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

stick slip motion and high speed ejecta in granular avalanches detected through a multi sensors flume abstract an oscillatory motion of dense dry granular flows is experimentally observed by means of a 5 5 m long densely instrumented flume an array of 35 sensing devices allowed recording kinematic and dynamic data of the entire flow with high spatial and temporal resolution dynamic data in addition to the kinematics provide valuable information to unveil stick slip motion that is proposed as the triggering mechanism for the appearance of periodic changes in compaction of the granular material called density waves periodic reverse graded strata after deposition of the flow accounts for such density waves besides internal interactions between different parts of the avalanche lead to the ejection of material and a high peak of the avalanche front velocity or an abnormal acceleration at the break slope and ejection of rocks from the flow was systematically observed evidencing internal interactions among different parts of the avalanche body while descending the inclined plane the velocity peak registered at the break in slope is interpreted as complementary evidence of these internal collisions and a non perfect inelastic collision simple model is assumed in order to explain the counter intuitive acceleration observed during the ejection process high speed ejection at the break in slope stick slip and expulsion from the flow are robust ubiquitous phenomena which do not strongly depend on the granulometric distribution used

signatures in flowing fluid electric conductivity logs flowing fluid electric conductivity logging provides a means to determine hydrologic properties of fractures fracture zones or other permeable layers intersecting a borehole in saturated rock the method involves analyzing the time evolution of fluid electric conductivity fec logs obtained while the well is being pumped and yields information on the location hydraulic transmissivity and salinity of permeable layers the original analysis method was restricted to the case in which flows from the permeable layers or fractures were directed into the borehole inflow recently the method was adapted to permit treatment of both inflow and outflow including analysis of natural regional flow in the permeable layer a numerical model simulates flow and transport in the wellbore during flowing fec logging and fracture properties are determined by optimizing the match between simulation results and observed fec logs this can be a laborious trial and error procedure especially when both inflow and outflow points are present improved analyses methods are needed one possible tactic would be to develop an automated inverse method but this paper takes a more elementary approach and focuses on identifying the signatures that various inflow and outflow features create in flowing fec logs the physical insight obtained provides a basis for more efficient analysis of these logs both for the present trial and error approach and for a potential future automated inverse approach inflow points produce distinctive signatures in the fec logs themselves enabling the determination of location inflow rate and ion concentration identifying outflow locations and flow rates typically requires a more complicated integral method which is also presented in this paper

a geophysical study of the castle mountain fault southcentral alaska abstract the castle mountain fault cmf lies less than 50 km from alaska s most populous city of anchorage and represents an important seismic hazard to the anchorage matanuska susitna valley region in southcentral alaska the character of seismicity varies along the cmf although the western cmf between 149 5 and 151 w shows evidence for late pleistocene or holocene reverse and dextral movement it has been seismically quiet over the past 50 years of local seismic network operation in contrast the cmf east of 149 5 w is associated with considerable background seismicity including the mw 5 81984 strike slip sutton earthquake we have used gravity and magnetic data constrained with results of previous seismic reflection and seismic tomography studies to model subsurface structure of the cmf in an effort to determine what may control the variation in its seismic behavior our models are consistent with a component of high angle reverse faulting northwest side up dip 85 to 87 that appears to have vertically offset late mesozoic rocks 2000 to 2500 m lack of data coverage precludes an estimate of its total strike slip motion holocene movement on the cmf appears to be associated with a region where both sides of the fault consist of sedimentary rocks as defined by a gravity and magnetic low if most of the vertical offset has occurred since the miocene in response to collision of the yakutat microplate with north america then our results are comparable to recent thermochronological and paleoseismic estimates of vertical slip rates subduction of the edge of the yakutat microplate appears to spatially influence seismic behavior along the cmf while the occurrence of the 1964 great alaska earthquake has also temporally affected local seismicity

active tectonics of the st elias orogen alaska observed with gps measurements 1 we use data from campaign and continuous gps sites in southeast and south central alaska to constrain a regional tectonic block model for the st elias orogen active tectonic deformation in the orogen is dominated by the effects of the collision of the yakutat block with southern alaska our results indicate that 37 mm yr of convergence is accommodated along a relatively narrow belt of n nw dipping thrust faults in the eastern half of the orogen with the present day deformation front running through icy bay and beneath the malaspina glacier near the bering glacier the collisional thrust fault regime transitions into a broad northwest dipping decollement as the yakutat block basement begins to subduct beneath the counterclockwise rotating elias block the location of this transition aligns with the gulf of alaska shear zone implying that the pacific plate is fragmenting in response to the yakutat collision our model indicates that the bering glacier region is undergoing internal deformation and could correspond to the final stage of offscraping and accretion of sediments from the yakutat block prior to subduction predicted block motions at the western edge of the orogen suggest that the crust is laterally escaping along the aleutian fore arc

new constraints on relative motion between the pacific plate and baja california microplate mexico from gps measurements summary we present a new surface velocity field for baja california using gps data to test the rigidity of this microplate calculate its motion in a global reference frame determine its relative motion with respect to the north american and the pacific plates and compare those results to our estimate for pacific north america motion determination of pacific plate motion is improved by the inclusion of four sites from the south pacific sea level and climate monitoring project these analyses reveal that baja california moves as a quasi rigid block but at a slower rate in the same direction as the pacific plate relative to north america this is consistent with seismic activity along the western edge of baja california the baja california shear zone and may reflect resistance to motion of the eastern edge of the pacific plate caused by the big bend of the san andreas fault and the transverse ranges in southern california

the role of rheology and slab shape on rapid mantle flow three dimensional numerical models of the alaska slab edge 1 away from subduction zones the surface motion of oceanic plates is well correlated with mantle flow direction as inferred from seismic anisotropy however this correlation breaks down near subduction zones where shear wave splitting studies suggest the mantle flow direction is spatially variable and commonly non parallel to plate motions this implies local decoupling of mantle flow from surface plate motions yet the magnitude of this decoupling is poorly constrained we use 3d numerical models of the eastern alaska subduction transform plate boundary system to further explore this decoupling in terms of both direction and magnitude specifically we investigate the role of the slab geometry and rheology on the mantle flow velocity at a slab edge the subducting plate geometry is based on wadati benioff zone seismicity and tomography and the 3d thermal structure for both the subducting and overriding plates is constrained by geologic and geophysical observations in models using the composite viscosity a laterally variable mantle viscosity emerges as a consequence of the lateral variations in the mantle flow and strain rate spatially variable mantle velocity magnitudes are predicted with localized fast velocities greater than 80 cm yr close to the slab where the negative buoyancy of the slab drives the flow the same models produce surface plate motions of less than 10 cm yr comparable to observed plate motions these results show a power law rheology i e one that includes the effects of the dislocation creep deformation mechanism can explain both observations of seismic anisotropy and decoupling of mantle flow from surface motion

tectonic drivers of the wrangell block insights on fore arc sliver processes from 3 d geodynamic models of alaska intracontinental shear zones can play a key role in understanding how plate convergence is manifested in the upper plate in regions of oblique subduction however the relative role of the driving forces from the subducting plate and the resisting force from within intracontinental shear zones is not well understood results from high resolution geographically referenced instantaneous 3d geodynamic models of flat slab subduction at the oblique convergent margin of alaska are presented these models investigate how viscosity and length of the denali fault intracontinental shear zone as well as coupling along the plate boundary interface modulate motion of the wrangell block forearc sliver and slip across the denali fault models with a weak denali fault 1017 pa s and strong plate coupling 1021 pa s were found to produce the fastest motions of the wrangell block 10 mm yr the 3d models predict along strike variation in offs et along the denali fault changing from dextral strike slip motion in the eastern segment to oblique convergence towards the fault apex models further show that the flat slab drives oblique motion of the wrangell block and contributes to 20 models with a short fault and 28 models with a long fault of the observed quaternary slip rates along the denali fault the 3d models provide insight into the general processes of forearc sliver mechanics and also offer a 3d framework for interpreting hazards in regions of flat slab subduction

tectonic block motion and glacial isostatic adjustment in southeast alaska and adjacent canada constrained by gps measurements 1 we use data from campaign and continuous gps sites in southeast alaska and the neighboring region of canada to constrain a regional tectonic block model that estimates block angular velocities and derives a self consistent set of fault slip rates from the block motions present day tectonics in southeast alaska is strongly influenced by the collision of the yakutat block our model predicts a velocity of 50 3 0 8 mm a toward n22 9 0 6 w for that block our results suggest that the eastern edge of the yakutat block is deforming along this edge the fairweather fault accommodates a large portion of the pacific north america relative plate motion through 42 9 0 9 mm a of dextral slip further south along the queen charlotte fault our model predicts an average of 43 9 0 6 mm a of dextral slip and a southward increasing amount of transpression strain from the yakutat collision is transferred far to the east of the strike slip system this strain transfer causes the region north of glacier bay to undergo a clockwise rotation south of glacier bay and inboard of the queen charlotte fault a smaller but clearly defined clockwise rotation is observed the heterogeneous block motion north and south of glacier bay may indicate the area is undergoing internal deformation and could explain regional patterns of diffuse seismicity the northern cordillera of canada displays a small northeasterly motion our block model suggests that the entire southeastern alaska northwestern canada margin is mobile

comparison of surface aquifer and pore waters from a mesozoic basin and its underlying palaeozoic basement southeast france chemical evolution of waters and relationships between aquifers abstract as part of the deep geology of france gpf ardeche project water samples were collected along the ardeche margin of the massif central crystalline shield water is contained within various rocks including early jurassic carbonate triassic sandstone and evaporite permian continental deposits and the crystalline basement three sample types were studied surface water from streams and springs formation water sampled from fractured zones aquifers at various depths and pore water from rocks cored in the morte merie scientific borehole drilled to a depth of 980 m in 1993 as part of the ardeche project three main water chemistry signatures are associated with the three major geological groups 1 hco 3 ca mg water occurs in early jurassic carbonate and late triassic sandstone with dolomitic cement 2 ca so 4 water occurs in triassic sulphated shale and sandstone 3 na cl water occurs in permian sandstone and crystalline basement the samples enable a comparison between waters that flow on the surface those that have been in the underlying geological formations for a short time and those that have resided in closed pores of the host rock for a long time saturation indices computed for surface and formation waters show that dissolution reactions progressively increase the concentration of elements until saturation is reached surface waters were saturated for quartz and carbonate and formation waters for quartz carbonate gypsum muscovite and k feldspar saline water 12 g l tds from the permian rocks is controlled by a mineralogical assemblage of quartz calcite anhydrite muscovite k feldspar and albite at temperatures 80 90 c although equilibrium was reached for the formation waters concentrations in the pore waters reflect a general enrichment as compared to free formation waters from the fractured zones of the corresponding formation which suggests introduction of mobile elements in the solution only in permian rocks was a stable equilibrium observed since pore waters show no enrichment as compared to formation waters no water mixing was observed except along faults that form pathways for the fluid between formations each geological group generally behaves as a closed system except the permian rocks that seem to be or were exposed to circulation from the crystalline basement

plateau subduction intraslab seismicity and the denali alaska volcanic gap tectonic tremors in alaska usa are associated with subduction of the yakutat plateau but their origins are unclear due to lack of depth constraints we have processed tremor recordings to extract low frequency earthquakes lfes and generated a set of six lfe waveform templates via iterative network matched filtering and stacking the timing of impulsive p compressional wave and s shear wave arrivals on template waveforms places lfes at 40 58 km depth near the upper envelope of intraslab seismicity and immediately updip of increased levels of intraslab seismicity s waves at near epicentral distances display polarities consistent with shear slip on the plate boundary we compare characteristics of lfes seismicity and tectonic structures in central alaska with those in warm subduction zones and propose a new model for the region s unusual intraslab seismicity and the enigmatic denali volcanic gap i e an area of no volcanism where expected we argue that fluids in the yakutat plate are confined to its upper crust and that shallow subduction leads to hydromechanical conditions at the slab interface in central alaska akin to those in warm subduction zones where similar lfes and tremor occur these conditions lead to fluid expulsion at shallow depths explaining strike parallel alignment of tremor occurrence with the denali volcanic gap moreover the lack of double seismic zone and restriction of deep intraslab seismicity to a persistent low velocity zone are simple consequences of anhydrous conditions prevailing in the lower crust and upper mantle of the yakutat plate

moho interface beneath yakutat terrane southern alaska 1 we use air gun shots recorded by ocean bottom and land seismometers to constrain a 3 d velocity structure and a moho interface depth for the yakutat terrane in southern alaska we use a tomographic inversion of 61 000 first arrival picks from 64 receivers to create a 3 d velocity model the average velocity depth function north of the coastline has velocities at the surface of 4 5 km s increasing to velocities of 6 km s at 12 13 km below the surface average velocities at the surface are slower near the coast 3 8 km s than under the highest topography 4 7 km s we carry out an interface inversion of 19 000 pmp reflection picks from 50 receivers to constrain a 2 d moho interface model the average moho depth of the yakutat terrane in the marine portion of our study area is 30 km but depth rapidly increases onshore to 40 45 km beneath the high topography of the chugach st elias mountains moho depths are consistent with airy isostasy beneath the orogen our data set supports a continuous moho at the base of the yakutat terrane with no evidence for pacific oceanic crust underthrusting the yakutat terrane we present several geologic models for crustal thickening beneath the chugach st elias orogen that are consistent with the seismic observations and surface geology and compare these models with geologic mapping in the region we argue that crustal thickening and topography at the chugach st elias mountains is obtained via a duplex system that produces a vertically growing antiformal stack of sedimentary and metasedimentary material

extending alaska s plate boundary tectonic tremor generated by yakutat subduction the tectonics of the eastern end of the alaska aleutian subduction zone are complicated by the inclusion of the yakutat microplate which is colliding into and subducting beneath continental north america at near pacific plate rates the interaction among these plates at depth is not well understood and further east even less is known about the plate boundary or the source of wrangell volcanism the drop off in wadati benioff zone wbz seismicity could signal the end of the plate boundary the start of aseismic subduction or a tear in the downgoing plate further compounding the issue is the possible presence of the wrangell slab which is faintly outlined by an anemic eastward dipping wbz beneath the wrangell volcanoes in this study i performed a search for tectonic tremor to map slow plate boundary slip in south central alaska i identified 11 000 tremor epicenters which continue 85 km east of the inferred pacific plate edge marked by wbz seismicity the tremor zone coincides with the edges of the downgoing yakutat terrane and tremors transition from periodic to continuous behavior as they near the aseismic wrangell slab i interpret tremor to mark slow semicontinuous slip occurring at the interface between the yakutat and north america plates the slow slip region lengthens the megathrust interface beyond the wbz and may provide evidence for a connection between the yakutat slab and the aseismic wrangell slab

depth dependent activity of non volcanic tremor in southwest japan 1 with a new location method we obtained a high resolution map of non volcanic tremor along the subducting philippine sea plate in southwest japan and clarified the depth dependent behavior of the tremor activity a bimodal distribution of tremor along dip is apparent in regions where short term slow slip events sses and very low frequency earthquakes are frequently detected the separation of bimodal peaks is 5 to 10 km in depth the updip tremor activity occurs episodically coincident with major bursts that often accompany geodetically detectable sses the downdip tremor activity is however rather stable with frequent minor bursts this depth dependent tremor activity likely reflects variation of interplate slip properties specifically weakening with increasing depth and temperature in westernmost shikoku anomalous tremor activity was detected in only the updip section in late 2003 this is interpreted as being triggered by a long term sse in the shallower edge of the tremor zone

possible relationship between nonvolcanic tremor and the 1998 2001 slow slip event south central alaska 1 we document the occurrence of nonvolcanic tremor nvt in south central alaska for 3 months of each year between 1999 and 2001 to provide a first order attempt to understand the relationship between nvt and a large slow slip event that occurred over a 2 to 3 year period between 1998 and 2001 the majority of the nvt signals observed after the onset of the slow slip event are bursts lasting between 10 and 15 min with frequencies ranging from 1 to 6 hz by the summer of 2001 the quantity of nvt has decreased dramatically from the previous summers and episodes rarely last up to 10 min the decrease in nvt activity in the summer of 2001 is coincident with the end of the slow slip event there is a clear spatial correlation between the observed nvt and the slow slip event with most of the nvt events located on the downdip edge of the region of highest slip depth estimates range widely over the region with approximately half concentrated near the interpreted north america yakutat pacific plate interface and the remainder located above the plate interface however owing to inadequate station coverage and poor knowledge of the local structure determining accurate depths is difficult and thus the relationship between the nvt and the plate interface is problematic this is the first study giving evidence that the relationship between slow slip events and nvt seen in cascadia and southwest japan may also exist in alaska

seismic anisotropy under central alaska from sks splitting observations 1 seismic anisotropy under central alaska is studied using shear wave splitting observations of sks waves recorded on the broadband experiment across the alaska range beaar 1999 2001 splitting results can be divided into two distinct regions separated by the 70 km contour of the subducting pacific plate waves that travel through the thicker mantle wedge show fast directions that are parallel to the strike of the slab these slab parallel directions appear to indicate along strike flow in the mantle wedge and splitting delay times increase with path length in the mantle wedge suggesting anisotropy of 7 9 0 9 the region of along strike flow corresponds to high seismic attenuation and hence high temperatures along strike flow here may be driven by secular shallowing of the slab driven by subduction of buoyant yakutat terrane crust or by toroidal flow around the east end of the aleutian slab waves traveling southeast of the 70 km contour sample the pacific plate and the nose of the mantle wedge they show fast directions that parallel the direction of plate motion these fast directions are most likely due to flow under the subducting pacific plate and or anisotropy within the subducting pacific lithosphere the high splitting delay times 0 8 1 7 s associated with these convergence parallel directions cannot be produced in the mantle wedge which is 10 30 km thick here thus anisotropy shows a sharp 90 change in fabric associated with the onset of high temperature wedge flow

wrangell benioff zone southern alaska the first unequivocal evidence for the existence of a benioff zone that may be related to the quaternary wrangell volcanoes comes from a set of 86 well located hypocenters for earthquakes smaller than about magnitude 4 in the region between lat 61 and 62 5 n and between long 142 and 145 5 w about half of the earthquakes occur at depths of 25 km or less below 40 km a clearly defined north northeast dipping zone of seismicity here termed the wrangell benioff zone extends to a depth of about 85 km and continues for about 115 km along strike subparallel to the volcanic trend the western end of the zone may be offset from the northern end of the much more active aleutian benioff zone where the benioff zone shoals to 30 to 40 km it becomes nearly horizontal and cannot be clearly distinguished from upper plate seismicity it is uncertain whether the subducted plate segment that contains the wrangell benioff zone is structurally part of the pacific plate or the yakutat block

evolution of interstitial waters along the passive margin of the southeast basin of france welcom well chemical on line monitoring applied to balazuc 1 well ardeche abstract as part of the geologie profonde de la france gpf deep geology of france programme investigating the passive margin of the southeast basin of france studies are being made on the possibility of modelling mass transfer in the summer of 1990 when the first hole in the area balazuc 1 was being drilled along a basement rooted fault chemical monitoring of the drilling fluids welcom enabled the composition of the interstitial fluids contained within the intersected rocks to be reconstructed the computations were compared to on core leaching carried out during the drilling following which the welcom results were calibrated the interstitial fluids from the drilled formations show very contrasted compositions from the top to the bottom of the hole it has been possible to distinguish diagenetically evolved seawater within the hettangian limestone modified continental fluids within the upper part of the triassic sandstone reservoirs and evaporated seawater within the middle triassic evaporites several zones of intensive fluid circulation are also indicated by dolomitization of the basal hettangian limestone circulation of fluids expelled from the evaporites within the upper part of triassic sandstone reservoirs and continental derived hydrothermal fluid flow within the lower triassic sandstone reservoir and carboniferous silty shale the results show that chemical logging of drilling fluids can provide valuable data concerning interstitial fluids where other techniques are not available

mapping the megathrust beneath the northern gulf of alaska using wide angle seismic data in the northern gulf of alaska and prince william sound we have used wide angle seismic reflection refraction profiles earthquake studies and laboratory measurements of physical properties to determine the geometry of the prince william and yakutat terranes the aleutian megathrust and the subducting pacific plate in this complex region the yakutat terrane is underthrust beneath the prince william terrane and both terranes are interpreted to be underlain by the pacific plate wide angle seismic reflection refraction profiles recorded along five seismic lines are used to unravel this terrane geometry modeled velocities in the upper crust of the prince william terrane to 18 km depth agree closely with laboratory velocity measurements of orca group phyllites and quartzofeldspathic graywackes the chief components of the prince william terrane to hydrostatic pressures as high as 600 mpa 6 kbar a landward dipping reflector at depths of 16 24 km is interpreted as the base of the prince william terrane this reflector corresponds to the top of the wadati benioff zone seismicity and is interpreted as the megathrust immediately beneath the megathrust is a 4 km thick 6 9 km s refractor which we infer to be the source of a prominent magnetic anomaly and which is interpreted by us and previous workers to be gabbro in eocene age oceanic crust of the underthrust yakutat terrane wide angle seismic data magnetic anomaly data and tectonic reconstructions indicate that the yakutat terrane has been underthrust beneath the prince william terrane for at least a few hundred kilometers wide angle seismic data are consistent with a 9 to 10 landward dip of the subducting pacific plate beneath the outer shelf and slope distinctly different from the inferred average 3 to 4 dip of the overlying 6 9 km s refractor and the wadati benioff seismic zone beneath the inner shelf our preferred interpretation of the geophysical data is that one composite plate composed of the pacific plate of a fairly uniform thickness and the yakutat plate of varying thickness is subducting beneath southern alaska

comparison of hydrogeochemical logging of drilling fluid during coring with the results from geophysical logging and hydraulic testing example of the morte merie scientific borehole ardeche france deep geology of france programme abstract a 980 m deep well was cored on the ardeche border of the southeastern basin of france as part of the deep geology of france gpf programme hydrogeochemical logging was carried out during drilling which involved the monitoring of physico chemical parameters ph eh temperature and conductivity and chemical parameters concentrations of he rn co 2 ch 4 o 2 ca cl and sio 2 of the drilling fluid permanently circulating in the well this logging programme was complemented by geophysical logging and two hydraulic tests the combination of these measurements enabled identification of a transmissive interval due to fractures in the jurassic carbonates and of fluid inflow both at the base of the porous and slightly permeable triassic sandstones and from an open fracture in the permian conglomerates these intervals are marked by changes in the drilling fluid chemistry such as an increase in chemical species content or a drop in ph the degree of modification depends on the natural permeability of the fractures and the salinity of the fluids the porous and permeable intervals are also marked by he anomalies which act as a tracer for these zones comparison between the geophysical and hydrogeochemical logs reveals that the latter provide information on the liquid phase whether the fractures are productive or not whereas the geophysical logs are more directly related to the solid phase

slow slip events and seismic tremor at circum pacific subduction zones 1 it has been known for a long time that slip accompanying earthquakes accounts for only a fraction of plate tectonic displacements however only recently has a fuller spectrum of strain release processes including normal slow and silent earthquakes or slow slip events and continuous and episodic slip been observed and generated by numerical simulations of the earthquake cycle despite a profusion of observations and modeling studies the physical mechanism of slow slip events remains elusive the concurrence of seismic tremor with slow slip episodes in cascadia and southwestern japan provides insight into the process of slow slip a perceived similarity between subduction zone and volcanic tremor has led to suggestions that slow slip involves fluid migration on or near the plate interface alternatively evidence is accumulating to support the notion that tremor results from shear failure during slow slip global observations of the location spatial extent magnitude duration slip rate and periodicity of these aseismic slip transients indicate significant variation that may be exploited to better understand their generation most slow slip events occur just downdip of the seismogenic zone consistent with rate and state dependent frictional modeling that requires unstable to stable transitional properties for slow slip generation at a few convergent margins the occurrence of slow slip events within the seismogenic zone makes it highly likely that transitions in frictional properties exist there and are the loci of slow slip nucleation slow slip events perturb the surrounding stress field and may either increase or relieve stress on a fault bringing it closer to or farther from earthquake failure respectively this paper presents a review of slow slip events and related seismic tremor observed at plate boundaries worldwide with a focus on circum pacific subduction zones trends in global observations of slow slip events suggest that 1 slow slip is a common phenomena observed at almost all subduction zones with instrumentation capable of recording it 2 different frictional properties likely control fast versus slow slip 3 the depth range of slow slip may be related to the thermal properties of the plate interface and 4 the equivalent seismic moment of slow slip events is proportional to their duration mo different from the mo 3 scaling observed for earthquakes

slab1 0 a three dimensional model of global subduction zone geometries 1 we describe and present a new model of global subduction zone geometries called slab1 0 an extension of previous efforts to constrain the two dimensional non planar geometry of subduction zones around the focus of large earthquakes slab1 0 describes the detailed non planar three dimensional geometry of approximately 85 of subduction zones worldwide while the model focuses on the detailed form of each slab from their trenches through the seismogenic zone where it combines data sets from active source and passive seismology it also continues to the limits of their seismic extent in the upper mid mantle providing a uniform approach to the definition of the entire seismically active slab geometry examples are shown for two well constrained global locations models for many other regions are available and can be freely downloaded in several formats from our new slab1 0 website http on doi gov d9arbs we describe improvements in our two dimensional geometry constraint inversion including the use of average active source seismic data profiles in the shallow trench regions where data are otherwise lacking derived from the interpolation between other active source seismic data along strike in the same subduction zone we include several analyses of the uncertainty and robustness of our three dimensional interpolation methods in addition we use the filtered subduction related earthquake data sets compiled to build slab1 0 in a reassessment of previous analyses of the deep limit of the thrust interface seismogenic zone for all subduction zones included in our global model thus far concluding that the width of these seismogenic zones is on average 30 larger than previous studies have suggested

repeated large slow slip events at the southcentral alaska subduction zone abstract we identify and study an ongoing slow slip event sse in the southcentral alaska subduction zone using gps measurements this is the second large sse in this region since modern geodetic measurements became available in 1993 we divide the ongoing sse into two phases according to their transient displacement time evolution their slip distributions are similar to each other but slip rates are slightly different this ongoing sse occurs downdip of the main asperity that ruptured in the 1964 alaska earthquake on the same part of the subduction interface as the earlier 1998 2001 sse the average slip rate of this sse is 4 5 cm yr with a cumulative moment magnitude of mw 7 5 mw 7 3 and mw 7 1 for phases i and ii respectively through the end of 2012 the time and space dependence of the gps displacements suggest that the slip area remained nearly the same during phase i while the slip rate increased with time the sses occur on a transitional section of the subduction plate interface between the fully locked updip part and the freely slipping deeper part during the 1964 earthquake slip on the region of the sse was much lower than slip in the updip region based on this observation and the repeated sses we conclude that this part of the interface slips repeatedly in sses throughout the interseismic period and does not build up a large slip deficit to be released through large slip in earthquakes

multi segment earthquakes and tsunami potential of the aleutian megathrust abstract large to great earthquakes and related tsunamis generated on the aleutian megathrust produce major hazards for both the area of rupture and heavily populated coastlines around much of the pacific ocean here we use paleoseismic records preserved in coastal sediments to investigate whether segment boundaries control the largest ruptures or whether in some seismic cycles segments combine to produce earthquakes greater than any observed since instrumented records began virtually the entire megathrust has ruptured since ad1900 with four different segments generating earthquakes m8 0 the largest was the m9 2 great alaska earthquake of march 1964 that ruptured 800 km of the eastern segment of the megathrust the tsunami generated caused fatalities in alaska and along the coast as far south as california east of the 1964 zone of deformation the yakutat microplate experienced two m8 0 earthquakes separated by a week in september 1899 for the first time we present evidence that earthquakes 900 and 1500 years ago simultaneously ruptured adjacent segments of the aleutian megathrust and the yakutat microplate with a combined area 15 greater than 1964 giving an earthquake of greater magnitude and increased tsunamigenic potential

alaska megathrust 2 imaging the megathrust zone and yakutat pacific plate interface in the alaska subduction zone we image the slab underneath a 450 km long transect of the alaska subduction zone to investigate 1 the geometry and velocity structure of the downgoing plate and their relationship to slab seismicity and 2 the interplate coupled zone where the great 1964 earthquake mw 9 2 exhibited the largest amount of rupture the joint teleseismic migration of two array data sets based on receiver functions rfs reveals a prominent shallow dipping low velocity layer at 25 30 km depth in southern alaska modeling of rf amplitudes suggests the existence of a thin layer vs of 2 1 2 6 km s that is 20 40 slower than underlying oceanic crustal velocities and is sandwiched between the subducted slab and the overriding plate the observed megathrust layer with vp vs of 1 9 2 3 may be due to a thick sediment input from the trench in combination with elevated pore fluid pressure in the channel our image also includes an unusually thick low velocity crust subducting with a 20 dip down to 130 km depth at 200 km inland beneath central alaska the unusual nature of this subducted segment results from the subduction of the yakutat terrane crust our imaged western edge of the yakutat terrane aligns with the western end of a geodetically locked patch with high slip deficit and coincides with the boundary of aftershock events from the 1964 earthquake it appears that this sharp change in the nature of the downgoing plate could control the slip distribution of great earthquakes on this plate interface

automated detection and location of cascadia tremor 1 a new autonomous seismic location and detection methodology enables real time opportunities for high resolution spatio temporal monitoring of non volcanic tremor combining a unique cross correlation technique with epicenter clustering analysis in northern cascadia automatically yields thousands of tremor epicenters from the may 2008 episodic tremor and slip ets event while routinely detecting and locating inconspicuous inter ets tremor bursts although ets events in this area produce about two weeks of continuous tremor we find a nearly equal amount of tremor during the last 15 month inter ets period the resulting ets and inter ets epicenters occur in the slow slip region where the plate interface is 30 45 km deep and have a sharp well resolved updip boundary about 75 km east of the downdip edge of the seismogenic megathrust zone this ability to track tremor with high spatio temporal resolution facilitates automatic tremor monitoring and the mapping of the transition zone and regions of locked zone stress accumulation