aseismic deformation associated with an earthquake swarm in the northern apennines italy analyzing the displacement time series from continuous gps cgps with an independent component analysis we detect a transient deformation signal that correlates both in space and time with a seismic swarm activity maximum m w 3 69 0 09 occurred in the hanging wall of the altotiberina normal fault northern apennines italy in 2013 2014 the geodetic transient lasted 6 months and produced a nw se trending extension of 5 3 mm consistent with the regional tectonic regime the seismicity and the geodetic signal are consistent with slip on two splay faults in the altotiberina fault atf hanging wall comparing the seismic moment associated with the geodetic transient and the seismic events we observe that seismicity accounts for only a fraction of the measured geodetic deformation the combined seismic and aseismic slip decreased the coulomb stress on the locked shallow portion of the atf while the transition region to the creeping section has been loaded

reinterpretation of late quaternary sediment chronology of lake biwa japan from correlation with marine glacial interglacial cycles a review of published stratigraphic records of pollen sediment grain size diatoms and organic matter composition from lake biwa japan identifies four pre holocene episodes of milder climate increased surface runoff and enhanced aquatic productivity indicating intervals of warmer and wetter conditions which are interpreted as being interglacial correlation of these episodes to times of marine interglacial periods revises the age scale of the lake biwa sediment sequence which has been based on fission track dating the revised chronostratigraphic scale proposes an age of ca 430 000 yr b p for the base of the 250 m thick t bed instead of the former age of ca 700 000 yr b p

microseismicity on patches of higher compression during larger scale earthquake nucleation in a rate and state fault model while many large earthquakes are preceded by observable foreshocks the mechanism responsible for the occurrence of these smaller scale seismic events remains uncertain one physical explanation of foreshocks with growing support is that they are produced by the interaction of slow slip with fault heterogeneity inspired by the suggestion from laboratory experiments that foreshocks occur on fault asperities bumps we explore rate and state fault models with patches of higher normal stress embedded in a larger seismogenic region by conducting 3 d numerical simulations of their behavior over long term sequences of aseismic and seismic slips the models do produce smaller scale seismicity during the aseismic nucleation of larger scale seismic events these smaller scale events have reasonable stress drops despite the highly elevated compression assigned to the source patches we find that the two main factors contributing to the reasonable stress drops are the significant extent of the rupture into the region surrounding the patches and the aseismic stress release just prior to the seismic events the smaller scale seismicity can only occur if a sufficient separation in nucleation scales between the foreshock like events and mainshocks is achieved our modeling provides insight into the conditions conducive for generating foreshocks on both natural and laboratory faults

aseismic deformations perturb the stress state and trigger induced seismicity during injection experiments fluid injections can trigger seismicity even on faults that are not optimally oriented for reactivation suggesting either sufficiently large fluid pressure or local stress perturbations understanding how stress field may be perturbed during fluid injections is crucial in assessing the risk of induced seismicity and the efficiency of deep fluid stimulation projects here we focus on a series of in situ decametric experiments of fluid induced seismicity performed at 280 m depth in an underground gallery while synchronously monitoring the fluid pressure and the activated fractures movements during the injections seismicity occurred on existing natural fractures and bedding planes that are misoriented to slip relative to the background stress state which was determined from the joint inversion of downhole fluid pressure and mechanical displacements measured at the injection we then compare this background stress with the one estimated from the inversion of earthquake focal mechanisms we find significant differences in the orientation of the stress tensor components thus highlighting local perturbations after discussing the influence of the gallery the pore pressure variation and the geology we show that the significant stress perturbations induced by the aseismic deformation which represents more than 96 per cent of the total deformation trigger the seismic reactivation of fractures with different orientations

late pleistocene and holocene paleoenvironments of the north pacific coast abstract unlike the north atlantic the north pacific ocean probably remained free of sea ice during the last glacial maximum lgm 22 000 to 17 000 bp following a eustatic low in sea level of ca 120 m at 19 000 bp a marine transgression had flooded the bering and chukchi shelves by 10 000 bp post glacial sea level history varied widely in other parts of the north pacific coastline according to the magnitude and timing of local tectonism and glacio isostatic rebound glaciers covered much of the continental shelf between the alaska peninsula and british columbia during the lgm maximum glacier extent during the lgm was out of phase between southern alaska and southern british columbia with northern glaciers reaching their outer limits earlier between 23 000 and 16 000 bp compared to 15 000 14 000 bp in the south glacier retreat was also time transgressive with glaciers retreating from the continental shelf of southern alaska before 16 000 bp but not until 14 000 13 000 bp in southwestern british columbia major climatic transitions occurred in the north pacific at 24 000 22 000 15 000 13 000 and 11 000 9000 bp rapid climate changes occurred within these intervals including a possible younger dryas episode an interval of climate warmer and drier than today occurred in the early holocene cooler and wetter conditions accompanied widespread neoglaciation beginning in some mountain ranges as early as the middle holocene but reaching full development after 3000 bp

role of orbital forcing in east asian monsoon climates during the last 350 kyr evidence from terrestrial and marine climate proxies from core rc14 99 proxy records of northeast asian precipitation marine pollen and northwest pacific sea surface temperatures marine fauna contain concentrations of variance frequency peaks coincident with those of orbital variations eccentricity obliquity and precession time series of these monitors of various components of the east asian monsoon system are coherent with changing solar insolation and climate boundary conditions ice volume snow cover albedo at 41 and 23 kyr frequencies winter sea surface temperature wsst maxima are in phase with global ice volume minima at all three milankovitch frequencies 100 41 and 23 kyr periods wsst maxima are also linearly related to summer insolation at 30 n lagging radiation maxima by 55 3 5 kyr across the precessional frequency band 23 kyr period our east asian monsoon rainfall indicator cryptomeria reaches highest values immediately following summer insolation maxima during periods of low ice volume interglacials across the eccentricity frequency band 100 kyr period cryptomeria maxima are in phase with ice volume minima at the higher frequency of orbital precession monsoon rainfall lags both summer radiation maxima 125 8 kyr and ice volume minima 60 3 8 kyr whereas much of the variation in northwest pacific wsst can be attributed to summer radiation forcing and changes in global climate mechanisms driving east asian monsoon precipitation are more complex involving other possibly internal factors

the influence of changing orbital parameters and surface boundary conditions on climate simulations for the past 18 000 years abstract general circulation model experiments at 3000 year intervals for the past 18 000 years were made to estimate the magnitude timing and pattern of the climatic response to prescribed changes of orbital parameters date of perihelion axial tilt eccentricity and glacial age lower boundary conditions ice sheets land albedo sea ice and sea surface temperature the experiments used the community climate model ccm of the national center for atmospheric research ncar the response of monsoon circulations and tropical precipitation to the orbitally produced solar radiation changes was much larger than the response to changes of glacial age boundary conditions the continental interior of eurasia was 2 4 k warmer in summer and summer monsoon precipitation of north africa south asia was increased by 10 20 between 12 000 and 6000 yr bp before present when perihelion occurred during northern summer rather than in winter as now and the earth s axial tilt was larger than now southern hemisphe

searching for hidden earthquakes in southern california earthquakes follow a well known power law size relation with smaller events occurring much more often than larger events earthquake catalogs are thus dominated by small earthquakes yet still missing a much larger number of even smaller events caused by signal fidelity issues to overcome these limitations we applied a template matching detection technique to the entire waveform archive of the regional seismic network in southern california this effort resulted in a catalog with 1 81 million earthquakes a factor of 10 increase which provides important new insights into the geometry of fault zones at depth foreshock behavior and nucleation processes and earthquake triggering mechanisms the extraordinary detail resolved in this type of catalog will facilitate a new generation of analyses of earthquakes and faults

monsoon fluctuations over the past 350 kyr high resolution evidence from northeast asia northwest pacific climate proxies marine pollen and radiolarians abstract high resolution analyses of pollen and radiolarians from northwest pacific cores v28 304 and rc14 99 provide continuous directly linked evidence of oceanic atmospheric climate processes through the past three pleistocene glacial interglacial cycles systematic fluctuations in marine pollen assemblages which reflect changes in the forest communities of japan are compatible with fluctuations in faunal assemblages and inferred oceanographic properties offshore each interglacial has distinguishable characteristics which imply that the sequence timing and magnitude of climatic change were not identical during the three most recent interglacial intervals most interglacials contain at least one 10 15 kyr period of exceptionally high percentages 20 of cryptomeria which we interpret as reflecting increased levels of precipitation in response to intensification of the summer monsoon with the exception of oxygen isotope substage 5e in rc14 99 interglacial summer sea surface temperatures were similar to or slightly warmer than today glacial environments in central japan and in the northern subtropical gyre were similar to those which now support cold temperate and boreal forests on northernmost japan and a dominant subpolar fauna and associated low sea surface temperatures offshore climatic change was apparently not as severe in southern japan where temperate vegetation largely replaced warm temperate flora or in the southern subtropical gyre where only winter ssts were cooler than present we attribute these changes in vegetation and surface water conditions to shifts in the atmospheric polar and oceanographic subarctic fronts in response to the seasonal variations in the siberian high maxima in cryptomeria systematically lag maxima in solar insolation at 30 n this correlation between our summer monsoon indicator and summer insolation substantiates the view that the strength of the asian monsoon is linked to variations in northern hemisphere solar radiation

rapid assessment of earthquake source characteristics recent studies emphasize the rapid assessment of earthquake source properties such as moment magnitude to help alleviate the impact of earthquakes depending on local crustal structure earthquakes occurring at different depths can differ greatly in high frequency motions which emphasizes the importance in constraining focal depth for the predictions of strong motions for large earthquakes assessing rupture directivity is also essential in estimating ground motion effects throughout the source region in this article we perform an in depth study on a group of recent earthquakes near the intersection of the san jacinto and san andreas fault systems in southern california we develop a systematic method to accurately estimate moment magnitude and focal mechanism within 3 6 s after the first p arrival focal depth can also be constrained within 10 s upon the arrival of s waves to determine the direction of fault rupture we implement a forward modeling method which takes smaller earthquake recordings as empirical green s functions to simulate the rupture direction of the beginning motion generated by larger events with a small event nearby we resolve the rupture characteristic of the 2014 m w 4 4 event using information at stations within 35 km from the epicenters and successfully predict the ground motion response at stations at farther distances where directivity effect is significant rupture direction of simulated earthquakes with larger magnitudes can also be accurately resolved using the method proposed opening a possibility to predict ground motions ahead of time in particular for hazardous regions

pollen and radiolarian records from deep sea core rc14 103 climatic reconstructions of northeast japan and northwest pacific for the last 90 000 years using modern pollen and radiolarian distributions in sediments from the northwest pacific and seas adjacent to japan to interpret floral and faunal changes in core rc14 103 44 02 n 152 56 e we recognize two major responses of the biota of eastern hokkaido and the northwest pacific to climatic changes since the last interglaciation relatively stable glacial environments 80 000 20 000 yr b p were basically cold and wet 8 c and 1200 mm mean annual temperature and precipitation respectively supporting climax broadleaf deciduous forest with quercus and ulmus zelkova with surface waters in the northwest pacific characterized by warm 1 5 c winter and cold 10 4 14 3 c summer temperatures climatic evidence from rc14 103 shows a high degree of local and regional variation within the context of global climatic change correlative ocean and land records provide the detailed input necessary to assess local regional responses to variations in other key elements i e solar radiation monsoonal variations of the northeast asian climate system

transient deformation in california from two decades of gps displacements implications for a three dimensional kinematic reference frame our understanding of plate boundary deformation has been enhanced by transient signals observed against the backdrop of time independent secular motions we make use of a new analysis of displacement time series from about 1 000 continuous global positioning system gps stations in california from 1999 to 2018 to distinguish tectonic and nontectonic transients from secular motion a primary objective is to define a high resolution three dimensional reference frame datum for california that can be rapidly maintained with geodetic data to accommodate both secular and time dependent motions to this end we compare the displacements to those predicted by a horizontal secular fault slip model for the region and construct displacement and strain rate fields over the past 19 years california has experienced 19 geodetically detectable earthquakes and widespread postseismic deformation we observe postseismic strain rate variations as large as 1 000 nstrain year with moment releases equivalent up to an mw6 8 earthquake we find significant secular differences up to 10 mm year with the fault slip model from the mendocino triple junction to the southern cascadia subduction zone the northern basin and range and the santa barbara channel secular vertical uplift is observed across the transverse ranges coastal ranges sierra nevada as well as large scale postseismic uplift after the 1999 mw7 1 hector mine and 2010 mw7 2 el mayor cucapah earthquakes we also identify areas of vertical land motions due to anthropogenic natural and magmatic processes finally we demonstrate the utility of the kinematic datum by improving the accuracy of high spatial resolution 12 day repeat cycle sentinel 1 interferometric synthetic aperture radar displacement and velocity maps

the 2012 brawley swarm triggered by injection induced aseismic slip it has long been known that fluid injection or withdrawal can induce earthquakes but the underlying mechanisms remain elusive for example the 2012 brawley swarm which produced two strike slip shocks with magnitudes larger than 5 3 and surface ruptures in the close vicinity of a geothermal field started with earthquakes about 5 km deeper than the injection depth 1 5 km this makes the causality between the injection and seismicity unclear here we jointly analyze broadband and strong motion waveforms uavsar leveling measurements and field observations to reveal the detailed seismic and aseismic faulting behaviors associated with the 2012 brawley swarm in particular path calibration established from smaller events in the swarm allows waveform inversion to be conducted up to 3 hz to resolve finite rupture process of the mw 4 7 normal event our results show that the 2012 earthquake sequence was preceded by aseismic slip on a shallow normal fault beneath the geothermal field aseismic slip initiated in 2010 when injection rate rapidly increased and triggered the following earthquakes subsequently including unusually shallow and relatively high frequency seismic excitations on the normal fault in this example seismicity is induced indirectly by fluid injection a result of mediation by aseismic creep rather than directly by a pore pressure increase at the location of the earthquakes

pliocene pleistocene evolution of the north pacific ocean atmosphere system interpreted from fossil diatoms the relative abundance of diatom taxa in 216 core tops has been quantified and compared using cluster analysis with assemblages in six cores located beneath different water masses of the north pacific ocean all but one sequence span at least 1 5 m y early pleistocene to holocene and one extends to 2 6 ma the quantitative abundance of each taxon and the space time occurrence of each cluster are interpreted as tracers of oceanographic conditions in addition to high frequency glacial interglacial oscillations the records display rapid steplike changes at 2 4 ma 1 6 1 5 ma 1 0 ma 0 8 0 7 ma and 0 35 ma two secondary transitions recorded only in the northwestern cores occur at 2 0 ma and 1 1 ma we conclude that both the high frequency oscillations and the stepwise transitions reflect variations in extent of subarctic water masses under the influence of the siberian high pressure and aleutian low pressure atmospheric cells we further conclude that 1 the subarctic water mass has developed progressively and attained its modern structure only in the late pleistocene 2 some stages of this evolution may have occurred earlier in the eastern subarctic 3 the holocene is an atypical warm extreme so that the present is not a very good key to the past 4 there were several glaciations between 2 4 and 2 0 ma and 5 the subtropical gyre is more conservative than the subarctic gyre and major changes in the region have been due to forcing from the north we propose a conceptual model of oscillating metastable climatic modes maintained by internal feedback and suggest that steplike changes may occur when one set of boundary conditions is temporarily exceeded

a seismic refraction survey of the imperial valley region california the u s geological survey conducted an extensive seismic refraction survey in the imperial valley region of california in 1979 the imperial valley is located in the salton trough an active rift between the pacific and north american plates forty shots fired at seven shot points were recorded by 100 portable seismic instruments at typical spacing of 0 5 1 km more than 1300 recording locations were occupied and more than 3000 usable seismograms were obtained we analyzed five profiles using a standard ray tracing program constructed a contour map of reduced travel times from our most widely recorded shot point and modeled an existing gravity profile across the salton trough results are itemized 1 all models have in common a sedimentary layer vp 1 8 5 0 km s a transition zone vp 5 0 5 65 km s a basement vp 5 65 km s in the imperial valley 5 9 km s on the bordering mesas and subbasement vp 7 2 km s 2 the sedimentary layer ranges in thickness along the axis of the salton trough from 3 7 km salton sea to 4 8 km u s mexican border on the bordering mesas it is quite variable in thickness 3 the transition zone is about 1 km thick in most places in the imperial valley there are no marked velocity discontinuities in this zone between the sedimentary layer and basement on the bordering mesas however there is a discontinuity at the top of this zone 4 there are apparently two types of basement on the bordering mesas basement is crystalline igneous and metamorphic rocks in the imperial valley basement is mostly lower greenshist facies sedimentary rocks based primarily on the smooth transition in character from sediment to basement arrivals the low value of basement velocity and the fact that deep 4 km wells in the valley penetrate only the upper part of the known cenozoic stratigraphic column for the salton trough 5 the subbasement or intermediate crustal layer ranges in depth along the axis of the salton trough from 16 km salton sea to 10 km u s mexican border gravity modeling requires that this layer deepen and or pinch out beneath the bordering mesas and mountain ranges based on its high velocity and the presence of intrusive basaltic rocks in the sedimentary section in the imperial valley the subbasement is thought to be a mafic intrusive complex similar to oceanic middle crust 6 several structures are seen that affect basement transition zone and deeper parts of the sedimentary layer they include a scarp along the imperial fault as much as 1 km down to the northeast and a scarp passing roughly along the topographic boundary between the imperial valley and the bordering mesa to the west as much as 3 km down to the east we interpret the latter scarp to be the suture or rift boundary between the older crystalline basement on the mesa and the younger metasedimentary basement in the imperial valley 7 on a contour map of reduced travel time from our most widely recorded shot point subtle patches of early arrivals among otherwise late arrivals in the central imperial valley correlate well with known geothermal resource areas having reservoir temperatures of more than 150 c apparently the salton trough is a location where new crust is being generated as the rift opens mafic intrusive rocks fill it from below as sedimentary rocks fill it from above rifting and intrusion produce high heat flow that metamorphoses the sedimentary rocks to shallow depth metasedimentary basement in the imperial valley and thus consolidates the new crust

uavsar observations of triggered slip on the imperial superstition hills and east elmore ranch faults associated with the 2010 m 7 2 el mayor cucapah earthquake the 4 april 2010 m 7 2 el mayor cucapah earthquake that occurred in baja california mexico and terminated near the u s mexican border caused slip on the imperial superstition hills and east elmore ranch faults the pattern of slip was observed using radar interferometry from nasa s uninhabited aerial vehicle synthetic aperture radar uavsar instrument collected on 20 21 october 2009 and 12 13 april 2010 right lateral slip of 36 9 and 14 2 mm occurred on the imperial and superstition hills faults respectively left lateral slip of 9 2 mm occurred on the east elmore ranch fault the widths of the zones of displacement increase northward suggesting successively more buried fault motion to the north the observations show a decreasing pattern of slip northward on a series of faults in the salton trough stepping between the el mayor cucapah rupture and san andreas fault most of the motion occurred at the time of the m 7 2 earthquake and the uavsar observations are consistent with field creepmeter gps and envisat observations an additional 28 1 mm of slip at the southern end of the imperial fault over a 1 km wide zone was observed over a 1 day span a week after the earthquake suggesting that the fault continued to slip at depth following the mainshock the total moment release on the three faults is 2 3 1023 1 2 1024 dyne cm equivalent to a moment magnitude release of 4 9 5 3 assuming shallow slip depths ranging from 1 to 5 km

creep burst coincident with faulting in marble observed in 4 d synchrotron x ray imaging triaxial compression experiments faults in carbonate rocks show both seismic and aseismic deformation processes leading to a wide range of slip velocities we deformed two centimeter scale cores of carrara marble at 25 c und

biogenic silica record in lake biwa of central japan over the past 145 000 years abstract the record of the biogenic silica flux bsf g cm 2 103yr 1 in lake biwa reflects changes in diatom productivity in the lake and provides information regarding changes in paleoclimatic conditions the bsf record of lake biwa demonstrates five periods over the past ca 145 000 yr when the bsf values were significantly greater than 7 5 g cm 2 103yr 1 and five intervals when they were lower the data imply that paleoclimatic conditions were warmer and wetter from ca 123 000 to 115 000 103 000 to 95 000 88 000 to 72 000 57 000 to 32 000 yr b p and around ca 6000 yr b p when the bsf values were greater and relatively dry and cold from ca 141 000 to 123 000 yr b p and during intervals between two of the five warm and wet episodes when the bsf values were lower time series of the bsf record can be correlated with the record of biogenic silica content in lake baikal and the marine oxygen isotope stages 1 through 6 furthermore the bsf values varied with much higher amplitude during the last interglaciation than during the last glaciation probably implying that the diatom productivity in lake biwa was likewise more variable and had a larger range under interglacial conditions than under glacial conditions

terrestrial ocean environmental change in the northwestern pacific from the glacial times to holocene abstract the mixed water region mwr between the oyashio current and the kuroshio extension and surrounding terrestrial region have been affected by the global climatic change the sedimentary core kr02 15 pc6 collected at 40 23 8871 n 143 29 8663 e in the mwr provides detailed records of pollen and spores and alkenone sea surface temperature sst during the last 15 kyr showing that both ocean and terrestrial environments have been appreciably linked abundance of picea a proxy for terrestrial cool climate fluctuated coinciding with the alkenone sst change during the interstadial period 15 0 7 7 cal kyr b p alkenone sst increased to the modern level at 8 0 cal kyr b p and remained almost constant until 2 0 kyr b p while the terrestrial warming still continued until 4 0 cal kyr b p the rainfall under terrestrial warm condition increased gradually from 7 9 cal kyr b p and rapidly from 2 0 cal kyr b p both terrestrial and marine environments cooled down during the last 2 kyr possibly due to the intensified cold oyashio current

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

when evaporites are not formed by evaporation the role of temperature and pco2 on saline deposits of the eocene green river formation colorado usa

climatic change at the end of the last glaciation in japan inferred from pollen in three cores from the northwest pacific ocean abstract late glacial pollen time series from high sedimentation rate marine cores kh79 3 c6 ch84 04 and ch84 14 show the rise of successional vegetation typified by betula during the replacement of boreal forest types picea and pinus by thermophilous quercus forests variations in these three marine pollen records replicate the trends and timing of pollen records from japan and the structure and timing of vegetation and climatic changes on the pacific coast of japan since the last glacial maximum in marine cores kh79 3 c6 ch84 04 and ch84 14 oxygen isotope and or marine faunal data have been interpreted as evidence of a cooling event in the northwest pacific ocean which is coeval with the younger dryas chronozone pollen records from these northwest pacific cores like those from japan do not exhibit a regionally replicated statistically robust pollen assemblage which can be unambiguously interpreted as evidence of a late glacial climatic reversal between ca 11 000 and 10 000 yr b p the apparent disparity between the terrestrial pollen and marine evidence for a climatic oscillation during the younger dryas chron in northeast asia further complicates the variable record of this brief late glacial event

last glacial holocene change in intermediate water ventilation in the northwestern pacific abstract the modern north pacific is the terminus for deep water circulation while no deep water mass is formed today the region is the source of north pacific intermediate water 300 800 m formed primarily in the sea of okhotsk however the source and strength of intermediate water in the glacial north pacific was likely different from the present intermediate water here we present microfossil evidence of late quaternary ventilation changes associated with changes in intermediate water intermediate water ventilation decreased drastically at the glacial termination when it switched to the modern circulation system the ventilation change appears to have been widespread and synchronous in the north pacific glacial microfossil assemblages indicate that there was relatively strong ventilation of intermediate water which seems to have been cold and well oxygenated as if produced by brine rejection during the formation of sea ice on the basis of the glacial distribution of microfossils in the north pacific we suggest that intermediate water was derived from the bering sea during the glacials rather than the sea of okhotsk

fluid controlled faulting process in the asal rift djibouti from 8 yr of radar interferometry observations the deformation in the asal rift djibouti is characterized by magmatic inflation diking distributed extension fissure opening and normal faulting an 8 yr time line of surface displacement maps covering the rift constructed using radar interferometry data acquired by the canadian satellite radarsat between 1997 and 2005 reveals the aseismic behavior of faults and its relation with bursts of microseismicity the observed ground movements show the asymmetric subsidence of the inner floor of the rift with respect to the bordering shoulders accommodated by slip on three of the main active faults fault slip occurs both as steady creep and during sudden slip events accompanied by an increase in the seismicity rate around the slipping fault and the fieale volcanic center slip distribution along fault strike shows triangular sections a pattern not explained by simple elastic dislocation theory these observations suggest that the asal rift faults are in a critical failure state and respond instantly to small pressure changes in fluid filled fractures connected to the faults reducing the effective normal stress on their locked section at depth

quaternary forest and climate history of hokkaido japan from marine sediments abstract pollen data from quaternary marine sediments deposited in central hokkaido northern japan provide insight into northeast asian vegetation and climatic changes over the last few million years during the early pleistocene coniferous forest dominated by picea and cryptomeria japonica and taiga composed of larix and picea developed under cool wet and cold dry climates respectively strong climatic contrasts are inferred from late pleistocene interglacial and glacial pollen assemblages which precede the last glacial cycle in the former cool temperate broad leaf forest mainly composed of fagus reflects a warmer and wetter climate than now in the latter taiga similar to that now found in northern sakhalin apparently flourished in hokkaido the composition of pollen assemblages correlated with oxygen isotope stage 5 changed from cool temperate forest of quercus ulmus and juglans substage 5e to picea larix taiga substage 5d cool temperate forest of quercus and ulmus substage 5c and picea abies forest substage 5b compared with present conditions climate during stage 5 in northern japan apparently fluctuated from warmer wetter to colder drier taiga composed of picea pinus and larix indicating colder dry conditions during stage 4 was replaced by picea abies forest and picea larix taiga in stage 3 suggesting relatively cool and cold dry environments taiga and mixed forest with taiga and cool temperate components characterize stage 2 holocene forests with juglans betula and quercus juglans were succeeded by picea and abies during the early holocene warm interval 7000 bp subsequently quercus ulmus and abies alnus assemblages reflect climatic deterioration pan mixed forest has been developed in hokkaido since 2000 bp

post large earthquake seismic activities mediated by aseismic deformation processes abstract two aseismic deformation processes are commonly invoked to explain the transient geodetic surface displacements that follow a major earthquake afterslip and viscoelastic relaxation both induce time dependent stress variations in the crust potentially affecting aftershock occurrence however the two mechanisms relative impacts on crustal deformation and seismicity remain unclear we find for the case of the 2010 mw 7 2 el mayor cucapah emc earthquake not only that afterslip likely drove clustered seismicity after the earthquake but also that long range earthquake interactions were likely modulated by viscoelastic relaxation at large scales in space 5 times the fault rupture length and time 7 yr this has important implications for the study of the seismic cycle and for seismic hazard estimation since post seismic deformation related to a single mw 7 2 earthquake affects interseismic velocities and regional seismicity rates for more than a decade

late pleistocene holocene radiolarian and pollen records from sediments in the sea of okhotsk in two cores with oxygen isotope stratigraphy from the southern okhotsk sea marine pollen and siliceous microfauna record concurrent late glacial through holocene variations in regional terrestrial and marine environments glacial vegetation around the southern okhotsk basin which resembles the present tundra steppe of the northwest coast of this marginal sea yields to spruce dominated boreal forests during the glacial interglacial transition temperate forest components such as oak peak during the mid holocene decreasing oak accompanied by increasing spruce reflects the effect of global cooling on local vegetation during the last 4 kyr although the radiolarian fauna in the okhotsk sea samples is similar to that present in the northwest pacific the dominant species in both regions differ concentrations of radiolarians are low in latest glacial samples with higher concentrations occurring above and below this interval cycladophora davisiana the dominant radiolarian species in the majority of holocene okhotsk sea sediments is present at lower percentages in late glacial samples from our two sites thus this species holocene latest pleistocene abundance pattern in sea of okhotsk sediments is the reverse of that recorded in high latitude open ocean sites the combined marine pollen and radiolarian records indicate changes in the sea of okhotsk s physical oceanographic conditions and surrounding vegetation during the late glacial which were associated with this region s response to global climate change

fluctuations in the east asian monsoon over the last 144ka in the northwest pacific based on a high resolution pollen analysis of images core md01 2421 abstract a high resolution pollen analysis of images core md01 2421 45 83 m from the northwest pacific off central japan was used to clarify the vegetation history of central japan over the past 144 ka an age model was constructed using the oxygen isotope stratigraphy of benthic foraminifera 12 accelerator mass spectrometry ams 14c datings and two tephra layers with known eruption ages the pollen temperature index t p 1 0 0 t w t c t w where tw is the sum of temperate taxa and tc the sum of subalpine taxa values were high during 129 119 115 100 82 76 53 49 and 15 0 ka cool temperate broad leaved forests developed during the high tp periods and subalpine conifer forests grew during the low tp periods the tp fluctuated synchronously with summer insolation at 36 n where the core was collected during periods with abundant cryptomeria or sciadopitys 120 118 115 89 78 70 and 4 0 3 ka the east asian summer monsoon was stronger and the annual precipitation was greater in central japan than at present 2000 vs 1500 mm fluctuations in the sea surface temperature sst calculated from the oxygen isotopes of foraminifera in core md01 2421 and changes in the strength of the summer monsoon were synchronous the sst was determined by the currents passing over the core site rather than by the strength of summer insolation northward movement high sst of the kuroshio current which is under the influence of the summer okhotsk high pressure was strong near the summer insolation minima when precipitation was high particularly around 116 94 and 71 ka thus the strengths of both summer insolation and the east asian summer monsoon have determined the vegetation history of central japan for the last 144 ka

aseismic motions drive a sparse seismicity during fluid injections into a fractured zone in a carbonate reservoir author s duboeuf l de barros l cappa f guglielmi y deschamps a seguy s abstract 2017 american geophysical union all rights reserved an increase in fluid pressure in faults can trigger seismicity and large aseismic motions understanding how fluid and faults interact is an essential goal for seismic hazard and reservoir monitoring but this key relation remains unclear we developed an in situ experiment of fluid injections at a 10 meter scale water was injected at high pressure in different geological structures inside a fault damaged zone in limestone at 280 m depth in the low noise underground laboratory france induced seismicity as well as strains pressure and flow rate was continuously monitored during the injections although nonreversible deformations related to fracture reactivations were observed for all injections only a few tests generated seismicity events are characterized by a 0 5 to 4 khz content and a small magnitude approximately 3 5 they are located within 1 5 m accuracy between 1 and 12 m from the injections comparing strain measurements and seismicity shows that more than 96 of the deformation is aseismic the seismic moment is also small compared to the one expected from the injected volume moreover a dual seismic behavior is observed as 1 the spatiotemporal distribution of some cluster of events is clearly independent from the fluid diffusion 2 while a diffusion type pattern can be observed for some others clusters the seismicity might therefore appear as an indirect effect to the fluid pressure driven by aseismic motion and related stress perturbation transferred through failure

review of major shale dominated detachment and thrust characteristics in the diagenetic zone part ii rock mechanics and microscopic scale abstract characterising large shale thrust zone behaviour down to the diagenetic metamorphic boundary is both simple and complex the task in critical taper analogue and numerical models has been successfully approximated using simple material parameters yet the weakness of shales thrusts on a case by case basis show great variability in key factors across a wide range of scales understanding of these variables and their relationships to different tectonic settings is patchy due to the different objectives of workers studying the various systems e g seismic hazards hydrocarbon exploration structural geology research and the types of available geological and geophysical data early research recognized that megathrusts feature creeping and locked patches which may be described using the rate and state formalism in addition to temperature differential stress and strain rate key controlling factors on thrust weakness are mineralogy amount of weak phase present structure localization mechanisms grain size and shapes porosity permeability and pore fluid pressure the smectite illite transition has been a focus of seismic hazard research due to its coincidence with the top of the seismogenic zone while there may be a relationship other factors such as pore fluid pressure variations or structure localization are also important the critical taper model is a simple means of determining whether basic rock mechanics data e g frictional strength pore fluid pressure is appropriate for natural wedges for example aseismic basal detachments of gravity driven systems smaller critical taper wedges appear to retain higher pore fluid pressures along the basal detachment than seismogenic basal detachments higher critical taper wedges in many continental and deltaic fold and thrust belts high organic carbon content is a very important factor in shale weakness due to 1 the overall more ductile and well cleaved nature of the shale when organic content is high 2 the presence of high overpressures due to maturation of organic material and 3 metamorphism of carbon to low friction graphite this multifaceted influence of organic carbon content is just one example of the diversity of potential influences on shale thrust zone weakness which enable shales to be weak despite considerable lateral deposition related and vertical burial related changes in composition some key variations between different types of fold and thrust belt gravity driven accretionary prism andean himalayan type lie in systematic variations in clay mineralogy magnitudes and origins of overpressures seismic versus aseismic detachments and different structural localization mechanisms further research is required to explore the viability of such distinctions and their impact on structural styles

seismicity related to the hydraulic stimulation of grt1 rittershoffen france the rittershoffen deep geothermal reservoir in northeastern france is well characterized and has been extensively studied by a multidisciplinary approach a hydraulic stimulation for the development of the geothermal reservoir was performed in june 2013 this injection of fluid led to seismic activity which was closely monitored by a dedicated set of seismic stations the seismic sequence started during the injection but showed an unusual long quiet period of 4 d after shut in before the occurrence of a second swarm of events here we take the opportunity of this well monitored activity to gain insight into the geomechanical factors favouring the development of induced earthquakes we apply a template matching approach and a relative relocation procedure to obtain a precise estimate of the geometries of the activated structures our approach shows that the induced events during the injection took place on two parallel planar structures it shows that details of the seismicity generally obtained from borehole seismic network are achievable from surface network when an appropriate analysis is performed the development of this induced seismicity is in good agreement with the known stress field and failure criterion proposed for the reservoir in particular the orientation of the activated structure associated focal mechanisms and the overpressure needed to initiate the seismic activity are all in line with the geomechanical model of the area the swarm of delayed events 4 d after shut in can be well explained by considering an aseismic slip on the imaged fault and the related static stress transfer we therefore suggest that the ability to monitor local slow aseismic movements at depth in conjunction with precise tracking of the seismicity is of primary importance to understand induced earthquake activity

evidence for coupled seismic and aseismic fault slip during water injection in the geothermal site of soultz france and implications for seismogenic transients summary we analysed the triggered seismicity recorded near 3 km in depth within granite during the 1993 water injection experiment at soultz france we selected all large multiplets associated with the largest dislocated fault identified on the borehole logging 4 3 cm slip and showed that each one consisted of the repeated rupture of a single asperity these asperities were forced to rupture due to fault creep around them so that their growing cumulative slip history reveals the creep history on the fault with a mean slip rate and a seismicity rate both decaying approximately as 1 t this is consistent with a rate strengthening friction law on the creeping faults and differs from the interpretation of omori type 1 t seismicity rates in terms of a weakening friction control of the unstable fault surfaces this model of asperity rupture forced by relaxation creep is easily generalized in seismogenic regions even for single ruptures of asperities on small creeping faults showing that a significant part of aftershock rates can be controlled by the strengthening friction properties and the creep of faults at all scales this lead us to introduce the concept of a critical asperity density above which dynamic interaction between neighbouring asperities can initiate large seismic ruptures at soultz the asperity density is subcritical but the neighbouring asperities nonetheless interact at distances up to a few source dimensions as revealed by their delayed cross triggering considering the seismic cloud in soultz at a global scale the strain produced by the injection experiment was mostly aseismic related to creep on major faults and causing large permeability changes influencing in turn the pore pressure diffusion and the creeping process our observations demonstrate that the identification and analysis of multiplets can provide accurate images of the geometry and kinematics of transient slip patches and indirectly detect pore pressure changes which should contribute to a better understanding of the coupling between transient fluid flow creep and microseismic activity in seismogenic regions

indications for a successively triggered rupture growth underlying the 2000 earthquake swarm in vogtland nw bohemia 1 the characteristics of earthquake swarms can neither be described by simple laws nor are the underlying mechanisms presently understood swarm activity is often assumed to be caused by an intrusion of fluids into the seismogenic zone we have studied the earthquake catalog of the large earthquake swarm that occurred in the year 2000 in vogtland se germany and nw bohemia an area well known for its episodic swarm generation we observe a significant decrease of the gutenberg richter b value during the swarm evolution as well as a fractal temporal clustering of the earthquakes the spatial spreading of the swarm s activity which is approximately confined to one plane cannot simply be explained by a process of fluid diffusion instead we observe a simple relationship between the spatial spreading and the seismic moment release which is in good agreement with empirical relationships derived for tectonically driven earthquakes and theoretical crack growth models this observation points to a progressively growing main fracture underlying the swarm activity in addition we find that the swarm earthquakes themselves trigger aftershocks near the border of their rupture area the stick slip behavior of the rupture propagation can be explained by stress transfers and induced fluid flows due to earthquakes in a fluid permeated critically loaded fault zone however during the first phase the temporal behavior is found to be different pointing to intrusion of fluids initiating the swarm activity

sea surface temperature estimates for the tropical western pacific during the last glaciation and their implications for the pacific warm pool twenty deep sea sediment cores from the western pacific between 30 n and 30 s provide evidence of sea surface temperature sst changes throughout the tropics and subtropics glacial ssts were estimated using the modern analog technique mat applied to planktonic foraminifers and planktonic foraminiferal 18o changes we used 18o to identify the last glacial maximum the mat method differs from the traditional transfer function approach in that it utilizes a global coretop database and estimates paleotemperature by finding analogs from the modern coretop samples in addition the mat approach appears to be less susceptible than the transfer function technique to biases introduced by carbonate dissolution our results indicate that tropical ssts differed by less than 2 c from present away from the tropics 30 n and 30 s ssts were at least 3 c cooler our results differ from those of previous studies in the western pacific by using a set of well preserved high sedimentation rate cores from shallow regions the results of this study clearly indicate that a western pacific warm pool existed during the last glacial maximum lgm providing a heat and moisture source for a walker circulation cell similar to that of today we propose that a steeper lapse rate existed during the last glacial maximum and that this can explain at least part of the discrepancy between marine and terrestrial temperature estimates adjacent to new guinea for the lgm

origin of depositional cycles in a permian saline giant the salado mcnutt zone evaporites of new mexico and texas two types of metre scale depositional cycles have been recognized within the mcnutt potash zone of the permian salado evaporites the cycles record progressive drawdown and concentration of brine in a shallow marginal marine basin type i cycles made of basal carbonate siliciclastic mudstone then anhydrite polyhalite pseudomorphous after primary gypsum overlain by halite and capped by muddy halite are interpreted as marine sea water dominated they formed by massive spillover of sea water through a connection with the permian ocean at high relative sea level stands lagoonal mudstone and anhydrite polyhalite after subaqueous gypsum followed by relative lowering of sea level and gradual basin restriction shallow saline lake and salt pan halite and ending with a desiccated basin isolated from the permian ocean salt pan halite and saline mudflat muddy halite cycle cap type ii cycles occur between the type i cycles and contain halite overlain transitionally by muddy halite they record a temporal evolution of environments from a shallow saline lake to an ephemeral salt pan saline mudflat complex and are interpreted as continental dominated sequences sourced by meteoric inflow from surrounding land areas that mixed with variable amounts of sea water either residual or introduced into the salado basin by seepage the vertical stacking of type i cycles is best explained by periodic invasions of sea water into the salado basin coincident with eustatic sea level rises the continental dominated type ii cycles formed during intervening periods of eustatic sea level fall and low stands the maximum time interval between major marine incursions is an average of 10 5 yr

intermittent slip along the alto tiberina low angle normal fault in central italy the alto tiberina normal fault atf in central italy is a 50 km long crustal structure that deepens at a low angle 15 20 events on the fault plane are about ten times less than those located i

controls on the ph of hyper saline lakes a lesson from the dead sea abstract the ph of aqueous environments is determined by the dominant buffer systems of the water defined operationally as total alkalinity ta the major buffer systems in the modern ocean are carbonic and boric acids of which the species bicarbonate carbonate and borate make up about 77 19 and 4 of the ta respectively during the course of seawater evaporation e g lagoons the residual brine loses considerable portion of the dissolved inorganic carbon dic and carbonate alkalinity ca already at the early stages of evaporation dic and ca decrease due to massive precipitation of caco3 while total boron tb increases conservatively turning borate to the dominant alkalinity species in marine derived brines in the present work we assess the apparent dissociation constant value of boric acid k b in saline and hypersaline waters using the dead sea ds as a case study we explain the ds low ph 6 3 and the effect of the boric and carbonic acid p k s on the behavior of the brine s buffer system including the ph increase that results from brine dilution the k b in ds was estimated from tb ta dic and ph data measured in this study and early empirical data on artificial ds brines containing just carbonic acid the k b value was corroborated by pitzer ion interaction model calculations using phreeqc thermodynamic code applied to the chemical composition of the ds our results show that k b increases considerably with the brine s ionic strength reaching in the ds to a factor of 100 higher than in mean seawater based on theoretical calculations and analyses of other natural brines it is suggested that brines composition is a major factor in determining the k b value and in turn the ph of such brines we show that the higher the proportion of divalent cations in the brine the higher the dissociation constants of the weak acids presumably due to formation of complexes the low ph of the dead sea is accordingly explained by its extremely high ionic strength tds 348 g l and the dominance of the divalent cation mg2 other natural hyper saline brines with high concentration of divalent cations such as kunteyi lake in china and don juan pond in antarctica follow the same general pattern in contrast the high ph of soda lakes results not only from their high ta but also by the dominance of the monovalent cation na our study emphasizes the strong control of brine composition on p k b and ph these factors should be taken into consideration when reconstructing past and present environmental evaporitic environments

seismic response to injection well stimulation in a high temperature high permeability reservoir author s hopp c sewell s mroczek s savage m townend j abstract 2019 american geophysical union all rights reserved fluid injection into the earth s crust can induce seismic events that cause damage to local infrastructure but also offer valuable insight into seismogenesis the factors that influence the magnitude location and number of induced events remain poorly understood but include injection flow rate and pressure as well as reservoir temperature and permeability the relationship between injection parameters and injection induced seismicity in high temperature high permeability reservoirs has not been extensively studied here we focus on the ngatamariki geothermal field in the central taup volcanic zone new zealand where three stimulation injection tests have occurred since 2012 we present a catalog of seismicity from 2012 to 2015 created using a matched filter detection technique we analyze the stress state in the reservoir during the injection tests from first motion derived focal mechanisms yielding an average direction of maximum horizontal compressive stress shmax consistent with the regional ne sw trend however there is significant variation in the direction of maximum compressive stress 1 which may reflect geological differences between wells we use the ratio of injection flow rate to overpressure referred to as injectivity index as a proxy for near well permeability and compare changes in injectivity index to spatiotemporal characteristics of seismicity accompanying each test observed increases in injectivity index are generally poorly correlated with seismicity suggesting that the locations of microearthquakes are not coincident with the zone of stimulation i e increased permeability our findings augment a growing body of work suggesting that aseismic opening or slip rather than seismic shear is the active process driving well stimulation in many environments

inferred rheological structure and mantle conditions from postseismic deformation following the 2010 mw 7 2 el mayor cucapah earthquake author s dickinson lovell h huang mh freed am fielding e burgmann r andronicos c abstract the author s 2017 the 2010mw7 2elmayor cucapah earthquake provides a unique target of postseismic study as deformation extends across several distinct geological provinces including the coldmesozoic arc crust of the peninsular ranges and newly formed hot extending lithosphere within the salton trough we use five years of global positioning system measurements to invert for afterslip and constrain a 3 d finite element model that simulates viscoelastic relaxation we find that afterslip cannot readily explain far field displacements more than 50 km from the epicentre these displacements are best explained by viscoelastic relaxation of a horizontally and vertically heterogeneous lower crust and upper mantle lower viscosities beneath the salton trough compared to the peninsular ranges and other surrounding regions are consistent with inferred differences in the respective geotherms our inferred viscosity structure suggests that the depth of the lithosphere asthenosphere boundary lab is 65 km below the peninsular ranges and 32 km beneath the salton trough these depths are shallower than the corresponding seismic lab this suggests that the onset of partial melting in peridotite may control the depth to the base of the mechanical lithosphere in contrast the seismic lab may correspond to an increase in the partial melt percentage associated with the change from a conductive to an adiabatic geotherm

evidence from north west canada for an early holocene milankovitch thermal maximum according to the milankovitch theory of global climatic change maximum summer solar radiation at high latitudes of the northern hemisphere occurred at 10 000 yr bp refs 1 2 in particular it predicts summer solstice radiation greater by 9 10 preliminary climate simulation experiments with these increased values of radiation confirm that high latitude land surfaces received maximal insolation at 10 000 yr refs 3 4 paradoxically however the large volume of fossil pollen and other evidence from north america indicates a maximum of holocene warmth at 7 000 6 000 yr ref 5 and a recent review of the evidence from new england suggests that the warming began at 9 000 and ended at 5 000 yr but also stresses the difficulties of interpretation in terms of climate change6 we summarize here data from sites in the north west corner of mainland canada fig 1 that directly support the milankovitch hypothesis

latest pleistocene and holocene palaeoenvironment of japan and its marginal sea abstract analyses of pollen and radiolarian abundance variations in a deep sea core from the sea of japan indicate that major vegetational changes on mainland japan during the last 80 000 years coincided with events of similar magnitude offshore in the marginal sea on land dry cold temperate conditions alternate with wet cold temperate periods throughout most of the last glacial period 80 000 10 000 yr b p offshore during glacial times of low winter precipitation the radiolarian fauna was dominated by assemblage similar to those present today along the subarctic front and throughout much of the subpolar gyre associated with cold winter and summer sea surface temperatures during most of the high precipitation stadials the dominant radiolarian assemblage was comparable with that existing in today s sea of okhotsk associated with cold winter and cool summer sea surface temperatures on the western coast of honshu warmer temperate conditions throughout the holocene were associated with a marine faunal assemblage similar to that living in waters overlying the core site today radiolarian abundance levels productivity were lower during most of the last glacial period compared to holocene values the presence of radiolaria throughout all but a portion of the early stage of the last glacial interval indicates that although restricted some degree of exchange between the southern sea of japan and north pacific waters took place throughout most of the last glacial period these data place major constraints on local reconstructions of sea level and of climate on the adjacent coast of honshu during this time

synoptic reconstruction of a major ancient lake system eocene green river formation western united states numerous 40ar 39ar experiments on sanidine and biotite from 22 ash beds and 3 volcaniclastic sand beds from the greater green river piceance creek and uinta basins of wyoming colorado and utah constrain 8 m y of the eocene epoch multiple analyses were conducted per sample using laser fusion and incremental heating techniques to differentiate inheritance 40ar loss and 39ar recoil when considered in conjunction with existing radioisotopic ages and lithostratigraphy biostratigraphy and magnetostratigraphy these new age determinations facilitate temporal correlation of linked eocene lake basins in the laramide rocky mountain region at a significantly increased level of precision to compare our results to the geomagnetic polarity time scale and the regional volcanic record the ages of eocene magnetic anomalies c24 through c20 were recalibrated using seven 40ar 39ar ages overall the ages obtained for this study are consistent with the isochroneity of north american land mammal ages throughout the study area and provide precise radioisotopic constraints on several important biostratigraphic boundaries applying these new ages average sediment accumulation rates in the greater green river basin wyoming were approximately three times faster at the center of the basin versus its ramp like northern margin during deposition of the underfilled wilkins peak member in contrast sediment accumulation occurred faster at the edge of the basin during deposition of the balanced filled to overfilled tipton and laney members sediment accumulation patterns thus reflect basin center focused accumulation rates when the basin was underfilled and supply limited accumulation when the basin was balanced filled to overfilled sediment accumulation in the uinta basin at indian canyon utah was relatively constant at 150 mm k y during deposition of over 5 m y of both evaporative and fluctuating profundal facies which likely reflects the basin margin position of the measured section the most rapid sediment accumulation for the entire system 1 m k y occurred between 49 0 and 47 5 ma when volcaniclastic materials from the absaroka and or challis volcanic fields entered the green river formation lakes from the north our new ages combined with existing paleomagnetic and biostratigraphic control permit the first detailed synoptic comparison of lacustrine depositional environments in all the green river formation basins coupled with previously published paleocurrent observations our detailed correlations show that relatively freshwater lakes commonly drained into more saline downstream lakes the overall character of eocene lake deposits was therefore governed in part by the geomorphic evolution of drainage patterns in the surrounding laramide landscape freshwater overfilled lakes were initially dominant 53 5 52 0 ma possibly related to high erosion rates of remnant cretaceous strata on adjacent uplifts expansion of balanced fill lakes first occurred in all green river formation basins at 52 0 51 3 ma and again between 49 6 and 48 5 ma evaporative underfilled lakes occurred in various basins between 51 3 and 45 1 ma coincident with the end of the early eocene climatic optima and subsequent onset of global cooling defined from marine record however evaporite intervals in the different depocenters were deposited at different times rather than being confined to a single episode of arid climate evaporative terminal sinks were initially located in the greater green river and piceance creek basins 51 3 48 9 ma then gradually migrated southward to the uinta basin 47 1 45 2 ma this history is likely related to progressive southward construction of the absaroka volcanic province which constituted a major topographic and thermal anomaly that contributed to a regional north to south hydrologic gradient the greater green river and piceance creek basins were eventually filled from north to south with absarokaderived detritus at sedimentation rates 1 2 orders of magnitude greater than the underlying lake deposits

on the relationship between fault permeability increases induced stress perturbation and the growth of aseismic slip during fluid injection author s cappa f guglielmi y nussbaum c birkholzer j abstract 2018 american geophysical union all rights reserved fluid injections into the deep subsurface can at times generate earthquakes but often they only produce aseismic deformations here we analyze the influence of fault hydromechanical properties on the growth of injection induced aseismic slip using hydromechanical modeling we show how permeability enhancement in addition to the background stress and frictional weakening has an important effect on the pressure diffusion and slip growth during injection we find that the more pronounced the fault permeability enhancement the stronger is the growth of the aseismic slip zone the effect of enhanced permeability is more pronounced when the fault is initially close to failure our results show that aseismic slip grows beyond the pressurized zone when the fault permeability increases while slip remains behind the pressurized zone when permeability does not vary from its initial preslip value thus fault permeability increases should be considered as complementary mechanism to current models of fluid induced aseismic slip

induced earthquake families reveal distinctive evolutionary patterns near disposal wells the timing of events in seismic sequences can provide insights into the physical processes controlling fault slip in southern kansas the rate of earthquakes rose rapidly starting in 2013 following expansion of energy production into the area demanding the disposal of large volumes of wastewater into deep wells seismicity catalogs that are complete to low magnitudes can provide insights into the physical processes that induce seismicity near wastewater disposal we develop a catalog of over 130 000 earthquakes recorded in southern kansas from mid march 2014 through december 2017 by applying a matched filter algorithm to an original catalog of 5 831 template earthquakes detections have nearly identical waveforms to their associated template event and represent slip on nearly co located sections of a fault we select template events with at least 100 associated detections and examine the characteristics of these prolific families of earthquakes we find that families located close 10 km to areas with significant volumes of injected fluids have near poissonian interevent times and the families remain active over longer durations families farther from high volume injection wells show strong clustering of interevent times and shorter sequence durations we conclude that increasing pore fluid pressures from nearby disposal of large volumes of wastewater is the primary driver of these long duration episodes with earthquake earthquake interactions driving sequences at greater distance from the wells

observations of static coulomb stress triggering of the november 2011 m5 7 oklahoma earthquake sequence in november 2011 a m5 0 earthquake occurred less than a day before a m5 7 earthquake near prague oklahoma which may have promoted failure of the mainshock and thousands of aftershocks along the wilzetta fault including a m5 0 aftershock the m5 0 foreshock occurred in close proximity to active fluid injection wells fluid injection can cause a buildup of pore fluid pressure decrease the fault strength and may induce earthquakes keranen et al 2013 links the m5 0 foreshock with fluid injection but the relationship between the foreshock and successive events has not been investigated here we examine the role of coseismic coulomb stress transfer on earthquakes that follow the m5 0 foreshock including the m5 7 mainshock we resolve the static coulomb stress change onto the focal mechanism nodal plane that is most consistent with the rupture geometry of the three m 5 0 earthquakes as well as specified receiver fault planes that reflect the regional stress orientation we find that coulomb stress is increased e g fault failure is promoted on the nodal planes of 60 of the events that have focal mechanism solutions and more specifically that the m5 0 foreshock promoted failure on the rupture plane of the m5 7 mainshock we test our results over a range of effective coefficient of friction values hence we argue that the m5 0 foreshock induced by fluid injection potentially triggered a cascading failure of earthquakes along the complex wilzetta fault system

small latitudinal shift in the kuroshio extension central pacific during glacial times evidence from pollen transport the mid latitude area of the central pacific is sensitive to ocean environmental change because latitudinal fluctuation in a transition zone between subtropical and subarctic waters has played an important role in climatic change in east asia the north pacific and north america higher amounts of pollen and spores were found in core h3571 on the hess rise during the glacials than during the interglacials pollen originating from broadleaf deciduous forest in warm and humid environments as well as from boreal conifers and tundra park tundra in cold and wet environments occurred during the glacials the boreal conifer pollen such as tsuga picea and haploxylon could originate from the central japanese archipelago that ephedra was supplied from the asian continent and that the main source regions for the rest of the pollen and spores were from the southern japanese archipelago to the area around the east china sea therefore ocean current transportation was important for the transportation of pollen and spores to the hess rise this evidence demonstrates a small southward shift in the kuroshio extension during the glacials it also suggests that terrestrial organic matter om deposited in the open sea may also be transported by ocean currents reflecting coastal terrestrial environments although it is widely believed that terrestrial om in open sea sediments is of aerosol origin

the scec southern california reference three dimensional seismic velocity model version 2 we describe version 2 of the three dimensional 3d seismic velocity model of southern california developed by the southern california earthquake center and designed to serve as a reference model for multidisciplinary research activities in the area the model consists of detailed rule based representations of the major southern california basins los angeles basin ventura basin san gabriel valley san fernando valley chino basin san bernardino valley and the salton trough embedded in a 3d crust over a variable depth moho outside of the basins the model crust is based on regional tomographic results the model moho is represented by a surface with the depths determined by the receiver function technique shallow basin sediment velocities are constrained by geotechnical data the model is implemented in a computer code that generates any specified 3d mesh of seismic velocity and density values this parameterization is convenient to store transfer and update as new information and verification results become available

seismicity controlled by a frictional afterslip during a small magnitude seismic sequence m l 5 on the chihshang fault taiwan we report evidence for frictional afterslip at shallow depths about 5 to 7 km during a small magnitude seismic sequence with ml 5 along the chihshang fault a main active structure of the longitudinal valley in southeast taiwan the afterslip which was recorded by a nearby borehole dilatometer lasted about a month with a cumulative geodetic moment magnitude of 4 8 0 2 the afterslip comprised two stages and controlled the aftershock sequence the first postseismic stage which followed a ml 4 6 earthquake lasted about 6 h and mostly controlled the ruptures of neighboring asperities e g multiplets near the hypocenter then a 4 week duration large afterslip event following a ml 4 9 earthquake controlled the rate of aftershocks during its first 2 days through brittle creep the study presents a rare case of simultaneous seismological and geodetic observations for afterslip following earthquakes with magnitude lower than 5 furthermore the geodetic moment of the postseismic phase is at least equivalent to the coseismic moment of the sequence

complementary slip distributions of the largest earthquakes in the 2012 brawley swarm imperial valley california we investigate the finite rupture processes of two m 5 earthquakes in the 2012 brawley swarm by joint inversion of nearby strong motion and high rate gps data waveform inversions up to 3 hz were made possible by using a small event m w3 9 for path calibration of the velocity structure our results indicate that the first m w5 3 event ruptured a strong concentrated asperity with offsets of 20 cm centered at a depth of 5 km the subsequent m w5 4 event occurred 1 5 h later with a shallower slip distribution that surrounds and is complementary to that of the earlier event the second event has a longer rise time and weaker high frequency energy release compared to the m w5 3 event both events display strong rupture directivity toward the southwest and lack of very shallow 2 km coseismic slip the hypocenters for these events appear to be near or in the bedrock but most of the slip is distributed at shallower depths 6 km and can explain a large part of the gps offsets for the swarm the complementary slip distributions of the two events suggest a triggering relationship between them with no significant creep needed to explain the various data sets

imbricated aseismic slip and fluid diffusion drive a seismic swarm in the corinth gulf greece the primary processes driving seismic swarms are still under debate here we study the temporal evolution of a seismic swarm that occurred over a 10 day period in october 2015 in the extensional rift of the corinth gulf greece using high resolution earthquakes relocations the seismicity radially migrates on a normal fault at a fluid diffusion velocity 125 m day however this migration occurs intermittently with periods of fast expansion 2 to 10 km day during short seismic bursts alternating with quiescent periods moreover the growing phases of the swarm illuminates a high number of repeaters the swarm migration is likely the results of a combination of multiple driving processes fluid up flow in the fault may induce aseismic slip episodes separated by phases of fluid pressure build up the stress perturbation due to aseismic slip may activate small asperities that produce bursts of seismicity during the most intense phase of the swarm

highly heterogeneous pore fluid pressure enabled rupture of orthogonal faults during the 2019 ridgecrest mw7 0 earthquake here we show that the 2019 mw7 0 ridgecrest mainshock as well as its mw6 5 foreshock ruptured orthogonal conjugate faults we invert the waveforms recorded by the dense strong motion network at re

eocene atmospheric co2 from the nahcolite proxy estimates of the atmospheric concentration of co 2 co 2 atm for the hothouse climate of the early eocene climatic optimum eeco vary for different proxies extensive beds of the mineral nahcolite nahco 3 in evaporite deposits of the green river formation piceance creek basin colorado usa previously established co 2 atm for the eeco to be 1125 ppm by volume ppm here we present experimental data that revise the sodium carbonate mineral equilibria as a function of co 2 and temperature co precipitation of nahcolite and halite nacl now establishes a well constrained lower co 2 atm limit of 680 ppm for the eeco paleotemperature estimates from leaf fossils and fluid inclusions in halite suggest an upper limit for co 2 atm in the eeco from the nahcolite proxy of 1260 ppm these data support a causal connection between elevated co 2 atm and early eocene global warmth but at significantly lower co 2 atm than previously thought which suggests that ancient climates on earth may have been more sensitive to a doubling of co 2 atm than is currently assumed

high fluid pressure and triggered earthquakes in the enhanced geothermal system in basel switzerland 1 we analyzed 118 well constrained focal mechanisms to estimate the pore fluid pressure field of the stimulated region during the fluid injection experiment in basel switzerland this technique termed focal mechanism tomography fmt uses the orientations of slip planes within the prevailing regional stress field as an indicator of the fluid pressure along the plane at the time of slip the maximum value and temporal change of excess pore fluid pressures are consistent with the known history of the wellhead pressure applied at the borehole elevated pore fluid pressures were concentrated within 500 m of the open hole section which are consistent with the spatiotemporal evolution of the induced microseismicity our results demonstrate that fmt is a robust approach being validated at the meso scale of the basel stimulation experiment we found average earthquake triggering excess pore fluid pressures of about 10 mpa above hydrostatic overpressured fluids induced many small events m 3 along faults unfavorably oriented relative to the tectonic stress pattern while the larger events tended to occur along optimally oriented faults this suggests that small scale hydraulic networks developed from the high pressure stimulation interact to load hydraulically isolated high strength bridges that produce the larger events the triggering pore fluid pressures are substantially higher than that predicted from a linear pressure diffusion process from the source boundary and shows that the system is highly permeable along flow paths that allow fast pressure diffusion to the boundaries of the stimulated region

late quaternary atmospheric and oceanographic variations in the western pacific inferred from pollen and radiolarian analyses abstract pollen and radiolarian analyses of sediment from four piston cores located along a south north transect 28 44 n off the east coast of japan yield detailed records of variations in terrestrial and marine climate of this region for the last 140 ka the last interglacial climate of the southern half of japan was characterized by increased temperature and precipitation at least across central japan compared with today off southern japan surface were cooler during summer than at present off central japan both summer and winter sea surface temperatures were cooler than today early glacial 115 71 ka bp climate across central and southern japan alternated between wet and dry warm temperate with surface waters offshore warmer in summer and winter than during the penultimate interglacial temperatures and precipitation in japan reached low levels early during the full glacial phase and remained relatively low throughout much of the full glacial 71 14 ka bp cold sea surface temperatures at all our sites coincided with these cold conditions on land temperatures across much of japan began to increase steadily during the deglacial with surface waters offshore remaining at or near their glacial lows holocene vegetation patterns which continued to reflect an increase in temperature reached a maximum during early to mid holocene surface waters offshore however remained relatively cool during the early holocene with temperature maxima at most western pacific sites occurring in mid to late holocene we propose specific changes in the seasonal positions of atmospheric pressure cells to explain these climate variations that have occurred across the northeast asian northwest pacific region through the most recent interglacial glacial cycle results of this exercise show that there are no major discrepancies between climate reconstructions for mainland japan inferred from pollen and those for the western pacific derived from radiolarians

aseismic transient slip on the gofar transform fault east pacific rise oceanic transform faults display a unique combination of seismic and aseismic slip behavior including a large globally averaged seismic deficit and the local occurrence of repeating magnitude m 6 earthquakes with abundant foreshocks and seismic swarms as on the gofar transform of the east pacific rise and the blanco ridge in the northeast pacific ocean however the underlying mechanisms that govern the partitioning between seismic and aseismic slip and their interaction remain unclear here we present a numerical modeling study of earthquake sequences and aseismic transient slip on oceanic transform faults in the model strong dilatancy strengthening supported by seismic imaging that indicates enhanced fluid filled porosity and possible hydrothermal circulation down to the brittle ductile transition effectively stabilizes along strike seismic rupture propagation and results in rupture barriers where aseismic transients arise episodically the modeled slow slip migrates along the barrier zones at speeds 10 to 600 m h spatiotemporally correlated with the observed migration of seismic swarms on the gofar transform our model thus suggests the possible prevalence of episodic aseismic transients in m 6 rupture barrier zones that host active swarms on oceanic transform faults and provides candidates for future seafloor geodesy experiments to verify the relation between aseismic fault slip earthquake swarms and fault zone hydromechanical properties

anthropogenic seismicity rates and operational parameters at the salton sea geothermal field geothermal power is a growing energy source however efforts to increase production are tempered by concern over induced earthquakes although increased seismicity commonly accompanies geothermal production induced earthquake rate cannot currently be forecast on the basis of fluid injection volumes or any other operational parameters we show that at the salton sea geothermal field the total volume of fluid extracted or injected tracks the long term evolution of seismicity after correcting for the aftershock rate the net fluid volume extracted injected provides the best correlation with seismicity in recent years we model the background earthquake rate with a linear combination of injection and net production rates that allows us to track the secular development of the field as the number of earthquakes per fluid volume injected decreases over time