topography and self gravitation interaction in elastic gravitational modeling changes in gravity due to volcanic loading of the crust are influenced by topography we investigate the relative importance of topography and self gravitation in the interpretation of gravity changes it is shown that modeling of gravity changes can be more precise with the introduction of topographic relief although it is neglected self gravitation of the medium this paper exploits this result by suggesting a mathematical simplification that could be useful in the future development of a numerical technique to accurately include topographic effects in the modeling of deformation and gravity changes finally we perform an inversion of the gravity changes observed at mayon volcano philippines between december 1992 and december 1996 including topographic effects by varying the depth of the source failure to account for topographic influences can bias estimates of source parameters particularly when the lateral extension of the relief is of the same order of magnitude as the source depth

3d multi source model of elastic volcanic ground deformation abstract developments in interferometric synthetic aperture radar insar and gnss global navigation satellite system during the past decades have promoted significant advances in geosciences providing high resolution ground deformation data with dense spatio temporal coverage this large dataset can be exploited to produce accurate assessments of the primary processes occurring in geologically active areas we present a new original methodology to carry out a multi source inversion of ground deformation data to better understand the subsurface causative processes a nonlinear approach permits the determination of location size and three dimensional configuration without any a priori assumption as to the number nature or shape of the potential sources the proposed method identifies a combination of pressure bodies and different types of dislocation sources dip slip strike slip and tensile that represent magmatic sources and other processes such as earthquakes landslides or groundwater induced subsidence through the aggregation of elemental cells this approach has the following features 1 simultaneous inversion of the deformation components and or line of sight los data 2 simultaneous determination of diverse structures such as pressure bodies or dislocation sources representing local and regional effects 3 a fully 3d context and 4 no initial hypothesis about the number geometry or types of the causative sources is necessary this methodology is applied to mt etna southern italy we analyze the ground deformation field derived from a large insar dataset acquired during the january 2009 june 2013 time period the application of the inversion approach models several interesting buried structures as well as processes related to the volcano magmatic plumbing system local subsidence within the valle del bove and seaward motion of eastern flank of the volcano

gravity changes and deformation due to a magmatic intrusion in a two layered crustal model we develop and extend theoretical and computational methods for the calculation of the deformation gravity and potential change due to a point source of magma injection into a multilayered elastic gravitational earth model in our calculations which are based upon the method outlined by rundle two distinct layers overlying a half space may be incorporated the source can be located in either of the layers or the half space the method is quite general and can be readily adapted to calculations in which stresses in either the layers or the half space relax by viscoelastic flow the results obtained indicate that the use of homogeneous half space to represent the earth may in some cases be too simple a model and that variations in elastic moduli have a more significant effect than variation in reference density on both the surface displacements and gravity changes as an example we calculate the displacement and gravity changes due to a subsurface mass injection in a crust mantle model appropriate to the volcanic island of lanzarote which is presently the subject of numerous geophysical experiments both historical and recent data indicate that lanzarote may be subject to some risk of volcanic eruption in the future thus our calculations may be useful in interpreting observations of preemption phenomena the results are discussed in terms of prediction versus measurement capabilities

study of volcanic sources at long valley caldera california using gravity data and a genetic algorithm inversion technique we model the source inflation of the long valley caldera california using a genetic algorithm technique and micro gravity data while there have been numerous attempts to model the magma injection at long valley caldera from deformation data this has proven difficult given the complicated spatial and temporal nature of the volcanic source recent work illustrates the effectiveness of considering micro gravity measurements in volcanic areas a genetic algorithm is a problem solving technique which combines genetic and prescribed random information exchange we perform two inversions one for a single spherical point source and another for two sources that might represent a more spatially distributed source the forward model we use to interpret the results is the elastic gravitational earth model which takes into account the source mass and its interaction with the gravity field the results demonstrate the need to incorporate more variations in the model including another source geometry and the faulting mechanism in order to provide better constraints on intrusion volumes future work should include the joint inversion of gravity and deformation data during the same epoch

geodetic methods for detecting volcanic unrest a theoretical approach in this paper we study the application of different geodetic techniques to volcanic activity monitoring using theoretical analysis this methodology is very useful for obtaining an idea of the most appropriate and efficient monitoring method mainly when there are no records of geodetic changes previous to volcanic activity the analysis takes into account the crustal structure of the area its geology and its known volcanic activity to estimate the deformation and gravity changes that might precede eruptions the deformation model used includes the existing gravity field and vertical changes in the crustal properties both factors can have a considerable effect on computed deformation and gravity changes topography should be considered when there is a steep slope greater than 10 the case study of teide stratovolcano tenerife canary islands for which no deformation or gravity changes are available is used as a test to avoid considering topography we worked at the lowest level of las canadas and examined a smaller area than the whole caldera or island therefore the results are only a first approach to the most adequate geodetic monitoring system the methodology can also be applied to active areas where volcanic risk is not associated with a stratovolcano but instead with monogenetic scattered centers especially when sites must be chosen in terms of detection efficiency or existing facilities the canary islands provide a good example of this type of active volcanic areas and we apply our model to the island of lanzarote to evaluate the efficiency of the monitoring system installed at the existing geodynamic station on this island topography is not important the results of our study show clearly that the most appropriate geodetic volcano monitoring system is not the same for all different volcanic zones and types and the particular properties of each volcano zone must be taken into account when designing each system

horizontal viscoelastic gravitational displacement due to a rectangular dipping thrust fault in a layered earth model calculations of horizontal displacements due to a rectangular finite thrust fault in a viscoelastic gravitational layered earth model are presented the earth model consists of a single elastic gravitational layer overlying a viscoelastic gravitational half space a review of the full three dimensional theoretical solutions is presented along with the explicit solutions for horizontal displacements several examples of computations for dipping faults with various angles and located at different depths are shown the results indicate that viscoelasticity introduces a long wavelength component into the interseismic deformation field which is not present in published elastic techniques and also that a proper consideration of gravity is necessary only for near field computations at longer periods of time a pattern is found in the cumulative displacement of cycled earthquakes which indicates that the viscoelastic displacements are visible for longer recurrence time events and that these may serve as a time index for the various stages between cycles

new results at mayon philippines from a joint inversion of gravity and deformation measurements in this paper we detail the combination of the genetic algorithm ga inversion technique with the elastic gravitational model originally developed by rundle and subsequently refined by fernandez and others a sensitivity analysis is performed for the joint inversion of deformation and gravity to each of the model parameters illustrating the importance of proper identification of both the strengths and limitations of any source model inversion and this technique in particular there is a practical comparison of the theoretical results with the inversion of geodetic data observed at the mayon volcano in the philippines where there are gravity changes without significant deformation after the 1993 eruption

mechanics of fold and thrust belts and accretionary wedges cohesive coulomb theory a critically tapered fold and thrust belt or submarine accretionary wedge is one that is on the verge of coulomb failure everywhere including its base where frictional sliding along a decollement is assumed to be occurring cohesion within a wedge can add significantly to the overall strength near the toe the effect of this is to decrease the near toe taper leading to a critical topographic profile that is concave upward if the decollement is planar we obtain an approximate self consistent solution for the state of stress within a thin skinned cohesive critical coulomb wedge and determine the relationship between the wedge taper and its strength and basal friction the theory is then applied to the presently deforming fold and thrust belt of western taiwan fitting of theoretical critical wedge shapes to topographic profiles and measurements of the step up angles of thrust faults from the basal decollement are used to constrain the taiwan wedge strength parameters an attractive assertion fully consistent with all the observations is that the mechanics of fold and thrust belts and accretionary wedges is governed by normal frictional and fracture strengths of rocks measured in the laboratory in particular if byerlee s law b 0 85 is adopted as the coefficient of sliding friction on the base we find a coefficient of internal friction 0 9 1 0 in the wedge and a wedge cohesion so 5 20 mpa other solutions having strengths and ambient stresses up to 4 times lower than this can also however satisfy the data

characterization of the composition of dust fallout and identification of dust sources in arid and semiarid north china abstract a source analysis to characterize the composition of dust fallout in arid and semiarid north china an important source area of dust for east asia was performed monthly samples were obtained from april 2001 to march 2002 at 29 sites in sandy and gobi deserts steppes and loess areas and the following elements were analyzed ce co cs eu fe hf lu nd rb sc ta tb th as la na sb sm u yb al ca mg mn ti and v although the dust compositions differed it was difficult to determine the potential dust source areas based solely on the elemental fingerprints of the dust principal components analysis showed that at most sites sm sc la ce eu and th were most strongly correlated r 0 7 with other elements whereas crustal elements such as al fe and ti were only strongly correlated with the other elements at a few sites of the 26 elements that we analyzed maybe only sb was representative of anthropogenic pollution but pollutant sources were unclear because at most sites in different months the crustal derived elements and those derived from anthropogenic pollutants always appeared synchronously creating difficulties and high uncertainties in source identification

seamount loading and stress in the ocean lithosphere 2 viscoelastic and elastic viscoelastic models analytical solutions are presented for the deformation and stress state of a horizontally stratified earth subject to normal loads of size and wavelength that are characteristic of seamounts the models investigated include layered elastic plates homogeneous viscoelastic plates and elastic over viscoelastic models in all cases the composite models overlie an inviscid half space the principal advantage of the laminated elastic models over homogeneous elastic plates is that they can result in a substantial reduction in the maximum stress differences in those parts of the plate least capable of supporting large stress differences authors

an upper limit to ground deformation in the island of tenerife canary islands for the period 1997 2006 continuous monitoring of ground deformation in the volcanic island of tenerife canary islands is based on gps networks since there are as yet no tiltmeter stations installed on the island however there is a world class astronomical observatory on the island the el teide observatory where four tiltmeters two aligned in the north south and the other two in the east west are monitoring the movements of the solar telescope themis themis heliographic telescope for the study of solar magnetism and instabilites is among the three largest solar telescopes in the world since themis is located a few kilometers from the main volcanic structures of the island in particular the el teide pico viejo stratovolcano and the precision of the inclinometers is comparable to those used in geophysical studies we carried out the analysis of the tilt measurements for the period 1997 2006 the tiltmeters at themis are placed in the seventh floor of a tower hence their sensitivity to geological processes is reduced compared to geophysical installations however themis measurements are the only terrestrial data available in tenerife for such a long period of observations which include the sustained increase in seismic activity that started in 2001 in this sense a significant change was found in the east west tilt of approximately 35 radians between the years 2000 and 2002 some theoretical models were calculated and it was concluded that such tilt variation could not be due to dike intrusions nor a volcanic reactivation below the el teide pico viejo volcano the most likely explanation comes from dislocations produced by a secondary fault associated to a major submarine fault off the eastern coast of tenerife in any case taking into account the nearly permanent data recording at themis they could be considered as a complement for any ground deformation monitoring system in the island

viscoelastic gravitational deformation by a rectangular thrust fault in a layered earth previous papers in this series have been concerned with developing the numerical techniques required for the evaluation of vertical displacements which are the result of thrust faulting in a layered elastic gravitational earth model this paper extends these methods to the calculation of fully time dependent vertical surface deformation from a rectangular dipping thrust fault in an elastic gravitational layer over a viscoelastic gravitational half space the elastic gravitational solutions are used together with the correspondence principle of linear viscoelasticity to give the solution in the laplace transform domain the technique used here to invert the displacements into the time domain is the prony series technique wherein the transformed solution is fit to the transformed representation of a truncated series of decaying exponentials purely viscoelastic results obtained are checked against results found previously using a different inverse transform method and agreement is excellent the major advantage in using the prony series technique is that deformations can be computed for arbitrary time intervals a series of results are obtained for a rectangular 30 dipping thrust fault in an elastic gravitational layer over viscoelastic gravitational half space time dependent displacements are calculated out to 50 half space relaxation times a or 100 maxwell times 2 m a significant effects due to gravity are shown to exist in the solutions as early as several a the difference between the purely viscoelastic solution and the viscoelastic gravitational solutions grows as time progresses typically the solutions with gravity reach an equilibrium value after 10 20 relaxation times when the purely viscoelastic solutions are still changing significantly additionally the length scaling which was apparent in the purely viscoelastic problem breaks down in the viscoelastic gravitational problem two independent length scales one of which changes with time are now seen to characterize the problem

progressive proglacial to subglacial deformation and syntectonic sedimentation at the margins of the mid pleistocene british ice sheet evidence from north norfolk uk abstract detailed analysis and interpretation of the stratigraphy and structures developed within polydeformed sediments exposed in the coastal section between west runton and sheringham eastern england has allowed the characterisation of the glacitectonic signature associated with the advance of a major mid pleistocene anglian ice sheet the sequence of pre glacial deposits and glacial sediments laid down during earlier southerly directed ice advances d1 d2 is deformed and disrupted by an ice advance from the west southwest that marks a major change in ice flow dynamics in northern east anglia the simplest interpretation of this deformation event d3 is in terms of a progressive proglacial to subglacial deformation model proglacial deformation occurred in advance of the ice margin and was dominated by thrusting positive topographic features which developed above the propagating thrusts controlled sediment dispersal patterns within outwash sandur leading to the formation of small sub basins between these morainic ridges the accretion of the wedge shaped proglacial thrust moraines to the main push moraine formed at the margin of the advancing glacier may have temporarily stalled forward motion of the ice thrusting and large scale folding associated with ice marginal deformation led to the stacking of material excavated from further up ice onto the stoss side of these accreted thrust related moraines that allowed the glacier to override the obstruction subglacial deformation was highly variable in its style and intensity ranging from heterogeneous folding and thrusting through to more pervasive ductile shearing associated with the formation of a subglacial shear zone the thickness and complexity of this shear zone increases up ice where it is characterised by a thick glacitectonic melange the pore water content of the deforming sediments controlled the pattern of deformation within the shear zone however an increase in the efficiency of the drainage system towards the front of the glacier would have led to a rapid thinning of this water enhanced zone of ductile shear evidence from north norfolk suggests that zones of preferential pore water flow within the glacier bed are a major controlling factor on the location of the subglacial shear zone consequently the bulk of the forward motion of the glacier may not be accommodated by shearing within the sediments immediately below its base but occur at a deeper level within the deforming bed

glacial isostatic adjustment i the forward problem summary the isostatic adjustment of a radially stratified visco elastic spheroid is treated using space time green functions for the associated surface mass load boundary value problem these impulse response functions are convolved with a heaviside function to give the time dependent deformation of the planet which would be produced by a unit point mass brought up from infinity at t 0 and allowed to remain on the surface the resulting heaviside green functions can be employed to simulate all of the important signatures of glacial isostatic adjustment given a space time dependent surface mass load consisting of ice sheet ablation histories and a model of the simultaneous filling of the ocean basins these source terms are simply convolved with the heaviside green function appropriate to a specific response signature a realistic model of the spatial distribution of the main late pleistocene ice loads and of their temporal disintegration is constructed the response of two visco elastic earth models is computed and compared to a global set of relaxation data relative sea level curves on the basis of this initial comparison of theory and observation the possibility that the lower mantle has a viscosity which is significantly in excess of the viscosity of the upper mantle is excluded in addition clear evidence of the presence of the lithosphere has been found in relaxation data from sites which were near the edge of the laurentide ice sheet such data should therefore prove useful as a basis for analysis of lateral variations in lithosphere thickness further extensions of the calculation are suggested

viscoelastic displacement and gravity changes due to point magmatic intrusions in a gravitational layered solid earth summary we present a method for the computation of time dependent geodetic and geophysical signatures deformation potential and gravity changes due to magmatic intrusions in a layered viscoelastic gravitational medium this work is an extension of a deformation model previously developed to compute effects due to volcanic loading in an elastic gravitational layered media the model assumes a planar earth geometry useful for near field problems and consists of welded elastic and viscoelastic layers overlying a viscoelastic half space every layer can either be considered elastic or viscoelastic the intrusion treated as a point source can be located at any depth in any of the layers or in the half space several examples of theoretical computations for different media are also presented we have found that in line with previous results obtained by other authors introducing viscoelastic properties in all or part of the medium can extend the effects displacements gravity changes etc considerably and therefore lower pressure increases are required to model given observed effects the viscoelastic effects seem to depend mainly on the rheological properties of the layer zone where the intrusion is located rather than on the rheology of the whole medium we apply our model to the 1982 1984 uplift episode at campi flegrei modelling simultaneously the observed vertical displacement and gravity changes the results clearly show that for a correct interpretation of observed effects it is necessary to include the gravitational field in the anelastic theoretical models this factor can change the value and pattern of time dependent deformation as well as the gravity changes explaining cases of displacement without noticeable gravity changes or vice versa cases with uplift and incremental gravity values and other cases the combination of displacement and gravity changes is found to be especially effective in constraining the possible characteristics of the magmatic intrusion as well as the rheology of the medium surrounding it

spherical and ellipsoidal volcanic sources at long valley caldera california using a genetic algorithm inversion technique abstract we model the second inflation period at long valley caldera california using a genetic algorithm technique and high quality geodetic measurements of elevation changes and baseline extensions we compare two source inversions for both spherical mogi point sources and the finite prolate ellipsoid of yang and davis a sensitivity analysis for the genetic algorithm is performed based upon synthetic data set inversions on similar sources in order to better constrain the areal location orientation and volume of the potential sources the spherical sources are well constrained the larger located at 9 9 km beneath the resurgent dome with a volume of 0 036 km 3 while the second at only 0 008 km 3 is located at a depth of 7 3 km beneath the south moat the depths to the ellipsoidal sources are switched with the larger source at a depth of 9 6 km and the smaller at 11 8 km with volumes of 0 037 and 0 002 km 3 respectively

deformation gravity and potential changes due to volcanic loading of the crust a method for calculating deformation gravity and potential changes induced by volcanic loads imposed within and on the earth s crust is presented the method involves application of techniques developed for earthquake loading problems in elastic gravitational earth models by considering the elastic gravitational equilibrium of the layered system the gravitational and displacement response due to intruding masses and to pressurized magma chambers can be computed for applications involving seamount loading variations in the height of sea level can be calculated by requiring that seawater lie along an equipotential in continental loading problems the change in potential can be used to calculate the orthometric height cahnge as distinct from the geometric height change for some plausible loading geometries the difference between these two qunatities can be significant results for various loads and earth structures are shown and discussed in particular a magmatic mass intruding into an elastic gravitational lithosphere overlying a compressible gravitating asthenosphere produces distinct gravity anomalies which depend on the depth of intrusion applications of this result can be made to problems of isostatic compensation the intrusion of a magmatic mass together with the associated pressurization of the magma chamber produces distinctive surface gravity and deformation in the near field gravity gradients more defined as surface gravity divided by uplift vary with distance from the source moreover orthometric elevations can be significantly 25 less than geometric elevations these results have clear application to data from events such as the posteruption deflation of kilauea volcano less

inflation or deflation new results for mayon volcano applying elastic gravitational modeling volcanic activity produces deformation and gravity changes that many times can be used as precursors of future eruptions applying geodetic techniques to monitoring activity involves interpretation using deformation models usually the observed changes of the deformation and gravity fields are interpreted seperately not in a joint inversion it can be difficult if not impossible to interpret the data coherently or correctly in terms of the characteristics of the intrusion or the deflation derived from the gravity changes with purely elastic models as in the case of mayon volcano phillipines we show that elastic gravitational models can be used to interpret these cases simultaneously leading to a result that is more plausible on the basis of the available information thus we may need to change the philosophy normally used to interpret geodetic observations interpretation as proposed in this work can significantly improve the possibility of predicting future eruptions

vertical distortion in long valley california associated with the january 1983 earthquake swarm beginning in the summer of 1982 a series of repeated high precision gravity measurements have been undertaken in long valley california benchmarks have been established from south of crowley lake outside the caldera to mono craters in the north stations are reobserved at frequent intervals with three model g lacoste romberg gravity meters we observed significant changes in surface gravity associated with the january 1983 earthquake swarm in the south moat of long valley caldera these changes indicate that the ground around the casa diablo hot springs area was uplifted at the time of the swarm the uplift pattern agrees with that predicted by the model of rundle and whitcomb that is injection of magma into two chambers at 5 to 8 km depth beneath long valley caldera

interpretation of 1992 1994 gravity changes around mayon volcano philippines using point sources significant gravity changes observed around the mayon volcano philippines between 1992 and 1994 at 26 stations are interpreted in terms of an increase of mass and pressure changes at several point sources modelled using a fast inversion process this inversion approach attempts to fit gravity and elevation changes by combining a random search for the positions of the sources and a linear least squares fit for the incremental mass pressure and possible common regional values for gravity or elevation changes some stabilizer terms are included in the misfit function models with one and two sources were tested against the observed changes at mayon models with only one source give a best fit for a shallow source with a positive mass increment horizontally displaced far from the summit the study using two sources gives a best fit that is similar to the one source model but in addition indicates anomalous behavior at stations in the sw neglecting the stations located southward from a local fracture the best fitting model suggests one central positive mass change source which is likely to be an intrusion of about 0 5 mu with a depth of about 5 km beneath the volcano standard deviation for the residuals ranges from 7 8 gal for one source models to 6 7 gal for models with two sources both of the cases are below the error value of 9 4 gal estimated for the gravity data so that it is not possible to discriminate between both possible interpretations without additional information

models of crustal deformation this review is principally concerned with theoretical models of crustal deformation developed during this quadrennium observational data as well as topics in lithospheric flexure and isostasy are covered in companion reviews in this volume progress has been made toward constructing both new inelastic and inhomogeneous elastic models of earthquake induced crustal deformation most of the inelastic models involve dislocations or green s functions in an elastic or anelastic lithosphere which overlies a maxwell viscoelastic asthenosphere

an overview of geodetic volcano research in the canary islands the canary islands are mostly characterized by diffuse and scattered volcanism affecting a large area with only one active stratovolcano the teide pico viejo complex tenerife more than 2 million people live and work in the 7 447 km2 of the archipelago resulting in an average population density three times greater than the rest of spain this fact together with the growth of exposure during the past 40 years increases volcanic risk with respect previous eruptions as witnessed during the recent 2011 2012 el hierro submarine eruption therefore in addition to purely scientific reasons there are economic and population security reasons for developing and maintaining an efficient volcano monitoring system in this scenario geodetic monitoring represents an important part of the monitoring system we describe volcano geodetic monitoring research carried out in the canary islands and the results obtained we consider for each epoch the two main existing constraints the level of volcanic activity in the archipelago and the limitations of the techniques available at the time theoretical and observational aspects are considered as well as the implications for operational volcano surveillance current challenges of and future perspectives in geodetic volcano monitoring in the canaries are also presented

modeling gravity and trilateration data in long valley california 1983 1984 during the period july 1982 through july 1984 a series of repeated high precision gravity measurements have been undertaken in and around long valley california data were collected at about 40 sites using three lacoste romberg model g gravity meters at the same time the u s geological survey was conducting a program of high precision line length measurements throughout the same area significant changes were observed with both types of data during the intervals 1982 1983 and 1983 1984 previous work by us has shown that deformation data during the interval 1975 1983 are consistent with a model for the inflation of long valley caldera which includes magma injection beneath the south central caldera at a depth of only 5 km simultaneous inversion of the trilateration and gravity data for the period 1983 1984 shows that most of the previous model is still reasonably consistent with the data and implies injected volumes of between 0 01 and 0 02 km3 additionally uplift during this period occurred along the inyo domes chain of vents and flows indicating perhaps a new source of inflation in the northwest part of the caldera this uplift amounts to a few centimeters and implies a volume increase of perhaps 0 004 km3 at reasonably shallow depth 3 km the total amount of uplift in the northwest is small in comparison to the total uplift centered on the central resurgent dome total vertical displacement well in excess of half a meter for purposes of comparison we examine several models one of which involves injection at the base of the crust this model implies much higher injected volumes as much as 0 15 0 2 km3

the interpretation of gravity changes and crustal deformation in active volcanic areas simple models like the well known point source of dilation mogi s source in an elastic homogeneous and isotropic half space are widely used to interpret geodetic and gravity data in active volcanic areas this approach appears at odds with the real geology of volcanic regions since the crust is not a homogeneous medium and magma chambers are not spheres in this paper we evaluate several more realistic source models that take into account the influence of self gravitation effects vertical discontinuities in the earth s density and elastic parameters and non spherical source geometries our results indicate that self gravitation effects are second order over the distance and time scales normally associated with volcano monitoring for an elastic model appropriate to long valley caldera we find only minor differences between modeling the 1982 1999 caldera unrest using a point source in elastic homogeneous half spaces or in elasto gravitational layered half spaces a simple experiment of matching deformation and gravity data from an ellipsoidal source using a spherical source shows that the standard approach of fitting a center of dilation to gravity and uplift data only excluding the horizontal displacements may yield estimates of the source parameters that are not reliable the spherical source successfully fits the uplift and gravity changes overestimating the depth and density of the intrusion but is not able to fit the radial displacements

development of sediment landform associations at cold glacier margins dry valleys antarctica hambrey m j fitzsimons s j 2010 development of sediment landform associations at cold glacier margins dry valleys antarctica sedimentology 57 3 857 882 michael hambrey is corresponding author sponsorship marsden fund of new zealand university of otago research committee nerc grant no ner a s 2000 01256

the growth of geological structures by repeated earthquakes 1 conceptual framework in many places earthquakes with similar characteristics have been shown to recur if this is common then relatively small deformations associated with individual earthquake cycles should accumulate over time to create geological structures following this paradigm we show that existing models developed to describe leveling line changes associated with the seismic cycle can be adapted to explain geological features associated with a fault in these models an elastic layer containing the fault overlies a viscous half space with a different density fault motion associated with an earthquake results in immediate deformation followed by a long period of readjustment as stresses relax in the viscous layer and isostatic equilibrium is restored deformation is also caused as a result of the loading and unloading due to sediment deposition and erosion in this paper the parameters that control the growth of dip slip structures are identified we find that the flexural rigidity of the crust or the apparent elastic thickness provides the main control of the width of a structure the loading due to erosion and deposition of sediment determines the ratio of uplift to subsidence between the two sides of the fault the flexure due to sediment load is much more important in this respect than whether the fault is normal or reverse in character we find that in general real structures are associated with apparent elastic thicknesses of 4 km or less and thus with very low flexural rigidities

correction to contrast of metamorphic and structural histories across the work channel lineament coast plutonic complex british columbia by maria luisa crawford and lincoln s hollister

an integrated approach to the study of glaciolacustrine landforms and sediments a case study from hagavatn iceland abstract this paper describes the landform assemblage associated with the neoglacial fluctuation of hagafellsjokull eystri into proglacial hagavatn iceland this landform assemblage is dominated by three components firstly a series of moraines formed both by thrusting within the glacier margin and by proglacial subglacial deformation the internal sedimentary architecture of these moraines ranges from stacked sediment slabs separated by listric thrusts to complexly folded and faulted sequences all in glaciolacustrine sediments the second component is a morainal bank and associated ice contact delta the morainal bank consists of a series of low amplitude ridges composed of laminated silts and clays which have been deformed proglacially during the neoglacial ice advance 1890 this morainal bank helped stabilise the 1890 ice limit within the proglacial lake and was the focus for subaqueous outwash first in the form of a subaqueous out wash fan and subsequently as an ice contact delta the third component is a series of lake bed kame terraces formed by rapid sedimentation in a canal like lake formed as the ice retreated away from the push moraines a range of glaciolacustrine facies is present within the lake bed kame terraces and the sedimentary architecture records a complex pattern of ice marginal oscillations and changes in lake level this detailed case study provides an important analogue for the interpretation of both glaciolacustrine and glaciomarine landform sediment assemblages of pleistocene age and illustrates a range of styles of glaciolacustrine sedimentation and glaciotectonic deformation

absolute gravity measurements in california 1984 1989 repeated absolute gravity measurements have been made at 12 sites in california between 1984 3 and 1989 7 as determined in laboratory tests the instrument used has an estimated accuracy of 10 gal approximately 10 8 g the repeatability of the measurements is consistent with this accuracy assessment no gravity changes above the limits set by instrumental uncertainty and environmental noise are observed in california during this period the field observations provide upper limits on the rates of secular gravity changes which could be attributed to crustal deformation with a resolution corresponding to vertical displacement rates of 1 2 cm yr

under pressure clastic dykes in glacial settings abstract clastic dykes are widespread in glacial settings and we provide examples from switzerland patagonia iceland and the antarctic ranging in age from tertiary to recent on the basis of these examples we establish the general characteristics of clastic dykes and proceed to establish the direction of propagation on sedimentological grounds micromorphological analysis reveals that sedimentation in the dykes is ruled by pressure gradients and that ordinary sedimentological rules do not apply clastic dykes act like safety valves in the subglacial hydraulic system their development depends on specific subglacial conditions like water volume and pressure the nature of the bed sediments or bedrock and the hydraulic properties of the bed a number of scenarios for clastic dyke development are presented as there is not just one set of conditions under which they form development of clastic dykes affects glaciodynamics like velocity and surging and landform formation like till thickness and bedrock disruption

joint interpretation of displacement and gravity data in volcanic areas a test example long valley caldera california volcanic activity produces deformation and gravity changes that many times can be used as precursors of future eruptions applying geodetic techniques to monitoring activity involves interpretation using deformation models usually gravity change data and displacement data are interpreted separately we show using modeling of deformation and gravity change data in long valley caldera california usa that this can lead to incorrect interpretations the results obtained show that displacements and gravity changes must be interpreted together whenever possible and that elastic gravitational models can be a far more appropriate approximation to problems of volcanic load in the crust than the more commonly used purely elastic models therefore it is necessary to change the philosophy normally used to interpret geodetic observations improving the possibility of predicting future eruptions

a hybrid model for the summit region of merapi volcano java indonesia derived from gravity changes and deformation measured between 2000 and 2002 three dimensional displacements and gravity changes were measured at 20 points between 2000 and 2002 at merapi volcano java indonesia former models focused on the modeling of a single magmatic source located in the summit region of the volcano such models do not fit to our measurements between 2000 and 2002 a new hybrid model approach is developed consisting of an elastic gravitational source described by a mass and energy term as well as a combined dip slip strike slip fault zone in the summit region both nonlinear optimization problems given by the common inversion of three dimensional displacements and gravity changes are solved by applying a genetic algorithm the hybrid model fits the measurements accurately tested by fisher test statistics furthermore our model for merapi volcano confirms previous structural models for this region so that the new model is statistically proven as well as physically reliable

shear wave velocity structure around teide volcano results using microtremors with the spac method and implications for interpretation of geodetic results deformation analysis and simulation of volcanic edifices require the construction of models of elastic properties of those structures in this paper we present an analysis of microtremor measurements recorded during the performance tests of two temporary seismic arrays installed in the eastern portion of the teide caldera in 1994 we take advantage of recent developments of the spac method and use spatial cross correlation computations to estimate phase velocity dispersion of rayleigh waves at the location of the arrays we show that the extension of the standard spac method is valid in the case of our data justifying its use and supporting the generalization of the spac method to single station pairs the phase velocity dispersion curve obtained was inverted to recover the shear wave profile at the site of the arrays our results indicate that the subsoil structure of the caldera is laterally homogeneous at the scale of a few km about the location of the arrays we obtained about 315 m of volcanic sediments overlying rocks with a shear wave velocity of 2 km s these results are robust and are a starting point to further modelling of deformation permanent or transient at this volcanic edifice which can be useful in the interpretation of different observed fields in fact the computation of deformations and gravity changes due to possible volcanic intrusions in two models one considering the volcanic sediments and the other without considering them provided different results in the near field

on postglacial sea level summary an exact method is presented for calculating the changes in sea level that occur when ice and water masses are rearranged on the surface of elastic and viscoelastic non rotating earth models the method is used to calculate the instantaneous elastic and delayed vi scoelastic sea level changes following the partial melting of late quaternary ice sheets we find that there can be large errors in the usual assumption that changes in sea level are uniform over the ocean basins if a quantity of ice equivalent to a uniform 100 m rise in sea level melts from the laurentide and fennoscandian ice sheets then in the south pacific the instantaneous rise in sea level can be as large as 120m in the north atlantic the instantaneous rise is always less than 100 m there is a zone in the north atlantic with almost no sea level change and near greenland and norway the sea level falls rather than rises by over 100 m one thousand years after the melting a forebulge migrating towards the ice loads causes water to flow from the south pacific into the north pacific suggesting that raised beaches should occur in the south pacific the gravitational attraction of an ice mass upon a nearby ocean tends to hold sea level high in the vicinity of the ice this extra load near the ice may have a significant influence on postglacial isostatic adjustment

gravity induced stresses near topography of small slope topographic modification of gravity induced near surface stresses results in significant departures from a lithostatic state a perturbation scheme provides approximate analytical solutions for plane strain of an elastic half space with an irregularly shaped free surface of small characteristic slope e the leading order effect of the topography is equivalent to that of a distributed normal load on a plane boundary and the correction at order e is due to a distributed shear traction on a plane boundary in the near surface region these two effects contribute at the same order to departures from the lithostatic stress field the contribution of the shearing has been neglected in most previous analyses we present explicit solutions for several particular geometries a symmetric ridge or valley an adjacent ridge and valley a shelf and a sharp crested ridge notable features include 1 for a sufficiently steep ridge the horizontal normal stress is compressive at the crest and decreases possibly becoming tensile with depth 2 large horizontal tension is induced in a valley bottom at greater depth these effects vanish and the stresses approach lithostatic similar analysis is applied to a half space under a far field tectonic compression or tension the result shows that the leading order effect of topography is equivalent to a distributed shear traction on a plane surface regional horizontal compression can be significantly reduced or even change to tension in the neighborhood of a topographic high

modeling of stress changes at mayon volcano philippines in this paper we analyze the stress change associated with the inverted volcanic source models at mayon volcano philippines where there are gravity changes without significant deformation after the 1993 eruption we detail the applicable data and the associated inversion techniques and models prior to calculating the appropriate stress changes it is determined that the stress change associated with the central magmatic source produces compressional stress changes at a secondary source to the northwest prompting a change in the local water storage in the underlying fractured rock

sensitivity test of the geodetic network in las canadas caldera tenerife for volcano monitoring abstract a 17 benchmark geodetic network in the volcanic area of the teide caldera canary islands has been utilised several times since 1982 to detect crustal movements associated with volcanic activity within the network as well as a procedure for solving configuration problems the network is located on the mid western side of the caldera where there are two different morphological zones that both have benchmarks the authors performed a sensitivity test of this geodetic network for volcano monitoring purposes to do so we use a deformation model to calculate surface displacement caused by a dike intrusion in a homogenous half space the depth and location of dike are changed to study the variation of the effects produced displacements the size and location of the intruded dike are found to play a major role in determining both the displacement pattern and magnitude when the dike is close to the surface there is an inversion of the surface displacement pattern and very large surface displacement at certain benchmarks such phenomena can serve as precursors of such dike eruptions our study show a clear need to extend the existing geodetic network to cover the full island for volcano monitoring purposes

the 1890 surge end moraine at eyjabakkajokull iceland a re assessment of a classic glaciotectonic locality abstract the glaciotectonic architecture and sequential evolution of the eyjabakkajokull 1890 surge end moraines in iceland were studied for understanding better the formation and evolution of glaciotectonic end moraines and their relation to glacier dynamics based on morphological geological and geophysical data from terrain cross profiles cross sections and ground penetrating radar profiles we demonstrate that three different qualitative and conceptual models are required to explain the genesis of the eyjabakkajokull moraines firstly a narrow single crested moraine ridge at the distal end of a marginal sediment wedge formed in response to decoupling of the subglacial sediment from the bedrock and associated downglacier sediment transport secondly large lobate end moraine ridges with multiple closely spaced narrow asymmetric crests formed by proglacial piggy back thrusting thirdly a new model shows that moraine ridges with different morphologies may reflect different members of an end moraine continuum this is true for the eastern and western parts of the eyjabakkajokull moraines as they show similar morphological and structural styles which developed to different degrees the former represents an intermediate member with decollement at 4 5 m depth and 27 33 shortening through multiple open anticlines that are reflected as moderately spaced symmetric crests on the surface the latter represents an end member with decollement at about 27 m depth and 39 horizontal shortening through multiple high amplitude overturned and overthrusted anticlines appearing as broadly spaced symmetric crests we propose that the opposite end member would be a moraine of multiple symmetric wide open anticlinal crests of low amplitude our data suggest that the glacier coupled to the foreland to initiate the end moraine formation when it had surged to within 70 190 m of its terminal position this indicates a time frame of 2 6 days for the formation of the end moraines

flexure of the ocean lithosphere from island uplift bathymetry and geoid height observations the society islands summary ln flexure models of the response of the ocean lithosphere to seamount loading three key unknowns must generally be considered the density distribution of the load the degree of fd in of the deflection created moat and the flexural rigidity the models are usually constrained by one of three types of observations gravity or geoicl height anomalies the moat and arch geometry and the amount of uplift of islands on this arch the determination of the model parameters from geoid anomalies is critically dependent on the interpretation of the broad and regional geoid rise that is seen over many of the younger seamount chains and likewise the flexure parameters deduced from the moat and arch geometry are a function of the interpretation of the associated bathymetric swell the uplift data require that the tectonic erosional and sea level history of the region be known although this requirement can be relaxed if rather than the uplift relative to sea level the change in uplift with distance from the load is used as the observed quantity all these types of observations have been used in this paper to constrain the flexure model for the society islands and while any one data type on its own does not lead to reliable flexure parameters a consistent solution is found when the three are taken together the results point to a relatively low load density of 2 5 g m apart from a high density core a moat that is partly fdled in with sediment or volcanic debris and a flexural rigidity of about 3 x dyne cm

tectonic evolution of bell regio venus regional stress lithospheric flexure and edifice stresses in order to understand the relationship between volcanic and tectonic processes and the stress state in the lithosphere of venus we analyzed the stress environments and resulting tectonic features associated with the major volcanic edifices in bell regio using magellan synthetic aperture radar sar images and altimeter measurements of topography the major volcanoes of bell regio tepev mons and nyx mons exhibit tectonic characteristics that are unique relative to other volcanic edifices on venus the most prominent distinction is the lack of large rift zones within the overall highland uplift which characterize many other highland rises on venus also previous studies have determined that many large venus volcanoes exhibit radial tectonic structures on their flanks but generally lack the circumferential graben which surround volcanoes on earth and mars tepev and nyx montes exhibit both the radial tectonic features associated with other venusian edifices and numerous concentric graben nyx mons implies a more distributed magmatic system by its broad shape radial chains of pit craters and expansive flow fields whereas tepev mons is a more centralized volcanic system with limited associated long flows we investigate the regional stresses associated with bell regio and structural features believed to be a consequence of lithospheric flexure due to volcanic loading modeling both nyx mons and tepev mons as axisymmetric loads with gaussian mass distributions on an elastic plate the relationship between the tectonic features surrounding tepev mons and stresses associated with magma chamber inflation are also examined through finite element analysis using topography data to model the shape of the volcano we determine that a horizontally ellipsoidal or tabular reservoir at a range of depths from approximately 20 to 40 km can satisfy the locations of graben formation observed in magellan images these results imply a shift in volcanic style within bell regio from an early phase of broad low shield formation to later steep sided more centralized edifice development such changes are consistent with an increase in the thickness of the lithosphere over time

lithospheric stress and deformation the study of the mechanisms magnitudes and modes of lithospheric stress and deformation occupies a central position in the discipline of tectonophysics it is therefore difficult in assembling a comprehensive review to place limits on what should be included for example one cannot discuss stress and deformation apart from considerations of the rheological models of the lithosphere which link the two and ultimately control the behavior of plates at their margins and in their interiors once admitting to the importance of rheological considerations in discussing stress and deformation one is then compelled to include information relating to the thermal state of the lithosphere since temperature is one of the foremost environmental variables controlling rheology furthermore lithospheric processes cannot be considered in isolation from those affecting the asthenosphere since surely there exists some coupling between the motion of the lithosphere and convection in the earth s interior in fact an understanding of lithospheric stress and deformation can be considered a prerequisite to solving problems in geodynamics because it is through the lithospheric filter that one detects the consequences of thermal and compositional anomalies at greater depth the topic of this report cannot even be cleanly separated from reviews in other disciplines such as seismology and geodesy the magnitude and orientation of lithospheric stress is often indicated by earthquakes while lithospheric strain can be observed geodetically the philosophy i have adopted here is that some overlap with other review papers in this series is unavoidable and probably desirable from the standpoint of emphasizing how recent work n other areas of geophysics has contributed to the advancement in our understanding of the lithosphere s state of stress and mechanisms of deformation i have however resisted the temptation to include extraterrestrial studies presumably covered in the planetary section despite the similar causes for deviatoric stress and deformational mechanisms operating on other terrestrial planets certainly ideas of how silicate materials behave and how lithosphere responds to internal forces benefit from the perspective of omparative planetology finally in defining the scope of this portion of the u s national report to the iugg i did not consciously exclude papers by non u s citizens work done at non u s institutions projects not funded by the u s government or however else foreign might be defined topics in geophysical research cannot be divided along political boundaries however i did not attempt to seek out articles written in languages other than english or published in journals not readily available in the united states and i apologise for this obvious shortcoming

numerical modelling of thrust structures in unconsolidated sediments implications for glaciotectonic deformation abstract the mechanics of thrust faulting induced by a differential vertical load has been studied by application of a dynamic finite element model the modelled scenario is analogous to the glaciostatic load imposed onto an unconsolidated sedimentary substrate by a stationary ice sheet the objective is to evaluate whether large scale glaciotectonic deformation may be induced by gravity spreading in front of a stationary glacier or if a push from the rear is required the model is capable of handling large strains and rotations combined with visco elastic plastic rheologies model parameters are derived from a pleistocene large scale glaciotectonic thrust complex in the eastern danish north sea the plastic behaviour of the unconsolidated sediments is described by a time and pressure dependent drucker prager yield criterion combined with a non associated flow law the modelling results show that gravity spreading in front of a stationary ice sheet can form strain localisations and possibly cause thrust faults to nucleate in unconsolidated sediments several kilometres beyond the snout of the ice sheet provided a decollement surface is situated at a suitable depth relative to the effective load of the ice sheet hence it is concluded that large scale glaciotectonic thrusting may be formed by gravity spreading alone and a push from the rear is not generally required to explain the observed deformation