cone penetration test calibration for erksak beaufort sea sand interpretation of the cone penetration test in sands is generally based on empirical calibrations from tests in large diameter calibration chambers although interpretation of these calibration data for clean sands in terms of the state parameter is expected to be broadly applicable to other sands material specific correlations are desirable for many projects this paper describes a series of calibration chamber tests carried out on a sand dredged from the beaufort sea for construction of artificial islands this erksak sand is a uniformly graded subrounded medium grained sand with a fines content of 3 6 the testing chamber described is 1 4 m in diameter and allows independent control of vertical horizontal and back pressures on the sand sample samples of the sand were prepared by moist compaction to preserve the fines content and then back pressure saturated the chamber test data are presented and confirm that the erksak sand fits the general trends observed for other sands very well a method i

spatial correlation of seismic slip at the hdr soultz geothermal site qualitative approach one major goal of monitoring seismicity accompanying hydraulic frac turing of a reservoir is to obtain information about the pattern size and orientation of fractures the traditional method is to analyze the pattern of locations of the induced microearthquakes to investigate whether additional information about the fracture pattern may be obtained from induced microearthquake datasets we applied variogram analysis to investigate the spatial distribution of shear displacement at the source of microearthquakes variography is a method for analyzing spatial interde pendence of a variable the method was applied to a set of induced microearthquakes observed in the vicinity of the gpk1 injection well at soultz sou forets hot dry rock geothermal site alsace france variograms obtained for 20 vertical slices zones along the wellbore were compared with the orientation of the fractures de rived from a formation micro imager which is a resistivity log for measuring po sition and orientation of fractures in a borehole we found that variograms exhibiting spatial dependency correlated well with zones where fractures belong to one domi nant orientation set and variograms with no or low spatial dependency corresponded to zones with two or more fracture orientations sets we propose that this correlation results from the relation between the spatial variation of shear displacement the physical properties of fractures and their orientations

reconsideration of case histories for estimating undrained shear strength in sandy soils when sandy soils respond in a strain softening manner to undrained loading an estimation of the resulting undrained shear strength su is required to determine the potential for flow liquefaction

a reinterpretation of seismicity associated with the january 1983 dike intrusion at kilauea volcano hawaii in january 1983 a dike intrusion fissure eruption generated a swarm of 375 magnitude 1 to 3 earthquakes along a 16 km segment of kilauea s middle east rift zone we searched the hawaiian volcano observatory catalog for multiplets of similar events from this region from 1980 through 1985 and obtained precise relative locations by waveform cross correlation over 150 of the intrusion earthquakes could be grouped into 14 multiplets of five or more events with sufficient similarity for accurate relocation some multiplets were active for only a few minutes during the downrift migration phase of the seismic swarm consistent with generation near the propagating dike tip while others were active for several days the two multiplets nearest the origin of the seismic swarm include events from the preceding days and months most multiplets span only 50 to 100 m following relocation are located at about 3 to 4 km depth and appear to deepen downrift the catalog depths of those earthquakes in multiplets and those not in multiplets are similar suggesting that most of the recorded seismicity may have come from a very limited depth interval despite the fact that the dike breached the surface by analogy with a mechanical model used to explain a similar clustering of background seismicity in the upper east rift in 1991 we infer that the earthquakes are generated in regions of high stress concentration immediately above kilauea s deforming deep rift body this conclusion is consistent with the depth of the top of the deep rift body inferred from geodetic data and with numerical calculations suggesting that a significant ambient differential stress is required for dikes to produce earthquakes larger than magnitude 1

slip parallel seismic lineations on the northern hayward fault california a high resolution relative earthquake location procedure is used to image the fine scale seismicity structure of the northern hayward fault california the seismicity defines a narrow near vertical fault zone containing horizontal alignments of hypocenters extending along the fault zone the lineations persist over the 15 year observation interval implying the localization of conditions on the fault where brittle failure conditions are met the horizontal orientation of the lineations parallels the slip direction of the fault suggesting that they are the result of the smearing of frictionally weak material along the fault plane over thousands of years

unstable behaviour of sand and its implication for slope instability results of some constant shear drained csd tests conducted on both loose and dense sand are presented using the critical state line and a modified state parameter a new framework for analysing the instability of granular soil slopes is proposed the test data were examined and interpreted using the new framework instability lines for sand with different void ratios were established within this framework the conditions for the occurrence of instability in both contractive and dilative granular soil slopes under various shear stress levels were examined using the proposed framework key words deformation laboratory tests liquefaction sands shear strength slope stability

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

monitoring velocity variations in the crust using earthquake doublets an application to the calaveras fault california we present a technique that greatly improves the precision in measuring temporal variations of crustal velocities using an earthquake doublet or pair of microearthquakes that have nearly identical waveforms and the same hypocenter and magnitude but occur on different dates we compute differences in arrival times between seismograms recorded at the same station in the freqency domain by cross correlation of short windows of signal a moving window analysis of the entire seismograms including the coda gives t the difference in arrival times versus running time along the seismogram the time resolution of the method is an order of magnitude better than the digitization interval the t technique is illustrated with a pair of microearthquakes m 1 7 and 2 0 that occurred before and after the coyote lake california earthquake m 5 9 of august 6 1979 and on the same segment of the calaveras fault that ruptured during the earthquake the coda wave arrivals for some stations are progressively delayed for the second earthquake in the doublet so that its seismogram appears as a stretched version of the earlier event we interpret this systematic variation in t along the coda as a change in the average s velocity in the upper crust in the time interval between the two doublets s wave velocities appear to have decreased by 0 2 in an oblong region 5 10 km in radius at the south end of the aftershock zone

yield strength ratio and liquefaction analysis of slopes and embankments a procedure is proposed to evaluate the triggering of liquefaction in ground subjected to a static shear stress i e sloping ground using the yield strength ratio su yield v0 thirty liquefaction flow failures were back analyzed to evaluate shear strengths and strength ratios mobilized at the triggering of liquefaction strength ratios mobilized during the static liquefaction flow failures ranged from approximately 0 24 to 0 30 and are correlated to corrected cone and standard penetration resistances these yield strength ratios and previously published liquefied strength ratios are used to develop a comprehensive liquefaction analysis for ground subjected to a static shear stress this analysis addresses 1 liquefaction susceptibility 2 liquefaction triggering and 3 post triggering flow failure stability in particular step 2 uses the yield strength ratio back calculated from flow failure case histories and the cyclic stress method to incorporate seismic loading

deep fault plane geometry inferred from multiplet relative relocation beneath the south flank of kilauea dense microearthquake swarms occur in the upper south flank of kilauea providing multiplets composed of hundreds of events the similarity of their waveforms and the quality of the data have been sufficient to provide accurate relative relocations of their hypocenters a simple and efficient method has been developed which allowed the relative relocation of more than 250 events with an average precision of about 50 m horizontally and 75 m vertically relocation of these events greatly improves the definition of the seismic image of the fault that generates them indeed relative relocations define a plane dipping about 6 northward although corresponding absolute locations are widely dispersed in the swarm a composite focal mechanism built from events providing a correct spatial sampling of the multiplet also gives a well constrained northward dip of about 5 to the near horizontal plane this technique thus collapses the clouds of hypocenters of single event locations to a plane coinciding with the slip plane revealed by previous focal mechanism studies we cannot conclude that all south flank earthquakes collapse to a single plane there may locally be several planes perhaps with different dips and depths throughout the south flank volume the 6 northward dipping plane we found is too steep to represent the overall flexure of the oceanic crust under the load of the island of hawaii this plane is probably an important feature that characterizes the basal slip layer below the upper south flank of kilauea volcano differences in seismicity rate and surface deformations between the upper and lower south flank could be related to the geometry of this deep fault plane the present work illustrates how high precision relative relocations of similar events in dense swarms combined with the analysis of geodetic measurements can help to describe deep fault plane geometry systematic selection and extensive relative relocation of similar earthquakes could be attempted in other well instrumented highly seismic areas to provide reliable basic information especially useful for understanding of earthquake generation processes

induced microearthquake patterns in hydrocarbon and geothermal reservoirs six case studies the injection or production of fluids can induce microseismic events in hydrocarbon and geothermal reservoirs by deploying sensors downhole data sets have been collected that consist of a few hundred to well over 10 000 induced events we find that most induced events cluster into well defined geometrical patterns in many cases we must apply high precision relative location techniques to observe these patterns at three sedimentary sites thin horizontal strands of activity are commonly found within the location patterns we believe this reflects fracture containment between stratigraphic layers of differing mechanical properties or states of stress at a massive carbonate and two crystalline sites combinations of linear and planar features indicate networks of intersecting fractures and allow us to infer positions of aseismic fractures through their influence on the location patterns in addition the fine scale seismicity patterns often evolve systematically with time at sedimentary sites migration of seismicity toward the injection point has been observed and may result from slip induced stress along fractures that initially have little resolved shear in such cases triggering events may be critical to generate high levels of seismic activity at one crystalline site the early occurrence of linear features that traverse planes of activity indicate permeable zones and possible flow paths within fractures we hope the continued development of microseismic techniques and refinement of conceptual models will further increase our understanding of fluid behavior and lead to improved resource management in fractured reservoirs

precise microearthquake locations and fluid flow in the geothermal reservoir at soultz sous forets france i relocated two microearthquake clusters induced by hydraulic stimulation of a hot dry rock geothermal reservoir in the rhine graben near soultz sous forets france the two clusters were chosen from a collection of clusters identified within a 16 000 event data set obtained in 1993 i determined p and s wave arrival times manually choosing distinctive peaks if waveforms were similar at a given station or first breaks if waveforms were emergent or nodal judging weights accordingly requiring a minimum of five arrival times yielded populous clusters of 226 and 355 events in both cases relocation revealed two distinct planar patches of activity 100 to 200 m across intersecting and truncating one another along a common edge linear segments traverse the planar patches and may mark intersections with seismically inactive fractures the earliest activity occurred along these segments these segments may therefore mark permeable zones that could be important components of the fluid flow network the interpretation of linear segments as flow paths is supported by path dimension constraints derived from fluid flow modeling studies and by the expected confining effects of hydrothermal sealing found in cored fractures orientations of the planar features are verified through consistency with orientations found in core and logging studies in addition focal mechanisms obtained by constraining slip planes parallel to active planes indicate normal to right lateral strike slip consistent with the measured stress field focal mechanisms indicate mass deficits at inside corners implying that the concentrations of activity at fracture intersections may result from slip on one fracture causing extension and a resulting permeability increase in the other the improved location precision results from a ten fold improvement in the precision of arrival time estimation for phases that were similar as estimated from the standard deviation of residuals grouped by station and phase before and after repicking only a two fold improvement was noted for poorly correlated or nodal phases for this data set the manual phase picking yielded more interpretable detail in the location patterns compared to results of an automatic cross correlation technique the manual results could be used to guide improvements to automatic techniques to obtain precise locations of the entire data set

stochastic evaluation of static liquefaction in a predominantly dilative sand fill the paper investigates the potential for liquefaction in a predominantly dilative hydraulic sand fill and in particular whether pockets of loose material could have been instrumental in the failure of the nerlerk underwater berm this has been achieved stochastically by linking random field theory for modelling spatial variability with finite elements for computing geostructural response specifically a double hardening soil model has been calibrated against data from 74 triaxial tests on erksak sand for a wide range of sand states while state parameter statistics have been derived from 71 cone penetration tests from two beaufort sea sand islands multiple realisations of structural performance have then been carried out by generating univariate random fields of state parameter from which the soil model parameters have been inferred the results demonstrate that it may be possible for a predominantly dilative fill to liquefy due to the presence of semi continuous loose zones arising from deposit

improved relative locations of clustered earthquakes using constrained multiple event location a new method for improving relative locations of clustered earthquakes is presented and applied to a suite of microearthquakes induced by hydraulic fracturing the method is based on the assumption that clustering of earthquake hypocenters is obscured by the uncorrelated scatter of individual hypocenters the method is implemented as an additional constraint in a joint hypocenter determination jhd scheme the method shifts event hypocenters toward the center of mass of the events within some volume surrounding the event location if the rms misfit between predicted and measured arrival times does not increase significantly the method uses the same basic assumption of jones and stewart 1997 which is that there is greater clustering in actual earthquake locations than there is in locations determined using conventional techniques our method differs in that it is implemented as part of the jhd process so it operates on raw travel time data rather than on derived hypocenters the method produces hypocenters from a demonstration field dataset that are similar to those obtained by phillips et al 1997 from time consuming precise manual repicking of relative arrival times of events the clustering constraint can easily be incorporated as an additional constraint in earthquake location velocity tomography codes and may lead to improved velocity structure determination and earthquake location pattern identification and interpretation

clustering and periodic recurrence of microearthquakes on the san andreas fault at parkfield california the san andreas fault at parkfield california apparently late in an interval between repeating magnitude 6 earthquakes is yielding to tectonic loading partly by seismic slip concentrated in a relatively sparse distribution of small clusters 20 meter radius of microearthquakes within these clusters which account for 63 of the earthquakes in a 1987 92 study interval virtually identical small earthquakes occurred with a regularity that can be described by the statistical model used previously in forecasting large characteristic earthquakes sympathetic occurrence of microearthquakes in nearby clusters was observed within a range of about 200 meters at communication speeds of 10 to 100 centimeters per second the rate of earthquake occurrence particularly at depth increased significantly during the study period but the fraction of earthquakes that were cluster members decreased

studies of the seismic coda using an earthquake cluster as a deeply buried seismograph array loosely speaking the principle of green s function reciprocity means that the source and receiver positions in a seismic experiment can be exchanged without affecting the observed seismograms consequently the seismograms observed at a single observation location o and caused by a cluster of microearthquakes at locations ei are identical to the time series that would be measured by an array of stress meters emplaced at positions ei recording waves generated by a source acting at o by applying array analysis techniques like slant stacking and frequency wave number analysis to these seismograms we can determine the directions and velocities of the component waves as they travel in the earthquake focal region rather than at the surface we have developed a computationally rapid plane wave decomposition which we have applied to single station recordings of aftershocks of the 1984 morgan hill california earthquake the analysis is applied to data from three seismic stations having considerably different site geologies one is a relatively hard rock station situated on franciscan metamorphics one is within the calaveras fault zone and one is on semiconsolidated sand and gravels we define the early coda to be the part of the coda initiating immediately after the direct s wave and ending at twice the s wave lapse time the character of the s wave and early coda varies from being impulsive at the first station to highly reverberative at the last we examine waves in sequential time windows starting at the s wave and continuing through the early part of the coda at all seismic stations the early coda is dominated by a persistent signal that must be caused by multiple scattering probably within 2 km of each seismic station despite clear station to station differences in the character of the early coda coda q values measured in the late coda greater than twice the s lapse time agree well among stations implying that the mechanisms causing the varying behavior of the early coda do not control the coda decay rate at the stations we have considered coda q values measured on horizontal components of motion agree within a factor of 2 with those measured on vertical components we have not been able to determine the composition of the late coda because of a low signal to noise ratio our analysis technique however is quite appropriate for such a task

influence of landslide geometry and kinematic deformation to describe the liquefaction of landslides some theoretical considerations abstract the generation of excess pore pressure and possible liquefaction can be explained by different mechanisms in literature less attention is given to the effects of landslide geometry and kinematic deformation on the generation of excess pore pressure and possible liquefaction of sliding blocks the objective of this paper is to discuss these factors by proposing a simple analytical model of landslide liquefaction using classic soil mechanics theory the model describes the initial state of failure and solves forces for each slice with the bishop s limit equilibrium method immediately after failure the difference in movement for each slice is calculated assuming a viscous shear band and using the coulomb viscous model the differential movements conduct to differential strains which are transferred to excess pore pressures in slides characterized by curved slip surfaces the lower parts showed compaction and increase in pore pressures during displacement while the upper parts showed dilatation and a decrease in pore pressures the potential liquefaction is then evaluated for each slice in relation to the displacement the model is applied to a slump type failure that occurred on the super sauze mudslide southeast france in compact clay rich material it was observed that the slump completely liquefied into a flow however the model simulations were not able to completely liquefy all the slices of the slump in case a decrease in pore pressures through dilatation was assumed in the upper part of the slump the decrease in pore pressures caused a rapid stabilisation of the remaining sliding body in case a neutral pore pressure was assumed in the upper part with dilatation movement and deformation of the remaining slices could continue leading to a nearly complete liquefaction of the slump model simulations for many geometries of curved slip surfaces reveal that the liquefied volume increases with steeper slopes and more curved slip surfaces it is discussed also how planar slides which in theory show small differential movement of the individual slices and hence no large compaction can completely liquefy through deformation at the toe

detailed joint structure in a geothermal reservoir from studies of induced microearthquake clusters microearthquake clusters form distinct planar patterns within five study regions of a geothermal reservoir undergoing hydraulic fracturing at fenton hill new mexico the patterns define individual slipping joint surfaces of dimension 40 120 m containing 80 150 events each sharp straight edges truncate the clusters we interpret these as marking intersections with aseismic joints each edge orientation is consistent with an intersection between the active joint and a plane oriented parallel to one of the other clusters we identify therefore it appears that cluster shapes constrain the geometry of seismic and aseismic joints both could be important components of the fluid flow network the distribution of inferred slip plane orientations is consistent with but fails to provide sufficient constraint to differentiate conclusively between two very different stress field estimates one measured using pressurization and wellbore breakouts the other using focal mechanisms of the largest microearthquakes an impermeable joint model requiring pore pressure in excess of the normal stress on a joint before slip can occur was inconsistent with many of the inferred slip plane orientations the high quality locations were possible because events from the same cluster generated nearly similar waveforms permitting the precise determination of relative arrival times standard deviations of arrival time residuals fall between 0 1 and 1 1 ms for these clusters major axes and aspect ratios of the 90 confidence ellipsoids range from 6 to 28 m and 1 5 to 8 respectively small events dominate the seismic energy release and thoroughly populate the identified active joints allowing the hypocenters to reflect details of the joint structure to further investigate the reservoir structure we applied a source array slant stack technique to waveforms from the well located clusters yielding directions that scattered energy left each cluster by studying paths of scattered waves we expected to pinpoint impedance contrasts that might have indicated concentrations of fluid filled joints however results show that scattered energy in the s wave coda left the source region in the same direction as the direct s wave direct waves may have excited borehole tube waves that became trapped in the vicinity of the geophone tool overwhelming any energy scattered from the reservoir

high precision relative locations of earthquakes at mount st helens washington several earthquake sequences have occurred at mount st helens as clusters of shallow events with nearly identical waveforms multiplets we present a technique that allows the relative relocation of events within a multiplet to at least an order of magnitude higher precision than is typically possible with traditional techniques a multiplet is studied in pairs of events called doublets each doublet is made up of a reference event and one other event from the multiplet the cross spectrum of a short window beginning just before the p arrival is used to compute differences in arrival times between seismograms from the same station for each doublet these time differences computed with a precision of 1 2 ms are then used to locate each earthquake relative to the reference event engineering explosions with well known locations are used to test the relocation technique explosions can be relocated with accuracy better than 20 m for events within 250 m of the reference explosion the relocation technique is applied to earthquakes preceding the september 10 1984 and the may june 1985 dome building eruptions of mount st helens forty events that occurred during a 12 hour period in september 1984 are located in a volume approximately 30 m in diameter beneath the lava dome the earthquakes following the extrusion do not occur in multiplets and appear to be distributed over a much larger volume in the may june 1985 eruption we recognize three multiplet sets that took place successively in time the multiplets are interpreted as repeated failure or slip within a relatively small volume due to high strain rates around the magma supply conduit

a method for determining significant structures in a cloud of earthquakes the interpretation of a cloud of earthquake hypocenters in terms of causative structures is not a simple task locations are subject to uncertainties which will not be the same for every earthquake the data should therefore not be interpreted simply by inspection which is difficult in the case of three dimensional data anyway instead we propose using the location uncertainties as a guide in processing the data earthquake locations are moved inside their uncertainty or confidence ellipsoids until a simplified picture of the earthquake cloud is obtained which can then be interpreted in terms of some simplified structure such as faults the aim of the approach is to give the simplest possible structure that is consistent with all the location and confidence ellipsoid data the method is applied to three synthetic sets of data these illustrate the potential and limitations of the method application to a real earthquake data set from rabaul caldera in papua new guinea gives an image of the caldera ring fault that suggests departures from the simple ring fault structure previously assumed sensitivity analysis on the rabaul data shows that the method is not unduly sensitive to the assumptions that have to be made in applying it

analysis of induced seismicity for stress field determination and pore pressure mapping the focal mechanisms of some one hundred microseismic events induced by various water injections have been determined within the same depth interval numerous stress measurements have been conducted with the htpf method when inverted simultaneously the htpf data and the focal plane solutions help determine the complete stress field in a fairly large volume of rock about 15 106 m3 these results demonstrate that hydraulically conductive fault zones are associated with local stress heterogeneities some of these stress heterogeneities correspond to local stress concentrations with principal stress magnitudes much larger than those of the regional stress field they preclude the determination of the regional stress field from the sole inversion of focal mechanisms in addition to determining the regional stress field the integrated inversion of focal mechanisms and htpf data help identify the fault plane for each for each of the focal mechanisms these slip motions have been demonstrated to be consistent with terzaghi s effective stress principle and a coulomb friction law with a friction coefficient ranging from 0 65 to 0 9 this has been used for mapping the pore pressure in the rock mass this mapping shows that induced seismicity does not outline zones of high flow rate but only zones of high pore pressure for one fault zone where no significant flow has been observed the local pore pressure has been found to be larger than the regional minimum principal stress but no hydraulic fracturing has been detected there

analysis of the microseismicity induced by fluid injections at the egs site of soultz sous forets alsace france implications for the characterization of the geothermal reservoir properties in june july 2000 a hydraulic stimulation experiment took place at the geothermal egs site of soultz sous forets alsace france in order to enhance the permeability of the fractured granitic massif at 5 km depth as it is well known that fluid injections tend to induce microseismic events a downhole and a surface seismological network have been installed to monitor the seismic activity during the stimulation test 23400 m3 of fluid have been injected in the rock volume through the open hole section 4400 m 5000 m of the well gpk2 at increasing rates of 30 l s 1 40 l s 1 and then 50 l s 1 more than 7200 microseismic events in the magnitude range 0 9 to 2 6 have been precisely located through a simultaneous inversion of the seismic velocity structure and location parameters the analysis of the behavior of the seismicity relative to the hydraulic parameters gives important information about the geothermal reservoir it appears that the evolution of the seismicity strongly depends on the variations of the injection rate an increase or a decrease leads to changes of the velocity structure the number and magnitude of microseismic events this involves different hydro mechanical processes between the fluid flow and the fracture planes which will control the final shape of the microseismic cloud moreover the study of the variations of the b value with time suggests that the stimulation experiment produces a large proportion of small earthquakes but records of events of magnitude higher than 2 indicate that fluid injection could reactivate structures whose dimensions allow the generation of such earthquakes

rupture geometry from high precision relative hypocentre locations of microearthquake clusters summary in 1987 two microearthquake sequences with a duration of about a week each and consisting of 37 and 46 events respectively occurred in the upper crust below the jura mountains of northern switzerland the seismograms within each sequence exhibit a high degree of similarity indicating tight clustering of hypocentres and similar focal mechanisms using a cross correlation technique applied to the seismograms in the time domain together with a new least squares adjustment procedure it was possible to determine relative hypocentre locations of the earthquakes in each cluster with a precision of a few tens of metres the results show that hypocentres of events with the same focal mechanism lie on a plane which coincides exactly with one of the nodal planes of the fault plane solution and that consequently swarm like sequences of similar earthquakes are due to repeated slip on the same fault in one case slip occurred as right lateral motion on a steeply dipping plane striking in wnw ese direction whereas the other case corresponds to left lateral slip on two almost vertical planes striking roughly n s in 1988 an additional earthquake triplet occurred on a wnw ese oriented normal fault nearby all three mechanisms are consistent with a general nnw sse oriented direction of maximum crustal shortening and a corresponding wsw ene oriented extension repeated slip on the same fault is indicative of a large degree of heterogeneity and of short term temporal variability of both frictional resistance and stress distribution on the fault an explanation for the occurrence of such swarm like seismic activity in terms of barriers or asperities would require that shear stress on the unbroken patches increase from one event to the next since however the overall shear stress would be expected to decrease as a consequence of the stress released in each event a more plausible mechanism involves pore pressure fluctuations caused by fluids under suprahydrostatic pressures migrating upward through pre existing zones of weakness in the crust

marine geotechnical engineering in canada marine geotechnical engineering in canada is over one hundred years old having started with overwater drilling and testing for bridges and nearshore structures its growth has been sporadic with not much attention being directed to the geotechnical properties of marine soils until the late 1970 s when design of artificial islands made up of large caissons started to develop for about the last 15 years marine geotechnical engineering has been driven by the oil and gas industry most of the action has been in the beaufort sea where complex site conditions have necessitated detailed geotechnical field drilling sampling programs and in situ testing very little geotechnical engineering research work or site invesigation has been carried out off the east coast except for the hibernia site on the grand banks in the coming years we can expect to see dramatic changes in site investigation methods the use of robotics and expert systems coupled with innovative geophysical techniques could dramatically change our methods of site charcterization and measurement of geotechnical properties

mineralization mechanisms in the shangfanggou giant porphyry skarn mo fe deposit of the east qinling china constraints from h o c s pb isotopes abstract the giant shangfanggou skarn porphyry mo fe deposit one of the largest mo deposits in the east qinling orogen is hosted by the neoproterozoic luanchuan group on the southern margin of the north china craton the mineralization occurs mainly as veinlets and in veinlet disseminated form within altered schists skarns hornfelses and or marbles the hydrothermal alteration and mineralization at shangfanggou took place over four stages stage 1 involved potassic alteration and silicification in the porphyry skarnization and magnetization in carbonate strata and hornfelsization in schists quartz molybdenite veins associated with phyllic alteration were produced in the porphyry during stage 2 along with sericitization chloritization serpentinization and silicification in the skarns hornfelses and or marbles quartz polymetallic sulfide veins related to phyllic alteration were produced during stage 3 and ore barren quartz calcite pyrite veins associated with weak carbonatation were produced during stage 4 c o and d isotope compositions of hydrothermal calcite dolomite magnetite phlogopite and quartz from different stages of mineralization during the formation of the shangfanggou deposit range from 12 9 to 8 8 3 2 to 22 7 and 100 to 80 respectively sulfur isotope compositions of sulfides from the ores of the shanfanggou deposit range from 3 6 to 4 4 206 pb 204 pb 207 pb 204 pb and 208 pb 204 pb ratios of 17 648 to 18 742 apart from one magnetite with a value of 20 78 15 526 to 15 690 and 38 197 to 39 823 in the shanfanggou deposit the evolution of the ore forming fluids in the shangfanggou deposit as revealed by 18 o d and 13 c isotope studies was one of progressive modification of the magmatic fluids through fluid wall rock interactions along conduits during fluid ascent and this signifies the involvement of formation strata water during the earlier stages of mineralization and the predominance of meteoric waters over magmatic fluids in the later stages the carbon sulfur and lead isotope compositions suggest mixing took place between the magmas and the host rocks within the region integrating the data obtained from studies of the regional geology ore geology fluid inclusions and c h o s pb isotope geochemistry we conclude that the shangfanggou mo fe deposit is a porphyry skarn type system that formed during a transition from compressional to extensional tectonics during the jurassic early cretaceous continental collision between the north china craton and yangtze craton the ore materials were sourced from magmatic ore forming fluids that mixed with components derived from carbonaceous wall rocks during their ascent and which were gradually mixed with meteoric waters especially in the later stages

evidence from a cluster of small earthquakes for a fault at 18 km depth beneath oak ridge southern california abstract a swarm of about 50 small earthquakes m 1 5 occurred for a month during 1989 beneath oak ridge southern california location accuracy using conventional analysis of arrival time picks is limited for these events by the weak emergent nature of arrivals on the available seismograms however waveform cross correlation techniques are found to provide precise relative event locations due to the similarity of the waveforms recorded at individual stations the relocated events form a small cluster about 1 km across at a depth of 18 km and are aligned along a plane that dips 35 to the northwest estimated standard errors for the locations are generally less than 50 m the time evolution of the sequence shows a gradual migration of activity away from its initiation point three additional events occurred several months later these align along the same plane but are displaced about 500 m to the southeast from the main swarm reliable fault plane solutions are difficult to obtain for these events due to the small number of station records available the limited range of takeoff angles and the weak initial arrivals on many of the seismograms stacking the records at each station over the different events greatly reduces prearrival noise levels and assists in resolving the average p first motions analysis of these first motion data indicates that the slip planes of probable focal mechanisms are not in agreement with the plane defined by the seismicity the seismicity alignment may represent the extension of the simi fault in which case some shallowing of the fault dip would be required to match the observed 35 dip at 18 km

drained instability of sand in plane strain flowslide or failure of loose granular soil slopes is often explained using liquefaction or instability data obtained from undrained triaxial tests however under static loading conditions the assumption of an undrained condition is not realistic for sand particularly clean sand case studies have indicated that instability of granular soil can occur under essentially drained conditions e g the wachusett dam failure in 1907 laboratory studies on changi sand by chu et al in 2003 have shown that sand can become unstable under completely drained conditions however these studies were carried out under axisymmetric conditions and thus cannot be applied directly to the analysis of slope failures in this paper experimental data obtained from plane strain tests are presented to study the instability behaviour of loose and dense sand under plane strain conditions based on these test data the conditions for the occurrence of drained instability in plane strain are established using the modified sta

hydraulic stimulation of natural fractures as revealed by induced microearthquakes carthage cotton valley gas field east texas we produced a high resolution microseismic image of a hydraulic fracture stimulation in the carthage cotton valley gas field of east texas we improved the precision of microseismic event locations four fold over initial locations by manually repicking the traveltimes in a spatial sequence allowing us to visually correlate waveforms of adjacent sources the new locations show vertical containment within individual targeted sands suggesting little or no hydraulic communication between the discrete perforation intervals simultaneously treated within an 80 m section treatment i e fracture zone lengths inferred from event locations are about 200 m greater at the shallow perforation intervals than at the deeper intervals the highest quality locations indicate fracture zone widths as narrow as 6 m similarity of adjacent source waveforms along with systematic changes of phase amplitude ratios and polarities indicate fairly uniform source mechanisms fracture plane orientation and sense of slip over

foreshock sequence of the 1992 landers california earthquake and its implications for earthquake nucleation the june 28 1992 landers california earthquake mw 7 3 was preceded for about 7 hours by a foreshock sequence consisting of at least 28 events in this study we examine the geometry and temporal development of the foreshocks using high precision locations based on cross correlation of waveforms recorded at nearby stations by aligning waveforms rather than trying to obtain travel time picks for each event independently we are able to improve the timing accuracy greatly and to make very accurate travel time picks even for emergent arrivals we perform a joint relocation using the improved travel times and reduce the relative location errors to less than 100 m horizontally and less than 200 m vertically with the improved locations the geometry of the foreshock sequence becomes clear the landers foreshocks occurred at a right step of about 500 m in the mainshock fault plane the nucleation zone as defined by the foreshock sequence is southeast trending to the south and nearly north trending to the north of the right step this geometry is confirmed by the focal mechanisms of the foreshock sequence which are right lateral and follow the trend as determined by the foreshock locations on the two straight segments of the fault and are rotated clockwise for foreshocks that occur within the step the extent of the foreshock sequence is approximately 1 km both vertically and horizontally modeling of the coulomb stress changes due to all previous foreshocks indicates that the foreshocks probably did not trigger each other this result is particularly clear for the mw 4 4 immediate foreshock since stress transfer in the sequence appears not to have played a significant role in its development we infer an underlying aseismic nucleation process probably aseismic creep other studies have shown that earthquake nucleation may be controlled by fault zone irregularities this appears to be true in the case of the landers earthquake although the size of the irregularity is so small that it is not detectable by standard location techniques

mapping the frequency magnitude distribution in asperities an improved technique to calculate recurrence times we hypothesize that highly stressed asperities may be defined by mapping anomalously low b values along the san andreas fault near parkfield the asperity under middle mountain with its b 0 46 can be distinguished from all other parts of the fault surface likewise along the calaveras fault the northern asperity of the morgan hill 1984 m6 2 rupture can be identified by its low b of 0 5 as a high stress patch along the fault we add further evidence to the observations that the b value of the frequency magnitude relationship of earthquakes is inversely proportional to stress by showing that it decreases with depth in the parkfield segment of the san andreas and along the calaveras fault in both of these areas b values above and below 5 km depth are 1 2 and 0 8 respectively we propose that probabilistic recurrence times tr based on the seismicity parameters a and b should be calculated from their values within asperities only instead of from the values of the entire rupture area of the maximum expected earthquake the strong patches on faults control the time of rupture because they are capable of accumulating larger stresses than the rest of the fault zone which slips along passively when an asperity breaks therefore no information on tr is contained in the passive fault segments only in the asperities at parkfield the probabilistic estimates of tr derived from the data in the whole rupture and in the asperity only are 72 18 24 and 23 12 18 years respectively compared to the historically observed repeat time of 22 years at morgan hill the tr estimates are 122 46 76 and 78 47 110 years respectively compared to the observed repeat time of 72 years

rates of aftershock decay and the fractal structure of active fault systems abstract aftershock activity on frequency decay against time is characterized by a power law the modified omori formula of an exponent p which differs with each aftershock sequence a theoretical study suggested that p which is a rate constant of aftershock decay is related to the fractal dimension of a pre existing fault system this has however never been checked aftershock activity on size distribution is also characterized by an exponential distribution against magnitude the gutenberg richter relation with a slope b although p is expected to be related to b which is related to the partitioning rate of earthquake energy the relationship has never been established here the relation between the p values and the fractal dimensions of the pre existing fault systems and that between the p values and the b values are explored using natural seismicity data and data of the observable fault systems the p and b values were estimated for fifteen aftershock sequences which occurred in japan in this paper aftershocks were identified on the basis of a phenomenological definition in the seismicity data the fractal capacity dimensions d0 are estimated for the pre existing active fault systems observed on the surface in the aftershock regions in the present paper the standard box counting method was adopted to get the d0 negative correlations between 1 p and d0 and 2 p and b were observed with some scattering observation 1 shows that the rate of aftershock decay p decreases systematically with increasing occupancy rate of the pre existing active fault system d0 and suggests that aftershock decay dynamics is constrained by the pre existing fracture field observation 2 shows that p certainly has a relation with b moreover we offer possible interpretation on these negative correlations and some scatters in both observations the scatters are interpreted as the scatter of the difference of two fractal dimensions between 3 d fracture construction in the crust and 2 d cross sectional surface observed active fault system supported by further tests this paper strongly suggests that the scaling for a natural fracture system is self affine with different fractal scalings in different directions rather than self similar which would be a manifestation of regional anisotropy of the fracture system and that the seismic parameters p and b depend on the 3 d construction of the fracture system in the crust

detailed fracture system of the soultz sous forets hdr field evaluated using microseismic multiplet analysis the reservoir structure of the soultz hdr field has been investigated by examining induced microearthquake multiplets microseismic events with similar waveforms have been selected from microseismic data obtained during a 1993 hydraulic fracturing experiment precise relative arrival times and source locations have been determined by cross spectrum analysis the cross spectrum analysis decreased the residual from 0 75 ms to 0 1 ms the estimated orientations of the multiplet planes are consistent with fracture orientations detected in soultz boreholes a comparison between the stress field and the orientation of structural planes suggests that the structural planes were under a critical condition of frictional slip

seismic imaging using microearthquakes induced by hydraulic fracturing abstractseismic imaging using microearthquakes induced by hydraulic fracturing produces a three dimensional 3 d s wave velocity model of the fractured zone improves the calculated locations of the microearthquakes and may lead to better estimates of fractureplane orientations fracture density and water flow paths such information is important for predicting the amount of heat energy that may be extracted from geothermal reservoir a fractured zone was created at the los alamos hot dry rock reservoir in north central new mexico within otherwise impermeable basement rock by injecting 21000 m3 of water into a borehole under high pressure at a depth of 3 5 km induced microearthquakes were observed using four borehole seismometers the p wave and s wave arrival times have been inverted to find the 3 d velocity structures and the microearthquake locations and origin times the inversion was implemented using the separation of parameters technique and constraints were incorporated to require smooth vel

joint hypocentral location in media with lateral velocity variations and interpretation of the station corrections abstract the application of a new implementation of the joint determination of hypocenters origin times and station correction terms jhd technique to data from the arkansas swarm usa the campi flegrei italy and the nazca plate argentina throws new light onto the problem of earthquake location in all these cases good quality p and s wave arrival times were available the main results are as follows 1 large lateral velocity variations llvv are generally associated with relatively large station corrections these corrections in turn are usually much larger than the average of the station residuals determined when the same set of events is located using a single event location sel method 2 the locations determined by the jhd and sel methods may be substantially different 3 since the effect of llvv on jhd locations is not well established simple 3 d velocity models are constructed so that the jhd technique applied to synthetic data generated using these models produce station corrections similar to those observed 4 the analysis of the synthetic data also shows that the locations determined by the jhd method are much closer to the true locations than the locations determined with the sel method the use of the weighted average of the sel station residuals as station corrections does not give better located events although there is a large decrease in the r m s residual computed for each event therefore the use of r m s residuals to estimate the quality of event locations is not always warranted in view of these results it is possible to conclude that the jhd station corrections can be used to detect lateral velocity variations and to produce locations substantially less affected by these variations than the locations determined by the sel method furthermore under appropriate conditions the jhd station corrections can also be used in a forward modeling scheme to get a semiquantitative velocity model such a model may be the only information that can be obtained from a data set when the station and event distributions are not adequate for 3 d velocity inversion

using automated high precision repicking to improve delineation of microseismic structures at the soultz geothermal reservoir an automatic adaptive correlation based algorithm for adjusting phase picks in large digital seismic data sets provides significant improvement in resolution of microseismic structures using only a small fraction of the time and manpower which would be required to re analyze waveforms manually or semi automatically we apply this technique to induced seismicity at the soultz sous forets geothermal site france the method is first applied to a small previously manually repicked subset of the catalogue so that we may compare our results to those obtained from painstaking visual cross correlation based techniques relative centroid adjusted hypocenters show a decrease in median mislocation from 31 to 7 m for preliminary and automatically adjusted picks respectively compared to the manual results narrow intersecting joint features not observed in the preliminary hypocenter cloud but revealed through manual repicking are also recovered using the automatic method we then address a larger catalogue of 7000 microearthquakes after relocating the events using automatic repicks the percentage of events clustering within 5 m of their nearest neighbor increases form 5 to 26 of the catalogue hypocenter relocations delineate narrow linear features previously obscured within the seismic cloud interpreted as faults or fractures which may correspond to fluid propagation paths or to changes in stress as a result of elevated pore pressures rms travel time residuals for the larger data set are reduced by only 0 2 however phase pick biases in the preliminary catalogue have influenced both the velocity model and station correction calculations which will affect location residuals these pick biases are apparent on the adjusted stacked waveforms and correcting them will be important prior to future velocity model refinements