a p wave velocity model of earth s core present earth core models derived from the retrieval of global earth structure are based on absolute travel times mostly from the international seismological centre isc and or free oscillation eigenfrequencies many core phase data are left out of these constructions e g pkp differential travel times amplitude ratios and waveforms this study is an attempt to utilize this additional information to construct a model of core p wave velocity which is consistent with the different types of core phase data available in conjunction with our waveform modeling we used 150 differential time measurements and 87 amplitude ratio measurements which were the highest quality observations chosen from a large population of global digital seismograph network gdsn records as a result of fitting these various data sets a one dimensional p wave velocity model of the core prem2 is proposed this model modified from the preliminary reference earth model prem dziewonski and anderson 1981 shows a better fit to the combined data set than any of the existing core models major features of the model include a sharp velocity discontinuity at the inner core boundary icb with a large jump 0 78 km s and a low velocity gradient at the base of the fluid core the velocity is nearly constant over the lower 100 km of the outer core the model features a depth dependent q structure in the inner core such that a constant t for the inner core fits the amplitude ratios and waveforms of short period waves moderately well this means the top of the inner core is more attenuating than the deeper part of the inner core in addition the p velocity in the lowermost mantle is reduced from that of prem as a baseline adjustment for the observed separations of the df and ab branches of pkp at large distances

on the visibility of the inner core shear wave phase pkjkp at long periods summary stacks of over 90 000 long period seismograms recorded by the global seismic networks resolve many seismic phases but fail to detect the inner core shear phase pkjkp we compare these results to synthetic seismograms computed for prem using the spectral element method and show that expected pkjkp amplitudes are over 10 times smaller than signal generated noise caused by high order p surface multiples and reverberations from upper mantle discontinuities indeed pkjkp can only be seen in synthetic seismograms when differences are taken between two sets of synthetics generated from earth models with slightly different innercore shear velocities these results suggest that routine observation of pkjkp is unlikely and that reported observations if real must have resulted from exceptional focusing effects or inner core attenuation much less that current models

observations of exotic inner core waves the seismic structure of earth s inner core is highly complex displaying strong anisotropy and further regional variations however few seismic waves are sensitive to the inner core and fundamental questions regarding the origin of the observed seismic features remain unanswered thus new techniques to observe different types of inner core waves are imperative to improve data coverage here we detail our method for detecting exotic inner core phases such as pkjkp and pkiikp using inner core compressional waves as proof of concept we use phase weighted stacking on long period data from a global distribution of stations and employ several synthetic methods including normal mode summation and specfem to identify and confirm the inner core phases we present evidence for two observations of exotic inner core compressional waves and apply the technique to a previously detected inner core shear wave a possible new inner core shear wave remains unconfirmed additionally we show how our method is important for rejecting potential observations and distinguishing between waves with similar traveltime and slowness the method is most successful for detecting exotic inner core compressional waves and will provide a new approach for studying the compressional wave structures in the upper inner core

observations of pkikp pcp amplitude ratios and implications for earth structure at the boundaries of the liquid core 1 mining of the database produced by seismic array stations of the international monitoring system has resulted in hundreds of new observations of precritical reflections from earth s inner core here we present short period amplitude ratios between these pkikp phases and corresponding reflections pcp from the core mantle boundary cmb pkikp pcp amplitude ratios are one of the few seismic observations that directly constrain the change in s velocity and density across the inner core outer core boundary we measure the amplitude ratios from optimally tuned array beams and use a bootstrap technique to estimate observational uncertainties we also use a model resampling technique to estimate uncertainties associated with the background reference model the optimal models have s velocities at the top of the inner core less than about 2 5 km s and density jumps across the inner core outer core boundary of less than about 0 45 g cm3 these values can be reconciled with the higher estimates from normal mode constraints if strong radial gradients are present in the top of the inner core or if the outermost inner core has material properties distinct from the bulk of the inner core we also find evidence for an ultralow velocity zone in the lowermost mantle beneath the eastern coast of australia a unique best fitting model cannot be determined but an example that is consistent with the data has a reduction in p velocity of 10 a reduction in s velocity of 35 and an increase in density of 20 this type of structure could be explained by the presence of partial melt and increased iron content just above the cmb

a deep earthquake aftershock sequence and implications for the rupture mechanism of deep earthquakes a distinguishing characteristic of deep earthquakes has been the absence of observable aftershock sequences1 2 here we report the first extensive deep earthquake aftershock sequence to be observed it was recorded by an array of eight broadband seismographs following the 9 march 1994 deep tonga earthquake the aftershocks show a power law decay with time following the main shock as is typical of shallow events most of the well located aftershocks are concentrated along a steeply dipping plane consistent with one of the nodal planes of the main shock mechanism and the mechanisms of three large aftershocks assuming these aftershocks denote the main shock rupture area they define a 50 65 km fault plane extending across the entire width of the active seismic zone and into the surrounding aseismic region the width of the aftershock zone is wider than the expected width of the metastable olivine wedge demonstrating that either the width of the metastable olivine material exceeds previous estimates or the aftershocks are not confined in such a wedge

the complex rupture process of the 1996 deep flores indonesia earthquake mw 7 9 from teleseismic p waves from an analysis of broadband teleseismic p waveforms we resolve the complex rupture characteristics of the 17 june 1996 flores earthquake mw 7 9 depth 590 km this earthquake was unusual because of its large rupture length and the variation in rupture velocity and stress drop the 20 s rupture propagated westward at 2 3 km s to a distance of 20 30 km and eastward at 4 km s over 75 km average static stress drop was about 15 mpa but the stress drop during the episode of main moment release was a factor of four higher the oblique normal faulting mechanism is consistent with the stress expected as the slab descends along a highly curved trench significant rupture complexity is also reported for the deep 1994 mw 7 7 fiji and mw 8 2 bolivia earthquakes and is evident in the source time functions of many smaller earthquakes at depths 300 km thus source complexity of deep earthquakes appears no less common than for shallow earthquakes and requires the existence of significant heterogeneity in the physical properties that control deep earthquake rupture

source rock characteristics of the lower cretaceous abu gabra formation in the muglad basin sudan and its relevance to oil generation studies organic rich shale and claystone are present within the lower cretaceous abu gabra formation of the muglad basin representing excellent oil source rocks the source rock potential of abu gabra organicrich whole rock samples from two oilfields in the muglad basin was investigated using bulk and quantitative pyrolysis techniques the analytical program included toc pyrolysis sra pyrolysis gc bulk kinetics elemental analysis and kerogen microscopy the results were used to characterize the kerogen composition and type of petroleum generated from these abu gabra organic rich sediments to clarify the structural variability of the organic matter in the abu gabra source rock the investigated abu gabra organic rich sediments proved to contain excellent quality lacustrine kerogens the samples have moderate to high hydrogen index hi values 267e837 mg hc g rock consistent with predominantly oil prone types i and ii kerogen with a minor contribution of type iieiii kerogens this is supported by the abundant liptinitic materials i e lipid rich structured algae structureless amorphous alginite and sporinite and high atomic hydrogen to carbon h c ratio however pyrolysis gc analysis proved that all the investigated abu gabra samples contain homogeneous type i kerogen that produces mainly waxy oil bulk kinetic experiments on these samples indicate that the source rock facies derived from a homogenous organic matter spans an extremely narrow distribution of activation energy ea ranges from 49 kcal mol to 51 kcal mol the magnitude order of frequency factors a also show a narrow distribution range from 10

tectonostratigraphic development of the interior sudan rifts central africa abstract in the muglad melut and blue nile rift basins of interior sudan three major episodes of rifting concomitant subsidence and nonmarine nonvolcanic sedimentation are recognized these three rifting cycles which spanned 140 to 95 ma fl 95 to 65 ma f2 and 65 to 30 ma f3 resulted in the accumulation of up to 5400 4200 and 5400 m of sediments respectively in the muglad basin the best known and largest of the sudan rift basins each rifting cycle consists of 1 a basal sandstone unit at least near rift margins that is followed by 2 an upward coarsening section of lacustrine shale grading through marginal lacustrine mudstone and sandstone into fluvial mudstone and sandstone and 3 a capping blanket of fluvial and alluvial sandstone the shale dominated portions of these cycles were deposited in a closed drainage basin during active faulting the fluvial and alluvial blanket sands were deposited in an open drainage basin during the thermal sag phase following each tectonic cycle the early cretaceous f1 intracontinental rifts of interior sudan were linked to major rifts spreading centres in the proto south atlantic by the dextral wsw trending central african shear zone and to the indian ocean via the nw trending anza rift in kenya in the muglad basin f1 deformation involved high strain rates rapid syn rift crustal stretching and subsidence and the formation of deep fault bounded tensional and transtensional pull apart basins during the f2 and f3 deformations the rates of subsidence and stretching were much lower and were focused within smaller geographic areas structural elements include asymmetric half grabens and less common full grabens with central highs the three superimposed tectonic episodes resulted in the subsidence of nnw to nw trending rift sub basins this gave rise to a wide variety of normal fault geometries displacements and growth histories planar domino style and listric normal f1 fault arrays are modeled the rotated f1 basement blocks typically are asymmetric and low standing and favour ne directed growth and material transport the f2 and f3 normal faults which have both ne and sw directed polarities often are listric and decouple younger syn rift strata from older f1 rotated and locked planar basement faults palinspastic restorations and forward modeling of three regional cross sections suggest that f1 faults account for 65 80 of total crustal extension stretching factors across the interior sudan rifts vary between 1 25 and 1 40 this range is considered to be a minimum since restored sections do not cross f3 depocenters total crustal extension across the muglad plus the melut rift basins exceeds 75 km

an automatic seismic event processing for detection and location the p m c c method we present a new method for automatic detection and location of seismic events recorded on a network it is based on a progressive study of the interstation correlation functions which leads to a consistent set of time delays when a seismic phase is present three different examples are processed on networks of different sizes

detection of pkjkp at intermediate periods by progressive multi channel correlation abstract we have identified the seismic phase pkjkp traveling through the inner core of the earth as a shear wave in intermediate period 2 10 s records of the deep 1996 flores sea earthquake at eight stations of the french seismic network this constitutes direct evidence of the solidity of the inner core which while generally recognized was until now only inferred from indirect evidence the arrival times on stacked seismograms require a shear wave velocity at the top of the inner core icb 3 65 km s in agreement with values suggested from normal mode observations julian et al s 1972 observation of a lower velocity 2 95 km s is easily reconciled with our result if interpreted as the surface reflection ppkjkp the high poisson ratio 0 44 can be reconciled with a normal crystalline structure without invoking partial melting on account of the overwhelming pressure at the center of the earth

organic geochemical and petrographic characteristics of neogene organic rich sediments from the onshore west baram delta province sarawak basin implications for source rocks and hydrocarbon generation potential abstract the neogene succession of the onshore petroleum prolific west baram province of north west borneo contains organic rich sediments particularly within sarawak basin bulk and quantitative pyrolysis results coupled with organic petrographic characteristics of neogene organic rich sediments have enabled investigation of the source rock characteristics and evaluation of the hydrocarbon generation potential the results were used to assess the quantity of organic matter kerogen composition thermal maturity and type of petroleum that could possibly be generated from these neogene sediments the total organic carbon toc contents of the neogene sediments range between 1 06 and 11 11 wt and hydrogen index hi values are largely below 105 mg hc g toc suggesting that the sediments are organically rich and contain gas prone type iii kerogen this kerogen type is supported by the abundant terrestrial materials i e vitrinite phytoclasts spores and pollen low atomic hydrogen to carbon atomic h c ratio and high abundance of aromatic hydrocarbons in pyrolysis gc pyrograms and would likely generate mainly condensate and gas the analysed samples have vitrinite reflectance in the range of 0 39 0 48 ro and pyrolysis t max in the range of 401 434 c which indicate that these neogene sediments contain immature to very early mature organic matter this implies that these onshore sediments have not been buried to a sufficient depth however the offshore stratigraphic equivalent of these sediments are known to have been buried to deeper depth and could therefore act as an effective petroleum source rock in particular for natural gas

a decision analysis framework for the assessment of likely post failure velocity of translational and compound natural rock slope landslides an integral component of the assessment of hazard and risk for landslides from large natural rock slopes is the examination of the likely consequences associated with failure this in turn is inherently related to the post failure velocity of the slide mass this paper presents a decision analysis framework for assessment of the post failure velocity of such slopes the paper includes discussion of characteristics that influence the post failure velocity and presents decision trees and supporting matrices to allow assessment of the likely post failure velocity of translational and internally sheared compound landslides these represent the most common classes of large rock landslides the framework is based on data gathered from a large number of landslides from natural rock slopes and incorporates information from a study of excavated rock slopes these landslides have been studied to determine the factors and characteristics of rock slope failures that influence the post failure velocity the framework

geological and morphological study of the daguangbao landslide triggered by the ms 8 0 wenchuan earthquake china abstract landslides are one of the most significant geomorphic processes in mountainous regions recently a gigantic landslide daguangbao dgb landslide with a volume of 1 2 109 m3 was triggered by the ms 8 0 wenchuan earthquake china and has attracted widespread attention this landslide 28 38 16 93 e 104 06 02 35 n is located 85 km north northeast nne of the epicenter and on the hanging wall side 4 km away from the surface rupture zone of the earthquake our long term 2008 present study which includes topographic interpretation and geological and geomorphological investigations allows us to define the geological model of the dgb landslide and estimate the initiation and traveling mechanisms the topography was studied by using high resolution digital elevation models arial images and abundant photos at different scales are used to performed geomorphological analysis the geology in the landslide area was studied by exploratory trenches a tunnel and terrestrial laser scanning tls the results show that the mass movement destabilized a folded slope along a deep seated average depth of 400 m bedding fault developed in the dolomite of the sinian formation the morphology of the landslide main scarp is characterized by steep 55 75 and high up to 730 m release surfaces resulting from the linkage of three joint sets an excess pore water pressure dependent loss of shear strength at the basal layer during the earthquake is assumed to have favored landslide initiation an internal shear running subparallel to the stratification surface is confirmed to have dominated the longitudinal mobility of the landslide and driven landslide mass thrusting to a height of 500 m on the slopes on the other side of the valley the dgb landslide as a transient destabilization and morphogenesis event has largely contributed to erosion in the study area

observations of high frequency scattered energy associated with the core phasepkkp stacks of global seismic network data reveal emergent high frequency 1 hz energy extending back from the pkkpc caustic at 72 to a distance of about 60 the arrival s emergent onset long duration 150 s apparent slowness and proximity to the core phase pkkp indicate a deep scattering origin however the amplitude and timing of the observations are difficult to explain with simple models of pkkp scattering

shear properties of earth s inner core constrained by a detection of j waves in global correlation wavefield seismic j waves shear waves that traverse earth s inner core provide direct constraints on the inner core s solidity and shear properties however these waves have been elusive in the direct seismic wavefield because of their small amplitudes we devised a new method to detect j waves in the earthquake coda correlation wavefield they manifest through the similarity with other compressional core sensitive signals the inner core is solid but relatively soft with shear wave speeds and shear moduli of 3 42 0 02 kilometers per second and 149 0 1 6 gigapascals gpa near the inner core boundary and 3 58 0 02 kilometers per second and 167 4 1 6 gpa in earth s center the values are 2 5 lower than the widely used preliminary earth reference model this provides new constraints on the dynamical interpretation of earth s inner core

three common source rock evaluation errors made by geologists during prospect or play appraisals geologists are frequently called on to evaluate the source rocks associated with their exploration prospects or plays the three most common questions asked and answered about the source rock during project reviews are what s the total organic carbon toc what kerogen type does rock eval indicate and what maturity level does the vitrinite reflectance data point to the answers to these seemingly innocuous questions may in fact be providing a false sense of security about the source rock in question understanding how this line of questioning can lead you astray and make you the victim of the toc myth if i have high toc i have a good source rock the rock eval fallacy the rock eval data tell me what kind of kerogen is in my source rock and the vitrinite reflectance deficiency vitrinite reflectance will tell me if my source rock is generating is important some of the solutions to these problems include fully integrating toc and rock eval data supplementing rock eval data with pyrolysis gas chromatography and using burial history diagrams to help interpret vitrinite reflectance harry dembicki jr is a senior geological advisor for geochemistry in the geological technology group at anadarko petroleum corporation where he provides technical support to both exploration and development teams he holds a b s degree 1973 in geology from the state university college of new york at new paltz and a ph d 1977 in geology with emphasis in organic geochemistry from indiana university he previously worked as an organic geochemist for conoco and marathon

zones of t wave excitation in the ne indian ocean mapped using variations in backazimuth over time obtained from multi channel correlation of ims hydrophone triplet data summary ground coupled hydro acoustic waves so called t waves observed at international monitoring system ims hydrophone triplet stations in the indian ocean were analysed for backazimuth and apparent wave speed by applying a progressive multi channel correlation method pmcc for t waves which propagate along topographically unblocked geodesic paths the three triplet channels generally show good signal correlation over sliding windows and various frequency bands a characteristic change in backazimuth over time in some cases combined with signs of dispersion is observed for many t waves generated by earthquakes from the margin of the indo australian plate between the sunda islands to the southeast and the andaman islands to the northwest backazimuths and arrival times of those pmcc detections are used to map point by point the areas where ground to water coupling takes place such areas are mostly linked to large gradients in the bathymetry predominantly at approximately the depth of the axis of the sound fixing and ranging sofar channel along island arcs edges of continental shelves and at comparatively small features like isolated islands or sea mountains six examples are discussed in this paper for the strongest events the area of detectable groundto water coupling often spans distances of more than 15 in one case even more than 26 and a range in backazimuths of up to 35 information on the accuracy of backazimuth determination on the average hydro acoustic wave speed along the wave path and on topographic blockage of waves can also be inferred from the results owing to the consistency and great detail of the mapped coupling zones for the study area it can be shown that it is predominantly seismic energy from p and or pn waves that couples efficiently into the sofar channel particularly for deep focus events the backazimuths determined for the highest amplitude segments of the signals can deviate considerably from the great circle azimuth between source and receiver and may therefore lead to inaccurate epicentre locations based on backazimuth measurements of t waves in some cases laterally reflected t waves are observed

geotechnical characteristics of large slow very slow and extremely slow landslides based on a study of 45 large slow moving landslides it is apparent that for a landslide to travel slowly after failure the sliding is most likely to be active or reactivated on a basal rupture surface at or close to residual strength the likelihood of slow movement after failure is also increased when the inclination of the basal rupture surface is less than the residual friction angle the slow moving landslides are all of low rock mass strength with varying degrees of disaggregation or they possess soil strength the influence of lateral margins on landslide restraint is generally small with landslide movement typically controlled by fluctuations in piezometric pressure the most commonly observed slow large landslides are mudslides and translational debris rock slides followed by particular forms of translational rock slides and internally sheared compound slides some mudslides display evidence of short periods of up to moderate velocities

geotechnical characteristics of large rapid rock slides based on the analysis of 51 case studies of large rapid rock slides for a landslide to travel rapidly after failure there has to be a significant loss of strength on the basal surface of rupture lateral margins and or internally within the slide mass or the factor of safety has to be maintained below 1 0 after failure by high groundwater pressures internally sheared compound slides and translational slides may all travel rapidly depending on their detailed geotechnical and geometric characteristics the characteristics of these landslides that suggest an increased likelihood of rapid failure have been identified all the rapid rock slides examined in this study involved relatively high strength rock masses most cases were considered to be first time landslides largely involving brittleness on the basal rupture surface however there were some cases considered to be reactivated or active landslides on pre sheared rupture surfaces for this latter group the loss of strength leading to rapid lands

normal mode constraints on shear and compressional wave velocity of the earth s inner core abstract free oscillation data are used to determine the average compressional and shear wave velocity structure of the earth s inner core and place tight constraints on their values the new data reinforce the argument for a solid inner core and the best data fit is obtained for average inner core velocities close to the prem reference model s 3 55 0 05 km s p 11 15 0 05 km s these values limit the time windows in which inner core shear waves like pkjkp may be observed inner core velocities for hcp and bcc iron at inner core conditions from ab initio molecular dynamics simulations and diamond anvil cell experiments are found to be incompatible with the seismological data in particular for the shear wave velocity when light elements are taken into account the misfit is worse than for a fluid inner core model the discrepancy between seismic and mineral physical values for the inner core shear wave velocity may be explained by an inner core temperature in excess of 6500 k the existence of fluid inclusions in the inner core the effect of viscoelastic weakening or crystal defects

inner core anisotropy in three dimensions the purpose of this paper is the investigation of cylindrical anisotropy in the inner core based on the travel time anomalies of the pkikp phase we use the arrival times reported in the international seismological centre bulletins for years 1964 1990 we select only earthquakes which have a good azimuthal coverage and a sufficiently large number of reporting stations the earthquakes are relocated using corrections for lateral heterogeneity computed for our most recent three dimensional mantle model we use a total of 313 422 observations of the df branch of pkp travel time anomalies within the epicentral distance ranges of 120 140 and 150 180 reported by 2335 stations for 26 377 earthquakes we process the data using an averaging procedure which we call cylindrical anisotropy stacking that enhances the effects of anisotropy but is expected to suppress those due to lateral heterogeneity and random errors the processed residuals show a remarkably consistent pattern this confirms the dominance of the cylindrical elastic anisotropy in the inner core with approximately a constant axis of symmetry this axis of symmetry is found to be tilted 10 5 1 from the earth s rotation axis in the direction 160 e 5 in the northern hemisphere in this new coordinate system we determine a four layer axisymmetric model of transverse anisotropy with each layer approximately 300 km thick the model shows that the anisotropy is strongest 3 within the innermost part of the core the travel time anomalies show significant 1 5 s longitudinal variations even when the tilt of the axis of symmetry is considered there is a substantial increase in the amplitude of the longitudinal variations which are dominated by the second and fourth harmonics for rays with bottoming depths exceeding 400 km below the inner core boundary the measurable tilt of the axis of symmetry and the presence of significant nonaxisymmetric signal may provide important clues with respect to the possible causes of anisotropy the increase in the anisotropy in the innermost part of the core departs from earlier inferences that anisotropy may be limited to the outermost 200 300 km of the earth s inner core

mars volatile evolution implications of the recent measurement of 17o in water from the snc meteorites escape of oxygen to space on mars is capable of producing a fractionation of oxygen isotopes in the remaining oxygen which is off of the fractionation line produced by the usual mass dependent exchange processes the magnitude of fractionation which can occur can be larger than that which was measured in oxygen in water derived from the snc meteorites thought to have come from mars in conjunction with the apparent lack of fractionation of 18o in the atmosphere this result suggests that less than 25 of the oxygen in the martian climate system has been lost over geologic time other mechanisms also might be able to produce such a fractionation so that this conclusion is not unique however it is consistent with other lines of evidence there is no requirement for an initial volatile inventory with an isotopic composition different from that of the bulk planet as might be the case for a late veneer of volatile rich material

an observation of pkjkp inferences on inner core shear properties the seismic phase pkjkp which traverses the inner core as a shear wave and would provide direct evidence for its solidity has been difficult to detect using stacked broadband records from the grafenberg array in germany we documented a high signal to noise phase the arrival time and slowness of which agree with theoretical predictions for pkjkp the back azimuth of this arrival is also consistent with predictions for pkjkp as is the comparison with a pseudoliquid inner core model envelope modeling of the pkjkp waveform implies a shear velocity gradient with depth in the inner core that is slightly larger than that in the preliminary reference earth model

bulk sound travel times and implications for mantle composition and outer core heterogeneity we present a new methodology for con straining mantle composition directly from observed seismic travel times by measuring travel times of pcp pcs scs and pkikp phases generated by the chi nese nuclear explosion of 21 may 1992 and recorded at cpiccntral distanccs of loo wc dircctly determine hulk sound travel li r es t for the mantle and outer core this eliminates the need to combine independcnt vp and vs profiles characterizing different paths and frequencies to obtain a reference vm profile our ob served piiikp pcp differential travel time indicates that the outer core model of ak135 is slow by 2 1 s that of iasp91 bv 2 3 sl while that of prem is slow by only 0 7 s and suggests through comparison with other data relative lateral homogeneity of the outer core furthermore we find that t for the crust and lanlle in this region exceeds the ak135 prediction by 3 5 s iasp91 by 3 9 s t1 o s since t he lowrr mnn tle contribution to this delay depends upon how much arises in the upper mantle we present two end member models for such a slower mantle vm in which the delay resides entirely above or below 660 km depth the lat ter yields best fitting lower mantle compositions which are less enriched in si than those fit to t for ak135 or iaspsi for the former and neither supports fe enrichment of the lower mantle applicability of such localized observations to the larger iirantle is suggested by tomographic results indicating that lateral hctcro geneity in i m is very small relative to that in 4 our results illustrate the potential utility of tom in constrain ing mantle composition

the observation of inner core shear waves summary although the earth s inner core has long been thought to be solid there have not as yet been unequivocal observations of inner core shear waves here we present observations of the phases ppkjkp and skjkp for the flores sea event of 1996 june 17 the observations support the value of approximately 3 6 km s 1 for the inner core shear wave velocity and open up new possibilities for exploring the anisotropic structure and the attenuation properties of the inner core the analysis and validation of the observation is based on a new method that can be used in the search for and identification of inner core shear waves in this method normal mode synthetics for a solid inner core are compared with those for a fluid inner core it is only by such comparisons that it is possible to be certain that inner core shear waves rather than interferences of other phases are responsible for observed energy maxima in stacked seismic records

hydrocarbon source potential of eocene miocene sequence of western sabah malaysia abstract an evaluation of the petroleum generating potential of onshore eocene miocene sequences of western sabah malaysia was performed based on organic petrological and geochemical methods the sequences analysed are the belait meligan temburong and west crocker formations of western sabah the belait formation which is stage iv equivalent in the offshore represents one of the major source rock reservoirs of the petroleum bearing sabah basin the eocene early miocene west crocker and temburong formations are deepwater turbidites whilst the miocene meligan and belait formations are shallow marine fluvio deltaic deposits the vitrinite reflectance and pyrolysis t max values show that the belait samples are generally immature for hydrocarbon generation whereas the meligan temburong and west crocker samples are in the mature to late maturity stage of hydrocarbon generation the overall bulk source rock properties of the belait and meligan show fair to good petroleum source rock potential with toc more than 1 wt hydrocarbon yield in the range of 400 1300 ppm and moderately high hi for many of the samples most of the samples representing the temburong and west crocker formations have toc less than 1 wt and have no to fair hydrocarbon generating potential interestingly the samples collected in the west crocker formation characterized by slump deposits mtd have toc 2 and possess good to excellent hydrocarbon generating potential the organic matter present in all of the studied formations is mainly of terrigenous origin based on the abundance of woody plant materials observed under the microscope consequently the analysed sequences are predominantly gas prone dominated by type iii and type iii iv kerogen except for minor occurrence of mixed oil gas prone type ii iii kerogen in the belait formation and in the slump mass transport deposits mtd of the west crocker formation

heterogeneity and anisotropy of earth s inner core seismic observations provide strong evidence that earth s inner core is anisotropic with larger velocity in the polar than in the equatorial direction the top 60 80 km of the inner core is isotropic evidence for an innermost inner core is less compelling the anisotropy is most likely due to alignment of hcp hexagonal close packed iron crystals aligned either during solidification or by deformation afterward the existence of hemispherical variations used to be controversial but there is now strong evidence from both seismic body wave and normal mode observations showing stronger anisotropy less attenuation and a lower isotropic velocity in the western hemisphere two mechanisms have been proposed to explain the hemispherical pattern either a inner core translation wherein one hemisphere is melting and the other is solidifying or b thermochemical convection in the outer core leading to different solidification conditions at the inner core boundary neither is yet able to explain all se