a physical basis for the frictional melting of some rock forming minerals abstract under conditions of coseismic slip 0 1 2 0 m s 1 within the upper crust differences in the shear yield strengths fracture toughnesses melting points and to a lesser extent thermal conductivities of rock forming minerals result in a hierarchy of friction melting susceptibilities in many so called pseudotachylytes it is observed that phyllosilicates and amphiboles are preferentially consumed to form the melt phase whilst quartz and feldspar tend to survive as clasts this can be explained in terms of the disequilibrium flash melting of those mineral phases possessing the lower shear yield strengths fracture toughnesses and thermal conductivities rather than by eutectic melting that would otherwise generate equilibrium minimum melts indicative of igneous processes at high strain rates typical of coseismic faulting the mechanical behaviour of minerals is primarily controlled by their fracture toughnesses with progressive comminution during slip leading to fusion the friction melting dependence on the mechanical properties of minerals indicates that there may be an important relationship between wall rock lithology and earthquake magnitude if frictional melting results in fault lubrication

spine growth and seismogenic faulting at mt unzen japan the concluding episode of activity during the recent eruption of mt unzen october 1994 to february 1995 was characterized by incremental spine extrusion accompanied by seismicity analysis of the seismic record reveals the occurrence of two dominant long period event families associated with a repeating nondestructive source mechanism which we attribute to magma failure and fault controlled ascent we obtain constraints on the slip rate and distance of faulting events within these families that analysis is complemented by an experimental thermomechanical investigation of fault friction in mt unzen dacitic dome rock using a rotary shear apparatus at variable slip rates and normal stresses a power density threshold is found at 0 3 mw m 2 above which frictional melt forms and controls the shear resistance to slip inducing a deviation from byerlee s frictional law homogenized experimentally generated pseudotachylytes have a similar final chemistry thickness and crystal content facilitating the construction of a rheological model for particle suspensions this is compared to the viscosity constrained from the experimental data to assess the viscous control on fault dynamics the onset of frictional melt formation during spine growth is constrained to depths below 300 m for an average slip event this combination of experimental data viscosity modeling and seismic analysis offers a new description of material response during conduit plug flow and spine growth showing that volcanic pseudotachylyte may commonly form and modify fault friction during faulting of dome rock this model furthers our understanding of faulting and seismicity during lava dome formation and is applicable to other eruption modes

the role of calcining and basal fluidization in the long runout of carbonate slides an example from the heart mountain slide block wyoming and montana u s a abstract in order to understand the movement of large rock masses or allochthons on low angle surfaces we have studied the 3400 km2 heart mountain slide block of northwestern wyoming and southwestern montana the heart mountain slide block was initiated on a 2 gradient with its toe thrust a minimum of 45 km across an early eocene landscape the slide block moved on a basal layer that ranges in thickness from a few tens of centimeters to several meters this basal layer commonly has a concrete like appearance of rounded mixed lithology grains in a fine grained carbonate matrix and in some locations it has features similar to sedimentary deposits including both normal and inverse grading flow banding turbidite like structures and clastic dikes containing pieces of carbonized wood nowhere did we observe crosscutting relationships in the basal layer or overlying clastic dikes as would be expected from incremental or noncatastrophic emplacement results from cathodoluminescence and 18o 13c and 8

identification of karst features using seismic p wave tomography and resistivity anisotropy measurements a football stadium with a capacity of a hundred thousand spectators is under construction over a karst terrain 10 km west of the old town of istanbul turkey a large cavity of approximately 30 m3 was detected beneath the sports field through a number of boreholes so that a geophysical survey was required to further investigate a portion of the sports field we utilized seismic refraction tomography and dc electrical method with rotated wenner array to delineate zones with solution voids and cavities total core recovery tcr was 5 15 from boreholes where zones with low velocities were identified through tomographic inversion whereas tcr values were above 60 in zones with higher velocities both low velocity zones in the tomographic images and increasing resistivity anisotropy with depth appear to indicate that the cavity extends toward the west and south at a depth of approximately 8 m although the southward and westward extension changes in character

application of seismic refraction tomography in karst terrane seismic refraction tomography field data were collected on several bridge foundation sites in pennsylvania in close proximity to geotechnical boring locations profiles determined from these field measurements were plotted against drilling data and these comparisons revealed the ability of seismic wave velocities to differentiate overburden soil from rock in addition foundation construction data were collected at each of the sites and compared with refraction test results determined prior to construction in particular top of rock revealed by an excavation and pile tip elevations at driving refusal were compared with refraction test results from these data it appears that seismic wave tomograms can characterize the soil rock interface and that it is possible to predict expected design pile lengths based upon a measured p wave velocity tomogram it can be concluded from these site comparisons that geophysical techniques such as seismic refraction tomography can provide important additional information to site characterization for bridge foundations in karst terrane however these techniques should not be viewed as a replacement but should be conducted during design stage site investigation to aid selection of borehole locations and other testing needs

bottom simulating reflectors seismic velocities and avo effects we obtain the wave velocities of ice and gas hydrate bearing sediments as a function of concentration and temperature unlike previous theories based on simple slowness and or moduli averaging or two phase models we use a biot type three phase theory that considers the existence of two solids grain and ice or clathrate and a liquid water and a porous matrix containing gas and water for consolidated berea sandstone the theory underestimates the value of the compressional velocity below 0 c including grain ice interactions and grain cementation yields a good fit to the experimental data strictly speaking water proportion and temperature are closely related fitting the wave velocity at a given temperature allows the prediction of the velocity throughout the range of temperatures provided that the average pore radius and its standard deviation are known the reflection coefficients are computed with a viscoelastic single phase constitutive model the analysis is carried out for the top and botto

synthetic sh seismograms in a laterally varying medium by the discrete wavenumber method summary we present a new method to calculate the sh wavefield produced by a seismic source in a half space with an irregular buried interface the diffractiog interface is represented by a distribution of body forces the green s functions needed to solve the boundary conditions are evaluated using the discrete wavenumber method our approach relies on the introduction of a periodicity in the source medium configuration and on the discretization of the interface at regular spacing the technique developed is applicable to boundaries of arbitrary shapes and is valid at all frequencies some examples of calculation in simple configurations are presented showing the capabilities of the method

failure of volcano slopes magmatic intrusions can initiate and sustain massive and catastrophic volcano collapse their role is twofold involving both driving and resisting forces first flank stability is diminished by magmastatic and magma overpressures and steepened slopes that accompany intrusion second excess pore pressures in potential failure zones can be generated as a result of intrusion related mechanical or thermal straining of the rock fluid medium pressurized retrograde boiling in high level magma chambers or hydrothermal fluid circulation also earthquakes may aid collapse through inertial forces and shaking induced pore pressure generation these excess pore pressures reduce the sliding resistance as shown for wedge shaped slide blocks for selected cases the destabilizing influence of mechanically induced pore pressures is maximized as the intruded width or corresponding overpressure of the intrusion is increased the destabilizing influence of thermally induced pore pressures is conditioned by the seve

volcanic drumbeat seismicity caused by stick slip motion and magmatic frictional melting during volcanic eruptions solidifying magma ascends through the volcanic conduit often accompanied by repetitive drum beat seismicity laboratory experiments on magma samples from soufriere hills volcano montserrat and mount st helens volcano usa show that viscous melt formed at the surface between the rising magma and conduit walls can temporarily halt magma ascent accentuating the cyclical seismicity

full frequency range transient solution for compressional waves in a fluid saturated viscoacoustic porous medium1 an analytical transient solution is obtained for propagation of compressional waves in a homogeneous porous dissipative medium the solution based on a generalization of biot s poroelastic equations holds for the low and high frequency ranges and includes viscoelastic phenomena of a very general nature besides the biot relaxation mechanism the viscodynamic operator is used to model the dynamic behaviour associated with the relative motion of the fluid in the pores at all frequency ranges viscoelasticity is introduced through the standard linear solid which allows the modelling of a general relaxation spectrum the solution is used to study the influence of the material properties such as bulk moduli porosity viscosity permeability and intrinsic attenuation on the kinematic and dynamic characteristics of the two compressional waves supported by the medium we also obtain snapshots of the static mode arising from the diffusive behaviour of the slow wave at low frequencies lntroduction the acoustics of porous media within the framework of petroleum geophysics have been receiving more attention in recent years regional exploration seismology aimed at the discovery of hydrocarbon reservoirs is based on simplified rheological models and ray representations of the wavefield in the past these approximations were sufficient since the degree of resolution required was not high in the present time when most reservoirs are delimited the need to increase the resolution and use not only the traveltimes but also the information contained in the amplitude and phase of the seismic wavefield has gradually emerged the new exploration scenario is confined to reservoir areas and involves the presence of oil wells and data from seismic logs and well seismics which have enough resolution to see the effects of bulk properties porosity permeability fluid content and fluid solid interaction on the seismic pulse in this case the correct

frictionite as evidence for a large late quaternary rockslide near kanchenjunga sikkim himalayas india implications for extreme events in mountain relief destruction abstract we present sedimentologic and petrographic field evidence of an extremely large 2 5 109 m3 late quaternary rockslide around dzongri 24 km s of kanchenjunga 8585 m a s l widespread occurrence of shattered leucogranites and migmatites deposited discordantly on top of undisturbed augen gneisses and separated by micro brecciated sliding surfaces indicate rapid movement during a large rockslide event occurrence of frictionite hyalomylonite in mineral samples indicates short term temperatures of 600 c in the moving rockslide mass along a 12 sliding plane from a sw direction of movement we infer a source 8 km ne of the deposit 5 km s of pandim 6691 m a s l where today a thick leucogranite intrusion marks a zone of weakness and failure of a postulated former mountain crest the mechanism of movement the dip of the sliding surface and the deposit preservation along ridge tops require that the dzongri rockslide ran out over an ice filled prek chu valley hence we prefer earthquake shaking over undercutting and glacial debuttressing as a possible trigger mechanism a regional review of other similarly large and catastrophic himalayan rockslides indicates that leucogranite intrusions are highly conducive to large scale failure in the higher himalayan crystalline hhc importantly high erosion rates have rendered this large rockslide deposit undetectable by remote sensing or digital elevation data which are commonly used for identifying evidence of such extreme events quantifying the contribution of such giant landslides in destroying some of the highest relief on earth will thus need further research attention

selective melting processes as inferred from experimentally generated pseudotachylytes abstract high speed friction experiments have been conducted on gabbros and granites to better constrain the process of frictional melting during seismogenic fault motion experiments were done on cylindrical specimens of 25 mm in diameter under a normal stress of 1 0 1 5 mpa and at slip rates up to 2 m s using a rotary shear high speed frictional testing machine the experimentally generated pseudotachylytes consist of a fused glassy matrix with abundant vesicles and angular or sub angular to rounded fragments these locally occur as injected network veins in the fractured rock x ray diffraction analysis has revealed the presence of as much as 40 70 wt glass the mineral contents of clasts in the experimental pseudotachylyte in granite as determined by x ray diffraction analysis indicate that quartz is the most resistant to melting biotite the least and feldspar is intermediate thus the sio2 depletion in natural pseudotachylyte glass is likely to be due to the selective melting of constituent materials during frictional melting

continuous wavelet transform theoretical aspects and application to aeromagnetic data at the huanghua depression dagang oilfield china we use the continuous wavelet transform based on complex morlet wavelets which has been developed to estimate the source distribution of potential fields for magnetic anomalies of adjacent sources they always superimpose upon each other in space and wavenumber making the identification of magnetic sources problematic therefore a scale normalization factor a n is introduced on the wavelet coefficients to improve resolution in the scalogram by theoretical modelling we set up an approximate linear relationship between the pseudo wavenumber and source depth the influences of background field random noise and magnetization inclination on the continuous wavelet transform of magnetic anomalies are also discussed and compared with the short time fourier transform results synthetic examples indicate that the regional trend has little effect on our method while the influence of random noise is mainly imposed on shallower sources with higher wavenumbers the source horizontal position will be affected by the change of magnetization direction whereas the source depth remains unchanged after discussing the performance of our method by showing the results of various synthetic tests we use this method on the aeromagnetic data of the huanghua depression in central china to define the distribution of volcanic rocks the spectrum slices in different scales are used to determine horizontal positions of volcanic rocks and their source depths are estimated from the modulus maxima of complex coefficients which is in good accordance with drilling results

the role of rock fragmentation in the motion of large landslides abstract by considering the implications of the comminution generally associated with very large landslides we arrive at a simple explanation for the remarkably low frictional resistance to motion demonstrated by large intact blockslides e g waikaremoana new zealand volcanic debris avalanches e g socompa chile and large rock avalanches e g falling mountain n z which allows such mass movements to achieve unexpectedly high velocities and long runout distances during rapid grain flow under high direct stress the overall grain motion generates stresses in many force chains that strain individual grains to failure most of the elastic strain energy accumulated in these force chains before failure is returned at failure to the resulting grain fragments resulting in apparent instantaneous pressures of 3q on the surroundings where q is the ambient strength of the previously intact grains gpa these intense pressures support some of the direct force on the shear layer so that the effective intergranular stress in the shear layer is reduced because frictional resistance is proportional to effective stress this reduces the overall frictional resistance to shear the steady state effective stress is that which just allows fragmentation to continue the resistance to motion estimated from this relationship explains to much better than order of magnitude accuracy the reported motions of the large rapid mass movements we also deduce that grain fragmentation can be sustained for sufficiently long to explain the phenomena without reducing the mean grain size by volume in the granular layer to unrealistically small values the presence of pore fluid does not appear to influence the effect of fragmentation dynamics in a major way the proposed mechanism requires further laboratory and simulation studies to reduce its current dependence on limited field data but its success suggests that it is worthwhile investigating further as an explanation for large mass movements in the types of brittle rock in which fragmentation occurs

potentially active volcanoes of peru observations using landsat thematic mapper and space shuttle imagery landsat thematic mapper tm images and space shuttle color photograph have been used to make a synoptic study of the volcanoes of southern peru 14 17 s the northernmost portin of the central volcanic zone cvz 14 28 s of the andes apart from providing consistent coverage the chief merit of the tm for this study has been the spatial resolution provided by the 30 m pixel size the optimal 20 m resolution variable lighting and viewing geometry and stereo capability of the shuttle photography provided an invaluable ancilliary data set at the resolution available subtle glacial morphological features such as valley and terminal moraines can be confidently identified and these features have been used to determine the relative ages of volcanoes volcanoes have been classified as potentially active if they have i a well preserved summit crater ii pristine lava flow texture and morphology iii flank lava flows with low albedo and iv evidence of postglacial 10 000 years activity eight major volcanoes are postulated to be potentially active most are large dominantly andesitic composite cones with edifice heights of up to 2500 m some of which threaten nearby settlements one of them sabancaya was active as recently as july 1988 other little known postglacial volcanic features include huaynaputina site of a major explosive rhyolitic eruption in 1600 a d and several fields of monogenetic scoria cones and lava flows the active volcanic front is some 200 km east of the peru chile trench and the volcanoes lie on a trenchparallel trend oblique to the ew subduction this narrow volcanic zone is thought to reflect the steep dip of the nazca plate through the zone of magma generation the break in the trend of the volcanic front in the northern extremity of the volcanic zone is thought to reflect the complexity of the crustal stress field above a major segment boundary in the subducting plate the fields of mafic monogenetic centers also occur in this region in comparison with the southern part of the cvz the general paucity of older volcanic edifices north of 17 s suggests a more recent onset of volcanism north of this latitude probably resulting from the oblique subduction of the nazca ridge and the consequent northward migration of its intersection with the pere chile trench this coupled with the lack of any large silicic caldera systems and youthful dacite domes like those found further south suggest that there are real differences between the volcanic evolution of different parts of the cvz

interaction of seismic waves with a viscous liquid layer abstract the interaction of seismic waves with a layer filled with a viscous fluid is studied this study is intended to provide the basis for designing active seismic experiments to detect the existence of hydraulically induced fractures in a hot dry rock geothermal energy system we compute transmission and reflection coefficients for p sv and sh waves incident at arbitrary angles onto a fluid layer embedded between two homogeneous half spaces we find that coefficients for sh waves at normal incidence can be written in terms of two dimensionless parameters one of these parameters i is the ratio of acoustic impedance of the fluid to the acoustic impedance of the solid the other dimensionless parameter d is a measure of the amount of energy the sh wave loses during one pass through the fluid layer we find that the amplitude of the sh wave transmitted through the fluid layer is equal to the amplitude of the incident sh wave if i is nearly 1 and d is small as d increases energy is lost due to viscous dissipation in the fluid and transmitted wave amplitude diminishes if i is not nearly 1 some energy is reflected by the fluid layer three dimensionless parameters are required for solution for the case of p waves normally incident on the fluid layer one parameter r is the ratio of the bulk modulus to effective shear modulus of the fluid the second parameter is the ratio of elastic impedance of the solid to the shear impedance of the fluid and the third is d we find that the value of r is a good measure of the importance of fluid viscosity on the propagation of p waves through the fluid detailed studies of the effects of fluid and solid physical properties on the amplitudes of transmitted and reflected waves when waves are normally incident provide valuable insight into the importance of physical properties in the calculations for non normal incidence finally reflection and transmission coefficients are computed for p and sv waves incident at arbitrary angle on a viscous fluid layer physical properties of fluid and rock are chosen to be those thought appropriate for the los alamos national laboratory hot dry rock geothermal test site located at fenton hill new mexico

fault rheology beyond frictional melting during earthquakes comminution and frictional heating both contribute to the dissipation of stored energy with sufficient dissipative heating melting processes can ensue yielding the production of frictional melts or pseudotachylytes it is commonly assumed that the newtonian viscosities of such melts control subsequent fault slip resistance rock melts however are viscoelastic bodies and at high strain rates they exhibit evidence of a glass transition here we present the results of high velocity friction experiments on a well characterized melt that demonstrate how slip in melt bearing faults can be governed by brittle fragmentation phenomena encountered at the glass transition slip analysis using models that incorporate viscoelastic responses indicates that even in the presence of melt slip persists in the solid state until sufficient heat is generated to reduce the viscosity and allow remobilization in the liquid state where a rock is present next to the melt we note that wear of the crystalline wall rock by liquid fragmentation and agglutination also contributes to the brittle component of these experimentally generated pseudotachylytes we conclude that in the case of pseudotachylyte generation during an earthquake slip even beyond the onset of frictional melting is not controlled merely by viscosity but rather by an interplay of viscoelastic forces around the glass transition which involves a response in the brittle solid regime of these rock melts we warn of the inadequacy of simple newtonian viscous analyses and call for the application of more realistic rheological interpretation of pseudotachylyte bearing fault systems in the evaluation and prediction of their slip dynamics

simulations of ground motion in the los angeles basin based upon the spectral element method we use the spectral element method to simulate ground motion generated by two recent and well recorded small earthquakes in the los angeles basin simulations are performed using a new sedimentary basin model that is constrained by hundreds of petroleum industry well logs and more than 20 000 km of seismic reflection profiles the numerical simulations account for 3d variations of seismic wave speeds and density topography and bathymetry and attenuation simulations for the 9 september 2001 m w 4 2 hollywood earthquake and the 3 september 2002 m w 4 2 yorba linda earthquake demonstrate that the combination of a detailed sedimentary basin model and an accurate numerical technique facilitates the simulation of ground motion at periods of 2 sec and longer inside the basin model and 6 sec and longer in the regional model peak ground displacement velocity and acceleration maps illustrate that significant amplification occurs in the basin

fusion by earthquake fault friction stick or slip field observations of pseudotachylites and experimental studies of high speed friction indicate that melting on a slipping interface may sig nificantly affect the magnitude of shear stresses resisting slip we investigate the effects of rock melting on the dynamic friction using theoretical models of shear heating that couple heat transfer thermodynamics of phase transitions and fluid mechanics results of laboratory experiments conducted at high order of m s slip velocities but low order of mpa normal stresses suggest that the onset of frictional melting may give rise to substantial increases in the effective fault strength presumably due to viscous effects however extrapolation of the modeling results to in situ conditions suggests that the efficiency of viscous braking is significantly reduced under high normal and shear stresses when transient increases in the dynamic fault strength due to fusion are not sufficient to inhibit slip decreases in the effective melt viscosity due to shear heating and melting of clasts drastically decrease the dynamic friction resulting in a nearly complete stress drop thermal runaway the amount of energy dissipation associated with the formation of pseudo tachylites is governed by the temperature dependence of melt viscosity and the average clast size in the fault gouge prior to melting clasts from a coarse grained gouge have lower chances of survival in a pseudotachylite due to a higher likelihood of non equilibrium overheating the maximum temperature and energy dissipation attainable on the fault surface are ultimately limited by either the rock solidus via viscous braking and slip arrest or liquidus via thermal runaway and vanishing resistance to sliding our modeling results indicate that the thermally activated fault strengthening and rupture arrest are unlikely to occur in most mafic protoliths but might be relevant for quartz rich rocks especially at shallow 5 7 km depths where the driving shear stress is relatively low

neogene and quaternary ignimbrites in the area of arequipa southern peru stratigraphical and petrological correlations abstract this study focuses on the correlation of four newly identified rhyolitic ignimbrites located around arequipa which were previously described as a single ignimbrite sheet 1 the rio chili ignimbrite ca 13 33 ma crops out in the rio chili canyon and consists of a cooling unit of non welded to partially welded massive crystal rich lapilli tuff this ignimbrite represents the base of the neogene ignimbrite succession in the arequipa area and may be stratigraphically equivalent to the 14 13 ma huaylillas ignimbrites in southern peru 2 the second voluminous 20 km3 and widespread la joya ignimbrite sheet ca 4 87 ma filled the arequipa depression its probable source is now buried underneath the chachani volcanic complex the la joya ignimbrite covers both the arequipa batholith toward the rio vitor piedmont and also part of the altiplano to the east and north of the chachani complex 3 the arequipa airport ignimbrite aai sheet ca 1 6 ma 18 km3 the third and latest infill of the arequipa basin consists of a lower white columnar jointed massive lapilli tuff indurated by vapor phase recrystallization and is overlain by an upper pink lithic rich non welded massive lapilli tuff the source of this ignimbrite is also buried underneath the chachani complex as indicated by anisotropy of magnetic susceptibility measurements and component lithology 4 the yura non welded pumice flow deposits ca 1 02 ma 1 5 km3 are restricted to the northern and western flanks of the chachani complex and may correlate with tuffs of the capillune formation on the altiplano all ignimbrites are high k calc alkaline to alkaline rhyolites which contain variable amounts of plagioclase biotite quartz sanidine and fe ti oxides the modal composition of mineral phases and chemistry of amphiboles and biotites are useful for distinguishing the ignimbrites specific geochemical fingerprints such as sr y rb ba cs ree and sr isotopes were effective discriminator elements magmatic differentiation crustal residence time and contamination and source melting processes are discussed in order to explain compositional variations the older la joya ignimbrite and rio chili ignimbrite reflect initial wetter crustal melts closer to granite composition whereas with time the younger arequipa airport ignimbrite and yura tuffs initial melts are slightly less evolved and dryer due to more extensive crustal melting the voluminous 40 km3 neogene ignimbrites of the arequipa area were produced by three major explosive volcanic pulses in the central volcanic zone of southern peru whose genetic relation with tectonic uplift and crustal thickening of the andean cordillera are still a matter of debate

analytic simulation of the elastic waves propagation in the neighborhood of fluid filled wells with monopole sources an analytic formulation to understand the scattering diffraction and attenuation of elastic waves at the neighborhood of fluid filled wells is presented an important and not widely exploited technique to carefully investigate the wave propagation in exploration wells is the logging of sonic waveforms fundamental decisions and production planning in petroleum reservoirs are made by interpretation of such recordings nowadays geophysicists and engineers face problems related to the acquisition and interpretation under complex conditions associated with conducting open hole measurements a crucial problem that directly affects the response of sonic logs is the eccentricity of the measuring tool with respect to the center of the borehole even with the employment of centralizers this simple variation dramatically changes the physical conditions on the wave propagation around the well recent works in the numerical field reported advanced studies in modeling and simulation of acoustic wave propagation around wells including complex heterogeneities and anisotropy however no analytical efforts have been made to formally understand the wireline sonic logging measurements acquired with borehole eccentered tools in this paper the graf s addition theorem was used to describe monopole sources in terms of solutions of the wave equation the formulation was developed from the three dimensional discrete wave number method in the frequency domain the cylindrical bessel functions of the third kind and order zero were re derived to obtain a simplified set of equations projected into a bi dimensional plane space for displacements and stresses this new and condensed analytic formulation allows the straightforward calculation of all converted modes and their visualization in the time domain via fourier synthesis the main aim was to obtain spectral surfaces of transfer functions and synthetic seismograms that might be useful to understand the wave motion produced by the eccentricity of the source and explain in detail the new arising borehole propagation modes finally time histories and amplitude spectra for relevant examples are presented and the validation of time traces using the spectral element method is reported

ground roll attenuation using the s and x f k transforms ground roll which is characterized by low frequency and high amplitude is an old seismic data processing problem in land based seismic acquisition common techniques for ground roll attenuation are frequency filtering f k or velocity filtering and a type of f k filtering based on the time offset windowed fourier transform these techniques assume that the seismic signal is stationary in this study we utilized the s x f k and t f k transforms as alternative methods to the fourier transform the s transform is a type of time frequency transform that provides frequency dependent resolution while maintaining a direct relationship with the fourier spectrum application of a filter based on the s transform to land seismic shot records attenuates ground roll in a time frequency domain the t f k and x f k transforms are approaches to localize the apparent velocity panel of a seismic record in time and offset domains respectively these transforms provide a convenient way to define offset or time varying reject zones on the separate f k panel at different offsets or times

frictional melt and seismic slip 1 frictional melt is implied in a variety of processes such as seismic slip ice skating and meteorite combustion a steady state can be reached when melt is continuously produced and extruded from the sliding interface as shown recently in a number of laboratory rock friction experiments a thin low viscosity high temperature melt layer is formed resulting in low shear resistance a theoretical solution describing the coupling of shear heating thermal diffusion and extrusion is obtained without imposing a priori the melt thickness the steady state shear traction can be approximated at high slip rates by the theoretical form ss n1 4 a under a normal stress n slip rate v radius of contact area r a is a dimensional normalizing factor and w is a characteristic rate although the model offers a rather simplified view of a complex process the predictions are compatible with experimental observations in particular we consider laboratory simulations of seismic slip on earthquake faults a series of high velocity rotary shear experiments on rocks performed for n in the range 1 20 mpa and slip rates in the range 0 5 2 m s 1 is confronted to the theoretical model the behavior is reasonably well reproduced though the effect of radiation loss taking place in the experiment somewhat alters the data the scaling of friction with n r and v in the presence of melt suggests that extrapolation of laboratory measures to real earth is a highly nonlinear nontrivial exercise

application of the continuous wavelet transform on seismic data for mapping of channel deposits and gas detection at the co2sink site ketzin germany conventional seismic data are band limited and therefore provide limited geological information every method that can push the limits is desirable for seismic data analysis recently time freque

on the transient behavior of frictional melt during seismic slip s n and g d t were supported by a european research council starting grant project acronym usems and by a progetti di eccellenza fondazione cassa di risparmio di padova e rovigo we are grateful to nick beeler and to an anonymous referee for their constructive reviews and their help to improve the clarity of the manuscript

electron microscopy study of hyalomylonites evidence for frictional melting in landslides abstract hyalomylonites from langtang nepal and kofels otz valley austria were investigated by transmission electron microscopy tem the matrix is glassy at both localities rarely it is crystallized and devitrified to dendrites and skeletal microlites of plagioclase alkali feldspar and biotite the matrix is chemically heterogeneous with schlieren and formed by partial to almost complete melting of host rocks of granitic to granodioritic composition locally glasses with pure quartz plagioclase and alkalifeldspar composition were found from sio 2 glass minimum temperatures of 1520 c are estimated at both hyalomylonite localities melting appears to be the result of frictional heating on the gliding plane of a large landslide the host rocks were deformed in a brittle mode microstructures typical of plastic deformation at high temperatures are displayed by inclusions and were probably inherited from previous tectonic events

frictional melting processes and products in geological materials introduction and discussion this special issue is the outcome of a theme session convened by the above authors entitled frictional melting processes and products in geologic materials held at the 1990 geological society of america annual meeting in dallas texas u s a the goals of the session were threefold to bring together researchers working on various aspects of frictional melting in rock to provide a forum for the exchange of new ideas and to encourage the production of a thematic set of papers dedicated to the topic of the eight papers presented here the first two spray swanson are primarily processand mechanism oriented the next magloughlin maddock o hara deal primarily with chemical aspects of host rock pseudotachylyte relations the last three mainly provide descriptions of naturally occurring koch and masch techmer et al and artificially produced kennedy and spray friction melts natural pseudotachylytes are described from strike slip zones magloughlin swanson thrusts and their listric counterparts koch and masch techmer et al and connecting lateral ramps o hara thus it appears that there exists an association between pseudotachylyte generation and relatively long lived largedisplacement faulting and shearing the prime objective of the meeting was to promote the integration of different approaches

extreme frictional processes in the volcanic conduit of mount st helens usa during the 2004 2008 eruption abstract the 2004 2008 eruption of mount st helens saw the extrusion of seven high viscosity spines and formation of discrete shear zones along the conduit margin at spine 7 this shear zone consists of four structurally distinct layers the outer surface gouge l1 crosscuts a dark banded layer l2 which grades into a moderately sheared layer l3 and undeformed rock l4 inside the spine field observations porosity measurements geochemistry mineralogy microstructure crystal size and shape distribution kinetic properties and magnetic analyses chart the evolution of deformation processes and products throughout the eruption gouge formation was concomitant with characteristic microseismic drumbeats at depths 0 5 1 km in addition the seismic record shows two larger earthquakes with similar seismic signatures in august 2006 which we conclude represent larger slip amounts along the conduit margin of spine 7 extensive slip resulted in frictional heating on the order of several hundreds of degrees melting the highly viscous crystalline ascending magma plug and forming a pseudotachylyte high ambient temperatures in the conduit resulted in near equilibrium melting and slow recrystallisation thus impeding the development of signature pseudotachylyte characteristics and hindering identification thus frictional melting and recrystallisation in ascending magma plugs may be a common but unidentified phenomena at composite volcanoes worldwide

a model for the rheology of particle bearing suspensions and partially molten rocks an edited version of this paper was published by agu copyright 2009 american geophysical union

vertical injectites of detachment carbonate ultracataclasite at white mountain heart mountain detachment wyoming carbonate ultracataclasite cuc is found as a veneer along the bedding plane portion of the eocene heart mountain detachment wyoming united states at white mountain where the cuc is thickest we report the discovery of six dikes as much as 1 m wide that were intruded vertically 120 m from the detachment into the overlying madison and bighorn formations the horizontal basal detachment and injectite material is texturally petrographically geochemically and isotopically identical containing sparse sand to pebble sized andesitic clasts various quartz calcite melt spherules and armored lapilli in a matrix 95 of fine grained calcite the relationship of hanging wall displacement to fault gouge generation and the presence of vertical 120 m fault gouge injectites makes the heart mountain slide anomalous to all fault systems especially as this fault system had only one episode of motion

sedimentology and geomorphology of the deposits from the august 2006 pyroclastic density currents at tungurahua volcano ecuador the deposits of the pyroclastic density currents from the august 2006 eruption of tungurahua show three facies associations depending on the topographic setting the massive proximal cross stratified and distal cross stratified facies 1 the massive facies is confined to valleys on the slopes of the volcano it contains clasts of 1 m diameter to fine ash material is massive and interpreted as deposited from dense pyroclastic flows its surface can exhibit lobes and levees covered with disk shaped and vesicular large clasts these fragile large clasts must have rafted at the surface of the flows all along the path in order to be preserved and thus imply a sharp density boundary near the surface of these flows 2 the proximal cross stratified facies is exposed on valley overbanks on the upper part of the volcano and contains both massive coarse grained layers and cross stratified ash and lapilli bedsets it is interpreted as deposited from a dense pyroclastic flows that overflowed the gentle ridges of valleys of the upper part of the volcano and b dilute pyroclastic density currents created from the dense flows by the entrainment of air on the steep upper flanks 3 the distal cross stratified facies outcrops as spatially limited isolated and wedge shaped bodies of cross stratified ash deposits located downstream of cliffs on valleys overbanks it contains numerous aggrading dune bedforms whose crest orientations reveal parental flow directions a downstream decrease in the size of the dune bedforms together with a downstream fining trend in the grain size distribution are observed on a 100 m scale this facies is interpreted to have been deposited from dilute pyroclastic density currents with basal tractional boundary layers we suggest that the parental flows were produced from the dense flows by entrainment of air at cliffs and that these diluted currents might rapidly deposit through pneumatic jumps three modes are present in the grain size distribution of all samples independently of the facies which further supports the interpretation that all three facies derive from the same initial flows this study emphasizes the influence of topography on small volume pyroclastic density currents and the importance of flow transformation and flow stripping processes

disappearing ink how pseudotachylytes are lost from the rock record abstract melt origin pseudotachylytes are the most widely accepted feature recording earthquake slip in the fault rock record however reports of pseudotachylytes are rare compared to the frequency and distribution of earthquakes in active faults suggesting melting occurs only under exceptional circumstances and therefore that pseudotachylytes are rarely formed in this paper we document the processes whereby pseudotachylytes are overprinted destroyed and otherwise removed from the rock record we present examples of recrystallized altered and cataclastically and crystal plastically deformed pseudotachylytes from a variety of ancient faults based on these observations we identify characteristics of pseudotachylytes that are resistant to change over geologic time and develop criteria to allow recognition of relict pseudotachylytes our results imply that pseudotachylytes are vastly under reported due to their vulnerability to destruction and the resulting difficulty in identification as a consequence the significance of frictional melting is underestimated the criteria we propose to distinguish relict pseudotachylytes can help to reconcile the observed frequency of earthquakes with the difficulty of demonstrating ancient seismic slip in the rock record

bubble collapse structure a microstructural record of fluids bubble formation and collapse and mineralization in pseudotachylyte abstracta complex microstructural feature has been discovered within centimeter scale pseudotachylyte veins and is here termed bubble collapse structure bcs three first order features of bcss are 1 a central quartz dominated monocrystal or polycrystal 2 a light colored reaction halo and 3 a generally radial but commonly curving pattern of opaque seams and or elliptical quartz amygdules two populations of bubbles were principally responsible for forming bcss one was a population of millimeter scale bubbles and the second involved much more numerous small bubbles mean diameter m the first population likely formed from liquid water interstitial to the precursory cataclasite or from melting of hydrous minerals whereas the second population formed by diffusional growth bcss began forming as the pseudotachylyte melt cooled and the pressure inside the bubbles decreased as the large bubbles flattened into oblate ellipsoids parallel to the vein margins melt flowed toward each collapsing bu

identification of karst features with spectral analysis on the seismic reflection data the use of high resolution seismic tools to investigate karst terrain has had limited success due to the ambiguous seismic events caused by lateral heterogeneities of the sedimentary cover as well as the superimposition of surface waves to address these problems a spectral analysis scheme is proposed on the seismic reflection data to characterize karst features in this paper first the s transform is applied to suppress the ground roll as a type of time frequency transform the s transform provides frequency dependent resolution while maintaining a direct relationship with the fourier spectrum application of a filter based on the s transform attenuates ground roll in a time frequency domain then the continuous wavelet transform is employed for the time frequency mapping of potential karst features which are featured as frequency differentiation anomalies synthetic model and real data example validate the efficiency of the spectral analysis scheme for the detection of karst features

valles marineris mars wet debris flows and ground ice abstract detailed study of the valles marineris equatorial troughs suggests that the landslides in that area contained water and probably were gigantic wet debris flows one landslide complex generated a channel that has several bends and extends for 250 km further support for water or ice in debris masses includes rounded flow lobes and transport of some slide masses in the direction of the local topographic slope differences in speed and emplacement efficiency between martian and terrestrial landslides can be attributed to the entrainment of volatiles on mars but they can also be explained by other mechanisms support that the wall rock contained water comes from the following observations 1 the water within the landslide debris must have been derived from wall rock 2 debris appears to have been transported through tributary canyons 3 locally channels emerged from the canyons 4 the wall rock apprarently disintegrated and flowed easily and 5 fault zones within the troughs are unusually resistant to erosion the study further suggests that in the equatorial region of mars material below depths of 400 800 m was not desiccated during the time of landslide activity within the last billion years of martian history therefore the martian ground water or groundice reservoir if not a relic from ancient times must have been replenished

geological constraints on the emplacement mechanism of the parinacota debris avalanche northern chile the holocene parinacota volcanic debris avalanche ca 8 000 years b p is located in the central andes of northern chile the avalanche formed by the sector collapse of a major stratovolcano adjacent to a lake basin in a single catastrophic event the deposit has an estimated volume of ca 6 km3 a run out of over 22 km and covers more than 140 km2 of the surrounding terrain the values of the heim coefficient 0 08 and the ratio a v 2 3 ca 50 where a is the area covered and v the volume of the deposit indicate high mobility of the avalanche debris in transport two avalanche units can be distinguished the lower unit consists mainly of blocks of rhyodacitic lavas and domes and pyroclastic flow deposits and glacial fluvial and lacustrine sediments the upper unit consists of a coarse grained breccia with little matrix largely composed of andesite blocks which are angular with little or no rounding by abrasion the avalanche displays pronounced hummocky topography in which hummock volume and amplitude as well as maximum block size within individual hummocks tends to decrease with transport distance and towards the lateral margins of the avalanche deposit some surfaces of individual breccia blocks are covered by tens to thousands of small scale impact marks indicating that neighbouring blocks were vibrating and colliding without significant shearing motion most of the deformation and shearing was instead accommodated in a basal layer of wet structureless sediments incorporated into the avalanche debris from the inundated lake basin we propose that the ancestral parinacota stratovolcano collapsed because of loading of underlying fluvioglacial and lacustrine sediments the edifice disintegrated during collapse along existing fractures into large rock domains volumes from 10 to greater than 1 106 m3 which were transported with little internal deformation and then fragmented into hummocks of breccia as they were deposited the decrease of hummock volume with distance suggests that material that travelled further broke up and had an initial greater kinetic energy

shear localisation strain partitioning and frictional melting in a debris avalanche generated by volcanic flank collapse abstract the arequipa volcanic landslide deposit to the east of arequipa peru originated from the pichu pichu volcanic complex covering an area 100 km2 the debris avalanche deposit exhibits internal flow structures and basal pseudotachylytes we present field microstructural and chemical observations from slip surfaces below and within the deposit which show varying degrees of strain localisation at one locality the basal shear zone is localised to a 1 2 cm thick extremely sheared layer of mixed ultracataclasite and pseudotachylyte containing fragments of earlier frictional melts rheological modelling indicates brittle fragmentation of the melt may have occurred due to high strain rates at velocities of 31 m s 1 and that frictional melting is unlikely to provide a mechanism for basal lubrication elsewhere we observe a

plane layered models for the analysis of wave propagation in reservoir environments1 the long wavelength propagation and attenuation characteristics of three geological structures that frequently occur in reservoir environments are investigated using a theoretical model that consists of a stack of fine and viscoelastic plane layers with the layers being either solid or fluid backus theory properly describes fine layering and a set of fluid filled microfractures under the assumption that interfaces between different materials are bonded the effects of saturation on wave attenuation are modelled by the relative values of the bulk and shear quality factors the anisotropic quality factor in a fine layered system shows a variety of behaviours depending on the saturation and velocities of the single constituents the wave is less attenuated along the layering direction when the quality factors are proportional to velocity and vice versa when inversely proportional to velocity fractured rocks have very anisotropic wavefronts and quality factors in particular for the shear modes which are strongly dependent on the characteristics of the fluid filling the microfractures 7hen the size of the boundary layer is much smaller than the thickness of the fluid layer the stack of solid fluid layers becomes a layered porous media of the biot type this behaviour is caused by the slip wall condition at the interface between the solid and the fluid as in biot theory there are two compressional waves but here the medium is anisotropic and the slow wave does not propagate perpendicular to the layers moreover this wave shows pronounced cusps along the layering direction like shear waves in a very anisotropic single phase medium

large scale landslide simulations global deformation velocities and basal friction the cause of the apparent small friction exhibited by long runout landslides has long been speculated upon in an attempt to provide some insight into the matter this paper describes results obtained from a discrete particle computer simulation of landslides composed of up to 1 000 000 two dimensional discs while simplified the results show many of the characteristics of field data the volumetric effect on runout preserved strata etc and with allowances made for the two dimensional nature of the simulation the runouts compare well with those of actual landslides the results challenge the current view that landslides travel as a nearly solid block riding atop a low friction basal layer instead they show that the mass is completely shearing and indicate that the apparent friction coefficient is an increasing function of shear rate the volumetric effect can then be understood with all other conditions being equal different size slides appear to travel with nearly the same average velocity however as the larger landslides are thicker they experience smaller shear rates and correspondingly smaller fractional resistance

frictional fusion due to coseismic landsliding during the 1999 chi chi taiwan ml 7 3 earthquake fused materials pseudotachylytes generated from landsliding during the 1999 chi chi taiwan ml7 3 earthquake are found on the glide plane in mio pliocene interbedded shale and siltstone the pseudotachylytes occur as thin layers on the glide plane and as veins injected into cracks in the host rocks which are a few mm to 1 cm in thickness typical melting textures within the pseudotachylyte include vesicles glassy matrices flow structures and rounded and embayed clast shapes powder x ray diffraction analysis has revealed a glass content of up to 50 wt within the pseudotachylyte physical conditions of pseudotachylyte formation are estimated to have been 1 5 mpa corresponding to ca 40 m depth at a temperature of at least 1100 1600 c the geological and petrological data suggests that these pseudotachylytes formed by frictional melting generated from coseismic landsliding during the chi chi earthquake

non newtonian rheological law for highly crystalline dome lavas volcanic eruption models are hampered by the lack of multiphase magmatic flow laws most rheological models estimate the viscosity of multiphase lavas via the einstein roscoe equation but this simplification cannot be used for high crystallinity and it does not consider the non newtonian strain rate dependence of viscosity we carried out parallel plate experiments on natural samples to simulate multiphase lava deformation under various stresses and strain rates multiphase lavas exhibit an important component of shear thinning and appear to invalidate the adequacy of einstein roscoe based formulations for highly crystalline lava rheology the remarkable singular dependence of viscosity on strain rate yields a novel universal rheology law at eruptive temperatures t i e log 0 993 8974 t 0 543 log our work reveals the importance of considering microcracking and viscous dissipation at very high strain rate 10 3 s 1 explaining the occurrence of seismic swarms along the conduit margins and consequently supporting plug like magma ascent models

effect of glass on the frictional behavior of basalts at seismic slip rates we performed 31 friction experiments on glassy basalts gb and glass free basalts gfb at slip rates up to 6 5 m s 1 and normal stress up to 40 mpa seismic conditions frictional weakening was associated to bulk frictional melting and lubrication the weakening distance dw was about 3 times shorter in gb than in gfb but the steady state friction was systematically higher in gb than in gfb the shorter dw in gb may be explained by the thermal softening occurring at the glass transition temperature tg 500 c which is lower than the bulk melting temperature tm 1250 c of gfb postexperiment microanalyses suggest that the larger crystal fraction measured in gb melts results in the higher steady state friction value compared to the gfb melts the effect of interstitial glass is to facilitate frictional instability and rupture propagation in gb with respect to gfb

elastic moduli evolution and accompanying stress changes with increasing crack damage implications for stress changes around fault zones and volcanoes during deformation summary the elastic moduli of rock in areas susceptible to crack damage such as within fault zones or volcanic edifices can be subject to large modifications knowledge of how elastic moduli may vary in such situations is important for both the reliable modelling of volcano deformation and stability and for linear and non linear elastic crack models for earthquake rupture furthermore it has previously been shown that changes in elastic moduli can induce changes in the stress field surrounding faults here we report both uniaxial experimental measurements of changes in elastic moduli during increasing amplitude cyclic stressing experiments on a range of different rock types basalts sandstones and granite and the results of modelled stress modifications the trend in elastic moduli evolution with increasing damage was remarkably similar for each rock type with the exception of essentially crack free intrusive basalt that exhibited very minor changes in general young s modulus decreased by between 11 and 32 per cent and poisson s ratio increased by between 72 and 600 per cent over the total sequence of loading cycles these changes are attributed to an increasing level of anisotropic crack damage within the samples our results also show that acoustic emission ae output during any loading cycle only commenced when new crack damage was generated this corresponded to the level of stress where ae ceased during the unloading portion of the previous cycle using the multilayer elastic model of faulkner et al we demonstrate that the damage induced changes in elastic moduli also result in significant decreases in differential stress increases in mean stress and rotation of the applied greatest principal stress relative to the orientation of the mechanical layering the similar trend in the evolution of the elastic moduli of all the rocks tested suggests that stress modification in the damage zone of faults might take the same form regardless of the lithology through which the fault runs these observations are discussed in terms of their applicability to both fault zones and deformation at volcanoes

low to high velocity frictional properties of the clay rich gouges from the slipping zone of the 1963 vaiont slide northern italy the final slip of about 450 m at about 30 m s of the 1963 vaiont landslide italy was preceded by 3 year long creeping phase which was localized in centimeter thick clay rich layers 60 70 smectites 20 30 calcite and quartz here we investigate the frictional properties of the clay rich layers under similar deformation conditions as during the landslide 1 5 mpa normal stress 2 10 7 to 1 31 m s slip rate and displacements up to 34 m experiments were performed at room humidity and wet conditions with biaxial torsion and rotary shear apparatus the clay rich gouge was velocity independent to velocity weakening in both room humidity and wet conditions in room humidity experiments the coefficient of friction decreased from 0 47 at v 0 70 m s full lubrication results from the formation of a continuous water film in the gouge the vaiont landslide occurred under wet to saturated conditions the unstable behavior of the landslide is explained by the velocity weakening behavior of the vaiont clay rich gouges the formation of a continuous film of liquid water in the slipping zone reduced the coefficient of friction to almost zero even without invoking the activation of thermal pressurization this explains the extraordinary high velocity achieved by the slide during the final collapse

decoupling of pyroclastic currents hazards assessments gravitational settling of fragments gas elutriation and boundary layer processes cause concentration values to change within different parts of sediment gravity flows during movement these processes result in flow transformations density stratification and decoupling of single currents into separate sediment gravity flows density can change by an increase in solids concentration in basal zones of currents by downward fall of particles or by incorporation of particles from the substrate thereby leaving their upper parts more dilute in some flows upward streaming gases and elutriation of fines cause dilute turbulent currents to develop at the top of a dense current increasing concentration dampens turbulent action transforming the turbulent to the nonturbulent state commonly at the current s base conversely dilute parts of currents become or remain turbulent currents consisting of turbulent and nonturbulent parts can decouple by shearing past one another because of differing flow properties with each part taking separate paths the manner by which a pyroclastic flow moves affects its predicted runout distance its distribution as continuous sheets or in isolated basins and whether it can cross barriers such as high mountain ranges or water bodies during the eruption of unzen volcano on june 3 1991 decoupling of a pyroclastic surge from the top of a pyroclastic flow caused the deaths of harry glicken maurice krafft katia krafft and 40 japanese citizens mapping volcanic hazard zones requires that consideration be given to decoupling processes to help prevent similar tragedies in the future

pseudotachylyte frictionite at the base of the arequipa volcanic landslide deposit peru implications for emplacement mechanisms abstract the arequipa volcanic landslide deposit peru displays a pseudotachylyte or frictionite at its basal contact with an older ignimbrite the pseudotachylyte consists of a dark 1 cm thick vitreous layer that shows striations on its upper surface it contains small mineral clasts from both the landslide rocks and the underlying ignimbrite embedded in an optically isotropic matrix tem observations revealed a clast melt suspension with a lower black obsidian like vein made of chemically heterogeneous glass the pseudotachylyte is interpreted as the result of partial melting due to frictional heating during landslide emplacement this is the third pseudotachylyte reported at the base of a landslide deposit and the first in a volcanic environment calculations show that basal melting only accounts for a small proportion of the total energy released during landslide emplacement indicating that landslide transport was dominated by dissipative stresses affecting the whole landslide body and not conce

laboratory simulations of tensile fracture development in a volcanic conduit via cyclic magma pressurisation during volcanic unrest high magma pressure induces cracking and faulting of the country rock providing conduits for the transport of magma and other fluids these conduits known as dykes are fundamental structures for the transport of magma to the surface in volcanically active regions the mechanics of dyke propagation is not yet fully understood but is crucial to better model dyke emplacement and eruption in volcanoes central to this need is a greater understanding of the mechanical properties of the magma country rock interaction as a function of known magmatic pressure temperature and stress here we report data from a series of experiments in which we cyclically compress viscoelastic rhyolitic magma at 828 c 892 c and 918 c inside a cylindrical conduit like shell of basalt from mt etna italy until fracture occurs the compression is performed under strain rates cyclically varying between 5 10 6 and 5 10 5 s 1 the resultant monitored axial loading and relaxation illustrates how the presence of a visco elastic fluid magma controls the stress induced at the conduit margin boundary this is achieved by analysing the viscoelastic relaxation through time to calculate an apparent modulus which is found to decrease with both increasing temperature and time in the 4 cycles before failure we find that the apparent modulus decreases from 180 to 40 gpa 80 to 20 gpa and 8 to 1 gpa for imposed stress cycles at 828 c 892 c and 918 c respectively we theoretically estimate a tensile strength at failure of approximately 7 11 mpa consistent with recent field data and in agreement with a model derived from the sample geometry and basic material parameters post experimental neutron computed tomography and microscopic analyses further reveal the fragmentation of the melt and generation of tuffisite veins inside the conduit due to spontaneous crack nucleation associated with conduit wall fracture the geometry of the rupture area inside the melt is akin to a mach cone associated with supershear fractures we discuss our findings in terms of magma rock interaction leading to dykes tuffisite veins and magma fragmentation

characterization of geological boundaries using 1 d wavelet transform on gravity data theory and application to the himalayas we investigate the use of the continuous wavelet transform for gravity inversion the wavelet transform operator has recently been introduced in the domain of potential fields both as a filtering and a source analysis tool here we develop an inverse scheme in the wavelet domain designed to recover the geometric characteristics of density heterogeneities described by simple shaped sources the 1 d analyzing wavelet we use associates the upward continuation operator and linear combinations of derivatives of any order in the gravity case we first demonstrate how to localize causative sources using simple geometric constructions both the upper part of the source and the whole source can be studied when considering low or high altitudes respectively the homogeneity degree of the source is deduced without prior information and allows us to infer its shape introducing complex wavelets we derive analytically the scaling behavior of the wavelet coefficients for the dyke and the step sources the modulus term is used in an inversion procedure to recover the thickness of the source the phase term provides its dip this analysis is performed on gravity data we measured along a profile across the himalayas in nepal good agreement of our results with well documented thrusting structures demonstrates the applicability of the method to real data also deeper less constrained structures are characterized

landslide mobility and hazards implications of the 2014 oso disaster abstract landslides reflect landscape instability that evolves over meteorological and geological timescales and they also pose threats to people property and the environment the severity of these threats depends largely on landslide speed and travel distance which are collectively described as landslide mobility to investigate causes and effects of mobility we focus on a disastrous landslide that occurred on 22 march 2014 near oso washington usa following a long period of abnormally wet weather the landslide s impacts were severe because its mobility exceeded that of prior historical landslides at the site and also exceeded that of comparable landslides elsewhere the 8 10 6 m 3 landslide originated on a gently sloping

a model for frictional melt production beneath large rock avalanches 1 two puzzling traits of giant rock avalanches sturzstroms are the decrease of the effective friction coefficient as a function of the volume volume effect and the remarkable preservation of large geological structures during the flow demonstrating that the upper cap of a sturzstrom travels coherently on top of a basal shear layer hence frictional heat is rapidly produced along the shear layer which could explain the formation of sheets of molten rock inside certain landslide deposits it has been conjectured that a molten layer could potentially self lubricate the base of the sturzstrom to theoretically investigate this scenario we consider the model of a rock slab sliding on an inclined surface we present a set of coupled differential equations to calculate the frictional heat produced the properties of the molten layer thickness temperature and velocity distribution and the motion of the slab our simulations illustrate the onset of self lubrication and show the volume effect when the melt viscosity is low corresponding to a simulated mafic composition of the rock for a felsic composition and to some extent also for intermediate melts we find that the melting introduces more resistance at the beginning of the melting process in close similarity with frictional melting in tectonic faults however in contrast to faults the rock avalanche is capable of overcoming the initial resistance in at least two situations if the rock is rigid and the landslide is sufficiently thick or else if the material of the landslide is disintegrated the simulations also show that although self lubrication is a viable possibility to explain the runout of sturzstroms there are rather stringent conditions for the formation of a molten layer of good lubricating qualities more generally we suggest that the properties of the coulomb frictional law at the interfaces may change radically during sliding and that the assumption of constant friction does not represent a good model in landslide calculations

natural and experimental evidence of melt lubrication of faults during earthquakes melt produced by friction during earthquakes may act either as a coseismic fault lubricant or as a viscous brake here we estimate the dynamic shear resistance f in the presence of friction induced melts from both exhumed faults and high velocity 1 28 meters per second frictional experiments exhumed faults within granitoids tonalites indicate low f at 10 kilometers in depth friction experiments on tonalite samples show that f depends weakly on normal stress extrapolation of experimental data yields f values consistent with the field estimates and well below the byerlee strength we conclude that friction induced melts can lubricate faults at intermediate crustal depths

seismic and ultrasonic velocities in permafrost we calculate the compressional and shear wave velocities of permafrost as a function of unfrozen water content and temperature unlike previous theories based on simple slowness and or moduli averaging or two phase models we use a biot type three phase theory that considers the existence of two solids solid and ice matrices and a liquid unfrozen water the compressional velocity for unconsolidated sediments obtained with this theory is close to the velocity computed with wood s model since biot s theory involves a wood averaging of the moduli of the single constituents moreover the model gives lower velocities than the well known slowness averaging theory wyllie s equation for consolidated berea sandstone the theory underestimates the value of the compressional velocity below 0 c computing the average bulk moduli by slowness averaging the ice and solid phases and wood averaging the intermediate moduli with the liquid phase yields a fairly good fit of the experimental data the proportion of unfrozen water and temperature are closely related fitting the wave velocity at a given temperature allows the prediction of the velocity at the whole range of temperatures provided that the average pore radius and its standard deviation are known