a tidal model for eastern juan de fuca strait and the southern strait of georgia a three dimensional barotropic finite element model is used to calculate the tidal flows in eastern juan de fuca strait and the southern strait of georgia the harmonics of eight constituents are computed and compared with those from previous finite difference models and those from historical tide gauge and current meter observations root mean square differences between observed and calculated sea level amplitudes are within 2 0 cm for all constituents and the phases are within 4 0 for all constituents except k2 horizontal currents from the model are found to reproduce the observed vertical variations in shear except in regions where stratification effects and internal tides exist in particular the model representation of currents at six stations in the canadian tide and current tables volume 5 is accurate the pattern of tidal residual currents has much more detail than previous coarser resolution models and numerous eddies are predicted computed energy flux fields reveal that over a 29 day period only 38 of the tidal power entering juan de fuca strait is transmitted into the southern strait of georgia and of the 39 entering haro strait 36 is dissipated within the strait itself

tide modulated gas emissions and tremors off sw taiwan abstract the continental margin off sw taiwan is in an incipient stage of orogeny and contains numerous active mud diapirs and mud volcanoes gas emissions out of the seabed off sw taiwan are revealed by acoustic images from 38 khz echo sounders or sub bottom profilers however the mechanism for gas emissions is still poorly understood in this study we show that the gas emissions out of the seabed and the associated tremors off sw taiwan are strongly correlated with the ocean tides especially with the diurnal and semidiurnal constituents particularly for each tidal day the strong gas emissions expulsions and long duration tremors occur mainly during both the rising periods to the higher high tides and the falling periods to the lower low tides both the gas emissions and tremor activities are generally quiescent near the tidal datum on average the daily intensity of gas emissions and the magnitude of tremors are positively proportional to the daily tidal range a larger slope site implies a greater concentration of gas in the shallow sediments most of the individual tremors and long duration tremors observed off sw taiwan occur as results of the strong gas expulsions out of the gas bearing seabed the high frequency components of the induced tremors quickly decay and are followed by horizontal low frequency 7 hz harmonic oscillations of the seabed long duration tremors may enhance seafloor instability and increase the potential for submarine landslides

controls on plate motion by oscillating tidal stress evidence from deep tremors in western japan deep tremors are considered to be shear slip on the plate interface and are often sensitive to tidal stress here we demonstrate that a small cluster of tremors is extremely well correlated with tide levels observed at nearby stations in western japan the correlation is interpreted as representing a nonlinear relationship between stress and slip which is similar to the rate dependent friction law an empirical relationship and observed tide records explain the temporal changes in tremor activity over 9 years the combination of the nonlinear fault rheology and oscillating tidal stress may control temporal changes in plate motion and earthquake occurrence remarkably the background seismicity is similar to the predicted tremor rate obtained from tidal observations over the past 50 years this mechanism may also explain the seasonality and decadal scale weak periodicity of large earthquakes and is likely to be helpful in probabilistic forecasting of future seismicity

oxygen isotope composition of modern and archaeological otoliths from the estuarine hardhead catfish ariopsis felis and their potential to record low latitude climate change abstract shells and otoliths fish ear bones from archaeological deposits of pine island southwest florida provide valuable archives of ecological patterns climate change and associated human responses many remains from these deposits that can be used for climate reconstruction are from estuarine animals the challenge in using oxygen isotope composition of their carbonate hard parts lies in deconvoluting the effects of temperature and salinity mixing of fresh and saltwater each having different isotopic compositions otoliths of the hardhead catfish ariopsis felis linneaus 1766 may provide a record of winter temperature without the complication of salinity variation because this fish spends winter months in waters of marine to near marine salinities hence 18 o water can be constrained when employing published temperature equations here we present geochemical data from modern and archaeological otoliths to evaluate whether they preserve winter temperature a modern catfish was caught near pine island sound and the otoliths lapilli removed archaeological otoliths from the 2nd 3rd century ad falling within the roman optimum ro and the 13th 14th century ad falling within the little ice age lia were obtained from the florida museum s collections oxygen isotope compositions were converted to temperature using published temperature equations and assuming 1 for gulf water isotopic compositions for the modern otolith range from 3 55 to 0 29 the lia otolith ranges from 3 92 to 0 52 and the ro otolith ranges from 1 80 to 0 84 all three otoliths record winter temperature 20 c similar to modern conditions calculated summer temperatures for the modern and lia otoliths 40 c are overestimated and reflect the combined influence of temperature and salinity when catfish inhabit brackish estuarine waters during their reproductive season in contrast summer temperature estimates for the ro otolith are similar to modern conditions indicating estuarine water during the summer was close to 1 this result suggests that seasonal rainfall patterns during the time period represented by the ro otolith were different than today such that the summer wet season was not prevalent

tidal sensitivity of shallow very low frequency earthquakes in the ryukyu trench we show that the activity between 2002 and 2014 of shallow very low frequency earthquakes vlfes which occur in shallow subduction zones of the ryukyu trench responds to ocean and earth tides tidal sensitivity is highest in the central portion of the ryukyu trench and lowest in the southwest the lag of peak vlfe activation behind the peaks of shear stress or normal stress is laterally heterogeneous along the ryukyu trench the lateral variation of the lag between the peaks of sensitivity and stresses can be explained by the dependence of vlfe activation on thrust encouraging shear stress on the plate the effective normal stress which is calculated through rock experiments and from the sensitivity of vlfe for shear stress is 0 25 mpa in the central ryukyu trench which implies that high pore pressure on the plate interface would induce the vlfes the lateral variation of the sensitivity can be explained by differences in pore pressure within the plate interface although tidal sensitivity is lowest in the southwestern ryukyu trench it increased temporarily during the middle of the decay of vlfe swarm activity this is interpreted as reflecting a temporary increase in pore pressure on the fault frictional heterogeneity or fault weakening during the slip of slow slip events

episodic slow slip events accompanied by non volcanic tremors in southwest japan subduction zone 1 episodic slow slip events have been recognized by means of tilt changes in the western shikoku area southwest japan the crustal tilt deformation was observed repeatedly with a recurrence interval of approximately six months coincident with the occurrences of major non volcanic deep tremor activities in this area observed tilt changes can be explained by slow slip events occurring around the source area of tremors in each episode the source of the slow slip event and tremor migrate simultaneously the spatial and temporal coincidence of tremors and slow slip events indicates that they both may be coupling phenomena reflecting the stress accumulation process at the subducting plate

geochemical variation in microstructural shell layers of the southern quahog mercenaria campechiensis implications for reconstructing seasonality abstract shells of the northern and southern quahogs mercenaria mercenaria and mercenaria campechiensis respectively from paleontological and archaeological deposits have been used to reconstruct climate environmental conditions and ecological relationships seasonal fluctuations in temperature and salinity are recorded in shell carbonate as variations in 18 o and 13 c values and sr ca ratios however these environmental proxies have not yet been calibrated for m campechiensis previous geochemical studies of quahog shells focused on the outer prismatic layer as an ecological archive the outer layer is often not preserved in fossil and archaeological shells moreover recent innovations in microsampling techniques allow high resolution sampling of the middle cross lamellar layer this study tests whether outer prismatic and middle cross lamellar layers record similar variations in 18 o and 13 c values and sr ca ratios in modern shells of m campechiensis and whether profiles are similar among individuals the last 2 years of shell growth from three individuals 6 7 and 9 years old collected alive near bokeelia southwest florida were microsampled for geochemical analyses 18 o varies seasonally relative to translucent summer and opaque winter growth increments variation of 18 o from outer and middle layers are identical within and among shells however the oldest individual did not preserve the most positive values represented in the two younger shells 13 c from both layers are similar within shells although the outer layer is more variable and the range of values varies somewhat among individuals sr ca ratios from the outer and middle layers within shells do not track each other well and profiles among individuals are different to evaluate whether a seasonal signal was present sr ca ratios were compared to 18 o values there was no co variation within the outer layer in any of the shells therefore this layer should be avoided when using sr ca ratios as a temperature proxy the middle layer from the 6 year old shell showed no co variation the 7 year old shell exhibited a moderate negative co variation r 2 0 55 p r 2 0 72 p 18 o and environmental interpretations made using 13 c values should be treated with caution

introduction to special section on phenomenology underlying processes and hazard implications of aseismic slip and nonvolcanic tremor 1 this paper introduces the special section on the phenomenology underlying processes and hazard implications of aseismic slip and nonvolcanic tremor by highlighting key results of the studies published in it many of the results indicate that seismic and aseismic manifestations of slow slip reflect transient shear displacements on the plate interface with the outstanding exception of northern cascadia where tremor sources have been located on and above the plate interface differing models of the plate interface there also need to be reconciled slow slip phenomena appear to result from propagating deformation that may develop with persistent gaps and segment boundaries results add to evidence that when tectonic deformation is relaxed via slow slip most relaxation occurs aseismically but with seismic signals providing higher resolution proxies for the aseismic slip instead of two distinct slip modes as suggested previously lines between fast and slow slip more appropriately may be described as blurry zones results reported also show that slow slip sources do not coincide with a specific temperature or metamorphic reaction their associations with zones of high conductivity and low shear to compressional wave velocity ratios corroborate source models involving pore fluid pressure buildup and release these models and spatial anticorrelations between earthquake and tremor activity also corroborate a linkage between slow slip and frictional properties transitional between steady state and stick slip finally this special section highlights the benefits of global and multidisciplinary studies which demonstrate that slow phenomena are not confined to beneath the locked zone but exist in many settings

late holocene climate change in the big belt mountains central montana usa carroll college and the helena national forest are working in a 6 year research partnership designed to investigate the relationship between paleoclimate change and human adaptation in the big belt mountains of central montana usa this ongoing project is designed to gather archaeological and paleoenvironmental data from three diverse ecosystems within one drainage basin high altitude park areas 1800 2100 m mid altitude conifer forests 1200 1500 m and low altitude locales under 1500 m along the missouri river these data will represent paleoecological and archaeological changes through time and will detect synchrony and diversity across an elevation gradient thus far excavation of two mid altitude sites dating to 2400 and 4500 bp and one high altitude site dated to 2400 bp revealed evidence of a significant drought period about 2000 years ago to date the excavated sites evidence a shift in pollen to drier species a shift to higher sedimentation rates and changes in snail and vertebrate

seasonal climate change across the roman warm period vandal minimum transition using isotope sclerochronology in archaeological shells and otoliths southwest florida usa abstract archaeological evidence suggests that southwest florida experienced variably warmer and wetter climate during the roman warm period rwp 300 bc 550 ad relative to the vandal minimum vm 550 800 ad this hypothesis was tested by reconstructing seasonal scale climate conditions for the latter part of the rwp 1 550 ad by using high resolution oxygen isotope ratios 18o of archaeological shells mercenaria campechiensis and otoliths ariopsis felis eight shells radiocarbon dated to 150 550 ad recorded that the rwp summers at 150 250 ad were insignificantly different from today and the rwp summers at 250 350 ad and 450 550 ad were drier relative to today eight otoliths indicate that the winters were variable during the rwp colder than today at 150 200 ad and 250 300 ad similar to today at 200 250 ad 300 350 ad and 450 500 ad and warmer than today at 500 550 ad the climate reconstructions agree with archaeological observations and are partially coherent with the history of sea level change with a drying and cooling trend at the 95 confidence level across the rwp vm transition the climate transition is not only consistent with falling sea level but also coherent with reduced solar radiation reduced solar radiation may have triggered a change in atmospheric circulation patterns that precipitated the observed climate transition

effective stress friction and deep crustal faulting author s beeler nm hirth g thomas a burgmann r abstract 2015 american geophysical union all rights reserved studies of crustal faulting and rock friction invariably assume the effective normal stress that determines fault shear resistance during frictional sliding is the applied normal stress minus the pore pressure here we propose an expression for the effective stress coefficient f at temperatures and stresses near the brittle ductile transition bdt that depends on the percentage of solid solid contact area across the fault f varies with depth and is only near 1 when the yield strength of asperity contacts greatly exceeds the applied normal stress for a vertical strike slip quartz fault zone at hydrostatic pore pressure and assuming 1 mm and 1 km shear zone widths for friction and ductile shear respectively the bdt is at 13 km f near 1 is restricted to depths where the shear zone is narrow below the bdt f 0 is due to a dramatically decreased strain rate under these circumstances friction cannot be reactivated below the bdt by increasing the pore pressure alone and requires localization if pore pressure increases and the fault localizes back to 1 mm then brittle behavior can occur to a depth of around 35 km the interdependencies among effective stress contact scale strain rate and pore pressure allow estimates of the conditions necessary for deep low frequency seismicity seen on the san andreas near parkfield and in some subduction zones among the implications are that shear in the region separating shallow earthquakes and deep low frequency seismicity is distributed and that the deeper zone involves both elevated pore fluid pressure and localization

pattern informatics and the soup of groups model of earthquakes a case study of italian seismicity an improved pattern informatics pi method inspired by the soup of groups model is developed in this study this improved method reveals its potential in reducing the noise that when the classical pi is applied can yield misleading conclusions about the existence of hotspots in the vicinity of the epicenter of a strong earthquake the application of this new method to italian seismicity from 1985 to 2018 properly reveals hotspots around the two strongest earthquakes that occurred in 2009 l aquila earthquake and 2016 norcia earthquake suggesting its utility in studies devoted to earthquake prediction

complex evolution of transient slip derived from precise tremor locations in western shikoku japan transient slip events which occur more slowly than traditional earthquakes are increasingly being recognized as important components of strain release on faults and may substantially impact the earthquake cycle surface based geodetic instruments provide estimates of the overall slip distribution in larger transients but are unable to capture the detailed evolution of such slip either in time or in space accompanying some of these slip transients is a relatively weak extended duration seismic signal known as nonvolcanic tremor which has recently been shown to be generated by a sequence of shear failures occurring as part of the slip event by precisely locating the tremor we can track some features of slip evolution with unprecedented resolution here we analyze two weeklong episodes of tremor and slow slip in western shikoku japan we find that these slip transients do not evolve in a smooth and steady fashion but contain numerous subevents of smaller size and shorter duration in addition to along strike migration rates of 10 km d observed previously much faster migration also occurs usually in the slab dip direction at rates of 25 150 km h over distances of up to 20 km we observe such migration episodes in both the updip and downdip directions these episodes may be most common on certain portions of the plate boundary that generate strong tremor in intermittent bursts the surrounding regions of the fault may slip more continuously driving these stronger patches to repeated failures tremor activity has a strong tidal periodicity possibly reflecting the modulation of slow slip velocity by tidal stresses

granulite formation is driven by magmatic processes in the deep crust abstract known examples of granulite facies metamorphism span at least 3 5 b y of earth history mineralogic geobarometry indicates that such metamorphism has occurred in the deep crust typically at 20 30 km 6 9 kbar geothermometry indicates that peak t 700 900 c and therefore that t was elevated by at least 200 c over an anorogenic geotherm of 15 20 c km 1 commonly invoked sources of heat include rising magmas radioactive decay insulated by continent continent collision mantle volatiles or crustal thinning present day crustal thicknesses are normal beneath exposed granulite terranes and the common absence of evidence for post metamorphic underplating suggests synmetamorphic thicknesses of 60 80 km thus granulites form in tectonically active regions of thickened crust and elevated geotherm xenolith suites suggest that granulite facies mineralogy persists in the deepest crust after tectonism in spite of declining temperature to greenshist amphibolite facies conditions

scaling of seismicity induced by nonlinear fluid rock interaction 1 fluid injections into geothermal systems sometimes can produce significant seismic events with magnitudes of up to 4 however in the case of hydraulic fracturing of hydrocarbon reservoirs such events occur extremely seldom in the last case in contrast to the former one the structure of rocks is being actively destroyed e g opening of tensile fractures and the fluid rock interaction is strongly nonlinear e g a strong increase of permeability what is the role of this nonlinearity we consider nonlinear pore pressure diffusion to explain features of seismicity we formulate seismicity triggering front its propagation is sensitive to a grade of nonlinearity to spatial dimension of diffusion and to the injection rate we show that a probability of an event with a magnitude larger than a given one increases proportionally to the injected mass an increase of this probability with time is insensitive to the nonlinearity we compare different borehole experiments in some cases the injection produces clearly nonlinear impact on rocks in others this impact is approximately linear we find a well agreement with our theory we observe an insensitivity of temporal increments of magnitude probability to the grade of nonlinearity these increments are controlled by injection rate increments in contrast nonlinear fluid rock interactions are characterized by a strong dominance of small earthquakes defects activated by a nonlinear diffusion possibly obey gutenberg richter statistics with anomalous high b values in the case of a linear diffusion magnitude distributions of events are probably inherited from pre existing fracture systems

low friction and fault weakening revealed by rising sensitivity of tremor to tidal stress at subduction zones deep parts of the fault can slip slowly generating tremor analysis of tremor in cascadia reveals increasing sensitivity of slip to tidal stresses over several days implying that the fault is weak and weakens as it slips

automatic detection and characterization of seismic tremors in northern cascadia 1 we develop an algorithm that automatically detects and characterizes seismic waveforms associated with episodic tremor and slip ets events in northern cascadia for each hour long seismogram the process begins with the calculation of moving average and scintillation index functions a logic chart is designed to sort the observed waveform patterns into a set of classes based on these functions an ets event is always manifest by many station hours with coherent tremor ct patterns automatic analysis of seismic waveforms recorded in the past three years gives results consistent with the work done by tedious visual inspection of seismograms our algorithm which is free from human oversight is ideal for an automatic tremor monitoring system to give immediate notice of an ets event

environmental controls on the stable isotopic composition of mercenaria mercenaria potential application to paleoenvironmental studies 1 we have investigated the environmental controls of seasonally resolved records of oxygen and carbon isotopes of modern mercenaria mercenaria bivalves collected live from five coastal sites along the east coast of north america seasonal profiles of 18o and 13c obtained by subsampling the incremental growth layers of aragonite were compared with in situ historical records of temperature and salinity we show that m mercenaria 18o profiles track accurately the seasonal variations of water temperature and that variations in growth rates do not affect the shell 18o values growth rates are strongly reduced or interrupted below water temperatures ranging from 8 to 10 c implying that only bivalves sampled in tropical areas track the full amplitude of seasonal variations although further measurements of water 18o and a better understanding of seasonal variations of the water 18o salinity relationships are necessary mercenaria mercenaria bivalves appear to precipitate their shell close to isotopic equilibrium whereas the amplitude of the seasonal profiles of 18o reflects variations in water temperature the annual average 18o decreases with latitude reflecting the trend of rainfall and riverwater 18o with latitude over the northern american continent

lithoprobe southern vancouver island cenozoic subduction complex imaged by deep seismic reflections reply the lithoprobe seismic reflection project on vancouver island was designed to study the large scale structure of several accreted terranes exposed on the island and to determine the geometry and structural characteristics of the subducting juan de fuca plate in this paper we interpret two lithoprobe profiles from southernmost vancouver island that were shot across three important terrane bounding faults leech river san juan and survey mountain to determine their subsurface geometry and relationship to deeper structures associated with modem subduction the structure beneath the island can be divided into an upper crustal region consisting of several accreted terranes and a deeper region that represents a landward extension of the modern offshore subduction complex in the upper region the survey mountain and leech river faults are imaged as northeast dipping thrusts that separate wrangellia a large mesozoic paleozoic terrane from two smaller accreted terranes the leech river schist mesozoic rock

cooler winters as a possible cause of mass extinctions at the eocene oligocene boundary the eocene oligocene boundary at about 33 7 myr ago marks one of the largest extinctions of marine invertebrates in the cenozoic period1 for example turnover of mollusc species in the us gulf coastal plain was over 90 at this time2 3 a temperature change across this boundary from warm eocene climates to cooler conditions in the oligocene has been suggested as a cause of this extinction event4 but climate reconstructions have not provided support for this hypothesis here we report stable oxygen isotope measurements of aragonite in fish otoliths ear stones collected across the eocene oligocene boundary palaeotemperatures reconstructed from mean otolith oxygen isotope values show little change through this interval in agreement with previous studies5 6 from incremental microsampling of otoliths however we can resolve the seasonal variation in temperature recorded as the otoliths continue to accrete new material over the life of the fish these seasonal data suggest that winters became about 4 c colder across the eocene oligocene boundary we suggest that temperature variability rather than change in mean annual temperature helped to cause faunal turnover during this transition

tidal modulation of continuous nonvolcanic seismic tremor in the chile triple junction region 1 we located continuous seismic tremor with coherent amplitude wave trains in the chile ridge subduction region 46 5 s in two clusters north and south of the chonos archipelago between the chile trench and the north patagonian fore arc tremor persisted from december 2004 to february 2007 the entire period of the chile ridge subduction project temporary seismic deployment and lasted 17 h on six occasions tremor in the more active southern cluster reached a maximum duration of 48 h and we observed no more than 3 continuous days without tremor activity the cluster locations coincide with the surface projections of subducted transform faults formed at the chile ridge we also detected simultaneous colocated low frequency microearthquakes with well defined impulsive waves within the tremor signals distributed from the surface to 40 km depth suggesting tremors and earthquakes are part of the same process the periodicity of tremor duration is strongly correlated with semidiurnal diurnal and long period tides m2 n2 k1 o1 p1 and mm 12 421 h 12 000 h 23 934 h 25 819 h 24 066 h and 27 555 days respectively we found a significant correlation between tremor occurrence and earth tides when tidal stress is calculated for the slip plane of a right lateral strike slip fault with strike n95 e which is near parallel to subducted transform faults n78 e of the chile ridge indicating that the very small stresses resulting from the combination of ocean loading and solid earth tides 1 kpa are sufficient to facilitate or suppress tremor production tremors occur when shear stresses are maximum and wane or are low when shear stresses are minimum

food for thought mathematical approaches for the conversion of high resolution sclerochronological oxygen isotope records into sub annually resolved time series abstract oxygen isotope 18 o records of incrementally banded marine calcifiers provide high resolution information about modern and past environmental conditions however given their biological origin these records are often distorted by ontogenetic and seasonal growth pattern to evaluate their reliability many studies correlate skeletal 18 o records with instrumentally measured time series of environmental conditions using a variety of methods to recalculate their temporal framework lacking consistency and a limited traceability of many temporal alignment methods underline the need for standardized and flexible method for the temporal alignment of sclerochronological records here two methods for the temporal alignment of sclerochronological data and their application on measured oxygen isotope signatures of a fish otolith and a marine bivalve shell are presented and compared the first method is a flexible approach using a linear interpolation between carefully selected temporal reference points for recalculating ontogenetic growth effects with an optional extension accounting for seasonal growth oscillations the second approach uses the seasonally oscillating von bertalanffy growth function parameterized based on the oxygen isotope record to reconstruct the underlying growth model and reconstruct thereby its temporal framework using these methods we re align 18 o based water temperature records of a carlarius heudelotii otolith and a venus crebrisulca shell with measured sea surface temperature time series and compare the resulting correlation as well as the different underlying growth models our results show that both methods represent useful tools for the temporal alignment of sclerochronological records however underlying growth models strongly differ depending on the temporal alignment method and the parameters used for the reconstruction of the temporal framework this underlines the importance of a careful selection of a particular alignment method depending on the complexity of distortion due to seasonal and ontogenetic growth trajectories moreover we show that both organisms represent reliable paleoenvironmental archives providing sub seasonally resolved water temperature records

ocean quahogs arctica islandica and atlantic surfclams spisula solidissima on the mid atlantic bight continental shelf and georges bank the death assemblage as a recorder of climate change and the reorganization of the continental shelf benthos abstract the degree to which evidence of range shifts in shelf biomass dominants atlantic surfclams and ocean quahogs as a function of climate change is examined by comparing the dissimilarity in distribution of the living community and the record of habitation ensconced in the death assemblage comparison of the distribution of live animals and dead shells reveals for both species that live animals are rarely found where dead shells were not collected but dead shells were collected at a substantively larger number of sites than where live animals were found the geographic footprint resolved by the dead shells was much broader than that of live animals extensive spatially coherent regions exist inshore and offshore of the present day habitat of occupation where evidence of previous occupation exists sites where ocean quahog shells were found without live ocean quahogs included a portion of the continental shelf inshore of the present day habitable range an area only habitable under colder climatic conditions than observed today surfclam shells were found offshore of the present day habitable region in deeper water additional warming of bottom waters offshore would be necessary for surfclams to occupy the region now occupied solely by dead shells the death assemblage shows that these biomass dominants have repositioned themselves across the continental shelf during the past and this repositioning certainly is driven by changes in bottom water temperature moreover the distribution of surfclam shells indicates that the death assemblage may provide a possible window into the future as movement of the present day population is towards these deeper water previously occupied regions overall the death assemblage may provide an important source of information on range shifts sparing the need to carry out extensive and frequent benthic surveys and may permit reconstruction of ongoing shifts in community composition as a product of climate change when adequate survey data are not available

clamr a statistical evaluation of isotopic and temperature records in sclerochronologic studies abstract isotope sclerochronology has been widely used to reconstruct paleoclimate from the hard part remains of a broad range of taxa from many different environmental settings and geological and cultural contexts oxygen isotope 18o time series derived from these ultra high resolution daily seasonal annual records have been used to estimate annual averages seasonal ranges and seasonal extremes these time series however inherently include uncertainties such as unconstrained environmental noise changes in seasonal growth rates resulting in weighting annual temperature estimates toward seasons of maximum growth growth cessation and reliance on the most extreme 18o values in the time series to estimate seasonal temperature range etc to better quantify uncertainties in paleoclimate reconstructions using sclerochronologic data we developed an open source r package clamr the clamr evaluation tool improves upon the previous best fit sinusoid approach by introducing additional statistical computation and analysis including discrete fourier transform to initialize parameters for the sinusoidal function nelder mead method to optimize parameters jackknife error estimation and window size calculation for sinusoidal smoothing it can automatically calculate and plot statistical errors for oxygen isotope or temperature data series and provide statistical estimation of temperature and isotopic variables such as annual averages seasonal ranges and seasonal extremes moreover it allows evaluation of the influence of environmental and or physiological noise added to the climate signal therefore clamr enables more comprehensive and justified comparison between paleoclimate reconstructions and modern instrument records and ultimately advances our interpretation of seasonal isotope records from biogenic hard parts

slow earthquakes and nonvolcanic tremor nonvolcanic tremor is observed in close association with geodetically observed slow slip events in subduction zones accumulating evidence points to these events as members of a family of slow earthquakes that occur as shear slip on the downdip extensions of fault zones in a regime that is transitional between a frictionally locked region above and a freely slipping region below by virtue of their locations and their properties slow earthquakes are certain to provide new insights into the behavior of earthquakes and faulting and into the hazard they embody

tidal modulation of nonvolcanic tremor episodes of nonvolcanic tremor and accompanying slow slip recently have been observed in the subduction zones of japan and cascadia in cascadia such episodes typically last a few weeks and differ from normal earthquakes in their source location and moment duration scaling the three most recent episodes in the puget sound southern vancouver island portion of the cascadia subduction zone were exceptionally well recorded in each episode we saw clear pulsing of tremor activity with periods of 12 4 and 24 to 25 hours the same as the principal lunar and lunisolar tides this indicates that the small stresses associated with the solid earth and ocean tides influence the genesis of tremor much more effectively than they do the genesis of normal earthquakes because the lithostatic stresses are 10 5 times larger than those associated with the tides we argue that tremor occurs on very weak faults

earthquakes stress and strain along an obliquely divergent plate boundary reykjanes peninsula southwest iceland earthquakes stress and strain along an obliquely divergent plate boundary the reykjanes peninsula southwest iceland

late holocene indian summer monsoon variations recorded at lake erhai southwestern china in this study we report changes in indian summer monsoon ism intensity during the past 3500 yr inferred from proxy indices at lake erhai southwestern china both the pollen concentrations and other proxy indices including sediment grain size total organic carbon contents toc and elemental contents e g fe al clearly indicate a long term decreasing trend in ism intensity over the late holocene during the period from approximately ad 750 to ad 1200 pollen concentrations of conifer and broadleaf trees and herbs reached the lowest levels over the past 3500 yr while the pollen percentages of both herbs and broadleaf trees increased suggesting a significant medieval drought the grain size toc and elemental contents also support an arid climate during the medieval period the little ice age lia at lake erhai was characterized as cold and wet the medieval and lia climatic patterns at lake erhai were similar to those over most of the ism areas but anti phase with those over east asian summer monsoon easm areas we suspect that sea surface temperature variations in the indo pacific oceans and the related land sea thermal contrasts may be responsible for such hydroclimatic differences between easm and ism areas

persistent tremor within the northern costa rica seismogenic zone 1 we identify tremor using a spectral detection method and characterize its occurrence over a period of four years 2006 2009 in the vicinity of the nicoya peninsula costa rica although a few major tremor events accompanied by geodetic slow slip occur much of the tremor record consists of minor episodes with short duration and no detectable geodetic slip its persistent occurrence suggests that some portion of the interface is experiencing slow slip nearly continuously driving small patches to fail in accelerated slip locations indicate that much of the tremor occurs at shallow depth in freely slipping regions of the seismogenic zone this result is significant in that locations of slow slip and tremor at other subduction zones are largely limited to the downdip frictional transition tremor locations may help to refine the heterogeneous distribution of locked and freely slipping patches within the costa rica seismogenic zone

regionally coherent little ice age cooling in the atlantic warm pool 1 we present 2 new decadal resolution foraminiferal mg ca sst records covering the past 6 8 centuries from the northern gulf of mexico gom these records provide evidence for a little ice age lia cooling of 2 c consistent with a published mg ca record from pigmy basin comparison of these 3 records with existing sst proxy records from the gom caribbean region show that the magnitude of lia cooling in the atlantic warm pool awp was significantly larger than the mean hemispheric cooling of 1 c we propose that a reduction in the intensity and spatial extent of the awp during the lia combined with associated changes in atmospheric circulation may account for the regional sst patterns observed in the gom caribbean region during the lia

isotopic evidence for climate change during the vandal minimum from ariopsis felis otoliths and mercenaria campechiensis shells southwest florida usa archaeological evidence from coastal southwest florida suggests this region and its local inhabitants the calusa were affected by drought and cooling during the vandal minimum climate episode ad 500 800 to test this hypothesis we reconstructed seasonal scale climate conditions using stable oxygen and carbon isotope ratios 18o and 13c preserved in ariopsis felis otoliths and mercenaria campechiensis shells comparing 18o records from both species distinguishes between cool versus warm and wet versus dry conditions 18o values from four otoliths indicate cooling of winter temperatures occurred in the early vandal minimum ad 500 600 and late half of the middle vandal minimum ad 650 700 persistent dry summers punctuated by occasional years with wet summers throughout the vandal minimum were detected from 18o values of eight archaeological shells our climate reconstructions are in good agreement with archaeological observations and with the cool and dry conditions documented in europe

laboratory triggering of stick slip events by oscillatory loading in the presence of pore fluid with implications for physics of tectonic tremor 1 the physical mechanism by which the low frequency earthquakes lfes that make up portions of tectonic also called non volcanic tremor are created is poorly understood in many areas of the world tectonic tremor and lfes appear to be strongly tidally modulated whereas ordinary earthquakes are not anomalous seismic wave speeds interpreted as high pore fluid pressure have been observed in regions that generate tremor here we build upon previous laboratory studies that investigated the response of stick slip on artificial faults to oscillatory tide like loading these previous experiments were carried out using room dry samples of westerly granite at one effective stress here we augment these results with new experiments on westerly granite with the addition of varying effective stress using pore fluid at two pressures we find that raising pore pressure thereby lowering effective stress can significantly increase the degree of correlation of stick slip to oscillatory loading we also find other pore fluid effects that become important at higher frequencies when the period of oscillation is comparable to the diffusion time of pore fluid into the fault these results help constrain the conditions at depth that give rise to tidally modulated lfes providing confirmation of the effective pressure law for triggering and insights into why tremor is tidally modulated while earthquakes are at best only weakly modulated

seasonal temperature variability of the neoglacial 3300 2500 bp and roman warm period 2500 1600 bp reconstructed from oxygen isotope ratios of limpet shells patella vulgata northwest scotland abstract seasonal sea surface temperature variability for the neoglacial 3300 2500 bp and roman warm period rwp 2500 1600 bp which correspond to the bronze and iron ages respectively was estimated using oxygen isotope ratios obtained from high resolution samples micromilled from radiocarbon dated archaeological limpet patella vulgata shells the coldest winter months recorded in neoglacial shells averaged 6 6 0 3 c and the warmest summer months averaged 14 7 0 4 c one neoglacial shell captured a year without a summer which may have resulted from a dust veil from a volcanic eruption in the katla volcanic system in iceland rwp shells record average winter and summer monthly temperatures of 6 3 0 1 c and 13 3 0 3 c respectively these results capture a cooling transition from the neoglacial to rwp which is further supported by earlier studies of pine history in scotland pollen type analyses in northeast scotland and european glacial events the cooling transition observed at the boundary between the neoglacial and rwp in our study also agrees with the abrupt climate deterioration at 2800 2700 bp also referred to as the subboreal subatlantic transition and therefore may have been driven by decreased solar radiation and weakened north atlantic oscillation conditions

laterally propagating slow slip events in a rate and state friction model with a velocity weakening to velocity strengthening transition we investigate the behavior of simulated slow slip events using a rate and state friction model that is steady state velocity weakening at low slip speeds but velocity strengthening at high slip speeds our simulations are on a one dimensional line fault but we modify the elastic interactions to mimic the elongate geometry frequently observed in slow slip events simulations exhibit a number of small events as well as periodic large events the large events propagate approximately steadily along strike and stress and slip rate decay gradually behind the propagating front their recurrence intervals can be determined by considering what is essentially an energy balance requirement for long distance propagation it is possible to choose the model parameters such that the simulated events have the stress drops slip velocities and propagation rates observed in cascadia

late holocene climate change for the eastern interior united states evidence from high resolution δ 18 o values of sagittal otoliths abstract stable oxygen isotope values were determined for freshwater drum aplodinotus grunniens sagittal otoliths recovered from the eastman rockshelter archaeological site in northeast tennessee to evaluate climate change for the eastern interior united states from 5500 calendar years ago to the present micromilled samples representing less than six days of otolith growth were extracted to acquire high resolution intra otolith variation in 18 o values freshwater drum sagittal otoliths form annual bands due to thermally induced growth cessation below 10 c 18 o h 2 o values can be calculated once a high resolution carbonate sample representing the beginning of the growing season is isolated maximum summer temperature can be calculated using the seasonal minimum 18 o caco 3 value and the 18 o h 2 o value maximum summer temperatures calculated from the freshwater drum sagittae suggest that summer temperatures generally decrease from 29 c at 5 5 ka to 22 c at 0 3 ka however warmer climates at 2 9 1 7 1 6 and 1 2 1 0 ka punctuate this trend a more complete picture of the climate is reconstructed because 18 o h 2 o values which are a function of the ratio of summer to winter precipitation are also calculated a relatively low average 18 o h 2 o value of 8 1 vsmow was calculated at 1 0 ka suggesting cold winters dry summers and or wet winters may have prevailed during part of the medieval warm period in tennessee contrary to studies suggesting that the holocene was extremely stable and the hypsithermal was invariably warm and dry additional evidence suggesting both significant climate variability and evidence for a wetter mid holocene is presented

three dimensional model simulations of tides and buoyancy currents along the west coast of vancouver island a three dimensional finite element model is used to calculate the barotropic tides and seasonal buoyancy flows off the western and northern coasts of vancouver island the model buoyancy currents and the harmonics of eight tidal constituents are compared with those from previous models and those from tide gauge and current meter observations the rms differences between observed and calculated sea level tidal amplitudes are within 2 3 cm for all constituents whereas the rms differences between observed and calculated phases are with the exception of q1 within 3 58 the model currents are more accurate than those from previous models of particular interest are the diurnal continental shelf waves it is shown that these waves are generated through the conservation of potental vorticity arising when the strong diurnal tidal currents in juan de fuca strait encounter the abrupt topography near the entrance to the strait these waves do not appear to propagate beyond brooks peninsula a large promontory cutting across the continental shelf a power budget analysis reveals that the reason for this is not the blocking effect of the peninsula but rather there is little energy left in the waves when they reach that point this energy loss is primarily through frictional dissipation in a series of trapped eddies along the shelf break the location of these eddies varies with the forcing frequency and appears to be related to the spacing of canyons it is also demonstrated that the strong diurnal currents observed over the shallow banks in queen charlotte sound to the north of brooks peninsula do not arise from the oscillatory diurnal flows in queen charlotte strait unlike the case for juan de fuca strait the region offshore of queen charlotte strait does not support diurnal coastally trapped waves seasonal changes in the wavelengths of the vancouver island shelf waves are shown to arise through an advective interaction doppler shift with the buoyancy driven vancouver island coastal current and the wind driven shelf break current

slow slip phenomena in cascadia from 2007 and beyond a review recent technological advances combined with more detailed analyses of seismologic and geodetic observations have fundamentally changed our understanding of the ways in which tectonic stresses arising from plate motions are accommodated by slip on faults the traditional view that relative plate motions are accommodated by a simple cycle of stress accumulation and release on locked plate boundary faults has been revolutionized by the serendipitous discovery and recognition of the significance of slow slip phenomena mostly in the deeper reaches of subduction zones the cascadia subduction zone located in the pacific northwest of the conterminous united states and adjacent canada is an archetype of exploration and learning about slow slip phenomena these phenomena are manifest as geodetically observed aseismic transient deformations accompanied by a previously unrecognized class of seismic signals although secondary failure processes may be involved in generating the seismic signals the primary origins of both aseismic and seismic phenomena appear to be episodic fault slip probably facilitated by fluids on a plate interface that is critically stressed or weakened in cascadia this transient slip evolves more slowly and over more prolonged durations relative to the slip in earthquakes and it occurs between the 30 and 40 km depth contours of the plate interface where information was previously elusive although there is some underlying organization that relaxes nearly all the accrued plate motion stresses along the entirety of cascadia we now infer that slow slip evolves in complex patterns indicative of propagating stress fronts our new understanding provides key constraints not only on the region where the slow slip originates but also on the probable characteristics of future megathrust earthquakes in cascadia herein we review the most significant scientific issues and progress related to understanding slow slip phenomena in cascadia and highlight some of their societal implications we provide a comprehensive review from the big picture as inferred from studies of regional scale monitoring data to the details revealed by innovative focused experiments and new instrumentation we focus on what has been learned largely since 2007 when several major investments in monitoring and temporary deployments dramatically increased the quality and quantity of available data

model of deep nonvolcanic tremor part i ambient and triggered tremor there is evidence of triggering of tremor by seismic waves emanating from distant large earthquakes the frequency content of triggered and ambient tremor are largely identical suggesting that tremor does not depend directly on the nature of the source we show here that the model of plate dynamics developed earlier by us is an appropriate tool for describing the onset of tremor in the framework of this model tremor is an internal response of a fault to failure triggered by external disturbances the model predicts generation of radiation in a frequency range defined by the fault parameters other specific features predicted are 1 the upper limit of the size of the emitting area is a few dozen kilometers 2 tremor accompanies earthquakes and aseismic slip 3 the frequency content of tremor depends on the type of failure the model also explains why a tremor has no clear impulsive phase in contrast to earthquakes a comparatively small effective normal stress hence a high fluid pressure is required to make the model consistent with observed tremor parameters our model indicates that tremor is not necessarily a superposition of low frequency earthquakes as commonly assumed although the latter may trigger tremor the approach developed complements the conventional viewpoint which assumes that tremor reflects a frictional process with low rupture speed essentially our model adds the hypothesis that resonant type oscillations exist inside a fault this addition may change our understanding of the nature of tremor in general and the methods of its identification and location in particular

model of deep nonvolcanic tremor part ii episodic tremor and slip abstract bursts of tremor accompany a moving slip pulse in episodic tremor and slip ets events the sources of this nonvolcanic tremor nvt are largely unknown we developed a model describing the mechanism of nvt generation according to this model nvt is a reflection of resonant type oscillations excited in a fault at certain depth ranges from a mathematical viewpoint tremor phonons and slip pulses solitons are two different solutions of the sine gordon equation describing frictional processes inside a fault in an ets event a moving slip pulse generates tremor due to interaction with structural heterogeneities in a fault and due to failures of small asperities observed tremor parameters such as central frequency and frequency attenuation curve are associated with fault parameters and conditions such as elastic modulus effective normal stress penetration hardness and friction model prediction of nvt frequency content is consistent with observations in the framework of this model it is possible to explain the complicated pattern of tremor migration including rapid tremor propagation and reverse tremor migration migration along the strike direction is associated with movement of the slip pulse rapid tremor propagation in the slip parallel direction is associated with movement of kinks along a 2d slip pulse a slip pulse pinned in some places can fragment into several pulses causing tremor associated with some of these pulse fragments to move opposite to the main propagation direction the model predicts that the frequency content of tremor during an ets event is slightly different from the frequency content of ambient tremor and tremor triggered by earthquakes

detection of triggered deep low frequency events from the 2003 tokachi oki earthquake 1 we show the level of increased decreased seismicity mapped across japan immediately following the 2003 tokachi oki earthquake mw 8 1 of september 25 2003 ut by use of the statistic significant dynamic triggering of events is found near the nankai subduction zone 900 1400 km from the earthquake the events are inferred to be dynamically triggered deep low frequency earthquakes of a type that often occur in this region the triggering appears to be caused by the long period oscillations of the surface waves which may be effective in triggering fluid related events the region that showed the highest level of triggered events was an area of elevated activity in the bungo strait where a slow slip event was in progress

new constraints on subduction zone structure in northern cascadia summary a detailed passive seismic experiment was carried out across southwestern british columbia and northwestern washington to investigate the structure of the subducting juan de fuca plate and mantle wedge in cascadia and its relation to intraslab seismicity as part of the polaris project 31 three component broad band stations were deployed in an approximately linear array spanning southern vancouver island the gulf and san juan islands watcom county and the british columbia lower mainland p wave coda from 41 teleseismic events have been employed in formal inversions for fine scale shear velocity structure our results indicate a structure very similar to that identified across a comparable profile in central oregon the continental moho is evident at the eastern end of the profile near 35 km depth but disappears towards georgia strait puget sound a prominent low s velocity zone is clearly evident below southern vancouver island dipping eastwards through georgia strait puget sound and coincides with the e reflection zone originally identified in lithoprobe studies structure below the e layer is much less prominent and varies intermittently along the array based on the observations and interpretations of similar structures beneath oregon alaska and south america and its projection to mantle depths we suggest that the low velocity e layer represents the dehydrating oceanic crust of the subducting juan de fuca plate this interpretation is consistent with recent seismicity studies that place shallow wadati benioff events within the oceanic mantle and implies that the oceanic crust is 6 8 km shallower beneath vancouver island than previously assumed as in oregon we interpret the diminished signature of oceanic crust below a depth of 45 km to signal the presence of eclogitization which in turn supplies water to serpentinize the overlying forearc mantle

a 1400 year high resolution record of atmospheric circulation over the north atlantic and asia major ion series developed from new subannual scale sampling of an ice core from central greenland are calibrated with instrumental series of atmospheric sea level pressure recording major marine icelandic low and terrestrial siberian high atmospheric circulation systems to provide proxy records of atmospheric circulation over the past 1400 years examination of the proxy records reveals major changes in behaviour of these systems c ad 1400 multidecadal and centennial scale periodic components characterization of mean sea level pressure anomaly fields during the little ice age and the mediaeval warm period the potential role of solar forcing coupled ocean atmosphere associations and a perspective within which the characteristics of instrumental era climate can be assessed

imaging slow slip fronts in cascadia with high precision cross station tremor locations 1 we apply a new method to obtain accurate locations of tremor sources beneath southern vancouver island unlike more standard cross time methods which compare waveforms from different time windows at the same station this cross station method compares waveforms from the same time window at widely separated stations it performs well relative to cross time methods when the response to an impulsive tremor source is dominated by the main arrival rather than coda and when multiple colocated sources are active within the time window examined we focus on a region roughly 10 km across that was monitored by the polaris deployment from 2003 to 2006 relative location errors appear to be 1 km allowing us to image in great detail rapid and small scale tremor migrations that arise behind the main slow slip front the secondary fronts tend to a start at or within about 1 km of the main tremor front and propagate back along strike at rates of 10 20 km h b less commonly do the reverse ending at the main front or c propagate up or downdip at or within 1 2 km of the main front estimated stress drops in the secondary events are comparable to that in the main event implying that their 25 50 times greater propagation speed results from a similarly greater slip speed

an 8 century tropical atlantic sst record from the cariaco basin baseline variability twentieth century warming and atlantic hurricane frequency 1 we present the first direct comparison and calibration of a downcore foraminiferal mg ca record to historical instrumental sea surface temperature sst mg ca measured on the planktic foraminifer globigerina bulloides from a cariaco basin sediment core strongly correlate with spring march may instrumental ssts between a d 1870 and 1990 a mg ca sst equation is derived and a paleo sst record is presented spanning the last 8 centuries an interval that includes the end of the medieval warm period and the little ice age the long term record displays a surprising amount of variability the temperature swings are not necessarily related to local upwelling variability but instead represent wider conditions in the caribbean and western tropical atlantic the mg ca sst record also captures the decadal and multidecadal variability observed in records of global land and sea surface temperature anomalies and atlantic tropical storm and hurricane frequency over the late nineteenth and twentieth centuries a divergence between the sst proxy record and atlantic storm frequency around 1970 appears to reflect a fundamental change in atlantic hurricane behavior noted in historical data on average twentieth century temperatures are not the warmest in the entire record but they do show the largest increase in magnitude and fastest rate of sst change over the last 800 a

correlation of tremor activity with tidal stress in the northern cascadia subduction zone 1 we analyze hourly data from five tremor episodes in the northern cascadia subduction zone over the period 2003 2005 provided by the tremor activity monitoring system tams all five tremor episodes correspond to slow slip events observed by gps fourier decomposition is used to separate the hourly tremor counts for each episode into long period 0 2 2 cpd components the tidal component of the observations is compared with theoretical stress variations at depths of 20 30 and 40 km with 40 km being the depth of the interpreted subduction thrust interface the stress variations are predicted by a 2 d ocean tide loading model combined with estimates of stress variations from earth tides we find that the shear stress in the thrust direction and the compressive normal stress on shallow dipping surfaces correlates with the data significantly better than the confining stress over the range of depths investigated the relative amplitudes of tidal shear stress and compressive normal stress result in positive coulomb stress favoring slip peak tremor activity occurs at times of maximum tidal shear stress in the thrust direction which would assist slow slip and would suggest that tidal tremor and slip are colocated the response of the tremor to tidal shear stress is roughly proportional to the mean activity level controlled by tectonic conditions of stress and pore pressure a significant nontidal daily variation in tremor activity of unknown origin is identified

periodic slow earthquakes from the cascadia subduction zone continuous geodetic measurements from convergent margins have shown that deep transient creep events can release large amounts of strain energy without detectable seismic shaking and they are thus known as slow or silent earthquakes because subduction zones generate the largest earthquakes

deep high amplitude reflections from a major shear zone above the subducting juan de fuca plate seismic reflection data show that a regionally extensive band of landward dipping reflections exists above the subducting juan de fuca plate at the western canadian continental margin the reflections truncate at depth a major terrane boundary mapped near the surface and must have a structural origin many reflections are very strong having reflection coefficients locally as high as 10 20 these amplitudes are consistent with theoretical calculations of reflections from sharp poirosity contrasts if the pores are very thin however seismic data from the accreted sedimentary melange farther seaward from which much of the deep reflective zone is derived suggest that significant porosity contrasts do not occur alone because higher reflection amplitudes are found in regions of inferred high strain both geometric and amplitude constraints imply that the deep reflective layering represents intensely sheared rocks possibly originating close to the subduction decollement

a revised dislocation model of interseismic deformation of the cascadia subduction zone 1 cas3d 2 a new three dimensional 3 d dislocation model is developed to model interseismic deformation rates at the cascadia subduction zone the model is considered a snapshot description of the deformation field that changes with time the effect of northward secular motion of the central and southern cascadia forearc sliver is subtracted to obtain the effective convergence between the subducting plate and the forearc horizontal deformation data including strain rates and surface velocities from global positioning system gps measurements provide primary geodetic constraints but uplift rate data from tide gauges and leveling also provide important validations for the model a locked zone based on the results of previous thermal models constrained by heat flow observations is located entirely offshore beneath the continental slope similar to previous dislocation models an effective zone of downdip transition from locking to full slip is used but the slip deficit rate is assumed to decrease exponentially with downdip distance the exponential function resolves the problem of overpredicting coastal gps velocities and underpredicting inland velocities by previous models that used a linear downdip transition a wide effective transition zone etz partially accounts for stress relaxation in the mantle wedge that cannot be simulated by the elastic model the pattern of coseismic deformation is expected to be different from that of interseismic deformation at present 300 years after the last great subduction earthquake the downdip transition from full rupture to no slip should take place over a much narrower zone

slow slip events in the early part of the earthquake cycle in february 2014 a mw 7 0 slow slip event sse took place beneath the nicoya peninsula costa rica this event occurred 17 months after the 5 september 2012 mw 7 6 earthquake and along the same subduction zone segment during a period when significant postseismic deformation was ongoing a second sse occurred in the middle of 2015 21 months after the 2014 sse and 38 months after the earthquake the recurrence interval for nicoya sses was unchanged by the earthquake however the spatial distribution of slip for the 2014 event differed significantly from previous events having only deep 40 km slip compared to previous events which had both deep and shallow slip the 2015 sse marked a return to the combination of deep plus shallow slip of preearthquake sses however slip magnitude in 2015 was nearly twice as large mw 7 2 as preearthquake sses we employ coulomb failure stress change modeling in order to explain these changes stress changes associated with the earthquake and afterslip were highest near the shallow portion of the megathrust where preearthquake sses had significant slip lower stress change occurred on the deeper parts of the plate interface perhaps explaining why the deep 40 km region for sses remained unchanged the large amount of shallow slip in the 2015 sse may reflect lack of shallow slip in the prior sse these observations highlight the variability of aseismic strain release rates throughout the earthquake cycle

tremor bands sweep cascadia 1 during the slow slip events in cascadia and japan a well documented feature of nonvolcanic tremor nvt is its puzzling slow along strike migration but the cause possible implications and underlying physics of this long term tremor migration and its relationship with slow slip remain elusive here we use tremor data recorded by a dense seismic array in cascadia and apply a beam backprojection technique to map the spatiotemporal evolution of tremor with high resolution it reveals that elongated slip parallel bands of tremor activity illuminate the slipping part of the plate interface over the time scale of several hours and sweep cascadia along strike from south to north we propose that small changes in static stress due to slow slip in a section of the fault cause slip and associated nvt activity in the adjacent section and the resulting progressive along strike transfer of stress is responsible for the long term tremor migration during a slow slip event

tidal modulation and triggering of low frequency earthquakes in northern cascadia we analyze the influence of earth and ocean tides on the triggering of low frequency earthquakes lfes in northern cascadia using three lfe catalogs for southern vancouver island and washington state from episodic tremor and slip events between 2003 and 2013 sensitivities of lfe families to tidally induced fault normal stress updip shear stress udss and corresponding time derivatives are computed and their geographic variability is mapped we find localized areas showing higher sensitivity to udss than their surroundings suggesting that tidal sensitivity depends on laterally heterogeneous physical properties such as variable pore fluid pressures and frictional properties along the plate interface we observe that sensitivity of lfes to udss rises dramatically from near zero on the first day of strong activity to a maximum 4 days later in addition the peak lfe rate transitions from a correlation with peak tidal shear stress rate to a correlation with peak tidal shear stress through large slow slip events we identify 64 rapid tremor reversals rtrs that start a few days after the main slip front the rtrs have an average stress drop of 0 8 kpa and a majority 72 occurs during periods of large positive udss the combined observations imply that rtrs play an important role in slow slip processes and that modulation of creep rate due to tidal stress and tidal triggering of secondary events are jointly responsible for the observed tidal sensitivity

developing oxygen isotope proxies from archaeological sources for the study of late holocene human climate interactions in coastal southwest florida abstract oxygen isotopes 18 o derived from archaeological mercenaria campechiensis shells and ariopsis felis otoliths potentially provide low latitude paleoclimate data for studying late holocene human climate interactions in coastal southwest florida specimens analyzed come from the pineland site complex deposits record abrupt and subtle environmental changes appearing to have been climate related and to have impacted the sedentary human residents one archaeological shell otolith set dates to 2nd 3rd century a d within the roman optimum ro climatic episode a second set dates to 13th 14th century a d within the little ice age lia a modern shell otolith set was analyzed for comparison 18 o aragonite of modern and lia shells suggest similar seasonal conditions ro shell is 1 more positive during summer suggesting higher estuarine salinity than in modern and lia times modern and lia otoliths also have similar 18 o aragonite estimated winter temperatures are within measured instrument records summer temperatures are overestimated reflecting summer migration into less saline water estimated summer temperatures for ro otolith are similar to today s suggesting elevated estuarine salinity and diminished rainy season consistent with similar aged zooarchaeological assemblages comparisons of two taxa aid in interpreting archaeological 18 o data however early results are mixed with expected profiles for ro specimens and unexpected profiles for lia specimens

late holocene variability in florida current surface density patterns and possible causes 1 planktonic foraminiferal 18o time series from three well dated high sedimentation rate cores near the florida keys 24 4 n 83 3 w exhibit repeated centennial to millennial scale oscillations during the late holocene isotopic shifts of 0 2 0 3 over the past 5200 years represent changes in sea surface temperature sst of 1 0 1 5 c or salinity variability of 1 2 psu the largest significant isotopic events are centered at approximately 200 2000 3200 and prior to 4000 calendar years bp high florida current 18o during the little ice age lia correlates with published records of high 18o in the sargasso sea and low sst off the coast of west africa an interval of generally low 18o in the florida straits from 1800 to 500 years bp is synchronous with the medieval warm period off west africa but leads low 18o in the sargasso sea by several hundred years synchronous cooling across the subtropical gyre during the lia is difficult to explain using interannual north atlantic oscillation patterns but may be consistent with the simulated effects of reduced solar irradiance at frequencies between 1 1000 and 1 300 years during the late holocene florida current 18o is coherent with a published estimate of 14c production rate radiocarbon production seems to lead 18o at these frequencies but uncertainty in the phase calculation precludes a clear lead lag relationship at frequencies lower than 1 300 years florida current 18o is coherent and in phase with atmospheric 14c the coherence of 14c and 18o at periods 1000 years implies oceanic circulation may play a role in modulating atmospheric radiocarbon on millennial timescales

reflection signature of seismic and aseismic slip on the northern cascadia subduction interface at the northern cascadia margin the juan de fuca plate is underthrusting north america at about 45 mm yr 1 ref 1 resulting in the potential for destructive great earthquakes2 3 the downdip extent of coupling between the two plates is difficult to determine because the most recent such earthquake thought to have been in 1700 4 occurred before instrumental recording thermal and deformation studies5 indicate that off southern vancouver island the interplate interface is presently fully locked for a distance of 60 km downdip from the deformation front great thrust earthquakes on this section of the interface with magnitudes of up to 9 4 5 have been estimated to occur at an average interval of about 590 yr ref 3 further downdip there is a transition from fully locked behaviour to aseismic sliding where high temperatures allow ductile deformation with the deep aseismic zone exhibiting slow slip thrust events6 here we show that there is a change in the reflection character on seismic images from a thin sharp reflection where the subduction thrust is inferred to be locked to a broad reflection band at greater depth where aseismic slip is thought to be occurring this change in reflection character may provide a new technique to map the landward extent of rupture in great earthquakes and improve the characterization of seismic hazards in subduction zones

florida current surface temperature and salinity variability during the last millennium surface water d 18 ow near dry tortugas increased 0 4 during the course of the little ice age lia 1200 1850 a d equivalent to a salinity increase of 0 8 1 5 on the great bahama bank where surface waters are influenced by the north atlantic subtropical gyre d 18 ow increased by 0 3 during the last 200 years although a portion 0 1 of this shift may be an artifact of anthropogenically driven changes in surface water sco2 the remaining d 18 ow signal implies a 0 4 1 increase in salinity after 200 years b p the simplest explanation of the d 18 ow data is southward migration of the atlantic hadley circulation during the lia scaling of the d 18 ow records to salinity using the modern low latitude d 18 ow s slope produces an unrealistic reversal in the salinity gradient between the two sites only if d 18 ow is scaled to salinity using a high latitude d 18 ow s slope can the records be reconciled variable atmospheric 14 c paralleled dry tortugas d 18 ow suggesting that solar irradiance paced centennial scale migration of the inter tropical convergence zone and changes in florida current salinity during the last millennium citation lund d c and w curry 2006 florida current surface temperature and salinity variability during the last millennium paleoceanography 21 pa2009 doi 10 1029 2005pa001218

three dimensional dislocation model for great earthquakes of the cascadia subduction zone there have been no historical cascadia great subduction thrust earthquakes but there is good recent evidence that very large earthquakes have occurred in the past and that strain is building up toward a future great event geodetic measurements in the coastal region from northern california to southern british columbia show vertical and horizontal deformation as expected for the strain accumulation of a locked thrust fault the segment of the subduction thrust that is locked and may rupture in future great events has previously been estimated through two dimensional 2 d elastic dislocation modeling of interseismic deformation geodetic data in this study a general 3 d dislocation model for thrust faults has been developed that accommodates curved fault geometry and nonuniform interseismic locking or coseismic rupture the model is based on die surface deformation due to shear faulting in an elastic half space the 3 d model of the cascadia subduction zone calculates the surface deformation for a locked zone or a rupture zone of variable width along the margin the bend in the margin trend and subducting slab end effects are included there is a downdip transition zone between interseismic completely locked and free slip portions of the fault or between coseismic full rupture and no displacement an initial 3 d model based upon 2 d dislocation models and upon thermal constraints was adjusted to optimize the fit of the predicted interseismic surface deformation to current deformation geodetic data the best fit model has the thrust locked along the whole margin with an average locked zone width of 60 km and a transition zone width of 60 km the two zones lie mainly offshore beneath the continental shelf and slope the locked and transition zone widths vary smoothly along the margin being greater off northern washington where the thrust dip is shallow and narrower off central oregon assuming that the locked plus transition zones approximate the maximum coseismic rupture area these widths permit amw 9 earthquake

spatial temporal patterns of seismic tremors in northern cascadia 1 we study in detail the two consecutive episodic tremor and slip ets events that occurred in the northern cascadia subduction zone during 2003 and 2004 for both sequences the newly developed source scanning algorithm ssa is applied to seismic waveform data from a dense regional seismograph array to determine the precise locations and origin times of seismic tremors in map view the majority of the tremors occurred in a limited band bounded approximately by the surface projections of the 30 km and 50 km depth contours of the plate interface the horizontal migration of tremor occurrence is from southeast to northwest with an average speed of 5 km d in cross section tremors in both sequences span a depth range of over 40 km across the interface with the majority occurring in the overriding continental crust in particular 50 55 of them are located within 2 5 km from the strong seismic reflector bands above the plate interface the lack of vertical migration implies that a slow diffusion process in the vertical direction cannot be responsible for tremor occurrences the source spectra of tremors clearly lack high frequency content 5 hz relative to local earthquakes we propose two possible models to explain the relationship between slip and tremors the first one regards ets tremors as the manifestation of hydroseismogenic processes in response to the temporal strain variation associated with the episodic slip along the lower portion of the plate interface downdip from the locked zone in the second model tremors and slip are associated with the same process along the same structure in a distributed deformation zone across the plate interface neither model can be dismissed conclusively at this stage

migration characteristics of seismic tremors in the northern cascadia margin 1 seismic waveforms from a dense regional array were analyzed to study episodic tremor and slip ets events in northern cascadia the april 2005 episode occurred mostly in northern vancouver island vi where the explorer plate subducts beneath the north america plate while the may 2005 episode was mainly in middle vi all tremor occurrences are positively correlated with the presence of subducted slabs besides the steady along strike migration and halting behavior found in previous ets events a new pattern jumping is found this time visual inspection of previous seismic records suggests that the jumping behavior is probably common to ets tremors in all regions of vi the majority of tremors occurred between 25 and 45 km depth in places where local seismicity is sparse or absent our observations are compatible with the interpretation that fluids released from dehydration of subducted materials are involved in tremor generation

caribbean sea surface temperatures two to three degrees cooler than present during the little ice age we determined the seasonal environmental conditions during the little ice age lia by interpreting isotope proxies in the coral skeleton of montastrea faveolata from the northeast caribbean the oxygen isotope composition was determined for three time intervals during the lia 1700 1705 1780 1785 1810 1815 thought to correspond to the coldest intervals the period 1984 1989 was used to represent modern calibration conditions we determined that ssts from the lia intervals are nearly 2 3 c cooler than present lia cooling in the caribbean may have resulted from regional oceanic and atmospheric circulation differences especially in winter we propose that a trough of cold air from the north atlantic may have extended farther south than present into the northern caribbean although there are indications from pacific corals that seasonality was greater during the lia this does not seem to be the case for the caribbean

seawater temperature seasonality in the south china sea during the late holocene derived from high resolution sr ca ratios of tridacna gigas temperature seasonality the difference between summer and winter temperature has significant influences on global terrestrial and marine ecosystems however most of proxy based climate records are of limited temporal resolution and thus insufficient to quantify the past temperature seasonality in this study high resolution sr ca ratios of modern live caught and fossil dead collected tridacna gigas shells from the south china sea scs were used to reconstruct the seawater temperature seasonality during the late holocene the averaged seawater temperature seasonality around 2165 75 bc 4 46 1 41 c derived from the data of 18 yr were similar to the seasonality of recent decade 4 41 0 82 c during ad 1994 2005 but the temperature seasonality around ad 50 40 3 69 1 37 c derived from the data of 48 yr and ad 990 40 3 64 0 87 c derived from the data of 11 yr was significantly lower than that during ad 1994 2005 the reduced seasonality around ad 990 40 was attributable to the unusually warm winter during the medieval times probably caused by the weakening of east asian winter monsoon our study highlighted the potential of t gigas shells in providing high resolution seasonality climate information during the late holocene

evidence for tidal triggering of high amplitude rapid tremor reversals and tremor streaks in northern cascadia 1 we provide a new link between tectonic tremor propagation tremor amplitude and tidal stresses by analyzing high resolution tremor locations and amplitudes determined by multibeam backprojection of data from an array of subarrays for two cascadia episodic tremor and slip events we observe repeating high amplitude rapid tremor reversals rtrs and tremor streaks they tend to occur when tremor amplitudes are highest and occur almost exclusively during periods of thrust encouraging tidally induced shear stress on the fault we speculate that thrust encouraging shear stress from tidal loading forces trigger rtrs and streaks that energetically rerupture the weakened fault behind the slow slip front the high rate and amplitude of tremor during rtrs and streaks stands in contrast to the hypothesis that activity at the leading edge of the slow slip zone is the most energetic and loudest this implies that the spatiotemportal pattern of slow earthquake slip migration is even more intricate than previously reported

temporal and spatial occurrence of deep non volcanic tremor from washington to northern california 1 regional network data reveal deep non volcanic tremor occurs in five independent sections along the u s section of the cascadia subduction zone with different recurrence intervals sizeable tremor episodes occur during periods with no measurable geodetic deformation as well as coincident with episodic slow slip events and the displacement amplitudes of the tremor with and without geodetic deformation are similar the tremor depths cover a wide range that does not coincide directly with the subducting slab interface the tremor can migrate bi directionally from the point of initiation and more than one spatially distinct tremor source can be active at a given time these results indicate that the tremor is not directly related to the slow slip event instead we suggest that the tremor is related to the presence and movement of fluids at depth which can explain the locations and episodic occurrence as well as the seismic signal characteristics themselves namely the limited frequency content small size emergent onsets and prolonged durations with and without geodetic deformation

southward migration of the intertropical convergence zone through the holocene titanium and iron concentration data from the anoxic cariaco basin off the venezuelan coast can be used to infer variations in the hydrological cycle over northern south america during the past 14 000 years with subdecadal resolution following a dry younger dryas a period of increased precipitation and riverine discharge occurred during the holocene thermal maximum since approximately 5400 years ago a trend toward drier conditions is evident from the data with high amplitude fluctuations and precipitation minima during the time interval 3800 to 2800 years ago and during the little ice age these regional changes in precipitation are best explained by shifts in the mean latitude of the atlantic intertropical convergence zone itcz potentially driven by pacific based climate variability the cariaco basin record exhibits strong correlations with climate records from distant regions including the high latitude northern hemisphere providing evidence for global teleconnections among regional climates

a silent slip event on the deeper cascadia subduction interface continuous global positioning system sites in southwestern british columbia canada and northwestern washington state usa have been moving landward as a result of the locked state of the cascadia subduction fault offshore in the summer of 1999 a cluster of seven sites briefly reversed their direction of motion no seismicity was associated with this event the sudden displacements are best explained by 2 centimeters of aseismic slip over a 50 kilometer by 300 kilometer area on the subduction interface downdip from the seismogenic zone a rupture equivalent to an earthquake of moment magnitude 6 7 this provides evidence that slip of the hotter plastic part of the subduction interface and hence stress loading of the megathrust earthquake zone can occur in discrete pulses

cascadia tremor polarization evidence for plate interface slip 1 new seismic measurements of the repeated phenomenon of episodic tremor and slip in northern cascadia indicate identical source processes of tremor and slow slip predicted polarization directions of upgoing s waves radiated from shear slip on the plate interface align with the relative motion between the juan de fuca and north american plates seismic observations from small aperture array data on the olympic peninsula of the cascadia subduction zone show uncharacteristically stable linear particle motion coincident with the passage of tremor sources beneath the array the azimuth of this horizontal ground motion matches expected polarizations from slip on the plate interface this finding suggests that cascadia tremor is shear slip on the plate interface implying that as in japan geodetically observed slow slip and seismically observed tremor are manifestations of the same phenomenon

evidence suggesting fluid flow beneath japan due to periodic seismic triggering from the 2004 sumatra andaman earthquake 1 we show that very large surface waves from the 2004 sumatra andaman earthquake m9 2 triggered deep low frequency dlf seismic tremors beneath japan over a 500 km wide region the triggered seismicity was periodically excited synchronized with the amplitudes and phases of the oscillatory surface waves incident on the region periodic excitation implies that the specific phase of the surface waves plays an important role for the triggering estimation of stress changes in the source regions showed that the volumetric dilatation larger than 10 8 was the predominant factor for triggering thereby strongly supporting the hypothesis that dlf events are caused by processes related to fluid flow

tidal triggering of low frequency earthquakes near parkfield california implications for fault mechanics within the brittle ductile transition 1 studies of nonvolcanic tremor nvt have established the significant impact of small stress perturbations on nvt generation here we analyze the influence of the solid earth and ocean tides on a catalog of 550 000 low frequency earthquakes lfes distributed along a 150 km section of the san andreas fault centered at parkfield lfe families are identified in the nvt data on the basis of waveform similarity and are thought to represent small effectively co located earthquakes occurring on brittle asperities on an otherwise aseismic fault at depths of 16 to 30 km we calculate the sensitivity of each of these 88 lfe families to the tidally induced right lateral shear stress rlss fault normal stress fns and their time derivatives and use the hypocentral locations of each family to map the spatial variability of this sensitivity lfe occurrence is most strongly modulated by fluctuations in shear stress with the majority of families demonstrating a correlation with rlss at the 99 confidence level or above producing the observed lfe rate modulation in response to shear stress perturbations requires low effective stress in the lfe source region there are substantial lateral and vertical variations in tidal shear stress sensitivity which we interpret to reflect spatial variation in source region properties such as friction and pore fluid pressure additionally we find that highly episodic shallow lfe families are generally less correlated with tidal stresses than their deeper continuously active counterparts the majority of families have weaker or insignificant correlation with positive tensile fns two groups of families demonstrate a stronger correlation with fault normal tension to the north and with compression to the south of parkfield the families that correlate with fault normal clamping coincide with a releasing right bend in the surface fault trace and the lfe locations suggesting that the san andreas remains localized and contiguous down to near the base of the crust the deep families that have high sensitivity to both shear and tensile normal stress perturbations may be indicative of an increase in effective fault contact area with depth synthesizing our observations with those of other lfe hosting localities will help to develop a comprehensive understanding of transient fault slip below the seismogenic zone by providing constraints on parameters in physical models of slow slip and lfes

regional climate variability in the western subtropical north atlantic during the past two millennia 1 western subtropical north atlantic oceanic and atmospheric circulations connect tropical and subpolar climates variations in these circulations can generate regional climate anomalies that are not reflected in northern hemisphere averages assessing the significance of anthropogenic climate change at regional scales requires proxy records that allow recent trends to be interpreted in the context of long term regional variability we present reconstructions of gulf stream sea surface temperature sst and hydrographic variability during the past two millennia based on the magnesium calcium ratio and oxygen isotopic composition of planktic foraminifera preserved in two western subtropical north atlantic sediment cores reconstructed sst suggests low frequency variability of 1 c during an interval that includes the medieval climate anomaly mca and the little ice age lia a warm interval near 1250 a d is distinct from regional and hemispheric temperature possibly reflecting regional variations in ocean atmosphere heat flux associated with changes in atmospheric circulation e g the north atlantic oscillation or the atlantic meridional overturning circulation seawater d 18 o which is marked by a fresher mca and a more saline lia covaries with meridional migrations of the atlantic intertropical convergence zone the northward advection of tropical salinity anomalies by mean surface currents provides a plausible mechanism linking carolina slope and tropical atlantic hydrology

dipping seismic reflectors electrically conductive zones and trapped water in the crust over a subducting plate the lithoprobe program across the northern cascadia subduction zone at vancouver island has obtained geophysical data that suggest a dipping zone of trapped free pore water in the overlying continental crust land and marine multichannel seismic reflection profiles show several bands of reflectors the primary one at a depth of about 30 km is about 5 km thick dips inland and appears to coincide with an electrically conductive layer defined by magnetotelluric data the downgoing oceanic crust is imaged as a thin reflector dipping at about 15 and 10 km deeper than the primary reflector a location that is consistent with seismicity and seismic refraction data both the reflectors and the conductor have been modeled by near horizontal lamellae with 1 4 saline water porosity detailed geothermal measurements defining heat flow that decreases inland indicate that the dipping bands are nearly isothermal at a temperature of 400 500 c it is suggested that free water generated by dehydration of the downgoing oceanic plate migrates upward until reduced temperature results in hydration reactions and mineral precipitation that forms an impermeable barrier low vertical permeability is required to keep the water from separating to the top of the layer this can be reconciled with the low electrical resistivity if pore interconnection is through thin grain boundary tubes as predicted by theoretical equilibrium pore geometry although very small effective grain size is necessary an abrupt transition from high permeability to very low permeability is predicted at a several percent porosity in agreement with the modeled porosity such pore geometry with low permeability may be restricted to temperatures above about 400 c i e in greenschist to amphibolite facies conditions where grains will deform to equilibrium geometry and cracks are annealed the region above the reflective and conductive band is estimated to be within blueschist conditions consistent with the inferred high seismic velocity from refraction data and high density from gravity data

fortnightly modulation of san andreas tremor and low frequency earthquakes earth tides modulate tremor and low frequency earthquakes lfes on faults in the vicinity of the brittle ductile seismic aseismic transition the response to the tidal stress carries otherwise inaccessible information about fault strength and rheology here we analyze the lfe response to the fortnightly tide which modulates the amplitude of the daily tidal stress over a 14 d cycle lfe rate is highest during the waxing fortnightly tide with lfes most strongly promoted when the daily stress exceeds the previous peak stress by the widest margin this pattern implies a threshold failure process with slip initiated when stress exceeds the local fault strength variations in sensitivity to the fortnightly modulation may reflect the degree of stress concentration on lfe producing brittle asperities embedded within an otherwise aseismic fault

tidal modulation of slow slip in cascadia 1 several studies have shown that the seismic tremor in episodic tremor and slip is tidally modulated suggesting a sensitivity to the rather small tidal stresses we address whether the slip rate in slow slip events is also tidally modulated by examining data from six borehole strainmeters in northwest washington and southern vancouver island we simultaneously fit data from multiple stations and from slow slip events occurring over a 3 year interval from january 2007 to june 2009 as we are unable to extract a meaningful signal from a single record we find modulation of the strain rate with a 12 4 h period that of the tide with the largest amplitude that is significant at the 99 level the amplitude of this modulation suggests that the slip rate during slow slip events oscillates on average 25 above and below its mean value during a tidal cycle tidal modulation estimates at three other periods are significant with more than 70 probability the phase of maximum strain rate in the 12 4 h m2 period coincides with the phase of the maximum tremor rate taken from a catalog in an overlapping region comparison with a simple tidal loading model shows that the phase of maximum strain rate in the m2 period may occur at the maximum shear stress or up to 90 before it depending on the location of slip in the subduction zone

widespread triggering of nonvolcanic tremor in california we identified seven locations on or near the transform plate boundary in california where nonvolcanic tremor was triggered by the 2002 denali earthquake this result implies that the conditions essential for nonvolcanic tremor exist in a range of tectonic environments models explaining tremor typically require conditions endemic to subduction zones that is high temperatures and fluid pressures because previously tremor was nearly exclusively documented in subduction zones the absence of tremor in geothermal areas is inconsistent with such models additionally we found no correlation between creeping or locked faults and tremor contrary to predictions of frictional models of tremor

early holocene to present palaeoenvironmental shifts and short climate events from the tropical wetland and lake sediments kukkal lake southern india geochemistry and palynology the kukkal basin tamil nadu india receives most of its rain from the southwest monsoon swm a sediment core from kukkal lake preserves a continuous sediment record from the early holocene to p

an integrated perspective of the continuum between earthquakes and slow slip phenomena slow slip a mechanism by which faults can relieve stress was thought to be distinct from earthquakes however a global review of slow slip phenomena suggests that instead there is a continuum between the two types of event