application of electrical resistivity techniques to detect weak and fracture zones during underground construction the scope of the electrical resistivity survey has recently been extended to various fields beyond groundwater and underground resource exploration electrical resistivity techniques were evaluated in two case studies to substantiate their applicability to geotechnical and environmental problems first electrical resistivity imaging eri was used to map the fractured zone ahead of the tunnel face during construction using the new australian tunneling method natm the eri technique could adequately modify tunnel support patterns in quasi real time on the basis of the field test results and could subsequently improve the stability of tunnel excavation second electrical resistivity tomography ert was used between two test boreholes in a research tunnel site to monitor the movement of brine after it was injected in one of the two boreholes a pair of low conductivity zones that were regarded as the pathway of groundwater flow between the two boreholes was clearly imaged because of enhancement of conductivity caused by diffusion of the brine the applicability of electrical resistivity techniques to geotechnical and environmental problems was successfully substantiated

sensitivity study of borehole to surface and crosswell electromagnetic measurements acquired with energized steel casing to water displacement in hydrocarbon bearing layers westudythetheoreticalresponseofelectromagneticallyenergized steel casing in the presence of subsurface variations of electrical resistivity casing is energized with a finite size solenoid antenna located along the axis of the borehole measurementsconsistoftheazimuthalcomponentoftheelectricfieldacquired either on the surface or in a separate well in the same hydrocarbonfield weassumetwo dimensional2daxisymmetric variations of subsurface electrical resistivity and casing excitation simulationsofelectromagneticemfieldsexcitedbyenergized steel casing are performed with a goal oriented hpadaptivefinite elementmethodthatautomaticallygeneratesasequence of optimal grids delivering exponential convergence rates in terms of the em fields at the receiver antennas against cpu time this advanced finite element method enables accurate modeling of problems with high conductivity contrasts in large computational domains numerical simulations quantify the measurement sensitivity to variations of frequency distance fromcasingtoreceivers resistivityofthetargetoil bearinglayer and pistonlike radial invasion of water within a target layer initially saturated with oil when receivers are placed in a nearby well numerical results indicate that measurements exhibit the largest sensitivity to the target oil saturated layer when the transmitter or receiver antenna is located just above the target layer andanotherantennaislocatedbelowthetargetlayer afrequency range from 5 30 hz provides optimal results for the detectionofoil bearinglayersandestimationofradialextentofwater invasion large horizontal distances up to 1500 m between transmitter and receivers and a background material with resistivity above 50 m also enhance the measurement sensitivity to radial variations of water invasion this sensitivity can be as largeas15 20 ofthemeasuredelectricfield

geochemistry and diagenesis of miocene lacustrine siliceous sedimentary and pyroclastic rocks mytilinii basin samos island greece abstract a late miocene non marine stratigraphic sequence composed of limestone opal ct bearing limestone porcelanite marlstone diatomaceous marlstone dolomite and tuffite crops out on eastern samos island this lacustrine sequence is subdivided into the hora beds and the underlying pythagorion formation the hora beds is overlain by the clastic mytilinii series which contains turolian late miocene mammalian fossils the lacustrine sequence contains volcanic glass and the silica polymorphs opal a opal ct and quartz volcanic glass predominantly occurs in tuffaceous rocks from the lower and upper parts of the lacustrine sequence opal a diatom frustules is confined to layers in the upper part of the hora beds beds rich in opal ct underlie those containing opal a the occurrence of opal ct is extensive encompassing the lower hora beds and the sedimentary rocks and tuffs of the pythagorion formation a transition zone between the opal a and opal ct zones is identified by x ray diffraction patterns that are intermediate between those of opal ct and opal a perhaps due to a mixture of the two polymorphs diagenesis was not advanced enough for opal ct to transform to quartz or for volcanic glass to transform to opal c based on geochemical and mineralogical data we suggest that the rate of diagenetic transformation of opal a to opal ct was mainly controlled by the chemistry of pore fluids pore fluids were characterized by high salinity moderately high alkalinity and high magnesium ion activity these pore fluid characteristics are indicated by the presence of evaporitic salts halite sylvite niter high boron content in biogenic silica and by dolomite in both the opal a and opal ct bearing beds the absence of authigenic k feldspar borosilicates and zeolites also support these pore fluid characteristics additional factors that influenced the rate of silica diagenesis were host rock lithology and the relatively high heat flow in the aegean region from miocene to holocene

centroid moment tensor solutions for july september 1998 abstract centroid moment tensor solutions are presented for 214 earthquakes that occurred during the third quarter of 1998 the solutions are obtained using corrections for aspherical earth structure represented by a whole mantle shear velocity model sh8 u4l8 of dziewonski and woodward dziewonski a m woodward r l 1992 acoustic imaging at the planetary scale in emert h harjes h p eds acoustical imaging plenum new york 19 785 797 a new model of anelastic attenuation of durek and ekstrom durek j j ekstrom g 1996 a radial model of anelasticity consistent with long period surface wave attenuation bull seism soc am 86 144 158 is used to predict the decay of the waveforms

high angle reverse faulting associated with the 1946 nankaido earthquake abstract analysis of vertical crustal deformation data in the southwestern part of shikoku southwest japan suggests that the nankaido earthquake of 1946 m w 8 1 which is a principal interplate thrust earthquake was accompanied by subsidiary faulting on a splay fault adjacent to the coast of shikoku discarding crustal movement resulting from the main thrusting of the nankaido earthquake local leveling data are explained by slip on a simple rectangular thrust fault located just offshore of shikoku although it is difficult to constrain the fault location a possible result is a high angle thrust dipping landward at an angle of about 70 with a dislocation of about 1 5 m and source dimensions of 30 13 km along strike and dip respectively this result indicates that the fault may be one of the steeply dipping subsidiary faults branching from the main low angle thrust as was the case in the alaska earthquake of 1964 although several lines of evidence suggest that this faulting occurred as slow aseismic slip its discrimination from the main seismic event is extremely difficult this kind of high angle thrusting just offshore of the coast would play an important role for the formation of the marine terraces during the late quaternary period

rapid determination of global moment tensor solutions in an effort to improve data services the national earthquake information center has begun a program in cooperation with the incorporated research institutions for seismology data management center iris dmc to produce rapid estimates of the seismic moment tensor for most earthquakes with a body wave magnitude of 5 8 or greater although this program is still undergoing testing and fine tuning an estimate of the moment tensor can usually be produced within 20 minutes of the arrival of the broadband p waveform data from the iris dmc although the speed with which this data can be obtained varies in many cases a solution can be obtained within two hours of the earthquake these solutions do not vary significantly from the final solutions determined using the entire network because of the manner in which the data and the synthetic seismograms are aligned the method is insensitive to the effects of timing errors epicentral mislocation and lateral heterogeneity in earth structure this procedure was implemented in may 1993 the results from that month are presented here

t waves from the 1998 papua new guinea earthquake and its aftershocks timing the tsunamigenic slump t waves recorded at hydrophone and seismic stations following the papua new guinea earthquake of 17 july 1998 and its aftershocks show that a small event at 09 02 gmt featured source properties incompatible with an elastic dislocation of appropriate body wave magnitude m b 4 4 these include an exceptional duration 47 s at the wake island hydrophone station wk31 a spectrum rich in high frequencies 7 to 12 hz and a generally low spectral amplitude these characteristics can be explained by the model of an underwater slump accelerating from a standstill and eventually slowing down the relocation of the 09 02 event is compatible with its location within an amphitheater inside which shipboard cruises in 1998 and 1999 documented the presence of a 4 c km3 geologically fresh slump we propose that the slump took place at 09 02 on 17 july 1998 i e 13 minutes after the mainshock and that it generated the locally catastrophic tsunami whose properties amplitude and distribution of runup timing could not be explained by a dislocation model

borehole to surface electrical resistivity monitoring of a salt water injection experiment a field experiment was conducted at the university of california richmond field station to demonstrate the sensitivity of borehole to surface resistivity measurements in groundwater investigations a quantity of saline water was injected into a fresh water aquifer while the resistivity was monitored using a multichannel borehole to surface system two experiments were conducted using pole pole and pole dipole receiver electrode arrays the data from the pole pole experiment were superimposed to simulate a dipole pole array and the data from the pole dipole array were superimposed to simulate a dipole dipole array this superposition of the data was done to enhance the anomaly and facilitate interpretation a numerical modeling study was performed in conjunction with the field experiment in order to interprete the results a three dimensional modeling program was used to simulate the geological setting of the field experiment and the salt water injection this modeling revealed that an asymmetric displacem

resistivity and induced polarization monitoring of salt transport under natural hydraulic gradients we demonstrate the use of resistivity induced polarization ip monitoring of salt transport under natural hydraulic loads electrical monitoring of saline tracer transport during forced injection has been demonstrated previously detection of tracer transport under natural hydraulic loading is difficult because neither the hydraulic load nor the tracer resistivity can be controlled in one study we identify the electrical response to salt transport in a dynamic beach environment resistivity ip imaging resolved the structure of the saltwater freshwater interface and evidence for tide induced groundwater transport resistivity increases in the near surface and at depth upbeach of the high tide mark accompanied by tidal transgression we attribute this to desaturation and decreasing salinity in the near surface and to decreasing salinity at depth despite tidal transgression monitoring of groundwater levels indicates a phase lag between the tide level and groundwater level supporting the electrical da

three dimensional controlled source electromagnetic modelling with a well casing as a grounded source a hybrid method of moments and finite element scheme steel well casings in or near a hydrocarbon reservoir can be used as source electrodes in time lapse monitoring using grounded line electromagnetic methods a requisite component of carrying out such monitoring is the capability to numerically model the electromagnetic response of a set of source electrodes of finite length we present a modelling algorithm using the finite element method for calculating the electromagnetic response of a three dimensional conductivity model excited using a vertical steel cased borehole as a source the method is based on a combination of the method of moments and the coulomb gauged primary secondary potential formulation using the method of moments we obtain the primary field in a half space due to an energized vertical steel casing by dividing the casing into a set of segments each assumed to carry a piecewise constant alternating current density the primary field is then substituted into the primary secondary potential finite element formulation of the three dimensional problem to obtain the secondary field to validate the algorithm we compare our numerical results with i the analytical solution for an infinite length casing in a whole space excited by a line source and ii a three layered earth model without a casing the agreement between the numerical and analytical solutions demonstrates the effectiveness of our algorithm as an illustration we also present the time lapse electromagnetic response of a synthetic model representing a gas reservoir undergoing water flooding

sources of tsunami and tsunamigenic earthquakes in subduction zones we classified tsunamigenic earthquakes in subduction zones into three types earth quakes at the plate interface typical interplate events earthquakes at the outer rise within the subducting slab or overlying crust intraplate events and tsunami earthquakes that generate considerably larger tsunamis than expected from seismic waves the depth range of a typical interplate earthquake source is 10 40km controlled by temperature and other geological parameters the slip distribution varies both with depth and along strike recent examples show very different temporal change of slip distribution in the aleutians and the japan trench the tsunamigenic coseismic slip of the 1957 aleutian earthquake was concentrated on an asperity located in the western half of an aftershock zone 1200km long this asperity ruptured again in the 1986 andreanof islands and 1996 delarof islands earthquakes by contrast the source of the 1994 sanriku oki earthquake corresponds to the low slip region of the previous interplate event the 1968 tokachi oki earthquake tsunamis from intraplate earthquakes within the subducting slab can be at least as large as those from interplate earthquakes tsunami hazard assessments must include such events similarity in macroseismic data from two southern kuril earthquakes illustrates difficulty in distinguishing interplate and slab events on the basis of historical data such as felt reports and tsunami heights most moment release of tsunami earthquakes occurs in a narrow region near the trench and the concentrated slip is responsible for the large tsunami numerical modeling of the 1996 peru earthquake confirms this model which has been proposed for other tsunami earthquakes including 1896 sanriku 1946 aleutian and 1992 nicaragua

numerical modelling of tsunami generation and propagation from submarine slumps the 1998 papua new guinea event summary deep and large submarine slumps may generate tsunamis as disastrous as tsunamis of tectonic origin such a landslide is likely to be the origin of the 1998 july 17 tsunami of papua new guinea the deadliest tsunami in the last 50 years water waves devastated a 20 km stretch of coastline wiping out three villages and killing more than 2200 people a numerical model has been developed to study the efficiency of deep slumps in producing tsunamis and has been applied to the papua new guinea event the landslide is treated as the flow of a homogeneous gravity driven continuum governed by a rheological law water waves are generated by sea bottom displacements induced by the landslide the shallow water approximation is adopted for both the landslide and the associated water waves the resulting differential equations are solved by a finite difference method based on shock capturing the shallow water hypothesis is tested by comparison with a model solving navier stokes equations for a mixture of water and sediments sensitivity tests carried out for a 2 d simplified geometry show that the water surface profile depends strongly on the constitutive law of the landslide the 1998 event is simulated numerically by the shallow water model testing different friction laws the observed inundation height distribution is well reproduced by the model for a volume of 4 km3 with its top located at a water depth of 550 m and sliding with a coulomb type friction law over a distance of 5 km

fluid injection monitoring using electrical resistivity tomography five years of co2 injection at ketzin germany between the years 2008 and 2013 approximately 67 kilotons of co2 have been injected at the ketzin site germany as part of the geophysical monitoring programme time lapse electrical resistivity tomography has been applied using crosshole and surface downhole measurements of electrical resistivity tomography the data collection of electrical resistivity tomography is partly based on electrodes that are permanently installed in three wells at the site one injection well and two observation wells both types of ert measurements consistently show the build up of a co2 related resistivity signature near the injection point based on the imaged resistivity changes and a petrophysical model co2 saturation levels are estimated these co2 saturations are interpreted in conjunction with co2 saturations inferred from neutron gamma loggings apart from the co2 brine substitution response in the observed resistivity changes significant imprints from the dynamic behaviour of the co2 in the reservoir are observed

the direct current response of electrically conducting fractures excited by a grounded current source abstracthydraulic fracture stimulation of low permeability reservoir rocks is an established and cross cutting technology for enhancing hydrocarbon production in sedimentary formations and increasing heat exchange in crystalline geothermal systems whereas the primary measure of success is the ability to keep the newly generated fractures sufficiently open long term reservoir management requires a knowledge of the spatial extent morphology and distribution of the fractures knowledge primarily informed by microseismic and ground deformation monitoring to minimize the uncertainty associated with interpreting such data we investigate through numerical simulation the usefulness of direct current dc resistivity data for characterizing subsurface fractures with elevated electrical conductivity by considering a geophysical experiment consisting of a grounded current source deployed in a steel cased borehole in doing so the casing efficiently energizes the fractures with steady current finite element

simulation of electrical conduction in geomaterials by spice electrical responses of the subsurface can be used to identify geologic strata locate anomalies detect and delineate contamination among many other applications all these applications depend on the spatial variations of electrical properties in the subsurface and the resulting flow pattern of electric current due to the heterogeneity of the subsurface and complex boundary conditions three dimensional electric current flow problems are not easy to analyze in particular when the response is frequency and or time dependent in this paper a method of electric circuit analogy is proposed to simulate the electrical responses of geomaterials using the circuit simulator spice the technique will allow simulation of more complex electrical conduction behavior of geomaterials without much extra effort the excellent agreement between simulated results and analytical solutions developed for surface geophysical techniques establishes the viability of the method limitations of the approach and potential solutions to relax these limitations and other potential applications of the technique in geosciences are also discussed

authigenic silicates and silica polymorphs in the miocene saline alkaline deposits of the karlovassi basin samos greece the lower neogene unit of the karlovassi basin samos island greece was deposited in a continental basin during miocene times and consists of four successions overlying a basal conglomerate the four successions are from the base upward carbonates tuffaceous rocks claystones and porcelanites volcanic glass was originally abundant in the tuffaceous succession but is now represented by its diagenetic products including boron bearing k feldspar the zeolites clinoptilolite analcite and mordenite smectite opal disordered tridymite cristobalite cristobalite and minor amounts of the zeolites erionite phillipsite and chabasite and tridymite evaporite minerals such as gypsum celestite and thenardite are present along with authigenic silicates in tuffaceous intervals into the claystone succession authigenic silica polymorphs represented by opal and chalcedony were identified in the uppermost succession of porcelaneous limestones to chert five irregular concentric zones related to the presence and kind of zeolites and k feldspar are recognized in the lower neogene unit 1 a marginal zone of carbonate and detrital silicate minerals nonauthigenic silicates 2 a clinoptilolite zone 3 a mixed clinoptilolite analcite zone 4 an analcite zone and 5 a central boron bearing k feldspar zone the general pattern of zonation and distribution of authigenic silicates as well as their chemical characteristics indicates the presence of a saline alkaline lake during miocene times this lake is analogous to those of the same age which existed in southern yugoslavia and western turkey where borate sulfate and double carbonate deposits were formed along with authigenic silicates it is possible that a large continental area in the eastern mediterranean underwent large scale dessication which took place during the miocene messinian salinity crisis resulting in the development of highly saline alkaline lacustrine environments

direct current and self potential monitoring of an evolving plume in partially saturated fractured rock abstract hole surface and hole hole mise a la masse malm measurements and surface self potential sp measurements were taken over a 173 day period during an 8 well radial injection tracer experiment in partially saturated fractured columbia river basalt a potassium chloride tracer stream was injected into the fractured basalt and was energized directly for the malm experiments the constant concentration tracer solution was injected for 76 days above a perched water table at an average rate of 10 07 l day tracer injection was followed by a 34 day period of tap water injection and a 63 day drainage period the associated changes in potential distributions and sp s over time indicate that an asymmetrical vadose zone plume evolved in the fractured basalt hole surface and sp measurements were used to track the lateral evolution of the tracer plume however there was some noise and variability in the sp data the hole hole measurements helped delineate the depth of preferential tracer migration in the fractured basalt

gps measurements of crustal deformation within the pacific australia plate boundary zone in irian jaya indonesia abstract global positioning system gps measurements made in 1991 1992 and 1993 provide preliminary estimates of slip distribution between the australian and pacific plates in irian jaya indonesia we interpret the gps results with constraints from earthquake mechanisms and slip vectors recent marine surveys and geology three gps sites in southeastern irian jaya show motions that are within 10 mm yr of the expected motion of australia a coast to coast n s baseline along 140 5 e crosses all known onland regions of active deformation but reveals no more than 15 mm yr of shortening and 20 mm yr of left lateral shear in the 27 month period the remaining 40 mm yr of expected convergence between the pacific and australian plates probably occurs at the new guinea trough gps sites on the island of biak at 136 e and at sorong near the western tip of bird s head at 131 e both move 90 100 mm yr in a wsw direction relative to irian jaya but less than 15 mm yr relative to each other these sites are on either side of the sorong fault and demonstrate that it is not presently the major boundary between the australian and pacific plates instead the plate boundary is now south of the sorong and biak sites earthquakes suggest possible structures that accomodate motion between bird s head and australia but the relative importance of them remains uncertain

spatial analysis of the la paca se spain 2005 seismic series through the relative location of multiplets and principal component analysis abstract on 29 january 2005 a m w 4 8 i max vi vii earthquake occurred near the village of la paca se spain the aftershock sequence shows distinct heterogeneity manifested in a non uniform temporal decay of activity and different source mechanisms for the main shock and the largest aftershocks we analysed 262 earthquakes of the seismic series in order to characterize the active seismic structures moving window cross correlation of the p and s waveforms recorded at local broad band stations and the application of a selection algorithm have allowed to identify events with similar waveforms multiplets and to classify them into 16 clusters of 3 25 earthquakes each in each multiplet cluster events have been relocated with respect to a master event by the linear inversion of cross correlation time lags for p and s waves clusters show epicentral alignments with a predominant direction n145 e and two secondary directions n6 e and n40 e spatio temporal patterns of the seismicity have been analysed using principal component analysis pca upon the relocated epicentre distribution and we have obtained three trends n42 e n14 e and n145 e present during all the sequence these directions inferred from relative location and pca are coincident with nodal planes of moment tensor solutions for the larger events within the series they can be interpreted as the simultaneous activity of conjugate strike slip faults under a n160 170 e orientation of the principal compressive stress 1

tectonic interpretation of aftershock relocations in eastern papua new guinea using teleseismic data and the arrival pattern method summary the arrival pattern ap method and teleseismic data have been used to relocate aftershocks following three major mw 7 8 interplate earthquakes that occurred in eastern papua new guinea in 2000 november the first event was an mw 8 0 strike slip earthquake that ruptured the weitin fault over a length of 100 km no aftershocks were located in the upper 15 km suggesting that the accumulated strain was fully released in this event the two subsequent mw 7 8 thrust events occurred on the new britain trench wadati benioff zones dipping 20 define the locations of the thrust events at 152 e and 153 e on fault planes with strikes of 75 and 65 respectively the plot of aftershocks defines a complex seismic zone beneath new ireland where events have occurred in the overriding pacific and south bismarck plates above the deeper zone of subduction of the solomon sea plate these events cluster in a broad zone to the northeast of the weitin fault rather than defining a linear feature that might have been expected following a near vertical major strike slip event

the aleutian earthquake of june 10 1996 mw 7 9 ruptured parts of both the andreanof and delarof segments the epicenter of the aleutian earthquake of june 10 1996 is located in the delarof segment where a large subduction earthquake is expected however the aftershock area of the earthquake is not only in the delarof segment but also in the andreanof segment where the 1986 andreanof earthquake occurred previously we estimate the fault parameters of the 1996 earthquake by numerically computing the tsunami and comparing the waveforms with that recorded at adak the fault width is 30 km or less and the average slip is about 4 m the observed far field tsunamis around the pacific are also explained by the synthetic tsunami computed using the above fault parameters the results indicate that the 1996 earthquake ruptured parts of both the delarof and andreanof segments however the 1996 earthquake did not rupture the region of the largest moment release by the 1986 earthquake

the 1998 papua new guinea earthquake and its fault plane estimated from relocated aftershocks the 1998 papua new guinea earthquake of m w 7 0 occurred near the wewak trench where the north bismarck plate is subducting beneath the australian plate its mechanism is thrust type and one of the nodal planes is almost parallel to the plate interface to determine which of the two nodal planes of the main shock is the fault plane we relocated the main shock and aftershocks using a method of modified joint hypocenter determination we combined and employed two types of data in this study firstly we used data reported by the national earthquake information center neic of the u s geological survey usgs which includes three stations at the northeastern edge of irian jaya and one station in northern papua new guinea from which the epicentral distances are less than 2 degrees secondly in addition to the above permanent station data we used data from temporary aftershock observations near the epicentral area around the sissano lagoon carried out by tsuji et al 1998 using three component seismometers they carried out observations from august 2 to october 2 1998 at three sites although the network did not record the main shock and immediate aftershocks the data obtained by temporary observation sites can clearly assist in identifying their absolute locations since it is possible to apply the joint hypocenter determination jhd method hypocenters were relocated between the coastline and the wewak trench distributed along a nodal plane dipping shallowly to the southwest therefore we can conclude that this nodal plane is the main shock fault and that the 1998 papua new guinea earthquake was an interplate earthquake between the north bismarck and australian plates

an integrated geophysical investigation of the hydrogeology of an anisotropic unconfined aquifer abstract the predictive capability of groundwater flow models is frequently restricted by insufficient characterisation of a typically heterogeneous and anisotropic subsurface trace levels of volatile organic compounds have been detected at municipal water supply wells in gray maine groundwater flow modelling based on available hydrogeologic data defines a dominant w e transport vector that is inconsistent with the apparent n40e transport of a plume emanating from a road salt storage facility as mapped with a terrain conductivity instrument a local scale geophysical study at an undisturbed site in the glacial marine delta deposit aquifer was conducted to investigate the possible influence of anisotropy on flow through these unconsolidated sediments ground penetrating radar and terrain conductivity measurements reveal evidence for structural features that are likely to promote preferential transport paths orientated in a general ne sw direction two conductive tracers one deep and one surficial were injected and monitored for direct evaluation of the groundwater flow vector using resistivity and self potential methods although interpretation was limited by an incomplete resistivity dataset the results and modelling of both methods supports a general n30e n40e flow vector furthermore consistent flow velocity estimates 0 15 m day are obtained from the two methods analysis of this integrated dataset suggests that anisotropy exerts a significant control on flow in this unconsolidated aquifer predictions of sources of groundwater contamination at municipal wells based on flow models not accounting for this anisotropy will likely be in error this study illustrates the potential value of an integrated geophysical study which will aid the development of accurate flow models for unconsolidated aquifers

evidence for active subduction at the new guinea trench 1 recent seismic tomography imaging shows clear evidence for southwestward subduction along the entire length of the new guinea trench ngt in indonesia and papua new guinea viewed in conjunction with the occurrence of large mw 7 thrust earthquakes that are known to have occurred on the trench this confirms conclusions of earlier studies that the ngt is an active inter plate boundary the 650 km long slab is visible to a depth of about 300 km and subducts with a dip angle that varies from 30 at 136 e to 10 at 143 e the improved clarity of the seismic tomography in this region stems from the use of a more accurate data set of p and s wave arrival times and hypocentral locations

a salt tracer test monitored with surface ert to detect preferential flow and transport paths in fractured karstified limestones in hard rock aquifers fractured zones constitute adequate drinking water exploitation areas but also potential contamination paths one critical issue in hydrogeological research is to identify characterize and monitor such fractured zones at a representative scale a tracer test monitored with surface electrical resistivity tomography ert could help by delineating such preferential flow paths and estimating dynamic properties of the aquifer however multiple challenges exist including the lower resolution of surface ert compared with crosshole ert the finite time that is needed to complete an entire data acquisition and the strong dilution effects we conducted a natural gradient salt tracer test in fractured limestones to account for the high transport velocity we injected the salt tracer continuously for four hours at a depth of 18 m we monitored its propagation with two parallel ert profiles perpendicular to the groundwater flow direction concerning the data acquisition we always focused

testing dioscorides medicinal clays for their antibacterial properties the case of samian earth earths were medicinal clays reported by authors of classical antiquity today there are no archaeological samples thereof at least with irrefutable proof that they were used as medicines therefore their mineral identity and potential pharmacological actions have to be investigated on the basis of field work laboratory testing and analysis as well as scrutiny of the relevant ancient texts this paper focuses on samian earth from the island of samos in the east aegean used in antiquity as an eye salve and for the cleaning of cloth previously samian earth has been equated with kaolin but we suggest its composition was probably more closely associated with the local borates to be found in the proximity of bentonitic clays microbiological testing of hydrated layered silicates kaolin and bentonite from samos and melos in the aegean in association with different borates colemanite tincalconite was carried out against common pathogens like staphylococcus aureus and pseudomonas aeruginosa experimental results showed that even a few hundred ppms of boron boric acid in the samos bentonitic clays can have a significant effect on the reduction of bacterial colonies this observation corroborates the assumption that the medicinal properties of the earths were integrally associated with the mineralogy of specific localities within the volcanic islands of their origin

the aitape 1998 tsunami reconstructing the event from interviews and field mapping on the evening of 17 july 1998 on the aitape coast of papua new guinea a strongly felt earthquake was followed some 10 25 minutes later by a destructive tsunami the tsunami comprised three waves each estimated to be about 4 m high the second of the three waves rose to a height of 10 15 m above sea level after it had crossed the shoreline and caused most damage maximum wave heights and the greatest damage were recorded along a 14 km sector of coast centered on sissano lagoon in this sector the wavefronts moved from east to west along the coast all structures were destroyed and in the two main villages 20 40 percent of the population was killed partial destruction extended 23 km to the southeast and 8 km to the northwest and effects of the tsunami were felt as far as 250 km to the west northwest beyond the international border more than 1600 people are known to have died with some estimates as high as 2200 1000 were seriously injured and 10 000 survivors were displaced this paper presents information from interviews with eye witnesses and from mapping of damage and inundation and includes new information on the height shape and timing of the waves on the possible escape of petroleum and other gases from beneath the seafloor before and during the tsunami on unusual sound effects that preceded the waves and lighting effects that followed on possible deep circulation to 250 m of sea water in the waves on subsidence of the order of 50 70 cm at the coastal sand barrier and on the resilience and potential protective capacity of certain species of trees eye witness accounts indicate that the tsunami reached the shore at between 09 00 and 09 08 ut which is earlier than is proposed in published models of the timing and location of the source of the tsunami

groundwater flow after heavy rain in landslide slope area from 2 d inversion of resistivity monitoring data in the interest of monitoring the flow of groundwater from heavy rains we conducted surface resistivity tomography through the vadose zone over several days the measured data were modeled by 2 d inversion a laboratory experiment was carried out to estimate the difference in geological characteristics we measured the effects of groundwater fluctuation using two tank models one using sand and one using bricks which represent unconsolidated sediments and jointed rocks respectively in the sand model we succeeded in monitoring water level fluctuation as the change in resistivity over time in the brick model the water level did not appear as a distinct boundary field experiments were carried out in an area in which the near surface conditions consisted of heavily weathered rocks with an extensive shear zone several tens of meters thick measurements were performed over 42 days during which we observed changes in resistivity associated with heavy rainfall it became clear that resistivity decreases of up to 8 were present in highly porous zones in heavily weathered layers this result suggests a connection between a decrease in resistivity and the infiltration of rainwater in particular a pronounced zone of minimum resistivity may indicate infiltration of rainwater into the vadose zone the relationship between resistivity changes and rainfall was inferred to depend on the permeability of geological structure

imaging and characterisation of subsurface solute transport using electrical resistivity tomography ert and equivalent transport models abstract we assess the usefulness of electrical resistivity tomography ert in imaging and characterising subsurface solute transport in heterogeneous unconfined aquifers a field tracer experiment was conducted at the krauthausen test site germany the spatial and temporal evolution of the injected nabr solute plume was monitored in a 2d ert image plane located downstream of the injection well for 90 days since ert maps changes in bulk electrical conductivity the reconstructed images at selected time intervals are first converted to solute concentration maps by postulating a linear relation the concentration maps are then analysed using an equivalent convection dispersion model cdm which conceptualises the aquifer as a homogeneous medium with a uniform mean flow velocity as demonstrated by associated synthetic model studies ert resolution in terms of recovered equivalent dispersivities is limited due to spatial smoothing inherent to the imaging algorithm since for heterogeneous media local concentrations within the plume deviate from those predicted by the equivalent cdm we also interpret the ert derived pixel breakthrough curves in terms of an equivalent stream tube model stm the stm represents transport in the aquifer by a set of 1d convection dispersion processes allowing the degree of mixing and the heterogeneity of transport within the plume to be quantified we believe that the observed tracer plume is satisfactorily described by the equivalent cdm probably because the tracer plume was small relative to the heterogeneity scale of the aquifer even though application of the stm revealed some deviation from the ideal homogeneous case the equivalent dispersivity in the stm matches the longitudinal dispersivity of the cdm closely consistent with predominantly homogeneous mixing however the stm analysis illustrates how ert results can be used to quantify the variability of parameters relevant to flow and transport in heterogeneous aquifers

fluid migration in the vadose zone from 3 d inversion of resistivity monitoring data the movement of a small plume of fresh water through the vadose zone was monitored using surface resistivity tomography and pole pole potential measurements sets of potential measurements on a square grid at several times throughout the experiment show gradual progressive and systematic development of low resistivity zones that are inferred to be loci of fluid concentration a procedure for inverting percentage changes in potentials is developed here and used to map maximum potential changes of 13 into resistivity decreases of up to 40 through 3 d resistivity inversion the resulting patterns are complex with both resistivity increases and decreases needed to match the observed data the resistivity reductions show a spatial connection to the plume s source and are suggestive of the fluid migration resistivity increases generally appear to form rims surrounding the decreases and may be artifacts of the inversion process however some isolated increases in the surface layer may be caused by evapora

a borehole to surface electromagnetic survey the results of a limited field trial confirm the usefulness of borehole to surface electromagnetic em measurements for monitoring fluid extraction a vertical em profiling experiment was done at the university of california richmond field station where we simulated a brine spill plume by creating a saline water injection zone at the depth of 30 m the data acquisition mode was analogous to the reverse vertical seismic profiling vsp configuration used for seismic measurements in that the em transmitter traversed the pvc cased borehole used for fluid injection and extraction while the receivers were deployed on the surface the em measurements were made at 9 6 khz with an accuracy of 1 in signal amplitude and 1 in signal phase observations were taken at 5 m intervals along two intersecting profiles that were centered on the injection well and extended for 60 m on either side of it the presence of the injected salt water at the expected 30 m depth was indicated clearly by differences between the p

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

a tracer test in a shallow heterogeneous aquifer monitored via time lapse surface electrical resistivity tomography we illustrate a case study of a saline tracer test in a shallow highly heterogeneous aquifer monitored by means of surface time lapse ert the test was aimed at identifying the system s hydraulic properties some of the expected limitations of the method particularly caused by the strong decrease in ert resolution with depth and the consequent problems with mass balance and moment calculation could be partly balanced by the use of direct measurements of groundwater electrical conductivity and tracer concentration at one selected location the vast heterogeneity of the system ranging in lithology from clay to gravel at a scale of meters to tens of meters reflects itself in the tracer migration and distribution over time the tracer is trapped in the low permeability regions and from these it is slowly released over time high resolution surface ert proves effective at picturing this system behavior over time the extreme heterogeneity is also a challenge in the attempt to translate bulk electrical

three dimensional massively parallel electromagnetic inversion ii analysis of a crosswell electromagnetic experiment summary a 3 d electromagnetic inversion scheme has been successfully applied to crosswell electromagnetic data collected at the richmond field station near berkeley california by comparing images of data collected before and after the injection of 50000 gallons of salt water a 3 d image of the plume has been developed which shows the location of zones of maximum permeability surrounding the injection well through which the salt water has migrated a resolution analysis has determined that the location of the plume is fairly accurate however the image of the geology will be distorted due to incomplete data coverage this latter problem is further complicated by the fact that data residuals indicate that the wells deviate from the vertical these deviations have been shown to cause artefacts within the images and thus further reduce the accuracy of the images with respect to the geology

the effect of bathymetry on tsunami characteristics at sisano lagoon papua new guinea the 1998 papua new guinea tsunami was greater than expected from its earthquake magnitude the area of significant impact was small approximately a 30 km stretch near the mouth of sissano lagoon papua new guinea to explain the localized nature of the event a submarine landslide has been conjectured to be responsible our study indicates that offshore bathymetry is critical to predicting tsunami coastal behavior model runs with newly obtained bathymetric data indicate that an earthquake fault source combined with the existing seafloor geometry may also explain the concentrated tsunami although the definitive cause of the papua new guinea tsunami remains uncertain local bathymetry had a notable effect on the wave behavior

subducting oceanic crusts of the philippine sea and pacific plates and weak zone normal compression in the kanto district japan summary oceanic crusts subducting into the mantle were detected by analyses of mantle earthquakes in the kanto district central japan earthquakes in a depth range of 30 80 km in the southwestern ibaraki prefecture were relocated by a modified method of joint hypocentre determination we obtained a good distribution map of hypocentres and focal mechanisms a boundary layer between the eurasian and philippine sea plates was found where thrust earthquakes with p axes in the nw se direction and of which low angle nodal planes dip northward occurred in a layer with a thickness of about 4 km the p wave velocity in this layer is estimated to be less than about 7 0kms l another boundary layer between the philippine sea and pacific plates exists about 15 km beneath the above boundary layer thrust earthquakes with p axes in the ew direction and of which low angle nodal planes dip westward occurred in this layer that also has a thickness of about 4km furthermore normal faulting earthquakes of which the p axes are almost perpendicular to the boundary layers were found immediately outside the boundary layers combining these results we can conclude that the boundary layers are oceanic crusts that exist at the top of the subducting philippine sea and pacific plates weak zone normal compression was proposed to result from the existence of low velocity oceanic crusts at plate boundaries this hypothesis can be explained because only stress caused by relative motion of the two plates is consumed inside the weak oceanic crust the remnant stress after subtracting the above stress from the tectonic one applied at the plate boundary is the stress of which the p axis is normal to the plate boundary

quick aftershock relocation of the 1994 shikotan earthquake and its fault planes the 1994 shikotan earthquake of mw 8 2 occurred near the western kurile trench where the pacific plate is subducting beneath the north american plate although its mechanism is thrust type it is not a typical low angle thrust event with a nodal plane parallel to the plate boundary that occurs at the plate boundary in order to determine which of the two nodal planes of the main shock was the fault plane we relocated the main shock and all aftershocks with m 5 3 using a modified joint hypocenter determination method earthquakes on the northwestern side of the aftershock area including the main shock are located along a plane dipping east southeastward with a dip of 70 this plane is about 80 to 150 km long and 70 km wide the main shock occurred at the north northeastern bottom of this plane which is almost parallel to one of the two nodal planes of the main shock determined by harvard university which has a strike of n51 e and a dip of 76 thus we conclude that this plane is the fault plane that the fault broke at the northeastern bottom of the fault plane and that the rupture propagated to the surface and also to the southeast in addition to the aftershocks aligned with this fault plane there is a secondary alignment which is subparallel to the main fault plane and about 50 km east where the largest aftershock of mw 7 3 occurred on oct 9 since several aftershocks occurred on this secondary fault plane on the same day as the main shock it seems reasonable to suppose that this secondary fault plane was generated together with the main fault plane at the time of the main shock

crosswell electromagnetic tomography system design considerations and field results electrical conductivity is an important petroleum reservoir parameter because of its sensitivity to porosity pore fluid type and saturation although induction logs are widely used to obtain the conductivity near boreholes the poor resolution offered by surface based electrical and electromagnetic em field systems has thus far limited obtaining this information in the region between boreholes low frequency crosswell em offers the promise of providing subsurface conductivity information at a much higher resolution than was previously possible researchers at lawrence livermore national lab llnl and lawrence berkeley laboratories lbl together with an industrial consortium recently began a program to conduct low frequency crosswell em surveys and develop suitable inversion techniques for interpreting the data in developing the field instrumentation we used off the shelf components whenever possible but custom designed induction coil transmitters and receivers were built for the field experiment

analysis of the far field tsunamis generated by the 1998 papua new guinea earthquake the tsunami generated by the 1998 papua new guinea earthquake was observed at several tide gauges and ocean bottom pressure gauges in japan the fault model of the 1998 papua new guinea earthquake was estimated using those tsunami waveforms observed in japan and coseismic subsidence observed along the coast of papua new guinea near the source region the numerical simulation of the tsunami using the linear boussinesq equation was carried out the tsunami waveforms in japan are explained by the fault model which is consistent with the harvard cmt solution including the seismic moment of 3 7 1019 nm the additional tsunami source such as a sediment slump is not needed to explain the observed tsunami in japan the mechanism of the earthquake was likely to be a steeply dipping reverse fault the 1998 papua new guinea earthquake was likely to occur within a small accretionary prism near the new guinea trench

empirical constraints on magnitude distance relationships for seismically induced submarine tsunamigenic landslides abstract seismically induced submarine landslide tsunamis here called silts attract growing attention due to their unique setting damage potential and short warning time a question of key importance especially for tsunami early warning is how far can an earthquake trigger a tsunamigenic slump here we investigate the relationships between earthquake magnitude and the maximal distance between the seismogenic fault and the tsunamigenic slumps rf and between the earthquake epicenter and the slump re and propose empirical constraints on these magnitude distance m d relations the 49 identified silts are spread in various seismotectonic and bathymetric settings in different seas around the globe we found that the maximal distance of the tsunamigenic submarine landslide from the parent earthquake grows with the magnitude and is bounded by an envelope constrained by mw as low as 4 9 for several kilometers the 1968 liguria coast italy and as far as 250 km for mw 7 7 the 1819 rann of kachchh india higher earthquake magnitudes also produce silts seemingly distances lower than 250 km however it is suspected that the available data is limited and unable to reflect the true nature of silt s generation generalized empirical relations between the earthquake magnitude mw and the maximal distance from the seismogenic fault to its generated silt rf in km are log rf 1 17 0 49 mw r2 0 78 the empirical distance between the earthquake epicenter and the corresponding tsunamigenic slump re in km is log re 0 87 0 45 mw r2 0 83 although many earthquakes within the m d bounding envelope did not produce tsunamis the successful events still enable the delineation of the m d zone vulnerable to tsunami generation which in turn can be applied to tsunami early warning procedures this is particularly important for near coast inland earthquakes as their tsunamigenic potential might be overlooked

estimation of current plate motions in papua new guinea from global positioning system observations plate tectonic motions have been estimated in papua new guinea from a 20 station network of global positioning system sites that has been observed over five campaigns from 1990 to 1996 the present velocities of the sites are consistent with geological models in which the south bismarck woodlark and solomon sea plates form the principal tectonic elements between the pacific and australian plates in this region active spreading is observed on the woodlark basin spreading centre but at a rate that is about half the rate determined from magnetic reversals the other major motions observed are subduction on the new britain trench seafloor spreading across the bismarck sea seismic lineation convergence across the ramu markham fault and left lateral strike slip across the papuan peninsula these motions are consistent with a 8 2 myr 1 clockwise rotation of the south bismarck plate about a pole in the huon gulf and a rotation of the woodlark plate away from the australian plate second order deformation may also be occurring in particular manus island and northern new ireland may be moving northward relative to the pacific plate at 5 8 mm yr 1 significant at the 95 but not at the 99 confidence level which may suggest the existence of a north bismarck plate

the july 1998 papua new guinea earthquake mechanism and quantification of unusual tsunami generation the unusual tsunami generated by the july 17 1998 papua new guinea earthquake was investigated on the basis of various geophysical observations including seismological data tsunami waveform records and on land and submarine surveys the tsunami source models were constructed for seismological high angle and low angle faults splay fault and submarine slumps far field and near field tsunamis computed from these models were compared with the recorded waveforms in and around japan and the measured heights along the coast around sissano lagoon respectively in order to reproduce the far field tsunami waveforms small sources such as splay fault or submarine slump alone were not enough and a seismological fault model was required relocated aftershock distribution and observed coastal subsidence were preferable for the low angle fault but the low angle fault alone could not reproduce the large near field tsunamis the low angle fault with additional source possibly a submarine slump is the most likely source of the 1998 tsunami although other possibilities cannot be excluded computations from different source models showed that the far field tsunami amplitudes are proportional to the displaced water volume at the source and the comparison with the observed tsunami amplitudes indicated that the displaced water volume at the 1998 tsunami source was 0 6 km3 the near filed tsunami heights on the other hand are determined by the potential energy of displaced water and the comparison with the observed heights showed that the potential energy was 2 x 1012 j

quantifying surface to reservoir electromagnetics for waterflood monitoring in a saudi arabian carbonate reservoir abstractwe modeled surface to borehole controlled source electromagnetics to assess the sensitivity of electromagnetic fields to the detection and evolution of the waterfront position in a saudi arabian carbonate reservoir we studied a test well drilled for research purposes at the edge of the current waterfront the 3d reservoir saturations were obtained by using a black oil simulator and later converted to resistivity using archie s empirical relation the anisotropic overburden model was derived from the upscaling of triaxial resistivity logs acquired from the surface to reservoir depth in the well the modeling study was performed by the combination of 3d finite element time domain and 3d finite difference frequency domain methods using surface galvanic sources in radial and transverse polarization modes with borehole receivers results indicated that the electric field components have the largest sensitivity to static reservoir resistivity distributions and to the time lapse resistivity changes the

electrical resistivity characterization of an industrial site using long electrodes an electrical resistivity survey was completed at the t tank farm at the hanford nuclear site in washington state u s a the purpose of the survey was to define the lateral extent of waste plumes in the vadose zone in and around the tank farm the t tank farm consists of single shell tanks that historically have leaked and many liquid waste disposal facilities that provide a good target for resistivity mapping given that the site is highly industrialized with near surface metallic infrastructure that potentially could mask any interpretable waste plume it was necessary to use the many wells around the site as long electrodes to accommodate the long electrodes and to simulate the effects of a linear conductor the resistivity inversion code was modified to assign low resistivity values to the well s location the forward model within the resistivity code was benchmarked for accuracy against an analytic solution and the inverse model was tested for its ability to recreate images of a hypothetical targe

near field modeling of the july 17 1998 tsunami in papua new guinea modest earthquakes may trigger large submarine landslides responsible for disastrous tsunami waves as demonstrated by the papua new guinea event of july 17 1998 the relatively small earthquake was followed by unexpectedly high waves up to 15 m wiping out 3 villages and killing more than 2200 people numerical simulations show that seismic dislocation sources are not energetic enough to reproduce the observed tsunami along the coast tsunami generation by a submarine landslide has been simulated by a finite difference model assimilating the landslide to a flow of granular material long wave approximation is adopted for both water waves and the slide numerical results show that observed inundation heights are well reproduced for a volume of 4 km located 20 km offshore sliding downslope with a coulomb type friction