stream driven high density gravelly traction carpets possible deposits in the trabeg conglomerate formation sw ireland and some theoretical considerations of their origin within high density flood flows a prominent mechanism of gravel transport and deposition is by stream driven high density traction carpet with a rheology similar to grain flow these gravel carpets are envisaged to form the basal portion of a bipartite high density flood flow decoupled from an overlying sand and silt laden turbulent flow several examples already documented in the literature are reviewed and an additional case from the lower old red sandstone of southwest ireland is presented two mechanisms of traction carpet initiation are discussed by rapid entrainment of gravel into suspension on rising stage followed by settling into the gravel traction carpet at peak and falling stage and by overconcentration of a normal low density bedload gravel entrainment suspension and traction carpet development are significantly easier if the flood water already carries a high concentration of sand and silt in suspension theoretical consideration further shows that gravelly traction carpets can be maintained in channels of relatively low gradient by the shear stress exerted by the high density sand bearing turbulent flood flow above this tangential shear stress is converted to dispersive pressure which aids buoyancy and quasi static grain to grain contacts in the support of the clasts within the gravel carpet the carpet is thought to have a quasi plastic rheology but behave much like a viscous fluid at high shear rates stream driven gravelly traction carpets are expected to produce sheet like units of clast to matrix supported conglomerate characterized by a parallel or an a p a i clast fabric these units may be ungraded normally or inversely graded depending on the rate of shear the viscosity of the flow and the celerity of deposition

scattered p p waves observed at short distances we detect previously unreported 1 hz scattered waves at epicentral dis tances between 30 and 50 and at times between 2300 and 2450 s after the earthquake origin these waves likely result from off azimuth scattering of pkpbc to pkpbc in the upper mantle and crust and provide a new tool for mapping variations in fine scale 10 km mantle heterogeneity array beams from the large aperture seismic array lasa clearly image the scattered energy gradually emerging from the noise and reaching its peak amplitude about 80 s later and returning to the noise level after 150 s stacks of transverse versus radial slowness t r show two peaks at about 2 2 and 2 2 s indicating the waves arrive along the major arc path 180 to 360 and significantly off azimuth we propose a mantle and surface pkpbc to pkpbc scattering mechanism for these observations because 1 it agrees with the initiation time and distinctive slowness signature of the scattered waves and 2 it follows a scattering path analogous to previously observed deep mantle pkkpscat tering chang and cleary 1981 the observed upper mantle scattered waves and pkkp waves fit into a broader set of scattered waves that we call p 0 dp 0 which can scatter from any depth d in the mantle

late ordovician volcanism in korea constrains the timing for breakup of sino korean craton from gondwana abstract in the early paleozoic the sino korean craton skc and south china craton scc were situated along the margin of east gondwana the skc was connected to core gondwana by an epeiric sea which was the site for deposition of lower paleozoic sequences of skc the skc and scc may have drifted away from core gondwana sometime during the mid paleozoic and would have been outboard microcontinents in the late paleozoic until they collided to form the east asian continent in the triassic the breakup of scc from gondwana was suggested to have taken place at 380 ma while no reliable suggestions have hitherto been made for breakup of skc from gondwana this study presents a convincing evidence for breakup of skc from gondwana based on the recognition of late ordovician volcanism in korea new shrimp u pb zircon ages 445 0 3 7 ma and 452 5 3 2 ma are obtained from trachytic rocks of the ongnyeobong formation of taebaeksan basin in korea which occupied the marginal part of the skc in the early paleozoic this late ordovician volcanism along with previous records of ordovician volcanic activities along the western margin of the skc is interpreted indicating the development of an incipient oceanic ridge the oceanic ridge uplifted the skc including the epeiric sea which subsequently resulted in terminating the early paleozoic sedimentation of the epeiric sea the paucity of lower paleozoic volcanic rocks across much of the skc however suggests that the oceanic ridge did not extend into the epeiric sea instead spreading of oceanic ridge entailed dextral movement of associated transform faults which may have played a major role in breakup of skc from mainland gondwana by the end of ordovician

structural style of the okcheon fold thrust belt in the taebaeksan zone korea abstract structural interpretation of the distinct map pattern defined by highly connected thrust traces in the map view of the taebaeksan zone provides insight into the structural style of the northeastern okcheon belt the map pattern can generally be explained by either a folded imbricate fan or a hinterland dipping duplex the same geometry could also be formed by a complex combination of major imbricate thrusts and their connecting splays having the structural architecture of a typical fold thrust belt however a folded imbricate fan model is not adequate to explain the absence of late paleozoic to early mesozoic strata i e the pyeongan supergroup between two major thrusts viz the pyeongchang and machari thrusts in this area this result further suggests that the yeongwol area the western part of the taebaeksan zone is a duplex that corresponds to a more internal and deeper hinterland part of the fold thrust belt while the imbricate thrusts with low connectivity in the taebaek area the eastern part of the taebaeksan zone indicate a more external and shallower foreland portion of the belt in addition cross cutting relations and newly obtained sensitive high resolution ion microprobe shrimp u pb zircon ages from a cross cutting dike and syntectonic sedimentary rocks suggest limited thrust reactivation after the early jurassic and early tertiary respectively in spite of this the original geometry of the fold thrust wedge in the taebaeksan zone remained well preserved

fractals in geology and geophysics the definition of a fractal distribution is that the number of objectsn with a characteristic size greater thanr scales with the relationn r d the frequency size distributions for islands earthquakes fragments ore deposits and oil fields often satisfy this relation fractals were originally introduced by mandelbrot to relate the length of a coastline to the length of the measuring stick this application illustrates a fundamental aspect of fractal distributions scale invariance the requirement of an object to define a scale in photographs of many geological features is one indication of the wide applicability of scale invariance to geological problems scale invariance can lead to fractal clustering geophysical spectra can also be related to fractals these are self affine fractals rather than self similar fractals examples include the earth s topography and geoid

inhomogeneities near the core mantle boundary inferred from short period scattered pkp waves recorded at the global digital seismograph network we analyze short period pkp precursor wave trains recorded at global digital seismograph network stations in the distance range 120 140 to infer the nature of inhomogeneities near the core mantle boundary travel times and particle motions are consistent with predictions of single scattered waves near the cmb the dominant frequencies are around 1 hz the regions best sampled are beneath indonesia north america central africa and south america based on first order scattering theory the characteristics of the wave number spectrum of the structural inhomogeneities are obtained for two hypotheses volume inhomogeneities and topographic irregularities for the range of wavelengths sampled by these data between 10 and 70 km the spectrum of inhomogeneities is best represented by a power law of index 5 3 for volume inhomogeneities and 6 8 for topographic irregularities if the scattering is due only to volumetric inhomogeneities we estimate the strength of the structural variations to be about 0 5 in p wave velocity for a 200 km thick layer if the scattering is due only to topographic irregularities the topography has an rms height of 280 m at present we can not distinguish between these two types of inhomogeneities

aseismic seismogenic coupling for a long strike slip fault summary a 2 d mechanical model for the elastic coupling between the upper seismogenic and lower aseismic parts of a long strike slip fault is presented the model spans the quasistatic and dynamic stages of the earthquake cycle by predicting the dynamic dislocation at the fault trace in terms of the quasistatic build up of average stress drop on the seismogenic zone aa toh w where w is the width of the seismogenic zone h is the thickness of the crust and to is the time dependent remote stress the stress drop aa z is predicted to be nearly uniform with depth z except near the base of the seismogenic zone where a stress concentration develops if coseismic slip is constrained to the crust then faults which are at least four times longer in the strike direction relative to the coseismic depth attain a mean dislocation which is independent of fault length the rise time may be as small as 6 s in the absence of coseismic movement beneath the seismogenic fault and increases to about 30 s for coseismic slip of the entire crust rapid post seismic creep on the lower aseismic fault is predicted by the model since the dislocation at the surface of the earth exceeds the pre seismic dislocation at the base of the plate the application of the model to contemporary small earthquakes near the southern segment of the san andreas fault leads to an interpretation that the 1857 seismic gap is locked at a depth of about 7 8 km by asperities which become unlocked by a maximum energy release rate of the order of lo7 j m this estimate for the maximum energy release rate is equal to that of tse dmowska rice 1985 and comparable to the estimate of li 1987 of 0 6 to 3 8 x lo7 j m 2 for a typicul san andreas great earthquake with a surface dislocation of 6m an average recurrence time of 150yr a relative plate velocity of 4cmyr and a stress rate of 0 1 bar yr the model predicts for w h 8 40 and 12 30 respectively a depth of coseismic slip of 12 and 30 km a stress drop of 75 and 38 bars and a critical energy release rate of 0 28 and 0 17 x lo7 j mp2 these lower energy release rates are more consistent with the estimate of rudnicki 1980 of 0 38 x lo7 j m and imply that a great earthquake may occur before the energy release rate reaches the maximum value of lo7 j m 2

velocity structure near the inner core boundary from waveform modeling a velocity model of the inner core boundary icb region is developed from broadband wave form modeling the data consist of long period and short period record sections gathered from the u s arrays wwssn and lrsm deep events beneath indonesia were used these sampled the icb structure beneath the north pacific the cagniard de hoop technique was used to generate the synthetics which allowed considerable flexibility in forward modeling these individual pkp phases our preferred model was developed from modifications of the preliminary reference earth model prem it contains a relatively low velocity gradient above the icb a sharp jump at the icb of about 0 78 km s and a relatively large gradient underneath these features are constrained largely by the differential travel times and amplitude ratios of pkikp and pkikp of the short period section further modification of prem in the fluid core was required to explain the long period observations associated with pkp waveforms our modeling results suggest a low velocity gradient at the bottom roughly 400 km of the fluid core a low q zone at the top of the inner core is required to fit the relative amplitudes of pkikp phases similar to earlier studies this model indicates possible inhomogeneity above the icb as suggested by other authors

shear and compressional velocity models of the mantle from cluster analysis of long period waveforms summary we present a new technique for the efficient measurement of the traveltimes of long period body wave phases the technique is based on the fact that all arrivals of a particular seismic phase are remarkably similar in shape for a single event this allows the application of cross correlation techniques that are usually used in a regional context to measure precise global differential times the analysis is enhanced by the inclusion of a clustering algorithm that automatically clusters waveforms by their degree of similarity this allows the algorithm to discriminate against unusual or distorted waveforms and makes for an extremely efficient measurement technique this technique can be applied to any seismic phase that is observed over a reasonably large distance range here we present the results of applying the algorithm to the long period channels of all data archived at the iris dmc from 1976 to 2005 for the seismic phases s and p from 23 to 100 and ss and pp from 50 to 170 the resulting large data sets are inverted along with existing surface wave and updated differential traveltime measurements for new mantle models of s and p velocity the resolution of the new model is enhanced particularly in the mid mantle where ss and pp turn we find that slow anomalies in the central pacific and africa extend from the core mantle boundary to the upper mantle but their direct connection to surface hotspots is beyond our resolution furthermore we find that fast anomalies that are likely associated with subducting slabs disappear between 1700 and 2500 km and thus are not continuous features from the upper to lower mantle despite our extensive coverage and high resolution of the mid mantle

density patterns of the upper mantle under asia and the arctic comparison of thermodynamic modelling and geophysical data based on the modified thermodynamic model we calculate the density of olivine pyroxene mixtures at different proportions of molecular masses in minerals at temperatures of 1000 1700 k and pressures up to 17 gpa the calculated density of the olivine pyroxene mixtures is compared with the prem model and the average density patterns of the asian and arctic regions estimated from the data on the rayleigh wave group velocity dispersion in upper mantle conditions taking into account the characteristic temperature profiles of different tectonic units in asia tibetan plateau khangay dome baikal rift and southern siberian platform and the arctic chukotka fold belt barents sea northern greenland and eurasia basin we discuss density patterns and features of the mantle composition underneath structures and to depths of 200 km where the most significant variations in their density patterns are observed the results obtained suggest some insights into the geodynamic evolution of the lithosphere in the study area the calculated density characteristics of the components in the upper mantle and the modelling of their composition are compared with average density patterns under the tectonic units in order to show the possibilities of previously developed equations of state it has been shown that the composition 0 9 mg0 9fe0 1 2sio4 0 1mgsio3 describes the prem model well in addition to the average velocity patterns of the study regions variations in mineralogical compositions are revealed between stable structures and the areas with high levels of tectonic and seismic activity the present paper could be of interest to geophysicists and mineralogists as it researches overlapping topics for both sciences indicating the relationship between seismicity and features of the deep structure of the upper mantle

dynamical links between small and large scale mantle heterogeneity seismological evidence abstract we identify pkp pkp scattered waves also known as p p from earthquakes recorded at small aperture seismic arrays at distances less than 65 p p energy travels as a pkp wave through the core up into the mantle then scatters back down through the core to the receiver as a second pkp p p waves are unique in that they allow scattering heterogeneities throughout the mantle to be imaged we use array processing methods to amplify low amplitude coherent scattered energy signals and resolve their incoming direction we deterministically map scattering heterogeneity locations from the core mantle boundary to the surface we use an extensive dataset with sensitivity to a large volume of the mantle and a location method allowing us to resolve and map more heterogeneities than have previously been possible representing a significant increase in our understanding of small scale structure within the mantle our results demonstrate that the distribution of scattering heterogeneities varies both radially and laterally scattering is most abundant in the uppermost and lowermost mantle and a minimum in the mid mantle resembling the radial distribution of tomographically derived whole mantle velocity heterogeneity we investigate the spatial correlation of scattering heterogeneities with large scale tomographic velocities lateral velocity gradients the locations of deep seated hotspots and subducted slabs in the lowermost 1500 km of the mantle small scale heterogeneities correlate with regions of low seismic velocity high lateral seismic gradient and proximity to hotspots in the upper 1000 km of the mantle there is no significant correlation between scattering heterogeneity location and subducted slabs between 600 and 900 km depth scattering heterogeneities are more common in the regions most remote from slabs and close to hotspots scattering heterogeneities show an affinity for regions close to slabs within the upper 200 km of the mantle the similarity between the distribution of large scale and small scale mantle structures suggests a dynamic connection across scales whereby mantle heterogeneities of all sizes may be directed in similar ways by large scale convective currents

petrology of late paleozoic early mesozoic pyeongan group sandstones gohan area south korea and its provenance and tectonic implications abstract carboniferous to triassic strata of the pyeongan group crop out in the gohan area northeastern south korea these strata consist in ascending order of the hongjeom sadong gobangsan and nogam formations sandstones in these formations comprise three distinct framework mineral suites suite 1 sandstones hongjeom formation through the middle member of gobangsan formation are quartz and quartzose arenites wackes that contain abundant quartz little or no feldspar and few acid volcanic clasts heavy minerals are mainly tourmaline rutile and zircon suite 2 sandstones upper member of gobangsan formation are lithic arenites wackes characterized by moderate quartz content low amounts of feldspar and moderate to abundant volcanic clasts sphene is the predominant heavy mineral suite 3 sandstones nogam formation are feldspathic arenites wackes distinguished by low quartz content moderate to abundant feldspar and low amounts of acid volcanic clasts the heavy mineral assemblage of the nogam formation is characterized particularly by epidote and sphene feldspar poor suite 1 sandstones were derived from a source terrain rich in quartzite and quartzose sandstone abundant quartz and stable heavy minerals were supplied initially during late carboniferous time to a shallow marine shelf which changed gradually near the end of carboniferous time to a nonmarine paralic platform setting electron probe microanalysis shows that suite 1 tourmaline was derived originally from li poor granitoids pegmatites and ca poor aplite and metapsammite petrographic evidence demonstrates that the scarcity of feldspars in suite 1 sandstones is not the result of diagenetic intrastratal solution major changes in mineralogy from suite 1 into suite 2 and suite 3 sandstone indicate changes in provenance suite 2 sandstones were derived from diorite granodiorite acid volcanic rocks and possibly some metamorphic rocks which furnished feldspars and sphene the appearance of feldspars and volcanic rock fragments in these sandstones reflects orogenic changes and uplift resulting from incipient collision of the asian mainland and the honshu block of southwest japan compositionally immature suite 3 sandstones were derived mainly from granite granodiorite and granitic gneiss indicating continuing uplift these source rocks provided quartz k feldspar plagioclase epidote and sphene acid volcanic rocks supplied minor amounts of rock fragments

a three dimensional semianalytic viscoelastic model for time dependent analyses of the earthquake cycle 1 exploring the earthquake cycle for large complex tectonic boundaries that deform over thousands of years requires the development of sophisticated and efficient models in this paper we introduce a semianalytic three dimensional 3 d linear viscoelastic maxwell model that is developed in the fourier domain to exploit the computational advantages of the convolution theorem a new aspect of this model is an analytic solution for the surface loading of an elastic plate overlying a viscoelastic half space when fully implemented the model simulates 1 interseismic stress accumulation on the upper locked portion of faults 2 repeated earthquakes on prescribed fault segments and 3 the viscoelastic response of the asthenosphere beneath the plate following episodic ruptures we verify both the analytic solution and computer code through a variety of 2 d and 3 d tests and examples on the basis of the methodology presented here it is now possible to explore thousands of years of the earthquake cycle along geometrically complex 3 d fault systems

north america pacific plate boundary an elastic plastic megashear evidence from very long baseline interferometry i investigate a number of lithospheric deformation models based upon the concept that the motions of points near the north america pacific plate boundary are a linear combination of north america and pacific velocities this concept entails a shear strain transition zone in the vicinity of the boundary the best of these models fit 95 of the variance in 139 very long baseline interferometry vlbi length and transverse velocity observations taken over 5 5 years and require only 90 of the relative plate motion predicted by rm2 residual misfits in the megashear models are largely explained by a 6 1 mm yr component of basin and range spreading perpendicular to the plate boundary instantaneous shear deformation associated with plate tectonics is apparently developing in a zone 450 km wide paralleling the san andreas fault some of this deformation will be recovered through elastic rebound the rest will be permanently set through plastic processes thus depending on the elastic plastic composition of the borderlands the width and pattern of strain accumulation in the megashear over geological time may or may not be significantly different than what is currently observed because vlbi data have been assembled for only a small fraction of the earthquake cycle plastic and elastic strains are indistinguishable other information will have to be brought to bear to discriminate elastic and plastic behaviors and reconcile instantaneous and geologic deformation near the north america pacific margin

quasi static propagator matrices creep on strike slip faults abstract this paper presents a method for computing viscoelastic flow in a layered earth by means of quasi static propagator matrices the method has advantages over approximate or purely numerical attacks in that exact semi analytical solutions are obtained the procedure enables a more rapid calculation than is possible with finite elements yet it does not sacrifice exactness as do analytical approximations to illustrate the technique i constructed a plausible model of the san andreas fault and investigated the time and space behavior of displacement displacement rate shear stress and shear strain rate at depth as well as at the surface viscoelastic relaxation speeds the restressing of the fault for events of magnitude 6 2 and 6 9 viscoelasticity reduces recharge time relative to the base strain rate by 15 and 50 respectively for events of magnitude 6 2 and less viscoelasticity has only a small influence and a linear extrapolation of stress accumulation will predict the time of recharge reasonably well relative plate velocities measured within 400 km of the fault are highly variable in space and time direct plate velocity measurements made as far as 100 km from a major fault could differ by a factor of two from the average rate features of the fault model at depth include stresses and strain rates which exceed surface values by a factor of three sign reversals in strain rates and positive coseismic stress drops induced for limited periods in narrow thin zones the latter feature could initiate and terminate aftershock sequences stress recharge does not occur simultaneously at all depths on the fault for all magnitude events recurrence times of earthquakes estimated from surface observations may thus be biased

constraining the short scale core mantle boundary topography beneath kenai peninsula alaska with amplitudes of core reflected pcp wave previous analysis of short period pcp with seismic array reported rapid variation of pcp amplitude and suggested small scale variation of core mantle boundary cmb topography beneath kenai peninsula alaska in order to constrain the length scale l and topographic height variation h in the region we quantitatively compute synthetic pcp seismograms using the seismic representation theorem for a core mantle boundary cmb with topography bump h 0 or depression h 0 we model pcp amplitudes for l in the range of 60 500 km h in the range of 6 km depression to 5 km bump it is observed that cmb depressions do produce amplification and cmb bumps generate de amplification for short period pcp amplitudes after computation for various combinations of l and h amplification in the range of 2 4 5 is observed in the above mentioned parameter ranges the topography model of a cmb depression h 6 km l 6 predicts 1 hz pcp amplification consistent with observed pcp amplitude variation beneath kenai peninsula however pcp amplitude can also be affected by heterogeneities in the crust and mantle the estimated topography could be less pronounced

rupture complexity of the 1994 bolivia and 2013 sea of okhotsk deep earthquakes the physical mechanism of deep earthquakes depth 300 km remains enigmatic partly because their rupture dimensions are difficult to estimate due to their low aftershock productivity and absence of geodetic or surface rupture observations the two largest deep earthquakes the recent great 2013 sea of okhotsk earthquake m 8 3 depth 607 km and the great 1994 bolivia earthquake m 8 3 depth 637 km together provide a unique opportunity to compare their rupture patterns in detail here we extend a travel time sub event location method to perform full teleseismic p waveform inversion this new method allows us to explain the observed broadband records with a set of sub events whose model parameters are robustly constrained without smoothing we find that while the okhotsk event is mostly unilateral rupturing 90 km along strike with a velocity over 4 km s the bolivia earthquake ruptured about half this distance at a slow velocity about 1 5 km s and displayed a major change in rupture direction we explain the observed differences between the two earthquakes as resulting from two fundamentally different faulting mechanisms in slabs with different thermal states phase transformational faulting is inferred to occur inside the metastable olivine wedge within cold slab cores whereas shear melting occurs inside warm slabs once triggered

viscosity estimates for the crust and upper mantle from patterns of lacustrine shoreline deformation in the eastern great basin the deformed shorelines of lake bonneville constitute a classic source of information on lithospheric elastic thickness and upper mantle viscosity we describe and apply a new model to a recently augmented data set new data better constrain both the complex spatio temporal pattern of the lake load and the crustal deformation response to that load the history of lake level fluctuations has been significantly refined and somewhat modified this is due to both more radiocarbon dates from within the bonneville basin and to an improved calibration of the radiocarbon timescale itself the data which constrain the crustal deformation pattern consist of ages and shoreline elevations from several hundred points which sample three major levels of lake bonneville and corresponding elevations from the high stands of three smaller lakes situated to the west of lake bonneville the data from the smaller lakes help elucidate the pattern of deflection which occurred beyond the edge of the big lake the geometry of the earth model incorporates an arbitrary number of layers overlying a half space and the rheology of each level can accommodate an arbitrary number of maxwell viscoelastic elements in parallel the inverse modeling comprises three complementary approaches for the simplest configurations we performed a direct search of the parameter space and delineated the irregular boundary of the subspace of acceptable models for more complex configurations we constrained the elastic parameters to their seismically determined values and then solved for viscosity versus depth profiles by either expressing the log viscosity versus log depth profile as a series of specially constructed orthogonal polynomials or by allowing each of 8 10 layers plus the half space to have an independently determined viscosity we found that the data do not strongly support nor can they conclusively exclude a more complex rheology than simple maxwell viscoelasticity the orthogonal polynomial solution exhibits an essentially monotonic decrease in viscosity with depth the most rapid change occurs at shallow depths decreasing from 1023 pa s at 3 km to 102o pa s at 30 km the decrease is much more gradual below with only another factor of 5 decrease between 30 and 300 km depth the unconstrained solution exhibits a rapid decrease in viscosity with depth from 2x 10 24 pa s in the top 10 km to 4x 1017 pa s at a depth of 40 km a nearly isoviscous asthenospheric region extends from 40 to 150 km and is underlain by a mantle lithospheric region with increased viscosity 2x 102o pa s extending from 150 to 300 km depth and by a uniform viscosity 1019 pa s half space below

the upper mantle transition zone discontinuities in the pacific as determined by short period array data short period array recordings from pacific earthquakes show precursors to pp produced by underside reflections of p waves off the discontinuities in the upper mantle we use these events to study the structure of the transition zone discontinuities in the central and northern pacific the discontinuities of the mantle transition zone at depths of 410 km and 660 km are particularly interesting for the interpretation of the chemistry and temperature structure of the mantle transition zone the pp reflections from these discontinuities are too small to be identified in unprocessed seismograms therefore array methods are used to detect and identify the pp underside reflections the data of several events show reflections from the 410 km discontinuity the topography of the reflector can be used to study the olivine to spinel phase transition in the central and northwestern pacific the mean depth of the reflector is 404 16 km with topography near the hawaiian islands and the kuriles forward modeling enables an estimate of the minimum impedance contrast and the maximum thickness of the discontinuity this study shows that the 410 km discontinuity must be sharper than 6 km assuming a simple linear gradient for the kcl phase change with an impedance contrast of 8 9 as in iasp91 to be in agreement with our data the minimum impedance contrast for a first order discontinuity would be 6 5 the 660 km discontinuity cannot be detected in this dataset using pp underside reflections in agreement with previous studies forward modeling shows that the non detection of the 660 can be explained by a discontinuity with a thickness of more than 12 km for the iasp91 impedance contrast or by a first order discontinuity with an impedance contrast of less than v9 5 2002 elsevier science b v all rights reserved

earthquake cycle deformation in the tibetan plateau with a weak mid crustal layer 1 geodetic observations of interseismic deformation across the tibetan plateau contain information about both tectonic and earthquake cycle processes time variations in surface velocities between large earthquakes are sensitive to the rheological structure of the subseismogenic crust and in particular the viscosity of the middle and lower crust here we develop a semianalytic solution for time dependent interseismic velocities resulting from viscoelastic stress relaxation in a localized midcrustal layer in response to forcing by a sequence of periodic earthquakes earthquake cycle models with a weak midcrustal layer exhibit substantially more near fault preseismic strain localization than do classic two layer models at short 50 mm yr postseismic velocities in the years following the coseismic ruptures we suggest that earthquake cycle models with a localized midcrustal layer can simultaneously explain both preseismic and postseismic geodetic observations with a single maxwell viscosity while the classic two layer model requires a rheology with multiple relaxation time scales

tracking paleozoic evolution of the south korean peninsula from detrital zircon records implications for the tectonic history of east asia abstract the southern part of the korean peninsula preserves important records of the paleozoic evolutionary history of east asia here we present shrimp u pb ages of detrital zircon grains from paleozoic metasedimentary successions okcheon and joseon supergroups yeoncheon group taean formation and pyeongan supergroup that are incorporated into the major phanerozoic mountain belts okcheon and hongseong imjingang belts in south korea providing new insights for provenances and paleotectonic evolution of the south korean peninsula during paleozoic time the zircon ages from our samples display two distinct spectra patterns in their presence absence of neoproterozoic and or paleozoic populations our results together with the available data from the korean peninsula suggest that 1 the early to middle paleozoic successions in the okcheon belt were deposited in continental margin setting s formed by neoproterozoic intracratonic rifting 2 the middle paleozoic metasedimentary rocks in the imjingang belt can be interpreted as molasse and flysch sediments along an active continental margin 3 the late paleozoic to early triassic taean formation along the western gyeonggi massif represents a syn to post collision deltaic complex of a remnant oceanic basin and 4 the late paleozoic to possibly early triassic pyeongan supergroup in the okcheon belt might represent a wedge top and or foreland basin the spatial and temporal discrepancy between the south korean peninsula and the central china orogenic belt during paleozoic might reflect lateral variations in crustal evolution history along the east asian continental margin during the paleo tethyan ocean closure

sharpness of upper mantle discontinuities determined from high frequency reflections an understanding of the nature of seismic discontinuities in the earth s upper mantle is important for understanding mantle processes in particular the amplitude and sharpness of these discontinuities are critical for assessing models of upper mantle phase changes and chemical layering so far seismic studies aimed at determining the thickness and lateral variability of upper mantle discontinuities have yielded equivocal results particularly for the discontinuity at 410km depth1 2 here we present short period 0 8 2 0 s recordings of upper mantle precursors to the seismic phase p p pkppkp from two south american earthquakes recorded by the 700 station short period array in california our results show that the 410 and 660 km discontinuities beneath the indian ocean are locally simple and sharp corresponding to transi tion zones of 4 km or less these observations pose problems for mineral physics models3 5 which predict a transitional thickness greater than 6 km for the peridotite to spinel phase transition in contrast to the results of long period studies6 7 we observe no short period arrivals from near 520 km depth

time dependent deformation and stress relaxation after strike slip earthquakes the quasi static time dependent behavior after strike slip earthquakes is studied using three dimensional finite element models the effects of lateral heterogeneities finite fault and nonuniform fault slip are included models of a great earthquake and a medium size earthquake are constructed using a set of possible viscosity structures deformation change after an earthquake is found to be sensitive to the viscosity structure located beneath the fault zone the presence of low viscosity beneath the fault concentrates the horizontal displacement near the fault zone and completely changes the character of vertical deformation thus leveling in addition to horizontal geodetic measurements after a strike slip event is important in determining the viscosity structure near fault zones the shear stress in front of the fault tip increases significantly within several decades after the event for models with a shallow low viscosity zone beneath the fault this accelerated stress accumulation is consistent with the observed phenomenon of earthquake migration along the north anatolian fault zone

crustal deformation the earthquake cycle and models of viscoelastic flow in the asthenosphere summary the crustal deformation patterns associated with the earthquake cycle can depend strongly on the rheological properties of subcrustal material substantial deviations from the simple patterns for a uniformly elastic earth are expected when viscoelastic flow of subcrustal material is considered the detailed description of the deformation pattern and in particular the surface displacements displacement rates strains and strain rates depend on the structure and geometry of the material near the seismogenic zone in the past few years various viscoelastic models of crustal deformation have been published these models differ in their predictions concerning the temporal and spatial patterns of crustal deformation in some cases these differences are due to varying choices for the physical mechanism under study in other cases however the differences are the result of the details of the mathematical treatment or the choice of model parameters we seek to resolve the origin of some of these differences by analysing several different linear viscoelastic models with a common finite element computational technique the models involve strike slip faulting and include a thin channel asthenosphere model a model with a varying thickness lithosphere and a model with a viscoelastic inclusion below the brittle slip plane the calculations reveal that the surface deformation pattern is most sensitive to the rheology of the material that lies below the slip plane in a volume whose extent is a few times the fault depth if this material is viscoelastic the surface deformation pattern resembles that of an elastic layer lying over a viscoelastic half space when the thickness or breadth of the viscoelastic material is less than a few times the fault depth then the surface deformation pattern is altered and geodetic measurements are potentially useful for studying the details of subsurface geometry and structure distinguishing among the various models in best accomplished by making geodetic measurements not only near the fault but out to distances equal to several times the fault depth this is where the model differences are greatest these differences will be most readily detected shortly after an earthquake when viscoelastic effects are most pronounced for a thin channel asthenosphere model we have found that the predicted displacements are less than those for a half space asthenosphere this result is contrary to recently published results based on analytical approximations the deficiencies of the latter work result from ignoring material below the asthenosphere and in using thickness averaged deformation parameters although the displacements predicted for a thin channel asthenosphere are less than those for a half space asthenosphere the post seismic strain rates at intermediate distances from the fault are greater in an absolute value sense in the former model

quantification of free gas in the kumano fore arc basin detected from borehole physical properties iodp nantroseize drilling site c0009 the kumano fore arc basin overlies the nankai accretionary prism formed by the subduction of the philippine sea plate beneath the eurasian plate offshore the kii peninsula sw honshu japan seismic surveys and boreholes within the framework of the nankai trough seismogenic zone experiment nantroseize project show evidence of gas hydrates and free gas within the basin here we use high quality borehole sonic data from integrated oceanic drilling program iodp site c0009 to quantify the free gas distribution in the landward part of the basin the brie theory is used to quantify gas content from sonic logs which are calibrated from laboratory measurements on drill cores first we show that the sonic data are mainly sensitive to the fluid phase filling the intergranular pores effective porosity rather than to the total porosity that includes water bound to clay minerals we then compare the effective porosity to lithodensity derived porosity that acts as a proxy for total porosity the combination of these two data sets also allows assessment of clay mineralogy of the sediments second we compute free gas saturation and find a gas rich interval that is restricted to a lithological unit characterized by a high abundance of wood fragments and lignite this unit at the base of the fore arc basin is a hydrocarbon source that should be taken into account in models explaining gas distribution and the formation of the bottom simulating reflector within the kumano fore arc basin

imaging the ramp decollement geometry of the chelungpu fault using coseismic gps displacements from the 1999 chi chi taiwan earthquake abstract we use coseismic gps data from the 1999 chi chi taiwan earthquake to estimate the subsurface shape of the chelungpu fault that ruptured during the earthquake studies prior to the earthquake suggest a ramp decollement geometry for the chelungpu fault yet many finite source inversions using gps and seismic data assume slip occurred on the down dip extension of the chelungpu ramp rather than on a sub horizontal decollement we test whether slip occurred on the decollement or the down dip extension of the ramp using well established methods of inverting gps data for geometry and slip on faults represented as elastic dislocations we find that a significant portion of the coseismic slip did indeed occur on a sub horizontal decollement located at 8 km depth the slip on the decollement contributes 21 of the total modeled moment release we estimate the fault geometry assuming several different models for the distribution of elastic properties in the earth homogeneous layered and layered with lateral material contrast across the fault it is shown however that heterogeneity has little influence on our estimated fault geometry we also investigate several competing interpretations of deformation within the e w trending rupture zone at the northern end of the 1999 ground ruptures we demonstrate that the gps data require a 22 to 35 km long lateral ramp at the northern end contradicting other investigations that propose deformation is concentrated within 10 km of the chelungpu fault lastly we propose a simple tectonic model for the development of the lateral ramp

the nature of the 660 kilometer upper mantle seismic discontinuity from precursors to the pp phase global seismic network data were used to image upper mantle seismic discontinuities stacks of phases that precede the pp phase thought to be underside reflections from the upper mantle discontinuities at depths of 410 and 660 kilometers show that the reflection from 410 kilometers is present but the reflection from 660 kilometers is not observed a continuous lame s constant lambda and seismic parameter at the 660 kilometer discontinuity explain the missing underside p reflections and lead to a p wave velocity jump of only 2 percent whereas the s wave velocity and density remain unchanged with respect to previous global models the model deemphasizes the role of lame s constant lambda with regard to the shear modulus and constrains the mineralogical composition across the discontinuity

the nature of the 660 kilometer discontinuity in earth s mantle from global seismic observations of pp precursors the 660 kilometer discontinuity which separates earth s upper and lower mantle has been detected routinely on a global scale in underside reflections of precursors to ss shear waves here we report observations of this discontinuity in many different regions using precursors to compressional pp waves the apparent absence of such precursors in previous studies had posed major problems for models of mantle composition we find a complicated structure showing single and double reflections ranging in depth from 640 to 720 kilometers that requires the existence of multiple phase transitions at the base of the transition zone the results are consistent with a pyrolite mantle composition

influence of lithosphere viscosity structure on estimates of fault slip rate in the mojave region of the san andreas fault system 1 it is well known that slip rate estimates from geodetic data are nonunique because they depend on model assumptions and parameters that are often not known a priori estimates of fault slip rate on the mojave segment of the san andreas fault system derived from elastic block models and gps data are significantly lower than estimates from geologic data to determine the extent to which the slip rate discrepancy might be due to the oversimplified models of the rheology of the lithosphere we develop a two dimensional linear maxwell viscoelastic earthquake cycle model and simultaneously estimate fault slip rates and lithosphere viscosity structure in the mojave region the model consists of episodic earthquakes in an elastic crust overlying layers with different viscosities that represent the lower crust uppermost mantle and upper mantle we use gps measurements of postseismic relaxation following the 1992 landers earthquake triangulation measurements spanning 1932 1977 gps measurements of the contemporary velocity field and paleoseismic data along the san andreas fault we infer lower crustal 15 30 km depth viscosity of 1019 10 20 pa s uppermost mantle 30 60 km viscosity of 10 20 22 pa s and underlying upper mantle viscosity of 10 18 10 19 pa s consistent with inferences from laboratory experiments of relatively high viscosity lithospheric mantle and lower viscosity lower crust and underlying asthenospheric mantle we infer a 20 30 mm yr slip rate on the san andreas fault in agreement with the lower end of geologic estimates inversions of geodetic data with models that do not incorporate layered viscosity structure may significantly misestimate slip rates

depositional environments and sequence stratigraphy of the late carboniferous early permian coal bearing successions shandong province china sequence development in an epicontinental basin abstract this study focuses on the late carboniferous early permian coal bearing successions in shandong province north china in order to understand the depositional processes and sequence stratigraphic framework in an epicontinental basin based on detailed analysis of eleven facies five facies assemblages fas were recognized in the studied succession fa1 3 are present mainly in the benxi and taiyuan formations and consist of mixed siliciclastic and carbonate lithofacies representing eluvial lagoon barrier lagoon and tidal flat environments fa4 occurs in the shanxi formation and consists mainly of interbedded medium to fine sandstone siltstone mudstone and coal lithofacies representing river dominated deltaic environments fa5 is characterized by interbeds of trough cross stratified coarse sandstone and silty mudstone mainly in the lower shihezi formation which was deposited in meandering river channel and floodplain three third order sequences were established based on the vertical arrangement of facies assemblages and identification of physical surfaces i e subaerial unconformity transgressive surface and regressive surface each sequence comprises a transgressive systems tract tst and a highstand systems tract hst tst of sequence 1 is composed of eluvial lagoonal deposits fa1 whereas hst formed in lagoon barrier and tidal flat settings fa2 and fa3 tst of sequence 2 formed in a barrier lagoon system fa2 whereas hst is characterized by repetitive accumulation of interbedded limestone sandstone mudstone and coal deposited under lagoonal and tidal flat settings fa2 and fa3 tst of sequence 3 comprises fa2 and hst mainly fa4 deposited in a river dominated shallow water delta system sequence 3 is overlain by a fluvial sequence fa5 the three third order sequences in the shandong region are generally correlated with those in the taebaeksan basin south korea the eastern part of the north china block the relative sea level curves established in the two regions show a generally similar long term rising trend

a perovskitic lower mantle inferred from high pressure high temperature sound velocity data determination of the shear wave velocities for silicate perovskite and ferropericlase under the pressure and temperature conditions of the deep lower mantle indicates that perovskite constitutes much more of the lower mantle than predicted by the conventional mantle model and is consistent with the chondritic earth model earth s upper mantle is apparently depleted of silicon when compared with meteorites which are thought to represent the material from which the earth formed this missing silicon problem has provoked intense debate it suggests that the deficit might be balanced by silicon in the core or that the upper mantle is not representative of the entire mantle and that the lower mantle is enriched in silicon murakami et al provide evidence to support the latter case they made laboratory measurements of sound wave transmission through silicate perovskite and ferropericlase minerals at pressures and temperatures matching those of the lower mantle and compared the resulting shear wave values with seismic data that sample the lower mantle they conclude that the mineralogical model that provides the best fit is one in which perovskite constitutes greater than 93 of the lower mantle this suggests that the lower mantle is enriched in silicon in comparison with the upper mantle consistent with the chondritic earth model and that there is limited mass transport between the upper and lower mantle the determination of the chemical composition of earth s lower mantle is a long standing challenge in earth science accurate knowledge of sound velocities in the lower mantle minerals under relevant high pressure high temperature conditions is essential in constraining the mineralogy and chemical composition using seismological observations1 but previous acoustic measurements were limited to a range of low pressures and temperatures here we determine the shear wave velocities for silicate perovskite and ferropericlase under the pressure and temperature conditions of the deep lower mantle using brillouin scattering spectroscopy2 the mineralogical model that provides the best fit to a global seismic velocity profile1 indicates that perovskite constitutes more than 93 per cent by volume of the lower mantle which is a much higher proportion than that predicted by the conventional peridotitic mantle model it suggests that the lower mantle is enriched in silicon relative to the upper mantle which is consistent with the chondritic earth model such chemical stratification implies layered mantle convection with limited mass transport between the upper and the lower mantle

seismological evidence for thermo chemical heterogeneity in earth s continental mantle abstract earth s thermo chemical structure exerts a fundamental control on mantle convection plate tectonics and surface volcanism there are indications that mantle convection occurs as an intermittent stage process between layered and whole mantle convection in interaction with a compositional stratification at 660 km depth however the presence and possible role of any compositional layering in the mantle remains to be ascertained and understood by interfacing inversion of a novel global seismic data set with petrologic phase equilibrium calculations we show that a compositional boundary is not required to explain short and long period seismic data sensitive to the upper mantle and transition zone beneath stable continental regions yet radial enrichment in basaltic material reproduces part of the complexity present in the data recorded near subduction zones and volcanically active regions our findings further indicate that 1 cratonic regions are characterized by low mantle potential temperatures and significant lateral variability in mantle composition and 2 chemical equilibration seems more difficult to achieve beneath stable cratonic regions these findings suggest that the lithologic integrity of the subducted basalt and harzburgite may be better preserved for geologically significant times underneath cratonic regions

on tsunami nucleation ii an instantaneous modulated line source abstract tsunami generation on a spherically symmetric self gravitating and elastic earth is investigated using normal mode summations and moment tensor line sources wave cancellation in a line source of length l substantially eliminates tsunamis whose horizontal wavenumber component along the fault exceeds 3 l this results in a preferential beaming of tsunami radiation perpendicular to the fault strike beaming from a source of fixed length occurs in the same fashion irrespective of slip mechanism tsunami radiation patterns from finite sources are thus more uniform than those from point sources the largest far field sea waves from any long shallow fault are likely to be found within 20 azimuth of the perpendicular bisecting great circle although line sources subordinate distinctions in radiation patterns focal mechanism is still a critical element in determining the extent of tsunami excitation the ratio of maximum tsunami amplitude from strike and dip slips of equal moment are 1 10 for faults 400 km in length finite faulting weakens strike slip tsunamis relative to dip slip tsunamis because the beaming and natural radiation directions of strike slips are severely misaligned using an empirical relation linking source process time fault length and moment i predict tsunami energies in the range 1010 1017 j for earthquake moments spanning 2 1018

reconciling pacific 410 and 660 km discontinuity topography transition zone shear velocity patterns and mantle phase transitions a r t i c l e i n f o article history we observe that the depths of the 410 and 660 km seismic discontinuities are on average slightly positively correlated globally this is due in large part to a modestly depressed 660 km discontinuity and a large depression of the 410 km discontinuity across the paci c the clapeyron slope dp dt the change in pressure depth of a phase transition with a change in temperature can be used to predict the depth of a phase transformation assuming lateral temperature variations the phase change of olivine to spinel is well understood experimentally almost certainly produces the 410 km discontinuity and has a positive clapeyron slope at the base of the transition zone both the olivine component of the mantle spinel and the pyroxene component garnet transform to perovskite and periclase observations of 660 km discontinuity depths are often consistent with the negative clapeyron slope of the spinel to perovskite and periclase transition with an apparent anti correlation with the depth of the 410 km discontinuity however under the paci c the depression of the 410 km discontinuity and slow seismic velocities indicate that the mantle is warmer than average using a negative clapeyron slope for the perovskite forming reaction the 660 km discontinuity is predicted to be shallow in this region however we observe that it is either depressed or has little de ection from its average depth we nd that if the clapeyron slope associated with the 660 km discontinuity changes sign from negative to positive between 1920 and 2020 k we can explain the correlation of discontinuity structure with seismic velocities in the transition zone this shift in sign is in accord with the dominant 660 km transition forming reaction shifting from spinel to garnet near this temperature

seismic evidence for small scale heterogeneity throughout the earth s mantle details in the amplitude structure of short period precursors to the seismic core phase pkp can be used to constrain the depth extent of mantle scattering the simplest model consistent with the observations invokes small 8 km weak r m s velocity perturbations of 1 random heterogeneities uniformly distributed throughout the mantle the data do not support previously proposed models that place an increase in the concentration of scattering sites near the base of the mantle and instead place an upper limit on the amplitude of any short wavelength topography at the core mantle boundary

reconciling pp and p p precursor observations of a complex 660 km seismic discontinuity high frequency precursors to p p almost invariably observe a narrow 660 km discontinuity whereas pp precursor studies at long periods struggle to detect a reflection from the 660 despite its apparent sharpness to p p to investigate these contradictory observations we compare pp and p p precursors in the same region using short period p p precursors we observe a sharp 660 km discontinuity which appears to vary in depth substantially the apparent topography on the 660 is too large to originate solely from thermal variations regardless of its cause therefore indicating chemical variations at the base of the mantle transition zone long period p p precursors show no 660 as they are sensitive to a larger area and thus average out the apparent topography in agreement with long period pp precursors instead we see some evidence in both long period data types for a reflection from 720 km depth which is likely to correspond to a phase change in the garnet system

postseismic deformation due to subcrustal viscoelastic relaxation following dip slip earthquakes the deformation of the earth following a dip slip earthquake is calculated by using a three layer rheological model and finite element techniques the three layers are an elastic upper lithosphere a standard linear solid lower lithosphere and a maxwell viscoelastic asthenosphere attention is focused on the magnitude of the postseismic subsidence and the width of the subsidence zone that develops due to the viscoelastic response to coseismic reverse slip detailed analysis for a fault extending from the surface to 15 km with a 45 dip reveals that postseismic subsidence is sensitive to the depth to the asthenosphere but is only weakly dependent on lower lithosphere depth the greatest subsidence occurs when the elastic lithosphere is about 30 km thick and the asthenosphere lies just below this layer asthenosphere depth 2 times the fault depth the extremum in the subsidence pattern occurs at about 5 km from the surface break of the fault and lies over the slip plane at this location the subsidence reaches 60 of the coseismic uplift after about 30 maxwell times unlike the horizontal deformation following a strike slip earthquake significant vertical deformation due to asthenosphere flow persists for many times the maxwell time of the asthenosphere as a consequence the relaxation of the lower lithosphere has only a secondary effect on uplift and subsidence it does however substantially increase horizontal straining the width of the postseismic subsidence zone also depends strongly on the depth to the asthenosphere and shows little sensitivity to the presence of a slowly relaxing lower lithosphere parametric adjustment of the lithosphere thickness and fault dip angle over a considerable range of values in a simple model of an elastic lithosphere and viscoelastic asthenosphere reveals that the postseismic subsidence is greatest when the fault penetrates through about one half the lithosphere previous estimates of the asthenosphere viscosity 1019 pa s and lithosphere thickness 30 40 km for the region of japan affected by the 1896 riku u earthquake are confirmed by model calculations

crustal velocity field of southwest japan subduction and arc arc collision we investigate crustal deformation in southwest japan over a 3 year period revealed by a permanent dense global positioning system gps array southwest japan is a part of the amurian plate a microplate moving about 10 mm yr toward the east with respect to the eurasian plate it overrides the philippine sea plate at the nankai trough and collides with the northeast japan arc in the central part of japan in this paper we first derive gps site velocities relative to the stable part of the amurian plate in order to isolate signals of crustal deformation caused by the subduction and or the collision the velocity field has a conspicuous feature indicating the interseismic elastic loading by the philippine sea plate slab at the nankai trough characterized by the northwestward movements of points throughout the studied area their amplitudes are the largest at the pacific coast and decay toward the japan sea coast with a subtle systematic shift of azimuths a model assuming an elastic half space the convergence rate at the nankai trough based on a refined euler vector and the strength of the coupling inferred from a thermal model could explain the velocity field in the western part of the studied area to a large extent those in the eastern part systematically deviate from them and the residual components there show east west shortening and north south extension this may represent crustal thickening and trenchward extrusion of crustal blocks caused by the collision between southwest and northeast japan this suggests that the collision between southwest and northeast japan gives rise to not only crustal thickening but also trenchward extrusion of crustal block a velocity contrast was found across the median tectonic line the largest inland active fault in japan but the current permanent gps network is not dense enough for us to discuss its coupling depth

utilization of observations of well bore failure to constrain the orientation and magnitude of crustal stresses application to continental deep sea drilling project and ocean drilling program boreholes

seismic velocity and density jumps across the 410 and 660 kilometer discontinuities the average seismic velocity and density jumps across the 410 and 660 kilometer discontinuities in the upper mantle were determined by modeling the observed range dependence in long period seismic wave arrivals that reflect off of these interfaces the preliminary reference earth model prem is within the computed 95 percent confidence ellipse for the 410 km discontinuity but outside the allowed jumps across the 660 kilometer discontinuity current pyrolite mantle models appear consistent with the constraints for the 410 kilometer discontinuity but overpredict amplitudes for the 660 kilometer reflections the density jump across the 660 kilometer discontinuity is between 4 and 6 percent below the prem value of 9 3 percent commonly used in mantle convection calculations

the role of an intracrustal asthenosphere on the behavior of major strike slip faults measurements of strain accumulation adjacent to the san andreas fault indicate that the zone of strain accumulation extends only a few tens of kilometers away from the fault such a narrow zone of cyclic strain accumulation and release is consistent with the measured coseismic strain and inferred stress drop during the 1906 earthquake the restricted zone of cyclic accumulation and release of elastic energy adjacent to major strike slip faults has been attributed to the damping effect of a viscoelastic asthenosphere however to explain the narrowness of the zone on the san andreas fault it is necessary to conclude that the thickness of the lithosphere is 10 20 km this does not appear to be consistent with the relatively low surface heat flow measurements in this paper an alternative four layer model is proposed to explain the behavior of the san andreas fault an upper elastic plate extends to a depth of about 15 km the depth of the deepest seismicity on and adjacent to the fault beneath this upper elastic plate is a soft intracrustal asthenosphere that exhibits a viscoelastic behavior the viscous behavior of these crustal rocks at relatively low temperatures is attributed to either the presence of quartz which is known to have a very soft rheology or the presence of water that can lead to pressure solution creep or to both effects beneath this soft layer is a second elastic layer made up of the tough lower crustal and upper mantle rocks and beneath this second elastic layer is the asthenosphere there is extensive geological and geophysical evidence for the existence of an intracrustal asthenosphere both in california and elsewhere we show that the damping due to the intracrustal asthenosphere can explain the observed narrow zone of cyclic strain accumulation and release on the san andreas fault

provenance derived from the geochemistry of late paleozoic early mesozoic mudrocks of the pyeongan supergroup korea late carboniferous early triassic pyeongan supergroup korea was deposited in paralic to nonmarine environments developed disconformably on a lower paleozoic platformal sequence pyeongan supergroup mudrocks show progressive upsection changes in major trace and rare earth element compositions mudrocks in the lower and middle parts of the pyeongan supergroup are strongly depleted in cao and na2o while those in the upper part are enriched in these elements in parallel with cao and na2o the ratio of k2o al2o3 in the lower and middle sections is less than 0 3 while uppermost strata are enriched in k2o having k2o al2o3 ratios greater than 0 3 the index of compositional variability a measure of compositional maturity is less than 0 6 in the lower to middle section whereas in the uppermost strata it is greater than 0 7 similar trends are reflected in a cn k space compared to paas mudrocks of the pyeongan supergroup except for those in uppermost units they are depleted in mn ca and na and are slightly depleted in mg and p contrasting major oxide trends between the lower and middle parts of the pyeongan and the uppermost units are due to decreasing proportions of clay minerals and a concomitant increase in the proportion of nonclay silicate minerals due to increasing input of first cycle detritus excursions marked by increases in mgo na2o and cao reflect large scale input of nonclay first cycle minerals from crystalline source rocks due to large scale basement uplift incompatible elements are generally enriched in mudrocks of the pyeongan supergroup relative to paas while transition metals co ni cr and v are progressively depleted in younger parts of the section total rare earth element concentrations are higher than paas but chondrite normalized patterns display the typical lree enriched pattern of paas eu anomalies for most mudrocks are close to that of paas the youngest mudrocks in the pyeongan supergroup have the most negative values these trends can be explained by a sedimentary system dominated by detritus derived from recycled highly weathered granitic materials in the lower to middle pyeongan section with an increased proportion of less weathered detritus derived from fractionated granitic materials in uppermost strata such an interpretation is consistent with the results of studies on coarse grained sediments of the pyeongan supergroup

reconciling seismic and geodetic models of the 1989 kilauea south flank earthquake 1 the inconsistency in depth between geodetic and seismic models of the 1989 kilauea earthquake has long been puzzling previous attempts to incorporate elastic heterogeneity have deepened geodetic models substantially bringing them closer to the seismic depth however recent studies that have included heterogeneity for other faults indicate that the effect is not so great we show here that elastic heterogeneity has a relatively minor effect on the geodetic model depth for this earthquake also however by combining three different sets of geodetic data we are able to get a more accurate estimate of the depth which does in fact coincide with the hypocentral depth at the 95 confidence level when we consider that static elastic parameter values are commonly less than dynamic values the agreement is even better furthermore the depth is consistent with the earthquake having occurred at the interface between the volcanic pile and the pre volcanic seafloor

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

tectonic and sedimentary evolution of the korean peninsula a review and new view abstract this review focuses on the tectonics and sedimentation of major sedimentary basins and orogenic belts late proterozoic neogene in the korean peninsula the korean peninsula is part of the amuria plate and represents an important link between continental blocks of north and south china and the island arcs of japan the basement rocks exposed in the kyonggi and yongnam massifs consist of 2 7 to 1 1 ga high grade gneiss and schist these massifs are separated by the okchon fold belt which comprises metasedimentary rocks and bimodal meta volcanic rocks the stratigraphy of the okchon group is unclear at present the okchon basin was probably initiated as an intraplate rift prior to the late proterozoic the hwanggangri formation clast bearing phyllite most likely represents deposition by subaqueous debris flows in slope environments of an enclosed basin the stratigraphic relationship between the okchon group and the choson supergroup cambro ordovician of the taebaeksan basin is poorly constrained the choson supergroup unconformably overlies the yongnam massif and consists mainly of carbonate sequence that formed mostly in shallow marine and tidal environments reflecting numerous sea level fluctuations the sequence is disconformably overlain by siliciclastic sequence of pyongan supergroup carboniferous triassic which formed most likely in shallow marine deltaic and fluvial environments the imjingang belt is an east trending fold and thrust zone and consists of metasedimentary rocks and volcaniclastics devonian carboniferous underlain unconformably by proterozoic basement rocks late proterozoic amphibolites of oceanic affinity were metamorphosed at about 8 13 kbar and 630 740 c during the late permian to the early triassic the south vergent contraction and top down to the north normal faulting are suggestive of a suture belt between the north china block sino korea craton and the south china block yangtze craton an extension of sulu belt across the yellow sea entire peninsula experienced strong deformation and metamorphism during the suturing event namely songrim orogeny during this orogenic event the kyonggi massif and the okchon basin accreted to the yongnam massif and taebaeksan basin along the south korean tectonic line running northeast southwest a series of northward trending thrust formed along the boundary zone to the east kaktong and kongsuwon thrusts and others piggyback basins locally developed along the thrust faults forming the taedong group the crustal deformation resumed in the early to late jurassic daebo event under contractional setting dextral ductile shearing associated with thrusting and folding continued in the mid southern part of the peninsula it was due to orthogonal northwestward subduction of the izanagi plate under the asian continent the yongnam massif experienced continuous dextral offset along the honam shear zone in the early cretaceous the izanagi plate began to subduct northward and caused formation of strike slip basins in retroarc setting i e kyongsang basin in the southeastern part and a number of small scale basins in the mid southwestern part of the peninsula small scale alluvial fans and fluvial channel networks formed in the basin margin and were transitional to ephemeral lacustrine systems under semiarid to arid conditions extensive intrusion of granitoids occurred from triassic to early tertiary with a gap between 160 and 100 ma representing continental magmatic arc in the tertiary the southeastern margin of the korean peninsula experienced back arc opening pull apart basins formed in the miocene bounded by the yangsan and hupo faults the yonil group sedimentary fill of the pohang basin comprises more than 1 km thick siliciclastic sequence which represents deposition in fan delta systems on the hanging wall of the yangsan fault thick more than 10 km thick sediments in the ulleung basin margin were deformed in the late miocene due to the northward movement of kyushu block quarternary volcanic events in cheju island represent intraplate hot spots

stress induced borehole elongation a comparison between the four arm dipmeter and the borehole televiewer in the auburn geothermal well the nature and origin of borehole elongation recorded by the four arm dipmeter calipers is studied utilizing information obtained from hydraulic fracturing stress measurements and borehole televiewer data taken in a well located in auburn new york a preferred orientation n10 w s10 e 10 and a less prominant e w orientation of borehole elongation was observed on two runs of the dipmeter comparisons of borehole geometry determined using the televiewer and the dipmeter show that both tools give the same orientation of borehole elongtion provided that the zone of elongation is longer than 30 cm comparisons of dipmeter caliper data with orientation of in situ stress and natural fractures obtained from hydrofracturing tests and televiewer data show that the n10 w s10 e borehole elongations 1 are axisymmetric 2 are aligned with the minimum horizontal stress sh and 3 are not associated with natural fractures intersecting the well these elongations are interpreted as stress induced well bore breakouts the e w elongation direction is characterized by an asymmetric borehole cross section in thinly bedded rocks and is not caused by breakouts this asymmetric geometry can be discriminated from breakouts using the oriented electric measurements provided by the dipmeter this study demonstrates that the dipmeter can be used to determine the orientation of sh by mapping breakouts confirming the results of earlier less detailed studies and provides a firm basis for mapping regional stress patterns using existing dipmeter data

global seismic data reveal little water in the mantle transition zone abstract knowledge of the earth s present water content is necessary to constrain the amount of water and other volatiles the earth acquired during its formation and the amount that is cycled back into the interior from the surface this study compares 410 and 660 km discontinuity depth with shear wave tomography within the mantle transition zone to identify regions with seismic signals consistent with water the depth of the 410 and 660 km discontinuities is determined from a large updated dataset of ss s410s and ss s660s differential travel times known as ss precursors the discontinuity depths measured from binning and stacking the ss precursor data are then compared to the shear velocity model hmsl s06 in the transition zone mapping all the possible combinations very few locations match the predictions from mineral physics for the effects of water on discontinuity depth and shear velocity the predictions although not yet measured at actual transition zone temperatures and pressures are a shallow 410 km discontinuity a deep 660 km discontinuity and a slow shear velocity only 8 of the bins with high quality data are consistent with these predictions and the calculated average water content within these bins is around 0 6 wt a few isolated locations have patterns of velocity topography that are consistent with water while there are large regional scale patterns consistent with cold hot temperature anomalies combining this global analysis of long period seismic data and the current mineral physics predictions for water in transition zone minerals i find that the mantle transition zone is generally dry containing less than one earth ocean of water although subduction zones could be locally hydrated the combined discontinuity and velocity data show no evidence that wadsleyite or ringwoodite have been globally hydrated by subduction or initial earth conditions

a global tomographic model of shear attenuation in the upper mantle we present a global three dimensional model of shear attenuation in the upper mantle based on the measurement of amplitudes of low frequency 100 300s rayleigh waves observed at stations of the geoscope and iris networks attenuation coefficients are measured on r1 and r2 paths using a method which minimizes the effects of focussing due to propagation in a three dimensional elastic earth through a series of tests which in particular involve the computation of synthetic models of attenuation and focussing we demonstrate that long wavelength lateral variations in attenuation in the first 400 500 km of the mantle can indeed be resolved the model is obtained in a two step procedure the first step consists in the computation of maps of rayleigh wave attenuation at different periods using an inversion method without a priori parametrisation which involves the introduction of a correlation length chosen here at 3000 km to optimize the trade off between resolution and variance in the model in the second step after corrections for shallow structure an inversion with depth is performed assuming lateral heterogeneity is confined to depths between 80 and 650 km the resulting model presents lateral variations in qp that are correlated with tectonic features in particular ridges and shields in the first 250 km of the upper mantle below that depth the pattern shifts and becomes correlated with the hotspot distribution particularly so if the buoyancy strength of hotspots is taken into account two major low velocity zones appear to be located in the central pacific and beneath northern africa in the depth range 300 500 km this pattern seems to continue at greater depth but resolution becomes insufficient below 500 km to draw definitive conclusions the smooth lateral variations retrieved are on the order of 50 down to 400 km we propose an interpretation in terms of plume lithosphere ridge interaction in the upper mantle arguing for deflection of the bulk of hot upwelling material from plumes towards ridges which may be occurring between 200 and 300 km depth

integrating borehole breakout dimensions strength criteria and leak off test results to constrain the state of stress across the chelungpu fault taiwan article the paper describes the computation of the maximum horizontal stress h magnitude in the vicinity of the chelungpu fault taiwan host of the slip zone during the chi chi earthquake mw 7 6 1999 the scientific hole b intercepts the chelungpu fault at 1136 m at the depths of logged breakouts 940 1310 m the vertical stress v as estimated from density logs increases linearly with depth from 22 to 31 mpa a series of leak off tests yielded two reliable shut in pressures 23 7 mpa at 1085 m and 29 8 mpa at 1279 m which are lower than the estimated v albeit by only 2 1 and 0 6 mpa respectively in our analysis the shut in pressures were considered to represent estimates of the least horizontal principal stresses h at the respective depths and consequently the test induced fractures were assumed to have been vertical principal stress directions had been previously determined by others 105 155 for the maximum horizontal stress h

splay fault branching along the nankai subduction zone seismic reflection profiles reveal steeply landward dipping splay faults in the rupture area of the magnitude m 8 1 tonankai earthquake in the nankai subduction zone these splay faults branch upward from the plate boundary interface that is the subduction zone at a depth of approximately 10 kilometers approximately 50 to 55 kilometers landward of the trough axis breaking through the upper crustal plate slip on the active splay fault may be an important mechanism that accommodates the elastic strain caused by relative plate motion

observations of pkkp precursors used to estimate small scale topography on the core mantle boundary stacks of global seismic data reveal the time and distance dependence of high frequency 1 hertz precursors to the seismic phasepkkp synthetic seismogram modeling shows that scattering from random small scale topography at the pkkpcore mantle boundary reflection point generates precursory arrivals similar to those seen in the data models with a root mean square core mantle boundary topography of 250 to 350 meters and correlation length of 7 to 10 kilometers explain the main features of the data however a systematic range dependent misfit between observed and predicted precursor power suggests that inner core scattering may contribute to the precursors

survey of precursors to p p fine structure of mantle discontinuities 1 the jumps in seismic velocity and density near 410 and 660 km depths have been postulated to mark phase changes in a locally chemically homogeneous mantle seismic estimates of upper mantle discontinuity thickness and lateral variability have varied posing difficulties for assessing models with chemical and phase transition layering observations of underside high frequency 1 hz p wave reflections from the 410 and 660 km discontinuity that precede the p p phase provide unique constraints on the physical properties of these dynamically critical features we have collected high quality recordings of p p and its precursors from three sources the california seismic network the large aperture seismic array in montana and the global seismic network the array and regional network data have great sensitivity to weak p p precursors whereas the global network recordings have good geographical distribution of bounce points the only consistently observed reflections originate from depths near 410 km and 660 km the reflector observed near 520 km depth with longer period waves which has been interpreted as the olivine phase transition is too small in impedance contrast or too thick to reflect 1 hz p waves data from all three networks indicate that the 1 hz p waves from the 660 are bigger than those from the 410 although large variability in p p and its precursors amplitudes prevents strong conclusions we show that the p p precursor amplitudes travel time dispersion and frequency content are consistent with a sharp 2 km 660 and a more diffuse 410 consistent with mineral physics predictions

a model of the earthquake cycle along the san andreas fault system for the past 1000 years 1 we simulate 1000 years of the earthquake cycle along the san andreas fault system by convolving best estimates of interseismic and coseismic slip with the green s function for a point dislocation in an elastic plate overlying a viscoelastic half space interseismic slip rate is based on long term geological estimates while fault locking depths are derived from horizontal gps measurements coseismic and postseismic deformation is modeled using 70 earthquake ruptures compiled from both historical data and paleoseismic data this time dependent velocity model is compared with 290 present day geodetic velocity vectors to place bounds on elastic plate thickness and viscosity of the underlying substrate best fit models rms residual of 2 46 mm yr require an elastic plate thickness greater than 60 km and a substrate viscosity between 2 1018 and 5 1019 pa s these results highlight the need for vertical velocity measurements developed over long time spans 20 years our numerical models are also used to investigate the 1000 year evolution of coulomb stress stress is largely independent of assumed rheology but is very sensitive to the slip history on each fault segment as expected present day coulomb stress is high along the entire southern san andreas because there have been no major earthquakes over the past 150 300 years animations s1 and s2 of the time evolution of vector displacement and coulomb stress are available as auxiliary material

detrital modes of the pyeongan supergroup late carboniferous early triassic sandstones in the samcheog coalfield korea implications for provenance and tectonic setting abstract medium to coarse sandstones of the carboniferous to early triassic pyeongan supergroup in the samcheog coalfield korea were studied to infer the provenance and tectonic settings of the source areas sandstone detrital modes change upwards stratigraphically sandstone types from the manhang to dosagog formations low to middle in the sequence are quartzarenite and sublitharenite to litharenite whereas sandstones of the gohan and donggo formations high in the sequence are feldspathic litharenite and arkose respectively using various ternary diagrams the provenance of the manhang to gohan formations is suggested to be a recycled orogen setting some gohan formation sandstones plot within the arc related setting field and the donggo formation sandstones plot within both continental block and recycled orogen fields results of quartz grain petrography are consistent with those of detrital modes quartz in sandstones of all units except the donggo formation indicates derivation from low rank metamorphic sources quartz in donggo sandstones was derived from medium to high rank metamorphic and plutonic source rocks considering the sandstone composition and palaeocurrent data the pyeongan supergroup probably was deposited in a molasse foreland basin and was derived from a synbasinal orogenic belt probably the akiyoshi orogen located in southwest japan

sandstone petrology of the pyeongan supergroup taebaeksan region korea implications for the carboniferous triassic tectonic history of east asia abstract sandstones of the pyeongan supergroup vary from quartzose to quartzo feldspathic in composition the introduction of significant amounts of plagioclase and k feldspar in upper formations of the pyeongan supergroup may be related to a change in tectonic stability of the source area from a relatively stable cratonic interior to an uplifted basement the absence of sandstones rich in lithic fragments in the korean peninsula including the pyeongan and daedong supergroups the latter of which is supposedly post collision between the north and south china blocks suggests that a recycled orogen had never been emplaced in korea reference of the tectonic divisions of korea to those of china or japan should be made with substantial care this includes the current attempts to relate the imjingang belt with the qinling dabieshan belt or the ogcheon belt with the hida belt

a multilayer model of time dependent deformation following an earthquake on a strike slip fault a multilayer half space model of the earth is used in finite element calculations of time dependent deformation and stress following an earthquake on an infinitely long strike slip fault the model involves shear properties of an elastic upper lithosphere a standard viscoelastic linear solid lower lithosphere a maxwell viscoelastic asthenosphere and an elastic mesosphere time dependent displacements strains and stresses are computed both at the surface of the earth and at depth the analysis includes both systematic variations of fault and layer depths and comparisons with simpler elastic lithosphere over viscoelastic asthenosphere calculations for conditions which may be appropriate for the earth the creep of both the lower lithosphere and the asthenosphere can contribute to the postseismic deformation the magnitude of the deformation is enhanced by a short distance between the bottom of the fault slip zone and the top of the creep layer but is less sensitive to the thickness of the creeping layer furthermore postseismic restressing is increased as the lower lithosphere becomes more viscoelastic but the tendency for the width of the restressed zone to grow with time is retarded

large scale characteristics of plate boundary deformations related to the post seismic readjustment of a thin asthenosphere summary the large scale response of an elastic lithosphere riding on a thin viscoelastic asthenosphere to periodically occurring ruptures at a transform or subduction type plate boundary is described approximately by appropriate limit cycle solutions for a plate foundation model introduced previously by rice the cyclic behaviour of thickness averaged displacements strains and strain rates their decay away from the plate boundary and a resolution into coseismic and post seismic alterations are obtained and their dependence on repeat time and a characteristic relaxation time investigated a comparison is made with existing periodic solutions for the surface deformations in a nur mavko half space model this suggests important effects due to viscosity stratification on post seismic rebound when earthquake repeat times exceed relevant relaxation times by at least one order of magnitude

rupture characteristics of the deep bolivian earthquake of 9 june 1994 and the mechanism of deep focus earthquakes the m w 8 3 deep 636 kilometers bolivian earthquake of 9 june 1994 was the largest deep focus earthquake ever recorded seismic data from permanent stations plus portable instruments in south america show that rupture occurred on a horizontal plane and extended at least 30 by 50 kilometers rupture proceeded at 1 to 3 kilometers per second along the down dip azimuth of the slab and penetrated through more than a third of the slab thickness this extent is more than three times that expected for a metastable wedge of olivine at the core of the slab and thus appears to be incompatible with an origin by transformational faulting these large events may instead represent slip on preserved zones of weakness established in oceanic lithosphere at the earth s surface

global mapping of topography on the 660 km discontinuity long period precursors to the ss seismic phase are used to produce global maps of topography for the discontinuity at 660 km depth in the upper mantle these maps indicate discontinuity depth variations of up to 30 km and suggest a correlation between regional depressions in the 660 km discontinuity and subduction zones a result more consistent with models in which the subducting slabs are deflected horizontally at the discontinuity than with models of unhindered slab penetration into the lower mantle

detailed structure of mantle transition zone beneath southeastern china and its implications for thinning of the continental lithosphere abstract this paper presents a new study on 3 d structure temperature and water content estimation of the mantle transition zone mtz by p wave receiver functions common conversion point ccp method on broadband array with 267 temporary stations and 203 permanent stations in southeastern china the results show different structural characteristics of the mtz to the north and south of the 29 n line in the northern part the 660 km discontinuity is generally deeper than globe models and there are two independent local depressions with characteristics of high velocity low temperature and water shortage we interpret them as two previous subducting plates stagnated in mtz possibly related to two separate subduction events at different times while in the southern part the 410 km discontinuity is locally depressed resulting in thinning of the mtz particularly in the cathaysian block south of the 29 n line based on the mtz structure and the estimation of temperature and water content we conside dehydration of the mtz as one of the important mechanisms of lithospheric thinning through interaction with the asthenosphere we then propose a dynamic model that combines paleo pacific flat slab subduction and upper mantle convection to explain the lithospheric extension and thinning magmatic rock distribution weak seismic activity and basin and range geomorphology this model differs from that north of the 29 n line in the north china block

gypsum a joint tomographic model of mantle density and seismic wave speeds 1 gypsum is a 3 d model of mantle shear wave s speeds compressional wave p speeds and density the model is developed through simultaneous inversion of seismic body wave travel times p and s and geodynamic observations while using realistic mineral physics parameters linking wave speeds and density geodynamic observations include the global free air gravity field divergence of the tectonic plates dynamic topography of the free surface and the flow induced excess ellipticity of the core mantle boundary gypsum is built with the philosophy that heterogeneity that most closely resembles thermal variations is the simplest possible solution models of the density field from earth s free oscillations have provided great insight into the density configuration of the mantle but are limited to very long wavelength solutions alternatively scaling higher resolution seismic images to obtain density anomalies generates density fields that do not satisfy geodynamic observations the current study provides a 3 d density model for the mantle that directly satisfies geodynamic and seismic observations through a joint seismic geodynamic inversion process notable density field observations include high density piles at the base of superplume structures supporting the general results of past normal mode studies however we find that these features are more localized and have lower amplitude than past studies would suggest when we consider both fast and slow seismic anomalies in gypsum we find that p and s wave speeds are strongly correlated throughout the mantle however we find a low correlation of fast s wave zones in the deep mantle 1500 km depth with the corresponding p wave anomalies suggesting a systematic divergence from simplified thermal effects in ancient subducted slab anomalies the cratonic lithosphere and d regions are shown to have strong compositional signatures however we argue that temperature variations are the primary cause of p wave speed s wave speed and density anomalies throughout most of the mantle

core mantle boundary topography from short period pcp pkp and pkkp data abstract we use a total of 839 369 pcp pkpab pkpbc pkpdf pkkpab and pkkpbc residual travel times from bull seism soc am 88 1998 722 grouped in 29 837 summary rays to constrain lateral variation in the depth to the core mantle boundary cmb we assumed a homogeneous outer core and the data were corrected for mantle structure and inner core anisotropy inversions of separate data sets yield amplitude variations of up to 5 km for pcp pkpab pkpbc and pkkp and 13 km for pkpdf this is larger than the cmb undulations inferred in geodetic studies and moreover the pcp results are not readily consistent with the inferences from pkp and pkkp although the source receiver ambiguity for the core refracted phases can explain some of it this discrepancy suggest that the travel time residuals cannot be explained by topography alone the wavespeed perturbations in the tomographic model used for the mantle corrections might be too small to fully account for the trade off between volumetric heterogeneity and cmb topography in a second experiment we therefore re applied corrections for mantle structure outside a basal 290 km thick layer and inverted all data jointly for both cmb topography and volumetric heterogeneity within this layer the resultant cmb model can explain pcp pkp and pkkp residuals and has approximately 0 2 km excess core ellipticity which is in good agreement with inferences from free core nutation observations joint inversion yields a peak to peak amplitude of cmb topography of about 3 km and the inversion yields velocity variations of 5 in the basal layer the latter suggests a strong trade off between topography and volumetric heterogeneity but uncertainty analyses suggest that the variation in core radius can be resolved the spherical averages of all inverted topographic models suggest that the data are best fit if the actual cmb radius is 1 5 km less than in the earth reference model used i e the average outer core radius would be 3478 km

equivalent strike slip earthquake cycles in half space and lithosphere asthenosphere earth models by virtue of the images used in the dislocation solution the deformation at the free surface produced throughout the earthquake cycle by slippage on a long strike slip fault in an earth model consisting of an elastic plate lithosphere overlying a viscoelastic half space asthenosphere can be duplicated by prescribed slip on a vertical fault embedded in an elastic half space for the case in which each earthquake ruptures the entire lithosphere thickness h the half space equivalent slip rate is as follows depth interval 0 h slip identical to that in lithosphere asthenosphere model i e abrupt coseismic slip and no subsequent slip depth interval 2n 1 h to 2n 1 h n 1 2 slip rate uniform in space and dependent upon time as fn t exp t a where fn is a n 1 degree polynomial in t a is twice the asthenosphere relaxation time and t is measured from the instant after the preceding earthquake the slip rate averaged over the seismic cycle in each depth interval equals the secular rate of relative plate motion for reasonable values of a slip rates below 5h do not vary much from that mean value and can be treated as constant thus the surface deformation due to the earthquake cycle in the lithosphere asthenosphere model can be calculated very simply from the half space model with time dependent slip in the two depth intervals h 3h and 3h 5h and uniform slip at a rate equal to the secular relative plate velocity below depth 5h inversion of 1973 1988 geodetic measurements of deformation across the segment of the san andreas fault in the transverse ranges north of los angeles for the half space equivalent slip distribution suggests no significant slip on the fault above 30 km and a uniform slip rate of 36 mm yr below 30 km one equivalent lithosphere asthenosphere model would have a 30 km thick lithosphere and an asthenosphere relaxation time greater than 33 years but other models are possible

seismic constraints on mantle flow and topography of the 660 km discontinuity evidence for whole mantle convection recent seismic models of three dimensional mantle structure and topography on the transition zone seismic discontinuities permit the direct evaluation of the buoyancy forces that drive large scale mantle flow this buoyancy distribution coupled with radial viscosity models that are consistent with the observed geoid predicts flow patterns with significant vertical flow through the 660 km phase boundary the observed topography on the 660 km discontinuity acts to inhibit convection across the boundary but is two to four times too small to prevent whole mantle convection

phanerozoic polyphase orogenies recorded in the northeastern okcheon belt korea from shrimp u pb detrital zircon and k ar illite geochronologies abstract we present the shrimp u pb detrital zircon and k ar illite 1m d 1m and 2m 1 ages suggesting new insight into the phanerozoic polyphase orogenies preserved in the northeastern okcheon belt korea since the initial basin formation during neoproterozoic rifting through several successive contractional orogens the u pb detrital zircon ages from the early paleozoic strata of the taebaeksan zone suggest a cambrian maximum deposition age and are supported by trilobite and conodont biostratigraphy although the age spectra from two sedimentary groups the yeongwol and taebaek groups show similar continuous distributions from the late paleoproterozoic to early paleozoic ages a grenville age hiatus 1 3 0 9 ga in the continuous stratigraphic sequence from the taebaek group suggests the existence of different peripheral clastic sources along rifted continental margin s in addition we present the k ar illite 1m d 1m ages of the fault gouges which confirm fault formation reactivation during the late cretaceous to early paleogene ca 82 62 ma and the early miocene ca 20 18 ma the 2m 1 illite ages at least those younger than the host rock ages provide episodes of deformation metamorphism and hydrothermal effects related to the tectonic events during the devonian ca 410 ma and permo triassic ca 285 240 ma these results indicate that the northeastern okcheon belt experienced polyphase orogenic events namely the okcheon middle paleozoic songrim late paleozoic to early mesozoic daebo middle mesozoic and bulguksa late mesozoic to early cenozoic orogenies reflecting the phanerozoic tectonic evolution of the korean peninsula along the east asian continental margin

spectral induced polarization characterization of rocks from the handuk iron mine south korea spectral induced polarization sip using the electrochemical reaction at the interface between mineral particle and groundwater is a powerful tool for the exploration of minerals however sip responses of rocks have not been fully characterized because it is influenced by various petrological properties in this study the relationship between sip responses and the petrological features of representative rocks from skarn deposits was analyzed for the evaluation of the sip responses chargeability and relaxation time of time domain induced polarization ip were calculated by an equivalent circuit analysis among various circuit models used for the analysis an existing circuit model was utilized for this study because it sufficiently describes the electrochemical reaction of water saturated rocks and is more suitable for the analysis of heterogeneous rocks than the other models the circuit model was found to be appropriate because the normalized root mean square error between the observed values and ones obtained through the model fittings reasonably low ranging from 4 18 to 0 05 the chargeability values of the mineralized rocks were higher than those of the non mineralized rocks igneous and carbonates and the relaxation time was related to the grain size of the magnetite it was found that the sip characteristics of the mineralized rocks are dependent on features of the ore minerals in the non mineralized rocks there was little difference in the chargeability whereas the variation in their relaxation time values was influenced by the feldspar content sericitization and the grain size of the calcite recrystallization the sip characteristics of the non mineralized rocks are considered to be dependent on the grade of the hydrothermal alteration

topography of the 660 km seismic discontinuity beneath izu bonin implications for tectonic history and slab deformation we analyze the p wave codas of 65 paths from deep northwestern pacific earthquakes recorded by arrays of stations in germany the western united states india and turkmenistan we identify a phase resulting from a near source s to p conversion at a nearly horizontal discontinuity ranging in depth from 650 to 730 km which we interpret as a thermally depressed spinel to perovskite and magnesiowustite phase transition we migrate these data along with 39 more from wicks and richards 1993 accounting for three dimensional ray bending by the sloping discontinuity to produce a high resolution topography map of the 660 km discontinuity in the izu bonin region assuming an equilibrium phase transition we interpret the discontinuity depth in terms of local temperatures the slab if defined by a thermal anomaly greater than 400 k is only about 100 km thick near 28 n suggesting the slab is penetrating into the lower mantle with little or no advective thickening farther to the north however cold material appears spread out over a wide region consistent with the slab having been laid down flat on the 660 km discontinuity as the trench retreated 2000 km eastward both the narrow slab to the south and the flat lying slab to the north are consistent with recent high resolution tomographic images the depression to 745 km along the arc is consistent with a maximum thermal anomaly of about 1100 k along the entire arc the depression occurs directly beneath the deepest earthquakes even where seismicity is dipping at 45 and stops at 450 km depth suggesting that the slab steepens to a vertical dip at the deepest seismicity this change to a vertical orientation suggests that the slab loses strength temporarily through a physical process which causes the seismicity to increase dramatically and then abruptly cease

lithostratigraphy and depositional environments of the pyeongan supergroup carboniferous permian in the taebaek area mid east korea abstract the pyeongan supergroup carboniferous permian consists of a thick siliciclastic sequence 1700 m thick recent sedimentological work in the taebaek area has refined the lithostratigraphic units manhang geumcheon jangseong hambaeksan dosagok gohan and donggo formations in ascending order the entire sequence is represented by thirteen sedimentary facies which can be organized into seven facies associations fa the lower part of the manhang formation fa 1 moscovian consists of crudely cross stratified conglomerate massive sandstone and gray homogeneous siltstone formed in shoreface off river mouth whereas purple siltstone and grainstone of the upper part fa 2 probably formed in a coastal plain environment the geumcheon jangseong formation moscovian artinskian consists of dark gray sandstone dark gray shale coal and bioturbated wackestone fa 3 formed in a lagoonal environment the hambaeksan formation kungurian comprises milky white crudely stratified conglomerate gray coarse sandstone and partly laminated black shale fa 4 representing a shoreface progradation the dosagok formation late permian is characterized by an alternation of purple fine sandstone and conglomerate fa 5 formed in a bedload dominated fluvial system the gohan formation late permian is mostly composed of upward fining units massive sandstone to dark gray siltstone fa 6 suggesting a restricted inter distributary bay environment the donggo formation late permian consists of cross stratified coarse sandstone and purple sandstone fa 7 interpreted as deposits of perennial sandy braided river system

nonlinear strain buildup and the earthquake cycle on the san andreas fault two contrasting models of the earthquake deformation cycle on strike slip faults predict significant temporal declines in shear strain rate near the fault accompanied by a progressive broadening of the zone of deformation adjacent to it in the thin lithosphere model transient deformation results from flow in the asthenosphere due to stress relaxation following faulting through most or all of the lithosphere for an earth model with a thick elastic lithosphere plate thickness depth of seismic slip transient motions are due to postearthquake aseisrnic slip below the coseismic fault plane data from the san andreas fault indicate a long term temporal decrease in strain rate that persists for at least 30 years and may extend through the entire earthquake cycle observations support a cycle long rate decrease and a temporal spreading of the deformation profile only if movement cycles on the northern and southern locked sections of the fault are basically similar if so the usually lower strain rates and broader deformation zone currently observed on the southern san andreas represent a later evolutionary stage of the northern locked section where a great earthquake is a more recent occurrence although the data allow some extreme models to be discarded no sufficiently strong constraints exist to decide between the thin and thick lithosphere models regardless of the appropriate model the geodetic observations themselves indicate that strain buildup is sufficiently nonlinear to cause significant departures from recurrence estimates based on linear strain accumulation and the time predictable model

reservoir induced deformation and continental rheology in vicinity of lake mead nevada lake mead is a large reservoir in nevada formed by the construction of the 221 m high hoover dam in the black canyon of the colorado river the lake encompasses an area of 635 km2 and the total volume of the reservoir is 35 5 km3 filling started in february 1935 on the basis of a first order leveling in 1935 several levelings were carried out to measure the deformation induced by the load of the reservoir subsidence in the central parts of the lake relative to the first leveling was around 120 mm 1941 218 mm 1950 and 200 mm 1963 the subsidence pattern clearly shows relaxation of the underlying basement due to the water load of the lake which ceased after 1950 modeling of the relaxation process by means of layered viscoelastic compressible flat earth models with a detailed representation of the spatial and temporal distribution of the water load shows that the thickness of the elastic crust underneath lake mead is 30 3 km the data are also consistent with a 10 km thick elastic upper crust and a 20 km thick viscoelastic lower crust with 1020 pa s as a lower bound for its viscosity the subcrust has an average viscosity of 1018 0 2 pa s a surprisingly low value the leveling data constrain the viscosity profile down to 200 km depth

inferring earth s discontinuous chemical layering from the 660 kilometer boundary topography topography or depth variation of certain interfaces in the solid earth can provide important insights into the dynamics of our planet interior although the intermediate and long range topographic variation of the 660 kilometer boundary between earth s upper and lower mantle is well studied small scale measurements are far more challenging we found a surprising amount of topography at short length scale along the 660 kilometer boundary in certain regions using scattered p p seismic waves our observations required chemical layering in regions with high short scale roughness by contrast we did not see such small scale topography along the 410 kilometer boundary in the upper mantle our ndings support the concept of partially blocked or imperfect circulation between the upper and lower mantle

present day principal horizontal stress orientations in the kumano forearc basin of the southwest japan subduction zone determined from iodp nantroseize drilling site c0009 a 1 6 km riser borehole was drilled at site c0009 of the nantroseize in the center of the kumano forearc basin as a landward extension of previous drilling in the southwest japan nankai subduction zone we determined principal horizontal stress orientations from analyses of borehole breakouts and drilling induced tensile fractures by using wireline logging formation microresistivity images and caliper data the maximum horizontal stress orientation at c0009 is approximately parallel to the convergence vector between the philippine sea plate and japan showing a slight difference with the stress orientation which is perpendicular to the plate boundary at previous nantroseize sites c0001 c0004 and c0006 but orthogonal to the stress orientation at site c0002 which is also in the kumano forearc basin these data show that horizontal stress orientations are not uniform in the forearc basin within the surveyed depth range and suggest that oblique plate motion is being partitioned into strike slip and thrusting in addition the stress orientations at site c0009 rotate clockwise from basin sediments into the underlying accretionary prism

shear wave anisotropy spatial and temporal variations in time delays at parkfield central california summary shear wave splitting is analysed on data recorded by the high resolution seismic network hrsn at parkfield on the san andreas fault central california during the three year period 1988 1990 shear wave polarizations either side of the fault are generally aligned in directions consistent with the regional horizontal maximum compressive stress at some 70 to the fault strike whereas at station mm in the immediate fault zone shear wave polarizations are aligned approximately parallel to the fault normalized time delays at this station are found to be about twice as large as those in the rock mass either side this suggests that fluid filled cracks and fractures within the fault zone are elastically or seismically different from those in the surrounding rocks and that the alignment of fault parallel shear wave polarizations are associated with some fault specific phenomenon temporal variations in time delays between the two split shear waves before and after a ml 4 earthquake can be identified at two stations with sufficient data mm within the fault zone and vc outside the immediate fault zone time delays between faster and slower split shear waves increase before the ml 4 earthquake and decrease near the time of the event the temporal variations are statistically significant at 68 per cent confidence levels earthquake doublets and multiplets also show similar temporal variations consistent with those predicted by anisotropic poroelasticity theory for stress modifications to the microcrack geometry pervading the rock mass this study is broadly consistent with the behaviour observed before three other earthquakes suggesting that the build up of stress before earthquakes may be monitored and interpreted by the analysis of shear wave splitting

postseismic relaxation theory on the spherical earth abstract postseismic displacements and strains observed at the earth9s surface can be explained through the relaxation of a viscoelastic asthenosphere underlying a purely elastic crust a theory is presented for modeling the effects of postseismic relaxation on a spherically symmetric earth for an earthquake point source located in the upper elastic layer the displacement field is decomposed into its toroidal and spheroidal components a linear maxwell rheology in the viscoelastic layers is assumed enabling the use of the correspondence principle for the solutions of the equations of static equilibrium displacement and strain fields are then calculated using normal mode summation computational results are presented for two simple earthquake sources a strike slip fault and a uniaxial thrust fault the patterns of postseismic displacements and strains are found to depend strongly on both the earth model and earthquake source geometry in particular the elastic plate thickness asthenosphere thickness fault type and fault length each play a major role in determining the spatial pattern of postseismic relaxation effects asthenospheric viscosity controls the temporal pattern of relaxation

stress state estimation by geophysical logs in nantroseize expedition 319 site c0009 kumano basin southwest japan 1 to understand the stress regime in the shallow portion of the nankai trough seismogenic zone we carefully investigated the resistivity image logs at iodp site c0009 that penetrated to 1600 meters below the sea floor mbsf in the central kumano forearc basin during the riser drilling several downhole measurements were run including image logs caliper and comprehensive geophysical logs sets borehole resistivity images obtained by a wireline logging tool were reprocessed in order to eliminate image artifacts generated by sticky tool movements etc the constraints on the possible magnitude and orientation of horizontal principal stresses are provided from the borehole images rock strength and logging data the absence of borehole breakouts above 1285 mbsf represents a small difference shmin

architectural analysis of fluvial sequences in the northwestern part of kyongsang basin early cretaceous se korea abstract the northwestern part of kyongsang basin early cretaceous largely comprises interbedded sandstones and mudstones of fluvial depositional environments with local basin margin conglomeratic deposits of alluvial fan systems these non marine successions are divided into 5 successive stratigraphic units each of which is unique in facies assemblages and architecture of sandstone bodies one stratigraphic unit sinpyong anpyong unit is documented in this paper with detailed architectural analysis of sandstone bodies the deposits of the sinpyong anpyong unit are divided into three major components thick sandstone thin sandstone and mudstone dominated bodies the thick sandstone bodies 2 47 m thick comprise stacked element groups bounded by laterally persistent erosional surfaces probably representing superposition of channel belts within individual element groups elements are laterally superposed indicating growth and superposition of bars and movement of associated channels the thickness of bar deposits and dip angles of laterally inclined strata suggest that channels were a few to 10 m in depth and 9 m to several tens of meters in width paleocurrent data indicate southward or southeastward draining channel systems the thin sandstone bodies generally the thick sandstone bodies formed in major channels and channel belts are characterized by lateral superposition of numerous bar and channel deposits limited extent of individual lateral accretion sets and the presence of mid channel bar deposits suggesting deposition in braided rivers detailed reconstruction of bars and channels reveals a range of processes including growth coalescence and erosion of bars and migration switching and filling of channels lateral accretion of bars and the associated channel migration might have been principal processes in the sinpyong anpyong river systems bars were commonly coalesced by lateral superposition forming large bar complexes

formative mechanisms depositional processes and geological implications of furongian late cambrian reefs in the north china platform abstract the cambrian series 3 furongian successions of the north china platform contain various microbial metazoan and microbial reefs this study focuses on furongian reefs of the platform in order to understand formative processes and the evolution of the reefs during cambrian epoch 3 and the furongian three types of furongian reefs were differentiated in the shandong region china maceriate reefs columnar stromatolitic reefs and small scale microbial reefs maceriate reefs show dm to m scale domal or flat bedded geometry and consist of cm scale maze like maceria structures made of siliceous sponges and microbial components microstromatolites girvanella and tarthinia columnar stromatolitic reefs are characterized by stromatolite columns of 10 100 cm in height and 5 50 cm in diameter they consist dominantly of girvanella with less conspicuous poorly preserved sponge spicule networks small scale microbial reefs commonly show cm to dm scale domal macrostructures and were constructed mainly by calcimicrobes girvanella and renalcis these three types of furongian reefs were deposited in various shallow marine settings in response to relative sea level changes the furongian reefs are markedly different in terms of macro and micro fabrics from the cambrian series 3 reefs that are dominated by thrombolites and dendrolites and were constructed mainly by epiphyton in the shandong region this difference is also recognized in the beijing region ca 500 km away the abrupt transition from the cambrian series 3 type to furongian type reefs coincidently with a decrease in calcified microbe diversity was most likely due to global euxinic oceanic conditions and a possible eustatic sea level drop rather than the highly diachronous platform wide drowning event i e drowning of the cambrian series 3 carbonate platform the abundant occurrence of sponge spicule networks in the furongian reefs suggests that metazoan reef builders i e sponges resurged and became actively involved in the reefal systems prior to the great ordovician biodiversification event this study may provide an important basis for further investigation into the evolution of reefal systems during the middle to late cambrian when metazoan reef builders were known to be scarce