interferometer studies of equatorial f region irregularities and drifts a radar interferometer technique developed at jicamarca peru and first used to study electrojet irregularities has now been used successfully to study plasma turbulence in the equatorial f region our first results have shown that the most turbulent echoes appear to come from a region that extends for tens of kilometers in altitude but for only a kilometer or less in the east west direction this slab may very well be the wall of a depleted region a plasma bubble sometimes the irregularities can be tracked as they move eastward or westward velocity profiles for the evening period obtained in this way show a strong shear with westward velocities at the lowest altitudes observed and eastward velocities above a plausible explanation for this shear is that the westward drifts are driven by electric fields produced by westward e region winds and mapped up along magnetic field lines while at higher heights where the electron density is greater the drifts are controlled by the f region dynamo driven by eastward winds

environmental conditions for the presence of magnetofossils in the last glacial maximum inferred from magnetic parameters of sediments from the ulleung basin east sea abstract magnetic characterization of sediments from the ulleung basin in the east sea japan sea was carried out to decipher changes in environmental conditions over the last 39 000 years magnetic susceptibility intensities of natural remanent magnetization nrm anhysteretic remanent magnetization arm partial arm parm and saturation isothermal remanent magnetization sirm were measured for selected samples irm acquisition hysteresis and first order reversal curve forc measurements were made the ratios of rock magnetic parameters such as arm sirm arm and s ratio were determined to identify magnetic grain size and mineralogical variations along with electron microscope observations of magnetic mineral extracts down core variations in rock magnetic parameters for the 5 21 m long sediment core reveal distinct intervals with different grain size concentration and composition of magnetic minerals the uppermost portion and the high magnetic intensity zone hiz in marine isotope stage mis 2 are characterized by higher concentrations of fine grained magnetite whereas the mis 1 and 3 intervals contain lower concentrations of coarser grained magnetic minerals with increasing influence of hematite and or iron sulphide minerals the hiz interval is inferred to contain high occurrences of fine grained bacterial magnetosomes based on geochemical proxies east sea conditions for the hiz interval coincident with the last glacial maximum lgm can be summarized as having low total organic carbon toc enhanced eolian contributions from terrestrial organic particles and iron bearing minerals under the influence of an intensified east asian winter monsoon along with iron reducing but not sulphidic conditions that favoured growth and preservation of magnetotactic bacteria the delicate balance between reductive dissolution of magnetofossils under sulphidic conditions and production and preservation of magnetotactic bacteria in overlying iron reducing sediments for the hiz interval is responsible for the resultant abundance variations of magnetosomes in the studied sediments

japan sea oxygen isotope stratigraphy and global sea level changes for the last 50 000 years recorded in sediment cores from the oki ridge abstract we obtained twenty ams accelerator mass spectrometry radiocarbon dates 2 tephra layer chronologies and a planktonic foraminiferal 18 o stratigraphy for the last 50 000 years from japan sea cores from the oki ridge in this paper we report ams 14 c results that allow us to reconstruct a high resolution chronology of the cores and discuss millennial scale climate changes recorded in japan sea sediments the sedimentation rate for the site increased dramatically from the glacial stage to the holocene as a result of significant hydrological changes associated with deglaciation and global sea level rise a lighter 18 o anomaly for the planktonic foraminifers was found during the lgm last glacial maximum this shift corresponds to a freshening of the japan sea surface waters and is mainly due to a global sea level drop rather than anomalously warm ssts sea surface temperatures as previously reported our record combined with the global sea level data suggests that the lgm started about 30 kyr ago and that the salinity of the japan sea became fresher than at present the ssts during mis marine oxygen isotope stage 3 were relatively stable and global sea level was not lower than ca 80 m the surface water of the japan sea attained normal saline levels following the younger dryas cold event and reached the present day 18 o values 7 kyr ago

evidence for prehistoric earthquakes on the superstition hills fault from offset geomorphic features offset geomorphic features along the superstition hills fault show evidence for at least one slip event prior to the 1987 surface rupture and possibly as many as four to five earlier prehistoric earthquakes we documented several geomorphic features that appeared offset by multiple events by making detailed topographic maps offset features were abundant along reaches of the fault with high topographic relief and large displacement slip distribution for the penultimate event as recorded by offset rills streams and shrub coppice dunes is very similar to the slip distribution from the 1987 earthquake through april 1988 this similarity may prove to be fortuitous if afterslip from the 1987 event continues to increase the total slip for this earthquake but if afterslip associated with the 1987 event ceases in the near future then the past two earthquakes were nearly identical in slip and the superstition hills fault may be expected to produce characteristic earthquakes of roughly magnitude 6

orbital scale stratigraphy and high resolution analysis of biogenic components and deep water oxygenation conditions in the japan sea during the last 640 kyr abstract paleoceanographic conditions in the japan sea changed drastically during the late quaternary in association with orbital and suborbital cycles and glacio eustatic sea level changes however few studies have examined long term sediment records older than 160 ka because of the lack of long and continuous cores and the difficulty in constructing high resolution age models in this study we first constructed an orbital scale stratigraphy of the sediments covering the last 640 kyr by comparing the specmap 18o curve and the 18o curve of planktonic foraminifera 18opf in the japan sea together with the combination zones of dominant planktonic foraminifera species then we reconstructed temporal variations in biogenic silica biosil and biogenic carbonate biocarb contents calculated from high resolution major element analysis data determined by an xrf microscanner in order to evaluate the deep water oxygenation conditions we also defined excess s as the difference between the content of s in the sediments and that for normal marine sediments calculated from the organic carbon content corg estimated from lightness l by assuming a total sulfur content stotal corg ratio of 0 36 and examined its variability biosil shows orbital scale variation and is generally low except during interglacial maxima when global sea level was high enough to allow a strong influx of the tsushima warm current biocarb shows orbital and suborbital scale variations and tends to be higher in dark layers deposited during glacial stages whereas the relationship is reversed during interglacial stages the low biocarb in dark layers deposited during interglacial stages is probably due to dissolution of biogenic carbonate caused by the increase in surface productivity as a result of the strong influx of nutrient rich east china sea coastal water and consequent increase in surface productivity and decomposition rate of organic matter in the intermediate water excess s tends to be higher in thicker dark layers deposited during glacial maxima when the sea level dropped below 90 m compared to adjacent light layers suggesting development of euxinic deep water conditions during these periods the results demonstrated the presence of orbital and suborbital scale variations in biosil and biocarb and their association with dark and light layers in the japan sea that reflect variations in the nature and strength of inflow through the tsushima strait controlled by both climatic and sea level changes whereas higher excess s reflects the development of euxinic deep water condition during glacial maxima in association with glacio eustatic sea level drops below 90 m during the last 640 kyr

response of vegetation in central japan to precession during the last 147 000 years a lignin record from lake biwa core biw08 b abstract to understand the responses of terrestrial vegetation in central japan to global climate changes we generated a record of lignin composition from core biw08 b in lake biwa central japan during the last 147 000 years by tmah pyrolysis gc ms lignin abundance was intermittently elevated and associated with a high ratio of cinnamyl c to vanillyl v phenols c v ratio of lignin suggesting episodic inflows of herbaceous plant derived organic matter into lake biwa the largest inflow occurred during the last deglaciation variation in the ratio of syringyl s to vanillyl v phenols s v ratio which is a contribution index of angiosperms against gymnosperms showed a precession like cycle was consistent with a pollen record from lake biwa and showed a pattern similar to the s v record from an offshore marine site in the northwestern pacific the variation reflected the regional replacement of cool temperate deciduous broadleaf forests subalpine conifer forests and japanese cedar forests in central japan caused by the repetition of warmer dry and cooler wet climates on a precession cycle

paleoenvironmental changes in the japan sea during the last 85 000 years five distinct changes in the paleoenvironment of the japan sea within the last 85 000 years are revealed from the sedimentary record of a piston core recovered from the oki ridge changes in both surface and deepwater conditions are registered by changes in lithology calcium carbonate content organic carbon content oxygen and carbon isotope ratios and microfossil assemblages including calcareous nannoplankton diatoms radiolaria and foraminifera between 85 and 27 ka the warm tsushima current did not flow into the japan sea and cold surface water conditions prevailed environments at the seafloor fluctuated between dysaerobic to weakly oxic conditions between 27 and 20 ka freshwater input to the japan sea probably from the huang ho river in china stratified the water column and the severe anoxic conditions eliminated most benthic fauna between 20 and 10 ka the cold oyashio current flowed into the japan sea through the tsugaru strait reestablishing deepwater ventilation shallow water benthic assemblages of the north pacific ocean subsequently colonized the japan sea and occupied the vacant niches of the deep basins between 10 and 8 ka the foraminifer compensation level fcl gradually rose to a depth shallower than 1000 m and bottom conditions changed from dysaerobic to oxic at 10 ka the warm tsushima current started to flow into the japan sea through the tsushima strait to establish the modern oceanographic regime which has existed since 8 ka the eustatic sea level during the last glacial maximum was above the sill depths 130 m of the tsushima and tsugaru straits assuming that tectonic movements at these straits were negligible for the last 20 ka

the flickering switch of late pleistocene climate change polar ice contains a unique record of past climate variations previous greenland ice cores have documented relatively warm interstadial periods during the last glaciation and short centuryscale returns to colder conditions during the glacial to interglacial warming see for example ref 1 these climate features have also been observed to varying degrees in ocean sediment cores2 4 and terrestrial pollen and insect records5 7 here we report electrical conductivity measurements from a new greenland ice core which confirm these previous observations and also reveal a hitherto unrecognized mode of rapid climate variation fluctuations in ice conductivity on the scales of 5 20 years reflect rapid oscillations in the dust content of the atmosphere this flickering between two preferred states would seem to require extremely rapid reorganizations in atmospheric circulation

three dimensional records of surface displacement on the superstition hills fault zone associated with the earthquakes of 24 november 1987 seven quadrilaterals constructed at broadly distributed points on surface breaks within the superstition hills fault zone were repeatedly remeasured after the pair of 24 november 1987 earthquakes to monitor the growing surface displacement changes in the dimensions of the quadrilaterals are recalculated to right lateral and extensional components at millimeter resolution and vertical components of change are resolved at 0 2 mm precision the displacement component data for four of the seven quadrilaterals record the complete fault movement with respect to an october 1986 base these data fit with remarkable agreement the power law u t u f b t 1 b t c where u t is a displacement component at time t after the second main shock and uf b and c are constants this power law permits estimation of the final displacement uf from the data obtained within the period of observation data from one quadrilateral located near the epicenter of the second main shock and northeast trending conjugate faults allow that about 5 cm of right lateral slip may have been associated with the first main shock there data from the other quadrilaterals confirm that the surface faulting on most of the superstition hills fault zone did initiate at the time of the second main shock of the 1987 earthquakes the three dimensional motion vectors all describe nearly linear trajectories throughout the observation period and they indicate smooth shearing on their respective fault surfaces the inclination of the shear surfaces is generally nearly vertical except near the south end of the superstition hills fault zone where two strands dip northeastward at about 70 surface displacement on these strands is right reverse another kind of deformation superimposed on the fault displacements has been recorded at all quadrilateral sites it consists of a northwest southeast contraction or component of contraction that ranged from 0 to 0 1 per cent of the quadrilateral lengths between november 1987 and april 1988

case studies of coupling between the e and f regions during unstable sporadic e conditions 1 simultaneous f region airglow e region coherent scatter radar and ionosonde observations were made in greece during the summer sporadic e season in 2002 in this paper we report on two case studies during which patchy sporadic e layers were accompanied by midlatitude spread f coherent vhf radar echoes including two stream echoes and traveling ionospheric disturbances registered by the airglow instrument we argue that these events give strong evidence that polarization electric fields are built up in the e region and are mapped upward to the f region creating rising and falling regions in the bottomside plasma the resulting structure creates conditions for midlatitude spread f as detected by the ionosonde this correlation between patchy sporadic e and midlatitude spread f is further supported in a companion paper upward coupling of this sort is particularly efficient in regions of f region plasma uplift and airglow depletion since the f region pedersen conductivity is low which reduces the electrical load on the e region generator

historic surface slip along the san andreas fault near parkfield california the parkfield earthquake prediction experiment is focusing close attention on the 44 km long section of the san andreas fault that last ruptured seismically in 1966 ms 6 0 the 20 km long central segment of the 1966 parkfield rupture extending from the mainshock epicenter at middle mountain southeastward to gold hill forms a 1 to 2 km salient northeastward away from the dominant n40 w strike following the 1966 earthquake afterslip aseismic slip has been nearly constant moderate parkfield earthquakes have recurred on average every 21 years since 1857 when a great earthquake m 8 ruptured at least as far north as the southern parkfield segment many measurements of slip have been made near parkfield since 1966 nevertheless much of the history of surface slip remained uncertain especially the total amount associated with the 1966 event in 1985 we measured accumulated slip on the four oldest cultural features offset by the fault along the 1966 parkfield rupture segment we interpret net slip on each feature as a sum of event slip sum of coseismic and rapid preseismic and postseismic slip from parkfield earthquakes and steady interseismic slip as measured over the last 20 years on nearby alinement arrays creep meters and trilateration lines we assumed for each site that event slip was identical for the 1922 1934 and 1966 parkfield events and that long term average rate of interseismic slip was constant between all events two fences on the southern segment southeast of gold hill indicate event slip of 13 and 15 cm and interseismic slip rate of 0 36 and 0 30 cm yr since 1959 and 1908 respectively at these sites redundant independent data support our assumption that both event and interseismic slip occur uniformly on the central segment near parkfield both the 1934 and the 1966 ruptures offset a bridge built in 1932 interseismic slip rate near the bridge has been about 1 1 cm yr since 1966 thus we deduce an average event slip of 31 cm for the 1934 and 1966 earthquakes on a parallel fault trace 1 km to the southwest slip was about 8 cm in 1966 thus total event slip summed across the entire fault zone near parkfield was nearly 40 cm on middle mountain 4 km north of the 1966 mainshock epicenter an offset fence indicates 17 cm of slip in 1966 and a 2 26 cm yr interseismic slip rate since circa 1946 thus the central segment of the 1966 rupture is characterized by much larger event slip 40 cm than both distal segments 15 cm this amount of surface slip per event is about twice what had been previously assumed larger 1966 surface slip in the central part of the rupture is geodetically compatible with a coseismic slip of 65 10 cm slip on a narrow buried asperity between middle mountain and gold hill that has been inferred from the depth distribution of early aftershocks assuming our characteristic surface slip model one can further deduce a deficit in slip since the great 1857 earthquake taking the long term slip rate as 3 3 cm yr the surface slip deficit is 3 0 2 m south of gold hill but only 0 3 0 3 m northward from parkfield

eolian dust input to the subarctic north pacific eolian dust is a significant source of iron and other nutrients that are essential for the health of marine ecosystems and potentially a controlling factor of the high nutrient low chlorophyll status of the subarctic north pacific we map the spatial distribution of dust input using three different geochemical tracers of eolian dust 4he 232th and rare earth elements in combination with grain size distribution data from a set of core top sediments covering the entire subarctic north pacific using the suite of geochemical proxies to fingerprint different lithogenic components we deconvolve eolian dust input from other lithogenic inputs such as volcanic ash ice rafted debris riverine and hemipelagic input while the open ocean sites far away from the volcanic arcs are dominantly composed of pure eolian dust lithogenic components other than eolian dust play a more crucial role along the arcs in sites dominated by dust eolian dust input appears to be characterized by a nearly uniform grain size mode at 4 m applying the 230th normalization technique our proxies yield a consistent pattern of uniform dust fluxes of 1 2 g m2 yr across the subarctic north pacific elevated eolian dust fluxes of 2 4 g m2 yr characterize the westernmost region off japan and the southern kurile islands south of 45 n and west of 165 e along the main pathway of the westerly winds the core top based dust flux reconstruction is consistent with recent estimates based on dissolved thorium isotope concentrations in seawater from the subarctic north pacific the dust flux pattern compares well with state of the art dust model predictions in the western and central subarctic north pacific but we find that dust fluxes are higher than modeled fluxes by 0 5 1 g m2 yr in the northwest northeast and eastern subarctic north pacific our results provide an important benchmark for biogeochemical models and a robust approach for downcore studies testing dust induced iron fertilization of past changes in biological productivity in the subarctic north pacific

possibility of biases in the estimation of earthquake recurrence and seismic hazard from geologic data abstract aseismic deformation is an integral part of the earthquake process and may lead to systematic biases in the estimation of earthquake size recurrence and attendant strong ground motions in seismic hazard analyses founded on the geologic description of the locations lengths and slip rates of active faults observations are reviewed and presented to suggest that large earthquakes systematically rupture to increasingly greater depths below the seismogenic layer and that the portion of slip on faults accommodated by aseismic processes may be inversely related to the length of rupture expected to occur on them if so the expected seismic moment per unit area of earthquakes on mapped faults may be systematically overestimated as a function of rupture length when derived from regressions of seismic moment and aftershock area and estimates of seismic moment rate derived from geologic measures of fault offset might be systematically overestimated as an inverse function of the length of rupture expected to recur on a fault

the elmore ranch and superstition hills earthquakes of 24 november 1987 introduction to the special issue on 24 november 1987 two significant earthquakes occurred along the southern san jacinto fault zone and related structural elements in southern california not far from the international border these two events the elmore ranch earthquake m 6 2 at 0154 gmt and the superstition hills earthquake m 6 6 at 1315 gmt both moment magnitudes from sipkin 1989 and their aftershocks have yielded a rich harvest of geological seismological and engineering data pertinent to the cause and effect of earthquakes in this region where the southern san jacinto fault zone enters the salton depression from the peninsula ranges bordering it on the southwest fig 1 this special issue of the bulletin presents 18 geologic and seismologic investigations of these earthquakes a collection of papers born in el centro california on 8 and 9 february 1988 at a meeting attended by approximately 60 scientists interested in these earthquakes for one reason or another

bulk friction modeling of afterslip and the modified omori law abstract afterslip data from the superstition hills fault in southern california a creep event on the same fault the modified omori law and cumulative moments from aftershocks of the 1957 aleutian islands earthquake all indicate that the original formulation by dieterich 1981 constitutive properties of faults with simulated gouge agu geophys monogr 24 103 120 for friction evolution is more appropriate for systems far from instability than the commonly used approximation developed by ruina 1983 slip instability and state variable friction laws j geophys res 88 10359 10370 to study instability the mathematical framework we use to test the friction models is a one dimensional massless spring slider under the simplifying assumption proposed by scholz 1990 the mechanics of earthquakes and faulting cambridge university press and used by marone et al 1991 on the mechanics of earthquake afterslip j geophys res 96 8441 8452 that the state variable takes on its velocity dependent steady state value throughout motion in response to a step in stress this assumption removes explicit state variable dependence from the model obviating the need to consider state variable evolution equations anti derivatives of the modified omori law fit our data very well and are very good approximate solutions to our model equations a plausible friction model with omori law solutions used by wesson 1988 dynamics of fault creep j geophys res 93 8929 8951 to model fault creep and generalized by rice 1983 constitutive relations for fault slip and earthquake instabilities pure appl geophys 121 443 475 to a rate and state variable friction model yields exactly omori s law with exponents greater than 1 but yields unstable solutions for omori exponents less than 1 we estimate from the dieterich formulation the dimensionless parameter a which is equal to the product of the nominal coefficient of friction and the more commonly reported friction parameter a we find that a is typically positive qualitatively consistent with laboratory observations although our observations are considerably larger than laboratory values however we also find good model fits for a when data correspond to omori exponents less than 1 a modification of the stability analysis by rice and ruina 1983 stability of steady frictional slipping j appl mech 50 343 349 indicates that a is not a consequence of our assumption regarding state variable evolution a consistent interpretation of a in terms of laboratory models appears to be that the data are from later portions of processes better characterized by two state variable friction models a is explained by assuming that our data cannot resolve the co seismic evolution of a short length scale state variable to a velocity weakening state our parameterization leads to an apparent negative instantaneous viscosity we estimate the largest critical slip distance associated with afterslip to be 1 10 cm consistent with other estimates for near surface materials we assume that our observed large values for a reflect the fact that our model ignores the geometrical complexities of three dimensional stresses in fractured crustal materials around a fault zone with frictional stresses that vary on a fault surface our one dimensional model parameters reflect spatially averaged bulk stress and frictional properties of a fault zone where we clearly cannot specify the details of the averaging process our analysis of omori s law suggests that bulk frictional properties of a fault zone are well described by our simple laboratory based models but they would need to change during the seismic cycle for a mainshock instability to recur unless a mainshock aftershock sequence were characterized by a process similar to the arrested instabilities possible in two state variable systems

timing duration and transitions of the last interglacial asian monsoon thorium 230 ages and oxygen isotope ratios of stalagmites from dongge cave china characterize the asian monsoon and low latitude precipitation over the past 160 000 years numerous abrupt changes in 18o 16o values result from changes in tropical and subtropical precipitation driven by insolation and millennial scale circulation shifts the last interglacial monsoon lasted 9 7 1 1 thousand years beginning with an abrupt less than 200 years drop in 18o 16o values 129 3 0 9 thousand years ago and ending with an abrupt less than 300 years rise in 18o 16o values 119 6 0 6 thousand years ago the start coincides with insolation rise and measures of full interglacial conditions indicating that insolation triggered the final rise to full interglacial conditions

a silent mw 4 7 slip event of october 2006 on the superstition hills fault southern california 1 during october 2006 the 20 km long superstition hills fault shf in the salton trough southern california slipped aseismically producing a maximum offset of 27 mm as recorded by a creepmeter we investigate this creep event as well as the spatial and temporal variations in slip history since 1992 using ers 1 2 and envisat satellite data during a 15 year period steady creep is punctuated by at least three events the first two events were dynamically triggered by the 1992 landers and 1999 hector mine earthquakes in contrast there is no obvious triggering mechanism for the october 2006 event field measurements of fault offset after the 1999 and 2006 events are in good agreement with the interferometric synthetic aperture radar data indicating that creep occurred along the 20 km long fault above 4 km depth with most of the slip occurring at the surface the moment released during this event is equivalent to a mw 4 7 earthquake this event produced no detectable aftershocks and was not recorded by the continuous gps stations that were 9 km away modeling of the long term creep from 1992 to 2007 creep using stacked ers 1 2 interferograms also shows a maximum creep depth of 2 4 km with slip tapering with depth considering that the sediment thickness varies between 3 km and 5 km along the shf our results are consistent with previous studies suggesting that shallow creep is controlled by sediment depth perhaps due to high pore pressures in the unconsolidated sediments

the response of northern hemisphere extratropical climate and vegetation to orbitally induced changes in insolation during the last interglaciation abstract the last interglaciation substage 5e provides an opportunity to examine the effects of extreme orbital changes on regional climates we have made two atmospheric general circulation model experiments p t approximated the northern hemisphere seasonality maximum near the beginning of 5e p t approximated the minimum near the end of 5e simulated regional climate changes have been translated into biome changes using a physiologically based model of global vegetation types major climatic and vegetational changes were simulated for the northern hemisphere extratropics due to radiational effects that were both amplified and modified by atmospheric circulation changes and sea ice feedback p t showed mid continental summers up to 8 c warmer than present mid latitude winters were 2 4 c cooler than present but in the arctic summer warmth reduced sea ice extent and thickness producing winters 2 8 c warmer than present the tundra and taiga biomes were displaced poleward while warm summer steppes expanded in the mid latitudes due to drought p t showed summers up to 5 c cooler than present especially in mid latitudes sea ice and snowpack were thicker and lasted longer polar desert tundra and taiga biomes were displaced equatorward while cool summer steppes and semideserts expanded due to the cooling a slight winter warming in mid latitudes however caused warm temperate evergreen forests and scrub to expand poleward such qualitative contrasts in the direction of climate and vegetation change during 5e should be identifiable in the paleorecord

the history and variability of the east asian paleomonsoon climate abstract changes in the east asian paleomonsoon reflect interactions between the global atmosphere ocean land and ice systems and are also an expression of their combined effect within the boundary conditions imposed by the east asian continent and solar radiation the history of the east asian monsoon is an alternation between dominance by the dry cold winter and warm humid summer monsoons high resolution eolian sequences preserved in the chinese loess plateau reveal that the east asian monsoon may have commenced at least 7 2 ma ago they also provide evidence indicating that the pulsed uplift of the tibetan plateau at about 3 4 and 7 2 ma may have played an important role in inducing climate change the palaeoclimatic records of the last glacial cycle show high frequency variability on time scales of 1000 year or even shorter and instability of the east asian paleomonsoon system the high frequency variability could be due to a non linear response to orbital forcing or a result of the coupling processes between different components of the global system cold air activity in northern high latitudes the trans equatorial air streams from the southern hemisphere and possibly enso may have played an important role in east asian monsoon variability the synchroneity of all the palaeoclimatic events along the polar equator polar pep transect is still an open question correlation of limited palaeoclimatic records for the last 30 kyr obtained from east asia and australia suggests that the trans equatorial air streams driven by the monsoon and trade winds may have had an influence on opposite hemispheres

probabilistic estimates of surface coseismic slip and afterslip for hayward fault earthquakes we examine the partition of long term geologic slip on the hayward fault into interseismic creep coseismic slip and afterslip using monte carlo simulations we compute expected coseismic slip and afterslip at three alinement array sites for hayward fault earthquakes with nominal moment magnitudes ranging from about 6 5 to 7 1 we consider how interseismic creep might affect the coseismic slip distribution as well as the variability in locations of large and small slip patches and the magnitude of an earthquake for a given rupture area we calibrate the estimates to be consistent with the ratio of interseismic creep rate at the alinement array sites to the geologic slip rate for the hayward fault we find that the coseismic slip at the surface is expected to comprise only a small fraction of the long term geologic slip the median values of coseismic slip are less than 0 2 m in nearly all cases as a result of the influence of interseismic creep and afterslip however afterslip makes a substantial contribution to the long term geologic slip and may be responsible for up to 0 5 1 5 m median plus one standard deviation s d of additional slip following an earthquake rupture thus utility and transportation infrastructure could be severely impacted by afterslip in the hours and days following a large earthquake on the hayward fault that generated little coseismic slip inherent spatial variability in earthquake slip combined with the uncertainty in how interseismic creep affects coseismic slip results in large uncertainties in these slip estimates

seasonal and longitudinal variation of large scale topside equatorial plasma depletions 1 we examine the large scale properties of three classes of equatorial topside plasma depletions referred to as channels in order of increasing zonal width and internal large scale substructuring we study simple channels multichannels and superchannels we find that peaks in channel activity are centered on 0 african sector and 180 western pacific sector superchannels are found to strongly dominate in the african sector whereas simple and multichannels dominate the pacific sector within the african sector the relative proportions of the three channel classes remain stable in all seasons in the pacific sector simple and multichannels are dominant in all seasons of activity though small but significant seasonal variations in channel widths and spacings are seen structure at a zonal scale size of about 100 km is found to be present in all channels examined observational and model evidence suggests that 100 km density structure represents channels such that all multichannels and superchannels consist of multiple contiguous simple channels since seeds that initiate channel formation necessarily influence large scale channel features we utilize our data to draw conclusions regarding bottomside seeding conditions in the various seasonal and longitudinal sectors specifically we find that strong long wavelength 1000 km seeds appear much more frequently in the african sector resulting in the prevalence of superchannels there when long wavelength seeds appear in the pacific sector they result in periodic trains of simple and multichannels a bottomside preseeded at a scale size near 100 km accounts for the ubiquity of 100 km scale size in the ae e data

sediment fabrics oxygenation history and circulation modes of japan sea during the late quaternary abstract the quaternary hemipelagic sediments of the japan sea are characterized by centimeter to decimeter scale alternations of heavily bioturbated organic poor light layers and finely laminated organic rich dark layers these dark and light layers which can be correlated throughout the deeper part of the basin are considered to reflect changes in bottom water oxygenation however depositional mechanisms responsible for individual dark layers and causes of oxygen depletion are not fully understood two possible settings for deposition of organic rich dark layers are recognized one is a stratified ocean like the black sea where limited vertical advection results in euxinic conditions in the deeper parts of the basin the other is an upwelling region like the arabian sea where the oxygen minimum zone is intensified by enhanced nutrient upwelling and surface productivity in this study fabrics of hemipelagic sediments deposited in the japan sea during the last 160 ka were studied in three cores collected from different latitudes and water depths fabrics were classified into 4 classes based on corresponding bottom water oxygenation level five dark layer types were defined based on the distribution patterns of sediment fabric classes within each dark layer comparison of dark layer types at shallower and deeper sites in a chronologic framework provided evidence for five different modes of deep water circulation these circulation modes which reflect relative intensities of upwelling and density stratification appear to be related to global sea level changes as well as climate impact on the nature of water influx through the tsushima strait

how well can we simulate past climates evaluating the models using global palaeoenvironmental datasets abstract global syntheses of palaeoenvironmental data are required to test climate models under conditions different from the present data sets for this purpose contain data from spatially extensive networks of sites the data are either directly comparable to model output or readily interpretable in terms of modelled climate variables data sets must contain sufficient documentation to distinguish between raw primary and interpreted secondary tertiary data to evaluate the assumptions involved in interpretation of the data to exercise quality control and to select data appropriate for specific goals four data bases for the late quaternary documenting changes in lake levels since 30 14 c kyr bp the global lake status data base vegetation distribution at 18 14 c kyr and 6 14 c kyr bp biome 6000 aeolian accumulation rates during the last glacial interglacial cycle dirtmap and tropical terrestrial climates at the last glacial maximum the lgm tropical terrestrial data synthesis are summarised each has been used to evaluate simulations of last glacial maximum lgm 21 calendar kyr bp and or mid holocene 6 cal kyr bp environments comparisons have demonstrated that changes in radiative forcing and orography due to orbital and ice sheet variations explain the first order broad scale in space and time features of global climate change since the lgm however atmospheric models forced by 6 cal kyr bp orbital changes with unchanged surface conditions fail to capture quantitative aspects of the observed climate including the greatly increased magnitude and northward shift of the african monsoon during the early to mid holocene similarly comparisons with palaeoenvironmental datasets show that atmospheric models have underestimated the magnitude of cooling and drying of much of the land surface at the lgm the inclusion of feedbacks due to changes in ocean and land surface conditions at both times and atmospheric dust loading at the lgm appears to be required in order to produce a better simulation of these past climates the development of earth system models incorporating the dynamic interactions among ocean atmosphere and vegetation is therefore mandated by quaternary science results as well as climatological principles for greatest scientific benefit this development must be paralleled by continued advances in palaeodata analysis and synthesis which in turn will help to define questions that call for new focused data collection efforts

experimental analysis of slip distribution along a fault segment under stick slip and stable sliding conditions abstract this paper presents the results of an experimental study of slip distribution along fault models with different sliding surface morphologies submitted to various orientations of fault and loading direction uniaxial compression tests were done on pmma plates to measure the relative displacement of markers perpendicular to the sliding surfaces slip distribution profiles were then constructed for different stages of shortening of the samples it was shown that fault morphology determines both the sliding regime and the slip distribution along the sliding surfaces along fault models with grounded surfaces fmgs stable sliding giving a symmetrical smooth distribution was observed for fault models with natural fracture surfaces fmns stick slip was observed in this case the slip distribution exhibited significant irregularities in a generally symmetrical profile analysis of this profile enabled four types of local slip behaviour to be identified which may provide a physical basis for the interpretation of coseismic slip distributions the local slip behaviours were interpreted in terms of interaction of irregular asperities and helped understand the discrepancy observed between theoretical slip distributions and the displacement measured along the active faults analysis of the slip distribution profiles along the fmgs and the fmns also showed that they evolved systematically after the appearance of branching for a large amount of shortening mode i branching was observed at the tips of the sliding surfaces after its development the global amount of slip along the faults increased and the slip gradient between the centre and the tips of the faults decreased this effect is consistent with numerical modelling studies finally the observed profiles were compared with the linear the tapered and the elliptic theoretical models using two different procedures we conclude that in the case of the fmns where the sliding surface topography is complex no model could correctly describe the slip distribution and that in both cases of fmns and fmgs branching caused a change in the shape of the slip distribution profiles

surface slip subsequent to the 24 november 1987 superstition hills california earthquake monitored by digital creepmeters three creepmeters of new design were operated on the superstition hills fault following the 24 november 1987 earthquake each creepmeter consists of a digital displacement sensor interrogated periodically by a computer at the end of each hour the computer determines a recording rate appropriate to the velocity of the slip on the fault in that hour no data are recorded if the fault is inactive data are recorded at a maximum rate of one sample per minute if slip on the fault is detected the resolution and range of the creepmeters are 10 m and 15 cm respectively fault activity is observed to be confined to periods of episodic slip creep events with mean amplitudes 3 to 6 mm and durations less than 4 hr a total of 80 creep events were recorded during the first week following the earthquake creep events occurred several times each day after 6 months events occurred every 3 weeks this increase in the mean time interval between creep events results in the observed decay in afterslip rate between creep events the fault is inactive although more than 200 microstrain of fault zone deformation may accumulate before each event although creep events were observed to propagate unilaterally in both directions along the fault the most impulsive events appeared to propagate bilaterally from a dilatant offset separating the northern and southern halves of the 24 km long fault zone maximum propagation velocities of 30 m sec were observed aftershocks 2 m 4 7 were observed to occur near the creepmeters following 6 to 9 cm of surface slip on the fault a future aftershock in this region is anticipated in mid 1989 based on afterslip rates in the year following the main shock

grain size of quartz as an indicator of winter monsoon strength on the loess plateau of central china during the last 130 000 yr the chinese loess paleosol sequence constitutes an important record of variations in asian monsoon climate over the past 2 4 myr magnetic susceptibility of loess and paleosols has been used as a proxy for summer monsoon intensity while median grain size has been regarded as a measure of the strength of winter monsoon winds that were responsible for most of the dust transport however median grain size is only an approximate index of winter monsoon strength because both paleosols and loess have been modified to various degrees by weathering processes that have produced pedogenic clay the quartz component of loess and paleosols is largely unaffected by weathering processes and therefore constitutes a more reliable proxy index of monsoon wind strength median grain size qmd and maximum grain size qmax values of monomineralic quartz isolated from the loess paleosol section at luochuan in the central loess plateau are characterized by two main intervals during the last ca 130 000 yr when these parameters were significantly greater than 9 and 85 m respectively and three main intervals when they were lower the data imply that the winter monsoon weakened during the intervals with low qmd and qmax values which coincide with marine oxygen isotope stages 5 3 and 1 and was strongest ca 67 000 and 20 000 yr ago during isotope stages 4 and 2 however both quartz grainsize records display second order high frequency high amplitude variations which are lacking in the magnetic susceptibility record that imply rapid and significant changes in atmospheric conditions that affect dust transport and deposition

asynchronous holocene optimum of the east asian monsoon abstract the spatial and temporal distribution of summer monsoon precipitation or effective moisture during the holocene has been reconstructed on the basis of geological data including lake levels pollen profiles and loess paleosol records in addition the summer july precipitation increment effective precipitation and monsoon strength index have been obtained from numerical modeling experiments both geological data and numerical modeling indicate that the holocene optimum as defined by peak east asian summer monsoon precipitation was asynchronous in central and eastern china reaching a maximum at different times in different regions e g ca 10 000 8000 yr ago in northeastern china 10 000 7000 yr ago in north central and northern east central china ca 7000 5000 yr ago in the middle and lower reaches of the yangtze river and ca 3000 yr ago in southern china in southwestern china the maximum appeared ca 11 000 yr ago but probably was related to the maximum landward extension of the indian summer monsoon the regional shift in the maximum precipitation belt from northwest to southeast over the past 10 000 yr is interpreted as a response to changing seasonality related to orbital forcing of the climate the southeastward shift of the east asian summer monsoon maximum is consistent with the progressive weakening of the summer monsoon as the summer solar radiation anomaly decreased progressively through the holocene and the east asian monsoon index declined while the early maximum in southwestern china matches the maximum of the indian monsoon index

nonstationary phase of the plio pleistocene asian monsoon paleoclimate records indicate that the strength of the asian summer monsoon is sensitive to orbital forcing at the obliquity and precession periods 41 000 and 23 000 years respectively and the extent of northern hemisphere glaciation over the past 2 6 million years the timing phase of strong monsoons has changed by 83 degrees in the precession and 124 degrees in the obliquity bands relative to the phase of maximum global ice volume inferred from the marine oxygen isotope record these results suggest that one or both of these systems is nonstationary relative to orbital forcing

longitudinal asymmetry of the occurrence of the plasma irregularities over african low latitude region this study presents the results of plasma irregularities over african equatorial and low latitude region under various solar geophysical conditions that gave rise to an east west longitudinal asymmetry the data used for this research were obtained from the ground based gnss receiver stations within african equatorial ionization anomaly region for 3 consecutive years 2011 2013 in the ascending phase of solar cycle 24 the study considered specific days of different geomagnetic activities in equinoctial month of october 2013 in addition the five most geomagnetically disturbed and quietest days in each month for the 3 consecutive years and the annual mean for each year were considered in this study rate of change of total electron content index roti was used to access the level of the ionospheric irregularities activity the presence of ionospheric irregularities was taken when the difference between the local daytime 0600 1800 and nighttime 1900 2400 mean roti is above 0 075 tecu min the study revealed that african equatorial ionospheric irregularities occurrence is larger in the west sector and that irregularities activity could be sometimes 4 40 lowered or inhibited during the disturbed conditions in the african equatorial eastern sector in comparison to the western region the asymmetry observed in the region could be attributed to transequatorial meridional winds and probably the east west asymmetry in the strength of the eej current in the region

monsoon climate of the early holocene climate experiment with the earth s orbital parameters for 9000 years ago values for the precession and obliquity of the earth 9000 years ago indicate that the global average solar radiation for july 9000 years ago was 7 percent greater than at present when the estimated solar radiation values are used in a low resulation climate model the model simulates an intensified continent scale monsoon circulation this result agrees with paleoclimatic evidence from africa arabia and india that monsoon rains were stronger between 10 000 and 5000 years ago than they are today

long term afterslip of the 2004 m 6 0 parkfield california earthquake implications for forecasting amount and duration of afterslip on other major creeping faults abstract we present the longest record of surface afterslip on a continental strike slip fault for the 2004 m 6 0 parkfield california earthquake from which we can derive critical information about the duration and predictability of afterslip relevant to urban displacement hazard applications surface slip associated with this event occurred entirely postseismically along the interseismically creeping 0 6 1 5 cm yr main trace of the san andreas fault using the first year of afterslip data the program after correctly predicted the cumulative surface afterslip maximum 35 cm eventually attained by 1 yr postearthquake observed afterslip had accumulated to only 74 of its modeled final value u f in units of length the 6 yr data suggested final slip would be reached everywhere by 6 12 yrs parkfield s afterslip lasted much longer 6 12 yrs than afterslip following a 2014 m 6 0 event in napa california where no interseismic creep was known and its afterslip neared completion 97 of u f by 1 yr the uncertainty in u f for the napa event fell to 2 cm in only three months versus in 2 yrs for the parkfield event mostly because duration of the power law stage of afterslip at parkfield is much longer 1000 493 1666 days versus 100 35 421 days for napa because the urban hayward fault near san francisco california like the parkfield section exhibits interseismic creep in a similar geological regime significant afterslip might last for up to a decade following an anticipated m 6 7 earthquake potentially delaying postearthquake recovery electronic supplement tables of afterslip observations and coefficients for computing afterslip

the greenville fault preliminary estimates of its long term creep rate and seismic potential abstract once assumed to be locked we show that the northern third of the greenville fault gf creeps at 2 mm yr based on 47 yr of trilateration net data this northern gf creep rate equals its 11 ka slip rate suggesting a low strain accumulation rate in 1980 the gf easternmost strand of the san andreas fault system east of san francisco bay produced an m w 5 8 earthquake with a 6 km surface rupture and dextral slip growing to 2 cm on cracks over a few weeks trilateration shows a 10 cm post 1980 transient slip ending in 1984 analysis of 2000 2012 crustal velocities on continuous global positioning system stations allows creep rates of 2 mm yr on the northern gf 0 1 mm yr on the central gf and 0 mm yr on its southern third modeled depth ranges of creep along the gf allow 5 25 aseismic release greater locking in the southern two thirds of the gf is consistent with paleoseismic evidence there for large late holocene ruptures because the gf lacks large 1 km discontinuities likely to arrest higher 1 m slip ruptures we expect full length 54 km ruptures to occur that include the northern creeping zone we estimate sufficient strain accumulation on the entire gf to produce m w 6 9 earthquakes with a mean recurrence of 575 yr while the creeping 16 km northern part has the potential to produce an m w 6 2 event in 240 yr it may rupture in both moderate 1980 and large events these two dimensional model estimates of creep rate along the southern gf need verification with small aperture surveys online material green net data file

magnetic declination control of the equatorial f region dynamo electric field development and spread f we have carried out a comparative study of the evening prereversal enhancements in the equatorial f region vertical ionization drift velocities vz over fortaleza 4 s 38 w brazil and jicamarca 12 s 77 w peru two magnetic equatorial stations in the american zone the results show profound dissimilarities in the seasonal trends in the times and widths of the vz prereversal peak which reflect in the spread f characteristics as well at the two stations the dissimilarities are shown to be arising mainly from the difference in the magnetic field declination angles that causes differences in the conjugate e region sunset durations and hence in the f region polarization electric field development rates at the two stations

dynamics of fault creep observations along the surface traces of active faults in california and elsewhere indicate that tectonic displacement can occur as seismic slip or as aseismic fault creep fault creep occurs as secular displacement and as displacement episodes called creep events which last a few hours to days and include from a millimeter or less to a few tens of millimeters of displacement instrumental measurements of displacement versus time during creep events show that many events have a characteristic simple form including a steep beginning followed by a gradual decay in the rate of displacement some creep events display small amounts of precursory slip and many seem to be composed of several discrete simple events propagation of creep events along the san andreas calaveras and imperial faults in california has been inferred from the nearly simultaneous observation of creep events at nearby creepmeters and from kinematic modeling of continuous measurements of strain during creep events fault creep can be viewed as arising from the interplay of three factors stress applied to the fault from external sources stress caused by the geometry and distribution of displacement on the fault arising from the elastic response of the surrounding medium to the displacements within the anelastic fault zone itself and the constitutive relations characterizing the resistance to slip on the fault analytic solutions are presented for a simple rectangular dislocation quasi static model of nonpropagating fault creep assuming viscous and quasi plastic power law creep fault zone rheology and for a multi element composed of several rectangular or striplike dislocation surfaces quasi static model assuming a viscous rheology viscous rheology implies solutions composed of exponentials that decay with time the simple one element quasi plastic model is in agreement with the form of creep events observed at melendy ranch california a matrix formulation is presented to calculate dislocation stresses on a fault zone in a half space or plate the formulation involves the division of the dislocation surface into strips or rectangles and the use of published solutions to calculate the stress resulting from displacement on each individual element results from the matrix method agree with analytic results for equilibrium displacements on stress free cracks the matrix formulation is then used as the basis for a numerical method to simulate one and two dimensional propagating creep assuming a quasi plastic rheology on the fault zone results from this method agree reasonably well with observations of afterslip from the 1966 parkfield 1975 oroville and 1979 imperial valley california earthquakes and of a propagating creep event observed along the southern calaveras fault central california during july 1977 this method of analysis and the assumption that creep at each point on the fault zone follows a power law rheology after the applied stress reaches a spatially varying yield stress can explain the secular and episodic nature of fault creep afterslip the simple shape of some individual events and the multiple composite shape of others and the propagation of creep events on the southern calaveras fault observations of propagating creep indicate a yield stress near zero at the surface and throughout much of the fault zone however they also indicate the presence of a zone at a depth of about 0 5 km and about 5 km long with a yield stress of about 15 bars 1 5 mpa the methods of solution presented here should be applicable to many problems in the dynamics of faulting

longitudinal variability of annual changes in activity of equatorial spread f and plasma bubbles global distribution maps of equatorial spread f esf activity for various annual periods were derived from the topside soundings by the ionosphere sounding satellite b iss b in 1978 1980 the esf activity during the northern winter period reveals maximum enhancement at the atlantic longitudes of large westward geomagnetic declination and during the northern summer at the pacific longitudes of large eastward declination on several orbits passing over the region of the esf activity enhancement abrupt depletions of the electron density or equatorial plasma bubbles were observed at the satellite altitude of about 1100 km it has also been found that the background electron density distributions tend to be symmetric with respect to the magnetic equator in the region of the enhanced esf activity and asymmetric in the region of the suppressed esf activity these observations are taken account of by the influence of a transequatorial thermospheric wind upon the suppression of the rayleigh taylor type plasma instability

orbital and millennial scale variations in asian dust transport path to the japan sea abstract orbital and millennial scale variations in the asian monsoon and its probable association with the dansgaard oeschger d o cycles have been demonstrated by previous studies however the origin and nature of such variations are poorly understood the japan sea is located down wind of the arid areas of the eurasian continent and thus receives significant amounts of aeolian dust consequently the hemipelagic sediments of the japan sea are expected to record a continuous aeolian dust accumulation which may provide information about the past variations in asian monsoon grain size flux and provenance of aeolian dust in the sediments were examined using two sediment cores obtained from the northern and southern parts of the japan sea in order to understand the spatial variability of asian monsoon since the silt fraction of the detrital materials in hemipelagic sediments of the japan sea is composed predominantly of aeolian dust the grain size flux and provenance of the silt fraction were examined the taklimakan desert loess plateau and siberia northeast china areas were identified as possible source areas of aeolian dust in the sediments of the japan sea based on the electron spin resonance esr signal intensity and crystallinity of quartz moreover the relative contribution of aeolian dust from each source area was estimated based on the esr signal intensity and crystallinity of quartz aeolian dust fluxes from the two source areas at the southern site were then estimated grain size and flux of eolian dust at the northern site and fluxes of aeolian dust from two source areas at the southern site show orbital scale variations in harmony with the insolation change at 30 n in june these results indicate orbital scale changes in the extent of the arid area and or frequency of dust storms in the taklimakan desert loess plateau and siberia northeast china areas and suggest that southward northward shifts of the westerly jet axis occurred together with either intensified weakened winter monsoon decreased increased winter precipitation in the siberia northeast china area or southeastward northwestward shifts of summer monsoon limit during periods of smaller larger insolation at 30 n in june in addition to these orbital scale variations millennial scale variations possibly associated with the d o cycles are observed in the grain size record of aeolian dust at the two sites based on analogy with orbital scale variations these millennial scale variations are considered to reflect millennial scale changes in the position of the westerly jet axis together with the changes either in winter monsoon intensity winter precipitation or position of summer monsoon limit our results suggest n s oscillations in the westerly jet and summer monsoon limit and changes in the intensity of the winter monsoon on orbital and millennial timescales

effects of the vertical plasma drift velocity on the generation and evolution of equatorial spread f we use radar observations from the jicamarca observatory from 1968 to 1992 to study the effects of the f region vertical plasma drift velocity on the generation and evolution of equatorial spread f the dependence of these irregularities on season solar cycle and magnetic activity can be explained as resulting from the corresponding effects on the evening and nighttime vertical drifts in the early night sector the bottomside of the f layer is almost always unstable the evolution of the unstable layer is controlled by the history of the vertical drift velocity when the drift velocities are large enough the necessary seeding mechanisms for the generation of strong spread f always appear to be present the threshold drift velocity for the generation of strong early night irregularities increases linearly with solar flux the geomagnetic control on the generation of spread f is season solar cycle and longitude dependent these effects can be explained by the response of the equatorial vertical drift velocities to magnetospheric and ionospheric disturbance dynamo electric fields the occurrence of early night spread f decreases significantly during equinox solar maximum magnetically disturbed conditions due to disturbance dynamo electric fields which decrease the upward drift velocities near sunset the generation of late night spread f requires the reversal of the vertical velocity from downward to upward for periods longer than about half an hour these irregularities occur most often at 0400 local time when the prompt penetration and disturbance dynamo vertical drifts have largest amplitudes the occurrence of late night spread f is highest near solar minimum and decreases with increasing solar activity probably due to the large increase of the nighttime downward drifts with increasing solar flux

long term creep rates on the hayward fault evidence for controls on the size and frequency of large earthquakes the hayward fault hf in california exhibits large m w 6 5 7 1 earthquakes with short recurrence times 161 65 yr probably kept short by a 26 78 aseismic release rate including postseismic its interseismic release rate varies locally over time as we infer from many decades of surface creep data earliest estimates of creep rate primarily from infrequent surveys of offset cultural features revealed distinct spatial variation in rates along the fault but no detectable temporal variation since the 1989 m w 6 9 loma prieta earthquake lpe monitoring on 32 alinement arrays and 5 creepmeters has greatly improved the spatial and temporal resolution of creep rate we now identify significant temporal variations mostly associated with local and regional earthquakes the largest rate change was a 6 yr cessation of creep along a 5 km length near the south end of the hf attributed to a regional stress drop from the lpe ending in 1996 with a 2 cm creep event north of there near union city starting in 1991 rates apparently increased by 25 above pre lpe levels on a 16 km long reach of the fault near oakland in 2007 an m w 4 2 earthquake initiated a 1 2 cm creep event extending 10 15 km along the fault using new better constrained long term creep rates we updated earlier estimates of depth to locking along the hf the locking depths outline a single 50 km long locked or retarded patch with the potential for an m w 6 8 event equaling the 1868 hf earthquake we propose that this inferred patch regulates the size and frequency of large earthquakes on hf online material 2007 event creep models plots of creepmeter data maps and cross sections of relocated microearthquakes and active fault traces and iterative solutions for depth of creep

daytime ionospheric longitudinal gradients seen in the observations from a regional beidou geo receiver network many studies have devoted to the longitudinal variations of the ionosphere globally however the ionospheric longitudinal variations in a small region are rarely reported in this paper we for the first time use tec data from a beidou geostationary orbit geo receiver network to observe and investigate ionospheric longitudinal variations within the zonal scale of 1000 km over central china 112 122 e 27 31 n 20 24 n magnetic latitudes during june 2015 december 2016 the beidou geo tec provides a good dataset to study longitudinal variations compared with non geo tec without contaminating the spatial variations and elevation changes due to satellite motion pronounced daytime longitudinal gradients within the distance of 1000 km are present in beidou geo tec it was found that the tec is generally larger in the west than in the east in some cases the tec gradient magnitude is larger than 45 tecu for most events the obvious daytime longitudinal gradients are accompanied by the tec enhancement the occurrence rate of daytime longitudinal gradients under different geomagnetic activities is similar whereas strong daytime longitudinal gradients mainly occur under the moderate and strong disturbance geomagnetic activities these observations suggest that the electric field disturbances could have significant effects on producing the observed ionospheric longitudinal gradients

radiocarbon calibration beyond 20 000 14c yr b p by means of planktonic foraminifera of the iberian margin we present a new set of 14c ages obtained by accelerator mass spectrometry ams on planktonic foraminifera from a deep sea core collected off the iberian margin md952042 this site at 37 n is distant from the high latitude zones where 14c reservoir age is large and variable many independent proxies alkenones magnetic susceptibility ice rafted debris foraminifera stable isotopes abundances of foraminifera pollen and dinoflagellates show abrupt changes correlative with dansgaard oeschger and heinrich events of the last glacial period the good stratigraphic agreement of all proxies from the fine to the coarse size fractions indicates that the foraminifera 14c ages are representative of the different sediment fractions to obtain reliable 14c ages of foraminifera beyond 20 000 14c yr b p we leached the shells prior to carbonate hydrolysis and subsequent analysis for a calendar age scale we matched the iberian margin u37k profile with that of greenland summit 18o both are proxies for temperature which in models varies synchronously in the two areas the match creates no spurious jumps in sedimentation rate and requires only a limited number of tie points except for ages older than 40 000 14c yr b p greenland s gisp2 and grip records yield similar calendars the 14c and imported calendar ages of the iberian margin record are then compared to data from lacustrine annual varves and from corals and speleothems dated by u th previously used to extend the calibration beyond 20 000 14c yr b p the new record follows a smooth pattern between 23 000 and 50 000 cal yr b p we find good agreement with the previous data sets between 23 000 and 31 000 cal yr b p in the interval between 33 000 and 41 000 cal yr b p for which previous records disagree by up to 5000 cal yr the iberian margin record closely follows the polynomial curve that was previously defined by an interpolation of the coral ages and runs between the lake suigetsu and the bahamian speleothem data sets

inverting measurements of surface slip on the superstition hills fault we derive and test a set of inversions of surface slip measurements based on the empirical relation u t uf 1 t t c proposed by sharp and saxton 1989 to estimate the final slip uf the power law exponent c and the power law duration t at short times sharp s relation behaves like the simple power law u t u 1 tc where u 1 is the initial slip that is the slip at 1 day after the earthquake at long times the slip approaches the final slip asymptotically the inversions are designed in part to exploit the accuracy of measurements of differential slip that is measurements of surface slip which are made relative to a set of nails or stakes emplaced after the earthquake we apply the inversions to slip measurements made at 53 sites along the superstition hills fault for the 11 months following the m 6 2 and 6 6 earthquakes of 24 november 1987 in general estimates of the initial slip and the power law exponent are well resolved while estimates of the power law durations and the final slip are less well resolved because the durations of the surface slip measurements are often less than the derived power law durations the slip on the three fault strands is a relatively smooth function of position the initial slip and final slip are well correlated the time dependence of surface slip at the 53 sites is roughly similar along the entire fault where the power law exponents are distributed as c 0 14 0 04 and the power law durations range from 100 t 1000 days

evidence for general instability of past climate from a 250 kyr ice core record recent results1 2 from two ice cores drilled in central greenland have revealed large abrupt climate changes of at least regional extent during the late stages of the last glaciation suggesting that climate in the north atlantic region is able to reorganize itself rapidly perhaps even within a few decades here we present a detailed stable isotope record for the full length of the greenland ice core project summit ice core extending over the past 250 kyr according to a calculated timescale we find that climate instability was not confined to the last glaciation but appears also to have been marked during the last interglacial as explored more fully in a companion paper3 and during the previous saale holstein glacial cycle this is in contrast with the extreme stability of the holocene suggesting that recent climate stability may be the exception rather than the rule the last interglacial seems to have lasted longer than is implied by the deep sea specmap record4 in agreement with other land based observations5 6 we suggest that climate instability in the early part of the last interglacial may have delayed the melting of the saalean ice sheets in america and eurasia perhaps accounting for this discrepancy

late pleistocene and holocene aeolian dust deposition in north china and the northwest pacific ocean abstract rates of dust deposition in the north pacific and the central loess plateau of china show a poor correlation during the last 30 000 yr although in both cases the dust was derived from deserts in northern china loess accumulation rates were high at the time of the last glacial maximum while dust flux to the north pacific was low at this time maximum dust flux to the north pacific is recorded in the mid holocene but holocene rates of loess accumulation have been low these differences are shown to reflect the different nature of the wind conditions responsible for dust transport to the loess plateau and the north pacific dust transport responsible for formation of the loess occurred mainly in the lower 1 5 km of the atmosphere and was accomplished by cold low level northwesterly winds associated with cold waves emanating from the mongolian anticyclone at present such conditions occur quite frequently in winter but during the coldest phases of the pleistocene they probably also occurred in the spring and summer long range dust transport from northern china to the north pacific requires that the dust is lifted to high levels above 3 km where it can be incorporated into the strong mid latitude westerlies strong vertical motions of the atmosphere occur most frequently in the spring when the mongolian anticyclone begins to weaken and frontal depressions move across the deserts of northern china such frontal depressions were probably more frequent during the climatic optimum of the mid holocene and during previous interglacials changes in continental aridity have probably played a minor role in controlling the magnitude of the dust flux to the north pacific

a high resolution absolute dated late pleistocene monsoon record from hulu cave china oxygen isotope records of five stalagmites from hulu cave near nanjing bear a remarkable resemblance to oxygen isotope records from greenland ice cores suggesting that east asian monsoon intensity changed in concert with greenland temperature between 11 000 and 75 000 years before the present yr b p between 11 000 and 30 000 yr b p the timing of changes in the monsoon as established with 230th dates generally agrees with the timing of temperature changes from the greenland ice sheet project two gisp2 core which supports gisp2 s chronology in this interval our record links north atlantic climate with the meridional transport of heat and moisture from the warmest part of the ocean where the summer east asian monsoon originates

slip along the superstition hills fault associated with the 24 november 1987 superstition hills california earthquake surficial slip along the entire mapped length of the superstition hills fault in southern california occurred in association with the superstition hills earthquake m s 6 6 of 24 november 1987 we made repeated measurements of surface slip at 36 sites along the fault and occupied 64 sites at least once at our sites dextral slip was as high as 48 5 cm 1 day after the earthquake and 71 cm 2 months after the measurements show that slip during the period from hr to several hundred hr following the event is described by a simple power law of time extrapolation to t 1 min indicates that co seismic slippage ranged from 5 to 23 cm at 10 of our best recorded sites suggesting that finite co seismic slippage occurred along the length of the fault these extrapolations are supported by a measurement made at imler road 30 min after the shock measurements are complete through october 1988 at many sites the form of slip rate was decay changed from power law to a function of log time during the interval between 300 and 500 hr after the earthquake logarithmic slip rate decay in time was observed for a period of several yr after the parkfield borrego mountain and imperial valley earthquakes those measurements may have begun too late to resolve power law behavior at early times if current logarithmic behavior of the superstition hills fault persists right lateral slippage will approach 90 cm 10 yr after the rupture changes in the along fault displacement profile correlate well with geometric features including a fault bend and a major fault step moreover slip behavior appears to be correlated to the thickness of sedimentary cover along the fault also the northern half of the fault is bounded by a large block of continental crystalline basement the presence of this block may have contributed to the relatively uniform early slip behavior observed there

eureka peak fault afterslip following the 28 june 1992 landers earthquake abstract although surface ruptures of the principal landers faults apparently slipped co seismically surface slip on the 10 km long eureka peak fault has continued at a decreasing rate during the year following the mainshock three creepmeters installed on the fault as early as 4 days after the mainshock have recorded afterslip amplitudes of more than 8 cm on the northern half of the mapped fault the maximum observed slip 1 yr after the earthquake is 23 2 cm and an additional 1 to 3 cm of afterslip may occur on the fault in the next decade if the current rate of slip decrease remains steady should this occur it will bring surface slip amplitudes close to the 25 cm of slip inferred from geodetic data to have occurred at depth on the northern 4 km of the fault creepmeters on the fault record both episodic creep events and slow background slip but although changes in creep rate occur they do not correlate well with seismic moment release in volumes near the fault zone as is the case with many afterslip processes and other creeping faults in california the eureka peak fault cuts through sediments it is possible that such sedimentary layers and corresponding depths to which afterslip is occurring are relatively shallow or that the fault lacks a well developed gouge zone near sites where episodic creep is absent

asian aridity and the zonal westerlies late pleistocene and holocene record of eolian deposition in the northwest pacific ocean rea d k and leinen m 1988 asian aridity and the zonal westerlies late pleistocene and holocene record of eolian deposition in the northwest pacific ocean palaeogeogr palaeoclimatol palaeoecol 66 1 8 a 30 000 year record of eolian deposition in the northwestern pacific ocean provides a history of the aridity of the asian source region and information on the changing latitude and intensity of the zonal westerlies the position of the maximum in eolian flux to the deep sea remained unchanged at 38 to 40 n during this entire time period but the dust flux record of aridity is greatest 6000 years ago at the holocene climatic optimum eolian grainsize data indicate that the northern margin of the westerly jet stream retreated northward during the holocene to a poleward extreme at about 6000 years ago and then moved back toward the equator the change in wind intensity across this margin was continually reduced throughout the holocene these sorts of data enhance our understanding of the behavior of the atmosphere during times of climate change and can be used to test computer generated models of past climatic conditions

surface faulting along the superstition hills fault zone and nearby faults associated with the earthquakes of 24 november 1987 the m 6 2 elmore desert ranch earthquake of 24 november 1987 was associated spatially and probably temporally with left lateral surface rupture on many northeast trending faults in and near the superstition hills in western imperial valley three curving discontinuous principal zones of rupture among these breaks extended northeastward from near the superstition hills fault zone as far as 9 km the maximum observed surface slip 12 5 cm was on the northern of the three the elmore ranch fault at a point near the epicenter twelve hours after the elmore ranch earthquake the m 6 6 superstition hills earthquake occurred near the northwest end of the right lateral superstition hills fault zone surface rupture associated with the second event occurred along three strands of the zone here named north and south strands of the superstition hills fault and the wienert fault for 27 km southeastward from the epicenter in contrast to the left lateral faulting which remained unchanged throughout the period of investigation the right lateral movement on the superstition hills fault zone continued to increase with time a behavior that was similar to other recent historical surface ruptures on northwest trending faults in the imperial valley region we measured displacements over 339 days at as many as 296 sites along the superstition hills fault zone and repeated measurements at 49 sites provided sufficient data to fit with a simple power law data for each of the 49 sites were used to compute longitudinal displacement profiles for 1 day and to estimate the final displacement that measured slips will approach asymptotically several years after the earthquakes the maximum right lateral slip at 1 day was about 50 cm near the south central part of the north strand of superstition hills fault and the predicted maximum final displacement is probably about 112 cm at imler road near the center of the south strand of the superstition hills fault the overall distributions of right lateral displacement at 1 day and the estimated final slip are nearly symmetrical about the midpoint of the surface rupture the average estimated final right lateral slip for the superstition hills fault zone is about 54 cm the average left lateral slip for the conjugate faults trending northeastward is about 23 cm the southernmost ruptured member of the superstition hills fault zone newly named the wienert fault extends the known length of the zone by about 4 km the southern half of this fault south of new river expressed only vertical displacement on a sinuous trace the maximum vertical slip by the end of the observation period there was about 25 cm but its growth had not ceased photolineaments southeast of the end of new surface rupture suggest continuation of the superstition hills fault zone in farmland toward mexico

high resolution mapping of near field deformation with airborne earth observation data a comparison study we present an investigation into different approaches for high resolution mapping of near field surface displacement for strike slip earthquakes airborne laser scanning als and optical imagery are two common sources of earth observation data available to geoscientists for earthquake documentation and studies optical image correlation and point cloud differencing techniques are among the most widely used methods for retrieving displacement signals in the near field we compare the performances of these techniques for estimating near field deformation using pre and postevent high resolution als and airborne imagery of the august 24 2014 mw 6 0 napa california earthquake estimates of deformation agree with field observations within a decimeter at the expected accuracy level of the data we show that the correlation of intensity images from als data can unveil the near field deformation successfully and outperforms optical image correlation in vegetated areas as well as in the absence of geodetic markers man made structures furthermore we illustrate that the point clouds generated with structure from motion perform comparably to als point clouds for retrieving the displacement signal in unvegetated areas overall we conclude that als data are generally better than imagery for estimating near field deformation regardless of the estimation methodology and that the iterative closest point algorithm was more effective at recovering the displacement signal

magnetospheric disturbance induced equatorial plasma bubble development and dynamics a case study in brazilian sector 1 equatorial ionospheric plasma bubble irregularity development and dynamics during the major magnetospheric storm of 26 august 1998 are investigated using the data collected by a multistation and multi instrument diagnostic network operated at equatorial and low latitude sites in brazil and auroral electrojet activity au al imf and dst indices a magnetospheric disturbance onset in the morning of 26 august 1998 was initiated by a solar wind shock and associated imf bz polarity reversals and ssc that were soon followed by a succession of substorm like auroral electrojet ae intensifications and dst development an imf bz southward turning and associated ae intensifications in the brazilian dusk sector produced intense prompt penetration eastward electric field that caused large f region vertical drift and consequently the developments of intense postsunset equatorial anomaly and a series of intense plasma bubbles the latter event lasting the entire night as observed by digital ionosondes at sao luis 2 33 s 315 8 e dip angle 5 and fortaleza 3 9 s 321 55 w dip angle 9 and an all sky imager two scanning photometers and a digisonde at the low latitude site cachoeira paulista 22 6 s 315 e dip angle 28 a notable aspect of the dynamics of the bubbles was their initially very low eastward drift velocity which turned into steadily increasing westward velocity that lasted till early morning hours the results show for the first time a relationship between the zonal drift velocities of optically observed large scale bubbles tens to hundreds of kilometers and that of the smaller scale kilometer sizes structures as observed by a digital ionosonde the results point to the dominant role of a disturbance dynamo associated westward thermospheric wind to maintain the plasma irregularity drift increasingly westward going into postmidnight hours as an important finding the results further show that significant contribution to the westward plasma bubble irregularity drift normally attributed to disturbance dynamo effect could arise from prompt penetration disturbance zonal electric field in the course of a disturbance sequence lasting several hours such effect is attributed to hall electric field arising from the primary disturbance zonal electric field under enhanced nighttime ionospheric conductivities produced possibly by storm associated particle precipitation in the brazilian longitude sector in agreement with recent evidences abdu et al 1998b

land ocean linkages over orbital and millennial timescales recorded in late quaternary sediments of the japan sea late quaternary sediments of the japan sea are characterized by centimeter to meter scale alternations of dark and light layers which are synchronous basinwide high resolution analyses of the sediments from ocean drilling program site 797 reveal that deposition of the meter scale alternations reflect variations in paleoceanographic conditions which were closely associated with glacio eustatic sea level changes through the modulation of the volume and character of the influx to the sea through the tsushima strait the centimeter to decimeter scale alternations reflect millennial scale variations which are possibly associated with dansgaard oeschger d o cycles with each dark layer appearing to correspond to an interstadial this variability is attributed to the development of a humid climate in central to eastern asia and the consequent increase in discharge from the huanghe and changjiang rivers during interstadials this caused expansion of the east china sea coastal water ecscw which penetrated more strongly into the japan sea the increased influence of the lower salinity nutrient enriched ecscw reduced deep water ventilation and enhanced the surface productivity leading to the development of anoxic bottom waters and deposition of the dark layers thus the centimeter to decimeter scale alternations of the dark and light layers record wet and dry cycles in central to eastern asia possibly associated with d o cycles

grain size distribution and depositional processes of the mineral component of abyssal sediments lessons from the north pacific grain size analyses of the mineral component of abyssal pacific surface sediments show two distinctly different size distributions that can be associated with sediments that are dominantly eolian and dominantly hemipelagic respectively in the range of 1 to 30 m eolian grains show a distinct size mode at about 2 m 9 and little material coarser than about 16 m 6 hemipelagic grains are characterized by a much flatter size distribution that has a broad size mode near 2 m 9 and important amounts of material coarser than 16 m 6 this ability to distinguish between hemipelagic and eolian grains will obviate some long standing concerns in the interpretation of deep sea sediments examples of the utility of this technique are given for the north pacific and south atlantic

surface slip associated with the 2004 parkfield california earthquake measured on alinement arrays although still continuing surface slip from the 2004 parkfield earth quake as measured on alinement arrays appears to be approaching about 30 35 cm between parkfield and gold hill this includes slip along the main trace and the southwest fracture zone swfz slip here was higher in 1966 at about 40 cm the distribution of 2004 slip appears to have a shape similar to that of the 1966 event but final slip is expected to be lower in 2004 by about 3 15 cm even when continuing slip is accounted for proportionately this difference is most notable at the south end at highway 46 where the 1966 event slip was 13 cm compared to the 2004 slip of 4 cm continuous global positioning system and creepmeters suggest that significant surface coseismic slip apparently occurred mainly on the swfz and perhaps on middle mountain the latter possibly caused by shaking langbein et al 2005 creepmeters indicate only minor 0 2 cm surface coseismic slip occurred on the main trace between parkfield and gold hill we infer that 3 6 cm slip accumulated across our arrays in the first 24 hr at highway 46 slip appears complete whereas the remaining sites are expected to take 2 6 years to reach their background creep rates following the 1966 event afterslip at one site persisted as much as 5 10 years the much longer recurrence intervals between the past two parkfield earthquakes and the decreasing slip per event may suggest that larger slip deficits are now growing along the parkfield segment

quantitative estimates of asian dust input to the western philippine sea in the mid late quaternary and its potential significance for paleoenvironment we present a new high resolution multiproxy data set of sr nd isotopes rare earth element soluble iron and total organic carbon data from international marine global change study core md06 3047 located in the western philippine sea we integrate our new data with published clay mineralogy rare earth element chemistry thermocline depth and delta c 13 differences between benthic and planktonic foraminifera in order to quantitatively constrain asian dust input to the basin we explore the relationship between philippine sea and high latitude pacific eolian fluxes as well as its significance for marine productivity and atmospheric co2 during the mid late quaternary three different indices indicate that asian dust contributes between similar to 15 and similar to 50 to the detrital fraction of the sediments eolian dust flux in core md06 3047 is similar to that in the polar southern pacific sediment coherent changes for most dust flux maximum minimum indicate that dust generation in interhemispheric source areas might have a common response to climatic variation over the mid late quaternary furthermore we note relatively good coherence between asian dust input soluble iron concentration local marine productivity and even global atmospheric co2 concentration over the entire study interval this suggests that dust borne iron fertilization of marine phytoplankton might have been a periodic process operating at glacial interglacial time scales over the past 700 ka we suggest that strengthening of the biological pump in the philippine sea and elsewhere in the tropical western pacific during the mid late quaternary glacial periods may contribute to the lowering of atmospheric co2 concentrations during ice ages

quiet time equatorial f region vertical plasma drift model derived from rocsat 1 observations 1 we have used five years of measurements on board the rocsat 1 satellite to develop a detailed quiet time global empirical model for equatorial f region vertical plasma drifts this model describes the local time seasonal and longitudinal dependence of the vertical drifts for an altitude of 600 km under moderate and high solar flux conditions the model results are in excellent agreement with measurements from the jicamarca radar and also from other ground based and in situ probes we show that the longitudinal dependence of the daytime and nighttime vertical drifts is much stronger than reported earlier especially during december and june solstice the late night downward drift velocities are larger in the eastern than in the western hemisphere at all seasons the morning and afternoon december solstice drifts have significantly different longitudinal dependence and the daytime upward drifts have strong wave number four signatures during equinox and june solstice the largest evening upward drifts occur during equinox and december solstice near the american sector the longitudinal variations of the evening prereversal velocity peaks during december and june solstice are anti correlated which further indicates the importance of conductivity effects on the electrodynamics of the equatorial ionosphere

correlation between climate events in the north atlantic and china during the last glaciation episodes of massive iceberg release heinrich events 1 3 into the north atlantic ocean during the last glaciation were associated with recurring episodes of unusually cold north atlantic surface water bond cycles 4 and cold air temperatures over greenland dansgaard oeschger events 5 6 four of the youngest of these cold events have also been reported in climate records from sites outside the north atlantic region7 but until now the entire suite has been identified only in north atlantic marine sediments greenland ice core records and tentatively in french lake sediments8 here we examine grain size data from chinese loess and intercalated accretionary palaeosols of last glacial age for evidence of similar climate signals remote from the north atlantic region we see grain size maxima with ages that match those of the last six heinrich events which we interpret as an indication of the changing strength of the east asian winter monsoon which largely controls the transport and deposition of central asian aeolian dust thus it seems that these heinrich events have left their signature in the chinese loess record this is consistent with simulations of the glacial climate9 which imply that the climates of the north atlantic and china were linked by the effect of westerly winds

study of equinoctial asymmetry in the equatorial spread f esf irregularities over indian region using multi instrument observations in the descending phase of solar cycle 23 1 in this paper we present the results of a morphological study of equatorial spread f esf irregularities over indian region based mainly on observations of 1 amplitude scintillations on gps l band signal and rate of tec index roti obtained using a network of gps receivers and 2 amplitude scintillations on a vhf signal using spaced receivers at tirunelveli an equatorial station occurrence of both amplitude scintillations on the gps l1 signal and occurrence of significant roti recorded at several stations has been investigated the latitudinal extent of l band scintillations shows that their strength is weak over the dip equator but stronger over equatorial ionization anomaly eia region preferentially during vernal equinox we find an equinoctial asymmetry in both the occurrence of scintillations and roti wherein their occurrence is greater in the vernal equinox than in the autumn equinox attempts have been made to understand the asymmetry in latitudinal extent using maximum cross correlation ci of intensity fluctuations obtained from the vhf spaced receivers observations the observations suggest that occurrence of ci less than 0 5 is more in the vernal equinox than in the autumn equinox suggesting that the maximum height of the equatorial plasma bubbles epbs during vernal equinox may be higher than that during autumn equinox timed guvi retrieved peak electron density during the same period also indicates that background electron density is higher and more symmetric during vernal equinox than autumn equinox hence our results suggest that background electron density may be playing a vital role in creating the equinoctial asymmetry

age dating and the orbital theory of the ice ages development of a high resolution 0 to 300 000 year chronostratigraphy using the concept of orbital tuning a continuous high resolution deep sea chronostratigraphy has been developed spanning the last 300 000 yr the chronology is developed using a stacked oxygen isotope stratigraphy and four different orbital tuning approaches each of which is based upon a different assumption concerning the response of the orbital signal recorded in the data each approach yields a separate chronology the error measured by the standard deviation about the average of these four results which represents the best chronology has an average magnitude of only 2500 yr this small value indicates that the chronology produced is insensitive to the specific orbital tuning technique used excellent convergence between chronologies developed using each of five different paleoclimatological indicators from a single core is also obtained the resultant chronology is also insensitive to the specific indicator used the error associated with each tuning approach is estimated independently and propagated through to the average result the resulting error estimate is independent of that associated with the degree of convergence and has an average magnitude of 3500 yr in excellent agreement with the 2500 yr estimate transfer of the final chronology to the stacked record leads to an estimated error of 1500 yr thus the final chronology has an average error of 5000 yr