surface stresses associated with arrested dykes in rift zones many theoretical models predict that arrested dykes may generate major grabens at rift zone surfaces arrested dyke tips in eroded rift zones however are normally not associated with major grabens or normal faults that could be generated by dyke induced stresses ahead of the tips and normal faults and grabens tend to be less common in those parts of eroded rift zones where dykes are comparatively abundant similarly there are feeder dykes as well as dykes arrested a few metres below the surface that do not generate faults or grabens at the surface here i propose that this discrepancy between theoretical models and field observations may be explained by the mechanical layering of the crust numerical models presented here show that abrupt changes in young s moduli layers with high dyke normal compressive stresses stress barriers and weak horizontal contacts have large effects on the dyke induced stress fields for the models considered the surface tensile stresses induced by arrested dykes are normally too small to lead to significant fault or graben formation at the rift zone surface the only significant dyke induced surface tensile stresses 2 mpa in these models are for a dyke tip arrested at 1 km depth below the surface of a rift zone with a weak contact at 400 m depth and subject to extension that tensile stress however peaks above the ends of the weak horizontal contact which in the model considered occur at distances of 4 km to either side of the dyke and shows no simple relation to the depth to the dyke tip thus for a layered crust with weak contacts straightforward inversion of surface geodetic data to infer dyke geometries may result in unreliable results

deep magma body beneath the summit and rift zones of kilauea volcano hawaii a magnitude 7 2 earthquake in 1975 caused the south flank of kilauea volcano hawaii to move seaward in response to slippage along a deep fault since then a large part of the volcano s edifice has been adjusting to this perturbation the summit of kilauea extended at a rate of 0 26 meter per year until 1983 the south flank uplifted more than 0 5 meter and the axes of both the volcano s rift zones extended and subsided the summit continues to subside these ground surface motions have been remarkably steady and much more widespread than those caused by either recurrent inflation and deflation of the summit magma chamber or the episodic propagation of dikes into the rift zones kilauea s magmatic system is therefore probably deeper and more extensive than previously thought the summit and both rift zones may be underlain by a thick near vertical dike like magma system at a depth of 3 to 9 kilometers

early cenozoic denudation of central west britain in response to transient and permanent uplift above a mantle plume upwelling mantle plumes beneath continental crust are predicted to produce difficult to quantify modest uplift and denudation the contribution of permanent and transient components to the uplift is also difficult to distinguish a pulse of denudation in britain in the early paleogene has been linked although with some controversy with the arrival of the proto iceland mantle plume in this contribution we show that combining apatite and zircon u th sm he and apatite fission track analyses from central west britain with numerical modeling clearly identifies a pulse of early cenozoic denudation the data indicate that rock uplift and denudation were centered on the northern east irish sea basin and 1 0 2 4 km of rocks were removed during the latest cretaceous early paleogene uplift and erosion appears to have started a few million years before the earliest magmatism in the region the regional denudation pattern mirrors the distribution of low density magmatic rocks that has been imaged in the deep crust however the injection of the underplating melt is not enough to account for the total denudation an additional regional uplift of at least 300 m is required which is consistent with a transient thermal effect from the hot mantle plume the rapid exhumation event ceased by 40 ma and the data do not require significant neogene exhumation

cenozoic vertical motions in the moray firth basin associated with initiation of the iceland plume 1 it is likely that the iceland mantle plume generated transient uplift across the north atlantic region when it initiated in earliest cenozoic time however transient uplift recorded in sedimentary basins fringing the region can be overprinted by the effects of permanent uplift identifying and quantifying transient uplift can only be achieved in areas which have a well constrained stratigraphic record and across which the relative importance of permanent and transient uplift varies e g the moray firth basin north sea by analyzing the subsidence of 50 boreholes from the moray firth basin mfb residual vertical motions unrelated to rifting have been isolated transient uplift of 180 425 m occurred during paleocene times the western mfb has also been affected by permanent cenozoic uplift with denudation decreasing from 1 3 0 1 km in the west of the basin to zero denudation east of 1 w dynamic support above the iceland plume led to transient uplift of the entire mfb in early paleocene times peaking in latest paleocene times in early eocene times the effect of the plume waned and subsidence occurred paleocene permanent uplift of the nw british isles is generally accepted to have been due to magmatic underplating of the crust emplaced during the british tertiary igneous province 61 58 5 ma the cause of neogene uplift events is poorly understood but it could also be associated with the iceland plume citation mackay l m j turner s m jones and n j white 2005 cenozoic vertical motions in the moray firth basin associated with initiation of the iceland plume tectonics 24 tc5004 doi 10 1029 2004tc001683

transformation of pyrite to pyrrhotite in the presence of au ag alloys at 500 c dry annealing of au x ag 1 x alloys 0 19 0 35 0 56 or of fineness 300 500 700 and pyrite was used to reveal the solubility of au ag in fes 2 and study phase equilibria in the fes 2 au x ag 1 x system at 500 c pyrrhotite acanthite and uytenbogaardtite and au ag alloys with increased fineness were established at the contacts of pyrite blocks with au ag plates the obtained results evidence the absence of solubility between fes 2 and au ag at 500 c the ag content in alloys influences the stability of pyrite and contributes to its transformation in pyrrhotite and sulfidation and ennobling of au ag alloys au ag sulfides and pyrrhotite may be present in the sulfide ores of metamorphogene deposits as annealing products of au ag pyrite bearing ores

reply to comment by hillis et al 2013 we agree that there is now convincing evidence which favours the idea that a region encompassing the british isles is dynamically supported by convective circulation beneath the lithospheric plate for example the coincidence of a long wavelength 800 km free air gravity anomaly with anomalously slow velocities beneath the lithospheric plate suggests that regional elevation of northern britain is maintained by a tongue of hot asthenosphere protruding away from iceland jones et al 2002a arrowsmith et al 2005 these observations are corroborated by the crustal thickness measurements of davis et al 2012 the icelandic plume initiated 62 ma and there is excellent evidence in the irminger and icelandic basins that this plume has waxed and waned with different periodicities jones et al 2002b poore et al 2009 this transient activity has manifest itself in geochemical and earthquake records along the reykjanes ridge poore et al 2011 parnell turner et al 2013 in the neogene record of deep water overflow across the greenland scotland ridge poore et al 2006 and along the fringing continental margins where spectacular buried ephemeral landscapes have been encountered shaw champion et al 2008 rudge et al 2008 hartley et al 2011 around the british isles there is considerable onshore and offshore evidence favouring a history of transient and or permanent vertical motions which may reflect palaeogene and neogene plume activity white lovell 1997 jones et al 2001 jones et al 2002a al kindi et al 2003 jones white 2003 mackay et al 2005 this regional pattern of epeirogeny is locally complicated by faulting and folding which is often difficult to date with precision

spatiotemporal model of kīlauea s summit magmatic system inferred from insar time series and geometry free time dependent source inversion k lauea volcano hawai i island has a complex magmatic system including summit reservoirs and rift zones kinematic models of the summit reservoir have so far been limited to first order analytical solutions with pre determined geometry to explore the complex geometry and kinematics of the summit reservoir we apply a multitrack wavelet based insar interferometric synthetic aperture radar algorithm and a novel geometry free time dependent modeling scheme to map spatiotemporally distributed surface deformation signals over k lauea s summit we process sar data sets from two overlapping tracks of the envisat satellite including 100 images during the period 2003 2010 following validation against global positioning system gps data we invert the surface deformation time series to constrain the spatiotemporal evolution of the magmatic system without any prior knowledge of the source geometry the optimum model is characterized by a spheroidal and a tube like zone of volume change beneath the summit and the southwest rift zone at 2 3 km depth respectively to reduce the model dimension we apply a principal component analysis pca scheme which allows for the identification of independent reservoirs the first 3 pcs explaining 99 63 8 28 5 and 6 6 respectively of the model include six independent reservoirs with a complex interaction suggested by temporal analysis the data and model presented here in agreement with earlier studies improve the understanding of k lauea s plumbing system through enhancing the knowledge of temporally variable magma supply storage and transport beneath the summit and verify the link between summit magmatic activity seismicity and rift intrusions

comparison of modern and geological observations of dynamic support from mantle convection the topographies of africa and antarctica form patterns of interlocking swells the relationship between topography and gravity indicates that these swells are dynamically supported by mantle convection with swell diameters of 1850 450 km and full heights between 800 and 1800 m the implication is that mantle convection not only supports swells surrounding hotspots but also influences topography across the entire surface areas of africa and antarctica we investigate whether dynamically supported swells are also observed throughout the geological record focusing on intensively studied mesozoic cenozoic sedimentary rocks around britain and ireland vertical motions of britain and ireland a typical piece of continental lithosphere far from a destructive plate boundary have been demonstrably affected by dynamic support for over half of the past 200 ma period the diameters and maximum heights of the mesozoic british swells and the modern african and antarctic swells are similar the ancient british swells grew in 5 10 ma and decayed over 20 30 ma suggesting vertical motion rates comparable with those estimated from geomorphological studies of africa igneous production rate and swell height are not correlated in the modern and the geological records mantle convection should be considered as a common control on regional sea level

formation and interpretation of dilatant echelon cracks the relative displacements of the walls of many veins joints and dikes demonstrate that these structures are dilatant cracks we infer that dilatant cracks propagate in a principal stress plane normal to the maximum tensile or least compressive stress arrays of echelon crack segments appear to emerge from the peripheries of some dilatant cracks breakdown of a parent crack into an echelon array may be initiated by a spatial or temporal rotation of the remote principal stresses about an axis parallel to the crack propagation direction near the parent crack tip a rotation of the local principal stresses is induced in the same sense but not necessarily through the same angle incipient echelon cracks form at the parent crack tip normal to the local maximum tensile stress further longitudinal growth along surfaces that twist about axes parallel to the propagation direction realigns each echelon crack into a remote principal stress plane the walls of these twisted cracks may be idealized as helicoidal surfaces an array of helicoidal cracks sweeps out less surface area than one parent crack twisting through the same angle thus many echelon cracks grow from a single parent because the work done in creating the array as measured by its surface area decreases as the number of cracks increases in cross sections perpendicular to the propagation direction echelon cracks grow laterally each crack overlapping its neighbors until the mechanical interaction of adjacent cracks limits this growth dilation of each crack pinches the tips of adjacent cracks into an asymmetrical form and introduces local stresses that can cause lateral growth along a curving sigmoidal path sigmoidal echelon cracks may link at tip to plane intersections leaving a step in the through going crack wall the geometry of dilatant echelon cracks may be used to infer spatial or temporal changes in the orientation of principal stresses in the earth

long term versus short term deformation processes at tenerife canary islands 1 several geophysical investigations have identified that the tenerife volcanic complex is affected by crustal deformation processes occurring at timescales of millions of years recently space based geodetic observations have also detected a short term surface deformation characterized by a broad subsidence pattern with maximum ground velocities of about 4 mm yr 1 for the purpose of investigating the relationship between these long term and short term deformation processes we performed an advanced fluid dynamic analysis fda we first carried out a standard dimensionless fda to discriminate the deformation style of tenerife and found that at million year timescales basement flexure mainly controls its long term structural evolution secondly to highlight the driving forces of the short term deformation process we simulated a numerical fda based on finite element models that include topography as well as vertical and lateral material heterogeneities our results show that the recent surface deformation is mainly caused by a progressive sagging of the denser less viscous core of the island onto the weaker but more viscous lithosphere moreover over periods comparable to the hypothesized age of loading of the oceanic crust beneath tenerife this tendency would result in a total flexure of about 3 4 km which is in agreement with independent estimations based on geophysical analyses our study shows that a unitary physical model may explain both the deformation recorded in deep geological structures and the current active ground deformation processes occurring at the tenerife volcano

linking paleogene denudation and magmatic underplating beneath the british isles a simple flexural model is used to explore the relationship between magmatic underplating and denudation first we show how denudation can be calculated as a function of underplating the distribution and density of underplate are obviously important parameters in determining the wavelength and amplitude of denudation however the denudational pattern can be considerably modulated by the flexural rigidity of the lithosphere several other parameters also play a significant role for example we show how variations in pre existing bathymetry and in present day topography affect denudational calculations we have applied our simple algorithm to the problem of paleogene underplating beneath the british isles forward and inverse modelling of travel time data from a wide angle seismic experiment which traversed the british isles suggests that a large pod of high velocity material occurs at moho depths beneath the irish sea the shape and inferred density of this pod are used to calculate the amplitude and wavelength of denudation for different flexural rigidities we compare our predictions with the observed pattern of paleogene denudation and conclude that the bulk of the observed denudation can be accounted for by magmatic underplating associated in a general way with the iceland plume notwithstanding this agreement there is compelling evidence for additional mild uplift events especially during the neogene these mild events may reflect fluctuating dynamic topography associated with the iceland plume

time dependent dike propagation from joint inversion of seismicity and deformation data dike intrusions both deform earth s surface and induce propagating earthquake swarms we develop methods to utilize both deformation and seismicity from brittle volcano tectonic earthquakes to image time dependent dike propagation dieterich s 1994 seismicity rate theory is used to relate dike induced stress changes to seismicity rate and is combined with elastic green s functions relating dike opening to deformation different space time patterns of seismicity develop if earthquakes occur at the same depth as the dike compared to above below the dike in the former seismicity initiates near the dike s leading edges but shuts off as the dike tips pass and seismogenic volumes fall into stress shadows in the latter seismicity continues at a decaying rate after the tips pass we focus on lateral propagation and develop a nonlinear inversion method that estimates dike length and pressure as a function of time the method is applied to the 2007 father s day intrusion in kilauea volcano seismicity is concentrated at 3 km depth comparable to geodetic estimates of dike depth and decays rapidly in time with lateral propagation only and a vertical dike tip line it is difficult to fit both gps data and the rapid down rift jump in seismicity suggesting significant vertical propagation for the events to have occurred below the dike requires a very short aftershock decay time hence unreasonably high background stressing rate the rapid decay is better explained if the dike extends somewhat below the seismicity we suggest that joint inversion is useful for studying the diking process and may allow for improved short term eruption forecasts

effects of loads in the upper crust on estimates of the elastic thickness of the lithosphere summary the admittance function and coherence relating gravity and topography are important constraints on the elastic thickness te of the lithosphere forsyth 1985 modelled them with a lithosphere loaded both externally by topography and internally by density contrasts such as initial undulations on the moho his approach has yielded thicknesses as high as 150 km for the continental lithosphere mckenzie fairhead 1997 argued that this method can only supply an upper bound on te because the response is biased by noise due to density variations in the upper crust we have used forsyth s approach to analyse the effect of shallow heterogeneities such as sedimentary basins and igneous intrusions simulating them by a thin layer with a laterally variable density the information content of the admittance and coherence is concentrated in the wavenumbers at which the two responses roll off to half their zero wavenumber values these two parameters are used to explore the interdependence of the retrieved elastic thickness and internal external loading ratio f provided the internal load is less than 10 per cent of the external it does indeed bias the response so that te is overestimated however for predominantly internal loads the reverse is the case and the value of te obtained by assuming equal internal and external loads is actually a lower bound it is particularly important to allow for the flexure due to upper crustal loads when the lithosphere is old and topography subdued due to prolonged erosion application of our approach to mckenzie fairhead s 1997 western australia data shows that the loading ratio depends strongly on wavenumber but that it is still possible to use the response data to constrain te which must be at least 90 km if the results obtained by conventional spectral estimation are accepted at least 40 km using the multitaper method

mechanical response of the south flank of kilauea volcano hawaii to intrusive events along the rift systems abstract increased earthquake activity and compression of the south flank of kilauea volcano hawaii have been recognized by previous investigators to accompany rift intrusions we further detail the temporal and spatial changes in earthquake rates and ground strain along the south flank induced by six major rift intrusions which occurred between december 1971 and january 1981 the seismic response of the south flank to individual rift intrusions is immediate the increased rate of earthquake activity lasts from 1 to 4 weeks horizontal strain measurements indicate that compression of the south flank usually accompanies rift intrusions and eruptions emplacement of an intrusion at a depth greater than about 4 km such as the june 1982 southwest rift intrusion however results in a slight extension of the subaerial portion of the south flank horizontal strain measurements along the south flank are used to locate the january 1983 east rift intrusion which resulted in eruptive activity the intrusion is modeled as a vertical rectangular sheet with constant displacement perpendicular to the plane of the sheet this model suggests that the intrusive body that compressed the south flank in january 1983 extended from the surface to about 2 4 km depth and was aligned along a strike of n66 e the intrusion is approximately 11 km in length extended beyond the january 1983 eruptive fissures which are 8 km in length and is contained within the 14 km long region of shallow rift earthquakes

evolution of dike opening during the march 2011 kamoamoa fissure eruption kīlauea volcano hawai i 1 the 5 9 march 2011 kamoamoa fissure eruption along the east rift zone of k lauea volcano hawai i followed months of pronounced inflation at k lauea summit we examine dike opening during and after the eruption using a comprehensive interferometric synthetic aperture radar insar data set in combination with continuous gps data we solve for distributed dike displacements using a whole k lauea model with dilating rift zones and possibly a deep decollement modeled surface dike opening increased from nearly 1 5 m to over 2 8 m from the first day to the end of the eruption in agreement with field observations of surface fracturing surface dike opening ceased following the eruption but subsurface opening in the dike continued into may 2011 dike volumes increased from 15 to 16 to 21 million cubic meters mcm after the first day eruption end and 2 months following respectively dike shape is distinctive with a main limb plunging from the surface to 2 3 km depth in the up rift direction toward k lauea s summit and a lesser projection extending in the down rift direction toward pu u at 2 km depth volume losses beneath k lauea summit 1 7 mcm and pu u 5 6 mcm crater relative to dike plus erupted volume 18 3 mcm yield a dike to source volume ratio of 2 5 that is in the range expected for compressible magma without requiring additional sources inflation of k lauea s summit in the months before the march 2011 eruption suggests that the kamoamoa eruption resulted from overpressure of the volcano s magmatic system

mechanical models for dikes a third school of thought abstract geological and geophysical data from continental volcanic centers and giant radial swarms and from oceanic shield volcanoes and rift zones indicate that dikes propagate laterally for distances that can be 10 to over 100 times their height what traps dikes within the shallow lithosphere and promotes these highly eccentric shapes gravity induced stress gradients in the surrounding rock and pressure gradients in the magma are the primary loading mechanisms pressure gradients due to magma flow are secondary to insignificant because the flow direction is dominantly horizontal this configuration of vertical blade shaped dikes with horizontal dike propagation and magma flow is fundamentally different from the two dike model configurations described in a recent review paper as two schools of thought for mechanical models of dikes in school i a dike is disconnected from its source and ascends under the influence of buoyancy in school ii a dike is connected to a magma reservoir and is driven upward by magma flux from the source we review the geological and geophysical data supporting the vertical dike horizontal flow propagation configuration and suggest the abundance and veracity of these data in many different geological settings and the modeling results that address this physical process warrant adding this as a third school of thought a new analytical solution for the boundary value problem of a homogeneous isotropic and linear elastic solid with a vertical fluid filled crack is used to investigate the effects of gravitationally induced stress and pressure gradients on the aperture distribution dike tip stress intensity and stable height model results indicate that in a homogeneous crust dikes can achieve stable heights greater than a kilometer only if the host rock fracture toughness k ic 100 mpa m 1 2 however density stratification of the crust is an effective mechanism for trapping kilometer scale dikes even if the host rock is very weak k ic 0 this analysis may explain why vertical dikes propagate laterally for great distances but reside within a narrow range of depths in the crust

rapid deformation of kilauea volcano global positioning system measurements between 1990 and 1996 campaign global positioning system gps measurements from 1990 to 1996 are used to calculate surface displacement rates on kilauea volcano hawaii the gps data show that the south flank of the volcano which has generated several large earthquakes in the past 3 decades is displacing at up to 8 cm yr to the south southeast the summit and rift zones are subsiding with maximum subsidence rates of 8 cm yr observed a few kilometers south of the summit caldera elastic dislocation modeling of the gps data suggests that the active sources of deformation include deep rift opening along the upper east and east rift zone fault slip along a subhorizontal fault near the base of the volcano and deflation near the summit caldera a nonlinear optimization algorithm was used to explore the parameter space and to find the best fitting source geometry there is a broad range of model geometries that fit the data reasonably well however certain models can be ruled out including those that have shallow rift opening or shallow fault slip some offshore aseismic slip on a fault plane that dips between 258 north northwest and 88 south southeast is required best fitting slip and rift opening rates are 23 28 cm yr although rates as low as 10 cm yr are permitted by the data

an assessment of the accuracy of admittance and coherence estimates using synthetic data previous work has shown that estimates of the admittance between topography and free air gravity anomalies are often biased by spectral leakage even after the application of multiple prolate spheroidal wavefunction data tapers despite this a number of authors who have used the free air admittance method to estimate the weighted average effective elastic thickness of the lithosphere te and to identify topography supported by mantle convection have not tested their methods using synthetic data with a known relationship between topography and gravity in this paper i perform a range of such tests using both synthetic surface data and synthetic line of sight los accelerations of satellites orbiting around an extra terrestrial planet it is found that spectral leakage can cause the estimated admittance and coherence to be significantly in error but only if the box in which they are estimated is too small the definition of small depends on the redness of the gravity spectrum there is minimal error in the whole box weighted average estimate of te if the admittance between surface gravity and topography is estimated within a box at least 3000 km wide when the synthetic uniform te is less than 20 km and the coherence is high the errors in te are mostly 5 km for all box sizes greater than 1000 km on the other hand when the true te is greater than 20 km and the box size is 1000 km the best fitting te is likely to be at least 5 10 km less than the true te however even when the coherence is high it is not possible to use elastic plate admittance models to distinguish between real and spurious small fractions of internal loading when the boxes are smaller than 2000 km in width noise in the gravity introduces error and uncertainty but no additional bias into the estimates of the admittance it does however bias estimates of te calculated using the coherence between bouguer gravity and topography the admittance at wavelengths between 1000 and 4000 km which is of interest when studying mantle convection is only well resolved when the box size is larger than 2000 km or the synthetic te is less than 15 km and the true long wavelength admittance is greater than 30 mgal km 1 when the box size is 1000 km it is not possible to distinguish between real and spurious convective support of long wavelength topography at the altitude of most orbiting satellites 200 400 km gravity is much redder than it is at ground level therefore it is necessary to use much larger boxes when using los accelerations to estimate the admittance than it is when using surface measurements however gradual changes in the altitude of the satellite or even occasional sudden changes make almost no difference to the estimate of the admittance finally three short investigations are undertaken concerning the effect on the admittance of the application of irregular windows to the data of lateral variations in te and of the infilling of flexural moats by low density sediment it is found that the bias due to the application of an irregular window is not significantly greater than the bias due to the application of a regular window of similar size that the best fitting te is strongly biased by the value associated with the highest amplitude topography and that sediment infill raises the admittance at wavelengths corresponding to the width of the moat

regional uplift associated with continental large igneous provinces the roles of mantle plumes and the lithosphere the timing and duration of surface uplift associated with large igneous provinces provide important constraints on mantle convection processes here we review geological indicators of surface uplift associated with five continent based magmatic provinces emeishan traps 260 million years ago ma siberian traps 251 ma deccan traps 65 ma north atlantic phase 1 61 ma and phase 2 55 ma and yellowstone 16 ma to recent all five magmatic provinces were associated with surface uplift surface uplift can be measured directly from sedimentary indicators of sea level in the north atlantic and from geomorpholocial indicators of relative uplift and tilting in yellowstone in the other provinces surface uplift is inferred from the record of erosion in the deccan north atlantic and emeishan provinces transient uplift that results from variations in thermal structure of the lithosphere and underlying mantle can be distinguished from permanent uplift that results from the extraction and emplacement of magma transient surface uplift is more useful in constraining mantle convection since models of melt generation and emplacement are not required for its interpretation observations of the spatial and temporal relationships between surface uplift rifting and magmatism are also important in constraining models of lip formation onset of surface uplift preceded magmatism in all five of the provinces biostratigraphic constraints on timing of uplift and erosion are best for the north atlantic and emeishan provinces where the time interval between significant uplift and first magmatism is less than 1 million years and 2 5 million years respectively rifting post dates the earliest magmatism in the case of the north atlantic phase 1 and possibly in the case of siberia the relative age of onset of offshore rifting is not well constrained for the deccan and the importance of rifting in controlling magmatism is disputed in the emeishan and yellowstone provinces in these examples rifting is not a requirement for onset of lip magmatism but melting rates are significantly increased when rifting occurs models that attempt to explain emplacement of these five lips without hot mantle supplied by mantle plumes often have difficulties in explaining the observations of surface uplift rifting and magmatism for example small scale convection related to craton or rift boundaries edge driven convection cannot easily explain widespread 1000 km scale transient surface uplift emeishan deccan north atlantic and upper mantle convection initiated by differential incubation beneath cratons the hotcell

an analysis of cotswold topography insights into the landscape response to denudational isostasy we have used the nextmap britain digital terrain model dtm to determine the lithospheric response to erosional unloading and the contribution of tectonics in the form of elastic plate flexure to the cotswold scarp and vale landscape the calculations take into account lithology variations and along strike changes in escarpment retreat we show that flexural rock uplift as a result of erosional unloading varies spatially and may contribute up to 50 of the relief in the cotswold region this is supported by morphometric analysis of concavity and steepness for 66 longitudinal river profiles that drain the scarp and dip slope of the escarpment viscoelastic plate models suggest that the uplift is initially rapid up to 8 m ka 1 and essentially complete within 50 ka these initial rates are compatible with an early post anglian incision rate inferred from the thames terraces the staircase terrace pattern suggests however that there have been a number of denudational isostatic events each associated with a climate cycle finally the analysis reveals an inherited proto landscape that has a subdued relief when compared with the modern dtm such a relief is consistent with an early extension of the river thames through the vale of moreton to the north of the present day cotswold hills

measuring plume related exhumation of the british isles in early cenozoic times mantle plumes have been proposed to exert a first order control on the morphology of earth s surface however there is little consensus on the lifespan of the convectively supported topography here we focus on the cenozoic uplift and exhumation history of the british isles while uplift in the absence of major regional tectonic activity has long been documented the causative mechanism is highly controversial and direct exhumation estimates are hindered by the near complete absence of onshore post cretaceous sediments outside northern ireland and the truncated stratigraphic record of many offshore basins two main hypotheses have been developed by previous studies epeirogenic exhumation driven by the proto iceland plume or multiple phases of cenozoic compression driven by far field stresses here we present a new thermochronological dataset comprising 43 apatite fission track aft and 102 u th sm he ahe dates from the onshore british isles inverse modelling of vertical sample profiles allows us to define well constrained regional cooling histories crucially during the paleocene the thermal history models show that a rapid exhumation pulse 1 2 5 km occurred focused on the irish sea exhumation is greatest in the north of the irish sea region and decreases in intensity to the south and west the spatial pattern of paleocene exhumation is in agreement with the extent of magmatic underplating inferred from geophysical studies and the timing of uplift and exhumation is synchronous with emplacement of the plume related british and irish paleogene igneous province bipip prior to the paleocene exhumation pulse the mesozoic onshore exhumation pulse is mainly linked to the uplift and erosion of the hinterland during the complex and long lived rifting history of the neighbouring offshore basins the extent of neogene exhumation is difficult to constrain due to the poor sensitivity of the ahe and aft systems at low temperatures we conclude that the cenozoic topographic evolution of the british isles is the result of plume driven uplift and exhumation with inversion under compressive stress playing a secondary role

new insights into kilauea s volcano dynamics brought by large scale relative relocation of microearthquakes 1 we investigated the microseismicity recorded in an active volcano to infer information concerning the volcano structure and long term dynamics by using relative relocations and focal mechanisms of microearthquakes there were 32 000 earthquakes of the mauna loa and kilauea volcanoes recorded by more than eight stations of the hawaiian volcano observatory seismic network between 1988 and 1999 we studied 17 000 of these events and relocated more than 70 with an accuracy ranging from 10 to 500 m about 75 of these relocated events are located in the vicinity of subhorizontal decollement planes at a depth of 8 11 km however the striking features revealed by these relocation results are steep southeast dipping fault planes working as reverse faults clearly located below the decollement plane and which intersect it if this decollement plane coincides with the pre mauna loa seafloor as hypothesized by numerous authors such reverse faults rupture the pre mauna loa oceanic crust the weight of the volcano and pressure in the magma storage system are possible causes of these ruptures fully compatible with the local stress tensor computed by gillard et al 1996 reverse faults are suspected of producing scarps revealed by kilometer long horizontal slip perpendicular lineations along the decollement surface and therefore large scale roughness asperities and normal stress variations these are capable of generating stick slip large magnitude earthquakes the spatial microseismic pattern observed in the south flank of kilauea volcano and hilina type instabilities rupture intersecting the decollement surface causing its large scale roughness may be an important parameter controlling the growth of hawaiian volcanoes

crustal structure of the british isles and its epeirogenic consequences crustal receiver functions have been calculated for a network of 51 three component broadband seismometers distributed across the british isles and nw europe over 3200 receiver functions were assembled for 1055 events for each station preliminary estimates of crustal thickness and vp vs ratio were obtained from h plots stacked receiver functions were then inverted to determine shear wave velocity as a function of depth each result was checked by guided forward modelling and by monte carlo error analysis in this way the robustness of our final calculated velocity profiles was carefully tested a set of depth migrated profiles was also constructed using an average of 50 events for each station over a range of backazimuths these profiles agree well with legacy wide angle crustal models our results show that crustal thickness varies between 24 and 36 km across the british isles thicker crust is found beneath north wales and beneath central scotland thinner crust occurs beneath northwest scotland and northwest ireland by combining our database with the results of controlled source wide angle experiments and with depth converted reflection profiles we have produced a detailed crustal thickness map for a region encompassing the british isles our synthesis of crustal thickness and structure has important implications for the tectonic and magmatic histories of this region complex moho structure with lower crustal p wave velocities of 7 km s 1 occurs beneath regions of cenozoic magmatism which may be consistent with magmatic underplating thin crust beneath northern britain suggests that present day long wavelength topography is maintained by regional dynamic support originating beneath the lithospheric plate

lithospheric flexure uplift and landscape evolution in south central england the high level river gravels in oxfordshire the northern drift group which range in age from early pleistocene to around 450 ka contain pebbles that were derived from a source area to the north near birmingham the pebbles could not have been transported across the upper triassic and lower jurassic clay outcrops of the midlands unless the region was at or close to sea level the present day cotswold escarpment ranges from 70 to 215 m this uplift must therefore have occurred after deposition of the northern drift group when the drainage of the midlands appears to have shifted from towards the thames basin to the bristol channel area it is concluded that lithospheric flexure due to the removal of 500 km 3 of soft late triassic and early jurassic clays and marls from large areas of the midlands and their re deposition in the celtic deep might account for this late pleistocene uplift uplift in the midlands is the likely explanation for both the tilted approximately 0 3 plateau surface in north oxfordshire and the change in strike of the jurassic beds sw of northamptonshire although some uplift occurred in se england during the early cenozoic and miocene we demonstrate here that there has been significant uplift of the region in the late pleistocene the tilted plateau surface in north oxfordshire may therefore be a relatively young i e post 450 ka feature related to tectonic uplift in the midlands

a transient subduction zone slip episode in southwest japan observed by the nationwide gps array 1 we investigate the spatiotemporal variation of fault slip on the subduction interface in southwest japan following the two 1996 hyuganada earthquakes m 6 7 using continuous gps observations a silent thrust slip event has been reported by hirose et al 1999 following these earthquakes approximately 100 km to the north beneath the bungo channel we employ the network inversion filter to rigorously invert for the fault slip distribution in space and time the gps time series is modeled as a sum of 1 secular deformation 2 coseismic station displacements 3 transient fault slip 4 random benchmark motion 5 reference frame shifts and 6 observational errors nonnegativity constraints effectively prohibit normal faulting on the subduction interface spatial and temporal smoothing parameters are estimated by the extended kalman filter the estimated fault slip rate images postseismic slip following the two hyuganada earthquakes slip associated with the silent thrust event began roughly 1 month after the second earthquake but initiated 100 km to the northeast of the hyuganada earthquakes the slow event propagated southwest and downdip beneath the bungo channel lasting approximately 1 year with maximum slip rates of 0 6 m yr the equivalent seismic moment was mw 7 2 we can rule out the possibility that slip propagated from the source region of the hyuganada earthquakes to the location of the silent earthquake however the timing of the events suggests a causal connection perhaps due to static stress transfer this kind of transient event or silent earthquake may reflect different fault zone characteristics and may be responsible for accommodating strain that would otherwise be released in large earthquakes

slip deficit on the san andreas fault at parkfield california as revealed by inversion of geodetic data a network of geodetic lines spanning the san andreas fault near the rupture zone of the 1966 parkfield california earthquake magnitude m 6 has been repeatedly surveyed since 1959 in the study reported here the average rates of line length change since 1966 were inverted to determine the distribution of interseismic slip rate on the fault these results indicate that the parkfield rupture surface has not slipped significantly since 1966 comparison of the geodetically determined seismic moment of the 1966 earthquake with the interseismic slip deficit rate suggests that the strain released by the latest shock will most likely be restored between 1984 and 1989 although this may not occur until 1995 these results lend independent support to the earlier forecast of an m 6 earthquake near parkfield within 5 years of 1988

growth and persistence of hawaiian volcanic rift zones hawaiian volcanic rift zones are modeled by representing the rifts and adjacent volcano flanks as long ridges with the geometry of flattened triangular prisms the intrusion of dikes along the axis of a rift requires a mechanism to generate the appropriate dike trapping stress field within the prism possible factors that affect the state of stress in the prism include multiple dike intrusion along the ridge axis faulting and gravitational sagging of the topography in extreme models with very steep slopes and high poisson s ratio corresponding to the gelatin models of rift zones by fiske and jackson 1972 results of finite element calculations indicate that gravity induced stresses are sufficient to trap a dike into propagating within the prism and parallel to the rift zone as proposed by fiske and jackson however the mechanism does not work for gently sloping flanks or a more acceptable poisson s ratio of about 0 25 additionally trapping stresses in the gravity loading and density stratification models will not persist after a few dike injection episodes therefore in mature hawaiian rift zones with possibly thousands of dikes additional processes must act to control the stresses that permit continued dike intrusion and rift persistence it is proposed that accommodation to dike emplacement occurs by slip on deep faults possibly of the type proposed for the 1975 kalapana hawaii earthquake as suggested by others for this earthquake the faults could coincide with the contact of the volcano with the seafloor within the weak seafloor sediments such faulting not only provides a means for the flanks to adjust continuously to intrusions but also generates the stress patterns needed to constrain future dikes to propagate along the rift axis other possible faulting mechanisms such as shallow gravity slides and normal faulting of the flanks do not appear to favor rift zone persistence in this model the horizontal stress generated by a standing column of magma at the time of dike emplacement the stresses in the ridges and the fault strength are coupled this results in a feedback between the maximum height that magma can rise along the rift fault friction and fault width through this feedback the slope of the volcano flank is controlled by the fault friction when applied to kilauea volcano the model yields an estimate for the coefficient of fault friction as high as 0 39 assuming normal hydrostatic pore fluid pressure an implication of this model supported by other studies is that rift intrusion and lateral spreading could be major contributors to volcano growth

joint analysis of geodetic and earthquake fault plane solution data to constrain magmatic sources a case study from kīlauea volcano abstract a joint analysis of geodetic and seismic datasets from k lauea volcano during a period of magmatic unrest in 2006 demonstrates the effectiveness of this combination for testing and constraining models of magma dynamics for a complex multi source system at the end of 2003 k lauea s summit began a four year long period of inflation due to a surge in magma supply to the volcano in 2006 for the first time since 1982 k lauea s southwest rift zone swrz also experienced inflation to investigate the characteristics of active magma sources and the nature of their interactions with faults in the swrz during 2006 we integrate through coulomb stress modeling contemporary geodetic data from insar and gps with a new catalogue of double couple fault plane solutions for volcano tectonic earthquakes we define two periods of inflation during 2006 based on the rate of deformation measured in daily gps data spanning february to 15 march 2006 period 1 and 16 march to 30 september 2006 period 2 insar data for these two periods are inverted to determine the position change in size and shape of inflation sources in each period our new models are consistent with microseismic activity from each period they suggest that during period 1 deformation in the swrz can be explained by pressurization of magma in a spherical reservoir beneath the south caldera and that during period 2 magma was also aseismically intruded farther to the southwest into the swrz along a sub horizontal plane our coulomb stress analysis shows that the microseismicity recorded in the swrz is induced by overpressurization of the south caldera reservoir and not by magma intrusion into the swrz this study highlights the importance of a joint analysis of independent geophysical datasets to fully constrain the nature of magma accumulation

volcano geodesy recent developments and future challenges abstract ascent of magma through earth s crust is normally associated with among other effects ground deformation and gravity changes geodesy is thus a valuable tool for monitoring and hazards assessment during volcanic unrest and it provides valuable data for exploring the geometry and volume of magma plumbing systems recent decades have seen an explosion in the quality and quantity of volcano geodetic data new datasets some made possible by regional and global scientific initiatives as well as new analysis methods and modeling practices have resulted in important changes to our understanding of the geodetic characteristics of active volcanism and magmatic processes from the scale of individual eruptive vents to global compilations of volcano deformation here we describe some of the recent developments in volcano geodesy both in terms of data and interpretive tools and discuss the role of international initiatives in meeting future challenges for the field

tectonic evolution of the north sea basin crustal stretching and subsidence summary the lithospheric stretching model for the formation of sedimentary basins was tested in the central north sea by a combined study of crustal thinning and basement subsidence patterns a profile of crustal structure was obtained by shooting a long range seismic experiment across the central graben the main axis of subsidence a seabed array of 12 seismometers in the graben was used to record shots fired in a line 530 km long across the basin the data collected during the experiment were interpreted by modelling synthetic seismograms from a laterally varying structure and the final model showed substantial crustal thinning beneath the graben subsidence data from 19 exploration wells were analysed to obtain subsidence patterns in the central north sea since jurassic times changes in water depth were quantified using foraminiferal assemblages where possible and observed basement subsidence paths were corrected for sediment loading compaction and changes in water depth through time the seismic model is shown to be compatible with the observed gravity field and the small size of observed gravity anomalies is used to argue that the basin is in local isostatic equilibrium both crustal thinning and basement subsidence studies indicate about 70 km of stretching across the central graben during the mid jurassic to early cretaceous extensional event this extension appears to have occurred over crust already slightly thinned beneath the graben and the seismic data suggest that total extension since the early permian may have been more than 100km the data presented here may all be explained using a simple model of uniform extension of the lithosphere

slow slip and tremor search at kilauea volcano hawaii 1 kilauea volcano hawaii has hosted a long series of slow slip events observed since the installation of the continuous gps network in 1996 kilauea s slow slip events are inferred to occur on the decollement fault at 8 km depth beneath its south flank with a location updip of the epicenters of large regular earthquakes fault slip typically lasts about two days and the events have magnitudes equivalent to mw 5 3 6 0 while slow slip events in subduction zones are commonly accompanied by tectonic tremor also called nonvolcanic tremor no tremor has yet been reported in association with kilauea s slow slip events instead there are swarms of small triggered earthquakes which is a characteristic only seen at select subduction zones e g boso and hikurangi a temporary array of seismometers was installed at kilauea in 2007 in anticipation of a slow slip event here we use several established methods to perform a systematic search for tectonic tremor during geodetically defined slow slip events as well as searching for tremor triggered by teleseismic surface waves we do not detect tectonic tremor using any of these methods although we are able to detect episodes of previously identified deep offshore volcanic tremor at 15 20 km depth and volcanic tremor from kilauea although kilauea s seismic network may not be adequate to observe tectonic tremor because hawaii is seismically noisy and its crust is highly attenuating it is also possible that the specific fault conditions on kilauea s decollement are not conducive to such tremor generation

kilauea slow slip events identification source inversions and relation to seismicity 1 several slow slip events beneath the south flank ofkilauea volcano hawaii have been inferred from transient displacements in daily gps positions to search for smaller events that may be close to the noise level in the gps time series we compare displacement fields on kilauea s south flank with displacement patterns in previously identified slow slip events matching displacement patterns are found for several new candidate events although displacements are much smaller than previously identified events one of the candidates 29 may 2000 is coincident with a microearthquake swarm as are all of the previously identified slow slip events the microearthquakes follow the onset of slow slip implying that they are triggered by stress changes during slip the new slow slip event brings the total number of events on kilauea between 1997 and 2007 to eight the smallest having m w 5 3 and the largest having m w 6 0 while the recurrence time between the four largest events is 2 11 0 01 years the repeat time for all eight events is 0 9 0 6 years we invert for the fault geometry and distribution of slip during the slow slip events the optimal source depths of 5 km assuming uniform slip dislocations in an elastic half space are considerably shallower than the accompanying swarm earthquakes 6 5 8 5 km which would place the earthquakes in a zone of decreased coulomb stress inversions including the effects of topography and layered elastic structure in the forward models favor depths comparable to microearthquake depths such that the earthquakes are located in a region of increased coulomb stress we also invert for time dependent fault slip directly from the 30 s gps phase observations constraining the source to the optimal uniform slip geometry on the basis of these inversions the larger events last between 1 5 2 2 days the data are unable to resolve migration of slip along the fault the temporal pattern of accompanying microearthquakes is consistent with the fault slip history assuming a seismicity rate theory based on rate and state friction making the swarm earthquakes coshocks and aftershocks of the slow slip events

a model for radial dike emplacement in composite cones based on observations from summer coon volcano colorado usa we mapped the geometry of 13 silicic dikes at summer coon an eroded oligocene stratovolcano in southern colorado to investigate various characteristics of radial dike emplacement in composite volcanoes exposed dikes are up to about 7 km in length and have numerous offset segments along their upper peripheries surprisingly most dikes at summer coon increase in thickness with distance from the center of the volcano magma pressure in a dike is expected to lessen away from the pressurized source region which would encourage a blade like dike to decrease in thickness with distance from the center of the volcano we attribute the observed thickness pattern as evidence of a driving pressure gradient which is caused by decreasing host rock shear modulus and horizontal stress both due to decreasing emplacement depths beneath the sloping flanks of the volcano based on data from summer coon we propose that radial dikes originate at depth below the summit of a host volcano and follow steeply inclined paths towards the surface near the interface between volcanic cone and basement which may represent a neutral buoyancy surface or stress barrier magma is transported subhorizontally and radially away from the center of the volcano in blade like dikes the dikes thicken with increasing radial distance and offset segments and fingers form along the upper peripheries of the intrusions eruptions may occur anywhere along the length of the dikes but the erupted volume will generally be greater for dike fed eruptions far from the center of the host volcano owing to the increase in driving pressure with distance from the source observed eruptive volumes vent locations and vent area intrusions from inferred post glacial dike fed eruptions at mount adams washington usa support the proposed model hazards associated with radial dike emplacement are therefore greater for longer dikes that propagate to the outer flanks of a volcano

localized quaternary uplift of south central england the early quaternary of south central england is characterized by uplift as is indicated by the river gravels that extend intermittently from oxfordshire through northamptonshire to lincolnshire the earliest of these gravels contain abundant quartz and quartzite clasts derived from lower triassic conglomerates in the west midlands but later deposits contain progressively larger amounts of locally derived jurassic sediments this compositional change is associated with the incision of the rivers that flowed eastwards from the west midlands subsequently the headwaters of some of these rivers were diverted towards the bristol channel and their suspended material was deposited on the outer parts of the uk continental shelf and slope the area of incised drainage gloucestershire to lincolnshire did not extend to east anglia in the east or to somerset in the west both these coastal regions contain several marine horizons showing that the area of uplift did not include the whole of southern england the uplift cannot therefore be attributed to eustatic changes in sea level the area of uplift is centred on the broad topographic depression of the english midlands and corresponds approximately to the outcrop of thick c 1 km upper triassic and lower jurassic mudrocks we have used an ordnance survey 50 m 50 m topographic grid to estimate the amount of mudrocks that has been removed from the depression and 2d flexural unloading models to calculate the tectonic uplift that resulted for various assumptions of the effective elastic thickness which is determined by the flexural rigidity of the lithosphere the amount of material removed is in accord with what is known of the volume of quaternary deposits offshore and the uplift accounts for the incised plateau surfaces of the flanking cotswold hills and the high ground of northamptonshire to the east and the forest of dean and the hills of herefordshire to the west

seismic evidence for a crustal magma reservoir beneath the upper east rift zone of kilauea volcano hawaii an anomalous body with low vp compressional wave velocity low vs shear wave velocity and high vp vs anomalies is observed at 8 11 km depth beneath the upper east rift zone of kilauea volcano in hawaii by simultaneous inversion of seismic velocity structure and earthquake locations we interpret this body to be a crustal magma reservoir beneath the volcanic pile similar to those widely recognized beneath mid ocean ridge volcanoes combined seismic velocity and petrophysical models suggest the presence of 10 melt in a cumulate magma mush this reservoir could have supplied the magma that intruded into the deep section of the east rift zone and caused its rapid expansion following the 1975 m7 2 kalapana earthquake

itrf2005 a new release of the international terrestrial reference frame based on time series of station positions and earth orientation parameters 1 unlike the past international terrestrial reference frame itrf versions where global long term solutions were combined the itrf2005 uses as input data time series weekly from satellite techniques and 24 h session wise from very long baseline interferometry of station positions and daily earth orientation parameters eops the advantage of using time series of station positions is that it allows to monitor station non linear motion and discontinuities and to examine the temporal behavior of the frame physical parameters namely the origin and the scale the itrf2005 origin is defined in such a way that it has zero translations and translation rates with respect to the earth center of mass averaged by the satellite laser ranging slr time series spanning 13 years of observations its scale is defined by nullifying the scale and its rate with respect to the very long baseline interferometry vlbi time series spanning 26 years of observations the itrf2005 orientation at epoch 2000 0 and its rate are aligned to the itrf2000 using 70 stations of high geodetic quality the estimated level of consistency of the itrf2005 origin at epoch 2000 0 and its rate with respect to the itrf2000 is respectively 0 1 0 8 5 8 mm and 0 2 0 1 1 8 mm yr along the x yand z axis we estimate the formal errors on these components to be 0 3 mm and 0 3 mm yr we believe that this low level of agreement between the two frame origins is most probably due to the poor slr network geometry and its degradation over time the itrf2005 combination involving 84 co location sites revealed a scale inconsistency of 1 ppb 6 3 mm at the equator at epoch 2000 0 and 0 08 ppb yr between the slr and vlbi long term solutions as obtained by the stacking of their respective time series possible causes of this inconsistency may include the poor slr and vlbi networks and their co locations local tie uncertainties systematic effects and possible inconsistent model corrections used in the data analysis of both techniques for the first time of the itrf history the itrf2005 rigorous combination provides self consistent series of eops including polar motion from vlbi and satellite techniques and universal time and length of day from vlbi only a velocity field of 152 sites with an error less than 1 5 mm yr is used to estimate absolute rotation poles of 15 tectonic plates that are consistent with the itrf2005 frame this new absolute plate motion model supersedes and significantly improves that of the itrf2000 which involved six major tectonic plates citation altamimi z x collilieux j legrand b garayt and c boucher 2007 itrf2005 a new release of the international terrestrial reference frame based on time series of station positions and earth orientation parameters j geophys res 112 b09401

earthquakes triggered by silent slip events on kīlauea volcano hawaii silent earthquakes or slow slip events happen so slowly that they cannot be detected by conventional seismographs but now the availability of gps data means that they can be followed in detail segall et al report on a series of small earthquakes on k lauea volcano hawaii the earthquakes at depths of 7 to 8 km appear to be triggered by otherwise silent slow slips though small triggered earthquakes of this type can be used to help quantify the increased hazard due to slow slip events slow slip events or silent earthquakes have recently been discovered in a number of subduction zones including the nankai trough1 2 3 in japan cascadia4 5 and guerrero6 in mexico but the depths of these events have been difficult to determine from surface deformation measurements although it is assumed that these silent earthquakes are located along the plate megathrust this has not been proved slow slip in some subduction zones is associated with non volcanic tremor7 8 but tremor is difficult to locate and may be distributed over a broad depth range9 except for some events on the san andreas fault10 slow slip events have not yet been associated with high frequency earthquakes which are easily located here we report on swarms of high frequency earthquakes that accompany otherwise silent slips on k lauea volcano hawaii for the most energetic event in january 2005 the slow slip began before the increase in seismicity the temporal evolution of earthquakes is well explained by increased stressing caused by slow slip implying that the earthquakes are triggered the earthquakes located at depths of 7 8 km constrain the slow slip to be at comparable depths because they must fall in zones of positive coulomb stress change triggered earthquakes accompanying slow slip events elsewhere might go undetected if background seismicity rates are low detection of such events would help constrain the depth of slow slip and could lead to a method for quantifying the increased hazard during slow slip events because triggered events have the potential to grow into destructive earthquakes

seismic velocity and attenuation structure of the east rift zone and south flank of kilauea volcano hawaii it has been proposed that a deep magma body beneath the east rift zone erz of kilauea volcano hawaii must be present in order to explain the observed deformation of the south flank from november 1999 to june 2000 29 iris passcal three component seismographs were operated across kilauea9s erz and south flank using local earthquakes recorded by these stations supplemented with data from the hawaiian volcano observatory stations we investigated the deep structure of the erz and south flank through two approaches seismic velocity tomography and seismic attenuation tomography results along two north northwest south southeast profiles are examined the western profile shows a low velocity region beneath and south of the hilina pali and earthquakes at depth are sandwiched between a high v p v s high q zone and a low v p v s low q zone the velocity and attenuation differences are interpreted to reflect the contrast in material properties between the overlying volcanic pile and the underlying fluid rich ocean sediments and fractured altered ocean crust beneath the south flank thrust fault the eastern profile shows an anomalous feature with low v p low v p v s high q p and low q s at about 7 km depth beneath the erz the low v p v s ratio is inconsistent with the presence of partial melt instead this anomaly is attributed to a trapped reservoir of co 2 our results do not support the existence of a sizable molten or partially molten body at depth beneath the erz if the deep magma body exists it must be relatively small based on synthetic resolution tests an estimated limit on the maximum allowable cross sectional size of the deep magma body is about 2 by 4 km

animated models of extensional basins and passive margins 1 we present animated models of the development of the san jorge north falkland and north sea extensional sedimentary basins and the orange pearl river mouth and voring passive continental margins these animations show the link between strain rate and subsidence and track both compaction and thermal development of the sediment pile calculations are based on a two dimensional inverse model for extracting the spatial and temporal variation of strain rate from stratigraphic profiles across extensional terrains this general algorithm requires no a priori assumptions about the number duration and intensity of the rifting episodes instead strain rate is allowed to vary smoothly through space and time until misfit between observed and predicted stratigraphy is minimized calculated 2 d and 1 d strain rate histories are corroborated by the number and duration of rifting episodes determined from independent stratigraphical and structural evidence the evolving temperature structure of the sediment pile is a function both of porosity which varies through time as compaction occurs and of heat flow into the base of the basin which is determined from the strain rate history we discuss the implications of the calculated strain rate histories for understanding the regional tectonic development of each basin and margin

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

the elastic thickness of the british isles free air gravity and topography data from the british isles have been analysed in the frequency domain to determine the mechanisms of topographic support first we calculate how the admittance between measured free air gravity and topography varies as a function of wavelength a simple model which consists of a crust with two layers of different densities overlying a higher density mantle was then used to calculate admittance functions the misfit between observed and calculated admittance was minimized by varying elastic thickness and the proportion of the total load due to internal loading at short wavelengths c 0 2 the general behaviour of the observed admittance suggests that topography is primarily supported by elastic stresses in the crust a small departure between observed and calculated admittance at the longest wavelengths 400

microearthquake streaks and seismicity triggered by slow earthquakes on the mobile south flank of kilauea volcano hawai i 1 we perform waveform cross correlation and high precision relocation of both background seismicity and seismicity triggered by periodic slow earthquakes at kilauea volcano s mobile south flank we demonstrate that the triggered seismicity dominantly occurs on several preexisting fault zones at the hilina region regardless of the velocity model employed the relocated earthquake epicenters and triggered seismicity localize onto distinct fault zones that form streaks aligned with the slow earthquake surface displacements determined from gps due to the unknown effects of velocity heterogeneity and nonideal station coverage our relocation analyses cannot distinguish whether some of these fault zones occur within the volcanic crust at shallow depths or whether all occur on the decollement between the volcano and preexisting oceanic crust at depths of 8 km nonetheless these hilina fault zones consistently respond to stress perturbations from nearby slow earthquakes

isostatic response of the australian lithosphere estimation of effective elastic thickness and anisotropy using multitaper spectral analysis gravity and topography provide important insights regarding the degree and mechanisms of isostatic compensation the azimuthally isotropic coherence function be tween the bouguer gravity anomaly and topography evolves from high to low for increasing wavenumber a diagnostic that can be predicted for a variety of lithospheric loading models and used in inversions for flexural rigidity thereof in this study we investigate the isostatic response of continental australia we consider the effects of directionally anisotropic plate strength on the coherelce the anisotropic coherence function is calculated for regions of australia that have distinctive geological and geophysical properties the coherence estimation is performed by the thomson multiple slepian taper spectral analysis method extended to two dimensional fields our analysis reveals the existence of flexural anisotropy in central australia indicative of a weaker n s direction of lower te this observation is consistent with the suggestion that the parallel faults in that area act to make the lithosphere weaker in the direction perpendicular to them it can also be related to the n s direction of maximum stress and possibly the presence of e w running zones weakened due to differential sediment burial rates we also demonstrate that the multitaper method has distinct advantages for computing the isotropic coherence function the ability to make many independent estimates of the isostatic response that are minimally affected by spectral leakage results in a coherence that is more robust than with modified periodogram methods particularly at low wavenumbers our analysis elucidates the reasons for discrepancies in previous estimates of effective elastic thickness te of the australian lithosphere in isotropic inversions for te we obtain values that are as much as a factor of 2 less than those obtained in standard inversions of the periodogram coherence using bouguer gravity and topography but greater than those obtained by inversions that utilize free air rather than bouguer gravity and ignore the presence of subsurface loads however owing to the low spectral power of the australian topography the uncertainty on any estimate of te is substantial

top down inflation and deflation at the summit of kīlauea volcano hawai i observed with insar 1 we use interferometric synthetic aperture radar insar to study deformation of the summit caldera at k lauea volcano during 2000 2008 which spanned both an east rift zone eruptive event in 2007 and the start of the ongoing summit eruption in 2008 the data set consists of small baseline subset sbas time series generated from 270 acquisitions on three separate beam modes from the radarsat 1 satellite we identify 12 time periods with distinct patterns of displacement that we attribute until late 2003 to secular tectonic driven deformation and from 2004 to 2008 to four different sources in the summit area we model the shallow magmatic system as a spherical reservoir at 1 9 0 1 km depth below the surface to the northeast of halemaumau source 1 and three vertically stacked sills at greater depths in the southern caldera area source 2 at the southern edge of the caldera at 2 9 0 2 km depth source 3 to the south southeast of the caldera at 3 4 0 5 km depth and source 4 south of the caldera at 3 6 0 4 km depth the sequence for filling of and withdrawal from these reservoirs reveals a top down process with sequences of both inflation and deflation initiating in the shallowest source inflation of source 3 is coincident with elevated seismic activity in the upper east rift zone in february 2006 and may 2007 source 4 is elongated toward the southwest rift zone and also shows elevated seismicity that extends toward the southwest rift zone

effects of a low viscosity lower crust on topography and gravity at convergent mountain belts during gravitational instability of mantle lithosphere we examine the gravitational stability of a stratified structure consisting of a low density crust through which viscosity decreases exponentially over a denser mantle lithosphere of constant viscosity which in turn overlies an inviscid slightly less dense layer like the asthenosphere the most important aspect of the viscosity structure is the contrast in viscosity at the moho surface uplift above a mantle downwelling is greatest when the viscosity contrast at the moho is negligible the surface is depressed when the viscosity of the lowermost crust is much greater than mantle viscosity for a wide range of viscosity structures calculated gravity anomalies and in particular admittances ratios of the fourier transform of gravity to that of topography produced by rayleigh taylor instability differ markedly from those observed across convergent mountain belts in particular whereas values of calculated admittance are negative or very small observed admittances are consistently positive thus if downwelling of mantle lithosphere directly beneath mountain ranges plays an important role in the construction of mountain belts it cannot be the main process that induces crustal thickening

moderate magnitude earthquakes induced by magma reservoir inflation at kīlauea volcano hawai i 1 although volcano tectonic vt earthquakes often occur in response to magma intrusion it is rare for them to have magnitudes larger than m4 on 24 may 2007 two shallow m4 earthquakes occurred beneath the upper part of the east rift zone of k lauea volcano hawai i an integrated analysis of geodetic seismic and field data together with coulomb stress modeling demonstrates that the earthquakes occurred due to strike slip motion on pre existing faults that bound k lauea caldera to the southeast and that the pressurization of k lauea s summit magma system may have been sufficient to promote faulting for the first time we infer a plausible origin to generate rare moderate magnitude vts at k lauea by reactivation of suitably oriented pre existing caldera bounding faults rare moderate to large magnitude vts at k lauea and other volcanoes can therefore result from reactivation of existing fault planes due to stresses induced by magmatic processes

magmatically triggered slow slip at kilauea volcano hawaii we demonstrate that a recent dike intrusion probably triggered a slow fault slip event sse on kilauea volcano9s mobile south flank our analysis combined models of advanced land observing satellite interferometric dike intrusion displacement maps with continuous global positioning system gps displacement vectors to show that deformation nearly identical to four previous sses at kilauea occurred at far field sites shortly after the intrusion we model stress changes because of both secular deformation and the intrusion and find that both would increase the coulomb failure stress on possible sse slip surfaces by roughly the same amount these results in concert with the observation that none of the previous sses at kilauea was directly preceded by intrusions but rather occurred during times of normal background deformation suggest that both extrinsic intrusion triggering and intrinsic secular fault creep fault processes can lead to sses

spontaneous and triggered aseismic deformation transients in a subduction fault model 1 aseismic deformation transients can emerge as a natural outcome of the rate and state friction processes revealed in laboratory fault sliding experiments when that constitutive formulation is applied to model subduction earthquake sequences transients can arise spontaneously for certain effective stress variations with depth we show that if interstitial fluids are present and pore pressure is near lithostatic around and downdip from the frictional stability transition transients with recurrence intervals of 1 year are predicted on the basis of laboratory friction parameters and their temperature hence depth variations the recurrence interval decreases with and reaches 14 months when is 2 3 mpa dimensional analysis and numerical studies show that the fault response primarily depends on a parameter w h here the high pore pressure zone extends distance w updip from the stability transition and h is the stable patch size for steady sliding evidence that such fluid conditions may actually be present is independently provided by the occurrence of nonvolcanic tremors as apparent responses to extremely small stress changes and by petrological constraints on expected regions of dehydration for the shallow dipping subduction zones where transients are observed transient sequences can also be triggered by a modest one time step like interseismic stress perturbation on the subduction fault due to nearby earthquakes or to pore pressure changes e g during episodes of metamorphic fluid release properties of triggered transients and future thrust earthquakes depend on the interseismic time when the perturbation is introduced its relative location along the subduction fault and its magnitude

volcano monitoring using gps developing data analysis strategies based on the june 2007 kīlauea volcano intrusion and eruption 1 the global positioning system gps is one of the most common techniques and the current state of the art used to monitor volcano deformation in addition to slow several centimeters per year displacement rates gps can be used to study eruptions and intrusions that result in much larger tens of centimeters over hours days displacements it is challenging to resolve precise positions using gps at subdaily time intervals because of error sources such as multipath and atmospheric refraction in this paper the impact of errors due to multipath and atmospheric refraction at subdaily periods is examined using data from the gps network on k lauea volcano hawai i methods for filtering position estimates to enhance precision are both simulated and tested on data collected during the june 2007 intrusion and eruption comparisons with tiltmeter records show that gps instruments can precisely recover the timing of the activity

constraints on magma chamber geometry at sierra negra volcano galapagos islands based on insar observations abstract we investigate the problem of estimating magma chamber geometry using insar observations of sierra negra volcano galapagos ascending and descending interferograms are combined to determine vertical and one horizontal component of displacement the ratio of maximum horizontal to vertical displacement suggests a sill like source spherical or stock like bodies are inconsistent with the data we estimate the geometry of the sill assuming a horizontal uniformly pressurized crack with unknown periphery and depth the sill is discretized into small elements that are either open and are subjected to the pressure boundary condition or remain closed we find the best fitting sill to be located beneath sierra negra s inner caldera at a depth of about 2 km using boundary element calculations we show that any magma chamber with a flat top coincident with the sill model fits the data equally well the data are insensitive to the sides and bottom of the magma chamber

fault frictional parameters and material properties revealed by slow slip events at kilauea volcano hawai i 1 we categorize slow slip events at kilauea volcano into two distinct families based on gps measurements of the surface displacement patterns an event correlation filter confirms that eastern and western families are statistically distinguishable with the western family notably self similar the western family exhibits quasi periodicity with regular repeat times while eastern family events are aperiodic or have complicated periodicity if the decollement is the source fault for both families of events it must have varying frictional properties at the 10 km scale of separation the temporal slip and spatial scaling behavior are consistent with a simplistic rate and state dependent frictional formalism provided that the characteristic slip distance for state evolution dc is of the order of millimeters rather than the 10 100 m typically found in lab studies and the shear rigidity is around 2 gpa consistent with fault gouge material

three dimensional modeling of the 1983 1984 eruption at piton de la fournaise volcano reunion island displacement vectors on 125 points over a 6 km 2 area were calculated zlotnicki et al 1990 for piton de la fournaise volcano reunion island from photogrammetric surveys conducted in september 1981 and again in september 1984 an eruptive crisis with two episodes occurred during the 3 years between the surveys we modeled the displacements from the photogrammetric surveys using a three dimensional mixed boundary element method the model shows that both eruptive episodes were fed by a single dike oriented 165 from north as the dike approached the ground surface it divided into segments that rotated into an en echelon pattern the model that best fits all observations suggests that the stress state within the volcano is quasi isotropic such that horizontal stresses equal the overburden these high horizontal stresses are incompatible with an elastic edifice loaded merely by gravitational forces however they may be attributed to the cumulative effect of repeated dike intrusions

pressurized magma reservoir within the east rift zone of kīlauea volcano hawai i evidence for relaxed stress changes from the 1975 kalapana earthquake we use 2000 2012 insar data from multiple satellites to investigate magma storage in k lauea s east rift zone erz the study period includes a surge in magma supply rate and intrusion eruptions in 2007 and 2011 the kupaianaha area inflated by 5 cm prior to the 2007 intrusion and the n pau crater area by 10 cm following the 2011 intrusion for the n pau crater area elastic modeling suggests an inflation source at 5 2 km depth or more below sea level the reservoir is located in the deeper section of the rift zone for which secular magma intrusion was inferred for the period following the 1975 mw7 7 decollement earthquake reservoir pressurization suggests that in this section of the erz extensional stress changes due to the earthquake have largely been compensated for and that this section is approaching its pre 1975 state reservoir pressurization also puts the molten core model into question for this section of k lauea s rift zone

magma compressibility and the missing source for some dike intrusions 1 dike intrusions are often accompanied by localized deflation interpreted as depressurizing magma chambers feeding the dike in some cases the inferred volume decrease is a factor of 4 or 5 less than the volume increase of the dike here we explore whether this discrepancy can be explained by compressibility of the magma combined with the fact that cracks are much more compliant than equidimensional magma chambers if pressure changes are small the magma compressibility m is constant and the dike ends up in hydrostatic equilibrium with an ellipsoidal magma chamber at the same depth the ratio rv of the volume of the crack to the volume lost by the chamber is rv 1 4 m 3 1 where is the host rock rigidity for gas poor magmas m 0 6 2 10 10 pa 1 and 3 25 gpa we find 1 2 rv 7 7 large changes in magma compressibility due to gas exsolution increase rv

january 30 1997 eruptive event on kilauea volcano hawaii as monitored by continuous gps a continuous global positioning system gps network on kilauea volcano captured the most recent fissure eruption in kilauea s east rift zone erz in unprecedented spatial and temporal detail the short eruption drained the lava pond at pueu oeo leading to a two month long pause in its on going eruption models of the gps data indicate that the intrusion s bottom edge extended to only 2 4 km continuous gps data reveal rift opening 8 hours prior to the eruption absence of precursory summit inflation rules out magma storage overpressurization as the eruption s cause we infer that stresses in the shallow rift created by the continued deep rift dilation and slip on the south flank decollement caused the rift intrusion

implications of deflation inflation event models on kīlauea volcano hawaiʻi abstract surface deformation of volcanic areas can reveal information about subsurface magma reservoirs and how magma is transported between them which is an important part of volcano monitoring for hazard mitigation one prominent style of deformation observed at k lauea volcano hawai i is episodic deflation inflation di events which are recorded in surface deformation data and characterized by deflation of the summit region over hours to days followed by rapid re inflation the exact cause of di events is unknown however a commonly proposed explanation is that a temporary blockage occurs in the conduit connecting the south caldera magma reservoir to the shallower halema uma u reservoir thus interrupting the influx of magma this model is investigated by testing the hypothesis that during the deflationary phase of a di event the volume of magma blocked from reaching the halema uma u reservoir is added to the south caldera reservoir using a mass balance approach and deformation modeling the expected deformation tilt pattern was predicted for the reservoirs and compared to tilt observations from 16 large 4 rad magnitude di events between 2010 and 2012 while the predicted tilts due to inflation from the south caldera reservoir are strong enough to be detected this signal is not seen in the tilt observations we also explore the possibility that the blockage occurs below the south caldera reservoir as well as alternative configurations that include a direct connection between the south caldera reservoir and the eruption site none of the simple two reservoir models we test are able to adequately satisfy the observations selected di events show that tilt vectors change in both magnitude and azimuthal direction over the course of deflation we conclude that the portion of the summit storage and plumbing system active during these di events is more complicated than two connected chambers and that it is more likely that these summit reservoirs have their own source conduits connecting in some complex way to the deep magma source

lispb revisited a new look under the caledonides of northern britain summary the lithospheric seismic profile in britain lispb shot in 1974 included a 700 km long north south profile of the crust and upper mantle of northern britain the wide angle seismic data from lispb was of exceptional quality and coverage making a reinterpretation using current modelling programs worthwhile this reinterpretation shows that the original crustal model published by bamford et al 1978 satisfies the observed first arrival traveltimes but that further detail of crustal velocity structure may be obtained by model shows strong variations in crustal velocity structure that appear to be correlated with geological and tectonic structures mapped at the surface the new lithospheric model is compatible with the observed gravity field when converted to appropriate densities and the variations in loading along the base of the density model show that the lithosphere is close to local isostatic equilibrium profiles of the variation of velocity and density with depth from the new model are compared with measurements of lewisian rocks made at confining pressures up to 8 kbar allowing the seismic model to be interpreted geologically a synthetic normal incidence profile of the new model is superimposed on the nearby nec deep seismic reflection profile and the features imaged by the two techniques are compared

geodetic evidence for en echelon dike emplacement and concurrent slow slip during the june 2007 intrusion and eruption at kīlauea volcano hawaii 1 a series of complex events at k lauea volcano hawaii 17 june to 19 june 2007 began with an intrusion in the upper east rift zone erz and culminated with a small eruption 1500 m3 surface deformation due to the intrusion was recorded in unprecedented detail by global positioning system gps and tilt networks as well as interferometric synthetic aperture radar insar data acquired by the envisat and alos satellites a joint nonlinear inversion of gps tilt and insar data yields a deflationary source beneath the summit caldera and an ene striking uniform opening dislocation with 2 m opening a dip of 80 to the south and extending from the surface to 2 km depth this simple model reasonably fits the overall pattern of deformation but significantly misfits data near the western end of an inferred dike like source three more complex dike models are tested that allow for distributed opening including 1 a dike that follows the surface trace of the active rift zone 2 a dike that follows the symmetry axis of insar deformation and 3 two en echelon dike segments beneath mapped surface cracks and newly formed steaming areas the en echelon dike model best fits near field gps and tilt data maximum opening of 2 4 m occurred on the eastern segment beneath the eruptive vent although this model represents the best fit to the erz data it still fails to explain data from a coastal tiltmeter and gps sites on k lauea s southwestern flank the southwest flank gps sites and the coastal tiltmeter exhibit deformation consistent with observations of previous slow slip events beneath k lauea s south flank but inconsistent with observations of previous intrusions slow slip events at k lauea and elsewhere are thought to occur in a transition zone between locked and stably sliding zones of a fault an inversion including slip on a basal decollement improves fit to these data and suggests a maximum of 15 cm of seaward fault motion comparable to previous slow slip events