how do asperities fracture an experimental study of unbroken asperities abstract the fracture of a shear fault containing several unbroken asperities in a granitic porphyry is examined in detail via acoustic emission ae data collected by a high speed multi channel waveform recording system the experimental results reveal that a quasi static nucleation of the shear faulting corresponds to the fracture of coupled asperities on the fault plan aes caused by the fracture of individual asperities exhibit similar characteristics to the sequence for natural earthquakes including foreshock mainshock and aftershock events foreshocks initiated at the edge of the asperity occur with an event rate that increases according to a power law of the temporal distance to the mainshock and with a decreasing b value from 1 1 to 0 5 one or a few mainshocks then initiate at the edge of the asperity or the front of the foreshocks the aftershock period is characterized by a remarkable increase and subsequent gradual decrease in b value and a decreasing event rate obeying the modified omori law which has been well established for earthquakes the fracture of neighboring asperities is then initiated after the mainshock of a particular asperity presumably due to redistribution of the strain energy accumulated within an asperity which is released by the mainshock resulting in enhancement of the stress concentration around the nearest neighboring intact asperities the progressive fracturing of multiple coupled asperities during the nucleation of shear faulting results in short term precursory fluctuations in both b value and event rate which may prove useful information in the prediction of failure of the main fault plane of seismic earthquakes

change in the probability for earthquakes in southern california due to the landers magnitude 7 3 earthquake the landers earthquake in june 1992 redistributed stress in southern california shutting off the production of small earthquakes in some regions while increasing the seismicity in neighboring regions up to the present this earthquake also changed the ratio of small to large events in favor of more small earthquakes within about 100 kilometers of the epicenter this implies that the probabilistic estimate for future earthquakes in southern california changed because of the landers earthquake the location of the strongest increase in probability for large earthquakes in southern california was the volume that subsequently produced the largest slip in the magnitude 7 1 hector mine earthquake of october 1999

similarities among the plio pleistocene terrestrial aeolian dust deposits in the world and in hungary abstract the widely distributed plio pleistocene aeolian dust deposits are one of the most important terrestrial archives of past climate and environmental changes the alternation of loess and palaeosol layers is regarded as evidence of the cyclic nature of pleistocene climate changes the loess succession is underlain by aeolian red clay which has been formed under warm humid climates according to the studies of red clay loess palaeosol sequences from china central asia alaska south america and central europe the mineral dust deposition has shown similar patterns since the pliocene the typical loess of the last one million years reflects glacial interglacial conditions whereas the old loess palaeosol sequences could be the product of shorter arid humid climate cycles the similarity of the sedimentary structures could be caused by the similar global climate conditions controlled by orbital forcing the investigated sections from hungary central europe have been affected by local and regional geomorphological and climate factors even so they can be correlated fairly well with the major global climate changes the hungarian aeolian dust deposits consist of three main groups of sedimentary formations 1 pliocene early pleistocene aeolian red clays 2 the oldest loess palaeosol sequences formed from the almost continuous early pleistocene dustfall and 3 the typical glacial interglacial loess deposits of the last one million years without remarkable dust deposition in the warmer periods

the middle pleistocene handaxe site of shuangshu in the danjiangkou reservoir region central china abstract the presence of acheulean tool types e g handaxes and cleavers in east asia has recently attracted considerable attention they challenge the long lasting concept that the early palaeolithic in east asia is characterized only by mode 1 technology and they reflect the diversity and complexity of palaeolithic culture during hundreds of thousands of years in this paper we present a detailed technological analysis of the in situ artifact assemblage at the shuangshu site danjiangkou reservoir region central china as well as intra and inter regional comparisons of some characteristic traits used to test the difference between handaxes in the east and the west the results show that there are two reduction sequences taking place one is expressed in the predominant use of quartz in the production the small to medium sized artifacts which is an expedient technology that dominates the whole assemblage and the other is represented by the predominant use of quartz phyllite and trachyte in the production of large cutting tools lcts the latter displays the technical criteria characteristic of acheulean technology although its origins are much debated in addition the number of lcts and total artifacts is generally low for the size of the excavation area which probably is a result of relatively small population size and the high mobility of hominids the thickness of handaxes has been shown not to be a reliable variable in demonstrating the difference between the east and the west

the geologic record of climatic change this paper reviews the principal results from paleoclimate studies and includes background material slanted toward climate modelers the inferred temperature history of the last 4 6 billion years indicates major changes in the components of the earth s climate system a secular change in global insolation receipt is due to a 20 30 increase in solar luminosity since the formation of the earth a co2 h2o greenhouse effect may have offset the lower luminosity during early earth history inferred fluctuations of global temperature have occurred over a broad range of time scales on time scales of 106 108 years paleogeographic factors e g continental drift and sea level changes have contributed significantly to temperature changes associated with transitions between nonglacial and glacial states preliminary modeling efforts indicate that additional factors e g co2 changes in atmospheric circulation must also be considered in order to explain the origin of nonglacial climates the origin of polar ice caps may result from ocean circulation changes that were caused by plate tectonic processes fluctuations of ice volume on a time scale of 10 105 years correlate with insolation variations caused by orbital perturbations feedback interactions within the land sea air ice system e g ocean circulation changes and bedrock dynamics have been responsible for a significant modulation of the orbital signal ice ages may be due to orbitally induced temperature changes superimposed on a global cooling of terrestrial origin

seismicity changes associated with the 2000 earthquake swarm in the izu island region a statistical method taking into account the information of magnitude occurrence time and location of earthquakes was applied to the earthquake data 1977 2000 of the japan meteorological agency jma to investigate seismicity changes in the izu island region the analysis indicated that a quiescence anomaly started about 1 5 years before the occurrence of the largest swarm in the summer of 2000 in the izu island region close investigations of the possible artifacts due to the selection of model parameters and the improvement of the seismological network lead to the conclusion that the above quiescence anomaly is unlikely a man made change the further stochastic test using 1000 random earthquake catalogs supports the idea that the above anomaly is significant the spatial distribution of the seismic quiescence which is quantified by a newly developed q parameter revealed a clear anomalous region around the epicentral area of the above earthquake swarm the seismicity revealed by the normalized parameter tends to increase just before the swarm as the first test of the above statistical method for investigating seismicity changes of earthquake swarms this study indicates that the increased rtl parameter would be a new potentially useful index for the risk alarm of earthquake swarms

holocene environmental change inferred from the loess palaeosol sequences adjacent to the floodplain of the yellow river china abstract chinese loess deposits are generally considered to be the product of dust storms and dust falls from the central asia arid zones that were transported across china by the northwesterly continental monsoon in contrast the zhengzhou loess found southeast of the loess plateau adjacent to the floodplain of the yellow river records a different eolian regime and dust source the zhengzhou loess was investigated by field observations measurements of magnetic susceptibility particle size distribution loss on ignition caco3 and chemical contents both field observations and the laboratory results indicate that during the last glacial the zhengzhou loess was supplied by two different eolian regimes and dust sources one was from the fresh flood deposits of the yellow river driven by the northeast winds from the low lying floodplain and the other was from the dust storms and dust falls that traveled across the loess plateau driven by the northwesterly continental monsoon from the central asian arid lands the early holocene 11 500 8500 a bp was a transition during the change in eolian regime and dust source because of the weakened northwesterly monsoon along with the global climatic amelioration following the retreat of the northwesterly monsoon from the onset of the mid holocene climatic optimum at 8500 a bp dust supply from the drifting sand zone on the yellow river floodplain became dominant because of the intensified strength of the northeast winds from the bohai sea from 3100 a bp onwards climatic aridity and extensive human disturbance have resulted in intensive eolian processes causing the incursion of the drifting sand into the zhengzhou loess zone these results show that loess accumulation is more complex than traditionally assumed the origin of loess deposits elsewhere outside the loess plateau may be related to dust sources derived from alluvial sediments of major river systems

pleistocene deglaciation and the earth s rotation implications for mantle viscosity summary recent results from the analysis of postglacial rebound data suggest that the viscosity of the earth s mantle increases through the transition region models which fit both relative sea level and free air gravity data have viscosities which increase from a value near 1022 poise in the upper mantle beneath the lithosphere to a value of about 1023 poise in the lower mantle in this paper we analyse the effect of deglaciation upon the earth s rotation and thereby show that the observed secular trend polar wander evident in the ils ipms pole path and measurements of the non tidal acceleration of the length of day are both consistent with the viscosity profile deduced from postglacial rebound the two analyses are therefore mutually reinforcing

sedimentological study of the stratigraphy at the site of homo erectus yunxianensis in the upper hanjiang river valley china abstract geomorphological and sedimentological investigations were carried out in the upper hanjiang river valley the sediments in the profile at the site of homo erectus yunxianensis were sampled systematically magnetic susceptibility loss on ignition particle size distribution and geochemical elements were analyzed in the laboratory the results show that the medium sand and gravel beds in the lower part of the profile are fluvial deposits of the third terrace land of the hanjiang river the upper part is a blanket of aeolian loess and palaeosol deposited from dust storms and dust falls according to stratigraphical correlation and palaeomagnetic dating the carbonate nodules encasing the fossils of h erectus yunxianensis and other mammalian faunas were formed during 800 785 ka the palaeosol overlying on the fossil layer is defined as the s8 that was developed during the mis 19 and the aeolian loess below the fossil layer is defined as l9 that was deposited during mis 20 these loess and palaeosol are similar to those over the chinese loess plateau and correlatable with those in the luochuan loess profile they are very different from the fluvial deposits in the hanjiang river valley these indicate that h erectus yunxianensis lived at a climatic transition from glacial to interglacial these results are very important in understanding the environment of h erectus yunxianensis in the upper hanjiang river valley

early human settlements in the southern qinling mountains central china abstract china is a key area of early human settlement in east asia with numerous paleolithic localities indicating an early pleistocene presence of hominins in northern and southern china considerable research has been devoted to determining possible migration routes for hominins linking the two areas in this paper we report the discovery of several loess covered paleolithic sites in the hanzhong and ankang basins along the hanjiang river in the southern piedmont of the qinling mountains qlm in central china a chronology is developed for these sections using a combination of detailed optically stimulated luminescence dating magnetostratigraphic analyses and pedostratigraphic correlation with the well dated loess paleosol sequence of the central chinese loess plateau the results indicate that the age of the oldest lithic assemblage at the longgangsi locality 3 paleolithic site in hanzhong basin is 1 20 ma thus making this locality as one of the oldest sites in central china our work also indicates that hominins occupied the hanjiang valley at several times 1 2 0 9 0 6 and 0 1 ma we propose that the hanjiang river valley was a probable hominin routeway through the qlm because many sites corresponding to these different phases were also discovered to the north of the qlm future study on the hanjiang river valley is important for verifying the hypothesis of an early human migration route between southern and northern china

pedostratigraphy of aeolian deposition near the yunxian man site on the hanjiang river terraces yunxian basin central china abstract since 2010 we have found stone artifacts at the houfang and dishuiyan loess sections on the second terrace of the hanjiang river and the wolonggang thick natural loess section on the fifth terrace of the same river near the xuetangliangzi site we dated dishuiyan and houfang loess sections by optically stimulated luminescence osl and thermally transferred osl tt osl methods respectively dating results showed that the loess paleosol deposited on the second hanjiang river terrace as l1 s1 l2 and s2 in sequence we dated the wolonggang loess section by high resolution paleomagnetostratigraphic analyses the jaramillo subchron was found at this section correlating with the central loess plateau we recognized the continuous loess paleosol sequence from l9 to l15 investigations showed that loess was continuously deposited on the terraces of the hanjiang river at yunxian basin since at least 1200 ka

has climate changed the earth s tilt have the ice ages secularly altered the obliquity axial tilt of the earth over geologic time the waxing and waning of ice caps in response to obliquity oscillations plus mantle adjustment to the weight of the caps alter the earth s dynamical flattening this affects the lunar and solar torques on the earth so as to secularly change the earth s axial tilt this mechanism is dubbed climate friction since analogous to tidal friction it arises from lags in the earth s response to cyclic external forcing but the existence of two processes ice cap waxing and waning and mantle viscous flow can lead to either an increase or decrease in the obliquity evidence indicates that the growth and decay of the ice caps greatly lag the orbital forcing this causes the axial tilt to increase with time but the ice cap effects are partly canceled by viscous compensation in the mantle low mantle viscosities about 1021 pa s lead to rapid compensation and have only a slight effect on obliquity high viscosities about 1022 pa s slow the compensation enough so that there could be significant secular change in the obliquity over geologic time perhaps explaining all of the present tilt of 23 5 however in addition to the current uncertainty as to the effective viscosity of the mantle knowledge of past ice ages is incomplete so that the amount of obliquity increase presently remains unknown

holocene paleofloods related to climatic events in the upper reaches of the hanjiang river valley middle yangtze river basin china abstract holocene slackwater deposits along the river channels were used to study the magnitude and frequency of the paleofloods that occurred prior to gaged and historical data sets all over the world paleoflood hydrological investigations were carried out in the upper reaches of the hanjiang river china four bedsets of paleoflood slackwater deposits were found interbedded in the holocene loess soil sequence within the cliff riverbanks they were studied by field observations and laboratory analysis including magnetic susceptibility particle size distribution and optically stimulated luminescence osl dating these provide a complete catalog of holocene flood events at a watershed scale that is very important in understanding the regional hydrological response to monsoonal climatic change four episodes of holocene overbank flooding have been recorded over the basin these hydroclimatic events were dated to 8500 8400 4200 4000 3200 2800 and 1800 1700 ybp by using the osl method in combination with pedostratigraphic correlations with the previously studied holocene pedostratigraphy in the hanjiang river basin the peak discharges of these flood episodes vary in a range from 26 610 to 47 900 m 3 s 1 as estimated by using the slope area method of streamflow measurement these flood events are therefore considered a regional expression of known climatic events and demonstrate holocene climatic instability the study provides a solid reference that magnitudes and recurrence frequencies of floods are highly sensitive to climate change in the monsoonal zone in other parts of the world

loading rate impact on fracturing pattern lessons from hydrocarbon recovery lacq gas field france using scaling parameters of induced seismicity in size and space domains seismic b value and spatial correlation dimension d respectively we analyze the fracturing pattern of the gas reservoir of lacq in correlation with the production rate on the basis of previous observations and a previous model segall et al 1994 we assume that the cause of induced seismicity is a poroelastic stressing such that the production rate can be viewed as a stress rate for the rocks adjacent to the reservoir during the 20 year study period the production rate has decreased dramatically leading to a change of poroelastic stress rate from 4 5 10 3 to 1 5 10 3 mpa yr accordingly we observe a significant decrease in the size of activated fractures and a reduction of the spatial clustering of fracturing both arguing for a stress rate impact on the fracturing pattern in the gas field we interpret these changes in terms of a change in the deformation mode of stressed rocks from a more brittle to a more ductile behavior as the stress rate was decreased this hypothesis is supported by independent evidence from a number of experimental numerical and field studies the loading rate thus appears as a possible candidate to drive changes of b and d in time and space the apparent sensitivity of the earth s crust fracturing pattern to loading rate variations of much lower frequency than the tidal variations suggests that the earth s crust deformation mode itself be frequency dependent also our observations may have strong implications in contexts where the loading rate is induced by human intervention e g hydrocarbon recovery mines suggesting the possibility of adjusting the loading rate so as to shape the fracturing pattern locally according to human needs

3 d spatial variation of b values of magnitude frequency distribution beneath the kanto district japan summary a method is developed for estimation and interpolation of 6 values in space a 3 d spline function is considered for the logarithm of the 6 value at each location in the space since many parameters for the spline coefficients are required to obtain a sensible estimate of the spatial variation of 6 values we consider the penalized log likelihood with the standard roughness penalties for the spline function further the error bands of the b value estimation at each location can be calculated using the current method the spatial distribution of 6 values beneath the kanto district down to the depth of 100km is determined based on hypocentral data of microearthquakes from the kanto tokai observational network of the national research center for disaster prevention the stability of the estimated pattern is checked by comparing with the results using alternative cut off magnitudes this is further ensured by comparison with the result obtained by an alternative model using equally divided blocks on the whole the vertical change in 6 value is greater than the horizontal one it is high in the crust of the eurasian plate especially above the upper boundary of the subducting pacific plate and in the northwest part or the volcanic area in the kanto district a steep decrease of the 6 values is seen to take place in perpendicular direction to the subducting pacific plate boundary also a similar change is seen in the boundary between the eurasian and phillippine sea plates especially beneath the southern part of the kanto plain the 6 value is low in the upper boundary of the subducting plates but high in the lower plane of the double seismic zone in the pacific plate it appears that even within a narrow area of aftershocks the 6 value can change significantly it is also found that the variation of the 6 value estimate is in good agreement with the structure of seismic wave fractional velocity perturbations the regions of high and low 6 values correspond respectively to the lower and higher parts of the p wave velocity the similar relationship is seen with the spatial structure of the seismic wave attenuation

search for reliable precursors a case study of the seismic quiescence of the 2000 western tottori prefecture earthquake 1 how to search for reliable precursors is one of the key problems of the study on earthquake forecast in this paper a method is presented to judge whether or not a precursor is reliable before a potential anomaly can be nominated as a reliable precursor it should pass or be proved by the following tests or analyses whether or not it is an artificial anomaly whether or not it correlates with an investigated event whether or not it is a random anomaly as a case study i have investigated the reliability of seismic quiescence for an m 7 3 earthquake which occurred in the western region of tottori prefecture japan on 6 october 2000 the earthquake data 1975 2000 of the japan meteorological agency jma were used in this study after analyzing the completeness of the catalog and removing aftershocks a statistical method which is called the rtl region time length algorithm and takes into account the information of magnitude occurrence time and location of earthquakes was applied to the above preprocessed earthquake data a clear seismic quiescence anomaly was detected before the 2000 western tottori prefecture earthquake close investigation indicated that the above anomaly is not due to artifacts of the selections of model parameters after quantifying the anomaly and making statistical analysis over the whole investigated spatiotemporal domain reasonable correlation between the above anomaly and the main shock in 2000 was recognized the stochastic test using synthetic randomized catalogs showed the above anomaly is unlikely due to chance thus the above seismic quiescence anomaly before the 2000 main shock should be a significant and reliable precursor and the research method revealed in this study can enhance the reliability of precursors

two current seismic quiescences within 40 km of tokyo summary two highly significant seismic quiescence anomalies that started in 1993 0 exist currently within about 40 km of tokyo they are located in central saitama province at 35 99 n 139 56 e and in tokyo bay south of funabashi at 35 59 n l39 94 e the radii of the anomalous volumes are approximately 15 km centred at about 25 and 20 km depth respectively the seismicity rate during the quiescence was less than 10 per cent background rate in both cases the significance of these quiescences measured by the standard deviate z test comparing the rate of the last three years to the backgound rate is higher than for any other rate changes present in the catalogue zmax 7 5 and 7 2 respectively however episodes of highly significant quiescences which could have been interpreted as precursors but were not followed by main shocks also exist in the data set a third seismic quiescence was found to be in progress since 1993 3 0 5 in nw saitama province at 36 18 n 139 22 e it has a radius of 14 km and is less significant than the other two anomalies zmax 6 8 in a polygon that covers the areas of all three quiescences defined above the seismicity rate since 1994 is only 30 per cent of the previous background rate i e 100 earthquakes that would normally have occurred did not this analysis is based on the earthquake catalogue of the national institute for earth science and disaster prevention for the years 1980 1996 2 and mmin 1 0 as well as for the years 1986 2 1996 2 with mmin 0 1 the anomalies are equally clear in the clustered and in the full catalogues to avoid contamination by explosions only nighttime data 19 00 to 7 00 hours local time were used the frequency magnitude distributions in the quiescent volumes at central saitama nw saitama and funabashi have b values of 1 3 1 5 and 1 1 respectively based on the hypothesis that crustal volumes with high b values may not be capable of m6 earthquakes these three quiescent volumes may be ruled out as source volumes for main shocks of these magnitudes using lilt seismic quiescence hypothesis alone it is a reasonable interpretation to suggest that m 6 5 0 5 earthquakes are expected to terminate each of the three quiescences within 1 year 1 year from now with a 50 per cent probability each the interpretation that all three quiet volumes could rupture together in a large earthquake seems less likely however based on the information that the quiescences are located in volumes with b values above the average b 0 8 it can be argued that the three current quiescences are false alarms the fact that these two lines of evidence allow opposing interpretations in these cases shows that neither hypothesis is sufficiently tested thus the quiescence hypothesis is not advanced enough for issuing earthquake predictions nevertheless it is important that scientific tests of prediction scenarios are formulated in real time so we can learn how to modify our hypotheses to make them useful for prediction in the future

mean magnitude variations of earthquakes as a function of depth different crustal stress distribution depending on tectonic setting 1 the mean magnitude of earthquakes in the gulf of corinth is found to increase strongly with depth b value decreases whereas the dip of fault planes decreases the b value difference of 0 25 between shallow and deep earthquake distributions is based on about 7 000 events and therefore is statistically highly significant the same is true in california but opposite patterns are observed in southern iceland and in western nagano japan because large mean magnitudes low b values are indicative of relatively high stress levels we propose that in the detachment layer at about 9 2 km depth earthquakes are generated at higher stresses than in the shallower parts of the crust the correlation of low b values with low faulting dips can be taken as line of evidence that low b values map high stress regimes

ice 3g a new global model of late pleistocene deglaciation based upon geophysical predictions of post glacial relative sea level change a new high resolution global model of late pleistocene deglaciation is inferred on the basis of geophysical predictions of postglacial relative sea level variations in which the ice ocean solid earth interaction is treated in a gravitationally self consistent fashion for the purpose of these analyses the radial viscoelastic structure of the planet is assumed known on the basis of previously published sensitivity tests on solutions of the forward problem only radiocarbon controlled relative sea level histories from sites that were actually ice covered with one or two additions are employed to constrain the model leaving relative sea level rsl data from sites that were not ice covered to be employed to confirm its consistency results for these confirmatory analyses are reported elsewhere here the new deglaciation model referred to as ice 3g is compared to previous models derived by several independent means and tested against a number of additional observations other than sea level histories including geologically controlled retreat isochrones oxygen isotope data from deep sea sedimentary cores and coral terrace elevations the latter two observations strongly constrain the net sea level rise that has occurred since the onset of deglaciation and therefore the mass of ice that melted during the last glacial interglacial transition

mars secular obliquity change due to the seasonal polar caps there is a weak positive feedback mechanism between the astronomy and meteorology of mars the mechanism is this the seasonal waxing and waning polar caps cause small changes in mars dynamical flattening because the changes in flattening are out of phase with the sun there is a net annual solar torque on the planet which increases the angle between the equatorial and orbital planes on the basis of viking observations of the present climate and simple atmospheric models of past climates these seasonal shifts of mass between the atmosphere and polar caps are capable of secularly increasing mars obliquity by about 1 or 2 since the origin of the solar system thus the climate driven largely by the axial tilt reacts back on the planet and slightly enhances the seasons on mars as time progresses more sophisticated models will probably not change this result much therefore this mechanism probably produced only minor changes in mars climate it causes negligible changes in the axial tilt and climate of the earth

second order moment of central california seismicity 1969 1982 the second order moment cross correlation function of earthquakes in the u s geological survey central california catalog between 1969 and 1982 was calculated with respect to a magnitude threshold m 4 0 over interevent distances up to 80 km and interevent times up to 320 days the statistical procedure results in a representation of the spatial temporal structure of the catalog associated with m 4 0 earthquakes and is capable of revealing patterns too weak to be detected in the space time distribution of seismicity for individual earthquake sequences a method is introduced for identifying aftershocks based on a physical two parameter model of the earthquake interaction process the results show that the aftershock process dominates the second order moment and may even obscure the statistical expression of a precursory process a concentration of foreshocks within 15 km and 3 days of m 4 0 main shocks exhibits an apparent migration toward the main shock loci with velocity 2 6 5 3 km d this concentration may be related to an observed tendency for m 4 0 events to cluster auto correlate over this interevent range with the identified aftershocks removed the residual catalog is poissonion in space and time when two m 4 0 earthquakes occur within 80 km and 40 days of each other aftershock productivity appears to be relatively enhanced in the earlier sequence this suggests that aftershock populations are not solely dependent on their main shocks and that unusually productive aftershock sequences may be predictors of future moderate earthquakes

the major asperities of the 1999 mw 7 4 izmit earthquake defined by the microseismicity of the two decades before it

north atlantic millennial scale climate variability 910 to 790 ka and the role of the equatorial insolation forcing abstract the mid pleistocene transition mpt was the time when quasi periodic 100 kyr high amplitude glacial variability developed in the absence of any significant change in the character of orbital forcing leading to the establishment of the characteristic pattern of late pleistocene climate variability it has long been known that the interval around 900 ka stands out as a critical point of the mpt when major glaciations started occurring most notably in the northern hemisphere here we examine the record of climatic conditions during this significant interval using high resolution stable isotope records from benthic and planktonic foraminifera from a sediment core in the north atlantic integrated ocean drilling program expedition 306 site u1313 we have considered the time interval from late in marine isotope stage mis 23 to mis 20 910 to 790 ka our data indicate that interglacial mis 21 was a climatically unstable period and was broken into four interstadial periods which have been identified and correlated across the north atlantic region these extra peaks tend to contradict previous studies that interpreted the mis 21 variability as consisting essentially of a linear response to cyclical changes in orbital parameters cooling events in the surface record during mis 21 were associated with low benthic carbon isotope excursions suggesting a coupling between surface temperature changes and the strength of the atlantic meridional overturning circulation time series analysis performed on the whole interval indicates that benthic and planktonic oxygen isotopes have significant concentrations of spectral power centered on periods of 10 7 kyr and 6 kyr which is in agreement with the second and forth harmonic of precession the excellent correspondence between the foraminifera 18 o records and insolation variations at the equator in march and september suggests that a mechanism related to low latitude precession variations advected to the high latitudes by tropical convective processes might have generated such a response this scenario accounts for the presence of oscillations at frequencies equal to precession harmonics at site u1313 as well as the occurrence of higher amplitude oscillations between the mis22 21 transition and most of mis 21 times of enhanced insolation variability

variable slip rupture model of the great 1923 kanto japan earthquake geodetic and body waveform analysis abstract the available geodetic and teleseismic data sets for the 1923 kanto earthquake m s 8 1 have been combined into a joint inversion for both temporal and spatial slip variations we assumed an initial faulting model to be consistent with the geometry determined by kanamori 1971 on the basis of first motion data aftershock area and the amplitude of surface waves at teleseismic distances and also to enclose the slipped area estimated by matsu9ura et al 1980 from the geodetic data employed here we then inverted for a heterogeneous distribution of slip of the fault plane the leveling routes and triangulation stations used consisting of 225 bench marks and 31 triangulation points are from matsu9ura et al 1980 we chose to first determine the overall static slip distribution by inverting the geodetic data alone we then proceeded to gradually increase the importance of the teleseismic data always requiring a good fit to the geodetic leveling and horizontal displacements in this way we could provide a constraint on the overall static slip characteristics from the geodetic data and provide stability for the teleseismic inversion yet determine the degree of slip heterogeneity and time history most suitable for matching the waveform data and for simulating strong ground motions our analysis yields a seismic moment of 7 to 8 10 27 dyne cm m w 7 8 to 7 9 with a maximum slip of approximately 8 m the most concentrated slip is in the shallow central and western portion of the fault the location of the concentrated slip on the fault plane has important consequences for the amplitude duration and frequency content of the resulting ground motions as documented by takeo and kanamori 1993

most likely locations of large earthquakes in the kanto and tokai areas japan based on the local recurrence times abstract we examined the hypothesis that minima in local recurrence time tl or equivalently maxima in local probability pl may map asperities in the kanto and tokai areas of japan where the earthquake catalog of the national research institute for earth science and disaster prevention nied is complete at the m 1 5 m1 5 level we mapped tl pl based on the a and b values of the nearest earthquakes within 20 km of every node of a grid spaced 0 01 for m7 target events only earthquakes within the top 33 km were used the b values increase strongly with depth in several areas therefore some of the tl pl anomalies are not revealed if data from the entire crustal seismogenic zone are mixed thus we mapped tl pl separately for the top 15 km and the rest of the depth range as well as for the entire seismogenic crust the resulting tl and pl maps show that approximately 12 of the total area shows anomalously short recurrence times out of six shallow target events with m 6 5 and which occurred since 1890 five are located within the anomalous areas with tl

on the structure and origin of major glaciation cycles 2 the 100 000 year cycle climate over the past million years has been dominated by glaciation cycles with periods near 23 000 41 000 and 100 000 years in a linear version of the milankovitch theory the two shorter cycles can be explained as responses to insolation cycles driven by precession and obliquity but the 100 000 year radiation cycle arising from eccentricity variation is much too small in amplitude and too late in phase to produce the corresponding climate cycle by direct forcing we present phase observations showing that the geographic progression of local responses over the 100 000 year cycle is similar to the progression in the other two cycles implying that a similar set of internal climatic mechanisms operates in all three but the phase sequence in the 100 000 year cycle requires a source of climatic inertia having a time constant similar to 15 000 years much larger than the other cycles similar to 5 000 years our conceptual model identifies massive northern hemisphere ice sheets as this larger inertial source when these ice sheets forced by precession and obliquity exceed a critical size they cease responding as linear milankovitch slaves and drive atmospheric and oceanic responses that mimic the externally forced responses in our model the coupled system acts as a nonlinear amplifier that is particularly sensitive to eccentricity driven modulations in the 23 000 year sea level cycle during an interval when sea level is forced upward from a major low stand by a milankovitch response acting either alone or in combination with an internally driven higher frequency process ice sheets grounded on continental shelves become unstable mass wasting accelerates and the resulting deglaciation sets the phase of one wave in the train of 100 000 year oscillations whether a glacier or ice sheet influences the climate depends very much on the scale the interesting aspect is that an effect on the local climate can still make an ice mass grow larger and larger thereby gradually increasing its radius of influence

revisiting the stratigraphic position of the matuyama brunhes geomagnetic polarity boundary in chinese loess article i nfo it is commonly accepted that the climate records in chinese loess can be correlated well with that in marine sediments however discrepancies for the stratigraphic position of paleomagnetic polarity reversal boundary seriously restrict an accurate teleconnection between these two archives for example the exact stratigraphic position of the whole matuyama brunhes mb transitional polarity zone remains uncertain in chinese loess in this study an accurate transitional zone of the mb reversal from the mangshan profile southeast margin of the chinese loess plateau clp was statistically determined using multiple subsets of parallel samples by integrating results from the central clp the whole mb transitional zone is consistently located across the pedostratigraphic and climatostratigraphic transitional zones between s8 and l8 over a wide region of the clp this conclusion further supports that the paleosol unit s8 should be teleconnected to the marine oxygen isotope stage 19 rather than 21 and thus unambiguously supplies an accurate age control in constructing a new loess time scale

a magnetostratigraphic reassessment of correlation between chinese loess and marine oxygen isotope records over the last 1 1 ma abstract we present a magnetic polarity based paleoclimatic correlation between chinese loess and marine oxygen isotope stage mis records over the last 1 1 ma this revised land ocean comparison indicates that inconsistent occurrence of the matuyama brunhes boundary which lies in mis 19 in marine sediments and occurs either at the base lower part of loess l8 or the uppermost part of soil s8 in chinese loess is due to regional and or local climate variability across the chinese loess plateau and does not need to be attributed to lock in effects of loess remanence acquisition associated with pedogenesis this result implies that the geomagnetic polarity boundaries in chinese loess in general are reliable chronostratigraphic time markers therefore astronomically tuned timescales for chinese loess that presume a downward shift of polarity boundaries due to a time lag in remanence acquisition may have overestimated ages of certain loess paleosol units

mars change in axial tilt due to climate the average tilt of mars equator with respect to its orbital plane may have increased significantly over the age of the solar system obliquity oscillations might have induced changes in the climate which altered the mass distribution and hence the solar torque on the planet viscous deformation attributable to loading by the large polar caps expected at low obliquity may have induced secular changes in the axial tilt earth like effective viscosities can account for virtually the entire present obliquity of 24 4 degrees thus the present average tilt of mars may not be primordial

carbon cycle instability as a cause of the late pleistocene ice age oscillations modeling the asymmetric response a dynamical model of the pleistocene ice ages incorporating many of the qualitative ideas advanced recently regarding the possible role of ocean circulation chemistry temperature and productivity in regulating long term atmospheric carbon dioxide variations has been constructed this model involves one additional term and free parameter beyond that included in a previous model b saltzman and a sutera 1987 providing the capacity for an asymmetic for example saw toothed response it is shown that many of the main features exhibited by the 18o derived ice record and the vostok core 13c derived carbon dioxide record in the late pleistocene can be deduced as a free oscillatory solution of the model including a rapid deglaciation during which a spike of high co2 and a rapid surge in north atlantic deep water production occurs it is expected that the addition of reasonable levels of external for example earth orbital forcing will enable the model to account for a significant amount of the remaining observed variance and covariance of the slow response climatic variables over the full pleistocene including the mid pleistocene transition

obliquity oblateness feedback are climatically sensitive values of obliquity dynamically unstable a new model is presented for feedback between rotational and climatic variations operative on time scales of 104 107 years due to the combined effect of planetary perturbations to the earth s orbit plane and luni solar torques on the oblate figure of the earth the obliquity varies by 1 on a 4 104 year time scale associated changes in the seasonal and latitudinal pattern of incident solar radiation cause major glaciations mass transport from the oceans to the polar ice sheets during these glaciations can change the gravitational oblateness of the earth by amounts approaching 1 as the rate of spin axis precession is directly proportional to the oblateness the climatically forced mass transport can by dynamically significant a simple parameterization of us coupled orbital rotational climatic system suggests that there is a strong tendency for the system to evolve away from climatically sensitive values of the obliquity this may explain the mid pleistocene transition from an obliquity dominated regime to the present regime in which most climatic variability is concentrated at longer 105 year periods

the nature origin and accumulation of loess abstract loess can be defined simply as a terrestrial clastic sediment composed predominantly of silt size particles which is formed essentially by the accumulation of wind blown dust there are three fundamental requirements for its formation 1 a sustained source of dust 2 adequate wind energy to transport the dust and 3 a suitable accumulation site most loess has been modified to some degree by local reworking bioturbation and syn depositional weathering but a process of loessification is not necessary for a dust deposit to qualify as loess the terms primary loess and secondary loess have previously been used to described wind deposited loess and redeposited loess respectively but it is more accurate to describe material reworked and redeposited by non aeolian processes as loess derived colluvium or loess derived alluvium during the quaternary loess formed in three main situations 1 mid continental shield areas beyond the limits of ice sheets periglacial loess 2 on the margins of high mountain ranges perimontane loess and 3 on the semi arid margins of some lowland deserts peridesert loess peridesert loess is relatively poorly developed partly due to the limited efficiency of silt generating mechanisms in low land deserts compared with glaciation but also important is the tendency in arid areas for dust to be dispersed over a wide area and to be rapidly reworked after deposition particularly in areas which experience frequent climatic changes the remarkably thick loess of china and central asia results from an unusual combination of conditions which has persisted for much of the last 2 3 million years namely rapid uplift of the tibetan plateau and surrounding mountain ranges high rates of sediment production and supply to adjacent basins a strong northwesterly and westerly wind regime and the existence of effective dust traps downwind of the source regions

multiphase timing of hominin occupations and the paleoenvironment in luonan basin central china thousands of paleolithic artifacts have been recovered from paleolithic sites in the luonan basin in the upper south luohe river of central china their discovery suggests that the basin was an important area for hominin settlement during the pleistocene however the initial timing of this occupation and the environmental conditions for this period are still largely unknown in addition the sediments are not well dated and most of the artifacts lie on the surface in an attempt to resolve these issues a new systemic paleomagnetic analysis was carried out on the loess deposits that contain in situ stone tools our detailed loess paleosol analyses of the stratigraphy of different sites in the basin and chinese loess plateau shows the accumulation of the loess since at least 1 1 million years ma ago moreover recently discovered in situ cores flakes and retouched stone tools in these deposits show that hominins used this region repeatedly from 0 8 0 7 ma to 0 4 0 3 and 0 2 0 1 ma pedostratigraphic analyses magnetic susceptibility and carbon isotope analyses also indicate that these hominins lived in a subtropical to warm temperate climate with broad needle leaf forest vegetation mixed with grasses c 2011 university of washington published by elsevier inc all rights reserved

correlating variations of b values and crustal deformations during the 1990s may have pinpointed the rupture initiation of the mw 7 4 izmit earthquake of 1999 august 17 summary the b value increases from 1 1 along straight segments to 1 7 along a releasing bend of the north anatolian fault system between 30 1 e and 30 8 e the tensional nature of the bend is corroborated by extension rates of 0 3 strain yr 1 as obtained from global positioning system gps data fault plane solutions in this area change from abundant right lateral strike slip to oblique slip with normal components in the central part of the bend compatible with the formation of a pull apart basin we suggest that this crustal volume is highly fractured corresponding to a short mean crack length due to the superposition of horizontal and normal faulting as a consequence of low normal stress on the existing cracks frictional sliding is assumed to be the predominant mechanism for the generation of seismic events resulting in high b values the lowest b values b 0 8 in the area investigated are found at the junction between the fault bend and the adjoining segment which runs through the epicentre of the 1999 izmit earthquake at the junction a localized stress concentration is expected from numerical models of seismicity along geometrical barriers thus the site of lowest b has been considered to be the most likely place for a major earthquake a conclusion that is confirmed by the izmit earthquake with epicentre located about 13 km from the anticipated site in early 1992 the spatially averaged b value started to increase along the central and northwestern parts of the fault bend and there was a corresponding period of intensified horizontal extension since no large earthquake was recorded in 1992 it is assumed that the anomalous extension and the associated change in stress have been caused by aseismic fault creep in view of the available seismotectonic information surface displacements due to a slow dislocation at depth were calculated the gps data are reasonably explained by a source of normal fault type at a depth of 10 km and equivalent magnitude mw 5 9 stress changes at seismogenic depths are calculated under the assumption that an increase in b is most likely to be observed along those segments where both deviatoric and mean stress are reduced while the coulomb stress change is positive that is the fault is brought closer to failure for right lateral strike slip the stress condition is fulfilled at the sites of the largest b value increase the surface rupture of the izmit earthquake is associated with known fault traces only in the west and in the east of the study area along the fault bend it detaches itself from mapped fault traces and runs through the regions of positive coulomb stress change caused by the inferred 1992 slow event maximum surface slip 5 m is observed in the immediate vicinity of sites of maximum coulomb stress change 3 bar indicating that the 1992 event could have partially unclamped the rupture plane of the subsequent izmit earthquake we propose that the strong differences in b observed along the complex fault bend can be used to characterize different states of tectonic deformation in space and time

source and path of magma for volcanoes in the subduction zone of northeastern japan the assumption that the source of magma for volcanoes in subduction zones is located in the mantle immediately above the top of the subducting slab at approximately 100 km depth and straight beneath the volcanoes is incorrect in northeastern japan the combination of evidence from velocity tomography in the mantle wedge above the slab and mapping of earthquake size distribution within it strongly points to a source of fluids at the top of the slab at 140 to 150 km depth from where material rises along an inclined path to the volcanoes

mapping the frequency magnitude distribution in asperities an improved technique to calculate recurrence times we hypothesize that highly stressed asperities may be defined by mapping anomalously low b values along the san andreas fault near parkfield the asperity under middle mountain with its b 0 46 can be distinguished from all other parts of the fault surface likewise along the calaveras fault the northern asperity of the morgan hill 1984 m6 2 rupture can be identified by its low b of 0 5 as a high stress patch along the fault we add further evidence to the observations that the b value of the frequency magnitude relationship of earthquakes is inversely proportional to stress by showing that it decreases with depth in the parkfield segment of the san andreas and along the calaveras fault in both of these areas b values above and below 5 km depth are 1 2 and 0 8 respectively we propose that probabilistic recurrence times tr based on the seismicity parameters a and b should be calculated from their values within asperities only instead of from the values of the entire rupture area of the maximum expected earthquake the strong patches on faults control the time of rupture because they are capable of accumulating larger stresses than the rest of the fault zone which slips along passively when an asperity breaks therefore no information on tr is contained in the passive fault segments only in the asperities at parkfield the probabilistic estimates of tr derived from the data in the whole rupture and in the asperity only are 72 18 24 and 23 12 18 years respectively compared to the historically observed repeat time of 22 years at morgan hill the tr estimates are 122 46 76 and 78 47 110 years respectively compared to the observed repeat time of 72 years

a multi index analysis of the extraordinary paleoflood events recorded by slackwater deposits in the yunxi reach of the upper hanjiang river china abstract paleoflood investigations were carried out on the first river terrace along the upper reaches of the hanjiang river a major tributary of the yangtze river in china several bedsets of paleoflood slackwater deposit swd were found within the eolian loess soil profiles in the yunxi reach of the upper hanjiang river the pedo stratigraphic sequences were studied using a multi index approach including magnetic susceptibility particle size distribution loess on ignition chemical elements and micro morphology both the sedimentary criteria and the analytical results show that the paleoflood swds were clearly differentiated from eolian loess and paleosol in the same profile by their abrupt vertical change in the pedo stratigraphy the studies indicate that these paleoflood swds were deposited from the suspended sediment load in floodwaters and hardly affected by the subsequent weathering and pedogenesis we have identified four episodes of extraordinary paleoflood events occurred on the hanjiang river during the last 18 000 years the paleoflood events were dated to 12 500 12 000 a b p 7500 7000 a b p 3100 3000 a b p and 1000 900 a b p respectively by using the osl method in combination with archeological dating of anthropogenic remnants and with pedo stratigraphic correlation with well dated profiles in the upper hanjiang river the flooding events are considered to respond to climate variability in relation with the monsoonal shift and coincide with the global climatic events recorded by other climatic proxies in different regions of the world this study is of great significance for understanding the interactions between hydro climatic systems and global change in sub humid regions

study on coseismic and postseismic crustal movements associated with the 1923 kanto earthquake abstract the kanto earthquake of 1923 m 7 9 occurred in the southern part of the kanto district japan this earthquake was accompanied by the transient crustal movements which follow instantaneous elastic deformations at the time of faulting the coseismic and postseismic crustal movements associated with the kanto earthquake are well interpreted by a dislocation source model in a composite medium which consists of an elastic surface layer lithosphere an intervening maxwellian viscoelastic layer asthenosphere and an elastic substratum an optimum fault model of the kanto earthquake is obtained from the coseismic crustal movements by using a method of inversion analysis in which effects of systematic errors caused by the movements of reference points in geodetic measurement are taken into account it is found that the fault motion of this earthquake is a reverse right lateral slip of 4 8 m with a slip angle of 140 on a fault plane which dips 25 towards n24 e where the slip angle is measured counterclockwise from the fault strike the fault length the fault width and the depth to the upper fault edge are determined as 95 km 54 km and 2 0 km respectively the postseismic transient crustal movements are considered to be controlled by a quasi static relaxation process of stress changes due to faulting in the earth s asthenosphere in such a quasi static problem the surface motion caused by a dislocation source consists of instantaneous elastic deformation at the time of faulting and transient viscoelastic movement after the event the viscoelastic part of the surface displacement field is calculated for the optimum fault model in a three layered composite medium with an intervening viscoelastic layer and compared with the observed data the transient crustal movements after the kanto earthquake are adequately explained by the present model taking the thickness of the lithosphere as 60 km and the thickness and viscosity of the asthenosphere as 180 km and 1020 poise respectively

most and least likely locations of large to great earthquakes along the pacific coast of mexico estimated from local recurrence times based on b values we mapped t l and p l local recurrence time and local probability density respectively for m max 7 2 earthquakes along the plate margin of the pacific coast of mexico in order to test two hypotheses the first is that the minima in t l or maxima in p l extracted probabilistically from the frequency magnitude distribution map asperities the second hypothesis is that recurrence times for characteristic events are estimated more correctly by local recurrence times than by the overall recurrence times of the zone comparing these results to the observed recurrence times for events of m 7 0 we find good agreement the coast of guerrero between longitude west 100 5 and 101 5 and the segment off the coast of southern chiapas show the shortest t l estimated as about 20 yr the location at longitude 98 5 near the boundary of guerrero with oaxaca the ometepec segment follows with estimates of about 30 yr as the next shortest t l along the coast of guerrero between 99 and 100 5 longitude t l is estimated as about 40 yr and finally in the segments off the oaxacan coast near 95 7 and 97 7 longitude t l ranges from 40 to 60 yr these volumes we define as asperities long local recurrence times are observed for the areas offshore from the isthmus of tehuantepec on the pacific plate off the coast of guerrero on land along the coast of most of oaxaca and along the northernmost 40 km of the guerrero coast if our ideas are correct then major moment release should emanate from the volumes we defined as asperities and relatively minor moment release should emanate from the volumes identified by the relatively long local recurrence times

earthquake scaling laws for creeping and non creeping faults the dependence of the summed moment release on the fault dimension differs between non creeping faults and creeping faults or volcanic regions this can be attributed to different earthquake scaling laws the number n of events with fault length l scales for non creeping faults as n l l 2 and for creeping faults as n l l 3 this difference offers a means for mapping the distribution of creep in the seismogenic crust

recognition of a locked state in plate subduction from microearthquake seismicity a tectonic state of a locked subduction is considered to be a possible source of a future interplate earthquake discriminating an actually locked state to verify its extent is therefore essential in constructing an accurate prospect against the forthcoming earthquake micorearthquake seismicity is an effective tool for such an analysis because it is considered to be a faithful indicator of the stress state and is expected to exhibit a characteristic pattern in the area where the locked state in the subduction appears with a certain stress concentration focusing on the microearthquake seismicity around the tokai district in central japan where a large interplate earthquake is feared to occur we tried to identify such an area of locked subduction on the philippine sea plate possibly related to the future earthquake we investigated the microearthquake seismicity from various perspectives first the hypocenter distribution was analyzed to identify the extent of the locked area the characteristic profile of the distribution was presumed to represent a stress concentrated area induced from the mechanical contact between both plates the second approach is to interpret stress patterns reflected in focal mechanisms the locked state was recognized and verified by a comparison of the p axis distribution pattern with that expected from a model imaging a partially locked subduction the third approach is to monitor the temporal change of the seismic wave spectrum analyzing predominant frequencies of p and s waves and monitoring their changes for a period of 10 years we found a trend of gradual increase common to both waves this means an increase of stress drop in microfracturings and in its turn implies accumulation of stress around the focus area the rate of the stress change converted from the frequency change was compared with the result derived from a numerical simulation the simulation performed on the basis of a constitutive friction law for a stick sliding on the plate interface computed a changing rate of the maximum shear stress around the locked zone and showed its spatial variation along the subduction axis thus the simulated result indicated a certain compatibility with the observed one although ambiguities and uncertainties still exist in the study all the results derived here seem to indicate an identical conclusion that the plate subduction is actually locked in this region at present

verification of our previous definition of preferred earthquake nucleation areas in kanto tokai japan abstract we have proposed that points of future initiation of rupture may be mapped based on minima in local recurrence times which are equivalent to local maxima in the probability for main shocks to occur these minima are often controlled by anomalously low b values log n a bm of the kanto tokai area approximately 12 showed anomalously short recurrence times and was proposed as asperities based on seismicity up to 1999 during the period 1999 2003 5 about 75 of the earthquakes with m 3 5 fell into the asperities earlier defined for example 19 out of 23 m 3 8 events the probability for this to occur by chance is approximately 2 10 14 this supports our idea that the most likely volumes to produce main shocks may be mapped by minima in local recurrence times

high resolution climate stratigraphy across the matuyama brunhes transition from palynological data of osaka bay sediments in southwestern japan abstract this study presents a high resolution palynological analysis of a sedimentary core from osaka bay japan straddling marine oxygen isotope stage mis 19 i e across the matuyama brunhes magnetic polarity boundary mbb comparison with the standard marine oxygen isotope curve bassinot f c labeyrie l d vincent e quidelleur x shackleton n j lancelot y 1994 the astronomical theory of climate and the age of the brunhes matuyama magnetic reversal earth and planetary science letters 126 91 108 demonstrates that variations in vegetation and the basinal environment coincided with global ice volume changes the late mis 20 is characterized by boreal climate with coniferous forest in mis 19 the forest was generally dominated by fagus and quercus lepidobalanus suggesting onset of humid climatic conditions slightly cooler than the present excluding coastal vegetation components climate during mis 19 can be subdivided into three stages the early stage including substage 19 3 is characterized by high seasonality in precipitation this contrasts with the very abundant year round precipitation that is inferred for the late stage from substage 19 2 to substage 19 0 which is characterized by cool temperate coniferous taxa including cryptomeria the very high precipitation rates of the latter persisted at least up to substage 18 4 there was no apparent vegetational response to the sea level highstand of 19 3 in contrast a short lived thermal maximum event took place ca 6 7 kyr later i e in middle mis 19 this event is characterized by increases in the warm temperate element quercus cyclobalanopsis the mbb the recommended criterion for defining the lower middle pleistocene boundary took place in middle mis 19 these lines of evidence indicate that the occurrence of the mbb corresponded with a shift towards warmer and wetter climatic conditions similar warming and wetting events across the mbb are also observed in pollen records from southern italy and central japan this possibly provides long distance correlation and may suggest a connection between the earth s magnetic field and climate

the ustic isohumisol chernozem distributed over the chinese loess plateau modern soil or palaeosol abstract the ustic isohumisol chernozem widely distributed over the chinese loess plateau is classified as a modern soil by agricultural pedologists and as a palaeosol by geoscientists high resolution investigations into this soil including field observations element analysis optically simulated luminescence dating and measurements of magnetic susceptibility and particle size distribution were carried out over the plateau uplands the results show that the formation of physico chemical properties and development of the soil profiles has kept pace with the land surface growth because of incessant dust accumulation during the holocene the continuously intensified weathering of accumulated dust from 11 500 a b p had resulted in an increased chemical differentiation through time during the early holocene the development of the ustic isohumisol occurred over the uplands between 8500 and 3100 a b p when the chemical differentiation reached its maximum because of increased precipitation and ample soil moisture in response to the mid holocene climatic optimum the soil formation had sustained for ca 5400 years and ceased at 3100 a b p a major pedogenic regression occurred from 3100 a b p because of climatic aridity and intensified dust accumulation over the loess plateau the newly accumulated loess and topsoil has the ustic isohumisol buried at a depth of ca 50 80 cm in general the pedogenic regression has been intensified by incorporation of the reworked components by increased runoff and erosion redeposition large scale land reclamation extended to the uplands at ca 2170 a b p an agricultural landscape of dry farming has formed since ca 1500 a b p thereafter the present topsoil has accumulated and has been affected by the intensified cultivation and addition of barnyard manure in history the solubles are retained in the topsoil because of dry climate and scant soil moisture

sedimentary records of extraordinary floods at the ending of the mid holocene climatic optimum along the upper weihe river china sedimentary records of the holocene extraordinary floods were investigated in the upper reaches of the weihe river a major tributary in the middle yellow river basin palaeoflood slackwater deposits swd were identified at several sites on the riverbanks these clayey silt beds are inserted into the holocene aeolian loess soil profiles and slope clastic deposits they have recorded the extraordinary palaeoflood events which occurred between 3200 and 3000 yr bp as dated by osl method and checked by the archaeological remains of the neolithic and bronze age retrieved from the profile the minimum flood peak discharges were estimated at between 22 560 and 25 960 m3 s by using palaeohydrological methods it is 4 5 5 0 times the largest gauged flood 5030 m3 s that has ever occurred since 1934 the palaeoflood slackwater deposits were found inserted into the pedostratigraphic boundary between the late holocene loess l0 and the mid holocene luvisol s0 in the riverbank profile this indicates that the ext

holocene climatic events recorded in palaeoflood slackwater deposits along the middle yiluohe river valley middle yellow river basin china abstract palaeohydrological investigations were carried out in the middle reaches of the yiluohe river a major tributary in the lower middle yellow river basin typical palaeoflood slackwater deposits swds were identified in the holocene pedostratigraphy on the cliffy river banks analytical results including magnetic susceptibility and grain size distribution data indicated that these swds were deposited from the suspended sediment load in flood water these swds are different from eolian loess soils and aeolian sands in the riverbank profile they recorded several episodes of extraordinary palaeoflood events in the longmenxia reaches of the yihe river valley these flood events were dated at 3100 3000 a 1800 1700 a 770 610 a and 420 340 a using the optically stimulated luminescence method in combination with the pedostratigraphic correlations in the longhutan reaches of the luohe river valley the palaeoflood events were dated at 1975 1466 a i e from the han to wei dynasties ad 25 534 during which the capital city on the river banks was flooded many times as recorded in the literature these extraordinary flood events are well correlated chronologically with the known holocene climatic events that occurred in the northern hemisphere thus the monsoonal climate was highly variable with both floods and droughts occurring frequently during these episodes these results are important for understanding the response of river systems in eastern asia to global changes

fluvial or aeolian unravelling the origin of the silty clayey sediment cover of terraces in the hanzhong basin qinling mountains central china this study is focused on a silty clayey sedimentary sequence on a terrace in the intramontane hanzhong basin located in the qinling mountains qlm central china traditionally the qlm are considered to have blocked dust transport from northwest to southeast china however in recent years geo archaeological studies have documented loess palaeosol sequences at numerous locations in and surrounding the qlm in the loess deposits overlying the terraces of the hanjiang river in the hanzhong ankang and yunxian basins abundant artefacts flakes stone tools e g scrapers and choppers and cores are commonly found the loess deposits have been deposited with lower sedimentation rates and they are finer grained and more intensely weathered compared to the loess deposits on the central loess plateau clp the loess deposits overly coarse sandy and gravely fluvial deposits terraces silty fluvial deposits are situated in between them discrimination between these two types of deposits could prove difficult because both deposits are fine grained silt and clay and can have similar grain size distribution characteristics this is however crucial for palaeo environmental interpretations during hominin occupation understanding fluvial morphodynamics and for pedostratigraphic correlation with the typical loess palaeosol sequences on the clp the aim of this research is to determine and characterize the transition of the fluvial to aeolian depositional environment in a fine grained sequence based on field observations organic matter and carbonate content grain size and shape analyses mineral content mica s and end member modelling of the grain size dataset in addition terrestrial cosmogenic nuclides tcn burial dating is used to determine the age of the basal coarse grained fluvial deposits the determined age 0 6 0 14 ma allows for a chronological correlation of the deposits to the loess palaeosol sequence on the clp independent from the pedostratigraphic correlation this age also gives insight in terrace abandonment and the fluvial morphodynamics of the hanjiang river the result indicates a clear distinction between sediments deposited in a fluvial environment and those formed in an aeolian depositional environment however the aeolian loess deposits show some atypical characteristics for example the end member model results show a coarsening in the five palaeosol layers this is in contrast with the fine grained nature of palaeosols on the clp the coarsening observed in the studied palaeosol layers is interpreted as the result of local surface runoff processes eroding fine sediment and or depositing relatively coarse material during interglacial periods because of the known depth of the fluvial aeolian transition and the absolute age of the tcn burial dated terrace deposits pedostratigraphic correlation of the palaeosol layers with the central loess plateau is possible the oldest palaeosol is correlated with s5 0 625 0 503 ma the transition from a fluvial to aeolian environment takes place in l6 between 0 625 and 0 693 ma this is consistent with the tcn age of 0 6 0 14 ma this age also marks the abandonment of the terrace caused by incision of the hanjiang river which is possibly related to an uplift phase of the qlm 2020 elsevier b v

minimum magnitude of completeness in earthquake catalogs examples from alaska the western united states and japan we mapped the minimum magnitude of complete reporting m c for alaska the western united states and for the junec earthquake catalog of japan mc was estimated based on its departure from the linear frequency magnitude relation of the 250 closest earthquakes to grid nodes spaced 10 km apart in all catalogs studied mc was strongly heterogeneous in offshore areas the mc was typically one unit of magnitude higher than onshore on land also mc can vary by one order of magnitude over distance less than 50 km we recommend that seismicity studies that depend on complete sets of small earthquakes should be limited to areas with similar mc or the minimum magnitude for the analysis has to be raised to the highest com mon value of mc we believe that the data quality as reflected by the mc level should be used to define the spatial extent of seismicity studies where mc plays a role the method we use calculates the goodness of fit between a power law fit to the data and the observed frequency magnitude distribution as a function of a lower cutoff of the magnitude data mc is defined as the magnitude at which 90 of the data can be modeled by a power law fit mc in the 1990s is approximately 1 2 0 4 in most parts of california 1 8 0 4 in most of alaska aleutians and panhandle excluded and at a higher level in the junec catalog for japan various sources such as ex plosions and earthquake families beneath volcanoes can lead to distributions that cannot be fit well by power laws for the hokkaido region we demonstrate how neglecting the spatial variability of m c can lead to erroneous assumptions about deviations from self similarity of earthquake scaling

reconstructing the palaeoflood events from slackwater deposits in the upper reaches of hanjiang river china abstract through investigation in the upper reaches of hanjiang river china an aeolian loess soil profile with four palaeoflood slackwater deposit swd interbeds was found on the cliffed riverbanks in yunxian county reach of hubei province based on field observation and laboratory analysis including magnetic susceptibility and particle size distribution the four palaeoflood swds were differentiated from aeolian loess and soil by sedimentary criteria and analytical results and recorded four episodes of palaeoflood events in the upper reaches of hanjiang river by using stratigraphic correlation and osl dating the four palaeofloods were dated to 12 600 12 400 a b p 11 600 11 400 a b p 5500 5000 a b p and 1000 900 a b p respectively according to the calculated maximum palaeoflood stage the maximum peak discharges of the palaeofloods events were reconstructed by using the hec ras one dimensional model the same hydrological method was used to calculate the peak discharge of the 2010 flood in the same reach the error between the calculated and gauged discharges was 4 9 showing that the reconstructed four palaeoflood discharges were reliable the flood peak discharge frequency relationship at 10 000 year timescale was established by a combination of the gauged flood historical flood and palaeoflood hydrological data in the upper reaches of the hanjiang river assessing reliability of peak discharge data in flood design for the water conservancy construction and flood mitigation

extraordinary floods of 4100 4000 a bp recorded at the late neolithic ruins in the jinghe river gorges middle reach of the yellow river china abstract holocene palaeohydrological investigations were carried out in the middle reach of the jinghe river that drains the central part of the loess plateau a set of palaeoflood slackwater deposits was found interbedded in the holocene loess soil sequence within the cliff riverbanks both the sedimentary criteria and the analytical results show that this sediment was sourced from a suspended sediment load of floodwater the major cultural layer of a late neolithic settlement 4300 4000 a bp occurring at the same site is blanketed by this flood deposit directly slopewash with pottery shards charcoal and burnt earth occurs in between the palaeoflood slackwater deposit beds it indicates that each of the slackwater deposit beds has recorded one individual flood event and that these extraordinary floods occurred when the late neolithic people occupied the riverbank terrace land this pre historical settlement was abandoned after the floods eventually due presumably to repeated inundation by overbank floodwater the flood events were osl dated to between 4100 and 4000 a bp and checked by archaeological dating of the anthropogenic remains retrieved from the sequences peak discharges of the floods were estimated to between 19 500 and 22 000 m3 s 1 which is several times gauged maximum floods during the 4200 4000 a bp climatic event severe droughts were documented in china s monsoonal regions and great floods were known from an ancient legend this study provides a well dated sediment record of pre historical floods which occurred at the transition from the neolithic to the bronze age in the yellow river basin it shows that extraordinary floods were part of the abrupt climatic variability during the 4200 4000 a bp climatic event the highly variable unstable and catastrophic climate typified by both droughts and floods resulted in settlement abandonment and possibly the decline of the highly developed late neolithic civilizations in china s monsoonal regions

investigating extreme flood response to holocene palaeoclimate in the chinese monsoonal zone a palaeoflood case study from the hanjiang river abstract palaeoflood events recorded by slackwater deposits swds were investigated extensively by sedimentological criteria of palaeohydrology along the upper hanjiang river valley modern flood swds were collected for comparison with palaeoflood swd in the same reaches three typical palaeoflood swds were observed within holocene loess soil blanket on the first river terrace land the grain size distributions of palaeoflood swds are similar to modern flood swds whereas they are different from eolian loess and soil palaeoflood swd lies in three major pedo stratigraphic boundaries ts l 0 l 0 s 0 and s 0 l t in the holocene loess soil profiles the chronology of three palaeoflood episodes was established by osl dating and pedo stratigraphic correlation with the well dated holocene loess soil profiles in the upper hanjiang river basin holocene palaeoflood events were dated to 9500 8500 3200 2800 and 1800 1700 a b p respectively palaeoflood discharges were estimated by the palaeoflood model i e slope area method and step backwater method the highest discharges are 51 680 53 950 m 3 s 1 at the 11 500 time scale in the xunyang reach of the upper hanjiang river valley holocene extraordinary hydroclimatic events in the hanjiang river often result from abnormal atmospheric circulations from southwest monsoons in the chinese monsoonal zone these results provide a regional expression of extreme flood response to holocene palaeoclimate to understand the effects of global climatic variations on the river system dynamics

correlating seismicity parameters and subsidence in the tokai region central japan 1 we demonstrate that transients in subsidence rate in the tokai area of central japan correlate with changes in the rate and size distribution of earthquakes three largely independent seismic catalogs cover this region national research institute for earth science and disaster prevention nied japanese meteorological agency jma and japan university network catalog junec comparing seismicity patterns between these three data sets offers a unique opportunity to verify seismicity anomalies based on independent sources a study of data quality magnitude reporting consistency and consistency across the three data sources reveals that the nied data for the period 1981 2002 are best suited for seismicity analysis we spatially and temporally map seismicity rates finding that a significant decrease in the earthquake rate of m 2 0 events coincides with an accelerated subsidence period however this anomaly disappears when including smaller magnitudes in the analysis this relative quiescence of larger events can readily be explained when interpreting the transient in seismicity in the framework of a change in the earthquake size distribution or b value the background b value of about 0 8 increased in the period 1987 5 1989 5 to a value of b 1 2 a highly significant change that can be confirmed in all three data sets the correlation between subsidence and b value change is significant stress tensor inversions of focal mechanism data for the anomalous period show an increase in thrusting type earthquakes while a unique interpretation of the relationship between subsidence and b value is not possible we propose that an increase in the locking stress a slow stick event is consistent with all observations

earthquake statistics at parkfield 1 stationarity of b values 1 in this paper paper 1 we quantitatively show that the heterogeneous pattern of b values of the gutenberg richter relation in the parkfield segment of the san andreas fault is to a high degree stationary for the past 35 years this prepares the grounds for paper 2 where we test the hypothesis that our model of spatially varying b values forecasts future seismicity more accurately than the approach in which one assumes a constant b value equal to the average regional value the method we develop to measure stationarity in the presence of spatial heterogeneity consists of the following steps 1 determine the optimal dimensions of the sampling volume by mapping b values with a wide range of radii and selecting the largest radius that gives the most detailed resolution of the b value heterogeneity along the selected fault segment the high data density permits the definition of the dominant dimensions of the seismotectonic fabric which is about 8 10 km 2 map the difference in b value between two periods selecting numerous possible catalog divisions 3 identify significant changes of b values by the utsu test utsu 1992 along the studied fault segment of 110 km length only one patch of radius 5 km showed a significant increase in b from below average to above as a function of time this change in b initiates around 1993 and thus correlates in space and time with a well documented episode of creep at depth using the derived spatial variable b value distributions we find that the highest probability for earthquakes with magnitude m 6 is in the middle mountain asperity where the 1966 parkfield earthquake nucleated and where all m 4 5 events in the data set occurred in contrast if only the regional average b value of 0 92 is used to predict future seismicity the creeping segment north of parkfield should produce major earthquakes most frequently a conclusion that contradicts the observations

post depositional remanent magnetization lock in and the location of the matuyama brunhes geomagnetic reversal boundary in marine and chinese loess sequences article i nfo pdrm lock in loess paleosol bioturbation disturbs detrital magnetic particles after deposition so accurate recording of the ancient geomagnetic field in bioturbated sediments is widely attributed to acquisition of a post depositional remanent magnetization pdrm whereby the geomagnetic field exerts a torque on a magnetic particle and aligns it with the field after the final mixing event experienced by the particle the relationship between the matuyama brunhes boundary mbb and oxygen isotope age tie points in marine sediments has been widely used to determine the depth at which the paleomagnetic signal is locked in however such analyses can be badly affected by age discrepancies among different paleoclimatic proxies and by varying isotopic compositions of seawater in different locations and from the presence of different water masses at different depths at the same location it is therefore necessary to separately compare paleomagnetic data with respect to either benthic or planktonic foraminiferal oxygen isotope records for sites from the same water mass to avoid inadvertently introducing age differences to the analysis when the global data set is subjected to such a rigorous analysis few reliable data remain for the mbb using two complementary approaches we estimate that the mbb is on average shifted 20 cm below its true position in marine sediments this offset is the sum of the thickness of the bioturbated surface mixed layer which is possibly dominant and the pdrm lock in depth there is also controversy concerning observed differences in the position of the mbb relative to paleoclimatic proxies in marine sediments and chinese loess deposits for the chinese loess quartz grain size is insensitive to pedogenic alteration and is a useful parameter for determining the true position of the mbb with respect to paleoclimatic boundaries we conclude that the mbb occurs late in marine oxygen isotope stage 19 and in the upper part of chinese paleosol unit s8 rather than at the mid or lower part of loess unit l8 our results require adjustment of the generally accepted positions for the mbb and resolve a longstanding chronological conundrum for marine and chinese loess sequences

the obliquity of mars and climate friction the mean obliquity of mars may have increased over geologic time due to climatic changes associated with obliquity oscillations this mechanism is dubbed climate friction given here is the mathematical theory of climate friction also a 10 m y numerical integration of the equations for a hypothetically large amount of climate friction is performed for the cases of the obliquity oscillations being 1 a single sinusoid and 2 a sum of three sinusoids theory and numerics agree in both cases within about 12 on the size of the secular increase in obliquity with most of the discrepancy coming from the theory giving obliquity amplitudes 10 too large further one possible mechanism of climate friction is investigated here postglacial rebound on mars the idea is that giant polar caps form when the obliquity is low these caps slowly squeeze out an equatorial bulge when the obliquity is high the caps disappear but the bulge takes some time to collapse due to mantle viscosity thus the equatorial bulge oscillates but is out of phase with the obliquity oscillations like tidal friction this causes a secular increase in the average obliquity using the preferred climate model of francois et al 1990 the total secular increase in the obliquity over the age of the solar system can amount to about 10 if mars mantle has an earthlike effective viscosity of 3 1021 pa s 3 1022 p the secular change is negligible for effective viscosities which differ by more than a factor of 10 from this value last how much climate friction tipped the earth is presently unknown

unlocking the ice house oligocene miocene oxygen isotopes eustasy and margin erosion oxygen isotope records and glaciomarine sediments indicate at least an intermittent presence of large continental ice sheets on antarctica since the earliest oligocene circa 35 ma the growth and decay of ice sheets during the oligocene to modern ice house world caused glacioeustatic sea level changes the early eocene was an ice free greenhouse world but it is not clear if ice sheets existed during the middle to late eocene doubt house world benthic foraminiferal 18o records place limits on the history of glaciation suggesting the presence of ice sheets at least intermittently since the earliest oligocene the best indicator of ice growth is a coeval increase in global benthic and western equatorial planktonic 18o records although planktonic isotope records from the western equatorial regions are limited subtropical planktonic foraminifera may also record such ice volume changes it is difficult to apply these established principles to the cenozoic 18o record because of the lack of adequate data and problems in stratigraphic correlations that obscure isotope events we improved oligocene to miocene correlations of 18o records and erected eight oxygen isotope zones oi1 oi2 mi1 mi6 benthic foraminiferal 18o increases which are associated with the bases of zones oil circa 35 8 ma oi2 circa 32 5 ma and mil circa 23 5 ma can be linked with 18o increases in subtropical planktonic foraminifera and with intervals of glacial sedimentation on or near antarctica our new correlations of middle miocene benthic and western equatorial planktonic 18o records show remarkable agreement in timing and amplitude we interpret benthic planktonic covariance to reflect substantial ice volume increases near the bases of zones mi2 circa 16 1 ma mi3 circa 13 6 ma and possibly mi5 circa 11 3 ma possible glacioeustatic lowerings are associated with the 18o increases which culminated with the bases of zone mi4 circa 12 6 ma and mi6 circa 9 6 ma although low latitude planktonic 18o records are required to test this these inferred glacioeustatic lowerings can be linked to seismic and rock disconformities for example we link 12 oligocene early late miocene inferred glacioeustatic lowerings with 12 of the sequence boundaries inferred eustatic lowerings of haq et al 1987

a systematic test of the hypothesis that the b value varies with depth in california we spatially map the shallow to deep b value ratio in the crust in california previous studies of the frequency magnitude distribution as a function of depth for selected crustal regions indicated that b decreases from b 1 1 in the 0 5 km depth range to b 0 8 in the depth range 7 15 km our detailed mapping confirms that this pattern can be established at the 99 significance level for about 32 of the entire seismically active crust about 2 of the crust displays the opposite b gradient one such area is the san francisco bay area we speculate that differences in stress levels are the main factor controlling the depth dependency of b these results confirm that the b value should not always be considered a constant in studies such as seismic hazard estimations

mars the regolith atmosphere cap system and climate change abstract a new model for predicting the behavior of the martian regolith atmosphere cap co 2 regime and describing its role in climate change is derived the model describes the time temperature histories of 90 regolith chunks on a latitude depth grid accounting for co 2 exchange by means of laboratory derived expressions relating temperature co 2 pressure p co 2 and adsorbed co 2 mass co 2 polar cap formation and sublimation is accounted for subject to the constraint of constant total co 2 in the atmosphere regolith cap system the influence of differences in regolith adsorption laws for basalt and clay and the influence of variations in regolith depth with latitude regolith thermal diffusivity and total exchangeable co 2 inventory on predicted variations in atmospheric pressure and cap mass are examined the following results are indicated 1 the atmosphere acts as a low capacity conduit through which flows between 10 and 100 times the current atmospheric mass of co 2 between two reservoirs a regolith ocean of adsorbed co 2 and a polar cap cryosphere 2 exchange between these reservoirs is driven by variations of obliquity with the polar cap the dominant co 2 sink at low and the regolith dominating at high atmospheric pressure ranges between 0 1 low and 15 mbar high pressures of up to 25 mbar could result from pre tharsis variations pressure up to 40 mbarare achieved only in models which also call for a huge quasi permanent present co 2 cap which is not apparent 3 at high the atmospheric pressure is buffered by the regolith and satisfies adsorption equilibrium for the 90 chunks as well as conservation of co 2 mass at low a potetially large co 2 cap appears and the atmospheric pressure is buffered by the cap not the regolith 4 the periodic reservoir flushing can account for the observation of simultaneous nonenrichment of 18 o and enrichment of 13 n 5 mars climate history may be divided into three parts a post tharsis formation history as described above b pre tharsis formation with qualitatively similar processes but larger oscillations between reservoirs and larger atmospheric pressure and cap mass variation and c the very early period of channel formation 6 the nature of the response of the three part regolith atmosphere polar cap martian climate system to surface insolation variations may be analogous to that of earth s ocean atmosphere cryosphere system

comparative study of the modern flood slackwater deposits in the upper reaches of hanjiang and weihe river valleys china abstract modern flood slackwater deposits swd were investigated and sampled in the upper reaches of hanjiang river and the weihe river valleys china magnetic susceptibility and grain size distribution were analyzed in the laboratory the results show that the magnetic susceptibility values of the modern flood swd vary between 20 10 8 m 3 kg 1 and 60 10 8 m 3 kg 1 very close to that of the malan loess over the weihe river basin these sediments were newly deposited and uninfluenced by weathering and pedogenesis the grain size distribution of the modern flood swd is dominated by silt with sand and clay indicating that these sediments were sourced from the suspended sediment load of floodwater however the grain size distribution of the modern flood swd has more sand sized sediments in the upper reaches of hanjiang river valley than that in the weihe river valley the modern flood swd are defined as sandy silt and silty sand in the upper reaches of hanjiang river valley whereas the modern flood swd are defined as silt sandy silt and clayey silt in the weihe river valley the modern flood swd have different sediment sources and transporting forces the modern flood swd are sourced mainly from the qinling and the bashan bedrock mountains and the related residual deposits slopewash and mud rock flow deposits in the upper reaches of hanjiang river valley during rainstorms torrential tributary rivers can bring much coarse deposits into the mainstream of the hanjiang river however the sources of the modern flood swd are the eolian loess and the related surface soil in the weihe river valley comparative study shows different sedimentary features between the modern flood swd in the upper reaches of hanjiang river valley and that in the weihe river valley these results give insight into the different sediment sources and transporting force of the modern flood swd which provide a basic reference to mitigate flood disasters and to soil and water conservation

provenance of loess deposits in the eastern qinling mountains central china and their implications for the paleoenvironment loess deposits in the eastern qinling mountains central china provide a detailed archive for reconstructing the paleoenvironment during early hominin occupation the study of the loess deposits also provides a unique opportunity to understand pleistocene atmospheric circulation in this transitional climatic zone however the provenance and formation of the loess deposits were not well understood until now in this paper we report on new geomorphologic investigations and depositional analyses of the loess deposits the results suggest that gobi deserts and drylands in northern and northwestern china were one of the dust sources these loess deposits show similar geochemical composition as the average upper crust ucc and may indicate that they experienced multiple sedimentary processes with the dust being well mixed before deposition however the higher sr 87 sr 86 ratios between 0 719650 and 0 721043 and extremely low nd 0 values between 11 98 and 18 97 which are different from the typical loess of the chinese loess plateau demonstrate that proximal clastic sediments that were apparently derived from the weathered qinling orogen bedrocks form the other important source for the loess deposits the chemical index of alteration cia al2o3 al2o3 cao na2o k2o x 100 and chemical proxy of alteration cpa 100 x al2o3 al2o3 na2o both in molar proportions show that the loess has experienced intense pedogenesis we conclude that the loess deposit has a mixed provenance the palaeoclimate in the eastern qinling mountains remained mild in the glacial periods due to the topography and unique geographic locations providing a suitable place for hominine occupation c 2012 elsevier ltd all rights reserved

geochemical characteristics of the eolian deposits in southern china and their implications for provenance and weathering intensity abstract the loess paleosol sequences in the middle lower reaches of the yantgze river are valuable geological records of quaternary environments that bear information about climate change for the subtropical zone of southern china type sections containing eolian deposits in this region mostly include the upper loess soil sequence referred to as xiashu loess formation the middle vermiculated red soil vrs and the underlying fluvial deposits or bedrock in this study xiashu loess paleosol formed in the xiashu loess and the vrs samples from xuancheng xc and jiujiang jj sections were analyzed for their elemental major and trace elements and isotopic sm nd geochemistry and compared with pleistocene loess and paleosol samples from the chinese loess plateau clp in northern china the results show an overall similarity in geochemical characteristics between the southern china loess and the average ucc indicating that the dust materials were derived from well mixed sedimentary protoliths which had undergone numerous upper crustal recycling processes in comparison with the loess of northern china the eolian deposits in southern china have higher tio2 zr hf and lower ba concentrations higher tio2 al2o3 u pb th pb and lower ba rb zr hf eu eu ce yb eu yb ratios and lower end 0 values with relatively greater range these features coincide with the complicated source rock compositions in the middle lower yangtze river which suggests local sources for the eolian deposits in this region the eolian deposits in southern china have experienced the intermediate k removal weathering stage ca sr na mg and k are the main mobile elements in the weathering process in comparison with the xiashu loess formation the vrs has greater depletion of na mg k and mn indicating a stronger weathering intensity or perhaps a longer period of weathering

paleofloods recorded by slackwater deposits in the upper reaches of the hanjiang river valley middle yangtze river basin china summary a paleo hydrological study was carried out along the upper reach gorges of the hanjiang river that drains from the qinling and dabashan mountains two bedsets of paleoflood slackwater deposits were found embedded in holocene loess soil sequences within riverbank cliffs all of these were studied by field observations and laboratory analyses including magnetic susceptibility particle size distribution and optically stimulated luminescence osl dating these analyses provided a complete catalog of holocene flood events on a watershed scale that is important for understanding the regional hydrological responses to monsoonal climatic change the results show that these hydro climatic events were dated to 9000 8500 and 3200 2800 a b p the paleoflood peak discharges were estimated to be 44 350 49 860 m 3 s by using the hec ras model and were verified by different approaches these results have extended the flood data sequence of the hanjiang river to a 10 000 year time scale the additional data allowed us to refine the flood frequency peak discharge curve and potentially increase its accuracy these results will play an important role in mitigating flood hazards and will be useful for hydraulic engineering and the development of water resources in the hanjiang river basin

holocene colluviation and its implications for tracing human induced soil erosion and redeposition on the piedmont loess lands of the qinling mountains northern china abstract colluvial components incorporated in loess soil sequences have preserved evidence of soil erosion and redeposition in the middle reaches of the yellow river drainage basin holocene loess soil sequences on the gentle sloped lands were studied by measuring magnetic susceptibility particle size distribution caco3 and extraction and identification of the non dust materials the analytical results indicate that in the early holocene soil erosion and redeposition by overland flow occurred even on the loess lands with small ground gradient in response to climatic amelioration linked to global climatic change no obvious soil erosion and redeposition events were found to correspond with the climatic fluctuations recorded in the loess soil sequence during the holocene climatic optimum the primary neolithic farming did not cause apparent erosion and redeposition because the loess landscape was mantled by well developed ustic luvisols and probably by forest vegetation both provided adequate resistance to sheet erosion by overland flow enhanced soil erosion and redeposition are traceable back to ca 4000 a b p it is attributed to intensified land use of arable farming and human settlement from the early bronze age onward a major event of sheet erosion and redeposition by overland flow occurred in the loess landscape during 4000 3600 a b p in the xia dynasty soil degradation and reduced resistance caused by climatic aridity and intensified dust accumulation may have played a secondary role in promoting soil erosion since 3100 a b p these results provide new insights into the history of soil erosion in the semi arid and semi humid loess regions and into the evaluation of human induced accelerated soil erosion against the background of the holocene natural erosion forced by monsoonal climatic fluctuation

frequency variations of the earth s obliquity and the 100 kyr ice age cycles variations in the earth s orbital parameters modulate the seasonal distribution of solar radiation and thereby induce changes in the earth s climate1 periodicities in the geological climate record with cycles of 100 41 and 23 kyr have been linked with changes in eccentricity obliquity and precession of the equinoxes respectively2 3 but although the eccentricity does vary with a 100 kyr period the effect on the incoming solar radiation is rather weak relative to the signals from obliquity and precession variations the 100 kyr signal in the climate record should therefore be of negligible intensity yet it is observed instead to dominate the record internal nonlinear processes within the climate system have been proposed to account for this fact4 14 in contrast i show here that variations in the frequency of the obliquity cycle can give rise to strong 100 kyr forcing of climate

new magnetostratigraphic dates of lantian homo erectus skeletal remains of homo erectus found in pleistocene loess at two sites near lantian in central china are of greatly different geologic age the cranium found in the fossil bearing strata at gongwangling is about 1 15 myr old whereas the remains found at the chenjiawo locality in middle pleistocene loess are about 0 65 myr old the dating is based on new paleomagnetic polarity determinations and on the lithostratigraphic position of the fossils in the loess paleosol sequence our results confirm that both localities are older than the first occupation of zhoukoudian new dates palaeoenvironmental settings and morphological features of the hominids from lantian localities have significant bearing on the understanding of adaptive radiations of the middle and late hominids in asia

migration of the antarctic polar front through the mid pleistocene transition evidence and climatic implications abstract the antarctic polar front is an important biogeochemical divider in the southern ocean laminated diatom mat deposits record episodes of massive flux of the diatom thalassiothrix antarctica beneath the antarctic polar front and provide a marker for tracking the migration of the front through time ocean drilling program sites 1091 1093 and 1094 are the only deep piston cored record hitherto sampled from the sediments of the circumpolar biogenic opal belt mapping of diatom mat deposits between these sites indicates a glacial interglacial front migration of up to 6 degrees of latitude in the early mid pleistocene the mid pleistocene transition marks a stepwise minimum 7 northward migration of the locus of the polar front sustained for about 450 kyr until an abrupt southward return to a locus similar to its modern position and further south than any mid pleistocene locus this interval from a 900 ka event that saw major cooling of the oceans and a 13c minimum through to the 424 ka mid brunhes event at termination v is also seemingly characterised by 1 sustained decreased carbonate in the sub tropical south atlantic 2 reduced strength of antarctic deep meridional circulation 3 lower interglacial temperatures and lower interglacial atmospheric co2 levels by some 30 per mil than those of the last 400 kyr evidencing less complete deglaciation this evidence is consistent with a prolonged period lasting 450 kyr of only partial ventilation of the deep ocean during interglacials and suggests that the mechanisms highlighted by recent hypotheses linking mid latitude atmospheric conditions to the extent of deep ocean ventilation and carbon sequestration over glacial interglacial cycles are likely in operation during the longer time scale characteristic of the mid pleistocene transition the cooling that initiated the 900 ka event may have been driven by minima in insolation amplitude related to eccentricity modulation of precession that also affected low latitude climates as marked by threshold changes in the african monsoon system the major thresholds in earth system behaviour through the mid pleistocene transition were likely governed by an interplay of the 100 kyr and 400 kyr eccentricity modulation of precession

astronomical timescale and palaeoclimatic implication of stacked 3 6 myr monsoon records from the chinese loess plateau abstract magnetic susceptibility and grain size records from two continuous red clay and loess palaeosol sequences on the chinese loess plateau have been generated to investigate the evolution and variability of the east asian monsoon eam during the late pliocene and pleistocene tuning the grain size records to orbital obliquity and precession yields an improved astronomical timescale for the loess palaeosol sequence 0 2 6 ma and an extended age model for the upper red clay formation 2 6 3 6 ma this timescale indicates older ages for a number of the magnetic polarity boundaries consistent with lock in depth offsets in loess sequences good site to site correlation enables generation of stacked grain size and susceptibility records spanning the last 3 6 myr these records indicate that monsoon evolution since the late pliocene can be subdivided into three phases 0 1 25 1 25 2 72 and 2 72 3 4 ma each phase is characterized by unique amplitude and frequency characteristics for both summer monsoon magnetic susceptibility and winter monsoon grain size spectral analyses of the stacked monsoon proxies indicate that characteristics of both the summer and winter monsoons are dominated mainly by variance in the eccentricity 410 and 100 kyr obliquity 41 kyr and precession 23 and 19 kyr bands over the past 3 4 myr implying a non linear response of the long term eam evolution to orbital and glacial forcing

variations in earthquake size distribution across different stress regimes the earthquake size distribution follows in most instances a power law1 2 with the slope of this power law the b value commonly used to describe the relative occurrence of large and small events a high b value indicates a larger proportion of small earthquakes and vice versa statistically significant variations of b values have been measured in laboratory experiments mines and various tectonic regimes such as subducting slabs near magma chambers along fault zones and in aftershock zones3 however it has remained uncertain whether these differences are due to differing stress regimes as it was questionable that samples in small volumes such as in laboratory specimens mines and the shallow earth s crust are representative of earthquakes in general given the lack of physical understanding of these differences the observation that b values approach the constant 1 if large volumes are sampled4 was interpreted to indicate that b 1 is a universal constant for earthquakes in general5 here we show that the b value varies systematically for different styles of faulting we find that normal faulting events have the highest b values thrust events the lowest and strike slip events intermediate values given that thrust faults tend to be under higher stress than normal faults we infer that the b value acts as a stress meter that depends inversely on differential stress

nucleation points of recent mainshocks in southern iceland mapped by b values the earthquake catalog in southern iceland between 20 25 w and 21 3 w is complete down to approximately mw 0 and shows no evidence for mag nitude shifts as a function of time since 1991 this means that 6902 earthquakes m 0 1 depth 20 km are available for studies of seismicity patterns preceding the two ms 6 6 mainshocks in 2000 in their source volumes and vicinity 20 25 w and 20 9 w the power law of the frequency magnitude relationship holds down to m0 detailed mapping including 3d mapping of the b value of the frequency magnitude distribution shows that variations from b 0 6 to 1 4 exist over distances of about 2 km this suggests that the tectonic fabric in southern iceland is hetero geneous on a small scale the hypocenters of the two ms 6 6 mainshocks and one additional m 4 5 mainshock are associated with low b values 0 6 0 8 statistically significantly different from volumes in their vicinity therefore one can expect future mainshocks in southern iceland to also emanate from volumes characterized by low b values however the small dimensions of these asperities may render it difficult to identify them before the mainshocks occur low values of estimated local recur rence times 500 2000 years map the two fault zones that ruptured in 2000 against a background of local recurrence times longer than 5000 years the first of the two m 6 6 mainshocks emanated from a volume of short estimated local recurrence time this supports the hypothesis that asperities with short local recurrence times control locations of major ruptures mapping of b values in cross sections shows anomalies of high b at the bottom of the seismogenic crust correlating with the change of its thickness in the middle of the study area these high b value anomalies and other pockets of such anomalies at shallower depths are best interpreted as caused by high pore pressure because evidence of fluids under high pressure is ubiquitous in this area

esr dating of tooth enamel from yunxian homo erectus site china abstract two almost complete fossil hominid crania ev9001 and ev9002 were found in 1989 and 1990 in middle pleistocene terrace deposit of han river yunxian county hubei province china they are classified as homo erectus nine fossil animal teeth stratigraphically associated with the skulls were selected for electron spin resonance esr dating the simple exponential function was used for determination of the accumulated dose de and its appropriateness was discussed on the base of the experimental study the closed system assumption was checked and the early uranium uptake model was applied to age determination a mean age value was yielded to be 581 93 ka it deviates from the palaeomagnetic dating result of 830 870 ka micro regional complete saturation of esr signal in enamel of very high u content may account for the underestimation of esr ages nevertheless both esr and palaeomagnetic dating results place yunxian crania in between the homo erectus of lantian and zhoukoudian which means that yunxian crania constitute an important link in the human evolutionary lineage of china

extraordinary floods related to the climatic event at 4200 a bp on the qishuihe river middle reaches of the yellow river china abstract palaeo hydrological study was carried out in the qishuihe river valley in the middle reaches of the yellow river several bedsets of flood slackwater deposit were identified in the holocene loess soil sequences on the riverbanks they were differentiated from aeolian loess and soils by the parallel and waving beddings and the distinctive stratigraphic breaks separating individual palaeoflood events chronology of the flood events was established by osl dating checked by archaeological identification of the anthropogenic remains retrieved from the sequences the results show that successive floods occurred between 4300 and 4000 a bp in association with the abrupt climatic event of 4200 a bp these overbank floods had the riverbank settlement inundated repeatedly another series of extraordinary floods occurred between 3200 and 3000 a bp when monsoonal climate shifted from the mid holocene climatic optimum toward late holocene dry conditions the climatic event of 4200 a bp and the climatic decline at 3100 a bp were believed to be characterized by droughts previously this work provides solid evidence that both severe droughts and extreme floods were parts of the climatic variability during abrupt climatic event and climatic decline in the semi arid to sub humid zones over the world

the procession constant of the earth variations through the ice age we directly calculate the history of variations in earth s precession constant h that are forced by variations in surface mass associated with late pleistocene ice age glaciation and deglaciation events our analyses show that the magnitude of delta h h sub zero is lower than that required to cause the recently hypothesized resonant reduction of the precession period

a comparison of seismicity characteristics and fault structure between stick slip experiments and nature fault zones contain structural complexity on all scales this complexity influences fault mechanics including the dynamics of large earthquakes as well as the spatial and temporal distribution of small seismic events incomplete earthquake records unknown stresses and unresolved fault structures within the crust complicate a quantitative assessment of the parameters that control factors affecting seismicity to better understand the relationship between fault structure and seismicity we examined dynamic faulting under controlled conditions in the laboratory by creating saw cut guided natural fractures in cylindrical granite samples the resulting rough surfaces were triaxially loaded to produce a sequence of stick slip events during these experiments we monitored stress strain and seismic activity after the experiments fault structures were imaged in thin sections and using computer tomography the laboratory fault zones showed many structural characteristics observed in upper crustal faults including zones of localized slip embedded in a layer of fault gouge laboratory faults also exhibited a several millimeter wide damage zone with decreasing micro crack density at larger distances from the fault axis in addition to the structural similarities we also observed many similarities between our observed distribution of acoustic emissions aes and natural seismicity the aes followed the gutenberg richter and omori utsu relationships commonly used to describe natural seismicity moreover we observed a connection between along strike fault heterogeneity and variations of the gutenberg richter b value as suggested by natural seismicity studies areas of low b value marked the nucleation points of large slip events and were located at large asperities within the fault zone that were revealed by post experimental tomography scans our results emphasize the importance of stick slip experiments for the study of fault mechanics the direct correlation of acoustic activity with fault zone structure is a unique characteristic of our laboratory studies that has been impossible to observe in nature

a sustainable review of the middle pleistocene benchmark sites including the ailuropoda stegodon faunal complex the proboscidean point of view abstract the different ecologies times of extinction and last stand of both elephas and stegodon in south east asia cover almost two million years in the middle pleistocene both taxa belong to the complex ailuropoda stegodon this regional complex is considered to have a chronological significance and further palaeoecological palaeobiogeographical or biochronological studies use this assemblage as a benchmark nevertheless such studies do not provide sufficient information regarding site formation and duration to be consistent enough to do so at an appropriate resolution mis timescale focussing attention on the occurrence of proboscideans a critical review of the robustness of the geological taphonomical and chronological data of middle pleistocene faunal assemblages suggests the necessity to undertake a deep reappraisal of this biochronological benchmark recommendations were provided in the 1980s not to use mixtures of faunal assemblages and progress in geochronology for two decades is available nevertheless a review of proboscideans suggests the necessity of a severe revision leading to scepticism concerning the use of the ailuropoda stegodon complex as an ecological marker extended to other taxa this review casts serious doubts on former and current paleoecological modellings and studies

viscous gravitational relaxation summary this paper is concerned with a detailed examination of the response of maxwell models of the planet to surface mass loads particular attention is devoted to an examination of the factors which determine the isostatic response since the understanding of this response is crucial in a number of different geodynamic problems one particular example which we discuss in detail is concerned with the prediction of free air gravity anomalies produced by large scale deglaciation events using the methods developed here we are able to provide the first direct assessment of the importance of initial isostatic disequilibrium on the observed relative sea level variations and free air gravity anomalies forced by the melting of the laurentide ice sheet we are therefore able to estimate the extent to which such initial disequilibrium might influence the inference of mantle viscosity from isostatic adjustment data our calculations establish that free air gravity data although they are sensitive to the degree of initial disequilibrium provide an extremely high quality constraint upon the viscosity of the lower mantle

pleistocene deglaciation and the global gravity field the present day global geoid and free air gravity anomaly signals induced by pleistocene deglaciation have been computed along with their secular variations a revised green function has been derived for the free air gravity anomaly and we find that an earth model with a lower mantle viscosity moderately larger than the upper mantle value satisfies observations of the anomaly over both hudson s bay and fennoscandia using this preferred earth model the predicted global geoid anomaly map is characterized by peak negative values of 36 7 9 4 and 21 9 m over hudson s bay northern europe and antarctica respectively and by a smooth small amplitude 2 5 m upwarping over the major ocean basins although the field has an order of magnitude less power than the observed there is a significant spatial correlation between the two inferences of mantle viscosity based upon comparisons between the observed geoid and the computed deglaciation induced anomaly are hampered by the large contribution from the convective circulation in the earth s mantle we have subtracted a predicted convection signal based on seismic tomography from the observed field however the residual geoid thus obtained is still too inaccurate to allow a useful comparison in contrast a filtered version of the observed geoid over canada which retains harmonic coefficients in the degree range 10 22 provides a relatively uncontaminated by convection datum that is indeed satisfied by the preferred earth model secular variations in the earth s gravitational field are naturally dominated by the signal from pleistocene deglaciation in this respect we compute zonal harmonics in the expansion of the present day rate of change of the geopotential and in particular we predict amplitudes comparable to that for the previously analysed j2 for j4 j5 j7 and j9 all of which reflect in large part the response due to the melting of the massive laurentide ice sheet this analysis suggests that measurement of these higher order secular variations of the zonal harmonics based upon analysis of long time series of lageos ranging data could provide very useful additional constraints on the radial variation of mantle viscosity these constraints along with all others described in this paper are shown to be relatively insensitive to assumptions concerning the deflection during the glacial isostatic adjustment process of the 400 and 670 km density discontinuities within the mantle

geochemical evidence for the provenance of middle pleistocene loess deposits in southern china the provenance of middle pleistocene loess in the middle and lower reaches of the yangtze river the most intensively investigated loess deposits outside the loess plateau region in china remains controversial identification of the provenance will provide crucial insight into the environmental implications of this valuable sedimentary archive and into the potential role of the east asian winter monsoon in transporting the dust from deserts in the asian interior in this study geochemistry was used to compare the provenance of loess in the lower reaches of the yangtze river in southern china with that inferred for loess deposits on the loess plateau in northern china compared with samples from the loess plateau the 20 mm fraction in the loess deposits of southern china has higher tio2 al2o3 zr nb zr al zr ti zr hf y al and lan smn ratios and lower eu eu th nb y nb and al nb ratios the clear distinction in immobile element ratios between samples from the two regions indicates that the loess deposits in the two regions have different provenances the inferred difference in source area is also supported by variations in the major element composition of bulk samples obtained in this study and collected from published data these lines of evidence indicate that the deserts in the asian interior are not the primary provenance for the southern loess it is suggested that the adjacent floodplains to the north of yangtze river are the dominant dust sources and the occurrence of sustained loess deposits in the lower reaches of the yangtze river currently an area of northern subtropical climate is an indication of local aridification and strengthened winter monsoon activity during glacial periods as a regional response to the middle pleistocene climate transition around 0 8 ma the role of the east asian winter monsoon in transporting the dust from northern deserts to southern china has been overestimated in previous studies

mapping asperities by minima of local recurrence time san jacinto elsinore fault zones minima of the local recurrence time tl m are correlated with the locations of historical main shocks in the san jacinto sj elsinore e fault zones of southern california we define tl m as the recurrence time calculated from the local b and a values of the frequency magnitude distribution earthquakes within 6 and 10 km from each point in the sj and e fault zones respectively we propose that anomalously low tl m values map asperities out of six historic main shocks 1899 1968 five ruptured substantial parts of four asperities mapped by our method which uses solely the modern earthquake catalog m 1 2 1981 0 1998 8 we estimate the probability for this correlation to occur at random as 10 2 to 10 3 depending on the scenario chosen it appears that the minima in tl m are tied to minima in b values more than to maxima in a values thus locations of low b values can also be used as an indication where asperities may be located and where main shocks are most likely the anza gap a segment of the san jacinto fault with low a values is mapped as an asperity by our method the heterogeneity in b values is strong throughout the study area the b values range from 0 5 to 1 8 over distances of 10 km volumes with approximately constant b values have radii of r 8 6 km our results suggest that detailed mapping of b values and local recurrence times in volumes with a few kilometers radius reveals important information about the local seismic hazard hitherto untapped by conventional seismicity analyses