estimates of the anomaly threshold in controlled source electromagnetics controlled source electromagnetics csem has been commercially applied for hydrocarbon exploration for more than 10 years the normalized amplitude response nar a common measure for csem anomaly strength is the ratio of the csem response at the target to the background response use of this measure allows anomaly strength to be quantified but leaves open the question of how strong the nar level needs to be before it can be considered significant for hydrocarbon exploration we apply three statistical approaches to determine the appropriate nar threshold for defining a csem anomaly and for estimating the overall significance of the csem method in hydrocarbon exploration the analysis is based on the published data in hesthammer et al 2010a 2010b referred to here as the hesthammer database this database reports nar levels and hydrocarbon exploration outcomes versus the depth to the target for a set of drilled prospects the database authors used an nar level of 1 15 or 15 for their anomaly t

boiling sand springs dismal river nebraska agents for formation of vertical cylindrical structures and geomorphic change boiling motion not temperature sand springs fed by ground water moving upward along distinct conduits occur along the dismal river in the nebraska sand hills the cylindrical conduits are developed in alluvium and are as large as 10 m in diameter and 44 m deep sides of the spring conduits are firm boiling sand is overlain in several places by a clear layer of water in the spring time varying wave patterns and boils can be observed along the interface between these layers sediment within the conduits is generally well sorted although some debris is present because of their large size firm sides and persistence in time the conduits have the potential for preservation as vertical cylindrical structures comparable to those reported in sedimentary rocks of several ages the discovery of preserved structures is evidence of paleo ground water discharge and therefore the structures are a useful mapping tool for determining position in landscape evolution

new statistical grain size method for evaluating the hydraulic conductivity of sandy aquifers abstract a new statistical grain size method of evaluating the hydraulic conductivity and transmissivity of sandy aquifers is presented the new equation is of the form k cd 2 10 and is similar to the existing equations but in this case the coefficient c which is normally taken as a constant is actually shown to be a variable that depends on the nature of the geologic environment source rock transportation deposition and post deposition history etc it is established that c for unconsolidated and poorly cemented sandy materials is 6 0 for moderately consolidated cemented rocks c 3 8 while for fairly well compacted and cemented rocks its value is about 2 0 with these coefficients the new statistical grain size method gives k and t values that compare favourably with those determined from pumping test methods

continuation of a deep borehole stress measurement profile near the san andreas fault 2 hydraulic fracturing stress measurements at black butte mojave desert california hydraulic fracturing stress measurements were obtained in the black butte drill hole 18 km northeast of the san andreas fault in the mojave desert at depths from 251 to 635 m in all tests the least and greatest horizontal principal stresses s h and s h respectively exceeded the vertical stress s indicating a thrust faulting stress regime a single good quality hydraulic fracture impression from 309 m depth indicates an s h direction of n41 e 10 this s h direction should be interpreted with caution because it is based on only one observation this orientation is fairly compatible with nearby surface stress measurements but is incompatible with most of the hydraulic fracturing stress orientations reported from comparable depths in the mojave desert and is not favorable for right lateral slip on either the san andreas fault or nw striking faults present farther to the east the stress regime measured in the black butte hole is comparable to that measured at nearby shallow depths but differs from the strike slip or transitional strike slip to thrust faulting stress regime present at similar depths in two nearby holes crystallaire 4 km northeast of fhe san andreas fault and hi vista 32 km northeast of the san andreas fault the s h direction measured in these holes is approximately 60 counterclockwise of that observed in the black butte hole the differences in stress magnitudes and orientation among these holes substantiate previous indications of local variations in stress in the upper kilometer of the crust in this area and cast doubt on the validity of linear elastic models in which the effects of the san andreas fault dominate the stress field in the western mojave desert

north atlantic sea surface temperatures for the last 1 1 million years summary a 1 2 ma time series of north east atlantic sea surface temperature sst has been assembled from the spliced record of piston core k 708 7 0 68 0 ma and hydraulic piston cores taken in nearby dsdp hole 552a 1 2 0 68 ma a no analogue fauna precludes making credible sst estimates in the interval 1 2 1 1 ma but the record above 1 1 ma is suitable for sst estimates and related time series analysis the amplitude of sst variation is considerably higher in the brunhes than in the upper matuyama this is due both to colder glacial sst minima after 0 85 ma and to increasingly warm interglacial sst maxima from 0 7 to 0 4 ma the dominant periodicity in the sst signal is centred near 95 000 years it increases in amplitude by a factor of four from the bottom of the record to the top with the largest increase occurring between 0 7 and 0 4 ma this suggests a relatively gradual evolution of 100 000 year power over half a million years of the late quaternary rather than a single abrupt change at 0 9 ma significant but progressively smaller spectral peaks occur at periods of 54 000 41 000 31 000 23 000 and 19 000 years both the 54 000 year and 31 000 year signals may be a response to insolation forcing by minor obliquity terms long term 18 o records show small responses by the ice sheets at or near these two periods indicating the probable initial response of the climate system to these insolation rhythms in phase relationships between 18 o and sst at these periods suggest that the ice sheets then impose these rhythms on the ocean with no lag the mechanism by which such small insolation and ice volume signals become enhanced in the sst record is not clear

stress anomaly accompanying the 1979 lytle creek earthquake implications for earthquake prediction an unusual stress transient was recorded 15 kilometers from the epicenter of the lytle creek earthquake in southern california it was observed at the recording site as an increased shear stress parallel to the fault surface and with the proper sense of shear to have triggered the earthquake the anomaly began 2 to 4 weeks before the earthquake and lasted for 3 months

strain on the san andreas fault near palmdale california rapid aseismic change frequently repeated strain measurements near palmdale california during the period from 1971 through 1980 indicate that in addition to a uniform accumulation of right lateral shear strain engineering shear 0 35 microradian per year across the san andreas fault a 1 microstrain contraction perpendicular to the fault that accumulated gradually during the interval 1974 through 1978 was aseismically released between february and november 1979 subsequently november 1979 to march 1980 about half of the contraction was recovered this sequence of strain changes can be explained in terms of south southwestward migration of a slip event consisting of the south southwestward movement of the upper crust on a horizontal detachment surface at a depth of 10 to 30 kilometers the large strain change in 1979 corresponds to the passage of the slip event beneath the san andreas fault

strain accumulation in southern california 1973 1980 frequent surveys of seven trilateration networks in southern california over the interval 1973 1980 suggest that a regional increment in strain may have occurred in 1978 1979 prior to 1978 and after late 1979 the strain accumulation has been predominantly a uniaxial north south compression this secular trend was interrupted sometime in 1978 1979 by an increment in both north south and east west extension in five of the seven networks the onset of this change appears to have occurred first in the networks farthest south the changes occurred without any unusual seismicity within the networks but the overall seismicity in southern california was unusually low prior to and has been unusually high since the occurrence the average principal strain rates for the seven networks in the 1973 1980 interval are 0 17 mu strain yr north south contraction and 0 08 mu strain yr east west extension although the observed increment in strain could be related to unidentifed systematic error in the measuring system a careful review of the measurements and comparison with three other measuring systems reveal no appreciable cumulative systematic error

ten years of marine csem for hydrocarbon exploration marine controlled source electromagnetic csem surveying has been in commercial use for predrill reservoir appraisalandhydrocarbonexplorationfor10 years althougha recent decrease has occurred in the number of surveys and publications associated with this technique the method has become firmly established as an important geophysical tool intheoffshoreenvironment thisisaconsequenceoftwoimportant aspects associated with the physics of the method first it is sensitive to high electrical resistivity which although not an unambiguous indicator of hydrocarbons is an important property of economically viable reservoirs second although the method lacks the resolution of seismic wave propagation it has a much better intrinsic resolution than potential field methods such as gravity and magnetic surveying which until now have been the primary nonseismicdatasetsusedinoffshoreexploration althoughbymany measures marine csem is still in its infancy the reliability and noise floors of the instrument systems have improved significantly over the last decade and interpretation methodology has progressed from simple anomaly detection to 3d anisotropic inversion of multicomponent data using some of theworld sfastestsupercomputers researchdirectionspresently include tackling the airwave problem in shallow water by applying time domain methodology continuous profiling tools and the use of csem for reservoir monitoring during production

hydrologic and geochemical properties of the san andreas fault at the stone canyon well the stone canyon well penetrates 600 m of highly fractured and severely altered quartz diorite intimately associated with the creeping segment of the san andreas fault of central california geophysical logs reveal a complex hydrology dominated by major fractures fluid pressure in some fractures is sufficient to prevent invasion of the formation by heavy drilling mud implying pore pressures at least 10 higher than hydrostatic ones at least three chemically distinct waters are encountered including a chloride brine clearly segregated from the shallow potable groundwater chemical alteration of the quartz diorite persists throughout the well far below the depth where the water rock reactions responsible for the ubiquitous chlorite and mixed layer clays can be considered weathering whole rock 18o analyses indicate significant interaction of the rocks with a low 18o fluid within some of the fractured and altered zones whereas a deeper sample shows18o enrichment high pore pressures encountered in stone canyon may be due to tectonic compression measurements of temporal variations in the pore pressure at the well may provide a means of predicting earthquakes along this segment of the san andreas fault

dating of late pleistocene interglacial and interstadial periods in the united kingdom from speleothem growth frequency abstract the growth of speleothems is indicative of interglacial and interstadial conditions in the united kingdom since their growth is dependent on two factors first the occurrence of significant diffuse groundwater recharge and second the biogenic production of carbon dioxide in the soil both are dependent on temperature and water availability the growth frequency of speleothems is examined using a cumulative distributed error frequency method applied to 341 uncontaminated uranium series age determinations the curves derived are shown to be statistically stable and the ages of the peaks are interpreted as the best estimates of the ages of interglacial and interstadial periods ten such periods are recognized during the interval 220 000 to 20 000 yr b p considerably more than are currently recognized in the uk pollen and coleoptera based quaternary stratigraphy correlations between the speleothem growth frequency peaks and last interglacial ipswichian sites can be made but correlations with last glacial devensian interstadial sites are limited because of the paucity of dates the speleothem growth frequency record provides a well dated terrestrial chronology for the past 140 000 yr b p which directly reflects regional palaeoclimatic conditions in britain and should prove very useful in unravelling the complex stratigraphy of the devensian and ipswichian stages

csem performance in light of well results during the past several years we have seen an increasing focus on the use of csem technology for hydrocarbon exploration in marine environments and recently a number of success stories have been published the technology has been demonstrated to aid both detection and delineation of hydrocarbon filled reservoirs

a strategy for short term prediction of earthquakes abstract physical processes leading to laboratory rupture have a nonlinear character which justifies optimism that earthquakes are predictable however nonlinear effects at the source of a smaller earthquake may be an insufficient basis for the prediction of an earthquake with rupture lengths tens to hundreds of kilometers thus a strategy for predicting such major or great events must depend on knowing the state of readiness of the entire length of the suspect fault the two most promising avenues are 1 to search for variations in shear and dilatational strains within the fault zone and in the bordering regions that signify the onset of a stuart instability and 2 to follow in detail the seismicity in response to the temporal variations of shear and normal strains as a measure of what parts of a long fault are at the point of failure an observational strategy based on these physical models requires detailed and frequent to continuous observation of strain within the fault and border zones focal mechanisms and accurate locations of earthquakes m 2 are needed to relate seismicity to a given configuration of the strain field with the exception of observations such as levels in water wells which carry information on the strain field a purely empirical search for earthquake precursors needs to be deemphasized

gas geochemistry and seismotectonics a review abstract publications on soil and spring gases have been examined regarding their relationships with both tectonic and seismic activities the main sources behaviours and uses of species detected in soils and springs are displayed and their mode of sampling and analysing briefly described the main patterns of degassing in soils are described and we outline the wide range of geochemical signatures as the result of both permeability and mineralogical contrasts because thermomineral waters have been in contact with great volumes of crustal rocks at various depths spring gases might be more representative of the local environment than soil gases moreover gas signature comparisons show that spring gases are much more enriched with deep gases and slightly contaminated by atmospheric gases therefore they can be considered as better samples for identifying precursors of earthquakes environmental perturbations are examined and it is shown from divergent cases that pressure temperature soil moisture or earth tides may generate very high perturbations of the degassing process such effects demonstrate that no systematic correction law can be proposed and that removing external contributions from gas concentrations must be performed case by case this demonstrates therefore the need for the simultaneous measurement of external parameters during gas monitoring a qualitative examination of about 150 claimed precursors proposed in the literature has been reviewed as noted by previous authors anomalies appear at distances sometimes much greater than typical source dimensions and occur in the field of strain higher than 10 9 most of them being in the field of strain higher than 10 8 taking into account the very high heterogeneity of such a set of data we can suggest that amplitudes of gas anomalies are independent of both magnitudes and epicentral distances of related earthquakes suggesting local conditions to control amplitudes on the contrary precursory time and duration of anomalies seem to increase both with magnitudes and epicentral distances abundant evidence demonstrates the major role of crustal fluids in the earthquake cycle many works have outlined the fact that crustal instabilities can appear as the result of low stress strain perturbations during loading it has been suggested that motion of fluids may occur at various scales from microcrack fluid transfer up to changes of hydraulic levels of water tables the study of subsequent anomalies is expected to supply a tool for earthquake prediction following previous authors we outline the need for further methodological improvements including the setting up of multiparameter station networks and the simultaneous recording of the main external parameters atmospheric pressure water and air temperature soil moisture for signal processing

palaeohydrogeological reconstructions of the north lincolnshire chalk uk for the last 140 000 years abstract the influence of climatic change on hydrogeology is investigated by studying the evolution of the north lincolnshire chalk aquifer system during the last 140 000 years a numerical modelling approach is adopted using a density coupled finite difference model to reconstruct past groundwater environments two major controls on groundwater circulation are considered the position of sea level which determines the base level condition and the amount of recharge associated with different climates the quaternary history of the region is used to define aquifer boundary conditions and climate analogue data are used to determine likely recharge amounts model results cannot be compared against groundwater flow volumes or head other than for the present day situation and so hydrochemical evidence is used to constrain the model simulations the main finding is that recharge to the chalk aquifer during the last 140 000 years has been restricted to periods when the climate and sea level position have been similar to those of the present day the devensian cold period experienced very minor recharge with no chalk permeability development forest clearance since about 5000 years ago is predicted to have permitted an increase in the volume of freshwater recharge which increased the rate of chalk permeability development the presence of saline water at depth in the aquifer is argued on the basis of the model behaviour to be contributed by a component of upward cross formational flow

accuracy and effectiveness of three dimensional controlled source electromagnetic data inversions abstractunconstrained 3d inversion of marine controlled source electromagnetic data csem data sets produces resistivity volumes that have an uncertain relationship to the true subsurface resistivity at the scale of typical hydrocarbon reservoirs furthermore csem scale resistivity is an ambiguous indicator of hydrocarbon presence not all resistivity anomalies are caused by hydrocarbon reservoirs and not all hydrocarbon reservoirs produce a distinct resistivity anomaly we have developed a method for quantifying the effectiveness of resistivities from csem inversion in detecting hydrocarbon reservoirs our approach uses probabilistic rock physics modeling to update information from a preexisting prospect assessment based on uncertain resistivities from csem the result is an estimate the probability of hydrocarbon presence that accounts for uncertainty in the resistivity and in rock properties examples using synthetic and real csem data sets demonstrate that the effectiveness of csem inversion in id

evolution of groundwater systems at the european coastline an overview is given of the status and origin of fresh and saline groundwaters in the sedimentary aquifers at or near the present european coastline results are presented as six regional maps summarizing as far as possible the conditions likely to have existed at the end of the pleistocene after the impact of glaciation when groundwaters might be expected to have reached their maximum offshore evolution prior to the encroachment of sea water during the holocene marine transgression in the eastern baltic the groundwater evolution was different to other european regions in that freshwater heads were higher than the present day promoting recharge during much of the late pleistocene near the north sea coasts there is generally evidence of freshwater movement to depths of 100 150 m but the absence of deeper freshwater palaeowater storage may relate to the low hydraulic gradients in the north sea basin in the southeastern part of the north sea brackish palaeowater is found between tertiary marine sediments c 300 m below the island of rcmo l 0 km off the danish west coast freshwater of pleistocene and holocene ages is found in aquifers at the english channel coast in several areas to depths in excess of 300 m offshore flow in the late pleistocene took place towards the central palaeovalley and some of this groundwater may be preserved off the present coastline in the two atlantic coastal areas of france and portugal spain a contrast exists due to the proximity of the continental margin and different hydraulic gradients in portugal freshwaters are found at the coastline and probably offshore that contain evidence of recharge during the lowered sea levels in most of the southwestern atlantic coast of spain fresh recent groundwater discharges along and beyond the coastline while in the old estuary of the guadalquivir river saline holocene water still encroaches the sediments on the mediterranean coast of france and spain some salinity encroachment took place during sea level rise in most of the spanish aquifers fresh recent groundwater has substituted for palaeowater except for the low lying areas ebro delta inca sa pobla plain where brackish holocene water is still present

late proterozoic periglacial aeolian deposits on the west african platform taoudeni basin western mali the late proterozoic bakoye 3 formation is a predominantly aeolian unit deposited in the glacially influenced cratonic taoudeni basin of western africa the bakoye 3 can be divided into five distal units two proximal units and a local upper massive sandstone the basal unit 1 shows a complex interfingering of aeolian and subaqueous structures and is interpreted as the precursor of the overlying erg sequences unit 2 consists of compound trough cosets of aeolian cross strata dominated by grain flow strata the unit is interpreted to represent draas with superimposed small crescentic dunes a super bounding surface marks the termination and planation of the erg unit 3 is distinguished from the underlying unit 2 by its larger overall simple sets of trough cross strata interpreted to represent simple large crescentic dunes unit 4 occurs only locally in laterally discontinuous large troughs in one case the trough is filled by small sets of tabular cross strata dominated by grain flow deposits at another section wedges of coarse grained wind ripple strata fill the trough unit 4 may represent remnants of ergs or more likely local deposition in depressions the depressions in the latter scenario formed with the development of a second super surface that truncates unit 3 unit 5 consists of very large sets of wind ripple cross strata with less common sets of grain flow deposits these deposits are believed to represent enormous dunes with large plinths and subordinate slip face development a third super surface separates unit 5 from overlying marine deposits together units 1 5 represent the core of the ergs in a distal position relative to adjacent upland source areas proximally aeolian deposits are simple smaller trough sets interpreted as moderate sized crescentic dunes coarse grained braided stream deposits are prominent locally the top of the bakoye 3 is marked by channelized mass flow deposits containing aeolian blocks and is believed to have resulted from iceberg grounding an overall environment for the bakoye 3 is one of uplands marked by ice sheets with outwash plains extending distally to aeolian ergs super surfaces all marked by polygonal fractures and coarsegrained sediment represent periods of erg termination that may be linked to glacial fluvial aeolian cycles

peat development sand cones and palaeohydrogeology of a spring fed mire in east yorkshire uk an archaeological dig near beverley east yorkshire uk revealed humified peat enclosing conical and cylindrical sand bodies sand cones which contained romano british greyware such sand cones have not been previously described in the literature below the peat upper and lower diamict units previously classified as holocene alluvium were reclassified as late devensian lodgement till and pre late devensian chalky head gelifluction deposits respectively enigmatic buried timbers dated dendrochronologically to 5840 bp were found partially buried within the till micromorphological evidence shows that the peat is autochthonous the sand cones are remains of former spring orifices which served as foci for groundwater discharge from the regional east yorkshire chalk aquifer which underlies the chalk head deposits in hydraulic continuity as a corollary it is suggested that the buried timbers subsided into the till penecontemporaneously with the death of the tree when an early period of vigorous groundwater discharge led to the temporary establishment of quicksand conditions peat accumulation and humification were intimately linked to variations in spring flows radiocarbon dates help to relate these variations to regional palaeohydrogeology in particular to holocene water table fluctuations which reflect changes in recharge rates a function of climatic change and sea level

groundwater chemistry in southeast suffolk u k and its relation to quaternary geology abstract east anglia has a complex pleistocene geological history having been affected both by major changes in the level of the adjacent north sea and by glacial processes the resulting geology has a profound effect on the distribution of water chemistry in the chalk aquifer which underlies the pleistocene deposits a detailed study of the chemistry of the chalk groundwater including strontium fluoride and iodide as well as major elements has shown that this chemistry results from three phases of saline intrusion early pleistocene to modern and at least two periods of freshwater flushing climatic changes and erosional history were important in controlling flushing periods

bedrock fracture parameters from the interpretation of well tides this paper presents a theory to account for the main features of the tidal response of an isolated plane fracture as revealed by the water level in an intersecting open borehole according to the theory the diurnal and semidiurnal tidal constituents both amplitude and phase of water level variations depend on the fracture aperture the orientation dip and strike and the radial extent of the fracture and the compressibility of the asperites the theory is applied to water level observations made in six open boreholes located in crystalline rock at a test site at the chalk river nuclear laboratories atomic energy of canada limited in chalk river ontario canada the boreholes were uncased and intersected many open fractures so that a definitive test of the theory could not be made however in four cases a fracture model could be found which fitted the observations within the experimental error

a study of the depth of weathering and its relationship to the mechanical properties of near surface rocks in the mojave desert weathered granite extends 70 m deep at hi vista in the arid central mojave desert of southern california the low strength of this granite is due to the alteration of biotite and chlorite montmorillonite deep weathering probably occurs in most granites although we cannot rule out some anomalous mechanisms at hi vista geophysical instruments set in these slightly altered rocks are limited by the unstable behavior of the rocks thus tectonic signals from instruments placed in shallow boreholes give vague results geophysical measurements of these weathered rocks resemble measurements of granitic rocks near major faults the rheology of the rocks in which instruments are placed limits the useful sensitivity of the instruments

estimating hydrogeological conditions over the last 120 ka an example from the sellafield area uk for a number of years united kingdom nirex limited investigated the suitability of the area around sellafield in nw england to assess its suitability to host a deep repository for intermediate level and some low level radioactive wastes resulting from britain9s nuclear programme the investigation programme collected a large amount of lithological hydrogeological and hydrochemical data from 18 boreholes up to 2000 m deep a potential route by which radionuclides may leave the repository and return to surface is the groundwater pathway it was recognized that the groundwater regime could be disturbed significantly by major climate changes particularly glacial interglacial cycles over the very long time scales considered in the assessment of the radiological safety of a repository available geological and hydrogeological data for the sellafield area are reviewed in the context of current thinking on glacial hydrogeology showing that disturbance of the hydrogeological regime is possible during glaciation and that there are significant uncertainties in determining the timing and magnitude of the effects caused by glaciation however the evidence available both from quaternary fracture filling minerals and from the chemistry of groundwater now present suggests that any disturbance to the deeper hydrogeological regime was relatively minor and that any subglacial recharge has been removed by the present flow regime there is a possibility that high hydraulic heads at depth in the low permeability basement rock considered as a host for the repository the borrowdale volcanic group of ordovician age beneath a cover of triassic sandstones may be residual

is the water still hot sustainability and the thermal springs at bath england the hot springs at bath are the largest natural thermal source in britain sustainable use of the waters for a spa requires maintenance of their temperature and flow rate together with smaller springs at hotwells bristol they form the outflow from a regional thermal aquifer that occurs where the carboniferous limestone is buried at depths 2 7 km in the bristol bath structural basin the aquifer is recharged via limestone outcrops forming the south and west portions of the basin rim current knowledge of the basin s structure is reviewed and important uncertainties identified concerning the hydrogeological role of thrust faults which may cut the limestone at depth a simple numerical model is used to determine the possible influence of thrusts upon groundwater flow within the thermal aquifer comparison of the modelled flow patterns with geochemical data and structure contours eliminates the hypothesis that thrusts completely disrupt the continuity of the aquifer the most successful model is used to simulate the possible impact of dewatering by large quarries at the limestone outcrops north and south of bath substantial reductions in modelled flow at bath result from proposed dewatering in the eastern mendips although the steady state approach adopted has severe limitations in that it does not take account of the incremental staging of actual dewatering nor allow for partial restitution of groundwater levels the geological uncertainties highlighted by the modelling could be addressed by future research into the effect of thrusts on the continuity of the carboniferous limestone more refined modelling to predict the timing of possible impacts of quarry dewatering will require measurements of the storativity of the thermal aquifer

in situ fluid pressure measurements for earthquake prediction an example from a deep well at hi vista california short term earthquake prediction requires sensitive instruments for measuring the small anomalous changes in stress and strain that precede earthquakes instruments installed at or near the surface have proven too noisy for measuring anomalies of the size expected to occur and it is now recognized that even to have the possibility of a reliable earthquake prediction system will require instruments installed in drill holes at depths sufficient to reduce the background noise to a level below that of the expected premonitory signals we are conducting experiments to determine the maximum signal to noise improvement that can be obtained in drill holes in a 592 m well in the mojave desert near hi vista california we measured water level changes with amplitudes greater than 10 cm induced by earth tides by removing the effects of barometric pressure and the stress related to earth tides we have achieved a sensitivity to volumetric strain rates of 10 9 to 10 10 per day further improvement may be possible and it appears that a successful earthquake prediction capability may be achieved with an array of instruments installed in drill holes at depths of about 1 km assuming that the premonitory strain signals are in fact present

regional deformation near palmdale california 1973 1983 the tehachapi trilateration network spans the intersection of the san andreas and garlock faults in southern california in the big bend region of the san andreas fault analysis of data from 1973 1983 shows strain differences between the northwest and southeast regions of the network and slip at depth on both faults the palmdale network spanning the san andreas fault entirely within the tehachapi network showed increases of about 1 strain in both east west and north south extension in late 1979 the tehachapi strains also jumped at this time but the magnitude of the increase was only about one third that of palmdale the principal strain rates for tehachapi over the time interval 1973 1983 are e 1 0 08 0 01 strain yr and e 2 0 12 0 01 strain yr with the 1 axis directed n76 e strains were also computed for two subregions the principal strain rates for the southeast tehachapi region are e 1 0 14 0 02 strain yr and e 2 0 16 0 02 strain yr with the 1 axis directed n73 e this result differs significantly from the principal strain rates at palmdale e 1 0 21 0 02 strain yr e 2 0 17 0 01 strain yr with the 1 axis directed n71 e for the northwest tehachapi region e 1 0 11 0 02 strain yr and e 2 0 06 0 02 strain yr with the 1 axis directed n93 e

recent localised sulphate reduction and pyrite formation in a fissured chalk aquifer reply reduction oxidation reactions in the london basin aquifer system how may they be investigated

anomalous water level changes and possible relation with earthquakes since late 1976 abandoned water wells have been monitored along the san andreas and san jacinto faults to detect water level changes which may be premonitory to earthquakes an m5 5 earthquake occurred 25 february 1980 within the san jacinto fault zone near anza the water level in a continuously recorded well in borrego valley 35 km from the epicenter rose 0 5 m and returned to its prior level during a four hour period beginning 88 hours before the earthquake the water level in this well had been remarkably steady compared to other wells being monitored another well in borrego valley showed a much smaller rise and fall in water level at the same time because these changes are unique for the long term records of these wells they may represent precursors to the earthquake several wells along the palmdale valyermo segment of the san andreas fault showed possibly anomalous long term water level changes which are not clearly related to rainfall between early 1979 and early 1980 water levels in six wells were 6 to 4 5 m higher and levels in two wells were about 3 m lower than would have been predicted based on the previous records the water level increases could have been the result of delayed response to seasonal rainfall following a long drought however it is interesting that the possibly anomalous water level changes first occurred at the same time as the reported changes in strain pattern from compression to expansion along the san andreas fault in the same area

hydrochemical and stable isotope evidence for the extent and nature of the effective chalk aquifer of north norfolk uk in eastern england the chalk aquifer is covered by extensive pleistocene deposits which influence the hydraulic conditions and hydrochemical nature of the underlying aquifer in this study the results of geophysical borehole logging of groundwater temperature and electrical conductivity and depth sampling for major ion concentrations and stable isotope compositions 18o and 2h are interpreted to reveal the extent and nature of the effective chalk aquifer of north norfolk it is found that the chalk aquifer can be divided into an upper region of fresh groundwater with a cl concentration of typically less than 100 mg l 1 and a lower region of increasingly saline water the transition between the two regions is approximately 50 m below sea level and results in an effective aquifer thickness of 50 60 m in the west of the area but less than 25 m where the eocene london clay boundary is met in the east of the area hydrochemical variations in the effective aquifer are related to different hydraulic conditions developed in the chalk where the chalk is confined by low permeability chalky boulder clay isotopically depleted groundwater 18o less than 7 5 is present in contrast to those areas of unconfined chalk where glacial deposits are thin or absent 18o about 7 0 the isotopically depleted groundwater is evidence for groundwater recharge during the late pleistocene under conditions when mean surface air temperatures are estimated to have been 4 5 c cooler than at the present day and suggests long groundwater residence times in the confined aquifer elevated molar mg ca ratios of more than 0 2 resulting from progressive rock water interaction in the confined aquifer also indicate long residence times a conceptual hydrochemical model for the present situation proposes that isotopically depleted groundwater occupying areas where confined groundwater dates from the late pleistocene is being slowly modified by both diffusion and downward infiltration of modem meteoric water and diffusive mixing from below with an old saline water body

water transfer cylindrical structures in the late proterozoic eolian sandstones in the taoudeni basin west africa abstract vertical cylindrical structures have already been described in literature but none in periglacial eolian dune deposits two types of vertical cylindrical structures have been observed in the late precambrian of western mali type 1 exhibits concentric laminae in subhorizontal transversal section and a cone in cone internal organization in type 2 laminations inherited from the parent sediments are partially preserved the two types are early post depositional cylindrical features both were caused by upward fluid flow responsible for liquefaction fluidization and entire type 1 or partial type 2 remobilization of eolian cross stratification in a proposed hypothetical reconstruction scheme a local overpressure caused by an unknown external impulse creates liquefaction cells which evolve either in an upward explosive way type 2 or in an upward moving liquefaction front type 1

palaeohydrology and future climate change since the mid 1980s there has been growing concern that increasing concentrations of so called greenhouse gases will lead to global warming changes to regional climates and hence impacts on the environment society and economy the united nations environment program and the world meteorological organization in 1987 set up the intergovernmental panel on climate change ipcc which has reported on climate change predictions ipcc 1990a 1992a the possible impacts of climate change ipcc 1990b 1992b and strategies for mitigating the effects of climate change ipcc 1991 the ipcc second assessment is scheduled for publication in 1996 climate change science is essentially predictive it is trying to predict conditions during the twenty first century by far the most common approach is based around the use of global climate models gcms these numerical simulation models are used to predict the global and regional climatic effects of changing greenhouse gas concentrations and many climate change impact studies use scenarios based in some way on gcm simulations these scenarios are then used to perturb current climatic time series and fed through a catchment hydrological model to simulate river flows and other hydrological properties e g bultot et al 1988 lettenmaier gan 1990 arnell reynard 1993 and many others the two major problems with this approach lie in the definition of credible catchment scale scenarios from gcm simulations and the development of realistic hydrological simulation models the latter problem is fundamental to hydrological simulation whilst the former is peculiar to climate change impact assessments and arises for two reasons first gcms do not at present represent all the climatic processes in a realistic manner particularly those relating to the development of clouds and the interactions between the atmosphere and the land surface and second gcms operate at a very coarse spatial resolution some important atmospheric processes such as the development of meso scale circulation patterns and convective storms are therefore not simulated particularly well and whilst gcms can simulate large scale atmospheric features well regional and local climates are often not well reproduced the coarse spatial resolution also means that gcm output has to be interpolated down to the catchment scale a variety of techniques of varying degrees of sophistication have been used or proposed ranging from simple statistical interpolation through empirical relationships between large scale and local climate to the use of nested regional climate simulation models but all rely ultimately on the reliability of the gcm simulations of large scale climatic features arnell 1995a the other popular approach to climate impact assessment uses the past as an analogue for the future one variant uses the instrumental period in practice the last century another uses historical data and a third uses palaeoclimatic reconstructions