a continuum of stress strength and slip in the cascadia subduction zone movement of the down going oceanic plate in subduction zones is accommodated by earthquakes slow slip and free slip with increasing depth analysis of accompanying tremor reveals a continuum of slow slip events in the cascadia subduction zone which suggests that deep free slip of the subducted plate may cause stress to be gradually transferred up the plate interface towards the seismogenic zone

seismic evidence for overpressured subducted oceanic crust and megathrust fault sealing water and hydrous minerals play a key role in geodynamic processes at subduction zones however there are few seismological constraints on the presence of water within the subducting plate audet et al model converted teleseismic waves to constrain the seismological properties of subducted oceanic crust from the cascadia continental margin to its intersection with the forearc mantle their observations suggest that water is pervasively present in fluid form at high pore pressures indicating that the megathrust is a low permeability boundary these results may hold important implications for our understanding of seismogenesis subduction zone structure and the mechanism of episodic tremor and slip this study models converted teleseismic waves to constrain the seismological properties of subducted oceanic crust from the cascadia continental margin to its intersection with the forearc mantle the observations suggest that water is pervasively present in fluid form at high pore pressures indicating that the megathrust is a low permeability boundary these results may hold important implications for our understanding of seismogenesis subduction zone structure and the mechanism of episodic tremor and slip water and hydrous minerals play a key part in geodynamic processes at subduction zones1 2 3 by weakening the plate boundary aiding slip and permitting subduction and indeed plate tectonics to occur4 the seismological signature of water within the forearc mantle wedge is evident in anomalies with low seismic shear velocity marking serpentinization5 6 7 however seismological observations bearing on the presence of water within the subducting plate itself are less well documented here we use converted teleseismic waves to obtain observations of anomalously high poisson s ratios within the subducted oceanic crust from the cascadia continental margin to its intersection with forearc mantle on the basis of pressure temperature and compositional considerations the elevated poisson s ratios indicate that water is pervasively present in fluid form at pore pressures near lithostatic values combined with observations of a strong negative velocity contrast at the top of the oceanic crust our results imply that the megathrust is a low permeability boundary the transition from a low to high permeability plate interface downdip into the mantle wedge is explained by hydrofracturing of the seal by volume changes across the interface caused by the onset of crustal eclogitization and mantle serpentinization these results may have important implications for our understanding of seismogenesis subduction zone structure and the mechanism of episodic tremor and slip

accumulation of mineral ballast on organic aggregates 1 to address whether the incorporation of suspended minerals drives the sedimentation of particulate organic carbon in the ocean or vice versa incubations of phytoplankton detritus aggregates were set up in rolling tanks containing seawater and suspended clay illite or calcium carbonate at concentrations ranging between 10 and 50 000 g l 1 the suspended minerals were efficiently scavenged by and incorporated into the organic aggregates the volume and porosity of aggregates decreased with increasing mineral concentrations and at suspended mineral concentrations higher than 500 g l 1 the initially medium sized aggregates were fragmented into thousands of tiny dense aggregates because radius and density have opposite effects on aggregate sinking rates the relationship between aggregate particulate organic carbon poc to mineral ratio and sinking rate is not a straightforward one that necessarily results in higher sinking rates with increased mineral content in these experiments the saturating capacity of organic aggregates for mineral particles appeared to be 97 to 98 weight percent mineral i e a poc to dry weight ratio of 0 02 to 0 03 g c g 1 this parallels the values of 0 05 g c g 1 observed for sinking particles in the deep sea and suggests that it is the flux of poc that determines the flux of minerals to the deep and not the other way around

late pleistocene relic ultisols and alfisols in an alluvial fan complex in coastal tuscany detailed stratigraphic sedimentary facies and palaeosol analyses were performed on an outcrop on late quaternary deposits in the coastal area of tuscany the outcrop was selected as representative of one of the major quaternary alluvial fan complexes of central italy the ancient cecina river fan and as showing contrasting if related palaeosols the oldest relic palaeosol was identified as an ultisol representative of the most developed soil type normally found as relic soil in italy and about whose possible ages only approximate interpretations presently exist osl dating set the whole succession of sediments palaeosols and geomorphic surfaces into a firm chronological setting as a result evolution of the cecina fan complex in late pleistocene could be fully reconstructed assessment of the age of the relic ultisol produced results contrasting with current interpretations showing how such a soil type can have developed in italian conditions in a relatively short time i e since about mis 5d

evidence of saharan dust in upper pleistocene reworked palaeosols of north west sardinia italy palaeoenvironmental implications abstract a multi disciplinary approach was followed to investigate two thick palaeosolstrata that alternate with wind blown dominated deposits developed along thealghero coast north west sardinia italy optically stimulated luminescenceages reveal that both palaeosols were developed during cooler drier periods the rst one at around 70 ka marine isotope stage 4 and the latter around 50 ka marine isotope stage 3 in contrast the pedological features indicate that thepalaeosols underwent heavy weathering processes under warm humid to sub humid conditions characteristic of the sardinian climate during the lastinterglacial stage marine isotope stage 5e to reconcile this apparent datadiscrepancy a range of sedimentological and pedological analyses wereconducted these analyses reveal that the palaeosols possess a complexhistory with accumulation and weathering occurring during marine isotopestage 5e and erosion colluviation and nal deposition taking place during thefollowing cold stages thus even if these reddish palaeosols were last formedduring the glacial period the sediments building up these strata probablyrecord the climate of the last interglacial stage marine isotope stage 5e traceelement and x ray diffraction analyses together with scanning electronmicroscope images reveal the presence of saharan dust in the parentmaterial of the palaeosols however no evidence of any far travelled africandust has been observed in the marine isotope stage 4 3 aeolian deposits it ispossible to conclude that in the west mediterranean islands saharan dustinput even if of modest magnitude is preserved preferentially in soilsaccumulated and weathered during interglacial stages keywords marine isotopic stage mediterranean osl dating trace elementgeochemistry xrd analysis sedimentology 2012 59 917 938

long term acceleration of aseismic slip preceding the mw 9 tohoku oki earthquake constraints from repeating earthquakes a decadal scale deformation transient preceding the 2011 mw 9 tohoku oki japan earthquake was reported from continuous gps data and interpreted as accelerating aseismic slip on the japan trench megathrust given the unprecedented nature of this transient independent confirmation of accelerating slip is required here we show that changes in the recurrence intervals of repeating earthquakes on the japan trench megathrust in the period 1996 to 2011 are consistent with accelerating slip preceding the tohoku oki earthquake all sequences of repeating earthquakes with statistically significant trends in recurrence interval at 95 confidence offshore south central tohoku occurred at an accelerating rate furthermore estimates of the magnitude of slip acceleration from repeating earthquakes are consistent with the completely independent geodetic estimates from a joint inversion of the gps and seismicity data we infer that a substantial portion of the megathrust experienced accelerating slip partly surrounding the eventual rupture zone of the mw 9 earthquake

kaolinitic paleosols in the south west of the iberian peninsula sierra morena region spain paleoenvironmental implications abstract this paper studies the physical and chemical characteristics of eight different soil profiles with paleohorizons rich in kaolinites and developed on different lithologies along the southern border of the hercinian iberian peninsula sierra morena region the paleohorizons of four of these soils are defined by low ph levels desaturation of the exchange complex and proportions of kaolinite of over 75 these characteristics are associated with subtropical pedogenic conditions during the pliocene period a further two soil profiles are contemporary and defined by the following features they occupy depression areas the clay fraction is dominated by kaolinites and smectites the exchange complex is saturated and the ph is above neutral values the last two soil profiles are developed on pliocene continental deposits and have more moderate pedogenic features their kaolinite levels are around 50 and their evolution is associated with shorter periods of exposure to these subtropical alteration conditions

a physics based approach of deep interseismic creep for viscoelastic strike slip earthquake cycle models most geodetic inversions of surface deformation rates consider the depth distribution of interseismic fault slip rate to be time invariant however some numerical simulations show down dip penetration of dynamic rupture into regions with velocity strengthening friction with subsequent up dip propagation of the locked to creeping transition recently bruhat segall 2017 developed a new method to characterize interseismic slip rates that allows slip to penetrate up dip into the locked region this simple model considered deep interseismic slip as a crack loaded at its down dip end and provided analytical expressions for stress drop within the crack slip and slip rate along the fault this study extends this approach to strike slip fault environments and includes coupling of creep to viscoelastic flow in the lower crust and upper mantle we employ this model to investigate interseismic deformation rates along the carrizo plain section of the san andreas fault this study reviews possible models elastic and viscoelastic for fitting horizontal surface rates using this updated approach we develop a physics based solution for deep interseismic creep which accounts for possible slow vertical propagation and investigate how it improves the fit of the horizontal deformation rates in the carrizo plain region

holocene earthquake records from the cascadia subduction zone and northern san andreas fault based on precise dating of offshore turbidites abstract we present preliminary evidence for a 10 000 year earthquake record from two major fault systems based on sediment cores collected along the continental margins of western north america new stratigraphic evidence from cascadia demonstrates that 13 earthquakes ruptured the entire margin from vancouver island to at least the california border since the eruption of the mazama ash 7700 years ago the 13 events above this prominent stratigraphic marker have an average repeat time of 600 years and the youngest event 300 years ago coincides with the coastal record we also extend the record of past earthquakes to the base of the holocene at least 9800 years ago during which 18 events correlate along the same region the sequence of holocene events in cascadia appears to contain a repeating pattern of events a tantalizing first look at what may be the long term behavior of a major fault system the northern california margin cores show a cyclic record of turbidite beds that may represent holoce

fault slip and seismic moment of the 1700 cascadia earthquake inferred from japanese tsunami descriptions 1 the 1700 cascadia earthquake attained moment magnitude 9 according to new estimates based on effects of its tsunami in japan computed coseismic seafloor deformation for hypothetical ruptures in cascadia and tsunami modeling in the pacific ocean reports of damage and flooding show that the 1700 cascadia tsunami reached 1 5 m heights at seven shoreline sites in japan three sets of estimated heights express uncertainty about location and depth of reported flooding landward decline in tsunami heights from shorelines and post 1700 land level changes we compare each set with tsunami heights computed from six cascadia sources each source is vertical seafloor displacement calculated with a three dimensional elastic dislocation model for three sources the rupture extends the 1100 km length of the subduction zone and differs in width and shallow dip for the other sources ruptures of ordinary width extend 360 670 km to compute tsunami waveforms we use a linear long wave approximation with a finite difference method and we employ modern bathymetry with nearshore grid spacing as small as 0 4 km the various combinations of japanese tsunami heights and cascadia sources give seismic moment of 1 9 1022 n m equivalent to moment magnitude 8 7 9 2 this range excludes several unquantified uncertainties the most likely earthquake of moment magnitude 9 0 has 19 m of coseismic slip on an offshore full slip zone 1100 km long with linearly decreasing slip on a downdip partial slip zone the shorter rupture models require up to 40 m offshore slip and predict land level changes inconsistent with coastal paleoseismological evidence

initiation and arrest of earthquake ruptures due to elongated overstressed regions the initiation of natural and induced earthquakes is promoted in fault areas where the shear stress is close to fault strength in many important situations these overstressed fault areas or asperities are very elongated for example in the case of a fault intersecting a reservoir subject to fluid injection or the stress concentration along the bottom of a seismogenic zone induced by deep fault creep theoretical estimates of the minimum overstressed asperity size leading to runaway rupture and of the final size of self arrested ruptures are only available for 2d problems and for 3d problems with an asperity aspect ratio close to one in this study we determine how the nucleation of ruptures on elongated asperities and their ensuing arrest depend on the size and aspect ratio of the asperity and on the background stress based on a systematic set of 3d dynamic rupture simulations assuming linear slip weakening friction we find that if the shortest asperity side is smaller than the 2d critical length the problem effectively reduces to a 2d problem in which rupture nucleation and arrest are controlled by the shortest length of the asperity otherwise nucleation and rupture arrest are controlled by the asperity area with a minor exception for asperities with shortest side slightly larger than the 2d critical length arrested ruptures are smaller than predicted by the asperity area the fact that rupture arrest is dominantly controlled by area even for elongated asperities corroborates the finding that observed maximum magnitudes of earthquakes induced by fluid injection are consistent with the theoretical relation between the magnitude of the largest self arrested rupture and the injected volume galis et al 2017 in context of induced seismicity our simulations provide plausible scenarios that could be either favourable or challenging for traffic light systems and provide mechanical insights into the conditions leading to these situations

shallow dynamic overshoot and energetic deep rupture in the 2011 mw 9 0 tohoku oki earthquake strong spatial variation of rupture characteristics in the moment magnitude mw 9 0 tohoku oki megathrust earthquake controlled both the strength of shaking and the size of the tsunami that followed finite source imaging reveals that the rupture consisted of a small initial phase deep rupture for up to 40 seconds extensive shallow rupture at 60 to 70 seconds and continuing deep rupture lasting more than 100 seconds a combination of a shallow dipping fault and a compliant hanging wall may have enabled large shallow slip near the trench normal faulting aftershocks in the area of high slip suggest dynamic overshoot on the fault despite prodigious total slip shallower parts of the rupture weakly radiated at high frequencies whereas deeper parts of the rupture radiated strongly at high frequencies

geochronology for some key sites along the coast of sardinia italy recent stratigraphic surveys and facies analyses have questioned long held interpretations of the development and furthermore the age of quaternary sediments along the coast of sardinia the matter of debate is whether the investigated sediments were deposited during the late wurmian and holocene or during marine isotope stage mis 5 and older stages optically stimulated luminescence standard blue optically stimulated luminescence osl post infrared ir pulsed blue osl and post ir infrared stimulated luminescence irsl dating was applied to shallow marine and aeolian deposits as well as radiocarbon dating to bulk organic material in palaeosols radiocarbon dates suggest sedimentation during the late wurmian and holocene whilst the luminescence results for both quartz and potassium feldspar indicate a depositional age for most of the investigated sites prior to and during mis 5 from a geochronological point of view the luminescence ages are considered reliable because they passed all quality tests furthermore there is good agreement of two dosimeters with different bleaching and luminescence properties the radiocarbon ages might suffer from underestimation due to some contamination with young carbon which however cannot be large enough to yield such young ages

soil chronosequence studies in temperate to subtropical low latitude low relief terrain with data from the eastern united states the coastal plain of the eastern united states is a low latitude low altitude low relief terrain composed primarily of gently dipping marine and marginal marine sediments that range in age from cretaceous to quaternary population density of the area is moderate and most of the population is concentrated along the coast inland of the coast agriculture including growing trees for pulp is the dominant economy in this region soils have developed along two different pathways one pathway is dominated by the dissolution and movement of oxyhydroxides and the accumulation of organic matter the other by the accumulation of clays and oxyhydroxyides and the adsorption or oxidation of organic matter the first pathway has resulted in the formation of spodosols the second in the development of ultisols no clearly distinguishable age trends have been identified in the spodosols but the properties of ultisols can be measured to quantify surface material alteration through time ultisols are therefore suited to order of magnitude chronostratigraphic interpretations potentially data derived through the study of ultisols can be used to develop models that predict how surface processes will change due to continued weathering and pedogenesis or as the result of climate change

genetically related alluvial deposits across active fault zones an example of alluvial fan terrace correlation from the upper quaternary of the southern po basin italy integrated studies of alluvial fan systems and related intramontane valley deposits provide potentially useful tools for understanding the character of alluvial sedimentation and its control in fault controlled piedmont zones an example is reported from the uppermost quaternary alluvial deposits of the northern apennines and the southern margin of the po basin a distinctive cyclicity characterizes both the outcropping and the buried units in the study area in intramontane valleys individual cycles consist of regular alternations of sections displaying high and low terrace preservation in the subsurface a rhythmic alternation of coarse grained bodies and laterally extensive pelitic horizons occurs at various scales and represents the basic cyclic motif of the depositional system the correlation between the terrace sequences and the depositional cycles in the subsurface allows the differentiation of distinct sequences with a characteristic internal architecture in the lower part of sequences poorly preserved terrace deposits are laterally correlatable with alluvial fan gravel bodies whereas highly preserved terrace deposits are correlated laterally with predominantly floodplain sediments in the upper part of sequences reliable correlation lines have been constructed using 14c dating thrust tectonics and climate exerted a major control on sequence development deep valley excavation with subsequent low terrace preservation occurred in response to relief rejuvenation during successive thrusting events on the other hand decreasing erosion related to periods of minor tectonic activity led to terrace preservation in the intramontane valleys the coeval episodes of alluvial fan growth and abandonment recorded at the basin margin are interpreted to reflect changes in the efficiency of the drainage system due to variations of tectonic uplift in the adjacent areas alternating phases of deglaciation and renewed glaciation however are inferred to have played a major role in controlling the amount and type of sediment delivered to the alluvial fan complexes

dynamic models of interseismic deformation and stress transfer from plate motion to continental transform faults thermal regime on geologic timescales 10 6 10 7 years as well as on timescales of the order of the earthquake recurrence 10 2 years strain localization in the viscoelastic medium results from thermomechanical coupling and power law dependence of strain rate on stress for conditions corresponding to the san andreas fault saf the predicted width of the shear zone in the lower crust is 3 5 km this shear zone accommodates more than 50 of the far field plate motion coupled thermomechanical models predict a single layer lithosphere in case of dry composition of the lower crust and upper mantle and a jelly sandwich lithosphere in case of wet composition deviatoric stress in the lithosphere in our models is relatively insensitive to the water content the far field loading rate and the fault strength and is of the order of 10 2 mpa thermomechanical coupling gives rise to an inverse correlation between the fault slip rate and the ductile strength of the lithosphere we show that our models are broadly consistent with geodetic and heat flow constrains from the saf in northern california models suggest that the regionally elevated heat flow around the saf may be at least in part due to viscous dissipation in the ductile part of the lithosphere

viscoelastic earthquake cycle models with deep stress driven creep along the san andreas fault system 1 we develop a two dimensional boundary element earthquake cycle model including deep interseismic creep on vertical strike slip faults in an elastic lithosphere coupled to a viscoelastic asthenosphere uniform slip on the upper part of the fault is prescribed periodically to represent great strike slip earthquakes below the coseismic rupture the fault creeps in response to lithospheric shear stresses within a narrow linear viscous fault zone the model is applied to the gps contemporary velocity field across the carrizo plain and northern san francisco bay segments of the san andreas fault as well as triangulation measurements of postseismic strain following the 1906 san francisco earthquake previous analysis of these data using conventional viscoelastic coupling models without stress driven creep segall 2002 shows that it is necessary to invoke different lithosphere asthenosphere rheology in northern and southern california in order to explain the data we show that with deep stress driven interseismic creep on the san andreas fault the data can be explained with the same rheology for northern and southern california we estimate elastic thickness in the range 44 100 km 95 confidence level fault zone viscosity per unit width of 0 5 8 2 1017 pa s m and asthenosphere relaxation time of 24 622 years 0 1 2 9 1020 pa s for northern and southern california we estimate a slip rate of 21 27 mm yr and recurrence time of 188 315 years for the northern san francisco bay san andreas fault and slip rate of 32 42 mm yr with recurrence time of 247 536 years for the carrizo plain

soil forming processes and rates on uplifted marine terraces in southwestern oregon usa soil chronosequences were examined on flights of tectonically uplifted marine terraces near cape blanco and cape arago southwestern oregon all of the soils contain abundant organic c and are strongly acidic ph in h2o 30 of the exchange sites saturated with al the soils in the two areas show a progression in development from spodosols to spodosols with clay enriched horizons and eventually to ultisols although the spodic and argillic horizons appear to be forming concurrently in the soils evidence is presented to support the concept that the spodic horizon is eventually masked by clay accumulation because of weathering in situ neoformation of clays and clay translocation the primary age related trends include increases in 1 the relative abundance of silt and clay 2 the ratio of quartz to feldspars in the very fine sand 100 50 m fraction and 3 the amounts of dithionite extractable fe and al and crystalline forms of fe in the profile

slip rate and tremor genesis in cascadia at many plate boundaries conditions in the transition zone between seismogenic and stable slip produce slow earthquakes in the cascadia subduction zone these events are consistently observed as slow aseismic slip on the plate interface accompanied by persistent tectonic tremor however not all slow slip at other plate boundaries coincides spatially and temporally with tremor leaving the physics of tremor genesis poorly understood here we analyze seismic geodetic and strainmeter data in cascadia to observe for the first time a large tremor generating slow earthquake change from tremor genic to silent and back again the tremor falls silent at reduced slip speeds when the migrating slip front pauses as it loads the stronger adjacent fault segment to failure the finding suggests that rheology and slip speed regulated stressing rate control tremor genesis and the same section of fault can slip both with and without detectable tremor limiting tremor s use as a proxy for slip

interseismic uplift rates for western oregon and along strike variation in locking on the cascadia subduction zone 1 we quantify the spatial pattern of uplift rate in western oregon and northernmost california using tidal and leveling records to better understand the pattern of interseismic locking on the cascadia subduction zone we extend relative sea level time series of the six primary noaa tide gauges to include all observations from 1925 to 2006 previously unidentified bench mark instability biases portions of tidal records by 1 6 mm a 1 before correction we determine precise relative uplift rates at the six tidal sites with an adjustment that includes rates of differenced time series as additional constraints our analysis of national geodetic survey leveling data between tide gauges corrects errors in 1941 leveling and 184 secondary ties double the number of highest quality uplift rate estimates relative uplift rates from leveling are adjusted to the tidal rates accounting for uncertainties in both data types tidal and leveling uplift rates agree within error for all but one of the coastal segments where we infer systematic leveling error affects the 1988 line uplift rates are made absolute using an interval and location specific geocentric sea level rise rate of 2 3 0 2 mm a 1 total propagated one sigma errors for the absolute uplift rates of bench marks are 0 4 mm a 1 along strike changes in uplift rate near 45 n and 42 8 n require two distinct changes in locking depth as inferred from elastic dislocation modeling the along strike changes in locking on this portion of the cascadia subduction zone interface correlate to the western and southern extent of the mafic siletzia block in the fore arc

a wrb based buried paleosol classification abstract present classification systems for buried paleosols are inadequately developed several classification systems for paleosols based on the us soil taxonomy have been developed recently but their use is still very limited we propose appilcation of the world reference base for soil resources which uses only substantial profile characteristics as a background for the development of a new buried paleosol classification the system was adapted for the use for buried paleosols dynamic criteria which could be altered by diagenesis were disregarded and the definitions of most horizons were modified a new prefix infra was applied for modified diagnostic horizons and properties and for refernce groups of buried paleosols as a result 11 diagnostic horizons 2 properties and 2 materials were left with their definitions and names 9 diagnostic horizons and 2 properties were modified and named with the prefix infra 14 diagnostic horizons 6 properties and 4 materials were excluded or joined with others and two new diagnostic horizons were proposed this relationship reflects the balance between stable and dynamic properties in the diagnostic criteria used by the wrb the number of soil units proposed for buried paleosols is fewer than for surface soils in the wrb 25 instead of 30 the use of wrb modifiers reflecting dynamic soil properties was tentatively recommended for the second level buried paleosols classification with prefixes pedo for pedogenically derived properties and dia for the properties caused by post burial processes the application of the proposed system to a set of paleosols previously described in the literature showed its utility for buried paleosol classification

viscosity of the asthenosphere from glacial isostatic adjustment and subduction dynamics at the northern cascadia subduction zone british columbia canada 1 late glacial sea level curves located in the cascadia subduction zone csz fore arc in southwestern british columbia show that glacial isostatic adjustment gia was rapid when the cordilleran ice sheet collapsed in the late pleistocene gia modeling with a linear maxwell rheology indicates that the observations can be equally well fit across a wide range of asthenospheric thicknesses provided that the asthenospheric viscosity is varied from 3 1018 pa s for a thin 140 km asthenosphere to 4 1019 pa s for a thick 380 km asthenosphere present day vertical crustal motion predicted by the gia models shows rates of a few tenths of a millimeter per year consistent with previous analyses the model viscosities largely pertain to the viscosity of the oceanic mantle beneath the subducting juan de fuca slab but include a contribution from the mantle wedge above the slab for comparison effective viscosities for the upper mantle due to the tectonic regime subduction were computed using the strain rates and temperatures of an independent geodynamic model of the csz with a wet olivine power law rheology the effective viscosities agree well with gia model viscosities of 1019 pa s or less corresponding to an asthenosphere of 100 or 200 km thickness the agreement suggests a significant role for power law flow in the gia response regardless of the microphysical mechanisms responsible for the gia response the viscosity values inferred from gia can be applied to studies of the megathrust earthquake cycle because both processes take place on comparable time scales

constraints on accumulated strain near the ets zone along cascadia abstract current national seismic hazard models for cascadia use the zone of episodic tremor and slip ets to denote the lower boundary of the seismogenic zone recent numerical models have suggested that an appreciable amount of long term strain may accumulate at the depth of ets and questions this assumption we use uplift rates from leveling campaigns spanning approximately 50 70 yrs in washington and oregon to investigate the amount of potential long term locking near the ets zone we evaluate the potential for deeper locking in cascadia by exploring a range of locking parameters along the subduction zone including the ets zone of the four east west leveling profiles studied three show a reduction in the misfit when secondary locking near the ets zone is included however the reduction in misfit values is only statistically significant for one profile this would suggest that models including a small amount of secondary locking are broadly indistinguishable from models without any secondary locking if secondary locking is considered the leveling data allow for locking up to 20 of the plate rate near the updip edge of the ets zone these results are consistent with but less resolved by gps observations

coupling on the northern cascadia subduction zone from geodetic measurements and physics based models kinematic inversions of gps and tide gauge leveling data display an unresolved gap between the downdip limit of the locked megathrust and the top of the episodic tremor and slip ets zone in northern cascadia this work combines physics based models of slow slip events with both mean ets displacements and decadal averaged deformation rates to explain the gap and determine how interseismic stress accumulates on the megathrust while physics based predictions match the average ets displacements they significantly misfit long term rates implying faster slip rates within both the gap and the ets region heterogeneous green s functions or velocity strengthening friction within the gap cannot explain the decadal rates the observed uplift rates require steeper gradients in slip rate at the base of the locked zone we invert for the smallest possible shear stress rate on the creeping megathrust below a locked zone that satisfactorily fits the data a nonzero shear stress rate within the ets zone reaching 2 5 kpa yr at a depth of 25 30 km is required finally of all the models that adequately fit both horizontal and vertical data only those with deep locking depths around 21 km significantly improve the fit to the uplift rates

reconciling viscoelastic models of postseismic and interseismic deformation effects of viscous shear zones and finite length ruptures we have developed a suite of earthquake cycle models for strike slip faults to investigate how finite ruptures and lithosphere scale viscous shear zones affect interseismic deformation in particular we assess whether localized and stationary interseismic deformation and large scale rapidly decaying postseismic transients may be explained with models incorporating either or both of these features models incorporating viscous shear zones give more stationary interseismic deformation than layered half space maxwell viscoelastic models producing similar early postseismic deformation in the near field this tendency is accentuated when the effective viscosity per unit width of the shear zone increases either with depth or with interseismic time models with finite 200 km long ruptures produce time dependent deformation similar to that from models with infinitely long ruptures though with smaller magnitude and somewhat more localized surface velocity fluctuations models incorporating a stiff lithosphere a low viscosity mantle asthenosphere and a crust to lithosphere scale viscous shear zone can replicate postseismic and interseismic deformation typical of large strike slip earthquakes such models require depth dependent power law or transient rheologies for the viscous shear zone material in the crust as long as the effective viscosity per unit shear zone width is approximately 1015 pa s m at crustal depths during the postseismic interval below the moho the shear zone effective viscosity per unit width must be higher throughout the seismic cycle at least over a short depth interval for example if shear zone viscosity per unit width is 5 1016 pa s m in the mantle lithosphere a model with a 50 km thick lithosphere and asthenosphere effective viscosities of 1 to 5 1018 pa s can reproduce reference velocity profiles for both postseismic and later interseismic deformation

seismic and geodetic constraints on cascadia slow slip 1 automatically detected and located tremor epicenters from episodic tremor and slip ets episodes in northern cascadia provide a high resolution map of washington s slow slip region thousands of epicenters from the past four ets events from 2004 to 2008 provide detailed map view constraints that correlate with geodetic estimates of the simultaneous slow slip each of these ets events exhibits remarkable similarity in the timing and geographic distribution of tremor density and geodetically inferred slip analysis of the latest 15 month inter ets period also reveals ageodetic tremor activity similar both in duration and extent to ets tremor epicenters from both ets and inter ets tremor are bounded between the 30 and 45 km plate interface depth contours and locate approximately 75 km east of previous estimates of the locked portion of the subducting juan de fuca plate inter ets tremor overlaps but is generally downdip of ets tremor and does not yet correlate with geodetically observed slip but this is likely because the slip is below current gps detection levels based on the tremor and slip correlation and the tremor duration and slip magnitude relationship we suggest that the well resolved sharp updip edge of tremor epicenters reflects a change in plate interface coupling properties the region updip of this boundary may accumulate stress with the potential for coseismic shear failure during a megathrust earthquake alternatively plate convergence in this region could be accommodated by continuous slow slip with no detectable tremor or by slow slip events with sufficiently long recurrence intervals that none have been detected during the past 10 years of gps observations

three dimensional surface motion maps estimated from combined interferometric synthetic aperture radar and gps data 1 we provide a technique to efficiently produce high resolution three dimensional surface motion maps by combining information about the motion of the earth s surface from interferometric observations of synthetic aperture radar images and repeated global positioning system gps geodetic measurements unwrapped interferograms showing pixel wise change in range from ground to satellite and sparse values of threedimensional movements are required as input the problem of finding the full threedimensional motion field is separated into two two dimensional problems initially the vertical component of the deformation field and its horizontal component in the look direction of the satellite are found later the look direction component is resolved into north and east components initial values for the motion fields are assigned to each pixel of interferograms from interpolation of available gps observations these values are then updated and optimized by comparison with the interferograms and the gps observations an additional constraint is an assumption of a smoothly varying motion field markov random field based regularization and simulated annealing algorithm are used for the optimization the technique is applied to create surface motion maps for the reykjanes peninsula sw iceland index terms 0933 exploration geophysics remote sensing 0910 exploration geophysics data processing 1206 geodesy and gravity crustal movements interplate 8155 8150 tectonophysics evolution of the earth plate boundary general 3040 8155 tectonophysics evolution of the earth plate motions general keywords remote sensing motion maps deformation data fusion interferometry gps

the ages and soils of two levels of rana surfaces in central spain abstract the geomorphology of two ranas and a specimen soil profile on each have been studied in the province of guadalajara central spain the ranas were first delineated on an aerial photograph then examined in the field for further identification and for the preparation of topographic profiles two soil profiles were described and sampled by horizons analyses were made of the samples for particle size distribution ph cation exchange relations and organic matter plus some observations on mineralogy of clay and fine sand fractions results of the study support earlier suggestions that the younger ran asurface s 1 is of donau age middle villafranchian but indicate that the second s 2 should be assigned to the middle upper pliocene lower villafranchian the soil profiles were found to be an alfisol on the younger and an ultisol on the older rana which is consistent with a greater age for the latter

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

deeper penetration of large earthquakes on seismically quiescent faults why many major strike slip faults known to have had large earthquakes are silent in the interseismic period is a long standing enigma one would expect small earthquakes to occur at least at the bottom of the seismogenic zone where deeper aseismic deformation concentrates loading we suggest that the absence of such concentrated microseismicity indicates deep rupture past the seismogenic zone in previous large earthquakes we support this conclusion with numerical simulations of fault behavior and observations of recent major events our modeling implies that the 1857 fort tejon earthquake on the san andreas fault in southern california penetrated below the seismogenic zone by at least 3 to 5 kilometers our findings suggest that such deeper ruptures may occur on other major fault segments potentially increasing the associated seismic hazard

juan de fuca slab geometry and its relation to wadati benioff zone seismicity 1 a new model of the subducted juan de fuca plate beneath western north america allows first order correlations between the occurrence of wadati benioff zone earthquakes and slab geometry temperature and hydration state the geo referenced 3d model constructed from weighted control points integrates depth information from earthquake locations and regional seismic velocity studies we use the model to separate earthquakes that occur in the cascadia forearc from those that occur within the underlying juan de fuca plate and thereby reveal previously obscured details regarding the spatial distribution of earthquakes seismicity within the slab is most prevalent where the slab is warped beneath northwestern california and western washington suggesting that slab flexure in addition to expected metamorphic dehydration processes promotes earthquake occurrence within the subducted oceanic plate earthquake patterns beneath western vancouver island are consistent with slab dehydration processes conversely the lack of slab earthquakes beneath western oregon is consistent with an anhydrous slab double differenced relocated seismicity resolves a double seismic zone within the slab beneath northwestern california that strongly constrains the location of the plate interface and delineates a cluster of seismicity 10 km above the surface that includes the 1992 m7 1 mendocino earthquake we infer that this earthquake ruptured a surface within the cascadia accretionary margin above the juan de fuca plate we further speculate that this earthquake is associated with a detached fragment of former farallon plate other subsurface tectonic elements within the forearc may have the potential to generate similar damaging earthquakes

determination of slow slip episodes and strain accumulation along the cascadia margin 1 continuous gps stations in the pacific northwest geodetic array network clearly record subduction related strain accumulation and slow slip episodes along the cascadia convergent margin many of the slow slip episodes have been correlated in time and space with seismic evidence for nonvolcanic tremor leading to the previous discovery of episodic tremor and slip ets in this study we use a hyperbolic tangent curve fitting technique for the identification of slow slip times and displacement magnitudes within the gps time series independent of seismic tremor data we then apply this technique to study the patterns of strain accumulation and release associated with ets events and characterize patterns of coupling associated with the locked and transition zones of the plate interface we demonstrate the effectiveness of this automated technique for both identification of slow slip observations and calculation of slow slip displacements recurrence patterns in the distribution of gps observations demonstrate coherence among neighboring stations over time and apparent along strike segmentation of the subduction interface when slow slip events are removed from the time series we can estimate the total site velocities between slow slip events these velocities decay as depth to the subduction interface increases but they diverge from the long term trends expected from the interseismic cycle at 30 60 km above the interface consistent with the location where slow slip displacements occur forward modeling of coupling on the plate interface reveals that in between slow slip events there is a patch of at least 30 coupling from 20 to 35 km depth which is needed to produce the observed back slip displacements intriguingly our best fitting models have a decrease in coupling down to 30 at 20 km depth followed by a peak of greater than 80 coupling at 30 35 km depth suggesting the source zone for ets events acts as a distinct locking zone that releases strain more frequently than the updip seismogenic locked zone although a zone of constant 30 coupling cannot be ruled out with this data set such a scenario indicates that frictional behavior with depth follows a more complex model than a simple temperature controlled transition we propose that coupling initially decreases with depth due to a decrease in strength of the overriding lower crust but then coupling increases again when the subducting plate comes in contact with the stronger overriding mantle

lower edge of locked main himalayan thrust unzipped by the 2015 gorkha earthquake faults are unlocked by earthquakes analysis of seismic data from the 2015 nepal earthquake shows that only part of the main himalayan thrust fault was unzipped by the quake leaving much of the fault locked and ready to slip in a future event

space time correlation of slip and tremor during the 2009 cascadia slow slip event 1 episodic tremor and slip ets involving transient deformations accompanied by emergent low frequency tremor occurs in subduction zones around the world ets events increase the shear stress on locked megathrusts and may potentially trigger damaging earthquakes despite the clear association of tremor and slip the physical relationship between them is unresolved tremor appears to result from slip on small asperities on the plate interface due to either creep on the surrounding fault or stress increases ahead of the propagating slow slip front previous studies of migrating slow slip events have not had sufficient spatial and temporal resolution to differentiate between these two models to address this we invert gps data from the august 2009 ets event in central cascadia for the space time evolution of fault slip rate we find a correlation in both space and time between tremor epicenters and the independently determined position of high fault slip rate this supports the first hypothesis that tremor asperities are loaded directly by slow slip rather than by stress increases ahead of the slip front and provides new insights into the mechanics of ets

optically stimulated luminescence dating of young sediments a review optically stimulated luminescence osl dating of young 1000 years sediments is used increasingly in a wide variety of late holocene studies as a mean of establishing contemporary sedimentation rates or the timing of sediment deposition this paper provides a summary of the basic principles of osl dating outlines the problems specific to the dating of young material and then uses recent applications to young sediments to illustrate the greatly increased scope and potential of the method in geomorphology and the geology of recent deposits the overall reliability of this new generation of osl ages is examined by comparing where possible osl ages with independent age control it is concluded that the osl ages are accurate in that there is no evidence for systematic over or under estimation it is our conclusion that osl dating should be regarded as a reliable chronological tool for determining the time of deposition of water lain sediments from the coastal zone and aeolian deposits from both coastal and inland environments our conclusion is supported by the growing popularity of osl dating in geomorphology and geology

an absolute chronology for the raised beach and associated deposits at sewerby east yorkshire england the raised beach sediments revealed in the cliffs at sewerby east yorkshire are widely regarded as ipswichian in age previously reported evidence for this dating is reviewed and new results from a range of luminescence dating techniques applied to the blown sand deposit overlying the raised beach are reported these provide the first absolute date for the sewerby site of 120 84 11 82 ka which places the blown sand at the boundary between oxygen isotope stages ois 5e and 5d as the underlying raised beach is little older than the blown sand it probably formed during ois stage 5e as suggested by the faunal evidence

soil chronosequences on quaternary marine terraces along the northwestern coast of calabria southern italy abstract two soil chronosequences representative of four orders of marine terraces from early to late pleistocene have been studied along the tyrrhenian coast of northern calabria in southern italy all soil profiles show a high degree of weathering although the degree of soil evolution varies according to the age of each terrace the soils are characterized by reddish to reddish brown colors clayey textures abundant clay coatings slickensides fe mn features or calcium carbonate concretions the dominance of kaolinite and illite among phyllosilicate clay minerals in all soil horizons the intense depletion in caco 3 na and k and the severe etching of quartz crystals in the older soils all record a highly leached pedogenic environment that is progressively more intense from younger to older soils despite the carbonate bedrock quartz feldspar and mica minerals also occur suggesting a partly allochthonous eolian origin of the parent material the major pedogenic features and their formative processes occurred polycyclically on the different orders of marine terraces and we interpret the soils to have mainly developed during repeated quaternary interglacials some surface a and bw horizons show quite different features suggesting a clear change in pedogenetic processes and possibly in climate and duration of soil formation these horizons have the typical field appearance of volcanic soils with andic properties brown colors loamy textures high porosity low bulk density high water retention thixotropy the occurrence of very small volcanic glass fragments and the possible presence of short range order aluminosilicate minerals confirmed some pyroclastic supply during soil formation

pedogenic approach to resolving the geomorphic evolution of the pakua river terraces in central taiwan abstract the southern part of the pakua tableland in taiwan comprises a series of wide unpaired river terraces that have as many as six altitude levels from pk 1 highest to pk 6 lowest the terrace surfaces are covered with lateritic soils this study described sampled and analyzed the soils from each terrace soil taxonomies are oxisol ultisol and inceptisol soil morphological characteristics were quantified as a profile development index pdi to determine the degree of soil development the chemical analyses included cation exchange capacity cec and selected extraction of fe in soils based on the degree of soil development surface deposits on terrace flights form the post incisive soil chronosequence supporting the hypothesis of terrace formation by fluvial processes soil ages were estimated based on iron crystallinity fed feo fet analytical results indicate that river terraces in the pakua tableland are aged 40 400 ka the long term uplift rate of the tableland can be estimated using terrace ages and folding geometry the variation of uplift rates demonstrates that the landscape underwent increased shortening of frontal thrusting by the changhua fault running beneath the tableland

time and size of a giant earthquake in cascadia inferred from japanese tsunami records of january 1700 geological evidence shows that great earthquakes have occurred in the recent prehistoric past in the cascadia subduction zone off the pacific coast of north america the most recent event or series of events is dated at about 300 years ago1 4 but the precise date and magnitude have not been determined geological investigations have not been able to distinguish a single giant earthquake from a series of great earthquakes occurring over a timespan of a decade or two4 although this information is important for the assessment of future hazard5 we have found several tsunami records in japan from ad 1700 with no indication of a local cause historical earthquake records and palaeoseismic evidence indicate the absence of a large earthquake in 1700 in south america alaska or kamchatka leaving cascadia as the most likely source of this tsunami the estimated time of the earthquake is the evening about 21 00 local time of 26 january 1700 the magnitude is estimated as 9 from the tsunami heights in which case the earthquake ruptured the entire length of the cascadia subduction zone2 these estimates are consistent with native american legends that an earthquake occurred on a winter night6

downdip landward limit of cascadia great earthquake rupture 1 this paper examines the constraints to the downdip landward limit of rupture for the cascadia great earthquakes off western north america this limit is a primary control for ground motion hazard at near coastal cities the studies also provide information on the physical controls of subduction thrust rupture globally the constraints are 1 locked transition zones from geodetic deformation gps repeated leveling tide gauges 2 rupture zone from paleoseismic coastal marsh subsidence paleogeodesy 3 temperature on the thrust for the seismic aseismic transition 4 change in thrust seismic reflection character downdip from thin seismic to thick ductile 5 fore arc mantle corner aseismic serpentinite and talc overlying the thrust 6 updip limit of episodic tremor and slip ets slow slip 7 rupture area associations with shelf slope basins 8 depth limit for small events on the thrust and 9 landward limit of earthquakes on the nootka transform fault zone the most reliable constraints for the limit of large rupture displacement 10 m are generally just offshore in agreement with thermal control for this hot subduction zone but well offshore central oregon and near the coast of northern washington the limit for 1 2 m rupture that can still provide strong shaking is less well estimated 25 50 km farther landward the fore arc mantle corner and the updip extent of ets slow slip are significantly landward from the other constraints surprisingly there is a downdip gap between the best other estimates for the great earthquake rupture zone and the ets slow slip in this gap plate convergence may occur as continuous slow creep

slow slip evolves into megathrust earthquakes in 2d numerical simulations 1 slow slip events sse in many subduction zones incrementally stress the adjacent locked megathrust suggesting that they could potentially either trigger or evolve into damaging earthquakes we explore this with 2d quasi dynamic simulations with rate state friction dilatancy and coupled 1d pore fluid and heat transport steady state weakening friction allows transient slip to nucleate but is inhibited by dilatant strengthening and destabilized by thermal pressurization sse spontaneously nucleate in low effective stress velocity weakening lesvw regions if the dimension of the lesvw is relatively small the sse are trapped at its updip end imparting a strong stress concentration in the locked zone after several centuries sse penetrate into the region of higher effective stress where thermal pressurization eventually leads to dynamic rupture for larger lesvw regions sse tend to increase in length with time ultimately higher slip speeds enhance thermal weakening leading to dynamic instability within the sse zone in both cases the onset of the ultimate sse is essentially indistinguishable from preceding events