segmented lateral dyke growth in a rifting event at barðarbunga volcanic system iceland crust at many divergent plate boundaries forms primarily by the injection of vertical sheet like dykes some tens of kilometres long1 previous models of rifting events indicate either lateral dyke growth away from a feeding source with propagation rates decreasing as the dyke lengthens2 3 4 or magma flowing vertically into dykes from an underlying source5 6 with the role of topography on the evolution of lateral dykes not clear here we show how a recent segmented dyke intrusion in the bar arbunga volcanic system grew laterally for more than 45 kilometres at a variable rate with topography influencing the direction of propagation barriers at the ends of each segment were overcome by the build up of pressure in the dyke end then a new segment formed and dyke lengthening temporarily peaked the dyke evolution which occurred primarily over 14 days was revealed by propagating seismicity ground deformation mapped by global positioning system gps interferometric analysis of satellite radar images insar and graben formation the strike of the dyke segments varies from an initially radial direction away from the bar arbunga caldera towards alignment with that expected from regional stress at the distal end a model minimizing the combined strain and gravitational potential energy explains the propagation path dyke opening and seismicity focused at the most distal segment at any given time and were simultaneous with magma source deflation and slow collapse at the bar arbunga caldera accompanied by a series of magnitude m 5 earthquakes dyke growth was slowed down by an effusive fissure eruption near the end of the dyke lateral dyke growth with segment barrier breaking by pressure build up in the dyke distal end explains how focused upwelling of magma under central volcanoes is effectively redistributed over long distances to create new upper crust at divergent plate boundaries

structure of tertiary and pleistocene normal faults in iceland normal faults were measured in three selected areas of the late tertiary and pleistocene lava pile in iceland the arithmetic mean throw of 315 faults is 8 2 m the minimum being 0 5 m and the maximum 150 m about 93 of the faults have throws of less than 20 m the mean strike of the faults is n31 e but the mode is n45 e the faults dip from 42 to 89 nearly 80 dip between 65 and 79 and the mean dip is 73 fault breccia is common and varies in thickness from 0 05 m to 2 m there is a positive linear relation between breccia thickness and throw the linear correlation coefficient being 0 78 it is proposed that the normal faults in iceland form by two basic mechanisms one is the development of faults from sets of inclined joints in the lava pile the initially vertical columnar joints in the lavas gradually decrease in dip with depth in the crust because the regional dip of the lavas increases by about 1 for every 150 170 m depth the inclined joints form sets of en echelon cracks that may link up through tension cracks that propagate from near the ends of the joints the other mechanism involves formation and growth of normal faults by coalescence of smaller tension fractures the great majority of fractures within the active rift zone are tension fractures but when they attain the length of several hundred meters they normally change into normal faults it is concluded that normal fault development in iceland commonly starts at depths of about 1 km in the crust

linked thrust and strike slip faulting during late cretaceous terrane accretion in the san juan thrust system northwest cascades orogen washington the san juan thrust system makes up the western elements of the late cretaceous northwest cascades orogen of washington a stack of metamorphic nappes with terranes ranging in age from early paleozoic to middle cretaceous the tectonic development of the nappes is an unresolved issue important to understanding plate convergent processes operating in the north american cordillera in the creta ceous as well as at other times two terrane bounding fault zones were studied in this project the lopez and the rosario fault zones the fault zone rocks were affected by two cataclastic plastic late cretaceous deformational events d1 and d2 that included accretion and lateral motion during blueschist facies metamorphic conditions d1 produced upright folds and a subvertical axial planar s1 foliation fabric in the lopez fault zone and southwest vergent folds and gently northeast dipping axial planar s1 foliation in the rosario fault zone in the lopez fault zone d2 produced northwest striking and subvertical strike slip shear zones s2 with dominant sinistral displacements whereas in the rosario fault zone d2 generated low angle s2 shear zones and various slip crenulation fabrics formed by northwest directed thrust motion the d1 fabrics are inferred to be related to initiation of subduction related accretion of the nappes by orogen normal southwest northeast shortening and accretionary tectonics the subsequent d2 fabrics developed as temporally overlapping subduction related low angle thrusts in the rosario fault zone and high angle sinistral strike slip faults in the lopez fault zone in an overall transpressive setting due to oblique convergence this model suggests that the high angle lopez fault zone d2 was located above a gently northeast dipping thrust detachment s2 expressed by the rosario fault zone that allowed the accreted nappes to move parallel to the orogen the kinematic model cannot validate regional scale dextral terrane translation of the san juan thrust system as inferred by paleomagnetic data elsewhere in the western united states but addresses important tectonic processes caused by oblique subduction and changing plate conditions

transformation of an archean craton margin during proterozoic basin formation and magmatism the albany fraser orogen western australia abstract the albany fraser orogen is a well preserved example of proterozoic modification of an archean craton margin the formation of two successive basin systems accompanied by magmatism along the southern and southeastern yilgarn craton margin in western australia reflect distinct changes in tectonic regimes resulting in significant transformations of the archean craton crust provenance analysis from detrital zircons indicates that the first basin system the c 1815 1600 ma barren basin was dominantly filled with neoarchean detritus derived from the yilgarn craton and paleoproterozoic detritus derived from coeval voluminous mostly felsic magmatism the abundance of locally derived sediment deposited onto a reworked archean yilgarn craton substrate coupled with the progressively more juvenile isotopic signature of magmas indicates a largely extensional tectonic setting consistent with either a continental rift basin or a long lived backarc basin system this extensional regime led to the formation of a passive margin and oceanic basin along the craton edge the c 1600 1305 ma arid basin and formation of an ocean continent transition in the most heavily modified outboard region of the craton margin the eastern nornalup zone a change in tectonic regime is denoted by the formation of an oceanic arc the c 1410 ma loongana arc preserved in the adjoining madura province oceanic subduction led to accretion of the loongana arc onto the craton edge recorded by the presence of exotic detritus derived from this arc deposited into a foreland basin uppermost arid basin this accretion event triggered crustal thickening and the earliest phase of magmatism of stage i of the albany fraser orogeny at c 1330 ma a change to west dipping subduction beneath the accreted portion of the loongana arc placed the orogen into a backarc setting into which the remainder of the recherche supersuite mafic and felsic magmas were intruded thus the albany fraser orogen is regarded as an archean craton margin that preserves a long history of proterozoic transformation dominated by extensional processes that resulted in the formation of orogen wide basin systems accompanied by magmatism the recognition that the albany fraser orogen has always been part of the west australia craton and the tectonic regimes that have affected it provide important constraints on reconstructions of the nuna and rodinia supercontinents

a reinterpretation of seismicity associated with the january 1983 dike intrusion at kilauea volcano hawaii in january 1983 a dike intrusion fissure eruption generated a swarm of 375 magnitude 1 to 3 earthquakes along a 16 km segment of kilauea s middle east rift zone we searched the hawaiian volcano observatory catalog for multiplets of similar events from this region from 1980 through 1985 and obtained precise relative locations by waveform cross correlation over 150 of the intrusion earthquakes could be grouped into 14 multiplets of five or more events with sufficient similarity for accurate relocation some multiplets were active for only a few minutes during the downrift migration phase of the seismic swarm consistent with generation near the propagating dike tip while others were active for several days the two multiplets nearest the origin of the seismic swarm include events from the preceding days and months most multiplets span only 50 to 100 m following relocation are located at about 3 to 4 km depth and appear to deepen downrift the catalog depths of those earthquakes in multiplets and those not in multiplets are similar suggesting that most of the recorded seismicity may have come from a very limited depth interval despite the fact that the dike breached the surface by analogy with a mechanical model used to explain a similar clustering of background seismicity in the upper east rift in 1991 we infer that the earthquakes are generated in regions of high stress concentration immediately above kilauea s deforming deep rift body this conclusion is consistent with the depth of the top of the deep rift body inferred from geodetic data and with numerical calculations suggesting that a significant ambient differential stress is required for dikes to produce earthquakes larger than magnitude 1

deflection of dykes into sills at discontinuities and magma chamber formation abstract many rift zones contain composite volcanoes central volcanoes most of which are supplied with magma from shallow crustal magma chambers volcanotectonic studies of eroded rift zones such as in iceland as well as geophysical studies indicate that many shallow magma chambers evolve from sills here i provide field description of sills and extinct magma chambers in the quaternary and tertiary palaeorift zones of iceland focusing on the felsic pluton of slaufrudalur southeast iceland as a fine example of a magma chamber developed through the injection of sills in this paper i review analyse and develop further two related mechanisms for the deflection of dykes into sills and thus the potential initiation of a magma chamber namely a cook gordon debounding delamination and b stress barriers and propose a third mechanism c favourable material toughness ratios due to elastic mismatch difference in young s moduli or stiffnesses of layers in contact in the cook gordon mechanism a weak contact opens up as a result of dyke induced tensile stress this mechanism is likely to operate primarily at shallow depths as is supported by field observations and numerical models a stress barrier is a layer where the local stress is unfavourable to a particular type of rock fracture here a dyke field observations and numerical models show that on meeting a stress barrier a dyke either changes into a sill or becomes arrested the material toughness mechanism indicates that when the upper layer at a contact has the same or less stiffness than the lower layer hosting the dyke there is little tendency for the dyke to become deflected into the contact however when the upper layer is stiffer such as when a stiff basaltic lava flow is on the top of a soft pyroclastic layer the dyke tends to become deflected into the contact to form a sill field results suggest that all these mechanisms may cause dyke deflection into sills and may operate together particularly where the rock consists of alternating soft and stiff layers since the quaternary lava pile in iceland has many more soft hyaloclastite layers than the tertiary lava pile these mechanisms were probably very efficient in generating sills and by implication shallow magma chambers during the quaternary this may be one reason why in comparison with the tertiary lava pile the quaternary lava pile contains so many sills and extinct plutons and active shallow magma chambers

paleomagnetism and geochronology of the ecstall pluton in the coast mountains of british columbia evidence for local deformation rather than large scale transport 1 samples for geochronologic geobarometric and paleomagnetic analyses were collected across the northern portion of the ecstall pluton southeast of prince rupert british columbia al in hornblende geobarometry indicates pressures from 740 10 to 840 30 mpa corresponding to crystallization depths of 25 to 30 km u pb analyses of zircons from western central and eastern localities within the pluton yield crystallization ages of 91 5 1 0 ma 90 8 1 0 ma and 90 5 1 0 ma respectively rock magnetic experiments reflected light microscopy and thermal demagnetization behavior suggest that natural remanent magnetism is carried by low ti titanohematite unblocking temperatures of the characteristic remanent magnetization chrm are dominantly in the 560 c to 630 c range with age of magnetization approximated by the 40ar 39ar hornblende ages of 84 2 0 10 ma on the western margin and 76 4 0 6 ma in the center of the pluton site mean chrm directions were isolated for paleomagnetic samples from 23 sites and are distributed along a small circle with subhorizontal axis at 340 azimuth chrm directions from the central portion of the pluton are concordant with the expected cretaceous magnetic field direction while chrm directions from the western margin are discordant by 70 folding of the ecstall pluton either during late cretaceous west directed thrust transport above the convex upward prince rupert shear zone or during younger deformation of the pluton and underlying shear zone can account for the paleomagnetic data and is consistent with the geochronologic geobarometric and structural geologic observations

stress gradient coupling in glacier flow iv effects of the t term the t term in the longitudinal stress equilibrium equation for glacier mechanics a double y integral of 2t xy x 2 where x is a longitudinal coordinate and y is roughly normal to the ice surface can be evaluated within the framework of longitudinal flow coupling theory by linking the local shear stress t xy at any depth to the local shear stress t b at the base which is determined by the theory this approach leads to a modified longitudinal flow coupling equation in which the modifications deriving from the t term are as follows 1 the longitudinal coupling length i is increased by about 5 2 the asymmetry parameter is altered by a variable but small amount depending on longitudinal gradients in ice thickness h and surface slope 3 there is a significant direct modification of the influence of local h and on flow which represents a distinct driving force in glacier mechanics whose origin is in pressure gradients linked to stress gradients of the type t xy x for longitudinal variations in h the t force varies as d 2h dx 2 and results in an in phase enhancement of the flow response to the variations in h describable for sinusoidal variations by a wavelength dependent enhancement factor for longitudinal variations in the force varies as d dx and gives a phase shifted flow response although the t force is not negligible its actual effect on t b and on ice flow proves to be small because it is attenuated by longitudinal stress coupling the greatest effect is at shortest wavelengths 2 5h where the flow response to variations in h does not tend to zero as it would otherwise do because of longitudinal coupling but instead because of the effect of the t force tends to a response about 4 of what would occur in the absence of longitudinal coupling if an effect of this small size can be considered negligible then the influence of the t term can be disregarded it is then unnecessary to distinguish in glacier mechanics between two length scales for longitudinal averaging of t b one over which the t term is negligible and one over which it is not longitudinal flow coupling theory also provides a basis for evaluating the additional datum state effects of the t term on the flow perturbations u that result from perturbations h and from a datum state with longitudinal stress gradients although there are many small effects at the 1 level none of them seems to stand out significantly and at the 10 level all can be neglected the foregoing conclusions apply for long wavelengths h for short wavelengths h effects of the t term become important in longitudinal coupling as will be shown in a later paper in this series

imaging magma transport during the 1997 seismic swarm off the izu peninsula japan the spatio temporal evolution of a propagating magma filled crack was estimated from inversion of global positioning system gps data tiltmeters and leveling the dike opened at a maximum rate of 50 millimeters per day and had a peak magma flux of 2 x 10 6 cubic meters per day although the spatial resolution was limited slow upward propagation was resolved during the 9 day long intrusion in contrast the earthquakes migrated rapidly upward during the first 12 hours of the swarm and nearly all of the seismic energy was released in the first 2 days comparison of inversion results with accurate hypocenter locations will lead to improved understanding of magma transport through the brittle crust and of the causes of volcanic seismicity

a scale independent approach to fracture intensity and average spacing measurement fracture intensity the number of fractures per unit length along a sample line is an important attribute of fracture systems that can be problematic to establish in the subsurface lack of adequate constraints on fracture intensity may limit the economic exploitation of fractured reservoirs because intensity describes the abundance of fractures potentially available for fluid flow and the probability of encountering fractures in a borehole traditional methods of fracture intensity measurement are inadequate because they ignore the wide spectrum of fracture sizes found in many fracture systems and the consequent scale dependence of fracture intensity an alternative approach makes use of fracture size distributions which allow more meaningful comparisons between different locations and allow microfractures in subsurface samples to be used for fracture intensity measurement comparisons are more meaningful because sampling artifacts can be recognized and avoided and because common thresholds of fracture size can be enforced for counting in different locations additionally quantification of the fracture size distribution provides a mechanism for evaluation of uncertainties estimates of fracture intensity using this approach for two carbonate beds in the sierra madre oriental mexico illustrate how size cognizant measurements cast new light on widely accepted interpretation of geologic controls of fracture intensity

southern continuation of the coast shear zone and paleocene strain partitioning in british columbia southeast alaska this paper documents the newly recognized southern continuation of the early tertiary coast shear zone extending its known length by 350 km to more than 1200 km three sites along the shear zone in british columbia douglas channel bella coola and machmell river have similar histories during the period ca 65 55 ma the shear zone is 2 11 km thick and is defined by well developed mylonite zones that strike northwest and dip steeply northeast motion on the shear zone was predominantly reverse with the northeast side up synkinematic plutons are common in the shear zone lower plate rocks high grade gneiss derived from an ancient continental margin assemblage show little evidence of the extensive deformation and plutonism in the shear zone north of bella coola high grade gneiss forms the upper plate but to the south weakly metamorphosed rocks of stikinia compose the upper plate geochronologic data show that the shear zone was active between ca 60 and 55 ma at douglas channel ca 62 and 56 ma at bella coola and after 66 and before 56 ma near the machmell river these features match those of the coast shear zone in southeast alaska and adjacent british columbia together the shear zones formed a continental scale reverse ductile fault in paleocene time plate reconstructions show an oblique component to the dominantly dextral transcurrent paleocene margin partitioning of this motion across the continental margin produced a regional system of strike slip faults and contraction on the coast shear zone

stress gradient coupling in glacier flow i longitudinal averaging of the influence of ice thickness and surface slope for a glacier flowing over a bed of longitudinally varying slope the influence of longitudinal stress gradients on the flow is analyzed by means of a longitudinal flow coupling equation derived from the vertically cross sectionally integrated longitudinal stress equilibrium equation by an extension of an approach originally developed by budd 1968 linearization of the flow coupling equation by treating the flow velocity u vertically averaged ice thickness h and surface slope in terms of small deviations u h and a from overall average datum values u 0 h 0 and 0 results in a differential equation that can be solved by green s function methods giving u x as a function of h x and x x being the longitudinal coordinate the result has the form of a longitudinal averaging integral of the influence of local h x and x on the flow u x u x u0 2l l 0 ln n nh n l exp x x l dx where the integration is over the length l of the glacier the operator specified deviations from the datum state and the term on which it operates which is a function of the integration variable x represents the influence of local h x x and channel shape factor x at longitudinal coordinate x on the flow u at coordinate x the influence being weighted by the influence transfer function exp x x l in the integral the quantity l that appears as the scale length in the exponential weighting function is called the longitudinal coupling length it is determined by rheological parameters via the relationship l 2h n n 3n where n is the flowlaw exponent n the effective longitudinal viscosity and n the effective shear viscosity of the ice profile n is an average of the local effective viscosity n over the ice cross section and n 1 is an average of n 1 that gives strongly increased weight to values near the base theoretically the coupling length l is generally in the range one to three times the ice thickness for valley glaciers and four to ten times for ice sheets for a glacier in surge it is even longer l 12h it is distinctly longer for non linear n 3 than for linear rheology so that the flow coupling effects of longitudinal stress gradients are markedly greater for non linear flow the averaging integral indicates that the longitudinal variations in flow that occur under the influence of sinusoidal longitudinal variations in h or with wavelength are attenuated by the factor 1 1 2 l 2 relative to what they would be without longitudinal coupling the short intermediate and long scales of glacier motion raymond 1980 over which the longitudinal flow variations are strongly partially and little attenuated are for 2l 2l 20l and 20l for practical glacier flow calculations the exponential weighting function can be approximated by a symmetrical triangular averaging window of length 4l called the longitudinal averaging length the traditional rectangular window is a poor approximation because of the exponential weighting the local surface slope has an appreciable though muted effect on the local flow which is clearly seen in field examples contrary to what would result from a rectangular averaging window tested with field data for variegated glacier alaska and blue glacier washington the longitudinal averaging theory is able to account semi quantitatively for the observed longitudinal variations in flow of these glaciers and for the representation of flow in terms of effective surface slope values exceptions occur where the flow is augmented by large contributions from basal sliding in the ice fall and terminal zone of blue glacier and in the reach of surge initiation in variegated glacier the averaging length 4l that gives the best agreement between calculated and observed flow pattern is 2 5 km for variegated glacier and 1 8 km for blue glacier corresponding to l h 2 in both cases if l varies with x but not too rapidly the exponential weighting function remains a fairly good approximation to the exact green s function of the differential equation for longitudinal flow coupling in this approximation l in the averaging integral is l x but is not a function of x effects of longitudinal variation of l are probably important near the glacier terminus and head and near ice falls the longitudinal averaging formulation can also be used to express the local basal shear stress in terms of longitudinal variations in the local stope stress with the mediation of longitudinal stress gradients

the shallow ice approximation for anisotropic ice formulation and limits ice sheet flow modeling is generally based on the shallow ice approximation sia developed for isotropic ice we extend this approximation to anisotropic ice and check its validity for both the isotropic and anisotropic cases by comparing the results of up to second order sia with those obtained from a model solving the full set of mechanical equations the theory is developed for a constitutive relation describing newtonian and non newtonian behavior but numerical results are shown only for a newtonian behavior the results are compared for plane flow of isothermal ice under steady state conditions sia gives an excellent representation of the newtonian flow of an isotropic ice sheet and a good description for the anisotropic case the zero order approximation is sufficient to describe ice flow precisely over flat bedrock for the anisotropic and isotropic cases even close to an ice divide for uneven bedrock the second order sia gives excellent results for isotropic ice and acceptable results for anisotropic ice finally we quantify the error introduced by using an enhancement factor to represent the anisotropy when longitudinal stresses are taken into account

角閃石中のアルミニウム圧力計を使って決定された ワシントン州 stuart山バソリスの広域的傾動 バハ ブリティシュコロンビアの北方への転移に関する意味

an overview of the 2009 eruption of redoubt volcano alaska abstract in march 2009 redoubt volcano alaska erupted for the first time since 1990 explosions ejected plumes that disrupted international and domestic airspace sent lahars more than 35 km down the drift river to the coast and resulted in tephra fall on communities over 100 km away geodetic data suggest that magma began to ascend slowly from deep in the crust and reached mid to shallow crustal levels as early as may 2008 heat flux at the volcano during the precursory phase melted 4 of the drift glacier atop redoubt s summit petrologic data indicate the deeply sourced magma low silica andesite temporarily arrested at 9 11 km and or at 4 6 km depth where it encountered and mixed with segregated stored high silica andesite bodies the two magma compositions mixed to form intermediate silica andesite and all three magma types erupted during the earliest 2009 events only intermediate and high silica andesites were produced throughout the explosive and effusive phases of the eruption the explosive phase began with a phreatic explosion followed by a seismic swarm which signaled the start of lava effusion on march 22 shortly prior to the first magmatic explosion early on march 23 2009 utc more than 19 explosions or events were produced over 13 days from a single vent immediately south of the 1989 90 lava domes during that period multiple small pyroclastic density currents flowed primarily to the north and into glacial ravines three major lahars flooded the drift river terminal over 35 km down river on the coast tephra fall deposited on all aspects of the edifice and on several communities north and east of the volcano and at least two and possibly three lava domes were emplaced lightning accompanied almost all the explosions a shift in the eruptive character took place following event 9 on march 27 in terms of infrasound signal onsets the character of repeating earthquakes and the nature of tephra ejecta more than nine additional explosions occurred in the next two days followed by a hiatus in explosive activity between march 29 and april 4 during this hiatus effusion of a lava dome occurred whose growth slowed on or around april 2 the final explosion pulverized the very poorly vesicular dome on april 4 and was immediately followed by the extrusion of the final dome that ceased growing by july 1 2009 and reached 72 m m 3 in bulk volume the dome remains as of this writing effusion of the final dome in the first month produced blocky intermediate to high silica andesite lava which then expanded by means of lava injection beneath a fracturing and annealing cooling surface crust in the first week of may a seismic swarm accompanied extrusion of an intermediate to high silica andesite from the apex of the dome that was highly vesicular and characterized by lower p 2 o 5 content the dome remained stable throughout its growth period likely due to combined factors that include an emptied conduit system steady degassing through coalesced vesicles in the effusing lava and a large crater pit created by the previous explosions we estimate the total volume of erupted material from the 2009 eruption to be between 80 m and 120 m m 3 dense rock equivalent dre the aim of this report is to synthesize the results from various datasets gathered both during the eruption and retrospectively and which are represented by the papers in this publication we therefore provide an overall view of the 2009 eruption and an introduction to this special issue publication

earthquake swarms and dike intrusions off the east coast of izu peninsula central japan abstract relationships between earthquake swarms and dike intrusions are investigated in the monogenetic volcano region off the east coast of the izu peninsula central japan hypocentral distribution of an earthquake swarm associated with the 1989 ito oki submarine eruption and those of eight major earthquake swarms for 7 years before the eruption in the same region are precisely relocated comparison of the hypocentral distribution with a dike model obtained from crustal movement measurements by okada and yamamoto 1991 ensures that hypocentral areas of the earthquake swarms can be used as reliable indicators of intruded dikes the epicentral area of each earthquake swarm shows an elliptic shape with a 3 5 km long axis and a 2 4 km short axis the long axis trending from a nw se to wnw ese direction the total hypocentral distribution of the nine swarms forms a seismic zone of about 20 km long and about 5 km wide with each of the swarm areas overlapping focal migrations from deep 10 km to shallow 3 km depths are found in the two largest events in 1988 and 1989 indicating that dikes propagated from deep to shallow areas in the upper crust these features of the hypocentral distributions suggest that the seismic swarms were induced by dike intrusions which ascended from a deep seated magma reservoir with dike like geometry located beneath the seismic zone solidification time of a dike with thickness comparable to that of the dike model of okada and yamamoto 1 45 m at the bottom of the dike is several days indicating that the dikes inducing the earthquake swarms solidified almost during the swarm period the physical mechanisms of the dike induced earthquake swarms are investigated for the izu region the focal depth migration and fault type of the earthquake swarm suggest that stress change in the region surrounding the dike due to dike emplacement is the most important factor for the cause of the earthquakes

paleomagnetism and tectonic significance of albian and cenomanian turbidites ochoco basin mitchell inlier central oregon 1 understanding continental growth and convergent margin dynamics associated with terrane accretion and modification of the cordilleran margin of north america is prevented by conflicts in paleogeographic models for major terranes oceanic plates and the north american margin we present new paleomagnetic data suggesting that the blue mountains superterrane located at an inboard portion of the cordilleran margin has undergone substantial northward translation and clockwise rotation relative to north america since mid cretaceous time positive baked contact conglomerate and fold tests provide evidence that the magnetization of these rocks dates from their deposition these results yield a mean direction of d 10 8 i 58 5 k 127 95 4 1 and n 11 comparison of magnetic inclinations and magnetic fabrics shows no evidence for inclination error a paleolatitude of 39 2 4 8 4 3 n is obtained indicating a paleolatitude anomaly of 15 9 4 1 northward translation of 1760 460 km and cw rotation of 37 7 3 with respect to north america since circa 93 ma application of an ad hoc 5 inclination error yields translation of 1200 460 km through comparison with other units in the western cordillera we infer that the mitchell inlier was located adjacent to the sierra nevada arc during mid cretaceous time and that the blue mountains province may correlate with the intermontane superterrane in british columbia other interpretations such as large inclination errors or an independent displacement history for the mitchell inlier are possible but unlikely more work is needed to fully test these hypotheses and resolve major questions of cordilleran tectonics

ground based and uav based photogrammetry a multi scale high resolution mapping tool for structural geology and paleoseismology this contribution reviews the use of modern 3d photo based surface reconstruction techniques for high fidelity surveys of trenches rock exposures and hand specimens to highlight their potential for paleoseismology and structural geology we outline the general approach to data acquisition and processing using ground based photographs acquired from standard dslr cameras and illustrate the use of similar processing approaches on imagery from unmanned aerial vehicles uavs it is shown that digital map and trench data can be acquired at ultra high resolution and in much shorter time intervals than would be normally achievable through conventional grid mapping the resulting point clouds and textured models are inherently multidimensional x y z point orientation colour texture archival and easily transformed into orthorectified photomosaics or digital elevation models dems we provide some examples for the use of such techniques in structural geology and paleoseismology while pointing the interested reader to free and commercial software packages for data processing visualization and 3d interpretation photogrammetric models serve to act as an ideal electronic repository for critical outcrops and observations similar to the electronic lab book approach employed in the biosciences this paper also highlights future possibilities for rapid semi automatic to automatic interpretation of the data and advances in technology

compaction corrected paleomagnetic paleolatitudes for late cretaceous rudists along the cretaceous california margin evidence for less than 1500 km of post late cretaceous offset for baja british columbia the paleolatitudinal distribution of bivalve rudists has important significance for the baja british columbia baja bc hypothesis that western canadian superterranes from british columbia have been displaced 3000 km since cretaceous time rudists are not observed in baja bc sedimentary rocks yet they are common in late cretaceous strata in california and baja california which have the same paleomagnetically determined paleolatitudes approximately 25 n as baja bc rocks of late cretaceous age in order to resolve this contradiction and to delimit more exactly the southern paleolatitudes of baja bc paleomagnetic inclinations corrected for the effects of burial compaction were used to determine the paleolatitudinal distribution of rudists along the california margin compaction corrected paleomagnetic data from the peninsular ranges and salinia terranes indicate that rudists were restricted to paleolatitudes between 34 and 40 n evidence of coastal upwelling in the latest cretaceous marca shale may explain the northern limit of the rudist distribution these data suggest that baja bc was no farther south than 40 n in the late cretaceous thus limiting its post cretaceous displacement to less than 1500 km and that burial compaction has also affected the paleomagnetism of nanaimo group sedimentary rocks from vancouver island this result also helps resolve the conflict between paleomagnetic results which show 1500 km of post late cretaceous offset between the insular coast plutonic complex superterrane and the intermontane superterrane and geologic observations which can allow only tens of kilometers of offset between these terranes in the methow tyaughton basin

dike induced faulting in rift zones of iceland and afar geodetic data and field observations demonstrate that the emplacement of dikes in volcanic rift zones frequently generates normal faulting and graben subsidence at the earth9s surface elastic modeling of the vertical ground surface displacements above dikes and faults indicates that the extent of graben subsidence can be achieved only if fault slip extends virtually to or beyond the dike plane at depth a mechanical model that includes dikes and frictional faults shows that dike opening tends to compress and lock faults located to either side of the dike therefore slip extending into or beyond the dike cavity must occur either 1 on faults that intersect the dike near its top above the zone of dike induced compression or 2 on faults that slip ahead of the dike as it propagates laterally data from iceland indicate that slip occurred on deep faults that presumably slipped in advance of the laterally propagating dike

rapid cooling and exhumation in the western part of the mesoproterozoic albany fraser orogen western australia abstract the albany fraser orogen of southwestern australia is an understudied orogenic belt which is interpreted to record the mesoproterozoic suturing of the yilgarn craton of western australia to the mawson craton of east antarctica during rodinia assembly previous u pb geochronology has dated peak amphibolite to granulite facies metamorphism in the orogen at ca 1180 ma here we report the first 40ar 39ar thermochronology of hornblende biotite and muscovite grains from a 360 km transect across the western albany fraser orogen and uncover a record of strikingly fast syn orogenic cooling and exhumation to the north muscovites from the northern foreland record cooling at ca 1159 ma in the central and southern domains of the orogen the biranup and nornalup zones hornblende yields ca 1169 ma cooling ages and biotite yields ca 1172 1144 ma cooling ages the new cooling ages imply that the three domains were exhumed rapidly following peak metamorphism at ca 1180 ma attained a similar structural level by ca 1159 ma and have experienced a uniform exhumation history since that time to constrain mineral closure temperatures and post peak metamorphic cooling rates we conducted a monte carlo simulation which fully propagates uncertainty and minimises error correlations modelling of cooling from hornblende to biotite closure temperatures ca 585 c and 365 c respectively in the nornalup and biranup zones yields fast cooling rates of 33 9 17 c ma and 22 5 7 c ma respectively these fast cooling rates imply rapid exhumation in an active tectonic setting undergoing peak metamorphism although the structural evolution of the albany fraser orogen remains poorly constrained the transpressional tectonic activity associated with deformation in the western part of the albany fraser orogen may have been an active driver of this fast exhumation this is distinctly different from exhumation models for granulite facies domains in other mesoproterozoic orogens which typically experience post orogenic slow 1 5 c ma cooling driven by mechanisms such as orogenic collapse and erosion we consider that the observed differences reflect the interpreted syn tectonic transpressional exhumation history of the albany fraser orogen which is an underrepresented tectonic regime in the mesoproterozoic cooling record

sheeted intrusion of the synkinematic mcdoogle pluton sierra nevada california field microstructural and geochronologic evidence indicates that the late cretaceous mcdoogle pluton located near the eastern margin of the sierra nevada batholith was emplaced as a subvertically sheeted complex into a steep reverse sense shear zone evidence of internal subvertical sheeting includes abundant concordant wall rock inclusions and screens that separate the pluton from adjacent jurassic plutons preservation of a ghost tectonostratigraphy in the distribution of the inclusions and rare interphase contacts the solid state tectonic fabric in the wall rocks and the magmatic submagmatic and weak solid state fabrics in the mcdoogle pluton all are concordant and record northeast southwest horizontal shortening subvertical extension and a significant component of northeast side up simple shear intrusive contacts generally are concordant with the fabrics but where discordances occur the wall rock fabric invariably is truncated by the contact however late synkinematic emplacement of the mcdoogle pluton is indicated by synintrusive boudinage of apophyses of the pluton and by the overall concordance of pluton fabrics including magmatic lineation zircon u pb isotope dates were obtained from the quartz monzodiorite central phase of the mcdoogle pluton 94 4 ma the mafic granodiorite border phase 94 8 0 6 ma and an older hornblende granodiorite included in the central phase 97 6 0 4 ma granodiorite orthogneiss in the wall rock yielded a u pb zircon date of 164 2 1 6 8 ma which we interpret to be the crystallization age and which is indistinguishable from a new age of 164 5 2 3 ma for the twin lakes pluton a u pb titanite date of 94 4 0 9 ma from the 164 ma orthogneiss sample may reflect thermal effects of the intruding mcdoogle pluton synkinematic growth of titanite in the shear zone or perhaps both the age of the sawmill lake shear zone that hosts the mcdoogle pluton is bracketed between 148 ma the age of the independence dike swarm and 92 ma the age of the lamarck pluton that crosscuts both the mcdoogle pluton and the shear zone fabrics regional evidence suggests a shear zone age younger than 110 ma but older deformation is possible the predominance of horizontal shortening over transcurrent motion and an age older than 90 ma exclude a direct relationship to the dextral sierra crest shear system which has been proposed to pass near the study area the location age constraints and kinematics of the shear zone are consistent with both the later stages of movement in the east sierran thrust system and isostatic sinking of the arc magmatic complex into its substrate

pluton emplacement within an extensional transfer zone during dextral strike slip faulting an example from the late archaean abitibi greenstone belt abstract the lake abitibi area within the late archaean abitibi greenstone belt exhibits an interlinked plutonic structural and metamorphic evolution that may characterize segmented strike slip faults at upper to mid crustal levels along the major southeastward propagating macamic d 2 dextral strike slip fault theological and preexisting d 1 structural heterogeneities induced the development of nnw trending dextral oblique splays which evolved into an extensional trailing fan and created an extensional nnw dipping stepover magma flowing upwards from deeper parts of the macamic fault spread towards the southeast at upper crustal levels along both the oblique slip and extensional d 2 splays and built several plutons in a pull apart domain between 2696 and 2690 ma different emplacement and material transfer mechanisms operated simultaneously in different parts of the system including fault dilation and wedging lateral expansion wall rock ductile flow and stoping transfer of movement between d 2 splays occurred under ductile conditions during syn emplacement amphibolite grade metamorphism 500 700 c during cooling d 2 faults appear to have been closely linked during the superior province wide late transpressional event

deciphering shallow paleomagnetic inclinations 1 implications from correlation of albian volcanic rocks along the insular intermontane superterrane boundary in the southern canadian cordillera 1 geologic and paleomagnetic data lead to two contradictory hypotheses regarding the paleoposition of the insular and intermontane superterranes that presently constitute the western canadian cordillera paleomagnetic data from the insular and intermontane superterranes suggest a southerly origin coinciding with the latitude of mexico and the northwest united states respectively during the mid cretaceous geologic evidence points to a northerly origin for these same tectonic entities during this period both models cannot be correct geologic and paleomagnetic data from the empire valley churn creek area in south central british columbia 51 5 n 122 5 w are critical to resolving these contradictory hypotheses late cretaceous rocks correlated to the insular superterrane with large paleomagnetic displacements unconformably overlie mid cretaceous rocks correlative to the spences bridge group of the intermontane superterrane we provide paleomagnetic evidence of this correlation based on similar magnetic properties opaque mineral assemblages demagnetization behavior fold test results mean inclinations clockwise vertical axes rotations and statistically indistinguishable paleomagnetic poles and displacement estimates this correlation and the observed geologic relationships in the empire valley churn creek area indicate that the insular and intermontane superterranes were linked by the mid cretaceous sites from the two previous spences bridge group studies are combined with their correlatives in the empire valley churn creek area to give 81 sites that yield a paleomagnetic pole of 60 5 n 304 5 e dp 3 7 dm 5 5 which corresponds to 1050 450 km of displacement from the south this new displacement estimate suggests that the spences bridge arc formed at the latitude of southern oregon during the mid cretaceous

mapping folds and fractures in basement and cover rocks using uav photogrammetry cape liptrap and cape paterson victoria australia abstract brittle and ductile deformation of alternating layers of devonian sandstone and mudstone at cape liptrap victoria australia resulted in upright folds with associated fold accommodation faults and multiple fracture sets structures were mapped at the fold stack locality at cape liptrap using high resolution aerial photographs acquired by a digital camera mounted on an unmanned aerial vehicle uav subsequent photogrammetric modelling resulted in georeferenced spatial datasets point cloud digital elevation model and orthophotograph with sub cm resolution and cm accuracy which were used to extract brittle and ductile structure orientation data an extensive dataset of bedding measurements derived from the dense point cloud was used to compute a 3d implicit structural trend model to visualise along strike changes of devonian tabberabberan folds at the fold stack locality and to estimate bulk shortening strain this model and newly collected data indicate that first generation shallowly south southwest plunging upright folds were gently refolded about a steeply plunging subvertical fold axis during a devonian low strain north south shortening event this also led to the local tightening of first generation folds and possibly strike slip movement along regional scale faults in order to distinguish fractures associated with devonian compression from those that formed during cretaceous extension and later inversion we compared the five fracture sets defined at cape liptrap to previously mapped joints and faults within the overlying sedimentary cover rocks of the cretaceous strzelecki group gippsland basin which crop out nearby an east southeast trending fracture set that is not evident in the strzelecki group can be linked to the formation of devonian folds additionally hinge line traces extracted from the fold stack dataset are aligned parallel to a dominant fracture set within the overlying cover sediments this suggests that basement structures folds and coeval parallel faults have an important influence on fault and joint orientations within cretaceous cover rocks

deciphering shallow paleomagnetic inclinations 2 implications from late cretaceous strata overlapping the insular intermontane superterrane boundary in the southern canadian cordillera 1 significant discrepancies exist between paleomagnetic and geologic estimates of the timing and magnitude of terrane displacement in the southern canadian cordillera lithostratigraphic palynological geochronologic geochemical and structural data to which we add paleomagnetic data demonstrate that upper cretaceous strata in churn creek are laterally equivalent facies of the silverquick powell creek spc succession these rocks therefore comprise a single overlap sequence linking the insular and intermontane superterranes by late albian cenomanian time 95 ma contradicting previous assertions based solely on paleomagnetic interpretation that major 2000 km latitudinal displacement separated the two regions the churn creek succession retains primary magnetic remanence as demonstrated by positive fold conglomerate and contact tests the sediments do not hold the anisotropy signature of compaction shallowed inclinations the mean inclination of all spc sites from both mount tatlow and churn creek is 55 6 2 3 n 36 sites corresponding to a paleolatitude of 36 1 2 4 this reflects northward translation of the composite insular intermontane superterrane of 3050 450 km between 85 and 50 ma the silverquick powell creek succession at churn creek unconformably overlies the northern end of the spences bridge group a late early cretaceous volcanic arc assemblage on the intermontane superterrane paleomagnetic data in the companion paper place it 1050 450 km south of its current position between 100 and 105 ma integration of these new data sets require that the insular and intermontane superterranes formed a single enormous crustal block that underwent complex episodic south north translation between circa 105 and 50 ma the timing rate and vectors of translation are problematic in terms of geologic constraints along the continental margin

the geologic history of redoubt volcano alaska abstract redoubt volcano is a composite cone built on continental crust at the northeast end of the aleutian arc magmas erupted at redoubt are medium k calc alkaline basalts andesites and dacites the eruptive history of the volcano can be divided into four parts the early explosive stage early cone building stage late cone building stage and post glacial stage the most silicic products of the volcano were erupted during the early explosive stage about 0 888 ma and include pumiceous pyroclastic flow deposits block and ash flow deposits and a dome or shallow intrusive complex basalt and basaltic andesite lava flows and scoria and ash flows were produced during the early cone building stage which was underway by 0 340 ma during the late cone building stage andesitic lava flows and block and ash flows were emplaced airfall deposits produced during post glacial eruptions are silicic andesite in composition since the early cone building stage magmas have become progressively more silicic but none are as silicic as those in the early explosive stage limited pb and sr isotopic data suggest that redoubt magmas were contaminated by north american continental crust

the paleomagnetic effects of reheating the ecstall pluton british columbia abstract paleomagnetic data of plutons from the western canadian cordillera are currently interpreted to indicate thousands of kilometers of latitudinal transport in situ tilting or post intrusion folding for the ecstall pluton of british columbia the inclination of magnetic remanence directions steepens to the east from 16 to 81 butler et al j geophys res 107 2002 between 24 and 12 km west of a thermal boundary with the coast mountains batholith cmb the cmb was at 700 800 c between 60 and 52 ma the stable remanent magnetization is in ilmenohematite grains with exsolved lamellae of ferrian ilmenite it has the characteristic properties of lamellar magnetism robinson et al nature 418 2002 517 520 which is acquired with exsolution in ilmenohematite below 390 c ghiorso phys chem minerals 25 1997 28 38 thus it is thermal chemical remanent magnetization tcrm our heat flow calculations show that the thermal effects of eocene cmb on the adjacent 91 ma ecstall pluton were enough to reset the remanent magnetization directions reheating to the temperatures necessary for tcrm is supported by k ar and ar ar cooling dates on hornblende and biotite which young from west to east towards the cmb in concert with the change in inclinations thus the progressive steepening of magnetization inclinations is attributed to reheating during the eocene of the 91 ma ecstall pluton by the cmb this reheating followed post solidification northward latitudinal displacement of the pluton the amount of translational displacement of the coastal terranes of british columbia prior to 60 ma hinges on the interpretation of discordant magnetizations from plutons that may have cooled slowly after emplacement in the mid to lower crust as was the case for the ecstall pluton many of these plutons contain ilmenohematite as an accessory magnetic phase our interpretation for the low temperature acquisition of tcrm in the ecstall pluton may have far reaching implications for understanding enigmatic discordant paleomagnetic directions reported from plutons of the western canadian cordillera

insights into the mechanics of en echelon sigmoidal vein formation using ultra high resolution photogrammetry and computed tomography abstract two novel techniques photo based reconstruction photogrammetry and computed tomography ct are used to investigate the formation of an exceptional array of sigmoidal veins in a hand sample from cape liptrap southern victoria and to provide constraint on models for their development the accuracies of the photogrammetric models were tested by comparison with a laser scan generated three dimensional 3d model the photogrammetric model was found to be accurate to at least 0 25 mm and substantially more detailed than the laser scan a methodology was developed by which 3d structural measurements could be extracted from the photogrammetric model this was augmented with the ct model which through its capacity to elucidate internal structure was used to constrain the geometry and linkage of structures within the rock volume the photogrammetric and ct data were then combined with detailed photomicrographs to evaluate the evolution of the sigmoidal veins in the sample the angle between the sigmoidal vein margins and an inferred shear zone as well as the orientations of the crystal fibres were found to imply a rotation of 27 however coeval pressure solution seams and older veinlets in the rock bridges between the veins were only found to have rotated by 10 an observation not easily explained using existing models for sigmoidal vein formation a new model is proposed in which a significant component of sigmoidal vein geometry is due to localised dilation caused by slip on the pressure solution seams the process involves strain partitioning onto pressure solution seams which leads to exaggeration of sigmoidal vein geometries if not accounted for the apparent vein rotation due to slip partitioning introduces errors into calculations of simple shear and volume strain based on sigmoidal arrays of this type furthermore the ct data demonstrated that in 3d the veins are continuous and channel like implying a far higher degree of connectivity and fluid transport than is suggested by their 2d form

evidence from the ad 2000 izu islands earthquake swarm that stressing rate governs seismicity magma intrusions and eruptions commonly produce abrupt changes in seismicity far from magma conduits that cannot be associated with the diffusion of pore fluids or heat such swarm seismicity also migrates with time and often exhibits a dog bone shaped distribution the largest earthquakes in swarms produce aftershocks that obey an omori type exponential temporal decay but the duration of the aftershock sequences is drastically reduced relative to normal earthquake activity here we use one of the most energetic swarms ever recorded to study the dependence of these properties on the stress imparted by a magma intrusion a 1 000 fold increase in seismicity rate and a 1 000 fold decrease in aftershock duration occurred during the two month long dyke intrusion we find that the seismicity rate is proportional to the calculated stressing rate and that the duration of aftershock sequences is inversely proportional to the stressing rate this behaviour is in accord with a laboratory based rate state constitutive law suggesting an explanation for the occurrence of earthquake swarms any sustained increase in stressing rate whether due to an intrusion extrusion or creep event should produce such seismological behaviour

stress gradient coupling in glacier flow ii longitudinal averaging of the flow response to small perturbations in ice thickness and surface slope as a result of the coupling effects of longitudinal stress gradients the perturbations u in glacier flow velocity that result from longitudinally varying perturbations in ice thickness h and surface slope are determined by a weighted longitudinal average of h h and where h and are influence coefficients that control the size of the contributions made by local h and to the flow increment in the longitudinal average the values of h and depend on effects of longitudinal stress and velocity gradients in the unperturbed datum state if the datum state is an inclined slab in simple shear flow the longitudinal averaging solution for the flow perturbation is essentially that obtained previously kamb and echelmeyer 1985 with equivalent values for the longitudinal coupling length l and with h n l and n where n is the flow law exponent calculation of the influence coefficients from flow data for blue glacier washington indicates that in practice differs little from n whereas h can differ considerably from n 1 the weighting function in the longitudinal averaging integral which is the green s function for the longitudinal coupling equation for flow perturbations can be approximated by an asymmetric exponential whose asymmetry depends on two asymmetry parameters and where is the longitudinal gradient of l dl dx the asymmetric exponential has different coupling lengths l and l for the influences from up stream and from down stream on a given point of observation if is in the range 1 5 2 2 as expected for flow perturbations in glaciers or ice sheets in which the ice flux is not a strongly varying function of the longitudinal coordinate x then when dl dx 0 the down stream coupling length l is longer than the up stream coupling length l and vice versa when dl dx 0 flow thickness and slope perturbation data for blue glacier obtained by comparing the glacier in 1957 58 and 1977 78 require longitudinal averaging for reasonable interpretation analyzed on the basis of the longitudinal coupling theory with 4l 1 6 km up stream decreasing toward the terminus the data indicate n to be about 2 5 if interpreted on the basis of a response factor 0 85 derived theoretically by echelmeyer unpublished for the flow response to thickness perturbations in a channel of finite width the data contain an apparent indication that the flow response to slope perturbations is distinctly smaller in relation to the response to thickness perturbations than is expected on a theoretical basis i e h n n 1 for a slab this probably indicates that the effective l is longer than can be tested directly with the available data set owing to its limited range in x

volcano deformation and eruption forecasting recent advances in global positioning system gps tilt and interferometric synthetic aperture radar insar have greatly increased the availability of volcano deformation data these measurements combined with appropriate source models can be used to estimate magma chamber depth and to provide information on chamber shape and volume change however kinematic models cannot constrain magma chamber volume and provide no predictive

a one dimensional finite element model for two dimensional glacier flow on presente une description de la reduction des equations d equilibres 2d vers une forme 1d a travers la methodologie de kantorovich et on traite un exemple qui demontre la capacite du modele numerique a fournir des solutions en accord avec celles obtenues par les modeles a elements finis 2d

paleomagnetism of the mount stuart batholith revisited again what has been learned since 1972 we have collected 20 new paleomagnetic sites from the mount stuart batholith and the adjacent beckler peak stock using thermal and low temperature demagnetization and rock magnetic tests we have found that the remanence in most of the batholith is carried by single domain magnetite the mean of the new mount stuart batholith sites is d 354 2 i 46 2 k 87 2 a95 4 6 n 11 and is similar to those of the beck and noson 1972 and beck and others 1981 studies examination of ar geochronology of hornblende and biotite from the mount stuart batholith finds that the southern part of the batholith cooled through the blocking temperature of magnetite at 91 ma the northern part cooled through the blocking temperature of magnetite at 86 ma and of pyrrhotite at 83 ma from these combined results we conclude that the paleomagnetic directions from the southern part of the batholith were acquired within 0 5 to 1 0 ma of the time at which the ah barometers cooled below their closure temperature use of the ah barometry to establish paleohorizontal for these rocks is thus well justified correcting the mount stuart direction for the tilt indicated by the aluminum in hornblende ah barometry the mean becomes d 355 9 i 50 6 this result places the mount stuart batholith at a latitude of 31 3 3 8 3 4 n at 91 ma by identifying the carrier of remanence in the mount stuart batholith as being single domain sd magnetite we have removed the major remaining uncertainty in interpreting the paleomagnetism of these rocks the characteristic magnetization repeatedly found in the mount stuart rocks clearly supports the microplate tectonic model of beck and noson 1972 presently manifest as the baja british columbia baja bc hypothesis

high resolution modeling of the advance of the younger dryas ice sheet and its climate in scotland abstract ice sheet modeling tightly constrained by empirical studies provides an effective framework to reconstruct past climatic and environmental conditions scotland was severely affected by the abrupt climate change associated with the younger dryas stade during which an extensive ice sheet formed across the west highlands after a period of ice free conditions here a quasi three dimensional time dependent ice flow mass balance model is developed and applied to scotland at 1 km resolution the flow model is based on the driving stress approximation with an additional longitudinal correction term essential at this scale of operation surface mass balance is driven by temperature and precipitation changes and further mass wastage is achieved through an empirically defined calving term the ice dynamics and mass balance components are coupled through the equation for mass continuity which is integrated through time over a finite difference grid which yields the geometric evolution of the ice sheet initial experiments reveal the model to be relatively insensitive to internal parameters but highly sensitive to mass balance furthermore these experiments indicate that scotland is readily susceptible to glaciation with large glaciers building up on the flanks of ben nevis after a temperature depression of 2 5 c under present day precipitation the younger dryas is modeled using a grip temperature series locally adjusted for amplitude and a systematic series of runs enables the isolation of the climate which best matches mapped ice limits this optimum fit configuration requires an annual temperature cooling of 8 c and the introduction of substantial west east and south north precipitation gradients of 40 and 50 respectively to the present day regime under these conditions a series of substantial independent regional ice centers develop in agreement with trimline studies and after 550 years the modeled ice sheet closely resembles the maximum limits as indicated by field mapping however modeled ice continues to expand beyond 550 yr in conflict with the mapped ice limits which suggest a prolonged period of stability this discrepancy may be explained by the onset of extreme aridity ca 400 yr into the stade associated with a southern migration of the polar front leading to a reduction in atmospheric circulation which effectively starved the ice sheet of its moisture source preventing further expansion introduction of an additional 20 reduction in precipitation to the optimum fit regime after 350 yr brings the modeled ice sheet to equilibrium substantiating this conclusion

stresses and displacements in layered rocks induced by inclined cone sheets abstract currently the sheet intrusion paths and geometries including the sheet opening thickness as well as the depth to sheet tip are commonly determined from geodetic surface data using elastic dislocation models these models assume the volcanic zone central volcano to be an elastic half space of uniform mechanical properties field observations however show that volcanic zones volcanoes are composed of numerous layers whose mechanical properties primarily young s modulus vary widely here we provide new numerical models on the effects of a typical variation in young s modulus in an active volcanic zone central volcano on the internal and surface stresses and displacements induced by a sheet intrusion whose tip is arrested at a depth below the surface of 100 m the sheet has a dip dimension height of 2 km its opening thickness depends on the magmatic overpressure sheet dimension and host rock young s modulus for the values used here sheet thickness would be in the range of 0 5 1 4 m similar to commonly measured sheet thicknesses in the field the only loading is internal magmatic overpressure in the sheet of 5 mpa the modelled crustal segment volcano consists of 5 layers all with the same poisson s ratio 0 25 each of the 4 uppermost layers is 10 m thick layer 1 the top or surface layer has a young s modulus of 3 gpa layer 2 a modulus of 20 gpa layer 3 a modulus of 30 gpa and layer or unit 5 a modulus of 40 gpa we vary the young s modulus or stiffness of the fourth layer from 10 gpa to 0 01 gpa while the dip of the sheet takes the following values 30 45 60 for an inclined sheet and 90 for a dike the resulting displacement and stresses are highly asymmetric across the sheet tip except for the dike with the main surface stresses and displacements being above the dipping sheet and highest for the 30 dipping sheet for comparison three elastic half space models of the same sheet configuration and loading but uniform young s modulus in each model 40gpa 20gpa and 10 gpa all yield much higher surface stresses and displacements than any of the layered models as the stiffness of layer 4 decreases the surface stresses gradually decrease while changes in vertical displacements are comparatively small but greater in horizontal displacements in particular as the stiffness of layer 4 decreases from 10 gpa to 0 01 gpa for the 30 dipping sheet the maximum surface shear stress decreases from about 6 6 mpa to 2 2 mpa and the maximum tensile stress from about 6 9 mpa to about 2 3 mpa thus even a single comparatively thin 10 m soft layer close to the surface of a central volcano volcanic zone where such layers are almost universal may cause a great change in the maximum sheet induced stresses at the surface and thereby in any sheet induced fracture pattern furthermore the stress peaks in the layered models do not coincide with the displacement peaks fracture formation is most likely at the location of the stress peaks the results have important implications for the correct interpretation of geodetic data and fracturing during unrest periods with magma chamber rupture and sheet injection

stress gradient coupling in glacier flow iii exact longitudinal equilibrium equation the vertically integrated exact longitudinal stress equilibrium equation of budd 1970 is developed further in such a way as to yield an equation that gives explicitly and exactly the contributions to the basal shear stress made by surface and bed slope surface curvature longitudinal stress deviators and longitudinal stress gradients in a glacier flowing in plane strain over a bed of longitudinally varying slope with this exact equation questions raised by various approximate forms of the longitudinal equilibrium equation can be answered decisively and the magnitude of errors in the approximations can be estimated to first order in the angle that describes fluctuations in the surface slope from its mean value the exact equilibrium equation reduces to 1 2sin 2 b pghsin 2g t b k where g and t are the well known stress deviator gradient and variational stress terms k is a longitudinal curvature term and b is a basal drag term that contributes a resistance to sliding across basal hills and valleys except for t these terms are expressed in simple form and evaluated for practical situations the bed slope relative to the mean slope is not assumed to be small which allows the effects of bedrock topography to be determined particularly through their appearance in the b term

paleomagnetic and geobarometric study of the mid cretaceous whitehorse pluton yukon territory this is the first of several lithoprobe paleomagnetic studies underway to examine geotectonic motions in the northern canadian cordillera except for one controversial study estimates for terranes underlying the intermontane belt in the yukon have been extrapolated from studies in alaska southern british columbia and the northwestern united states the whitehorse pluton is a large unmetamorphosed and undeformed tonalitic body of mid cretaceous age 112 ma that was intruded into sedimentary units of the whitehorse trough in the stikinia terrane geothermobarometric estimates for eight sites around the pluton indicate that postmagnetization tilting has been negligible since cooling through the hornblende crystallization temperature and that the pluton is a high level intrusion paleomagnetic measurements for 22 of 24 sites in the pluton yield a well defined characteristic remanent magnetization chrm direction that is steeply down and northwards the chrm direction gives a paleopole of 285 5 e 81 7 n

polyphase brittle and ductile deformation of late jurassic ophiolitic basalt argillite matrix melange and stratigraphic overlap sequence northwestern washington state abstract a belt of jurassic to cretaceous ophiolitic rocks borders the western margin of the u s cordillera and stretches from central california to northwestern washington state the northern end of this belt lies between the san juan islands and the northwest cascades within this region ophiolitic rocks consist of a succession of oceanic and arc affinity igneous and sedimentary rocks which form a sedimentary melange and sedimentary overlap sequence which is imbricated during the mid cretaceous the melange contains blocks and olistoliths of peridotite plagiogranite chert basalt and volcanoclastic conglomerate which range in size from a meter to over 1 km and are contained within a matrix of argillite and volcanoclastic breccia and conglomerate peridotites were exposed to the sub aqueous surface along serpentinized shear zones prior to their incorporation into the melange and the sedimentary matrix of the melange underwent brittle deformation during the earliest stages of its structural history melange rocks are overlain in angular unconformity by a jura cretaceous arc sourced sedimentary succession which is at least 500 meters thick and passes upward from a basal breccia containing clasts of plagiogranite gabbro tonalite chert and basalt into argillite containing late jurassic radiolarians the argillite is overlain by poorly sorted greywacke and conglomerate with clast populations similar to those of the basal breccia the conglomerate fines upward into a massive to bedded feldspathic lithic arenite and greywacke that yields mid cretaceous detrital zircons the overlap succession and the melange are deformed by two generations of highly penetrative structures d1a and d1b which produced north to east vergent tight to isoclinal folds and axial planar pressure solution cleavages all units are further deformed by three generations of penetrative structures the successively younger nne to nw ne and e w to wnw trending folds have foliations that cross cut the earlier structural fabrics and faults formation of the melange required differential elevations during the time of deposition and the presence of rocks which are sourced from both arc and oceanic crust extension within the forearc provides a mechanism to exhume peridotites and generate differential topography for arc and oceanic affinity rocks to erode and be incorporated into the melange as part of olistostromal deposits

review of drones photogrammetry and emerging sensor technology for the study of dykes best practises and future potential abstract dykes play a major role in transporting magma through the crust to subsurface storage reservoirs or eruption sites at the surface the geometry connectivity and internal textures of dykes preserve an important record of dyke emplacement linkage and magma flow dynamics unravelling these facets of dyke evolution is critical to interpreting signals of magma migration in active volcanoes as well as tectonic processes including crust formation and continental break up during hazard assessment unfortunately our ability to develop new insights is limited by the continuity of high precision data that can be extracted from the field the emergence of unmanned aerial vehicles uavs a k a drones photogrammetry and other sensor techniques are set to greatly improve our field capabilities by collecting data at higher density and with greater precision here we present a workflow emphasising best practise in uav survey design the construction of photogrammetric models and standardised reporting of those models emphasis is given to the factors that should be considered in order to resolve the geological features of interest in any study e g wall rock fractures chilled margins magmatic breccias dyke apertures etc a point to raster technique is documented that measures spatial error in the rasters that are derived from photogrammetric models e g orthomosaics and digital elevation models using three case studies we show how dyke swarms can be mapped accurately over areas approaching 1 km2 at sub centimetre resolution the data illustrate how questions about dyke induced deformation host rock controls on segmentation and aperture variation may be addressed and we present a method for the high density high precision measurement of dyke apertures in 3d we also review semi automated mapping tools and emerging uav sensing techniques including hyperspectral and aeromagnetic sensors and the potentially important contributions they will make to the study of intrusive systems and volcanology more broadly

structural and geochemical interactions between magma and sedimentary host rock the hovedoya case oslo rift norway two end member conceptual models are used to describe deformation of the earth s crust induced by magma intrusion mode i fracturing assumes tensile or opening mode elastic deformation while mode ii fracturing assumes plastic shear mode deformation around a viscous indenter field observations of both mechanisms exist but it remains unclear which mechanism dominates in which conditions we describe intrusion geometries host rock deformation and geochemical magma host rock interactions around 53 exceptionally preserved tephrite basanite permian dike segments of 0 5 to 30 cm thickness these thin dikes that is dikelets intruded late ordovician carbonate rich sedimentary rocks on hovedoya island oslo rift norway dikelets emplaced in preexisting fractures dominantly created cavities ahead of their narrow tapering tips and are associated with bent host rock broken bridges and stepped segmented geometries other tips are blunt with dense brittle fracturing around them also cross sectional intrusion segment opening profiles deviate from parabola shaped profiles typical for elastic media the observations demonstrate that dominant opening mode host rock deformation can coexist with shear mode deformation locally alignment of most dikelet segments along the dominant host rock fracture directions highlights the control of local structural orientations on magma emplacement analysis of bulk major and trace element compositions in situ micro xrf sample analysis and carbon and oxygen stable isotope compositions suggests that thermochemical interactions between magma and the carbonate rich host rock produced a low viscosity mixture of magma pore water and gas we propose that such low viscosity hybrid fluid may assist in the intrusion of magma in sedimentary rocks by filling the cavity ahead of propagating sheet intrusion tips

semi automatic mapping of dyke and dyke related fractures using uav based photogrammetric data a case study from sijiao island coastal southeastern china abstract mapping dyke and dyke related fractures is important for magma propagation and emplacement mechanisms analysis here we propose a semi automatic workflow for dyke and fracture mapping using unmanned aerial vehicle uav based photogrammetric data our workflow integrates mean shift and grabcut in one cut gcoc algorithms to segment dykes and harnesses the phase symmetry algorithm and a series of follow up actions to detect fractures sijiao island of zhejiang province se china is examined as a case study to validate the approaches with our workflow the generated dyke map attains more than a 97 recall rate when compared with the results of expert interpretation and the ratio of the number of detected false fracture segments to the number of total segments is less than 18 the dyke strike and fracture strike calculation match well with field measurements moreover by combining visual interpretation and the resulting geometric information our results manifest that dyke magma invaded along pre existing fractures to form dykes on sijiao island and the difference between dyke fractures and host rock fractures may be because of the effect of major changes of regional stress this workflow has great potential for high resolution terrestrial mapping

geothermobarometry and fluid inclusions of dioritic rocks in bangladesh implications for emplacement depth and exhumation rate abstract application of hornblende thermobarometry and fluid inclusion studies to the palaeoproterozoic 1 7 ga basement rocks from maddhapara nw bangladesh provide information on the pressure and temperature p t conditions of crystallization the emplacement depth and composition of magmatic fluid the basement rocks are predominantly diorite or quartz diorite with a mineral assemblage of plagioclase hornblende biotite quartz k feldspar titanite and secondary epidote and chlorite the calculated p t conditions of the dioritic rocks are 680 725 c and 4 9 6 4 kbar which probably correspond to crystallization conditions fluid inclusion studies suggest that low to medium salinity 0 6 4 wt nacl eq h 2 o rich fluids are trapped during the crystallization of quartz and plagioclase the isochore range calculated for primary aqueous inclusions is consistent with the p t condition obtained by geothermobarometry the basement rocks likely crystallized at a depth of 17 22 km with a minimum average exhumation rate of 12 15 m ma during palaeoproterozoic to lopingian time such slow exhumation indicates low relief continental shield surface during this period

palaeomagnetic dating and tectonic significance of dolerite intrusions in the albany mobile belt western australia abstract dolerite dykes and sills in the mesoproterozoic albany mobile belt and neoproterozoic stirling range formation metasediments in southwestern australia provide evidence for extensional events between australia east antarctica and greater india paleomagnetic analysis shows that primary remanence was carried by single domain magnetite for samples from seven localities palaeomagnetic poles for the majority of sites fall close to the earliest cambrian part of the australian apparent polar wander path apwp the interpreted earliest cambrian dykes intrude both extensional dominant and shear fractures indicating nne ssw extension between the western australian and east antarctic shields and a horizontal ese wnw maximum compressive stress dyke emplacement appears to be contemporaneous with mafic volcanism in central and northern australia and igneous intrusion in once contiguous parts of the east antarctic shield these features are interpreted as being related to gondwanaland assembly and may represent a response to far field stresses resulting from the collision between east and west gondwanaland a second suite of nw striking mid carboniferous dykes is related to ne sw extension and rifting between greater india and the western australian shield during early stages in the formation of the perth basin in a sinistral transtensional regime along the southern western australian margin a palaeopole from the primary remanence in a nnw striking dolerite dyke falls on the poorly defined triassic to early cretaceous part of the australian apwp indicating a possible third phase of dyke emplacement regional tectonic constraints for rifting in the perth basin suggest that this youngest dyke most likely intruded during the triassic

evidence for dyke parallel shear during syn intrusion fracturing abstract dyke intrusion is a highly dynamic process with seismicity preceding and accompanying magma emplacement on timescales of hours to days recent surveys of microseismicity indicate shear failure along fault planes parallel to the orientation of intruding dykes however the precision of earthquake hypocentre locations is typically limited to tens or hundreds of meters and cannot resolve whether the hypocentres relate to strain of wall rock fragments within the dykes fault damage around the intrusions or peripherally in the country rock here we present high resolution three dimensional 3d reconstructions of outstanding coastal exposures of a swarm of 19 dolerite dykes near albany western australia using an unmanned aerial vehicle and structure from motion photogrammetry it is observed that the number of faults and joints increases towards the dyke swarm which alongside mutually overprinting relationships indicate that dyke emplacement and faulting were coeval the faults contain cataclasites and are parallel to the dykes in contrast mohr coulomb theory predicts shear failure on strike parallel faults inclined 30 to the dyke plane the faults and joints form a damage zone associated with the dyke swarm even though the dykes themselves occupy mode i extension fractures these results confirm the recent geophysical evidence for dyke parallel shear failure that can occur in the host rocks around intruding dykes we suggest that coeval dyke parallel seismicity both reactivated existing fracture networks and nucleated new fractures based on the premise that host rock fracturing induces changes in elastic properties remote stresses can reorientate locally leading to shear failure this model provides for the first time an explanation for the origin of double couple failure that is parallel in 3d strike and dip to dykes during their emplacement

evolution of the queen charlotte basin further paleomagnetic evidence of tertiary extension and tilting abstract the queen charlotte islands form the northwestern margin of the queen charlotte basin the basin which was formed by extension contains numerous mid tertiary lavas plutons and dykes referred to as the masset igneous complex and eocene to present marine and non marine sedimentary rocks throughout its history the basin has been bounded on the west by a north northwest oriented transform plate boundary the queen charlotte fault initially motion along this fault was transtensional phase 1 then more purely transform phase 2 and finally transpressive phase 3 most of the masset igneous complex appears to have been formed under transtension phase 1 middle eocene through early miocene previous paleomagnetic studies of the complex 129 sites mainly from the southern queen charlotte islands and new results herein 102 sites mainly from the northern islands illustrate magnetizations with inclinations generally steeper than those expected from coeval rocks of continental north america indicating north south extension segmentation and tilting of fault bound slivers along the western margin of the basin we argue that this north south extension occurred in phase 2 during the middle and or late miocene long after the main east west extension of phase 1 results from the northwest corner of the queen charlotte islands although commonly anomalous are not oversteepened and may delineate a structural domain separate from the rest of the archipelago as a by product this study provides two reference paleopoles for north america one for the late eocene early oligocene from ramsay island lavas 78 1 n 119 9 e a 95 7 0 and one of lesser reliability for the early miocene from the lavas of dinan bay 83 3 n 137 8 e a 95 9 8 a second by product is that the magnetic polarities and radiometric ages are consistent with the cande and kent global geomagnetic polarity time scale

emplacement of the final lava dome of the 2009 eruption of redoubt volcano alaska abstract after more than 8 months of precursory activity and over 20 explosions in 12 days redoubt volcano alaska began to extrude the fourth and final lava dome of the 2009 eruption on april 4 by july 1 the dome had filled the pre 2009 summit crater and ceased to grow by means of analysis and annotations of time lapse webcam imagery oblique image photogrammetry techniques and capture and analysis of forward looking infrared flir images we tracked the volume textural effusive style and temperature changes in near real time over the entire growth period of the dome the first month of growth april 4 may 4 produced blocky intermediate to high silica andesite lava 59 62 3 wt sio 2 that initially formed a round dome expanding by endogenous growth breaking the surface crust in radial fractures and annealing them with warmer fresh lava on or around may 1 more finely fragmented and scoriaceous andesite lava 59 8 62 2 wt sio 2 began to appear at the top of the dome coincident with increased seismicity and gas emissions the more scoriaceous lava spread radially over the dome surface while the dome continued to expand from endogenous growth and blocky lava was exposed on the margins and south side of the dome by mid june the upper scoriaceous lava had covered 36 of the dome surface area vesicularity of the upper scoriaceous lava range from 55 to 66 some of the highest vesicularity measurements recorded from a lava dome we suggest that the stability of the final lava dome primarily resulted from sufficient fracturing and clearing of the conduit by preceding explosions that allowed efficient degassing of the magma during effusion the dome was thus able to grow until it was large enough to exceed the magmastatic pressure in the chamber effectively shutting off the eruption

glacier volume estimation as an ill posed inversion estimating a glacier s volume by inferring properties at depth e g bed topography or basal slip from properties observed at the surface e g area and slope creates a calculation instability that grows exponentially with the size of the glacier random errors from this inversion instability can overwhelm all other sources of error and can corrupt thickness and volume calculations unless problematic short spatial wavelengths are specifically excluded volume area scaling inherently filters these short wavelengths and automatically eliminates the instability while numerical inversions can also give stable solutions by filtering the correct wavelengths explicitly as is frequently done when regularizing a model each of the scaling and numerical techniques has applications to which it is better suited and there are trade offs in resolution and accuracy but when calculating volume neither the modeling nor the scaling approach offers a fundamental advantage over the other both are significantly limited by the inherently ill posed inversion and even though both provide stable volume solutions neither can give unique solutions

dyke diatreme transition in monogenetic volcanoes insights from the hillier bay volcanic complex western australia the factors controlling phreatomagmatism and diatreme formation are still poorly constrained and understood here we describe the field relationships between mafic intrusions and volcaniclastic deposits observed at hillier bay western australia and discuss the implications for the formation of monogenetic basaltic volcanoes involving both phreatomagmatic and magmatic eruption phases the hillier bay volcanic complex consists of a series of basaltic sheeted dykelets and larger dykes injected within the metamorphic basement volcaniclastic lithologies also occur usually trapped between basaltic dykes and the basement these vary between mixtures of juvenile basaltic fragments metamorphic basement fragments and quartz feldspar sand in different relative amounts based on the textures of the clastic lithologies we argue that initial phreatomagmatic phases resulted from sequential injections of thin dykelets due to ascending magma struggling to open a path to the surface the relatively lower magma water ratio maximises the efficiency of premixing leading to phreatomagmatic explosions later as the main body of magma reaches the shallow conduit through wider dykes magma overcomes water availability and the eruption style switches to magmatic effusive this implies that magma flux may be a determining factor controlling eruption style in at least some monogenetic volcanoes

time scales of pluton construction at differing crustal levels examples from the mount stuart and tenpeak intrusions north cascades washington deciphering the magmatic history of continental magmatic arcs in general and the growth history of individual intrusions in particular is key to understanding the complex history of magma generation segregation and transport that define the dynamics of crustal growth we utilize high precision u pb geochronology to resolve a detailed magmatic history from two composite intrusions the 2 4 kbar mount stuart batholith and the 7 10 kbar tenpeak pluton emplaced in the cretaceous north cascades arc this temporal framework provides a way to evaluate models of pluton growth that explain common features of intrusions such as concentric compositional zoning and internal magmatic contacts u pb zircon crystallization ages were obtained from 12 samples of the mount stuart batholith and 8 samples of the tenpeak intrusion representing the range of compositional diversity and geographical extent these dates indicate that the mount stuart batholith was constructed over a 5 5 m y time period that was punctuated by four intervals of high magma flux the durations of the high flux periods are short a few hundred thousand years relative to the duration of the batholith the consistent pattern of magmatic fabrics and the lack of distinct contacts in the batholith may be explained by the juxtaposition of melt rich and mush zones with subtle contacts between mineralogically and texturally similar tonalite and time transgressive magma fabrics in contrast the tenpeak intrusion was constructed over a 2 6 m y time period with magma influx distributed throughout the intrusive history and texturally distinct magma bodies the tenpeak intrusion lacks distinct age domains which suggests that any magma reservoir was smaller in size and potentially more ephemeral although the distinct age domains and discrete compositional and textural phases indicate that pluton growth occurred incrementally neither pluton bears resemblance to a purely end member incremental growth model whereby a pluton is constructed from hundreds to thousands of discrete magma pulses that have little if any interaction in particular ages from the youngest domain of the mount stuart batholith indicate that a melt rich magma reservoir of 520 km 3 existed over a 170 90 k y time span

rethinking yellowstone in yukon and baja british columbia paleomagnetism of the late cretaceous swede dome stock northern canadian cordillera 1 paleomagnetic results obtained from the 69 8 ma swede dome stock emplaced into the pericratonic yukon tanana terrane ytt west of dawson yukon indicate a minimal northward translation of 360 575 km and a clockwise rotation of 20 23 with respect to north america in accord with the displacement of 425 km along the nearby tintina fault coeval carmacks group volcanics in contrast have previously indicated 1900 km northward translation and minimal rotation and have been proposed to be a displaced manifestation of the fixed yellowstone hot spot thus providing an independent estimate of the late cretaceous paleoposition of the baja british columbia terranes of western north america a compilation of recent mid and late cretaceous paleomagnetic results from the ytt and intermontane belt imb terranes reveals that the carmacks group paleomagnetic result is anomalous the ytt and imb terranes which form the bulk of baja british columbia appear instead to have experienced 1000 km northward translation with respect to north america since 70 ma consistent with geological estimates of motion along plausible accommodating faults in addition past mobility of the hawaii emperor hot spot implies that the pacific hot spots may have experienced 1200 km of southward motion from 81 to 47 ma if so then the paleoposition of the yellowstone hot spot if it existed at 70 ma would likely have produced the carmacks magmatism 1000 km north of yellowstone s current latitude consistent with a moderate 1000 km post 70 ma northward translation of the ytt and imb terranes to their present position in north america

stress transferred by the 1995 mw 6 9 kobe japan shock effect on aftershocks and future earthquake probabilities the kobe earthquake struck at the edge of the densely populated osaka kyoto corridor in southwest japan we investigate how the earthquake transferred stress to nearby faults altering their proximity to failure and thus changing earthquake probabilities we find that relative to the pre kobe seismicity kobe aftershocks were concentrated in regions of calculated coulomb stress increase and less common in regions of stress decrease we quantify this relationship by forming the spatial correlation between the seismicity rate change and the coulomb stress change the correlation is significant for stress changes greater than 0 2 1 0 bars 0 02 0 1 mpa and the nonlinear dependence of seismicity rate change on stress change is compatible with a state and rate dependent formulation for earthquake occurrence we extend this analysis to future mainshocks by resolving the stress changes on major faults within 100 km of kobe and calculating the change in probability caused by these stress changes transient effects of the stress changes are incorporated by the state dependent constitutive relation which amplifies the permanent stress changes during the aftershock period earthquake probability framed in this manner is highly time dependent much more so than is assumed in current practice because the probabilities depend on several poorly known parameters of the major faults we estimate uncertainties of the probabilities by monte carlo simulation this enables us to include uncertainties on the elapsed time since the last earthquake the repeat time and its variability and the period of aftershock decay we estimate that a calculated 3 bar 0 3 mpa stress increase on the eastern section of the arima takatsuki tectonic line attl near kyoto causes fivefold increase in the 30 year probability of a subsequent large earthquake near kyoto a 2 bar 0 2 mpa stress decrease on the western section of the attl results in a reduction in probability by a factor of 140 to 2000 the probability of a mw 6 9 earthquake within 50 km of osaka during 1997 2007 is estimated to have risen from 5 6 before the kobe earthquake to 7 11 afterward during 1997 2027 it is estimated to have risen from 14 16 before kobe to 16 22

the dynamic response of kennicott glacier alaska usa to the hidden creek lake outburst flood glacier sliding is commonly linked with elevated water pressure at the glacier bed ice surface motion during a 3week period encompassing an outburst of ice dammed hidden creek lake hcl at kennicott glacier alaska usa showed enhanced sliding during the flood two stakes 1 2 km from hcl revealed increased speed in two episodes both associated with uplift of the ice surface relative to the trajectory of bed parallel motion uplift of the surface began 12 days before the flood initially stabilizing at a value of 0 25m two days after lake drainage began further uplift reaching 0 4m occurred while surface speed peaked at 1 2md maximum surface uplift coincided with peak discharge from hcl high water level in a down glacier ice marginal basin and low solute concentrations in the kennicott river each of these records is consistent with high subglacial water pressure we interpret the ice surface motion as arising from sliding up backs of bumps on the bed which enlarges cavities and produces bed separation the outburst increased water pressure over a broad region promoting sliding inhibiting cavity closure and blocking drainage of solute rich water from the distributed system pressure drop upon termination of the outburst drained water from and depressurized the distributed system reducing sliding speeds expanded cavities then collapsed with a 1 day time scale set by the local ice thickness