early middle paleozoic intraplate orogeny in the ogcheon belt south korea a new insight on the paleozoic buildup of east asia the polycyclic ogcheon belt of south korea represents the boundary between two precambrian blocks investigation on the timing and kinematics of the block agglomeration is of considerable bearing on the understanding of the constitution of the asian continent we report here structural evidence showing that the earlier tectonic event dates back to early middle paleozoic the ogcheon tectonism or orogeny the ductile piling up of nappes of the ogcheon belt corresponds to an intracontinental orogeny involving the opening and the subsequent closure of an aborted rift and not of a wide oceanic area the nappes contain unequivocal evidence for ductile shearing with a northwest over southeast sense of movement field evidence includes the presence of s1 and s1 2 foliations bearing an extensive stretching lineation perpendicular to the belt associated with a strongly noncoaxial deformation regime the f1 isoclinal folds are commonly a type and sheath folds whose axes are parallel to the stretching lineation whereas the southeast facing f2 recumbent folds have subhorizontal axes parallel to the belt all lines of evidence unconformity superposed deformations age of the metamorphism etc imply that the d1 2 ogcheon tectonism is pre middle carboniferous late silurian early devonian the subsequent indosinian middle triassic f3 upright synfolial folds that trend nne ssw and later structures clearly overprint the middle paleozoic ductile thrusts and isoclinal folds the early paleozoic ogcheon supergroup is formed of a thick volcanosedimentary pile deposited above an early platform sequence in a rift basin on the basis of the geochemical characteristics of the metavolcanics it appears that oceanization did not occur and ogcheon rift aborted soon after it was formed we suggest that middle paleozoic ductile nappe structures have been formed by the structural inversion of the rift extensional features during the ductile stacking episode the early formed foliation and isoclinal folds have been folded in a continuum during the same tectonic event middle carboniferous terrigenous formations have been deposited unconformably upon folded and thrust older rocks a tentative correlation with early paleozoic imjingang qinling and cathaysian belts within the asian continent reveals that ogcheon rift was emplaced within the south china plate and that imjingang belt should represent the limit between north and south china blocks in the korean peninsula

simulated annealing inversion of teleseismic p wave slowness and azimuth for crustal velocity structure at long valley caldera simulated annealing a non linear global search algorithm is used to invert teleseismic p wave slowness and azimuth data for crustal velocity structure synthetic tests show that simulated annealing is able to locate low p wave velocity zones with reasonable accuracy in space and recovers almost 70 of the target velocity perturbations testing suggests that significant results can be obtained with as few as two stations inversion of ray direction data from long valley caldera finds an asymmetrical low velocity zone beneath the resurgent dome at 8km depth having a perturbation of 25 from the background this zone extends to the east and south to depths of at least 24km with a perturbation of about 10 these features generally agree with previous results from teleseismic travel time inversion and forward modeling of ray direction and are probably associated with the residual long valley caldera magma chamber

continental crust composition constrained by measurements of crustal poisson s ratio deciphering the geological evolution of the earth s continental crust requires knowledge of its bulk composition and global variability the main uncertainties are associated with the composition of the lower crust seismic measurements probe the elastic properties of the crust at depth from which composition can be inferred of particular note is poisson s ratio this elastic parameter can be determined uniquely from the ratio of p to s wave seismic velocity and provides a better diagnostic of crustal composition than either p or s wave velocity alone1 previous attempts to measure have been limited by difficulties in obtaining coincident p and s wave data sampling the entire crust2 here we report 76 new estimates of crustal spanning all of the continents except antarctica we find that on average increases with the age of the crust our results strongly support the presence of a mafic lower crust beneath cratons and suggest either a uniformitarian craton formation process involving delamination of the lower crust during continental collisions followed by magmatic underplating or a model in which crust formation processes have changed since the precambrian era

a meteorological overview of the second pacific exploratory mission in the tropics meteorological conditions over the central pacific basin are summarized during nasa s second pacific exploratory mission in the tropics pem b which was conducted during february april 1999 mean flow patterns during pem b are described important features near the surface include subtropical anticyclones the south pacific convergence zone spcz and the intertropical convergence zone itcz the itcz is found to exhibit a double structure with branches at 5 n and 5 s both the itcz and spcz are areas of widespread cloudiness and convection extensive lightning occurs over the land masses surrounding the pacific basin and over the central south pacific ocean itself pem b occurs during a la nina period of relatively cold sea surface temperatures in the tropical pacific compared to climatology the pem b period exhibits deep convection located west of its typical position stronger than normal easterly trade winds a relatively strong weak northern southern hemispheric jet stream the spcz located west of its normal position and an upper tropospheric cyclonic wind couplet that straddles the equator circulation patterns during pem b are compared with those of pem a which occurred during august september 1996 pem b is found to exhibit a less organized itcz a comparatively weak jet stream in the southern hemisphere a relatively strong jet stream in the northern hemisphere and enhanced convection over the central pacific finally meteorological conditions for selected flights are discussed utilizing streamlines 10 day backward trajectories thermodynamic soundings and satellite imagery air parcels sampled by the aircraft are found to originate or pass over diverse regions including asia south america southern africa and australia some parcels remain over the pacific ocean during the preceding 10 day period

investigation of a large scale mode of ocean atmosphere variability and its relation to tropical pacific sea surface temperature anomalies abstract by examining the linearly coupled atmospheric and oceanic signals related to interannual variability in sea surface temperatures and upper air wind fields a hemispheric scale ocean atmosphere teleconnection mode is isolated that is significantly correlated with equatorial pacific ssts 12 months later the interannual component of this teleconnection mode is related to a basin scale dipole in the upper air wind fields stretching across the extratropical pacific with additional anomalies extending from the eastern tropical pacific over north america and into the atlantic basin in addition it is related to variability in the sst field with warm anomalies found over the tropical subtropical western pacific as well as the equatorial eastern pacific also there are related cold anomalies over the extratropical central north pacific that extend down into the central subtropical tropical pacific diagnostic studies investigating the ocean atmosphere structure for this mode of variability indicate th

crustal velocity structure in italy from analysis of regional seismic waveforms abstract in this article we use regional seismic waveforms recorded by the recently installed istituto nazionale di geofisica e vulcanologia ingv national network and the mediterranean very broadband seismographic network mednet stations to develop 1d crustal velocity models for the italian peninsula about 55 000 p wave and 35 000 s wave arrival times from 4727 events are used to derive average seismic parameters in the crust and uppermost mantle we define four regions according to geological constraints and recent travel time tomography results based on the average seismic parameters we combine broadband seismic waveforms and travel times of regional phases to model crustal structures for the four regions by applying the genetic algorithm our results indicate smooth velocity gradients with a depth beneath the apennines and a deep moho beneath the central alps green s functions from the regionalized 1d velocity models are used to determine source depths and focal mechanisms for 37 events with a magnitude larger than 3 5 by a grid search technique our results show that normal and strike slip faulting source mechanisms dominate the apenninic belt and that most thrust faulting events occur in the adriatic sea and the outer margin of the northern apennines

full waveform tomography for radially anisotropic structure new insights into present and past states of the australasian upper mantle article i nfo we combine spectral element simulations and adjoint techniques in a non linear full seismic waveform tomography for the radially anisotropic structure of the australasian upper mantle our method allows us to explain 30 s waveforms in detail and it yields tomographic images with locally 2 lateral resolution in the course of 19 conjugate gradient iterations the total number of exploitable waveforms increased from 2200 to nearly 3000 the final model amsan 19 thus explains data that were not initially included in the inversion this is strong evidence for the effectiveness of the inversion scheme and the physical consistency of the tomographic model amsan 19 confirms long wavelength heterogeneities found in previous studies and it allows us to draw the following inferences concerning the past and present states of the australian upper mantle and the formation of seismic anisotropy 1 small scale neutral to low velocity patches beneath central australia are likely to be related to localised paleozoic intraplate deformation 2 increasing seismic velocities between the moho and 150 km depth are found beneath parts of proterozoic australia suggesting thermochemical variations related to the formation and fragmentation of a centralian superbasin 3 radial anisotropy above 150 km depth reveals a clear ocean continent dichotomy we find strong vshnvsv beneath the coral and tasman seas the anisotropy is strongest at the top of the inferred asthenospheric flow channel where strain is expected to be largest radial anisotropy beneath the continent is weaker but more variable localised patches with vshbvsv appear in accord with small scale intraplate deformation 4 the ocean continent dichotomy disappears gradually between 150 and 250 km depth where the continental lithospheric mantle and the oceanic asthenosphere pass into the underlying convecting mantle 5 significant anisotropy exists below 250 km depth its character can be explained by sublithospheric small scale convection and a change in the dominant glide system of olivine

adjoint tomography of the southern california crust using an inversion strategy based on adjoint methods we developed a three dimensional seismological model of the southern california crust the resulting model involved 16 tomographic iterations which required 6800 wavefield simulations and a total of 0 8 million central processing unit hours the new crustal model reveals strong heterogeneity including local changes of 30 with respect to the initial three dimensional model provided by the southern california earthquake center the model illuminates shallow features such as sedimentary basins and compositional contrasts across faults it also reveals crustal features at depth that aid in the tectonic reconstruction of southern california such as subduction captured oceanic crustal fragments the new model enables more realistic and accurate assessments of seismic hazard

crustal structure in southern korea from joint analysis of teleseismic receiver functions and surface wave dispersion we estimated crustal structures under 18 broadband stations in southern korea by combining receiver functions and surface wave dispersion with the genetic algorithm ga estimated crustal structures were analyzed together with previously determined structures under four stations gkp incn snu and tjn in chang et al 2004 the trend of moho depths estimated from the ga inversion generally coincides with the surface topography ranging from 26 km to 36 km in the inland however the moho depth distribution does not agree with the topography in the region around the chugaryeong fault which extends approximately north northeast south southwest in the central korean peninsula the shallow moho depth under this region may be related to consequential crustal thinning processes along the fault caused by extensional tectonic movements another discrepancy is found in the gyeongsang basin formed in a retroarc setting by the subduction of the izanagi plate in the early cretaceous a thick crust observed in the basin may be caused by two factors maturity of the basin and underplating of magma materials average crustal velocities vary from 6 02 km sec to 6 51 km sec in southern korea this variation indicates that crustal structures in southern korea involve diverse velocity profiles that change rapidly with distance remarkably a clear velocity discontinuity is observed at the depth range of 8 10 km under several stations

southern hemisphere circulation features associated with el nino southern oscillation events abstract composite seasonal mean and anomaly fields prepared from operational numerical analyses have been used to describe the southern hemisphere sh circulation features associated with el nino southern oscillation enso events the period of analyses available 1972 83 has limited the composites to include only three enso events the reliability and stability of the composites has been tested using multiple permutation methods and by comparison with the results obtained using a longer period 1950 79 of sh rawinsonde station data in the sh winter a weak equivalent barotropic wavetrain pattern of anomalies extends over australia and the south pacific ocean to south america this wavetrain pattern is quite variable in amplitude and location between enso events although it is more stable over the subtropical pacific in the sh summer the circulation anomalies are more zonally symmetric with increased height at low and high latitudes and decreased height in middle latitudes the circulation anoma

using a genetic algorithm to model broadband regional waveforms for crustal structure in the western united states in this study we analyze regional seismograms to obtain the crustal structure in the eastern great basin and western colorado plateau adopting a for ward modeling approach we develop a genetic algorithm ga based parameter search technique to constrain the one dimensional crustal structure in these regions the data are broadband three component seismograms recorded at the 1994 95 iris passcal colorado plateau to great basin experiment cpgb stations and supple mented by data from u s national seismic network usnsn stations in utah and nevada we use the southwestern wyoming mine collapse event m 5 2 that occurred on 3 february 1995 as the seismic source we model the regional seis mograms using a four layer crustal model with constant layer parameters timing of teleseismic receiver functions at cpgb stations are added as an additional constraint in the modeling ga allows us to efficiently search the model space a carefully chosen fitness function and a windowing scheme are added to the algorithm to prevent search stagnation the technique is tested with synthetic data both with and without random gaussian noise added to it several separate model searches are carried out to estimate the variability of the model parameters the average colorado plateau crustal struc ture is characterized by a 40 km thick crust with velocity increases at depths of about 10 and 25 km and a fast lower crust while the great basin has approximately 35 km thick crust and a 2 9 km thick sedimentary layer

climate dynamics along the arid northern coast of chile the 1997 1998 dinamica del clima de la region de antofagasta diclima experiment 1 the diclima field experiment was designed to test and quantify the hypothesis of an afternoon enhancement of the coastal subsidence in the extremely arid northern chile because of solar heating over the west slope of the andes ten day campaigns near antofagasta 23 s were carried out in january 1997 july 1997 and january 1998 significant diurnal cycles in temperature mixing ratio and wind from about 1000 to 4000 m above sea level were observed this layer was decoupled from the marine boundary layer circulation below by the subsidence inversion when its base was under the average height of the coastal mountain range the solar heating cycle over the andes and associated circulation resulted in a mean afternoon zonal divergence above the subsidence inversion base of about 30 10 6 s 1 exceeding by a factor of 5 typical subtropical west coast divergences the corresponding early morning convergence was particularly intense during the austral winter experiment in spite of the very strong el nino conditions that prevailed during the july 1997 and january 1998 experiments the overwhelming control that radiation exerts on the daily cycles of the atmospheric circulation over the west slope of the andes seems to guarantee the general validity of the results

low crustal velocities and mantle lithospheric variations in southern tibet from regional pnl waveforms we report low average crustal p wave velocities 5 9 6 1 km s poisson s ratio 0 23 0 27 thickness 68 76 km in southern tibet from modelling regional pnl waveforms recorded by the 1991 1992 tibetan plateau experiment we also find that the mantle lithosphere beneath the indus tsangpo suture and the lhasa terrane is shield like pn velocity 8 20 8 25 km s lid thickness 80 140 km positive velocity gradient 0 0015 0 0025 s 1 analysis of relative pn travel time residuals requires a decrease in the mantle velocities beneath the northern lhasa terrane the banggong nujiang suture and the southern qiangtang terrane tectonic and petrologic considerations suggest that low bulk crustal velocities could result from a thick 50 60 km felsic upper crust with vertically limited and laterally pervasive partial melt these results are consistent with underthrusting of indian shield lithosphere beneath the tibetan plateau to at least the central lhasa terrane

planetary and synoptic scale signatures associated with central american cold surges abstract motivated by outstanding issues from a previous case study of a midlatitude cold surge that affected mexico and central america the climatology of central american cold surges is examined in this paper an independently derived listing of 177 cold surge events is employed for which the following properties are tabulated onset date duration time between cold surge events latitude of maximum equatorward penetration min and 48 h maximum surface temperature change at merida mexico t these data show that 75 of the cold surges have durations of 2 6 days the same timescale as mobile disturbances in the westerlies also there does not appear to be any relationship between t and the duration of the event although cold surges that penetrate to low latitudes min 7 10 n have a weak tendency to persist longer than those that do not penetrate to low latitudes min 15 20 n in addition the reding data indicate that the cold surges tend to reach their most equatorward extent where

the principal nonseasonal modes of variation of global sea surface temperature abstract thirty five million ship reports for the period 1949 79 have been used to construct global monthly mean sea surface temperature fields for 5 5 latitude longitude regions the monthly means have been subjected to eigenvector analysis to bring out the nonseasonal modes of variation the el nino mode is the most important and its eigenvector time series is identical to that found previously by weare et al for the pacific alone addition of data from the other oceans adds unexplained variance so that the percentage of the variance explained by the el nino mode is smaller in the global case than for the pacific alone the second most important eigenvector pattern shows evidence of a cooling trend for the north pacific and north atlantic in the 1964 79 period this is in agreement with previous work an zonal mean sea surface temperature by the authors with recent work on the north pacific by douglas et al and with a polar cap cooling in the lower troposphere for the same period reported by boer

vhf echoes from the high latitude mesosphere and lower thermosphere observations and interpretations abstract recently published data ecklund and balsley describing vhf radar echo characteristics from the arctic mesosphere and lower thermosphere show a remarkable seasonal dependence of both the echo height and echo intensity during the three month period around the summer solstice intense and nearly continuous echoes are returned from a narrow 2 km half power region centered at 86 km during the remainder of the year however the echoes are much weaker more sporadic and occur at a much lower altitude 70 km 9 km in this paper we present additional data that suggest that the summer echoes are primarily the result of shear instability of low frequency tidal motions in the region of high stratification above the arctic summer mesopause while the winter echoes arise from the nonlinear breakup of upward propagating gravity waves

broad band modelling of regional seismograms the basin and range crustal structure three component broad band displacement seismograms with paths sampling the basin and range province are studied to constrain the crustal structure to find an average model that fits the data in both absolute time and waveform we generate broad band reflectivity synthetics and conduct sensitivity tests on different parts of a layered crustal model where only a few layers are involved generalized rays are used to help identify the various phases it proves useful to decompose a regional seismogram into segments so that the impact of model parameters on each segment can be clearly identified thus for mid crustal earthquakes it is established that the top crustal layer controls the rayleigh wave the airy phase in shape over the range from 300 to 600 km and the crustal layer just above the source depth controls its timing the p nl waves the p n and p l portion are controlled in broad band character by the mid crust while the top layer contributes to their long period motion these crustal parameters control the tangential motion similarly the sv wave the segment between the p nl wave and the rayleigh wave is mostly controlled by the shear velocity of the lower crust in judging the goodness of fit between the array observations and synthetic waveforms we allow individual data segments to shift relative to the 1 d synthetics by a few seconds to account for some lateral variation the amount of time shift is found by the cross correlation in displacement between the data segment and the synthetics applying these tests in a forward modelling approach we find that a simple two layer crustal model is effective in explaining this data set in this model the main crustal layer has p and s velocities of 6 1 km s 1 and 3 6 km s 1 similar to those found by langston helmberger 1974 a surface layer of thickness 2 5 to 3 5 km is required to fit the rayleigh waves the refined model can be used as a reference model for further studies in this region

moho depth and crustal vp vs variation in southern korea from teleseismic receiver functions implication for tectonic affinity between the korean peninsula and china we estimated moho depths and v p v s ratios of the crust under 21 broadband stations in southern korea by using a grid search in the crustal thickness v p v s ratio h domain the moho depth varies from 25 9 km to 32 5 km and the v p v s ratio ranges from 1 71 to 1 82 inland moho depths in the southernmost area of the korean peninsula were estimated shallower than those of the previous results obtained assuming a poisson solid in the joint analysis of receiver functions and surface wave dispersion this southernmost area is roughly in accord with the yeongnam massif where relatively high v p v s ratios of 1 78 1 82 are estimated on the contrary comparatively low v p v s ratio measurements 1 71 1 76 are generally distributed in the gyeonggi massif which is located in the central area of the korean peninsula the major factor for the high v p v s ratios in the yeongnam massif is thought to be the plagioclase rich mafic composition of the lower crust rather than partial melting or crustal fluids because high crustal s wave velocities are reported in the yeongnam massif the mafic composition might have been supplied by the magmatic underplating from the clearly divided feature of v p v s ratios in southern korea and the v p v s ratio similarities between southern korea and china it seems that the yeongnam massif might be related to the sino korea craton whereas the gyeonggi massif is related to the yangtze craton

pn travel time tomography of the paleo continental collision and rifting zone around korea and japan abstract a recent dense deployment of seismic stations in south korea and japan allows regional seismic imaging of the far east asian region that experienced continental collisions and riftings we perform seismic imaging based on a mantle lid p wave pn travel time tomography to exploit the tectonic imprints in the lithosphere the average pn velocity in the region is estimated to be 7 95 0 03 km sec the inverted pn velocities illuminate the tectonic structures high velocities of 8 15 km sec are observed in the precambrian massif regions while low velocities of 7 8 km sec are associated with the fold belt and sedimentary basin regions in the southern korean peninsula the pn velocity is estimated to be low in the backarc basins including the ulleung and the yamato basins while it is estimated to be higher on the continental fragments including the south korea plateau and the oki bank the high velocity structures along the japanese islands support the separation of the japanese province from the eurasia plate the high velocity anomaly along the east coast of the korean peninsula around the hupo bank suggests intrusion and solidification of high density material in the lower crust and mantle lid

modified frequency wavenumber algorithm for regional seismograms using filon s quadrature modelling of lg waves in eastern north america summary the main focus of this study is to develop an efficient frequency wavenumber code to synthesize high frequency say 10 hz regional seismograms up to a distance of more than 1000 km in a medium consisting of a large number of crustal layers and investigate effects of regional waveguides on lg waves in this newly developed code the frequency wavenumber response is evaluated by using the filon s quadrature at high frequency and the polynomial approximation of bessei s functions implementing trapezoidal integration at low frequency this has reduced the computation time by several folds compared to the time needed for the trapezoidal integration using this algorithm both broad band seismograms at harvard and short period ectn eastern canadian telemetered network seismograms from 1988 november 25 saguenay earthquake were successfully modelled a moment magnitude of 5 9 was used initially an average waveguide was calibrated to successfully excite the regional pnl and snl waves at hrv its near surface structure constrained by matching the recorded frequency content the crust mantle transition zone was constrained by modelling the strength of the broad band snl waves consisting of sn ssmsnsmssms and ssmssms phases relative to the initial pnl waves the model was modified to consist of thin layers with an alternating high and low velocity distribution to match the high frequency ectn lg waves observed from 300 to 600 km away in addition the effect of a near surface irregular receiver structure on the duration of lg waves was also investigated by convolving its response with the regional lg seismograms initial study suggests this method as viable for modelling the entire lg waves including the coda numerical studies suggest that the shapes and peak amplitudes on lg seismograms depend more strongly on the source depth anelasticity and crustal waveguide than do the pnl seismograms

long term observations of the arctic mesosphere with the mst radar at poker flat alaska in this report we summarize the results of 22 months of observations of arctic mesosphere echoes with the 50 mhz radar at poker flat alaska operation with a partially complete system began in february 1979 and has continued on a nearly continuous basis to the present time the altitude range of the mesospheric echoes obtained during this period shows a pronounced seasonal variation during summer months the mesospheric echoes are relatively continuous in time and extend from about 80 to 100 km with an unexpectedly strong peak in signal to noise ratio at about 85 km in contrast in nonsummer months mesospheric echoes are less intense and occur at lower altitudes in the range from 55 to 80 km these lower altitude nonsummer echoes are observed primarily during daytime hours when energetic auroral particle precipitation as determined by the poker flat 30 mhz riometer is present

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

heterogeneous modification and reactivation of a craton margin beneath the korean peninsula from teleseismic travel time tomography abstract margins of old continental lithosphere are likely prone to ongoing modification processes therefore constraining detailed structures beneath the margin can be essential in understanding the evolution of the continental lithosphere the eastern margin of the eurasian plate is a natural laboratory that allows us to study the strong effects from multiple episodes of continental collision and subduction of different oceanic plates since their formation to reveal the detailed evolution of cratons at their margins we describe for the first time the upper mantle structures beneath the southern korean peninsula skp based strictly on teleseismic relative arrival time data from densely deployed local seismic arrays which allows us to constrain the details of the lithospheric structures beneath the archean proterozoic basement we imaged a thick 150 km high velocity anomaly mainly beneath the proterozoic yeongnam massif with large velocity contrasts dlnvp 4 0 and dlnvs 6 0 at its boundaries suggesting the presence of a long lasting cratonic root in the southwestern skp on the other hand low velocity anomalies were found beneath the proterozoic gyeonggi massif gyeongsang arc back arc basin and along the eastern margin of the skp indicating significantly modified regions the possible existence of a remnant cratonic root beneath the skp and contrasting lithospheric structures across the different precambrian massifs suggests the highly heterogeneous modification of cratonic lithosphere at the eastern eurasian plate margin strong velocity reductions which indicate a thermally elevated upper mantle potentially with partial melts correspond to areas of cenozoic basalts high surface heat flow and high topography along the eastern kp margin we interpret this coincidence as a result of recent reactivation of a craton margin which is controlled by intense interaction between the convective upper mantle and heterogeneous continental lithosphere

broadband modeling of local earthquakes three component broadband waveforms of two small earthquakes near upland california recorded on the pasadena broadband high dynamic range instrument were modeled to obtain useful green s functions for this path and to examine the sensitivity of the synthetic seismograms to perturbations of the crustal model we assumed that the source of each event was both simple and known as determined from the caltech usgs array first motions a trapezoidal time function was chosen to fit the width of the direct s wave generalized rays reflectivity and finite difference techniques were used to compute the synthetic seismograms we found that a simple layer over a half space model is an adequate approximation of the upper crust along this profile in particular the waveforms are controlled by a relatively slow 4 km thick surficial layer 4 5km s 1 2 6 km s 1 over a faster layer 5 9 km s 1 3 5 km s 1 the relative amplitudes of direct and multiple s indicate that the main shock occurred at a depth of 6 km while the aftershock occurred at a depth of 8 to 9 km sensitivity analyses indicate that for distances less than 50 km and for periods longer than 1 sec the synthetic seismograms are not very sensitive to perturbations of the deep crustal structure analysis of upper crustal model perturbations revealed that the surficial layer is between 3 to 5 km thick in addition the contact between this layer and the underlying material can be smoothed with a 2 km wide velocity gradient without adversely affecting the fit to the data two dimensional finite difference calculations show that a ridge structure beneath the recorder acts as a lowpass filter the lower frequency phases are largely unaffected other two dimensional models with ridges between the source and receiver clearly did not fit the data synthetic seismograms computed for the best fitting model were used to estimate a long period moment of 6 2 1022 dyne cm ml 4 6 and 1 1022 dyne cm ml 3 7 with identical triangular source time durations of 0 3 sec assuming the same fault dimension of 0 4 km from standard scaling laws stress drop estimates of 410 and 70 bars are obtained for the two events respectively generally we found that it is possible to reproduce local waveforms at frequencies up to 1 hz without a complete knowledge of fine structural detail resulting green s functions can be useful in studying historic events and in simulations of large events from a given source region

advancement in source estimation techniques using broadband regional seismograms one important constraint on source retrieval from regional seismograms comes from the amplitude difference between various phases such as pnl surface wave sv sh because the misfit errors used in some waveform inversions are normalized by the data and synthetics the amplitude information in the data has not been fully utilized in this article we modify the cut and paste source estimation technique zhao and helmberger 1994 by removing this type of normalization it is shown that the modified method increases the stability and resolution of inversion when multiple stations at different distance ranges are used a distance scaling factor is introduced to compensate for the amplitude decay with distance by applying the technique to the terrascope data we have determined source mechanisms and depths of 335 southern californian events with m l 3 5 the amplitude decays with distance are r 1 13 for pnl r 0 55 for love waves and r 0 74 for rayleigh waves in contrast to generally shallow source depths reported by the southern california short period network the depth distribution from waveform inversion shows a strong peak around 12 km with few earthquakes occurring above 5 km and below 20 km

observed relationships between the el nino southern oscillation and the extratropical zonal mean circulation abstract there is increasing evidence indicating that the climate response to variations in the el nino southern oscillation enso includes not only thermally forced zonal wind anomalies in the subtropics but also eddy driven zonal wind anomalies that extend into the mid high latitudes of both hemispheres in this study new insights into the observed seasonally varying signature of enso in the extratropical zonal mean circulation are provided and the associated linkages with the dominant patterns of extratropical variability are examined the zonal mean extratropical atmospheric response to enso is characterized by two principal features an equivalent barotropic dipole in the southern hemisphere sh zonal mean zonal flow with centers of action located near 40 and 60 during austral summer and a weaker but analogous dipole in the northern hemisphere nh with centers of action located near 25 and 45 during early and late boreal winter both structures are accompanied by eddy momentum flux ano

crustal structure of the south central andes cordillera and backarc region from regional waveform modelling summary we investigate the crustal structure in the andes cordillera and its backarc region using regional broadband waveforms from crustal earthquakes we consider seismic waveforms recorded at regional distances by the chile argentina geophysical experiment charge during 2000 2002 and utilize previous seismic moment tensor inversion results for each single station earthquake pair we fixed the source parameters and performed forward waveform modelling using ray paths that sample the crust of the highest elevation cordillera and the accreted terranes in the backarc region our investigation indicates that synthetic seismograms for our earthquake station geometry are most sensitive to crustal parameters and less sensitive to mantle parameters we performed a grid search around crustal thickness p wave seismic velocity vp and p t os wave seismic velocity ratio vp vs fixing mantle parameters we evaluated this waveform analysis by estimating an average correlation coefficient between observed and synthetic data over the three broadband components we identified all acceptable crustal models that correspond to high correlation coefficients that provide best overall seismogram fits for the data and synthetic waveforms filtered mainly between 10 and 80 s our results indicate along strike variations in the crustal structure for the north south high cordillera with higher p wave velocity and thickness in the northern segment north of 33 s and persistently high vp vs ratio 1 85 in both segments this is consistent with a colder mafic composition for the northern segment and a region of crustal thickening above the flat slab region in contrast the results for the current volcanic arc south of 33 s agree with a warmer crust consistent with partial melt related to quaternary volcanism presumably of an intermediate to mafic composition a distinctive feature in the backarc region is the marked contrast between the seismic properties of the cuyania and pampia terranes that correlates with their heterogeneous crustal composition the cuyania terrane composed of mafic ultramafic rocks exhibits high vp high vp vs and a thicker layered crust versus the thinner more quartzrich crust of the eastern sierras pampeanas associated with low vp and low vp vs these differences may have some effect on the mechanism that unevenly generates crustal seismicity in the upper 30 km in this active compressional region in particular the seismic properties of the cuyania terrane which shows evidence for a high vp and high vp vs crust may be reflecting the complex tectonic evolution history of this terrane including accretion rifting and re accretion processes since the palaeozoic that promote a high level of crustal seismicity in the upper 30 km enhanced by the flat slab subduction in the segment between 31 s and 32 s another possible mechanism could be directly related to the presence of a strong lower crust above the flat slab that efficiently transfer stresses from the slab to the upper crust generating higher seismicity in the cuyania terrane between 30 s and 34 s

assessment of southern oscillation sea level pressure indices abstract monthly sea level pressure anomalies at easter island rapa tahiti and darwin for the period 1951 79 are analysed to reveal their temporal characteristics and the coherence and time lead lag relationships among them for interannual scale oscillations the pressure variations at rapa and easter island lead those at tahiti and those of opposite phase at darwin by 2 8 months where the large lead times are associated with lower frequency oscillations of the four stations rapa has the smallest percentage of its variance in the range of periods containing the southern oscillation darwin has the largest spatial smoothing by combining stations enhances the percentage of variance in the longer periods combining tahiti and darwin gives a substantial increase combining rapa and easter island much less normalization of the time series through division by the monthly standard deviations is also treated the combination of tahiti and darwin is recommended as a southern oscillation index for diagno

the effect of el chichon on wind variability in the troposphere stratosphere and mesosphere over alaska data from the poker flat alaska mst radar combined with standard nws balloon observations at fairbanks alaska show that low frequency 3 11 day wind fluctuations within the troposphere and lower stratosphere for the period january march 1983 were noticeably weaker than those for other similar periods between 1979 1984 similar effects can be detected in the higher frequency 1 6 hr and 8 48 hr wind fluctuations obtained from the radar data alone in contrast to these decreases in the troposphere and lower stratosphere wind variations the magnitude of the tidal period 8 48 hr atmospheric wind fluctuations observed by radar in the mesosphere during june july were significantly increased in 1983 relative to surrounding years all of these variations appear to be reasonably well associated with the presence of enhanced aerosol concentrations in the lower stratosphere following the explosion of el chichon volcano in april 1982

imaging the three dimensional crust of the korean peninsula by joint inversion of surface wave dispersion and teleseismic receiver functions abstract a detailed study of the 3d variation of shear wave velocities in thesouthern part of the korean peninsula is made by combining high frequency surface wave tomography results of cho et al 2006b with teleseismic p wave receiverfunctions at 80 locations on the peninsula receiver functions were derived fromhigh gain acceleration short period and broadband digital data streams of the koreameteorological administration kma and korean institute for geosciences andmineral resources kigam networks vertical cross sections trace the lateral vari ation in the depth to the moho the variation of low velocities near the surface andthe variable thickness of the transition from surface velocities to midcrustal veloci ties the derived crustal structure provides new insights on the evolution of thekorean crust introduction geophysics and seismology in particular provides in direct means for assessing the larger to local scale present day architecture of continental masses through remote sens ing bostock 1999 although eld geology has providedvast information on the upper crust mapping variations instructure in depth through geophysical investigation is aprincipal step in unraveling and understanding the evolutionof the continental lithosphere in an area whose genetic pro cess is relatively unknown such as the korean peninsula itis important to add geophysical constraints to reveal the con tinental evolution the korean peninsula fig 1 situated at the easternmargin of the eurasian continent is a tectonic assemblageof two phanerozoic mobile belts the imjingang belt and theokcheon fold belt three precambrian basement terrains nangrim gyeonggi and yeongnam massifs from north tosouth and one volcanoclastic basin that is gyeongsang ba sin reedmann and um 1975 cluzel

on the annual variation of tropospheric zonal winds observed above christmas island in the central equatorial pacific observations of tropospheric winds have been made nearly continuously since early 1986 in the altitude range 2 18 km using a 50 mhz vhf wind profiler at christmas island 2 n 157 w tropospheric zonal winds observed at christmas island show a pronounced annual variation in the middle to upper troposphere with westerly winds typically observed during northern winter the annual variation is strongest during la nina and weakest during el nino the amplitude of the cycle has a broad peak in the upper troposphere empirical orthogonal function eof analysis of the vertical structure of the annual variation shows that the principal mode explains nearly 90 of the variance in the 90 to 365 day frequency band we attribute the annual variation in zonal winds to the annual variation in deep tropical heating associated with deep convection the annual variation in tropical convection gives rise to annual variations in the surface pressure and pressure difference between darwin and tahiti the pressure difference is greatest during northern hemisphere winter months other measures of the annual variation in tropical convection are provided by the tropical tropopause height and by highly reflective clouds hrc the tropical tropopause is highest during the northern hemisphere winter months when convection is most active over the maritime continent western pacific warm pool region and lowest in northern summer when convection is most active over the land masses of the northern hemisphere the hrc show an annual migration in the centers of active convection the annual latitudinal migration of the active centers of convection over the western pacific with respect to the equatorial waveguide appears to be an important factor in determining the annual variation evident in the remote response of the zonal winds observed over christmas island

further analysis of the relationship between circulation anomaly patterns and tropical convection tropical extratropical connections are investigated for 250 mbar stream function fluctuations in both intraseasonal and interannual bands the principal modes of anomalous 250 mbar stream function are computed and related to anomalous outgoing longwave radiation olr which is used as a proxy for deep tropical convection the leading mode for both boreal winter and summer displays a large zonally symmetric component which appears in both the intraseasonal is and interannual ia bands in the is band the dominant mode is an oscillation with a period of 48 days correlations between the principal component of this mode and olr anomalies indicate that this pattern is directly related to convection in the tropical pacific the second mode for the boreal winter consists of a wave train from the pacific ocean east northeastward to western north america and then east southeastward to the subtropical atlantic ocean this mode also exists in both ia and is bands simultaneous and lagged correlations between the amplitude time series of this mode and olr anomalies indicate that extreme amplitudes of this wave train are preceded by extremes in the olr anomalies cloud band activity in the subtropical north pacific enhanced cloud band activity in the vicinity of hawaii associated with an anomalousmore cyclonic 250 mbar circulation in the same region precedes the maximum development of a 250 mbar ridge south of the aleutian islands trough over western north america and another ridge along the east coast of the united states the second mode for boreal summer june august is associated with variations of the asian monsoon 36 refs 11 figs 1 tab less

regional wave propagation in tanzania east africa 1 crust and upper mantle structure under tanzania east africa is investigated using broadband waveforms and phase travel times collected from regional events recorded by the 1994 1995 tanzania broadband seismic experiment broadband displacement waveforms from the ml 5 9 rukwa graben earthquake 18 august 1994 are modeled using a wave number integration algorithm and a new phase time inversion technique to infer a very simple crustal and upper mantle model that can be used for waveform studies of other regional earthquakes in the area displacement amplitudes for all phases in the data are predicted quite well using source parameters determined from a previous study of teleseismic waveforms the crust is parameterized by a linear gradient in velocity defined by surface and moho p velocities poisson s ratio and crustal thickness this simple parameterization is sufficient to explain arrival times and waveshapes of the three component waveforms recorded between 200 and 800 km at stations located on the craton and mozambique belt the s wave train consists of sn multiple sn and critically reflected s wave multiples in the crustal waveguide in addition to the fundamental mode rayleigh wave high phase velocity critical s wave reflections are seen to form the low group velocity lg phase prominent sp depth phases are seen in the regional waveform data which can be used to infer accurate source depths for events in the region the tanzania craton and adjacent mozambique belt crustal structure is simple and laterally homogeneous showing few effects of rift disruption high wave velocities in the uppermost mantle suggest little thermal modification from rifting processes of the east african rift

estimation of crustal structure in central and west japan from waveform modeling of regional pl waves an inverse method of modeling the regionalpl waveform with the predominant period of about 20 s was developed to estimate the averages velocity structure of the upper crust applicability of the waveform modeling was confirmed by the results of the numerical experiments thepl waveform is most sensitive to thes velocity in the upper crust whereas it is not affected significantly by errors involved in the focal mechanism solution and focal depth determination when thepl wave is well developed the method was applied to the observed seismograms recorded in central japan from the earthquakes with epicentral distances 300 500 km as a result distinct regional differences were found in the upper crustals velocity in particular between the southern shikoku district west japan and the southern chubu district central japan and between the mountainous and the coastal areas in the southern chubu district these differences are in agreement with the general features ofp velocity structures obtained by explosion experiments and by analyses of natural earthquakes our method is effective to the extent that the crustal structure along the propagation path can be assumed a horizontally layered structure it is not applicable when the sensitivity of thepl waveform to the error in the focal mechanism solution is exceptionally high

the relationship between large scale vertical motion highly reflective cloud and sea surface temperature in the tropical pacific region vertical motion fields at 850 mbar over the tropical pacific region are calculated from the 1963 1973 mean wind fields for 4 months of the year and for october 1972 the peak month in the 1972 1973 el nino event these vertical motion fields are derived using the projective separation technique which has the unique property of separating vertical motion into components due to meridional wind convergence and zonal wind convergence this separation permits investigation of the response of the hadley and walker circulations to annual and interannual variation of the sea surface temperature in the tropical pacific the large scale features of the computed vertical motion fields are in agreement with those of highly reflective clouds which indicate the locations of deep convection examination of the annual cycle of the vertical motion and its components shows no strong variation of the walker circulation with the east west gradient of sea surface temperature on the other hand a strong correlation is found between meridional overturning in the eastern pacific and the local equatorial sea surface temperature during el nino events the eastern and central pacific contribution to the hadley circulation tends to increase

calibration of the tibetan plateau using regional seismic waveforms we use the recordings from 51 earthquakes produced by a passcal deployment in tibet to develop a two layer crustal model for the region starting with their isc locations we iteratively fit the p arrival times to relocate the earthquakes and estimate mantle and crustal seismic parameters an average crustal p velocity of 6 2 6 3 km s is obtained for a crustal thickness of 65 km while the p velocity of the uppermost mantle is 8 1 km s the upper layer of the model is further fine tuned by obtaining the best synthetic sh waveform match to an observed waveform for a well located event green s functions from this model are then used to estimate the source parameters for those events using a grid search procedure average event relocation relative to the isc locations excluding two poorly located earthquakes is 16 km all but one earthquake are determined by the waveform inversion to be at depths between 5 and 15 km this is 15 km shallower on average than depths reported by the isc the shallow seismicity cut off depth and low crustal velocities suggest high temperatures in the lower crust thrust faulting source mechanisms dominate at the margins of the plateau within the plateau at locations with surface elevations less than 5 km source mechanisms are a mixture of strike slip and thrust most events occurring in the high plateau where elevations are above 5 km show normal faulting this indicates that a large portion of the plateau is under ew extension

mapping the upper mantle three dimensional modeling of earth structure by inversion of seismic waveforms a method is presented for the inversion of waveform data for the three dimensional distribution of seismic wave velocities the method is applied to data from the global digital networks international deployment of accelerometers global digital seismograph network the selected data set consists of some 2000 seismograms corresponding to 53 events and 870 paths the moment tensors of the earthquakes are determined through an iterative procedure which minimizes the corrupting influence of lateral heterogeneity a global model is constructed for shear wave velocity expanded up to degree and order 8 in spherical harmonics and described by a cubic polynomial in depth for the upper 670 km of the earth s mantle although no a priori information is incorporated the model predictions reproduce much of what is known about the dispersion of mantle waves for example high phase velocities for shields low velocities at ridges and a strong degree 2 pattern for rayleigh waves since the method makes use of complete waveforms overtone data are also included it is shown that the model is reproducible in that substantially the same model can be constructed from each half of the total data set considered independently the model shows that shields and ridges are major features in the depth interval 25 250 km the ridges of the southern pacific and the larger shields persist to 350 km but the southeast indian rise is underlain by a high velocity anomaly at this depth as is much of the mid atlantic ridge at 450 650 km the major features are a broad region of high velocities incorporating south america much of the south atlantic and parts of west africa a broad region of low velocities in the central and eastern pacific high velocities in the western pacific and a low velocity anomaly beneath the red sea and the gulf of aden in the absence of a crustal correction degrees 2 and 3 show a high positive correlation with the geoid paradoxically this is largely destroyed when the distribution in crustal thickness is taken into account spherical harmonic degrees 4 7 show a significant negative correlation

the interrelationship between temperature changes in the free atmosphere and sea surface temperature changes fields of sea surface temperature anomalies from the global ocean surface temperature atlas gosta and microwave sounding measurements msu of temperature in the troposphere are examined separately and together for the 1979 1988 period global correlation patterns of both sets of fields are investigated at a range of leads and lags up to 6 months and exhibit a wide range of correlation structure there are regions such as the tropical eastern pacific where sea surface temperature anomalies persist for several months and are associated with local air temperature anomalies in this particular example about 0 7 c air temperature change is associated with a 1 0 c sea temperature change by contrast some ocean regions and many atmospheric regions mostly in middle and high latitude show only local spatial correlations that disappear completely in a month or two the most persistent and extensive spatial correlation patterns are quite different for the sea and the air in the sea the butterfly pattern of the pacific is the most important and reverses sign between the eastern equatorial pacific and the western pacific and subtropics in the warm phase the temperature anomalies associated with this pattern are similar to the correlation pattern for the atmosphere the main correlation pattern is an equatorial belt with no sign changes in the tropics this pattern is linked to the oceanic el nino mode in the warm phase the temperature anomalies show peak values on both sides of the equator in the eastern and central pacific based mainly on the results from the spatial patterns certain regions are selected for intercomparison of time series in the tropical eastern pacific the sea leads the air by about a month while in the gulf stream and kuroshio regions the sequence is reversed

crustal velocity structure across the southern korean peninsula from seismic refraction survey 1 the first crustal scale controlled source seismic refraction experiment in the southern korean peninsula kcrust2002 was carried out along a 300 km long profile across this peninsula in december 2002 iterative processing and modeling produced a laterally varying layered crustal velocity model the crust is thickest 34 km below the okcheon fold belt in the middle of the transect and thinnest 28 km at the eastern end where the cretaceous gyeongsang basin is characterized by 5 km of low velocity material that constitutes the upper crust the p velocities in upper and lower crust range from 5 4 to 6 0 km s and from 6 4 to 6 7 km s respectively the average crustal poisson s ratio is found to be 0 25 0 27 vp vs 1 73 1 78 along the profile a mid crustal velocity discontinuity is recognized in the northwestern part of the transect the underlying mantle has velocities in the range of 7 9 8 1 km s

forward waveform modelling procedure for 1 d crustal velocity structure and its application to the southern korean peninsula summary we propose a full grid search procedure for broad band waveform modelling to determine a 1 d crustal velocity model the velocity model can be more constrained because of the use of broad band waveforms instead of traveltimes for the crustal phases although only a small number of event station pairs were employed despite the time consuming nature of the full grid search method to search the whole model parameter space the use of an empirical relationship between the p and s wave velocities can significantly reduce computation time the proposed method was applied to a case in the southern korean peninsula broad band waveforms obtained from two inland earthquakes that occurred on 2007 january 20 mw 4 6 and 2004 april 26 mw 3 6 were used to test the method the three layers over half space crustal velocity model of the p and s wave velocities was estimated comparisons of waveform fitness between the final model and previously published models demonstrate advancements in the average value of waveform fitness for the inland earthquakes in addition 1 d velocity models were determined for three distinct tectonic regions namely the gyonggi massif the okcheon belt and the gyeongsang basin which are all located inside the study area a comparison between the three models demonstrates that the crustal thickness of the southern korean peninsula increases from nw to se and that the lower crustal composition of the okcheon belt differs from that of the other tectonic regions

velocity structure of upper mantle transition zones beneath central eurasia from seismic inversion using genetic algorithms summary we present velocity constraints for the upper mantle transition zones beneath central siberia based on observations of the 1982 rift deep seismic sounding dss profile the data consist of seismic recordings of a nuclear explosion in north western siberia along a 2600 km long seismic profile extending from the yamal peninsula to lake baikal we invert seismic data from the mantle transition zones using a non linear inversion scheme using a genetic algorithm for optimization and the wkbj method to compute the synthetic seismograms a statistical error analysis using a graphbinning technique was performed to provide uncertainty values in the velocity models our best model for the upper mantle velocity discontinuity near 410 km depth has a two stage velocity gradient structure with velocities increasing from 8 70 9 25 km s over a depth range of 400 415 km a gradient of 0 0433 s and from 9 25 9 60 km s over a depth range of 415 435 km a gradient of 0 0175 ski this derived model is consistent with other seismological observations and mineral physics models the model for the velocity discontinuity near 660 km depth is simple sharp and includes velocities increasing from 10 15 km s l at 655 km depth to 10 70 km s at 660 km depth a gradient of 0 055 s

lithospheric structure of the arabian shield and platform from complete regional waveform modelling and surface wave group velocities summary regional seismic waveforms reveal significant differences in the structure of the arabian shield and the arabian platform we estimate lithospheric velocity structure by modelling regional waveforms recorded by the 1995 1997 saudi arabian temporary broadband deployment using a grid search scheme we employ a new method whereby we narrow the waveform modelling grid search by first fitting the fundamental mode love and rayleigh wave group velocities the group velocities constrain the average crustal thickness and velocities as well as the crustal velocity gradients because the group velocity fitting is computationally much faster than the synthetic seismogram calculation this method allows us to determine good average starting models quickly waveform fits of the jon and sn body wave arrivals constrain the mantle velocities the resulting lithospheric structures indicate that the arabian platform has an average crustal thickness of 40 km with relatively low crustal velocities average crustal p and s wave velocities of 6 07 and 3 50 km s 1 respectively without a strong velocity gradient the moho is shallower 36 km and crustal velocities are 6 per cent higher with a velocity increase with depth for the arabian shield fast crustal velocities of the arabian shield result from a predominantly mafic composition in the lower crust lower velocities in the arabian platform crust indicate a bulk felsic composition consistent with orogenesis of this former active margin p and s wave velocities immediately below the moho are slower in the arabian shield than in the arabian platform 7 9 and 4 30 km s 1 and 8 10 and 4 55 km s respectively this indicates that the poisson s ratios for the uppermost mantle of the arabian shield and platform are 0 29 and 0 27 respectively the lower mantle velocities and higher poisson s ratio beneath the arabian shield probably arise from a partially molten mantle associated with red sea spreading and continental volcanism although we cannot constrain the lateral extent of a zone of partially molten mantle

whole mantle sh velocity model constrained by waveform inversion based on three dimensional born kernels summary a whole mantle sh velocity model is obtained by using a unique data set and techniques body and surface waveforms including major and multi orbit phases are used as a data set and are inverted by using 3 d born kernels the resultant model sh18ce reveals the different natures of the two major upwelling systems the strong low velocity anomalies beneath africa extend for more than 1000 km from the core mantle boundary cmb whereas those beneath the pacific are restricted to 300 400 km from the cmb the results also show the variable natures of stagnant slabs on the 670 discontinuity around japan the depths of the strongest high velocity anomalies within the stagnant slabs are different region by region which is consistent with the detailed delay time tomography model in this area

source estimation from broadband regional seismograms recently developed source inversion techniques do not take full advantage of the broadband nature of regional seismograms the reason is that green s functions generated from flat layered models are not correct for the complicated propagational phenomena associated with realistic crustal structure the inversion is usually performed by removing short periods and inverting only selected portions of the records in this article we introduce a source estimation technique that allows for better use of the entire broadband record when only imperfect green s function are available the procedure desensitizes the timing between the principal crustal arrivals by fitting portions of the green s functions independently the preferred source is the orientation that minimizes the average l1 and l2 norms in term of the four parameters m 0 strike dip and rake the l2 error emphasizes the longer period surface waves while the l1 error weights the shorter period body waves we obtain estimates of duration by modeling long period and broadband signals the depth determination can be obtained directly from the surface reflected phases sp mp or ss ms or by cycling through the depth dependent green s functions in addition to the source parameters we obtain t phase alignments shifts that can be used as green s function corrections for relocating other events or as a guide to deriving new crustal models

simulation of enso related surface wind anomalies with an atmospheric gcm forced by observed sst the ecmwf t21 atmospheric gcm is forced by observed near global sst from january 1970 to december 1985 its response in low level winds and surface wind stress over the pacific ocean is compared with various observations the time dependent sst clearly induces a southern oscillation so in the model run which is apparent in the time series of all variables considered the phase of the gcm so is as observed but its low frequency variance is too weak and is mainly confined to the western pacific because of the gcm s use as the atmospheric component in a coupled ocean atmosphere model the response of an equatorial oceanic primitive equation model to both the modeled and observed wind stress is examined the ocean model responds to the full observed wind stress forcing in a manner almost identical to that when it is forced by the first two low frequency eofs of the observations only these first two eofs describe a regular eastward propagation of the so signal from the western pacific to the central pacific within about a year the ocean model s response to the modeled wind stress is too weak and similar to the response when the observed forcing is truncated to the first eof only in other words the observed so appears as a sequence of propagating patterns but the simulated so as a standing oscillation the nature of the deviation of the simulated wind stress from observations is analyzed by means of model output statistics mos it is shown that a mos corrected simulated wind stress if used to force an ocean gcm leads to a significant enhancement of low frequency sst variance which is most pronounced in the western pacific

crustal structure of the altiplano from broadband regional waveform modeling implications for the composition of thick continental crust we have modeled the full waveforms from six intermediate depth and two shallow earthquakes recorded at regional distances by the banjo broadband andean joint experiment banjo and seismic exploration of the deep altiplano seda portable seismic networks in the central andes in this study we utilize data from those banjo and seda stations located within the altiplano and eastern cordillera we used reflectivity synthetic seismograms and a grid search to constrain four parameters of the altiplano eastern cordillera lithosphere crustal thickness average crustal velocity vp and crustal and upper mantle poisson s ratios crust and mantle using our grid search we investigated the crustal and upper mantle structure along 36 individual event station paths and applied forward modeling to 56 event station paths robust models for the altiplano that provide the best overall fit between the data and synthetic seismograms are characterized by an average vp of 5 75 6 25 km s crustal thicknesses of 60 65 km crust 0 25 and mantle 0 27 0 29 we find a north south variation in the structure of the altiplano with the crust south of the banjo transect characterized by either lower than average crustal p wave velocities or a slightly higher crust relative to crust north of the banjo transect these results are consistent with a model of crustal thickening caused predominantly by tectonic shortening of felsic crust rather than by underplating or magmatic intrusion from the mantle

linkages between 200 mb tropical and extratropical circulation anomalies during the 1986 1989 enso cycle abstract nmc operational wind analyses have been used to document the 200 mb circulation anomalies during the solstice seasons of the 1987 1989 enso cycle using the one level vorticity balance diagnostic approach the 200 mb rossby wave anomalous source distribution was derived as departures from a three year mean for the single warm phase season january march 1987 the effective rossby wave anomaly sources were found to be generally quite small within 15 of the equator poleward of about 15 the anomalous 200 mb divergence through the planetary vorticity divergence anomaly stretching term is the dominant factor in determining the anomalous 200 mb vorticity source distribution its jfm standard deviation around 30 35 n was an order of magnitude larger than that found in the deep tropics the january march and june august 200 mb circulation differences between the warm and cold phase of the 1987 1989 enso cycle are described the enso cycle linkages between the equatorial pacific convection anomali

impact of broadband seismology on the understanding of strong motions most analyses of strong motion attenuation assume simple whole space type geometrical spreading namely 1 r or its modified form e kr r however broadband data presently becoming available suggests a more complex behavior with substantial crustal effects events such as the sierra madre event m 5 8 triggered the strong motion channels at all of the terrascope stations allowing for 0 01 sec sampling of the wavefield we find that most of the well defined crustal bodywave arrivals defined and modeled in the 1 to 0 1 hz bandpass also contain high frequency energy by comparing the triggered channels with the continuous channels we see that several of the more distant stations triggered on the depth phase sp m p these phases as well as the depth phase ss m s are obvious in velocity and quite apparent in accelerations our best models for southern california contain a relatively thick low velocity layer at the surface roughly 5 km thick with shear velocities below 3 km sec this layer or zone because it appears to vary considerably controls the wavefield at nearly all frequencies out to about 60 km and yields attenuation decay faster than 1 r at large ranges the lower crustal triplications dominate and the attenuation curve flattens adding random scatters to these layered models adds additional complexity but does not alter the basic flat layer predictions

waveform modelling of teleseismic s sp sspmp and shear coupled pl waves for crust and upper mantle velocity structure beneath africa summary we describe a waveform modelling technique and demonstrate its application to determine the crust and upper mantle velocity structure beneath africa our technique uses a parallelized reflectivity method to compute synthetic seismograms and fits the observed waveforms by a global optimization technique based on a very fast simulated annealing vfsa we match the s sp sspmp and shear coupled pl phases in seismograms of deep 200 800 km moderate to large magnitude 5 5 7 0 earthquakes recorded teleseismically at permanent broad band seismic stations in africa using our technique we produce p and s wave velocity models of crust and upper mantle beneath africa additionally our use of the shear coupled pl phase wherever observed improves the constraints for lower crust and upper mantle velocity structure beneath the corresponding seismic stations our technique retains the advantages of receiver function methods uses a different part of the seismogram is sensitive to both p and s wave velocities directly and obtains helpful constraints in model parameters in the vicinity of the moho the resulting range of crustal thicknesses beneath africa 21 46 km indicates that the crust is thicker in south africa thinner in east africa and intermediate in north and west africa crustal p 4 7 8 km s 1 and s wave velocities 2 5 4 7 km s 1 obtained in this study show that in some parts of the models these are slower in east africa and faster in north west and south africa anomalous crustal low velocity zones are also observed in the models for seismic stations in the cratonic regions of north west and south africa overall the results of our study are consistent with earlier models and regional tectonics of africa

tropical and subtropical north atlantic vertical wind shear and seasonal tropical cyclone activity abstractgiven recent insights into the role of anticyclonic rossby wave breaking awb in driving subseasonal and seasonal north atlantic tropical cyclone tc activity this study further examines

the tropical tropopause and the el nino of 1982 1983 an earlier study of the behavior of the tropical tropopause during 1982 is extended through 1984 the earlier study focused on the influence of the el chichon volcanic eruption but it also considered the influence of the 1982 1983 el nino event during its onset phase in the latter half of 1982 here we present anomalies of tropopause height tropopause potential temperature and lower stratospheric potential temperature through 1984 these anomalies clearly show a much warmer than normal tropopause potential temperature over the western tropical pacific associated with el nino the abnormally warm tropopause potential temperature which was evident in late 1982 reaches a peak in early 1983 and continues abnormally warm until about october 1983 during this period the tropopause is also abnormally high but the lower stratospheric potential temperature is near normal

lithospheric structure of the qiangtang terrane northern tibetan plateau from complete regional waveform modeling evidence for partial melt we report models of p and s wave velocity and attenuation for the the crust and uppermost mantle of the qiangtang terrane northern tibetan plateau inferred by fitting reflectivity synthetic seismograms to observed complete regional waveforms the data are three component broadband seismograms recorded by the 1991 1992 iris passcal incorporated research institutions for seismology program for array seismic studies of the continental lithosphere tibetan plateau experiment and global seismic network stations in the region the qiangtang terrane has thick crust 65 5 km with p and s wave velocities of 6 1 6 3 and 3 34 3 43 km s respectively yielding an anomalously high crustal poisson s ratio of 0 29 0 02 seismic velocities of the upper mantle of the qiangtang terrane are normal for p waves and slow for s waves 8 10 and 4 35 4 41 km s respectively with a high mantle poisson s ratio of 0 29 0 01 attenuation in the crust and upper mantle is high qp 100 200 and qs 44 89 modeling of the broadband p waveforms suggests that a decrease in mantle velocity occurs at about 160 km depth in the mantle however this is not unambiguously supported by the data and modeling the crust and uppermost mantle of the qiangtang terrane probably contains partial melt based on the high poisson s ratio low shear wave velocities and low q the absence of high frequency sn and the presence of volcanism of mantle lithospheric origin support the presence of partial melt crustal and uppermost mantle structure in the qiangtang terrane is different from that for the lhasa terrane immediately to the south based on results of our previous studies the average crustal p and s wave velocities are 4 faster and 2 slower respectively in the qiangtang terrane relative to the lhasa terrane this yields a significant difference in the crustal poisson s ratio with values of 0 29 for the qiangtang terrane and 0 25 for the lhasa terrane differences in the uppermost mantle p and s wave velocities and poisson s ratios of these two adjacent terranes cannot be explained by temperature differences alone using the mantle temperature estimates of mcnamara et al 1997 we suggest that partial melt of an ultramafic composition beneath the qiangtang terrane fits the velocity and poisson s ratio estimates

site response modelling by non linear waveform inversion microearthquake waveforms and spectra are well known to be strongly influenced by the shallow subsurface conditions at the recording site we make use of this fact to determine optimum site models from sh wave microearthquake seismograms using a non linear waveform inversion technique based on simulated annealing site models are optimized in terms of thicknesses s wave velocities and densities of the uppermost layers 100 m for 1d plane layer models in addition the source parameters in terms of brune model source time functions are optimized simultaneously the synthetic seismograms are calculated using a modification of haskell s plane sh wave algorithm using aftershock recordings of the loma prieta earthquake a 1d plane layer model has been obtained for a selected site in central california which has been occupied during the aftershock experiment for this dataset cross correlation coefficients between optimized synthetics and observed records reach values above 0 8 the site model at the selected station for varying sources is fairly stable especially for the uppermost layers we observe systematic variations of layer parameters with back azimuth which would be in agreement with slightly dipping layer interfaces

large amplitude moho reflections sms from landers aftershocks southern california closely spaced aftershocks of the 28 june 1992 landers earthquake m w 7 3 were used to make event record sections that show the transverse components of s and sms arrivals at a distance of 70 to 170 km for the data recorded toward the north in the mojave desert large sms phases are observed with amplitudes 2 to 5 times greater than the direct s for similar distances to the south the sms arrival is comparable to or smaller than the s comparisons to synthetic seismograms indicate that the large amplitude sms phases are produced by the simple crustal structure of the mojave desert that allows a large moho reflection in contrast the more complex geologic structure to the south partitions the seismic energy into a more complicated set of seismic phases so that the moho reflection is diminished in amplitude the large sms phases observed in the mojave enhance the overall ground motions by a factor of 2 to 3 this suggests that when damaging earthquakes occur in other regions of simple crustal structures moho reflections will produce amplified strong motions at distance ranges around 100 km depending on the local structure

a new approach to paleoclimatic research using linear programming abstract one of the most frequently attempted correlations in quaternary research is between insolation and paleoclimatic data yet there are a large number of insolation time series that could potentially explain a quaternary dataset individually or in combination we computed 342 insolation time series varying by latitude time of year and time of day for fitting to four different paleoclimatic records foraminiferal 18 o from specmap temperatures inferred from vostok antarctica ice cores marine accumulation rates of a freshwater diatom melosira originating from tropical africa lakebeds and 18 o variations in calcite at devil s hole nevada we developed two inductive linear programming models that solve for the weighted combination of insolation curves that minimize either the average or maximum residual from the proxy curve each of the four proxy records lagged and unlagged was solved by both model types on average our composite insolation curves fit the proxy records 48 76 better than does june daily insolation at 60 n the key insolation curve of the milankovitch paradigm globally high latitude insolation 60 70 n and s and insolation at specific times of day noon or non noon as opposed to daily dominated the results regionally the model tended to select insolation curves from absolute latitudes similar to those of the proxy records the fact that these results are plausible given known biophysical processes combined with the fact that a small number of curves repeatedly accounted for a disproportionate share of the explanation suggest strongly that the correlations found are not happenstance despite the inductive method used

earthquake source mechanism and rupture directivity of the 12 september 2016 mw 5 5 gyeongju south korea earthquakeshort note

application of very fast simulated annealing to the determination of the crustal structure beneath tibet summary the simulated annealing method has recently been applied to several multiparameter optimization problems including those of geophysical inversion a new variant of simulated annealing called very fast simulated annealing vfsa overcomes some of the drawbacks of a conventional simulated annealing it has been found to be a practical tool for geophysical inversion sen stoffa 1995 the method is particularly useful for non linear problems with multiple parameters where a grid search method is prohibitively expensive here we have applied vfsa to retrieve the crustal structure beneath seismic stations in tibet using teleseismic body waveform data our approach is to compare the radial component records with generalized ray synthetics directly in the time domain for any given crustal structure we have formulated a direct relationship between the radial and the vertical component signal so that we can generate synthetic radial component data from recorded vertical component seismograms zhao frohlich 1996 we have tested the vfsa inversion algorithm using synthetics and confirmed that it works very well i e it finds solutions very close to the true solution using the algorithm we have determined the crustal structures beneath 11 stations in tibet from south to north the total crustal thickness is quite uniform our tectonic interpretation of these crustal models is that they may represent crust from the eurasian plate injected beneath the crust of the converging indian plate certain features of the models are consistent with the presence of a small convection cell or plume beneath north central tibet as suggested by molnar 1990

inversion of strong ground motion and teleseismic waveform data for the fault rupture history of the 1979 imperial valley california earthquake a least squares point by point inversion of strong ground motion and teleseismic body waves is used to infer the fault rupture history of the 1979 imperial valley california earthquake the imperial fault is represented by a plane embedded in a half space where the elastic properties vary with depth the inversion yields both the spatial and temporal variations in dislocation on the fault plane for both right lateral strike slip and normal dip slip components of motion inversions are run for different fault dips and for both constant and variable rupture velocity models effects of different data sets are also investigated inversions are compared which use the strong ground motions alone the teleseismic body waves alone and simultaneously the strong ground motion and teleseismic records the inversions are stabilized by adding both smoothing and positivity constraints the moment is estimated to be 5 0 10 25 dyne cm and the fault dip 90 5 dislocation in the hypocentral region south of the united states mexican border is relatively small and almost dies out near the border dislocation then increases sharply north of the border to a maximum of about 2 m under interstate 8 dipslip motion is minor compared to strike slip motion and is concentrated in the sediments the best fitting constant rupture velocity is 80 per cent of the local shear wave velocity however there is a suggestion that the rupture front accelerated from the hypocenter northward the 1979 imperial valley earthquake can be characterized as a magnitude 5 earthquake at the hypocenter which then grew into or triggered a magnitude 6 earthquake north of the border

partitioned fault movement and aftershock triggering evidence for fault interactions during the 2017 mw 5 4 pohang earthquake south korea

the relationship between interannual variability in the 200 mb tropical wind field and the southern oscillation abstract the interannual variability in the upper tropospheric tropical wind field is described through empirical orthogonal functions teleconnections and composite analyses the data used are 11 years of mean monthly analyzed fields of zonal and meridional components of the 200 mb wind on a 5 mercator grid extending from 48 1 n to 48 1 s derived from the national meteorological center s operational tropical analysis a substantial portion of the interannual variability in the 200 mb circulation is shown to be related to the southern oscillation the anomalous circulation in the pacific is characterized by a pair of anticyclonic cyclonic anomalies straddling the equator during periods of low high southern oscillation index zonal wind differences of 8 11 m s 1 between low and high index phases of the so were found near 25 n 25 s and near the equator in the central pacific composites relative to el nino events during different seasons reveal that anomalous anticyclonic circulations in the pacific are

crustal structure in southern korea from joint analysis of regional broadband waveforms and travel times regional broadband waveforms and travel times of seismic phases are combined to model crustal structure in regions where the signal to noise ratio snr of waveforms is low the utilization of travel time data enables us to overcome the problem occurring in waveform inversion with low snr data the distortion of deep velocity structure the genetic algorithm ga adopted as a search algorithm is useful in regions where there is little a priori information about crustal structure after verifying the robustness of the joint inversion technique by numerical tests we applied the technique to southern korea in order to get a simple one dimensional average crustal model using broadband waveforms bandpassed between 0 03 and 0 3 hz and travel times of pg pmp and pn waves recorded at ten broadband and five short period stations from the 2 june 1999 gyeongju earthquake m l 3 4 korea the p wave velocities in the resulting three layered crustal model are 5 67 0 06 6 05 0 05 6 67 0 02 and 7 88 0 02 km sec from the top layer to the half space respectively and the depths of layers are 5 1 0 8 16 7 1 0 and 31 9 1 0 km synthetic waveforms and travel time curves corresponding to the resulting velocity model fit observed seismograms generally well the synthetics are preceded by the observed waveforms in the southwestern part of korean peninsula inferring the presence of a high velocity zone in that area

the 25 november 1988 saguenay quebec earthquake source parameters and the attenuation of strong ground motion the saguenay earthquake of 25 november 1988 occurred close to the southern margin of the saguenay graben in southern quebec it was caused by almost purely dip slip faulting centered at a depth of 26 km with a p axis oriented northeast southwest this faulting mechanism is similar to those of the larger historical earthquakes in eastern north america but the focal depth is substantially greater than all but one of these events the seismic moment estimated from regional pni waves and teleseismic long period body waves is 5 10 24 dyne cm corresponding to a moment magnitude of 5 8 the source duration of the earthquake is estimated to be 1 8 sec corresponding to a stress drop of 160 bars which is not significantly higher than the average stress drop of 120 bars estimated from previous large earthquakes in eastern north america in order to simultaneously match the recorded ground motion amplitudes of strong motion acceleration strong motion velocity and teleseismic short period and long period body waves it is necessary to use a source function having a complex shape that implies the presence of asperities and larger local stress drops the large set of strong motion recordings of the saguenay earthquake has been used to validate a procedure for estimating strong ground motion attenuation based on a simple wave propagation model the most important feature of the recorded strong motions is that their peak amplitudes do not decay significantly with distance inside 120 km but then decay abruptly beyond 120 km profiles of recorded accelerograms with absolute times indicate that at distances beyond 64 km the peak ground motions are due to strong postcritical reflections from velocity gradients in the lower crust the principal shear wave arrivals and the variation of their peak amplitudes with distance were reproduced in synthetic seismograms generated using a regional crustal structure model the critical distances for the postcritical reflections were short because of the deep focal depth of the event causing the elevation of ground motion amplitudes out to 120 km similar studies of earthquakes in other regions of eastern north america indicate that the strength of the postcritical reflections and the distance ranges over which they are dominant are controlled by the focal depth and crustal structure regional variations in crustal structure thus give rise to predictable regional variations in strong ground motion attenuation

crustal thickness and upper mantle velocities in the tibetan plateau region from the inversion of regional pnl waveforms evidence for a thick upper mantle lid beneath southern tibet the crustal thickness and upper mantle velocity variation in tibet and surrounding regions was mapped through the inversion of 130 individual long period pnl waveforms the 130 paths crisscross the tibetan plateau hindu kush karakoram southwest china burma and northern india regions we regionalized these areas on the basis of topographic and geologic expression and determined the average upper mantle velocity and crustal thickness value for each block or region through a linear least squares inversion of the 130 parameter values crustal thicknesses in the tibetan plateau karakoram and hindu kush regions range from 63 to 72 km and pn velocities are 0 10 0 20 km s faster beneath these regions than those beneath northern india we observed impulsive first arrivals evidence for positive upper mantle gradients on seismograms recorded at distances between 1000 and 1400 km the paths of these waves crossed portions of tibet the hindu kush and east india regions simple modeling of the long period pn wave form and amplitude requires fairly high upper mantle gradients of 0 18 0 25 km s per 100 km beneath the pamir hindu kush region and requires an upper mantle lid in excess of 100 km thickness the southern half of tibet also requires a lid of about 100 km thickness a thinner upper mantle lid 50 km provided a poor match to the tibetan observations even with a very high gradient of 0 2 km s per 100 km the upper mantle structure of east india appears to be similar to the southern half of tibet 100 km thick positive gradient zone both the increase in pn velocity from india into tibet and the evidence for a thick upper mantle lid beneath tibet are consistent with the model in which indian lithosphere has underthrust southern tibet due to poor path coverage the structure beneath northern tibet cannot be resolved and thus underthrusting beyond central tibet cannot be constrained the rapid increase in upper mantle velocity from northern india into tibet can be explained by the pressure increase alone produced by the double thick crust and indicates that the indian lithosphere which underlies tibet is out of thermal equilibrium