locating and quantifying geological uncertainty in three dimensional models analysis of the gippsland basin southeastern australia abstract geological three dimensional 3d models are constructed to reliably represent a given geological target the reliability of a model is heavily dependent on the input data and is sensitive to uncertainty this study examines the uncertainty introduced by geological orientation data by producing a suite of implicit 3d models generated from orientation measurements subjected to uncertainty simulations the resulting uncertainty associated with different regions of the geological model can be located quantified and visualised providing a useful method to assess model reliability the method is tested on a natural geological setting in the gippsland basin southeastern australia where modelled geological surfaces are assessed for uncertainty the concept of stratigraphic variability is introduced and analysis of the input data is performed using two uncertainty visualisation methods uncertainty visualisation through stratigraphic variability is designed to convey the complex concept of 3d model uncertainty to the geoscientist in an effective manner uncertainty analysis determined that additional seismic information provides an effective means of constraining modelled geology and reducing uncertainty in regions proximal to the seismic sections improvements to the reliability of high uncertainty regions achieved using information gathered from uncertainty visualisations are quantified in a comparative case study uncertainty in specific model locations is identified and attributed to possible disagreements between seismic and isopach data further improvements to and additional sources of data for the model are proposed based on this information finally a method of introducing stratigraphic variability values as geological constraints for geophysical inversion is presented

a geophysically constrained litho structural analysis of the eburnean greenstone belts and associated granitoid domains burkina faso west africa abstract interpretation of airborne geophysical data integrated with field structural and lithological observation was successfully employed in the creation of the litho structural framework in a poorly exposed paleoproterozoic granite greenstone terrain of the west african craton the geophysical data portray with sufficient detail all of the lithological units and structural features present the results suggest that the granitoid domains are formed by numerous small to medium sized plutons the existence of several generations of magmatic episodes has a significant impact on the development of a regional tectonic model the magnetic data provided a better definition of the actual pluton shapes and several highly magnetic late orogenic plutons were reliably identified relic f1 fold hinges were recognized in the hounde and boromo greenstone belts the d1 penetrative structures are generally affected by the d2 transcurrent shear zones which often form as well the granite greenstone belt boundaries previously unreported s2 shear zones including the bossie shear zone transecting the sideradougou granitoid domain and abundant small scale shear zones affecting all of the lithologies represent prospective areas for gold exploration airborne gamma ray spectrometry data aided in the mapping process in areas with less regolith cover including erosional ridges and parts of the banfora greenstone belt the magnetic data revealed at least three generations of doleritic dykes crosscutting the western burkina faso

constrained 3d modeling of the mesoproterozoic benagerie volcanics australia abstract the benagerie volcanics form part of a hotspot track that affected large sections of eastern australia during the mesoproterozoic understanding the location and controls on eruption centres of the benagerie volcanics and coeval plutons is difficult because they do not outcrop and are known only from limited drillhole data we have applied various combinations of forward and inversion modeling of magnetic and gravity to well constrained petrophysics and drillholes areas to characterize the 3d geometry and extent of the volcanic province and its crustal architecture thereby adding to a better understanding of the emplacement mechanisms involved we interpret the sw limit of the benagerie shear zone corridor to be a major terrane boundary separating relatively magnetic crust to the sw from crust with low magnetic susceptibility to the ne 2d and 3d models show a pronounced thickening of felsic material coincident with the shear zone that may be interpreted as a plutonic root thereby corroborating interpretations that this shear zone acted as a structural conduit for the ascent and emplacement of magma

uncertainty estimation for a geological model of the sandstone greenstone belt western australia insights from integrated geological and geophysical inversion in a bayesian inference framework

three dimensional model and late stage warping of the plattengneis shear zone in the eastern alps abstract the plattengneis shear zone is a 250 600 m thick flat lying cretaceous eclogite facies mylonitic shear zone with north over south transport direction that is exposed over almost 1000 km2 in the koralpe region along the eastern margin of the alps although the shear zone is one of the largest in the alps its role in the eoalpine metamorphic evolution and the subsequent exhumation of the region remain enigmatic and its large scale geometry is not well understood the outcrop pattern suggests that the shear zone is made up of a single sheet that is folded into a series of open syn and antiforms with wavelengths of about 10 km eclogite bodies occur above within and below the shear zone and there is no metamorphic grade change across the shear zone in the south the fold axes strike east west and plunge shallowly to the east in the north the fold axes are oriented in north south direction and form a dome shaped structure of the shear zone total shortening during this late stage warping event was of the order of 5 indirect evidence constrains this folding event to have occurred between 80 and 50 ma and the fold geometry implies that the final exhumation in the koralpe occurred somewhat later than further north interestingly the shear zone appears to strike out of the topography in the south and dip into the topography in the north so that north of the shear zone only hanging wall rocks are exposed and south of it only foot wall rocks possibilities for the geometric relationship of the plattengneis shear zone with the surrounding south dipping detachments are discussed

inversion of complex body waves we have developed a method that inverts seismic body waves to determine the mechanism and rupture pattern of earthquakes the rupture pattern is represented as a sequence of subevents distributed on the fault plane this method is an extension of our earlier method in which the subevent mechanisms were fixed in the new method the subevent mechanisms are determined from the data and are allowed to vary during the sequence when subevent mechanisms are allowed to vary however the inversion often becomes unstable because of the complex trade offs between the mechanism the timing and the location of the subevents many different subevent sequences can explain the same data equally well and it is important to determine the range of allowable solutions some constraints must be imposed on the solution to stabilize the inversion we have developed a procedure to explore the range of allowable solutions and appropriate constraints in this procedure a network of grid points is constructed on the i plane where and i are respectively the onset time and the distance from the epicenter of a subevent the best fit subevent is determined at all grid points then the correlation is computed between the synthetic waveform for each subevent and the observed waveform the correlation as a function of and i and the best fit mechanisms computed at each i grid point depict the character of allowable solutions and facilitate a decision on the appropriate constraints to be imposed on the solution the method is illustrated using the data for the 1976 guatemala earthquake

method and analysis for the upscaling of structural data abstract 3d geological models are created to integrate a set of input measurements into a single geological model there are many problems with this approach as there is uncertainty in all stages of the modelling process from initial data collection to the approach used in the modelling scheme itself to calculate the geological model this study looks at the uncertainty inherent in geological models due to data density and introduces a novel method to upscale geological data that optimises the information in the initial dataset this method also provides the ability for the dominant trend of a geological dataset to be determined at different scales by using self organizing maps som s to examine the different metrics used to quantify a geological model we allow for a larger range of metrics to be used compared to traditional statistical methods due to the som s ability to deal with incomplete datasets the classification of the models into clusters based on the geological metrics using k means clustering provides a useful insight into the models that are most similar and models that are statistical outliers our approach is guided and can be calculated on any input dataset of this type to determine the effect that data density will have on a resultant model these models are all statistical derivations that represent simplifications and different scales of the initial dataset and can be used to interrogate the scale of observations

basin centered asperities in great subduction zone earthquakes a link between slip subsidence and subduction erosion 1 published areas of high coseismic slip or asperities for 29 of the largest circum pacific megathrust earthquakes are compared to forearc structure revealed by satellite free air gravity bathymetry and seismic profiling on average 71 of an earthquake s seismic moment and 79 of its asperity area occur beneath the prominent gravity low outlining the deep sea terrace 57 of an earthquake s asperity area on average occurs beneath the forearc basins that lie within the deep sea terrace in sw japan slip in the 1923 1944 1946 and 1968 earthquakes was largely centered beneath five forearc basins whose landward edge overlies the 350 c isotherm on the plate boundary the inferred downdip limit of the locked zone basin centered coseismic slip also occurred along the aleutian mexico peru and chile subduction zones but was ambiguous for the great 1964 alaska earthquake beneath intrabasin structural highs seismic slip tends to be lower possibly due to higher temperatures and fluid pressures kilometers of late cenozoic subsidence and crustal thinning above some of the source zones are indicated by seismic profiling and drilling and are thought to be caused by basal subduction erosion the deep sea terraces and basins may evolve not just by growth of the outer arc high but also by interseismic subsidence not recovered during earthquakes basin centered asperities could indicate a link between subsidence subduction erosion and seismogenesis whatever the cause forearc basins may be useful indicators of long term seismic moment release the source zone for cascadia s 1700 a d earthquake contains five large basin centered gravity lows that may indicate potential asperities at depth the gravity gradient marking the inferred downdip limit to large coseismic slip lies offshore except in northwestern washington where the low extends landward beneath the coast transverse gravity highs between the basins suggest that the margin is seismically segmented and could produce a variety of large earthquakes

vein mineralization at the damang gold mine ghana controls on mineralization abstract two distinct styles of au mineralization occur at the damang gold mine palaeoproterozoic sediments of the tarkwaian group host both one style of mineralization is stratabound within quartz lithic conglomerates of the banket series the second style of mineralization is associated with an extensive low displacement fault fracture mesh that formed in a compressional stress regime late in the deformational history and after the peak metamorphism regional deformation within the tarkwaian involved initial nw se directed shortening d 1 a major nne trending f 1 anticline hosts the damang orebody broadly n s shortening during d 2 resulted in the formation of e w trending thrusts with small displacements the d 3 shortening direction was similar to that of d 1 steep d 1 faults were reactivated and a new set of low angle thrusts and associated flat lying extension veins were formed the bulk of the mineralization observed at damang is associated with the low displacement d 3 fault fracture mesh the presence of flat lying extensional veins and the reactivation of some misoriented d 1 structures is indicative of periodic episodes of supralithostatic fluid pressures low differential stress and fault valve behavior towards the end of the deformation history

uncertainty reduction through geologically conditioned petrophysical constraints in joint inversion abstractwe have developed a joint geophysical inversion workflow that aims to improve subsurface imaging and decrease uncertainty by integrating petrophysical constraints and geologic data in this framework probabilistic geologic modeling is used as a source of information to condition the petrophysical constraints spatially and to derive starting models the workflow then uses petrophysical measurements to constrain the values retrieved by geophysical joint inversion the different sources of constraints are integrated into a least squares framework to capture and integrate information related to geophysical petrophysical and geologic data this allows us to quantify the posterior state of knowledge and to calculate posterior statistical indicators to test this workflow using geologic field data we have generated a set of geologic models which we used to derive a probabilistic geologic model in this synthetic case study we found that the integration of geologic information and petrophysical con

age constraints on tarkwaian palaeoplacer and lode gold formation in the tarkwa damang district sw ghana two major epigenetic gold forming events are recorded in the world class gold province of southwest ghana a pre tarkwaian event was the source of the world class tarkwa palaeoplacers whereas post birimian and tarkwaian deformation which was related to the eburnean orogeny gave rise to the world class e g prestea to giant e g obuasi orogenic gold deposits which have made the region famous for more than 2 500 years a maximum age of 2133 4 ma for tarkwaian sedimentation is provided by 71 of 111 concordant shrimp ii u pb dates from detrital zircons in tarkwaian clastic rocks from damang and bippo bin northeast of tarkwa the overall data distribution broadly overlaps the relatively poorly constrained ages of birimian volcanism and associated dixcove type granitoid emplacement indicating syntectonic development of the tarkwaian sedimentary basin these zircon ages argue against derivation of the palaeoplacer gold from an orogenic gold source related to the compressional phase of an orogeny significantly older than the eburnean orogeny instead they suggest that the gold source was either orogenic gold lodes related to an earlier compressional phase of a diachronous eburnean orogeny or ca 2200 2100 ma intrusion related gold lode the co2 rich fluid inclusions in associated vein quartz pebbles are permissive of either source at the damang deposit an epigenetic orogenic lode gold system clearly overprinted and sulphidised low grade palaeoplacer hematite magnetite gold occurrences in the banket series conglomerate within the tarkwaian sedimentary sequence gold mineralisation is demonstrably post peak metamorphism as gold related alteration assemblages overprint metamorphic assemblages in host rocks in alteration zones surrounding the dominant subhorizontal auriferous quartz veins there are rare occurrences of hydrothermal xenotime which give a shrimp u pb age of 2063 9 ma for gold mineralisation the similar structural timing of epigenetic gold mineralisation in tarkwaian host rocks at damang to that in mainly birimian host rocks elsewhere in southwest ghana particularly at obuasi suggests that 2063 9 ma is the best available age estimate for widespread orogenic gold mineralisation in the region argon argon ages of 2029 4 and 2034 4 ma for hydrothermal biotite from auriferous quartz veins appear to represent uplift and cooling of the region below about 300 c as estimates of the temperature of gold mineralisation are higher at around 400 c if peak metamorphism with temperatures of about 550 c is assumed to have occurred at about 2100 ma the biotite ages in combination with the xenotime age suggest a broadly constant uplift rate for the region of about 1 km per 10 million years from about 2100 to 2025 ma

slip history of the 1994 sanriku haruka oki japan earthquake deduced from strong motion data abstract we analyzed the seismic waves of the 1994 sanriku haruka oki earthquake m w 7 7 which occurred in the aftershock area of the 1968 tokachi oki earthquake m w 8 2 applying a multiple time window inversion scheme to near source strong motion data we obtained a detailed spatiotemporal rupture process and compared it with that of the tokachi oki earthquake the fault geometry is constructed based on the aftershock distribution the obtained rupture model is consistent with the cmt solution even for a non double couple component the total seismic moment is 4 0 10 20 n m large slips are concentrated in three asperities the first asperity centers about 40 km south and 50 km west from the hypocenter with a maximum slip of 4 4 m the second one centers about 60 km west from the hypocenter with a maximum slip of 2 2 m and the third one lies about 110 km west from the hypocenter with a maximum slip of 2 6 m the obtained moment rate and the duration on the first and second asperities are lower and much longer than those on the third asperity respectively the first asperity does not overlap with an area of large slip during the tokachi oki earthquake but the second or third seem to overlap with or be adjacent to the asperity of the tokachi oki earthquake our inversion result also shows an abrupt change of the rupture velocity from 1 8 to 3 0 km sec at the central part of the fault plane a difference of the seismic coupling between the oceanic and the continental lithospheres at the trenchward side and at the landward side of the 143 e meridian seems to affect the rupture process of this earthquake

stochastic fracture generation accounting for the stratification orientation in a folded environment based on an implicit geological model article i nfo this paper presents a new approach in generating stochastic discrete fracture networks the particularity of the approach isthatitallows us tosimulate thetheoreticalfamiliesoffractures thatare expected ina foldedenviron ment the approach produces fractures that are consistent with the local stratigraphic orientation the fractures are modeled as simplerectangular planarobjects whenthey are modeled they arerotatedaccordingtothe local stratigraphic orientation as the stratigraphy is modeled using an implicit approach we use the gradient of this geological potential field to retrieve the information about the geological orientation the fracture number and size are following user defined probability density functions 2015 elsevier b v all rights reserved

parameter estimation and fault detection by three component seismic and geoelectrical surveys in a coal mine three component seismic and geoelectrical in mine surveys were carried out in lyukobanya colliery near miskolc hungary to determine the in situ petrophysical parameter distributions and to detect inhomogeneities in the coal seam the seismic measurements comprise an underground vertical seismic profile using body waves and an in seam seismic amplitude depth distribution and transmission survey using channel waves the geoelectrical measurements are based on the drift and seam sounding method interval traveltime amplitude multiple filter and polarization analysis methods are applied to the seismic data they lead to a five layer model for the strata including the coal seam the coal seam and two underlying beds act as a seismic waveguide the layer sequence supports the propagation of both normal and leaky mode channel waves of the love and rayleigh type a calculation of the total reflected energy for each interface using knott s energy coefficients shows that the velocity ranges of high reflection energy and of normal and leaky mode wavegroups coincide the excitation of wavegroups strongly depends on the seismic source a simultaneous inversion of a geoelectrical drift and seam sounding survey prevents misinterpretations of the seismic data by clearly identifying the low velocity coal seam as a high resistivity bed calculations of dispersion and sounding curves improve the resolution of the slowness and resistivity in each layer both diminished amplitudes and distortions in the polarization of transmission seismo grams and decreasing resistivities in a geoelectrical pseudosection of the coal seam are related to an inhomogeneity a calculation of synthetic seismograms for love and rayleigh channel waves with the finite difference and the alekseev mikhailenko method agrees well with the field data for the main features i e particular arrivals in the wave train wavegroups velocities and symmetries or asymmetries this in mine experiment demonstrates that the simultaneous acquisition processing and interpretation of seismic and geoelectrical data improve the lithological interpretation of petrophysical parameter distributions coal seam inhomogeneities can also be detected more reliably by the two independent surveys than by one alone

the rupture process and asperity distribution of three great earthquakes from long period diffracted p waves moment tensor source mechanisms for the largest twenty nine shallow earthquakes from 1981 m s 6 5 have been determined using long period rayleigh wave spectra and p wave first motions recorded by the international deployment of accelerograms ida global digital seismic network gdsn and world wide standardised seismic network wwssn these are compared with the centroid moment tensor mechanisms presented by dziewonski and woodhouse which were obtained in a contrasting manner in most cases the source is well represented by a single double couple mechanisms with good agreement of scalar moment and orientation between the two studies apparent mismatches for other cases may be interpreted in terms of source complexity we emphasise the objectivity of comparing moment tensor elements apparent discrepancies in the moment and orientation of double couple fault plane solutions are usually due to differences in the mxz and myz moment tensor elements which are poorly constrained by long period data

geodiversity exploration of 3d geological model space abstract the process of building a 3d model necessitates the reconciliation of field observations geophysical interpretation geological data uncertainty and the prevailing tectonic evolution hypotheses and interpretations uncertainty is compounded when clustered data points collected at local scales are statistically upscaled to one or two points for use in regional models interpretation is required to interpolate between sparse field data points using ambiguous geophysical data in covered terranes it becomes clear that multiple interpretations are possible during model construction the various interpretations are considered as potential natural representatives but pragmatism typically dictates that just a single interpretation is offered by the modelling process uncertainties are introduced into the 3d model during construction from a variety of sources and through data set optimisation that produces a single model practices such as these are likely to result in a model that does not adequately represent the target geology a set of geometrical geodiversity metrics are used to analyse a 3d model of the gippsland basin southeastern australia after perturbing geological input data via uncertainty simulation the resulting sets of perturbed geological observations are used to calculate a suite of geological 3d models that display a range of geological architectures the concept of biodiversity has been adapted for the geosciences to quantify geometric variability or geodiversity between models in order to understand the effect uncertainty has models geometry various geometrical relationships depth volume contact surface area curvature and geological complexity are used to describe the range of possibilities exhibited throughout the model suite end member models geodiversity metrics are classified in a similar manner to taxonomic descriptions further analysis of the model suite is performed using principal component analysis pca to determine important geometrical characteristics the configuration of the model space is determined through identifying outlier model examples which potentially represent undiscovered model species

analysis and interpretation of the heterogeneous rupture process application of the empirical green s function method and nonlinear inversion technique to large earthquakes abstract heterogeneous rupture processes were revealed using an empirical green s function egf method and a nonlinear inversion technique three events the 1980 east izu peninsula earthquake the 1983 japan sea earthquake and the 1987 east chiba earthquake are studied kernel events used as empirical green s functions were selected among the foreshocks and aftershocks the dimension and orientation of the fault plane were evaluated from the aftershock distribution and main shock fault plane solution a moment ratio between the main shock and the kernel event was estimated in order to identify the number of subfaults strong motion waveforms recorded at near distances were inverted to estimate moment release rupture time and rise time at each subfault with the stress drop calculated from the moment release and rise time distributions of these faulting parameters can be related to the aftershock distribution and geological structures general features are that the moment release was large where the aftershock activity was low that the irregular rupture propagations detected here were related to geological structures such as a ridge junction seamount chains and other tectonic plate boundaries and that stress drop distributions show some relation to the pattern of aftershocks an exception is the small moment release at the bending corner of the 1983 japan sea earthquake where the aftershock activity was low with this method it is possible to extract not only the detailed source history but also information on geophysical structures

directivity analysis of the december 28 1994 sanriku oki earthquake mw 7 7 japan on december 28 1994 a segment along the northern japan trench failed in a mw 7 7 underthrusting earthquake the sanriku oki earthquake less than 30 years earlier the great tokachi oki underthrusting earthquake of may 16 1968 mw 8 2 occurred in the same region we examine the rupture process of the recent event using teleseismic body and surface wave data and compare our results to the rupture characteristics of the tokachi oki earthquake as estimated by various authors in previous studies we use an empirical green function technique to obtain relative source time functions spanning a large range of the directivity parameter the strong azimuthal dependence of the durations of these source time functions indicates a significant unilateral component of rupture in a down dip direction west northwest the main rupture initiated about 35 km southwest of the epicenter approximately 20 seconds after the onset of a low energy precursor the main tokachi oki rupture was also preceded by low moment release however it is unclear whether the low moment release preceding both earthquakes represents part of the rupture process or a distinct foreshock the main rupture areas asperities of the sanriku oki and the tokachi oki earthquakes do not significantly overlap

inversion of geological knowledge for fold geometry abstract the process of building three dimensional 3d geological models can be framed as an inverse problem where a model describing the 3d distribution of rock units is non uniquely derived from geological observations the inverse problem theory provides a powerful framework for inferring these parameters from all geological observations in a similar way to how a geologist can iteratively update their structural interpretation while mapping existing geological knowledge is usually indirectly incorporated into 3d models using the geologist s non unique interpretation as form lines cross sections and level maps these approaches treat constraints derived from geological knowledge in the same way as direct observations diluting and confusing both information provided by geological knowledge and hard data resulting in significant subjectivity we present a geological inversion using bayesian inference where geological knowledge can be incorporated directly into the interpolation scheme with likelihood functions and informative prior distributions we demonstrate these approaches on a series of synthetic fold shapes as a proof of concept and a case study from the proterozoic davenport province in the northern territory australia the combined inversion of geological data and knowledge significantly reduces the uncertainty in possible fold geometries where data is sparse or highly ambiguous this could be used by geologists while mapping to propagate information about uncertainties throughout the mapping model building process and would allow for different structural interpretations to be rapidly tested for targeted data collection

simultaneous inversion of waveform and geodetic data for the rupture process of the 1984 naganoken seibu japan earthquake summary a simultaneous inversion method of strong motion seismograms and geodetic data for inferring earthquake rupture process was developed we assumed a source model composed of many point sources of which slip vectors and rupture times are unknown parameters in addition to observed data we introduced smoothing constraints to determine many parameters without instability since the leastsquares solution depends on the relative weights of the smoothing constraints to a data misfit function we determined their values by minimizing akaike s bayesian information criterion abic by using abic we can objectively choose a unique model this inversion method was applied to the naganoken seibu japan earthquake of 1984 dividing a 15 x 10 km fault into 150 subfaults we obtained the minimum abic model with a seismic moment of 2 7 x los dyne cm this model has a slip peak in the eastern and shallow area of the assumed fault the high slip area is just under the areas where thrown out boulders were found by umeda et al 1987 and iio yoshioka 1988 comparing the aftershock distribution with the estimated slip distribution we found that the high slip area had few aftershocks this suggests that aftershocks are caused by the stress generated in the marginal region around the main shock slip the inversion analysis also revealed that there was a slight change in slip angle during the earthquake the high slip area has some amount of dip slip component while the slips in the other areas are almost purely right lateral

dynamic rupture scenarios of anticipated nankai tonankai earthquakes southwest japan 1 we investigated dynamic rupture scenarios of anticipated megathrust earthquakes on the nankai tonankai subduction zone southwest japan to improve the scenario reliability the model parameters should be constrained by available data or derived from their analysis we employed the three dimensional plate interface geometry and the slip deficit rate on the interface accumulated slip deficit was used to obtain the stress drop distribution of anticipated earthquakes the estimated stress drop distribution is consistent with the seismogenic asperity locations known from the analysis of past earthquakes fault friction constitutive parameters however had to be assumed from indirect observations because they cannot be constrained directly by the data based on various geophysical observations we defined three regions where larger fracture energy is required these are the eastern edge of the tonankai area the western edge of the nankai area and the region between the tonankai and nankai areas beneath the kii peninsula such lateral heterogeneity promoted the segmented rupture along the nankai trough with predefined stress drop and constitutive parameters various rupture scenarios for tonankai and nankai asperities were obtained for different initiation locations in some cases a single segment is ruptured while in other cases all the segments are broken due to dynamic linkage at the segment boundary causing a giant earthquake the initiation location is a critical parameter that controls the rupture propagation across the segment boundary these scenarios will be extremely useful to evaluate deterministically the strong ground motions and tsunami hazards caused by the next major earthquakes in southwest japan

detection of guided waves between gas wells for reservoir characterization guided seismic waves can be used to predict continuity and discontinuity of reservoir structures between wells with the low velocity beds acting as waveguides we relate guided wave signatures to waveguide targets using experimental data acquired at the stratton gas field in southeast texas the observed seismic data indicate the presence of trapped energy in low velocity shale markers between wells 145 and 151 guided waves in the form of leaky modes are excited transmitted and detected in the low velocity shale markers at a well separation of 1730 ft 527 m dispersion analysis modeling frequency amplitude depth curves well logs and lithological information all support the results specifically the characterization of two low velocity shale markers v2 and v5 demonstrates that v2 is more heterogeneous than v5 between the source well 151 and detector well 145 finally images of synthetic and real data show the potential applications of the guided wave technology as a tool for reservoir charact

3d modeling of the ashanti belt southwest ghana evidence for a litho stratigraphic control on gold occurrences within the birimian sefwi group abstract a three dimensional model of the gold rich paleoproterozoic ashanti greenstone belt has been built with a hybrid geological modeling method using geomodeller and gocad then inverted using vpmg software the model helps to identify the main regional scale controls leading to abundant gold mineralization in the southeast of the belt by highlighting the lithological distribution and geometry of geological structures the three dimensional geological model shows that 85 of gold occurrences in the ashanti greenstone belt are proximal to a specific tholeiitic metabasaltic horizon bv1 this result is noteworthy given that the relatively thin 300 m thick bv1 layer represents only 10 by volume of the modeled sefwi group stratigraphy a map of distance between the topography and the bv1 layer is produced and identifies areas showing a high probability to host gold deposits in the southeast of the ashanti belt possible structural controls performed by the bv1 tholeiitic metabasaltic rocks on the location of gold occurrences are discussed and we hypothesize that the bv1 layer acted as a mineralization trap or source of gold both hypotheses agree with examples from the literature and explain the observed distribution of the mineralized sites

a multidisciplinary study of a syntectonic pluton close to a major lithospheric scale fault relationships between the montmarault granitic massif and the sillon houiller fault in the variscan french massif central 2 gravity aeromagnetic investigations and 3 d geologic modeling 1 new gravity and aeromagnetic investigations have been carried out to understand the emplacement mechanisms of a granitic pluton and the relationships with a nearby lithospheric scale fault this paper concerns the second part of a methodological multidisciplinary study and complements previous geochronologic and anisotropy of magnetic susceptibility ams studies on the same pluton in the northern part of the variscan french massif central fmc the montmarault massif crops out along the sillon houiller fault shf bouguer and aeromagnetic anomaly maps imply thickening of the pluton along the shf and suggest laccolitic spreading northwestward on the basis of petrophysical measurements direct two dimensional 2 d joint gravity and magnetic modeling has been performed along 10 cross sections in order to quantitatively constrain the 3 d pluton geometry and its relationships with surrounding geologic units these geophysical cross sections new structural information field and ams measurements and petrophysical data have been integrated into a regional 3 d geological and geophysical model altogether the results obtained from geochronology petromagnetic fabrics part 1 gravity and aeromagnetic investigations as well as 3 d modeling part 2 demonstrate that the montmarault pluton was emplaced during the namurian period along the shf our results further show that at that time in response to a nw se regional extension if the shf existed it behaved as a normal fault mylonites attesting for synmagmatic normal motion on the northeastern part of the montmarault pluton strengthen this tectonic scenario during the late carboniferous the fmc experienced ne sw extension along the shf by 80 km of brittle left lateral wrench offset this second tectonic event is well recorded in the stephanian coal basins which were formed along nw se listric brittle faults and constrain the present day shape of the montmarault pluton

waveform inversion for rupture processes of two deep earthquakes in the izu bonin region abstract using a waveform inversion method we studied the rupture processes of two deep earthquakes in the izu bonin region the earthquake source was modelled by space time dependent slip on a fault plane the fault plane was divided into many subfaults and the source was expressed in terms of the final dislocations on the subfaults the rupture starting times at the subfault corners and the rise time of source function from p wave seismograms recorded by the global digital seismograph network we first obtained the displacement waveforms by deconvolution techniques next we inverted these waveform data to determine the model parameters for the earthquake near torishima on march 6 1984 non homogeneous stress distribution and variation in rupture velocity were revealed the rupture initiated at a corner of a 54 36 km 2 fault and high stress drop occurred in the middle region of the fault about 30 km away from the initiation the earthquake south off honshu of april 24 1984 did not have as complex a rupture process the rupture propagated unilaterally with almost constant velocity

stochastic structure constrained image guided inversion of geophysical data abstractinverse modeling of geophysical data involves the recovery of a subsurface structural model and the distribution of petrophysical properties independent information regarding the subsurface structure is usually available with some uncertainty from the expertise of a geologist and possibly accounting for sedimentary and tectonic processes we have used the available structural information to construct a model covariance matrix and to perform a structure constrained inversion of the geophysical data to obtain a geophysical tomogram m we have considered that the geologic models y were built from random variables and were described with a priori probability density function in the bayesian framework we have explored for the a posteriori probability density of the geologic models i e the structure of the guiding image with the markov chain monte carlo method and we inverted at the same time in a deterministic framework the geophysical data the sampling of the geologic models was performed

wide band analysis of the 3 march 1985 central chile earthquake overall source process and rupture history we apply a linear finite fault waveform inversion scheme to the near source strong motion records the teleseismic body waves and the long period rayleigh waves recorded for the 3 march 1985 chile earthquake to recover the mainshock rupture history the data contain periods between about 2 and 350 sec and are inverted by allowing a variable dislocation rise time at each point on the fault the results indicate that the mainshock had a seismic moment of 1 5 1028 dyne cm mw 8 0 and ruptured mainly updip and to the south of the hypocenter for a distance of about 150 km along the nazca south america plate boundary a smaller northward component of propagation is also evident giving a total rupture length of about 200 km the total source duration of the mainshock is 70 sec with the majority of the slip occurring within the first 40 sec in a broad 100 km wide zone in the northern half of the rupture area slip in this region extends from a depth of 55 km to within about 10 km of the surface and contains two areas of maximum slip 2 3 and 2 9 m with rise times of approximately 14 sec slip in the southern portion of the fault reaches lower peak values 1 8 m and extends downdip to depths no greater than 30 km an independent variable rise time inversion of the teleseismic body waves alone yields similar results indicating that a significant component of slow fault motion is not required for this earthquake the mainshock was preceded by several smaller precursors the largest of which is an mw 6 6 thrust earthquake occurring at a depth of 22 km in the shallow 15 dipping portion of the plate interface

evolution of the mount woods inlier northern gawler craton southern australia an integrated structural and aeromagnetic analysis structural mapping integrated with interpretation and forward modelling of aeromagnetic data form complimentary and powerful tools for regional structural analysis because both techniques focus on architecture and overprinting relationships this approach is used to constrain the geometry and evolution of the sparsely exposed mount woods inlier in the northern gawler craton the mount woods inlier records a history of poly phase deformation high temperature metamorphism and syn and post orogenic magmatism between ca 1736 and 1584 ma the earliest deformation involved isoclinal folding and the development of bedding parallel and axial planar gneissic foliation s1 this was accompanied by high temperature upper amphibolite to granulite facies metamorphism at ca 1736 ma during subsequent north south shortening d2 open to isoclinal south southeast oriented f2 folds developed as the palaeoproterozoic successions of the inlier were thrust over the archaean nuclei of the gawler craton the syn d2 engenina adamellite was emplaced at ca 1692 ma the post d2 history involved shear zone development and localised folding exhumation of metamorphic rocks and deposition of clastic sediments prior to the emplacement of the ca 1584 ma granite balta suite the mount woods inlier is interpreted as the northern continuation of the kimban orogen

three dimensional mineral prospectivity modeling for targeting of concealed mineralization within the zhonggu iron orefield ningwu basin china abstract the zhonggu iron orefield is one of the most important iron orefields in china and is located in the south of the ningwu volcanic basin within the middle and lower yangtze metallogenic belt of eastern china here we present the results of new 3d prospectivity modeling that enabled the delineation of areas prospective for exploration of concealed and deep seated baixiangshan type mineralization and yangzhuang type mineralization within the zhonggu orefield both of these deposits are kiruna type fe apatite deposits but are hosted by different formations within the ningwu basin the modeling approach used during this study involves 3 steps 1 combining available geological and geophysical data to construct 3d geological models 2 generation of 3d predictive maps from these 3d geological models using 3d spatial analysis and 3d geophysical methods 3 combining all of the 3d predictive maps using logistic regression to create a prospectivity map this approach integrates a large amount of available geoscientific data using 3d methods including 3d geological modeling 3d 2d geophysical methods and 3d spatial analysis and data integration methods the resulting prospectivity model clearly identifies highly prospective areas that not only include areas of known mineralization but also a number of favorable targets for future mineral exploration the 3d prospectivity modeling approach showcased within this study provides an efficient way to identify camp scale concealed and deep seated exploration targets and can easily be adapted for regional and deposit scale targeting

transmission and detection of guided seismic waves in attenuating media we can use guided seismic waves to map properties of reservoirs between wells with the low velocity layers acting as waveguides when guided waves are detected they are an indication of the continuity of the bed examined guided waveforms are characterized by time frequency representations to study important physical properties of the beds acting as waveguides we used full waveform seismic modeling in viscoelastic media to examine the required velocity contrasts and distances over which guided wave signals can be used in one set of models sandstones are the central waveguide lithology in another set shales we applied these models referred to here collectively as shaly sandstone waveguides to a range of geological circumstances where either the sands or the shales represent the low velocity layers within a reservoir to study the distances over which guided waves can be detected we compared the amplitudes of the signals computed for the models using a realistic source strength to the signal levels determined from published borehole noise studies in shaly sandstone waveguides we find it is feasible to use particle velocity measurements to record guided waves above seismic noise levels in the frequency range of 60 to 800 hz at well separations exceeding a distance of 800 m however pressure detectors such as hydrophones may only be useful up to distances of 400 m between wells in addition to the issues of shaly sandstone waveguides and practical distances between wells we present an application of guided waves using crosswell seismic data from the gypsy test site in oklahoma a site originally established by british petroleum in this field example within a sandstone reservoir we demonstrate the sensitivity of leaky mode amplitudes to source receiver location another telltale characteristic of continuity in the type of reservoir studied at the gypsy test site where there is a low shear velocity contrast between the host medium and the waveguide is the head wave followed by the leaky mode

guided seismic waves in layered poroviscoelastic media for continuity logging applications model studies1 the gas industry is continuing to concentrate its research and development efforts on new and advanced technology to improve reservoir descriptions through the producing life and development history of heterogeneous gas reservoirs a very important aspect of this need is the ability to reduce the uncertainty of estimating probable reserves and to lower the operating costs to recover incremental reserves in producing and depleted gasfields established methods for reducing uncertainty in heterogeneous reservoir compartments such as vsp and cross well techniques may enhance resolution but they are currently not economically justifiable in on shore gasfields continuity logging using guided waves is an alternative approach to analysing inter well seismic data to confirm the continuity of heterogeneous gas reservoir compartments in particular the continuity of sand and shale stratigraphy in gas reservoirs the solution of a coupled system of differential equations based on biot and homogenization theories is adapted to calculate guided seismic waves trapped in low velocity layers the general solution is for a 3d source in a horizontally layered poroviscoelastic medium having isotropic and laterally homogeneous material properties a unified representation of the medium that includes fluid solid interactions and viscoelastic losses is incorporated into the solution the guided wave part of the vector wave field and fluid pressure of the complete wave motion in layered dissipative media is verified and used to simulate dispersion and attenuation of guided seismic waves for continuity logging applications the results of this work suggest that the multimode wave solution is appropriate to simulate guided seismic wave signatures to indicate continuity of layered earth structures in poroviscoelastic reservoirs in particular the normal mode information can be used for planning continuity logging surveys and for interpreting the corresponding seismic data further fluid pressure waveforms show that maximum amplitude normal modes can be detected at layer interfaces in fluid filled porous media and the corresponding airy phase wave groups may carry information on the formation permeability

regional dome evolution and its control on ore grade distribution insights from 3d implicit modelling of the navachab gold deposit namibia abstract we introduce a novel approach to analyse and assess the structural framework of ore deposits that fully integrates 3d implicit modelling in data rich environments with field observations we apply this approach to the early palaeozoic navachab gold deposit which is located in the damara orogenic belt namibia compared to traditional modelling methods 3d implicit modelling reduces user based modelling bias by generating open or closed surfaces from geochemical lithological or structural data without manual digitisation and linkage of sections or level plans instead a mathematically defined spatial interpolation is used to generate 3d models that show trends and patterns that are embedded in large drillhole datasets in our 3d implicit model of the navachab gold deposit distinctive high grade mineralisation trends were identified and directly related to structures observed in the field the 3d implicit model and field data suggest that auriferous semi massive sulphide ore shoots formed near the inflection line of the steep limb of a regional scale dome where shear strain reached peak values during fold amplification this setting generated efficient conduits and traps for hydrothermal fluids and associated mineralisation that led to the formation of the main ore shoots in the deposit both bedding parallel and highly discordant sets of auriferous quartz sulphide veins are interpreted to have formed during the later lock up stage of the regional scale dome additionally pegmatite dykes crosscut and remobilise gold mineralisation at the deposit scale and appear to be related to a younger joint set we propose that kilometre scale active folding is an important deformation mechanism that influences the spatial distribution and orientation of mineralisation in ore deposits by forming structures traps and pathways for fluids at different preferred sites and orientations we also propose that areas that experience high shear strain located along the inflection lines of folds can act as preferred sites for syn deformational hydrothermal mineralisation and should be targeted for regional scale exploration in fold and thrust belts our research also suggests that examination of existing drillhole datasets using 3d implicit modelling is a powerful tool for spatial analysis of mineralisation patterns when combined with fieldwork this approach has the potential to improve structural understanding of a variety of ore deposits

towards an integrated inversion of geoscientific data what price of geology abstract the inversion of multiple geoscientific datasets to define structures in hard rock terrains has for the most part been limited to geophysical methods supported by rock property constraints in this paper we expand the range of constraints available to geological modellers by defining a series of misfit functions that are used to define the quality of a given geological model with respect to the available geological data these misfit functions encompass both spatial and temporal observations and include primary data such as the location of an outcrop or bore hole location of a given rock type the orientation of its different generations of foliations as well as secondary geologic observations such as age relationships when we combine geologic conditions with geophysical misfit functions which already exist for many geophysical measures we have the potential to better constrain two and 3d models of the earth as a first test a subset of these misfit functions are applied to a set of synthetic three dimensional volumetric models built with an implicit surface modelling scheme by perturbing the input structural data within a narrow range we can simulate a range of significantly different three dimensional models for which we can then apply both geological and geophysical misfit functions several joint geological geophysical inversion schemes may be developed based on this methodology with the ultimate goal being an inversion scheme that simultaneously minimizes both geological and geophysical misfit

defining folds on three dimensional surfaces we present a new method for the structural analysis of folded surfaces the method requires a generalized definition of a fold as a patch consisting of contiguous points with gaussian curvature and mean curvature of consistent sign four classes of folds result from this definition antiforms and synforms each of synclastic and anticlastic forms this new analysis is illustrated with reference to several examples

towards incorporating uncertainty of structural data in 3d geological inversion abstract all geological models are subject to several kinds of uncertainty these can be classified into three different types data imprecision and quality inherent randomness and incomplete knowledge with our approach we address uncertainties introduced by input data quality in complex three dimensional 3d models of subsurface structures geological models as input data we consider parameters of geological structures i e formation and fault boundary points and orientation measurements our method consists of five steps construction of an initial geological model with an implicit potential field method assignment of probability distributions to data positions and orientation measurements simulation of several input data sets construction of several model realisations based on these simulated data sets and finally the visualisation and analysis of the uncertainties we test our approach in two generic models a simple graben setting and a complex dome structure the first model shows that our approach can evaluate uncertainties from different structures and their interaction furthermore it indicates that the final uncertainty of the model is not simply the sum of all input data uncertainties but complex interactions exist the second example demonstrates that our approach can handle full three dimensional settings with overturned surfaces results of the uncertainty simulation can be visualised and analysed in several ways ranging from borehole histograms to uncertainty maps for complex 3d visualisation and analysis we use indicator functions when we apply these we can treat the visualisation of uncertainties in complex settings in a self consistent manner with our simulation method it is possible to analyse and visualise the uncertainties directly introduced by imprecision in the input data our approach is intuitive and straight forward and suitable in both simple and complex geological settings it enables detailed insights into the model quality even for the non expert in cases where a geological model is the basis for geophysical simulation it opens up the way to geological data driven ensemble modelling and inversion

seismogram envelope inversion for the spatial distribution of high frequency energy radiation from the earthquake fault application to the 1994 far east off sanriku earthquake japan incoherency of high frequency seismic waves leads to the idea to analyze seismogram envelopes disregarding phase information for the source study we develop an inversion method for estimating high frequency above 1 hz energy radiation from the earthquake fault and site amplification factors from observed mean square s wave seismogram envelopes the inversion is executed by using the s wave envelope green function from the onset to coda for a point shear dislocation source in a scattering medium which is formulated based on an extended version of the radiative transfer theory the use of the envelope green function enables us to estimate the spatial distribution of high frequency energy radiation on a fault plane this has been difficult by conventional waveform inversion methods the rupture velocity and the duration time of energy radiation on each subfault are also estimated by grid search method we apply this new method to the 1994 far east off sanriku northeastern japan earthquake mw 7 7 which ruptured a 90 km segment of the plate boundary along the japan trench inverting observed seismogram envelopes at 10 strong motion stations in japan it is concluded that above 90 of the high frequency energy was radiated from the western half of the fault with the largest energy radiation near the deep side edge the rupture velocity is estimated to be 2 7 km s the estimated site amplification factors ranging between 0 3 and 15 are consistent with those independently estimated by the coda normalization method

heterogeneity of the 1980 izu hanto toho oki earthquake rupture process summary the rupture process of the 1980 izu hanto toho oki japan earthquake is examined by inverting strong motion seismic waveform records synthetic seismograms for waveform inversion are calculated using the empirical green s function technique after selecting the optimum small events for the empirical green s function the rupture starting time moment release and rise time at each sub fault are estimated in this procedure the results are as follows in the northern part of the fault surface where the swarm activity occurred the rupture propagation is irregular less moment is released and the rise time is short the local stress drop distribution is also estimated using the results of the inversion it is found that the heterogeneities of the rupture propagation moment release distribution and stress drop distribution have some relation to the geological setting in this area or to the seismic swarm activity

high stress drops of short period subevents from the 1968 tokachi oki earthquake as observed on strong motion records strong motion records of the 1968 tokachi oki earthquake were examined and two very high stress drop subevents were identified the first subevent had been previously located by nagamune 1969 and the second subevent was located in this study using p waves recorded on short period wwssn records estimates of source parameters revealed small source dimensions 1 per cent of the aftershock area and very high dynamic and static stress drops in the kilobar range for both of the subevents it is suggested that these subevents are important in driving the main rupture of this earthquake the two subevents also produced the dominant accelerations on the strong motion records and it is shown that high peak accelerations 150 to 200 cm sec2 were recorded even at relatively large distances 100 to 200 km

source tomography by simulated annealing using broad band surface waves and geodetic data application to the mw 8 1 chile 1995 event summary we invert surface wave and geodetic data for the spatio temporal complexity of slip during the mw 8 1 chile 1995 event by simulated annealing this quasi global inversion method allows for a wide exploration of model space and retains the non linearity of the source tomography problem complex source spectra are obtained from 5 to 45 mhz from first and second orbit fundamental mode rayleigh waves using an empirical green s function cross correlation technique coseismic displacement vectors were measured at 10 gps sites near antofagasta they are part of a french chilean experiment which monitors the northern chile seismic gap the spectra together with the geodetic data are inverted for the moment distribution on a 2 d dipping fault under the physical constraints of slip positivity and causality marginal a posteriori distributions of the model parameters are obtained from several independently inverted solutions in general features of the slip model are well resolved data are well fitted by a purely unilateral southward rupture with a nearly uniform velocity around 2 5 3 0 km s 1 and a total duration of 65 s several regions of moment release were imaged one near the hypocentre a major one 80 km south of it and a minor one 160 km south of it the major patch of moment release seemed to have propagated to relatively shallow depths near the trench 100 km ssw of the epicentre the region of major slip is located updip of the 1987 mw 7 5 earthquake suggesting a causal relationship most of the slip occurred updip of the hypocentre 36 km but the entire coupled plate interface 20 40 km ruptured during the chile 1995 event

waveform inversion using abic for the rupture process of the 1983 hindu kush earthquake abstract an inversion method was developed to infer earthquake rupture process from far field velocity waveforms we devise a source model that has variable slip and variable rupture velocity the fault plane is divided into many subfaults slip amplitude is assumed to be dependent on the subfaults and slip velocity at a point is assumed to be a triangle function of time rupture time is expressed by an interpolation equation using the rupture times at the corners of the subfaults the slip distribution and the rupture front motion are estimated by constrained least squares inversion we incorporate smoothing constraints on slip distribution and on rupture propagation into the observed data the degree of the constraints is controlled by hyperparameters the optimal values of the hyperparameters are determined by minimizing akaike s bayesian information criterion abic under the assumption of abic we can obtain a unique solution with reasonable resolution we apply this inversion method to the hindu kush earthquake of 30 december 1983 with a depth of 212 km we found that the rupture process of this earthquake was composed of two subevents the first subevent occurs near the initiation point of the rupture the centre of the second subevent region is approximately 20 km to the west of the first subevent the released moment of the second subevent is about seven times larger than that of the first subevent

that s why it s called interpretation impact of horizon uncertainty on seismic attribute analysis in the late 1960s early 1970s seismic stratigraphy revolutionized the petroleum industry by providing an objective meaningful technique for describing the stratigraphic record and predicting the distribution of potential reservoir source and seal facies within the last 10 years the uses of seismic data have evolved from sequence interpretation and qualitative assessment of reservoir trends to evaluations that include more quantitative prediction of reservoir properties throughout the industry seismic attribute analysis has become a commonly utilized tool for quantitative evaluation of reservoir properties from seismic data

influence of fault plane heterogeneity on the seismic behavior in the southern kurile islands arc the seismic behavior in the southern kurile islands arc is strongly influenced by spatial heterogeneity in the mechanical properties of the plate interface maps showing sites of maximum seismic moment release for the great underthrusting earthquakes of 1958 1963 1969 and 1973 provide a first order image of the major regions of enhanced strength or asperities hypocenters of these and an additional 83 smaller earthquakes with mb 5 3 and known underthrusting mechanisms were recomputed using the method of joint hypocenter determination in order to assess better the influence that the strength distribution exerts on the interplate seismicity patterns nearly all of the smaller magnitude earthquakes locate outside of the principal asperities of the great earthquakes this observation is consistent with substantial release of accumulated strain energy in asperity regions during the great earthquakes and a redistribution of stress in adjacent areas following their rupture an along dip depth dependent component of strength heterogeneity appears to influence the seismicity patterns the asperities of the 1958 and 1973 great earthquakes and hypocenters of most of the ms 7 earthquakes occur near the downdip edge of the 100 km wide seismically active plate interface this would be expected if shear resistance on the interface increases monotonically with lithostatic pressure up to the brittle ductile or stick slip stable slip transition that defines the base of the seismogenic zone the asperities of the 1963 and 1969 earthquakes however appear to be located well above the downdip edge of the coupled plate interface the occurrence of large asperities in middepth ranges of the seismogenic interface suggests the influence of along dip changes in other parameters besides lithostatic pressure that control shear resistance along strike segmentation of the kurile islands thrust zone may be a consequence of along strike alternation in the location of the largest asperities between the deep interface and the midinterface

inversion of intermediate period rayleigh waves for source characteristics of the 1968 tokachi oki earthquake a least squares inversion technique was applied to rayleigh waves with periods of 10 25 s to determine the distribution of moment release within the source region of the 1968 tokachi oki earthquake the inversion procedure attempts to produce synthetic seismograms which match the data by solving for the amount of moment generated from each point of a grid spaced at 40 km the data were recorded on low gain mechanical seismometers that were located 70 200 km from the source region assuming simple unilateral and bilateral rupture models the inversion was run for different values of constant rupture velocity resulting in a best fit to the data at 3 0 3 1 km s for both models the calculated surface wave synthetics depended strongly on the crustal velocity model by using a velocity structure obtained from a refraction survey the waveforms of the synthetics became significantly different depending on whether we used discontinuities or linear gradients to connect the depth points for which the survey gives a refractor p velocity neither a structure of only discontinuities nor a structure of only gradients was found to produce satisfactory synthetics therefore an intermediate structure with a linear gradient near the surface and discontinuities below was used the results of the inversion show that the data can be modeled with a source consisting of two strong subevents which dominate the radiation of these surface waves the relative location of the two subevents is consistent with the locations of the two subevents of high stress drop that were seen on strong motion records

the sanriku oki japan earthquake of december 28 1994 mw 7 7 rupture of a different asperity from a previous earthquake fault geometry depth and slip distribution of the sanriku oki earthquake of december 28 1994 ms 7 5 are estimated from seismic waveforms geodetic measurements and tsunami waveforms and compared with those of the 1968 tokachi oki earthquake mw 8 2 the most recent large earthquake in the epicentral region seismic wave inversions indicate a shallowly dipping thrust type mechanism and the focal depth of 22 28 km representing an underthrust event at the subduction interface the source time function has an initial stage of 20 s followed by a main pulse of 30 s duration a shape similar to that of the 1968 tokachi oki earthquake joint inversion of geodetic and tsunami data shows that the region of the largest slip 1 7 m corresponds to a region of relatively small slip for the 1968 tokachi oki earthquake furthermore the joint inversion shows that the region of the largest asperity of the 1968 earthquake had essentially zero slip during the 1994 sanriku oki earthquake these results indicate that the dominant asperities ruptured by the 1994 sanriku and 1968 tokachi oki earthquakes are different the result of the joint inversion also shows that the aseismic zone near the japan trench was not ruptured by the 1994 earthquake

high heat geodynamic setting during the palaeozoic evolution of the mount painter province sa australia evidence from combined field structural geology and potential field inversions