self similarity properties of seismicity in the southern aegean area we investigate the time self similarity properties of seismicity in the hellenic are which is one of the most rapidly deforming and seismically active regions of the mediterranean area the presence of time scale invariance properties in the shallow and intermediate depth seismicity is revealed in particular 1 f beta fluctuations are detected from the analysis of earthquake sequences using the counting statistics methodology the shallow seismicity is characterized by a time clustering effect and shows a beta value that is a typical fingerprint of self similar behaviours whereas the intermediate seismicity can be considered as a realization of a purely poissonian process the investigations cover instrumentally recorded earthquakes occurring between 1964 and 1996 and the analyses have been carried out selecting different magnitude thresholds the beta value for shallow seismicity decreases from almost 0 5 to 0 2 as the threshold magnitude increases from 3 3 to 4 5 c 2000 elsevier science b v all rights reserved

a fractal model for crustal deformation abstract we hypothesize that crustal deformation occurs on a scale invariant matrix of faults for simplicity we consider a two dimensional pattern of hexagons on which strike slip faulting occurs the behavior of the system is controlled by a single parameter the fractal dimension deformation occurs on all scales of faults the fractal dimension determines the fraction of the total displacement that occurs on the first order or primary faults the value of the fractal dimension can be obtained from the frequency magnitude relation for earthquakes our results are applied to the san andreas fault system in central california earthquake studies give d 1 90 we associate the main strand of the san andreas fault with the primary faults of our fractal system we predict that the relative velocity across the main strand is 2 93 cm yr the remainder of the relative velocity of 5 5 cm yr between the pacific and north american plates occurs on higher order faults the predicted value is in reasonably good agreement with the value 3 39 0 29 cm yr obtained from geological studies

fractal structure of spatial distribution of microfracturing in rock summary a constant stress fracture experiment of oshima granite was carried out at the confining pressure of 40mpa hypocentres of 2064 acoustic emissions were located during the experiment using the correlation integral we found that the spatial distribution of hypocentres of acoustic emission is a fractal and that the fractal dimension decreases with the evolution of rock fracturing the spatial distribution of earthquake s hypocentres reveals fractals ranging from regional to worldwide distribution if we extrapolate from laboratory measurements it is possible to predict the occurrence of large earthquakes by the decrease in the fractal dimension

identifying space time clustering properties of the 1983 1997 irpinia basilicata southern italy seismicity abstract the fractality of the earthquake sequence 1983 1997 of irpinia basilicata southern italy one of the most seismically active regions of the mediterranean area has been analysed by temporal and spatial fractal tools the fractal exponent estimated by the allan factor method characterises the time clustering behaviour of the set of earthquakes while the correlation dimension d c calculated by means of the correlation integral method gives information on the space clustering behaviour of the sequence of seismic events analysing the variations of both the parameters we recognised the presence of a strong space time clusterisation associated with the major events that occurred in the investigated area

compressional and shear wave velocities as a function of confining stress in dry sandstones a laboratory study was carried out to investigate the influence of confining stress on compressional and shear wave velocities for a set of rock samples from gas producing sandstone reservoirs in the cooper basin south australia the suite of samples consists of 22 consolidated sublitharenites with helium porosity ranging from 2 6 to 16 6 we used a pulse echo technique to measure compressional and shear wave velocities on dry samples cylindrical 4 6 2 cm at room temperature and at elevated confining stress 60 mpa compressional and shear wave velocities in samples increase non linearly with confining stress a regression equation of the form v a be dp gives a good fit to the measured velocities with improved prediction of velocities at high confining stresses compared with equations suggested by other studies the predicted microcrack closure stresses of the samples show values ranging from 70 mpa to 95 mpa and insignificant correlation with porosity permeability or clay content there is a positive correlation between change in velocity with core porosity and permeability but this association is weak and diminishes with increasing confining stress experimental results show that pore geometry grain contact type and distribution and location of clay particles may be more significant than total porosity and clay content in describing the stress sensitivity of sandstones at in situ reservoir effective stress the stress dependence of cooper basin sandstones is very large compared with data from other studies the implication of our study for hydrocarbon exploration is that where the in situ reservoir effective stress is much less than the microcrack closure stress of the reservoir rocks the variation of reservoir effective stress could cause significant changes in velocity of the reservoir rocks the velocity changes induced by effective stress in highly stress sensitive rocks can be detected at sonic log and probably surface seismic frequencies

a generalized biot gassmann model for the acoustic properties of shaley sandstones1 we obtain the wave velocities of clay bearing sandstones as a function of clay content porosity and frequency unlike previous theories based simply on slowness and or moduli averaging or two phase models we use a biot type three phase theory that considers the existence of two solids sand grains and clay particles and a fluid the theory which is consistent with the critical porosity concept uses three free parameters that determine the dependence of the dry rock moduli of the sand and clay matrices as a function of porosity and clay content testing of the model with laboratory data shows good agreement between predictions and measurements in addition to a rock physics model that can be useful for petrophysical interpretation of wave velocities obtained from well logs and surface seismic data the model provides the differential equation for computing synthetic seismograms in inhomogeneous media from the seismic to the ultrasonic frequency bands

the evolution of seismicity at parkfield observation experiment and a fracture mechanical interpretation we compare observations of local seismicity sequences with acoustic emissions during rock fracture and find similarities in the distribution of event magnitudes which lead us to consider a model of seismicity which is characterized by fracture growth laws derived from the field of fracture mechanics and which include both negative and positive feedback processes we find that the model predicts the observed negative correlation between the seismic b value and the fractal dimension of the earthquake epicentres the simple short range interactions described in the model give rise to a system with a long range order similar to current models of critical processes

temporal variations in the fractal properties of seismicity in the north anatolian fault zone between 31 e and 41 e we investigate the nature of temporal variations in the statistical properties of seismicity associated with the north anatolian fault zone between longitudes 31 41 e during the instrumental period 1900 1992 temporal variations in the seismicb value and the fractal correlation dimensiondc of earthquake epicenters are examined for earthquakes of magnitudems 4 5 using sliding windows of 100 consecutive events b varies temporally between 0 6 and 1 0 anddc between 0 6 and 1 4 both representing significant fluctuations above the errors in measurement technique a strong negative correlation r 0 85 is observed betweenb anddc consistent with previous observation of seismicity in japan and southern california major events early in this century ms 7 are associated with lowb and highdc respectively consistent with greater stress intensity and greater spatial clustering of epicenters both implying a greater degree of stress concentration at this time

lithospheric density structure beneath the tarim basin and surroundings northwestern china from the joint inversion of gravity and topography abstract intraplate strain generally focuses in discrete zones but despite the profound impact of this partitioning on global tectonics geodynamics and seismic hazard the processes by which deformation becomes localized are not well understood such heterogeneous intraplate strain is exemplified in central asia where the indo eurasian collision has caused widespread deformation while the tarim block has experienced minimal cenozoic shortening the apparent stability of tarim may arise either because strain is dominantly accommodated by pre existing faults in the continental suture zones that bound it essentially discretizing eurasia into microplates or because the lithospheric scale strength i e viscosity of the tarim block is greater than its surroundings here we jointly analyze seismic velocity gravity topography and temperature to develop a 3 d density model of the crust and upper mantle in this region the tarim crust is characterized by high density v s v p and v p v s consistent with a dominantly mafic composition and with the presence of an oceanic plateau beneath tarim low density but high velocity mantle lithosphere beneath southern southwestern tarim underlies a suite of permian plume related mafic intrusions and a type granites sourced in previously depleted mantle lithosphere we posit that this region was further depleted dehydrated and strengthened by permian plume magmatism the actively deforming western and southern margins of tarim the tien shan kunlun shan and altyn tagh fault are underlain by buoyant upper mantle with low velocity we hypothesize that this material has been hydrated by mantle derived fluids that have preferentially migrated along paleozoic continental sutures such hydrous material should be weak and herein strain focuses there because of lithospheric scale variations in rheology rather than the pre existence of faults in the brittle crust thus this world class example of strain partitioning arises not simply from the pre existence of brittle faults but from the thermo chemical and therefore rheological variations inherited from prior tectonism

misalignment of the orientation of fractures and the principal axes for p and s waves in rocks containing multiple non orthogonal fracture sets summary azimuthal anisotropy in rocks can result from the presence of one or more sets of partially aligned fractures with orientations determined by the stress history of the rock a shear wave propagating in an azimuthally anisotropic medium splits into two components with diverent polarizations if the source polarization is not aligned with the principal axes of the medium in the presence of two or more non orthogonal sets of vertical fractures the symmetry of the medium may be approximated as monoclinic with a horizontal plane of mirror symmetry if in the absence of fractures the rock is transversely isotropic ti with the symmetry axis perpendicular to the bedding plane for such a medium the fast and slow polarization directions for vertically propagating shear waves are not parallel or perpendicular to any of the fracture planes but lie in directions given by the principal axes of a second rank fracture compliance tensor this tensor is independent of the normal compliance of the fractures it follows that for vertical propagation of shear waves in a vertically fractured ti medium any number of arbitrarily oriented vertical fracture sets is equivalent to two mutually perpendicular fracture sets provided that the seismic wavelength is large compared to the size of the fractures for ovsets typical of surface seismic acquisition the p wave velocity at fixed ovset varies with azimuth as cos 2 w w 0 where w is the azimuth measured with respect to the fast polarization direction for a vertically polarized shear wave w 0 depends on both the normal and the shear compliance of the fractures and may diver from zero if the ratio of the normal to shear compliance of the fractures varies significantly between fracture sets if this ratio is similar for all fractures w 0 0 and the principal axes of the variation in p wave velocity with azimuth for fixed ovset are determined by the principal axes of the second rank fracture compliance tensor

rock assemblages in central asia and the evolution of the southern asian margin by looking in detail at the rock record in central asia it is possible to map rock assemblages that are diagnostic of particular plate settings simplest of the assemblages include the rocks of the tadjik depression where mesozoic and paleogene sediments record the development of a south facing passive continental margin analysis of igneous activity in central asia and of the timing of deformation of these miogeoclinal rocks indicates that the paleotethyan ocean to the south was in the mesozoic subducting to the south beneath a migratory arc consisting of parts of iran afghanistan and the pamir only in the late tertiary does the tadjik depression develop a peripheral foreland assemblage which indicates any deformation of the miogeocline this presumably occurred as a result of the closing of the paleotethyan ocean and accretion of this portion of the arc to the southern margin of asia it appears unlikely that the depression passive margin sequence developed in a normal rift margin setting analysis of assemblages in the hercynian orogen tien shan to the north indicates that unlike the uralian section of the orogen the deformation here occurred due to the closure of a marginal basin and overthrusting of its basement rocks over a south facing arc thus considering depression basement composition it appears that the passive margin assemblage is superimposed over either a late paleozoic forearc or paleozoic ocean floor paleozoic rocks exposed north of the herat suture in afghanistan may require the forearc basement interpretation noting that the geometry of subduction and the timing of paleotethyan suturing seem to have varied along strike in the orogen a more complicated model of tectonic accretion is required

controls on acoustic properties of upper jurassic siliciclastic rocks boulonnais northern france more than 200 plugs from outcrop and a nearby borehole in a carbonaceous siliciclastic interval of late jurassic kimmeridgian to tithonian age were quantitatively analyzed for texture mineralogy and acoustic properties our primary goal was to study the effect of clay fraction smaller than 8 m silt sand fraction larger than 8 m and carbonate on the acoustic properties the quantitative nature and volume of the data made it possible to observe four dimensional relationships in contoured ternary diagrams primary control on the acoustic properties is exerted by porosity but the trend of this relationship significantly deviates from popular velocity transforms the contribution of clay silt sand and carbonate particular material and cement explains the remaining variation in acoustic properties although no clear linear thresholds are defined a general trend is that clay and carbonate content have opposite and overlapping effects on acoustic properties the influence of clay content progressively increases with decreasing carbonate content and visa versa with increasing carbonate content the variation of acoustic velocity at a given porosity value increases to nearly twice of that in the clay dominated sediment traditional classification boundaries are present but strongly overprinted by this interplay between clay and carbonate this study may have important implications for porosity and lithofacies prediction from wireline logs in similar mixtures of sediment in addition the quantitative character of the textural and mineralogical data may provide a direct link from acoustic properties to the primary depositional system and sequence stratigraphy

a discussion of hidden subduction in orogenic belts the mckenzie et al 2019 model concerning the cause of the deep earthquakes in the hindu kush region in asia greatly resembles the hidden subduction model proposed earlier however in the case o

seismic and electrical properties of unconsolidated permafrost1 a model has been developed to relate the velocities of acoustic waves vp and vs in unconsolidated permafrost to the porosity and extent of freezing of the interstitial water the permafrost is idealized as an assemblage of spherical quartz grains embedded in a matrix composed of spherical inclusions of water in ice the wave scattering theory of kuster and toksoz is used to determine the effective elastic moduli and hence the acoustic velocities the model predicts vp and vs to be decreasing functions of both the porosity and the water to ice ratio the theory has been applied to laboratory measurements of vp and vs in 31 permafrost samples from the north american arctic although no direct measurements were made of the extent of freezing in these samples the data are consistent with the predictions of the model electrical resistivity measurements on the permafrost samples have demonstrated their essentially resistive behaviour the ratio of resistivity of permafrost in its frozen state to that in its unfrozen state has been related to the extent of freezing in the samples electromagnetic and seismic reflection surveys can be used together in areas of permafrost firstly an em survey to determine the extent of freezing and then the acoustic velocity model to predict the velocities in the permafrost the necessary transit time corrections can thus be made on seismic reflection records to compensate for the presence of permafrost

the east anatolian fault an oblique collisional belt abstract the tectonic setting for the area around the arabia africa anatolia triple junction is described from combined landsat spot satellite image analysis and field observations since the late miocene the motion along the east anatolian fault generated major structures corresponding to shortening with a sinistral slip component the 150 km wide area of the triple junction is highly deformed by folding and thrusting distributed mainly on the border of the anatolian block in addition kinematic reconstructions confirm that the arabia anatolia relative motion is both sinistral and convergent the sinistral strike slip faults of the east anatolian fault zone are of second order and local consequences of the n s arabia anatolia collision

seismicity changes associated with the 2000 earthquake swarm in the izu island region a statistical method taking into account the information of magnitude occurrence time and location of earthquakes was applied to the earthquake data 1977 2000 of the japan meteorological agency jma to investigate seismicity changes in the izu island region the analysis indicated that a quiescence anomaly started about 1 5 years before the occurrence of the largest swarm in the summer of 2000 in the izu island region close investigations of the possible artifacts due to the selection of model parameters and the improvement of the seismological network lead to the conclusion that the above quiescence anomaly is unlikely a man made change the further stochastic test using 1000 random earthquake catalogs supports the idea that the above anomaly is significant the spatial distribution of the seismic quiescence which is quantified by a newly developed q parameter revealed a clear anomalous region around the epicentral area of the above earthquake swarm the seismicity revealed by the normalized parameter tends to increase just before the swarm as the first test of the above statistical method for investigating seismicity changes of earthquake swarms this study indicates that the increased rtl parameter would be a new potentially useful index for the risk alarm of earthquake swarms

fractals in geology and geophysics the definition of a fractal distribution is that the number of objectsn with a characteristic size greater thanr scales with the relationn r d the frequency size distributions for islands earthquakes fragments ore deposits and oil fields often satisfy this relation fractals were originally introduced by mandelbrot to relate the length of a coastline to the length of the measuring stick this application illustrates a fundamental aspect of fractal distributions scale invariance the requirement of an object to define a scale in photographs of many geological features is one indication of the wide applicability of scale invariance to geological problems scale invariance can lead to fractal clustering geophysical spectra can also be related to fractals these are self affine fractals rather than self similar fractals examples include the earth s topography and geoid

reconciling physical properties with surface seismic data from a layered mafic intrusion abstract compositional layering of intrusive rocks is often cited as a source of seismic reflectivity in the crystalline crust direct evidence for this is based primarily on synthetic seismograms calculated from laboratory measurements of rock velocity and density or estimates of aggregate rock properties from measurements of mineral velocities and densities little is known about how in situ effects such as fracturing chemical alteration or anisotropy may change the reflectivity character of the surface seismic data an ideal dataset for examining the hazards of using physical properties data for estimating crustal reflectivity occurs at the nellie intrusion a middle proterozoic age layered mafic intrusion that lies beneath the permian basin of west texas due to a well that penetrated 4 5 km of the intrusion we have a dataset that spans the scale from compositional data on the intrusion derived from well cuttings to log data to surface reflection data sonic and density log data from the well measure velocities and densities 10 to 15 below the values calculated from modal mineralogy we attribute this difference primarily to pervasive post emplacement alteration and fracturing of the rock mass in situ thus this unique dataset provides a quantitative estimate of the magnitude of difference between observed and theoretical velocities that can be expected for crystalline rocks in the upper crust and its cause despite the difference analysis of synthetic seismograms shows that primary compositional variation of the intrusion is still responsible for sub horizontal layered reflectivity in both the log based and petrology based synthetic seismograms boundaries of intrusive cycles are characterized by large negative reflection coefficients due to the juxtaposition of mafic rich basal layers against plagioclase rich layer tops in detail only the log based synthetic provides a good match to the surface seismic reflection data this suggests that physical properties from modal mineralogy are useful in obtaining a generalized model for reflectivity but that differences in bulk physical properties of the rock mass preclude the possiblity of obtaining a one to one match with surface seismic data

effects of diagenesis and clays on compressional velocities in rocks experimental results at ultrasonic frequencies in brine or water saturated samples cut perpendicular to bedding demonstrate that compressional velocities vary linearly with porosity and volume fraction clay in detrital silicate rocks characterized by pores with low aspect ratios p wave velocity is more sensitive to porosity than clay content obeying the empirically derived expression vp 2 4c 8 6 5 8 at 800 bars confining pressure and 400 bars pore pressure where the units of vp are kilometers per second is the volume fraction pores and c is the volume fraction clay deviations from this equation are less than 2 with the exception of the high pore aspect ratio st peter sandstone which has a compressional velocity that is 17 higher than the predicted value the equation is insensitive to the chemical compostion of the dominant clay mineral and apparently insensitive to the location of the clay grains with respect to the mineral framework e g in free pore space or in contact zones between mineral grains of lower compressibilities

fractal dimension and b value on creeping and locked patches of the san andreas fault near parkfield california we tested the hypotheses 1 that the fractal dimension d of hypocenters are different in a locked and a creeping segment of the san andreas fault and 2 that the relationship d 2b holds approximately where b is the slope of the frequency magnitude relationship the test area was the 30 to 50 km fault segment north of park eld for which two earthquake catalogs exist the borehole high resolution seismic network data and the u s geological survey data which have a minimum magnitude of completeness of mc 0 4 and mc 1 0 1 2 respectively the relative location errors in the two catalogs are estimated as 0 25 km and less than 1 km respectively the periods of high quality data available extend from 1987 to 1998 5 and 1981 to 2000 2 respectively furnishing 2609 and 3775 events for analysis in the two catalogs in the locked part 0 5 b 0 7 and 0 96 d 1 14 whereas in the creeping segment 1 1 b 1 6 and 1 45 d 1 72 however the spatial distribution of the hypocenters in the creeping segment is not well approximated by a fractal distribution we conclude 1 that the frequency magnitude distribution as described by b as well as the fractal dimension d are different in the locked and creeping segments near park eld 2 that the spatial distribution in the creeping segment is not well approximated by a fractal distribution and 3 that the relationship d 2b holds in the locked segment where both parameters can be measured accurately thus we propose that the heterogeneity of seismogenic volumes lead to differences in d and b and that these differences where established by high quality data may furnish clues concerning properties of fault zones

fractal dimension of fault systems in japan fractal structure in rock fracture geometry at various scales based on fault maps whether or not the fracture geometry of rocks is self similar was examined by using a box counting algorithm the statistical self similarity fractal structure of the fault fracture systems holds well at the scale of about 2 to 20 km the fractal dimension in japan varied from 1 05 to 1 60 the fractal dimension is about 1 5 1 6 at the central part of the japan arc and decreases with distance from the center at a smaller scale the fractal structure also holds well in the rock fracture geometry the fractal dimension of the north izu peninsula fault system branching faults is 1 49 at the scale of 0 625 to 10 km the fractal dimension of rock fracture geometry at the scale order of 10 1 to 10 2 meters is about 1 49 1 61 the upper limit of the fractal dimension of rock fracture geometry is about 1 6 judging from the estimation of fractal dimension on actual fracture geometry of rocks this value may impose a restraint on modeling of faulting and the fracture process of rocks

velocities and quality factors of sedimentary rocks at low and high effective pressures summary techniques for measuring acoustic velocities and quality factors q of sedimentary rocks in the laboratory are sufficiently accurate to establish closely fitting regression curves which represent the variation of these acoustic properties with pressure ultrasonic p and s wave measurements of velocity v v and q q q were made on 16 different water saturated sandstone samples at various effective pressures using an ultrasonic reflection technique and the data were fitted using a simple regression equation containing a constant plus linear and exponential pressure dependent terms the redundancy of the linear term in the regression of q data suggests that microcracks alone govern the pressure variation of q whereas velocities are additionally dependent on another mechanism consistent with the changes in elastic moduli caused by intergranular compression causing small reductions in porosity the implied rates of microcrack closure with increasing effective pressure in all samples were found to be comparable the regression equations describe the data closely enough to enable the extrapolation of acoustic properties to both low and high effective pressures this is of practical use since laboratory techniques can produce uncertain results at low pressures due to coupling problems and low signal strengths whilst high pressures require large confining vessels low pressure and high pressure data are applicable to shallow seismic surveys and hydrocarbon exploration respectively

velocity porosity clay content systematics of poorly consolidated sandstones compressional velocities have been measured as a function of confining pressure for 14 west delta block louisiana sandstone cores the dry velocity data for these poorly consolidated sandstones at 10 mpa confining pressure plot on a linear velocity density trend with well consolidated sandstones but not loose sands the dry velocity data also show linear trends of decreasing velocity with increasing porosity along contours of constant clay content similar to those obtained at 40 mpa by tosaya and nur 1982 for saturated sandstones the spacing between clay contours indicates that a large portion of the velocity variation with clay content is due to microporosity which is not included in point counting within the clays the slope of the velocity porosity trends indicates that cementation increases with decreasing porosity

velocities of compressional and shear waves in limestones carbonate rocks are important hydrocarbon reservoir rocks with complex textures and petrophysical properties porosity and permeability mainly resulting from various diagenetic processes compaction dissolution precipitation cementation etc these complexities make prediction of reservoir characteristics e g porosity and permeability from their seismic properties very difficult to explore the relationship between the seismic petrophysical and geological properties ultrasonic compressional and shear wave velocity measurements were made under a simulated in situ condition of pressure 50 mpa hydrostatic effective pressure at frequencies of approximately 0 85 mhz and 0 7 mhz respectively using a pulse echo method the measurements were made both in vacuum dry and fully saturated conditions in oolitic limestones of the great oolite formation of southern england some of the rocks were fully saturated with oil the acoustic measurements were supplemented by porosity and permeability measurements petrological and pore geometry studies of resin impregnated polished thin sections x ray diffraction analyses and scanning electron microscope studies to investigate submicroscopic textures and micropores it is shown that the compressional and shear wave velocities vp and vs respectively decrease with increasing porosity and that vp decreases approximately twice as fast as vs the systematic differences in pore structures e g the aspect ratio of the limestones produce large residuals in the velocity versus porosity relationship it is demonstrated that the velocity versus porosity relationship can be improved by removing the pore structure dependent variations from the residuals the introduction of water into the pore space decreases the shear moduli of the rocks by about 2 gpa suggesting that there exists a fluid matrix interaction at grain contacts which reduces the rigidity the predicted biot gassmann velocity values are greater than the measured velocity values due to the rock fluid interaction this is not accounted for in the biot gassmann velocity models and velocity dispersion due to a local flow mechanism the velocities predicted by the raymer and time average relationships overestimated the measured velocities even more than the biot model

precursory seismicity changes associated with the mw 7 4 1999 august 17 izmit turkey earthquake summary we investigated precursory seismicity in and around the epicentral zone of the mw 7 4 1999 august 17 izmit turkey earthquake by applying a statistical method the rtl region time length algorithm to earthquake catalogues derived from that for the period 1981 1999 of kandilli observatory and earthquake research institute koeri the derived catalogues are complete for events md 3 in most of western turkey after declustering aftershocks we investigated the seismicity patterns preceding the izmit event at local izmit tectonic zone and national turkey scales the rtl parameter indicates that a period of seismic quiescence started at the end of 1995 and reached a minimum in december 1996 an activation phase lasting about three months followed the main shock in izmit and vicinity did not occur when the seismicity returned to its background level but occurred with a delay of nearly 2 5 yr we present a new parameter to quantify the spatial distribution of seismic quiescence the results from both catalogues indicate that a significant quiescence anomaly appeared in 1996 around the epicenter of the izmit earthquake the primary characteristics of the seismicity patterns prior to the izmit earthquake are similar to those obtained for large events in russia and japan the variations of seismicity patterns revealed by the rtl algorithm may offer better understanding of the physical nature of seismo tectonics and provide useful information for seismic hazard estimation the varying characteristics of the izmit and other events may reflect the difference between seismo tectonics in turkey and in other regions such as russia and japan

laboratory measurements of the acoustic and transport properties of carbonate rocks and their link with the amount of microcrystalline matrix laboratory data and computer tomography ct scan image analysis of carbonate rocks were combined demonstrating a quantitative link between acoustic and transport properties the fraction of microcrystalline calcite micrite in the matrix and the grain to micrite matrix ratio samples from the monte acuto formation gargano italy a transgressive system tract tst whose microstructure ranges from basal pelagic mudstones to coarse calciturbidites were analyzed results indicate that high micrite rocks with low grain to micrite matrix ratios typical of low energy depositional settings are relatively stiffer and more impermeable in contrast lower amounts of micrite due to high energy depositional settings or its removal from intergranular macropores by progressive leaching of the matrix leads to high grain to micrite matrix ratios this process will increase porosity and reduce rock stiffness both of which reduce velocity decreasing micrite content correlates well with increasing macroporosity

a proposed super thick sedimentary basin bay of bengal a super thick 22km sedimentary basin under the northern bay of bengal is proposed the hypothesis is based on data from surface wave dispersion seismic refraction sn attenuation and geology we present new high frequency sn data which indicate a cold upper mantle beneath the bay of bengal we propose that the oceanic crust in this region is in fact nearly normal and that the sedimentary section is at least 6 km thicker than previously thought with velocities at the base of the sediments having been increased to near 6 5 km sec by high pressure metamorphism reinterpretation of the refraction data indicate a post india asia collision thickness of over 16 km

spatial variations of the fractal properties of seismicity in the anatolian fault zones abstract the anatolian fault zones are seismically active strike slip fault zones transcending the anatolian plate in e w and n s directions we investigate the spatial variations of seismicity along these zones in an attempt to investigate fault complexity along strike quantified by the gutenberg richter b value and the fractal correlation dimension of earthquake epicentres using the maximum likelihood method and the correlation integral respectively the investigation covers instrumentally recorded carthquakes of magnitude m 4 5 occurring between 1900 and 1992 we find systematic spatial variations which may be related to structural or mechanical variability along strike in particular the large change in strike at the northern apex of the north anatolian fault zone is associated with the highest correlation dimension and lowest b value for seismicity this century the correlation dimension and b value show a negative correlation with respect to each other similar to results reported in other regional studies of japan and southern california this statistical correlation is stronger when more objective seismic zoning is carried out based on number of events rather than more subjective seismotectonic zoning in common use in seismic hazard analysis

partitioning of strike slip and convergent motion between eurasia and arabia in eastern turkey and the caucasus the plate motion model nuvel 1 de mets et al 1990 predicts a strongly oblique component to the convergence between arabia and eurasia at the longitude of the caucasus earthquake focal mechanisms suggest that this oblique convergence is partitioned into pure right lateral strike slip motion in eastern turkey and pure shortening by thrusting in the greater caucasus such partitioning offers an explanation for the apparent eastward continuation of the right lateral faulting of the north anatolian fault from turkey into iran from a summation of seismic moment tensors between 1911 and 1991 it appears that most of the right lateral strike slip motion in eastern turkey is accommodated by faulting in large earthquakes while most of the shortening in the caucasus appears to occur aseismically

a statistical space time magnitude analysis on the aftershocks occurrence of the july 21th 2017 mw 6 5 bodrum kos turkey earthquake abstract in this study a detailed space time magnitude assessment on the aftershock sequence of july 21th 2017 mw 6 5 bodrum kos earthquake turkey is carried out by focusing on the analyses of aftershock parameters b value p value dc value and mamax b value is estimated as 0 90 0 05 with a completeness magnitude mc 1 6 and this relatively small b value may be resulted from the abundance of aftershocks with magnitude ml 4 0 however it is well represented by the gutenberg richter law with a typically b 1 0 p value is estimated as 1 04 0 02 with a c value 0 224 0 039 and is well characterized nearly close to the global p 1 0 this relatively high p value may be a result of the relative fast decay rate of the aftershock activity dc value is calculated as 1 74 0 09 and it means that aftershocks are homogeneously distributed temporal distribution of b value shows that small b values may be due to a stepwise increase in effective stress before the occurrence of larger aftershocks regional changes range from 0 5 to 1 2 in b value from 0 4 to 1 3 in p value and from 3 0 to 5 2 in mamax the smallest b values are found in and around mainshock including karaada bodrum akyarlar and turgutreis and these regions have high stress as well as coseismic deformation the largest p values are found in and around the mainshock epicenter including karaada and it is interpreted that this situation may be caused by coseismic deformation mamax values larger than 4 4 are observed in and around mainshock epicenter including bodrum and akyarlar and there is a clear correlation between spatial variations of b values and mamax these results show that stress changes and coseismic deformation seem highly effective on b and p value variations therefore a special interest needs to be given to these anomaly regions since aftershock hazard is highly associated with these parameters and may be developed considering their space time magnitude distribution

loading rate impact on fracturing pattern lessons from hydrocarbon recovery lacq gas field france using scaling parameters of induced seismicity in size and space domains seismic b value and spatial correlation dimension d respectively we analyze the fracturing pattern of the gas reservoir of lacq in correlation with the production rate on the basis of previous observations and a previous model segall et al 1994 we assume that the cause of induced seismicity is a poroelastic stressing such that the production rate can be viewed as a stress rate for the rocks adjacent to the reservoir during the 20 year study period the production rate has decreased dramatically leading to a change of poroelastic stress rate from 4 5 10 3 to 1 5 10 3 mpa yr accordingly we observe a significant decrease in the size of activated fractures and a reduction of the spatial clustering of fracturing both arguing for a stress rate impact on the fracturing pattern in the gas field we interpret these changes in terms of a change in the deformation mode of stressed rocks from a more brittle to a more ductile behavior as the stress rate was decreased this hypothesis is supported by independent evidence from a number of experimental numerical and field studies the loading rate thus appears as a possible candidate to drive changes of b and d in time and space the apparent sensitivity of the earth s crust fracturing pattern to loading rate variations of much lower frequency than the tidal variations suggests that the earth s crust deformation mode itself be frequency dependent also our observations may have strong implications in contexts where the loading rate is induced by human intervention e g hydrocarbon recovery mines suggesting the possibility of adjusting the loading rate so as to shape the fracturing pattern locally according to human needs

fractals in studies of faulting and seismicity in the baikal rift zone abstract fractal analyses have been carried out for spatial patterns of faulting including over 3000 faults and seismicity of more than 60 000 earthquakes in the baikal rift zone brz it is concluded that faulting and seismicity are in balance in the whole brz and out of balance in its flanks by analysing fractal dimensions of seismicity in time it has been revealed that the out of balance state of the processes is predetermined by the fact that development of the spatial patterns of epicentral fields has not been completed yet in the brz flanks

correlation of seismotectonic variables and gps strain measurements in western turkey period extending from 1981 to 1998 are examined in the eastern mediterranean and western turkey area this analysis was conducted in three tectonic subdivisions corresponding to regions dominated by shear extensional and compressional deformation the region of shear coincides with the northern anatolian fault zone nafz the region of extension with the aegean back arc region and the region of compression to the aegean subduction zone between the african and anatolian plates the median b value in the region of extension is larger than those observed in the regions of shear and compression and suggests that large magnitude earthquakes are less probable in this region than along the nafz and aegean subduction zone a significant correlation is observed between d2 and d15 with dilatation over the 10 40 km range in the back arc region of extension a marginal correlation between gps derived strain and b value is observed only in the region of compression where it correlates negatively with shear and positively with dilatation a significant positive correlation is observed between d and b along the nafz a clear relationship between d and b does not exist in regions deformed by extension and compression the relationship between d and b along the nafz may also be an indicator of increased seismic hazard since the positive relationship between d and b is a recent characteristic of the nafz observed only in the 20 year period preceding the izmit earthquake index terms 7215 seismology earthquake parameters 7209 seismology earthquake dynamics and mechanics 7223 seismology seismic hazard assessment and prediction 7230 seismology seismicity and seismotectonics keywords gps strain fractal dimension b value

variations in petrophysical properties along a mixed siliciclastic carbonate ramp upper jurassic ricla ne spain abstract a multi scale petrophysical study was performed on an upper jurassic siliciclastic carbonate ramp system near the village of ricla spain a combination of textural field observations thin section and grain size analysis chemical mineralogical thermo gravimetric analysis and physical porosity gamma ray and velocity measurements properties was used to capture the heterogeneity of this mixed sedimentary system subsequently synthetic seismic sections with varying resolution were created to show the characteristics of the internal ramp structures the translation from the measured petrophysical properties to a synthetic seismic section helps to better understand subsurface seismic although upscaling problems are a recurring issue the homogeneity of the samples and the continuity of the outcrop and facies reduce the number of uncertainties acoustic properties are generally controlled by the amount and type of pore spaces due to the low porosities the ramp geometry is characterized by an overall lateral homogeneity and vertical heterogeneity textural sedimentological and stratigraphic transitions in the outcrop are related to the defined facies each has its own unique mineralogical signature amplitude variations in the synthetic seismic profile are primarily caused by changes in mineral composition thus facies transitions

elastic properties of hydrate bearing sediments using effective medium theory accurate and detailed models of the seismic velocity structure of gas hydrate bearing sediments may be determined by careful analysis of controlled source seismic data however interpretation of these velocities in terms of hydrate saturation of the pore space has hitherto relied on semiempirical formulas and or simple effective medium theory we develop a rigorous theoretical scheme to relate the seismic properties of a clay rich hydrate bearing sediment to its porosity mineralogy microstructural features and hydrate saturation we consider separately the two possible end members for the distribution of hydrate in the pore space 1 hydrates are unconnected and located in the pore voids without appreciable grain contact and 2 connected hydrates are forming cement binding around the grains the scheme is transversely isotropic to allow for anisotropy due to alignment of clay platelets and is based on a combination of a self consistent approximation a differential effective medium theory and a method of smoothing for crystalline aggregates we have applied the scheme to lithological and seismic velocity data from ocean drilling program site 995 on the blake ridge southeastern u s continental margin to make estimates of the hydrate saturation it was found that the hydrates are probably unconnected and their volume concentration varies between approx 0 at 100 m below the seabed and approx 9 at 400 m depth just above the bottom simulating reflector if the clay platelet orientation distribution resembles the function we have used

predicting lithology and transport properties from acoustic velocities based on petrophysical classification of siliciclastics based on the recently developed petrophysical classification of siliciclastics which takes into account the amount of the volumetric clay content c and textural position of clay it is shown that acoustic velocities can be fairly accurate tools in predicting lithology porosity and ultimately transport properties of these rocks four major petrophysical groups of carbonate and organic poor siliciclastics are distinguished 1 clean arenites c 35 percent the compressional velocity versus porosity relation for consolidated rocks in each of these groups is found to be linear with very high correlation coefficients this allows for remarkably accurate porosity estimates or lithology prediction in consolidated siliciclastics from acoustic velocities compared to the widely used time average wyllie equation or its improved modification raymer equations both of which neglect textural factors

magnitude of completeness b value and spatial correlation dimension of earthquakes in the south baikal basin baikal rift system abstract magnitude of completeness b value and correlation dimension of spatial epicenter distribution were estimated for the south baikal basin using earthquake catalogue for the period of digital observations all estimated parameters were mapped with a one for all approach that allowed revealing their spatial variability the value of the completeness magnitude which was evaluated on the frequency magnitude distribution was found to range from mc 1 0 to 1 6 over the basin depending on network configuration change with the average value of 1 1 0 1 then b value in the gutenberg richter relation was estimated by maximum likelihood method based on the catalogue with m 1 1 earthquakes the lower b value 0 81 0 03 was revealed for the southern part of the basin which is under transtension stress regime in contrast to pure extension characteristic for the rest of the territory the higher b value 1 01 0 01 was obtained for the area to the north east of the selenga delta where two of the largest baikal earthquakes occurred in the last 150 years and which is characterized by more heterogeneous crust structure correlation dimension in the southern part of the basin was found to be closed to 1 that is interpreted as a tendency of epicenters to be distributed along a line whereas the central part is characterized by a higher value that corresponds to a tendency of epicenters to be distributed over a plane rather than along lineaments a comparison of the southern and central basins which make up the tectonically single south baikal basin shows that seismicity of the central basin is characterized by higher b values and correlation dimension that may imply different stress level and or faulting type

fractal geometry in the san andreas fault system it has been noted that the spatial distribution of earthquakes and the mode of strain release in the san andreas fault system is related to the complexity of fault geometry because of their rough appearance over many length scales faults can be regarded as fractal surfaces direct estimates of fractal dimension d of portions of the san andreas fault system between the northern gabilan range and the salton sea including the postulated extent of the great 1857 fort tejon earthquake are obtained from measured fault lengths analogous to the lengths of coastlines as discussed by mandelbrot regions characterized by complicated fault geometry are associated with larger values of d based on fault traces mapped at a scale of 1 750 000 d is 1 3 for this reach of the fault defined as a 30 km wide band about a main fault trace for that part near parkfield which could be associated with the nucleation of the 1857 earthquake d is 1 1 at this same scale d is 1 4 for the san andreas and related faults near san bernardino where the 1857 rupture stopped compared to 1 2 for the san andreas san juan fault segments near the point of arrest of the 1966 parkfield earthquake at finer map scales 1 24 000 and 1 62 500 critical lengths of 500 m and 1 km are identified which might relate to the extent of off san andreas fault offsets the critical lengths also suggest that fault geometry is not self similar if this fractal geometry persists through the seismic cycle it may be possible to use a quantitative measure of complexity to explain the occurrence of great and characteristic earthquakes along a given reach of fault

mesozoic ophiolites sutures and arge scale tectonic movements in afghanistan abstract the tectonic history of afghanistan appears to be the result of successive accretion of fragments of gondwana to the active margin of laurasia since the end of the paleozoic the margin in afghanistan lies along the present herat and panjshir faults south of hindu kush swings around the central pamirs and can presumably be traced along the present western altyn tagh and kunlun faults in tibet north of this boundary paleozoic rocks have been deformed in the upper paleozoic whereas south of it there is no trace of the hercynian orogeny the first collision of gondwanian fragments with laurasia probably occurred in the early mesozoic along the hindu kush and kunlun to the south ophiolites along the panjao and pangong nu chiang sutures respectively in central afghanistan and central tibet testify for another suturing event in the upper jurassic or lower cretaceous the indus tsangpo suture between india and tibet corresponds in eastern afghanistan to two ophiolite subbelts near kabul and khost both ophiolite complexes have been emplaced between maestrichtian and lower eocene by choking of two northward dipping subduction zones after complete contact between the indian and asian continents was achieved presumably in the end of eocene the penetration of india into asia caused large scale intra continental shortening a large part of the shortening was accommodated by strike slip faulting along mesozoic and more ancient sutures central afghanistan in particular was extruded to the west along the herat suture by the protrusion of the pamir wedge it subsequently collided with the lut block

mathematical modelling of anisotropy of illite rich shale summary the estimation of illite rich shale anisotropy to account for the alignment of clays and gas or brine filled cracks is presented via mathematical modelling such estimation requires analysis to interpret the dominance of one effect over another this knowledge can help to evaluate the permeability in the unconventional reservoir stress orientation and the seal capacity for the conventional reservoir effective media modelling is used to predict the elastic properties of the illite rich shale and to identify the dominant contributions to the shale anisotropy we consider two principal reasons of the shale anisotropy orientation of clay platelets and orientation of fluid filled cracks in reality both of these two factors affect the shale anisotropy the goal of this study is first to separately analyse the effect of these two factors to reveal the specific features in p and s wave velocity behaviour typical of each of the factors and then consider a combined effect of the factors when the cracks are horizontally or vertically aligned to do this we construct four models of shale the behaviour of p and s wave velocities is analysed when gas and water filled cracks embedded in a host matrix are randomly oriented or horizontally or vertically aligned the host matrix can be either isotropic or anisotropic of vti symmetry in such a modelling we use published data on mineralogy and clay platelet alignment along with other micromechanical measurements in the model where the host matrix is isotropic the presence of a singularity point when the difference changes its sign in shear wave velocities is an indicator of brine filled aligned cracks in the model with the vti host matrix and horizontally aligned cracks filled with gas an increase in their volume concentration leads to that the azimuth at which the singularity is observed moves toward the symmetry axis in this case if the clay content is small around 20 per cent the singularity point may even vanish the thomsen parameters are helpful in fluid type indication in shale an indicator of gas filled aligned cracks is if aligned cracks in illite rich shale are brine filled negative value of indicates brine filled cracks in illite rich shale a shale with brine filled cracks exhibits higher vp vs ratio in the vertical direction as compared to the gas filled shale a disorientation of clay platelets and brine filled cracks may lead to that the singularity point is absent for brine saturated shale as well in this case one can also observe and decreased values of vp vs in the vertical direction as in the case of gas filled cracks in the presence of vertically aligned cracks shales exhibit distinctly revealed features of orthorhombic symmetry the results have important applications where seismic measurements are applied to predict the maturity state of the shale

aftershocks properties of the 2013 shonbe m w 6 3 earthquake central zagros iran abstract the spatial and temporal seismicity parameters stress state as well as the partitioning of the seismic energy of the shonbe earthquake sequence have been investigated the geodetic data and the stress tensor inversions of the focal mechanisms before and after the shonbe main shock indicate the same ne sw trend of the greatest principal stress this stress orientation demonstrates a non heterogeneous stress state in that region of the central zagros which can be confirmed by the fractal dimension and the estimated p value the aftershock focal mechanisms show a diversity which may be associated with the approximately uniaxial stress field acting nearly perpendicular to the main shock fault plane in which the co seismic stress release is nearly complete the spatial distributions of the b and p values have been investigated and compared the high p value regions e g far to the southeast south and southwest of the main shock are approximately consistent with the high b value regions and the low p value regions e g the limited areas at the north northeast of the main shock are nearly consistent with the low b value regions the limited areas surrounding the main shock and also at the east southeast of the main shock the p values are not in agreement with the b values which may be attributed to the local tectonic features in those regions the seismic moment ratio and the bath s law have been used to constrain the energy partitioning between the main shock and the aftershocks it is found that a high fraction of the energy is released by the shonbe main shock and nearly one third of the energy released by the aftershocks this may be associated with the high stress imparted by the blind thrust main shock to the overlying crust in which promotes failure in the surrounding area and is often relieved by secondary faults and typically produce a high number of aftershocks

late palaeozoic to triassic evolution of the turan and scythian platforms the pre history of the palaeo tethyan closure abstract a number of en echelon arranged southwest facing arc fragments of palaeozoic to jurassic ages sandwiched between two fairly straight east northeast trending boundaries constitute the basement of the scythian and the turan platforms located between the laurasian and tethyside units they have until now largely escaped detection owing to extensive jurassic and younger cover and the inaccessibility of the subsurface data to the international geological community these units are separated from one another by linear gently curved faults of great length and steep dip those that are exposed show evidence of strike slip motion the arc units originally constituted parts of a single silk road arc located somewhere south of the present day central asia for much of the palaeozoic although by the late carboniferous they had been united into a continental margin arc south of the tarim basin and equivalent units to the west and east they were stacked into their present places in northern afghanistan turkmenistan caucasus and the northern black sea by large scale right lateral strike slip coastwise transport along arc slicing and arc shaving strike slip faults in the triassic and medial jurassic simultaneously with the subductive elimination of palaeo tethys this gigantic dextral zone the silk road transpression was a trans eurasian structure and was active simultaneously with another similar system the gornostaev keirogen and greatly distorted eurasia the late palaeozoic to jurassic internal deformation of the dniepr donets aulacogen was also a part of the dextral strain in southern europe when the emplacement of the scythian and turan units was completed the elimination of palaeo tethys had also ended and neo tethyan arcs were constructed atop their ruins mostly across their southern parts the western end of the great dextral zone that emplaced the turan and scythian units horsetails just east of north dobrudja and a small component goes along the tornquist teisseyre lineament

size scaling relationships in the active fault networks of japan and their correlation with gutenberg richter b values fractal properties of active fault systems in japan are evaluated and compared to gutenberg richter b values properties of the active fault network and seismicity were evaluated at 20 km intervals along three lines oriented along the length of honshu the main island of japan fractal dimensions for the active fault network are calculated using the box counting method the box curves often reveal the presence of an abrupt transition in slope at 8 km scales this transition separates linear regions in the box curves that span box sizes of 17 5 to 8 5 km and 7 75 to 2 km power law coefficients were computed for the 17 5 to 8 5 km dl and 7 75 to 2 km ds range of box sizes from overlapping 70 70 km regions of the active fault complex the maximum likelihood method is used to estimate b value from earthquakes occurring in the seismogenic zone upper 20 km the correlation between d and b value are found to vary considerably throughout japan in general d and b are negatively correlated which suggests that increased complexity in the active fault network accommodates rupture along fault planes of relatively larger surface area areas of significant positive correlation are also observed in japan the positive correlations arise through joint increases in b and d in such areas the probability of large magnitude earthquakes decreases in response to increased fragmentation of the active fault network and increased possibility that stress release will take place along faults of smaller surface area negative correlations between b and d generally occur when increases in d are paralleled by decreases in b negative correlation areas bound the intensely faulted region of central japan an area of negative correlation also occurs in the intensely faulted high d area of central japan where continued increases in d are paralleled by decreases in b in general these observations suggest that as fault complexity increases as measured by d interconnected planes of larger and larger surface area will accommodate strain release however with continued rise in fault complexity strain release begins to occur on smaller fragments resulting in higher b and lower magnitude seismicity the analysis may provide insights into the relationship between seismicity associated with large scale faults populations and earthquake hazard assessment

anisotropy correction for deviated well sonic logs application to seismic well tie borehole sonic logs acquired in deviated wells penetrating the hrz and colville shales in the niakuk field in alaska s north slope are seen to be significantly faster than vertical well logs these differences are attributed to shale anisotropy an iterative inversion scheme was created to invert for shale anisotropy parameters using multiple wells penetrating shale sections at different angles the inversion involves fitting the sonic log data at a range of borehole angles to the compressional wave group velocity surface the result is an estimate of the anisotropy parameters e and and the vertical p wave velocity the results show that the shales are strongly anisotropic with compressional wave anisotropy thomsen s parameter e on the order of 40 and the anisotropy parameter relates vertical velocity to short offset nmo velocity around 10 this large anisotropy can affect seismic imaging avo and time depth calculations a procedure was created to estimate the anisotropy corrected vertical s

correlating variations of b values and crustal deformations during the 1990s may have pinpointed the rupture initiation of the mw 7 4 izmit earthquake of 1999 august 17 summary the b value increases from 1 1 along straight segments to 1 7 along a releasing bend of the north anatolian fault system between 30 1 e and 30 8 e the tensional nature of the bend is corroborated by extension rates of 0 3 strain yr 1 as obtained from global positioning system gps data fault plane solutions in this area change from abundant right lateral strike slip to oblique slip with normal components in the central part of the bend compatible with the formation of a pull apart basin we suggest that this crustal volume is highly fractured corresponding to a short mean crack length due to the superposition of horizontal and normal faulting as a consequence of low normal stress on the existing cracks frictional sliding is assumed to be the predominant mechanism for the generation of seismic events resulting in high b values the lowest b values b 0 8 in the area investigated are found at the junction between the fault bend and the adjoining segment which runs through the epicentre of the 1999 izmit earthquake at the junction a localized stress concentration is expected from numerical models of seismicity along geometrical barriers thus the site of lowest b has been considered to be the most likely place for a major earthquake a conclusion that is confirmed by the izmit earthquake with epicentre located about 13 km from the anticipated site in early 1992 the spatially averaged b value started to increase along the central and northwestern parts of the fault bend and there was a corresponding period of intensified horizontal extension since no large earthquake was recorded in 1992 it is assumed that the anomalous extension and the associated change in stress have been caused by aseismic fault creep in view of the available seismotectonic information surface displacements due to a slow dislocation at depth were calculated the gps data are reasonably explained by a source of normal fault type at a depth of 10 km and equivalent magnitude mw 5 9 stress changes at seismogenic depths are calculated under the assumption that an increase in b is most likely to be observed along those segments where both deviatoric and mean stress are reduced while the coulomb stress change is positive that is the fault is brought closer to failure for right lateral strike slip the stress condition is fulfilled at the sites of the largest b value increase the surface rupture of the izmit earthquake is associated with known fault traces only in the west and in the east of the study area along the fault bend it detaches itself from mapped fault traces and runs through the regions of positive coulomb stress change caused by the inferred 1992 slow event maximum surface slip 5 m is observed in the immediate vicinity of sites of maximum coulomb stress change 3 bar indicating that the 1992 event could have partially unclamped the rupture plane of the subsequent izmit earthquake we propose that the strong differences in b observed along the complex fault bend can be used to characterize different states of tectonic deformation in space and time

subduction and vertical coastal motions in the eastern mediterranean convergence in the eastern mediterranean of oceanic nubia with anatolia and the aegean is complex and poorly understood large volumes of sediment obscure the shallow structure of the subduction zone and since much of the convergence is accommodated aseismically there are limited earthquake data to constrain its kinematics we present new source models for recent earthquakes combining these with field observations published gps velocities and reflection seismic data to investigate faulting in three areas the florence rise sw turkey and the pliny and strabo trenches the depths and locations of earthquakes reveal the geometry of the subducting nubian plate ne of the florence rise a bathymetric high that is probably formed by deformation of sediment at the surface projection of the anatolia nubia subduction interface in sw turkey the presence of a strike slip shear zone has often been inferred despite an absence of strike slip earthquakes we show that the gps derived strain rate field is consistent with extension on the orthogonal systems of normal faults observed in the region and that strike slip faulting is not required to explain observed gps velocities further sw the pliny and strabo trenches are also often interpreted as strike slip shear zones but almost all nearby earthquakes have either reverse faulting or normal faulting focal mechanisms oblique convergence across the trenches may be accommodated either by a partitioned system of strike slip and reverse faults or by oblique slip on the aegean nubia subduction interface the observed late quaternary vertical motions of coastlines close to the subduction zone are influenced by the interplay between 1 thickening of the material overriding the subduction interface associated with convergence which promotes coastal uplift and 2 subsidence due to extension and associated crustal thinning long wavelength gravity data suggest that some of the observed topographic contrasts in the eastern mediterranean are supported by mantle convection however whether the convection is time dependent and whether its pattern moves relative to nubia are uncertain and its contribution to present day rates of vertical coastal motions is therefore hard to constrain the observed extension of the overriding material in the subduction system is probably partly related to buoyancy forces arising from topographic contrasts between the aegean anatolia and the mediterranean seafloor but the reasons for regional variations are less clear

earthquakes in the garhwal himalaya of the central seismic gap a study of historical and present seismicity and their implications to the seismotectonics the historical and the present seismicity catalogues of the garhwal himalaya have been studied for their spatio temporal variations and their implications on the seismotectonics of the region the micro seismicity fractal dimensions dc and frequency magnitude distribution b value coupled with the available literature on geology geomorphology and geophysics have been used to derive the seismotectonics and stress level changes in the region the seismic cross sections for the relocated micro seismicity focal mechanisms and the swath profiles for the presence of physiographic transition 2 pt2 at the foothill of the higher himalaya indicate the constant presence of the mid crustal ramp mcr in the detachment plane and its active seismogenic nature the comparison of this scenario suggests the constant presence of seismogenically active mcr structure throughout the central seismic gap the seismic cross sections further reveal that the sensu stricto main central thrust munsiari thrust is also a site of generation of the micro seismicity in few segments due to its reactivation by thrusting along the mcr the high fractal dimension value dc 1 47 suggests the heterogeneous nature of the region owing to the presence of local faults and transverse tectonics the high stress accumulation in the garhwal himalaya with low b value b 0 70 suggests the high probability of occurrence of a larger or greater earthquake in the near future further the study also reveals that the 2011 chamoli earthquake of m 5 0 preceded by a quiescence period of nearly a year shows different stress levels before and after its occurrence which is well constrained with the increased moderate earthquake activity around the chamoli region this increased seismic activity and stress conditions in the chamoli region suggest the high possibility of the occurrence of major earthquakes hence the study recommend for a detailed seismic hazard evaluation of the region

geophysical properties of cap rocks in qiongdongnan basin south china sea abstract based on measured petrophysical properties and statistical methods relationship between petrophysical properties and well log and seismic parameters are established empirically to evaluate the quality of cap rocks in qiongdongnan basin good cap rocks show high density and low sonic travel time four zones can be divided vertically according to displacement pressures in qiongdongnan basin best seal quality is found in the depth range of 2000 4000 m the ya 13 1 structure has excellent cap rock which contributes to its abundant gas accumulation

space time correlations of seismotectonic parameters examples from japan and from turkey preceding the izmit earthquake analysis of the correlation between fractal attributes of complex seis motectonic variables may offer insights into seismic hazard assessment the guten berg richter moment magnitude and moment source area relations yield a direct fractal relationship among the gutenberg richter b value occurrence rate and the characteristic linear dimension of the fault plane square root of fault surface area in contrast temporal variation in the correlation dimension of epicenters dc i s found in several studies to correlate negatively with the b value in different regions of the world spatial variations between the b value and dc also tend to oppose each other in japan negative correlations are also observed in the regional scale com parisons of the capacity dimension do of active fault systems and the b value however at local scales the relationship yields both positive and negative correla tion the occurrence of positive or negative correlation appears to be controlled by different modes of failure within the active fault complex spatial variations between the b value and dc along the northern anatolian fault zone nafz suggest that on average from 1900 to 1992 earthquake magnitudes were higher and epicenters more scattered within the central nafz than in its eastern and western segments temporal analysis reveals that the relationship between the b value and dc are nonstationary temporal correlations are generally negative a period of positive correlation is observed between 1976 and 1988 during the last 3 yr of this period 1985 1988 both the b value and d c rose significantly suggesting that stress release occurs through increased levels of low magnitude and increasingly scattered seismicity this dispersed pattern of seismicity in combination with higher slip rates in the central nafz may be one that did not adequately relieve stress along the main fault zone this change in behavior and the tendency during the last century for the seismicity to migrate westward along the nafz may point to an increased risk of larger magnitude events such as the i zmit earthquake

fractal analysis applied to characteristic segments of the san andreas fault fractal theory is applied in a quantitative analysis of the san andreas fault saf geometry the method which directly measures the increase in total fault length with a decrease in ruler size gives the fractal dimension d and scaling properties for the chosen length band 0 5 1000 km a physical interpretation of d is that it measures the irregularity of the fault trace in the selected band the fault is subdivided into six segments of distinctive seismic behavior a main fault trace which shows either maximum coseismic slip or creeping was selected for analysis with three alternative branches examined for the saf system south of san bernardino branches of the fault trace are not considered in this work fractal dimensions calculated for the different segments range from 1 0008 to 1 0191 and are different from 1 0 to the 95 confidence interval these small changes reflect the overall smoothness of the main fault trace significant variations in d among segments indicate heterogeneities in the fault smoothness along strike d also changes significantly from the short length band to the long length band where the demarcation point ranges from 1 to 2 km the short length band has larger d values a slight correlation is obtained between the fractal dimension of the main trace and the extent of subparallel faulting this indicates some correspondence between the main fault trace irregularity and the complexity of subsidiary fault traces in plan view

the accommodation of large strains in the upper lithosphere of the earth and other solids by self similar fault systems the geometrical origin of b value plate tectonics has provided a method of visualizing the geometry of the deformation of the earth s lithosphere on a large scale the description is so concise that for many purposes it provides an explanation of geological processes that overshadows the need to understand the driving processes the mechanics of the zones between the plates are less well understood particularly in continental regions where large areas are subject to deformation both continuous and discontinuous models have been tried but both have obvious drawbacks

the major asperities of the 1999 mw 7 4 izmit earthquake defined by the microseismicity of the two decades before it

estimation of marine sediment bulk physical properties at depth from seafloor geophysical measurements a combination of geophysical techniques can yield estimates of several physical properties versus depth an example is presented for a thick sequence of sediments in middle valley near the present spreading axis of the juan de fuca ridge we have computed the porosity temperature and thermal conductivity versus depth by combining the results of seafloor electrical and heat flow surveys the electrical resistivity of the sediments is empirically related to the porosity of the medium and to the pore fluid electrical conductivity which is in turn sensitive to the temperature the temperature profile is determined from the heat flow and the thermal conductivity the latter is determined from calculated porosity and estimates of the constituent mineral and pore fluid thermal conductivities the measured surface heat flow is assumed to be and the resistivity has been determined to be approximately constant with depth the computation of the variation of temperature porosity and thermal conductivity with depth yields physically realistic and reasonable results other physical properties void ratio bulk density water content compressional wave velocity are estimated from the porosity the shear wave velocity is calculated empirically from the compressional wave velocity and poisson s ratio is then computed from the compressional and shear wave velocities the results are in good agreement with values derived for similar rapidly deposited sediment sequences elsewhere but the model calculations indicate that deep sea drilling project measurements may be biased toward higher porosity samples

lattice preferred orientation and seismic anisotropy in sedimentary rocks summary although it is well known that sedimentary rocks can be seismically anisotropic there have been few detailed investigations of the underlying cause of such anisotropy here we investigate anisotropy due to the preferred orientation of minerals or lattice preferred orientation lpo in a suite of sedimentary rocks seismic properties are predicted by averaging single crystal elastic constants of minerals according to their crystal orientation and modal volume fraction in the rock aggregate both electron backscattered diffraction ebsd and x ray texture goniometry xtg are tested as quantitative techniques for measuring the lpo of sedimentary rocks although ebsd has promise for future lpo measurements in polymineralic sedimentary rocks problems currently remain in measuring low symmetry phases e g feldspars and very small clay or mica particles however the lpo of very fine grained phyllosilicates can be measured using xtg and the lpo of low symmetry minerals can be measured using manual ebsd pattern analysis here we use such a hybrid approach to estimate lpo in a suite of sedimentary samples the seismic properties calculated from lpo data show anisotropy values for p waves ranging from 1 5 per cent in sandstones to over 3 5 per cent in a siltstone to 12 per cent in a shale the effect of thin multilayering on long wavelength propagation in a siltstone is predicted by applying backus type averaging the layering does not enhance the anisotropy because of the small differences in density and in elasticity between the two layer types the lpo of phyllosilicates and to a lesser extent dolomite and siderite seem to contribute significantly to the seismic anisotropy of phyllosilicate rich rocks siltstones and shales the weak lpo of quartz in sandstones causes a few per cent anisotropy cumulatively our results suggest that field observations of seismic anisotropy have the potential to be used as an indicator of rock lithology

continental collisions and the origin of subcrustal continental earthquakes the existence of subcrustal continental earthquakes beneath the alpine himalayan belt was recognised more than 60 years ago there is general agreement that most of those beneath the western part o

spatial variability of the time correlated behaviour in italian seismicity abstract using the national institute of geophysics and volcanology seismic catalogue an analysis of the time clustering behaviour of the instrumental seismicity of italy was performed the time span of the analysed catalogue is from 1986 to 2001 and only the events with magnitude m 2 4 were considered the analysis carried out on the full and aftershock depleted catalogues was performed using detrended fluctuation analysis which permits the identification of correlated temporal structures in time series even in the presence of trends or non stationarities our findings confirm the presence of long range behaviour in the temporal distribution of seismicity data of both full and depleted catalogues suggesting that the clustering phenomenon is not due only to the generation of aftershocks following the occurrence of large shocks but relies on the underlying time structure of the seismicity of italian areas

strike slip fault geometry in turkey and its influence on earthquake activity the geometry of turkish strike slip faults has been reviewed and described from this data set it appears that fault geometry the distribution of discontinuities such as bends and stepovers along the main fault trace plays an important role in controlling the location of large earthquake rupture segments along the fault zones large earthquake ruptures generally do not propagate past individual stepovers that are wider than 5 km or bends that have angles greater than about 30 more important than the size of each discontinuity however is the total geometric pattern i e the distribution of adjacent bends and stepovers based not only on distance from one another but also on relative discontinuity size certain geometric patterns restraining single or double bends are particularly common and can be viewed as responsible for strain accumulation along portions of the fault zone fault geometry not only plays a role in the extent of earthquake rupture but also in characteristics of earthquake behavior for example large earthquake epicenters often occur near restraining bends or double bends furthermore aftershocks and swarm activity can often be associated with releasing areas areas along the strike slip fault that are undergoing a relatively large amount of extension

research on b values based on fault buffers the b value is closely related to the crustal stress by studying the b value trends of regions before large earthquakes we can obtain the evolution of crustal stress which is generally considered useful earthquake precursor information a quake is closely related to fault tectonic movement in the past the traditional b value calculation method did not consider the spatial distribution of the fault here we propose a new algorithm based on the fault s buffer area combining the spatial distribution and trend of the fault this algorithm can accurately calculate the b value changes for a specific fault using the fault as the basic independent unit this method provides a useful reference for earthquake hazard judgment based on this algorithm we use a total of 428 963 earthquakes from 1980 to 2013 after removal of the aftershock sequences and combine these quakes with the active fault distribution data to study the b value changes before major earthquakes in western sichuan the results show that the b values of the fubianhe fault longmenshan main fault and shuangshi pengguan fault in western sichuan decreased for at least 2 years before the earthquakes the longmenshan main fault area began to decrease slowly 5 years before the wenchuan ms8 0 earthquake and sharply decreased in the year before the quake which reflects a significant change in crustal stress during this time this conclusion and the method are available for long term earthquake hazard assessment as a reference

accreted terranes in the northern part of the philippine archipelago the philippine archipelago consists of a complex array of ophiolites continental fragments and island arc elements that can be identified as accreted terranes similar to those increasingly recognized as components of orogenic zones the northern philippines including luzon mindoro and nearby smaller islands can be divided into at least six of these tectonic elements from west to east across central luzon there are the neogene accretionary prism of the west luzon arc the eocene zambales ophiolite the cretaceous angat ophiolite and a late cretaceous early paleogene volcanic arc built on an older metamorphic basement this arc terrane is repeated by offset along the philippine fault to the south the western luzon terranes are juxtaposed against the metamorphic basement block of mindoro which itself is colliding with the north palawan microcontinental fragment the ophiolites appear to have originated in back arc basins rather than in oceanic plateaus and the metamorphic belts have protoliths indicating deformation along active margins perhaps deep within accretionary prisms the philippine terranes are interpreted as fragments that originated within the complex pacific eurasian plate boundary rather than as intra pacific basin units these terranes have been assembling at least since the oligocene by strike slip and convergent displacements strike slip displacement either along transcurrent faults or as a component of convergence played a very important if not dominant role in this assembly most terranes identified in the northern philippine appear to be plate fragments with attached crust and upper mantle their characteristics contrast with those usually interpreted for terranes in the north american cordillera where near orthogonal convergence and shallow dipping terrane sutures are favored

seismic velocities for hydrate bearing sediments using weighted equation a weighted equation based on the three phase time average and wood equations is applied to derive a relationship between the compressional wave p wave velocity and the amount of hydrates filling the pore space the proposed theory predicts accurate p wave velocities of marine sediments in the porosity range of 40 80 and provides a practical means of estimating the amount of in situ hydrate using seismic velocity the shear s wave velocity is derived under the assumption that the p to s wave velocity ratio of the hydrated sediments is proportional to the weighted average of the p to s wave velocity ratios of the constituent components of the sediment in the case that all constituent components are known a weighted equation using multiphase time average and wood equations is possible however this study showed that a three phase equation with modified matrix velocity compensated for the clay content is sufficient to accurately predict the compressional wave velocities for the marine sediments this theory was applied to the laboratory measurements of the p and s wave velocities in permafrost samples to infer the amount of ice in the unconsolidated sediment the results are comparable to the results obtained by repeatedly applying the two phase wave scattering theory the theory predicts that the poisson s ratio of the hydrated sediments decreases as the hydrate concentration increases and the porosity decreases in consequence the amplitude versus offset avo data for the bottom simulating reflections may reveal positive negative or no avo anomalies depending on the concentration of hydrates in the sediments

fundamentals of seismic rock physics during the past 50 years or so tremendous progress has been made in studying physical properties of rocks and minerals in relation to seismic exploration and earthquake seismology during this period many theories have been developed and many experiments have been carried out some of these theories and experimental results have played important roles in advancing earth sciences and exploration technologies this tutorial paper attempts to summarize some of these results

the effect of systematic diagenetic changes on the mechanical behavior of a quartz cemented sandstone abstracta key goal of petrophysical studies of sandstones is to relate common field measurements particularly seismic or sonic velocities to parameters defining the rock s mechanical and hydrologic characteristics these include elastic and inelastic mechanical properties porosity and permeability we explored relationships among these properties in variably quartz cemented mature arenites of the st peter sandstone with porosities ranging from 9 to 25 in a previous paper we described microstructural changes accompanying progressive quartz cementation and related porosity and permeability reduction in this sample suite here we report ultrasonic velocities ultrasonic velocities dynamic and static elastic properties confined compressive strength and tensile strength analyses of these data demonstrated that factors controlling permeability also fundamentally determined the elastic and inelastic mechanical properties we found that the number of grain contacts or bonds per number of grains vi

evolution of the temporal multifractal scaling properties of the chiayi earthquake ml 6 4 taiwan abstract variations in the fractal dimension of earthquakes have been suggested to be a precursor of a large earthquake however the physical characteristics and seismicity are always different along a large fault system and it is difficult to segment a large fault for further investigating therefore the fractal dimension of earthquakes on a given fault only reflects the average seismic characteristics of the area and may be unrelated to precursory activity in this paper the evolution of the temporal generalized fractal dimension dq of a seismic cluster within a small fault system associated with the chiayi earthquake ml 6 4 taiwan is investigated the earthquakes of this sequence are confined in small source volume and reflect the behavior of the local fault system our results show that the dq curve of the background stage is smooth with a low multifractal degree 0 36 and the seismicity is nearly monofractal in the chiayi region during the foreshock stage the seismicity becomes active such that not only the dq curve exhibits greater variability especially for the steep slope of dq curve at q 0 but also the temporal fractal dimension changes from nearly monofractal to multifractal in the aftershock stage the fluctuation of dq is large and the multifractal degree is up to 1 0 the temporal multifractal property becomes more pronounced as well finally when the seismicity returns to the background stage the dq curve becomes smooth and nearly monofractal again therefore the fluctuations in the dq spectrum of an earthquake cluster associated with a large earthquake not only give a clear picture of the temporal alterations in the seismogenic regimes but also illustrate their variability through time for a large earthquake in addition the variation of the slope of dq curve at q 0 in the foreshocks may be used as a precursor of a large earthquake

spatial bias in b value of the frequency magnitude relation for the hong kong region abstract the onshore and offshore regions in south guangdong around hong kong exhibit different b values of the g r relation the two regions have yielded b values of 0 85 and 0 67 respectively based on the most complete seismic database for the period 1970 1995 tests on the completeness of the seismic catalogue and dominance of local source zones suggest a fundamentally complete record for m 3 events and the spatial bias in the b values cannot be explained entirely in terms of these two factors the subcatalogue of onshore events with focal depth 6 km has yielded an essentially identical b value as that for the offshore region thus revealing a weak upper crust with diffused seismicity overlying a relatively strong lower crust the present study shows that spatial bias in the b value can be resolved by a proper analysis of the seismic data the interpretation is also consistent with the model that the relative motion between south china and the south china sea is diffused over a broad fault zone along the coast with a higher b value in the upper crust and the lack of a single wrench fault

diagnostics of seismic time lapse effects of sandstones based on laboratory data we evaluated a viscoelastic modeling of p and s wave velocity dispersion attenuation pressure and fluid effects for a set of siliciclastic rock samples our analysis used a published laboratory data set of 63 sandstones with a wide range of compositional heterogeneities we observed a notable correlation between the velocity and attenuation pressure sensitivity and the abundance lack of quartz in the samples we included compliant pores low aspect ratio proportionally to the content of secondary minerals to account for the differential sensitivity to pressure the observed velocity and attenuation were well reproduced by the applied viscoelastic modeling we found that pores of significantly different scale required pore fluid relaxation time constants of proportionally different magnitudes to reproduce the velocity and attenuation measurements the relaxation time constant of crack sized pores can be one order of magnitude smaller than the constant of mesopores moreover the velocity dispersion and attenuation signatures revealed that a pore textural model dependent on lithological composition is critical in the prediction of time lapse fluid and pressure responses

interpretation of low seismicity in the eastern anatolian collisional zone using geophysical seismicity and aeromagnetic and geological data the eastern anatolia is a continental collisional zone between the arabia eurasia plates and is currently being accompanied by the westward escape of the anatolian crustal block to the west southwest along two major strike slip fault zones the natf and the eatf although these major fault zones have experienced historical earthquakes with moderate to high magnitude notably there is a low seismicity zone on the active eatf between the bitlis and poturge massifs the low seismicity zone is characterized by thinner crustal structure relative to its environs the shallow curie point depth scpd ca 12 14 km in between 39 40 e and 38 5 39 n in the easternmost part of the anatolian plate and moderate to high b values more than 0 7 we consider that the shallow cpd and moderate to high b values in the low seismicity zone characterized by thinner crustal area are closely related with the higher thermal structure of the crust which most probably resulted from crust hot asthenospheric mantle interactions