predicting the elastic response of organic rich shale using nanoscale measurements and homogenisation methods determination of the mechanical response of shales through experimental procedures is a practical challenge due to their heterogeneity and the practical difficulties of retrieving good quality core samples here we investigate the possibility of using multiscale homogenisation techniques to predict the macroscopic mechanical response of shales based on quantitative mineralogical descriptions we use the novel peakforce quantitative nanomechanical mapping technique to generate high resolution mechanical images of shales allowing the response of porous clay organic matter and mineral inclusions to be measured at the nanoscale these observations support some of the assumptions previously made in the use of homogenisation methods to estimate the elastic properties of shale and also earlier estimates of the mechanical properties of organic matter we evaluate the applicability of homogenisation techniques against measured elastic responses of organic rich shales partly from published data and also from new indentation tests carried out in this work comparison of experimental values of the elastic constants of shale samples with those predicted by homogenisation methods showed that almost all predictions were within the standard deviation of experimental data this suggests that the homogenisation approach is a useful way of estimating the elastic and mechanical properties of shales in situations where conventional rock mechanics test data cannot be measured

velocity porosity relationships predictive velocity model for cemented sands composed of multiple mineral phases computer simulations are used to calculate the elastic properties of model cemented sandstones composed of two or more mineral phases two idealized models are considered a grain overlap clay quartz mix and a pore lining clay quartz mix unlike experimental data the numerical data exhibit little noise yet cover a wide range of quartz cement ratios and porosities the results of the computations are in good agreement with experimental data for clay bearing consolidated sandstones the effective modulus of solid mineral mixtures is found to be relatively insensitive to microstructural detail it is shown that the hashin shtrikman average is a good estimate for the modulus of the solid mineral mixtures the distribution of the cement phase is found to have little effect on the computed modulus porosity relationships numerical data for dry and saturated states confirm that gassmann s equations remain valid for porous materials composed of multiple solid constituents as noted previously the krief relationship successfully describes the porosity dependence of the dry shear modulus and a recent empirical relationship provides a good estimate for the dry rock poisson s ratio from the numerical computations a new empirical model which requires only a knowledge of system mineralogy is proposed for the modulus porosity relationship of isotropic dry or fluid saturated porous materials composed of multiple solid constituents comparisons with experimental data for clean and shaly sandstones and computations for more complex three mineral quartz dolomite clay systems show good agreement with the proposed model over a very wide range of porosities

detailed observations of california foreshock sequences implications for the earthquake initiation process we find that foreshocks provide clear evidence for an extended nucleation process before some earthquakes in this study we examine in detail the evolution of six california foreshock sequences the 1986 mount lewis ml 5 5 the 1986 chalfant ml 6 4 the 1986 stone canyon ml 4 7 the 1990 upland ml 5 2 the 1992 joshua tree mw 6 1 and the 1992 landers mw 7 3 sequence typically uncertainties in hypocentral parameters are too large to establish the geometry of foreshock sequences and hence to understand their evolution however the similarity of location and focal mechanisms for the events in these sequences leads to similar foreshock waveforms that we cross correlate to obtain extremely accurate relative locations we use these results to identify small scale fault zone structures that could influence nucleation and to determine the stress evolution leading up to the mainshock in general these foreshock sequences are not compatible with a cascading failure nucleation model in which the foreshocks all occur on a single fault plane and trigger the mainshock by static stress transfer instead the foreshocks seem to concentrate near structural discontinuities in the fault and may themselves be a product of an aseismic nucleation process fault zone heterogeneity may also be important in controlling the number of foreshocks i e the stronger the heterogeneity the greater the number of foreshocks the size of the nucleation region as measured by the extent of the foreshock sequence appears to scale with mainshock moment in the same manner as determined independently by measurements of the seismic nucleation phase we also find evidence for slip localization as predicted by some models of earthquake nucleation

the mw 5 8 mineral virginia earthquake of august 2011 and aftershock sequence constraints on earthquake source parameters and fault geometry the mw 5 8 earthquake of 23 august 2011 17 51 04 utc moment m0 5 7 10 17 n m occurred near mineral virginia within the central virginia seis mic zone and was felt by more people than any other earthquake in united states history the u s geological survey usgs received 148 638 felt reports from 31 states and 4 canadian provinces the usgs pager system estimates as many as 120 000 people were exposed to shaking intensity levels of iv and greater with approximately 10 000 exposed to shaking as high as intensity viii both regional and teleseismic moment tensor solutions characterize the earthquake as a northeast striking reverse fault that nucleated at a depth of approximately 7 2 km the distri bution of reported macroseismic intensities is roughly ten times the area of a similarly sized earthquake in the western united states horton and williams 2012 near source and far field damage reports which extend as far away as washington d c 135 km away and baltimore maryland 200 km away are consistent with an earthquake of this size and depth in the eastern united states eus within the first few days following the earthquake several government and aca demic institutions installed 36 portable seismograph stations in the epicentral region making this among the best recorded aftershock sequences in the eus based on modeling of these data we provide a detailed description of the source parameters of the mainshock and analysis of the subsequent aftershock sequence for defining the fault geometry area of rupture and observations of the aftershock sequence mag nitude frequency and temporal distribution the observed slope of the magnitude frequency curve or b value for the aftershock sequence is consistent with previous eus studies b 0 75 suggesting that most of the accumulated strain was released by the mainshock the aftershocks define a rupture that extends between approxi mately 2 8 km in depth and 8 10 km along the strike of the fault plane best fit modeling of the geometry of the aftershock sequence defines a rupture plane that strikes n36 e and dips to the east southeast at 49 5 moment tensor solutions of the mainshock and larger aftershocks are consistent with the distribution of aftershock locations both indicating reverse slip along a northeast southwest striking southeast dipping fault plane

cosmogenic 10 be constraints on little ice age glacial advances in the eastern tian shan china abstract presumed little ice age lia glacial advances represented by a set of fresh sharp crested boulder covered and compact moraines a few hundred meters downstream from modern glaciers have been widely recognized in the central asian highlands however few studies have constrained the formation ages of these moraines we report 31 10 be exposure ages from presumed lia moraines in six glacial valleys in the urumqi river headwater area and the haxilegen pass area of the eastern tian shan china our results reveal that the maximum lia glacial extent occurred mainly around 430 100 yr a cold and wet period as indicated by proxy data from ice cores tree rings and lake sediments in central asia we also dated a later glacial advance to 270 55 yr however 10 be exposure ages on several presumed lia moraines in front of small thin glaciers are widely scattered and much older than the globally recognized timing of the lia historical topographic maps indicate that most glaciers were more extensive in the early 1960s and two of our 10 be sample sites were located close to the ice front at that time boulders transported by these small and thin glaciers may be reworked from deposits originally formed prior to the lia glacial advances producing apparently old and widely scattered exposure ages due to varied nuclide inheritance other published ages indicated an earlier lia advance around 790 300 yr in the easternmost tian shan but in our study area the more extensive advance around 430 100 yr likely reworked or covered deposits from this earlier event

improving local earthquake locations using the l1 norm and waveform cross correlation application to the whittier narrows california aftershock sequence experiments with different earthquake location methods applied to aftershocks of the october 1 1987 whittier narrows earthquake in california ml 5 9 suggest that local event locations can be greatly improved through the use of the l1 norm station corrections and waveform cross correlation the whittier narrows sequence is a compact cluster of over 500 events at 12 to 18 km depth located within the dense station coverage of the southern california seismic network scsn a telemetered network of several hundred short period seismographs scsn travel time picks and waveforms obtained through the southern california earthquake center are examined for 589 earthquakes between 1981 and 1994 in the vicinity of the mainshock using a smoothed version of the standard southern california velocity model and the existing travel time picks improved location accuracy is obtained through use of the l1 norm rather than the conventional least squares l2 norm approach presumably due to the more robust response of the former to outliers in the data a large additional improvement results from the use of station terms to account for three dimensional velocity structure outside of the event cluster to achieve greater location accuracy waveforms for these events are resampled and low pass filtered and the p and s wave cross correlation functions are computed at each station for every event pair for those events with similar waveforms differential times may be obtained from the cross correlation functions these times are then combined with the travel time picks to invert for an adjusted set of picks that are more consistent than the original picks and include seismograms that were originally unpicked locations obtained from the adjusted picks show a further improvement in accuracy location uncertainties are estimated using a bootstrap technique in which events are relocated many times for sets of picks in which the travel time residuals at the best fitting location are used to randomly perturb each pick improvements in location accuracy are indicated by the reduced scatter in the residuals smaller estimated location errors and the increased tendency of the locations to cluster along well defined fault planes median standard errors for the final inversion are 150 m in horizontal location and 230 m in vertical location although the relative locations within localized clusters of similar events are better constrained seismicity cross sections resolve the shallow dipping fault plane associated with the mainshock and a steeply dipping fault plane associated with a ml 5 3 aftershock these fault planes appear to cross and activity began on the secondary fault plane prior to the large aftershock

anisotropy of experimentally compressed kaolinite illite quartz mixtures the anisotropy of physical properties is a well known characteristic of many clay bearing rocks this anisotropy has important implications for elastic properties of rocks and must be considered in seismic modeling preferred orientation of clay minerals is an important factor causing anisotropy in clay bearing rocks such as shales and mudstones that are the main cap rocksofoilreservoirs thepreferredorientationofclaysdepends mostly on the amount of clays and the degree of compaction to studytheeffectoftheseparameters wepreparedseveralsamples compressingattwoeffectiveverticalstressesamixtureofclays illite and kaolinite and quartz silt with different clay quartz ratios the preferred orientation of the phases was quantified with rietveld analysis on synchrotron hard x ray images pole figures for kaolinite and illite display a preferred orientation of clay platelets perpendicular to the compaction direction increasing in strength with clay content and compaction pressure quartz particles have a random orientation distribution aggregate elastic properties can be estimated by averaging the singlecrystal properties over the orientation distribution obtained from the diffraction data analysis calculated p wave velocity anisotropy ranges from 0 pure quartz sample to 44 pure clay sample highly compacted but calculated velocities are much higher than measured velocities this is attributed to uncertainties about single crystal elastic properties and oriented micropores and limited grain contacts that are not accounted for in themodel inthiswork wepresentaneffectivemethodtoobtain quantitative data helping to evaluate the role of clay percentage and compaction pressure on the anisotropy of elastic properties ofclay bearingrocks

crustal rheology from focal depths in the north china basin abstract in order to investigate earthquakes in the lower crust of north china basin ncb we develop a new method of resolving very accurately the focal depth for local earthquakes in the sedimentary regions by using p and s to p converted wave sp at the sedimentary interface theoretical analysis shows clearly that the travel time difference between the sp and p wave almost linearly correlates with the focal depth this finding provides tight constraints on the depth with this method we obtain well constrained depths of 44 events in the ncb with uncertainties in the depth of about 2 km such a fine resolution can have great potential in asking questions regarding the crustal rheology the depth distribution shows abundance of earthquakes in depth interval of 20 km with some events in the lower crust but also reveals the absence of seismicity deeper than 25 km we find a good fit between the depth frequency distribution in this region and the yield strength envelope yse in the baikal rift systems brs we infer that the seismogenic thickness is 25 km in the ncb and the main deformation mechanism is brittle fracture we further hypothesize that 1 the rheological layering of dominant rheology in the ncb is similar to that of the brs which can be explained with a quartz rheology at 0 10 km depth and a diabase rheology at 10 35 km depth 2 the temperature is moderate in the seismogenic zone of crust we emphasize that many accurately resolved earthquake locations can shed light on the local nature of the crustal rheology and this strategic method can be employed in other sedimentary regions which are seismically active

automated procedure for point and kinematic source inversion at regional distances 1 the development of fast automatic routines for the retrieval of point source parameters of medium to large earthquakes was convincingly established in the last years and decades providing an increasing number of focal mechanism solutions original applications at teleseismic distances have been successively accompanied by specific routines for regional data sets the majority of these methods are based on the fit of low passed time traces we present here a new technique for the automatic retrieval of point source parameters and highly parameterized kinematic rupture models at regional distances assuming the recently proposed eikonal model to describe the extended source in our approach we use a larger set of information to better constrain the source parameters including the fit of amplitude spectra and displacements at different phases and frequency ranges the time consumption of the inversion process is significantly improved thanks to the implementation of green s functions databases we adopt a multistep inversion approach finally providing the focal mechanism magnitude and centroid location of the point source for events with magnitude higher than a threshold of mw 5 5 source geometry rupture extension and average slip may be additionally retrieved we discuss the methodology and the inversion stability showing applications to significant earthquakes in two case areas we focus on germany and greece and their neighboring areas considering major shallow earthquakes in the last 5 years the proposed method is currently implemented for automatic data processing at the seismological observatory of the federal institute for geosciences and natural resources in germany

local earthquake wave propagation through mississippi embayment sediments part ii influence of local site velocity structure on qp qs determinations elastic near surface structure and receiver depth effects are seen to control body wave amplitude spectra in the band from 2 to 50 hz for local earthquake observations in the new madrid seismic zone p and s wave spectral peaks are created by resonance in shallow low velocity zones and spectral nulls are created by interference of direct and free surface reflections due to receiver depth these wave propagation effects dominate sp s spectral ratios and mimic anelastic attenuation effects by making it appear that s waves are deficient in higher frequencies relative to sp waves there is no evidence from sp s spectral ratios that unconsolidated sediments of the mississippi embayment are highly attenuating dominance of p and s wave resonance suggests that the unconsolidated sediments amplify rather than attenuate seismic waves at high frequency this has important implications for estimating hazards from strong ground motions in the area in the absence of any identifiable anelastic attenuation effect in the spectral ratio the only allowable q p q s relationship for embayment sediments is that q s 3 q p based on consideration of wave travel times manuscript received 11 march 2003

effective elastic properties of solid clays clay minerals are perhaps the most abundant materials in the earth s upper crust as such their elastic properties are extremely important in seismic exploration seismic reservoir characterization and sonic log interpretation because little exists in the literature on elastic properties of clays we have designed a method of measuring effective elastic properties of solid clays clays without pores in this method clay minerals are mixed with a material with known elastic properties to make composite samples elastic properties of these clay minerals are then inverted from the measured elastic properties of the composite samples using the weighted hashin shtrikman average using this method we have measured 66 samples of 16 types of clays in this paper we present a comprehensive data set of elastic properties of solid clays that commonly occur in or are related to petroleum reservoirs although uncertainties up to 10 exist the data set reported here is by far the most comprehensive set of e

global compilation of interferometric synthetic aperture radar earthquake source models 1 comparisons with seismic catalogs 1 while many earthquakes have now been studied using interferometric synthetic aperture radar insar data a full assessment of the quality and additional value of insar source parameters compared to seismological techniques is still lacking we compile a catalog of source models obtained using insar and estimate the corresponding centroid moment tensor cmt parameters we refer to this compilation as the icmt archive we compare source parameters from over 70 insar studies of 57 global earthquakes with those in the global cmt gcmt international seismological centre isc and engdahl hilst buland ehb seismic catalogs we find an overall good agreement between fault strike dip and rake values in the gcmt and icmt archives likewise the differences in seismic moment between these two archives are relatively small and we do not find support for previously suggested trends of insar leading to larger moments than seismic data however epicentral locations show substantial discrepancies which are larger for the gcmt median differences of 21 km than for the ehb and isc catalogs median differences of 10 km since insar data have a high spatial resolution and thus should map epicentral locations accurately this allows us to obtain a first independent estimate of epicentral location errors in the seismic catalogs earthquake depths from insar are systematically shallower than those in the ehb catalog with a median of differences of 5 km while this trend may be partly due to unmodeled crustal complexity it is also compatible with the observation that the rupture of crustal earthquakes tends to propagate upward in the seismogenic layer

resolving focal depth in sparse network with local depth phase spl a case study for the 2011 mineral virginia earthquake sequenceresolving focal depth in sparse network with local depth phase spl

on an improved method to obtain the moment tensor and depth of earthquakes from the amplitude spectrum of rayleigh waves abstract a new method is presented to invert for the moment tensor and depth using the amplitude spectra of vertical component rayleigh waves in the period range 20 to 100 sec the technique follows a similar approach to that suggested by romanowicz 1982a to invert for the moment tensor from the complex spectra of rayleigh waves and presents some distinct advantages to the method proposed originally by mendiguren 1977 it eliminates some biases and errors in the data arising for example from inaccurate propagation corrections furthermore it is substantially faster computationally and permits us to study independently the variance reduction as a function of depth of each of the momenttensor elements resulting in better focal depth resolution the method is applied to three earthquakes in the tien shan mountains of central asia the eastern cordillera of peru and the gibbs transform fault in the north atlantic in all three cases the results of the moment tensor inversion agree with those determined using long period body wave modeling

an updated stress map of the continental united states reveals heterogeneous intraplate stress knowledge of the state of stress in earth s crust is key to understanding the forces and processes responsible for earthquakes historically low rates of natural seismicity in the central and eastern united states have complicated efforts to understand intraplate stress but recent improvements in seismic networks and the spread of human induced seismicity have greatly improved data coverage here we compile a nationwide stress map based on formal inversions of focal mechanisms that challenges the idea that deformation in continental interiors is driven primarily by broad uniform stress fields derived from distant plate boundaries despite plate boundary compression extension dominates roughly half of the continent and second order forces related to lithospheric structure appear to control extension directions we also show that the states of stress in several active eastern united states seismic zones differ significantly from those of surrounding areas and that these anomalies cannot be explained by transient processes suggesting that earthquakes are focused by persistent locally derived sources of stress such spatially variable intraplate stress appears to justify the current spatially variable estimates of seismic hazard future work to quantify sources of stress stressing rate magnitudes and their relationship with strain and earthquake rates could allow prospective mapping of intraplate hazard

rock physics templates for clay rich source rocks shale source rocks are composed of various minerals mainly smectite and illite depending on the burial depth and they can be described as transversely isotropic media the pore space may contain kerogen water oil and gas determined by the in situ conditions a petroelastic description is based on the following smectite illite transformation as a function of depth is described by a fifth order kinetic reaction backus averaging to mix isotropic smectite and anisotropic illite is then used to obtain the elasticity constants of the mineral composing the frame porosity is obtained from density and water is part of the mineral whose elasticity constants are obtained from gassmann equations oil and gas generated from kerogen are assumed to saturate the kerogen phase the bulk modulus of the oil gas mixture is calculated by a mesoscopic loss model and the stiffnesses of the kerogen fluid mixture are obtained with the kuster and toksoz model assuming that the fluid is included in a kerogen matrix two models are considered to obtain the seismic velocities of the shale namely backus averaging and the gassmann equation generalized to the anisotropic case with a solid pore infill we built rock physics templates rpts containing only kerogen immature and kerogen plus hydrocarbons mature pore pressure effects were modeled and used as templates we considered the kimmeridge shale at different depths to model kerogen oil and oil gas conversions we assumed a basin evolution model with a constant sedimentation rate geothermal gradient and a first order kinetic arrhenius reaction the detection of the hydrocarbons was investigated from rpts built with wave velocities impedances lame constants density poisson ratio young modulus and anisotropy parameters for varying kerogen content fluid saturations and pore pressure moreover the amplitude variation with offset intercept and gradients were computed corresponding to the seismic response of a source rock layer for varying kerogen content and fluid saturation

t matrix approach to shale acoustics summary the t matrix approach of quantum scattering theory is used here to place many long wavelength equivalent medium approximations for porous composites polycrystals and cracked media on a common footing and to indicate their limitations but also to derive some new results based on two point statistics in this way we have obtained an insight into the difficult problem of elastic inclusions at finite concentrations which is of foremost relevance when estimating the effective material parameters of porous cracked shales involving stacks of more or less horizontally aligned clay platelets mixed together with more rounded silt minerals and with fluid filling the spaces a rather involved perturbative analysis of the effects of interactions between or structural correlations among the various inclusions minerals and cavities making up a real shale of hexagonal symmetry was performed in an attempt to obtain a better match between theoretical predictions based on a combination of coherent and optical potential approximations and experimental results recovered from ultrasonic wave speeds for the effective elastic stiffness tensor for the particular data set considered in this study the t matrix approach was able to match the data better than the approach of hornby et al but the match was not completely satisfactory further progress in theoretical shale modelling may come from a better knowledge of the elastic properties of pure clay minerals a more detailed knowledge of the microstructure of shales the incorporation of constraints obtained from comparisons between theoretical predictions and experimental results as well as a continuing development of the t matrix approach numerical results also for the effect of bedding parallel microcracks on the elasticity of such a real shale have value in illustrating the importance of taking into account the effects of spatial distribution when trying to deal with non dilute mixtures of highly contrasting material properties

the aftershock sequence of the 2011 mineral virginia earthquake temporal and spatial distribution focal mechanisms regional stress and the role of coulomb stress transfer abstract the aftershocks of the 23 august 2011 m w 5 7 mineral virginia earthquake were recorded by 36 temporary stations installed by several institutions we located 3960 aftershocks from 25 august 2011 through 31 december 2011 a subset of 1666 aftershocks resolves details of the hypocenter distribution we determined 393 focal mechanism solutions aftershocks near the mainshock define a previously recognized tabular cluster with orientation similar to a mainshock nodal plane other aftershocks occurred 10 20 km to the northeast a large percentage of the aftershocks occurred in regions of positive coulomb static stress change and 80 of the focal mechanism nodal planes were brought closer to failure however the aftershock distribution near the mainshock appears to have been influenced strongly by rupture directivity aftershocks at depths less than 4 km exhibit reverse mechanisms with north northwest trending nodal planes most focal mechanisms at depths greater than 6 km are similar to the mainshock with north northeast trending nodal planes a concentration of aftershocks in the 4 6 km depth range near the mainshock are mostly of reverse type but display a 90 range of nodal plane trend those events appear to outline the periphery of mainshock rupture where positive coulomb stress transfer is largest the focal mechanisms of aftershocks at depths less than 4 km and those greater than 6 km along with the mainshock point to the possibility of a depth dependent stress field prior to the occurrence of the mainshock analysis of earthquake occurrence using a new magnitude scale indicates a gutenberg richer law b value of 0 864 and an omori law p value of 1 085 indicative of a typical aftershock sequence online material catalogs of aftershock location magnitude and focal mechanisms

elastic moduli of anisotropic clay claymineralsareimportantcomponentsinshales controlling their elastic properties and anisotropy the elasticity of crystalline clay minerals differs significantly from that of clay in situ because of the ability of clay particles to bind water in the majority of published works only isotropic moduli for in situ clays are reported however anisotropy is inherent in the clay elasticity we develop an inversion technique for determination of thestiffnesstensorofinsituclayfromtheshale sstiffnesstensor as an example we obtain the stiffness tensor of a water clay composite from the data on the water saturated greenhorn shale sample whose clay composition consists of almost equal amounts of illite and smectite and comparable amounts of kaolinite and chlorite the stiffness tensor of the water clay composite is found for the greenhorn shale with step by step inversion based upon an effective medium theory the inversion uses a nonlinear optimization technique with bounds imposed on the estimated parameters in the inversion we apply different approaches of the effective medium theory using a published method referred to here as the generalized singular approximation gsa the gsa method makes it possible to take into account the microstructure of shales the resulting elasticity constants of the anisotropic transversely isotropic in situ clay composite are c11 23 7 c33 8 5 c44 0 8 c66 5 7 and c13 3 1 in gpa and the density equals 2 17 g cm 3 the thomsen parameters for the clay composite are 0 89 3 10 and 0 34 the elasticity constants found for this clay composite can be used in the theoretical analysis of shales that have a similar composition of clay but with different mineral compositions the inversion technique developed can be used for general shale water clay composites when the mineral composition and orientation of the clay platelets are known

analysis of similar event clusters in aftershocks of the 1994 northridge california earthquake 1 we perform waveform cross correlation on over 14 000 aftershocks of the 1994 northridge mw 6 7 earthquake in southern california as recorded by short period stations of the southern california seismic network scsn approximately 10 30 of the events belong to similar event clusters depending upon the similarity criteria that are applied we relocate events within 218 of these clusters to a relative location accuracy of about 30 m using the differential times obtained from the cross correlation these relocated event clusters often show planar features suggestive of faults at depth and we apply principal parameter analysis to characterize the shape of each cluster and to compute best fitting planes in several cases these planes are parallel to the main shock fault plane however more generally the seismicity planes exhibit a wide range of orientations suggesting complexity in the aftershock faulting composite focal mechanisms can be obtained for each cluster by combining the p polarity data from individual events a comparison of polarity measurement differences within similar event clusters provides constraints on the error rate in the individual focal mechanisms for some clusters we are able to resolve the primary versus auxiliary fault plane ambiguity by comparing the computed focal mechanisms with the best fitting seismicity planes individual event focal mechanisms are in general agreement with the composite focal mechanisms for the similar event clusters events occurring along the main shock rupture plane are mainly thrust whereas events in the hanging wall are predominately strike slip

joint inversion for earthquake depths using local waveforms and amplitude spectra of rayleigh waves reliable earthquake depth is fundamental to many seismological problems in this paper we present a method to jointly invert for centroid depths with local distance 5 seismic waveforms and regional distance of 5 15 rayleigh wave amplitude spectra on sparse networks we use earthquake focal mechanisms and magnitudes retrieved with the cut and paste cap method to compute synthetic amplitude spectra of fundamental mode rayleigh wave for a range of depths then we grid search to find the optimal depth that minimizes the joint misfit of amplitude spectra and local waveforms as case studies we apply this method to the 2008 wells nevada mw6 0 earthquake and a mw5 6 outer rise earthquake to the east of japan trench in 2013 uncertainties estimated with a bootstrap re sampling approach show that this joint inversion approach constrains centroid depths well which are also verified by independent teleseismic depth phase data

upscaling of elastic properties of anisotropic sedimentary rocks summary in this paper the term upscaling means the theoretical prediction of rock s elastic properties at lower frequency seismic or cross well data using higher frequency logging data on sonic velocities vp vs1 and vs2 porosity and density the mineral composition and water saturation derived from other logs are used due to the special treatment of sonic logging data provided by the dipole sonic probe all the sonic velocities are obtained in the principal coordinate system of the rock s stiffness tensor the upscaling procedure includes two steps the first step involves the solution of an inverse problem on reconstruction of the parameters of the rock s microstructure from the logging data the inversion is based on the effective medium theory as a result of the inverse problem solution the effective stiffness tensor is found for depths at which the sonic wave velocities are measured at the second step the velocities of waves at given lower frequencies are calculated as propagating in a layered medium the number of layers in the medium depends on the given frequency and logging step each layer of the medium has the stiffness tensor found at the first step this upscaling procedure has been applied to a wellbore for which the dipole sonic data are available the rocks penetrated by the well are shales in general the resulting medium exhibits orthorhombic symmetry at sonic frequency this symmetry results from the preferential orientation of clay platelets and grain related cracks and vertical cracks the existence of the latter is indicated by the dipole sonic tool depending on the microstructure parameters orientation of clay platelets and cracks pore crack connectivity and shale mineralogical composition the shales at lower frequency have either transversely isotropic symmetry with the vertical axis of symmetry a k a vti or orthorhombic symmetry

clay squirt local flow dispersion in shale bearing sandstones abstractdispersion of elastic wave velocity is common in sandstone and larger in shaly sandstone than in clean sandstone dispersion in fluid saturated shaly sandstone often exceeds the level expected from the stress dependent elastic moduli of dry sandstone the large dispersion has been coined clay squirt and is proposed to originate from a pressure gradient between the clay microporosity and the effective porosity we have formulated a simple model that quantifies the clay squirt effect on bulk moduli of sandstone with homogeneously distributed shale laminae or dispersed shale the model predictions were compared with the literature data for sandstones with dispersed shale agreement was found whereas other sandstones have larger fluid saturated bulk modulus possibly due to partially load bearing shales or heterogeneous shale distribution the data that agree with the clay squirt model indicated nonuniform pore pressure in the high frequency regime and uniform pore pressure in the low frequency regi

near source geometrical spreading in the central virginia seismic zone determined from the aftershocks of the 2011 mineral virginia earthquake we used aftershocks of the 2011 mineral virginia earthquake to study geometrical spreading at hypocentral distances less than 60 km in the central virginia seismic zone sixty nine aftershocks occurring from 25 august 2011 through 24 december 2011 provided the data we used the coda normalization method to estimate the attenuation coefficient associated with geometrical spreading we filtered the time domain signals in several octave wide frequency bands and examined attenuation of peak s wave amplitude in the 1 0 30 0 hz frequency range amplitude was assumed to decrease as a function of hypocenter distance r according to r the coefficient of attenuation was examined for the three component s wave amplitudes with corrections for sh and sv radiation patterns we observed no systematic frequency dependence of the coefficient of attenuation for the radial and transverse components assuming infinite quality factor q derived as a weighted mean over the entire range of frequencies 1 30 hz are both 1 51 0 05 the weighted mean value of the attenuation coefficient on the vertical component over the same range of frequencies is 1 45 0 05 slightly less than for the horizontal components we corrected the data assuming three q models the estimated geometrical spreading coefficients are in the 1 30 1 46 range depending on the assumed q model and component which is only slightly less than the estimates of determined assuming infinite q the estimated attenuation coefficients differ significantly from the value of 1 0 expected for a whole space the results for the horizontal components are in agreement with previous full wavefield modeling however the observed vertical component attenuation is substantially less than that predicted by the synthetics the depths of the earthquakes are less than 8 km so these results may not be representative of geometrical spreading in parts of eastern north america where earthquakes occur at greater depths online material table of earthquake hypocenters and focal mechanisms

elastic anisotropy modeling of kimmeridge shale 1 anisotropy of elastic properties in clay rich sedimentary rocks has been of long standing interest these rocks are cap rocks of oil and gas reservoirs as well as seals for carbon sequestration elasticity of shales has been approached by direct velocity measurements and by models based on microstructures here we are revisiting the classical kimmeridge shale studied by hornby 1998 by first quantifying microstructural features such as phase volume fractions grain shapes and grain orientations and pore distributions with advanced analytical methods and then using this information in different models to explain bulk elastic properties it is shown that by application of a self consistent algorithm based on eshelby s 1957 model of inclusions in a homogeneous medium it is possible to explain most experimental elastic constants though some discrepancies remain which may be due to the interpretation of experimental data using a differential effective medium approach an almost perfect agreement with experimental stiffness coefficients can be obtained though the physical basis of this method may be questionable the influence of single crystal elastic properties grain shapes preferred orientation and volume and shapes of pores on elastic properties of shale is explored

geomechanics field characterization of woodford shale and barnett shale with advanced logging tools and nano indentation on drill cuttings the woodford shale and barnett shale have emerged as prolific gas plays in the us midcontinent however the intrinsically low permeability of these gas shales hinders profitable pro duction unless horizontal well drilling and multistage hydraulic fracturing are employed the success of these operations depends on accurate de terminations of the anisotropic elastic and poroelastic properties of these shale formations

the nanogranular acoustic signature of shale a multiscale micromechanics model has been developed for the prediction of anisotropic acoustic properties of shale the model is based on the recently identified nanogranular mechanical response of shale through indentation experiments it recognizes the dominant role of the anisotropic elastic properties of compacted clay in the anisotropic elasticity of shale at different length scales compared to contributions of shape and orientation of particles following a thorough validation at multiple length scales using mineral elasticity data nanoindentation experiment results and ultrasonic pulse velocity tests the model predictions compare adequately with measurements on kerogen free and kerogen rich shales and shaley sandstones the acoustic signature of shale thus is found to be controlled by two volumetric parameters that synthesize the porosity and mineralogy information the clay packing density and the silt inclusion volume fraction through a series of dimensionless isoparametric plots the micromechanics model predicts trends of increasing elastic anisotropy with increasing clay packing density or decreasing porosity which correspond to the intrinsic mechanical response of unfractured shale and quantifies the stiffness reduction induced by the presence of kerogen

texture and anisotropy analysis of qusaiba shales scanning and transmission electron microscopy synchrotron x ray diffraction microtomography and ultrasonic velocity measurements were used to characterize microstructures and anisotropy of three deeply buried qusaiba shales from the rub alkhali basin saudi arabia kaolinite illite smectite illite mica and chlorite show strong preferred orientation with 001 pole figure maxima perpendicular to the bedding plane ranging from 2 4 6 8 multiples of a random distribution m r d quartz feldspars and pyrite crystals have a random orientation distribution elastic properties of the polyphase aggregate are calculated by averaging the single crystal elastic properties over the orientation distribution assuming a nonporous material the average calculated bulk p wave velocities are 6 2 km s maximum and 5 5 km s minimum resulting in a p wave anisotropy of 12 the calculated velocities are compared with those determined from ultrasonic velocity measurements on a similar sample in the ultrasonic experiment which measures the effects of the shale matrix as well as the effects of porosity velocities are smaller p wave maximum 5 3 km s and minimum 4 1 km s the difference between calculated and measured velocities is attributed to the effects of anisotropic pore structure and to microfractures present in the sample which have not been taken into account in the matrix averaging

monitoring the earthquake source process in north america with the implementation of the usgs national earthquake information center prompt assessment of global earthquakes for response system pager rapid determination of earthquake moment magnitude is essential especially for earthquakes that are felt within the contiguous united states we report an implementation of moment tensor processing for application to broad seismically active areas of north america this effort focuses on the selection of regional crustal velocity models codification of data quality tests and the development of procedures for rapid computation of the seismic moment tensor we systematically apply these techniques to earthquakes with reported magnitude greater than 3 5 in continental north america that are not associated with a tectonic plate boundary using the 0 02 0 10 hz passband we can usually determine with few exceptions moment tensor solutions for earthquakes with m w as small as 3 7 the threshold is significantly influenced by the density of stations the location of the earthquake relative to the seismic stations and of course the signal to noise ratio with the existing permanent broadband stations in north america operated for rapid earthquake response the seismic moment tensor of most earthquakes that are m w 4 or larger can be routinely computed as expected the nonuniform spatial pattern of these solutions reflects the seismicity pattern however the orientation of the direction of maximum compressive stress and the predominant style of faulting is spatially coherent across large regions of the continent

depth of faulting during the 1968 meckering australia earthquake sequence determined from waveform analysis of local seismograms waveforms for 11 foreshocks and 48 aftershocks of the ms 6 8 meckering earthquake recorded at the world wide standard seismograph network station mundaring are analyzed to determine the depth distribtion of faulting during this unusual intraplate earthquake sequence clear depth phases including sp and rg are seen in the local seismograms at distances of 60 95 km and are studied using synthetic seismograms computed using generalized ray theory and wave number integration techniques large rg s ratios seen on the vertical component short period data for many events imply source depths less than 2 km the short period p waveform contains the best depth estimator in the form of sp so that depth can be estimated to within an uncertainty of about 1 km for most events the foreshocks cluster at less than 2 km depth and most aftershocks occur within 1 km of the surface a few aftershocks occur as deep as 7 km these results are consistent with a previous teleseismic waveform study in which faulting was inferred to start near the surface at 1 5 km depth with rupture proceeding downward and not exceeding 6 km depth these results coupled with previous stress studies in the australian shield and models of crustal strength show that faulting in a cold shield area is a near surface phenomenon and implies that most of the crust is too strong to be fractured

mechanical properties of organic matter in shales mapped at the nanometer scale abstract the mechanical properties of organic matter strongly affect the way shales deform and fracture however the way organic matter responds to mechanical stresses is poorly understood representing a critical obstacle to assessing oil and gas production in shale formations little is known about the mechanical properties of organic matter in fine grained rocks primarily because it often occupies tiny nanometer scale voids between the mineral grains which cannot be accessed using standard mechanical testing techniques here we use a new atomic force microscopy technique peakforce qnm to map the mechanical properties of organic and inorganic components at the nanometer scale we find that the method is able to distinguish between different phases such as pyrite quartz clays and organic matter moreover within the organic component young s modulus values ranged from 0 to 25 gpa in 3 different samples all of which come from thermally mature type ii iii source rocks in the dry gas window a modal value of 15 16 gpa was measured with additional peaks measured at 10 gpa in addition the maps suggest that some porous organic macerals possess a soft core surrounded by a harder outer shell 50 100 nm thick thus our results demonstrate that the method represents a powerful new petrographic tool with which to characterize the mechanical properties of organic rich sedimentary rocks

source mechanism and rupture directivity of the 18 may 2009 mw 4 6 inglewood california earthquake on 18 may 2009 an m w 4 6 earthquake occurred beneath inglewood california and was widely felt though source mechanism and its location suggest that the newport inglewood fault nif may be involved in generating the earthquake rupture directivity must be modeled to establish the connection between the fault and the earthquake we first invert for the event s source mechanism and depth with the cut and paste method in the long period band 5 s because of the low velocity shallow sediments in the los angeles la basin we use two velocity models in the inversion for stations inside and outside the la basin however little difference is observed in the resolved source mechanism m w 4 6 strike 246 145 dip 50 77 rake 17 138 and depth 7 to 9 km compared to an inversion using the standard southern calfornia model with the resolved source parameters we calibrate the amplitude anomaly of the short period 0 5 2 hz p waves with amplitude adjustment factors aaf these aafs are used as corrections when retrieving source mechanisms of the smaller aftershocks using short period p waves alone most of the aftershocks show similar source mechanisms as that of the mainshock providing ideal empirical green s functions egfs for studying its rupture process we use a forward modeling approach to retrieve rupture directivity of the mainshock consistent with movement on the nif with rupture toward the southeast although we focus on p waves for analyzing rupture directivity the resolved unilateral pattern is also confirmed with the azimuthal variation of the duration of sh waves observed in the basin the high rupture velocity near the shear velocity and relatively low stress drop are consistent with the hypothesis of rupture on a mature fault

identification and inversion of converted shear waves case studies from the european north atlantic continental margins summary wide angle shear wave arrivals converted from compressional to shear waves at crustal interfaces enable crustal vp vs ratios to be determined which provide valuable constraint on geological interpretations analysis of the converted shear wave phases represents the next logical step in characterizing the crustal structure and composition following multichannel seismic structural imaging and tomographic inversion of the wide angle compressional wave phases in this offshore study across two passive margins extending from stretched continental to fully oceanic crust the high data density 2 10 km ocean bottom seismometer obs spacing and a consistent efficient conversion interface produced shear wave data sets suitable for traveltime inversion the shear waves were recorded by three orthogonal geophones in each obs arrival phases visible to 180 km offset were identified using their arrival times moveout velocities and particle motions across the north atlantic volcanic rifted continental margins studied breakup was accompanied by the eruption of large volumes of basalts of the north atlantic igneous province the interface between post volcanic sediments and the top of the basalts provides the dominant conversion boundary across the oceanic crust and the continent ocean transition however the shear wave data quality was significantly diminished at the continental ends of the profiles where the thick basalt flows and hence this conversion interface feathers out and crustal attenuation increases initial modelling of the converted shear wave phases was carried out using a layer based approach with arrivals converted on the way up used to constrain the vp vs ratio of the post volcanic sedimentary sequence beneath each obs to produce a model with continuous crustal s wave velocities the compressional wave velocities beneath the sediment top basalt interface were transformed into starting shear wave velocities using a constant value of vp vs and the inversion carried out by specifying the appropriate ray path once the data set had been fully interpreted correction of the traveltimes to effective symmetric ray paths enabled us to apply a regularized grid inversion such inversions are less subjective than the layer based approach and yield more robust minimum structure results with quantifiable errors except in the vicinity of a known subbasalt low velocity zone encountered on the faroes margin monte carlo analyses were performed for this approach the average model from multiple inversions using randomized starting models and traveltimes shows the structure required by the traveltimes and the model standard deviation gives an estimate of uncertainty model and inversion parametrizations were fully tested and optimum parameters chosen for compressional and shear wave inversions this allows after appropriate model smoothing an estimate to be made of the spatial variation of the vp vs ratio within the crust there are marked gradients in vp vs and vp vs ratio across the continent ocean transition which may result from intrusion of high magnesium mafic igneous material into the crystalline continental crust the vp vs ratio used in conjunction with vp also provides constraints on the subbasalt lithologies forming the low velocity zone we conclude from such an analysis that this zone is unlikely to be composed entirely of igneous hyaloclastite material some proportion of clastic sedimentary rocks is likely to be present the vp vs and vp properties of the units underlying the low velocity zone are inconsistent with crystalline

focal depths for small to moderate earthquakes mn 2 8 in western quebec southern ontario and northern new york regional depth phase modeling is a useful technique to constrain earthquake focal depths for events within sparse networks we demonstrate how regional depth phases can be used to obtain focal depths for hundreds of earthquakes with m n 2 8 that occurred from 1980 to 2004 in southern ontario western quebec and northern new york state we discuss the development of regional depth phases with distance their use in focal depth determinations by matching waveforms to synthetics and possible sources of error in general focal depths can be determined to within about 3 km when there is at least one record at regional distances with clearly identifiable depth phases such as spmp or spg in southwestern ontario and northern new york focal depths range from 2 to 15 km in areas of western quebec and along the ottawa river valley in ontario focal depths range from 2 to 25 km more than half of the earthquakes in a cluster of activity near maniwaki in western quebec are deeper than 20 km all earthquakes deeper than 20 km occurred north of about 45 3 n there is an intriguing tendency for earthquake depths to cluster near 8 km 12 km 15 km and 22 km another interesting observation is that there are several earthquake pairs or small groups with very similar epicenters but quite different depths the most active regions in western quebec and along the ottawa river valley tend to exhibit a relatively wide range of focal depths along broad zones that trend roughly northwest suggesting that seismicity is occurring along diffuse northwest trending faults throughout the crust the wide range of focal depths may indicate the potential for a larger maximum scale of fault rupture and serve as a contemporary marker of locations where large events have occurred in the recent geologic past

seismic modeling to monitor co2 geological storage the atzbach schwanenstadt gas field 1 we develop a petro elastical numerical methodology to compute realistic synthetic seismograms and analyze the sensitivity of the seismic response when injecting carbon dioxide co2 in a depleted gas reservoir the petro elastical model describes the seismic properties of the reservoir rock saturated with co2 methane and brine and allows us to estimate the distribution and saturation of co2 during the injection process the gas properties as a function of the in situ pressure and temperature conditions are computed with the peng robinson equation of state taking into account the absorption of gas by brine wave attenuation and velocity dispersion are based on the mesoscopic loss mechanism which is simulated by an upscaling procedure to obtain an equivalent viscoelastic medium corresponding to partial saturation at the mesoscopic scale having the equivalent complex and frequency dependent bulk dilatational modulus we include shear attenuation and perform numerical simulations of wave propagation at the macroscale by solving the viscoelastic differential equations using the memory variable approach the pseudo spectral modeling method allows general material variability and provides a complete and accurate characterization of the reservoir the methodology is used to assess the sensitivity of the seismic method for monitoring the co2 geological storage at the atzbach schwanestadt depleted gas field in austria the objective of monitoring is the detection of the co2 plume in the reservoir and possible leakages of co2 the leakages are located at different depths where the co2 is present as gaseous liquid and supercritical phases even though the differences can be very subtle this work shows that seismic monitoring of co2 from the surface is possible while the identification of shallow leakages is feasible the detection of the plume and deep leakages located in the caprock just above the injection formation is more difficult but possible by using repeatability metrics such as the normalized rms nrms images considering real data conditions affected by random noise a reference detection threshold for deep leakages and the co2 plume in the reservoir corresponds to a signal to noise ratio of about 10 db

rupture model of the 2011 mineral virginia earthquake from teleseismic and regional waveforms 1 we independently invert teleseismic p waveforms and regional crustal phases to examine the finite fault slip model for the 2011 mw 5 8 mineral virginia earthquake theoretical and empirical green s functions are used for the teleseismic and regional models respectively both solutions show two distinct sources each about 2 km across and separated by 2 5 km the source at the hypocenter is more localized in the regional model leading to a higher peak slip of 130 cm and higher average stress drop of 250 bars compared with 86 cm and 150 bars for the same source in the teleseismic model both sources are centered at approximately 8 km depth in the regional model largely below the aftershock distribution in the teleseismic model the sources extend updip to approximately 6 km depth into the depth range of the aftershocks the rupture velocity is not well resolved but appears to be near 2 7 km s

shear wave velocity of the sedimentary basin in the upper mississippi embayment using s to p converted waves from mid october 1989 to august 1992 40 three component panda portable array for numerical data acquisition stations were deployed in the central new madrid seismic zone three component digital seismograms recorded by the panda stations in the region are characterized by 1 the very weak direct s arrivals on the vertical component which can be identified unambiguously from the two horizontal components and 2 at least two prominent secondary arrivals between the direct p and s arrivals one sp dominant on the vertical component and another ps with smaller amplitude on the two horizontal components travel time differences between the sp and s and between the p and ps are the same for different earthquakes recorded at the same station but are different at different stations even for the same event polarization analyses of three component seismograms and travel time measurements confirm the interpretation that these two secondary arrivals are the p to s ps and s to p sp converted waves that occur at the bottom of the sedimentary basin beneath each station since abundant well log data are available in the upper mississippi embayment the thickness of the sediments beneath each seismic station can be estimated travel time differences between the direct and the converted waves can be used to calculate average shear wave velocity for the sediments beneath each station the estimated shear wave velocities of the sediments beneath panda stations vary from 0 45 to 0 67 km sec the higher shear wave velocity associated with thicker sediments can be interpreted as a consequence of increasing compaction of unconsolidated sediments due to increasing overburden

focal depth determination for moderate and small earthquakes by modeling regional depth phases spg spmp and spn there are three usable regional depth phases spg spmp and spn and their corresponding reference phases pg pmp and pn the differential time between each depth phase and its reference phase can be used to estimate earthquake focal depth we have developed a method to determine focal depth for moderate and small earthquakes by using a regional depth phase modeling rdpm method we used a default focal mechanism to generate the differential times for all earthquakes to estimate the reliability of the modeled focal depths we compared our solutions with those obtained by other methods and found the consistency is good because the focal depths estimated by rdpm are model dependent we tested the extent of the dependency and found that a 10 error in the crustal model may generate a 10 15 error in the modeled depth the absolute error is determined by the error in the crustal model and the focal depth itself we found that earthquake location errors have only a small effect on the modeled focal depths by analyzing synthetic and observed waveforms we found a distance window within which spmp and pmp are well developed and within the window the p portion of the waveform is relatively simple and spmp and pmp are easy to identify we also demonstrated that the assumptions of spmp and pmp are correct that regional depth phases are not developed or not discernible in some regions and that regional depth phases have special features that can be used to identify those phases

experimental mechanical compaction of clay mineral aggregates changes in physical properties of mudstones during burial dry and brine saturated clay aggregates ranging from pure smectite to pure kaolinite were compacted in the laboratory experiments were conducted by increasing vertical effective stress up to 50 mpa to study the changes in physical properties of mudstones during burial the results suggest that the physical properties porosity density acoustic velocity etc of mudstones vary greatly with increasing effective stress clay mineralogy and fluid content kaolinite aggregates are much more compressible than those composed of smectite brine saturated clay mixtures are much more compressible than dry clay mixtures brine may soften and lubricate the clay matrix compared to dry clays resulting in higher compressibility in the brine saturated state the lesser degree of compaction of dry smectite compared to dry kaolinite aggregates can be explained by the differences in grain size as kaolinitic clays have much larger grains than smectitic clays the extremely fine grained nature of smectite implies that the imposed vertical stress is distributed over a very large number of grain contacts so that the force per contact area is very low in smectite compared to that in coarse grained kaolinite at 20 mpa effective stress corresponding to about 2 km burial depth with hydrostatic pore pressure brine saturated pure kaolinite compacted to 20 porosity while pure smectite retained 41 porosity brinesaturated clay mixtures show higher vp and lower vs than dry clay mixtures a pronounced difference in vs was observed among the brinesaturated clay mixtures the lowest vs as a function of vertical effective stress was found for pure smectite for a given porosity value smectitic clays have higher velocities and elastic moduli than the kaolinitic clays the vp vs ratio is significantly higher in smectite than in kaolinite aggregates treating mudstones as a uniform class of rocks introduces significant errors in estimates of physical properties which are strongly affected by the clay mineralogy grain size the amount of other minerals present and fluid content our results have implications for well log interpretation and mudstone and shale property determinations from seismic data at shallow burial depth o 2k m 801c above depths where significant chemical compaction takes place r 2007 elsevier ltd all rights reserved

earthquake source mechanism and rupture directivity of the 12 september 2016 mw 5 5 gyeongju south korea earthquakeshort note

three dimensional compressional wavespeed model earthquake relocations and focal mechanisms for the parkfield california region we present a new three dimensional 3d compressional wavespeed v p model for the parkfield region taking advantage of the recent seismicity associated with the 2003 san simeon and 2004 parkfield earthquake sequences to provide increased model resolution compared to the work of eberhart phillips and michael 1993 epm93 taking the epm93 3d model as our starting model we invert the arrival time data from about 2100 earthquakes and 250 shots recorded on both permanent network and temporary stations in a region 130 km northeast southwest by 120 km northwest southeast we include catalog picks and cross correlation and catalog differential times in the inversion using the double difference tomography method of zhang and thurber 2003 the principal v p features reported by epm93 and michelini and mcevilly 1991 are recovered but with locally improved resolution along the san andreas fault saf and near the active source profiles we image the previously identified strong wavespeed contrast faster on the southwest side across most of the length of the saf and we also improve the image of a high v p body on the northeast side of the fault reported by epm93 this narrow body is at about 5 to 12 km depth and extends approximately from the locked section of the saf to the town of parkfield the footwall of the thrust fault responsible for the 1983 coalinga earthquake is imaged as a northeast dipping high wavespeed body in between relatively low wavespeeds 5 km sec extend to as much as 10 km depth we use this model to derive absolute locations for about 16 000 earthquakes from 1966 to 2005 and high precision double difference locations for 9 000 earthquakes from 1984 to 2005 and also to determine focal mechanisms for 446 earthquakes these earthquake locations and mechanisms show that the seismogenic fault is a simple planar structure the aftershock sequence of the 2004 mainshock concentrates into the same structures defined by the pre 2004 seismicity confirming earlier observations waldhauser et al 2004 that the seismicity pattern at parkfield is long lived and persists through multiple cycles of mainshocks online material 3d v p model and earthquake relocations

prediction of sonic velocities in shale from porosity and clay fraction obtained from logs a north sea well case study abstractprediction of sonic velocities in shales from well logs is important for seismic to log ties if the sonic log is absent for a shaly section for pore pressure anomaly detection and for data quality control an anisotropic differential effective medium dem was used to simulate elastic properties of shales from elastic properties and volume fractions of silt and wet clay a hypothetical composite material that includes all clay minerals and water anisotropic elastic coefficients of the wet clay were assumed as a first order approximation to be linearly dependent on wet clay porosity wcp here by wcp we mean a ratio of a pore volume occupied by water to a total volume of the wet clay effects of silt inclusions on elastic coefficients of shales were taken into account by using the anisotropic differential effective medium model silt inclusions were modeled as spherical quartz particles simulated elastic coefficients of shales were used to calculate compressional and shear velocities and th

earthquake hypocenters and focal mechanisms in central oklahoma reveal a complex system of reactivated subsurface strike slip faulting the sharp increase in seismicity over a broad region of central oklahoma has raised concern regarding the source of the activity and its potential hazard to local communities and energy industry infrastructure since early 2010 numerous organizations have deployed temporary portable seismic stations in central oklahoma in order to record the evolving seismicity in this study we apply a multiple event relocation method to produce a catalog of 3639 central oklahoma earthquakes from late 2009 through 2014 regional moment tensor rmt source parameters were determined for 195 of the largest and best recorded earthquakes combining rmt results with relocated seismicity enabled us to determine the length depth and style of faulting occurring on reactivated subsurface fault systems results show that the majority of earthquakes occur on near vertical optimally oriented ne sw and nw se strike slip faults in the shallow crystalline basement these are necessary first order observations required to assess the potential hazards of individual faults in oklahoma

improved location procedures at the international seismological centre summary the international seismological centre isc is a non governmental non profit organization with the primary mission of producing the definitive account of the earth s seismicity the isc bulletin covers some 50 yr 1960 2011 of seismicity the recent years have seen a dramatic increase both in the number of reported events and especially in the number of reported phases owing to the ever increasing number of stations worldwide similar ray paths will produce correlated traveltime prediction errors due to unmodelled heterogeneities in the earth resulting in underestimated location uncertainties and for unfavourable network geometries location bias hence the denser and more unbalanced the global seismic station coverage becomes the less defensible is the assumption that is the observations are independent which is made by most location algorithms to address this challenge we have developed a new location algorithm for the isc that accounts for correlated error structure and uses all iaspei standard phases with a valid ak135 traveltime prediction to obtain more accurate event locations in this paper we describe the new isc locator and present validation tests by relocating the ground truth events in the iaspei reference event list as well as by relocating the entire isc bulletin we show that the new isc location algorithm provides small but consistent location improvements considerable improvements in depth determination and significantly more accurate formal uncertainty estimates we demonstrate that the new algorithm through the use of later phases and testing for depth resolution considerably clusters event locations more tightly thus providing an improved view of the seismicity of the earth