the mutual interaction between continental scale ice sheets and atmospheric stationary waves the great continental ice sheets of the pleistocene represented significant obstacles to the northern hemisphere midlatitude westerlies they must therefore have forced large changes in the atmospheric circulation and consequently also in the patterns of accumulation and melting over the ice sheets themselves a simplified threedimensional coupled ice sheet stationary wave model is developed in order to understand the ice sheet s response to the circulation changes that it induces consistent with ice age climate simulations the ice sheet topography induces an anticyclonic circulation over the ice sheet causing a slight warming over the western slopes and a stronger cooling over the remainder the modeled feedbacks significantly affect the ice sheet configuration with the most important influences being the patterns of summer temperature and the topographically induced precipitation field the time evolution of the ice sheet is also changed by the atmospheric feedbacks and the results suggest the possibility of multiple equilibrium solutions

statistical analysis of the induced basel 2006 earthquake sequence introducing a probability based monitoring approach for enhanced geothermal systems summary geothermal energy is becoming an important clean energy source however the stimulation of a reservoir for an enhanced geothermal system egs is associated with seismic risk due to induced seismicity seismicity occurring due to the water injection at depth have to be well recorded and monitored to mitigate the seismic risk of a damaging event an appropriate alarm system needs to be in place for each individual experiment in recent experiments the so called traffic light alarm system based on public response local magnitude and peak ground velocity was used we aim to improve the pre defined alarm system by introducing a probability based approach we retrospectively model the ongoing seismicity in real time with multiple statistical forecast models and then translate the forecast to seismic hazard in terms of probabilities of exceeding a ground motion intensity level one class of models accounts for the water injection rate the main parameter that can be controlled by the operators during an experiment by translating the models into time varying probabilities of exceeding various intensity levels we provide tools which are well understood by the decision makers and can be used to determine thresholds non exceedance during a reservoir stimulation this however remains an entrepreneurial or political decision of the responsible project coordinators we introduce forecast models based on the data set of an egs experiment in the city of basel between 2006 december 2 and 8 approximately 11500 m 3 of water was injected into a 5km deep well at high pressures a six sensor borehole array was installed by the company geothermal explorers limited gel at depths between 300 and 2700 m around the well to monitor the induced seismicity the network recorded approximately 11200 events during the injection phase more than 3500 of which were located with the traffic light system actions where implemented after an ml 2 7 event the water injection was reduced and then stopped after another ml 2 5 event a few hours later an earthquake with ml 3 4 felt within the city occurred which led to bleed off of the well a risk study was later issued with the outcome that the experiment could not be resumed we analyse the statistical features of the sequence and show that the sequence is well modelled with the omori utsu law following the termination of water injection based on this model the sequence will last 31 29 14 years to reach the background level we introduce statistical models based on reasenberg and jones and epidemic type aftershock sequence etas models commonly used to model aftershock sequences we compare and test different model setups to simulate the sequences varying the number of fixed and free parameters for one class of the etas models we account for the flow rate at the injection borehole we test the models against the observed data with standard likelihood tests and find the etas model accounting for the on flow rate to perform best such a model may in future serve as a valuable tool for designing probabilistic alarm systems for egs experiments

the thermomechanical response of the greenland ice sheet to various climate scenarios using a three dimensional numerical model for land based ice sheets in the shallow ice approximation simulations are performed to determine the velocity and temperature distributions within the greenland ice sheet through time for various climate scenarios the ice is treated as a rheologically nonlinear heat conducting viscous fluid and the substrate is a heat conducting rigid solid this system is fed from above by prescribing as the climatic inputs the atmospheric temperature and the accumulation ablation rate functions at the free surface and from below by the geothermal heat we present the governing equations in the shallow ice approximation discuss the parameterizations used in the descriptions of the ice surface temperature and accumulation ablation functions briefly state how the complicated initial boundary value problem is numerically solved and how the input data that are available from measurements are implemented results of preliminary calculations disclose how the model performs and delimit its validity we study the role played by basal sliding and make clear that sliding should be accounted for where ever the basal ice is temperate and that the frictional heat generated in this sliding is thermomechanically significant we also study the reaction of the greenland ice sheet to various climate scenarios and make clear that today s thermal regime depends significantly upon the prior climate history moreover the thermomechanical properties of the ice are equally significant as is the thermal interaction of the ice sheet with the rockbed beneath

the influence of changing orbital parameters and surface boundary conditions on climate simulations for the past 18 000 years abstract general circulation model experiments at 3000 year intervals for the past 18 000 years were made to estimate the magnitude timing and pattern of the climatic response to prescribed changes of orbital parameters date of perihelion axial tilt eccentricity and glacial age lower boundary conditions ice sheets land albedo sea ice and sea surface temperature the experiments used the community climate model ccm of the national center for atmospheric research ncar the response of monsoon circulations and tropical precipitation to the orbitally produced solar radiation changes was much larger than the response to changes of glacial age boundary conditions the continental interior of eurasia was 2 4 k warmer in summer and summer monsoon precipitation of north africa south asia was increased by 10 20 between 12 000 and 6000 yr bp before present when perihelion occurred during northern summer rather than in winter as now and the earth s axial tilt was larger than now southern hemisphe

the importance of tropical sea surface temperature patterns in simulations of last glacial maximum climate abstract prescribed sst experiments are performed using the national center for atmospheric research s community climate model version 3 general circulation model to isolate the contribution of the tropical ssts reconstructed by the climate long range investigation mapping and prediction study climap to the modeled global atmospheric circulation anomalies at the last glacial maximum lgm the changes in tropical sst patterns cause changes in tropical convection that force large 300 m in 500 mb geopotential height changes in northern hemisphere wintertime circulation these midlatitude circulation changes occur despite the small 1 c change in the mean tropical sst between the present and the climap reconstruction in fact the midlatitude circulation changes due to the difference in the tropical sst pattern between the present and the climap reconstruction are greater than the circulation changes due to a uniform tropical sst cooling of 3 c or those due to the presence of the lgm ice sheets the

improving local earthquake locations using the l1 norm and waveform cross correlation application to the whittier narrows california aftershock sequence experiments with different earthquake location methods applied to aftershocks of the october 1 1987 whittier narrows earthquake in california ml 5 9 suggest that local event locations can be greatly improved through the use of the l1 norm station corrections and waveform cross correlation the whittier narrows sequence is a compact cluster of over 500 events at 12 to 18 km depth located within the dense station coverage of the southern california seismic network scsn a telemetered network of several hundred short period seismographs scsn travel time picks and waveforms obtained through the southern california earthquake center are examined for 589 earthquakes between 1981 and 1994 in the vicinity of the mainshock using a smoothed version of the standard southern california velocity model and the existing travel time picks improved location accuracy is obtained through use of the l1 norm rather than the conventional least squares l2 norm approach presumably due to the more robust response of the former to outliers in the data a large additional improvement results from the use of station terms to account for three dimensional velocity structure outside of the event cluster to achieve greater location accuracy waveforms for these events are resampled and low pass filtered and the p and s wave cross correlation functions are computed at each station for every event pair for those events with similar waveforms differential times may be obtained from the cross correlation functions these times are then combined with the travel time picks to invert for an adjusted set of picks that are more consistent than the original picks and include seismograms that were originally unpicked locations obtained from the adjusted picks show a further improvement in accuracy location uncertainties are estimated using a bootstrap technique in which events are relocated many times for sets of picks in which the travel time residuals at the best fitting location are used to randomly perturb each pick improvements in location accuracy are indicated by the reduced scatter in the residuals smaller estimated location errors and the increased tendency of the locations to cluster along well defined fault planes median standard errors for the final inversion are 150 m in horizontal location and 230 m in vertical location although the relative locations within localized clusters of similar events are better constrained seismicity cross sections resolve the shallow dipping fault plane associated with the mainshock and a steeply dipping fault plane associated with a ml 5 3 aftershock these fault planes appear to cross and activity began on the secondary fault plane prior to the large aftershock

characterization of hydraulic properties of rocks using probability of fluid induced microearthquakes the use of borehole fluid injections is typical for exploration and development of hydrocarbon or geothermal reservoirs such injections often induce small magnitude earthquakes the nature of processes leading to triggering of such microseismicity is still not completely understood here we consider induced microseismicity using as examples two case studies of geothermal reservoirs in crystalline rocks and one case study of a tight gas sandstone reservoir in all three cases we found that the probability of induced earthquakes occurring is very well described by the relaxation law of pressure perturbation in fluids filling the pore space in rocks this strongly supports the hypothesis of seismicity triggered by pore pressure moreover this opens additional possibilities of using passive seismic monitoring to characterize hydraulic properties of rocks on the reservoir scale with high precision

application of a polythermal three dimensional ice sheet model to the greenland ice sheet response to steady state and transient climate scenarios abstract steady state and transient climate change computations are performed with the author s three dimensional polythermal ice sheet model simulation code for polythermal ice sheets for the greenland ice sheet the distinctive feature of this model is the detailed consideration of the basal temperate ice layer in which the water content and its impact on the ice viscosity are computed its transition surface to the cold ice region is accounted for by continuum mechanical jump conditions on this interface the simulations presented include steady states subject to a range of physical parameters and two different climates present and glacial conditions as well as three types of transient scenarios namely i sinusoidal milankovic period forcing ii paleoclimatic forcing from the greenland ice core project core reconstruction and iii future greenhouse warming forcing

a one dimensional model for the interaction between continental scale ice sheets and atmospheric stationary waves the great continental ice sheets of the pleistocene represented a significant topographic obstacle to the westerly winds in northern midlatitudes this work explores how consequent changes in the atmospheric stationary wave pattern might have affected the shape and growth of the ice sheets themselves a one dimensional 1 d model is developed which permits an examination of the types and magnitudes of the feedbacks that might be expected when plausible temperature perturbations are introduced at the ice sheet margin which are proportional to the stationary wave amplitude the equilibrium shape of the ice sheet is significantly altered and depends on the sign of the perturbation the proposed feedback also affects the response of the ice sheet to time varying climate forcing the results suggest that the evolution of a continental scale ice sheet with a land based margin may be significantly determined by the changes it induces in the atmospheric circulation

a look inside the san andreas fault at parkfield through vertical seismic profiling the san andreas fault observatory at depth pilot hole is located on the southwestern side of the parkfield san andreas fault this observatory includes a vertical seismic profiling vsp array vsp seismograms from nearby microearthquakes contain signals between the p and s waves these signals may be p and s waves scattered by the local geologic structure the collected scattering points form planar surfaces that we interpret as the san andreas fault and four other secondary faults the scattering process includes conversions between p and s waves the strengths of which suggest large contrasts in material properties possibly indicating the presence of cracks or fluids

microseismic reflection imaging and its application to the basel geothermal reservoir we have developed a new approach for reflection seismic imaging using microseismic waveform data we took the specific character of microseismic downhole data into account and were able to image regions in the direct vicinity or inside of a seismically active zone we used a directional migration method that reduced imaging artifacts caused by the low aperture of the data but required estimation of the wavefield polarization we also used hodogram analysis to identify parts of data that provided reliable polarization estimates only these parts were then used for imaging whereas the rest of the data are excluded the approach was successfully applied to microseismic waveforms recorded during and after the stimulation of the enhanced geothermal system in basel switzerland this data set included more than 2000 events recorded at five sparsely distributed borehole sensors the reflection images revealed a distinct network of reflectors in the vicinity of the open hole section within the injection well the results were compared with the injection borehole ultrasonic image revealing a quite good agreement combined analysis of imaged reflectors event locations and event focal mechanisms indicated that the approach resolved mostly aseismic highly permeable fluid pathways whereas most of the seismicity occurred in the second order fractures

faulting induced by forced fluid injection and fluid flow forced by faulting an interpretation of hydraulic fracture microseismicity carthage cotton valley gas field texas we analyzed precisely located microearthquake data detected during five hydraulic fracture treatments in the carthage gas field of east texas the treat ments were conducted in two adjacent boreholes within interbedded sands and shales of the upper cotton valley formation the microearthquakes were induced within narrow horizontal bands that correspond to the targeted sandstone layers events throughout all the treatments show strike slip faulting occurring uniformly along vertical fractures trending close to maximum horizontal stress direction these events are consistent with the reservoir s prevalent natural fractures known to be isolated within the sands and trending subparallel to the expected hydraulic fracture orien tation when this uniform fracture system was activated exclusively the detected shear deformation measured as the moment release per unit volume of fluid injected was constant independent of various fluid viscosities and flow rates used within the base of the upper cotton valley formation anomalous event counts and moment release occurred within dense clusters that delineate bends or jogs in the fracture zones the mechanisms are also strike slip but the fault planes are more favorably oriented for failure the dense clusters show location patterns diverging in time suggesting the expulsion of fluids from compressive fault jogs fluid flow forced by the adjacent slip induced loading appears to initially extend the treatments but the loading also tends to lock up and concentrate stress at the jogs as evident by fewer but larger events populating the structures as treatments progress as a result effec tive drainage lengths from the boreholes may be shorter than would be inferred from the seismicity extending past the jogs these high moment asperities are similar to dense patches of seismicity observed along creeping sections of the san andreas fault where they have been attributed to localized zones of strength or stress con centration surrounded by larger regions undergoing stable aseismic slip this sim ilarity plus large moment deficits in terms of volume injected suggests a large component of aseismic slip is induced by the cotton valley treatments

new and revised radiolarian biochronology for the sedimentary cover of ophiolites in the lesser caucasus armenia in order to improve our understanding of the palaeogeographic and geodynamic evolution of the tethyan realms preserved in the lesser caucasus we here review the existing data for the sedimentary cover of ophiolites preserved in armenia particular attention is given to those dated sedimentary rocks that are in direct genetic contact with ophiolitic lavas as they provide constraints for submarine oceanic activity the oldest available ages come from the sevan akera suture zone that point to a late triassic oceanization data from both the sevan and vedi ophiolites provide evidence for middle jurassic bajocian submarine activity that continued until at least the late jurassic mid late oxfordian to late kimmeridgian early tithonian as dated recently in stepanavan and in this study for the vedi ophiolite

initiation and development of the laurentide and cordilleran ice sheets following the last interglaciation abstract fossil records from sites overridden by or adjacent to the laurentide ice sheet indicate that the climate of the last interglaciation oxygen isotope substage 5e ca 130 116 ka was warmer than today following the last interglaciation the laurentide ice sheet first developed during stage 5 over keewatin quebec and baffin island along its northern margin the ice sheet reached its maximum extent of the last glaciation during stage 5 the ice sheet advanced across baffin island onto the continental shelf early during stage 5 5d whereas the advance into the western canadian arctic occurred late during stage 5 5b the ice sheet also may have advanced into the st lawrence lowland during substage 5b although this event may be younger stage 4 the hudson bay lowland became ice free during substage 5a retreat of the ice sheet on baffin island occurred during late stage 5 probably substage 5a the exact timing of retreat from the western canadian arctic is unknown but it occurred before 48 ka the southern sector including the st lawrence lowland was ice free during late stage 5 the hudson bay lowland may have remained ice free through stage 4 and much of stage 3 because of conflicting chronologies however it is more likely that this area was glaciated throughout stage 3 and perhaps stage 4 nevertheless the data demonstrate that the lowland was ice free during part of the last glaciation an independent ice cap developed over the appalachian uplands and advanced across nova scotia during stage 4 perhaps as far as the edge of the continental shelf the ice cap remained active over nova scotia as a setellite to the laurentide ice sheet throughout the remainder of the last glaciation the ice sheet advanced into the st lawrence lowland during stage 4 and subsequently overwhelmed the local ice cap in the appalachian uplands advancing perhaps into northern new england but not farther south the lowland remained covered by the ice sheet until late stage 2 the ice sheet may also have advanced into the lake ontario basin during stage 4 the position of the northern margin of the laurentide ice sheet during stage 4 is not known but it remained an unknown distance behind its maximum position reached during stage 5 cores from baffin bay indicate a substantial decrease in high latitude glaciation during stage 4 following retreat the keewatin sector of the ice sheet may have remained over much of northwestern canada as a quasi stable ice mass until it readvanced during stage 2 similarly the baffin island sector of the ice sheet may have remained largely intact the southern margin of the ice sheet may have advanced into the lake ontario basin and upper mississippi valley during the middle of stage 3 ca 50 ka reaching its maximum extent of the last glaciation during stage 2 ca 18 21 ka advance of the northern margin was younger ca 8 13 ka than that of the southern margin this advance was less extensive than the penultimate advance stage 5 paleoenvironmental records indicate that the last interglaciation in areas covered by and near the cordilleran ice sheet was as warm as or warmer than present the cordilleran ice sheet appears to have developed during stage 5 or 4 at that time it advanced over southern british columbia and into the northern puget lowland there is no record of this event in northern areas that were later covered by the ice sheet the ice sheet disappeared before 59 ka at the beginning of a lengthy nonglacial interval paleoenvironmental records indicate that climate was similar to the present during part of this interval the ice sheet was absent and glaciers probably were confined to mountain areas throughout stage 3 climatic deterioration marking the end of this nonglacial interval may have begun as early as 29 ka by 14 15 ka the ice sheet had achieved its maximum extent of the last glaciation because there are few suitable dating methods capable of resolving events beyond the radiocarbon limit and because sites that preserve a record of events from the last glaciation are spatially restricted we consider this synthesis as tentative and subject to significant revision as dating methods improve nevertheless this perspective of the north american ice sheets through the last glaciation demonstrates their complex and dynamic behavior and attendant rapid fluctuations in ice volume

fresnel volume migration of single component seismic data standard implementations of kirchhoff prestack depth migration psdm distribute the recorded wavefield along two way traveltime isochrons and an image is generated by constructive interference of these isochrons along the actual reflector elements beside the recent developments of wave equation based approaches kirchhoff psdm is still considered widely as a state of the art technique in obtaining high quality images of the subsurface particularly for highly irregular survey layouts and target oriented imaging tasks however for sparse sampling or limited aperture the resulting image is affected by significant migration noise as a result of limited constructive interference of the back propagated wavefield some modifications have been proposed to reduce these artifacts these modifications include constructing a specular path of wave propagation derived from estimates of the emergent angle of coherent phases in the seismogram section and the mainly heuristic restriction of the imaging operator to the neighborhood of that wavepath our approach uses fresnel volumes to restrict the migration operator in a physically frequency dependent way using the emergent angle at the receiver determined by a local slowness analysis a ray is propagated into the subsurface the back propagation of the wavefield is restricted to the vicinity of this ray according to its approximated fresnel volume this so called fresnel volume migration approach enhances image quality significantly compared with standard kirchhoff psdm because of the inherent focusing and the restriction of the back propagation to the region around the actual reflection point

the sensitivity of stationary waves to variations in the basic state zonal flow abstract a linear primitive equation stationary wave model having high vertical and meridional resolution is used to examine the sensitivity of orographically forced primarily by himalayas stationary waves at middle and high latitudes to variations in the basic state zonal wind distribution we find relatively little sensitivity to the winds in high latitude but remarkable sensitivity to small variations in the subtropical jet fluctuations well within the range of observed variability in the jet can lead to large variations in the stationary waves of the high latitude stratosphere and to large changes even in tropospheric stationery waves implications for both sudden warmings and large scale weather are discussed

a simple ice sheet model yields realistic 100 kyr glacial cycles records of global ice volume for the past 700 kyr based on oxygen isotopic data from deep sea cores and reflecting mainly the changing northern hemispheric ice sheets show a dominant cycle of roughly 100 kyr period the records also show smaller amplitude oscillations with spectral peaks at roughly 40 and 20 kyr periods which are well correlated with the milankovich insolation variations due to perturbations in the earth s orbital parameters however no model has accurately simulated the 100 kyr glacial cycle recently birchfield et al 1 and oerlemans2 have obtained encouraging agreement with some features of the glacial cycle by using a simple ice sheet model with a realistic time lag in the response of the bedrock to the ice load this study extends their basic model first by including topography to represent high ground in the north improved results can then be obtained but only with unrealistic parameter values and for some aspects of the record further improvements areobtained by crudely parameterizing possible calving at the equatorward ice sheet tip during deglaciation by proglacial lakes and or marine incursions from the atlantic as emphasized by andrews3 the resulting ice volume curves agree fairly well with the observed records and their power spectra over the past 700 kyr

high resolution microseismic imaging abstract we examine the feasibility of high resolution microseismic imaging of unconventional reservoirs given frequencies in typical downhole microseismic data that are almost an order of magnitude higher than in seismic reflection data a comparable increase in image resolution might be expected bringing potential resolution of downhole microseismic images to a few meters we demonstrate that such a resolution is indeed achievable and present two case studies illustrating the reservoir features that can be imaged our first example constructed with p waves recorded in the woodford field reveals internal fabric of the woodford reservoir and formations surrounding it allowing us to discriminate the stimulated and unstimulated zones of the lower woodford shale encouraged by those results in our second example this time from the bakken field we use the slow shear waves which are more sensitive to fluids than p waves to find out whether hydraulic fractures themselves could be imaged our seismic v

rupture directivity of fluid induced microseismic events observations from an enhanced geothermal system the rupture process of fluid induced microseismic events is still poorly understood mainly due to usually small magnitudes and sparse monitoring geometries the high quality recordings of the earthquake sequence 2006 2007 at the enhanced geothermal system at basel switzerland constitute a rare exception allowing a systematic directivity study of 195 events using the empirical green s function method we observe clear directivity signatures for about half the events which demonstrates that rupture directivity persists down to small magnitudes ml 1 the predominant rupture behavior is unilateral we further find evidence that directivity is magnitude dependent and varies systematically with distance from the injection source whereas pore pressure seems to play the dominant role close to the injection source and no preferred rupture direction is observable directivity aligns parallel to the event distribution with increasing distance 100 m and is preferably oriented away from the injection point the largest analyzed events ml 2 show a distinct behavior they rupture toward the injection source suggesting that they nucleate in the vicinity of the pressure front and propagate backward into the perturbed volume this finding is of particular relevance for seismic hazard assessment of georeservoirs since it implies that maximum event size is related to dimension of the fluid perturbed volume our study also resolves rupture complexities for a small group of events this shows that small fault heterogeneities exist down to a scale of a few tens of meters the observation of directivity and complexity in induced microseismic events suggest that future source studies account for these phenomena

a comparison of competing explanations for the 100 000 yr ice age cycle there currently exists no consensus as to the cause of the ice ages of the late pleistocene many of the competing hypotheses have been formulated into mathematical models which enables a rigorous comparison to be made spectral analysis fails to distinguish rival models using regression analysis we examine the relative performance of several models each representative of a different type of modeling approach as explanations of both the global ice volume and also the time rate of change of the global ice volume we find there is no objective evidence in the record in favor of any particular model the respective merits of the different theories must therefore be judged on physical grounds

fresnel volume migration of multicomponent data if the aperture of a seismic reflection experiment is strongly limited kirchhoff migration suffers from strong artifacts attributable to incomplete summation this can be overcome by restricting the migration operator to the region that physically contributes to a reflection event examples of such limited aperture experiments include data acquisition in boreholes tunnels and mines we present an extension to three component 3c kirchhoff prestack depth migration where the migration operator is restricted to the fresnel volume of the specular reflected raypath we use the measured polarization direction at a 3c receiver to determine points of specular reflection in homogeneous media the polarization angle of 3c data can be used directly to decide whether a certain image point belongs to the fresnel volume of a specular reflection in heterogeneous media the fresnel volume around an image point is approximated by means of paraxial ray tracing the method is tested on a synthetic vertical seismic profiling experiment with strongly limited aperture migration artifacts and crosstalk effects from converted waves are strongly reduced compared with standard migration schemes the method is successfully applied to seismic data acquired in a tunnel

statistics of fracture strength and fluid induced microseismicity 1 in this paper we develop an approach for estimating the strength of rocks by analyzing fluid induced microseismicity the strength corresponds to the value of critical pressure in the pore space that must be exceeded in order to activate preexisting fractures i e to trigger earthquakes we assume that during hydraulic injection experiments in boreholes microseismicity is mainly triggered by a diffusive process of pore pressure perturbation an analytical solution can be applied to find time dependent pore pressure perturbations in rocks caused by fluid injections characteristics of the spatiotemporal evolution of microseismic clouds can be then used to estimate minimum and maximum pressures necessary to trigger earthquakes moreover we present a method for reconstruction of the full spectrum of rock strength that is we show how to estimate the probability density function of the critical pressure we verify the approach using numerical data and apply it to real data of injection induced microseismicity from two hot dry rock tests in crystalline rocks and one hydraulic fracturing experiment in a sedimentary rock the results show that such an analysis of microseismicity is able to provide us with a completely new feature of natural fractured rocks in situ namely the statistics of their strength we find that very low critical pressures in the range 0 001 1 mpa characterize the strength of preexisting cracks for all data sets analyzed the range of critical pressures is broadly distributed within 3 to 4 orders of magnitude however the probability density functions of critical pressure change very quickly from the zero level to significant values and from significant values to the zero level at the lower and upper limits of their nonvanishing value ranges respectively the lower bound of critical pressure is possibly defined by the magnitude of tidal induced stresses permanently occurring and relaxing in the earth

petroleum reservoir characterization using downhole microseismic monitoring imaging of microseismic data is the process by which we use information about the source locations timing and mechanisms of the induced seismic events to make inferences about the structure of a petroleum reservoir or the changes that accompany injections into or production from the reservoir a few key projects were instrumental in the development of downhole microseismic imaging most recent microseismic projects involve imaging hydraulic fracture stimulations which has grown into a widespread fracture diagnostic technology this growth in the application of the technology is attributed to the success of imaging the fracture complexity of the barnett shale in the fort worth basin texas and the commercial value of the information obtained to improvecompletions and ultimately production in the field the use of commercial imaging in the barnett is traced back to earlier investigations to prove the technology with the cotton valley imaging project and earlier experiments at the m site in the piceance

microseismic imaging of a geothermal reservoir stimulation exploitation of geothermal heat energy from rocks at depths of several km has been the goal of vari ous projects since the mid 1970s to exploit the energy in these deep rocks poses technical challenges in drilling well completion creation of the heat exchange reservoir at depth and control of seismicity in spite of the difficulties what are now known as enhanced engineered geothermal systems egs offer almost limitless clean energy so it is not surprising that this technology continues to attract investors however commercial energy production from the greatest potential resource hot rock at depths 5 km or temperatures 200 c remains elusive

stationary waves of the ice age climate abstract a linearized steady state primitive equation model is used to simulate the climatological zonal asymmetries stationary eddies in the wind and temperature fields of the 18 000 ybp climate during winter we compare these results with the eddies simulated in the ice age experiments of broccoli and manabe who used climap boundary conditions and reduced atmospheric co2 in an atmospheric general circulation model gcm coupled with a static mixed layer ocean model the agreement between the models is good indicating that the linear model can be used to evaluate the relative influences of orography diabatic heating and transient eddy heat and momentum transports in generating stationary waves we find that orographic forcing dominates in the ice age climate the mechanical influence of the continental ice sheets on the atmosphere is responsible for most of the changes between the present day and ice age stationary eddies this concept of the ice age climate is complicated by the sensitivity of t

reflection imaging of deep reservoir structure based on three dimensional hodogram analysis of multicomponent microseismic waveforms 1 we have applied a type of reflection technique in which natural or induced microseismicity is used as a wave source and is processed in the time frequency domain to data from the soultz hot dry rock site to image deep structures within the reservoir that may be associated with flow paths among three wells we selected and analyzed 119 good waveforms observed in 2003 the distribution of these 119 events was not strongly inclined and although the selected number of events was much smaller than the total microseismic events located we still succeeded in applying the reflection analysis the reflection images obtained using waveforms from 2003 are in agreement with those obtained using data from 1993 and 2000 finally detailed three dimensional reflection images were created by an integration of estimates using all available waveform data reflectors appear around the deep geothermal wells and one of the dipping reflectors seems to be an obstacle to flow connection that shows a clear correlation with a microseismic cloud created during hydraulic stimulation in 2004 from these analyses we succeeded in interpreting the roles of preexisting structures in the development of flow connection among wells which is an essential factor in a hot dry rock system