seismic imaging of subduction zone metamorphism combined analysis of high resolution seismic images of the alaska and cascadia subduction zones reveals where metamorphic fl uids are released both images show the subducted oceanic crust as a dipping low velocity layer with a clear termination depth however in alaska the crust is thicker 15 20 km compared to 8 km and terminates at greater depth 120 km com pared to 40 km than in cascadia based on metamorphic reaction estimates and geodynamic models we demonstrate that the termination depth corresponds to eclogitization of the crust triggered by dehydration of water bearing minerals and that the location of this reaction is dependent on the thermal structure of the subducted slab

identifying time temperature and mineralogical effects on chemical compaction in shales by rock physics relations the seismic response of a shale is a direct result of the original mineral composition textural configuration at deposition and degree of compaction the aim of this article is to show how the compactional processes and mineralogical effects can be directly identified by rock physics techniques and to emphasize the importance of having a thorough geological understanding when doing rock physics analysis to succeed we must first understand the fundamental relationships between sedimentology the compactional processes and the expected rock physics response that are not restricted to a particular basin or data set to achieve this we used wireline logs from 100 wells on the mid norwegian shelf to establish robust rock physics background trends in shales that were compared with the local responses in and around a target area the target was the tulipan well in the southwestern part of the mid norwegian shelf where thick deposits from the glacial marine north sea fan are located

interpretation of porosity and lwd resistivity from the nankai accretionary wedge in light of clay physicochemical properties evidence for erosion and local overpressuring in this study we used porosity to assess the compaction state of the nankai accretionary wedge sediments and any implications for stress and pore pressure however hydrous minerals affect porosity measurements and accounting for them is essential toward defining the interstitial porosity truly representative of the compaction state the water content of sediments was measured in core samples and estimated from logging data using a resistivity model for shale we used the cation exchange capacity to correct the porosity data for the amount of water bound to clay minerals and to correct the porosity estimates for the surface conductivity of hydrous minerals the results indicate that several apparent porosity anomalies are significantly reduced by this correction implying that they are in part artifacts from hydrous minerals the correction also improves the fit of porosity estimated from logging while drilling lwd resistivity data to porosity measured on cores low overall porosities at the toe of the accretionary wedge and in the splay fault area are best explained by erosion and we estimated the quantity of sediments eroded within the splay fault area by comparing porosity effective stress relationships of the sediments to a reference curve additionally a comparison of lwd data with core data resistivity and p wave velocity obtained at site c0001 landward of the mega splay fault area suggested a contribution from the fracture porosity to in situ properties on the formation

quartz cementation in late cretaceous mudstones northern north sea changes in rock properties due to dissolution of smectite and precipitation of micro quartz crystals abstract late cretaceous mudstones from two wells located in the northern north sea and the norwegian sea have been examined with respect to quartz cement two different types of quartz cement type 1 and type 2 have been identified using sem eds cl analysis of drill bit cuttings at depths 2370 2670 m 80 85 c type 1 appears as relatively large aggregates 30 100 m of depth temperature related crypto or microcrystalline to macrocrystalline irregular quartz cement formed by local re crystallization of biogenic silica the cl responses of type 1 quartz cement give a clear indication of an authigenic origin type 2 quartz cement represents relatively high amounts of extremely fine grained micro sized 1 3 m crystals embedded as discrete short chains or small clusters nests within the illitized clay matrix the cl responses of micro quartz crystals indicate an authigenic origin the micro quartz is most probably sourced from silica released during the smectite to illite dissolution precipitation reaction the petrographic evidence indicates that most of the silica released by the smectite to illite reaction has not been exported out of the mudstones the silica released produce a subtle inter connected micro quartz network interlocked with aggregates of micro quartz and authigenic clay crystals this micro quartz cementation process causes a significant and sharp change in the mudstone stiffness at the onset of the chemical compaction regime this is indicated by an abrupt increase in well log velocity vp and change in seismic facies close to 2500 m 80 85 c

geometry of the subducted plate near kodiak island and lower cook inlet alaska determined from relocated earthquake hypocenters abstract using observations from 28 seismograph stations in southern alaska we have used the jhd method to relocate 341 well recorded events with focal depths beneath about 40 km which occurred between 56 4 n and 60 5 n and between 151 6 w and 156 5 w these hypocenters show that the wadati benioff zone has a dip of about 45 however its strike changes by about 15 beneath lower cook inlet at about 59 n near where the volcanic line also bends northward near this bend there is also a distinctly higher level of seismic activity than in the area to the southwest of 59 n a few events are situated about 20 km beneath the main wadati benioff zone in cook inlet and a focal mechanism we have determined for one of these differs from other mechanisms for events in this area focal mechanisms available from previous work show that at intermediate focal depths the area between 59 n and 60 5 n is controlled by horizontal north south compression and as such differs from the region to the southwest relying primarily on the observed change in strike and apparent thickness of the wadati benioff zone we interpret these data to suggest that the subducted lithophere separates into two distinct segments as it subducts beneath cook inlet because the direction of subduction is not perpendicular to the volcanic arc the events situated beneath the wadati benioff zone in cook inlet may be part of the southwestern plate segment although the geometry and available focal mechanisms for events beneath cook inlet are similar to what would be expected in a double wadati benioff zone we suggest instead that these observations result because we are at the boundary between two adjacent segments of the subducting plate

development and applications of double difference seismic tomography double difference dd tomography is a generalization of dd location it simultaneously solves for the three dimensional velocity structure and seismic event locations dd tomography uses a combination of absolute and more accurate differential arrival times and hierarchically determines the velocity structure from larger scale to smaller scale this method is able to produce more accurate event locations and velocity structure near the source region than standard tomography which uses only absolute arrival times we conduct a stability and uncertainty analysis of dd tomography based on a synthetic data set currently three versions of the dd tomography algorithms exist tomodd tomofdd and tomoadd tomodd assumes a flat earth model and uses a pseudo bending ray tracing algorithm to find rays between events and stations while tomofdd uses a finite difference travel time algorithm and the curvature of the earth is considered both codes are based on a regularly distributed inversion grid with the former for a local scale and the latter for a regional scale in contrast tomoadd adapts the inversion mesh to match with the data distribution based on tetrahedral and voronoi diagrams we discuss examples of applying dd tomography to characterize fault zone structure image high resolution structure of subduction zones and determine the velocity structure of volcanoes

ultrasonic velocity and anisotropy of hydrocarbon source rocks an experimental study of the physical properties of black kerogen rich shales also including maturation analysis scanning electron microscope sem observations and physical modeling revealed fairly peculiar petrophysical parameters specifically these rocks have very low porosity and density but most importantly both p and s ultrasonic velocities normal to bedding are extremely low whereas they are much higher parallel to bedding giving rise to a strong anisotropy even at high confining pressures we found that these parameters primarily reflect kerogen content microstructure and maturation level of these rocks we found also that microcracks inferred from ultrasonic velocity measurements occur only in mature shales these microcracks are parallel to the bedding plane and further enhance strong intrinsic anisotropy notably at low effective pressure our results show that on a small scale kerogen rich shales are transversely isotropic rocks and can be effectively modeled using the thin laye

revealing hydrocarbon migration pathways in this paper a general concept for revealing hydrocarbon migration pathways in rock sequences is introduced the concept uses a multidisciplinary approach based on a geochemical and a petrophysical or mineralogical index these two indices provide together the migration plot which shows the direction of hydrocarbon movement

alternatives to core mantle boundary topography abstract nuclear explosions at the french test sites in the south pacific have been recorded at the regional seismic networks in the western united states a total of approximately 600 good quality short period seismograms were selected from an initial set of 900 the dense receiver spacing particularly in california allows the division of the networks into numerous subarrays and the data from each subarray can be analysed using conventional array techniques such as beam forming and frequency wave number analysis the seismic rays provide dense sampling of a small area of the core mantle boundary cmb beneath the eastern pacific from 5 to 13 n and 133 to 126 w pcp has a shallow incidence angle on the cmb at an epicentral distance of 65 and d is sampled over a large swathe from 2 s to 24 n and from 134 to 123 w beam traces have been formed for the p and pcp phases for each of the subarrays using slowness and azimuth values derived from array methods good quality beams have been selected for further analysis by applying a matched filter to the beamed traces an accurate set of pcp p differential travel times has been determined and compared with iasp91 the residuals show a smooth trend over the area sampled for the given epicentral distances p and pcp have similar paths through the crust and upper mantle so we make the assumption that near source and near receiver structures have negligible effect on the differential times we also assume that the midmantle is relatively homogenous many previous studies have interpreted pcp p residuals in terms of cmb topography by mapping the residuals directly to topography a range in elevation of 40 km over a lateral extent of about 700 km results alternatively we attempted to interpret the residuals in terms of velocity heterogeneity in d a range of d models have been tested including lateral velocity variation in a d layer with constant thickness the pcp p residuals may be explained by allowing the p wave velocity to vary laterally by a factor of 2 over the region sampled with most of the region being marginally fast this suggests that d heterogeneity has large spectral power at relatively short wavelengths in this scenario previous tomographic inversions for cmb topography will have large errors since in these inversions corrections for d structure are based on low order spherical harmonic models

alaska megathrust 1 seismicity 43 years after the great 1964 alaska megathrust earthquake 1 the largest moment release during the 1964 mw 9 2 alaska earthquake was on the portion of the megathrust under the eastern kenai peninsula and the prince william sound the area is currently locked geodetically and corresponds to where the yakutat terrane is subducting in 2006 2009 a seismic array consisting of 34 broadband seismometers was deployed in the region an automatic algorithm was used to detect 12 563 local earthquakes using 13 months of data from the experiment of these 9427 good quality earthquakes could be relocated in a joint inversion for hypocenters and velocity structure they were then relocated by double difference to generate a final catalog of 8308 hypocenters these microearthquakes delineate a deeper steeply dipping wadati benioff zone contiguous with an 11 km wide seismic zone dipping at 3 between 20 km and 40 km depth along the 1964 earthquake s rupture zone focal mechanisms do not show interplate thrust faulting events but mostly normal faulting events with t axes generally parallel the slab dip direction indicating them to be intraslab seismicity the shallow narrow band of seismicity lies within the subducting yakutat terrane and right below the thrust zone possibly thrust faulting has not yet resumed yet in this early phase of the earthquake cycle thick subducted sediments overlying the yakutat terrane could also form a large strong contact zone on a relatively smooth plate boundary which does not favor seismic sliding on small patches but ruptures homogenously in great earthquakes

smectite dehydration its relation to structural development and hydrocarbon accumulation in northern gulf of mexico basin a comparison of clay diagenesis data obtained from a study of tertiary shales from the brazos colorado river system of texas the mississippi river system of louisiana and the niger river system of nigeria illustrates significant differences in temperature intervals over which smectite diagenesis occurs the threshold temperature required to initiate diagenesis ranges from about 160 f 71 c in mississippi river sediments to more than 300 f 150 c in the niger delta water expelled from smectite into the pore system of the host shale during the process of diagenesis may migrate out of the shale early or may be totally or partially trapped and released slowly through time in either situation the water can act as a vehicle for hydrocarbon migration p ovided hydrocarbons are present in a form and in sufficient quantities to be transported observations from the northern gulf of mexico basin indicate a close relation between buildup of high fluid pressure and the smectite illite transformation process abnormal pressures exert partial control on the type and quantity of hydrocarbons accumulated because pressure potential determines the direction of fluid flow and overpressuring partly controls the geometry of growth faults and related folds in basins where shale structures are the dominant type formed the depths to which growth faults can penetrate and the angle of dip that these faults assume at depth are largely dependent on fluid pressure in the sedimentary section at the time of faulting dips of some faults in texas have been observed to change abruptly within the interval of smectite diagenesis and some faults formed in the overpressured miocene and younger sections become beddingplane types at depths where the temperature is near that required for thermal generation of petroleum although these faults may be important for fluid redistribution in shallow sandstone shale sections they are a minor factor in moving hydrocarbons out of shale below the faults in much of the texas offshore area fluid movement upward through microfracture systems in the deeply buried overpressured section overlying and extending upward from fault trends in the sub tertiary section is proposed as a mechanism for flushing hydrocarbons from the deeper portion of the northern gulf of mexico basin this flushing process would be enhanced by smectite diagenesis because water derived from smectite that was trapped during basin subsidence would cause the flushing process to continue for longer periods of time and to extend to greater depths than could be attained if only remnants of original pore water were present shale tectonism is also the primary mechanism for structural development in the tertiary section of the niger delta however seismic data indicate that the rate of dip change of seaward dipping listric growth faults is commonly less than that observed in texas where dips as low as 10 15 can occur at depths as shallow as 10 000 15 000 ft 3 048 4 572 m syndepositional faults in nigeria are formed in sandstone shale sections where the clay composition of shale is primarily kaolinite and where little water of smectite diagenesis has been added to the pore system of the host sedimentary section subtle differences in structural styles in the tertiary sections of texas and nigeria are probably the result of differences in clay composition of the shaly sections being deformed

seismicity of the wrangell and aleutian wadati benioff zones and the north american plate along the trans alaska crustal transect chugach mountains and copper river basin southern alaska the configuration of the aleutian and wrangell wadati benioff zones in southern alaska between longitudes 142 w and 148 w is determined from regionally recorded earthquakes from 1971 to 1986 the earthquakes are located with a simple velocity model calibrated with seismic refraction measurements conducted for the trans alaska crustal transect tact west of the transect meridian approximately 145 20 w and beneath the chugach mountains shocks in the depth range 25 60 km compose the shallow part of the northwest to north dipping aleutian zone this zone can be traced updip and seaward beneath prince william sound east of the transect meridian and north of 61 n latitude the weakly active north northeast dipping wrangell zone extends to a depth of at least 100 km beneath the wrangell volcanoes and along strike for at least 150 km the two zones appear to be continuous at least in the depth range 20 45 km and may define adjacent limbs of a buckle in the subducted oceanic lithosphere north of 61 n focal mechanisms in the shallow aleutian zone are compatible with a uniform stress field characterized by in plane least compressive stress directed toward the steeply dipping deeper part of the aleutian zone north of cook inlet stress orientation in the wrangell zone is unresolved because of the low level of seismicity no focal mechanisms corresponding to slip on a gently northward dipping megathrust have been observed along the transect meridian a change of focal mechanism with depth near the top of the dipping seismic zone is inferred to reflect the interplate boundary beneath the chugach mountains this boundary coincides with a band of strong reflectors imaged by tact vertical seismic profiling the overriding plate appears to be aseismic beneath the northern chugach mountains but minor shallow seismicity occurs beneath the copper river basin first motion patterns for these shallow shocks suggest the most compressive stress within the overriding plate is oriented subhorizontally and approximately north south

resistivity velocity transforms revisited velocity and density measured in a well are crucial for synthetic seismic generation which is in turn a key to interpreting real seismic amplitude in terms of lithology porosity and fluid because velocity and density curves are sometimes of poor quality or simply absent in older wells it is important to be able to reconstruct these curves from reliable measurements such as resistivity and gamma ray gr a recent example of this approach is by xu et al 2003 where mechanical compaction curves and velocity porosity relations are used to reconstruct a full suite of the needed log data the earliest attempt to reconstruct a sonic curve from resistivity is by faust 1953 where both the velocity and resistivity are empirically related to depth and lithology from these two relations an equation follows that links the sonic velocity to the depth and formation factor where the formation factor is defined as usual as the ratio of the resistivity of water saturated rock to the resistivity of water

new evidence for segmentation of the alaska subduction zone the purpose of this article is to provide additional evidence for segmentation of the subducted plate in alaska and to introduce a catalog of the relocated earthquakes for future studies we used the joint hypocenter determination method to relocate 14 099 subduction zone earthquakes that occurred from july 1988 to july 1998 and were located between 58 n and 65 n latitude the earthquake data were taken from the alaska earthquake information center catalog the selected earthquakes were divided into 16 blocks on the basis of their hypocentral locations and each block was relocated separately average epicenter shift was 3 8 km and average upward and downward depth shifts were 4 1 and 4 4 km respectively roughly the same number of earthquakes shifted upward 47 and downward 53 the overall change with respect to the initial locations is that the seismicity became more compact revealing details about the fine structure of the wadati benioff zone in particular we were able to identify more precisely the boundary between the kenai and mckinley blocks of the subducting plate in addition there is evidence for plate segmentation within the mckinley block manuscript received 15 november 2000

cross property rock physics relations for estimating low frequency seismic impedance trends from electromagnetic resistivity data estimating the low frequency seismic impedance trend is critical for reservoir characterization based on seismic inversions conventional seismic reflection data have an information gap between 2 and 10 hz and do not contain information about the background impedance trend on the other hand controlled source electromagnetic csem data are typically low resolution and contain information about the earth s resistivity structure thus cross property rock physics relations between elastic and electrical properties can extract information from the csem data to provide constraints on the low frequency seismic impedance trend this concept is tested with well log data and applied to a resistivity section inverted from csem data results show that appropriate cross property rock physics relations can capture the background low frequency impedance trend and provide useful constraints on models for inversion

tectonic drivers of the wrangell block insights on fore arc sliver processes from 3 d geodynamic models of alaska intracontinental shear zones can play a key role in understanding how plate convergence is manifested in the upper plate in regions of oblique subduction however the relative role of the driving forces from the subducting plate and the resisting force from within intracontinental shear zones is not well understood results from high resolution geographically referenced instantaneous 3d geodynamic models of flat slab subduction at the oblique convergent margin of alaska are presented these models investigate how viscosity and length of the denali fault intracontinental shear zone as well as coupling along the plate boundary interface modulate motion of the wrangell block forearc sliver and slip across the denali fault models with a weak denali fault 1017 pa s and strong plate coupling 1021 pa s were found to produce the fastest motions of the wrangell block 10 mm yr the 3d models predict along strike variation in offs et along the denali fault changing from dextral strike slip motion in the eastern segment to oblique convergence towards the fault apex models further show that the flat slab drives oblique motion of the wrangell block and contributes to 20 models with a short fault and 28 models with a long fault of the observed quaternary slip rates along the denali fault the 3d models provide insight into the general processes of forearc sliver mechanics and also offer a 3d framework for interpreting hazards in regions of flat slab subduction

the role of rheology and slab shape on rapid mantle flow three dimensional numerical models of the alaska slab edge 1 away from subduction zones the surface motion of oceanic plates is well correlated with mantle flow direction as inferred from seismic anisotropy however this correlation breaks down near subduction zones where shear wave splitting studies suggest the mantle flow direction is spatially variable and commonly non parallel to plate motions this implies local decoupling of mantle flow from surface plate motions yet the magnitude of this decoupling is poorly constrained we use 3d numerical models of the eastern alaska subduction transform plate boundary system to further explore this decoupling in terms of both direction and magnitude specifically we investigate the role of the slab geometry and rheology on the mantle flow velocity at a slab edge the subducting plate geometry is based on wadati benioff zone seismicity and tomography and the 3d thermal structure for both the subducting and overriding plates is constrained by geologic and geophysical observations in models using the composite viscosity a laterally variable mantle viscosity emerges as a consequence of the lateral variations in the mantle flow and strain rate spatially variable mantle velocity magnitudes are predicted with localized fast velocities greater than 80 cm yr close to the slab where the negative buoyancy of the slab drives the flow the same models produce surface plate motions of less than 10 cm yr comparable to observed plate motions these results show a power law rheology i e one that includes the effects of the dislocation creep deformation mechanism can explain both observations of seismic anisotropy and decoupling of mantle flow from surface motion

rupture process of the 1964 prince william sound alaska earthquake from the combined inversion of seismic tsunami and geodetic data 1 four great earthquakes 1952 1960 1964 and 2004 have occurred since seismic monitoring began and only two since the installation of a global seismic network a reexamination of the 1964 m 9 2 prince william sound pws alaska earthquake is timely due to the 2004 sumatra earthquake because it adds constraints to the potential range of source parameters for these types of infrequent events and aids in the ability to predict the ground motions for other subduction zone including cascadia we first measured the durations of high frequency energy radiation from teleseismic p wave codas recorded by short period world wide standardized seismographic network wwssn sp instruments to put constraints on the earthquake rupture length the durations ranged between 250 and 600 s and are shorter in time between azimuths of 190 and 260 the fault length is estimated to range from 540 to 740 km rupturing at average speeds of 1 4 2 km s in a 220 238 direction we developed a multiple time window kinematic rupture model for the pws earthquake from the least squares inversion of teleseismic p waves tsunami tide gauge records and geodetic leveling survey observations based on the green s function technique we assume three major fault segments for the subduction zone dipping 6 12 based on geologic data the subfault size on the megathrust was set to 50 50 km the patton bay fault pbf imbricate thrust was assigned a 60 dip with a subfault size of 20 20 km we estimated a seismic moment of 5 52 1022 n m mw9 12 we identified three areas of major moment release on the pws segment near montague and middleton islands extending out to the trench beneath the portlock anticline on the cook segment between 58 n fracture zone and the kodiak bowie seamount chain and finally on the katmai segment off the coast of kodiak island extending to the trench our preferred rupture model has a peak slip of 14 9 m along the megathrust and 17 4 m along the pbf the addition of the pbf resulted in an 8 improvement in residuals and also had a significant effect on the overall slip distribution moment release occurred as deep as 50 km depth slab contour near the 350 c isotherm and mantle fore arc wedge which is about 10 20 km deeper than previous coupling depths

intermediate and deep seismicity and lateral structure of subducted lithosphere in the circum pacific region in this paper we present a region by region review of the wadati benioff zone structure of most of the world s seismically active subduction zones focusing primarily on the intermediate and deep seismicity lateral changes in wadati benioff zone structure are common in every major subduction zone in this study we use these changes to define possible boundaries between portions or segments of lithosphere with differing subduction geometries although earthquake data seldom have the resolution to show conclusively whether these boundaries separate independent blocks of lithosphere the available data indicate that the active process at most of these segment boundaries is ductile deformation of the subducting plate rather than tearing we found the strongest evidence for the existence of tears where tears are geometrically necessary such as where a transform boundary terminates a trench as at the new hebrides tonga and south sandwich trenches weak evidence suggesting other tears does exist in some regions such as taiwan the japan izu bonin corner and the philippines the causes of these changes in structure are in most cases unclear only about 34 of the possible segment boundaries coincide with subducting bathymetric features some boundaries occur where there is apparent lateral strain caused by anomalous trench geometry we have designed a simple modeling procedure which incorporates published plate motion and the observed geometry of trenches and wadati benioff zones to estimate the lateral strain in subduction zones throughout the circum pacific region although no observed subduction zone has a perfectly strain free geometry there is a broad range of geometries for which the lateral strain is small indeed the observed geometry of most subduction zones involve relatively little lateral strain comparison with centroid moment tensor focal mechanisms indicates that in zones where the modeling predicted little lateral strain the mechanisms of intermediate and deep earthquakes show no effects of lateral stress and downdip stresses are clearly dominant in regions such as the mariana arc where the model predicts very large lateral extension lateral tension is very evident in the focal mechanisms in regions such as the hokkaido corner where the modeling predicts large compressional strains the plate appears to buckle and bending stresses parallel to the trench are evident in general this study finds that subducted lithosphere is remarkably cohesive and rigid and only rarely deforms by breaking or stretching

additional evidence for down dip tension in the pacific plate beneath central alaska abstract small intermediate depth earthquakes cluster in a volume about 20 km in diameter beneath gold king a landing strip on the northern flanks of the alaska range these events almost 600 km from the aleutian trench are the northern most which can be identified as being associated with the benioff zone extending inland from cook inlet west of anchorage first motion observations of the gold king events at local stations can be combined to determine a tensional axis dipping steeply to the north at an azimuth just west of north this composite mechanism suggests that the slab is subjected to down dip tensional forces probably as a result of gravitational sinking

source rock potential toc hydrogen index evaluation by integrating well log and geochemical data abstract evaluation of source rock potential using well log data alone e g density or sonic log is limited to the assessment of total organic carbon toc content well logs that directly measure the most important source quality parameter the hydrogen content of the kerogen do not exist therefore a method is proposed that combines log derived toc data with calibration schemes relating toc content to hydrogen index and maturity for individual source rock sets the method has been applied to the compositionally heterogeneous kimmeridge clay formation of the north sea and the homogeneous lower toarcian shale of n germany the combination of well log and geochemical data greatly improves the accuracy with which the lateral and vertical distribution of source rocks and their potential can be predicted on a basin and prospect level

subduction geometry beneath south central alaska and its relationship to volcanism the southern alaskan margin captures a transition between compression and strike slip dominated deformation accretion of the over thickened yakutat terrane termination of aleutian arc magmatism and the enigmatic wrangell volcanic field the extent of subduction and mantle structure below this region is uncertain with important implications for volcanism we present compressional and shear wave mantle velocity models below south central alaska that leverage a new seismometer deployment to produce the most complete image of the subducting pacific yakutat plate to date we image a steeply dipping slab extending below central alaska to 400 km depth which abruptly terminates east of 145 w there is no significant slab anomaly beneath the nearby wrangell volcanoes a paucity of volcanism is observed above the subducting yakutat terrane but the slab structure below 150 km depth and wadati benioff zone here are similar to those along the aleutian alaska arc features of the mantle wedge or overlying lithosphere are thus responsible for the volcanic gap

shallow seismicity of the anchorage alaska region 1964 1999 we have relocated over 4200 shallow 40 km earthquakes occurring in the anchorage region for 35 years following the 1964 great m w 9 2 alaska earthquake the shallowest 20 km earthquakes delineate several faults within the crust including one associated with mapped folds located north of upper cook inlet inversion of first motion data for the stress field orientation in upper cook inlet indicates east west oriented horizontal 1 and near vertical 3 a condition favoring reverse faulting along north south striking faults with trends similar to the orientation of mapped faults and fault cored anticlines within the inlet 1 is rotated 60 to 90 counterclockwise from the direction of plate convergence in agreement with global positioning system gps geodesy studies that indicate the western portion of the kenai peninsula and upper cook inlet do not appear to be moving in the direction of plate motion due to a change in coupling across the plate interface the stress regime north of the castle mountain fault is conducive to strike slip or normal faulting along faults striking east northeast or north northwest similar to previous studies we observed a persistent aseismic zone in the upper crust that appears to be located above and immediately downdip of the portion of the plate interface that slipped 20 25 m in the 1964 mainshock deeper 20 40 km earthquakes indicate intense deformation and a rapidly changing stress field near the boundary between the kenai and mckinley segments of the subducted slab the 1943 m w 7 0 susitna lowlands earthquake may have been associated with this region of complex deformation

estimation of strong ground motion from the great 1964 mw 9 2 prince william sound alaska earthquake we are generating physically plausible near field synthetic ground motions for the great 1964 prince william sound alaska earthquake compatible with available seismological data tectonic information and eyewitness accounts the first objective of this study is the simulation of the low frequency i e f 0 03 hz strong ground motions on selected locations and on a dense grid of observation points extending over the shallow dipping causative fault of the 1964 alaska earthquake in order to accomplish this task we are utilizing the slip model proposed by johnson et al 1996 based on a joint inversion of tsunami waveforms and geodetic data the calculations are carried out using the discrete wavenumber representation method bouchon and aki 1977 bouchon 1979 and the generalized transmission and reflection coefficient technique luco and apsel 1983 the second objective of this study is the reconstruction of the strong ground motion time histories and response spectra that the city of anchorage experienced during the 1964 alaska earthquake the low frequency i e f 0 03 hz ground motions are generated using the methodology described previously the intermediate frequency i e 0 03 f 0 50 hz ground motions are simulated by convolving green s functions generated by the discrete wavenumber representation method with far field radiation pulses of circular cracks sato and hirasawa 1973 dong and papageorgiou 2002a the high frequency i e 0 5 f 8 0 hz ground motions are simulated using the stochastic modeling approach the three independently derived ground motion components are then properly combined to generate synthetic broadband ground motion time histories and response spectra for the city of anchorage due to the 1964 prince william sound earthquake the third objective of this study is the validation of the synthetic strong ground motions for the 1964 alaska earthquake against observed tectonic deformation ground motion estimates inferred from descriptions of structural damage and eyewitness accounts in summary the analysis presented in this study contributes to a better understanding of the seismological aspects of the 1964 alaska earthquake and provides synthetic time histories and response spectra for engineering applications compatible with all available information i e seismological tectonic and eyewitness accounts it should be noted however that the generated strong ground motions are not necessarily unique nor do they reflect the entire uncertainty that characterizes the problem under investigation

organic facies and maturation of jurassic cretaceous rocks and possible oil source rock correlation based on pyrolysis of asphaltenes scotian basin canada abstract this paper establishes source rock characterization and oil oil and oil source rock correlations of selected organic rich shale source rocks and selected light oils and condensates from jurassic and cretaceous formations of the scotian basin multiple source rocks of kerogen types iia oil prone iia iib oil and condensate prone iib condensate and gas prone iii gas prone and iv nonsource are identified in various stratigraphic horizons vitrinite reflectance and t inmax data indicate variable maturation histories in different parts of the basin which are related to differences in lithology related heat conductivity and the presence of older sediments closer to areas of rifting multiple linear regression and cluster analyses of aromatic hydrocarbon ratios reveal two oil families some kerogen type iib rock extracts match many of the light oil and condensates in terms of the aromatic hydrocarbon distributions a second family of oils could not be correlated with any of the analyzed source rock extracts pyrolysis gas chromatography of asphaltenes from the cohasset a 52 and sable island 3h 58 wells are significantly different in n alkane aromatics and phenol content the asphaltene pyrolyzates of samples from venture b 52 and s desbarres o 76 have a high aromatic content low content of n alkanes and high phenol values s desbarres which is typical of a terrestial source they correlate well with one another and also with sable island light oil the n triumph g 43 whole rock and extract asphaltene pyrolyzates are dominated by normal hydrocarbons with aromatic phenolic and thiophenic compounds in low concentrations suggesting an algal source algal type organic matter may have made a contribution to the cohasset petroleum as its asphaltene pyrolyzate is also dominated by normal hydrocarbons

studies of wadati benioff zone seismicity of the anchorage alaska region we have relocated over 8600 earthquakes occurring between 1964 and 1999 at depths 25 km within 100 km of anchorage alaska using the double difference technique the relocated seismicity reveals important details of the subducting pacific plate and yakutat blocks including clustering of seismicity within the pacific plate mantle northeast and northwest striking near vertical faults within the pacific plate crust and a region of intense deformation associated with the southwestern edge of the yakutat block stress analyses from the direct inversion of first motion data and from inversion of focal mechanisms for 713 events indicates a rotation of the maximum compressive stress direction from a trench parallel direction northeast in the southwestern portion of the study area to an east west direction near the southwestern edge of the yakutat block located just north of anchorage regions of the pacific plate mantle that produced m w 6 4 earthquakes in 1934 and 1954 continue to be seismically active

seismic anisotropy under central alaska from sks splitting observations 1 seismic anisotropy under central alaska is studied using shear wave splitting observations of sks waves recorded on the broadband experiment across the alaska range beaar 1999 2001 splitting results can be divided into two distinct regions separated by the 70 km contour of the subducting pacific plate waves that travel through the thicker mantle wedge show fast directions that are parallel to the strike of the slab these slab parallel directions appear to indicate along strike flow in the mantle wedge and splitting delay times increase with path length in the mantle wedge suggesting anisotropy of 7 9 0 9 the region of along strike flow corresponds to high seismic attenuation and hence high temperatures along strike flow here may be driven by secular shallowing of the slab driven by subduction of buoyant yakutat terrane crust or by toroidal flow around the east end of the aleutian slab waves traveling southeast of the 70 km contour sample the pacific plate and the nose of the mantle wedge they show fast directions that parallel the direction of plate motion these fast directions are most likely due to flow under the subducting pacific plate and or anisotropy within the subducting pacific lithosphere the high splitting delay times 0 8 1 7 s associated with these convergence parallel directions cannot be produced in the mantle wedge which is 10 30 km thick here thus anisotropy shows a sharp 90 change in fabric associated with the onset of high temperature wedge flow

cross property relations between electrical conductivity and the seismic velocity of rocks cross property relations are useful when some rock properties can be measured more easily than other properties relations between electrical conductivity and seismic velocity stiffness moduli and density can be obtained by expressing the porosity in terms of those properties there are many possible ways to combine the constitutive equations to obtain a relation each one representing a given type of rock the relations depend on the assumptions to obtain the constitutive equations in the electromagnetic case the equations involve archie s law and its modifications for a conducting frame the hashin shtrikman hs bounds and the self similar and complex refraction index method crim models in the elastic case the stress strain relations are mainly based on the time average equation the hs bounds and the gassmann equation also expressions for dry rocks and for anisotropic media using backus averaging are analyzed the relations are applied to a shale saturated with brineoverburden and to a sandstone saturated with oilreservoir tests with sections of a north sea well log show that the best fit is given by the relation between the gassmann velocity and the crim selfsimilar and archie models for the conductivity

guidelines for evaluating petroleum source rock using programmed pyrolysis rock eval pyrolysis is used to rapidly evaluate the petroleum generative potential and thermal maturity of rocks accurate conclusions require programs every 30 60 ft 9 18 m understanding of interpretive pitfalls and supporting data such as visual kerogen vitrinite reflectance and elemental analyses the generative potential of coals is commonly overestimated by pyrolysis and is best determined by elemental analysis and organic petrography most coals show high s2 s3 5 and low hi values 300 mg hc g toc migrated oil and mud additives which alter rock eval data can sometimes be removed by special processing for immature rocks bimodal s2 peaks and pi values over 0 2 indicate contamination pyrolysis downgrades organic poor clay rich rocks which show lower hi and higher tmax values than isolated kerogen because of adsorption of pyrolyzate on the clays tmax values for small s2 peaks 0 2 mg hc g toc are unreliable tmax is affected by maturation organic matter type contamination and the mineral matrix s3 is sensitive to inorganic and adsorbed carbon dioxide and to instrumentation problems acidification of carbonate rich samples and proper maintenance improves s3 measurement constant sample weights 100 mg are recommended below a threshold weight tmax increases by up to 10 c and other parameters decrease organic rich samples which overload the detector can be diluted with carbonate detector linearity is determined by pyrolyzing various weights of an organic rich rock

subduction zone magnetic anomalies and implications for hydrated forearc mantle continental mantle in subduction zones is hydrated by release of water from the underlying oceanic plate magnetite is a significant byproduct of mantle hydration and forearc mantle cooled by subduction should contribute to long wavelength magnetic anomalies above subduction zones we test this hypothesis with a quantitative model of the cascadia convergent margin based on gravity and aeromagnetic anomalies and constrained by seismic velocities and find that hydrated mantle explains an important disparity in potential field anomalies of cascadia a comparison with aeromagnetic data thermal models and earthquakes of cascadia japan and southern alaska suggests that magnetic mantle may be common in forearc settings and thus magnetic anomalies may be useful in mapping hydrated mantle in convergent margins worldwide

estimation of clay content in soil based on resistivity modelling and laboratory measurements the determination of clay content in near surface formations is crucial for geotechnical hydrogeological and oil contamination studies we have developed a technique for estimating clay content that consists of the minimization of the difference between the theoretically calculated and measured soil resistivities as a function of water salinity to calculate the resistivity we used a model that takes into account the electrochemical processes in the clay micropores the experimental measurements of soil resistivity were performed on soil samples completely saturated by brines at different concentrations of nacl salt in the range 0 6 100 g l to obtain the resistivity versus salinity curve the parameters obtained with this curve inversion are the clay content the total porosity and the cation exchange capacity to verify the new technique we determined clay concentrations of artificial mixtures of calibrated sand and clay the relative mean error in the clay content does not exceed 20 for a 5 fitting error of the resistivity versus salinity curves such evaluations allow the correct separation of the main lithological groups sand sandy loam loam and light medium and heavy clay we applied this technique to estimate the petrophysical parameters of soils clay content porosity and cation exchange capacity at various sites in mexico the results improved the interpretation of the vertical electrical soundings the lithological soil characterization and the delineation of oil contaminated areas

details of stress directions in the alaska subduction zone from fault plane solutions we used the cumulative misfit method to divide a data set with heterogeneous stress orientations into subsets with homogeneous stress directions we propose that slope changes of the cumulative misfit as a function of earthquake number pinpoint the boundaries of homogeneous stresses using a synthetic data set of 50 fault plane solutions composed of two halves corresponding to two incompatible stress tensors we tested the validity and efficacy of the cumulative misfit method our acceptance criteria for results of stress tensor inversions are 1 the directions must be well constrained that is the 95 confidence regions of the greatest and least principal stresses do not overlap and 2 there must be evidence for homogeneity in the sample that is the average misfit of the inversion is less than 6 we estimated stress directions in the alaska wadati benioff zone wbz using 470 fault plane solutions which we determined for earthquakes with ml 3 and 67 published fault plane solutions for earthquakes with ms 5 we succeeded in subdividing the data set of the small and large earthquakes into 25 and 3 subsets with the average misfit ranging from 3 2 to 5 5 the average misfits of the subsets we accept as satisfying the assumption of homogeneity are smaller than the average misfit of the overall data set f 10 by factors of 2 to 3 we estimated the stress fields at two scales along the alaska wbz the stress directions measured by the large earthquakes ms 5 were homogeneous over large volumes with extension downdip and the direction of greatest compression along strike this unusual orientation of the greatest principal stress is attributed to the bend of the slab under central alaska which generates compressive stresses along strike the stress orientations revealed by small earthquakes in contrast exhibited a great deal of heterogeneity as a function of space although their general trend confirms the overall stress directions obtained from the large events we propose that the ratio of the dimensions of the stress field sensed by earthquakes to the rupture dimensions is about 20 to 50 the estimated stress directions of the crustal earthquakes corresponded to the following mechanisms 1 strike slip faulting with the greatest principal stress oriented n s near fairbanks and 2 thrusting with the greatest principal stress oriented nw se near mount mckinley

a semiautomatic calibration method applied to a small aperture alaskan seismic array small to medium aperture 25 km or less seismic arrays are of great importance for event location and characterization effective use of these arrays requires calibration preferably with large numbers of events to account for local and distant structural and propagation effects we implement a cross correlation method as a semiautomatic procedure applicable to any small array able to process thousands of events with several days of computer time on a sun blade 1000 workstation we analyze a database of 1228 p and pcp arrivals recorded between 1997 and 1998 at a 19 element alaskan seismic array the arrivals are picked by the prototype international data centre for events well located by the united states geological survey backazimuth and horizontal velocity residuals are calculated for all events complicated geology beneath the elements and elevation differences among the array stations make static corrections necessary we use 328 core phases including pcp pkikp pkp pkkp to determine the static corrections we present first order structural interpretations of our calibration results including a moho discontinuity dipping to the north with a 10 5 dip angle and a strike of 109 our method allows for resolution of phase arrivals within 2 3 sec and has potential to be used as an automatic detector of primary and secondary seismic phases

earthquake location in island arcs abstract a comprehensive data set of selected teleseismic p wave arrivals and local network p and s wave arrivals from large earthquakes occurring at all depths within a small section of the central aleutians is used to examine the general problem of earthquake location in island arcs reference hypocenters for this special data set are determined for shallow earthquakes from local network data and for deep earthquakes from combined local and teleseismic data by joint inversion for structure and location the high velocity lithospheric slab beneath the central aleutians may displace hypocenters that are located using spherically symmetric earth models the amount of displacement depends on the position of the earthquakes with respect to the slab and on whether local or teleseismic data are used to locate the earthquakes hypocenters for trench and intermediate depth events appear to be minimally biased by the effects of slab structure on rays to teleseismic stations however locations of intermediate depth events based on only local data are systematically displaced southwards the magnitude of the displacement being proportional to depth shallow focus events along the main thrust zone although well located using only local network data are severely shifted northwards and deeper with displacements as large as 50 km by slab effects on teleseismic travel times hypocenters determined by a method that utilizes seismic ray tracing through a three dimensional velocity model of the subduction zone derived by thermal modeling are compared to results obtained by the method of joint hypocenter determination jhd that formally assumes a laterally homogeneous velocity model over the source region and treats all raypath anomalies as constant station corrections to the travel time curve the ray tracing method has the theoretical advantage that it accounts for variations in travel time anomalies within a group of events distributed over a sizable region of a dipping high velocity lithospheric slab in application jhd has the practical advantage that it does not require the specification of a theoretical velocity model for the slab considering earthquakes within a 260 km long by 60 km wide section of the aleutian main thrust zone our results suggest that the theoretical velocity structure of the slab is presently not sufficiently well known that accurate locations can be obtained independently of locally recorded data using a locally recorded earthquake as a calibration event jhd gave excellent results over the entire section of the main thrust zone here studied without showing a strong effect that might be attributed to spatially varying source station anomalies we also calibrated the ray tracing method using locally recorded data and obtained results generally similar to those obtained by jhd

petrophysical implications of source rock microfracturing abstract hydrocarbon generation induced microfracturing in source rocks is important affecting both primary migration of hydrocarbons and unconventional shale plays in this study petrographic observations rock eval and total organic carbon content toc data and log derived physical properties were analyzed in order to evaluate eventual petrophysical implications of microfracturing induced by hydrocarbon generation petrographically evidences of microfracturing both normal and parallel to bedding have been found horizontal microfractures typically cross cut each other at an angle between 30 and 90 horizontal microfractures are readily imaged compared to vertical microfractures vertical microfractures were clearly observed only in rare cases in samples with a high degree of microfracturing in the case of moderate microfracturing the vertical component of microfractures may be too small to be detectable using conventional microscopy techniques longer vertical components of the microfractures may be facilitated by higher toc and particularly dense laminated organic matter fabric as well as higher thermal maturity levels clay minerals particularly smectites are also playing a role in reducing permeability and thereby increasing the local pressure generated by hydrocarbon generation eventually resulting in microfracturing log derived petrophysical properties particularly p wave velocity vp and formation resistivity can give information on microfracturing potential even though the techniques can t resolve the microfractures directly vp has been postulated to be sensitive to organic matter quantity and fabric whereas formation resistivity is largely governed by fluid content and clay minerals a reverse trend of increasing resistivity with decreasing vp was found and is linked to higher hydrocarbon saturation and toc and or dense laminated fabric of organic matter favoring microfractures the implications of the log derived petrophysical results are in agreement with the direct petrographic observations formation resistivities in the source rocks however are lower than those observed in non clay dominated hydrocarbon saturated intervals this indicate that low permeable organic rich source rocks with a high clay content particularly smectites may facilitate formation of the hydrocarbon filled vertical microfractures even at relatively low thermal maturities

filling the gap in a double seismic zone intraslab seismicity in northern chile abstract double seismic zones dszs of intermediate depth intraslab seismicity are observed in many subduction zones around the globe and have been related to dehydration reactions in the downgoing crust and mantle lithosphere these reactions occur at to first order constant temperatures which explains the observed linear arrangements of seismicity that appear to follow isotherms of thermal models intermediate depth seismicity in northern chile however exhibits a pattern of intraslab seismicity that substantially deviates from a classical dsz whereas two parallel seismicity planes are present in the updip part of the slab these abruptly change into a 25 30 km thick homogeneously seismogenic volume at a depth of 80 100 km seismicity rate and moment release significantly increase in this depth interval in order to understand which processes evoke this configuration and what distinguishes the northern chile subduction zone from more conventional subduction zone settings e g japan we performed a detailed seismological investigation of slab seismicity in northern chile using data from the ipoc permanent network we determined 600 moment tensors of intraslab earthquakes processed and evaluated location uncertainties for 8 years of high resolution earthquake hypocenter data and performed statistical analysis of the different seismicity populations we observe that earthquakes both in the highly active cluster and the dsz above exhibit consistently downdip extensive source mechanisms that align with the dip angle and direction of the slab this implies strong slab pull which is also evident from slab steepening outlined by hypocenters towards the downdip termination of the highly active cluster moreover events in the cluster show a very weak aftershock productivity and a high background event rate which leads to a temporal distribution of seismicity that is close to a purely random process we find that the position of the highly seismogenic volume spatially coincides with 1 the disappearance of the velocity contrast between oceanic crust and the underlying mantle in receiver function images 2 the transition from the cold nose i e the stagnant part to the hot part of the mantle wedge as evidenced by seismic attenuation images and 3 with an increase of the slab dip angle based on these different pieces of evidence we speculate that high tensile stresses and heat input from above could lead to a sudden burst of kinetically delayed metamorphic reactions there that then enables the observed increased seismicity rates since these reactions have overall a negative volume change that leads to slab densification and hence further increases slab pull the spatial pattern of seismicity we observe could result from a runaway type process which would explain its abrupt start and high moment release rates

seismic velocity structure and anisotropy of the alaska subduction zone based on surface wave tomography southcentral alaska is a complex tectonic region that transitions from subduction of pacific crust to flat slab subduction and collision of overthickened yakutat crust because much of the yakutat crust has been subducted seismic imaging is needed in order to understand the crustal and upper mantle structural framework for this active tectonic setting here we use teleseismic rayleigh waves to image large scale variations in shear wave structure our imaging technique employs a two plane wave representation with finite frequency sensitivity kernels our 3 d isotropic model reveals several features the subducting pacific yakutat slab slow wave speeds characterizing the onshore yakutat collision zone slow wave speeds of the wrangell subduction zone and a deep tomographic contrast at the eastern edge of the pacific yakutat slab we produce anisotropic phase velocity maps that exhibit variations in the fast direction of azimuthal anisotropy these maps show the dominance of the yakutat slab on the observed pattern of anisotropy west of the yakutat slab the fast directions are approximately aligned with the plate convergence direction in the region of the yakutat slab the pattern is more complicated along the margins of the slab the fast directions are roughly parallel to the margins we identify notable differences and similarities with published sks splitting measurements integrative modeling using 3 d anisotropy models and different seismic measurements will be needed in order to establish a detailed 3 d anisotropic velocity model for alaska this study provides a large scale starting point for such an effort

hydrocarbon generation induced microcracking of source rocks laboratory measurements of ultrasonic velocity and anisotropy in kerogen rich black shales of varying maturity suggest that extensive bedding parallel microcracks exist in situ in most mature source rocks undergoing the major stage of hydrocarbon generation and migration given the normal faulting regime with the vertical stress being the maximum principal stress typical of most sedimentary basins this microcrack alignment cannot be accounted for using simplified fracture mechanics concepts this subhorizontal microcrack alignment is consistent with 1 a model of local principal stress rotation and deviatoric stress reduction within an overpressured formation undergoing hydrocarbon generation and with 2 a strong mechanical strength anisotropy of kerogen rich shales caused by bedding parallel alignment of kerogen microlayers microcracks originate within kerogen or at kerogen illite interfaces when pore pressure exceeds the bedding normal total stress by only a few mpa due to the extremely low fractu

on the accuracy of modelling hydrocarbon generation and migration the egersund basin oil find norway abstract quantitative estimates of kerogen transformation and hydrocarbon charge to the structure of block 9 2 norwegian north sea were obtained by integrated basin modelling a probability distribution was assigned to each input parameter and the sensitivity to these parameters was investigated by subsequently varying each parameter within the assigned ranges the inaccuracy in the modelling results were mainly due to imprecise knowledge of hydrocarbon generation kinetics depth conversion and present day virgin rock temperature kerogen transformation modelling and source rock richness thickness areal extent volumetric charge calculations monte carlo latin hypercube sampling based on the probability distribution of each parameter was performed giving a 40 probability for a dry structure a mean value of 10 7 106sm3 recoverable oil and a considerable high side potential 4 probability for more than 50 106sm3

primary migration by oil generation microfracturing in low permeability source rocks application to the austin chalk texas fracturing of low permeability source rocks is induced by pore pressure changes caused by the conversion of organic matter to less dense fluids oil and gas these fractures increase the permeability and provide pathways for hydrocarbon migration an equation for the pressure change is derived using four major assumptions 1 the permeability of the source rock is negligibly small 0 01 d 10 20 m2 so that the pore pressure buildup by the conversion is much faster than its dissipation by pore fluid flow 2 the stress state is isotropic so that horizontal and vertical stresses are equal the source rock fails when the pore pressure equals the overburden pressure 3 the properties of the rock organic matter and fluids remain constant during oil generation this assumption is valid when the change in depth i e pressure and temperature is small 4 only two reaction rates are required for the conversions a low temperature reaction rate for the kerogen oil conversion e approx 24 kcal mol a approx 1014 m y and a high temperature reaction rate for oil gas conversion e approx 52 kcal mol a approx 5 5 1026 m y the equations for generation rate and pressure change are applied to the austin source rock by adjusting the several variables to fit geochemical data core saturations and observed levels of oil and gas production this application demonstrates that the equations are easily applied in calculating depths of primary migration for low permeability source rocks

geochemical effects of petroleum migration and expulsion from toarcian source rocks in the hils syncline area nw germany for mature oil prone source rocks of toarcian age in the hils syncline area nw germany the geochemical effects of primary migration of petroleum are shown expulsion has occurred at high efficiencies primarily via a network of macro and micro fractures the effects of this fracture controlled expulsion with respect to gross and molecular composition of c15 soluble organic matter are documented samples from fractured intervals have expelled total c15 soluble organic matter more efficiently than adjacent unfractured intervals a systematic comparison of samples taken at cm intervals away from macro fractures reveals compositional gradients which are interpreted to reflect preferential depletion of saturated and aromatic hydrocarbons from the source rock shale into the fractures extracts of shale samples directly at fracture walls are enriched in nso compounds and highly polar asphaltene like fractions the composition of residual petroleum fluids extracted from the fracture fill materials is variable in some cases there is a close match with that of the shale at some distance away from the fractures in other cases there is geochemical evidence to suggest that petroleum fluids were chemically altered during lateral flow along the fractures based on available geological and geochemical evidence a conceptual model is proposed to explain fracture development and fluid flow processes rapid heating by a nearby intrusive body at shallow depths when the toarcian sediments still contained about 15 20 pore water has played an important role overpressuring of aqueous pore fluids with abundant dissolved carbonate caused intense fracturing of the rich intervals in the mature toarcian sections finally the closely interdependent relationships between petroleum generation and petroleum migration processes are documented especially the evolution of these relationships with maturity progress from immature 0 48 rm to mature 0 68 and 0 88 rm and overmature 1 45 rm stages is shown for example in the maturity interval from 0 68 to 0 88 rm most of the measured shale compaction and porosity decrease is achieved by expulsion of petroleum for some samples there is an inverse relationship between kerogen quality and extractable hydrocarbon yields suggesting that expulsion efficiencies were higher from the better quality intervals because the petroleum achieved higher saturations and hence higher relative permeabilities

the effect of kerogen on the elastic anisotropy of organic rich shales abstractthe elastic properties of reservoir rocks are important for geomechanics applications the most important of which are analysis of stress changes due to production analysis of rock deformation and failure wellbore trajectory optimization and the design of hydraulic fractures organic rich shales are often observed to be strongly anisotropic due to the partial alignment of anisotropic clay minerals and the bedding parallel lamination of organic material within the shale neglecting shale anisotropy may lead to incorrect estimates of the in situ stress or stress changes resulting from production as a result isotropic models may fail to describe geomechanical behavior correctly the distribution of the organic phase plays an important role in determining the elastic properties of organic rich shales and this has a significant effect on production induced stress changes the presence of kerogen leads to a decrease in all of the elastic moduli and has a significant effect on the geomechanical b

lateral velocity variations in the andean foreland in argentina determined with the jhd method abstract lateral velocity variations in the andean foreland near san juan province argentina were detected by analyzing the station corrections computed as part of the joint location of local earthquake data the events recorded by a portable network panda have intermediate and shallow depths about 100 km and less than 40 km respectively the jhd technique was applied to intermediate depth events and to two subsets of shallow events that concentrate on two distinct geologic units precordillera and pampean ranges the computed station corrections have a strong dependence on the data processed analysis of the different patterns of corrections shows that the corrections are consistent with the presence of large scale lateral velocity variations bounded by major fault systems based on these corrections a qualitative velocity model is proposed that has relatively high velocities between the eastern precordillera and a westerly dipping plane on the eastern edge of pie de palo one of the mountain blocks of the pampean ranges velocities are lower immediately east of this plane and between the central and eastern precordillera this model has important tectonic implications because it suggests that there is a major boundary between the central and eastern precordillera and that the pampean basement whose extent is unknown underlies the eastern precordillera the existence of large velocity variations across the precordillera is consistent with a westward shift of almost 10 km of the relocated intermediate depth events and with the removal of an apparent westward dip opposite to the direction of subduction observed in the wadati benioff zone as determined from single event location the analysis of the intermediate depth events also exemplifies the deleterious effect on the jhd results introduced by the cancellation of small singular values in the computation of the station corrections

new geophysical insight into the origin of the denali volcanic gap summary volcanic gaps are segments of subduction zones that lack the volcanic activity usually found at these convergent margins they are regions where the necessary conditions to produce melt may appear favourable but where volcanoes are surprisingly absent from the surface in this study we present a new model that can explain the occurrence of such volcanic gaps it is based on seismic imaging and geodynamic modelling of the denali volcanic gap a 400 km wide region at the eastern end of the alaska aleutian subduction zone here the thick crust of the pacific plate and yakutat terrane subduct at shallow angle beneath north america a high resolution seismic profile clearly images the subducting crust undergoing progressive dehydration between 50 and 120 km depth and a negative subhorizontal velocity contrast at 60 km depth in the overlying mantle wedge we interpret this 60 km discontinuity as marking the top of a layer of partial melt that pools at the base of the overriding plate in steadystate subduction models melt accumulates at the apex of a vaulted mantle wedge the pinch zone from where it may break through the overlying lithosphere to the surface beneath the denali volcanic gap the pinch zone is absent or greatly reduced because shallow subduction of the yakutat terrane progressively cools the system and causes the slab to advance and replace the hot core of the mantle wedge this regime can be seen as the opposite of subduction rollback it prevents the formation of a pinch zone reduces the length of the melting column and causes melt to pool at the base of the overriding plate thus inhibiting magma generation and extraction

seismotectonics of the central denali fault alaska and the 2002 denali fault earthquake sequence in this article we analyze the spatial and temporal variations in the seismicity and stress state within the central denali fault system alaska before and during the 2002 denali fault earthquake sequence seismicity for 30 years prior to the 2002 earthquake sequence along the denali fault was very light with an average of four events with magnitude m l 3 per year we observe a significant increase in the seismicity rate prior to the m w 7 9 event of 3 november 2002 within its epicentral region starting about 8 months before its occurrence the majority of the aftershocks of the m w 7 9 event are located within the upper 11 km of the crust and form several persistent clusters with a few aseismic patches along the ruptured fault the most active aftershock source is associated with the epicentral region of the earthquake the overall b value of the aftershock sequence is 0 96 with the highest b values within the epicentral region we estimate that it will take 14 years for the seismicity rate to drop back to the background level the stress regime across the region varies in space and time the inferred stress regime prior to the 2002 sequence is predominately strike slip along the central part of the rupture zone the orientations of the least and intermediate stress axes are reversed after the 2002 earthquake sequence the maximum compressive stresses along the denali fault rotate clockwise by up to 35 the greatest rotations occur in the area of the rupture step over from the denali to the totschunda fault the inferred stress regime after the 2002 sequence reflects an interchanging thrusting and strike slip faulting along the ruptured fault the thrust faulting is concentrated in the epicentral region of the m w 7 9 event and along the rupture segments showing the largest surface offsets

rock physics of organic shales several publications over the last 20 years have established that black organic shales are generally characterized by strong velocity anisotropy low velocity in the bedding normal direction and relatively low density and porosity e g vernik and nur 1992 vernik and liu 1997 these rock properties are of interest in seismic attribute studies but even more so in geomechanical applications related to reservoir characterization and hydraulic fracture stimulation organic shales typically but not necessarily express strong vertical transverse isotropy vti with axis of symmetry perpendicular to the bedding parallel lamination and clay particle preferred orientation high resolution sem imaging figure 1 immediately reveals all these textural features in addition to silt grains and the lenticular distribution of the solid organic matter kerogen which in turn is characterized by significant intraparticle porosity in mature shales any ti medium is described by the five independent elastic consta

microfabric and rock properties of experimentally compressed silt clay mixtures abstract oedometric mechanical compaction tests were performed on brine saturated synthetic samples consisting of silt clay mixtures to study changes in microfabric and rock properties as a function of effective stress the silt consisted of crushed quartz 100 with grain size range between 4 and 40 m whereas the clay consisted of 81 kaolinite 14 mica illite and 5 microcline of grain size between 0 4 and 30 m five sample pairs ranging in composition from pure silt to pure clay were compacted to 5 and 50 mpa effective stress respectively sem studies were carried out to investigate microfabric changes in the mechanically compacted silt clay mixtures the degree of alignment of the different minerals present quartz mica illite and kaolinite were computed by using an image analysis software experimental compaction have measured the changes in the rock properties such as porosity and velocity as a function of effective stress for different mixtures of clay and silt clay rich samples showed a higher degree of mineral orientation and lower porosity compared to silt dominated samples as a function of effective stress pure clay sample had 11 porosity at 50 mpa effective stress whereas the pure silt sample retained about 29 porosity at the same effective stress the experiments showed that low porosity down to 11 is possible by mechanical compaction only a systematic increase in strain was observed in the silt clay mixtures with increasing clay content but the porosity values found for the 50 50 silt clay mixture were lower than that of 25 75 silt clay mixture no preferential mineral orientation is expected before compaction owing to the high initial porosity suggesting that the final fabric is a direct result of the effective stress both p and s wave velocities increased in all silt clay mixtures with increasing effective stress the maximum p and s wave velocities were observed in the 25 75 silt clay mixture whereas the minimum vp and vs were recorded in the pure silt mixture at 50 mpa effective stress p wave velocities as high as 3 km s resulted from experimental mechanical compaction alone the results show that fine grained sediment porosity and velocity are dependent on microfabric which in turn is a function of grain size distribution particle shape sediment composition and stress at 5 mpa effective stress quartz orientation increased as a function of the amount of clay indicating that clay facilitate rotation of angular quartz grains adding clay from 25 to 75 in the silt clay mixtures at 50 mpa effective stress decreased the quartz alignment the clay mineral orientation increased by increasing both the amount of clay and the effective stress the mica illite fabric alignment being systematically higher than that of kaolinite even small amount of silt 25 added to pure clay reduced the degree of clay alignment significantly this study demonstrates that experimental compaction of well characterized synthetic mudstones can be a useful tool to understand microfabric and rock properties of shallow natural mudstones where mechanical compaction is the dominant process

subduction of oceanic asthenosphere a critical appraisal in central alaska song and kawakatsu 2012 have shown that the sub slab fast splitting pattern observed in most subduction zones can be a direct consequence of subduction of the oceanic asthenosphere that has strong radial anisotropy this model not only explains the non intuitive trench parallel splitting pattern in most of subduction zones but also predicts the trench normal behavior fast polarization direction sub parallel to the absolute plate motion of the incoming plate observed in several shallow subduction zones the general validity of such a scenario is crucial to fundamental understandings of the development of mantle anisotropy in sub lithosphere or and sub slab conditions the nature and formation of oceanic asthenosphere as well as the flow pattern and mass transport near subduction zones to validate this scenario we examine sks splitting patterns observed across the fore arc in central alaska here the fast splitting direction varies from plate motion sub parallel near the trench to mostly trench parallel beyond the 100 km slab isodepth contour while being strongly variable in between after taking into account the rotation of anisotropy symmetry in the oceanic asthenosphere with respect to the local plate motion obliquity and down dip variations in the slab dip we reproduce a general 90 degree switch in fast splitting direction as well as the back azimuth dependent splitting pattern across the entire fore arc the current validation further augments the idea that apart from anisotropy in the mantle wedge and the subducting slab subduction of the oceanic asthenosphere is likely to be the dominant source of seismic anisotropy in central alaska and potentially in many subduction zones furthermore this result also provides alternative views to models of seismic anisotropy in the mantle wedge and on the length scale in which the 3d mantle flow may be important

a comprehensive study of the seismicity of the kenai peninsula cook inlet region south central alaska abstract we compare 30 yr of background seismicity of the kenai peninsula cook inlet region extending from eastern prince william sound kayak island to west of the cook inlet volcanic arc to potential field gravity magnetics tomographic global positioning system geodesy and geologic information to better determine factors controlling seismicity we also compare the occurrence of m w 5 events over the past 80 100 yr to background seismicity in an effort to determine how reflective background seismicity is of the regional seismic hazard our results indicate that contrasts in upper plate rheology leading to changes in density magnetic susceptibility and velocity of the upper plate serve to concentrate seismicity the southwestern edge of the subducting yakutat microplate has a strong influence on both upper and lower plate seismicity density and velocity contrasts also indicate changes in lower plate rheology that influence the location of deeper 30 km seismicity and the occurrence of a double seismic zone within the subducting pacific plate

microscopic and sedimentologic evidence for the generation and migration of hydrocarbons in toarcian source rocks of different maturities abstract this study is part of a comprehensive research program on the generation and migration of petroleum from the organic rich posidonia shale lower toarcian jurassic of the hils syncline northern germany four cores of the complete posidonia shale with varying amounts of underlying pliensbachian and overlying aalenian mudstones provided the sample base depending upon their distance from a presumed subjacent heat source the vlotho massif the cores display progressive levels of increasing thermal maturation with r 0 values 0 48 0 68 0 88 and 1 45 which span the limits of the oil generation window primary stratigraphic lithologic and petrographic attributes of the four sections are all very similar each includes a lower marlstone member about 5 m thick overlain by 11 31 m of calcareous clay shale clay minerals calcite pyrite kerogen and quartz are the principal constituents thus there is no evidence that depositional conditions of the posidonia shale varied significantly over the sampled area the omnipresence of framboidal pyrite clearly formed from the activity of sulphate reducing bacteria at or near the depositional interface is strong evidence that uniform reducing anoxic conditions were persistent at all localities this conclusion supports the assumption that initially each section was identical in overall properties and that significant differences observed in geochemistry organic macerals and other properties are directly related to the variable levels of thermal maturation kerogen from the least mature section r o 0 48 is type ii and composed of alginite a alginite b liptodetrinite bituminite and some terrestrial sporinite vitrinite and inertinite macerals with increasing maturation the alginite macerals exhibit a progressive change in morphology and fluorescence properties alginite of the least mature section displays a strong green fluorescence at 0 68 r o alginite macerals exhibit yellow orange fluorescence and are structurally well preserved although geochemical data indicate generation and loss of large amounts of oil at 0 88 r o hydrocarbon generation is almost complete and few primary alginites remain they have been transformed into secondary liptinites designated as metaalginite which have similar fluorescence colours at the highest maturation level 1 45 r o metaalginites are only weakly fluorescent with a shift toward red colours calcite and or bitumen filled bedding plane micro and macrofractures occur exclusively in the organic rich posidonia shale at maturity levels of 0 68 r o and above such features are totally absent in the immature posidonia section and in the adjacent organic poor mudstones this observation indicates that the fractures developed in direct response to overpressuring i e pore pressure exceeding lithologic load related to oil and gas generation in the source rock the fractures undoubtedly provided important expulsion conduits for generated products

a practical model for organic richness from porosity and resistivity logs a practical method the delta log r technique for identifying and calculating total organic carbon in organic rich rocks has been developed using well logs the method employs the overlaying of a properly scaled porosity log generally the sonic transit time curve on a resistivity curve preferably from a deep reading tool in water saturated organic lean rocks the two curves parallel each other and can be overlain since both curves respond to variations in formation porosity however in either hydrocarbon reservoir rocks or organic rich non reservoir rocks a separation between the curves occurs using the gamma ray curve reservoir intervals can be identified and eliminated from the analysis the separation in organic rich intervals results from two effects the orosity curve responds to the presence of low density low velocity kerogen and the resistivity curve responds to the formation fluid in an immature organic rich rock where no hydrocarbons have been generated the observed curve separation is due solely to the porosity curve response in mature source rocks in addition to the porosity curve response the resistivity increases because of the presence of generated hydrocarbons the magnitude of the curve separation in non reservoirs is calibrated to total organic carbon and maturity and allows for depth profiling of organic richness in the absence of sample data this method allows organic richness to be accurately assessed in a wide variety of lithologies and maturities using common well logs

recurring patterns of total organic carbon and source rock quality within a sequence stratigraphic framework sequence stratigraphy has been combined with total organic carbon toc analysis from well logs core and cuttings to develop a model of toc accumulation in marine source rocks routine well profiling of toc in marine source rocks has revealed that recurrent patterns in the vertical distribution of toc occur that can be explained with sequence stratigraphic concepts the model assumes that the principle controls on organic carbon accumulation are 1 the presence of low oxygen conditions at the sediment water interface and 2 sedimentation rate under these circumstances toc will vary inversely with terrigenous clastic influx if accommodation is high clastic influx is low in distal locations and the resulting weight percent toc in basinal sediments is increased th maximum toc in a vertical profile through a single marine sequence probably correlates to the maximum flooding surface toc decreases above this surface due to increasing sediment dilution during highstand progradation and decreases below it with the higher sedimentation rate of the older transgressive systems tract commensurate with toc increase towards the maximum flooding surface the organic matter type becomes more marine and therefore increasingly oil prone several marine source rock examples are presented as well as a lacustrine example which also conforms to the marine model

a review of the geodynamic evolution of flat slab subduction in mexico peru and chile abstract subducting plates around the globe display a large variability in terms of slab geometry including regions where smooth and little variation in subduction parameters is observed while the vast majority of subduction slabs plunge into the mantle at different but positive dip angles the end member case of flat slab subduction seems to strongly defy this rule and move horizontally several hundreds of kilometers before diving into the surrounding hotter mantle by employing a comparative assessment for the mexican peruvian and chilean flat slab subduction zones we find a series of parameters that apparently facilitate slab flattening among them trench roll back as well as strong variations and discontinuities in the structure of oceanic and overriding plates seem to be the most important however we were not able to find the necessary and sufficient conditions that provide an explanation for the formation of flat slabs in all three subduction zones in order to unravel the origin of flat slab subduction it is probably necessary a numerical approach that considers also the influence of surrounding plates and their corresponding geometries on 3d subduction dynamics

unusual mantle poisson s ratio subduction and crustal structure in central alaska 1 subduction zones alter the upper plate in a variety of ways including metasomatism via slab derived fluids and accretion of exotic terranes these processes should produce distinctive seismic signatures as seismic velocities are sensitive to compositional variations a new method is developed to estimates depths to interfaces and poisson s ratio vp vs ratio for dipping layered structures by stacking teleseismic receiver functions it also estimates crustal vp vs and thickness using this method we analyze a broadband data set from the central alaska subduction zone to seek evidence for mantle wedge composition crustal thickness varies from 27 to 45 km and crustal vp vs indicates an intermediate to mafic composition expected for these accreted island arc terranes inversions for mantle structure confirm the presence of a 15 20 km thick low velocity zone atop of the downgoing plate to 130 km depth perhaps subducted crust of an exotic terrane vp vs in the mantle wedge allows for 15 15 serpentinization where the slab is 80 km deep and the wedge is cold where the slab is deeper vp vs for the mantle wedge is unusually low 1 7 this value is lower than predicted for any common mantle mineral and may indicate significant quantities of quartz provided that past physical properties measurements are not grossly in error these results suggest that the mantle wedge in subduction zones can occasionally differ substantially in bulk composition from normal subcrustal mantle perhaps because collisions of exotic terranes cause tectonic mixing of crustal material into the mantle

relocation of earthquakes in the cook inlet area south central alaska using the joint hypocenter determination method abstract the joint hypocenter determination jhd method was used to relocate 1604 earthquakes that occurred during 1988 to 1993 in the wadati benioff zone wbz beneath the cook inlet in south central alaska the study utilizes both p and s wave arrivals recorded by a recently improved regional seismic network and it provides an improvement over previous studies the jhd locations of the events allowed improved delineation of the geometry of the subducted slab and the detection of a double seismic zone within the wbz in the 40 to 100 km depth range the jhd station corrections obtained correlate with the major surface geological features in the study area slow velocity sedimentary basins as well as with crustal and mantle structure high velocity subducting slab and low velocity anomalies beneath the active volcanoes to investigate the dependence of the jhd relocation procedure on factors such as the hypocentral depths of the events used the velocity model the p s ratio and random and systematic errors in travel time readings synthetic travel times were calculated using an exact raytracing technique a three dimensional tomographic p wave velocity model the present network configuration and the actual seismicity distribution then the synthetic events were located with the jhd algorithm the synthetic experiments showed that the jhd procedure is rather insensitive to the choice of plane layered velocity model and p s ratio preserves relative hypocenter locations well and can handle systematic and large random reading errors effectively

compaction processes and rock properties in uplifted clay dominated units the egersund basin norwegian north sea abstract a thick succession of fine grained sediments in any sedimentary basin can serve as source if organic rich and top seals both sealing and petroleum generation capacity of any fine grained succession is dependent on compaction history mechanical and chemical compactions of the sediments in the egersund basin a thick succession of fine grained sediments of upper jurassic lower cretaceous age overly middle jurassic reservoir sands the egersund basin however has experienced a complex depositional and tectonic history particularly late exhumation neogene which complicates the overall burial thermal and pressure history in this study petrophysical and acoustic properties bulk density and p wave velocity of 10 exploration wells from two neighboring blocks in the egersund basin were utilized to investigate compaction processes in the area in addition x ray diffraction xrd and scanning electron microscopy sem analyses from selected wells and available total organic carbon toc data were used as guide to interpret the compaction processes and resulting rock properties the results show that the transition from mechanical to chemical compaction is not sharp the onset of chemical compaction imposes a measurable deviation in the burial depth trends of the petrophysical properties expected from purely mechanical compaction the continuation of the depth related trends however indicates that chemical compaction may occur in concurrent with continuing mechanical compaction the observed compaction varies between the different clay dominated stratigraphic units indicating that the major control on both mechanical and chemical compaction is the primary sediment composition

crustal earthquakes in the cook inlet and susitna region of southern alaska abstract several large m 6 earthquakes have occurred in the vicinity of anchorage alaska within the past century the presence of the underlying subducting pacific plate makes it difficult to determine the origin of these older earthquakes as either crustal slab or the subduction plate interface we perform a seismological study of historical and modern earthquakes within the cook inlet and susitna region west of anchorage we first estimate hypocenters for historical large earthquakes in order to assess their likelihood of origin as crustal slab or plate interface we then examine modern crustal seismicity to better understand the style of faulting and the location of active structures including within and beneath the cook inlet and susitna basins we perform double couple moment tensor inversions using high frequency body waves 1 10 hz for small to moderate m 2 5 crustal earthquakes depth 30 km occurring from 2007 to 2017 our misfit function combines both waveforms differences as well as first motion polarities in order to obtain reliable moment tensor solutions the three focus regions beluga upper cook inlet and susitna exhibit predominantly thrust mechanisms for crustal earthquakes indicating an overall compressive regime within the crust that is approximately consistent with the direction of plate convergence mechanisms within upper cook inlet have strike directions aligned with active anticlines previously identified in cook inlet from active source seismic data our catalog of moment tensors is helpful for identifying and characterizing subsurface faults from seismic lineaments and from faults inferred from subsurface images from active source seismic data

alaska megathrust 2 imaging the megathrust zone and yakutat pacific plate interface in the alaska subduction zone we image the slab underneath a 450 km long transect of the alaska subduction zone to investigate 1 the geometry and velocity structure of the downgoing plate and their relationship to slab seismicity and 2 the interplate coupled zone where the great 1964 earthquake mw 9 2 exhibited the largest amount of rupture the joint teleseismic migration of two array data sets based on receiver functions rfs reveals a prominent shallow dipping low velocity layer at 25 30 km depth in southern alaska modeling of rf amplitudes suggests the existence of a thin layer vs of 2 1 2 6 km s that is 20 40 slower than underlying oceanic crustal velocities and is sandwiched between the subducted slab and the overriding plate the observed megathrust layer with vp vs of 1 9 2 3 may be due to a thick sediment input from the trench in combination with elevated pore fluid pressure in the channel our image also includes an unusually thick low velocity crust subducting with a 20 dip down to 130 km depth at 200 km inland beneath central alaska the unusual nature of this subducted segment results from the subduction of the yakutat terrane crust our imaged western edge of the yakutat terrane aligns with the western end of a geodetically locked patch with high slip deficit and coincides with the boundary of aftershock events from the 1964 earthquake it appears that this sharp change in the nature of the downgoing plate could control the slip distribution of great earthquakes on this plate interface

insights into mantle structure and flow beneath alaska based on a decade of observations of shear wave splitting sks shear wave splitting measurements from three program for array seismic studies of the continental lithosphere experiments broadband experiment across the alaska range alaska receiving cross transect of the inner core and multidisciplinary observations of subduction which form a north south transect across alaska show a remarkably simple pattern of two large anisotropy domains in the northern domain extending from the 70 km contour of the subducting pacific plate north to the arctic ocean fast directions are consistently in the ne sw direction these directions are essentially parallel to the absolute plate motion direction in northern alaska and parallel to the strike of the subducting plate above the mantle wedge suggesting that they represent some combination of plate scale asthenospheric flow in the upper mantle and flow along the subducting plate in the mantle wedge a strong wedge component beneath the alaska range is required to explain systematics of splitting delay times in the southern domain which extends south from the 70 km depth contour to the subducting plate fast directions are in the nw se direction a 90 rotation from the northern domain these fast directions are parallel to the dip of the subducting plate in the direction of convergence and represent entrained flow beneath the subducting slab the pacific plate absolute motion approximately parallels local convergence two major factors seem to control flow in these regions absolute plate motion in the north and the subduction of the pacific plate in the south although both subduction driven wedge flow and absolute plate motion contribute to the southern part of the northern regime

joint hypocentral location in media with lateral velocity variations and interpretation of the station corrections abstract the application of a new implementation of the joint determination of hypocenters origin times and station correction terms jhd technique to data from the arkansas swarm usa the campi flegrei italy and the nazca plate argentina throws new light onto the problem of earthquake location in all these cases good quality p and s wave arrival times were available the main results are as follows 1 large lateral velocity variations llvv are generally associated with relatively large station corrections these corrections in turn are usually much larger than the average of the station residuals determined when the same set of events is located using a single event location sel method 2 the locations determined by the jhd and sel methods may be substantially different 3 since the effect of llvv on jhd locations is not well established simple 3 d velocity models are constructed so that the jhd technique applied to synthetic data generated using these models produce station corrections similar to those observed 4 the analysis of the synthetic data also shows that the locations determined by the jhd method are much closer to the true locations than the locations determined with the sel method the use of the weighted average of the sel station residuals as station corrections does not give better located events although there is a large decrease in the r m s residual computed for each event therefore the use of r m s residuals to estimate the quality of event locations is not always warranted in view of these results it is possible to conclude that the jhd station corrections can be used to detect lateral velocity variations and to produce locations substantially less affected by these variations than the locations determined by the sel method furthermore under appropriate conditions the jhd station corrections can also be used in a forward modeling scheme to get a semiquantitative velocity model such a model may be the only information that can be obtained from a data set when the station and event distributions are not adequate for 3 d velocity inversion

influence of geometry and eclogitization on oceanic plateau subduction abstract subduction is driven by the negative buoyancy of the slab which depends on both the temperature and composition of the lithospheric plate in the case of subduction of an oceanic plateau larger thickness of the lower density crust and harzburgite layers can locally decrease the negative buoyancy available to drive subduction however the ability of a plateau to have an impact on subduction depends on the total buoyancy of the slab and therefore also depends on size of the plateau and the basalt to eclogite transition which substantially increases the density of the crust using 2 d numerical finite element models of subduction we investigate the role of eclogitization and oceanic plateau size thickness and length in the process of oceanic plateau subduction model results show that eclogitization of the crust substantially increases the chances that a plateau will be subducted because the extra buoyancy of larger plateaus is lost through the phase transition for kinematically driven models all plateaus are subducted regardless of the thickness or width extrapolation of these results to 3 d geometry shows that sufficient slab buoyancy is available to sustain subduction for narrow plateaus with slab widths 6 7 times the plateau width depending on plateau thickness and length in dynamically driven models subduction of oceanic plateaus of various sizes can substantially slow subduction and large plateaus 200 km long and 25 km thick can lead to break off of the slab and underplating of the plateau

historical seismicity 1918 1964 of the kodiak island region i have relocated 35 earthquakes and conducted waveform modeling studies of 12 events located primarily within the kodiak portion of the 1964 great alaska earthquake rupture zone and the northeasternmost portion of the 1938 semidi earthquake rupture zone these results show that there is considerable similarity between earthquakes occurring before the 1964 mainshock pre 1964 mainshock seismicity and after the 1964 mainshock post 1964 mainshock seismicity persistent seismicity has occurred for the past 85 years at the southwestern end of the 1964 rupture zone a region where global positioning system gps geodesy studies indicate the plate interface is currently locked earthquakes also occurred frequently within the kennedy entrance region where the transition between the kodiak and kenai block of the subducting pacific plate occurs the seismic moment rate for post 1964 mainshock seismicity is about two times larger than for premainshock seismicity this is in contrast to the prince william sound portion of the 1964 rupture zone where post 1964 mainshock moment rates are orders of magnitude lower than pre 1964 mainshock rates and the pattern of seismicity has changed considerably with time these observations reinforce previous studies that indicate the behavior of plate subduction beneath the kodiak island region is much different from that beneath the prince william sound region

modelling of hydrocarbon generation patterns in the egersund sub basin north sea abstract hydrocarbon generation in the egersund sub basin has been modelled using empirical lopatin type and kinetic models and two prototypes of source rocks from wells 9 4 4 and 18 11 1 the amount of oil generated changes with initial heat flow type of generation model activation energies and source rock richness but does not follow a straightforward pattern for example at lower thermal histories the amount of oil generated up to the present changes exponentially with initial heat flow variation due to change of activation energy distribution is linear to exponential depending on heating rate and variation due to source rock potential is linear the empirical model for oil generation is less sensitive to temperature and more sensitive to time than the kinetic models and appears to overestimate the amount of oil generated at low heating rates but underestimates it at high heating rates hydrocarbon yields predicted by the empirical model are usually 4 5 times higher than those predicted by the kinetic models for the drainage area of well 9 2 1 variation of initial heat flow between 1 15 and 1 25 hfu heat flow units results in a variation of output yield by a factor three if a minimum oil saturation of the pore volume of 10 is required for long distance migration the empirical model should have resulted in accumulations or oil shows also in the marginal drainage areas although not unambiguous the present hydrocarbon distribution can be explained best by generation from the kinetic model at thermal histories represented by initial heat flow between 1 20 and 1 30 hfu

three dimensional elastic dislocation modeling of the postseismic response to the 1964 alaska earthquake 1 gps velocity observations from the kenai peninsula and kodiak island alaska display a pattern of spatial variability suggesting the presence of multiple active processes on the underlying pacific north american plate interface velocities of sites on the eastern kenai peninsula and kodiak island are consistent with elastic strain accumulation at the plate interface whereas velocities of sites on the western kenai peninsula and cook inlet are oriented in the opposite direction and suggest an ongoing postseismic response to the 1964 alaska earthquake we can reproduce the observed velocities using a three dimensional elastic dislocation model to estimate the variation in coupling between the pacific and north american plates two different inversion schemes are examined to check the robustness of the results we find that the gps data can be satisfied by the presence of a locked area near southwest prince william sound a locked area near southwest kodiak island and an area of postseismic reverse slip beneath and north of the western kenai peninsula the shallow plate interface trenchward of the western kenai peninsula does not appear to be locked the locked areas correspond to the prince william sound and kodiak island asperities that ruptured in 1964 and the area of postseismic slip lies downdip of the 1964 rupture area the correspondence between the present shallow coupling distribution and the 1964 slip distribution suggests that the locked regions repeat from one earthquake cycle to another