fracture fluid and saturation effects on the seismic attributes of rocks from the southern negros geothermal field philippines abstract seismic based geophysical methods are seeing increased usage in evaluating geothermal resources in order to maximize resource potential however interpreting geophysical data such as velocities and dynamic modulus and fracture density alignment generated from geothermal reservoirs remains difficult here we present the results of a new laboratory study measuring seismic attributes of fresh and hydrothermally altered rocks from a philippine geothermal field southern negros geothermal project sngp during triaxial deformation two types of rocks were obtained by sub coring samples of low porosity 1 andesite and higher porosity 10 volcaniclastic samples from the sngp samples were prepared with two offset drill holes to allow a natural fracture to permit fluid flow along the fracture an embedded array of acoustic emission ae sensors allows elastic wave and induced microseismic data to be collected we measure a significant reduction in elastic wave velocities and moduli with the exception of poisson s ratio after shear fracture development an initially pre fractured permeability of approximately 10 17 m2 is measured we find that the permeability decreases from 2 0 10 14 m2 to lower than 7 4 10 15 m2 as the confining pressure is increased from 5 mpa to 30 mpa a concomitant increase in p and s wave velocities dynamic bulk and young s moduli are also measured finally we simulate a geothermal venting situation by intentionally releasing the high pore fluid water pressure from 10 to 50 mpa to ambient pressure generating a swarm of ae that increases in duration with higher pore pressure we postulate that this is due to fluid phase change liquid to gas and movement along the natural fracture plane and damage zone

quantifying damage saturation and anisotropy in cracked rocks by inverting elastic wave velocities crack damage results in a decrease of elastic wave velocities and in the development of anisotropy using non interactive crack effective medium theory as a fundamental tool we calculate dry and wet elastic properties of cracked rocks in terms of a crack density tensor average crack aspect ratio and mean crack fabric orientation from the solid grains and fluid elastic properties using this same tool we show that both the anisotropy and shear wave splitting of elastic waves can be derived two simple crack distributions are considered for which the predicted anisotropy depends strongly on the saturation reaching up to 60 in the dry case comparison with experimental data on two granites a basalt and a marble shows that the range of validity of the non interactive effective medium theory model extends to a total crack density of approximately 0 5 considering symmetries up to orthorhombic in the isotropic case kachanov s 1994 non interactive effective medium model was used in order to invert elastic wave velocities and infer both crack density and aspect ratio evolutions inversions are stable and give coherent results in terms of crack density and aperture evolution crack density variations can be interpreted in terms of crack growth and or changes of the crack surface contact areas as cracks are being closed or opened respectively more importantly the recovered evolution of aspect ratio shows an exponentially decreasing aspect ratio and therefore aperture with pressure which has broader geophysical implications in particular on fluid flow the recovered evolution of aspect ratio is also consistent with current mechanical theories of crack closure in the anisotropic cases both transverse isotropic and orthorhombic symmetries were considered anisotropy and saturation patterns were well reproduced by the modelling and mean crack fabric orientations we recovered are consistent with in situ geophysical imaging

combination of precise leveling and insar data to constrain source parameters of the mw 6 5 26 december 2003 bam earthquake we used new precise leveling data acquired 40 days after the bam earthquake in combination with radar interferometry observations from both ascending and descending orbits to investigate static deformation associated with the 2003 bam earthquake we invert this geodetic data set to gain insight into the fault geometry and slip distribution of the rupture the best fitting dislocation model is a steeply east dipping right lateral strike slip fault that has a size of 11 by 8 km and strikes n2 w we find that such smooth geometry fits available geodetic data better than previously proposed models for this earthquake our distributed slip model indicates a maximum strike slip of 3 m occurring about 3 to 5 km deep the slip magnitude and depth of faulting taper to the north where the fault approaches the bam city inclusion of crustal layering increases the amount of maximum slip inferred at depth by about 4

fault source of the 2 september 2009 mw 6 8 tasikmalaya intraslab earthquake indonesia analysis from gps data inversion tsunami height simulation and stress transfer abstract we estimate the fault model of the 2 september 2009 tasikmalaya intraslab earthquake based on the gps data available in western java indonesia the focal mechanism of the earthquake was used to help construct two possible fault models a west dipping fault with a strike of 160 8 and an east dipping fault with a strike of 34 0 in this study vertical information from gps data is crucial for constructing the top depth of the fault the subsidence information from gps data located near the epicenter suggests that the earthquake involved a deeper fault model while the amount of the moment release of the east dipping fault model dipe is equivalent to mw 6 9 the moment release of the west dipping fault model dipw is equivalent to mw 6 8 the gps data inversion indicates that model dipw produces a better fit than model dipe the tsunami simulation indicates that the tsunami height generated by the east dipping fault is smaller than that generated by the west dipping fault implying that the maximum tsunami height of the latter is closer to agreement with the reported one unlike model dipe the stress transfer analysis of model dipw indicates that most of the aftershocks were located in the region where cff is positive suggesting positive stress from the ruptured triggered aftershocks the combined analysis of gps data tsunami simulation and stress transfer suggests that the fault ruptured during the 2009 earthquake was dipping westward with a steep dip angle

deep downward fluid percolation driven by localized crust dilatation in iceland from a detailed seismic survey on a transform like plate setting in iceland we propose a spatial relationship between highly deformed crustal columns and areas of low vp vs ratio which are best explained by high fluid pressures at the base of the seismogenic crust combined with geological observations our seismic data suggest transient and local increases in crust permeability at specific highly dilating areas triggered by dynamical stresses from high magnitude regional earthquakes fluids are then trapped at supercritical conditions in the deep brittle crust which in turn increases the capacity of the rocks to deform through cracking and faulting

possible splay fault slip during the 1946 nankai earthquake this paper considers seafloor deformation associated with the 1946 nankai earthquake which occurred in the nankai trough subduction zone off the coast of southwest japan we note that recent high resolution determinations of the slip distribution assumed to be confined to the plate boundary result in a pronounced maximum in seafloor displacement midway between the coast of shikoku and the trough axis we show that this feature could be due to slip on a splay fault rather than the plate boundary such a model for the western part of the slip distribution is able to account for the main features of the tsunamigenic seafloor deformation obtained in previous studies with a maximum slip consistent with the plate convergent rate and history of earthquake recurrence at the nankai trough

fault slip distribution of the 2014 iquique chile earthquake estimated from ocean wide tsunami waveforms and gps data we applied a new method to compute tsunami green s functions for slip inversion of the 1 april 2014 iquique earthquake using both near field and far field tsunami waveforms inclusion of the effects of the elastic loading of seafloor compressibility of seawater and the geopotential variation in the computed green s functions reproduced the tsunami traveltime delay relative to long wave simulation and allowed us to use far field records in tsunami waveform inversion multiple time window inversion was applied to tsunami waveforms iteratively until the result resembles the stable moment rate function from teleseismic inversion we also used gps data for a joint inversion of tsunami waveforms and coseismic crustal deformation the major slip region with a size of 100 km 40 km is located downdip the epicenter at depth 28 km regardless of assumed rupture velocities the total seismic moment estimated from the slip distribution is 1 24 1021 n m mw 8 0

investigation of the best coseismic fault model of the 2006 java tsunami earthquake based on mechanisms of postseismic deformation abstract we investigate three available coseismic fault models of the 2006 m7 8 java tsunami earthquake as reported by fujii and satake 2006 bilek and engdahl 2007 and yagi and fukahata 2011 in order to find the best coseismic model based on mechanisms of postseismic deformation associated with viscoelastic relaxation and afterslip we construct a preliminary rheological model using vertical data obtaining a final rheological model after we include horizontal and vertical components of afterslip in the further process our analysis indicates that the coseismic fault model of fujii and satake 2006 provides a better and more realistic result for a rheological model than the others the best fit rheological model calculated using the coseismic fault model of fujii and satake 2006 comprises a 60 5 km elastic layer thickness with a viscosity of 2 0 1 0 10 17 pa s in the asthenosphere also we find that afterslip is dominant over the horizontal displacements while viscoelastic relaxation is dominant over the vertical displacement additionally in comparison to the coseismic displacement found through gps data taken at bako station our calculation indicates that fujii and satake 2006 modeled coseismic displacements with less gps data misfit than the other examined models finally we emphasize that our methodology for evaluating the best coseismic fault model can satisfactorily explain the postseismic deformation of the 2006 java tsunami earthquake

splay fault rupture during the 2014 mw7 1 molucca sea indonesia earthquake determined from gps measurements abstract the coseismic slip of the 2014 molucca sea indonesia earthquake moseq is investigated using gps data from continuously monitoring stations coseismic fault models are compared between the main fault with a 25 west dipping plane and the 65 west dipping splay fault plane in analyzing this earthquake with fine faults sized resolution and homogenous fault models we find that a splay fault ruptured during the mainshock our finding suggests that the 2014 moseq occurred on an unmapped fault although we have limited gps data available in the region our results for coseismic slip are sufficient to explain the available gps data our estimation suggesting that a maximum coseismic slip of around 36 cm occurred near the hypocenter with cumulative seismic moment of 4 70 1019 n m mw 7 1

delineating fracture zones using surface tunnel surface seismic data p s and s p mode conversions a surface tunnel surface seismic experiment was conducted at the aspo hard rock laboratoryto study the seismic response of major fracture systems intersecting the tunnel a newly developedthree com

elastic wave velocities and permeability of cracked rocks abstract cracks play a major role in most rocks submitted to crustal conditions mechanically cracks make the rock much more compliant they also make it much easier for fluid to flow through any rock body relying on fracture mechanics and statistical physics we introduce a few key concepts which allow to understand and quantify how cracks do modify both the elastic and transport properties of rocks the main different schemes which can be used to derive the elastic effective moduli of a rock are presented it is shown from experimental results that an excellent approximation is the so called non interactive scheme the main consequences of the existence of cracks on the elastic waves is the development of elastic anisotropy due to the anisotropic distribution of crack orientations and the dispersion effect due to microscopic local fluid flow at a larger scale macroscopic fluid flow takes place through the crack network above the percolation threshold two macroscopic fluid flow regimes can be distinguished the percolative regime close to the percolation threshold and the connected regime well above it experimental data on very different rock types show both of these behaviors

coseismic and early postseismic deformation of the 5 january 2013 mw 7 5 craig earthquake from static and kinematic gps solutions static low rate 30 s and kinematic high rate 1 s global positioning system solutions are employed to investigate the near field coseismic and early postseismic deformation associated with the 5 january 2013 craig m w 7 5 earthquake based on the static solutions the coseismic slip distribution has an average slip of 6 m a geodetic moment m of 1 5 1020 n m and a magnitude m w of 7 4 a comparison of the static and kinematic results indicates that early first 4 days postseismic deformation was small compared to the coseismic deformation the postseismic transient can be characterized by a logarithmic decay function with an average decay time constant of about 56 days substantial postseismic deformation is observed over the first 1 6 yrs of the earthquake and can be explained by afterslip on an adjacent segment of the fault to the southeast of the main coseismic rupture additional study will be needed to confirm whether afterslip is indeed the dominant mechanism causing postseismic motions or if another mechanism is also active online material figures showing high rate global positioning system time series and model fits for selected sites

α β phase transition in quartz monitored using acoustic emissions summary it is usually suggested that thermal cracking in a quartz bearing rock results from the anomalously high volumetric expansion coefficients of quartz e g simmons cooper 1978 it has also been recognized that thermal expansion mismatch and mineral anisotropy contribute to thermal cracking in materials that consist of a polycrystalline aggregate composed of several anisotropic minerals even in the absence of a temperature gradient friedrich wong 1986 experiments investigating thermal cracking in rocks commonly involve imaging and quantitative stereology of crack populations induced in rocks treated to various peak temperatures e g friedrich johnson 1978 homand etienne troalan 1984 atkinson mcdonald meredith 1984 meredith atkinson 1985 here we report on acoustic emission experiments that monitor the process of thermal cracking as it occurs during heating supported by measurements of crack surface area pore fluid permeability porosity and surface conductivity carried out on rock samples treated to various peak temperatures the acoustic emission measurements show a strong peak of microcracking at the phase transition temperature for quartz 573 c superimposed upon a background of microcracking due to thermal expansion there is also a clear peak of microcracking at higher temperatures 800 c that can be attributed to oxidation dehydroxylation reactions of hornblende and chlorite measurements of fluid permeability pore surface area porosity and electrical conductivity made on samples that have been heat treated to various maximum temperatures show increases associated with a major episode of cracking in the 500 600 c temperature range indicating that the new cracks form a well interconnected network this has been confirmed by sem and optical microscopy these results have implications for the electrical conductivity of the continental crust providing a mechanism enabling the high pore fluid connectivity needed to explain zones of high electrical conductivity at depth providing that cracks opened in this way remain open at the high pressures existing at depth it should be recognized however that th se measurements are limited in their direct application since they were obtained under initially dry conditions at laboratory pressures

fluids and frequency dependent seismic velocity of rocks summary compressional and shear velocities of rocks are dependent on frequency and this dispersion may be significant even within the seismic band the amount and position of dispersion will be largely a function of fluid properties distribution and motion in the pores velocities are thus directly coupled to rock permeability and pore compliance propagation often will be in the high frequency regime even at a few tens of hertz static or low frequency models such as gasmann will fail under such conditions in addition biot theory will not correctly model wave propagation in many cases

ultrasonic velocities acoustic emission characteristics and crack damage of basalt and granite acoustic emissions ae compressional p shear s wave velocities and volumetric strain of etna basalt and aue granite were measured simultaneously during triaxial compression tests deformation induced ae activity and velocity changes were monitored using twelve p wave sensors and eight orthogonally polarized s wave piezoelectric sensors volumetric strain was measured using two pairs of orthogonal strain gages glued directly to the rock surface p wave velocity in basalt is about 3 km s at atmospheric pressure but increases by 50 when the hydrostatic pressure is increased to 120 mpa in granite samples initial p wave velocity is 5 km s and increases with pressure by 20 the pressure induced changes of elastic wave speed indicate dominantly compliant low aspect ratio pores in both materials in addition etna basalt also contains high aspect ratio voids in triaxial loading stress induced anisotropy of p wave velocities was significantly higher for basalt than for granite with vertical velocity components being faster than horizontal velocities however with increasing axial load horizontal velocities show a small increase for basalt but a significant decrease for granite using first motion polarity we determined ae source types generated during triaxial loading of the samples with increasing differential stress ae activity in granite and basalt increased with a significant contribution of tensile events close to failure the relative contribution of tensile events and horizontal wave velocities decreased significantly a concomitant increase of double couple events indicating shear suggests shear cracks linking previously formed tensile cracks

numerical investigation of rock heterogeneity effect on rock dynamic strength and failure process using cohesive fracture model abstract in this study a cohesive fracture model cfm which assumes rock material as assemblage of deformable grains joining together at their cohesive boundaries is developed to simulate rock fracture and failure behavior in terms of mineral and cement properties to better represent the structural bonds between the particles and the heterogeneity of rock material a user defined material model umat for the cohesive element with stochastic strengths is incorporated into the developed cfm the capability of the developed model for rock fracture problems under both static and dynamic loads is first explored based on the developed model the heterogeneity effect of rock on its dynamic failure process and dynamic strength is then studied the results demonstrate that the developed cfm can be used to investigate the rock fracture problems under both static and dynamic loads the heterogeneity of rock material not only affects the rock dynamic failure process but also leads to an increase of rock dynamic strength

a comprehensive model of postseismic deformation of the 2004 sumatra andaman earthquake deduced from gps observations in northern sumatra abstract we investigate the postseismic deformation of the 2004 sumatra andaman earthquake sae using 5 years of global positioning system gps data located in northern sumatra continuous gps data from northern sumatra suggest that the relaxation time in the vertical displacement is longer than horizontal displacements this implies that there are multiple physical mechanisms that control the postseismic deformation which refer to afterslip and viscoelastic relaxation in this study we introduce an analysis strategy of postseismic deformation to simultaneously calculate multiple mechanisms of afterslip and viscoelastic relaxation the afterslip inversion results indicate that the distribution of the afterslip and the coseismic slip are compensatory of each other also afterslip has a limited contribution to vertical deformation in northern sumatra in our rheology model we use a gravitational maxwell viscoelastic response and the result indicates that the elastic layer thickness is 65 5 km and the maxwell viscosity is 8 0 1 0 1018 pa s we find that afterslip plus maxwell viscoelastic relaxation are appropriate to explain the deformation in northern sumatra we also find that our rheology model reproduces the long term features of the gps time series in thailand applying our rheology model to the data in andaman islands our afterslip estimation is located at the down dip part of the plate boundary finally we showed that our rheology model is applicable to the gps datasets of postseismic deformation of the 2004 sae located in northern sumatra thailand and andaman nicobar respectively

tsunami wave analysis and possibility of splay fault rupture during the 2004 indian ocean earthquake the 2004 indian ocean tsunami was observed by two satellites close in space and time that traversed the indian ocean 2 h after the sumatra andaman earthquake but which observed different tsunami lead wave morphologies the earlier satellite jason 1 recorded a lead wave with two peaks of similar amplitude and wavelength while the later satellite topex poseidon recorded a lead wave with only one longer wavelength uplift to resolve this disparity we examine the travel paths of long wavelength waves over the seafloor bathymetry waves traveling from the margin will traverse significantly different paths to arrive at the two satellite transects the result is that the satellites are sensitive to different parts of the margin jason 1 is highly sensitive to the margin in the area of the epicenter while topex is sensitive to a more northerly section by developing solutions of the ocean gravity wave equations accounting for dispersion we show that the double peak of the jason 1 satellite observations are consistent with coseismic rupture of a splay fault of limited along strike extent located north of simeulue island the doubly peaked morphology can be reproduced with co activation of the subduction zone interface and the splay fault which creates a seafloor uplift pattern with two distinct areas of uplift the jason 1 satellite is sensitive to a splay fault in this portion of the margin whereas the topex satellite would not be significantly affected by this uplift pattern by back projecting satellite observation points to the margin we constrain the location of the proposed splay fault and find that it correlates with a bathymetric high the aftershock locations uplift of corals on simeulue island and a fault scarp on pulau salaut besar are also consistent with the activation of a splay fault in the area delimited by the back projection our work also shows that it is critical to fully capture gravity wave dispersion in order to represent features of the lead wave profile that may not be as well characterized by the shallow water long wavelength model it is also necessary to account for dispersion so as to precisely assess wavefront travel times this leads us to conclude that the rupture must have reached very near to the trench and propagated with an updip rupture velocity of order 2 0 km s or more

characterisation and multifaceted anisotropy assessment of corvio sandstone for geological co2 storage studies we present a comprehensive characterisation of the physical mineralogical geomechanical geophysical and hydrodynamic properties of corvio sandstone this information together with a detailed assessment of anisotropy is needed to establish corvio sandstone as a useful laboratory rock testing standard for well constrained studies of thermo hydro mechanical chemical coupled phenomena associated with co2 storage practices and for geological reservoir studies in general more than 200 core plugs of corvio sandstone 38 1 and 50 mm diameters 2 1 length to diameter ratio were used in this characterisation study with a rock porosity of 21 7 1 2 dry density 2036 32 kg m 3 and unconfined compressive and tensile strengths of 41 3 28 and 2 3 0 14 mpa respectively geomechanical tests show that the rock behaves elastically between 10 and 18 mpa under unconfined conditions with associated young s modulus and poisson s ratio of 11 8 2 8 gpa and 0 34 0 01 gpa respectively permeability abruptly decreases with confining pressure up to 10 mpa and then stabilises at 1 md ultrasonic p and s wave velocities vary from about 2 8 3 8 km s 1 and 1 5 2 4 km s 1 respectively over confining and differential pressures between 0 1 and 35 mpa allowing derivation of associated dynamic elastic moduli anisotropy was investigated using oriented core plugs for electrical resistivity elastic wave velocity and attenuation permeability and tracer injection tests corvio sandstone shows weak transverse isotropy symmetry axis normal to bedding of 10 for velocity and 20 for attenuation

frequency and fluid effects on elastic properties of basalt experimental investigations 1 in order to investigate the effects of fluid and frequency on the elastic properties we performed hydrostatic experiments on an icelandic basalt specimen under both dry and saturated conditions this basalt is characterized by a bimodal porosity i e cracks and equant pores the elastic properties bulk moduli in our case were investigated under high pressure through two experimental methods 1 a classical one using ultrasonic p and s waves velocities frequency 106 hz 2 and a new one using oscillation tests frequency 10 2 hz in dry condition experimental data show no significant difference between high hf and low lf frequency bulk moduli however in saturated conditions two effects are highlighted a physico chemical effect emphasized by a difference between drained and dry moduli and a squirt flow effect evidenced by a difference between hf and lf undrained moduli

anisotropy of elastic moduli p wave velocities and thermal conductivities of asan gneiss boryeong shale and yeoncheon schist in korea abstract this paper presents the anisotropic characteristics of the elastic moduli p wave velocities and thermal conductivities of three types of anisotropic rocks i e asan gneiss boryeong shale and yeoncheon schist occurring in korea the experiments were conducted on rock samples that show clear evidence of transverse isotropy cylindrical core samples with different anisotropy angles were prepared by coring at 15 degree intervals from the transversely isotropic plane using the laboratory directional coring system established for this study elastic moduli p wave velocities and thermal conductivities were determined along the sample axis for different anisotropy angles the anisotropy ratio is defined as the ratio of the properties parallel to the transversely isotropic plane to those perpendicular to the plane and the anisotropy ratios for the thermal conductivities k 90 k 0 of asan gneiss boryeong shale and yeoncheon schist were 1 4 2 1 and 2 5 respectively the p wave velocity anisotropy ratios v p 90 v p 0 for asan gneiss boryeong shale and yeoncheon schist were 1 2 1 5 and 2 3 respectively the elastic moduli p wave velocities and thermal conductivities that were obtained were compared with theoretical predictions by mean prediction error mpe the correlations between the measured properties were evidently correlated with some minor scatter in the data the degree of anisotropy measured in this study suggests that ignoring anisotropy in rock properties may mislead to erroneous results the application of tensorial transformation evaluations revealed that the three types of rocks chosen for this study can be modeled effectively by a transversely isotropic model

isolating along strike variations in the depth extent of shallow creep and fault locking on the northern great sumatran fault the great sumatran fault system in indonesia is a major right lateral trench parallel system that can be divided into several segments most of which have ruptured within the last century this study focuses on the northern portion of the fault system which contains a 200 km long segment that has not experienced a major earthquake in at least 170 years in 2005 we established the aceh gps network for the sumatran fault system agness across this segment agness observes large displacements which include significant postseismic deformation from recent large megathrust earthquakes as well as interseismic deformation due to continued elastic loading of both the megathrust and the strike slip system we parameterize the displacements due to afterslip on the megathrust using a model based on a rate and state dependent friction formalism using this approach we are able to separate afterslip from other contributions we remove predicted deformation due to afterslip from the observations and use these corrected time series to infer the depth of shallow aseismic creep and deeper locked segments for the great sumatran fault in the northern portion of this fault segment we infer aseismic creep down to 7 3 4 8 km depth at a rate of 2 0 0 6 cm year in the southwestern portion of the segment we estimate a locking depth of 14 8 3 4 km with a downdip slip rate of 1 6 0 6 cm year this portion of the fault is capable of producing a magnitude 7 0 earthquake

microfracture analysis of fault growth and wear processes punchbowl fault san andreas system california abstract fabric and timing relations of mode i microfractures are used to test current hypotheses for the origin of damage along large displacement faults by the processes of fault growth and wear oriented samples 0 075 m to 1 km from the punchbowl fault surface i e ultracataclasite layer document an increase in development of preferred orientation and increase in density of microfractures towards the ultracataclasite layer defining a zone of fault related microfracture damage about 100 m thick a distinct microfracture set that is perpendicular to the slip direction of the fault is present throughout the damage zone this implies that the average orientation of the maximum principal compressive stress within the damage zone was nearly normal to the fault surface two additional microfracture sets are present one oriented at low angles to the fault within meters of the ultracataclasite layer and another low angle set that occurs in the outermost damage zone the preferred orientations and timing relations are most consistent with local damage accumulation from stress cycling associated with slip on a geometrically irregular relatively weak fault surface low angle microfractures nearest the ultracataclasite layer also may record wear associated with the passage of earthquake ruptures and those in the outermost damage zone may be consistent with andersonian fault formation and subsequent fault weakening

numerical methods in rock mechanics the purpose of this civilzone review paper is to present the techniques advances problems and likely future development directions in numerical modelling for rock mechanics and rock engineering

nonlinear viscoelastic behavior of sedimentary rocks part ii hysteresis effects and influence of type of fluid on elastic moduli uniaxial stress cycling experiments were conducted on dry brine saturated and hexadecane saturated berea sandstone samples to observe in detail the hysteresis in stress strain diagrams and to understand the influence of different fluids on the strain amplitude dependence of elastic moduli and attenuation cycling experiments were also conducted with sandstone samples saturated with ctab a cationic surfactant that renders the mineral surfaces hydrophobic hexadecane and ctab were selected so as to investigate the relative contributions of adhesion hysteresis and stick slip sliding on attenuation in sedimentary granular rocks young s moduli and poisson s ratios obtained from the cycling tests show a significant dependence on strain amplitude on dry as well as water and hexadecane saturated samples bow tie shaped diagrams are obtained when loading and unloading tangent moduli are plotted against strain the type of fluid in the pore space and at the grain contacts has a large influence on the hysteresis observed in the stress strain diagrams

seismic wave attenuation and dispersion resulting from wave induced flow in porous rocks a review one major cause of elastic wave attenuation in heterogeneous porous media is wave induced flow of the pore fluid between heterogeneities of various scales it is believed that for frequencies below 1 khz the most important cause is the wave induced flow between mesoscopic inhomogeneities which are large compared with the typical individual pore size but small compared to the wavelength various laboratory experiments in some natural porous materials provide evidence for the presence of centimeter scale mesoscopic heterogeneities laboratory and field measurements of seismic attenuation in fluid saturated rocks provide indications of the role of the wave induced flow signatures of wave induced flow include the frequency and saturation dependence of p wave attenuation and its associated velocity dispersion frequency dependent shear wave splitting and attenuation anisotropy during the last four decades numerous models for attenuation and velocity dispersion from wave induced flow have been developed with varying degrees of rigor and complexity these models can be categorized roughly into three groups according to their underlying theoretical framework the first group of models is based on biot s theory of poroelasticity the second group is based on elastodynamic theory where local fluid flow is incorporated through an additional hydrodynamic equation another group of models is derived using the theory of viscoelasticity though all models predict attenuation and velocity dispersion typical for a relaxation process there exist differences that can be related to the type of disorder periodic random space dimension and to the way the local flow is incorporated the differences manifest themselves in different asymptotic scaling laws for attenuation and in different expressions for characteristic frequencies in recent years some theoretical models of wave induced fluid flow have been validated numerically using finite difference finite element and reflectivity algorithms applied to biot s equations of poroelasticity application of theoretical models to real seismic data requires further studies using broadband laboratory and field measurements of attenuation and dispersion for different rocks as well as development of more robust methods for estimating dissipation attributes from field data

the evolution of elastic moduli with increasing crack damage during cyclic stressing of a basalt from mt etna volcano article i nfo volcanic edifices such as mt etna italy are commonly subject to repeated cycles of stress over time due to the combination of magma emplacement from deep reservoirs to shallow depths and superimposed tectonic stresses such repeated stress cycles lead to anisotropic deformation and an increase in the level of crack damage within the rocks of the edifice and hence changes to their elastic moduli which are a key parameter for reliable modelling of deformation sources we therefore report results of changes in elastic moduli measured during increasing amplitude cyclic stressing experiments on dry and water saturated samples of etna basalt in all experiments the young s modulus decreased by approximately 30 over the total sequence of loading cycles and the poisson s ratio increased by a factor of approximately 3 0 5 microseismicity in terms of acoustic emission ae output was also recorded throughout each experiment our results demonstrate that ae output only re commences during any loading cycle when the level of stress where ae ceased during the unloading portion of the previous cycle is exceeded a manifestation of the kaiser stress memory effect in cycles where no ae output was generated we also observed no change in elastic moduli this result holds for both mechanical and thermal stressing our results are interpreted in relation to measurements of volcano tectonic seismicity and deformation at mt etna volcano

fracture toughness and subcritical crack growth during high temperature tensile deformation of westerly granite and black gabbro abstract the double torsion testing method has been used to determine catastrophic and subcritical crack propagation parameters for pre cracked specimens of westerly granite and black gabbro under a number of environmental conditions the critical stress intensity factor for catastrophic crack propagation fracture toughness of granite and gabbro has been measured at temperatures from 20 to 400 c in a vacuum at 20 c the fracture toughness of westerly granite was 1 79 0 02 mpa m 1 2 and for two blocks of black gabbro it was 3 03 0 08 mpa m 1 2 and 2 71 0 15 mpa m 1 2 respectively these values are very close to those reported by other investigators for tests conducted in air of ambient humidity at room temperature for both rocks fracture toughness at first increased slightly and then decreased steadily on raising the temperature above ambient conditions this behaviour is explained in terms of the density and distribution of thermally induced microcracks as determined by quantitative optical microscopy subcritical crack growth behaviour has been studied at temperatures up to 300 c and under water vapour at pressures of 0 6 to 15 kpa both the load relaxation and incremental constant displacement rate forms of the double torsion testing method were utilised to generate stress intensity factor crack velocity diagrams crack growth was measured over the velocity range 5 10 3 to 10 7 m s 1 increasing both temperature and water vapour pressure resulted in substantially higher crack growth rates the overall effect of raising the temperature over the range studied here 20 300 c was to increase the crack growth rate in granite and gabbro by 5 and 7 orders of magnitude respectively at constant stress intensity factor and vapour pressure of water for both rocks the slopes of stress intensity factor crack velocity curves were sensitive to changes in both temperature and water vapour pressure at low values of the latter parameter slopes fell substantially on raising the water vapour pressure but were relatively insensitive to changes in temperature at these higher pressures no subcritical crack growth limit was encountered estimates of the uncertainty in our experimental data are given from the results of multiple load relaxation experiments on westerly granite specimens we estimate the uncertainty in position of stress intensity factor crack velocity curves along the stress intensity axis to be c 10 of the fracture toughness and the uncertainty in slope of such curves to be c 12 problems associated with the extrapolation of our experimental data to regions of higher effective confining pressure in the earth s crust are discussed

splay fault branching along the nankai subduction zone seismic reflection profiles reveal steeply landward dipping splay faults in the rupture area of the magnitude m 8 1 tonankai earthquake in the nankai subduction zone these splay faults branch upward from the plate boundary interface that is the subduction zone at a depth of approximately 10 kilometers approximately 50 to 55 kilometers landward of the trough axis breaking through the upper crustal plate slip on the active splay fault may be an important mechanism that accommodates the elastic strain caused by relative plate motion

mapping active faults offshore portugal 36 n 38 n implications for seismic hazard assessment along the southwest iberian margin swath bathymetry and acoustic backscatter data from the southwest iberian margin which hosts the present day boundary between the european and african plates reveal the surficial expression of several fault structures 100 km offshore of portugal high resolution and multichannel seismic reflection profiles collected perpendicular to these structures show folding and reverse faulting of the quaternary units suggesting present day tectonic activity successive submarine landslide deposits at the base of the scarps provide evidence of cyclic fault activity the location and dimension of these newly identified structures agree with the modeled source suggested for the a d 1755 lisbon earthquake and tsunami possibly the most destructive event in western europe during historical time these fault escarpments and deformed seafloor sediments associated with a cluster of shallow seismicity suggest that these thrusts are active and may pose a significant earthquake and tsunami hazard to the coasts of portugal spain and morocco

fluid mobility and frequency dependent seismic velocity direct measurements the influence of fluid mobility on seismic velocity dispersion is directly observed in laboratory measurements from seismic to ultrasonic frequencies a forceddeformation system is used in conjunction with pulse transmission to obtain elastic properties at seismic strain amplitude 10 7 from 5 hz to 800 khz varying fluid types and saturations document the influence of pore fluids the ratio of rock permeability to fluid viscosity defines mobility which largely controls pore fluid motion and pore pressure in a porous medium high fluid mobility permits pore pressure equilibrium either between pores or between heterogeneous regions resulting in a low frequency domain where gassmann s equations are valid in contrast low fluid mobility can produce strong dispersion even within the seismic band here the low frequency assumption fails since most rocks in the general sedimentary section have very low permeability and fluid mobility shales siltstones tight limestones etc most rocks are not in the lowfrequency domain even at seismic frequencies only those rocks with high permeability porous sands and carbonates will remain in the low frequency domain in the seismic or sonic band

coseismic slip resolution along a plate boundary megathrust the nankai trough southwest japan geodetic survey measurements are used to estimate the coseismic slip distribution in the 1944 tonankai mw 8 1 and 1946 nankaido mw 8 3 earthquakes and to assess quantitatively the degree to which this slip is resolved on the plate boundary megathrust data used include 798 angle changes from triangulation surveys 328 leveling section differences and 5 coseismic tidal gage offsets many of the nominally coseismic triangulation data span 50 years nearly half the earthquake cycle and correction for interseismic deformation using post 1950 observations is applied microseismicity is used to define the configuration of the plate boundary interface and approximate it with a continuous multisegment fault model because the onshore geodetic data have very limited resolving power for offshore fault segments offshore coseismic slip was constrained by satake s 1993 estimation based on tsunami data the majority of the coseismic slip occurs between 15 and 25 km depth although resolution declines toward the trench axis it is sufficiently good to define two distinct high slip regions one off southeastern shikoku island 11 m maximum and the other offshore of kii peninsula 3 m maximum the slip magnitude off southeastern shikoku coupled with the plate convergence rate would imply an recurrence interval of about 270 years much longer than the average repeat time of 120 years for historical great earthquakes on the nankai trough however the maximum coseismic slip is sensitive to the assumed fault geometry and slippage on trough parallel splay faults could significantly decrease the maximum slip to about 6 m

coseismic slip distributions of the 26 december 2004 sumatra andaman and 28 march 2005 nias earthquakes from gps static offsets static offsets produced by the 26 december 2004 m 9 sumatra andaman earthquake as measured by global positioning system gps reveal a large amount of slip along the entire 1300 km long rupture most seismic slip inversions place little slip on the andaman segment whereas both near field and far field gps offsets demand large slip on the andaman segment we compile available datasets of the static offset to render a more detailed picture of the static slip distribution we construct geodetic offsets such that postearthquake positions of continuous gps sites are reckoned to a time 1 day after the earthquake and campaign gps sites are similarly corrected for postseismic motions the newly revised slip distribution m w 9 22 reveals substantial segmentation of slip along the andaman islands with the southern quarter slipping 15 m in unison with the adjacent nicobar and northern sumatran segments of length 700 km we infer a small excess of geodetic moment relative to the seismic moment a similar compilation of gps offsets from the 28 march 2005 nias earthquake is well explained with dip slip averaging several meters mw 8 66 distributed primarily at depths greater than 20 km online material offset estimation procedure comparison of results to other stud ies and simpler solutions and tables of coseismic offsets

dynamic and static moduli static and dynamic bulk moduli ks and kd are measured as continuous functions of pressure from zero to 2 3 kilobars for two sandstones a tuff limestone granite and oil shale results for the sandstones and granite are in good agreement with previously reported data with ks kd varying from about 0 5 at atmospheric pressure to close to unity at pressures 2 kilobars and above for rocks behaving elastically under static loading the ks kd ratio is inversely related to the microcrack density for the limestone time dependent deformation associated with pore collapse results in ks kd ratios approaching 0 1 at high pressure upon unloading while initially high 1 0 at high pressures ks kd becomes lower than values obtained during loading at low pressures 1 kilobar due to opening of microcracks generated during pore collapse for the oil shale in which few microcracks exist ks kd remains relatively constant with pressure at a value of about 0 7

the effect of fracture density and stress state on the static and dynamic bulk moduli of westerly granite elastic properties are key parameters during the deformation of rocks they can be measured statically or dynamically but the two measurements are often different in this study the static and dynamic bulk moduli kstatic and kdynamic were measured at varying effective stress for dry and fluid saturated westerly granite with controlled fracture densities under isotropic and differential stress states isotropic fracturing of different densities was induced in samples by thermal treatment to 250 450 650 and 850 c results show that fluid saturation does not greatly affect static moduli but increases dynamic moduli under isotropic loading high fracture density and or low effective pressure results in a low kstatic kdynamic ratio for dry conditions kstatic kdynamic approaches 1 at low fracture densities when the effective pressure is high consistent with previous studies stress induced anisotropy exists under differential stress state that greatly affects kstatic compared to kdynamic as a result the kstatic kdynamic ratio is higher than that for the isotropic stress state and approaches 1 with increasing axial loading the effect of stress induced anisotropy increases with increasing fracture density a key omission in previous studies comparing static and dynamic properties is that anisotropy has not been considered the standard methods for measuring static elastic properties such as poisson s ratio young s and shear modulus involve subjecting the sample to a differential stress state that promotes anisotropy our results show that stress induced anisotropy resulting from differential stress state is a major contributor to the difference between static and dynamic elasticity and is dominant with high fracture density

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

high precision slip distribution of the 1944 tonankai earthquake inferred from tsunami waveforms possible slip on a splay fault abstract inversion of tsunami waveforms is a well established technique for estimating the slip distributions of subduction zone earthquakes with some of the most detailed results having been obtained for earthquakes in the nankai trough sw japan the present study although it uses a method and tsunami waveform data set almost identical to previous study aims to improve on previous work by using a more precise specification of initial conditions for the calculation of tsunami green s functions specifically we incorporated four improvements in the present study 1 we used a realistic plate model based only on seismic survey results and assumed it to be the fault plane of the 1944 tonankai earthquake 2 the smallest subfaults consistent with the long wavelength approximation were used in the tsunami inversion analysis 3 we included the effect of horizontal displacement of the ocean bottom on tsunami generation and 4 we performed a checkerboard resolution test as obtained in previous studies a zone of high slip 2 0 m was resolved off the shima peninsula however the more precise calculation of tsunami green s functions has revealed additional detail that was not evident in previous studies which we demonstrate is resolvable and correlates with the position of known faults in the accretionary prism while there was little or no slip near the trench axis in the eastern part of the rupture zone there was up to 1 5 m of slip resolved within 30 km of the trough axis in the western part along the coast of the kii peninsula this troughward slip zone coincides with the position of a large splay fault mapped in multichannel reflection surveys furthermore it is also clear that the upper edge of the enshu fault off shima and atsumi peninsulas is consistent with the up dip limit of slip in the eastern part of our model we tested the possibility that slip occurred on the former splay fault instead of on the plate interface during the 1944 tonankai earthquake and find that slip on this splay fault is also consistent with the data although we cannot distinguish whether slip was dominant on the splay fault or on the plate interface we further suggest that the position of the enshu fault may be determined by the subduction of topographic highs and that such faults may have an important influence on the up dip rupture limit of the 1944 tonankai and potentially other subduction zone earthquakes

is there a best source model of the sumatra 2004 earthquake for simulating the consecutive tsunami summary many studies have attempted to invert the fault source of the sumatra 2004 event whereas they mostly consider the same fault geometry they lead to a wide range of potential slip distributions using tsunami modelling with geowave a model based on fully non linear boussinesq equations we investigate the influence of five distinct source models of various origins and the influence of rupture kinematics on the generated tsunami the simulation results are considered both at ocean scale and at country scale we then compare the results along the jason 1 track to the corresponding sea surface height anomaly ssha profile and examine the patterns of maximum sea surface elevation around the bay of bengal and on the eastern and southern coastlines of sri lanka in most cases the synthetic ssha profiles are not very consistent with the observed one although they all display a prevailing first wave the divergence in maximum sea surface elevation appears in particular along the sri lankan coast where three of the models lead to a clearly underestimated tsunami impact the best models derive from purely seismic and geodetic studies that did not consider any tsunami modelling thus suggesting that the methods to invert a fault model from tsunami data still need some adjustment especially concerning the handling of coastal data in addition it is important to consider the rupture kinematics along such a long fault as the generated tsunami is more significant than when considering an instantaneous rupture in the case of the sumatra 2004 event the tsunami impact on sri lanka is notably underestimated if modelled without the rupture kinematics we conclude that for tsunami modelling a complex description of the fault source model is not absolutely necessary but some significant parameters such as rupture kinematics should be taken into account

geodetic data inversion using a bayesian information criterion for spatial distribution of fault slip summary we developed a new inversion method to reconstruct static images of seismic sources from geodetic data using akaike s bayesian information criterion abic coseismic surface displacements are generally related with a slip distribution on a fault surface by linear integral equations parametric expansion of the fault slip distribution by a finite number of known basis functions yields a set of observation equations expressed in a simple vector form incorporating prior constraints on the smoothness of slip distribution with the observation equations we construct a bayesian model with unknown hyperparameters the optimal values of the hyperparameters which control the structure of the bayesian model are objectively determined from observed data by using abic once the values of hyperparameters are determined we can use the maximum likelihood method to find the optimal distribution of fault slip we examined the validity of this method through a numerical experiment using theoretical data with random noise we analysed geodetic data associated with the 1946 nankaido earthquake ms 8 2 by using this method the result shows that the fault slip distribution of this earthquake has two main peaks of 4 and 6 m located off kii peninsula and muroto promontory these two high slip areas are clearly separated by a low slip zone extending along kii strait such a slip distribution corresponds with the fact that the rupture process of this earthquake in the western part is notably different from that in the eastern part

wave velocities in hydrocarbon saturated rocks experimental results this paper contains laboratory measurements of the temperature dependence of velocities determined by ultrasonic pulse transmission methods in hydrocarbon liquids and rock samples saturated by the liquids the samples discussed include 26 hydrocarbons of varying molecular weight nine mixtures of these hydrocarbons four heavy oils tar three saturated sandstones and a saturated sand the data provide encouragement that high frequency high resolution seismic techniques may infer formation temperature changes thereby detecting the progress of thermal enhanced oil recovery processes

interplate coupling model off the southwestern coast of java indonesia based on continuous gps data in 2008 2010 abstract we present an interplate coupling model of the australia java plate interface off the southwestern coast of java indonesia based on data from the indonesian permanent gps station network from 2008 to 2010 the majority of vertical data indicate uplift while the baseline change rate indicates coastal contraction in the middle of the network and coastal extension in the eastern part of the network using the rate of baseline length changes and the absolute rate of vertical displacements we apply a geodetic inversion method by yabuki and matsu ura 1992 from the inversion result we interpret the main source of the observed velocity in west java as resulting from contributions of 1 interplate coupling off ujung kulon pelabuhan ratu at 20 to 40 km depth with a slip rate range from 48 to 56 mm yr 2 interplate coupling off pangandaran at 37 to 45 km depth with a slip rate of 48 to 55 mm yr 3 afterslip off pangandaran within the rupture area of the 2006 m7 8 java earthquake in the depth range of 15 20 km with a slip excess rate of 57 61 mm yr the absence of a megathrust earthquake for at least 300 years in this region implies seismic moment accumulation during this time period of 1 6 10 21 nm mw 8 7 off ujung kulon pelabuhan ratu and 3 9 10 21 nm mw 8 3 off pangandaran unless episodic slow slips release tectonic stress