kinematics fabrics and geochronology analysis in the medog shear zone eastern himalayan syntaxis abstract the uplift history and tectonic evolution of the eastern himalayan syntaxis ehs have been extensively studied in the last several decades the medog shear zone the eastern boundary of the ehs has preserved considerable significant information on the structural and tectonic evolution of the ehs in this study we report kinematics fabrics and geochronology data of the medog shear zone in the ehs analyses of the crystallographic preferred orientation cpo of quartz ebsd analysis demonstrated that there are three major slip systems 1 basal slip 2 prism c slip and 3 prism slip these slip systems are consistent with microstructures of low temperature shearing medium temperature shearing and high temperature shearing respectively zircons from the two gneiss samples possess inherited magmatic cores and metamorphic overgrown rims yielding a metamorphic age of 29 4 28 6 ma it is suggested that the dextral shearing along the medog shear zone was not earlier than the early oligocene the 40ar 39ar analysis indicates that the medog shear zone experienced three thermo tectonic events from the late oligocene to the pliocene e g 23 4 ma 16 9 12 6 ma and 5 3 ma we correlate the oligocene metamorphic event and the late oligocene to the pliocene multi stage thermo tectonic events that resulted from subduction of the northeast corner of the india plate

preliminary results from the sprites94 aircraft campaign 2 blue jets initial observations of a newly documented type of optical emission above thunderstorms are reported blue jets or narrowly collimated beams of blue light that appear to propagate upwards from the tops of thunderstorms were recorded on b w and color video cameras for the first time during the sprites94 aircraft campaign june july 1994 the jets appear to propagate upward at speeds of about 100 km s and reach terminal altitudes of 40 50 km fifty six examples were recorded during a 22 minute interval during a storm over arkansas we examine some possible mechanisms but have no satisfactory theory of this phenomenon

geometry and distribution of regional joint sets in a non homogeneous stress field case study in the ebro basin spain abstract three regional joint sets striking n s e w and wnw ese affect the tertiary rocks of the central ebro basin from analysis of their chronological relationships and spatial distribution it is concluded that they correspond to two different tectonic events the n s set oldest and the e w set younger are present in the southern and central sectors while the wnw ese joint set predominates in the northern one the n s joints propagated in response to joint normal and fluid loads under an intraplate stress field with shmax oriented near n s related to forces caused by the convergence of africa iberia and europe and rifting at the valencia trough during the sedimentary infilling of the basin these joints are only present in the southern part of the area the e w joint set in the southern central sector records the same fracturing event as the wnw ese set does in the northern one its orientation was modified by the presence of the older n s set in the south which perturbed the regional stress field the younger wnw ese and e w joint sets are interpreted as unloading joints these propagated as a consequence of flexural uplift and exhumation related to isostatic rebound at the pyrenees and the ebro foreland basin a numerical approach is used to explain the inhomogeneous distribution of the n s joint set in terms of their absence being controlled by the depth of the water table at the time of their formation

salman farsi dam reservoir a successful project on a karstified foundation sw iran the salman farsi dam is constructed on the ghareh aghaj river at the northern limb of changal anticline sw iran the anticline is composed of the calcareous asmari formation af sandwiched between two marly formations the pabdeh gurpi pgf and razak rf the af is divided into three units lower laf marl and limestone middle maf karstified limestone and upper uaf marl and marly limestone the dam is constructed on the maf and the reservoir is in direct contact with the maf uaf and rf a huge relict cave was discovered during excavation of grouting galleries in the maf in this research the potential leakage passage plp is defined as parts of the karst aquifer located lower than the normal water level nwl of reservoir in which the reservoir water has potential to be leaked toward downstream assuming no grout curtain construction the plp is composed of the inlet windows transfer passage and discharge zones at the salman farsi dam the plp is determined by three alternative schematic models considering hydrogeological and geological settings at this dam site the grout curtain was properly designed from the maf toward the downstream laf at the narrowest part of the plp and bypassing the huge cave the grout curtain was successful in blocking the plp based on the negligible leakage and high differences between water level in the pair piezometers at the upstream and downstream sides of the grout curtain it is recommended to determine the plp in future dam construction in karst terrains

natural deformation fabrics of plagioclase implications for slip systems and seismic anisotropy abstract the optical and tem microstructures and fabrics of twelve naturally deformed plagioclase containing rocks of compositions from an0 an80 have been studied with a view to determining the deformation mechanisms the optical indicatrix fabrics have been recorded in all samples with respect to the foliation and lineation in general and form a girdle in the foliation plane with a high concentration of normal to the foliation in some cases the orientation of 010 and 001 cleavages or albite and pericline twins has allowed the construction of pole figures in all cases 010 has been shown to be the dominant slip plane with either 001 or 100 the dominant slip direction tem shows that the dominant slip system is 010 001 with secondary 010 100 the seismic p wave anisotropy has been calculated for the first time from the lpo data of plagioclase the anisotropy coefficient is high at around 15 the minimum p velocity is normal to the lineation in the foliation plane and the maximum is sub parallel to the foliation normal the combined information on deformation kinematics and seismic anisotropy is valuable for interpretations of deep crustal seismic sections

monitoring and characterizing the deformation of an earth dam in guangxi province china abstract failures and severe deformation of earth dams have been reported frequently in the past decades extensive studies have been performed to monitor dam displacements to develop dam remediation plans however the long term monitoring of dam displacements and the effects of remediation on dam deformation are rarely studied in this study the vertical and lateral displacements of an earth dam in guangxi province southwestern china were monitored over an 18 year period the piezometric pressure was measured for the analysis of triggered seepage furthermore acoustic testing and borehole television tests were performed to examine the integrity of the cutoff wall that was built to prevent dam leakage and excessive deformation the results show that the largest lateral displacement of 65 8 mm and the maximum settlement of 178 mm are both located at the center of the dam and that the lateral displacement and settlement decrease gradually from the center to both abutments moreover greater settlements were observed on the side of the dam upstream of the cutoff wall the lateral displacements are dominated by the hydraulic pressure of the impounded water the dam settlements are generally determined by the thickness of the compacted soil along the longitudinal section the analysis shows that the greater settlements on the upstream side of the dam are attributed to dynamic seepage induced by the water level changes in the reservoir indicating that the cutoff wall effectively alleviated the seepage effects on the downstream side of the dam thus the dam s upstream face should be remediated to minimize the dynamic water level effects

a new magma chamber model based on structural studies in the oman ophiolite abstract structural mapping in the mafic ultramafic transition zone and in the overlying crustal section of the oman ophiolite has revealed the importance of magmatic flow in the formation of layering in the gabbros and the mechanical coupling between this flow and the asthenospheric flow of the underlying peridotites the crustal section near the spreading axis and in particular the magma chamber are fed by two independent melts a dominant gabbroic melt episodically injected from depth and a subordinate wehrlitic crystal mixture produced by compaction of the transition zone layering in the gabbros can be partly produced by tectonic transposition of the gabbroic and wehrlitic mixtures during magmatic flow whatever its origin the layering orientation in the newly created crust does not necessarily reflect its original attitude the final orientation of the layering is determined by the attitude of the magmatic flow plane at the time it was frozen a new magma chamber model is proposed which solves some of the physical difficulties of previous models and accounts for the seismic imaging of magma chambers beneath oceanic ridges

a review on natural and human induced geohazards and impacts in karst karst environments are characterized by distinctive landforms related to dissolution and a dominant subsurface drainage the direct connection between the surface and the underlying high permeability aquifers makes karst aquifers extremely vulnerable to pollution a high percentage of the world population depends on these water resources moreover karst terrains frequently underlain by cavernous carbonate and or evaporite rocks may be affected by severe ground instability problems impacts and hazards associated with karst are rapidly increasing as development expands upon these areas without proper planning taking into account the peculiarities of these environments this has led to an escalation of karst related environmental and engineering problems such as sinkholes floods involving highly transmissive aquifers and landslides developed on rocks weakened by karstification the environmental fragility of karst settings together with their endemic hazardous processes have received an increasing attention from the scientific community in the last decades concurrently the interest of planners and decision makers on a safe and sustainable management of karst lands is also growing this work reviews the main natural and human induced hazards characteristic of karst environments with specific focus on sinkholes floods and slope movements and summarizes the main outcomes reached by karst scientists regarding the assessment of environmental impacts and their mitigation

on the structure of grain boundaries in tectonites abstract grain boundaries in several tectonites have been examined using high voltage and scanning transmission electron microscopy on a gross scale grain boundaries are observed to differ from the host crystal in exhibiting faster rates of preferential etching during ion beam thinning and faster rates of ionization damage during exposure to the electron beam grain boundary features can be grouped according to decreasing size as follows grain junction voids that can form linked networks of tubules arrays of isolated voids and inclusions along the grain boundary surface and a narrow grain boundary film of distorted crystal structure the presence of inclusions in voids and the propensity for electron damage along the boundary suggests that the former were initially fluid filled and that the latter may be hydrated initial microchemical analyses using stem indicate that no compositional difference exists between the grain boundaries and host crystals the overall complex grain boundary structure in tectonites suggests that the effective grain boundary width for intercrystalline diffusion is much greater than that proposed based on metals and that diffusion path lengths along grain boundaries are much less than the theoretical maximum the net effect is to greatly enhance deformation mechanisms dependent on intercrystalline mass transport

pore fluid effects on seismic velocity in anisotropic rocks a simple new technique predicts the high and low frequency saturated velocities in anisotropic rocks entirely in terms of measurable dry rock properties without the need for idealized crack geometries measurements of dry velocity versus pressure and porosity versus pressure contain all of the necessary information for predicting the frequency dependent effects of fluid saturation furthermore these measurements automatically incorporate all pore interaction so there is no limitation to low crack density the velocities are found to depend on five key interrelated variables frequency the distribution of compliant crack like porosity the intrinsic or noncrack anisotropy fluid viscosity and compressibility and effective pressure the sensitivity of velocities to saturation is generally greater at high frequencies than low frequencies the magnitude of the differences from dry to saturated and from low frequency to high frequency is determined by the compliant or crack like porosity predictions of s

accelerating thinning of kenai peninsula glaciers alaska 1 temperate mountain glaciers are thinning at high rates and significantly contributing to sea level rise due to these glaciers remote locations remote sensing and digital elevation models dems are an effective way to calculate their thinning rates and contribution to sea level rise comparisons of 1950s united states geological survey usgs and 2000 shuttle radar topographic mission srtm dems with dems produced from lidar profiles of glacier center lines indicate thinning rates from the mid 1990s to 1999 0 72 0 13 m y 1 accelerated by a factor of 1 5 as compared with 1950 to mid 1990s 0 47 0 01 m y 1 for glaciers on the harding icefield overall comparison of usgs and srtm dems indicate the harding icefield and grewingk yalik glacier complex alaska are thinning 0 61 0 12 m y 1 from 1950 to 1999

accuracy of the lightning mapping array 1 the location accuracy of the new mexico tech lightning mapping array lma has been investigated experimentally using sounding balloon measurements airplane tracks and observations of distant storms we have also developed simple geometric models for estimating the location uncertainty of sources both over and outside the network the model results are found to be a good estimator of the observed errors and also agree with covariance estimates of the location uncertainties obtained from the least squares solution technique sources over the network are located with an uncertainty of 6 12 m rms in the horizontal and 20 30 m rms in the vertical this corresponds well with the uncertainties of the arrival time measurements determined from the distribution of chi square values to be 40 50 ns rms outside the network the location uncertainties increase with distance the geometric model shows that the range and altitude errors increase as the range squared r2 while the azimuthal error increases linearly with r for the 13 station 70 km diameter network deployed during steps the range and height errors of distant sources were comparable to each other while the azimuthal errors were much smaller the difference in the range and azimuth errors causes distant storms to be elongated radially in plan views of the observations the overall results are shown to agree well with hyperbolic formulations of time of arrival measurements e g proctor 1971 two appendices describe 1 the basic operation of the lma and the detailed manner in which its measurements are processed and 2 the effect of systematic errors on lightning observations the latter provides an alternative explanation for the systematic height errors found by boccippio et al 2001 in distant storm data from the lightning detection and ranging system at kennedy space center

multi channel seismic imaging of a crustal magma chamber along the east pacific rise a reflection observed on multi channel seismic profiles along and across the east pacific rise between 8 50 n and 13 30 n is interpreted to arise from the top of a crustal magma chamber located 1 2 2 4 km below the sea floor the magma chamber is quite narrow 4 6 km wide but can be traced as a nearly continuous feature for tens of kilometres along the rise axis

modelling the anisotropic seismic properties of partially molten rocks found at mid ocean ridges abstract the problem of modelling the seismic properties of mid ocean ridge rocks of the axial magma chamber amc and the low velocity triangle lvt immediately below it has been addressed using two samples from oman ophiolite as examples the specimens are a layered gabbro from the lower oceanic crustal sequence and a harzburgite from the upper most mantle section at the palaeo ridge axis the seismic properties have been simulated at a temperature of 1200 c and pressure of 200 mpa so that the basalt melt is above its solidus various effective medium methods are discussed in the perspective of modelling rocks that have a strong background elastic anisotropy due to crystal preferred orientation cpo and an introduced anisotropy due to oriented melt filled inclusions calculations using various methods show a wide range of predicted melt fractions for a given seismic velocity the self consistent scheme scs and differential effective medium dem are compared in some detail a tensorial model was developed using a poro elastic method of gassman at low seismic frequency and a standard dem with isolated basalt inclusions at high frequency at low frequency the basalt pore fluid is considered to be everywhere connected and the pressure uniform whereas at high frequency basalt inclusions are isolated assuming the medium to be a standard linear solid the low and high frequency velocities were used to calculate the anisotropy of attenuation calculations with spherical basalt inclusions show that the seismic velocities decrease and attenuation increase with increasing melt fraction the symmetry of the background anisotropy due to cpo is preserved but gradually reduced with increasing melt fraction for the seismic velocities observed for the axial magma chamber amc with v p of 3 5 to 4 7 km s the model predicts 50 70 melt for the low velocity triangle lvt below the amc with v p of 4 8 5 6 km s the model predicts 35 50 melt predictions from the observed attenuations q 1 at the amc of 0 05 0 02 and in the lvt of 0 02 0 01 are around 60 and 45 melt respectively seismic anisotropy has been modelled with ellipsoidal basalt pancake shaped inclusions with their circular sections in the xy foliation plane only a 2 3 of ellipsoidal basalt inclusions are required to over print the anisotropy of the background medium there is a rapid decrease in v p and increase of q 1 for propagation normal to the foliation z with increasing axial ratio of the inclusions with increasing axial ratio the model predicts decreasing amounts of melt for given velocity v p in the z direction for the lvt only 15 25 melt is predicted for a 10 1 inclusion instead of the 35 50 of the spherical inclusion

a gps based three dimensional lightning mapping system initial observations in central new mexico a gps based system has been developed that accurately locates the sources of vhf radiation from lightning discharges in three spatial dimensions and time the observations are found to reflect the basic charge structure of electrified storms observations have also been obtained of a distinct type of energetic discharge referred to as positive bipolar breakdown recently identified as the source of trans ionospheric pulse pairs tipps observed by satellites from space the bipolar breakdown has been confirmed to occur between the main negative and upper positive charge regions of a storm and found to be the initial event of otherwise normal intracloud discharges the latter is contrary to previous findings that the breakdown appeared to be temporally isolated from other lightning in a storm peak vhf radiation from the energetic discharges is observed to be typically 30 db stronger than that from other lightning processes and to correspond to source power in excess of 100 kw over a 6 mhz bandwidth centered at 63 mhz

identifying the boundaries of sinkholes and subsidence areas via trenching and establishing setback distances abstract one of the most effective mitigation strategies in sinkhole areas is the exclusion of sinkholes and their vicinity to construction the application of this preventive measure requires precise mapping of the boundaries of the areas affected by subsidence and the establishment of adequate setback distances which is an important policy issue with significant economic implications through the investigation of several buried sinkholes in the mantled evaporite karst of the ebro valley by trenching this work illustrates that the actual extent of the subsidence areas may be much larger than that inferred from surface mapping and geophysical surveys the objective and accurate subsurface information acquired from trenches on the outer edge of the deformed ground revealed sinkhole radii 2 3 times larger than initially estimated increasing one order of magnitude the sinkhole area trenches can therefore help to reduce mapping uncertainties and the size of setbacks moreover the trenching technique in combination with geochronological data and retrodeformation analyses provides critical information on the subsidence phenomena and the characteristics of the sinkholes relevant to hazard assessment since recommended setback distances found in the existing literature are highly variable and rather arbitrary we include a discussion here on the main factors that should be considered when defining setback zones for sinkholes

paleoflood records from sinkholes using an example from the ebro river floodplain northeastern spain 53 pags 10 figs the definitive version is available at https www cambridge org core journals quaternary research

glauberite halite association of the zaragoza gypsum formation lower miocene ebro basin ne spain glauberite is the most common mineral in the ancient sodium sulphate deposits in the mediterranean region although its origin primary or diagenetic continues to be a matter of debate a number of glauberite deposits of oligocene miocene age in spain display facies characteristics of sedimentologic significance in particular those in which a glauberite halite association is predominant in this context a log study of four boreholes in the zaragoza gypsum formation lower miocene ebro basin ne spain was carried out two glauberite halite lithofacies associations a and b are distinguished association a is composed of bedded cloudy halite and minor amounts of massive and clastic glauberite association b is made up of laminated to thin bedded clear macrocrystalline massive clastic and contorted lithofacies of glauberite and small amounts of bedded cloudy halite transparent glauberite cemented by clear halite as well as normal graded and reverse graded glauberite textures are common this type of transparent glauberite is interpreted as a primary subaqueous precipitate gypsum thenardite or mirabilite are absent in the two associations the depositional environment is interpreted as a shallow perennial saline lake system in which chloride brines association a and sulphate chloride brines association b are developed the geochemical study of halite crystals bromine contents and fluid inclusion compositions demonstrates that conditions for co precipitation of halite and glauberite or for precipitation of na sulphates mirabilite thenardite were never fulfilled in the saline lake system

reinterpretation of seismic reflection data over the east pacific rise multichannel seismic reflection data over the axial region of the east pacific rise are depth migrated using detailed velocity information from laboratory measurements of ophiolite samples the data are from the lamont doherty geological observatory s line 17 shot across the rise at 9 sup 0 n the migrated data are interpreted to show the structure of the seafloor and what we believe is the magma chamber roof the polarity and apparent root mean squared velocity of the magma chamber roof are asymmetric with respect to the topographic axis of the ridge the asymmetry is probably real and not an artifact of data collection modeling of the magnetic data gathered along the line shows that spreading has not been proceeding normally a reasonable explanation for the asymmetry is the possibility that the line intersects a transform fault or an abandoned ridge segment near the ridge axis the shape of the roof reflection is convex upward with an approximate slope of 10 sup 0 and a width of 4 km if extrapolated symmetrically to the other side of the ridge axis the magma chamber roof event is consistent with the funnel shaped chamber proposed by pallister and hopson 1981 for the samail ophiolite if the chambermore roof steepens rapidly beyond the extent of the reflection it would be consistent with the mush filled model of sleep 1975 1978 and dewey and kidd 1977 less

crystallographic preferred orientation magnetic and seismic anisotropy in rocks from the finero peridotite ivrea verbano zone northern italy interplay of anisotropy contributions from different minerals abstract mineral alignment can provide valuable information on a rock s geological history many structural tectonic or geodynamic studies rely on determining the preferred orientation of rock forming minerals either by direct texture determination or using anisotropy measurements as proxies robust interpretations of anisotropy require detailed understanding of its relationship with texture this study investigates the texture magnetic and seismic anisotropies of ultramafic rocks from the ivrea verbano zone ivz northern italy with a special focus on the interplay between anisotropy contributions carried by different minerals texture was obtained from electron backscatter diffraction magnetic anisotropy from low and high field anisotropy of susceptibility measurements and seismic anisotropy from p and s wave velocities along the three principal directions of the macroscopic fabric using 22 mm diameter cores texture based models of magnetic anisotropy agree well with corresponding measurements larger variability is observed for seismic anisotropy possible explanations are 1 velocities were measured in three directions insufficient to determine the full elasticity tensor and 2 seismic anisotropy depends on grain boundaries pores and cracks in addition to crystallographic preferred orientation the contributions to magnetic and seismic anisotropy of each constituent mineral can interfere positively leading to a larger overall anisotropy or negatively resulting in a weaker anisotropy seismic anisotropy is mostly controlled by olivine whereas magnetic anisotropy can be dominated by olivine pyroxene or hornblende this study illustrates that although the relationship between texture and anisotropy can be complex it is possible to quantitatively predict magnetic and to a lesser degree seismic anisotropy from texture data even though both magnetic and seismic anisotropies are common proxies for texture they are not coaxial and no simple relationship between the degree of magnetic and seismic anisotropy was found these results underline the importance of understanding different minerals contributions to anisotropy in upper mantle rocks

heterogeneous deformation and quartz crystallographic fabric transitions natural examples from the moine thrust zone at the stack of glencoul northern assynt quartz crystallographic fabric transitions in well exposed mylonites immediately beneath the moine thrust at the stack of glencoul nw scotland have been investigated by optical microscopy x ray texture goniometry and orientation distribution function analysis a progressive change is observed from asymmetrical kinked single girdle c axis fabrics at 0 5 cm beneath the moine thrust through asymmetrical type i cross girdle fabrics to symmetrical type i cross girdle fabrics at 30 cm beneath the thrust this c axis fabric transition is accompanied by a transition from asymmetrical single a axis maximum fabrics 0 5 cm beneath the thrust through asymmetrical two maxima fabrics to essentially symmetrical two maxima a axis fabrics odf analysis of these s l and l s tectonites indicates that c axis positions on the leading edge of the fabric skeleton are related by a common a direction oriented within the xz plane at a moderate angle to the lineation x in contrast c axis positions on the peripheral trailing edge are related by a positive r rhomb pole oriented close to z a directions lying within this common rhomb plane progressively change through 180 in orientation traced around the c axis fabric skeleton such contrasting single crystal rhomb a preferred orientations on the leading and trailing edges of the fabric skeleton are interpreted as indicating localized grain scale plane strain and flattening deformation respectively they result in tectonites with essentially symmetrical c and a axis fabrics which display strongly asymmetrical positive r and negative z rhomb pole figures the observed transition in quartz c and a axis fabrics is interpreted as indicating an increasing importance of non coaxial plane strain deformation as the moine thrust is approached even immediately 1 cm beneath the thrust however flow has still significantly departed from bulk simple shear and involved an important heterogeneous component of contemporaneous flattening deformation

3d transient numerical flow simulation of groundwater bypass seepage at the dam site of dongzhuang hydro junction abstract hydrogeological conditions at the dongzhuang hydro junction site are complex and include underground water divides a hanging river and hydraulic drops along faults the site suffers from seepage because of its location in karst terrain this study addresses dam bypass leakage at the dongzhuang site and deficiencies in the regional groundwater seepage model a hydrological conceptual model is generated as well as a regional numerical simulation of groundwater flow based on analysis of the geology and hydrogeology of the dam site and surrounding area from the analysis a detailed 3d model of the groundwater flow field at the dam site is established in which permeability and precipitation infiltration parameters are corrected using the inversion method leakage quantities are calculated for three different conditions natural state regular dam impoundment with an impervious curtain and regular dam impoundment without an impervious curtain the results show that underground water flows from west to east during all three conditions the leakage quantity bypassing the dam region without anti seepage treatment is 220 000 m3 d with seepage concentrated around the dam foundation dam abutments and the river bend of the reservoir head leakage in these areas accounts for 72 of the total leakage in the study area however when an impervious curtain is included in the model the total leakage quantity is reduced to 51 000 m3 d and seepage concentrates along the banks of the reservoir the 3d numerical model of regional groundwater flow is promising in that it can simulate complex hydrogeological conditions and the accuracy and confidence levels improve when a detailed 3d model of groundwater flow at the dam site is added to the regional model

contribution of spectral coherency analysis and tracer test to study leakage at the doosti dam reservoir iran and turkmenistan the doosti dam was built across the harirood river on the border between turkmenistan and iran during the reservoir impounding leakage occurred as new springs through the sandstone layers of the pesteleigh aquifer and limy sandstone and limestone layers of the neyzar kalat aquifer at the right abutment of the dam to evaluate the grout curtain operation a tracer test was carried out by injection of uranine in a borehole located at the upstream of grout curtain in the pesteleigh aquifer tracer test results demonstrated a diffuse flow component through the grout curtain in the pesteleigh aquifer but no tracer was detected at the main leakage point sp1 spring emerged downstream of grout curtain from the neyzar kalat aquifer using the spectral coherency function the lag time between changes in the water level of the injection borehole and water level in the tracer detected boreholes or discharge of the tracer detected springs was determined linear regression analyses indicated that the estimated lag time by the time series analysis was close to the first arrival time of the tracer therefore the estimated velocities based on the lag time of time series could be considered close to the calculated velocities based on the first arrival time of the tracer the estimated groundwater velocities based on the time series analysis ranged from 3 91 to 20 31 m h 1 showed that diffuse flow dominated pathways from the reservoir toward the downstream boreholes in the neyzar kalat aquifer while conduit flow was present within the pathways toward the sp1 spring regarding the reservoir volume the negligible amount of leakage at the maximum water level of the reservoir confirmed well overall operation of the grout curtain at the dam site

variability of the rebound hardness as a proxy for detecting the levels of continuity and isotropy in archaeological quartz abstract the equotip hardness tester is applied to different types of quartz and other lithic raw materials in order to determine if variations in the rebound hardness measured by this device may serve as a proxy for detecting the levels of continuity and isotropy of toolstones continuity the amount of cracks and other internal defects and isotropy the measure of the directional properties of a raw material are known to have important effects on the level of consistency and predictability of fractures which in turn is traditionally considered a main factor for defining the flaking quality of a given raw material the results demonstrate the existence of differences among the raw materials analysed in both the average value and the variability of the rebound hardness while cryptocrystalline samples show the most homogeneous results quartz and metamorphic rocks display a comparatively higher variance in the specific case of quartz such variability seems to be mainly caused by the presence of internal planes and discontinuities while anisotropy although also active had played a comparatively modest role the results achieved by the equotip hardness tester suggest that this device could be successfully used for a basic or preliminary estimating of some of the physical and mechanical properties of stone raw materials therefore it is a potential index test for complementing other more accurate laboratory methods

thermal diffusivity of olivine single crystals and polycrystalline aggregates at ambient conditions a comparison 1 heat transfer is a key process for the mantle dynamics however analysis of experimental data on thermal transport properties of upper mantle materials highlights a large scatter of absolute values of thermal diffusivity in particular conduction of heat in single crystals is systematically higher than in polycrystalline samples here we present new thermal diffusivity measurements on san carlos olivine single crystals and mantle rocks at 300k measured components of the olivine thermal diffusivity tensor along the 100 010 and 001 directions are 2 73 1 70 and 2 49 mm 2 s 1 respectively measurements of thermal diffusivity of peridotites as a function of structural orientation show absolute values and anisotropy in good agreement with those predicted by petrophysical models based on the crystal preferred orientation of olivine and the above thermal diffusivity tensor this suggests that the upper mantle thermal diffusivity is up to 50 higher than indicated by previous measurements on mantle rocks

upward electrical discharges from thunderstorms blue jets gigantic jets cloud to cloud discharges and cloud to ground lightning are all electrical discharges from thunderclouds an analysis of numerical simulations and observations of these phenomena places them all in a unifying framework thunderstorms occasionally produce upward discharges called blue jets and gigantic jets that propagate out of the storm top towards or up to the ionosphere1 2 3 4 whereas the various types of intracloud and cloud to ground lightning are reasonably well understood the cause and nature of upward discharges remains a mystery here we present a combination of observational and modelling results that indicate two principal ways in which upward discharges can be produced the modelling indicates that blue jets occur as a result of electrical breakdown between the upper storm charge and the screening charge attracted to the cloud top they are predicted to occur 5 10 s or less after a cloud to ground or intracloud discharge produces a sudden charge imbalance in the storm an observation is presented of an upward discharge that supports this basic mechanism in contrast we find that gigantic jets begin as a normal intracloud discharge between dominant mid level charge and a screening depleted upper level charge that continues to propagate out of the top of the storm observational support for this mechanism comes from similarity with bolt from the blue discharges5 and from data on the polarity of gigantic jets6 we conclude that upward discharges are analogous to cloud to ground lightning our explanation provides a unifying view of how lightning escapes from a thundercloud

seismic structure of the southern east pacific rise seismic data from the ultrafast spreading 150 to 162 millimeters per year southern east pacific rise show that the rise axis is underlain by a thin less than 200 meters thick extrusive volcanic layer seismic layer 2a that thickens rapidly off axis also beneath the rise axis is a narrow less than 1 kilometer wide melt sill that is in some places less than 1000 meters below the sea floor the small dimensions of this molten body indicate that magma chamber size does not depend strongly on spreading rate as predicted by many ridge crest thermal models however the shallow depth of this body is consistent with an inverse correlation between magma chamber depth and spreading rate these observations indicate that the paradigm of ridge crest magma chambers as small sill like midcrustal bodies is applicable to a wide range of intermediate and fast spreading ridges

anisotropic effective medium modeling of the elastic properties of shales shales are complex porous materials normally consisting of percolating and interpenetrating fluid and solid phases the solid phase is generally comprised of several mineral components and forms an intricate and anisotropic microstructure the shape orientation and connection of the two phases control the anisotropic elastic properties of the composite solid we develop a theoretical framework that allows us to predict the effective elastic properties of shales its usefulness is demonstrated with numerical modeling and by comparison with established ultrasonic laboratory experiments the theory is based on a combination of anisotropic formulations of the self consistent sca and differential effective medium dem approximations this combination guarantees that both the fluid and solid phases percolate at all porosities our modeling of the elastic properties of shales proceeds in four steps first we consider the case of an aligned biconnected clay fluid composite composed of ellipsoidal inclusion

mechanical properties of quartz at the α β phase transition implications for tectonic and seismic anomalies 1 the anelastic response of single crystal and polycrystalline quartz and quartz rich sandstones to applied stress at low frequencies has been investigated by dynamic mechanical analysis and force torsion pendulum measurements the dynamic modulus was measured on heating and cooling through the phase transition under shear and bending stress applied at low frequency 1 hz single crystal quartz shows highly anisotropic properties in both the real and imaginary part of the modulus polycrystalline novaculite quartz displays the phase transition temperatures tc around 8 c higher than seen in single crystal quartz due to the pinning stress effect of grain boundaries the properties of the sandstone vary with heating and cooling cycles as the cementation and microfracturing of the grain structure changes at high temperature the phase transition in quartz is ferrobielastic and as such energy differences between domains in the transformation microstructure arise under conditions of applied shear stress pre transition softening and an increase in anelastic loss above tc are attributed to ferrobielastic switching of incipient domain microstructures that arise in the silica microstructure the influence of temperature on this microstructure is to induce increased switching of domains as a response to thermal stress inherent in the anisotropic thermal expansion of the polycrystalline structure these results indicate that ferrobielastic switching in quartz is an important mechanism in controlling changes in mechanical properties as such we anticipate that it will induce measurable anomalies in seismic signatures of quartz rich portions of the earth s crust in regions of high thermal flux the transition may also be responsible for observed seismic velocity reductions and tectonic weakening in western north america and in certain parts of tibetan plateau

dam sites in soluble rocks a model of increasing leakage by dissolutional widening of fractures beneath a dam abstract water flowing through narrow fissures and fractures in soluble rock e g limestone and gypsum widens these by chemical dissolution this process called karstification sculptures subterranean river systems which drain most of their catchment close to dam sites unnaturally high hydraulic gradients are present to drive the water impounded in the reservoir downstream through fractures reaching below the dam under such conditions the natural process of karstification is accelerated to such an extent that high leakage rates may arise which endanger the operation of the hydraulic structure model simulations of karstification below dams by coupling equations of dissolutional widening to hydrodynamic flow are presented the model scenario is a dam 100 m wide in limestone or gypsum the modelling domain is a two dimensional slice 1 m wide directed perpendicular to the dam it extends 375 m vertically and 750 m horizontally the dam is located in its center this domain is divided by fractures and fissures into blocks of 7 5 7 5 1 m the average aperture width of the fractures is 0 02 cm we performed model runs on standard scenarios for a dam site in limestone with the height h of impounded water 150 m a horizontal impermeable apron of width w 262 m and a grouting curtain reaching down to a depth of g 97 m in a second scenario we changed these construction features to g 187 m and w 82 m to calculate widening of the fractures well established experimental data on the dissolution of limestone and gypsum have been used as they occur in such geochemical settings all model runs show similar characteristic behaviour shortly after filling the reservoir exhibits a small leakage of about 0 01 m 3 s 1 which increases steadily until a breakthrough event occurs after several decades with an abrupt increase of leakage to about 1 m 3 s 1 within the short time of a few years then flow in the fractures becomes turbulent and the leakage increases to 10 m 3 s 1 in a further time span of about 10 years the widths of the fractures are visualized in various time steps small channels propagate downstream and leakage rises slowly until the first channel reaches the surface downstream then breakthrough occurs the laminar flow changes to turbulent and a dense net of fractures which carry flow is established we performed a sensitivity analysis on the dependence of breakthrough times on various parameters determining breakthrough these are the height of impounded water h the depth g of grouting the average aperture width a 0 of the fractures and the chemical parameters which are c eq the equilibrium concentration of ca with respect to calcite and the ca concentration c in of the inflowing water the results show that the most critical parameter is a 0 at fracture aperture widths of 0 01 cm breakthrough times are above 500 years for values of a 0 0 02 cm however breakthrough times are within the lifetime of the structure we have also modelled dam sites in gypsum which exhibit similar breakthrough times however after breakthrough owing to the much larger dissolution rates of gypsum the time until unbearable leakage is obtained is only a few years the modelling can be applied to complex geological settings as phreatic cave conduits below the dam or a complex stratigraphy with varying properties of the rock with respect to hydraulic conductivity and solubility a few examples are given in conclusion our results support the assumption that increasing leakage of dam sites may be caused by dissolutional widening of fractures

the nature of seismic reflections from deep crustal fault zones deep seismic reflection profiles have recorded reflections from ductile shear zones within the crystalline basement perhaps the best example is the consortium for continental reflection profiling cocorp wind river line in wyoming which shows the wind river thrust fault to be a strong reflector from the surface to depths of about 30 km to identify the physical properties responsible for the seismic reflections from fault zones we report measurements of compressional wave velocity and velocity anisotropy in mylonites recovered from exhumed ductile shear zones these rocks are characterized by extensive ductile deformation of plastic minerals brittle deformation of the more rigid minerals grain size reduction and development of a strong fabric average velocity and density were not found to change significantly and systematically between the mylonites and the adjacent undeformed rock seismic anisotropy of 7 or greater is present in several mylonites dependent upon their composition and fabric using our data on mylonite properties and models for the crustal structure near the wind river line we compute true amplitude synthetic reflection seismograms and compare them to true amplitude plots of the cocorp wind river reflection data when anisotropy and the finely laminated structure of the fault zone are considered our modeling indicates fairly strong reflections from mylonite zones in most cases we also show that elevated pore pressure in shear zones may produce strong reflections however a permeability of the order of 10 16 darcy is required to maintain sufficient pore pressure to produce a velocity anomaly in a fault zone which has long been inactive

seismic propagation across the east pacific rise finite difference experiments and implications for seismic tomography we use a full waveform acousto elastic finite difference technique to investigate seismic propagation across the east pacific rise at 9 30 n for a two dimensional velocity model based on that proposed by vera and others 1990 the primary feature of the model is an upper crustal low velocity region corresponding to the axial magma chamber which includes a small magma body located 1 6 km beneath the seafloor at the rise axis the high velocity gradients in this region result in a complex pattern of propagation which includes considerable scattering of energy above and below the magma chamber a qualitative comparison of finite difference seismograms with data collected by receivers located 9 km and 20 km off axis during a tomography experiment at 9 30 n shows generally good agreement for paths that cross the rise axis the first arrival in the finite difference solutions diffracts above the magma chamber this phase has a very low amplitude and at larger offsets falls below the ambient noise levels observed during the tomography experiment in such cases the first arrival with significant energy is a diffraction from below the magma chamber a high amplitude moho turning pmp phase which results from the large velocity change across the moho beneath the rise axis is apparent in both the finite difference solutions and the observations ray theoretical calculations of the paths of the diffracted arrivals are very unstable and for the diffractions above the magma chamber no solution can be found with a single precision algorithm synthetic delay time inversions using an approximate ray tracing algorithm demonstrate the importance of ensuring that picked arrival times are assigned to paths that pass to the correct side of the magma body synthetic inversions of spectral estimates of t show that q 1 models are compromised not only if the ray paths are incorrect but also if t estimates include significant contributions from more than one phase deterministic scattering from the magma chamber may contribute noticeably to spectral estimates of t but the results of the finite difference experiments imply that high levels of attenuation observed for phases passing below the magma chamber are predominantly the result of intrinsic attenuation

review on sinkhole monitoring and performance of remediation measures by high precision leveling and terrestrial laser scanner in the salt karst of the ebro valley spain abstract the need to apply sinkhole remediation and monitoring programs is increasing concurrently with the rising engineering impacts of sinkholes in many regions however there is a significant gap in the scientific literature regarding the assessment of the performance of remedial works through subsidence monitoring monitoring techniques have experienced significant advances in the last few years thanks to the advent of new technologies this work presents a review of sinkhole monitoring methods and discusses some practical considerations about their capabilities and limitations it also documents a monitoring program high precision leveling and terrestrial laser scanner and the concurrent remedial works cement based and polyurethane grouting carried out in a highly active sinkhole that affects a flood control dike and the adjacent village of alcala ne spain the subsidence activity in the sinkhole is characterised by progressive sagging and the development of catastrophic nested collapses monitoring data reveal subsidence expansion and acceleration in the sector of the dike treated by polyurethane grouting above the main cavities in contrast subsequent cement based grouting of the large cavities significantly reduced subsidence rates displacement data also indicate substantial subsidence enhancement following flood recession and the associated water table drop buoyancy loss this case study illustrates that high precision leveling and terrestrial laser scanning are adequate complementary methods for monitoring specific sinkholes characterised by very high accuracy and detailed spatial resolution respectively

polystage deformation of the gaoligong metamorphic zone structures 40ar 39ar mica ages and tectonic implications abstract the gaoligong metamorphic zone is located southeast of the eastern himalayan syntaxis in western yunnan china the zone is characterized by four stages of deformation d1 d4 d1 structures record early compressive deformation during the indosinian orogeny which formed tight to isoclinal f1 folds of bedding with a penetrative s1 foliation developed parallel to fold axial planes mid crustal horizontal shearing during d2 resulted in overprinting of d1 structures d1 and d2 structures are associated with granulite facies metamorphism d3 doming resulted in late crustal thickening and the development of a regional nw se trending f3 antiform synchronous with or slightly subsequent to d3 deformation the zone experienced d4 ductile strike slip shearing resulting in its exhumation to shallow crustal levels and retrograde metamorphism granitic d4 mylonites predominantly yield 40 ar 39 ar mica ages of 15 16 ma indicating that d4 dextral strike slip shearing occurred in the miocene weakly deformed leucogranite and protomylonite yield 40 ar 39 ar ages of 10 11 ma suggesting that ductile strike slip shearing continued to the late miocene the new 40 ar 39 ar data indicate that escape related deformation along the gaoligong strike slip shear zone occurred in the miocene in association with recent geophysical studies and on the basis of the structural crystal preferred orientation cpo and geochronological data presented in this paper we suggest that the gaoligong metamorphic zone formed in response to intracontinental transpression in the southeast of tibet characterized as intense deformation and metamorphism at middle upper crustal levels

identification of leakage and potential areas for internal erosion combining ert and ip techniques at the negratin dam left abutment granada southern spain abstract at the negratin dam southern spain two main springs derived from the water reservoir were detected on the west side of the mountain ridge matching the location of the left abutment of the dam the seepages appear when the level of the stored water exceeds 622 m above sea level m a s l where some paleochannels are embedded in the silts the water level was at 631 m a s l on the day of the measurements 13 12 23 close to the historical maximum 633 78 m a s l although the water crossing the leaks does not drag particles nowadays this sector may potentially cause internal erosion or piping phenomena implying a loss of water resources and slope instability problems the infiltration areas were evaluated by electrical resistivity and induced polarization methods measured along one profile on the mountain ridge between the water reservoir and the springs we determine that the infiltrations zones are characterized by low resistivity and high chargeability distributed in small areas we demonstrate that these methods are a reliable tool to detect and characterize infiltration zones and they are the first step to planning mitigation actions to avoid the piping phenomena

causes of the catastrophic failure of an earth dam built on gypsiferous alluvium and dispersive clays altorricon huesca province ne spain this paper analyses the causes of the catastrophic failure of an earth dam that took place on 21 january 2001 during the first filling test in the ne of spain altorricon village huesca province the san juan reservoir with a capacity of 850 000 m3 was built in 1999 on gypsiferous mantled pediment deposits overlying tertiary dispersive clay sediments the basin of the reservoir was excavated in the alluvial cover and tertiary bedrock an earth dam was constructed on the pediment surface along the perimeter of the artificial basin the dam has a core of compacted clay material derived from the excavation which is indented 1 m in the tertiary shales of the bedrock cutting the highly pervious alluvial mantle field observations analysis of the basin and dam materials and eyewitnesses accounts have helped to infer the processes involved in the failure of the earth dam these processes include 1 subsidence and ravelling suffosion processes induced by the dissolution of the 4 m thick detrital cover with a gypsum content of around 40 2 piping processes affecting the embankments and core of the dam built with dispersive clays that have high exchangeable sodium percentage esp and show active pipes and 3 water circulation through biogenic burrows in the pediment deposits this case study demonstrates the frequently hidden limitations that evaporite sediments and dispersive clay materials pose to the construction of dams it also shows that highly permeable surficial deposits should be stripped before the construction of the dam structure

reflection characteristics of a mylonite zone based on compressional wave velocities of rock samples summary a combined field and laboratory study of the seismic reflection response and seismic properties of the mylonite zone capping the kettle dome metamorphic core complex provides important constraints on reflectivity of mylonites because of its structural and petrologic characteristics this mylonite zone can be regarded as a model for mid to deep crustal mylonite zones cdp reflection profiling revealed that the mylonite zone is reflective laboratory measurements of compressional wave velocities v at high confining pressures in samples collected directly up dip from the cdp reflection line revealed a wide variation of v in common mid crustal lithologies mafic and carbonate rock mean v values range from 6 67 to 7 31 km s at 600 mpa and quartzite and quartzo feldspathic values range from 6 16 to 6 52 km s seismic anisotropy at low pressures can be related to open microcracks and preferred mineral orientation whereas the latter effect controls anisotropy at high pressures the laboratory data provide the basis for a seismic model which indicates that the kettle dome mylonite zone can generate reflections from zones where high and low velocity lithologies are interlayered these reflections correlate with those observed on the cdp data thus demonstrating that the reflectivity of the mylonite zone is a direct result of its lithologic diversity and layered nature in this case it is not necessary to explain the reflections by the effects of anisotropy retrogression high pore pressure or constructive interference

a thermodynamic kinematic and microphysical analysis of a jet and gigantic jet producing florida thunderstorm this paper presents a meteorological analysis of a storm that produced two jets four gigantic jets gj and a starter which were observed by two radars as well as the kennedy space center 4 dimensional lightning surveillance system on 3 august 2013 in central florida the work is the first application of dual polarization data to a jet producing storm and is the fifth case related to a tropical disturbance the storm environment is consistent with the moist tropical paradigm that characterizes about three quarters of the surface and aircraft observed jet and gj events the most unstable mu convective available potential energy is not unusual for florida summer convection and is below the climatological mean for these events an unusual speed shear layer is located near the storm equilibrium level el and the storm exhibits a tilted structure with cgs displaced upshear the turbulence as measured by the eddy dissipation rate is extreme near the storm top during the event window consistent with the gj mixing hypothesis the individual events are collocated with and track along the center axis of the divergent outflow at the el and occur within the region of the coldest goes ir temperatures placing the events within the overshoot the dual polarization data indicate a deep graupel column extending above the mixed phase layer to a 13 km altitude

blue starters brief upward discharges from an intense arkansas thunderstorm this paper documents the first observations of a new stratospheric electrical phenomenon associated with thunderstorms on the night of 30 june ut 1 july 1994 30 examples of these events which we have called blue starters were observed in a 6 m 44 s interval above the very energetic arkansas thunderstorm where blue jets were first observed the blue starters are distinguished from blue jets by a much lower terminal altitude they are bright and blue in color and protrude upward from the cloud top 17 18 km to a maximum 25 5 km 83 655 ft in altitude all blue starters events were recorded from two small areas near texarkana texas arkansas where hail 7 0 cm in diameter was falling comparison to cloud to ground cg lightning flashes revealed 1 blue starters were not observed to be coincident with either positive or negative cg flashes but they do occur in the same general area as negative cg flashes 2 cumulative distributions of the negative cg flashes in 5 s before and after the starter and within a radius of 50 km shows a significant reduction for about 3 s following the event in the two cells where starters and jets were observed the energy deficit is approximately 109 j it is possible that blue starters are a short lived streamer phenomenon

the origin typology spatial distribution and detrimental effects of the sinkholes developed in the alluvial evaporite karst of the ebro river valley downstream of zaragoza city ne spain three types of sinkhole have been mapped in a 50 km2 stretch of the ebro river valley downstream of zaragoza large collapse sinkholes large shallow subsidence depressions and small cover collapse sinkholes the sinkholes relate to the karstification of evaporitic bedrock that wedges out abruptly downstream giving way to a shale substratum twenty three collapse sinkholes up to 50 m in diameter by 6 m deep and commonly hosting saline ponds have been identified in the floodplain they have been attributed to the upward stoping of dissolutional cavities formed within the evaporitic bedrock by rising groundwater flows twenty four large shallow subsidence depressions were mapped in the floodplain these may reach 850 m in length and were formed by structurally controlled interstratal karstification of soluble beds halite or glauberite and gypsum by rising groundwater flow and the progressive settlement of the overlying bedrock and overburden sediments a total of 447 small cover collapse or dropout sinkholes have been recognized in a perched alluvial level along the southern margin of the valley these sinkholes result from the upward propagation of voids through the alluvial mantle caused by the downward migration of detrital sediments into dissolutional voids the majority of these sinkholes commonly 1 5 2 m in diameter are induced by human activities over the karstic bedrock there is a significant increase in sinkhole density downstream this is interpreted as being a result of the evaporitic bedrock wedging out and the convergence of the groundwater flow lines in the karstic aquifer the collapse sinkholes in this area locally with a probability of occurrence higher than 140 sinkholes km2 year cause substantial damage to the linear infrastructures buildings and agriculture and they might eventually cause the loss of human lives copyright 2006 john wiley sons ltd

large depressions thickened terraces and gravitational deformation in the ebro river valley zaragoza area ne spain evidence of glauberite and halite interstratal karstification abstract in the studied reach of the ebro valley the terrace and pediment sediments deposited over glauberite and halite bearing evaporites show local thickenings 50 m recording dissolution induced synsedimentary subsidence recent data on the lithostratigraphy of the evaporite sequence allow relating the alluvium thickenings with either halite or glauberite dissolution the alluvium filled dissolution basin underlying the youngest terraces t8 t11 is ascribed to halite karstification the top of a halite unit approximately 75 m thick is situated 40 15 m below the valley bottom the thickenings of terrace t1 t7 and pediment sediments are attributed to interstratal glauberite karstification 1 coincidence between the elevation range of the terraces and that of the glauberite rich unit glauberite beds reach 30 and 100 m in single bed and cumulative thickness respectively 2 the exposed bedrock underlying thickened alluvium shows abundant subsidence features indicative of interstratal karstification the most common structure corresponds to hectometer scale sag basins with superimposed collapses in the central sector of each basin the subsided bedrock is frequently transformed into dissolution collapse breccias showing a complete textural gradation from crackle packbreccias to chaotic floatbreccias and karstic residues 3 paleokarst exposures show evidence of karstification confined to specific beds made up of secondary gypsum after precursory glauberite partly dissolved and partly replaced despite the magnitude of the subsidence recorded by the thickened alluvium and unlike nearby tributaries the terraces show a continuous and parallel arrangement indicating that the fluvial system was able to counterbalance subsidence by aggradation a number of kilometer size flat bottom depressions have been developed in the valley margin typically next to and inset into thickened terrace and pediment deposits the subsidence structures exposed in artificial excavations excavated in the bottom of some depressions and the correlation between the altitudinal distribution of these basins and that of the glauberite rich unit reveal that subsidence related to interstratal glauberite karstification is the main process involved in their genesis this research ascribes for the first time the thickenings and deformation of specific terrace levels and pediment levels and the development of large karstic depressions to interstratal karstification of exceptionally thick glauberite units

the structure of mid ocean ridges recent research results on the structure of midocean ridges are reviewed the new view of ridge axis crustal structure obtained from high resolution seismology is reviewed emphasizing the variation of that structure with spreading rate and along axis at a given spreading rate recent results on upper mantle structure beneath ridges are examined including variations with seafloor age indications from anisotropy for directions of mantle flow and long wavelength along axis variations in structure and their implications for lateral heterogeneity in mantle temperature and composition

local atomic structure of fontainebleau sandstone evidence for an amorphous phase 1 rocks are traditionally viewed as crystallite aggregates in general the treatment of the composition and mechanical properties never includes solid non crystalline components such glass like materials are difficult to detect in small quantities by standard techniques e g thin section polarimetry x ray diffraction but if they exist at critical locations i e grain contacts they could affect the behavior of rocks considerably neutron scattering measurements on a solid sample of fontainebleau sandstone have shown clear evidence for the presence of an unexpected glass like component atomic pair distribution function pdf analysis shows significant local structural deviations from pure quartz these deviations appear as an excess of 5 10 of nearest neighbor nn si o and o o bonds which is consistent with a 5 10 volume fraction of vitreous silica these measurements may provide significant information about the still unexplained causes for the peculiar mechanics and dynamics of sedimentary rocks

seismic evidence for a crustal magma reservoir beneath the upper east rift zone of kilauea volcano hawaii an anomalous body with low vp compressional wave velocity low vs shear wave velocity and high vp vs anomalies is observed at 8 11 km depth beneath the upper east rift zone of kilauea volcano in hawaii by simultaneous inversion of seismic velocity structure and earthquake locations we interpret this body to be a crustal magma reservoir beneath the volcanic pile similar to those widely recognized beneath mid ocean ridge volcanoes combined seismic velocity and petrophysical models suggest the presence of 10 melt in a cumulate magma mush this reservoir could have supplied the magma that intruded into the deep section of the east rift zone and caused its rapid expansion following the 1975 m7 2 kalapana earthquake

anticipating and managing engineering problems in the complex karst environment karst environments are characterized by distinctive landforms and a peculiar hydrologic behavior dominated by subsurface drainage karst systems can be extremely complex heterogeneous and unpredictable due to the wide range of geological and hydrological controlling factors the great variability results in serious problems for engineers and in difficulties to characterize the karstified rock masses and in designing the engineering works to be performed the design and development of engineering projects in karst environments require specific approaches aimed at minimizing the detrimental effects of hazardous processes and environmental problems further karst aquifers that provide approximately 20 25 of the world s drinking water are extremely vulnerable to pollution due to the direct connection between the surface and the subsurface drainage the rapidity of the water flow in conduit networks and the very low depuration capability sinkholes are the main source of engineering problems in karst environments and may cause severe damage in any human structure the strategies and solutions that may be applied to mitigate sinkhole problems are highly variable and largely depend on the kind of engineering structure the karst setting and the typology and size of the sinkholes a sound geological model properly considering the peculiarities of karst and its interactions with the human environment is essential for the design of cost effective and successful risk reduction programs due to the unique direct interaction between surface and subsurface environments and the frequent ground instability problems related to underground karstification management of karst environments is a very delicate matter disregarding such circumstances in land use planning and development inevitably results in severe problems with high economic impacts karst environments require specific investigation methods in order to properly manage and safeguard the sensitive geo ecosystems and natural resources associated with them

consistent modeling of the electrical and elastic properties of sedimentary rocks an effective medium theory is formulated which reproduces many of the observed electrical and elastic characteristics of sedimentary rocks within a unified framework the effective medium consists of fluid solid and cement components with the component material properties related to those of the composite through a differential effective medium dem scheme the resulting microstructure of the composite both conducts electricity through the fluid phase and supports shear besides deriving archie s law the theory gives an excellent account of the shear wave and compressional wave velocity correlations and predicts corrections to the wyllie equation that are consistent with observed deviations the three component dem also accommodates clay conductivity and finite frequency dielectric behavior

the seismic attenuation structure of a fast spreading mid ocean ridge the two dimensional p wave attenuation structure of the axial crust of the east pacific rise was obtained from an inversion of waveform spectra collected during an active source seismic tomography experiment the structure shows that attenuation near the surface is high everywhere but decreases markedly within 1 to 3 kilometers of the rise axis the near axis variation is attributed to the thickening of the surface basalt layer and possibly to in situ changes in porosity related to hydrothermal circulation high attenuation is also observed beneath the rise axis at depths ranging from about 2 kilometers less than 1 kilometer beneath the axial magma lens to the base of the crust the levels of attenuation in this deeper region require at most only a small fraction of partial melt

representing anisotropic subduction zones with isotropic velocity models a characterization of the problem and some steps on a possible path forward despite the widely known fact that mantle flow in and around subduction zones produces the development of considerable seismic anisotropy most p wave tomography efforts still rely on the assumption of isotropy in this study we explore the potential effects of erroneous assumption on tomographic images and explore an alternative approach we conduct a series of synthetic tomography tests based on a geodynamic simulation of subduction and rollback the simulation results provide a self consistent distribution of isotropic thermal anomalies and seismic anisotropy which we use to calculate synthetic delay times for a number of realistic and hypothetical event distributions we find that anisotropy induced artifacts are abundant and significant for teleseismic local and mixed event distributions the occurrence of artifacts is not reduced and indeed can be exacerbated by increasing richness in ray path azimuths and incidence angles the artifacts that we observe are in all cases important enough to significantly impact the interpretation of the images we test an approach based on prescribing the anisotropy field as an a priori constraint and find that even coarse approximations to the true anisotropy field produce useful results using approximate anisotropy fields can result in reduced rms misfit to the travel time delays and reduced abundance and severity of imaging artifacts we propose that the use of anisotropy fields derived from geodynamic modeling and constrained by seismic observables may constitute a viable alternative to isotropic tomography that does not require the inversion for anisotropy parameters in each node of the model

seismic analysis of the axial magma chamber reflector along the southern east pacific rise from conventional reflection profiling the thickness and internal properties of the magma sill located at the top of the axial magma chamber amc along the southern east pacific rise epr have been investigated through a combination of waveform modeling the near vertical incidence reflections from this body and analysis of reflection amplitude variation as a function of source receiver offset or slowness our results show that the amc reflector observed along the southern epr is best modeled by a thin 100 m thick sill of partial melt vs 0 km s sandwiched between higher velocity material and that the thickest sills are generally associated with the lowest p and s wave velocities the comparatively high p wave velocities and nonzero shear wave velocities inferred for this sill indicate that it is filled with partially molten magma which in some locations has a high crystal content this may have important implications for eruption mechanisms and along axis mixing of magma at the epr there is no simple relationship between morphologic indicators of magma supply e g axial depth or volume and sill thickness depth or velocity magma sill properties may be closely tied to the eruption and replenishment cycle of the amc and thus may vary on a much shorter spatial and temporal scale than axial morphology which reflects longer term variations in magma supply to the ridge

an illustration of the advantages of a complete texture analysis described by the orientation distribution function odf using quartz pole figure data abstract the preferred orientation of eight crystal directions of quartz was measured with an x ray texture goniometer for selected quartz bearing tectonites with a clear pattern of c axis preferred orientation the advantages of data analysis by means of calculations of the orientation distribution function and other forms of data presentation derived from the odf are demonstrated

defect microdynamics in minerals and solid state mechanisms of seismic wave attenuation and velocity dispersion in the mantle the propagation of seismic waves in the earth s mantle can be significantly affected by relaxation processes causing attenuation and velocity dispersion reduction this paper reviews the solid state mechanisms of relaxation processes based on the theory of defect microdynamics in solids together with some experimental observations on defects in minerals particularly in olivine for a given mechanism to have a significant effect on seismic wave propagation both the density and the mobility of the defects must be in an appropriate range the examination of the densities and geometry and mobilities of defects in olivine shows that dislocation and or grain boundary mechanisms can have a significant effect on seismic wave propagation although wide distributions of geometrical factors such as spacing of pinning points and of mobilities are required to explain all available data point defect mechanisms however are unlikely to be important because their densities are too small and or their mobilities are too large since the dislocation density and or grain size are determined in most cases by the long term tectonic stress seismic wave attenuation and velocity dispersion reduction involving these defects are likely to depend on the magnitude of the tectonic stress as well as the temperature theoretical considerations suggest a wide range of dependence of seismic wave attentuation and velocity dispersion on the long term tectonic stress this is particularly the case for dislocation mechanisms and warrants careful experimental investigation dislocations and or grain boundaries cause anelastic behavior relaxation peaks when they are pinned or blocked at some points pinning or blocking becomes ineffective at high temperatures and or low frequencies causing a transition to viscoelastic behavior both laboratory and seismological observations of internal friction are dominated by the high temperature background where internal friction increases monotonically with temperature which can be interpreted as a gradual transition to viscoelastic behavior or to a wide distribution of relaxation times however in most experimental studies to date the dislocation densities or the grain sizes were not well controlled making it difficult to identify the attenuation mechanisms and preventing any quantitative applications to earth the need for better characterization of defect microstructures in experimental specimens is emphasized

the calculated seismic properties of quartz mylonites with typical fabrics relationship to kinematics and temperature summary quartz mylonites produced by intense ductile deformation in shear zones are often invoked as seismic reflectors in the lower continental crust the seismic properties vp vsl v av and polarization planes of v and v have been calculated for five quartz mylonites that display typical lattice preferred orientations lpos all specimens display considerable seismic anisotropy with v anisotropy coefficients of between 8 and 12 per cent there are good correlations between the lpo of the a axes and the minimum v direction and the c axes and the maximum v direction the other seismic properties are not reliable indicators of lpo as the a axis is the major flow direction in quartz a correlation between the ductile flow direction and the v minimum can be made with increasing temperature and pressure alpha quartz transforms to beta quartz in the beta field quartzites are seismically transverse isotropic furthermore there is a considerable increase in v from 6 km s l in the alpha field to nearly 7 km s in the beta field the transition is instantaneous and hence will result in a sharp seismic discontinuity with a reflection coefficient of 0 08 between pure aggregates of alpha and beta phases however under typical conditions of the continental crust the seismological importance of this phase transition will be limited by the presence of secondary minerals and partial melting

photographic and lightning mapping observations of a blue starter over a new mexico thunderstorm 1 on 4 august 2010 a small blue starter was observed over an active thunderstorm in west central new mexico the storm was of normal polarity with upper positive charge over midlevel negative charge the event was visually observed and photographed and mapped by the lightning mapping array lma at langmuir laboratory the blue starter occurred during a seven stroke negative cloud to ground cg flash that was detected by the national lightning detection network nldn and data from the lma show that it initiated between upper positive charge and inferred negative screening charge at the cloud top upward positive streamers of the blue starter emerged from the cloud top at 15 2 km altitude and reached a terminal altitude of 17 km the observation confirms that blue starters can be initiated by the electric field changes associated with cg flashes which enhance the electric field between upper positive charge and negative screening charge it also confirms that the upward leaders and streamers of blue starters in normal polarity storms are of positive polarity

absorption band q model for the earth body wave surface wave and normal mode data are used to place constraints on the frequency dependence of q in the mantle with a simple absorption band model it is possible to satisfy the shear sensitive data over a broad frequency range the quality factor qs is proportional to in the band and to and 1 at higher and lower frequencies respectively as appropriate for a relaxation mechanism with a spectrum of relaxation times the parameters of the band are q min 80 0 15 and width 5 decades the center of the band varies from 101 seconds in the upper mantle to 1 6 103 seconds in the lower mantle the shift of the band with depth is consistent with the expected effects of temperature pressure and stress high qs regions of the mantle are attributed to a shift of the absorption band to longer periods to satisfy the gravest fundamental spheroidal modes and the scs data the absorption band must shift back into the short period seismic band at the base of the mantle this may be due to a high temperature gradient or high shear stresses a preliminary attempt is also made to specify bulk dissipation in the mantle and core specific features of the absorption band model are low q in the body wave band at both the top and the base of the mantle low q for long period body waves in the outer core an inner core qs that increases with period and low qp qs at short periods in the middle mantle the short period qs increases rapidly at 400 km and is relatively constant from this depth to 2400 km the deformational q of the earth at a period of 14 months is predicted to be 463

experimental evidence of transformation plasticity in silicates minimum of creep strength in quartz abstract mechanical weakening due to solid state transformation of mineral phases has long been proposed to be a significant mechanism for localization of deformation in the earth s lithosphere and the mantle transition zone however experimental observations confirming such a proposition are lacking here we present a novel approach to prove the existence of a minimum in the creep strength of quartz at the transition by observing the deformation of fluid inclusions in a quartz crystal using a hydrothermal diamond anvil cell pressure differences required for permanent deformation of the quartz around fluid inclusions were significantly lower at the phase transition than in either the stability fields of or quartz these results indicate that transformation plasticity of silicates can indeed cause a considerable localized reduction in the strength of the earth s crust and mantle

development of shape and lattice preferred orientations application to the seismic anisotropy of the lower crust abstract we review the physical basis of the development of fabrics in plastic and viscous flow and illustrate the typical fabrics formed by these processes in the main rock forming silicates of the lower crust feldspar quartz pyroxene and amphibole the orientation process in plastic deformation where a single slip is dominant is recalled and the role of the constraint of neighbouring grains is emphasized the fabric development of anisometric crystals in viscous flow is discussed as a function of the main controlling parameters shear strain aspect ratio and interference between crystals the same sense of fabric asymmetry is introduced by plastic and viscous flow between the flow plane and the shape preferred orientation and hence coherent kinematic analysis can be undertaken in both modes of flow in order to assess the role of such fabrics in the seismic laminations of the lower continental crust we have calculated the seismic p wave properties of typical fabrics for hypothetical monomineralic and polymineralic rocks the calculations show that the strongest anisotropies develop in monomineralic rock with values between 5 and 16 compared with 5 and 8 for typical rock compositions the strongest anisotropies for layered monomineralic rocks generated by fabrics is only 6 compared to the 14 suggested by model studies of the observed seismic laminations we suggest that other effects such as compositional layering and or constructive interference of seismic waves are responsible for augmenting the apparent anisotropy

sinkholes in the salt bearing evaporite karst of the ebro river valley upstream of zaragoza city ne spain geomorphological mapping and analysis as a basis for risk management abstract a detailed sinkhole map has been produced in a stretch of the ebro valley 40 8 km2 including the western sector of zaragoza city ne spain during the last few decades around 70 of the original sinkhole area has been filled with anthropogenic sediments causing the disappearance of 137 ha of wetlands the interstratal karstification of salts halite and glauberite and a wnw ese trending joint set have played a major control in the development of sinkholes three morphometric types of sinkholes have been differentiated each attributed to a specific subsidence mechanism inferred from the paleosinkholes exposed in the surrounding of zaragoza city sagging of bedrock and cover collapse of bedrock and cover and collapse of cover material related to the downward migration of particles through dissolutional conduits each type of sinkhole is characterised by a distinctive behaviour in terms of controlling factors spatio temporal distribution and kinematics and consequently the proposed differentiation may have a practical utility the vast majority of the subsidence damage identified in the area occurs within the boundaries of pre existing sinkholes identifiable in old aerial photographs and topographical maps this fact demonstrates that the application of preventive planning strategies based on detailed geomorphological maps would have allowed avoidance of most of the large financial losses caused by subsidence in the area of the order of hundreds of thousands of euros per year

preferred orientation of phyllosilicates in phyllonites and ultramylonites abstract x ray texture goniometry operated in the transmission mode has been applied to fine grained phyllosilicate rich sc mylonites from the santa rosa mylonite zone california the whipple mountains core complex california and the austroalpine nappes of the eastern alps austria basal planes 001 phyllosilicate pole figures depart in two respects from orthorhombic symmetry a the maximum pole density deviates from the pole to the mylonitic foliation and lies along a great circle which is normal to the foliation and contains the mylonitic lineation and b the contours of equal pole density are more widely spaced on one side of the 001 maximum than on the other measured along the mylonitic lineation optical microscopy reveals s and c surfaces and sets of shear bands sb characteristic of non coaxial deformation the pole figures are used for two purposes a the first is strain estimation after the march model by imposing orthorhombic symmetry the resulting march strains are more or less the same in all californian samples this is interpreted as evidence for a steady state foliation b the second is shear sense determination it is demonstrated that consistently asymmetric preferred orientations reflect structures which are typical of non coaxial deformation it is concluded that x ray analysis of phyllosilicate rich mylonites can in addition to providing an estimate of total strain give information about deformation regime and shear sense furthermore the study documents the heterogeneous nature of deformation on macroscopic and microscopic scales and the importance of non coaxial deformation in accommodating large strains

rapid subsidence in damaging sinkholes measurement by high precision leveling and the role of salt dissolution abstract investigations dealing with subsidence monitoring in active sinkholes are very scarce especially when compared with other ground instability phenomena like landslides this is largely related to the catastrophic behaviour that typifies most sinkholes in carbonate karst areas active subsidence in five sinkholes up to ca 500 m across has been quantitatively characterised by means of high precision differential leveling the sinkholes occur on poorly indurated alluvium underlain by salt bearing evaporites and cause severe damage on various human structures the leveling data have provided accurate information on multiple features of the subsidence phenomena with practical implications 1 precise location of the vaguely defined edges of the subsidence zones and their spatial relationships with surveyed surface deformation features 2 spatial deformation patterns and relative contribution of subsidence mechanisms sagging versus collapse 3 accurate subsidence rates and their spatial variability with maximum and mean vertical displacement rates ranging from 1 0 to 11 8 cm yr and 1 9 to 26 1 cm yr respectively 4 identification of sinkholes that experience continuous subsidence at constant rates or with significant temporal changes and 5 rates of volumetric surface changes as an approximation to rates of dissolution induced volumetric depletion in the subsurface reaching as much as 10 900 m3 yr in the largest sinkhole the high subsidence rates as well as the annual volumetric changes are attributed to rapid dissolution of high solubility salts

rapid mantle flow beneath the tonga volcanic arc abstract flow in the earth s asthenospheric mantle is typically assumed to be driven by motions of the overlying and adjacent plates suggesting flow rates comparable to plate velocities however arc parallel shear wave splitting and geochemical observations imply along strike flow in the lau basin presenting a challenge to geodynamic models of plate driven subduction systems as plate driven flow models predict arc perpendicular fast direction with simple a type mineral texturing although b type mineral texturing would result in the fast directions developing 90 relative to a type and likely occurs in the forearc mantle such texturing is unlikely in the asthenosphere wedge where higher temperatures and weak rheology likely prevail by tracking mineral texturing development within geodynamic flow models patterned after the tongan system in the lau basin that include along strike flow we find that the observations are best explained by models including rapid along arc flow within the subarc mantle the effect of melt on the anisotropy does not appear to be a primary control but needs to be investigated more fully the best fit to the observations is a model with along strike flow within a low viscosity channel beneath the arc at a rate of nearly 50 cm yr several times the plate motion velocities

3d seismic study of a ductile shear zone from laboratory and petrofabric data saint barthelemy massif northern pyrenees france in order to constrain interpretations of seismic reflection records more effectively the seismic properties of a middle crustal section exposed in the saint barthelemy massif have been determined the massif transected by a 200 m thick shear zone has been systematically sampled for density measurements and modal analysis has been performed in order to define the spatial variations of physical properties seismic velocities vp v5 shear wave birefringence have been measured on five representative samples to 600 mpa and 600 c simultaneously in the three structural directions x y and z for two samples the expep mental data have been compared with calculated values based on petrofabric analyses the lattice preferred orientation lpo is determined using universal stage electron channelling microscopy and neutron diffraction goniometry using the experimental and calculated velocity data we establish a lateral homogeneous anisotropie model

variations in axial magma lens properties along the east pacific rise 9 30 n 10 00 n from swath 3 d seismic imaging and 1 d waveform inversion we use three dimensional multistreamer seismic reflection data to investigate variations in axial magma lens aml physical properties along the east pacific rise between 9 30 n and 10 00 n using partial offset stacks of p and s converted waves reflecting off the top of the aml we image four 2 4 km long melt rich sections spaced 5 10 km from each other one dimensional waveform inversion indicates that the aml in a melt rich section is best modeled with a low vp 2 95 3 23 km s and vs 0 3 1 5 km s indicating 70 melt fraction in contrast the aml in a melt poor section requires higher vp 4 52 4 82 km s and vs 2 0 3 0 km s which indicates 40 melt fraction the thicknesses of the aml are constrained to be 8 32 m and 8 120 m at the melt rich and poor sites respectively based on the aml melt mush segmentation imaged in the area around the 2005 2006 eruption we infer that the main source of this eruption was a 5 km long section of the aml between 9 48 n and 51 n the eruption drained most of the melt in this section of the aml leaving behind a large fraction of connected crystals we estimate that during the 2005 2006 eruption a total magma volume of 9 83 106 m3 was extracted from the aml with a maximum of 71 106 m3 left unerupted in the crust as dikes from this we conclude that an eruption of similar dimensions to the 2005 2006 one would be needed with a frequency of years to decades in order to sustain the long term average seafloor spreading rate at this location

effect of crystal preferred orientations on the thermal diffusivity of quartz polycrystalline aggregates at high temperature article i nfo thermal diffusivity of synthetic quartz single crystals and natural polycrystalline aggregates were measured using a modified angstrom method at ambient pressure and up to 800 c in order to investigate the effect of crystal preferred orientation on thermal diffusivityof quartz rich rocks the thermal diffusivitytensorof quartz was determined by measuring the thermal diffusivity of an oriented synthetic quartz single crystal along the 100 and 001 directions a naturally deformed fine grained quartzite mylonite was used to compare the single crystalproperties with aggregate properties using thecrystal preferred orientations cpo measuredby the electron back scattered diffraction ebsd method and the measured thermal diffusivity tensor of quartz the three dimensional aggregate thermal diffusivity was modelled using volume averaging models in order to test the validity of these models that are only based on the properties of the constituent minerals the thermal diffusivity was then measured on oriented cores as a function of temperature along three orthogonal directions parallel to the x lineation y z pole to foliation structural frame both modelled and direct measurement of thermal diffusivity show an anisotropy of thermal diffusivity heat transport being more effective parallel to y direction and less effective parallel to the lineation x direction thermal diffusivities measured in a given direction on the natural rock are lower by less than 10 than the modelled thermal diffusivity in the same direction showing that rock imperfections have a weak effect on heat transport in addition the modelled thermal diffusivity anisotropy based on the characterization of crystal orientations and thermal diffusivity tensor shows a good agreement with measurements in both and stability field this validation of the petrophysical simulation allows for evaluating the 3d thermal diffusivity of quartz rich rocks in different crustal conditions the 3d thermal diffusivity of five naturally deformed quartzites displaying quartz fabrics expected in different crustal pressure and temperature ranges were simulated the resulting thermal diffusivity anisotropies of quartzites range between 40 and 10 depending on temperature crystallographic fabric patterns and fabric strength under crustal conditions quartzites deformed in the granulite facies display a high thermal diffusivity in the xz foliation plane whereas quartzites deformed in greenschist facies have highest thermal diffusivity in the z direction normal to the foliation plane

high temperature experiments on the elastic and anelastic behaviour of magmatic rocks measurements of the complex shear modulus have been performed on various ultrabasic and basic rocks dunite peridotite gabbro and basalts and a synthetic forsterite at temperatures between 600 and 1500 c depending on the sample material and in the frequency range from 0 003 to 30 hz under forced torsional oscillations the maximum shear stress was 0 3 mpa and the strains were of the order 5 10 6 to 5 10 5 measurements of the electrical resistivity as a function of temperature have been carried out together with the mechanical experiments to indicate the beginning of partial melting the absolute values of the shear modulus below tm are comparable with the results of other authors the onset of melting shows up in a rapid decrease of both shear modulus and electrical resistivity at high temperatures t 0 8 tm the absorption factor q 1 follows a power law q 1 exp a rt with 0 15 0 30 and a between 100 and 200 kj mol 1 towards lower temperatures this high temperature background is superimposed by a flat absorption peak which shifts from high to low frequencies with falling temperature this peak can often be described by a lognormal distribution of simple relaxation processes with a standard deviation of about three and a mean relaxation time exp a rt with a 400 600 kj mol 1 above tm a third contribution to q 1 is observed that can be regarded as independent of frequency between 1 and 30 hz this last component which contributes 50 to the total absorption is attributed to the melt phase in the samples an explanation for the high temperature background and the peak is proposed which is based on the relaxation of pinned dislocation lines by some coupling mechanism via the reorganisation of the stress field with increasing deformation this process may be responsible for both features at very high temperatures and low frequencies a small influence of steady state flow on q 1 is observed and below t 0 6 tm thermal cracking or thermoelastic losses may contribute to q 1 the influence of lithostatic pressure on q 1 is estimated and the extrapolation of the experimental data to the p t conditions of the uppermost mantle are in good agreement with published earth models an attempt is made to establish a general q t relationship from the experimental data

microscopic evidence of stishovite generated in low pressure shock experiments on porous sandstone constraints on its genesis it has been almost exactly half a century since the first synthesis of stishovite in shock experiments on quartz was reported but its formation conditions during shock is still under debate here we present direct transmission electron microscopic observation of stishovite within material recovered from high explosive shock experiments on porous sandstone shocked at 7 5 and 12 5 gpa our observations allow for new conclusions on the genesis of stishovite in a close to nature environment the formation of stishovite in short time shock experiments proves that its crystallization is ultrafast 1 s crystals were found only embedded in amorphous veins indicating homogeneous nucleation crystallization from melt rather than from glass can be concluded from the observation of roundish defect free crystals up to 150 nm in diameter embedded in nondensified glass the formation of stishovite at 7 5 gpa is in accordance with the phase diagram of silica if rapid undercooling is present that becomes only possible by the existence of small hot spots in an otherwise cold material which is supported by transient heat calculation the absence of coesite at 7 5 gpa suggests kinetic hindrance of its crystallization from melt and thus smaller critical cooling rates compared to stishovite where critical cooling rates are estimated to be as large as 1011 k s 1 while the amorphous veins containing stishovite represent unambiguously hot spots no associated pressure amplification could be verified within these veins the rapid liquidus crystallization of stishovite only in hot spots generated in porous material is an alternative formation mechanism to the widely accepted theory of solid solid transition from quartz to stishovite and might represent the more general mechanism occurring in nature for low shock pressure events

gypsum karst problems in constructing dams in the usa gypsum is a highly soluble rock and is dissolved readily to form caves sinkholes disappearing streams and other karst features that typically are also present in limestones and dolomites gypsum karst is widespread in the usa and has caused problems at several sites where dams were built or where dam construction was considered gypsum karst is present at least locally in most areas where gypsum crops out or is less than 30 60 m below the land surface these karst features can compromise on the ability of a dam to hold water in a reservoir and can even cause collapse of a dam gypsum karst in the abutments or foundation of a dam can allow water to pass through around or under a dam and solution channels can enlarge quickly once water starts flowing through such a karst system the common procedure for controlling gypsum karst beneath the dam is a deep cut off trench backfilled with impermeable material or a close spaced grout curtain that hopefully will fill all cavities in oklahoma the proposed upper mangum dam was abandoned before construction because of extensive gypsum karst in the abutments and impoundment area catastrophic failure of the quail creek dike in southwest utah in 1989 was due to flow of water through an undetected karstified gypsum unit beneath the earth fill embankment the dike was rebuilt at a cost of us 12 million with construction of a cut off trench 600 m long and 25 m deep other dams in the usa with severe gypsum karst leakage problems in recent years are horsetooth and carter lake dams in colorado and anchor dam in wyoming

sinkhole investigation in an urban area by trenching in combination with gpr ert and high precision leveling mantled evaporite karst of zaragoza city ne spain abstract sinkhole risks are becoming particularly severe in urban areas that lack careful planning and where karst depressions are frequently filled and developed these built up areas are the most challenging for sinkhole investigation they are the ones that require the highest priority and the application of novel approaches aimed at reducing the epistemic uncertainties associated with hazard assessments this work illustrates the strengths of the rarely used trenching technique for the investigation of sinkholes in mantled karst areas the approach has been tested on a buried sinkhole in the evaporite karst of zaragoza city analysing and comparing data gathered by trenching ground penetrating radar gpr using shielded and unshielded antennas with different frequencies electrical resistivity tomography ert and high precision leveling the sinkhole is located beneath a street and has led to the demolition of buildings creating a risk situation that requires careful assessment and management trenching provided the largest amount of objective data required for hazard assessment 1 precise location of the sinkhole edges 2 internal structure cumulative displacement subsidence mechanisms and their contribution the trench exposed an asymmetric structure with a minimum vertical displacement of 6 2 m comprising a complex collapse with different generations of faults and two marginal zones affected by gentle inward tilting collapse faulting accommodates at least 70 of the subsidence 3 age of the sinkhole and average subsidence rate the sinkhole was initiated sometime before or within 337 435 cal yr ad indicating a long term subsidence rate of ca 3 7 4 2 mm yr 4 kinematic style characterised by episodic collapse events as supported by leveling data the retrodeformation analysis together with geochronological data indicates four collapse events with a recurrence of around 400 years and suggests enhanced activity since ca 1950 ad the performance of gpr was highly variable depending mainly on the type of antenna and the timing of data acquisition the best quality data were obtained with shielded antennas and during relatively drier conditions the rather poor performance of ert commonly an adequate method for resolving subsidence structures at depth is attributed to the complex structure of the collapse sinkhole with spatially dense and abrupt resistivity changes in resistivity this case study strongly substantiates the implementation of the relatively inexpensive and highly objective trenching technique in sinkhole investigations

structure of young oceanic crust at 13 n on the east pacific rise from expanding spread profiles we present the results of the analysis of expanding spread profiles esps collected on and near the axis of the east pacific rise at 13 n these profiles were collected at 0 1 1 2 1 3 6 and 9 5 km from the rise axis and all but the most distant profile show a distinct low velocity zone lvz located within layer 3 of the oceanic crust at the ridge crest the top of the magma chamber is at the base of layer 2 while 3 6 km off axis the roof of the lvz is 1 1 km below the top of layer 3 the profile farthest from the ridge could possibly have a residual lvz confined to the lower 1 5 km of the crust the total width of the lvz as determined from the esp data is at least 6 km and possibly much greater this wide lvz apparently contradicts multichannel seismic data which show cross axis reflections from the magma chamber with a width of 5 km we suggest that a resolution of this apparent contradiction lies in a model of the rise axis with a small and transient central magma chamber of high partial melt fraction surrounded by a much larger and permanent region of hot rock with only isolated pockets of partial melt the esp data are sensitive to this larger region while the reflection data accurately map the presence or absence of the central magma chamber with its high impedance contrast we identify the presence of a layer at the top of the oceanic crust with initial p wave velocities between 2 35 and 2 6 km s while the s wave velocity is estimated as being 0 8 km s the layer thickness lies between 100 and 200 m these velocities are consistent with previous estimates for the pacific and recent results for the atlantic the thickness of this layer is consistent with that of layer 2a determined from geophysical measurements at deep sea drilling project hole 504b

leakage problems in dams built on evaporites the case of la loteta dam ne spain a reservoir in a large karstic depression generated by interstratal salt dissolution abstract la loteta reservoir with a storage capacity of 105 hm 3 is located in a large karst depression around 6 km long on the southern margin of the ebro river valley ne spain geomorphological mapping and borehole data indicate that the development of the basin is related to subsidence due to interstratal dissolution of the underlying halite and glauberite bearing evaporites the dam site corresponds to the water gap carved by the small drainage that captured the formerly internally drained depression here the foundation and abutments of the dam include a horizontal and laterally extensive gypsum unit 11 m thick this sedimentary package showed considerable evidence of karstification in the excavation carried out during the construction of the dam especially in the left abutment where it was largely removed the watertightness system of the ca 1 5 km long earth dam includes a vertical clay core a horizontal clay blanket a cut off wall and grout curtains 675 m and 255 m long on the left and right abutments respectively multiple data including leakage discharge measured in the different zones of the drainage system seepage points mapped downstream of the dam borehole and piezometric data and an equipotential map reveal that leakage essentially occurs through the gypsum unit the main leakage occurs beneath and next to the left edge of the dam body this water loss and the associated enlargement of karst conduits are also supported by settlement measured on the dam crest and the occurrence of sinkholes within the reservoir next to the left abutment additional seepage across the grout curtain in both abutments is also identified although unlikely there is also the potential for the water to escape towards an adjacent watershed where the base level is located below the maximum water level of the reservoir an additional cut off wall has been projected to block the main leakage path