonic styles of the neoproterozoic to paleozoic accretionary processes of the altaids are discussed the western altaids is the main focus of the study which was mainly composed of several independent linear components such as arcs and microcontinents with proterozoic basement and cover rocks various kinds of arcs existed in the paleo asian ocean including a complicated type of arc alaskan type which is a combination of the japan and mariana type intra oceanic arcs and the cordillera type continental arcs these linear components rotated and collided with each other with multiple subduction polarities which could have been an important result of multiple linear element amalgamation and which has contributed greatly to the architecture of the eurasian continent the basic tectonic styles of the altaids can be summarized as arc arc collision oroclinal bending and large scale rotation and multiple subductions with a complicated archipelago paleogeography these basic features of accretionary orogens in general can be attributed to the amalgamation of complicated multiple linear elements some mesozoic to cenozoic accretionary orogens in the world are also characterized by processes of multiple linear element amalgamation more attention should be paid to the multiple linear element amalgamation of ancient accretionary orogens which will shed light on lateral and vertical continental growth

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

asymmetric vegetation responses to mid holocene aridity at the prairie forest ecotone in south central minnesota abstract the mid holocene ca 8000 4000 cal yr bp was a time of marked aridity throughout much of minnesota and the changes due to mid holocene aridity are seen as an analog for future responses to global warming in this study we compare the transition into ca 9000 7000 yr ago and out of ca 5000 2500 yr ago the mid holocene mh period at kimble pond and sharkey lake located along the prairie forest ecotone in south central minnesota using high resolution 5 36 yr sampling of pollen charcoal sediment magnetic and loss on ignition properties changes in vegetation were asymmetrical with increasing aridity being marked by a pronounced shift from woodland forest dominated landscape to a more open mix of grassland and woodland savanna in contrast at the end of the mh grassland remained an important component of the landscape despite increasing effective moisture and high charcoal influxes median 2 7 4 0 vs 0 6 1 7 mm 2 cm 2 yr 1 at start of mh suggest the role of fire in limiting woodland expansion asymmetric vegetation responses variation among and within proxies and the near absence of fire today suggest caution in using changes associated with mid holocene aridity at the prairie forest boundary as an analog for future responses to global warming

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

fracture controlled fluid circulation and dissolutional weathering in sinkhole prone carbonate rocks from central italy abstract fractures karstic cavities and calcite precipitates are analysed on mesozoic carbonate strata from the cornicolani mountains central italy to quantify the relationships between fractures and related karstic cavities and to infer the fracture controlled fluid pathways the study area is characterized by active sinkholes and other karstic caves which are among the deepest ones in the world results show a clear control of fractures on the process of dissolutional weathering and therefore on the fluid circulation a model is proposed in which two different modes of dissolutional weathering coexist i a mode of diffuse weathering consisting in the dissolutional enlargement of closely spaced joints and bedding surfaces this process affects the strata situated at depths of up to 5 m ii a mode of more concentrated weathering active along highly permeable fault damage zones at depths of at least 70 m these processes are mostly connected with the shallow circulation of calcite dissolving meteoric waters and are controlled by the disparity of permeability between the fault damage zones and the surrounding jointed strata some calcite precipitates along the studied fault damage zones may be connected with a dissolutional process operated by waters that interacted with the adjacent quiescent volcanic district such calcite dissolving waters and the presence of high permeable fault damage zones along which the waters may ascent are probably the cause for the development of some of the deep sinkholes along faults in the study area

deep karst conduits flooding and sinkholes lessons for the aggregates industry abstract limestone aggregate quarries in deeply penetrating karst terrain are often at considerable risk of artesian inflow from groundwater or surface water channeled through the karstic aquifer the inflow occurs through what are likely to be complex conduits that penetrate hundreds of feet into bedrock rates of inflow can exceed the operation s pumping capabilities proving to be uneconomic to manage over the long term over time inflow rates can increase dramatically as turbulent flow through the conduit erodes its soft residual clay rich fill one recent investigation observed an inflow rate of more than 40 000 gpm from a surface water source floodwater persistently laden with sediment is an indicator of conduit washout and implies increasing inflow rates over time conduits carrying floodwater can exist in a variety of forms along deeply penetrating geologic faults joints or following the path of preferentially eroded bedding preferential structural deformation along faults or bedding can enhance dissolution during subsequent interaction with groundwater the resulting conduit may be a complex combination of many geological features making the exploration and remediation of the pathway difficult sinkholes at the site can occur within several contexts pre existing subsidence structures can reactivate and subside further forming new collapse sinkholes within soil directly overlying the conduit cover collapse sinkhole development can be a direct result of increasing downward groundwater velocities and subsurface erosion associated with the enlargement of a conduit normal operation events such as a quarry blast can also provide a significant new linkage between the groundwater and the quarry allowing rapid drainage of the groundwater reservoir with such drainage and erosion of karst fill sinkholes will develop over localized water table depressions most significantly over enhanced permeability zones associated with fractures paradoxically although the rise in quarry water level will lead to regional reduction in the hydraulic gradients on local scales drainage of the groundwater reservoir increases gradients and leads to the development of cover collapse sinkholes recommended methods for preliminary site investigation can include a detailed review of geological literature and drilling logs to compile a conceptual model of the site a fracture trace analysis with em geophysics can confirm the locations of major faults and fractures fingerprinting of the various water sources to the quarry and the water in the quarry is an inexpensive and effective means of identifying the source and likely direction of the groundwater and surface water flow automated geophysical equipment on the market for performing rapid resistivity and microgravity surveys speeds up the site screening process during reconnaissance exploration for deep structure it is recommended that mine planning fully incorporate this information so that quarry operators can take proactive measures to avoid catastrophic and costly flooding events

earth fissures triggered by groundwater withdrawal and coupled by geological structures in jiangsu province china earth fissures in jiangsu province china have caused serious damages to properties farmlands and infrastructures and adversely affected the local or regional economic development under the geological and environmental background in jiangsu province this paper presents the earth fissures caused by excessive groundwater withdrawal and coupled by distinctive geological structures such as ancient yellow river fault in xuzhou karst area and ancient yangtze river course and bedrock hills in suzhou wuxi and changzhou area although all the earth fissures are triggered by groundwater exploitation the characteristics are strongly affected by the specific geological and hydrogeological settings in particular in the water thirsty xuzhou city the cone of depression caused by groundwater extraction enlarged nearly 20 times and the piezometric head of groundwater declined 17 m over a decade as groundwater is extracted from the shallowly buried karst strata in the ancient yellow river fault zone the development of earth fissures is highly associated with the development of karstic cavities and sinkholes and their distribution is controlled by the ancient yellow river fault with all the 17 sinkholes on the fault on the other hand in the rapidly developing southern jiangsu province groundwater is mainly pumped from the second confined aquifer in the quaternary which is distributed neither homogeneously nor isotropically the second confined aquifer comprises more than 50 m thick sand over the ancient yangtze river course but this layer may completely miss on the riverbank and bedrock hills with a typical drawdown rate of 4 6 m per annum the piezometric head of groundwater in the second confined aquifer has declined 76 m at maocunyuan since 1970s and 40 m at changjing since mid 1980s and a large land subsidence e g 1 100 mm at maocunyuan is triggered coupled with the dramatic change of the bedrock topography that was revealed through traditional geological drilling and modern seismic reflection methods the geological structure controlled differential settlement and earth fissures are phenomenal in this area

the high p t sambagawa extrusional wedge japan abstract a metamorphic inversion along the asemigawa section of the besshi unit in the sambagawa high p t metamorphic zone has been explained previously by s vergent major recumbent folding or thrusting through careful structural field investigations however we recognize the d2 asemigawa detachment fault at the boundary of the highest grade oligoclase biotite zone thermal culmination in the belt we have also discovered a series of normal faults in the hanging wall of the major detachment in the upper domain and a series of thrust faults bounding every metamorphic mineral zone of the footwall in the lower domain outcrop scale d2 asymmetric folds are closely associated with axial planar pressure solution cleavages and are genetically related to the above d2 normal faulting and thrusting as fault propagation folds northward fold vergence is found only in the upper domain and southward vergence is found only in the lower domain exceptions to this rule occur only for parasitic folds in the overturned limbs of mesoscopic folds which indicates flexural slip as a likely fold mechanism we propose an extrusion wedge model for the inverted metamorphism and accordingly this mechanism may also account for a large part of the exhumation of the sambagawa metamorphic rocks although westward shear at the time of d1 stretching lineation has partly contributed to the exhumation by counter flow in the accretionary wedge we infer that m1 with its retrograde actinolite schists represents a d1 ductile shear zone but it contributes as much as a component of the d2 asemigawa detachment other normal and thrust faults and asymmetric folds as reactivated brittle shear zones thus shear direction had changed orthogonally and drastically between ductile d1 stretching and ductile brittle transition to brittle d2 extrusion we infer that this transition reflects the collision of an actively spreading mid ocean ridge and is a consequence of increased coupling of plates and orogen normal stress followed by oblique subduction d0 and d 1 record eastward down flow during the oblique underthrusting of oceanic plate before peak metamorphism m1

implications of mylonitic microstructures for the geotectonic evolution of the median tectonic line central japan the median tectonic line mtl the most prominent onshore fault in japan demarcates the cretaceous hiji quartz dioritic gneiss of the ryoke belt on the west from the high p t type sambagawa metamorphic rocks on the east in the takato area toward the mtl the hiji gneiss grades into strongly mylonitized rocks characterized by grain size reduction of quartz in the mylonitic rocks the development of fluxion banding sm is remarkably influenced by the existence of k feldspar forming a myrmekitic intergrowth brittle microstructures indicative of truly cataclastic deformation are observed only in mylonitic rocks close to the mtl early deep level ductile deformation apparently gave way to shallower brittle deformation at a later stage the attitude of stretching lineations lm and asymmetric microstructures observed in the mylonites suggest that sinistral strike slip shearing with a subordinate component of vertical slip took place during mylonitization in mid cretaceous time the mylonitic rocks and their protolith supposed to have constituted the eastern limb of the shear zone were probably eroded out and lost by upheaval of the sambagawa belt relative to the ryoke belt

development of collapse sinkholes in areas of groundwater discharge abstract collapse sinkholes are found in groundwater recharge zones throughout the world they cause substantial loss of property each year and occasional fatalities in such settings the formation of these features occurs through the downward migration of regolith into karst voids the presence of a void in the bedrock and sufficient seepage pressure or gravitative force in the regolith is required for their creation we investigated the development of cover collapse sinkholes in an unusual setting areas of groundwater discharge rather than recharge upward hydraulic gradients and the likelihood of groundwater saturated with respect to calcite are difficult to reconcile with standard models for collapse development short flowpaths or renewed groundwater aggressivity towards calcite via mischungskorrosion thermally driven circulation or deep seated gaseous sources are hypothetical mechanisms that could generate the subsurface voids that are needed to allow cover collapse development in discharge areas for the two field sites in central italy that we investigated calculated carbon dioxide partial pressures in springs ranged from 7 38 10 2 to 7 29 10 1 atm this indicates that deep seated gaseous sources are most likely the mechanism allowing the development of the sinkholes groundwater is recharged in surrounding limestone massifs the water moves through the carbonates and becomes saturated with calcite as it circulates deeply in to the adjacent valleys it mixes with deep seated waters and gaseous fluxes from major fault systems acquiring renewed aggressivity towards calcite finally the water ascends into confined aquifers in the valley fill and dissolves carbonate material present within leading to surface collapse

geomechanics of subsurface water withdrawal and injection land subsidence and uplift ground ruptures and induced seismicity are the principal geomechanic effects of groundwater withdrawal and injection the major environmental consequence of groundwater pumping is anthropogenic land subsidence the first observation concerning land settlement linked to subsurface processes was made in 1926 by the american geologists pratt and johnson who wrote that the cause of subsidence is to be found in the extensive extraction of fluid from beneath the affected area since then impressive progress has been made in terms of a recognizing the basic hydrologic and geomechanic principles underlying the occurrence b measuring aquifer compaction and ground displacements both vertical and horizontal c modeling and predicting the past and future event and d mitigating environmental impact through aquifer recharge and or surface water injection the first milestone in the theory of pumped aquifer consolidation was reached in 1923 by terzaghi who introduced the principle of effective intergranular stress in the early 1970s the emerging computer technology facilitated development of the first mathematical model of the subsidence of venice made by gambolati and freeze since then the comprehension measuring and simulation of the occurrence have improved dramatically more challenging today are the issues of ground ruptures and induced triggered seismicity which call for a shift from the classical continuum approach to discontinuous mechanics although well known for decades anthropogenic land subsidence is still threatening large urban centers and deltaic areas worldwide such as bangkok jakarta and mexico city at rates in the order of 10 cm yr

stability charts for predicting sinkholes in weakly cemented sand over karst limestone forty nine physical models of sinkhole development were constructed and tested using a geotechnical centrifuge to replicate full scale sinkhole development in the small models the soil profile studied was weakly cemented sand overlying cavities in karst limestone with uncemented sand over the cemented sand layer in half the models in configurations with no uncemented soil overburden the parameters critical to predicting failure were the unit weight of the cemented sand c the thickness of the cemented sand overlying the karst cavity hc the true cohesion of the weakly cemented sand c and the diameter of the underlying karst cavity d brittle collapse of the cemented soil into the underlying cavity took one of two forms depending on geometry when hc d was less than or equal to 0 25 the plug of soil that fell into the cavity penetrated through the full thickness of the cemented layer leaving an open hole when hc d was greater than or equal to 0 31 the plug of soil that fell into the cavity did not penetrate through the full thickness of the cemented layer but left behind a stable arch a dimensionless stability chart was developed based on model results relating chc c and hc d at failure that chart can be used to predict the onset of failure extrapolating to configurations and soil cementation strengths not specifically tested in this research a study was also made of the influence of uncemented sand overburden on hastening sinkhole development for configurations with ratios of hc d less than or equal to 0 25 the thickness of the uncemented overburden was varied at the brink of sinkhole development there was significant arching within the uncemented sand and the influence of the overburden on hastening sinkhole failure was much less than the full geostatic overburden the maximum uncemented overburden pressure bearing down on the breakthrough plug never exceeded the weight of a cone of sand of diameter d and height 1 25d where d equals the diameter of the top of that inclined plug

exhumation of the sanbagawa blueschist belt sw japan by lateral flow and extrusion evidence from structural kinematics and retrograde p t t paths

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

the role of the 1999 chamoli earthquake in the formation of ground cracks abstract the moderate magnitude chamoli earthquake that occurred in the garhwal higher himalaya in the early hours of march 29 1999 caused intense damage to the ground and mountain slopes of the alaknanda mandakini river valley and adjoining region a systematic survey of this induced damage was conducted immediately after the earthquake occurred prominent shallow cracks of significant length negligible width and indeterminate vertical extent conspicuously tensile in nature with little or no slip across the crack planes were observed in the ground at several places along the surveyed route these cracks had formed in the dynamic phase of the chamoli earthquake process that is in the period of time during which the earthquake generated seismic waves were passing through the geographic region of interest however we use the theory of earthquake induced static or long time stress changes to visualize such cracks at some selected sites where ground damage was relatively more intense and varied to suggest lower bound estimates of the dynamic stress contributions of the main shock for their formation based on the results of our analysis we conclude that just prior to the earthquake occurrence under the influence of the local ambient stress field the ground at these sites was already near failure in tension to this in its dynamic phase the chamoli earthquake induced stress perturbations having across the planes of the cracks i shear components which were nearly equal and opposite to similar components of the ambient stress field and ii normal tensile components necessary for triggering tensile failure of the ground the 3 or minimum principal stress component of the resultant perturbed failure stress field thus became sufficiently tensile while the transverse stresses became sufficiently insignificant this facilitated formation of major tensile cracks in the ground there our static estimates of the tensile stress changes at the different sites are in essence estimates of the minimal triggering stress perturbations that was provided by the chamoli earthquake in the dynamic state for the formation of the tensile cracks there

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

long term land subsidence and strata compression in changzhou china abstract changzhou city underlain by a multi layered aquifer system in quaternary sediments in the great yangtze river delta region experienced a maximum land subsidence rate of 147 mm year in the early 1980s due to excessive groundwater extraction a large scale monitoring station of 11 borehole extensometers was established in the city in 1983 to investigate land subsidence nine strata were predetermined in the quaternary depth interval and monitored by borehole extensometers presented in this paper are the long term observations of land subsidence strata compression and groundwater level in four aquifers from 1984 to 2002 and discussion on strata compression based on the measured data with reference to the stratigraphy soil properties groundwater withdrawn and literature of similar situations the compression of strata varies significantly and is strongly influenced by groundwater drawdown in the second confined aquifer or ca2 the groundwater level in ca2 declined from 55 m in 1981 to 76 m in 1994 and the land subsidence rate remained high after the city government enforced restrictions on groundwater extraction in 1995 the extraction rate sharply reduced the groundwater level in ca2 steadily recovered to 56 m until 2003 and the land subsidence rate declined to 10 mm year in 2002 from 1984 to 2002 the land subsidence was mainly attributed to the consolidation of the thick aquitard overlying ca2 in the future to prevent the subsidence rate from rising it is vital to stop groundwater drawdown in aquifers

distribution and morphology of sinkholes triggered by flooding following tropical storm alberto at albany georgia usa abstract flooding of the flint river in july 1994 triggered the collapse of at least 312 sinkholes in the karstic dougherty plain at albany georgia we examined the distribution and morphology of these new sinkholes to evaluate the mode of formation to characterize early stages of the evolution of sinkhole form and to estimate the lowering of the surface associated with the development of new sinkholes eighty eight percent of sinkholes occur inside the limits of flooding especially in areas of sandy overburden and they often follow joint controlled linear trends sinkhole dimensions are log normally distributed with median values of circumference 5 7 m length 1 8 m width 1 6 m and depth 0 7 m asymmetry l w 1 2 cross sectional forms range from narrow cylinders to large bowls with many sinkholes having undercut sides flooding triggered the formation of sinkholes by saturating and liquefying overburden which caused soil arches to collapse and flow into cavities in bedrock the prevalence of sinkholes near the periphery of flooding suggests that drainage and loss of buoyant support as flood waters subsided may also have contributed to failure a volume ratio index is used to quantify the three dimensional geometric form of sinkholes initially small cylindrical shafts open over a bedrock joint followed by progressive slumping that leads to widening and increases in volume to a final bowl form estimates of the aggregate volume of overburden transported underground in flooded areas range from 7 990 to 11 130 m3 averaged over flooded areas this accounts for 0 26 to 0 37 mm km2 lowering of the surface based on a 500 year recurrence interval for the flood event values for lowering of the surface range from 0 52 to 0 74 mm per 1 000 years these values are an order of magnitude less than estimates of carbonate dissolution and suggest that transport of overburden underground is limited by triggering events

earth fissures in jiangsu province china and geological investigation of hetang earth fissure earth fissures are a geohazard in jiangsu province china they can be caused by earthquakes and active faults underground mining groundwater extraction and landslides in order to establish a provincial rehabilitation plan in jiangsu a range of monitoring programs surveys geological investigations and modeling have been implemented or planned one of the focuses of the project is the land subsidence and earth fissures caused by excessive groundwater withdrawal in suzhou wuxi and changzhou su xi chang area southern jiangsu province hetang earth fissure within the su xi chang area was first reported in 1995 and a series of investigation has been conducted since then the site investigations and geophysical survey in 1997 have recognized the causative factor as the excessive groundwater drawdown coupled by the underlying bedrock ridge an open trench excavation in 2007 and a plane strain analysis suggest that hetang earth fissures may have cracked from the bedrock ridge to ground surface geological drilling in 2007 has further confirmed the existence and configuration of the ridge and extracted soil samples for laboratory tests to obtain soil parameters for numerical analyses and modeling of land subsidence and earth fissures in the su xi chang area jiangsu china the laboratory tests are currently in progress and the result of numerical analyses and modeling is expected to be presented in the near future

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

mechanism of deep cracks in the left bank slope of jinping first stage hydropower station abstract the proposed jinping first stage hydropower station is located on the middle reach of the yalongjiang river sichuan province pr china it consists of a double curvature arch dam with a maximum height of 305 m which will be the highest in the world cracks are well developed in the left bank slope of the pusiluogou the dam site of jinping first stage hydropower station some cracks are even developed at the horizontal distance into rock face in this paper the term horizontal depth was used to describe the horizontal distance into face of the slope beyond 200 m and these cracks are here referred to as deep cracks the distribution of these deep cracks is far beyond people s experiences in common unloading zones so the mechanism of the deep cracks is put forward as a new subject since these cracks are significant for the stability of the slope their mechanism becomes one of the key engineering geology problems a comprehensive study is made in this paper on the distribution characteristics of the cracks as well as their deformation features the factors that influence their distribution and deformation feature are also analyzed by means of geology mechanics and numerical simulation an important conclusion is consequently reached that deep cracks occurred as a result of release of high ground stress including gravitational stress and tectonic stress the formation of the deep cracks in the slope is a result of unloading process under favorable geology conditions fast crust uplift and quick river cutting and high tectonic stress are indispensable regional geological condition steep and high geometry condition provides favorable geometry condition hard at the lower part and soft at the upper part of the slope offers suitable rock combination condition and back facing bending planes and consequent discontinuities supply suitable structure of the slope

land subsidence in the cerro prieto geothermal field baja california mexico from 1994 to 2005 an integrated analysis of dinsar leveling and geological data abstract cerro prieto is the oldest and largest mexican geothermal field in operation and has been producing electricity since 1973 the large amount of geothermal fluids extracted to supply steam to the power plants has resulted in considerable deformation in and around the field the deformation includes land subsidence and related ground fissuring and faulting these phenomena have produced severe damages to the local infrastructure such as roads irrigation canals and other facilities in this paper the technique of differential synthetic aperture radar interferometry dinsar is applied using c band envisar asar data acquired between 2003 and 2006 to determine the extent and amount of land subsidence in the mexicali valley near cerro prieto geothermal field the dinsar results were compared with published data from precise leveling surveys 1994 1997 and 1997 2006 and detailed geological information in order to improve understanding of the temporal and spatial distributions of anthropogenic subsidence in the mexicali valley the leveling and dinsar data were modeled to characterize the observed deformation in terms of fluid extraction the results confirm that the tectonic faults control the spatial extent of the observed subsidence these faults likely act as groundwater flow barriers for aquifers and reservoirs the shape of the subsiding area coincides with the cerro prieto pull apart basin in addition the changes in spatial pattern and rate of the subsidence are correlated with the development of the cerro prieto geothermal field

orogeny and relative plate motions example of the japanese islands abstract the paleogeography of the eastern margin of asia near japan for the past 250 ma has been reconstructed on the basis of the relative motions between the oceanic plates and the eurasian plate engebretson et al 1982 and on land geology the relationships between the plate kinematics and orogeny are as follows calc alkaline magmatism is related to the presence of subduction when a plate boundary is a transform fault there is no volcanism very slow convergence rates do not give rise to magmatism migration of rft type triple junctions or ridge subduction produces forearc volcanism near the trench and also a wider volcanic zone uplift of low p t type regional metamorphic belts is related to collision episodes the uplift of the high p t blueschist belts on the contrary is not contemporaneous with them they appear to be related to the start of the subduction of a young plate after the migration of an rft type triple junction because the formation of a voluminous accretionary complex is contemporaneous with this and thrusting of this young accretionary complex beneath the uplifted metamorphic belt is often observed the underplating of the young accretionary complex beneath the older accretionary complex would be the cause of the uplift of the high p t type metamorphic belt the subduction of a young plate would thus be an important factor causing these orogenic events highly oblique convergence also results in formation of a serpentinite melange zone with fragments of blueschists presumably along a mechanical plate boundary in the forearc

earth fissures and localized differential subsidence long linear tension cracks associated with declining groundwater levels at four sites in subsiding areas in south central arizona fremont valley california and las vegas valley nevada occur near points of maximum convex upward curvature in subsidence profiles oriented perpendicular to the cracks profiles are based on repeated precise vertical control surveys of lines of closely spaced bench marks association of these fissures with zones of localized differential subsidence indicates that linear earth fissures are caused by horizontal tensile strains probably resulting from localized differential compaction horizontal tensile strains across the fissures at the point of maximum convex upward curvature ranging from approximately 100 to 700 microstrains 0 01 to 0 07 per year were indicated based on measurements with a tape or electronic distance meter

characteristics of aquifer system deformation in the southern yangtse delta china excessive groundwater pumpage has caused regional cones of depression and severe land subsidence in the southern yangtse delta china the characteristics of aquifer system compaction are complex because of the difference in the types compositions and structures of the soils that the hydrostratigraphic units are composed of and in the histories of groundwater level change the hydrostratigraphic units have experienced based on the data measured from extensometer groups and observation wells the characteristics of deformation for individual hydrostratigraphic units are analyzed the results show that different hydrostratigraphic units have different kinds of deformation and that an identical unit may also present different deformation characteristics such as elasticity elasto plasticity and visco elasto plasticity at different sites of the cone of depression or in different periods if the groundwater level rises continuously and remains constant later the aquifers and the aquitard units that consist of hard clay primarily exhibit elastic behaviour but the aquitard units that consist of soft clay deform plastically and by creep and exhibit visco elasto plastic behaviour if the groundwater level falls but is much higher than the previous lowest value aquifers and aquitards consisting of hard clay exhibit elasto plastic behaviour if the groundwater level falls below the previous lowest value aquifers and aquitards consisting of hard clay deform plastically and by creep and exhibit visco elasto plastic behaviour

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

century scale paleoclimatic reconstruction from moon lake a closed basin lake in the northern great plains estimates of past lake water salinity from fossil diatom assemblages were used to infer past climatic conditions at moon lake a climatically sensitive site in the northern great plains a good correspondence between diatom inferred salinity and historical records of mean annual precipitation minus evapotranspiration p et strongly suggests that the sedimentary record from moon lake can be used to reconstruct past climatic conditions century scale analysis of the holocene diatom record indicates four major hydrological periods an early holocene transition from an open freshwater system to a closed saline system by 7300 b p which corresponds with a transition from spruce forest to deciduous parkland to prairie and indicates a major shift from wet to dry climate a mid holocene period of high salinity from 7300 to 4700 b p indicating low effective moisture p et a transitional period of high salinity from 4700 to 2200 b p characterized by poor diatom preservation and a late holocene period of variable lower salinity during the past 2 200 yr indicating fluctuations in effective moisture

sinkhole formation above underground limestone quarries a case study in south limburg belgium abstract historical records were used for the compilation of a database of sinkholes resulted from collapses of abandoned shallow underground limestone quarries mines in two villages in belgian south limburg during the last 350 years the formation of such sinkholes caused at least 38 casualties but more often it caused a change in topography and damage to public and private property the objective of this study is to better understand the spatial and temporal patterns of quarry collapse related sinkholes in the study area apart from sinkhole locations and ages the compiled database provides information on the dimensions of the area affected and the damage caused by sinkhole formation as well as the causal factors of sinkholes one hundred seventy three sinkholes have been reported since 1665 but most 80 reported sinkholes postdate 1965 sinkhole dimensions provided information on the type of collapse seven large sinkholes displacing a total sediment volume of 480 000 m3 resulted from large scale roof breakdown after pillar failure the smaller sinkholes were the result of fall of the overburden into galleries after local roof collapse or suffosion of a solution pipe in total these small sinkholes displaced 12 300 m3 of sediment at present almost all large underground quarries in the study area have been affected by sinkholes these features were caused by natural and anthropogenic factors and occur in zones with thin roofs where pillars were affected by pillar robbing or on locations with inappropriate sewerage systems above quarries the formation of sinkholes was often reported in spring during years with high moisture contents in the overburden caused by high groundwater recharge or above average precipitation with increasing time since quarry abandonment quarries become more susceptible to pillar creep and bending of the roof hence if no appropriate mitigation measures are taken to reduce such deterioration processes the number of sinkholes is expected to increase

a 900 year pollen inferred temperature and effective moisture record from varved lake mina west central minnesota usa abstract drought is endemic to the north american great plains causing severe economic consequences however instrumental climate data only exist from ca ad 1890 and limited tree ring paleolimnological archeological and eolian records document the last two millennia to address this lack of monitoring and paleoclimatic data the pollen preserved in the varved sediments of lake mina minnesota on the northeastern border of the great plains were analyzed may and february mean monthly temperatures and annual precipitation minus potential evapotranspiration were reconstructed at a 4 year resolution using a pre settlement pollen climate calibration set the period of the so called little ice age lia ad 1500 1870 was colder than the medieval climate anomaly mca ad 1100 1500 in west central minnesota winter temperatures in the lia declined more than summer ones the pollen record suggests that the lia occurred in three phases an initial cold phase from ad 1505 to ad 1575 a warmer phase and then a very cold phase from ad 1625 to ad 1775 there were severe droughts detected in the lake mina record from ad 1660 to ad 1710 and ad 1300 to ad 1400 suggesting that high resolution pollen records can detect events previously defined from the tree ring records this latter century scale drought is concurrent with the widely reported ad 1250 1400 mega drought which exceeds the severity of 20th century droughts

stable carbon isotope behaviour of natural seepage of deep underground 13c rich methane detected along a fault zone and adsorbed in mudstone tokyo bay area japan abstract gas was sampled regionally including by drilling into faults in the south kanto gas field around tokyo bay japan gas samples were collected from cores in a gas sampling container immediately after drilling a value of 13c1 44 3 was obtained for gas in the container and 13c1 36 3 for seeping gas in a fault zone however typical ch4 in this dissolved in water gas field is mainly depleted in 13c and 13c1 values range from 66 to 68 owing to microbial degradation of organic material 13c rich ch4 is so far uncommon in the south kanto gas field seepages were observed from the surface along the north south fault zone the natural gas is stored below the sandstone layer by impermeable mudstone underlying the boundary at a depth of 30 m gas seepages were not observed below a depth of 40 m gas rises along the fault zone dissolved in groundwater up to the shallow region and then separates from the groundwater 13c rich ch4 adsorbed ch4 was found to have desorbed from drilled mudstone core samples taken at depths of 1400 1900 m in the main gas production strata similarly 13c rich ch4 was found in black shale overlying the oceanic crust forming part of a sedimentary accretionary prism underling the tokyo region it also appears in the spring water of spa wells originating at a depth of 1200 1500 m along a tectonic line methane generated by microbial degradation of organic material through co2 reduction in the south kanto gas field mainly originates as biogenic gas mixed with a small amount of 13c rich ch4 derived from thermogenic gas without oil components in strata it is assumed that 12c rich ch4 is easily detached from core or pore water through gas production whereas 13c rich ch4 is strongly adsorbed on the surfaces of particles the 13c rich ch4 rises along the major tectonic line or up the 50 m wide normal fault zone from relatively deep sources in the kanto region

restoration of exotic terranes along the median tectonic line japanese islands overview abstract this paper reviews recent progress on the geotectonic evolution of exotic paleozoic terranes in southwest japan namely the paleo ryoke and kurosegawa terranes the paleo ryoke terrane is composed mainly of permian granitic rocks with hornfels mid cretaceous high grade metamorphic rocks associated with granitic rocks and upper cretaceous sedimentary cover they form nappe structures on the sambagawa metamorphic rocks the permian granitic rocks are correlative with granitic clasts in permian conglomerates in the south kitakami terrane whereas the mid cretaceous rocks are correlative with those in the abukuma terrane this correlation suggests that the elements of northeast japan to the northeast of the tanakura tectonic line were connected in between the paired metamorphic belt along the median tectonic line southwest japan the kurosegawa terrane is composed of various paleozoic rocks with serpentinite and occurs as disrupted bodies bounded by faults in the middle part of the jurassic chichibu terrane accretionary complex it is correlated with the south kitakami terrane in northeast japan the constituents of both terranes are considered to have been originally distributed more closely and overlay the jurassic accretionary terrane as nappes the current sporadic occurrence of these terranes can possibly be attributed to the difference in erosion level and later stage depression or transtension along strike slip faults the constituents of both exotic terranes especially the ordovician granite in the kurosegawa south kitakami terrane and the permian granite in the paleo ryoke terrane provide a significant key to reconstructing these exotic terranes by correlating them with paleozoic granitoids in the eastern asia continent

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

liquefaction induced ground failure a study of the chi chi earthquake cases abstract the 1999 chi chi taiwan earthquake caused great destruction to buildings bridges and other facilities and a death toll of more than 2400 lessons should be learned from this event which albeit disastrous represents a rare full scale experimentation in geotechnical engineering and related fields of particular interest to geotechnical engineers is the phenomenon of soil liquefaction that caused significant damage to buildings lifelines and harbor facilities these liquefaction phenomena in the forms of sand boils lateral spreads tilting and settlement of buildings and ground settlement were observed in the chi chi event shortly after the earthquake an extensive field investigation in the yuanlin area including in situ tests and laboratory tests was conducted by moh and associates and other parties these in situ and laboratory tests along with ground performance observations form the basis for the present study in this paper 24 cases of ground performance in the areas that suffered the most from liquefaction are studied the ground performance in selected cases of the 24 cases is accounted for through a series of liquefaction analyses the analysis of the potential of liquefaction and ground failure is performed using cone penetration test cpt data the results of the analyses show that the field observations of ground performance in the yuanlin area in the chi chi event can be accounted for satisfactorily using the evaluation procedure by ishihara ishihara k 1985 stability of natural deposits during earthquakes proc 11th int conf on soil mechanics and foundation engineering san francisco ca vol 1 pp 321 376

engineering geology ground surface movement and fissures induced by underground mining in the jinchuan nickel mine the jinchuan nickel mine is the largest underground mine with cut and fill mining in china in 1999 there appeared evident ground surface movement and many ground fissures in jinchuan no 2 mine following an introduction to the engineering geology and mechanical properties of the rock mass in the jinchuan mine areas this paper reveals the features of the measured in situ stresses and puts emphasis on an analysis of the mechanism of surface movement and ground fissures induced by the underground mining with backfill it is indicated that both the fault structures and the alteration contact zones are well developed as the dominant engineering geological characteristics in the jinchuan mine areas the stress redistribution in surrounding rocks resulting from the mining the low stiffness of the filling body the existence of the void space and the influence of on going mining activities is the main reason for the occurrence of surface movement and ground fissures

a chronological framework for the holocene vegetational history of central minnesota the steel lake pollen record abstract paleorecords from minnesota and adjacent areas have often been used to evaluate large scale climatic processes in the mid continent of north america however most of these records are compromised by chronological flaws making problematic any comparisons with climatic interpretations based on other records e g gisp2 in greenland we report here a high resolution pollen record with a secure chronology constrained by 26 14 c dates on terrestrial macrofossils from steel lake central minnesota about 11 2 ka cal bp 11 000 calibrated yr before present the late glacial picea forest near steel lake was succeeded abruptly by pinus banksiana and or resinosa the pinus forest began to open 9 4 ka cal bp with the expansion of prairie taxa and a pine parkland or savanna prevailed until about 8 ka cal bp when quercus replaced pinus to become the dominant tree in the prairie areas for 4500 yr the close chronological control permits the correlation of key vegetational changes with those at other reliably dated sites in the eastern dakotas and in minnesota suggesting that the abrupt decline of the spruce forest was time transgressive from southwest to northeast during 2000 yr and that the development of prairie was time transgressive in the same direction over 2600 yr correlation of key pollen horizons at steel lake with those in the high resolution pollen profiles of elk lake ca 50 km northwest of steel lake suggests that the well known elk lake varve chronology for the early holocene is about 1000 yr too young

a method to predict the group fissuring and faulting caused by regional groundwater decline ground fissuring is a recurrent problem in many countries where water extraction surpasses the natural recharge of aquifers due to differential settlement the soil layer undergoes deformation and cracks with serious consequences for civil infrastructure here we propose an approximate analysis of the fissuring process that can be used to predict the location of cracks which increasingly affect some middle and large sized cities in the world for that purpose the ground loss theory is applied to sediments overlying a sinusoidal shaped graben this analysis shows the existence of a tensile zone at the border of the graben with maximal values on its shoulder where tension cracks are more likely to appear it also shows that soil deformation under differential settlement may evolve into ground faulting if water withdrawal continues finally when a crack has completely developed the tensile zone shifts towards the center of the graben creating a new area for potential cracking and faulting

microtectonic evidence for eastward ductile shear in the jurassic orogen of sw japan abstract two jurassic deformation phases are responsible for the thrust and nappe structures in the infrastructure of the outer belt of the mesozoic chain of sw japan the first phase was synmetamorphic and took place under hp lt conditions microtectonic analysis shows that the penetrative deformation corresponded to a ductile shear directed from w to e parallel to the stretching and mineral lineation at the regional scale the first phase corresponded to the obduction of the greenschist nappes upon the kurosegawa continent during the second phase the greenschist nappes were sliced leading to an apparent reverse metamorphic zoning the first phase structures were then locally reworked by folds giving rise to an apparent westwards sense of shear

clockwise 180 rotation of slip direction in a superficial nappe pile emplaced upon a high p t type metamorphic terrane in central japan abstract understanding the exhumation process of deep seated material within subduction zones is important in comprehending the tectonic evolution of active margins the deformation and slip history of superficial nappe pile emplaced upon high p t type metamorphic rocks can reveal the intimate relationship between deformation and transitions in paleo stress that most likely arose from changes in the direction of plate convergence and exhumation of the metamorphic terrane the kinshozan atokura nappe pile emplaced upon the high p t type sanbagawa sambagawa metamorphic rocks is the remnant of a pre existing terrane located between paired metamorphic terranes along the median tectonic line mtl of central japan intra and inter nappe structures record the state of paleo stress during metamorphism and exhumation of the sanbagawa terrane the following tectonic evolution of the nappes is inferred from a combined structural analysis of the basal fault of the nappes and their internal structures the relative slip direction along the hanging wall rotated clockwise by 180 from s to n in association with a series of major tectonic changes from mtl normal contraction to mtl parallel strike slip and finally mtl normal extension this clockwise rotation of the slip direction can be attributed to changes in the plate induced regional stress state and associated exhumation of the deep seated sanbagawa terrane from the late cretaceous coniacian to the middle miocene

rotation of slip direction of the atokura nappe viewed from microstructural analyses of brittle shear zones in the sambagawa belt southwest japan abstract the atokura nappe is mainly composed of late cretaceous fore arc sediments atokura formation and overlies the mikabu greenstones of the sambagawa belt in the kanto region southwest japan meso and microstructures of the foliated cataclastic fault rocks along the base of the nappe klippes are described and slip directions are determined movement of the nappe is divided into three stages based on a difference in fault rocks the slip direction of the nappe has rotated clockwise from wnw subparallel to the trend of geologic belts to n perpendicular to the trend movement of the atokura nappe may have changed from a strike slip to an extensional tectonic setting

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