microseismic event location for monitoring co2 injection using double difference tomography increases in pore pressure and volume caused by co2 injection will perturb the ambient stress field and possibly trigger brittle failure on small fractures or faults resulting in microearthquakes monitoring this induced seismicity can help understand the migration of the co2 front and the stress and strain changes in the reservoir miyazawa et al 2008 as part of research efforts of the southwest regional partnership on carbon sequestration supported by the u s department of energy and managed by the national energy technology laboratory a large number of microseismic events have been recorded since early 2008 using a geophone string cemented into a well for monitoring co2 injection at the aneth oil field in utah we use double difference tomography to obtain high precision locations of microseismic events and improve the spatial resolution of the velocity structure simultaneously the double difference seismic tomography method was developed for improving earthquake source locations and tomograph

direct determination of the timing of sea level change during termination ii an outcrop within the last interglacial terrace on barbados contains corals that grew during the penultimate deglaciation or termination ii we used combined 230th and231pa dating to determine that they grew 135 8 0 8 thousand years ago indicating that sea level was 18 3 meters below present sea level at the time this suggests that sea level had risen to within 20 of its peak last interglacial value by 136 thousand years ago in conflict with milankovitch theory predictions orbital forcing may have played a role in the deglaciation as may have isostatic adjustments due to large ice sheets other corals in the same outcrop grew during oxygen isotope 18o substage 6e indicating that sea level was 38 5 meters below present sea level about 168 0 thousand years ago when compared to the 18o signal in the benthic v19 30 v19 28 record at that time the coral data extend to the previous glacial cycle the conclusion that deep water temperatures were colder during glacial periods

atmospheric oxygen 18 and sea level changes past isotopic composition of atmospheric oxygen 18oatm can be inferred from the analysis of air bubbles trapped in ice caps the longest record covers the last 420 ka thousand of years at the vostok site in east antarctica it shows a strong modulation by the precession and striking similarities but also noticeable differences with the deep sea core oxygen 18 record from which changes in the oxygen content of sea water 18osw and in sea level can be derived indeed 18oatm is driven by complex fractionation processes occuring during respiration and photosynthesis both 18oatm and its difference with respect to 18osw the dole effect are influenced by factors such as the ratio of oceanic and terrestrial productivities which may have significantly changed between different climates also the response time of 18oatm to oceanic changes should be taken in consideration but this parameter itself depends on biospheric activity we review the various aspects of the link between the 18oatm and the 18osw signals we also examine the approach followed by shackleton science 2000 for deriving sea level change from the 18oatm vostok record assuming that the phase between this record and insolation changes is constant and that the dole effect is a fraction of the precessional component of the 18oatm signal glaciological constraints on the vostok chronology and the complexity of the dole effect show that those two assumptions are quite probably too simplistic

a penultimate glacial monsoon record from hulu cave and two phase glacial terminations oxygen isotope records of three stalagmites from hulu cave china extend the previous high resolution absolute dated hulu asian monsoon record from the last to the penultimate glacial and deglacial periods the penultimate glacial monsoon broadly follows orbitally induced insolation variations and is punctuated by at least 16 millennial scale events we confirm a weak monsoon interval between 135 5 1 0 and 129 0 1 0 ka prior to the abrupt increase in monsoon intensity at asian monsoon termination ii based on correlations with both marine ice rafted debris and atmospheric ch 4 records we demonstrate that most of marine termination ii the full rise in antarctic temperature and atmospheric co 2 and much of the rise in ch 4 occurred within the weak monsoon interval when the high northern latitudes were probably cold from these relationships and similar relationships observed for termination i we identify a two phase glacial termination process that was probably driven by orbital forcing in both hemispheres affecting the atmospheric hydrological cycle and combined with ice sheet dynamics

tomographic images of the el asnam fault zone and the evolution of a seismogenic thrust related fold the p wave velocity structure of the upper 9 km of the el asnam algeria fault zone the site of the ms7 3 earthquake october 10 1980 is obtained by inverting arrival times from 310 selected aftershocks computed crustal structure and relocation of aftershocks yield new insight on the structural geology of the area and help to clarify the evolution of fault related folding and the complexity of the rupture episodes during the el asnam earthquake the correlation between tomograms and geologic structures observed at the surface and inferred at depth delineates local heterogeneities of the upper crust there is evidence for distinct large scale structural trends consisting of two main thrusts with antithetic reverse faults seismic tomography provides reasonable constraints on the el asnam fault related fold geometry pointing out a complex preexisting structure along which the rupture evolution is controlled by the heterogeneous crust we propose that the main shock originated along an inverted normal fault bordering the pre neogene basement lateral lithologic heterogeneities obtained by seismic tomography reflect the fault segmentation and geometrical discontinuities along strike in agreement with the tectonic pattern

changes in atmospheric co2 and its carbon isotopic ratio during the penultimate deglaciation abstract the largest natural increases in atmospheric co 2 concentration as recorded in ice cores occur when the earth climate abruptly shifts from a glacial to an interglacial state open questions remain regarding the processes at play the sequences of events and their similarities along different glacial interglacial transitions here we provide new combined data of atmospheric co 2 and its carbon isotopic ratio 13 co 2 for the penultimate glacial interglacial transition termination ii from the antarctic epica dome c ice core together with the strongest antarctic warming this transition bears the largest co 2 increase 104 ppmv of the last nine terminations ending with an overshoot of 21 ppmv occurring within 300 y and leading to higher levels than those of the late pre industrial holocene the full co 2 rise is accompanied by an overall decrease of the 13 co 2 minimum values on which three positive excursions are superimposed peak to peak 13 co 2 changes in our record can reach 1 the ice core atmospheric 13 co 2 appears more depleted by 0 2 during termination ii compared to termination i paralleling a similar carbon isotopic depletion recorded in marine data during both terminations most of co 2 and 13 co 2 variations are attributed to southern ocean stratification breakdown and decreased efficiency of the biological pump compared to termination i termination ii ice core data point to different timings of decrease in iron supply and sea ice extent suggesting that they could account for distinct patterns of the carbon cycle

seismic imaging of arc magma and fluids under the central part of northeastern japan abstract a dense seismic network was temporarily deployed during 1997 1999 in the central part of northeastern japan by japanese university research groups using the local earthquake arrival time data recorded by the network we have determined high resolution three dimensional images of p wave velocity vp s wave velocity vs and vp vs ratio in this area our results show that low vp low vs and high vp vs areas are extensively distributed in the uppermost mantle along the volcanic front in the lower crust low vp low vs and high vp vs areas are visible but they are confined to the individual volcanic areas in contrast the upper crust of volcanic areas shows low vp low vs and low vp vs rather than high vp vs these observations suggest that partial melting materials exist in the uppermost mantle along the volcanic front and they spread up to the midcrust of the volcanic areas low vp low vs and low vp vs in the upper crust of the volcanic areas suggest the presence of h2o rather than melt there deep low frequency microearthquakes perhaps caused by the rapid movement of fluids are located mostly at the edge of partial melting zones particularly at their upper surface distinct s wave reflectors bright spots with large reflection coefficients are distributed in the midcrust with slightly low vp vs suggesting that most of them are filled with h2o

large heterogeneous structure beneath the atotsugawa fault central japan revealed by seismic refraction and reflection experiments abstract a high strain rate zone termed the niigata kobe tectonic zone is located in central japan and contains an active right lateral fault called the atotsugawa fault we present the results of an explosive source seismic experiment that focused on identifying the formation mechanisms of the fault the experiment used seven explosive sources and 1108 seismic stations and was undertaken during october 2007 in the area of the atotsugawa fault the seismic stations were set up on a survey line with a length of 170 km oriented orthogonal to the strike of the fault the linear array was used to identify the seismic structure of the fault zone and the deeper parts of the crust in the study area yielding fine details of the seismic structure of the crust along the profile line including lateral variations in p wave velocity and the configuration of layers in the crust a relatively low p wave velocity reflective zone was detected beneath the fault at depths of 15 25 km this zone also has extremely low s wave velocities directly underlies three active faults and contains three low resistivity zones that underlie these faults these reflective and low resistivity zones are thought to represent fluid within the crust and the data obtained during this study are consistent with a weak zone model for the formation of the active faults in the study area this suggests that the reflective layer represents a weak zone in the lower crust that is responsible for the concentration of deformation within the upper crust the presence of abundant fluids beneath the atotsugawa fault could also reduce the strength of the lower crust again focusing deformation related to the regional stress regime in areas that overlie these fluid containing zones the results suggest that the reflective layer was an important factor in the formation of the atotsugawa fault

abrupt change of antarctic moisture origin at the end of termination ii the deuterium excess of polar ice cores documents past changes in evaporation conditions and moisture origin new data obtained from the european project for ice coring in antarctica dome c east antarctic ice core provide new insights on the sequence of events involved in termination ii the transition between the penultimate glacial and interglacial periods this termination is marked by a north south seesaw behavior with first a slow methane concentration rise associated with a strong antarctic temperature warming and a slow deuterium excess rise this first step is followed by an abrupt north atlantic warming an abrupt resumption of the east asian summer monsoon a sharp methane rise and a co 2 overshoot which coincide within dating uncertainties with the end of antarctic optimum here we show that this second phase is marked by a very sharp dome c centennial deuterium excess rise revealing abrupt reorganization of atmospheric circulation in the southern indian ocean sector

seismic structure of the northeastern japan convergent margin a synthesis many studies recently made on the basis of seismic observations have revealed a detailed structure of the crust and the upper mantle beneath the northeastern japan arc and its relationship to seismic and volcanic activity spatial distributions of the depths to the conrad and the moho discontinuities estimated from shallow earthquake data and seismic explosion data show that both discontinuities are deep in the middle of the land area and shallow toward the coastlines of the japan sea and the pacific ocean the pn velocity has a lateral variation it is as low as 7 5 km s beneath the land area while that beneath the japan sea and the pacific ocean is 8 0 8 2 km s it changes abruptly at the transition zones which are located along the coastlines precise structure and location of the subducted pacific plate beneath the land area is inferred from converted or reflected seismic waves at the top or bottom of the plate the pacific plate is composed of a thin 5 km low velocity upper layer and a thick high velocity lower layer its total thickness being 80 90 km the upper plane seismicity of the double seismic zone is confined to the thin low velocity upper layer which probably corresponds to the subducted former oceanic crust the lower plane seismicity lies at the middle of the high velocity lower layer and the lower half of the plate below it is incapable of generating earthquakes the shallower portion of the upper surface of the plate beneath the pacific ocean along which major seismicity with low angle thrust faultings is actually occurring is also located by seismic observations on land and in the sea the pacific plate subducts at an extremely low angle of 5 for the first 25 km depth and then the dip steepens rather abruptly to 30 normal fault type events at the top of the plate have not been detected in the portion where the downward bending is the largest but have been ditected near the trench axis where it is rather small tomographic inversions for seismic velocity structure clearly delineate the inclined high velocity pacific plate with a thickness of 80 90 km and low velocity zones in the crust and the mantle wedge beneath active volcanoes seismic attenuation tomography also shows similar zones of low q value beneath active volcanoes although its spatial resolution is much lower the low velocity zones with 2 6 velocity lows are continuously distributed from the upper crust just beneath active volcanoes to a depth of 100 150 km in the mantle wedge and are approximately parallel to the dip of the underlying pacific plate these low velocity zones probably reflect the pathway of magma ascent from a depth in the mantle wedge to the earth s surface corresponding to a portion of the subduction induced secondary mantle wedge flow

basin inversion in central taiwan and its importance for seismic hazard proyectos intramurales 2006 301010 ministerio de ciencia e innovacion cgl2009 11843 bte and the csic predoctoral program junta para la ampliacion de estudios jae predoc

imaging the heterogeneous source area of the 2003 m6 4 northern miyagi earthquake ne japan by double difference tomography abstract a shallow m6 4 inland earthquake occurred on 26 july 2003 in the northern part of miyagi prefecture northeastern japan this earthquake was a typical inland thrust earthquake a type that is common in ne japan we obtained a detailed seismic velocity structure in the focal area of this earthquake by the double difference tomography method arrival time data came from temporary seismic stations deployed above the mainshock fault plane both the p wave and s wave velocities in the hanging wall were lower than those in the footwall aftershocks were aligned along a zone where the seismic velocity changes rapidly this is consistent with the interpretation that the 2003 northern miyagi earthquake occurred along a fault that acted as a normal fault in the miocene and has been reactivated as a reverse fault under the present compressional stress regime the large slip area by the main shock rupture asperity corresponds to an area with relatively high p and s wave velocities a zone with low vp vs was detected along the aftershock area one of the possible causes of this low vp vs zone is the existence of high aspect ratio pores that contain water hypocenters of the main shock largest foreshock and largest aftershock are also located within the low vp vs zone

nucleation process of an m2 earthquake in a deep gold mine in south africa inferred from on fault foreshock activity using a network of sensitive high frequency acoustic emission sensors we observed foreshock activity of an mw 2 2 earthquake main shock in a deep gold mine in south africa foreshock activity which selectively occurred on a part of the rupture plane of the forthcoming main shock lasted for at least 6 months until the main shock rock samples recovered from the main shock source region showed evidence of ancient hydrothermal alteration on the main shock rupture plane suggesting that the foreshock activity occurred on a preexisting weakness the foreshocks during 3 months before the main shock were concentrated in three clusters f1 f3 which we interpret as representing localized preslip at multiple sites while the location of mining area the source of stress perturbations changed with time the locations of foreshock clusters did not change suggesting that the preslip patches were controlled by strength heterogeneity rather than stress distribution activity over the entire foreshock area was generally constant but the largest cluster f2 showed accelerated activity starting at least 7 days before the main shock while mining stress did not increase in this period the main shock initiated at a point close to f1 away from f2 all the six foreshocks during the final 41 h occurred in f1 and f2 and in between these suggest that in the last stage of the preparation process of the main shock preslip patches interacted with each other through the stress concentration ahead of the expanding preslip patch f2 which should be the only driving force of the preparation process under the constant external load

constraint of the co2 rise by new atmospheric carbon isotopic measurements during the last deglaciation 1 the causes of the 80 ppmv increase of atmospheric carbon dioxide co2 during the last glacial interglacial climatic transition remain debated we analyzed the parallel evolution of co2 and its stable carbon isotopic ratio 13co2 in the european project for ice coring in antarctica epica dome c ice core to bring additional constraints agreeing well but largely improving the taylor dome ice core record of lower resolution our 13co2 record is characterized by a w shape with two negative 13co2 excursions of 0 5 during heinrich 1 and younger dryas events bracketing a positive 13co2 peak during the bolling allerod warm period the comparison with marine records and the outputs of two c cycle box models suggest that changes in southern ocean ventilation drove most of the co2 increase with additional contributions from marine productivity changes on the initial co2 rise and 13co2 decline and from rapid vegetation buildup during the co2 plateau of the bolling allerod

three dimensional structure of vp vs and vp vs beneath northeastern japan implications for arc magmatism and fluids we estimated both p v p and s wave velocity v s structures beneath northeastern japan by applying a tomographic method to 169 712 p and 103 993 s wave arrival time data from 4338 local events the average value of v p v s ratio is 1 69 in the upper crust 1 75 in the lower crust and 1 77 in the uppermost mantle these differences in v p v s ratio may mainly reflect the lithological variations with depth low v p low v s and high v p v s zones are extensively distributed along the volcanic front in the uppermost mantle and are downward to the back arc side in the mantle wedge here the low v p low v s and high v p v s values are interpreted because of partial melting materials which imply the presence of a vast amount of melt in the uppermost mantle in the lower crust low v p low v s and high v p v s zones are not continuously visible along the volcanic front but are confined to individual volcanic areas which suggests that melting of lower crustal materials occurs just beneath each active volcano in contrast the upper crust beneath active volcanoes exhibits low v p low v s and low v p v s these results suggest that the partial melting zones under northeastern japan spread out from the uppermost mantle along the volcanic front up to the midcrust right beneath active volcanoes the low v p low v s and low v p v s features in the upper crust suggest the existence of h 2 o rather than melt right beneath active volcanoes

effect of pore geometry on vp vs from equilibrium geometry to crack seismic wave velocities of melt or aqueous fluid containing systems are studied over a wide range of pore shapes including oblate spheroids tubes cracks and an equilibrium geometry controlled by a dihedral angle the relative role of liquid compressibility and pore geometry on the v p v s velocity ratio is clarified the result clearly indicates that p and s velocity structures determined by seismic tomography can be used to verify whether interfacial energy controlled melt or fluid geometry equilibrium geometry is achieved relationships between the diverse models are clearly established by relating each model to the oblate spheroid model in terms of the equivalent aspect ratio as a function of the aspect ratio a significant effect of pore geometry on d in v s d in v p the ratio of the fractional changes in v s and v p is shown equilibrium geometry of the partially molten rocks characterized by a dihedral angle of 20 40 corresponds to an aspect ratio of 0 1 0 15 the value of d in v s d in v p expected for the texturally equilibrated partially molten rocks is shown to be 1 1 5 which is much smaller than that expected for cracks and dikes with an aspect ratio of 10 2 10 3 in the upper mantle low velocity regions the seismologically obtained value of d in v s d in v p is within this range beneath the bolivian andes 1 1 1 4 but is as high as 2 beneath iceland 1 7 2 3 and beneath northeastern japan 2 0 the former region can be regarded as a region where equilibrium geometry is achieved and the latter regions can be regarded as regions where dikes and veins typical of a system far from the textural equilibrium dominate

the 1995 kobe earthquake seismic image of the source zone and its implications for the rupture nucleation in order to understand what may have triggered the 1995 kobe japan earthquake and how the rupture proceeded after initiation we determined high resolution three dimensional 3 d p and s wave velocity and poisson s ratio structures in the kobe epicentral area and relocated the aftershocks with the obtained 3 d velocity model we used 64 337 p and 49 200 s wave high quality arrival times from 3634 kobe aftershocks and local microearthquakes recorded by both permanent seismic networks and portable stations that were set up following the kobe mainshock significant velocity variations of up to 6 are revealed in the aftershock area we found that areas with high aftershock activity are generally associated with low poisson s ratio which may be the strong and competent parts of the fault zone and were apt to generate aftershocks the kobe mainshock hypocenter is located in a distinctive zone characterized by low p and s wave velocities and a high poisson s ratio this anomaly exists in the depth range of 16 to 21 km and extends 15 to 20 km laterally this anomaly may be due to a fluid filled fractured rock matrix that contributed to the initiation of the kobe earthquake our interpretation has been supported by many pieces of evidence from hydrological geochemical seismological and geophysical investigations conducted at the kobe earthquake region

sediment transport and siltation of brown trout salmo trutta l spawning gravels in chalk streams deposition rates of fine sediment into brown trout spawning gravels were measured at monthly intervals for a period of one year in a small channel of the river test hampshire data were also collected on stream discharge water depth flow velocity and suspended sediment concentrations deposition rates followed a seasonal pattern and were maximal during periods of high discharge in the late winter early spring when suspended sediment concentrations were high the material deposited in the spawning gravels included silts and fine sands 250 m that were transported in suspension and coarser fragments of low density tufalike material that were transported as bed load the ecological implications of fine sediment deposition for salmonid egg survival in chalk streams are considered

frictional constraints on crustal faulting we consider how variations in fault frictional properties affect the phenomenology of earthquake faulting in particular we propose that lateral variations in fault friction produce the marked heterogeneity of slip observed in large earthquakes we model these variations using a rate and state dependent friction law where we differentiate velocity weakening behavior into two fields the strong seismic field is very velocity weakening and the weak seismic field is slightly velocity weakening similarly we differentiate velocity strengthening behavior into two fields the compliant field is slightly velocity strengthening and the viscous field is very velocity strengthening the strong seismic field comprises the seismic slip concentrations or asperities the two intermediate fields weak seismic and compliant have frictional velocity dependences that are close to velocity neutral these fields modulate both the tectonic loading and the dynamic rupture process during the interseismic period the weak seismic and compliant regions slip aseismically while the strong seismic regions remain locked evolving into stress concentrations that fail only in main shocks the weak seismic areas exhibit most of the interseismic activity and aftershocks but can also creep seismically this mixed frictional behavior can be obtained from a sufficiently heterogeneous distribution of the critical slip distance the model also provides a mechanism for rupture arrest dynamic rupture fronts decelerate as they penetrate into unloaded complaint or weak seismic areas producing broad areas of accelerated afterslip aftershocks occur on both the weak seismic and compliant areas around a fault but most of the stress is diffused through aseismic slip rapid afterslip on these peripheral areas can also produce aftershocks within the main shock rupture area by reloading weak fault areas that slipped in the main shock and then healed we test this frictional model by comparing the seismicity and the coseismic slip for the 1966 parkfield 1979 coyote lake and 1984 morgan hill earthquakes the interevent seismicity and aftershocks appear to occur on fault areas outside the regions of significant slip these regions are interpreted as either weak seismic or compliant depending on whether or not they manifest interevent seismicity

what drives the millennial and orbital variations of δ18oatm abstract the isotopic composition of atmospheric oxygen 18oatm is a complex marker that integrates changes in global sea level water cycle and biosphere productivity a strong signature of orbital precession has been identified leading to the use of low resolution measurements of 18oatm to date ice core records however the drivers of these 18oatm variations are still poorly known here we combine records of millennial and orbital scale variations on the northgrip vostok and epica dome c edc ice cores to explore the origin of 18oatm variations we show that superimposed on the dominant precession signal millennial 18oatm variations record systematic decreases during warm phases of the dansgaard oeschger events and systematic increases during the cold phases we show that at both timescales 18oatm is strongly related to the monsoon activity itself influenced by precessional and millennial shifts in intertropical convergence zone itcz then we show that despite its simplicity the dole effect defined as the difference between 18oatm and 18o of global sea level enables one to remove the obliquity signal within the 18oatm record and is a good indicator of hydrological cycle and biosphere productivity finally we compare the 18oatm records to past changes in atmospheric composition recorded in ice cores and conclude that 18oatm responds much more than ch4 to precession signal in contrast with earlier views similarities observed at orbital timescales between co2 and 18oatm reveal a stronger coupling than previously thought between the carbon and the oxygen cycles

comparison of source areas of m4 8 0 1 repeating earthquakes off kamaishi ne japan are asperities persistent features abstract m4 8 0 1 earthquakes have occurred regularly since 1957 with a recurrence interval of 5 52 0 68 yr at the same location of the plate boundary off kamaishi iwate prefecture the last event m4 7 occurred on 11 13 2001 16 44 jst and the previous one m4 8 on 3 11 1995 10 30 jst waveforms of these events are similar to each other to examine the hypothesis that this characteristic earthquake sequence is caused by repeating ruptures of an asperity frictionally locked patch surrounded by creeping areas we compared the rupture area of the 2001 event with that of the 1995 event by a waveform inversion method estimated spatial extents of the rupture areas of the 2001 and 1995 events are almost the same and are estimated to be about 1 5 1 5 km 2 the rupture area of the 2001 event is almost completely overlapped with that of the 1995 event although the ruptures of the two events were initiated from different points the present observations clearly show that the 1995 and 2001 events are caused by the repeating ruptures of the same asperity patch and support the hypothesis of persistent asperities

orbital and millennial antarctic climate variability over the past 800 000 years a high resolution deuterium profile is now available along the entire european project for ice coring in antarctica dome c ice core extending this climate record back to marine isotope stage 20 2 800 000 years ago experiments performed with an atmospheric general circulation model including water isotopes support its temperature interpretation we assessed the general correspondence between dansgaard oeschger events and their smoothed antarctic counterparts for this dome c record which reveals the presence of such features with similar amplitudes during previous glacial periods we suggest that the interplay between obliquity and precession accounts for the variable intensity of interglacial periods in ice core records

receiver function images of the distorted philippine sea slab contact with the continental crust implications for generation of the 1891 nobi earthquake mj 8 0 abstract the 28 october 1891 nobi earthquake was one of the largest intraplate earthquakes in japan with an estimated magnitude of 8 0 determined by the japan meteorological agency it occurred in central japan on the eurasian plate beneath which the young philippine sea plate is subducting the geometry of this plate is not smooth rather beneath western japan it appears distorted over a relatively short lateral distance beneath the kinki region of central japan the subduction angle is approximately horizontal and the nobi earthquake occurred just above the horizontal section of the philippine sea slab temporary seismic stations were deployed in this area to investigate local seismic structure and its possible relationship to the cause of the earthquake crustal structure was investigated using receiver function analysis with a spatially dense temporary seismic network a clear image of the subducted philippine sea slab was resolved with ridge like structures beneath the epicentral area of the nobi earthquake the ridge like structure is in contact with the continental crust and the fault plane of the nobi earthquake is located at the edge of one such structure i e in the contact area the unique structure of the area is inferred to cause stress concentration and strain accumulation on local faults which resulted in the large size of the nobi earthquake

atmospheric δ13co2 and its relation to pco2 and deep ocean δ13c during the late pleistocene the ratio of the stable carbon isotopes of atmospheric co2 13co2 contains valuable information on the processes which are operating on the global carbon cycle however current 13co2 ice core records are still limited in both resolution and temporal coverage as well as precision in this study we performed simulations with the carbon cycle box model bicycle with special emphasis on atmospheric 13co2 proposing how changes in 13co2 might have evolved over the last 740 000 years we furthermore analyze the relationship between atmospheric 13co2 pco2 and deep ocean 13c of dissolved inorganic carbon dic 13cdic in both our modeling framework and proxy records when available our analyses show that mean ocean and deep pacific 13cdic are mainly controlled by the glacial interglacial uptake and release of carbon temporarily stored in the terrestrial biosphere during warmer climate periods in contrast glacial interglacial changes in pco2 and 13co2 represent mainly a mixture of ocean related processes superimposed on the slow glacial interglacial change in terrestrial carbon storage the different processes influencing atmospheric 13co2 largely compensate each other and cancel all variability with frequencies of 1 100 kyr 1 large excursions in 13co2 can a priori be expected as any small phase difference between the relative timing of the dominant and opposite sign processes might create large changes in 13co2 amplitudes in 13co2 caused by fast terrestrial uptake or release during millennial scale climate variability depend not only on the amount of transferred carbon but also on the speed of these changes those which occur on timescales shorter than a millennium are not detectable in 13co2 because of gas exchange equilibration with the surface ocean the 13co2 signal of fast processes on the other hand is largely attenuated in ice core records during the firnification and gas enclosure we therefore suggest to measure 13co2 with priority on ice cores with high temporal resolution and select times with rather fast climatic changes

ice age terminations 230th dated oxygen isotope records of stalagmites from sanbao cave china characterize asian monsoon am precipitation through the ends of the third and fourthmost recent ice ages as a result am records for the past four glacial terminations can now be precisely correlated with those from ice cores and marine sediments establishing the timing and sequence of major events in all four cases observations are consistent with a classic northern hemisphere summer insolation intensity trigger for an initial retreat of northern ice sheets meltwater and icebergs entering the north atlantic alter oceanic and atmospheric circulation and associated fluxes of heat and carbon causing increases in atmospheric co2 and antarctic temperatures that drive the termination in the southern hemisphere increasing co2 and summer insolation drive recession of northern ice sheets with probable positive feedbacks between sea level and co2

seismic activity and deformation process of the overriding plate in the northeastern japan subduction zone abstract we estimated the temperature distribution within the crust of the northeastern japan arc from p wave velocity perturbations obtained by travel time tomography by comparing the estimated temperature distribution with the focal depth distribution of shallow precisely relocated microearthquakes we found that the brittle to ductile or stick slip to stable sliding transition occurs at the 400 c isotherm and that the transition depth has considerable lateral variations the brittle seismogenic zone the upper portion of the crust becomes locally thin in the p wave low velocity areas where the temperature is estimated to be relatively high concentration of shallow microearthquakes high topography and relatively large contractile deformation of the crust are also observed in these low velocity areas active faults are not distributed in the low velocity areas but lie just along the edge of those areas or outside them all these observations suggest that earthquake occurrence and deformation within the crust is governed to a considerable degree by the thermal regime of this volcanic arc which is characterized by a horizontally inhomogeneous distribution of temperature

interhemispheric atlantic seesaw response during the last deglaciation the asynchronous relationship between millennial scale temperature changes over greenland and antarctica during the last glacial period has led to the notion of a bipolar seesaw which acts to redistribute heat depending on the state of meridional overturning circulation within the atlantic ocean here we present new records from the south atlantic that show rapid changes during the last deglaciation that were instantaneous within dating uncertainty and of opposite sign to those observed in the north atlantic our results demonstrate a direct link between the abrupt changes associated with variations in the atlantic meridional overturning circulation and the more gradual adjustments characteristic of the southern ocean these results emphasize the importance of the southern ocean for the development and transmission of millennial scale climate variability and highlight its role in deglacial climate change and the associated rise in atmospheric carbon dioxide

carbon isotope constraints on the deglacial co2 rise from ice cores the stable carbon isotope ratio of atmospheric co2 13catm is a key parameter in deciphering past carbon cycle changes here we present 13catm data for the past 24 000 years derived from three independent records from two antarctic ice cores we conclude that a pronounced 0 3 per mil decrease in 13catm during the early deglaciation can be best explained by upwelling of old carbon enriched waters in the southern ocean later in the deglaciation regrowth of the terrestrial biosphere changes in sea surface temperature and ocean circulation governed the 13catm evolution during the last glacial maximum 13catm and atmospheric co2 concentration were essentially constant which suggests that the carbon cycle was in dynamic equilibrium and that the net transfer of carbon to the deep ocean had occurred before then

double difference tomography the method and its application to the hayward fault california we have developed a double difference dd seismic tomography method that makes use of both absolute and relative arrival times by reducing systematic errors using the more accurate relative arrival times the method produces an improved velocity model simultaneously it yields event locations of a quality equivalent to those of the dd location method while avoiding simplifying assumptions of that method we test this method on a synthetic dataset and find that it produces a more accurate velocity model and event locations than standard tomography we also test this method on a hayward fault california earthquake dataset spanning 1984 1998 the earthquakes relocated by this method collapse to a thin line along the fault trace consistent with previous results the dd velocity model has sharper velocity contrasts near the source region than the standard tomography model

the dole effect and its variations during the last 130 000 years as measured in the vostok ice core we review the current understanding of the dole effect the observed difference between the delta sup 18 o of atmospheric o sub 2 and that of seawater and its causes extended the record of variations in the dole effect back to 130 kyr before present using data on the delta sup 18 o of o sub 2 obtained from studying the vostok ice core and discuss the significance of temporal variations the dole effect reflects oxygen isotope fractionation during photosynthesis respiration and hydrologic processes evaporation precipitation and evapotranspiration our best prediction of the present day dole effect 20 8 per thousand is considerably lower than the observed value 23 5 per thousand and we discuss possible causes of this discrepancy during the past 130 kyr the dole effect has been 0 05 per thousand lower than the present value on average the standard deviation of the dole effect from the mean has been only per thousand and the dole effect is nearly unchanged between glacial maxima and interglacial periods the small variability in the dole effect suggests that relative rates of primary production in the land and marine realms have been relatively constant most periodic variability in the dole effect is in the precession band suggesting that changes in this global biogeochemical termmore reflects variations in low latitude land hydrology and productivity or possibly variability in low latitude oceanic productivity 65 refs 4 figs 3 tabs less

climatic pause during termination ii identified in shallow and intermediate waters off the iberian margin the sequence of termination ii from the end of marine isotopic stage 6 mis 6 to mis 5e is observed through an isotopic study 18o of planktic and benthic foraminifera in core md99 2331 42 09 n 09 41 w collected in the north atlantic on the iberian margin first to build an approximate time scale a record of the planktic 18o signal is achieved from the top of the core holocene to mis 6 the remarkable similarity of this planktic record to the greenland ice core project ice core 18o record allows a rough dating of our core a focus on termination ii reveals one standstill in the benthic record this pause can be linked either to a perturbation of north atlantic oceanic circulation pattern as a slowing down of the north atlantic deep water formation or to an interruption in polar ice sheet melting which could be a more global phenomenon

synchronising edml and northgrip ice cores using δ18o of atmospheric oxygen δ18oatm and ch4 measurements over mis5 80 123 kyr abstract water isotope records from the epica dronning maud land edml and the northgrip ice cores have revealed a one to one coupling between antarctic isotope maxima aim and greenland dansgaard oeschger do events back to 50 kyr in order to explore if this north south coupling is persistent over marine isotopic stage 5 mis 5 a common timescale must first be constructed here we present new records of 18o of o2 18oatm and methane ch4 measured in the air trapped in ice from the edml 68 147 kyr and northgrip 70 123 kyr ice cores we demonstrate that through the period of interest ch4 records alone are not sufficient to construct a common gas timescale between the two cores millennial scale variations of 18oatm are evidenced over mis 5 both on the antarctic and greenland ice cores and are coupled to ch4 profiles to synchronise the northgrip and edml records they are shown to be a precious tool for ice core synchronisation with this new dating strategy we produce the first continuous and accurate sequence of the north south climatic dynamics on a common ice timescale for the last glacial inception and the first do events of mis 5 reducing relative dating uncertainties to an accuracy of a few centuries at the onset of do events 24 to 20 this edml northgrip synchronisation provides new firm evidence that the bipolar seesaw is a pervasive pattern from the beginning of the glacial period the relationship between antarctic warming amplitudes and their concurrent greenland stadial duration highlights the particularity of do event 21 and its antarctic counterpart our results suggest a smaller southern ocean warming rate for this long do event compared to do events of mis 3

glacial terminations as southern warmings without northern control the timing and mechanisms of the transition from a glacial to an interglacial state are controversial an analysis of antarctic ice core records indicates that glacial terminations may begin as millennial scale warmings in the southern hemisphere that unlike previous events are not reversed by abrupt warming in the northern hemisphere

modification of fluvial gravel size by spawning salmonids salmonids salmon and trout winnow fine sediment from streambed gravels during construction of the nest or open quotes redd close quotes used for spawning and incubation of fertilized eggs the gravels and interstitial fine sediments excavated during this process are exposed to currents and differently transported gravels move a short distance while the fine sediments are swept further downstream from the redd to quantify the resultant modification of particle size distributions in redds the authors sampled redds and adjacent undisturbed gravels to document changes in size distributions these data were compiled with previously published observations to analyze the general nature of size modification during spawning the final percentage finer than 1 mm in the gravels p1 sub f is related to the initial percentage finer than 1 mm p1 sub i by the equation p1 sub f 0 63 p1 sub i hydraulic variables water surface slope mean column velocity depth shear stress unit stream power explained little of the variance and did not appear in the optimal models because fisheries biologists are called upon to evaluate gravels as potential spawning sites these findings should prove useful in such evaluations 44 refs 5 figs 4 tabs

the last glacial termination a major puzzle of paleoclimatology is why after a long interval of cooling climate each late quaternary ice age ended with a relatively short warming leg called a termination we here offer a comprehensive hypothesis of how earth emerged from the last global ice age a prerequisite was the growth of very large northern hemisphere ice sheets whose subsequent collapse created stadial conditions that disrupted global patterns of ocean and atmospheric circulation the southern hemisphere westerlies shifted poleward during each northern stadial producing pulses of ocean upwelling and warming that together accounted for much of the termination in the southern ocean and antarctica rising atmospheric co2 during southern upwelling pulses augmented warming during the last termination in both polar hemispheres

evolution of strength recovery and permeability during fluid rock reaction in experimental fault zones abstract physical and chemical fluid rock interactions are implicated in controlling earthquake nucleation and recurrence in particular interseismic compaction sealing and healing of fractured fault rocks can lead to strength recovery and stabilisation of fault zones in contrast these same processes can also assist increases in pore fluid pressures and consequent destabilisation of faults here we present high temperature hydrothermal experiments designed to assess the evolution of strength of fault zones in previously intact rock and also characterise the associated changes to porosity and permeability cores of fontainebleau sandstone were initially loaded to failure in a high pressure gas medium apparatus the failed specimens were then hydrothermally reacted at 927 c for variable duration under isostatic conditions and subsequently re fractured to determine the interseismic strength recovery in the most extreme case hydrothermally induced gouge compaction cementation and crack healing resulted in 75 strength recovery after reaction for 6 h isostatic hydrothermal treatment also resulted in dramatic reduction in porosity and permeability strength of the fault zone following hydrothermal reaction appears to be closely correlated to porosity consistent with previous studies on brittle failure of porous aggregates the experimental results show how hydrothermal reactions in fault zones may lead to two competing time dependent effects fault strengthening due to increased cohesion in the fault zone and fault weakening arising from elevated pore pressures within a well cemented low permeability gouge layer

paleocean circulation during the last deglaciation a bipolar seesaw hughen et al 1998 have documented that during the first 200 years of younger dryas time the 14c content of atmospheric co2 increased by 50 and that during the remainder of this 1200 year duration cold event it steadily declined the initial increase in 14c c was likely the result of a reduction in the atlantic s conveyor circulation however were the subsequent radiocarbon decline due to the rejuvenation of this potent heat pump then it is difficult to understand why the climate conditions in the northern atlantic basin remained cold throughout the younger dryas modeling exercises by stocker and wright 1996 mikolajewicz 1998 and schiller et al 1998 show that if the conveyor is terminated the transfer of radiocarbon into the deep sea shifts to the southern ocean thereby stabilizing the atmospheric 14c c ratio paleoclimatic evidence from the antarctic continent suggests that this model based scenario might have been played out in the real world while the younger dryas cooling has been documented in many places around the world including new zealand denton and hendy 1994 sowers and bender 1995 using their 18o in o2 based correlation between the ice core 18o in ice records for antarctica and greenland have demonstrated that in antarctica the younger dryas was a time of maximum warming the point of this paper is that the steep rise in 18o rise in antarctic ice which commenced close to the onset of the younger dryas might have been caused by heat released to the atmosphere in response to an increase in deep sea ventilation in the southern ocean

imaging the source area of the 1995 southern hyogo kobe earthquake m7 3 using double difference tomography abstract to understand the generation process of inland earthquake we determined the seismic velocity structure in and around the source area of the 1995 southern hyogo kobe earthquake m7 3 in sw japan we adopted the double difference dd tomography method zhang h and c thurber double difference tomography the method and its application to the hayward fault california bull seism soc am 93 2003 1875 1889 we inverted arrival times recorded by a dense temporary seismic network for aftershocks and seismic networks routinely operated by japanese universities obtained results are summarized as follows 1 low velocity zones of a few kilometers width are distributed along the fault or along the aftershock alignment suggesting that the fault of the 1995 earthquake is located primarily in a low velocity zone 2 amount of velocity decrease within this low velocity zone varies along the strike of the fault most of large slip areas asperities seem to correspond to higher velocity areas relative to the surroundings on the fault rather than to lower velocity areas

two phase change in co2 antarctic temperature and global climate during termination ii the end of the last glacial maximum termination i roughly 20 thousand years ago ka was marked by cooling in the northern hemisphere a weakening of the asian monsoon a rise in atmospheric co2 concentrations and warming over antarctica the sequence of events associated with the previous glacial interglacial transition termination ii roughly 136 ka is less well constrained here we present high resolution records of atmospheric co2 concentrations and isotopic composition of n2 an atmospheric temperature proxy from air bubbles in the epica dome c ice core that span termination ii we find that atmospheric co2 concentrations and antarctic temperature started increasing in phase around 136 ka but in a second phase of termination ii from 130 5 to 129 ka the rise in atmospheric co2 concentrations lagged that of antarctic temperature unequivocally we suggest that during this second phase the intensification of the low latitude hydrological cycle resulted in the development of a co2 sink which counteracted the co2 outgassing from the southern hemisphere oceans over this period

a field method for the concurrent measurement of fine sediment content and embryo survival in artificial salmonid redds the infiltration cube method presented in this paper allows concurrent field measurement of fine sediment content and embryo survival in an incubating environment reproducing as closely as possible the morphology and grain size composition of a natural salmonid redd an infiltration cube is made up of a rectangular 30 cm square and 20 cm high steel frame with no walls which has a folded plastic bag attached to its base each infiltration cube is buried in the substrate using a procedure aimed at reproducing as closely as possible the construction and morpho sedimentological structure of a natural salmonid redd using a tripod installed on the river bed or at the surface of the ice the infiltration cube method provides a quick easy and robust way to pull relatively large samples approximately 65 kg out of underwater substrate even during tough winter field conditions the absence of walls on the cube also precludes bias in infiltration rates by both allowing lateral sediment transport within substrate and preventing loss of fine particles during retrieval from underwater copyright 2006 john wiley sons ltd

relations among fault behavior subsurface geology and three dimensional velocity models the development of three dimensional p wave velocity models for the regions surrounding five large earthquakes in california has lead to the recognition of relations among fault behavior and the material properties of the rocks that contact the fault at seismogenic depths regions of high moment release appear to correlate with high seismic velocities whereas rupture initiation or termination may be associated with lower seismic velocities these relations point toward a physical understanding of why faults are divided into segments that can fail independently an understanding that could improve our ability to predict earthquakes and strong ground motion

firn processes and δ15n potential for a gas phase climate proxy abstract in order to quantify the sequence of events between changes in atmospheric composition and climate changes recorded in ice cores we must accurately account for the age difference between ice and gas at a given depth this gas age ice age difference depends on the age of the ice at the bottom of the firn layer where the bubbles are closed off firn densification models are used to calculate how this age difference varied in the past but have an uncertainty on the order of 1000 years for central antarctic sites here we explore the possibility that 15 n of n 2 is a gas phase proxy of climate which can be used to synchronize gas and ice records we present the 15 n record from the epica dome c edc ice core covering the last three glacial terminations and five glacial interglacial cycles between 300 and 800 ka previous studies have shown that gravitational settling enriches 15 n as a function of the diffusive column height in the firn if densification models prediction of deeper firn close off under glacial conditions is correct then we would expect heavier 15 n during glacial periods and a negative correlation with temperature instead edc 15 n is positively correlated with the ice deuterium content a proxy for temperature as previously reported at vostok dome fuji and epica dronning maud land we propose a mechanism that links accumulation rate firn permeability and convective mixing in the top meters of the firn to explain this correlation between 15 n and ice deuterium content the tightest correlation is observed over glacial terminations supporting the idea that 15 n is a property in the gas phase that records changes in surface conditions linked to deglacial warming

stochastic resonance in the north atlantic large abrupt changes between warm and cold modes of north atlantic climate exhibit spectral power at 1500 years yet some climatic changes were linked to outburst floods and other events that are unlikely to have been truly periodic we hypothesize that a weak periodic forcing has combined with noise from ice sheet related events to cause the observed mode switches this stochastic resonance hypothesis predicts a recurrence pattern between warmings that is distinct from the predictions of simple periodic and stochastic models and at least some other models the ice isotopic data from central greenland ice cores are consistent with the stochastic resonance hypothesis but not with other models we have tested we thus support arguments for the existence of a periodicity of 1500 years in the north atlantic climate system and for the importance of ice sheet events in forcing north atlantic changes

the deuterium excess records of epica dome c and dronning maud land ice cores east antarctica new high resolution deuterium excess d data from the two epica ice cores drilled in dronning maud land edml and dome c edc are presented here the main moisture sources for precipitation at edc and edml are located in the indian ocean and atlantic ocean respectively the more southward moisture origin for edml is reflected in a lower present day d value compared to edc the edml and edc isotopic records 18o and d show the main climate features common to the east antarctic plateau and similar millennial scale climate variability during the last glacial period however quite large 18o and d differences are observed during mis5 5 and the glacial inception with a long term behaviour a possibility for this long term difference could be related to uncertainties in past accumulation rate which are used in the glaciological models regional climate anomalies between the two sites during mis5 5 could also be consistent with the observed edml edc 18o and d gradient anomalies simulations performed with the general circulation model echam4 for different time slices provide a temporal temperature isotope slope for the edml region in fair agreement to the modern spatial slope tsite and tsource records are extracted from both ice cores using a modelling approach after corrections for past 18o seawater and elevation changes a limited impact of d on antarctic temperature reconstruction at both edml and edc has been found with a higher impact only at glacial inception the aim antarctic isotope maximum events in both ice cores are visible also after the source correction suggesting that these are real climate features of the glacial period the different shape of the aim events between edc and edml as well as some climate features in the early holocene points to a slightly different climate evolution at regional scale a comparison of our temperature reconstruction profiles with the aerosol fluxes show a strong coupling of the nssca fluxes with antarctic temperatures during glacial period and a tighter coupling of 18o and tsite with ssna flux at edml compared to edc during the glacial period and mis5 5

three dimensional velocity structure seismicity and fault structure in the parkfield region central california this study examines the three dimensional velocity structure in a 60 by 80 km region containing the parkfield segment of the san andreas fault we use local earthquake and shot p arrival times in an iterative simultaneous inversion for velocity and hypocentral parameters using the three dimensional model we relocated 5251 events that occurred from 1969 to 1991 as well as the 1966 aftershocks and computed 664 fault plane solutions the san andreas fault saf characterized by a sharp across fault velocity gradient is the primary feature in the velocity solution there is a 5 20 lateral change in velocity over a 4 km width the contrast being sharper where there is better resolution the model also shows significant variations in the velocity and in the complexity of the velocity patterns along the saf the largest across fault velocity difference is below middle mountain where a large volume of low velocity material impinges on the saf from the northeast this material is inferred to be overpressured and may be key to understanding the unusual behavior in the parkfield preparation zone a 20 km long high velocity slice is imaged northeast of the saf near gold hill its along fault length corresponds to the length of the maximum slip in 1966 the relocated seismicity shows that the san andreas fault is a planar vertical fault zone at seismogenic depths ninety percent of the fault plane solutions that are on or near the saf were right lateral strike slip on subvertical fault planes that parallel the saf thus the surface fault complexities do not appear to extend to depth and therefore do not explain the rupture character at parkfield at parkfield variations in material properties play a key role in fault segmentation and deformation style our observations suggest that there may be a general relation between increasing velocity and increasing ability of the rocks to store strain energy and release it as brittle failure

synchronous volcanic eruptions and abrupt climate change 17 7 ka plausibly linked by stratospheric ozone depletion glacial state greenhouse gas concentrations and southern hemisphere climate conditions persisted until 17 7 ka when a nearly synchronous acceleration in deglaciation was recorded in paleoclimate proxies in large parts of the southern hemisphere with many changes ascribed to a sudden poleward shift in the southern hemisphere westerlies and subsequent climate impacts we used high resolution chemical measurements in the west antarctic ice sheet divide byrd and other ice cores to document a unique 192 y series of halogen rich volcanic eruptions exactly at the start of accelerated deglaciation with tephra identifying the nearby mount takahe volcano as the source extensive fallout from these massive eruptions has been found 2 800 km from mount takahe sulfur isotope anomalies and marked decreases in ice core bromine consistent with increased surface uv radiation indicate that the eruptions led to stratospheric ozone depletion rather than a highly improbable coincidence circulation and climate changes extending from the antarctic peninsula to the subtropics similar to those associated with modern stratospheric ozone depletion over antarctica plausibly link the mount takahe eruptions to the onset of accelerated southern hemisphere deglaciation 17 7 ka

vp and vp vs images in the mw 6 0 colfiorito fault region central italy a contribution to the understanding of seismotectonic and seismogenic processes 1 in 1997 the umbria marche apennines central italy was struck by a series of moderate magnitude normal faulting earthquakes accompanied by a prolonged sequence of aftershocks seismological analysis revealed a 40 km long nw trending structure composed by several low angle normal fault segments in this paper we present the three dimensional 3 d vp and vp vs structure of the fault zone determined by the inversion of p and s wave arrival times from 1982 aftershocks the high resolution tomographic images reveal strong heterogeneity along and across the fault zone and allow us along with the 3 d location of earthquakes to define the fault geometry at depth and to improve our understanding on the seismotectonics of this part of the northern apennines thrust and fold belt the relocated aftershocks suggest that the main ruptures occurred on planes slightly steeper than previously hypothesized and at depths shallower than those evidenced by 1 d locations we find that the preexisting structure which developed during the neogene compressional tectonics plays an important role in the earthquake generation and rupture evolution of the normal faulting events we propose that the main shocks whose hypocenters are all located at 6 km depth originated along a shallow decollement of the meso cenozoic cover thrust over the metamorphic basement geometrical discontinuities and lateral steps along the inherited structures control the lateral fault extent and determine fault segmentation this study offers a good example of how lithological heterogeneities and the complexity of the upper crust structure strongly affect the faulting process

deep structure of the northeastern japan arc and its implications for crustal deformation and shallow seismic activity abstract seismic tomography studies in the northeastern japan arc have revealed the existence of an inclined sheet like seismic low velocity and high attenuation zone in the mantle wedge at depths shallower than about 150 km this sheet like low velocity high attenuation zone is oriented sub parallel to the subducted slab and is considered to correspond to the upwelling flow portion of the subduction induced convection the low velocity high attenuation zone reaches the moho immediately beneath the volcanic front or the ou backbone range running through the middle of the arc nearly parallel to the trench axis which suggests that the volcanic front is formed by this hot upwelling flow aqueous fluids supplied by the subducted slab are probably transported upward through this upwelling flow to reach shallow levels beneath the backbone range where they are expelled from solidified magma and migrate further upward the existence of aqueous fluids may weaken the surrounding crustal rocks resulting in local contractive deformation and uplift along the backbone range under the compressional stress field of the volcanic arc a strain rate distribution map generated from gps data reveals a notable concentration of east west contraction along the backbone range consistent with this interpretation shallow inland earthquakes are also concentrated in the upper crust of this locally large contraction deformation zone based on these observations a simple model is proposed to explain the deformation pattern of the crust and the characteristic shallow seismic activity beneath the northeastern japan arc

sediment transport and resulting deposition in spawning gravels north coastal california incubating salmonid eggs in streambeds are often threatened by deposition of fine sediment within the gravel to relate sedimentation of spawning gravel beds to sediment transport infiltration of fine sediment 2 mm in diameter into clean gravel beds bed material size distributions scour fill depths and sediment transport during 10 storm flow events were measured in three streams of north coastal california although suspended sediment comprised most 75 94 of the clastic load during storm flows bed load material 0 25 2 mm accounted for most 70 78 of the fine sediment accumulated in experimental gravel implanted in the streambeds sand trapped in the interstices of the top several centimeters formed a seal that impeded deeper deposition of very fine sand and finer material the seal was responsible at least in part for a decrease in the rate of fine sediment accumulation with increasing cumulative bed load transport areas of the streambeds commonly scoured or filled 0 1 m or more during storm flows and thus scour and fill commonly created a sandy layer at least as thick as the seal formed by sediment infiltration scour could erode eggs laid in the bed and expose deeper levels of the bed to infiltration by fine sediment but at the same time could allow fine sediment to be winnowed away great temporal and spatial variation in sedimentation in these streams suggests that individual storms of moderate size pose a threat to eggs in many but not all areas selected by fish for spawning

two dimensional seismic image of the san andreas fault in the northern gabilan range central california evidence for fluids in the fault zone a joint inversion for two dimensional p wave velocity vp p to s velocity ratio vp vs and earthquake locations along the san andreas fault saf in central california reveals a complex relationship among seismicity fault zone structure and the surface fault trace a zone of low vp and high vp vs lies beneath the saf surface trace safst extending to a depth of about 6 km most of the seismic activity along the saf occurs at depths of 3 to 7 km in a southwest dipping zone that roughly intersects the safst and lies near the southwest edge of the low vp and high vp vs zones tests indicate that models in which this seismic zone is significantly closer to vertical can be confidently rejected a second high vp vs zone extends to the northeast apparently dipping beneath the diablo range another zone of seismicity underlies the northeast portion of this vp vs high the high vp vs zones cut across areas of very different vp values indicating that the high vp vs values are due to the presence of fluids not just lithology the close association between the zones of high vp vs and seismicity suggests a direct involvement of fluids in the faulting process

ductile creep compaction and rate and state dependent friction within major fault zones the shear traction on major strike slip faults during earthquakes is much lower than that expected on a frictionally sliding surface in equilibrium with hydrostatic pressure the low shear traction is explained if the fluid pressure at the time of the earthquake is much greater than hydrostatic pressure ductile creep within mostly sealed fault zones compacts the matrix and thus increases fluid pressure between earthquakes frictional dilatancy during earthquakes decreases fluid pressure below hydrostatic and over the earthquake cycle the fault zone is in long term equilibrium with the country rock this ductile mechanism is formally unified with rate and state theory for time dependent friction when the difference between a critical porosity where the rock loses all strength and the actual porosity of cracks is used as a state variable this choice is justified by percolation theory of mostly broken lattices time dependent behavior associated with changes in normal traction in the laboratory is explained by the formalism instability earthquakes sometimes occurs in the numerical experiments however fairly small amounts of frictional dilatancy during initial frictional creep decrease fluid pressure and preclude unstable sliding two coupled mechanisms for producing dilatancy on faults once an instability is well underway are evident 1 expansion of pore fluids associated with frictional heating increases fluid pressure offsetting the effects of increased pore volume during earthquakes there is some tendency for pore volume increase to balance fluid expansion so that fluid pressure stays relatively constant 2 production of isolated voids that do not immediately decrease fluid pressure throughout the fault zone during earthquakes can occur to the extent that the fault zone is not significantly strengthened although the extent of both processes is constrained by energy considerations the variation of fluid pressure during earthquakes is not yet well enough understood to predict stress drop from observable material properties

detailed imaging of the fault planes of the 2004 niigata chuetsu central japan earthquake sequence by double difference tomography abstract imaging of the hypocentral faults of the niigata chuetsu earthquake sequence was performed by double difference tomography using data obtained by a temporary aftershock observation network densely deployed in the hypocentral region two parallel unfavorly oriented fault planes steeply inclined to the wnw are revealed that of the main shock and that of the largest aftershock as well as a zone of velocity change between the high velocity footwall and the low velocity hanging wall for both p and s waves this suggests that the main shock and the largest aftershock are caused by the reactivation of normal faults in the miocene under the current compressional stress regime parts of the fault planes are also found to be located within the low velocity zone this low velocity zone continues to the lower crust which is imaged by an inversion from the regional data and would correspond with highly fractured zone around the fault plane with high fluid pressure which reactivated the unfavorly oriented fault and triggered the present earthquake large coseismic slip area appears to extend to the northeastern portion with relatively high velocity this suggests that the asperity large coseismic slip area of the main shock possibly correspond with a higher velocity region along the fault plane

ventilation of the deep southern ocean and deglacial co2 rise past glacial interglacial increases in the concentration of atmospheric carbon dioxide co2 are thought to arise from the rapid release of co2 sequestered in the deep sea primarily via the southern ocean here we present radiocarbon evidence from the atlantic sector of the southern ocean that strongly supports this hypothesis we show that during the last glacial period deep water circulating around antarctica was more than two times older than today relative to the atmosphere during deglaciation the dissipation of this old and presumably co2 enriched deep water played an important role in the pulsed rise of atmospheric co2 through its variable influence on the upwelling branch of the antarctic overturning circulation