exploiting the airwave for time lapse reservoir monitoring with csem on land in the application of controlled source electromagnetics for reservoir monitoring on land repeatability errors in the source will mask the time lapse signal due to hydrocarbon production when recording surface data close to the source we demonstrate that at larger distances the airwave will still provide sufficient illumination of the target the primary airwave diffuses downward into the earth and then is scattered back to the surface the time lapse difference of its recorded signal reveals the outline on the surface of the resistivity changes in a hydrocarbon reservoir under production however repeatability errors in the primary airwave can destroy the signal to noise ratio of the time lapse data we present a simple and effective method to remove the primary airwave from the data which we call partial airwave removal for a homogeneous half space and a delta function type of source the surface expression of the airwave does not depend on frequency for this reason the primary airwave can be subtracted from the data using recordings at two frequencies one low enough with a skin depth of the order of the reservoir depth that is sensitive to the reservoir the other high enough to only sense the near surface the method does not affect secondary airwave components created by signals that have propagated through the earth and returned to the surface we show that the method provides a direct indicator of production related time lapse changes in the reservoir we illustrate this for several models including a general 3d heterogeneous model and one with strong surface topography for situations where survey repeatability errors are large

the fallacy of the shallow water problem in marine csem exploration the recent explosion of activity in offshore controlled source electromagnetic csem exploration has shown both theoretically and in practice for the time harmonic case that shallow water environments depths less than say 300 m can pose a significant challenge for detection and characterization of thin resistive targets in the subsurface because the weakly attenuated atmospheric response overprints the weaker target response as an alternative the transient csem experiment is considered to explore the nature of the airwave signature when viewed from the perspective of csem time series the signature of a thin isolated resistive horizon is computed by using the quasi analytic solution for a 1d earth in response to excitation by a horizontal electric dipole antenna that signature clearly seen in the transient data generally lies in the time interval between the arrivalof the airwave and the late time seawater response the fact that either decreasing the water depth or increasing the source r

dislocation models of interseismic deformation in the western united states 1 the gps derived crustal velocity field of the western united states is used to construct dislocation models in a viscoelastic medium of interseismic crustal deformation the interseismic velocity field is constrained by 1052 gps velocity vectors spanning the 2500 km long plate boundary zone adjacent to the san andreas fault and cascadia subduction zone and extending 1000 km into the plate interior the gps data set is compiled from u s geological survey campaign data plate boundary observatory data and the western u s cordillera velocity field of bennett et al 1999 in the context of viscoelastic cycle models of postearthquake deformation the interseismic velocity field is modeled with a combination of earthquake sources on 100 known faults plus broadly distributed sources models that best explain the observed interseismic velocity field include the contributions of viscoelastic relaxation from faulting near the major plate margins viscoelastic relaxation from distributed faulting in the plate interior as well as lateral variations in depth averaged rigidity in the elastic lithosphere resulting rigidity variations are consistent with reduced effective elastic plate thickness in a zone a few tens of kilometers wide surrounding the san andreas fault saf system primary deformation characteristics are captured along the entire saf system eastern california shear zone walker lane the mendocino triple junction the cascadia margin and the plate interior up to 1000 km from the major plate boundaries

an elastic plate model for interseismic deformation in subduction zones geodetic observations of interseismic surface deformation in the vicinity of subduction zones are frequently interpreted using simple kinematic elastic dislocation models edm in this theoretical study we develop a kinematic edm that simulates plate subduction over the interseismic period the elastic subducting plate model espm having only 2 more degrees of freedom than the well established back slip model bsm an elastic plate thickness and the fraction of flexural stresses due to bending at the trench that are released continuously unlike the bsm in which steady state deformation in both plates is assumed to be negligible the espm includes deformation in the subducting and overriding plates owing to plate thickness while still preserving the correct sense of convergence velocity between the subducting and overriding plates as well as zero net steady state vertical offset between the two plates when integrated over many seismic cycles the espm links elastic plate flexure processes to interseismic deformation and helps clarify under what conditions the bsm is appropriate for fitting interseismic geodetic data at convergent margins we show that the espm is identical to the bsm in the limiting case of zero plate thickness thereby providing an alternative motivation for the bsm the espm also provides a consistent convention for applying the bsm to any megathrust interface geometry even in the case of nonnegligible plate thickness the deformation field predicted by the espm reduces to that of the bsm if stresses related to plate flexure at the trench are released either continuously and completely at shallow depths during the interseismic period or deep in the subduction zone below 100 km however if at least a portion of these stresses are not continuously released in the shallow portion of the subduction zone via seismic or aseismic events then the predicted surface velocities of these two models can differ significantly at horizontal distances from the trench equivalent to a few times the effective interseismic locking depth

oblique convergence and deformation along the kuril and japan trenches the hypothesis that present day deformation within the southern kuril forearc is driven by oblique subduction of the pacific plate is tested using 397 horizontal slip directions derived from shallow thrust earthquakes from the kuril and japan trenches for the period 1963 1991 a simple two plate model fits the 397 slip vectors significantly worse than a model that permits strike slip motion of the southern kuril forearc relative to the overlying plate weighted mean slip directions along the southern kuril trench are systematically rotated toward the direction orthogonal to the trench which implies that the net convergence is partitioned into less oblique subduction and trench parallel displacement of the southern kuril forearc the angular discrepancy between the observed slip direction and the direction predicted by the nuvel 1 pacific north america euler vector implies that the southern kuril forearc translates 6 11 mm yr 1 to the southwest relative to the overlying north american plate these results are consistent with geologically geodetically and seismologically observed convergence at the leading edge of the forearc sliver in southern hokkaido and with previously inferred extension at the trailing edge of the sliver which is located at the bussol strait at 46 n the percentage of the oblique component of the rigid plate convergence vector that is transferred into forearc strike slip motion is only 30 which may be evidence that the hokkaido honshu bend in the trench hinders southwest forearc motion or that the greater strength of oceanic forearcs impedes motion along forearc strike slip faults

post seismic and interseismic fault creep ii transient creep and interseismic stress shadows on megathrusts we use idealized subduction megathrust models to examine aseismic frictional fault creep throughout the interseismic period we consider rate dependent and rate and state dependent friction when there is significant post seismic creep surrounding locations of coseismic slip the creep rates surrounding an asperity may be lower than the plate convergence rate late in the seismic cycle this lowering of the creep rates is due to stress shadows forming around the interseismically locked asperities the size of the stress shadows increases as there is more transient post seismic creep larger asperities produce larger interseismic stress shadows and multiple asperities can act together to produce a stress shadow larger than the sum of the effects of the individual asperities for rate state frictional megathrusts there is a wide range of transient post seismic creep that occurs from pulses of post seismic creep with decreasing creep rates through time to delayed post seismic creep delayed post seismic creep may occur well into the interseismic period with transient creep lasting over a significant portion of the seismic cycle delayed post seismic creep is generally favoured in velocity strengthening regions with either a larger magnitude of the frictional direct effect or a larger effective normal stress in addition regions of the fault undergoing delayed post seismic creep must be above steady state following coseismic slip

source model of the 2007 mw 8 0 pisco peru earthquake implications for seismogenic behavior of subduction megathrusts we use interferometric synthetic aperture radar teleseismic body waves tsunami waveforms recorded by tsunameters field observations of coastal uplift subsidence and runup to develop and test a refined model of the spatiotemporal history of slip during the mw 8 0 pisco earthquake of 15 august 2007 our preferred solution shows two distinct patches of high slip one patch is located near the epicenter while another larger patch ruptured 60 km further south at the latitude of the paracas peninsula slip on the second patch started 60 s after slip initiated on the first patch we observed a remarkable anticorrelation between the coseismic slip distribution and the aftershock distribution determined from the peruvian seismic network the proposed source model is compatible with regional runup measurements and open ocean tsunami records from the latter data set we identified the 12 min timing error of the tsunami forecast system as being due to a mislocation of the source caused by the use of only one tsunameter located in a nonoptimal azimuth the comparison of our source model with the tsunami observations validate that the rupture did not extend to the trench and confirms that the pisco event is not a tsunami earthquake despite its low apparent rupture velocity 1 5 km s we favor the interpretation that the earthquake consists of two subevents each with a conventional rupture velocity 2 4 km s the delay between the two subevents might reflect the time for the second shock to nucleate or alternatively the time it took for afterslip to increase the stress level on the second asperity to a level necessary for static triggering the source model predicts uplift offshore and subsidence on land with the pivot line following closely the coastline this pattern is consistent with our observation of very small vertical displacement along the shoreline when we visited the epicentral area in the days following the event this earthquake represents to our knowledge one of the best examples of a link between the geomorphology of the coastline and the pattern of surface deformation induced by large interplate ruptures

geodetic imaging of plate motions slip rates and partitioning of deformation in japan 1 interseismic deformation in japan results from the combined effects of tectonic processes including rotation of crustal blocks and the earthquake cycle process of elastic strain accumulation about upper plate faults and subduction zone interfaces we use spherical linear block theory constrained by geodetic observations from densely spaced global positioning system gps stations to estimate plate motions fault slip rates and spatially variable interplate coupling on the japan kuril sagami and nankai subduction zones the reference model developed in this paper consists of 20 blocks produces a mean residual velocity magnitude of 1 84 mm yr at 950 stations and accounts for 96 of the observed interseismic deformation signal we estimate fault slip rates in excess of 15 mm yr along the niigata kobe tectonic zone and itoigawa shizuoka tectonic line through central japan confirming their hypothesized roles as major tectonic boundaries oblique convergence across the nankai trough is partitioned with 3 4 of the 30 mm yr of trench parallel motion accommodated by strike slip motion on the subduction interface and the remaining 1 4 accommodated by right lateral slip on the median tectonic line in contrast our models suggest negligible slip partitioning in eastern hokkaido where oblique slip on the japan kuril subduction interface accommodates all of the trench parallel component of relative plate motion inferred spatial variations in the rake and magnitude of slip deficit on subduction zone interfaces reflect the influences of megathrust geometry and earthquake cycle processes such as enhanced elastic strain accumulation about seismic asperities and coseismic sense fault motion indicative of silent slip events or afterslip following large earthquakes

an asperity model for fault creep and interseismic deformation in northeastern japan we explore the potential geodetic signature of mechanical stress shadows surrounding inferred major seismic asperities along the japan kurile subduction megathrust such stress shadows result from a decrease in creep rates late in the interseismic period we simplify the rupture history along this megathrust as the repeated rupture of several asperities each with its own fixed recurrence interval in our models megathrust creep throughout the interseismic period evolves according to velocity strengthening friction as opposed to common kinematic back slip models of locked or partially locked i e coupled regions of the megathrust such backslip models are usually constrained by onshore geodetic data and typically find spatially extensive and smooth estimates of plate coupling a likely consequence of model regularization necessitated by poor model resolution of course these large coupled regions could also correspond to seismogenic asperities some of which have not experienced a significant earthquake historically a subset of existing kinematic models of coupling along the japan trench particularly those that use both horizontal and vertical geodetic data have inferred a surprisingly deep 100 km locked zone along the megathrust or have called upon complex poorly constrained megathrust processes such as subduction erosion to explain the geodetic observations here we posit two scenarios for distributions of asperities on a realistic 3 d megathrust interface along the japan kurile trench off ne japan these scenarios reflect common assumptions made before and after the 2011 m w 9 tohoku oki earthquake we find that models that include two shallow m9 class asperities one corresponding to the 2011 tohoku oki earthquake and one offshore of hokkaido and associated stress shadows can explain geodetic observations of interseismic strain along the eastern halves of honshu and hokkaido specifically models including localized fault creep can explain most of the observed long term vertical subsidence in this region during the past century and thus appealing to processes such as deep locking or subduction erosion may not be required

post seismic and interseismic fault creep i model description we present a model of localized aseismic fault creep during the full interseismic period including both transient and steady fault creep in response to a sequence of imposed coseismic slip events and tectonic loading we consider the behaviour of models with linear viscous non linear viscous rate dependent friction and rate and state dependent friction fault rheologies both the transient post seismic creep and the pattern of steady interseismic creep rates surrounding asperities depend on recent coseismic slip and fault rheologies in these models post seismic fault creep is manifest as pulses of elevated creep rates that propagate from the coseismic slip these pulses feature sharper fronts and are longer lived in models with rate state friction compared to other models with small characteristic slip distances in rate state friction models interseismic creep is similar to that in models with rate dependent friction faults except for the earliest periods of post seismic creep our model can be used to constrain fault rheologies from geodetic observations in cases where the coseismic slip history is relatively well known when only considering surface deformation over a short period of time there are strong trade offs between fault rheology and the details of the imposed coseismic slip geodetic observations over longer times following an earthquake will reduce these trade offs while simultaneous modelling of interseismic and post seismic observations provide the strongest constraints on fault rheologies

interseismic coupling and asperity distribution along the kamchatka subduction zone 1 gps measurements of interseismic horizontal surface velocities reveal the degree of kinematic coupling of the plate boundary thrust along the kamchatka subduction zone from about 51 degrees to 57 degrees n latitude inversions for the distribution of aseismic slip rate along the similar to 15 degrees nw dipping underthrust suggest a nonslipping plate interface in southern kamchatka above similar to 50 km depth along the segment that ruptured in the m w 9 1952 earthquake north of similar to 53 degrees n the subduction interface experiences significant aseismic slip consistent with the lower seismic moment release in m 8 5 earthquakes along this portion of the subduction zone the gps velocities are consistent with a boundary element forward model in which historic earthquake rupture zones are represented as locked asperities surrounded by a zero shear stress subduction interface loaded by plate convergence models in which the complete rupture zones of historic earthquakes are considered locked greatly overpredict the degree of kinematic coupling reducing the area of the locked model asperities to the central 25 area of historic rupture zones fits the data well suggesting that large earthquakes involve small fully locked core asperities surrounded by conditionally stable portions of the plate interface areas of low aseismic slip rate appear to be roughly correlated with areas of low isostatic gravity anomalies over offshore forearc basins while less coupled portions of the kamchatka subduction zone coincide with high gravity anomalies offshore of two peninsulas possibly related to the subduction of the emperor meji seamount chain and the kruzenstern fracture zone

interplate coupling beneath ne japan inferred from three dimensional displacement field 1 the northeastern japan arc is located in a typical subduction zone and is a seismically active region where large interplate earthquakes have occurred repeatedly the nationwide gps network has made it possible to investigate the crustal deformation in unprecedented detail however vertical displacements are less accurate than the horizontal ones and have not been used to constrain interplate coupling models in this study gps carrier phase data are analyzed in order to estimate three components of site displacements the result indicates uplift along the japan sea coast and subsidence along the pacific ocean coast using the vertical site velocities together with the horizontal ones as the data for a geodetic inversion method a new model of interplate coupling is constructed to explain both the horizontal and vertical velocities for the interseismic period from 1997 to 2001 the model demonstrates strong coupling in the area off miyagi and in the area off aomori through the area off tokachi including the areas of asperities the downdip limit of the locked fault zone on the plate boundary has been estimated seismologically to be at a depth of 50 60 km in northeastern japan and the distribution of slip deficits derived in this study indicates that the transition zone extends down to a depth of about 100 km

optimizing em data acquisition for continental shelf exploration the controlled source electromagnetic csem method has been applied to oil and gas exploration and production for more than 10 years during this time most of the focus has been on derisking deep and ultradeep water drilling decisions in this article we will consider how em methods can be optimized for continental shelf applications which represent approximately 80 of offshore discoveries historically applications of em on the continental shelf have been limited for two principal reasons

effects of the airwave in time domain marine controlled source electromagnetics in marine time domain controlled source electromagnetics csem there are two different acquisition methods with horizontal sources for fast and simple data acquisition or with vertical sources for minimizing the effects of the airwave illustrations of the electric field as a function of space and time for various source antenna orientations based on analytical formulation of the electric field in two half spaces provide insights into the properties of the airwave and the nature of diffuse electric fields observing the development of the electric field over time and space reveals that diffusive fields exhibit directionality therefore techniques that have thus far mostly been applied to wavefields can be adapted for csem examples range from the well known up down decomposition to beam steering vertical sources have the advantage of not creating an airwave on the other hand it is quite difficult to achieve perfect verticality of the source antenna results using a numerically modeled data set to analyze the impact of the airwave on a signal from a subsurface reservoir in the case of a slightly dipping vertical source indicate that already for a dip of 0 05 the airwave contributes 20 to the complete electric field in our configuration of reservoir depth water thickness and conductivity values

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

structural factors controlling the coseismic rupture zone of the 1973 nemuro oki earthquake the southern kuril trench seismogenic zone 1 the kuril trench is an active seismogenic zone where historic great earthquakes have occurred repeatedly with temporal and spatial regularities this paper presents the results of a wide angle ocean bottom seismographic obs survey across the coseismic rupture zone of the 1973 nemuro oki earthquake mw 7 8 together with thermal modeling the main purpose of this study is to understand the crustal and thermal controls on the kuril seismogenic zone revealing structures that can be controlling factors of a megathrust earthquake helps in estimating earthquake hazards we focus specifically on the precise structure of the seismogenic interface our imaged subduction structure clearly indicates that the coseismic rupture of the 1973 event occurred between the subducting oceanic crust and the kuril island arc crust at 15 30 km depth a thermally determined updip limit of the seismic rupture 100 c corresponds to the seismically determined updip limit 15 km depth an analysis of amplitude variations of wide angle reflections demonstrated a highly reflective plate interface immediately trenchward of the coseismic rupture zone shallower than 15 km depth while a weakly reflective interface is observed at the coseismic rupture zone from the observed amplitude variation with offsets a thin low velocity layer 4 5 km s is observed at the top of the highly reflective interface this suggests the presence of fluid which would indicate weak coupling updip of the rupture zone we also deduced from these observations that a weakly reflective interface in the coseismic slip zone represents a strongly coupled zone pending the next megathrust earthquake

the shikotan earthquake of october 4 1994 lithospheric earthquake a large m w 8 2 earthquake occurred off shikotan is one of the kurile is on october 4 1994 we inverted 32 body wave records to determine the rupture pattern using an iterative deconvolution method the mechanisms of the subevents were allowed to vary during rupture the source parameters obtained are the location of the initial break 43 48 n 147 40 e the centroid depth 56 km strike dip rake 49 75 125 for the total source the seismic moment m o 2 6 10 21 nm m w 8 2 source time duration t 42 s the average rupture velocity 2 5 km s we also determined the mechanism using long period love and rayleigh waves from 14 stations the solution for a finite source distributed over a depth range from 0 to 90 km is strike dip rake 54 76 129 with mo 2 3 10 21 nm in good agreement with that from body waves referring to the extent of the aftershock area and the subevent distribution we estimated the fault area s 120 60 km the average slip d 5 6m and the stress drop 11 mpa we computed synthetic waveforms as well as static displacements using either the steep or the low angle plane as the fault plane and found that the steep dip fault model fits the data better our result the mechanism large centroid depth high stress drop strongly suggests that the 1994 shikotan earthquake is a lithospheric earthquake an intra plate event that ruptures through a substantial part of the subducting oceanic lithosphere this type of lithospheric earthquake is relatively common

splitting marine controlled source electromagnetic responses into sea and subseafloor contributions grounding the air wave abstractwe have found how the effects of the air wave in marine controlled source electromagnetic csem methods gradually vanish in the sea for shallow waters and how at the same time they gradually grow below the seafloor in an effort to comprehend existing detectability definitions the transition from sea to land is smooth because the sea becomes a thin conductive layer when the water depth is smaller than the skin depth in the sea we consider the problem of detecting resistive layers at depth associated with hydrocarbon reservoirs particularly in shallow water explorations and specifically on how the air wave affects detection our analysis is based on an integral representation of the electric field in terms of its sensitivity to changes in the electrical conductivity of a 1d profile two dimensional images of the integrands are obtained by plotting the integrand as a function of depth for different offsets results include the expected growth of the inhibiting effect of the sea as the water d

towards inferring earthquake patterns from geodetic observations of interseismic coupling ultimately seismotectonic studies seek to provide ways of assessing the timing magnitude and spatial extent of future earthquakes ample observations document the spatial variability in interseismic coupling defined as a degree of locking of a fault during the period of stress build up between seismic events fully or nearly locked fault patches are often surrounded by aseismically creeping areas however it is unclear how these observations could help assess future earthquakes here we simulate spontaneous seismic and aseismic fault slip with a fully dynamic numerical model our simulations establish the dependence of earthquake rupture patterns and interseismic coupling on spatial variations of fault friction we consider the long term evolution of slip on a model fault where two seismogenic locked segments are separated by an aseismically slipping patch where rupture is impeded we find that the probability for a large earthquake to break through the rupture impeding patch is correlated with the interseismic coupling averaged over this patch in addition the probability that an earthquake breaks through the rupture impeding patch and interseismic coupling are both related to fault friction properties through a single non dimensional parameter our study opens the possibility of predicting seismic rupture patterns that a fault system can produce on the basis of observations of its interseismic coupling and suggests that regions of low interseismic coupling may reveal permanent barriers to large earthquakes

on the mechanics of earthquake afterslip we propose a model for earthquake afterslip based on rate and state variable friction laws in the model afterslip is attributed to the interaction of a velocity weakening region at depth within which earthquakes nucleate with an upper region of velocity strengthening frictional behavior the existence of this upper region is supported by independent seismologic observations and the results of laboratory friction experiments in our model afterslip is the result of relaxation of a stress perturbation within the velocity strengthening region which arises when an earthquake propagates into that region from below we derive the stress perturbation and its decay from the friction constitutive law using a simple 1 degree of freedom approximation for the elastic interaction between the fault and its surroundings this approximation is based on thickness averaged displacements and slip velocities within the velocity strengthening region which is assumed to slip as a rigid block coseismic and postseismic slip are coupled through the thickness averaged stiffness k of the velocity strengthening region we assume k to be inversely proportional to the thickness of this region which means that thicker velocity strengthening regions have a greater tendency to arrest coseismic slip we model the afterslip time histories of the 1966 parkfield and 1987 superstition hills earthquakes and relate the model parameters to physical parameters which may govern the rheologic behavior of the faults in accord with field observations our model predicts 1 that afterslip on some faults scales with the thickness of the unconsolidated sedimentary cover and 2 that proportionally more afterslip occurs for earthquakes in which coseismic surface slip is small compared with coseismic slip at depth velocity strengthening frictional behavior is to be expected for faults within poorly consolidated sediments and for those that contain significant gouge zones about 500 m within their shallow regions 3 5 km combining our results with those of recent laboratory friction studies indicates that relatively young faults with little accumulated fault gouge should exhibit little afterslip

randomness of megathrust earthquakes implied by rapid stress recovery after the japan earthquake the 2011 tohoku oki earthquake released stress within a subduction zone analysis of seismic data shows that stresses returned to pre quake levels within a few years implying that large quakes could occur more often than previously thought

use of marine controlled source electromagnetic sounding for sub basalt exploration the problem of imaging sedimentary structure obscured by high velocity layers such as carbonate basalt or salt using conventional seismic techniques is well known when this problem is encountered in offshore areas marine electromagnetic data can provide valuable alternative and complementary constraints on the structure we concentrate on the use of marine controlled source electromagnetic csem sounding in the frequency domain the feasibility of mapping sub basalt sedimentary structure using this technique is explored by means of modelling studies which mimic a type of survey which could readily be employed in practice as a starting point the problem is addressed in terms of 1d resistivity structure we show that sub basalt sediments can be detected and their depth of burial quantified to within 200 m in the examples shown the presence of small scale inhomogeneities in the basalt which cause much of the scattering in seismic data is shown to have no appreciable effect on the ability of the csem data to detect the sediments the modelling is then extended to 2 5 dimensions again the presence of sub basalt sediments can be readily detected and their properties and geometry quantified especially if the electromagnetic data are combined with constraints from complementary geophysical techniques

deep crustal reflectors under reydarfjordur eastern iceland crustal accretion above the iceland mantle plume summary deep seismic reflection profiling on the faroe iceland ridge experiment fire imaged a sequence of dipping events in the upper to crust beneath the tertiary lava pile in reydarfjordur eastern iceland these events dip towards the spreading centre at which the crust was formed and continue down to 6 s two way time corresponding to depths down to 15 18 km similar crustal reflections have been observed previously within the crust in other areas of iceland although the reflective events located by previous surveys have not been interpreted rigorously in this study we calculate synthetic seismograms from modelled sequences of lava flows to examine the reflective character of a lava le the synthesized lava pile sections are based on field measurements made in the reydarfjordur area the 1 km vertical exposures on the sides of the fjord are composed of lava flows within stratigraphic units which have a range of compositions and some intercalated tuffaceous clastic horizons we compare the synthetic seismograms with our seismic reflection data to test the interpretation that the deep dipping reflections are caused by a gently dipping sequence of subaerially erupted lavas we conclude that the upper and mid crustal reflections that we observe can be interpreted as lava flow sequences similar to those seen at the surface with the main reflections resulting from packets of flows of similar thicknesses the reflectors that we have imaged beneath iceland are similar to those defining the seaward dipping reflectors on the volcanic continental margins and we therefore suggest that the seaward dipping reflections commonly result from packets of lavas with similar distributions of thicknesses the occurrence of lavas down to 15 18 km beneath reydarfjordur can be explained partly by multiple episodes of accretion of the upper crust although the volcanic processes forming the crust in iceland generally lead to advection of extrusive material to mid crustal levels the production of an average extrusive layer totalling 15 km thickness is within reasonable estimates of the current volcanic productivity the advection of frozen lava flows to mid crustal levels contributes to the maintenance of the subsolidus crust that is observed on iceland and the zeolite minerals within the extrusive sequence may be responsible for the crustal low resistivity zone that has been observed using magnetotelluric techniques

transient and permanent deformation of central japan estimated by gps 1 interseismic loading and subduction kinematics abstract we analyze continuous global positioning system gps data to estimate the kinematics of the philippine sea plate subduction below southern central japan using a back slip dislocation model we invert the strain rate tensors derived from the gps velocity field to obtain the velocity of the downgoing slab with respect to the tokai and kanto forearcs along the eastern nankai suruga and sagami troughs respectively in both cases these velocities are smaller and slightly rotated with respect to the philippine sea plate subduction velocity in central nankai this result implies strain partitioning between the subduction thrusts and on land and or offshore deformation zones in both the eastern nankai suruga and the sagami area in southern kanto we predict 20 mm yr 1 of dextral shear in agreement with motion observed along the boso strike slip fault in the tokai region the slip deficit accumulated since the last earthquake 1854 ranges between 6 and 3 m considering the extent of the locked zone it would correspond to a magnitude m w 8 15 earthquake if the slip deficit were to be released now during a single event

late quaternary glacial and sedimentary history of bonavista bay northeast newfoundland high resolution seismic profiles and core data from bonavista bay northeast newfoundland show that the sedimentary package above acoustic basement was deposited during the deglaciation of the late wisconsinan ice sheet during the late wisconsinan maximum 20 000 bp bonavista bay was occupied by a grounded ice sheet that extended farther offshore deglaciation of the bay was rapid and occurred prior to 13 500 bp during a time of rising sea level a basal till was deposited beneath the grounded ice and after lift off an ice shelf developed over the outer basins where diamicton was deposited the inner bay gradually deglaciated as the ice margin retreated to the present day shoreline by 13 000 bp and fine grained outwash sediments transported by interflows were rapidly deposited the inner bay remained under the influence of one or more remnant ice centres until 10 000 bp with ice positioned on the bonavista and gander peninsulas normal marine conditions were established in the outer bay by

vertical deformation of the japanese islands 1996 1999 1 the interseismic vertical deformation field of the japanese islands is derived from the global positioning system gps data between 1996 and 1999 although vertical components of the gps velocities have rarely been used as important information because of their higher noise level information on the vertical deformation field will enable us to separate rigid plate motions from deformation due to interplate coupling because horizontal displacements contain both effects whereas vertical displacements contain only the interplate coupling effect the results show that 1 the precision of the vertical velocity is generally better than 2 mm yr 2 the existence of clear uplift peaks of about 8 mm yr in the shikoku and tokai regions is consistent with strong coupling with a gradual brittleplastic transition zone at the nankai and the suruga trough respectively 3 clear uplift peaks do not seem to exist in the tohoku region because the japan trench plate boundary is too far oceanward from the gps sites 4 significant uplift is obtained in the western part of hokkaido which may be associated with the long term postseismic deformation due to the 1983 japan sea and the 1993 hokkaido nansei oki m 7 6 earthquakes and 5 uplift in northeastern japan along the japan sea coast is apparently associated with distributed compression due to incipient subduction

small interseismic asperities and widespread aseismic creep on the northern japan subduction interface the canonical model of fault coupling assumes that slip is partitioned into fixed asperities that display stick slip behavior and regions that creep stably we show that this simple asperity model is inconsistent with gps derived deformation in northern japan associated with interseismic coupling on the subduction interface and the transient response to mw 6 3 7 2 earthquakes during 2003 2011 comparisons of gps data with simulations of earthquakes on asperities and associated velocity strengthening afterslip require that afterslip overlaps areas of the fault that ruptured in previous earthquakes including the 2011 mw 9 tohoku oki earthquake whereas about 55 of the plate interface ruptured in earthquakes during 2003 2011 we infer that only 9 of the plate interface was fully locked between earthquakes inferred locked asperities are roughly 25 the size of rupture areas determined by seismic source inversions these smaller asperities are consistent with interseismic strain accumulation in 2009 although more extensive locking is required a decade earlier in 1998

source process of the mw 8 3 2003 tokachi oki japan earthquake and its aftershocks summary investigation of the sh wave seismograms indicates that rupture occurred on a shallowly dipping fault propagating in all directions from the hypocentre the average rupture velocity in the downdip and updip directions are 2 0 3 and 1 0 km s 1 respectively the maximum slip is found to be 12 m and is located downdip of the earthquake s hypocentre taken over the fault as a whole the average stress drop is 0 55 mpa used in conjunction with relocated aftershocks we find that two barriers constrain the faulting extent of slip creating a rupture area of 165 km 140 km these barriers coincide with submarine topographic features are domain boundaries for the seismic gaps along the arc and have high concentrations of large aftershocks near them the high slip regions align with the orientation of the subducting plate and resemble in size and shape the many seamounts about to subduct the 2003 tokachi oki earthquake was the largest earthquake to occur globally in that year and reruptured the portion of the kuril japan trench that last broke in the great tokachi oki earthquake of 1952 hamada suzuki 2004 the abundance of local data in this region coupled with the large magnitude of the event has led to a range of models for the rupture being proposed these solutions are summarised in table 1 all of these solutions have the total moment for the earthquake significantly below that obtained from the long period seismological data by the global cmt gcmt solution with some solutions having less than one third of the gcmt moment this study aims to address this anomaly by first investigating the long period moment tensor solution and then by finding a rupture model which is consistent with both broad band teleseismic data and the long period solution

heterogeneous coupling of the sumatran megathrust constrained by geodetic and paleogeodetic measurements geodetic and paleogeodetic measurements of interseismic strain above the sumatran portion of the sunda subduction zone reveal a heterogeneous pattern of coupling annual banding in corals provides vertical rates of deformation spanning the last half of the 20th century and repeated gps surveys between 1991 and 2001 and continuous measurements at gps stations operated since 2002 provide horizontal velocities near the equator the megathrust is locked over a narrow width of only a few tens of kilometers in contrast the locked fault zone is up to about 175 km wide in areas where great interplate earthquakes have occurred in the past formal inversion of the data reveals that these strongly coupled patches are roughly coincident with asperities that ruptured during these events the correlation is most spectacular for rupture of the m w 8 7 nias simeulue earthquake of 2005 which released half of the moment deficit that had accumulated since its previous rupture in 1861 suggesting that this earthquake was overdue beneath the mentawai islands strong coupling is observed within the overlapping rupture areas of the great earthquakes of 1797 and 1833 the accumulated slip deficit since these events is slowly reaching the amount of slip that occurred during the 1833 earthquake but already exceeds the slip that occurred during the 1797 earthquake thus rerupture of part of the mentawai patch in september 2007 was not a surprise in contrast coupling is low below the batu islands near the equator and around enggano island at about 5 s where only moderate earthquakes m w 8 0 have occurred in the past two centuries the correlation of large seismic asperities with patches that are locked during the interseismic period suggests that they are persistent features this interpretation is reinforced by the fact that the large locked patches and great ruptures occur beneath persistent geomorphologic features the largest outer arc islands depth and convergence rate dependent temperature might influence the pattern of coupling through its effect on the rheology of the plate interface but other influences are required to account for the observed along strike heterogeneity of coupling in particular subduction of the investigator fracture zone could be the cause for the low coupling near the equator

lipid biogeochemistry of plankton settling matter and sediments in trinity bay newfoundland i lipid classes abstract seawater settling particles and sediments were sampled in trinity bay a fjord like bay on the east coast of newfoundland to determine the nature and rates of lipid inputs at the height of the spring bloom diatom triacylglycerol storage increased in response to lowered nitrate and silicate concentrations this was followed by increased concentrations of phospholipids which coincided with biomass increases in dinoflagellates and zooplankton sediment trap results from 50 100 m show that planktonic lipids appear to be transferred with little alteration through the water column to benthic and demersal food webs fluxes are high especially in spring and incorporation into the food web seems to be very efficient with little loss through burial in the sediments much higher lipid concentrations are seen in sediments closer to shore where terrestrial plants are likely to be an important contributor to the lipids the sediment trap results also show that the use of poisons can cause an overestimation of fluxes of some acyl lipid classes while leaching during deployment may cause an underestimation of fluxes of most lipid classes

spatial correlation of interseismic coupling and coseismic rupture extent of the 2011 mw 9 0 tohoku oki earthquake 1 imaging the extent to which the rupture areas of great earthquakes coincide with regions of pre seismic interplate coupling is central to understanding patterns of strain accumulation and release through the earthquake cycle both geodetic and seismic estimates of the coseismic rupture extent for the march 11 2011 mw 8 9 9 0 earthquake tohoku oki earthquake may be spatially correlated 0 26 0 05 to 0 82 0 05 with a region estimated to be partially to fully coupled in the interseismic period preceding the earthquake though there is substantial variation in the estimated distribution and magnitude of coseismic slip the 400 km long region estimated to have slipped 4 m corresponds to an area of the subduction zone interface that was coupled at 30 of long term plate convergence rate with peak slip near a region coupled 80 the northern termination of rupture is collocated with a region of relatively low 20 interseismic coupling near the epicenter of the 1994 mw 7 6 sanriku oki earthquake and near a region of potential long term low coupling or ongoing slow slip slip on the subduction interface beneath the coastline 40 50 km depth is best constrained by the land based gps data and least constrained on the shallowest portion of the plate interface due to the 230 km distance between geodetic observations and the japan trench

remote sensing of hydrocarbon layers by seabed logging sbl results from a cruise offshore angola detecting and assessing hydrocarbon reservoirs without the need to drill test wells is of major importance to the petroleum industry seismic methods have traditionally been used in this context but the results can be ambiguous another approach is to use electromagnetic sounding methods that exploit the resistivity differences between a reservoir containing highly resistive hydrocarbons and one saturated with conductive saline fluids modeling presented by eidesmo et al 2002 demonstrates that by using seabed logging sbl a special application of frequency domain controlled source electromagnetic csem sounding the existence or otherwise of hydrocarbon bearing layers can be determined and their lateral extent and boundaries can be quantified such information provides valuable complementary constraints on reservoir geometry and characteristics obtained by seismic surveying

independent active microplate tectonics of northeast asia from gps velocities and block modeling 1 independent okhotsk and amurian microplate motions are tested using velocities from 123 gps sites 80 from within the proposed okh and amu plate boundaries used to constrain the plate kinematics of northeast asia a block modeling approach is used to incorporate both rigid block rotation and near boundary elastic strain accumulation effects in a formal inversion of the gps velocities models include scenarios with and without independent okh and amu plate motion our modeling favors scenarios with independent okh and amu motion based on the application of f test statistics the independent okh plate rotates 0 231 deg myr clockwise with respect to north america about a pole located north of sakhalin the modeled amu plate rotates 0 298 deg myr counterclockwise with respect to nam about a pole located west of the magadan region the plate motion parameters of the independent plates are consistent with the kinematics inferred from earthquake focal mechanism solutions along their boundaries

controlled electromagnetic sources for measuring electrical conductivity beneath the oceans 1 forward problem and model study exact closed form expressions for the electromagnetic induction fields produced by vertical and horizontal current sources in the conducting ocean overlying a one dimensional earth are derived from the maxwell equations numerical methods for the evaluation of the solutions are given including correction for the finite size of real sources simple models of the electrical conductivity structure of the ocean crust and lithosphere are deduced from geologic petrologic and laboratory data and their electromagnetic response is modeled horizontal electric dipole sources produce much larger field amplitudes than their vertical counterparts for a given frequency and range and the horizontal electric field offers superior received signal performance reflections of electromagnetic waves from the sea surface and thermocline must be considered for low enough frequencies or long ranges estimates of the ambient noise level from natural electromagnetic sources in the frequency range 0 01 10 hz are presented the ability of controlled sources to determine features of the conductivity of the ocean crust and upper mantle especially low conductivity zones is demonstrated if the mantle conductivity is low enough horizontal ranges of 50 km and conductivity estimates to over 20 km depth can be achieved

space time distribution of afterslip following the 2003 tokachi oki earthquake implications for variations in fault zone frictional properties 1 gps time series following the september 25 2003 ut tokachi oki earthquake m w 8 0 reveal significant deformation we use the network inversion filter to invert for the spatial and temporal evolution of afterslip in the 30 days following the earthquake afterslip is concentrated adjacent to the coseismic rupture zone between the 2003 rupture and the inferred source regions of the 1968 tokachi oki and the 1973 nemuro oki earthquakes the inversion shows a rapid decay of slip rate in the 2003 rupture zone with slower deceleration in the surrounding regions the stress velocity paths for the afterslip regions approximately follow d d in v 0 6 mpa suggestive of steady state velocity strengthening friction the complementary spatial pattern of coseismic rupture and afterslip may indicate along strike spatial variations of frictional properties although other interpretations can not be ruled out

interseismic uplift at the nankai subduction zone southwest japan 1951 1990 uplift as a function of time from 1951 through 1990 has been deduced from annual mean sea level measured at 15 tide gages along the nankai subduction zone southwest japan the recurrence interval for rupture of the nankai subduction zone is about 100 years and the most recent rupture was in late 1946 thus the 1951 1990 uplift record covers most of the first half of the earthquake cycle the precision of the uplift record is better than could be obtained currently by annual global positioning system gps measurements the pre 1960 uplift record shows rapid deformation that appears to terminate in 1959 after 1959 the uplift record is remarkably linear in time significant curvature in the uplift versus time plots is detected at only three of the 15 tide gages the inferred uplift rates are not quantitatively consistent with the predictions of either the viscoelastic coupling or elastic half space models of subduction but the agreement is sufficient to suggest that the causative physical mechanisms have been identified the immediate postseismic response is controlled by the propagation of slip downward along the downdip extension of the coseismic rupture and the interseismic response is caused by the accumulation of a slip deficit on the main thrust zone asthenosphere relaxation is not required to explain the observations

frictional afterslip following the 2005 nias simeulue earthquake sumatra continuously recording global positioning system stations near the 28 march 2005 rupture of the sunda megathrust moment magnitude m w 8 7 show that the earthquake triggered aseismic frictional afterslip on the subduction megathrust with a major fraction of this slip in the up dip direction from the main rupture eleven months after the main shock afterslip continues at rates several times the average interseismic rate resulting in deformation equivalent to at least a m w 8 2 earthquake in general along strike variations in frictional behavior appear to persist over multiple earthquake cycles aftershocks cluster along the boundary between the region of coseismic slip and the up dip creeping zone we observe that the cumulative number of aftershocks increases linearly with postseismic displacements this finding suggests that the temporal evolution of aftershocks is governed by afterslip

space geodetic observation of deep basal subduction erosion in northeastern japan abstract observation of tectonic erosion von huene and scholl rev geophys 29 1991 279 316 in a subduction zone has been difficult as it leaves little geological and geophysical evidence three dimensional velocity profiles of crustal movement obtained by global positioning system across ne and sw japan agree well with those predicted by the elastic loading of the subducting slabs however vertical velocities in the ne japan forearc show significant negative deviation relative subsidence this may indicate loss of material at the plate interface that can be attributed to the erosion of the upper plate by the underthrusting slab basal subduction erosion the estimated rate 15 mm yr down to a slab depth of 90 km is somewhat faster than the geological average the erosion speed may be variable being controlled by the surface roughness of subducting slabs

the 2011 magnitude 9 0 tohoku oki earthquake mosaicking the megathrust from seconds to centuries geophysical observations from the 2011 moment magnitude m w 9 0 tohoku oki japan earthquake allow exploration of a rare large event along a subduction megathrust models for this event indicate that the distribution of coseismic fault slip exceeded 50 meters in places sources of high frequency seismic waves delineate the edges of the deepest portions of coseismic slip and do not simply correlate with the locations of peak slip relative to the m w 8 8 2010 maule chile earthquake the tohoku oki earthquake was deficient in high frequency seismic radiation a difference that we attribute to its relatively shallow depth estimates of total fault slip and surface secular strain accumulation on millennial time scales suggest the need to consider the potential for a future large earthquake just south of this event

frictional slip of granite at hydrothermal conditions sliding on faults in much of the continental crust likely occurs at hydrothermal conditions i e at elevated temperature and elevated pressure of aqueous pore fluids yet there have been few relevant laboratory studies to measure the strength sliding behavior and friction constitutive properties of faults at hydrothermal conditions we slid laboratory granite faults containing a layer of granite powder simulated gouge velocity stepping experiments were performed at temperatures of 23 to 600 c pore fluid pressures ph2o of 0 dry and 100 mpa wet effective normal stress of 400 mpa and sliding velocities v of 0 01 to 1 m s 0 32 to 32 m yr conditions were similar to those in earlier tests on dry granite to 845 c by lockner et al 1986 the mechanical results define two regimes the first regime includes dry granite up to at least 845 and wet granite below 250 c in this regime the coefficient of friction is high 0 7 to 0 8 and depends only modestly on temperature slip rate and ph2o the second regime includes wet granite above 350 c in this regime friction decreases considerably with increasing temperature temperature weakening and with decreasing slip rate velocity strengthening these regimes correspond well to those identified in sliding tests on ultrafine quartz we infer that one or more fluid assisted deformation mechanisms are activated in the second hydrothermal regime and operate concurrently with cataclastic flow slip in the first cool and or dry regime is characterized by pervasive shearing and particle size reduction slip in the second hot and wet regime is localized primarily onto narrow shear bands adjacent to the gouge rock interfaces weakness of these boundary shears may result either from an abundance of phyllosilicates preferentially aligned for easy dislocation glide or from a dependence of strength on gouge particle size major features of the granite data set can be fit reasonably well by a rate and temperature dependent three regime friction constitutive model chester this issue we extrapolate the experimental data and model fit in order to estimate steady state shear strength versus depth along natural slipping faults for sliding rates as low as 31 mm yr we do this for two end member cases in the first case pore pressure is assumed hydrostatic at all depths shallow crustal strength in this case is similar to that calculated in previous work from room temperature friction data while at depths below about 9 13 km depending on slip rate strength becomes less sensitive to depth but sensitive to slip rate in the second case pore pressure is assumed to be near lithostatic at depths below 5 km strength is low at all depths in this case 20 mpa in agreement with observations of weak faults such as the san andreas the predicted depth of transition from velocity weakening to velocity strengthening lies at about 13 km depth for a slip rate of 31 mm yr in rough agreement with the seismic aseismic transition depth observed on mature continental faults these results highlight the importance of fluid assisted deformation processes active in faults at depth and the need for laboratory studies on the roles of additional factors such as fluid chemistry large displacements higher concentrations of phyllosilicates and time dependent fault healing

enhanced subsurface response for marine csem surveying one of the main challenges of using marine controlled source electromagnetic csem sounding for hydrocarbon detection has been a relatively low resolution and restricted depth penetration in addition the use of csem in shallow waters has been perceived as particularly difficult a new robust method for enhancing marine csem subsurface response is particularly useful in shallow waters the method is designed to reduce acquisition imprints and attenuate the dominant primary airwave contribution synthetic examples show that it is possible to detect thin deeply buried 3d resistive bodies in a shallow water environment with a complex resistivity structure the results highlight the importance of a sufficient signal to noise ratio

lipid biogeochemistry in the laurentian trough ii changes in composition of fatty acids sterols and aliphatic hydrocarbons during early diagenesis abstract interfacial sediments of the 300 m deep laurentian trough contained 3 2 11 1 2 6 2 0 4 2 4 0 2 0 5 mg g 1 oc of fatty acids unresolved hydrocarbons ucm sterols and resolved aliphatic hydrocarbons respectively reflecting a 46 93 loss relative to settling particles intercepted at 150 m depth a further 22 66 lipid loss was observed between 0 3 and 35 cm depth in the sediments lipid accumulation efficiencies in the top 3 cm sediment inventory averaged 21 29 of water column fluxes and indicated a clear reactivity trend pheopigments sterols fatty acids total lipids resolved hydrocarbons ucm however within each lipid class marine derived components were as highly reactive as pheopigments whereas terrestrial compounds behaved akin to the ucm extremely labile marine lipids that were enriched in settling particles such as pristane 24 methylcholesta 5 22e dien 3 ol and heneicosahexaene were quickly lost near the sediment water interface only moderately reactive components 16 0 16 1 fatty acids squalene and the more stable 22 0 and 24 0 acids fichtelite and ucm persisted deep enough to preserve the geographical trends observed for rapidly settling particles i e predominance of terrestrial and petrogenic compounds at a landward site and prevalence of marine lipids at a station located 120 km further seaward the preferential decay of marine components continued with depth in the cores resulting in similar residual lipid patterns at 35 cm depth however each site could still be discriminated clearly by its fatty acid and hydrocarbon composition in situ sedimentary processes such as the vertical distribution of bacteria and the production of coprostanol were also recorded in the lipid composition of these deep coastal sediments

a physical model for interseismic erosion of locked fault asperities the conventional asperity model posits that faults are partitioned into fixed velocity weakening vw patches asperities that are locked interseismically and velocity strengthening vs regions that creep stably without accumulating stress however studies of gps derived deformation in northern japan have shown that interseismic strain in the tohoku region did not accumulate at a constant rate as expected but gradually decreased from 1996 to 2011 this change in strain rate is consistent with locked asperities shrinking by 75 in area during this period here we consider a modification to the conventional asperity model such that thermal pressurization tp is active over an area that encompasses a vw region and part of the surrounding vs region in our quasi dynamic simulations tp causes shear stress during rapid slip to decrease to very low levels during the interseismic period stress gradually recovers to steady state friction at the plate rate at which point stable creep initiates the creep front propagates inward effectively eroding the locked asperity for uniform properties the locked area shrinks roughly linearly in time through the vs region locked asperities shrink more slowly with higher nominal friction coefficient or background effective normal stress in the vs region lower hydraulic diffusivity and larger tp zones lateral heterogeneity in properties can give rise to nonlinear erosion predictions from this model can be compared against gps data to test whether the model can explain the observed changes in interseismic strain rate in tohoku

focused source electromagnetic survey versus standard csem 3d modeling in complex geometries a novel focused source electromagnetic fsem method focusestheemfieldintheverticaldirectiontoprovidedeepreadingresistivitydata fsemoffersbetterspatialresolution and greater depth of investigation than the conventional controlled source electromagnetic csem method for land and marine em surveys we have proven the high efficiency of fsem by analyzing 3d models of various complex geologic formations in the presence of seafloor bathymetry shallow resistive gas hydrate overburdens and secondary gas reservoirs formed above deeper oil reservoirs combining the powerofourfocusingtechniquewiththepowerofour3dnumerical modeling method we have developed exceptionally challenging test cases to conclude that fsem automatically cancels unwanted shallow effects and allows simple visual interpretationofdeepreservoirresponses inaddition fsem is insensitive to imperfections in the setup geometry we achievetheseadvantagesusingapropercombinationofmeasurementsacquiredinthereceiverexcitedbytransmitterssituated at different space points the method is promising in anisotropicformationsaswell

fault plane geometry in the source region of the 1994 sanriku oki earthquake abstract we present the results of a seismic refraction experiment conducted off eastern aomori northeastern japan forearc region where the detailed crustal structure was poorly known an objective analysis using high quality survey data allowed us to obtain the seismic velocity structure to about 30 km depth and in particular to obtain a well constrained geometry of the plate boundary in the source region of the 1994 sanriku oki earthquake our results show that the subducting pacific oceanic plate increases its dip from about 5 to approximately 15 around the longitude of 143 5 e 80 km landward of the trench axis near the latitude of 40 n the location of this bend in the plate is 40 km east of the bending point previously proposed on the basis of hypocenter distribution a cluster of aftershocks of the 1994 sanriku oki earthquake occurred around the bending point this is because the bending of the subducting plate appears to affect the stress state in the vicinity of the plate boundary furthermore the plate geometry is also considered to be related to the coupling or slip features along the plate boundary as the bending point correlates with the spatial distribution of repeating earthquakes our results will lead to more reliable determinations of asperity areas because an accurate dip angle of the fault plane is necessary for slip distribution studies

numerical simulation of recurrence of asperity rupture in the sanriku region northeastern japan 1 a numerical simulation study is presented for the recurrence of great earthquakes and aseismic sliding in the sanriku region northeastern japan where the pacific plate subducts beneath northern honshu and m8 class earthquakes have occurred approximately every 100 years the friction on the plate interface is assumed to obey a rate and state dependent friction law and the spatial distribution of constitutive parameters of the friction law is estimated so that the simulated slip histories mimic those estimated from seismic and geodetic observations by introducing two large asperities that have velocity weakening frictional properties earthquakes similar to the 1968 tokachi oki earthquake mw 8 2 and the 1994 sanriku oki earthquake mw 7 7 can be modeled the former broke both the large asperities and the latter broke one of them the ruptures of the two simulated large earthquakes started from almost the same location and their nucleation processes are similar to each other two smaller asperities were introduced to represent smaller earthquakes one of the small asperities is for the largest aftershock mw 6 9 of the 1994 sanriku oki earthquake which was located westward from the 1994 main shock area and took place 10 d after the main shock the present simulation suggests that the largest aftershock was triggered by stress caused by propagation of postseismic sliding in the simulation the area of greatest intensity of postseismic sliding is located in the region between the main shock slip area and the largest aftershock area which is consistent with the estimation from gps data analyses for the postseismic sliding of the 1994 sanriku oki earthquake some important characteristics of seismic and aseismic processes as estimated from observations are reproduced in the model this suggests that spatially nonuniform frictional properties on the plate interface can be estimated to some extent by comparison between model results and observed data

extensional structure in northern honshu arc as inferred from seismic refraction wide angle reflection profiling a recent extensive seismic wide angle experiment revealed a new image of crustal and uppermantle structure across northern honshu arc japan the western part of the arc recorded the crustal deformation by the miocene back arc spreading of the sea of japan the crust is composed of highly deformed tertiary sedimentary layers a relatively low velocity 5 75 5 9 km s crystalline basement and a 15 km thick lower crust with a velocity of 6 6 7 0 km s clear westward crustal thinning from 32 to 27 km represents the extensional deformation by the backarc spreading the crust attains the maximum thickness 32 35km east of the backbone range for which the magmatic intrusion underplating since 10 15 ma is a predominant factor the eastern part of the arc has a less deformed upper crust and a reflective middle lower crust probably remaining a stable block since the time of the backarc spreading

what controls interplate coupling evidence for abrupt change in coupling across a border between two overlying plates in the ne japan subduction zone article i nfo interplate coupling in the southernmost extent of the northeast japan subduction zone east off kanto japan is investigated in detail using a large data set of small repeating earthquakes in this region of the trench trench trench type triple junction the subducting pacific plate is in contact with two different overlying plates the north american and philippine sea plates the border between the two overlying plates extending northwestward from the triple junction is identified along the upper surface of the pacific plate based on the slip vectors of many interplate events including small repeating earthquakes the interplate coupling coefficient estimated from the cumulative slip of small repeating earthquakes for the period from 1993 to 2007 reveals a distinct change from south ca 0 3 to north ca 0 7 across the border this border also corresponds to the southern limit of the source areas of mn7 interplate earthquakes in the last 80 years along the japan trench again indicating the stronger coupling to the north we also investigate hypocenter distribution and seismic velocity structure along the plate boundary from a large number of travel time data obtained from the nationwide seismograph network the results reveal a distinct low velocity zone just above the pacific plate and low seismicity along the plate boundary in the region overlain by the philippine sea plate whereas there are no low velocity zones and the seismicity is high in the region overlain by the north american plate these observations imply that the geological difference of overlying plate controls large scale coupling at the plate interface

structural characteristics off miyagi forearc region the japan trench seismogenic zone deduced from a wide angle reflection and refraction study abstract the japan trench subduction zone located east of ne japan has regional variation in seismicity many large earthquakes occurred in the northern part of japan trench but few in the southern part off miyagi region is in the middle of the japan trench where the large earthquakes m 7 with thrust mechanisms have occurred at an interval of about 40 years in two parts inner trench slope and near land a seismic experiment using 36 ocean bottom seismographs obs and a 12 000 cu in airgun array was conducted to determine a detailed 2d velocity structure in the forearc region off miyagi the depth to the moho is 21 km at 115 km from the trench axis and becomes progressively deeper landward the p wave velocity of the mantle wedge is 7 9 8 1 km s which is typical velocity for uppermost mantle without large serpentinization the dip angle of oceanic crust is increased from 5 6 near the trench axis to 23 150 km landward from the trench axis the p wave velocity of the oceanic uppermost mantle is as small as 7 7 km s this low velocity oceanic mantle seems to be caused by not a lateral anisotropy but some subduction process by comparison with the seismicity off miyagi the subduction zone can be divided into four parts 1 seaward of the trench axis the seismicity is low and normal fault type earthquakes occur associated with the destruction of oceanic lithosphere 2 beneath the deformed zone landward of the trench axis the plate boundary is characterized as a stable sliding fault plain in case of earthquakes this zone may be tsunamigenic 3 below forearc crust where p wave velocity is almost 6 km s and larger this zone is the seismogenic zone below inner trench slope which is a plate boundary between the forearc and oceanic crusts 4 below mantle wedge the rupture zones of thrust large earthquakes near land e g 1978 off miyagi earthquake are located beneath the mantle wedge the depth of the rupture zones is 30 50 km below sea level from the comparison the rupture zones of large earthquakes off miyagi are limited in two parts plate boundary between the forearc and oceanic crusts and below mantle wedge this limitation is a rare case for subduction zone although the seismogenic process beneath the mantle wedge is not fully clarified our observation suggests the two possibilities earthquake generation at the plate boundary overridden by the mantle wedge without serpentinization or that in the subducting slab

controlled source electromagnetic sounding in shallow water principles and applications the marine controlled source electromagnetic csem method is being applied to the problem of detecting and characterizing hydrocarbons in a variety of settings until recently its use was confined to deepwater water depths greater than approximately 300 m because of the interaction of signals with the atmosphere in shallower water depths the purpose of this study was to investigate using a simple 1d analytical analysis the physics of csem in shallow water this approach demonstrates that it is difficult to simply decouple signals that have interacted with the earth from those that have interacted with the air using either frequency domain or time domain methods stepping away from wavelike approaches which if applied without care can be misleading for the diffusive fields of csem we demonstrate an effective way to mitigate the effect of the air in shallow water surveys by decomposing the em signal into modes and using only the mode least affected by interaction with the atmosphere such decompos

fault stability inferred from granite sliding experiments at hydrothermal conditions seismicity on crustal faults is concentrated in the depth interval 1 3 to 12 15km tse and rice 1986 suggested that the lower bound on seismicity is due to a switch with increasing temperature from velocity weakening destabilizing to velocity strengthening stabilizing friction they inferred this transition from friction data for dry granite however pore fluids exist at elevated temperatures throughout the crust and may strongly influence strength and sliding behavior we present new data from sliding experiments on granite at elevated t 23 to 600 plus elevated ph2o 100 mpa our results show velocity strengthening at room temperature but velocity weakening from 100 to 350 c except at 250 from 350 to 600 there are systematic trends from velocity weakening to strong velocity strengthening and from high to low friction neither trend was seen in tests on dry granite the velocity dependence data imply the potential for unstable slip in the interval 100 to 350 using a geotherm to map temperature to depth this interval closely matches the observed earthquake distribution

3d inversion of marine csem and mt data an approach to shallow water problem abstractthe application of the marine controlled source electromagnetic csem technique for shallow water hydrocarbon exploration is challenged by the effect of an airwave that masks the response from the reservoir at depth we applied gauss newton based 3d inversion method to synthetic csem and magnetotelluric mt data to demonstrate the capability of 3d inversion to recover thin resistive targets in shallow water environments the experiment on the model with water depth of 300 m shows that the target signals at 0 25 hz are significant enough to resolve the reservoir at a burial depth of 1 km for the given noise level 6 of the electric field amplitude for the 100 m water depth case the high resistivity zone recovered is located much deeper and thicker than the true reservoir suggesting that the airwave component obscures the target signal more seriously however inverting inline and broadside data together or adding inline data at a different frequency 0 1 hz is quite effective in improving t

the marine controlled source electromagnetic method in shallow water we analyzed marine controlled source electromagnetic csem acquisition in shallow water by analytic and numerical calculations the problem at hand was the fact that the amplitude of the airwave due to a horizontal electric dipole becomes larger as the water depth is reduced the amplitude of the scattered field from a buried thin resistor would be difficult to extract from the increased total field if the scattered field amplitude were independent of water depth however we identified and explained a compensating effect where the amplitude of the scattered field increases with reduced water depth this amplification effect makes marine csem surveys in shallow water feasible we derived an approximate expression for the total field for a simple but realistic conductivity model this expression explains why the amplitudes of the term that describes the background field contribution and the term that gives the scattered field from the thin resistor increase when the water depth is reduced our results and sensitivity analysis indicated that the sensitivity of marine csem data acquired in a water depth of 40 m is comparable to the sensitivity of marine csem data acquired in a water depth of 300 m

interplate seismogenic zones along the kuril japan trench inferred from gps data inversion stress accumulation between earthquakes results from slip that is insufficient to fully accommodate plate movement an inverse analysis of gps data from the kuril japan trench reveals a trench parallel belt of stress accumulation with six peaks in the depth range of 10 40 km suggesting potential source regions for future earthquakes in the subduction zones around japan where four plates interact with one another large earthquakes have occurred repeatedly1 these interplate earthquakes are part of the process of tectonic stress accumulation and release that is driven by relative plate motion2 3 4 stress accumulation between earthquakes results from slip deficit slip that is insufficient to fully accommodate plate movement for the prediction of large earthquakes it is therefore important to monitor the distribution of slip deficit on plate interfaces here we apply an inversion method based on bayesian modelling using direct and indirect prior information on the magnitude and distribution of fault slip5 to horizontal and vertical velocities from global positioning system data for the seismically calm period between 1996 and 2000 we obtain a precise distribution of slip deficit rates on the interface between the north american and pacific plates around japan which reveals a trench parallel belt of slip deficit with six peaks in the depth range of 10 40 km these peaks agree with the source regions of past large interplate earthquakes along the kuril japan trench we conclude that the slip deficit zones identified with our method are potential source regions of large earthquakes

a dislocation model of strain accumulation and release at a subduction zone strain accumulation and release at a subduction zone are attributed to stick slip on the main thrust zone and steady aseismic slip on the remainder of the plate interface this process can be described as a superposition of steady state subduction and a repetitive cycle of slip on the main thrust zone consisting of steady normal slip at the plate convergence rate plus occasional thrust events that recover the accumulated normal slip because steady state subduction does not contribute to the deformation at the free surface deformation observed there is completely equivalent to that produced by the slip cycle alone the response to that slip is simply the response of a particular earth model to embedded dislocations for a purely elastic earth model the deformation cycle consists of a coseismic offset followed by a linear in time recovery to the initial value during the interval between earthquakes for an elastic viscoelastic earth model elastic lithosphere over a viscoelastic asthenosphere the postearthquake recovery is not linear in time records of local uplift as a function of time indicate that the long term postseimic recovery is approximately linear suggesting that elastic earth models are adequate to describe the deformation cycle however the deformation predicted for amore simple elastic half space earth does not reproduce the deformation observed along the subduction zones in japna at all well if stick slip is restricted to the main thrust zone as recognized earlier by shimazaki seno and kato the uplift profiles could be explained if stick slips were postulated to extend along the plate interface beyond the main thrust zone to a depth of perhaps 100 km but independent evidence suggests that stick slip at such depths if unlikely less

optimized 3d synthetic aperture for controlled source electromagnetics locating offshore hydrocarbon reservoirs has become more challenging with smaller deeper or shallow water targets in complicated environments controlled source electromagnetics csem is a geophysical method used to find reservoirs in marine settings the diffusive nature of csem fields means that the signal from the target is only a small part of the total field to reduce the impact of the complicated settings and to improve the detecting capabilities of csem we have applied a synthetic aperture to csem data the synthetic aperture virtually increased the length and width of the csem source by combining the responses from multiple individual sources applying a weight to each source steered or focused the synthetic aperture source array in the inline and crossline directions we have developed an optimization method to find the optimal weights for synthetic aperture arrays that adapted to the information about the reservoirs in the csem data to demonstrate the benefits of a weighted synthetic aperture we have applied a 2d synthetic aperture array and a crossline only synthetic aperture array to noisy simulated electromagnetic fields both synthetic aperture arrays reduced the noise and increased the detectability of the modeled reservoirs when compared with the original csem response the crossline only synthetic aperture array also preserved the structural information within the measurements

seismic and aseismic slip on the central peru megathrust slip on a subduction megathrust can be seismic or aseismic with the two modes of slip complementing each other in time and space to accommodate the long term plate motions although slip is almost purely aseismic at depths greater than about 40 km heterogeneous surface strain suggests that both modes of slip occur at shallower depths with aseismic slip resulting from steady or transient creep in the interseismic and postseismic periods thus active faults seem to comprise areas that slip mostly during earthquakes and areas that mostly slip aseismically the size location and frequency of earthquakes that a megathrust can generate thus depend on where and when aseismic creep is taking place and what fraction of the long term slip rate it accounts for here we address this issue by focusing on the central peru megathrust we show that the pisco earthquake with moment magnitude m w 8 0 ruptured two asperities within a patch that had remained locked in the interseismic period and triggered aseismic frictional afterslip on two adjacent patches the most prominent patch of afterslip coincides with the subducting nazca ridge an area also characterized by low interseismic coupling which seems to have repeatedly acted as a barrier to seismic rupture propagation in the past the seismogenic portion of the megathrust thus appears to be composed of interfingering rate weakening and rate strengthening patches the rate strengthening patches contribute to a high proportion of aseismic slip and determine the extent and frequency of large interplate earthquakes aseismic slip accounts for as much as 50 70 of the slip budget on the seismogenic portion of the megathrust in central peru and the return period of earthquakes with m w 8 0 in the pisco area is estimated to be 250 years

seismic structure and seismogenesis off sanriku region northeastern japan summary in 1997 a seismic experiment using an airgun array and ocean bottom seismographs obss was performed in the forearc region of the northeastern japan nej arc the objectives of this experiment were to clarify seismic structures of the forearc region off sanriku japan using airgun obs data and to understand the nature of the japan trench seismogenic zone fundamental features of the structure are as follows i the subduction angle becomes steeper from east to west from 3 to 8 to 11 with the top of the plate located at depths of 11 km 40 km west from the trench 21 km 120 km west from the trench and 28 km 140 km west from the trench respectively ii the nej moho beneath the forearc is defined at a depth of approximately 20 km iii p wave velocity of the island arc upper mantle is approximately 8 km s 1 iv the p wave velocity of the cretaceous sedimentary layer exhibits significant lateral variability 4 0 5 5 km s 1 i nthe e w direction v the upper crust of nej forearc also has the significant lateral heterogeneity 5 0 6 3 km s 1 i nthe e w direction but not in the n s direction vi the middle crust defined on land extends in some locations 40 km east of the coastline vii lateral variability in the p wave velocity of the lower crust 6 7 7 0 km s 1 i ssmall compared with that of the upper crust according to these results it is suggested that the rupture areas of large earthquakes m7 in this region are limited within the contact zone between the nej arc crust and the subducting oceanic crust although a thin layer with low velocity is probably present within this contact zone the serpentinization of uppermost mantle wedge of the nej arc by reaction between the mantle materials and the water from the thin layer beneath forearc region is limited this might indicate that a significant volume of water and sediments subduct with the slab to depths of over 20 km

vertical vertical controlled source electromagnetic instrumentation and acquisition abstract vertical vertical controlled source electromagnetic is an alternative to other techniques for providing three dimensional resistivity images of the subsurface it utilizes a large and powerful vertical dipole transmitter and arrays of e field receivers with vertical and horizontal dipole sensors the necessary instrumentation and acquisition procedures which differ strongly from other controlled source electromagnetic methods are described in the paper

an introduction to marine controlled source electromagnetic methods for hydrocarbon exploration early development of marine electromagnetic methods dating back about 80 years was driven largely by defense military applications and use for these purposes continues to this day deepwater frequency domain electric dipole dipole controlled source electromagnetic csem methods arose from academic studies of the oceanic lithosphere in the 1980s and although the hydrocarbon exploration industry was aware of this work the shallow water environments being explored at that time were not ideally suited for its use low oil prices and increasingly successful results from 3d seismic methods further discouraged investment in costly alternative geophysical data streams these circumstances changed in the late 1990s when both statoil and exxonmobil began modeling studies and fieldtrials of csem surveying in deep water around 1000 m or deeper specifically for characterizing the resistivity of previously identified drilling targets trials offshore angola in 2000 2002 by both these companies showed that

decomposition of electromagnetic fields into upgoing and downgoing components this paper gives a unified treatment of electromagnetic em field decomposition into upgoing and downgoing components forconductiveandnonconductivemedia wheretheelectromagneticdataaremeasuredonaplaneinwhichtheelectricpermittivity magneticpermeability andelectricalconductivityareknown constants with respect to space and time above and below the plane of measurement the medium can be arbitrarily inhomogeneousandanisotropic in particular the proposed decomposition theory applies to marine em low frequency data acquired for hydrocarbon mapping where the upgoing components of the recordedfield guided and refracted from the reservoir that are of interest for the interpretation the direct source field the refracted airwave induced by the source the reflected field from the sea surface and most magnetotelluric noise traveling downward just below the seabed are field components that are considered to be noise in electromagneticmeasurements the viability and validity of the decomposition method is demonstrated using modeled and real marine em data also termed seabed logging sbl data the synthetic data are simulated in a model that is fairly representative of the geologic area wheretherealsblwerecollected theresultsfromthesynthetic data study therefore are used to assist in the interpretation of the realdatafromanareawith320 mwaterdepthaboveaknowngas province offshore norway the effect of the airwave is seen clearly in measured data after field decomposition just below the seabed the upgoing component of the recorded electric field has almost linear phase indicating that most of the effect of the airwavecomponenthasbeenremoved

geodetic imaging of potential seismogenic asperities on the xianshuihe anninghe zemuhe fault system southwest china with a new 3 d viscoelastic interseismic coupling model we use gps and interferometric synthetic aperture radar insar measurements to image the spatial variation of interseismic coupling on the xianshuihe anninghe zemuhe xaz fault system a new 3 d viscoelastic interseismic deformation model is developed to infer the rotation and strain rates of blocks postseismic viscoelastic relaxation and interseismic slip deficit on the fault surface discretized with triangular dislocation patches the inversions of synthetic data show that the optimal weight ratio and smoothing factor are both 1 the successive joint inversions of geodetic data with different viscosities reveal six potential fully coupled asperities on the xaz fault system among them the potential asperity between shimian and mianning which does not exist in the case of 1019 pa s is confirmed by the published microearthquake depth profile besides there is another potential partially coupled asperity between daofu and kangding with a length scale up to 140 km all these asperity sizes are larger than the minimum resolvable wavelength the minimum and maximum slip deficit rates near the moxi town are 7 0 and 12 7 mm yr respectively different viscosities have little influence on the roughness of the slip deficit rate distribution and the fitting residuals which probably suggests that our observations cannot provide a good constraint on the viscosity of the middle lower crust the calculation of seismic moment accumulation on each segment indicates that the songlinkou selaha s4 shimian mianning s7 and mianning xichang s8 segments are very close to the rupture of characteristic earthquakes however the confidence level is confined by sparse near fault observations

nucleation and early seismic propagation of small and large events in a crustal earthquake model 1 earthquake nucleation and early seismic propagation are studied in a two dimensional strike slip fault model with depth variable properties the fault is governed by the dieterich ruina rate and state friction law we use an efficient and rigorous numerical procedure for elastodynamic analysis of earthquake sequences on slowly loaded faults developed by lapusta et al 2000 we find that for decreasing values of the characteristic slip distance of the friction law small events appear at the transition from the locked to creeping behavior toward the bottom of the seismogenic zone small and large events have very similar nucleation phases in our simulations here by nucleation phase we mean gradually accelerating aseismic slip in a small slowly expanding zone before the breakout of the dynamic seismically detectable event moment acceleration to which velocity seismograms are proportional in early stages of seismic propagation exhibits irregular fluctuations in the form of speedups and slowdowns in the moment release rate consistently with observations as reported by ellsworth and beroza 1995 our simulations show that such irregular moment acceleration can at least in part be due to the heterogeneous stress distribution imprinted on the fault by the arrest of previous small events and by stress concentrations at the borders of creeping regions and to partial arrest of the rupture in velocity strengthening fault regions which inhibit seismic slip index terms 7209 seismology earthquake dynamics and mechanics 7260 seismology theory and modeling 3220 mathematical geophysics nonlinear dynamics 7230 seismology seismicity and seismotectonics 3230 mathematical geophysics numerical solutions 8164 tectonophysics stresses crust and lithosphere keywords earthquake nucleation phase event clustering irregular moment release stress concentrations rate and state friction earthquake sequences

a bayesian source model for the 2004 great sumatra andaman earthquake the 2004 m w 9 1 9 3 sumatra andaman earthquake is one of the largest earthquakes of the modern instrumental era despite considerable efforts to analyze this event the different available observations have proven difficult to reconcile in a single finite fault slip model in particular the critical near field geodetic records contain variable and significant postseismic signal between 2 weeks and 2 months worth while the satellite altimetry records of the associated tsunami are affected by various sources of uncertainties e g source rupture velocity and mesoscale oceanic currents in this study we investigate the quasi static slip distribution of the sumatra andaman earthquake by carefully accounting for the different sources of uncertainties in the joint inversion of available geodetic and tsunami data to this end we use nondiagonal covariance matrices reflecting both observational and modeling uncertainties in a fully bayesian inversion framework modeling errors can be particularly large for great earthquakes here we consider a layered spherical earth for the static displacement field nonhydrostatic equations for the tsunami and a 3 d megathrust interface geometry to alleviate some of the potential epistemic uncertainties the bayesian framework then enables us to derive families of possible models compatible with the unevenly distributed and sometimes ambiguous measurements we infer two regions of high fault slip at 3 n 4 n and 7 n 8 n with amplitudes that likely reach values as large as 40 m and possibly larger these values are a factor of 2 larger than typically found in previous studies potentially an outcome of commonly assumed forms of regularization finally we find that fault rupture very likely involved shallow slip within the resolution provided by the existing data we cannot rule out the possibility that fault rupture reached the trench

3 d simulation of steady plate subduction with tectonic erosion current crustal uplift and free air gravity anomaly in northeast japan free air gravity anomaly in plate subduction zones characterized by island arc high trench low and outer rise gentle high reflects the cumulative effects of long term crustal uplift and subsidence in northeast japan the island arc high of observed free air gravity anomaly takes its maximum about the eastern coastline on the other hand the current vertical crustal motion estimated from geological and geomorphological observations shows a gentle uplift in the land area and steep subsidence in the sea area with the neutral point near the eastern coastline such a discrepancy in spatial patterns between the free air gravity anomaly and current vertical crustal motion can be ascribed to a change in the mode of crustal uplift and subsidence associated with the initiation of tectonic erosion at the north american pacific plate interface we developed a realistic 3 d simulation model of steady plate subduction with tectonic erosion in northeast japan on the basis of elastic viscoelastic dislocation theory through numerical simulations with this model we found that simple steady plate subduction brings about the crustal uplift characterized by island arc high with its maximum about the eastern coastline while steady plate subduction with tectonic erosion which is represented by the landward retreat of the plate interface brings about gentle uplift in the land area and steep subsidence in the sea area with the neutral point near the eastern coastline therefore if we suppose that tectonic erosion started 3 4 million years ago after the long duration of simple steady plate subduction we can consistently explain both patterns of free air gravity anomaly and current crustal uplift in northeast japan

marine controlled source electromagnetic interferometry in marine controlled source electromagnetics a boat tows an electric source whose signal is travelling on various paths to the receiver stations at the ocean bottom unfortunately the signal does not only travel via the subsurface to the receivers but also directly through the water and via the air water interface signals travelling on the latter two travelpaths do not contain any information about the subsurface on the contrary they cover a possible response from a subsurface reservoir therefore one aims to suppress the signal travelling along those paths interferometry by multidimensional deconvolution replaces the overburden by a homogeneous halfspace suppressing any interactions with the air water interface furthermore the direct field is removed and the source is redatumed to a receiver position since interferometry by multidimensional deconvolution is a data driven method no information about the ocean or the subsurface is needed except the material parameters at the receiver level this thesis investigates the benefits and limitations of interferometry by multidimensional deconvolution applied to marine controlled source electromagnetic data

convenient formulas for determining dip slip fault parameters from geophysical observables abstract simple equations are presented for estimating slip magnitude fault dip angle width of the zone of compression and other co seismic parameters from geologic seismic and geodetic observations made in subduction zone and continental dip slip environments these equations are easy to memorize and use without computational aids

three methods for mitigating airwaves in shallow water marine controlled source electromagnetic data in the past several years marine controlled source electromagnetic mcsem techniques have been applied successfully in deep water depth 1 km for oil and gas exploration the application of this technology in shallow water is challenged however because of airwaves that mask the signal from the target reservoir at depth based upon the understanding that an airwave is a lateral wave which can be analytically expressed in a dual half space resistivity model we propose three airwave mitigation approaches to reduce the effects of these airwaves on mcsem data in the em x bucking approach the effect of the airwaves can be bucked out from two measurements by using the analytic expression of the airwave the frequency derivative de dfreq approach takes advantages of the unique characteristics of the airwaves in frequency domain enhancing the reservoir signals while suppressing the airwave the magnetotelluric mt stripping method uses the plane wave feature of the airwaves and subtraction of

static deformation of a uniform half space due to a long dip slip fault summary closed form expressions for the displacements and stresses at an arbitrary point of a homogeneous isotropic perfectly elastic half space caused by a dip slip line source obtained earlier are integrated analytically to derive the elastic residual field due to a long dip slip fault of finite width the results are valid for an arbitrary dip of the fault and for arbitrary receiver locations inside the medium the variation of the displacement and stress field with the distance from the fault is studied numerically contour maps showing the stress field around a long dip slip fault are obtained permanent surface deformations which occur as a result of faulting can be measured from geodetic surveys carried out before and after an earthquake these observations can be used to obtain the fault parameters dip slip width depth by inversion using the theoretical expressions given in the paper the features of the observational data which are diagnostic of the source properties are the asymmetry of the data the magnitude of various components of deformation and the rate of fall of these components with distance the asymmetry depends mainly on the dip the magnitude on the slip and the rate of fall on the depth of the fault

seismic consequences of warm versus cool subduction metamorphism examples from southwest and northeast japan warm and cool subduction zones exhibit differences in seismicity seismic structure and arc magmatism which reflect differences in metamorphic reactions occurring in subducting oceanic crust in southwest japan arc volcanism is sparse and intraslab earthquakes extend to 65 kilometers depth in northeast japan arc volcanism is more common and intraslab earthquakes reach 200 kilometers depth thermal petrologic models predict that oceanic crust subducting beneath southwest japan is 300 to 500 c warmer than beneath northeast japan resulting in shallower eclogite transformation and slab dehydration reactions and possible slab melting

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