investigation of groundwater contamination using electric and electromagnetic methods at an open waste disposal site a case study from isparta turkey geophysical methods when integrated with soil chemical and hydrogeological methods can be used to investigate groundwater contamination direct current dc resistivity geo electrical sounding and very low frequency electromagnetic vlf em data were collected at an open waste site used by the municipality of the city of isparta turkey the groundwater at shallow depths in alluvium which is composed of gravel sand and clay were expected to be hazardously contaminated under and around the open waste disposal site in which both household and industrial wastes are known to be disposed of improperly in this study we mapped the spread of groundwater contamination using a vlf em method which allows fast and inexpensive data collection the method complements the results of geo electrical sounding there is a good correlation between the results of the vlf em and the dc resistivity methods employed for the investigation of subsurface structure of the site where soil chemical and previous hydrogeological surveys have indicated high levels of chemical concentrations

linear filtering of vlf dip angle measurements the suggested interpretation technique is based on discrete linear filtering of vlf data the output of the described filtering results is expressed in terms of an equivalent current density at a specified depth that would cause the measured magnetic field the most practical six point filter gives an accuracy of 8 the filter is an extension of the commonly used fraser filter to process vlf dip angle data filtering the same data set for various depths gives an idea about the change of current density with depth areas with high current density correspond to good conductors the conductor dip can also be determined the use of the technique is illustrated on theoretical and field examples in all cases a good correlation with original models and other types of geophysical measurements was obtained as shown in the last example the filtering technique is also applicable in interpretation of other electromagnetic methods

gravity data as a tool for landfill study this paper shows the potential of gravity data to map a buried landfill bottom topography to this end a gravity inversion method is presented for estimating the landfill s bottom depths at discrete points assuming a decrease of the density contrast with depth according to a hyperbolic law the method s efficiency was tested using synthetic data from simulated waste landfills producing estimated bottom topographies very close to the true ones the method s potentiality has been further evaluated in applying it to the gravity data from the abandoned thomas farm landfill site indiana usa whose bottom topography is known the estimated topography showed close agreement with the known thomas farm landfill s bottom topography

leachate detection via statistical analysis of electrical resistivity and induced polarization data at a waste disposal site northern israel landfill site is an intensely heterogeneous medium in which application of 2 d geophysical techniques frequently does not enable its accurate examination due to the lack of correlation between different geophysical profiles the study was aimed to eliminate such difficulty hereafter the leachate detection methodology is presented including 2 d smoothness constrained inversion of geoelectrical raw data collected in situ the inverted data normalization and statistical examination to eradicate influence of high heterogeneity of the landfill body the generalized statistical model of the entire site was created including the likelihood analysis of the entire normalized data set three geoelectrical parameters were involved in the analysis inversed electrical resistivity inversed chargeability ip and the ratio of inversed chargeability to inversed electrical resistivity ip res the study was combined with the synthetic modeling the analysis of bulk versus fluid electrical resistivity relationship and test borehole drillings such generalized analysis ensures independency of the results from the locality of sampling measurements it was shown that leachate detection can be correctly performed utilizing the ip res ratio while the anomaly s likelihood is higher than 90

the influence of fluid type on elastic wave velocity and attenuation in volcanic rocks abstract volcano seismic signatures are the convolution of source and path effects the source signature provides important information about the dynamic rock deformation and fluid resonance processes within the volcano but path effects are the result of the volcanic plumbing the edifice physical conditions and the complex geological structure complicating the inversion of seismic data further is the influence of fluid properties here we use ultrasonic experiments to understand the effect of variable fluid viscosity and bulk modulus on p wave attenuation and velocity for volcanic rocks from white island volcano whakaari new zealand our experimental conditions for high porosity ash tuff and low porosity lava resemble shallow and deep volcano facies respectively p wave velocity vp and quality factor qp increase with the viscosity and bulk modulus of the saturating fluid and decrease with porosity and fracture volume tuffs are highly sensitive to saturating fluid with variations in vp of up to 67 and qp of 383 vp and qp in fractured lavas are slightly less sensitive to fluids 24 and 296 respectively but vp can be used to identify lithology for these tuff vs lavas comparison of the experimental data with rock physics models suggests that squirt flow is the dominant attenuation mechanism for viscosities greater than that of water while scattering losses may be important in gas saturated rocks our results have significant implications for the interpretation of seismic tomography studies and for volcano hazard monitoring based on the characteristics of detected seismicity

volcanic coseismic and seasonal changes detected at white island whakaari volcano new zealand using seismic ambient noise ambient noise interferometry is becoming increasingly popular for studying seismic velocity changes such changes contain information on the structural and mechanical properties of earth systems application to monitoring however is complicated by the large number of processes capable of inducing crustal velocity changes we demonstrate this at white island volcano over a 10 year period containing multiple well documented eruptions using individual seismic stations we detect velocity perturbations that we ascribe to volcanic activity large earthquakes and seasonality distant seismic stations capture widespread nonvolcanic changes that are also present at the volcano comparison between velocity changes recorded by distant and local stations then allows us to distinguish volcanic phenomena from seasonality through this we resolve distinct features in ambient noise derived velocity changes that relate to volcanic unrest and a phreatic eruption illustrating the strength of the approach plain language summary detecting small changes in physical properties at volcanoes is important toward effectively forecasting volcanic eruptions one approach is to monitor the speed of seismic waves at the earth s surface which are sensitive to changes in the rock they pass through at volcanoes such changes may manifest through subsurface pressure increases preceding eruptions correctly interpreting these changes however is complicated many other nonvolcanic processes are also capable of producing similar wave speed perturbations at white island volcano new zealand we detect changes associated with volcanic activity large earthquakes and weather related processes using seismometers located on the volcano we demonstrate that volcanic and nonvolcanic features can be distinguished by comparing changes recorded at the volcano with those recorded at large distances where volcanic changes are not expected to be observed through this we resolve distinct differences that can be related to volcanic activity illustrating the strength of this approach

variability of passive gas emissions seismicity and deformation during crater lake growth at white island volcano new zealand 2002 2006 1 we report on 4 years of airborne measurements of co2 so2 and h2s emission rates during a quiescent period at white island volcano new zealand beginning in 2003 during this time a significant crater lake emerged allowing scrubbing processes to be investigated co2 emissions varied from a baseline of 250 to 2000 t d 1 and demonstrated clear annual cycling that was consistent with numbers of earthquake detections and annual changes in sea level the annual variability was found to be most likely related to increases in the strain on the volcano during sea level highs temporarily causing fractures to reduce in size in the upper conduit so2 emissions varied from 0 to 400 t d 1 and were clearly affected by scrubbing processes within the first year of lake development scrubbing caused increases of so42 and cl in lake waters and the ratio of carbon to total sulphur suggested that elemental sulphur deposition was also significant in the lake during the first year careful measurements of the lake level and chemistry allowed estimates of the rate of h2o g and hcl g input into the lake and suggested that the molar abundances of major gas species h2o co2 so2 and hcl during this quiescent phase were similar to fumarolic ratios observed between earlier eruptive periods the volume of magma estimated from co2 emissions 0 015 0 04 km3 was validated by cl increases in the lake suggesting that the gas and magma are transported from deep to shallow depths as a closed system and likely become open in the upper conduit region the absence of surface deformation further leads to a necessity of magma convection to supply and remove magma from the degassing depths two models of convection configurations are discussed

twin sources of high frequency volcanic tremor of izu oshima volcano japan the 1986 fissure eruption of izu oshima volcano was preceded and followed by strong volcanic tremor activities the post eruption tremor activity consists of an alternating sequence of a tremor episode lasting about 10 min and the subsequent quiescence of about 40 50 min the authors observed this post eruption activity by a 24 channel seismic array deployed on the caldera floor the semblance analysis of the recorded data revealed that high frequency 5 hz components of the tremor were radiated from two separated sources beneath the caldera the tremor first occurred at one source and then migrated to the other source in a transition time of about a few minutes during each tremor episode this transition suggests that the two sources are dynamically linked with each other in a magma filled crack or conduit

the use of crustal higher modes to constrain crustal structure across central asia summary we investigate the feasibility of observing crustal higher mode surface wave dispersion and applying these observations to improve estimates of crustal structure because crustal overtones propagate most efficiently and are excited best in regions with thick crust and deep crustal seismicity the study concentrates on central and southern asia and parts of the middle east we develop a new data set of observations of the group velocities of rayleigh and love wave first crustal overtones between a 7 and 18 s period across this region and present dispersion maps for the first crustal overtone between periods of 10 and 17 s a monte carlo inversion of the first higher mode together with fundamental mode dispersion at several locations demonstrates that the higher modes significantly reduce the range of acceptable crustal models and improve the resolution of the crust from the mantle general application of the method across continents worldwide is probably not feasible as a result of the low likelihood of observing large numbers of first overtones in regions of normal continental crustal thickness devoid of deep crustal seismicity

infrasonic waves and volcanic tremor at stromboli the origin of the volcanic tremor is still under debate many theories have been proposed in the last years but none has yet been completely accepted in 1993 highly sensitive pressure sensors 2 175 pa volt used to monitor the explosive activity at stromboli have revealed unexpected correlation between small spike shaped pressure signals 1 2 pa and volcanic tremor these pressure pulses repeat regularly in time with a recurrent period of ca 1 s video camera images allowed us to correlate the pressure pulses with small gas bursts occurring at one of the active vents the striking correlation 0 971 between infrasonic and seismic energy fluctuations is particularly meaningful in the frequency domain infrasonic and seismic signal share the same spectral content 3 hz for every station within a range of 700 m around the craters correlations in time and frequency domain remained unaltered during the 1994 field experiments moreover during 1994 the increased degassing activity has been followed by an increase in pressure release 7 8 pa and by a shift towards higher frequencies 8 hz both in the infrasonic and seismic records infrasonic waves and volcanic tremor show similar energy fluctuations and frequency contents appearing therefore to be produced by the same dynamical process on this basis we claim that volcanic tremor at stromboli originates by continuous outbursting of small gas bubbles in the upper part of the magmatic column

thermal infrared mapping of white island volcano new zealand abstract the first aerial thermal infrared tir survey of white island volcano was successfully performed during the early morning of 15 april 1992 high spatial resolution 1 2 m tir imagery representative of surface temperatures and simultaneous visible video imagery were obtained over approximately 75 of the exposed portion of this active volcano surface temperatures ranging from ambient 11 8 c to active 95 7 c were measured at 12 sites for image calibration purposes the tir imagery clearly depicts structurally complex thermal areas within main crater regions of thermal activity along the northern crater rim and on the northwest north and northeast crater flanks were also detected one thermal seepage was observed on the north coast west of north east point a close correlation is demonstrated between the tir thermal anomalies and present vent locations prehistoric subcrater boundaries and the geohydrology of the hydrothermal system hosted in main crater most of the active 1978 90 crater complex was mapped as a high temperature anomaly except for one relatively cool area which developed soon after by subsidence and collapse into a major new vent princess crater impermeable crater lake sediments are believed to cap the hydrothermal system in parts of the central and eastern subcraters where the tir map shows appreciable areas at ambient temperatures an area of high heat flow is located in the south side of the eastern subcrater where steam and gas escape through fractured lavas the distribution of thermal anomalies in the eastern subcrater suggests that there may have been two smaller craters located within the larger now filled in structure

seismicity associated with the reactivation of nevado del ruiz colombia july 1985 december 1986 abstract renewed activity of nevado del ruiz was first evidenced in november 1984 by increased fumarolic activity and felt earthquakes this increased activity prompted an installation of seismometers on the volcano in july 1985 earthquakes recorded in 1985 indicate that most of the seismic activity prior to the eruption on november 13 1985 was confined to an l shaped epicentral zone beneath the summit of the volcano a swarm prior to the november eruption originated west of the summit telemetered stations installed after the eruption enabled better locations of post eruptive activity majority of located post eruptive earthquakes originate within 5 km of the summit at a depth less than 7 km and only few exceeded magnitude 3

a probabilistic assessment of resolution in the sasw test and its impact on the prediction of ground vibrations summary the spectral analysis of surface waves sasw method is a technique for the identification of the thickness dynamic shear modulus and damping ratio of shallow soil layers the method consists of an in situ experiment to determine the dispersion curve of the soil and the solution of an inverse problem where the corresponding soil profile is identified the sasw method has been used to investigate pavement systems to assess the quality of ground improvement to determine the thickness of waste deposits and to identify the dynamic soil properties for the prediction of ground vibrations in this paper the focus is on the last application the information on the dynamic soil properties provided by the dispersion curve is limited the dispersion curve is insensitive to variations of the soil properties on a small spatial scale and at a large depth as a result the solution of the inverse problem in the sasw method is non unique and hence uncertain the prediction of ground vibrations is therefore based on a soil model with uncertain properties in this study a bayesian approach is followed to solve the inverse problem in the sasw method a prior stochastic soil model is first formulated using the information that is available before the sasw test is performed a markov chain monte carlo method is used to transform the prior model into a posterior stochastic soil model that accounts for the sasw test results finally the prediction of ground vibrations is addressed the posterior soil model is used to assess the robustness of the predicted vibrations accounting for the uncertainty on the results of the sasw test as an example the free field vibrations due to a hammer impact on a concrete foundation are considered more complicated problems such as the prediction of road and rail traffic induced vibrations can be addressed in a similar way

the s velocity structure of the east asian mantle from inversion of shear and surface waveforms summary the structure of the mantle beneath east asia down to 800 km depth is investigated using full waveforms of seismic shear and surface waves epicentral distances are limited to less than 40 in contrast with previous waveform inversions we avoid ray theoretical or path integral approaches instead we use 1 exact 3 d waveform sensitivity kernels that correctly reflect off path sensitivity and the existence of fresnel zones we apply 2 an accurate 3 d forward modelling technique based on a coupled mode multiple forward scattering approach allowing us 3 to iterate the inversion procedure through several 3 d models and 4 to evaluate the true misfit between the data and the synthetics for the 3 d model average lateral resolution of the model in regions with good path coverage is 400 km throughout the upper mantle in the depth range from 100 to 250 km the lateral resolution even approaches 200 km since wave front healing is taken into account the amplitudes of velocity perturbations are larger than in other tomographic models moreover the waveform sensitivity kernels provide an intrinsic physical smoothing of the model stabilizing the inversion finally owing to the use of exact sensitivities better resolution can be achieved with a given set of seismograms major features of the model are high velocity subducting slabs along the west pacific subduction zones stagnating at the 660 km discontinuity a strong low velocity zone between 80 and 250 km depth in the west pacific backarc regions a plume like low velocity feature beneath the southern tip of the baikal rift zone extending into the transition zone a low velocity region under the tien shan with connection into the transition zone and thick crust under tibet reaching its maximum thickness of approximately 80 km close to the 35th parallel the lithospheric mantle underneath southern tibet is very fast indicating underthrusting of the indian lithosphere in contrast the upper mantle beneath northern tibet exhibits average to slow values from the moho down to the 660 km discontinuity very high s velocities are again observed beneath the tarim basin the high velocity mantle lithospheres under southern tibet and the tarim join beneath the karakorum range at the western tip of the tibet plateau

subband decomposition and reconstruction of continuous volcanic tremor abstract a new method of analyzing volcanic tremor is presented which uses properties of undecimated wavelet packet transforms to filter decompose and recover signals from continuous multichannel data the method preserves many standard properties that are used to characterize tremor such as wavefield polarization and seismic energy in this way we can better understand the potentially many seismic sources that combine to form continuous volcanic tremor and we can specifically address the problem of what causes changing tremor spectral content tests on synthetic data suggest that sdr can recover multiple quasi continuous signals that differ from one another by an order of magnitude even in noisy environments tests on real data recorded at erta ale in 2002 suggest that sdr can recover signals with geophysically meaningful interpretations and corroborates existing seismic and multiparametric work by harris et al 2005 jones et al 2006 and harris 2008 we suggest that this algorithm could effectively detect subtle changes in the time frequency content of volcanic tremor and recover signals from real seismic sources that appear buried in background noise and or partly masked by one another such an algorithm could allow volcanologists much greater insight into the dynamics of volcanic systems and could detect subtle signals that might help address the possibility of unrest

a continent wide map of 1 hz lg coda q variation across eurasia and its relation to lithospheric evolution 1 we present new maps of lg coda q qo and its frequency dependence at 1 hz that cover virtually all of eurasia qo is relatively high up to 650 or more in the east european siberian indian and kazakh platforms but is surprisingly low 300 500 in the arabian platform and western portion of the siberian platform as well as in great britain and the northwestern portion of mainland europe it is generally low throughout the tethysides orogenic belt but there too it displays substantial regional variations 150 400 most qo anomalies appear to be related to the tectonic history of the eurasian crust the four regions with lowest values coincide with four of eurasia s most active concentrations of earthquake activity observed eurasian qo values are consistent with a previously determined empirical plot of global values in which qo in any region is proportional to the time elapsed since the most recent episode of tectonic or orogenic activity there comparisons of the new qo map with maps of rayleigh wave velocity temperature subducted lithosphere and seismicity lead us to infer that lg coda wave attenuation is most easily explained by energy lost in moving fluids through permeable rock or in being scattered from fluid enhanced zones the fluids are likely to have originated by hydrothermal release from subducting lithosphere or other upper mantle heat sources anomalies in qo and other lithospheric properties in some cases extend well outside the tethysides belt and other regions where upper mantle heat sources are known to occur possible explanations include earlier episodes of subduction activity crustal deformation due to collision of the afro arabian and indian plates or broader than expected back arc activity beneath eurasia

a preliminary seismic study of taal volcano luzon island philippines abstract the very active taal volcano lies in the southern part of luzon island only 60 km from manila the capital of the philippines in march 2008 we deployed a temporary seismic network around taal that consisted of 8 three component short period seismometers this network recorded during the period from march to november 2008 about 1050 local events in the early data processing stages unexpected linear drifting of clock time was clearly identified for a number of stations the drifting rates of each problematic station were determined and the errors were corrected before further processing initial location of each event was derived by manually picked p s phases arrival times using hypo71 and a general velocity model based on ak135 since the velocity structure beneath taal is essentially unknown we used travel times of 338 well located events in order to derive a minimum 1d velocity model using velest the resulting locations show that most events occurred at the shallow depth beneath the taal volcano and two major earthquake groups were noticed with one lying underneath the western shore of taal lake and the other one spread around the eastern flank of the taal volcano since there is no reported volcano activities during the operation period of our seismic array we are still not confident to interpret these findings in terms of other natures of volcano at the current stage however our work represents an important pioneer step towards other more advanced seismic studies in taal volcano

insights into fluid transport mechanisms at white island from analysis of coupled very long period vlp long period lp and high frequency hf earthquakes the august 2012 to october 2013 white island unrest sequence included 5 explosive volcanic eruptions and emplacement of a small dome these events were linked to an overall increase in so2 and h2s gas flux and rsam seismic tremor which began in late 2011 prior to this unrest a small swarm of 25 events was observed on 19 21 august 2011 and captured on a temporary seismic array including 14 broadband sensors each event comprised coupled pulses having distinct high frequency hf 2 5 hz long period lp 0 5 1 1 hz and very long period vlp 0 03 0 125 hz or 8 30 s earthquakes for each coupled event we compute the source locations origin times and related uncertainties by application of standard arrival time locations for the hf earthquakes and waveform semblance for the lp and vlp earthquakes results suggest that the events are centred beneath the active vent at depths generally 1 5 km the hf and lp earthquakes have shallow depths 1 km while vlp have slightly deeper source locations 0 8 1 5 km emergent onsets for lp and vlp sources make an analysis of the absolute origin times problematic but waveform matching of vlp to lp and hf components suggests that the main vlp pulse precedes the hf and lp source processes waveform inversion for the vlp source is consistent with the rupture of a high angle east west oriented crack opening either in a purely tensile or shear tensile manner the moment of the isotropic component is estimated at 1 2 1012 nm and the corresponding volumetric change is in the range 145 450 m3 results are interpreted as an upward migration of fluids which first excite the vlp from a high angle crack in the magma carapace followed by the excitation of lp and hf source processes in the overlying hydrothermal system

the 1976 1982 strombolian and phreatomagmatic eruptions of white island new zealand eruptive and depositional mechanisms at a wet volcano white island is an active andesitic dacitic composite volcano surrounded by sea yet isolated from sea water by chemically sealed zones that confine a long lived acidic hydrothermal system within a thick sequence of fine grained volcaniclastic sediment and ash the rise of at least 106 m3 of basic andesite magma to shallow levels and its interaction with the hydrothermal system resulted in the longest historical eruption sequence at white island in 1976 1982 about 107 m3 of mixed lithic and juvenile ejecta was erupted accompanied by collapse to form two coalescing maar like craters vent position within the craters changed 5 times during the eruption but the vents were repeatedly re established along a line linking pre 1976 vents the eruption sequence consisted of seven alternating phases of phreatomagmatic and strombolian volcanism strombolian eruptions were preceded and followed by mildly explosive degassing and production of incandescent blocky juvenile ash from the margins of the magma body phreatomagmatic phases contained two styles of activity a near continuous emission of gas and ash and b discrete explosions followed by prolonged quiescence the near continuous activity reculted from streaming of magmatic volatiles and phreatic steam through open conduits frittering juvennile shards from the margins of the magma and eroding loose lithic particles from the unconsolidated wall rock the larger discrete explosions produced ballistic block aprons downwind lobes of fall tephra and cohesive wet surge deposits confined to the main crater the key features of the larger explosions were their shallow focus random occurrence and lack of precursors and the thermal heterogeneity of the ejecta this white island eruption was unusual because of the low discharge rate of magma over an extended time period and because of the influence of a unique physical and hydrological setting the low rate of magma rise led to very effective separation of magmatic volatiles and high fluxes of magmatic gas even during phreatic phases of the eruption while true strombolian phases did occur more frequently the decoupled magmatic gas rose to interact with the conduit walls and hydrothermal system producing phreatomagmatic eruptions the form of these wet explosions was governed by a delicate balance between erosion and collapse of the weak conduit walls if the walls were relatively stable fine ash was slowly eroded and erupted in weak near continous phreatomagmatic events when the walls were unstable wall collapse triggered larger discrete phreatomagmatic explosions

case study a 3d resistivity and induced polarization imaging from downstream a waste disposal site in brazil a contaminated site from a downstream municipal solid waste disposal site in brazil was investigated by using a 3d resistivity and induced polarization ip imaging technique this investigation purpose was to detect and delineate contamination plume produced by wastes the area was selected based on previous geophysical investigations and chemical analyses carried out in the site indicating the presence of a contamination plume in the area resistivity model has successfully imaged waste presence 31 mv v water table depth and groundwater flow direction a higher chargeability zone m 31 mv v outside wastes placement and following conductive anomaly was interpreted as a contamination plume normalized chargeability mn m confirmed polarizable zone which could be an effect of a salinity increase contamination plume and the clay presence in the environment

rayleigh wave tomography of china and adjacent regions 1 this paper presents a tomographic study on the s wave velocity structure of china and adjacent regions group velocity dispersions of fundamental rayleigh waves along more than 4000 paths were determined with frequency time analysis the study region was divided into a 1 1 grid and velocities in between grid nodes were calculated by bilinear interpolation the occam s inversion scheme was adopted to invert for group velocity distributions this method is robust and allows us to use a fine grid in model parameterization and thus helps to restore a more realistic velocity pattern checkerboard tests were carried out and the lateral resolution was estimated to be 4 6 in china and its eastern continental shelves the resulting group velocity maps from 10 to 184 s showed good correlation with known geological and tectonic features the pure path dispersion curves at each node were inverted for shear wave velocity structures the three dimensional velocity model indicates thick lithospheres in the yangtze and tarim platforms and hot upper mantles in baikal and western mongolia coastal area and continental shelves of eastern china and indochina and south china sea regions the tibetan plateau has a very thick crust with a low velocity zone in its middle beneath the crust a north dipping high velocity zone mimicking a subducting plate reaches to 200 km in depth and reaches to the kunlun mountains northward in northern tibet a low velocity zone immediately below the moho extends eastward then turns southward along the eastern edge of the plateau until it connects to the vast low velocity area in indochina and the south china sea

experimental constraints on phreatic eruption processes at whakaari white island volcano vigorous hydrothermal activity interspersed by sequences of phreatic and phreatomagmatic eruptions occur at whakaari white island volcano new zealand here we investigate the influence of sample type hydrothermally altered cemented ash tuffs and unconsolidated ash lapilli and fragmentation mechanism steam flashing versus gas expansion on fragmentation and ejection velocities as well as on particle size and shape our rapid decompression experiments show that fragmentation and ejection speeds of two ash tuffs cemented by alunite and amorphous opal increase with increasing porosity and that both are significantly enhanced in the presence of steam flashing ejection speeds of unconsolidated samples are higher than ejection speeds of cemented tuffs as less energy is consumed by fragmentation fragmentation dominated by steam flashing results in increased fragmentation energy and a higher proportion of fine particles particle shape analyses before and after fragmentation reveal that both steam flashing and pure gas expansion produce platy or bladed particles from fracturing parallel to the decompression front neither fragmentation mechanisms nor sample type show a significant influence on the shape our results emphasize that under identical pressure and temperature conditions eruptions accompanied by the process of liquid water flashing to steam are significantly more violent than those driven simply by gas expansion therefore phase changes during decompression and cementation are both important considerations for hazard assessment and modeling of eruptions in hydrothermally active environments

surface geoelectrics for groundwater pollution and protection studies abstract surface geoelectrical methods are currently used in solving a range of hydrogeological problems involving both quality and quantity issues this is the first of two papers devoted to the use of applied geophysics in solving problems of groundwater protection and pollution detection in this paper attention is focused on the fundamental principles of geophysical surveying for pollution and protection studies geoelectrical methods in particular resistivity methods which are the most widely applicable geophysical method are analysed in detail relations between geoelectrical and hydrogeological parameters are discussed with a view to groundwater pollution as well as methods of measurements and the principles of geophysical and hydrogeological interpretation of results several examples are given to illustrate the principles a future paper will be devoted to presentation of case histories

automated detection and characterization of harmonic tremor in continuous seismic data harmonic tremor is a common feature of volcanic hydrothermal and ice sheet seismicity and is thus an important proxy for monitoring changes in these systems however no automated methods for detecting harmonic tremor currently exist because harmonic tremor shares characteristics with speech and music digital signal processing techniques for analyzing these signals can be adapted i develop a novel pitch detection based algorithm to automatically identify occurrences of harmonic tremor and characterize their frequency content the algorithm is applied to seismic data from popocatepetl volcano mexico and benchmarked against a month long manually detected catalog of harmonic tremor events during a period of heightened eruptive activity from december 2014 may 2015 the algorithm detects 1465 minutes of harmonic tremor which generally precede periods of heightened explosive activity these results demonstrate the algorithm s ability to accurately characterize harmonic tremor while highlighting the need for additional work to understand its causes and implications at restless volcanoes

temporal geophysical signatures from contaminant mass remediation we have previously documented changes in bulk electrical conductivity self potential sp and ground penetrating radar gpr reflections in a field setting caused by biogeochemical transformations of hydrocarbon contaminated media these transformations are associated with hydrocarbon biodegradation the results of surface geophysical surveys acquired in 1996 2003 and 2007 document changes in geophysical signatures associated with removing hydrocarbon mass in the contaminated zone initial investigations in 1996 showed that relative to background the contaminated area was characterized by higher bulk electrical conductivity positive sp anomaly and attenuated gpr reflections repeated surveys in 2003 and 2007 over the contaminated area showed that in 2007 the bulk electrical conductivityhad reverted to near background conditions the positive sp anomaly became more negative and the zone of attenuated gpr reflections showed increased signal strength removal of hydrocarbon mass in the vadose zone o

magnetic susceptibility and vlf r investigations for determining geothermal blowout contaminated area a case study from alasehir manisa turkey western turkey is one of the most spectacular regions of widespread active continental extension in the world the most prominent structures of this region are e w trending gediz and buyuk menderes grabens geothermal activity around city of manisa in gediz graben has been investigated by many researchers and many geothermal boreholes were drilled in order to produce electricity in the middle of may 2012 a geothermal blowout occurred 150 m away from the deep drilling depth 1 100 m in alkan village of alasehir resort in city of manisa after that four big blowouts took place at the same area and thermal water had been diverted to alkan stream for almost 4 months the boron b and fe levels of thermal water are 87 and 11 2 ppm where the background b and fe values of topsoil vary between 0 2 1 5 ppm and 3 08 5 63 ppm respectively the objective of this study was to utilize joint magnetic susceptibility and vlf r investigations to determine possibly contaminated area with b related to high fe level on the topsoil and thermal water in the subterranean layers it is observed that magnetic susceptibility values vary between 500 and 790 cgs 10 6 in the vicinity of blowouts and 150 340 cgs 10 6 at a distance of 50 m around where the background average value is 20 cgs 10 6 by using the data collected at 346 stations besides the vlf r studies were carried out along 18 profiles at three different frequencies laterally constrained two layer inversion was applied to each station in addition to the inversion of all profiles for each frequency all lines were stacked 2 d resistivity maps were obtained and the contaminated area was determined approximately as 35 000 m2 the results show not only satisfactory agreement between magnetic susceptibility and vlf r data but also provide fast and valued interpretation of geochemical and geophysical properties of the geothermal contaminated area

volcano topography structure and intrinsic attenuation their relative influences on a simulated 3d visco elastic wavefield the seismic wavefield recorded on volcanoes can be significantly influenced by path effects scattering from the topography and internal volcanic structure can play a dominant role in the recorded seismograms intrinsic attenuation is also thought to play an important role in the characteristics of volcano seismic signals we use 3d numerical modelling of wave propagation in elastic and visco elastic media including complex velocity models and topography to investigate the scattering and attenuation characteristics of synthetic seismograms we generate 5 distinct volcano models and simulate wave propagation through these models using shallow and deep double couple broadband sources we then analyse 129 synthetic seismograms calculated on the free surface the synthetic seismograms resemble vt a and vt b events the scattering effect of the topography alone is capable of producing complex seismograms the introduction of an internal velocity structure increases the duration of these seismograms while the introduction of intrinsic attenuation decreases the duration but not the complexity we fitted our synthetic seismograms to the diffusion in a half space model to quantify the scattering and attenuation coefficients the scattering quality factor measured on all 129 stations for all 5 volcano models was similar therefore we deduce that the topography appears to be the dominant scatterer the intrinsic attenuation quality factor for each of the specific models cannot be accurately recovered using the diffusion in a half space model the measured quality factor is not only sensitive to the attenuation properties but also to the structural properties in all cases the scattering is more dominant than the intrinsic attenuation

new insights into banded tremor from the 2008 2009 mount etna eruption 1 we investigated the banded tremor activity occurring at mt etna volcano between august october 2008 during the 2008 2009 eruption the banded tremor occurred in episodes lasting 25 30 min with intervals in between the episodes of about 25 min seismic signal analyses showed that the banded tremor was characterized by spectral contents wavefields and source locations that differed from the ordinary volcanic tremor the infrasound recordings exhibited an intermittent infrasonic tremor alternating with the banded tremor episodes finally nonlinear analyses suggested that a banded tremor system can be considered chaotic implying 1 sensitive dependence on initial conditions suggesting not only that a banded tremor system requires particular conditions to generate but also that slight variations of these conditions are able to greatly change the features of the banded tremor or even to stop it and 2 long term unpredictability that is the impossibility to forecast the long term evolution of the banded tremor on the basis of all these results and analogies with geyser models we suggest a model of banded tremor that invokes alternating recharge discharge phases banded tremor is due to perturbations in shallow aquifers such as fluid movement and bubble growth or collapse due to hydrothermal boiling triggered by the heat and hot fluid transfer from the underlying magma bodies this heat fluid transfer also causes an increasing pressure in the aquifer leading to fluid discharge during this process the seismic radiation decreases and if the fluid discharge is well coupled with the atmosphere acoustic signals are generated

crust and upper mantle shear velocity structure beneath the tibetan plateau and surrounding regions from interevent surface wave phase velocity inversion average a priori shear velocity models are constructed for the tien shan tarim basin pamir hindu kush himalaya and ne india these models are shown to account for most of the lateral velocity heterogeneity at wavelengths 1000 km interevent fundamental mode rayleigh and love wave phase velocities were measured in the period range 32 200 s and were inverted for path averaged shear velocity structures these in turn were regionalized to estimate average isotropic structures beneath the six regions listed above low upper mantle velocities are observed beneath the western and eastern tien shan the tarim basin structure is poorly constrained but exhibits very low upper crustal velocities probably due to deep sedimentary accumulation and either very high upper mantle velocities exist 4 8 km s in a layer 70 km thick or the lithosphere is very thick 180 km low upper mantle velocities are observed beneath the chang thang region the central and the northeast plateau but not beneath the southern or southeastern plateau the crustal velocity gradient with depth is zero in the east central plateau consistent with lower crustal basaltic intrusions there but is positive to the west and southeast of this zone upper mantle structures show that the indian lithosphere could have subducted beneath the entire plateau only if either 1 mantle in the depth range 115 185 km has been altered or removed to reduce its average velocity or 2 the indian lithosphere is only 85 km thick

mapping the moho with seismic surface waves a review resolution analysis and recommended inversion strategies abstract the strong sensitivity of seismic surface waves to the moho is evident from a mere visual inspection of their dispersion curves or waveforms rayleigh and love waves have been used to study the earth s crust since the early days of modern seismology yet strong trade offs between the moho depth and crustal and mantle structure in surface wave inversions prompted doubts regarding their capacity to resolve the moho here we review surface wave studies of the moho with a focus on early work and then use model space mapping to establish the waves sensitivity to the moho depth and the resolution of their inversion for it if seismic wavespeeds within the crust and upper mantle are known then moho depth variations of a few kilometres produce large 1 perturbations in phase velocities however in inversions of surface wave data with no a priori information wavespeeds not known strong moho depth shear speed trade offs will mask 90 of the moho depth signal with remaining phase velocity perturbations 0 1 only in order to resolve the moho with surface waves alone errors in the data must thus be small up to 0 2 for resolving continental moho with larger errors moho depth resolution is not warranted and depends on error distribution with period an effective strategy for the inversion of surface wave data alone for the moho depth is to first constrain the crustal and upper mantle structure by inversion in a broad period range and then determine the moho depth in inversion in a narrow period range most sensitive to it with the first step results used as reference prior information on crustal and mantle structure reduces the trade offs and thus enables resolving the moho depth with noisier data such information should be used whenever available joint analysis or inversion of surface wave and other data receiver functions topography gravity can reduce uncertainties further and facilitate moho mapping

integrated geophysical studies in the east indian geothermal province integrated geophysical surveys using vertical electrical sounding ves very low frequency vlf em radiation counting total magnetic field and self potential sp measurements are carried out to characterize the geothermal area around a hot spring in the nayagarh district orissa india that lies in the east indian geothermal province the study was performed to delineate the fracture pattern contaminated groundwater movement and possible heating source ves interpretations suggest a three to four layer structure in the area resistivity survey near the hot spring suggests that weathered and fractured formations constitute the main aquifer system and extend to 60 m depth current flow measured at various electrode separations normalized by the applied voltage suggests that fractures extend to a greater depth detailed vlf study shows that fractures extend beyond 70 m depth vlf anomaly has also very good correlation with the total magnetic field measured along the same profiles study results suggest that a gridded pattern of vlf survey could map the underground conductive fracture zones that can identify the movement of contaminated groundwater flow therefore precautionary measures can be taken to check further contamination by delineating subsurface conducting structures self potential sp measured over the hot spring does not show a large anomaly in favor of the presence of a sulphide mineral body a small positive 5 15mv sp anomaly is measured which may be streaming potential due to subsurface fluid flow a high radiation is measured about four kilometers from the hot spring suggesting possible radiogenic heating however the exact nature of the heating source and its depth is not known in the area deep resistivity followed by a magneto telluric survey could reveal the deeper structures

high resolution geophysical characterization of shallow water wetlands we describe a procedure for rapid characterization of shallow water contaminated wetlands terrain conductivity tc vertical magnetic gradiometry and surface waterchemistry data were obtained from a shallow draft paddleboat operable in as little as 0 3 m of water measurements were taken every 2 s with data acquisition rates exceeding 10 kmofline12 000datapointsper8 hrfieldday we applied this procedure to an urban wetland that is affected by point and nonpoint sources of pollution we used a one dimensional laterally constrained inversion algorithm toinverttheapparent conductivitydatasetobtainedfromthe tcsurveyandtocreateapseudo 2dimageofsedimentconductivity the continuously recorded surface water depth and conductivity values were input as a priori information in theinversion weusedsoilchemistrydeterminedfor28sediment samples collected from the site as well as lithologic logs from across the wetland to constrain interpretation of thegeophysicaldata theinvertedsedimentconductivitydescribes a pattern of contamination probably attributable to leachates from adjacent landfills and or to saltwater ingress from a partial tidal connection that is not obvious in the surface water data magnetic gradiometry values and the inphasecomponentofanem31responsebothreflectprimarily thedistributionofjunkmetalassociatedwithalegacyofillegal dumping historic aerial photographs suggest that this distribution reflects land use history and defines the maximum previous extent of an adjacent landfill and a pattern of dumpingcorrelatedwithhistoricroadways

passcal instrument performance during the tibetan plateau passive seismic experiment summary the passcal instrumentation performed very well in the tibetan plateau seismic experiment this experiment has demonstrated the viability of recording high quality broadband data at temporary sites in extreme environments it also highlights some areas where further development is needed primarily more effort is needed to develop more versatile triggering options for the passcal instruments such developments could both increase the instrument9s success at recording low magnitude teleseismic events for travel time studies and save disk space when recording local events thus further increasing the feasibility of long deployments in remote regions although the use of the passcal instrument9s calibration circuitry for sensor recentering is a valuable technique more experience is needed in the construction of sensor pads to minimize tilt problems that require site visits to relevel the seismometer such as we experienced at a few sites in the winter this may also lead to improved low frequency noise levels although signals with periods greater than 200 sec can be recovered from these sites the most exciting aspect of the data we have collected is its broad frequency content and spatial density we anticipate that this type of experiment will be increasingly useful in the study of lithospheric interactions as well as deep earth structure this data was delivered to the iris data management center in early september 1993 and is available to the community two other broadband passive seismic experiments the baikal rift experiment gao et al 1992 and the rocky mountain front experiment sheehan et al 1992 should be delivered to the iris dmc in the fall of 1993 as well temporary broadband seismic experiments represent an extension of the permanent global seismic network gsn we encourage the seismological community to incorporate these data into any research using gsn data in order to maximize the potential utility of this new mode of seismic recording

the 1989 earthquake swarm beneath mammoth mountain california an initial look at the 4 may through 30 september activity abstract mammoth mountain is a 50 000 to 200 000 year old cumulovolcano standing on the southwestern rim of long valley in eastern california on 4 may 1989 two m 1 earthquakes beneath the south flank of the mountain marked the onset of a swarm that has continued for more than 6 months in addition to its longevity noteworthy aspects of this persistent swarm include 1 an exponential like increase in the rate of activity through the first month 2 a vertically oriented planar distribution of hypocenters at depths between 6 and 9 km with a north northeast strike roughly perpendicular to the average t axis orientation for the swarm earthquakes 3 recurring spasmodic bursts rapid fire sequences of similar sized earthquakes with overlapping coda and occasional earthquakes with enhanced low frequency energy 4 a uniform temporal distribution of the four largest m 3 events over the first 4 months of the swarm with a cumulative seismic moment for the entire sequence through 30 september corresponding to a single m 4 earthquake 5 a b value of 1 2 and 6 submicrostrain perturbations on the nearby borehole dilatometer the first of which led the onset of swarm activity by more than 2 weeks these aspects of the swarm together with its location along the southern extension of the youthful mono inyo volcanic chain which last erupted 500 to 600 years ago point to a magmatic source for the modest but persistent influx of strain energy into the crust beneath mammoth mountain

rayleigh wave phase velocity maps of tibet and the surrounding regions from ambient seismic noise tomography ambient noise tomography is applied to the significant data resources now available across tibet and surrounding regions to produce rayleigh wave phase speed maps at periods between 6 and 50 s data resources include the permanent federation of digital seismographic networks five temporary u s program for array seismic studies of the continental lithosphere passcal experiments in and around tibet and chinese provincial networks surrounding tibet from 2003 to 2009 totaling 600 stations and 150 000 interstation paths with such a heterogeneous data set data quality control is of utmost importance we apply conservative data quality control criteria to accept between 5000 and 45 000 measurements as a function of period which produce a lateral resolution between 100 and 200 km across most of the tibetan plateau and adjacent regions to the east misfits to the accepted measurements among passcal stations and among chinese stations are similar with a standard deviation of 1 7 s which indicates that the final dispersion measurements from chinese and passcal stations are of similar quality phase velocities across the tibetan plateau are lower on average than those in the surrounding nonbasin regions phase velocities in northern tibet are lower than those in southern tibet perhaps implying different spatial and temporal variations in the way the high elevations of the plateau are created and maintained at short periods 20 s very high velocities are imaged in the tarim basin the ordos block and the sichuan basin these phase velocity dispersion maps provide information needed to construct a 3 d shear velocity model of the crust across the tibetan plateau and surrounding regions

seismic events at vulcano italy during 1988 1992 abstract a classification of seismic events is proposed that originate on vulcano aeolian islands southern tyrrhenian sea and adjacent regions into four broad classes 1 shocks that exhibit single peaked spectra 2 typical earthquakes with distinct p and s phases 3 irregular shaped events with ill defined to undetectable s phases and 4 long period events with dominant frequency peak less than 2 hz a hypothesis is put forward that the shocks occurring within the volcanic cone of la fossa are mainly related to intense fumarolic activity of high temperature more than 650 c in october 1992 estimation of seismic energy release within two distinct sectors one including la fossa cone the other external to it during 1988 1992 has been developed in order to evaluate the level of seismic activity of the system over the time here analysed the rate of seismic energy density release at la fossa was 4 71 1014 erg km 2 yr 1 that is significantly larger than that of the surrounding areas furthermore the energy partition estimate indicates that within la fossa seismic energy release associated with rock failure processes is on the whole about 3 6 times larger than that of fluid driven shocks the latter appear to be concentrated at rather shallow depths 400 1000 m where geochemical analyses and geothermal surveys indicate the sealing action of hydrothermal minerals estimated b values of the gutenberg richter magnitude frequency relation range between 0 81 0 27 and 1 45 0 29 within la fossa whereas a value around 1 6 has been calculated for the external sector the comparison between data presented in this paper and those from recent geophyical and geochemical investigations shows that appreciable increments in the rate of seismicity are accompanied with significant modifications in the chemistry of fumarolic gases and in the ground deformation pattern recorded at the base of the active cone

peculiarities of surface wave propagation across central eurasia abstract the recent installation of six broadband digital iris ida seismic stations in the ussr has provided new opportunities for studying surface wave propagation across eurasia group velocities of fundamental rayleigh and love modes between epicenters and these stations were determined for 35 events that occurred since april 1989 to the middle of july 1990 near eurasia differential phase velocities were found for the same arrivals along paths between several pairs of stations group and phase velocities were obtained in the period range from 15 to 300 sec frequency time polarization analysis was used for studying polarization properties of surface waves in some cases significant anomalies in the particle motion for periods up to 100 sec were observed they are attributed to surface wave refraction and scattering due to lateral inhomogeneities at the boundaries and inside the eurasia continent

3d behaviour of contamination in landfill sites using 2d resistivity ip imaging case studies in portugal aiming at defining a valid spatial contamination model resistivity and induced polarization ip measurements were used to investigate contamination plumes in the vicinity of two municipal landfills ovar and ilhavo previous geophysical surveys and underground water samples confirmed the contamination however 2d resistivity ip surveys enabled in obtaining a more accurate spatial model the ovar survey consisted of two profiles with nine wenner soundings each the ilhavo survey was carried out along two individual lines using a wenner standard pseudo section in both situations negative ip values were found associated with positive ip values which can be explained mainly by 2d or 3d geometric effects caused by the presence of the conductive plumes the data were modelled using a 2d inversion program res2dinv and the resulting resistivity and chargeability distributions were displayed as pseudo sections the resistivity and chargeability pseudo sections define the contamination plumes and the sedimentary structure these case studies illustrate the advantages of 2d resistivity ip surveys for the mapping of shape and dimension of contamination associated with landfills

evolution of the taupo hikurangi subduction system abstract the present day taupo hikurangi subduction system is a southward extension of the tonga kermadec arc system into a sediment rich continental margin environment it consists of a shallow structural trench the hikurangi trough a 150 km wide imbricate thrust controlled accretionary borderland the continental slope shelf and coastal hills of eastern north island a frontal ridge the main greywacke ranges of north island and a volcanic arc and marginal basin the taupo volcanic zone structural elements become progressively more elevated and subduction more oblique towards the south the whole nne trending system is truncated at a largely strike slip transform boundary that extends along the southwestern part of the hikurangi trough and the hope fault of south island to the main alpine fault the volcanic arc is 200 270 km from the structural trench and comprises a nne trending chain of andesite dacite volcanoes extending along the eastern side of the taupo volcanic zone most of the andesites are olivine bearing and have been erupted within the last 50 000 years it is suggested the taupo hikurangi margin has evolved by rotation of accretionary elements from an original nw trending subduction system north of new zealand the older elements of the prism were associated with subduction of a re entrant of the pacific plate and perhaps the south fiji basin in mid tertiary times they subsequently became separated from their nw trending volcanic arc by dextral strike slip movement along curved faults east of the main greywacke ranges during the plio pleistocene oblique subduction and accretion intensified as the taupo hikurangi margin rotated into line with the nne trending kermadec system and a marginal basin was developed along a similar trend to form the taupo volcanic zone within the last 50 000 years olivine bearing andesite volcanism has commenced along the eastern side of the taupo volcanic zone

characterization of active and closed landfill sites using 2d resistivity ip imaging case studies in penang malaysia an interpretation approach for analysis of electrical resistivity and chargeability inverse models generated at two upgraded semi aerobic landfill sites was developed the inverse models produced from a 2d inversion program res2dinv were used to set up a grid of electrical resistivity and chargeability imaging at the landfill sites the investigations confirmed a high chargeability unit 70 ms depicting waste deposits and a saturated clayey layer while the leachate plume showed low resistivity 10 m and weak chargeability zone 20 ms moreover the ip responses of a diffused leachate plume downstream of a separate semi aerobic landfill site in a similar geological setting were evaluated obtaining an analogous result the ion dominated plume that exhibited a weak chargeability promoted membrane polarization rather than electrode polarization in its ip responses however the high concentration of ions in the diffused leachate restrained the ionic polarization diminishing the ip effects in host sediments the interpretation of the resistivity and chargeability profiles at the characterization sites allowed delineating the different zones of the subsurface strata in particular comparison of the leachate zones at the two locations revealed that the active landfill with a lesser proportion of waste deposits contained a greater accumulation of leachate than the closed site the results in this study support the effectiveness of contaminant plume monitoring through the joint application of resistivity and ip methods these non invasive rapid and cost effective geophysical techniques could lead to a promising reconnaissance tool for remediation or reclamation of solid waste disposal sites

rayleigh wave group velocity tomography of siberia china and the vicinity rayleigh waves are used in a tomographic inversion to obtain group velocity maps of east asia 40 e 160 e and 20 n 70 n the period range studied is 30 to 70 seconds seismograms used for this study were recorded at cdsn stations at a temporary broadband seismic array in tibet at several sro stations and kirnos equipped stations established in asia by the former soviet union in siberia in the sakhalin and in mongolia altogether more than 1200 paths were available in the tomographic inversion the study area includes the angara craton the geologically ancient core of asia and the subsequently accreted units the altaids a paleozoic collision complex the sino korean platform a chain of archaen terranes separated by belts of active structures the south china platform a collage of precambrian paleozoic and mesozoic metamorphic and igneous terranes as well as the tibetan plateau an active tectonic feature created in late cenozoic through collision of the indian subcontinent and the asian continent many of these main units are recognizable in the tomographic images as distinctive units tibet appears as a prominent low velocity about 15 from the average structure with western and central tibet often appearing as the areas with the lowest velocities the central asian fold belt and the angara craton are consistently high group velocity areas some lesser tectonic features are also recognizable for example lake baikal is seen as a high velocity feature at periods greater than 40 seconds however the high group velocity feature does not stop near the southern end of lake baikal it extends south southwestward across mongolia the north china plain a part of the platform where extensional tectonics dominate is an area of high velocities as a result of relatively thin crust the south china block the least tectonically active region of china is generally an area of high velocity for periods longer than 40 seconds a nne trending high group velocity gradient clearly exists in eastern china the velocities are noticeably higher in the east from the group velocity maps average dispersion curves at twelve locations were determined and inverted to obtain velocity structures main results of group velocity inversion include 1 a tibetan crust of around 60 km thick with low crustal and upper mantle shear velocities at 3 3 km s and 4 2 km s respectively 2 with the moho constrained at 40 43 km the angara craton and the central asian foldbelt have a v s in excess of 4 6 km s 3 relatively low shear velocities are obtained for tectonically active areas in many parts of the study area where precambrian basement is exposed the process in the crust and upper mantle due to recent tectonic activities have modified the crust and upper mantle velocity structures under the precambrian terranes they are no longer underlain by high velocity crust and mantle

thinning and flow of tibetan crust constrained by seismic anisotropy intermediate period rayleigh and love waves propagating across tibet indicate marked radial anisotropy within the middle to lower crust consistent with a thinning of the middle crust by about 30 the anisotropy is largest in the western part of the plateau where moment tensors of earthquakes indicate active crustal thinning the preferred orientation of mica crystals resulting from the crustal thinning can account for the observed anisotropy the middle to lower crust of tibet appears to have thinned more than the upper crust consistent with deformation of a mechanically weak layer that flows as if confined to a channel

assessing preferential seepage and monitoring mortar injection through an earthen dam settled over a gypsiferous substrate using combined geophysical methods abstract for several decades the sant llorenc de montgai reservoir has experienced different problems that could affect the safety of the engineering structure for this reason several corrective actions have been taken over the years here we present a study involving complementary geophysical methods including electrical resistivity tomography seismic refraction tomography and frequency domain electromagnetic surveys the analysis of the inverted electrical resistivity tomography cross sections combined with the seismic refraction results and land subsidence monitoring data show the likely mechanism of abnormal seepage the areas where mortar injections were applied as a corrective measure are also clearly delineated in addition the evolution of the state of the embankment has been established from two successive electrical resistivity tomography surveys in the last two decades the results show areas where corrective mortar injections have been effective while in other areas new abnormal seepage has been detected the lithological heterogeneity of the bedrock especially the dissolution of gypsum rich rocks induced subsidence effects and caused abnormal seepage in different areas along the embankment our results indicate how corrective solutions can be optimized to reduce the cost of corrective engineering interventions

characterization of seismic waveforms and classification of seismic events using chirplet atomic decomposition example from the lacq gas field western pyrenees france summary in the present paper we present a generalization of the wavelet transform known as chirplet transform specially designed to quantify the morphological attributes of individual seismic sections packets constituting the seismic waveforms the proposed transform relies on an atomic decomposition of individual seismograms based on local multiscale chirps swept frequency wave packets of various shape and duration we developed an algorithm that provides an optimal representation of the waveform packets in terms of i arrival time ii central frequency iii modulus iv phase v duration vi envelope shape and vii frequency modulation compacting the information contained in each seismogram into a reduced set of parameters particularly well suited to describe seismic waveforms in the present work we focus on the ability of atomic decomposition to classify seismic events we illustrate the developed methodology and resulting hierarchical classification scheme agglomerative clustering displayed as a dendrogram to seismograms of the induced seismicity recorded in the lacq gas field between 1989 and 1997 by a local seismic network for the present case study the resulting classification reveals different levels of similarity between seismic events of a same swarm accurate analysis of the subsequences of seismic events associated to an injection well shows temporal changes in the morphological attributes of the recorded seismic waveforms these changes are highly correlated with water over pressure records of the reservoir demonstrating the capability of the method to guide investigation of the underlying processes properties of propagation media source rupture processes and in a general manner the physical properties of the reservoir

in situ measurements of shear wave velocity in sediments with higher mode rayleigh waves a seismic survey was carried out on a tidal flat in the sw netherlands in order to determine shear wave velocities in sediments by means of higher mode rayleigh waves the dispersion properties of these rayleigh waves were measured in the 2 d amplitude spectrum or f k spectrum and resulted in phase velocities for six different modes as a function of frequency 5 30 hz these observed phase velocities were inverted for a nine layer model for the shear wave velocity to a depth of 50 m

effects of longitudinal variability of soil on a continuous spread footing abstract a simple model describing the soil foundation interaction for continuous wall footing and which takes longitudinal variations in soil s properties into account is presented in this paper this model has been developed using a finite element representation in which a 1d structure continuous spread footing rests on a spatially variable soil described by winkler type springs characterized by the subgrade reaction coefficient geotechnical pressuremeter tests and geophysical vlf r very low frequency resistivity mode surveys performed over a selected study area resting on an alluvial terrace were used to provide information on the soil s variability and to reveal the presence of clayey soil three kinds of natural variability are considered natural soil variations rapid variations in the soil s properties and shrinkage of clayey soil a relationship between the coefficient of subgrade reaction and the resistivity was observed the spatial variability of the coefficient of subgrade reaction was analyzed using geostatistics and then used in the model to derive differential settlements and bending moment values of a continuous spread footing which cannot be predicted if the soil is assumed to be homogeneous or if shrinkage under the continuous wall footing is not taken into account results show that as is often the case in practice when the longitudinal soil variability is not taken into account the design may be unsafe

volcanic earthquakes and their relationship to eruptions at ruapehu and ngauruhoe volcanoes abstract crustal earthquakes near ruapehu and ngauruhoe fall into two classes each of which can be subdivided on the one hand there are high frequency events 3 hz with sharp well defined phases mainly concentrated beneath ruapehu crater lake low frequency events the low frequency events resemble minakami s b type and explosion earthquakes but sometimes occur where no vent exists and rather deeper than his formal definition difficulty in applying minakami s classification rigorously and the fact that low frequencies may be due to abnormal attenuation of higher frequencies along the path rather than to their suppression or absence at the source has led to reclassification of earthquakes near the volcanoes into two broad groups tectonic and volcanic the former includes all high frequency earthquakes and those discrete events in which dominant low frequencies are due to path effects the latter includes multiple and emergent events which show evidence of prolonged or repetitive source mechanism dominant low frequencies are ascribed to occurrence in heat weakened material and high frequencies to instantaneous source mechanisms operating in competent rock the term volcano tectonic describes tectonic earthquakes within some arbitrary distance of a volcano at ngauruhoe and ruapehu volcanic earthquakes accompany explosive vent clearing eruptions subsequent open vent degassing and ash emission however although often powerful and prolonged usually occurs without earthquakes such activity is however frequently accompanied by volcanic tremor at ruapehu under closed vent conditions when lake temperature is low low frequency earthquakes up to magnitude ml 3 4 have occurred without any eruption five types of phreatic eruptions are identified at ruapehu each having a distinctive seismic pattern the three most explosive types appear to be generated by a chain reaction process and all involve flashing of water to steam the first by failure of the roof with little precursory seismicity after a closed vent period during which lake temperature decreases the second after prolonged heating of the lake and much preliminary volcanic tremor interpreted as due to rising magma and the third under open vent conditions in the wake of one of the two preceding types a fourth probably occurs in wet sediments near the base of the lake as a result of upward migration of hot gas and a fifth aseismic or accompanied by very weak volcanic tremor is associated with convective overturn within crater lake

crater lake controls on volcano stability insights from white island new zealand many volcanoes around the world host summit crater lakes but their influence on the overall stability of the edifice remains poorly understood here i use satellite radar data acquired by terrasar x from early 2015 to july 2017 over white island new zealand to investigate the interaction of the crater lake and deformation of the surrounding edifice an eruption in april 2016 was preceded by a period of uplift within the crater floor and drop in the lake level modeling of the uplift indicates a shallow source located at 100 m depth in the vicinity of the crater lake likely coinciding with the shallow hydrothermal system in addition to the drop in the lake level stress changes induced by the inflation suggest that the pressurization of the shallow hydrothermal system helped promote failure along the edge of the crater lake which collapsed during the eruption after the eruption and almost complete removal of the crater lake large areas of the crater wall and lake edge began moving downslope at rates approaching 400 mm yr the coincidence between the rapid increase in the displacement rates and removal of the crater lake suggests that the lake provides a physical control on the stability of the surrounding edifice

mechanical behaviour and failure modes in the whakaari white island volcano hydrothermal system new zealand abstract volcanic hydrothermal systems host a prodigious variety of physico chemical conditions the physico chemical state and mechanical behaviour of rocks within is correspondingly complex and often characterised by vast heterogeneity here we present uniaxial and triaxial compression experiments designed to investigate the breadth of mechanical behaviour and failure modes dilatant or compactant for hydrothermally altered lava and ash tuff deposits from whakaari white island volcano in new zealand a volcano with a well documented and very active hydrothermal system our deformation experiments show that the failure mode of low porosity lava remains dilatant over a range of depths up to pressures corresponding to depths of about 2 km upon failure shear fractures the result of the coalescence of dilatational microcracks are universally present the high porosity ash tuffs switch however from a dilatant to a compactant failure mode driven by progressive distributed pore collapse at relatively low pressure corresponding to a depth of about 250 m we capture the salient features of the dynamic conditions e g differential stress effective pressure in a schematic cross section for the whakaari hydrothermal system and map for the different lithologies areas susceptible to either dilatant vs compactive modes of failure the failure mode will impact for example the evolution of rock physical properties e g porosity permeability and elastic wave velocity and the nature of the seismicity accompanying periods of unrest we outline accordingly the potential implications for the interpretation of seismic signals outgassing ground deformation and the volcanic structural stability for whakaari and similar hydrothermally active volcanoes worldwide

crust and upper mantle tomography in tibet using surface waves we have obtained maps of lateral variations of structure in the crust and lithosphere in tibet and surrounding regions by inversion of single station measurements of fundamental mode rayleigh wave phase velocities in the period range 25 100 sec for earthquakes located in central asia and observed at teleseismic digital stations in eurasia phase velocity maps are obtained using a tomographic method without a priori constraints on region boundaries the lateral variations of s velocity reveal a symmetric pattern on each side of crustal low velocity zone centered on the chang tang region north central tibet this zone is bounded by rather steep velocity gradients to the south and east about 250 and 400 km north and west of the frontal thrusts of the himalayas and lungmen shan respectively the northern boundary of the zone crosses the northern limit of the tibet plateau altyn tagh and kunlun extending into the southwest tarim and qaidam basins the low crustal velocities are consistent with a thick hot crust in the central part of tibet consistent with quaternary volcanism in chang tang the steep gradients towards higher velocities in the south and in the north are compatible with the documented continental subduction in the south and suggest that a similar situation might exist in the north

investigation of seawater intrusion in the dibdibba aquifer using 2d resistivity imaging in the area between al zubair and umm qasr southern iraq electrical resistivity surveying for delineating seawater intrusion was performed in the dibdibba aquifer in the area between the cities of al zubair safwan and al zubair umm qasr in the vicinity of khor al zubair channel basrah governorate southern iraq fourteen 2d resistivity profiles with a total length of 14 km were collected in the study area the resistivity sections were compared with lithological data extracted from 11 boreholes thirty nine groundwater samples were collected within the area and analyzed for chemical constituents internal hydrogeological reports and unpublished studies were also evaluated results reveal the existence of three major resistivity layers ranging from 0 1 to 130 m at various depths and locations the first layer has very low electrical resistivity 0 1 5 m representing a layer saturated with saltwater intruded from khor al zubair channel the second layer shows resistivity in the range of 5 130 m attributed to a transition zone and an unaffected zone saturated with brackish groundwater the last resistivity layer 3 m represents coarse grain sediments saturated with saline groundwater furthermore a hard clay bed jojab appears with a resistivity of 3 7 m in all 2d imaging lines within a depth of 20 28 m electrical conductivity ec measurements from seven wells collected in 2014 and 2016 show a positive ec difference increasing landward with an average increase of 1927 s cm in addition six chemical relationships na cl ca mg hco3 so4 so4 hco3 so4 cl mg ca and cl hco3 co3 are used to detect the source of salinity in groundwater this study proves that extensive use of high resolution 2d imaging sections alongside lithological and hydrogeological data can serve as a useful tool to delineate the boundaries between aquifers identify hydraulic boundaries between groundwater with different salinities and allocate hard clay layers between the upper and lower dibdibba aquifer in general the combination of 2d imaging and hydrochemistry enables conceptualization of the hydrogeological situation in the subsurface and characterization of the salinity source here seawater intrusion in the study area there have been no studies published so far on the characteristics of saltwater intrusion in the study area and this study is considered to be important for monitoring and studying the intrusion and regression of seawater

mapping groundwater contamination using dc resistivity and vlf geophysical methods a case study geophysical methods can be helpful in mapping areas of contaminated soil and groundwater electrical resistivity and very low frequency electromagnetic induction vlf surveys were carried out at a site of shallow hydrocarbon contamination in utah county utah previously installed monitoring wells facilitated analysis of water chemistry to enhance interpretation of the geophysical data the electrical resistivity and vlf data correlate well and vertical cross sections and contour maps generated from these data helped map the contaminant plume which was delineated as an area of high interpreted resistivities

upper mantle beneath southeast asia from s velocity tomography 1 we present a three dimensional s velocity model of the se asian western pacific upper mantle with 400 km lateral resolution using the novel automated multimode inversion technique we processed 4038 vertical component seismograms and extracted 22 708 linear equations with uncorrelated uncertainties that constrain upper mantle structure we used time frequency windows to select signal with negligible proportion of scattered energy the windows included the fundamental rayleigh mode and s and multiple s waves the observed range of s velocity variations is the widest 17 18 in the upper 150 km of the mantle high velocity continental roots can reach beyond the present extent of the overlying archean proterozoic crust by 500 km beneath some precambrian units the roots are absent which can be attributed to deformation and gradual destruction of the ancient lithosphere at 120 150 km s velocity beneath some cratons reaches 4 8 km s this can be accounted for by thermal and compositional effects beneath the hainan island area a low velocity anomaly is observed from near the surface to the bottom of our model the hot spot type volcanism here may be caused by the deep mantle hainan plume a low velocity mantle domain underlies the south central sea of japan surrounded on the surface by intraplate volcanoes a deep seismicity gap is present near 40 n in the pacific slab subducting below and may result from a plume slab interaction a high velocity anomaly is present in the transition zone beneath the northern boundary of the yangtze craton we propose that the anomaly corresponds to subducted continental lithosphere stagnant atop the 660 km discontinuity

waveform tomography at a groundwater contamination site surface reflection data wehaveappliedacoustic waveformtomographyto452d seismic profiles to image the 3d geometry of a buried paleochannel at a groundwater contamination site at hill air force base in utah the paleochannel which is incised into an alluvium covered clay aquitard acts as a trap for dense nonaqueous phase liquids dnapls that contaminate the shallowest groundwater system in the study area the 2d profiles were extracted from a 3d surface reflection data set first arrival traveltime tomography provided initial velocity models for the waveform tomography we inverted for six frequency components in the band 30 90 hz of the direct and refracted waves to produce 45 2d velocity models the flanks and bottom of a channel with a maximum depth of about 15 m were well modeled in most of the 45 parallel 2d slices whichallowedustoconstructa3dimageofthechannel by combining and interpolating between the 45 image slices the 3d model of the channel will be useful for siting extraction wells within the site remediation program the alluvium that fills the channel showed marked vertical and lateral velocity heterogeneity traveltime tomography and waveform tomography can be complementary approaches used together they can provide high resolution images of complicatedshallowstructures

mapping the flow pathways and contaminants transportation around a coal washing plant using the vlf em geo electrical and ip techniques a case study ne iran coal washing operation is now being carried out in the alborz sharghi plant located in northeast of iran this can in effect create a number of environmental problems in this research different geophysical surveys were conducted to investigate the leachate flow pathways and time dependent transportation of contaminants in downstream of the plant which is situated between a coal waste pile and tailings impoundments the very low frequency survey identified the most likely contamination zones and flow pathways furthermore two dimensional resistivity models obtained by the inversion of geoelectrical data measured with the use of a dipole dipole array incorporating a time laps technique showed the contaminated plumes with low resistivity values 1 m to carry out a time laps technique 2 d geoelectrical surveys were repeated at same profiles by a time interval of 6 months the results distinguished a time dependent movement of the plume in a lateral and longitudinal form as well as its further extension to the deeper layers towards the groundwater table this was also verified by the results obtained by the induced polarization measurements

high frequency earthquakes at white island volcano new zealand insights into the shallow structure of a volcano hydrothermal system abstract volcano tectonic earthquakes at white island are concentrated in a single seismically active zone southeast of the active vents and at depths of less than 1 km a few deeper earthquakes also occur beneath the active vents a composite focal mechanism indicates that the stress regime in the shallow seismic zone is n s extensional shallow seismicity occurs within the main volume of the volcano hydrothermal system that underlies the main crater floor and we interpret this as a region where the rocks have been weakened by past magmatic intrusions elevated pore fluid pressure and physico chemical effects of acid volcanic fluids thereby allowing preferential seismic failure brittle seismic failure within this region requires a temperature less than about 400 c and implies high horizontal temperature gradients close to the active craters and fumaroles spasmodic bursts events are also a result of brittle failure but occur close to zones of significant permeability in response to changes in local fluid pressure

b type volcanic earthquakes at white island volcano new zealand abstract b type volcanic earthquakes at white island have almost all their energy in the band 0 5 4 hz around a dominant spectral peak of about 2 hz a high degree of similarity in the waveforms suggests that the earthquakes originate from a volume of about 100 m 3 and that the process that generates them is repetitive at a distance of 1 km from the active crater the particle motion of b type events suggests an initial p wave followed 0 5 seconds later by a horizontally polarised s wave and then a wave of unknown type the exact mechanism for b type events is unknown however the absence of higher harmonics implies they cannot be caused by the resonance of gas or magma within a pipe like structure and the p and s waves suggest a simple shear induced rock fracture in a hot ductile medium

seismicity at white island volcano new zealand a revised classification and inferences about source mechanism the classification of earthquakes at white island volcano new zealand has been revised to address problems in existing classification schemes to better reflect new data and to try to focus more on source processes seismicity generated by the direct involvement of magmatic or hydrothermal fluids are referred to as volcanic and that generated by fault movement in response to stresses caused by those fluids regional stresses thermal effects and so on are referred to as volcano tectonic spasmodic bursts form a separate category as we have insufficient information to classify them as volcanic or volcano tectonic volcanic seismicity is divided into short duration long period volcanic earthquakes long duration volcanic earthquakes and harmonic and non harmonic volcanic tremor while volcano tectonic seismicity is divided into shallow and deep volcano tectonic earthquakes harmonic volcanic tremor is related to sub surface intrusive processes while non harmonic volcanic tremor originates close to active craters at shallow depth and usually occurs during eruptive activity short duration long period volcanic earthquakes come from a single source close to the active craters but originate deeper than non harmonic volcanic tremor and are not related to eruptive activity long duration volcanic earthquakes often accompany larger discrete eruptions the waveform of these events consists of an initial low frequency part from a deep source and a later cigar shaped part of mixed frequencies from a shallow crater source

fast imaging of subsurface conductors using very low frequency electromagnetic data the study presents a fast imaging technique for the very low frequency data interpretation first an analytical expression was derived to compute the vertical component of the magnetic field at any point on the earth s surface for a given current density distribution in a rectangular block on the subsurface current density is considered as exponentially decreasing with depth according to the skin depth rule in a particular block subsequently the vertical component of the magnetic field due to the entire subsurface was computed as the sum of the vertical component of the magnetic field due to an individual block since the vertical component of the magnetic field is proportional to the real part of very low frequency anomaly an inversion program was developed for imaging of the subsurface conductors using the real very low frequency anomaly in terms of apparent current density distribution in the subsurface imaging results from the presented formulation were compared with other imaging techniques in terms of apparent current density and resistivity distribution using a standard numerical forward modelling and inversion technique efficacy of the developed approach was demonstrated for the interpretation of synthetic and field very low frequency data the presented imaging technique shows improvement with respect to the filtering approaches in depicting subsurface conductors further results obtained using the presented approach are closer to the results of rigorous resistivity inversion since the presented approach uses only the real anomaly which is not sensitive to very small isolated near surface conducting features it depicts prominent conducting features in the subsurface

evaluation of landfill disposal boundary by means of electrical resistivity imaging this paper deals with an employment of electrical resistivity imaging eri for survey of leachate content on the waste disposal site in northern israel the research consisted of conducting ten eri lines and drilling investigation wells data simulation used a 2d earthimager inversion program analysis of 2d eri interpretation results shows that determination of the boundary between the landfill body bottom intensively saturated with leachates and underlying layers of highly water saturated fat nonconsolidated clays presents a challenge however statistical analysis of eri data indicates that standard deviation and confidence interval of a set of resistivity data measured in the landfill body are significantly larger than those in underlying clays moreover maximum changes of these parameters are found on the boundary between landfill body and underlying soil thus reflecting natural differences in scattering of resistivity data measured in these two objects

crustal structure of northern and southern tibet from surface wave dispersion analysis 1 group and phase velocities of fundamental mode rayleigh waves in the period range of 10 to 70 s are obtained for southern and northern tibet significant variations in crustal velocity structure are found the group velocity minimum for tibet occurs at 33 s and the minimum is 0 12 km s lower for southern tibet than for northern tibet at periods greater than 50 s however group velocities are up to 0 2 km s faster in southern tibet the group and phase velocities are inverted for layered s wave models the dispersion observations in southern tibet can only be fit with a low velocity layer in the middle crust in contrast the velocity models for northern tibet do not require any lowvelocity zone in the crust the s wave velocity of the lower crust of southern tibet is 0 2 km s faster than the lower crust of northern tibet in southern tibet the sub moho velocity increases with a positive gradient that is similar to a shield while there is no velocity gradient beneath northern tibet the high velocity lower crust of southern tibet is consistent with the underthrusting of indian continental lithosphere the most plausible explanation of the mid crustal low velocity zone is the presence of crustal melt resulting from h2o saturated melting of the interplate shear zone between the underthrusting indian crust and overflowing asian crust the lack of a pronounced crustal low velocity zone in northern tibet is an indication of a relatively dry crust the low s wave velocity in the lower crust of northern tibet is interpreted to be due to a combination of compositional differences high temperatures presumably caused by a high mantle heat flux and possibly small amounts of partial melt combined with all available observations in tibet the new surface wave results are consistent with a hot and weak upper mantle beneath northern tibet index terms 7205 seismology continental crust 1242 7218 seismology lithosphere and upper mantle 7255 seismology surface waves and free oscillations 8102 tectonophysics continental contractional orogenic belts keywords tibet crustal velocity structure surface wave rayleigh waves continental collision

phase velocity structure from rayleigh and love waves in tibet and its neighboring regions deep geodynamic processes involved in the continental collision between india and asia are still controversial to address this issue phase velocities of 619 rayleigh waves and 254 love waves have been inverted by using an anisotropic tomographic technique such a technique enables us not only to retrieve phase velocity distributions but also to map azimuthal anisotropy on a large scale only phase velocity anomalies in the period range 50 200 s are dealt with here but the azimuthal anisotropy has been taken into account in the inversion process moreover because of the important influence of shallow layers on the inversion results an inversion of phase velocities corrected for shallow layers has been performed to correct raw phase velocities the 3smac crust heterogeneous reference earth model has been used the comparison of phase velocity distributions for love and rayleigh waves with and without corrections of surficial layers implies that much of the low velocity zone visible at short periods in central tibet can be explained by unusually thick crust at periods longer than 100 s tibet is overall characterized by high velocity anomalies such anomalies seem to converge toward the center of the plateau as period increases we conclude that the phase velocity structure beneath tibet results at short periods from thick crust and possible partial melting in the uppermost lithosphere and at long periods from the inward plunge of the cold lithospheric mantle surrounding the high plateau

a very low frequency electromagnetic study of the geo environmental hazardous areas in taiwan this study utilized the very low frequency electromagnetic vlf em technique a passive electromagnetic prospecting method working in the very low frequency range 15 30 khz to investigate the geo environmental problems of shallow low conductivity sedimentary layers in taiwan field examples successfully demonstrate the advantages of using this method in locating non mineralized shallow fault zones the zero crossings of in phase and quadrature measurements in 2 d contour maps clearly locate the position of subsurface anomalous source bodies further analysis of the measured vlf single profile peaks reveals that this method is useful in determining subsurface structures and conductivity the advantages of nondestructive noninvasive and low consumption of power make this method extremely friendly to the environment the authors anticipate this method will have more profound impacts on the interactions between prospecting technology and the earth

earthquake classification location and error analysis in a volcanic environment implications for the magmatic system of the 1989 1990 eruptions at redoubt volcano alaska abstract determination of the precise locations of seismic events associated with the 1989 1990 eruptions of redoubt volcano posed a number of problems including poorly known crustal velocities a sparse station distribution and an abundance of events with emergent phase onsets in addition the high relief of the volcano could not be incorporated into the hypoellipse earthquake location algorithm this algorithm was modified to allow hypocenters to be located above the elevation of the seismic stations the velocity model was calibrated on the basis of a posteruptive seismic survey in which four chemical explosions were recorded by eight stations of the permanent network supplemented with 20 temporary seismographs deployed on and around the volcanic edifice the model consists of a stack of homogeneous horizontal layers setting the top of the model at the summit allows events to be located anywhere within the volcanic edifice detailed analysis of hypocentral errors shows that the long period lp events constituting the vigorous 23 hour swarm that preceded the initial eruption on december 14 could have originated from a point 1 4 km below the crater floor a similar analysis of lp events in the swarm preceding the major eruption on january 2 shows they also could have originated from a point the location of which is shifted 0 8 km northwest and 0 7 km deeper than the source of the initial swarm we suggest this shift in lp activity reflects a northward jump in the pathway for magmatic gases caused by the sealing of the initial pathway by magma extrusion during the last half of december volcano tectonic vt earthquakes did not occur until after the initial 23 hour long swarm they began slowly just below the lp source and their rate of occurrence increased after the eruption of 01 52 ast on december 15 when they shifted to depths of 6 to 10 km after january 2 the vt activity migrated gradually northward this migration suggests northward propagating withdrawal of magma from a plexus of dikes and or sills located in the 6 to 10 km depth range precise relocations of selected events prior to january 2 clearly resolve a narrow steeply dipping pencil shaped concentration of activity in the depth range of 1 7 km which illuminates the conduit along which magma was transported to the surface a third event type named hybrid which blends the characteristics of both vt and lp events originates just below the lp source and may reflect brittle failure along a zone intersecting a fluid filled crack the distribution of hybrid events is elongated 0 2 0 4 km in an east west direction this distribution may offer constraints on the orientation and size of the fluid filled crack inferred to be the source of the lp events

surface wave group velocity tomography of east asia abstract group velocities of both rayleigh and love waves are used in a tomographic inversion to obtain group velocity maps of east asia 60 140 e and 20 60 n the period range studied is 30 70 s the tibetan plateau a region undergoing intense north south compression appears as a prominent low velocity about 15 from the average structure in this area central tibet appears as the area with the lowest velocities and southern tibet south of the zangbo suture zone and the himalayas is an area of high velocities the tibet low velocity area extends northward to the southern tarim basin the north china korean platform an area traditionally recognized as the oldest platform in china does not have a consistent crust and upper mantle velocity signature the north china plain a part of the platform where extensional tectonics dominates is an area of high velocities probably as a result of thin crust the other parts of the platform have relatively low velocities the south china block the least tectonically active region of china is generally an area of high velocity for periods longer than 40 s a high group velocity gradient clearly exists along longitude 105 e the velocities are noticeably higher east of this longitude than west of it this transition corresponds closely to that in the bouguer gravity map in general processes in the crust and upper mantle owing to recent tectonic activities rather than the age of the basement rocks seem to have dominant control of crust and upper mantle velocity structures

crustal radial anisotropy across eastern tibet and the western yangtze craton 1 phase velocities across eastern tibet and surrounding regions are mapped using rayleigh 8 65 s and love 8 44 s wave ambient noise tomography based on data from more than 400 program for array seismic studies of the continental lithosphere and chinese earthquake array stations a bayesian monte carlo inversion method is applied to generate 3 d distributions of vsh and vsv in the crust and uppermost mantle from which radial anisotropy and isotropic vs are estimated each distribution is summarized with a mean and standard deviation but is also used to identify highly probable structural attributes which include 1 positive midcrustal radial anisotropy vsh vsv across eastern tibet spatial average 4 8 1 4 that terminates abruptly near the border of the high plateau 2 weaker 1 0 1 4 negative radial anisotropy vsh vsv in the shallow crust mostly in the songpan ganzi terrane 3 negative midcrustal anisotropy 2 8 0 9 in the longmenshan region 4 positive midcrustal radial anisotropy 5 4 1 4 beneath the sichuan basin and 5 low vs in the middle crust 3 427 0 050 km s of eastern tibet midcrustal vs 3 4 km s perhaps consistent with partial melt is highly probable only for three distinct regions the northern songpan ganzi the northern chuandian and part of the qiangtang terranes midcrustal anisotropy provides evidence for sheet silicates micas aligned by deformation with a shallowly dipping foliation plane beneath tibet and the sichuan basin and a steeply dipping or subvertical foliation plane in the longmenshan region near vertical cracks or faults are believed to cause the negative anisotropy in the shallow crust underlying tibet

three dimensional crustal s wave velocity structure in japan using microseismic data recorded by hi net tiltmeters 1 we developed a three step method for three dimensional 3 d s wave velocity tomography by fitting synthetic cross spectra to the observed ones of ambient seismic noise we applied this method to the recording of hi net tiltmeters in japan at 679 stations from june 2004 to december 2004 first we calculated normalized cross spectra between radial components and those between transverse components for every pair of stations the first step is local 1 d s wave velocity inversion for each station assuming small lateral heterogeneity under a 100 km circle of a station we measured the dispersion curves of fundamental rayleigh waves fundamental love waves and first overtone of love waves by fitting the synthetic cross spectra to the observed ones between pairs of stations within the circle we inverted the measured dispersion curves for obtaining a 1 d s wave velocity model the second step is the inversion of the observed cross spectra for obtaining path averaged 1 d s wave velocity structure the third step is the inversion of the resultant path averaged structures for obtaining 3 d s wave velocity structure 0 1 0 1 1 km grid from the surface to a depth of 50 km using ray approximation the resultant s wave velocity structures show clear low velocity anomalies along tectonic lines from the surface to a depth of 20 km in particular along the hidaka mountain range we observed s wave perturbation more extreme than 20 they also show low velocity anomalies under volcanoes in kyusyu and tohoku in the southwestern part of shikoku our results show a clear low velocity anomaly corresponding to an accretional belt shimanto belt below 20 km we observe a low velocity anomaly in the center of japan which suggests a thick crust citation nishida k h kawakatsu and k obara 2008 three dimensional crustal s wave velocity structure in japan using microseismic data recorded by hi net tiltmeters j geophys res 113 b10302 doi 10 1029 2007jb005395

a volcanic tremor monitoring system abstract the digitising system installed at the chateau observatory in the north island of new zealand to monitor ruapehu and ngauruhoe volcanoes is used to digitise the seismic records from three seismometers and to calculate the power spectra of volcanic tremor in real time with the smoothed power spectra being recorded every 5 minutes on magnetic disk the 5 minute averages are later processed to remove the effects of earthquakes and interference before hourly averages are calculated this system has a better dynamic range than visual chart records and analysis of the data requires much less labour

crustal and uppermost mantle velocity structure beneath northwestern china from seismic ambient noise tomography summary in this paper we conduct ambient noise seismic tomography of northwestern china and adjacent regions the data include 9 months 2009 january to 2009 september three component continuous data recorded at 146 seismic stations of newly upgraded china provincial digital seismic networks and regional kyrgyzstan and kazakhstan networks empirical rayleigh and love wave green s functions are obtained from interstation cross correlations group velocity dispersion curves for both rayleigh and love waves between 7 and 50 s periods were measured for each interstation path by applying the multiple filter analysis method with phase matched processing the group velocity maps show clear lateral variations which correlate well with major geological structures and tectonic units in the study region shear wave velocity structures are inverted from rayleigh wave and love wave dispersion maps the results show that the tibetan plateau has a very thick crust with a low velocity zone in its mid lower crust along the northern margin of the plateau where a steep topographic gradient is present the low velocity zone does not extend to the tarim basin which may indicate that crustal materials beneath the tarim basin are colder and stronger than beneath the plateau therefore inhibit the extension of mid lower crustal flow and deformation of the tibetan plateau resulting in very sharp topography contrasts in the northeastern margin with a gentle topographic gradient toward the ordos platform the low velocity zone diminishes around the eastern kunlun fault meanwhile our results reveal obvious lateral velocity changes in the crust beneath the tarim basin in the upper crust the manjaer depression in the eastern tarim basin is featured with very low velocities and the bachu uplift in the western tarim basin with high velocities in the mid lower crust the northern tarim basin in general displays lower velocities than the southern part along latitude 40 n with an east west striking which is consistent with the high magnetic anomaly zone and may be related to the central suture belt connecting the south and north of tarim basement blocks together in pre sinian

an integrated magnetotelluric and gamma exploration of groundwater in fractured granite for small scale freshwater supply a case study from the boshan region shandong province china exploration and use of groundwater in hard rocks is a difficult but yet a significant issue especially when the local surface water source is polluted in this study integrated geophysical and nuclear methods are used to delineate groundwater bearing zones in a granite terrain in the boshan region shandong province china structural analysis showed that fractures extend in a nw se direction which is the same as the direction of river valley a controlled source audio frequency magnetotelluric survey conducted along the river valley indicated several different low resistivity anomalies or potential water bearing fracture zones they are seated at depth ranges down to 400 m from the surface along the river valley the locations of deep water bearing zones were further confirmed by higher gamma radiation measurements found near the river valley a fault with a nw se strike near the river was deduced as an anomalous water bearing zone two tube wells were drilled targeting at the water bearing zone that has achieved single well water yield greater than 360 m3 day the well water was sampled for water chemistry and stable isotope analyses shallow groundwater samples show similar water chemistry and isotopic feature to river water indicating connection between the two deep groundwater from the water bearing fracture zones is not hydraulically connected with shallow groundwater ensuring safety of the deep groundwater in the granite from being affected by the polluted shallow groundwater or river water integrated geophysical and gamma exploration methods helped to identify two disconnected groundwater systems offering an alternative freshwater source for the region if shallow groundwater or surface water is polluted

using volcanic tremor for eruption forecasting at white island volcano whakaari new zealand abstract eruption forecasting is a challenging task because of the inherent complexity of volcanic systems despite remarkable efforts to develop complex models in order to explain volcanic processes prior to eruptions the material failure forecast method ffm is one of the very few techniques that can provide a forecast time for an eruption however the method requires testing and automation before being used as a real time eruption forecasting tool at a volcano we developed an automatic algorithm to issue forecasts from volcanic tremor increase episodes recorded by real time seismic amplitude measurement rsam at one station and optimised this algorithm for the period august 2011 january 2014 which comprises the recent unrest period at white island volcano whakaari new zealand a detailed residual analysis was paramount to select the most appropriate model explaining the rsam time evolutions in a hindsight simulation four out of the five small eruptions reported during this period occurred within a failure window forecast by our optimised algorithm and the probability of an eruption on a day within a failure window was 0 21 which is 37 times higher than the probability of having an eruption on any day during the same period 0 0057 moreover the forecasts were issued prior to the eruptions by a few hours which is important from an emergency management point of view whereas the rsam time evolutions preceding these four eruptions have a similar goodness of fit with the ffm their spectral characteristics are different the duration amplitude distributions of the precursory tremor episodes support the hypothesis that several processes were likely occurring prior to these eruptions we propose that slow rock failure and fluid flow processes are plausible candidates for the tremor source of these episodes this hindsight exercise can be useful for future real time implementation of the ffm at white island a similar methodology could also be tested at other volcanoes even if only a limited network is available