extension of tube wave detection for quality evaluation of pile foundation abstract based on the theory of tube wave propagation in a fluid filled borehole this paper proposes a new method for detecting the integrity of pile foundation and overcomes some limitations of the existing pile integrity tests the basic principle of detecting the pile integrity by the tube wave testing equipment and concrete quality evaluation of piles are introduced the feasibility of the tube wave detection for geological exploration of a bridge pile in a karst development area is verified by field tests through some test cases of prestressed high strength concrete pipe piles cast in place piles and rock socketed piles with defects the accuracy of the tube wave detection and other methods is compared then some issues of the application of the tube wave for detecting pile defects are discussed finally the content of this paper is summarized and some suggestions on further research are put forward

tree ring evidence of the widespread effects of explosive volcanic eruptions tree ring evidence from 97 sites over north america and europe are used to develop a chronology of widespread cool summers since 1600 averaging annual maximum density information from the chronologies provides an index that correlates with northern hemisphere summer temperatures to 0 44 over 1851 1975 a number of the extreme low density years occur in both north america and europe suggesting a common response to high frequency forcing the analysis was repeated with ring width information but the results are markedly less coherent of the five common extreme low density years 1601 1641 1669 1699 and 1912 four are known to be coincident with the year or year following major volcanic eruptions other extreme low density indices in the continental series are also clear coincident with known volcanoes the density indices clearly demonstrate great potential for quantifying the climate effectiveness and perhaps establishing precise calendar dates of large explosive volcanoes 30 refs

the importance of atmospheric dynamics in the northern hemisphere wintertime climate response to changes in the earth s orbit milankovitch proposed that variations in the earth s orbit cause climate variability through a local thermodynamic response to changes in insolation this hypothesis is tested by examining variability in an atmospheric general circulation model coupled to an ocean mixed layer model subjected to the orbital forcing of the past 165 000 yr during northern hemisphere summer the model s response conforms to milankovitch s hypothesis with high low insolation generating warm cold temperatures throughout the hemisphere however during northern hemisphere winter the climate variations stemming from orbital forcing cannot be solely understood as a local thermodynamic response to radiation anomalies instead orbital forcing perturbs the atmospheric circulation in a pattern bearing a striking resemblance to the northern annular mode the primary mode of simulated and observed unforced atmospheric variability the hypothesized reason for this similarity is that the circulation response to orbital forcing reflects the same dynamics generating unforced variability these circulation anomalies are in turn responsible for significant fluctuations in other climate variables most of the simulated orbital signatures in wintertime surface air temperature over midlatitude continents are directly traceable not to local radiative forcing but to orbital excitation of the northern annular mode this has paleoclimate implications during the point of the model integration corresponding to the last interglacial eemian period the orbital excitation of this mode generates a 1 2 c warm surface air temperature anomaly over europe providing an explanation for the warm anomaly of comparable magnitude implied by the paleoclimate proxy record the results imply that interpretations of the paleoclimate record must account for changes in surface temperature driven not only by changes in insolation but also by perturbations in atmospheric dynamics

permeability variations within mining induced fractured rock mass and its influence on groundwater inrush this paper is concerned with the evaluation of permeability of fractured rock mass due to the cover stress re establishment which is a major factor in controlling water and gas flow rate induced by mining operations in fractured rock the case study considered in this paper is based on the results of observations of groundwater inrush and a decrease in water inflow from the fractured roof strata due to mining advancing in the taiping coalmine shandong province china a conceptual model of an effective porous media was used to assess the permeability distribution in the fractured zone induced by coal mining the cover stress re establishment in gob fractured rock mass was evaluated using an empirical formula based on the surface subsidence a simplified conceptual model of the fractured zone was used to evaluate the deformation of fractured zone along with the evaluation of changes in the rock permeability above the gob due to the cover stress re establishment these data were then used to calculate the water inflow rate into the panel predicted water inflow rates have been found to be in good agreement with those from monitoring data this study improved the understanding of the mechanisms of the post mining cover stress re establishment on permeability change of the overburden fracture rock strata these results can then be applied for numerical simulations of the process of overburden failure and consequent groundwater inrush due to coal mining

evidence for a volcanic cooling signal in a 335 year coral record from new caledonia although volcanic cooling events have been detected in tree ring records their occurrence in marine records has received much less attention herein we report results from a 335 year oxygen isotope record 1657 1992 from a new caledonia coral indicating that as many as 16 interannual scale cooling events occur within 1 year of a volcanic eruption as determined by ice core records there are also pentadal decadal scale cooling events beginning in 1675 1813 and 1903 that immediately postdate volcanic eruptions however the interannual correspondences are complicated by the fact that some of the cooling events also coincide with el ninos which cause cooling in this part of the western south pacific if our conclusions are substantiated by further work occurrence of distinct volcanic cooling signals may enable refinement of coral chronologies by use of the event stratigraphic approach with the most promising correlation horizons being associated with the following eruptions 1808 unknown 1813 1821 several eruptions 1835 coseguina 1883 krakatau and possibly 1963 agung

acoustic characterization of fracture permeability at chalk river ontario this study was undertaken to test recently formulated acoustic analysis methods for fracture interpretation the study area was selected because surface outcrops of igneous and metamorphic rocks have numerous interconnected fractures and major lithology changes in situ acoustic refraction data were obtained by digitally recording the entire pressure signal received by a conventional acoustic borehole logging system the acoustic energy source had a centerband frequency of 34 khz and data were obtained at 60 and 90 cm source receiver spacing borehole geometry produces waveforms with strong shear arrivals and high amplitudes associated with the fundamental guided fluid mode known as the tube wave waveforms refracted across fractures that are open on the borehole have shear mode excitation and tube wave attenuation effects similar to previously described effects for isolated fractures in very uniform lithologies independent permeability data for the chalk river boreholes are available in the form of ef

sage ii measurements of early pinatubo aerosols sage ii satellite measurements of the mt pinatubo eruption cloud in the stratosphere during june july and early august 1991 show that aerosols in the tropics reached as high as 29 km altitude with most of the cloud between 20 and 25 km the most optically thick portions of the cloud covered latitudes from 10 s to 30 n during the early part of this period by late july high stratospheric optical depths were observed to at least 70 n with the high values north of about 30 n from layers below 20 km high pressure systems in both hemispheres were observed to be correlated with the movement of volcanic material at 21 km into the westerly jet stream at high southern latitudes and similarly to high northern latitudes at 16 km by august the entire southern hemisphere had experienced a 10 fold increase in optical depth relative to early july due to layers above 20 km initial mass calculations using sage ii data place the aerosol produced from this eruption at 20 to 30 megatonnes well above the 12 megatonnes produced by el chichon

major volcanic eruptions and climate a critical evaluation abstract this paper examines whether major volcanic eruptions of the past century have had a significant impact on surface land and ocean temperatures surface pressure and precipitation both multieruption composites and individual eruption time series are constructed and analyzed included in this work is an attempt to remove one source of interannual variability the el nino southern oscillation enso these exercises indicate that only the largest eruptions in terms of producing a stratospheric dust cloud are suggested in the climatic record removing the enso signal in the composite and individual eruption series enhances the apparent volcanic effect of the largest eruptions no volcanic signal is obvious in pressure and precipitation records

the volcanic signal in surface temperature observations abstract climate records of the past 140 years are examined for the impact of major volcanic eruptions on surface temperature after the low frequency variations and el nino southern oscillation signal are removed it is shown that for 2 years following great volcanic eruptions the surface cools significantly by 0 1 0 2 c in the global mean in each hemisphere and in the summer in the latitude bands 0 30 s and 0 30 n and by 0 3 c in the summer in the latitude band 30 30 60 n by contrast in the first winter after major tropical eruptions and in the second winter after major high latitude eruptions north america and eurasia warm by several degrees while northern africa and southwestern asia cool by more than 0 5 c because several large eruptions occurred at the same time as enso events the warming produced by the enso masked the volcanic cooling during the first year after the eruption the timescale of the enso response is only 1 year while the volcanic response timescale is 2 years so the coo

acoustic modes of propagation in the borehole and their relationship to rock properties acoustic waveform measurements in boreholes have important applications in fracture hydrology and radioactive waste disposal but ambiguities in existing interpretation techniques remain a problem we have addressed the problem by using residue theory to predict the relative excitation of various modes contained in experimental waveforms a plane geometry model involving a layer of fluid between two elastic half spaces is shown to provide velocity dispersion curves for propagating modes that are very similar to those for the fluid filled borehole we use the plane geometry model to illustrate the effects of the confined borehole fluid on surface and body waves traveling along the borehole in the elastic solid we also computed excitation functions for some of the lowest order symmetric modes calculated the time domain response of the trapped modes following the shear head waves and compared them to waveforms recorded in boreholes through several homogeneous formations the insight into the mode composit

sub alpine trees testify late 20th century rapid retreat of gangotri glacier central himalaya abstract our understanding on glacier climate link in the himalayan region is constrained due to lack of long term observational and high resolution proxy records hostile weather conditions and difficult approaches to access glaciers due to rough terrains largely limit observational studies on glaciers in the himalaya sub alpine trees and shrubs close to glaciers growth of which is very sensitive to fluctuations in temperature provide precise continuous record on climate and glacier behaviour to supplement the observational records back to several centuries to unfold the gangotri glacier dynamics in the past we developed tree ring chronologies and studied the colonization pattern of the trees in the region tree ring chronologies of himalayan birch and himalayan pine developed from their respective upper tree line ecotone in the gangotri glacier forefields showed impact of temperature on the growth variations a comparison of himalayan pine chronology with temperature proxies revealed regional and hemispheric scale temperature signal using tree ring chronologies we show expansion retreat of the gangotri glacier during cool warm phases that are also in agreement with the glacier fluctuation records from central asia and southern tibet moreover using tree colonization pattern in the glacier forefields we established for the first time that the gangotri glacier terminus receded 1 853 km since the late 16th century 1571 c e major part of which 1 79 km receded since 1935 c e the glacier retreat associated with the onset of 20th century warming got accelerated since 1957 c e 1 567 km in view of our findings the gangotri glacier might further face accelerated recession in the 21st century under the projected warming

measurements of seismic anisotropy and fracture compliances in synthetic fractured media ultrasonic velocities were measured on a stack of synthetic material plexiglass at low 90 120 khz long wavelength range and high 480 khz short wavelength range frequencies plates were pressed together with uniaxial normal stress these measurements were repeated under different uniaxial pressures for two cases 1without circular rubber inclusions between synthetic fractures and 2with circular rubber inclusions between fractures calculation of anisotropy parameters and also normal and shear interface fracture compliances using linear calculus show reasonable variations anisotropy and compliances decreases as overburden pressure increases suggesting that anisotropy is caused by compliances at higher frequencies synthetic fractures seem to be stiffer than at lower frequencies for the long and short wavelength ranges similar variations were observed for anisotropy parameters and fracture compliances vs measurements in different directions show that for the case without rubber inclusions there is a good approximation of vti medium whereas for the case with inclusions there is a significant difference between vs travelling in directions parallel and perpendicular to the plates

the global impact of the minoan eruption of santorini greece the minoan eruption of santorini was a large magnitude natural event however in terms of scale it ranks smaller in erupted volume and eruptive intensity than the historical eruption of tambora in 1815 ad and smaller in sulphur emission and by inference climatic effects than both the tambora and mt pinatubo 1991 eruptions eruption statistics for the past 2000 years indicate that minoan size eruptions typically occur at a rate of several per thousand years eruptions resulting in a minoan scale injection of sulphur to the stratosphere occur far more frequently at a rate of one or two per century inferences of massive sociological religious and political impacts from such eruptions owe more to mythology than reality

climatic variability in the eastern united states over the past millennium from chesapeake bay sediments salinity oscillations caused by multidecadal climatic variability had major impacts on the chesapeake bay estuarine ecosystem during the past 1000 yr microfossils from sediments dated by radiometry 14 c 137 cs 210 pb and pollen stratigraphy indicate that salinity in mesohaline regions oscillated 10 15 ppt during periods of extreme drought low fresh water discharge and wet climate high discharge during the past 500 yr 14 wet dry cycles occurred including sixteenth and early seventeenth century megadroughts that exceeded twentieth century droughts in their severity these droughts correspond to extremely dry climate also recorded in north american tree ring records and by early colonists wet periods occurred every 60 70 yr began abruptly lasted 20 yr and had mean annual rainfall 25 30 and fresh water discharge 40 50 greater than during droughts a shift toward wetter regional climate occurred in the early nineteenth century lowering salinity and compounding the effects of agricultural land clearance on bay ecosystems

assessment of southern oscillation sea level pressure indices abstract monthly sea level pressure anomalies at easter island rapa tahiti and darwin for the period 1951 79 are analysed to reveal their temporal characteristics and the coherence and time lead lag relationships among them for interannual scale oscillations the pressure variations at rapa and easter island lead those at tahiti and those of opposite phase at darwin by 2 8 months where the large lead times are associated with lower frequency oscillations of the four stations rapa has the smallest percentage of its variance in the range of periods containing the southern oscillation darwin has the largest spatial smoothing by combining stations enhances the percentage of variance in the longer periods combining tahiti and darwin gives a substantial increase combining rapa and easter island much less normalization of the time series through division by the monthly standard deviations is also treated the combination of tahiti and darwin is recommended as a southern oscillation index for diagno

the volcanic signal in goddard institute for space studies three dimensional model simulations abstract transient calculations of the goddard institute for space studies general circulation model for the climatic signal of volcanic eruptions are analyzed by compositing the output for two different volcanoes for scenario a and five different volcanoes for scenario b the natural variability is suppressed and the volcanic signals am extracted significant global mean surface air temperature cooling and precipitation reduction are found for several years following the eruptions with larger changes in the northern hemisphere nh than in the southern hemisphere the global average temperature response lasts for more than four years but the precipitation response disappears after three years the largest cooling in the model occurs in the nh summer of the year after spring eruptions significant zonal average temperature reductions begin in the tropics immediately after the eruptions and extend to 45 s 45 n in the year after the eruptions in the second year cooling is still seen from 30 s to 30 n

was the 2003 european summer heat wave unusual in a global context 1 we place the european summer heat wave of 2003 in the context of other extreme summer tropospheric temperature events from 22 n to 80 n since 1979 as well as globally using annual averages the analysis is performed in terms of standard deviations sd exceeded and correlations between regional extremes and temperatures at larger spatial scales as has been pointed out previously the heat wave was statistically unusual and was a deep tropospheric phenomenon in this analysis we also find the following 1 extreme warm anomalies equally or more unusual than the 2003 heat wave occur regularly 2 extreme cold anomalies also occur regularly and occasionally exceed the magnitude of the 2003 warm anomaly in terms of the value of sd 3 there is a correlation between global and hemispheric average temperature and the presence of warm or cold regional anomalies of the same sign i e warmer than average years have more regional heat waves and colder than average years have more cold waves 4 natural variability in the form of el nino and volcanic eruptions appear to be of much greater importance in causing extreme regional temperature anomalies than a simple upward trend in time extreme temperature anomalies in the wake of the 1997 98 el nino were larger than the anomalies seen in summer 2003 both in area affected and sd extremes exceeded 5 regression analyses do not provide strong support for the idea that regional heat waves are increasing with time

impacts of a pinatubo size volcanic eruption on enso observations and model simulations of the climate responses to strong explosive low latitude volcanic eruptions suggest a significant increase in the likelihood of el nino during the eruption and post eruption years though model results have been inconclusive and have varied in magnitude and even sign in this study we test how this spread of responses depends on the initial phase of el nino southern oscillation enso in the eruption year and on the eruption s seasonal timing we employ the gfdl cm2 1 global coupled general circulation model to investigate the impact of the pinatubo 1991 eruption assuming that in 1991 enso would otherwise be in central or eastern pacific el nino la nina or neutral phases we obtain statistically significant el nino responses in a year after the eruption for all cases except la nina which shows no response in the eastern equatorial pacific the eruption has a weaker impact on eastern pacific el ninos than on central pacific el ninos we find that the ocean dynamical thermostat and to a lesser extent wind changes due to land ocean temperature gradients are the main feedbacks affecting el nino development after the eruption the el nino responses to eruptions occurring in summer are more pronounced than for winter and spring eruptions that the climate response depends on eruption season and initial enso phase may help to reconcile apparent inconsistencies among previous studies

dendrochemical analysis of a tree ring growth anomaly associated with the late bronze age eruption of thera the most marked tree ring growth anomaly in the aegean dendrochronological record over the last 9000 years occurs in the mid 17th century bc and has been speculatively correlated with the impact of the late bronze age eruption of thera santorini if such a connection could be proved it would be of major interdisciplinary significance it would open up the possibility of a precise date for a key archaeological geological and environmental marker horizon and offer a direct tie between tree ring and ice core records some 3600 years ago a volcanic explanation for the anomaly is highly plausible yet in the absence of a scientifically proven causal connection the value of the proposed correlation is limited in order to test the hypothesis dendrochemical analysis via synchrotron radiation scanning x ray fluorescence microscopy sxfm inductively coupled plasma atomic emission spectroscopy icp aes and inductively coupled plasma mass spectroscopy icp ms was carried out on growth ring series from four trees displaying the anomaly increases of sulfur calcium and rare earth elements following the onset of altered growth plus concentration spikes of zinc and hafnium in the first affected growth ring provide promising new evidence in support of a volcanic causal factor although a volcanic association is implied the new data are not sufficient to prove a link to the exact eruption source

volcanic eruptions cool summers and famines in the northeastern part of japan abstract during the last 300 years most of the poor rice harvests caused by unusual cool summers and leading to famine conditions in the tohoku district the northeastern part of japan took place just after the great volcanic eruptions an analysis of instrumental observations in the past century on the kinkasan island indicates that though the standard deviation in the summer air temperature is 1 1 c for 1882 1985 the summer air temperature averages 1 3 0 5 c lower than normal during the summer following the great volcanic eruptions the mid latitudinal mean surface air temperature in the northern hemisphere decreased only about 0 2 c this result indicates that the summer air temperature in tohoku district tends to be particularly sensitive to such eruptions in all the cool summers a blocking high persisted over the ocean northeast of japan and impeded the northward movement of the raiu front the stagnating polar front during the early summer exceptionally cool summers occurred frequently w

volcanic forcing of climate over the past 1500 years an improved ice core based index for climate models 1 understanding natural causes of climate change is vital to evaluate the relative impacts of human pollution and land surface modification on climate we have investigated one of the most important natural causes of climate change volcanic eruptions by using 54 ice core records from both the arctic and antarctica our recently collected suite of ice core data more than double the number of cores ever used before reduces errors inherent in reconstructions based on a single or small number of cores which enables us to obtain much higher accuracy in both detection of events and quantification of the radiative effects we extracted volcanic deposition signals from each ice core record by applying a high pass loess filter to the time series and examining peaks that exceed twice the 31 year running median absolute deviation we then studied the spatial pattern of volcanic sulfate deposition on greenland and antarctica and combined this knowledge with a new understanding of stratospheric transport of volcanic aerosols to produce a forcing data set as a function of month latitude and altitude for the past 1500 years we estimated the uncertainties associated with the choice of volcanic signal extraction criteria ice core sulfate deposition to stratospheric loading calibration factor and the season for the eruptions without a recorded month we forced an energy balance climate model with this new volcanic forcing data set together with solar and anthropogenic forcing to simulate the large scale temperature response the results agree well with instrumental observations for the past 150 years and with proxy records for the entire period through better characterization of the natural causes of climate change this new data set will lead to improved prediction of anthropogenic impacts on climate the new data set of stratospheric sulfate injections from volcanic eruptions for the past 1500 years as a function of latitude altitude and month is available for download in a format suitable for forcing general circulation models of the climate system

dynamic winter climate response to large tropical volcanic eruptions since 1600 1 we have analyzed the mean climate response pattern following large tropical volcanic eruptions back to the beginning of the 17th century using a combination of proxy based reconstructions and modern instrumental records of cold season surface air temperature warm anomalies occur throughout northern eurasia while cool anomalies cover northern africa and the middle east extending all the way to china in north america the northern portion of the continent cools with the anomalies extending out over the labrador sea and southern greenland the analyses confirm that for two years following eruptions the anomalies strongly resemble the arctic oscillation northern annular mode ao nam or the north atlantic oscillation nao in the atlantic eurasian sector with our four century record the mean response is statistically significant at the 95 confidence level over much of the northern hemisphere land area however the standard deviation of the response is larger than the mean signal nearly everywhere indicating that the anomaly following a single eruption is unlikely to be representative of the mean both the mean response and the variability can be successfully reproduced in general circulation model simulations driven by the solar heating induced by the stratospheric aerosols these models produce enhanced westerlies from the lower stratosphere down to the surface the climate response to volcanic eruptions thus strongly suggests that stratospheric temperature and wind anomalies can affect surface climate by forcing a shift in the ao nam or nao

european summer temperature response to annually dated volcanic eruptions over the past nine centuries the drop in temperature following large volcanic eruptions has been identified as an important component of natural climate variability however due to the limited number of large eruptions that occurred during the period of instrumen tal observations the precise amplitude of post volcanic cooling is not well constrained here we present new evidence on summer temperature cooling over europe in years following volcanic eruptions we compile and analyze an updated net work of tree ring maximum latewood density chronologies spanning the past nine centuries and compare cooling sig natures in this network with exceptionally long instru mental station records and state of the art general circu lation models results indicate post volcanic june august cooling is strongest in northern europe 2 years after an eruption 0 52 0 05 c whereas in central europe the temperature response is smaller and occurs 1 year after an eruption 0 18 0 07 c we validate these estimates by comparisonwith the shorter instrumental network and evaluate the statistical significance of post volcanic summer tempera ture cooling in the context of natural climate variability over the past nine centuries finding no significant post volcanic temperature cooling lasting longer than 2 years our results question the ability of large eruptions to initiate long term temperature changes through feedback mechanisms in the climate system we discuss the implications of these findings with respect to the response seen in general circulation models and emphasize the importance of considering well documented annually dated eruptions when assessing the

a dynamic model for fluid flow in open borehole fractures the attenuation of stoneley waves by an open borehole fracture is closely related to fluid flow in the fracture we consider the dynamic response of a viscous fluid in a borehole fracture to the oscillating pressure excitation of stoneley waves at the fracture opening a dynamic model has been developed to describe the fluid motion in the fracture this model relates both viscous shear effects at the fracture surface and the acoustic wave propagation in the fracture fluid the dynamic conductivity is derived to characterize the fluid conduction through the fracture this model is applied to study stoneley wave attenuation across a horizontal and along a vertical borehole fracture in the horizontal fracture case the theory is found to agree with laboratory fracture modeling data after minimizing scattering effects due to the fracture in the vertical fracture case where the scattering effects are minimal the theory is in excellent agreement with the laboratory data

fracture compliance estimation using borehole tube waves abstractwe tested two models one for tube wave generation and the other for tube wave attenuation at a fracture intersecting a borehole that can be used to estimate fracture compliance fracture aperture and lateral extent in the tube wave generation model we consider tube wave excitation in the borehole when a p wave is incident on the fracture the amplitude ratio of the pressure due to the tube wave to that of the incident p wave is a function of fracture compliance aperture and length similarly the attenuation of a tube wave in the borehole as it crosses a fracture intersecting the borehole is also a function of fracture properties numerically solving the dispersion relation in the fracture we study tube wave generation and the attenuation coefficient as a function of frequency we observed that measuring amplitude ratios or attenuation near a transition frequency can help constrain the fracture properties the transition frequency corresponds to the regime in which the viscous skin depth in

regional effects of the mount pinatubo eruption on the middle east and the red sea the 1991 eruption of mount pinatubo had dramatic effects on the regional climate in the middle east though acknowledged these effects have not been thoroughly studied to fill this gap and to advance understanding of the mechanisms that control variability in the middle east s regional climate we simulated the impact of the 1991 pinatubo eruption using a regional coupled ocean atmosphere modeling system set for the middle east and north africa mena domain we used the coupled ocean atmosphere wave sediment transport coawst framework which couples the weather research and forecasting model wrf model with the regional oceanic modeling system roms we modified the wrf model to account for the radiative effect of volcanic aerosols our coupled ocean atmosphere simulations verified by available observations revealed strong perturbations in the energy balance of the red sea which drove thermal and circulation responses our modeling approach allowed us to separate changes in the atmospheric circulation caused by the impact of the volcano from direct regional radiative cooling from volcanic aerosols the atmospheric circulation effect was significantly stronger than the direct volcanic aerosols effect we found that the red sea response to the pinatubo eruption was stronger and qualitatively different from that of the global ocean system our results suggest that major volcanic eruptions significantly affect the climate in the middle east and the red sea and should be carefully taken into account in assessments of long term climate variability and warming trends in mena and the red sea

the effects of mylonitization and fractures on elastic wave velocities in crystalline rock examples from the cajon pass scientific drillhole sonic compressional and shear wave velocities were calculated from full waveforms recorded in the cajon pass drillhole from 250 to 1829 m depth a complete suite of schlumberger logs was also recorded over the same interval compressional velocities in the sediments 250 495 m range from 3 3 to 4 0 km s shear velocities are unreliable shallow crystalline basement has low velocities vp 4 8 vs 2 8 km s and resistivities due to minor alteration below 708 m vp is 5 5 to 6 0 km s and vs is 3 2 to 3 5 km s velocities are generally lower in more felsic rocks in gneisses sonic waveforms are more distorted semblance coherence is lower and physical properties are more variable mylonitized zones and fractured intervals have distinctly lower velocities but different aggregate log response lower velocities are found within a zone of fractures within the gneiss at about 840 m porosity increases only at one large fracture within the interval in a mylonitized shear zone at 1440 m the velocity reduction and the porosity increase occur across the zone

explosive volcanic eruptions the el nino southern oscillation and u s climate variability abstract a study was conducted to identify and separate possible signals of volcanic eruptions and of the el nino southern oscillation enso in u s surface climate records anomalies of monthly mean surface air temperature and total precipitation taken from the u s historical climatology network were composited averaged over years of major explosive volcanic eruptions enso warm events and enso cold events since the year 1900 it was assumed that volcanic eruptions and enso events occur independently of each other all composite anomalies were assessed for significance with regard to several statistical and physical criteria the composite enso related anomalies were then subtracted from anomalies of temperature and precipitation associated with the volcanic eruptions removal of large magnitude and highly significant anomalies associated with the enso warm and cold events is found to facilitate detection of volcanic signals in monthly records of u s temperature and precipitation volcanic signals

application of diffraction tomography to fracture detection two diffraction tomography techniques are applied to crosshole field data to detect fractures in granitic rock the techniques used are the conventional back propagation method and a new quadratic programming method incorporating constraints in this formulation the born approximation is used for linearization of the inverse problem two dimensional 2 d pseudo spectral finite difference synthetic data are generated to demonstrate the inversion methods and justify use of the born approximation also using 2 d born synthetic data the velocity sensitivity of the inversion algorithm and reduction of fracture generated tube waves and s waves are investigated the inversion methods are applied to field data from the grimsel test site in switzerland the data are collected from a 10 21 5m rectangular area where fractures are known to exist data acquisition with 0 5 m spacing of three component receivers and a piezoelectric source is carried out so as to obtain a nearly complete coverage of the region cros

modeling of low frequency stoneley wave propagation in an irregular borehole a fast modeling method is formulated for low frequency stoneley wave propagation in an irregular borehole this fast modeling method provides synthetic waveforms which include the effects of two borehole irregularities diameter changes washout and formation property changes the essential physics of the low frequency stoneley waves are captured with a simple 1 d model a mass balance boundary condition and a propagator matrix are used to express stoneley wave interactions with the borehole irregularities the accuracy of the proposed method was confirmed through comparison with existing finite difference and boundary integral modeling methods that yielded cross correlations greater than 0 98 comparison of synthetic records calculated for an actual borehole with field records showed qualitative agreement in the major reflections because of the washout zones but showed some disagreements in the reflections caused by the fractures since the synthetic records include only information relating to the borehole geometry and the elastic properties of formation the reflection caused by the fracture will appear only in the field record these results suggest the possibility of distinguishing stoneley wave reflections caused by fractures from those caused by borehole irregularities further the fast computational speed of this method over 300 times faster than either boundary integral or finite difference methods makes it quite suitable for field application

surface temperature patterns associated with the southern oscillation abstract the typical global and large scale regional temperature patterns associated with the low warm and high cold phases of the southern oscillation so are investigated a total of 12 separate regions were found to have consistent temperature patterns associated with low phase of the so while 11 areas were found to have temperature patterns associated with the high phase of these areas 9 have expected temperature patterns during both phases of the so in the tropics temperature anomalies are of the same sign as the so related sea surface temperature sst anomaly in all land regions except for one area in the west pacific three extratropical responses to the low phase of the so are found over north america and one is found in japan high so temperature patterns were found in the extratropies for japan western europe and northwestern north america the identified temperature responses are more consistent in tropical regions than in the extratropies the so can influence the estimation of

fracture parameter inversion from passive seismic shear wave splitting a validation study using full waveform numerical synthetics abstract fractures are pervasive features within the earth s crust and they have a significant influence on the multi physical response of the subsurface the presence of coherent fracture sets often leads to observable seismic anisotropy enabling seismic techniques to remotely locate and characterise fracture systems since fractures play a critical role in the geomechanical and fluid flow response there has been significant interest in quantitatively imaging in situ fractures for improved hydro mechanical modelling in this study we assess the robustness of inverting for fracture properties using shear wave splitting measurements we show that it is feasible to invert shear wave splitting measurements to quantitatively estimate fracture strike and fracture density assuming an effective medium fracture model although the sws results themselves are diagnostic of fracturing the fracture inversion allows placing constraints on the physical properties of the fracture system for the single seismic source case and optimum receiver array geometry the inversion for strike has average errors of between 11 and 25 whereas for density has average errors between 65 and 80 for the single fracture set and 30 and 90 for the double fracture sets for real microseismic datasets the range in magnitude of microseismicity i e frequency content spatial distribution and variable source mechanisms suggests that the inversion of fracture properties from sws measurements is feasible

investigation of permeable fracture zones by tube wave analysis summary in vertical seismic profiling tube waves are generally classified as noise they have however useful applications tube waves can be generated by compressional waves at fluid filled cracks crossing the wall of the borehole in this case the permeability of the fracture zone can be estimated from the amplitude ratio of the incident p wave and the generated tube wave in the present study an improved model for tube wave amplitude interpretation is presented while former models assumed isolated cracks now the consideration of fracture zones of a certain porosity permeability and width is allowed master curves are used to check the sensitivity of the amplitude ratio of tube and p waves with respect to the formal parameters of computation it is shown moreover that mainly those parts of a fracture contribute to the tube wave generation which are within a radius of about 1 m of the borehole the problem of localization and characterization of fracture zones by tube waves was investigated with several complementary field experiments in shallow boreholes in crystalline rocks as vertical seismic profiling vsp with three component borehole geophones and hydrophones televiewer measurements well tests and temperature measurements it turned out that fracture zones were met at all depths where tube waves were generated however not all of them were found to be hydraulically activated during well tests and temperature measurements this means that fractures detected by tube wave vsp are not necessarily of hydrological importance transmissivity values based on tube wave analysis are therefore an upper limit for the well under consideration on the other hand the transmissivity values derived from the well tests agreed quite well with those of the tube wave analysis if only the open fracture zones were considered a fact which seems to confirm our theoretical model

modulation of enso evolution by strong tropical volcanic eruptions the simulated responses of the el nino southern oscillation enso to volcanic forcings are controversial and some mechanisms of these responses are not clear we investigate the impacts of volcanic forcing on the enso using a long term simulation covering 1400 1999 as simulated by the bergen climate model bcm and a group of simulations performed with the community atmosphere model version 4 0 cam4 and the bcm s ocean component miami isopycanic coordinated ocean model micom the analysis of the long term bcm simulation indicates that enso has a negative positive negative response to strong tropical volcanic eruptions sves which corresponds to the different stages of volcanic forcing in the initial forcing stage a brief and weak la nina like response is caused by the cooling along the west coast of the south american continent and associated enhancement of the trade winds in the peak forcing stage westerly wind anomalies are excited by both reduced east west sea level pressure gradients and weakened and equatorward shifted tropical convergence zones these westerly wind anomalies extend to the equatorial eastern pacific leading to an el nino like response at the same time easterly wind anomalies west of 120 e and strong cooling effects can promote a discharged thermocline state and excite an upwelling kelvin wave in the western pacific in the declining forcing stage forced by the recovered trade winds the upwelling kelvin wave propagates eastward and reaches the equatorial eastern pacific through the bjerknes feedback a strong and temporally extended la nina like response forms additional cam4 simulations suggest a more important role of the surface cooling over the maritime continent and surrounding ocean in shaping the westerly wind anomalies over the equatorial central eastern pacific and the easterly wind anomalies west of 120 e which are key to causing the el nino like responses and subsequent la nina like responses respectively the micom sensitivity simulations confirm that sve induced tropical atmospheric circulation anomalies play a dominant role in regulating post eruption enso evolution in the observation while the influences of anomalous buoyance forcing heat and freshwater fluxes are secondary therefore sves play an important role in modulating the enso evolution compared with proxy data the simulated el nino like responses and subsequent la nina like responses are consistent with the reconstructed enso responses to sves however the simulated initial brief la nina like response which is reproduced by most models is seen in only one proxy dataset and is absent in most of the reconstructed ensos and those observed the reason for this model data mismatch will require further investigation

finite difference synthetic acoustic logs the finite difference method is a powerful technique for studying the propagation of elastic waves in boreholes even for the simple case of an open borehole with vertical homogeneity the snapshot format of the method displays clearly the interaction between the borehole and the rock and the origin and evolution of phases we present an outline of the finite difference method applied to the acoustic logging problem including a boundary condition formulation for liquid solid cylindrical interfaces which is correct to second order in the space increments absorbing boundaries based on the formulations of reynolds 1978 and clayton and engquist 1977 were used to reduce reflections from the grid boundaries results for a vertically homogeneous sharp interface model are compared with the discrete wavenumber method and excellent agreement is obtained the technique is also demonstrated by considering sharp and continuous transitions damaged zones at the borehole wall and by considering the effects of wa

hydrological aspects of geophysical borehole measurements in crystalline rocks of the black forest abstract one of six wells drilled into the crystalline rock of the black forest basement during the german continental deep drilling project ktb site survey has been used to detect hydraulically active fractures and to identify their character by a variety of logging tools such as caliper and televiewer logging vertical seismic profiling vsp and electrical and thermal measurements in addition to standard logging recordings in the 265 m moosengrund well drilled into the triberg granite body these methods were applied successfully to discriminate between fractures and breakouts and to identify open and closed fractures and water consuming or water expelling fractures respectively fracture strike dip and width were determined from televiewer data vsp measurements were used to determine the seismic velocities in the unfractured rock and the fracture zones estimates of permeability 10 55 darcy and transmissivity 0 1 1 0cm 2 s 1 of the fracture zones were obtained by the analysis of p waves and tube waves in the vsp records the summed values of the transmissivity yield an upper estimate of the overall transmissivity determined by a pumping test

influence of various forcings on global climate in historical times using a coupled atmosphere ocean general circulation model the results of a simulation of the climate of the last five centuries with a state of the art coupled atmosphere ocean general circulation model are presented the model has been driven with most relevant forcings both natural solar variability volcanic aerosol and anthropogenic greenhouse gases sulphate aerosol land use changes in contrast to previous gcm studies we have taken into account the latitudinal dependence of volcanic aerosol and the changing land cover for a period covering several centuries we find a clear signature of large volcanic eruptions in the simulated temperature record the model is able to simulate individual extreme events such as the year without a summer 1816 warm periods in the early seventeenth century and the second half of eighteenth century occur in periods of increased solar irradiation strong warming is simulated after 1850 in particular over land going along with an increase of the positive north atlantic oscillation nao phase consistent circulation anomalies are simulated in multidecadal means with similarity to observed and reconstructed anomalies for example during the late seventeenth and early eighteenth century the model is able to reproduce some of the observed or reconstructed regional patterns we find that cooling around 1700 and at the end of the eighteenth century is less than in other studies due to the relatively small variations in solar activity and the relatively modest volcanic forcing applied here these cooling events are not restricted to europe and north america but cover most of the northern hemisphere colder than average conditions for example during the late seventeenth and early eighteenth centuries go along with a decrease in pressure difference between low and high latitudes and a decrease of the north atlantic oscillation this favours positive sea ice anomalies east of greenland and around iceland leading to widespread negative temperature anomalies over europe we also find characteristic blocking patterns over western europe in particular during autumn which contribute to the advection of cold air

the response of the north pacific decadal variability to strong tropical volcanic eruptions in this study the effects of volcanic forcing on north pacific climate variability on interannual to decadal time scales are examined using climate model simulations covering the last 600 years the model used is the bergen climate model a fully coupled atmosphere ocean general circulation model it is found that natural external forcings such as tropical strong volcanic eruptions sves and variations in total solar irradiance play an important role in regulating north pacific decadal variability npdv in response to tropical sves the lower stratospheric pole to equator temperature gradient is enhanced the north polar vortex is strengthened which forces a significant positive arctic oscillation at the same time dipole zonal wind anomalies associated with strong polar vortex propagate downward from the lower stratosphere through positive feedbacks in the troposphere the surface westerly winds across the central north pacific are significantly weakened and positive sea level pressure anomalies are formed in the north pacific this anomalous surface circulation results in changes in the net heat fluxes and the oceanic advection across the north pacific as a result of this warm water converges in the subtropical western north pacific where the surface waters in addition are heated by significantly reduced latent and sensible heat fluxes from the ocean in the eastern and high latitude north pacific the ocean loses more heat and large scale decreases in sea surface temperatures are found the overall response of this chain of events is that the north pacific enters a negative phase of the pacific decadal oscillation pdo and this negative phase of the pdo is maintained for several years it is thus concluded that the volcanic forcing plays a key role in the phasing of the pdo the model results furthermore highlight the important role of troposphere stratosphere coupling tropical extratropical teleconnections and extratropical ocean atmosphere interactions for describing npdv

fracture characterization from vertical seismic profiling data in vertical seismic profiling vsp data large amplitude borehole stoneley waves are observed at depths where fractures intersect the borehole the authors present a model which predicts the amplitudes of these stoneley waves as a function of certain parameters of the fractures namely the fracture aperture width the orientation and the degree of stiffness and roughness of the fracture the proposed mechanism for the generation of these borehole stoneley waves is coupling of a guided mode induced in the fracture by an incident plane wave typically a p wave to the borehole the model expresses the borehole stoneley wave amplitude normalized by the amplitude of the direct p wave as a function of frequency in terms of the fracture parameters the model is used as the basis for an inversion scheme employing a nonlinear least squares algorithm to estimate the fracture parameters the inversion is then applied to vsp data where borehole stoneley waves are observed at depths where fractures are known to intersect the borehole the results of the inversion indicate that the aperture and vertical component of the orientation i e dip of the fracture can be accurately estimated but the horizontal component of the orientation i e strike is notmore well resolved these conclusions are based on comparisons with independent estimates of these parameters from flow tests and borehole televiewer measurements in addition stiffness and roughness of the fractures are important effects which must be considered in order to obtain realistic estimates for the other parameters especially the fracture aperture 27 refs 14 figs 21 tabs less

ocean response to volcanic eruptions in coupled model intercomparison project 5 simulations we examine the oceanic impact of large tropical volcanic eruptions as they appear in ensembles of historical simulations from eight coupled model intercomparison project phase 5 models these models show a response that includes lowering of global average sea surface temperature by 0 1 0 3 k comparable to the observations they show enhancement of arctic ice cover in the years following major volcanic eruptions with long lived temperature anomalies extending to the middepth and deep ocean on decadal to centennial timescales regional ocean responses vary although there is some consistent hemispheric asymmetry associated with the hemisphere in which the eruption occurs temperature decreases and salinity increases contribute to an increase in the density of surface water and an enhancement in the overturning circulation of the north atlantic ocean following these eruptions the strength of this overturning increase varies considerably from model to model and is correlated with the background variability of overturning in each model any cause effect relationship between eruptions and the phase of el nino is weak

quantifying the pinatubo volcanic signal in south polar snow recent snow and firn core samples from south pole contain increased sulfate so42 concentrations during 1992 1994 as a result of the june 1991 pinatubo eruption and the august 1991 cerro hudson eruption in chile traces of pinatubo tephra volcanic ash were identified in the 1993 and 1994 snow layers supporting the conclusion that increased so42 in 1993 1994 is from the pinatubo eruption although the pinatubo eruption preceded hudson its so42 signal in south polar snow follows and is resolved from that of hudson the deposition of the pinatubo so42 aerosol was delayed due to the long transport to the high southern latitudes and its initial existence at high altitudes in the antarctic atmosphere multi year multi site sampling demonstrates that the volcanic signals are well preserved and spatially consistent measurements on 2 firn cores show that the south pole so so42 flux from pinatubo is 10 9 1 2 kg km 2 over 2 2 years while the hudson flux is 3 2 0 6 kg km 2 in 1 1 years these results when combined with satellite determined pinatubo sulfur dioxide so2 emission make it possible to link quantitatively the atmospheric aerosol mass loading from a low latitude volcanic eruption to its signal in polar ice cores

the reliability of anisotropy of magnetic susceptibility ams data as flow direction indicators in friable base surge and ignimbrite deposits italian examples abstract the base surge deposits in linosa and procida islands italy show minimum axes k3 of the anisotropy of magnetic susceptibility ams that are mostly parallel to the flow directions inferred from field evidence but sometimes perpendicular to them samples from different heights above the base of an ignimbrite bed vulsini area italy showing a coarse tail reverse grading and a fine grained basal layer have different magnetic fabrics at 10 and 40 cm from the base the declinations of maximum axes k1 of the ams are approximately 90 from the theoretical flow direction whereas at 60 and 75 cm from the base the k1 axes are approximately parallel to the flow direction this bed also shows a decrease upward of the magnetic foliation lineation and degree of anisotropy suggesting that the ams data could be used to obtain information about flow mechanisms the airm data in the case of the ignimbrite bed show that the long shape axes of the ferromagnetic grains are probably aligned with the maximum axes of the ams for this reason the change in the magnetic fabric at different distances from the base is probably due to differences in the flow behaviour rather than the domain state of magnetite grains this study shows that the ams lineations can indicate the flow direction in base surge and ignimbrite deposits but other geological and magnetic information is necessary to assess if these lineations are flow perpendicular or flow parallel

ice cores as an index of global volcanism from 1850 to the present to evaluate an important cause of past climate change climate researchers need reliable estimates of volcanic aerosol loading in the atmosphere previous indices the dust veil index volcanic explosivity index and those by mitchell 1970 sato et al 1993 and khmelevtsov et al unpublished manuscript 1993 all have drawbacks ice core acidity and sulfate records because they contain physical evidence of atmospheric loading are a promising source of information on past volcanic aerosols but these records contain large nonvolcanic signals as well we have compared northern hemisphere nh and southern hemisphere sh annual average versions of five indices with eight nh and six sh ice core records for the period 1850 to the present in an attempt to identify the volcanic signal common to all records the indices are all highly correlated with each other for the nh although the individual ice core records are in general not well correlated with each other or with any of the indices a composite derived from averaging the cores the ice core volcano index ivi shows promise as a new index of volcanic aerosol loading this new index correlates well with the existing non ice core volcanic indices and with high frequency temperature records for the sh the individual ice cores and indices are better correlated the shivi is again highly correlated with all indices and individual ice cores but not with high frequency temperature records for both hemispheres the southern oscillation index shows no significant correlation with the volcanic indices ice cores or the ivi thus providing no evidence for the impact of volcanic eruptions on el nino southern oscillation events

volcanic eruptions large scale modes in the northern hemisphere and the el nino southern oscillation abstract the author analyzes the impact of 13 major stratospheric aerosol producing volcanic eruptions since 1870 on the large scale variability modes of sea level pressure in the northern hemisphere winter the paper focuses on the arctic oscillation ao and the north atlantic oscillation nao to address the question about the physical nature of these modes the hypothesis that the phase of the el nino southern oscillation enso may control the geographical extent of the dominant mode in the northern hemisphere is also investigated as well as the related possibility that the impact of the eruptions may be different according to the phase of enso the author finds that both the ao and the nao are excited in the first winter after the eruptions with statistical significance at the 95 level both the signal and the significance are larger for the nao than for the ao the excitation of the ao and the nao is connected with the excitation of a secondary mode which resembles an augmented pacific north ame

a 970 year long summer temperature reconstruction from rogen west central sweden based on blue intensity from tree rings to assess past climate variability in west central scandinavia a new 972 year long temperature reconstruction based on adjusted delta blue intensity biadj was created presently it is the longest blue intensity chronology in fennoscandia and the third longest in the northern hemisphere measurements were obtained from 119 tree line scots pine pinus sylvestris l samples from rogen in the central scandinavian mountains sweden early and latewood blue intensity absorption data were used to create biadj the data were detrended using a signal free regional curve standardization method rsfi to minimize biological noise and maximize low frequency climate information the rogen biadj chronology has a substantially stronger temperature signal at inter annual timescales than the corresponding tree ring width rw chronology and it displays good spatial representation for the south central parts of scandinavia the biadj summer june through august temperature reconstruction extending back to 10

fracture characterization by means of attenuation and generation of tube waves in fractured crystalline rock at mirror lake new hampshire results are presented from experiments carried out in conjunction with the u s geological survey at the hubbard brook experimental forest near mirror lake new hampshire the study focuses on our ability to obtain orientation and transmissivity estimates of naturally occurring fractures the collected data set includes a four offset hydrophone vertical seismic profile full waveform acoustic logs at 5 15 and 34 khz borehole televiewer temperature resistivity and self potential logs and borehole to borehole pump test data borehole televiewer and other geophysical logs indicate that permeable fractures intersect the mirror lake boreholes at numerous depths but less than half of these fractures appear to have significant permeability beyond the annulus of drilling disturbance on the basis of acoustic waveform log analysis the vertical seismic profiling vsp data indicate a single major permeable fracture near a depth of 44 m corresponding to one of the most permeable fractures identified in the acoustic waveform log analysis vsp data also indicate a somewhat less permeable fracture at 220 m and possible fractures at depths of 103 and 135 m all correspond to major permeable fractures in the acoustic waveform data set pump test data confirm the presence of a hydraulic connection between the mirror lake boreholes through a shallow dipping zone of permeability at 44 m in depth effective fracture apertures calculated from modeled transmissivities correspond to those estimated for the largest fractures indicated on acoustic waveform logs but are over an order of magnitude larger than effective apertures calculated from tube waves in the vsp data set this discrepancy is attributed to the effect of fracture stiffness a new model is presented to account for the mechanical strength of asperities in resisting fracture closure during the passage of seismic waves during the generation of vsps

determination of in situ attenuation from full waveform acoustic logs method for the determination of in situ p and s wave attenuation from full waveform acoustic logs are developed for p waves the peak amplitude ratios of the refracted p waves from two different receivers can be used with geometrical spreading taken into account for s waves owing to the contamination by the guided waves its attenuation cannot be determined directly instead s wave attenuation is determined from the attenuation of the guided waves using the partition coefficients normalized partial derivatives of the phase velocity with respect to the body wave velocities analytical forms of these partition coefficients are presented here along with examples for a number of different rock formations granite limestone sandstone and soft sediments the results show that in high velocity rocks the fluid attenuation controls the guided wave attenuation except near the cut off frequency of the pseudo rayleigh wave for low velocity rock formations especially in the case where the s wave velocity is lower than the fluid velocity the s wave attenuation is the main contributor to the guided wave attenuation synthetic microseisgmogram calculated with the measured body wave attenuation agrees well with the actual microseismograms

the impact of wave mean flow interaction on the northern hemisphere polar vortex after tropical volcanic eruptions the current generation of earth system models that participate in the coupled model intercomparison project phase 5 cmip5 does not on average produce a strengthened northern hemisphere nh polar vortex after large tropical volcanic eruptions as suggested by observational records here we investigate the impact of volcanic eruptions on the nh winter stratosphere with an ensemble of 20 model simulations of the max planck institute earth system model we compare the dynamical impact in simulations of the very large 1815 tambora eruption with the averaged dynamical response to the two largest eruptions of the cmip5 historical simulations the 1883 krakatau and the 1991 pinatubo eruptions we find that for both the tambora and the averaged krakatau pinatubo eruptions the radiative perturbation only weakly affects the polar vortex directly the position of the maximum temperature anomaly gradient is located at approximately 30 n where we obtain significant westerly zonal wind anomalies between 10hpa and 30hpa under the very strong forcing of the tambora eruption the nh polar vortex is significantly strengthened because the subtropical westerly wind anomalies are sufficiently strong to robustly alter the propagation of planetary waves the average response to the eruptions of krakatau and pinatubo reveals a slight strengthening of the polar vortex but individual ensemble members differ substantially indicating that internal variability plays a dominant role for the tambora eruption the ensemble variability of the zonal mean temperature and zonal wind anomalies during midwinter and late winter is significantly reduced compared to the volcanically unperturbed period

forward modeling of fracture induced sonic anisotropy using a combination of borehole image and sonic logs we develop a methodology to model and interpret borehole dipole sonic anisotropy related to the effect of geologic fractures using a forward modeling approach we use a classical excess compliance fracture model that relies on the orientation of the individual fractures the elastic properties of the host rock and the normal and tangential fracture compliance parameters orientations of individual fractures are extracted from borehole image log analysis the model is validated using borehole resistivity image and sonic logs in a gas sand reservoir over a 160 ft 50 m vertical interval of a well significant amounts of sonic anisotropy are observed at three zones with a fast shear azimuth fsa exhibiting 60 of variation and slowness difference between 2 and 16 numerous quasivertical fractures with varying dip azimuths are identified on the image log at the locations of strong sonic anisotropy the maximum horizontal stress direction given by breakouts and drilling induced fractures is shown not

a numerical investigation of head waves and leaky modes in fluid filled boreholes although synthetic borehole seismograms can be computed for a wide range of borehole conditions the physical nature of shear and compressional head waves in fluid filled boreholes is poorly understood this paper presents a series of numerical experiments designed to explain the physical mechanisms controlling head wave propagation in boreholes these calculations demonstrate the existence of compressional normal modes equivalent to shear normal modes or pseudo rayleigh waves with sequential cutoff frequencies spaced between the cutoff frequencies for the shear normal modes major contributions to head wave spectra occur in discrete peaks at frequencies just below mode cutoff for both compressional and shear modes this result is confirmed by calculations with synthetic waveforms at frequencies corresponding to mode cutoff and by branch cut integrals designed to yield independent spectra for the compressional mode for soft formations where shear velocity falls below acoustic velocity in the borehole

borehole stoneley wave propagation across permeable structures this study investigates the propagation of borehole stoneley waves across permeable structures by modeling the structure as a zone intersecting the borehole a simple 1d theory is formulated to treat the interaction of the stoneley wave with the structure this is possible because the stoneley wave is a guided wave with no geometric spreading as it propagates along the borehole the interaction occurs because the zone and the surrounding formation possess different stoneley wavenumbers given appropriate representations of the wavenumber the theory can be applied to treat a variety of structures including a fluid filled fracture of special interest are the cases of permeable porous zones and fracture zones the results show that while stoneley wave reflections are generated strong stoneley wave attenuation is produced across a very permeable zone this result is particularly important in explaining the observed strong stoneley wave attenuation at major fractures where it has been difficult to explain the attenuation in terms of the single planar fracture theory in addition by using a simple and sufficiently accurate theory to model the effects of the permeable zone a fast and efficient method is developed to characterize the fluid transport properties of a permeable fracture zone

earth s spin and volcanic eruptions evidence for mutual cause and effect interactions the angular velocity of earth s rotation shows decadal oscillations due to the lunisolar gravitational torque as well as inter or intra annual changes arising from the angular momentum exchange between the atmosphere and the solid earth the energies involved in the length of day lod variations may affect the crustal deformation rate and seismic energy release on a global scale we found significant correlation between the occurrences of major volcanic eruptions and the lod pattern since ad 1750 on a multiyear scale eruption frequency worldwide increases with lod changes moreover the injection of sulphur gases into the atmosphere during major eruptions is accompanied by significant inter annual lod variations this provides evidence of complex mutual cause and effect interactions stress changes induced by multiyear variations in earth s spin may affect climactic volcanic activity also the atmosphere s dynamic response to volcanic plumes may result in global changes of wind circulation and climate with consequent lod variations

volcanic cooling signal in tree ring temperature records for the past millennium the authors acknowledge the national science foundation for funding much of the research presented herein rw s scottish work is currently funded through the uk leverhulme trust and natural environment research council nerc projects relic reconstructing 8000 years of environmental and landscape change in the cairngorms f 00 268 bg and scot2k reconstructing 2000 years of scottish climate from tree rings ne k003097 1

climatic response to high latitude volcanic eruptions 1 strong volcanic eruptions can inject large amounts of so2 into the lower stratosphere which over time are converted into sulfate aerosols and have the potential to impact climate aerosols from tropical volcanic eruptions like the 1991 mount pinatubo eruption spread over the entire globe whereas high latitude eruptions typically have aerosols which remain in the hemisphere in which they where injected this causes their largest radiative forcing to be extratropical and the climate response should be different from that of tropical eruptions we conducted a 20 member ensemble simulation of the climate response to the katmai eruption 58 n of 6 june 1912 using the nasa goddard institute for space studies modele climate model we also produced an additional 20 member ensemble for a 3 times katmai 3x katmai eruption to see the impact the strength of the eruption has on the radiative as well as the dynamical responses the results of these simulations do not show a positive arctic oscillation response like past simulations of tropical volcanic eruptions but we did find significant cooling over southern asia during the boreal winter the first winter following katmai and the second winter following 3x katmai showed strong similarities in lower stratospheric geopotential height anomalies and sea level pressure anomalies which occurred when the two cases had similar optical depth perturbations these simulations show that the radiative impact of a high latitude volcanic eruption was much larger than the dynamical impact at high latitudes in the boreal summer however strong cooling over the northern hemisphere landmasses caused a decrease in the asian monsoon circulation with significant decreases of up to 10 in cloud cover and warming over northern india thus the main dynamical impact of high latitude eruptions is in the summer over asia

elastic wave propagation in a fluid filled borehole and synthetic acoustic logs the propagation and dispersion characteristics of guided waves in a fluid filled borehole are studied using dispersion curves and modeling full wave acoustic logs by synthetic microseismograms the dispersion characteristics of the pseudo rayleigh reflected and stoneley waves in a borehole with and without a tool in the center are compared effects of different tool properties are calculated the effect of a rigid tool is to make the effective borehole radius smaller as an approximation dispersion characteristics of the guided waves in a borehole with a tool can be calculated as a purely fluid filled borehole with a smaller effective radius theoretical waveforms microseismograms of elastic waves propagating in a borehole are calculated using a discrete wavenumber integration with an appropriate choice of parameters our results look similar to the acoustic waveforms recorded in a limestone and a shale formation several factors affect the shape of an acoustic log microseismogram the effective rad

simulation of holocene cooling events in a coupled climate model three potential mechanisms behind centennial scale holocene cooling events are studied in simulations performed with the coupled climate model ecbilt clio 1 internal variability 2 solar forcing and 3 freshwater forcing in experiments with constant preindustrial forcings three centennial scale cooling events occur spontaneously in 15 000 years these rare events represent an unstable internal mode of variability that is characterised by a weaker thermohaline circulation a more southward location of the main site of deep water formation expanded sea ice cover and cooling of 101c over the nordic seas this mode is visited more frequently when the climate is cooled by abruptly reducing the solar constant by 5 or 3 wm 2 prescribing a solar forcing of the same magnitude but following a sinusoidal function with a period of 100 or 1000 years does not result in any centennial scale cooling events the latter forcing does however result in more frequent individual cold years in the north atlantic region that are related to local weakening of the deep convection and sea ice expansion adding realistic freshwater pulses to the labrador sea is also able to trigger centennial scale cooling events with temperature anomalies resembling proxy evidence for the cooling event at 8 2 kyr bp suggesting that freshwater forcing is a valid explanation for early holocene cooling events r 2007 elsevier ltd all rights reserved

field measurements of normal and shear fracture compliance abstract field estimates of the normal and shear compliance of water saturated fractures were obtained from a seismic experiment carried out on a wave cut platform of upper caithness flagstone on the north coast of scotland the rocks are cut by two orthogonal sets of vertical fractures vertical geophones were glued to the rock surface and seismic waves were generated by striking the surface with a sledge hammer first arrival traveltimes were obtained for source receiver distances up to 30 m differences of compressional velocity with direction across the platform were interpreted as resulting from the compliance of the fractures intersected by the transmitted waves the average normal compliance for fractures at this site is 4 0 10 12 1 0 10 12 m pa there is much less certainty about the precise value of shear compliance however the normal shear compliance ratio is determined to be 0 1

experimental development of low frequency shear modulus and attenuation measurements in mated rock fractures shear mechanics due to asperity contact area changes with normal stress abstractreservoir core measurements can help guide seismic monitoring of fluid induced pressure variations in tight fractured reservoirs including those targeted for supercritical co2 injection we have developed the first seismic frequency room dry measurements of fracture specific shear stiffness using artificially fractured standard granite samples with different degrees of mating a well mated tensile fracture from a dolomite reservoir core as well as simple roughened polymethyl methacrylate pmma surfaces we have adapted a low frequency 0 01 100 hz shear modulus and attenuation apparatus to explore the seismic signature of fractures and understand the mechanics of asperity contacts under a range of normal stress conditions our instrument is unique in its ability to measure at low normal stresses 0 5 20 mpa simulating open fractures in shallow or high fluid pressure reservoirs the accuracy of our instrument is demonstrated by calibration and comparison with ultrasonic measurements and

3 d seismic endoscopy multiscale analysis and dynamic azimuthal filtering of borehole waves summary we previously proposed a method of seismic endoscopy and a related prototype tool to acquire directional information and to produce three dimensional 3 d seismic images in a cylindrical volume surrounding a borehole with an investigation radius of several metres basic imaging algorithms were developed where the azimuthal move out amo process is combined to a timescale method to refocus directional information and analyse the surrounding medium further processing tools however were necessary for separating the various types of waves recorded the present paper describes a multiscale and dynamic azimuthal filtering to separate the far field waves from borehole or tube waves generated by the pipe we call this filter stoneley move out smo because it characterizes stoneley waves associated with the tube it is then possible to reconstruct details of the far field by an inverse wavelet transform the comparison with classical methods such as the covariance method is discussed applications on noisy synthetic and experimental data are presented

hydraulic properties of closely spaced dipping open fractures intersecting a fluid filled borehole derived from tube wave generation and scattering fluid filled fractures and fissures often determine the pathways and volume of fluid movement they are critically important in crustal seismology and in the exploration of geothermal and hydrocarbon reservoirs we introduce a model for tube wave scattering and generation at dipping parallel wall fractures intersecting a fluid filled borehole a new equation reveals the interaction of tube wavefield with multiple closely spaced fractures showing that the fracture dip significantly affects the tube waves numerical modeling demonstrates the possibility of imaging these fractures using a focusing analysis the focused traces correspond well with the known fracture density aperture and dip angles testing the method on a vsp data set obtained at a fault damaged zone in the median tectonic line japan presents evidences of tube waves being generated and scattered at open fractures and thin cataclasite layers this finding leads to a new possibility for imaging characterizing and monitoring in situ hydraulic properties of dipping fractures using the tube wavefield

acoustic televiewer log images of natural fractures and bedding planes in the toa baja borehole puerto rico although borehole conditions made acoustic televiewer logging difficult in the toa baja borehole more than 180 meters of continuous acceptable quality televiewer logs were obtained in the intervals from 730 to 880 meters and from 2 515 to 2 675 meters in depth indicating the presence of fractures that appear to be open in situ most of the largest possibly open fractures in these intervals are either nearly parallel to directions given by the dipmeter log and may represent solution openings or minor washouts along bedding planes or dip steeply to the south or southwest across bedding the televiewer log confirms the presence of an apparently open set of fractures near 867 meters in depth where circulation was lost during drilling and in the interval from 2 600 to 2 650 meters in depth where the temperature log indicates anomalous heat flow in the surrounding formation

detection of open fractures with vertical seismic profiling in vertical seismic profiling surveys tube waves are generated by compressional waves impinging on subsurface fractures or permeable zones the problem of generation of these waves by a nonnormal incident p wave for an inclined borehole intersecting a tilted parallel wall fracture is formulated theoretically the amplitude of tube waves depends on the permeability the length of the fracture and the frequency the relative effects of these parameters are studied individually the problem is also formulated for a thin oblate ellipsoidal penny shaped fracture the results for the two fracture models are compared and contrasted field data from tyngsboro massachusetts are shown for open fractures in granite from tube wave amplitudes normalized to p wave amplitudes calculated permeabilities are of the order of 100 mdarcy

a semblance guided median filter r eiter e c t oksoz m n and p urdy g m 1992 a semblance guided median filter geophysical prospecting 41 15 41 a slowness selective median filter based on information from a local set of traces is described and implemented the filter is constructed in two steps the first being an estimation of a preferred slowness and the second the selection of a median or trimmed mean value to replace the original data point a symmetric window of traces defining the filter aperture is selected about each trace to be filtered and the filter applied repeatedly to each time point the preferred slowness is determined by scanning a range of linear moveouts within the user specified slowness passband semblance is computed for each trial slowness and the preferred slowness selected from the peak semblance value data points collected along this preferred slowness are then sorted from lowest to highest and in the case of a pure median filter the middle point s selected to replace the original data point the output of the filter is therefore quite insensitive to large amplitude noise bursts retaining the well known beneficial properties of a traditional 1d median filter energy which is either incoherent over the filter aperture or lies outside the slowness passband may be additionally suppressed by weighting the filter output by the measured peak semblance this approach may be used as a velocity filter to estimate coherent signal within a specified slowness passband and reject coherent energy outside this range for applications of this type other velocity estimators may be used in place of our semblance measure to provide improved velocity estimation and better filter performance the filter aperture may also be extended to provide increased velocity estimation but will result in additional lateral smearing of signal we show that in addition to a velocity filter our approach may be used to improve signal to noise ratios in noisy data the median filter tends to suppress the amplitude of random background noise and semblance weighting may be used to reduce the amplitude of background noise further while enhancing coherent signal we apply our method to vertical seismic profile data to separate upgoing and downgoing wavefields and also to large offset ocean bottom hydrophone data to enhance weak refracted and post critically reflected energy

using flowmeter pulse tests to define hydraulic connections in the subsurface a fractured shale example cross borehole flowmeter pulse tests define subsurface connections between discrete fractures using short stress periods to monitor the propagation of the pulse through the flow system this technique is an improvement over other cross borehole techniques because measurements can be made in open boreholes without packers or previous identification of water producing intervals the method is based on the concept of monitoring the propagation of pulses rather than steady flow through the fracture network in this method a hydraulic stress is applied to a borehole connected to a single permeable fracture and the distribution of flow induced by that stress monitored in adjacent boreholes the transient flow responses are compared to type curves computed for several different types of fracture connections the shape of the transient flow response indicates the type of fracture connection and the fit of the data to the type curve yields an estimate of its transmissivity and storage coefficient the flowmeter pulse test technique was applied in fractured shale at a volatile organic contaminant plume in watervliet new york flowmeter and other geophysical logs were used to identify permeable fractures in eight boreholes in and near the contaminant plume using single borehole flow measurements flowmeter cross hole pulse tests were used to identify connections between fractures detected in the boreholes the results indicated a permeable fracture network connecting many of the individual boreholes and demonstrated the presence of an ambient upward hydraulic head gradient throughout the site

identification and separation of mount pinatubo and el nino southern oscillation land surface temperature anomalies empirical data analyses are performed to detect and separate the signals of the volcanic eruption and el nino events in the observed surface air temperature sat anomalies over land for the 2 years following the pinatubo eruption composite analyses of surface temperatures for the 1950 1997 period excluding the 2 years following each of the three major volcanic eruptions agung el chichon and pinatubo show that the distribution of sat anomalies over most land areas for the el nino composite is opposite to that for the la nina composite the pattern of sat anomalies changes from season to season this feature is more prominent over north america than over the other continents singular value decomposition analyses show that following the pinatubo eruption el nino signals were weak over eurasia but relatively strong over the other continents over north america the 1991 1992 el nino event contributed more than 50 to the observed surface cooling of about 1 0 c in june july and august 1992 globally averaged the maximum cooling over land with the el nino southern oscillation signals removed is 0 5 c in september october and november 1992 and september october and november 1993