band limited heterogeneous fractal structure of earthquakes and acoustic emission events summary generalized correlation integral functions of the spatial distribution of earthquake epicentres have been determined for the chinese earthquake catalogue these correlation integral functions have three distinct power law regimes bands showing that the spatial distribution of earthquakes has band limited heterogeneous fractal structure we also found similar results in the hypocentre distribution of acoustic emission events in coarse grained granite under triaxial compression testing these results show that the fractal structure in rock fracturing is very complex they are heterogeneous in space and also band limited in scale the spatial distribution of fractures shows different patterns corresponding to different scale ranges microcracks in rock samples earthquake epicentres in seismic clusters seismic clusters along active fault zones boundary of crustal block for the most cases and active fault zones in the earth s crust the fractal dimension differs corresponding to the scale bands indicating there are some intrinsic characteristic scales existing in the fracturing system such as grain size and size of crustal blocks

how do asperities fracture an experimental study of unbroken asperities abstract the fracture of a shear fault containing several unbroken asperities in a granitic porphyry is examined in detail via acoustic emission ae data collected by a high speed multi channel waveform recording system the experimental results reveal that a quasi static nucleation of the shear faulting corresponds to the fracture of coupled asperities on the fault plan aes caused by the fracture of individual asperities exhibit similar characteristics to the sequence for natural earthquakes including foreshock mainshock and aftershock events foreshocks initiated at the edge of the asperity occur with an event rate that increases according to a power law of the temporal distance to the mainshock and with a decreasing b value from 1 1 to 0 5 one or a few mainshocks then initiate at the edge of the asperity or the front of the foreshocks the aftershock period is characterized by a remarkable increase and subsequent gradual decrease in b value and a decreasing event rate obeying the modified omori law which has been well established for earthquakes the fracture of neighboring asperities is then initiated after the mainshock of a particular asperity presumably due to redistribution of the strain energy accumulated within an asperity which is released by the mainshock resulting in enhancement of the stress concentration around the nearest neighboring intact asperities the progressive fracturing of multiple coupled asperities during the nucleation of shear faulting results in short term precursory fluctuations in both b value and event rate which may prove useful information in the prediction of failure of the main fault plane of seismic earthquakes

interaction of parallel strike slip faults and a characteristic distance in the spatial distribution of active faults summary a numerical simulation of the activities of many parallel strike slip faults is performed to explore the effect of the interaction of fault slip on the spatial distribution of active faults in the model a large number of faults with random strengths are embedded in an elastic layer lithosphere over a maxwell type viscoelastic half space asthenosphere and shear loading of a constant strain rate is applied when slip takes place on a model fault shear stress is decreased around the fault and then recovered with time due to the viscoelastic response of the asthenosphere the decrease in shear stress prohibits the occurrence of another earthquake around the slipped fault resulting in the existence of a characteristic distance between active faults this characteristic distance is found to be controlled by the thickness of the elastic layer the strain rate and the viscoelastic relaxation time the density of simulated active faults increases with the strain rate consistent with observations of active faults in japan furthermore the present simulation result may explain the characteristic distance which breaks the fractal structure of the spatial distribution of active faults in japan which was discovered by lei kusunose 1999

scale dependence in earthquake processes and seismogenic structures we provide a positive answer to the question whether large earthquakes can be separated from small ones using various observations on the earthquake processes and seismogenic structures for california the boundary of separation is at m 5 this conclusion leads to the possibility of deterministic modeling of earthquake occurrence for prediction we recognize however that the system of earthquake occurrence involves nonlinear physics with many degrees of freedom we suggest that the geometrical barriers and asperities may be a good starting point for the modeling we also discuss the implication of our finding on the numerical simulation of earthquake rupture propagation and conclude that the model fault zone must be made thicker for a more realistic simulation of major earthquakes

multiscaling of shear zones and the evolution of the brittle to viscous transition in continental crust 1 a new method is introduced for quantifying the scale and the intensity of strain localization from maps of natural shear zones the method employs autocorrelation functions to determine local areal scales of geometric homogeneity these homogenization scales are used to calculate scale dependent localization fractions of deformed rock the strain localization intensity is quantified from measurements of mean relative to maximum shear strain this approach is used to analyze shear zones on different scales from an exposure cap de creus spain of the fossil brittle to viscous transition bvt changes in the scaling characteristics of shear zones are interpreted to reflect a time sequence of localization during the evolution of the continental bvt we show that shear zone scaling is related to inherited anisotropies older schistosity lithological layering pegmatite bodies and to the predominant mode of deformation brittle viscous the length to width ratio of shear zones increases with their length up to the meter scale and decreases for larger length scales as they evolve from isolated shear fractures to interconnected mylonitic shear zones variations in strain localization intensity calculated along a single shear zone indicate that such shear zones weakened from their brittle tips to their mylonitic centers thus driving their propagation and growth to larger scales our results imply that the bvt evolves by network widening a process whereby strain localizes on progressively larger scales until a dense network of weak mylonitic layers tens to hundreds of meters wide and hundreds to thousands of meters long forms subparallel to the regional shearing plane

seismicity patterns in the himalayan plate boundary and identification of the areas of high seismic potential abstract space time distribution of earthquakes along the himalayan plate boundary has been investigated with a view to discerning fluctuations in seismicity rates associated with great earthquakes the possibilities of epicentre migration and gaps in seismic activity data from 1800 to 1976 were considered this study shows that all great earthquakes m 8 0 were preceded by seismically quiescent periods of at least 19 years furthermore earthquake quiescence has also been recognised to follow the great earthquakes three possible trends of migration of epicentres of great earthquakes have been recognised 1 1 the first trend starts from the 1905 kangra earthquake the epicentres of subsequent earthquakes migrating eastwards along the plate boundary 2 2 the second trend of migration starts from the great nepal earthquake of 1833 associated with eastward migration 3 3 the third trend commences from the great assam earthquake of 1897 and shows a westward migration of earthquake epicentres the middle section of the himalayan convergent plate boundary 80 e to 90 e in general displays a relatively low level of seismicity as compared to the adjacent sections a remarkable decrease in seismicity following the year 1970 has been observed along a section of the himalaya which lies to the east of the rupture zone of the great 1905 kangra earthquake since 1970 the seismicity rate has also dropped in the region lying in between the rupture zones of the great assam earthquakes of 1897 and 1950 as has earlier been reported by khattri and wyss 1978 such decreases in the level of seismicity along active plate boundaries have been demonstrated to be indicative of building up of stresses leading to future great earthquakes mogi 1969 mccann et al 1979

semi empirical estimation of peak ground acceleration from large earthquakes abstract a simplified method is proposed for synthesizing ground acceleration from a large earthquake the present method is based on the semi empirical method of irikura 1986 which is consistent with the square source model but is much simplified for engineering use in this method the fault of the large earthquake is divided into small elements and the acceleration envelope waveforms instead of the time histories from the elements are simply determined using the empirical relations the envelope waveforms from the elements are summed to synthesize the envelope waveform of a large earthquake the peak acceleration of the large earthquake is obtained from the maximum value of the summed envelope to test the present method the peak accelerations are calculated for the 1985 central chile earthquake ms 7 8 during which a considerable number of the strong motion records were obtained close to the source the calculated accelerations are in good agreement with the observed ones the attenuation characteristics of the calculated peak accelerations for earthquakes of different magnitudes are examined the results show that 1 1 the shortest distance from the fault plane is an appropriate definition for source distance 2 2 the peak acceleration becomes independent of magnitude in the near field and 3 3 the source direction effect on the peak acceleration is not negligible

the hierarchical rupture process of a fault an experimental study abstract we describe the detailed faulting process of a naturally healed fault containing geometric and mechanical asperities in a granitic porphyry sample based on data collected with a high speed acoustic emission ae waveform recording system asperity failure is examined using the detailed spatio temporal distribution of ae hypocenters the initial phase of ae activity is also examined using high dynamic range waveforms our experimental results indicate that quasi static nucleation of the heterogeneous fault is associated with the failure of asperities on the fault plane the fracturing of an asperity is characterized by a dense spatial clustering of ae events and a changing b value b hereinafter which is manifest in three typical stages of failure as follows 1 foreshocks exhibiting a decrease in b 2 a period of mainshocks corresponding to a minimum in b and 3 aftershocks of increasing b the progressive fracture of several coupled asperities results in short term precursory fluctuations in both b and ae rate furthermore some ae events possess similar dynamic rupture features to those of earthquakes having an initial phase associated with the transition from quasi dynamic to dynamic rupture we conclude based on these experimental observations that fault rupture has hierarchical characteristics quasi static nucleation of fault rupture represents dynamic fracture of the asperities on the fault plane likewise a quasi static nucleation process characterized by dynamic microfracturing precedes the fracture of an asperity since dynamic motions are easier to detect remotely than static deformations understanding the hierarchical processes underlying fault rupture may thus be helpful for elucidating quasi static nucleation at larger scales in terms of the dynamic rupture of the asperities at smaller scales careful studies of asperity failure in the lab may guide future seismic studies of large asperities on natural faults potentially making it possible to recognize the final preparation stage before a large earthquake

identifying an asperity through 3 d mapping of the frequency magnitude distribution following the idea introduced by wiemer and wyss 1997 here is an attempt to map the seismic hazard in terms of the b value in the frequency magnitude distribution in a region with moderate seismic activity bearn region french pyrenees in this area the complexity of the geology makes it necessary to perform a 3 d mapping b values are computed within 5 km radius spherical volumes that contain an average of 140 events strong lateral variations between 0 45 and 1 8 are observed at short scales in the whole investigated volume the minimum of the b value is clearly correlated with a historically active zone which last ruptured in 1980 mb 5 1 interpretating low b values in terms of high stresses may lead us to consider this minimum b patch as a 5 km radius asperity this study allows to define its location and dimensions

nucleation process of an m2 earthquake in a deep gold mine in south africa inferred from on fault foreshock activity using a network of sensitive high frequency acoustic emission sensors we observed foreshock activity of an mw 2 2 earthquake main shock in a deep gold mine in south africa foreshock activity which selectively occurred on a part of the rupture plane of the forthcoming main shock lasted for at least 6 months until the main shock rock samples recovered from the main shock source region showed evidence of ancient hydrothermal alteration on the main shock rupture plane suggesting that the foreshock activity occurred on a preexisting weakness the foreshocks during 3 months before the main shock were concentrated in three clusters f1 f3 which we interpret as representing localized preslip at multiple sites while the location of mining area the source of stress perturbations changed with time the locations of foreshock clusters did not change suggesting that the preslip patches were controlled by strength heterogeneity rather than stress distribution activity over the entire foreshock area was generally constant but the largest cluster f2 showed accelerated activity starting at least 7 days before the main shock while mining stress did not increase in this period the main shock initiated at a point close to f1 away from f2 all the six foreshocks during the final 41 h occurred in f1 and f2 and in between these suggest that in the last stage of the preparation process of the main shock preslip patches interacted with each other through the stress concentration ahead of the expanding preslip patch f2 which should be the only driving force of the preparation process under the constant external load

shear rupture under constant normal stiffness boundary conditions abstract a grain based distinct element method and its embedded grain based method are used to simulate the fracturing processes leading to shear rupture zone creation in a calibrated massive non jointed brittle rock specimen deformed in direct shear under constant normal stiffness boundary conditions under these boundary conditions shear rupture zone creation relative to the shear stress versus applied horizontal displacement load displacement curve occurs pre peak before the maximum peak shear strength is reached this is found to be the result of a normal stress feedback process caused by the imposed shear displacement which couples increases in normal stress due to rupture zone dilation with shear stress producing a complex normal shear stress path that reaches and then follows the rock s yield strength envelope while the yield envelope is followed the shear strength increases further and shear stress oscillations repeated stress drops followed by re strengthening periods in the load displacement curves occur due to fracture creation as the rupture zone geometry smoothens once the maximum peak strength is reached after a series of shear stress oscillations the largest stress drops occur as the ultimate or residual shear strength is approached the simulation results provide insight into the fracturing process during rupture zone creation and improve the understanding of the shear stress versus applied horizontal displacement response as well as the stick slip behaviour of shear rupture zones that are being created under constant normal stiffness boundary conditions

characteristic features of local breakdown near a crack tip in the transition zone from nucleation to unstable rupture during stick slip shear failure abstract characteristic features of local breakdown near a propagating crack tip during slip failure nucleation and its transition process to unstable rupture under mode ii conditions are experimentally studied using a rock sample with a simulated fault the size of which is large compared with the size of the breakdown zone in addition distinctive features in the nucleation zone are compared with those in the zone of steady dynamic rupture propagation it is found that the local breakdown stress drop the local dynamic stress drop the local stress increase immediately before the slip weakening process the dimensionless parameter s defined by das and aki and the shear fracture energy are functions of crack length in the transition zone from nucleation to unstable rupture i e they all increase with crack growth in the nucleation zone this is contrasted with the observations in the zone of steady dynamic rupture propagation where these physical parameters do not depend on crack length an increase in the magnitudes of these parameters with crack growth in the nucleation zone results in increasing resistance to crack extension with crack growth in the nucleation zone the reason for the increase in crack growth resistance in this zone is that a slip failure nucleus is formed at a point or zone where the local strength and the shear fracture energy are at a minimum this basic physical information can provide the key to earthquake prediction since the nucleation itself is a precursory phenomenon the ratio of the size of the breakdown zone to the crack length decreases abruptly beyond the critical crack length rupture velocity v accelerates with crack growth and reaches the shear wave velocity or super shear and v is found to be expressed empirically as a function of crack length in the nucleation zone a positive correlation is found between s and v in the nucleation zone v increases with increasing s however no such correlation was observed in the zone of steady dynamic rupture propagation where v seems to have reached the shear wave velocity of super shear for s 0 5 this is consistent with das and aki s numerical result the interrelationships between shear stress slip displacement slip velocity and acceleration near the crack tip during the breakdown in the nucleation zone are revealed and they are compared with those in the zone of dynamic rupture propagation the present experiments suggest that the relationship between shear stress and slip displacement is more fundamental during the breakdown process than the relationship between shear stress and slip velocity a model is presented to describe the breakdown process in the nucleation zone

modelling of active lineaments for predicting a possible earthquake scenario around dehradun garhwal himalaya india abstract the doon valley which consists of the doon gravels and siwalik rocks is surrounded by the main boundary thrust mbt in the north the main frontal thrust mft mohand thrust and bhimgoda thrust in the south the ganga tear fault in the east and the yamuna tear fault in the west lineaments identified from the aerial photographs show that a few of them trend parallel to the himalayan orogen and the others are transverse to it the effect of the neotectonic activity is clearly reflected in the doon valley implying that the doon valley is tectonically unstable today and that the possibility of earthquakes in this region cannot be ruled out the ruptures along identified active lineaments are modelled three dimensionally peak accelerations are obtained by using a methodology based on the semi empirical method of irikura which was used by midorikawa the efficacy of this modelling technique for the himalayan region is established by simulating peak ground accelerations for the uttarkashi earthquake of 20 october 1991 and comparing it with recorded one a seismic study of the region shows that it is prone to moderate as well as great earthquakes the technique of midorikawa has been applied for the preparation of zonation maps in this seismically active region two different zonation maps showing respectively the effects of moderate as well as great earthquakes in this region are presented in this paper the zonation map for moderate earthquakes shows that the region can experience peak ground accelerations around 310 cm s2 this value is close to the peak ground acceleration of 304 cm s2 recorded for the uttarkashi earthquake ms 7 1 at uttarkashi station which is about 60 km north of dehradun the prepared map shows that among all identified active lineaments rupture along four lineaments can cause major damage in the region among these four three lineaments are transverse to the major tectonic zones viz the mft and mbt in the region and one extends along the mft lying south of dehradun the zonation map for great earthquakes m 8 has been prepared by modelling a rupture in the central gap region of the himalaya seven different possibilities of rupture nucleation within the rupture plane are modelled and a zonation map containing three different zones is prepared the prepared zonation map for this worst possible scenario shows that cities like tehri uttarkashi srinagar deoprayag pauri and dehradun fall within zone 1 and can experience ground accelerations bigger than 600 cm s2 the region like hardwar and rishikesh fall within zone 2 and can experience ground accelerations around 300 cm s2 the zonation map shows that tehri can experience accelerations up to 0 84g and this value is comparable with that obtained by other researchers this study confirms that for very long periods the destruction in the region will be dominantly affected by ruptures having longer lengths and least effected by shorter ruptures therefore special consideration about the longer ruptures should be taken while considering effect of earthquake hazards in this region

evidence for a constant b value above magnitude 0 in the southern san andreas san jacinto and san miguel fault zones and at the long valley caldera california the cumulative b value the slope of the gutenberg richter relationship between earthquake occurrence rate and magnitude is commonly found to be constant 1 network catalogues however reveal a decrease at small magnitudes 3 some recent studies have suggested that this decrease in b value is not just an artifact of catalogue incompleteness but that small earthquakes are really not as numerous as a constant b value extrapolated from larger events would predict brune allen 1967 recorded microseismicity in both the san andreas and san jacinto fault zones in southern california calculating that they were complete to magnitude 0 reyes et al 1975 performed a similar study of the san miguel fault zone baja california estimating completeness above magnitude 0 5 we compare the results of these studies with the occurrence rates of earthquakes on the same faults recorded by the southern california and resnor seismic networks the observed microseismicity rates are in good agreement with the rates predicted by extrapolating the b values of the larger earthquakes in a new microseismicity survey at the long valley caldera mammoth lakes california microearthquakes were recorded and counted within 24 km of stations clk and chs this study is estimated to be complete above 0 6 m at clk and 0 9 m at chs and the microseismicity rates are found to be in good agreement with the rate predicted by extrapolating the b value from the local network recorded seismicity the constant b value in the magnitude range 0 to 5 observed in all four areas considered is consistent with a scale invariant earthquake rupture process

time dependent cracking and brittle creep in crustal rocks a review abstract rock fracture under upper crustal conditions is driven not only by applied stresses but also by time dependent chemically activated subcritical cracking processes these subcritical processes are of great importance for the understanding of the mechanical behaviour of rocks over geological timescales a macroscopic manifestation of time dependency in the brittle field is the observation that rocks can deform and fail at constant applied stresses a phenomenon known as brittle creep here we review the available experimental evidence for brittle creep in crustal rocks and the various models developed to explain the observations laboratory experiments have shown that brittle creep occurs in all major rock types and that creep strain rates are extremely sensitive to the environmental conditions differential stress confining pressure temperature and pore fluid composition even small changes in any of these parameters produce order of magnitude changes in creep strain rates and times to failure three main classes of brittle creep model have been proposed to explain these observations phenomenological statistical and micromechanical statistical and micromechanical models explain qualitatively how the increasing influence of microcrack interactions and or the increasing accumulated damage produces the observed evolution of macroscopic deformation during brittle creep however no current model can predict quantitatively all of the observed features of brittle creep experimental data are limited by the timescale over which experiments are realistically feasible clearly an extension of the range of available laboratory data to lower strain rates and the development of new modelling approaches are needed to further improve our current understanding of time dependent brittle deformation in rocks

a way to synchronize models with seismic faults for earthquake forecasting insights from a simple stochastic model abstract numerical models are starting to be used for determining the future behaviour of seismic faults and fault networks their final goal would be to forecast future large earthquakes in order to use them for this task it is necessary to synchronize each model with the current status of the actual fault or fault network it simulates just as for example meteorologists synchronize their models with the atmosphere by incorporating current atmospheric data in them however lithospheric dynamics is largely unobservable important parameters cannot or can rarely be measured in nature earthquakes though provide indirect but measurable clues of the stress and strain status in the lithosphere which should be helpful for the synchronization of the models the rupture area is one of the measurable parameters of earthquakes here we explore how it can be used to at least synchronize fault models between themselves and forecast synthetic earthquakes our purpose here is to forecast synthetic earthquakes in a simple but stochastic random fault model by imposing the rupture area of the synthetic earthquakes of this model on other models the latter become partially synchronized with the first one we use these partially synchronized models to successfully forecast most of the largest earthquakes generated by the first model this forecasting strategy outperforms others that only take into account the earthquake series our results suggest that probably a good way to synchronize more detailed models with real faults is to force them to reproduce the sequence of previous earthquake ruptures on the faults this hypothesis could be tested in the future with more detailed models and actual seismic data

fractal approaches in investigating the time dynamics of self potential hourly variability fractal tools have been used to investigate the time dynamics of hourly self potential data recorded during the year 2001 by five geoelectrical stations located in one of the most seismic areas of southern italy scaling behaviour has been revealed by means of different statistics the lomb periodogram method the detrended fluctuation analysis the higuchi analysis and the mean distance spanned within the time l the values of the scaling exponents estimated by means of these methods indicate that the temporal fluctuations of the geoelectrical signals are not typical of purely random stochastic processes i e white noise but evidence the presence of long range correlations furthermore it is found that these correlations are linear

compressive failure of mudstone samples containing quartz veins using rapid ae monitoring the role of asperities this paper presents the results of an ongoing experimental investigation of compressive failure of homogeneous and heterogeneous rocks we used a rapid data acquisition system to monitor the spatio temporal distribution of acoustic emission ae during fault nucleation under conditions of either constant rate loading or static loading in order to examine the effect of asperities on faulting we conducted a series of experiments on mudstone with quartz veins the bedding planes of the mudstone were oriented at an angle of 30 with the maximum compressive stress and were expected as the fracture plane the quartz veins are much stronger than the bedding plane of mudstone and thus the samples model faults having strong asperities experimental results show that 1 ae activity initiated close to the peak stress and almost all ae hypocenters appeared at the intersections of the veins and the fault planes suggesting that the vein asperities control faulting 2 the b value changed with time and shows multiple large and short term fluctuations 3 the change of the b value correlated closely with the spatio temporal hierarchy of the fracture process and 4 fault segments along the bedding plane show behavior of slip having large compressive deformation before the peak stress while the vein asperities show large precursor dilatancy prior to dynamic rupture these experimental results are helpful for the understanding of seismic precursor phenomena associated with strain localization dilatancy change in level of ground water as well as the b value

premonitory acoustic emissions and stick slip in natural and smooth faulted westerly granite 1 a stick slip event was induced in a cylindrical sample of westerly granite containing a preexisting natural fault by loading at constant confining pressure of 150 mpa continuously recorded acoustic emission ae data and computer tomography ct generated images of the fault plane were combined to provide a detailed examination of microscale processes operating on the fault the dynamic stick slip event considered to be a laboratory analog of an earthquake generated an ultrasonic signal that was recorded as a large amplitude ae event first arrivals of this event were inverted to determine the nucleation site of slip which is associated with a geometric asperity on the fault surface ct images and ae locations suggest that a variety of asperities existed in the sample because of the intersection of branch or splay faults with the main fault this experiment is compared with a stick slip experiment on a sample prepared with a smooth artificial saw cut fault surface nearly a thousand times more ae were observed for the natural fault which has a higher friction coefficient 0 78 compared to 0 53 and larger shear stress drop 140 compared to 68 mpa however at the measured resolution the ultrasonic signal emitted during slip initiation does not vary significantly between the two experiments suggesting a similar dynamic rupture process we propose that the natural faulted sample under triaxial compression provides a good laboratory analogue for a field scale fault system in terms of the presence of asperities fault surface heterogeneity and interaction of branching faults

india eurasia collision chronology has implications for crustal shortening and driving mechanism of plates the motion of the indian plate is determined in an absolute frame of reference and compared with the position of the southern margin of eurasia deduced from palaeomagnetic data in tibet the 2 600 900 km of continental crust shortening observed is shown to have occurred in three different episodes subduction of continental crust intracontinental thrusting and internal deformation and lateral extrusion the detailed chronology of the collision and plate reorganizations in the indian and pacific oceans supports the hypothesis that slab pull is a dominant driving mechanism of plate tectonics

indicators of critical point behavior prior to rock failure inferred from pre failure damage abstract to investigate possible indicators of critical point behavior prior to rock failure the statistical properties of pre failure damage were analyzed based on acoustic emission events ae recorded during the catastrophic fracture of typical rock samples under differential compression aes were monitored using a high speed 32 channel waveform recording system time dependent statistics including the energy release rate b value of the magnitude frequency distribution fractal dimension and spatial correlation length scl of the ae hypocenters were calculated for each data set each parameter is a function of the time to failure and thus can be treated as an indicator of the critical point it is clear that the pre failure damage evolution prior to catastrophic failures in several common rock types is generally characterized by 1 accelerated energy release 2 a decrease in fractal dimension and scl with a subsequent precursory increase and 3 a decrease in b value from 1 5 to 0 5 for hard rocks and from 1 1 to 0 8 for soft rocks such s c cataclasite however each parameter also reveals more complicated temporal evolution due to either the heterogeneity of the rock mass or the micro mechanics of shear fracturing this confirms the potential importance of integrated analysis of two or more parameters for successfully predicting the critical point the decreasing b value and increasing energy release may prove meaningful for intermediate term prediction while the precursory increase in fractal dimension and scl may facilitate short term prediction

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

preslip and cascade processes initiating laboratory stick slip recent modeling studies have explored whether earthquakes begin with a large aseismic nucleation process or initiate dynamically from the rapid growth of a smaller instability in a cascade up process to explore such a case in the laboratory we study the initiation of dynamic rupture stick slip of a smooth saw cut fault in a 76 mm diameter cylindrical granite laboratory sample at 40 120 mpa confining pressure we use a high dynamic range recording system to directly compare the seismic waves radiated during the stick slip event to those radiated from tiny m 6 discrete seismic events commonly known as acoustic emissions aes that occur in the seconds prior to each large stick slip the seismic moments focal mechanisms locations and timing of the aes all contribute to our understanding of their mechanics and provide us with information about the stick slip nucleation process in a sequence of 10 stick slips the first few microseconds of the signals recorded from stick slip instabilities are nearly indistinguishable from those of premonitory aes in this sense it appears that each stick slip begins as an ae event that rapidly 20 s grows about 2 orders of magnitude in linear dimension and ruptures the entire 150 mm length of the simulated fault we also measure accelerating fault slip in the final seconds before stick slip we estimate that this slip is at least 98 aseismic and that it both weakens the fault and produces aes that will eventually cascade up to initiate the larger dynamic rupture

accelerating moment release of acoustic emission during rock deformation in the laboratory the accelerating moment release amr of seismicity before large earthquakes has been discussed by an increasing number of seismologists over recent years however most of their research is concentrated on theoretical descriptions based on statistical physics in this paper we investigate the laboratory amr phenomenon of acoustic emission ae and attempt to understand the physical mechanism of amr behavior from the point of view of rock deformation ae data used in this paper are from a granitic porphyry gp sample with heterogeneous structure including grains of different size and a naturally healed joint based on a stochastic amr model the microfracturing activity during rock deformation is analyzed three stages pre amr amr and nucleation that cover the entire deformation period are defined according to their different microfracturing features the fractal structure of each stage is investigated our results indicate that the ae activity is highly sensitive to both the stress load and the rock structure the amr stage in which the moderate ae events demonstrated typical amr behaviors features a process of stress concentration and stress transfer on the fault plane the amr stage had a constant stress load condition and was characterized by a much earlier increase of ae rate than the elevation of mean ae magnitude both of which are consistent with the results derived from the damage rheology model ben zion and lyakhovsky 2002 the amr stage was immediately followed by the nucleation stage caused by quasi static dynamic fracture of the main fault therefore regarding the gp sample the amr stage is a long term preparatory process for dynamic fault fracture

fracture in westerly granite under ae feedback and constant strain rate loading nucleation quasi static propagation and the transition to unstable fracture propagation new observations of fracture nucleation are presented from three triaxial compression experiments on intact samples of westerly granite using acoustic emission ae monitoring by conducting the tests under different loading conditions the fracture process is demonstrated for quasi static fracture under ae feedback load a slowly developing unstable fracture loaded at a slow constant strain rate of 2 5 10 6 s and an unstable fracture that develops near instantaneously loaded at a fast constant strain rate of 5 10 5 s by recording a continuous ultrasonic waveform during the critical period of fracture the entire ae catalogue can be captured and the exact time of fracture defined under constant strain loading three stages are observed 1 an initial nucleation or stable growth phase at a rate of 1 3 mm s 2 a sudden increase to a constant or slowly accelerating propagation speed of 18 mm s and 3 unstable accelerating propagation in the 100 ms before rupture the high level of ae activity as seen on the continuous record prevented the location of discrete ae events a lower bound estimate of the average propagation velocity using the time to rupture and the existing fracture length suggests values of a few m s however from a low gain acoustic record we infer that in the final few ms the fracture propagation speed increased to 175 m s these results demonstrate similarities between fracture nucleation in intact rock and the nucleation of dynamic instabilities in stick slip experiments it is suggested that the ability to constrain the size of an evolving fracture provides a crucial tool in further understanding the controls on fracture nucleation

quasi static fault growth and cracking in homogeneous brittle rock under triaxial compression using acoustic emission monitoring this paper describes the localization of deformation acceleration in the period prior to dynamic failure in hornblende schist rock under triaxial compression using acoustic emission ae monitoring rather than stabilize the failure process by controlling axial stress to maintain a constant rate of ae for monitoring ae hypocenters as in previous works e g lockner et al 1991 we have instead developed a rapid multichannel data collection system this enables us to elucidate the dynamics of fault nucleation under condition of constant stress creep loading which is a better approximation to low strain rate condition in the earth and allows both quasi static and dynamic crack growth to occur the waveforms of more than 8000 ae events which occurred mainly during a 15 s period were recorded on 32 channels with a sampling rate of 50 ns and mask time of 200 s hypocentral locations of ae sources revealed that the fault initiated at one end of the core and then propagated into the unfaulted rock with a process zone fault front of intense cracking we found that there were two different processes operating during the quasi static nucleation of a shear fault namely a process zone in front of the fault tip and a wake of damage zone following the process zone the process zone had the following features 1 major tensile cracking 2 low b value and fewer larger events and 3 strong self excitation the mechanism of crack interaction and fault growth was therefore a mutual enhancement on dilatation due to tensile cracking on the other hand the damage zone was characterized by 1 major shear cracking 2 low b value and more larger events and 3 weak self excitation indicating that in the damage zone following the development of a shear fault linkage between cracks became the major mechanism of crack interaction and fault development the mutual changes of b value and self exciting strength observed in our experiments seem to occur as a result of the hierarchy of fault growth which was not observed under slowed down loading conditions therefore our experimental results under a realistic approximation of the dynamic condition of the earth are meaningful for the problems of earthquakes as well as rock bursts

detailed analysis of acoustic emission activity during catastrophic fracture of faults in rock abstract the detailed time space distribution of acoustic emission ae events during the catastrophic fracture of rock samples containing a pre existing joint or potential fracture plane is obtained under triaxial compression using a high speed 32 channel waveform recording system and the results are discussed with respect to the prediction and characterization of catastrophic fault failure ae activity is modeled quantitatively in terms of the seismic b value of the magnitude frequency relation the self excitation strength of the ae time series and the fractal dimension of ae hypocenters consistent with previous studies on rock samples containing a fracture plane with several asperities the present analyses reveal three long term phases of ae activity associated with damage creation on heterogeneous faults each clearly identifiable based on the above parameters a long term decreasing trend and short term fluctuation of the b value in the phase immediately preceding dynamic fracture are identified as characteristic features of the failure of heterogeneous faults based on the experimental results it is suggested that precursory anomalies related to earthquakes and other events associated with rock failure are strongly dependent on the heterogeneity of the fault or rock mass a homogeneous fault or rock mass appears to fracture unpredictably without a consistent trend in precursory statistics while inhomogeneous faults fracture with clear precursors related to the nature of the heterogeneity

fractal analysis of three dimensional spatial distributions of earthquakes with a percolation interpretation although many studies have shown that faults and fractures are self similar over a large range of scales none have tested the fault structure for self similarity in three dimensions in this study earthquake hypocentral locations in central and southern california were used to illuminate three dimensional 3 d fault structures for which we measured the fractal capacity dimension d0 3 d hypocentral distributions from the joshua tree big bear and upland aftershock sequences as well as background seismicity at parkfield were found to be fractal where d0 3 d increased with increasing event density asymptotically approaching a stable value the joshua tree data set stabilized at d0 3 d 1 92 0 02 the parkfield data set asymptotically approached d0 3 d 1 82 and the big bear data set approached d0 3 d 2 01 as a test of the effects of location errors upon the measured value of d0 3 d the upland aftershock data were located with both the southern california hadley and kanamori 1977 h k velocity model and the more accurate hauksson and jones 1991 h j velocity model events located with the h k model asymptotically approached d0 3 d 2 07 and events located with the h j model approached d0 3 d 1 79 suggesting that improved hypocentral locations may decrease the measured fractal dimension one interpretation of our results of d0 3 d 2 0 for all of the hypocentral data is that earthquakes only occur on the percolation backbone of a fault network i e the active part of the network that accommodates finite strain deformation sahimi et al 1993 we show that a percolation model that allows for healing of previously broken bonds is consistent with this interpretation

great earthquakes seismicity gaps and potential for earthquake disaster along the himalaya plate boundary abstract analysis of the space time patterns of seismicity in the himalaya plate boundary has established the existence of three seismic gaps 1 1 the kashmir gap lying west of the 1905 kangra earthquake 2 2 the central gap situated between the 1905 kangra and the 1934 bihar earthquakes 3 3 the assam gap between the 1897 and 1950 assam earthquakes this study has shown that the above great earthquakes were preceded as well as followed by long periods 19 years of decreased levels of seismic activity in the epicentral regions remarkable decrease in the seismicity following the year 1970 has been observed in the western half of the central gap as well as in the assam gap local seismic investigation in the assam gap confirms this feature and the seismicity suggests the existence there of an asperity the local seismic investigations in garhwal himalaya have shown that the small earthquakes are confined to the upper 6 8 km of the crust and may have strike slip motions these earthquakes occur in a region where teleseismically recorded events were few

the seismic hazard at tehri dam abstract the proposed 265 m high tehri dam in india would lie in one of the most hazardous areas in the world with respect to earthquakes a magnitude 8 or greater earthquake may be expected under the dam due to the unique tectonic setting and lack of detailed studies little is known about the expected ground in motion but indirect evidence suggests acceleration of over l g can be expected in these circumstances the dam design should be subject to the most rigorous dynamic analysis

microseismic investigation of mining induced brittle fault activation in a chinese coal mine abstract the process whereby a brittle fault was activated by mining is not only significant for disaster prediction but also for earthquake prediction thus it was necessary to study their activation process in this study stress state ae acoustic emission ms microseismic activities during brittle fault activation stages of brittle fault activation and the relation between ae ms activities and brittle fault parameters were analysed and it was feasible to identify buried brittle faults determine their parameters and activation process based on ms monitoring the no 22517 working face in the dongjiahe coalmine was taken as an example firstly a buried brittle fault was identified in no 22517 working face by the ms monitoring method secondly the buried brittle fault parameters were determined its azimuth angle was 307 5 in the orbital roadway and 357 5 on the haulage roadway its dip angle was 73 and it was a reverse fault thirdly the activation process of the buried brittle fault was determined the buried brittle fault was not affected by the mining activities when the distance from mining activities to the buried brittle fault was over 300 m the disturbance stage was from 300 m to 80 m and the local activation stage from 100 m to 30 m and the whole activation stage around 30 m the b value decreased during the process of brittle fault activation and reached a minimum value at the whole activation stage it was concluded that these changes are related to the stress distribution around the brittle fault the results demonstrated that ms monitoring technology can detect small buried brittle faults ahead of the working face and is also an effective method to study the process and mechanism of brittle fault activation

asperities barriers characteristic earthquakes and strong motion prediction recent results from paleoseismology suggest that earthquakes recurrent on a given fault may often have the same characteristic length and amount of slip stable asperities and barriers which survive many earthquakes can explain these results the activity of volcano usu japan since 1977 which produced a dacite dome with a total upheaval of 180 m offered a great opportunity to study the recurrence behavior of a fault seismologists at hokkaido university revealed a family of repeated earthquakes with nearly the same amount of slip generated from the same fault plane on the crater wall along which the dome moved upward this family can be explained by the existence of a stable asperity on the crater wall and is called the asperity type family they found however another type of family of earthquakes which share the same fault plane but show a great range of variation in the amount of slip the behavior of the latter family can be explained by the presence of weak barriers over a fault plane defined by strong stable barriers and this family is referred to as the barrier type family this type of earthquake model has been used successfully in the interpretation of observed strong motion acceleration spectra from california and the results reveal the stability of local stress drop among different earthquakes the agreement found between local stress drops estimated from strong motion data and those inferred from geological observation supports the possibility for predicting earthquake strong motion directly from geological observation of the causative fault

electro magnetic earthquake bursts and critical rupture of peroxy bond networks in rocks abstract we propose a mechanism for the low frequency electromagnetic emissions and other electromagnetic and electric phenomena which have been associated with earthquakes the mechanism combines the critical earthquake concept and the concept of crust acting as a charging electric battery under increasing stress the electric charges are released by activation of dormant charge carriers in the oxygen anion sublattice called peroxy bonds or positive hole pairs php where a php represents an o 3 x oo yo 3 with x y si 4 al 3 i e o in a matrix of o 2 of silicates we propose that php are activated by plastic deformations during the slow cooperative build up of stress and the increasingly correlated damage culminating in a large critical earthquake recent laboratory experiments indeed show that stressed rocks form electric batteries which can release their charge when a conducting path closes the equivalent electric circuit we conjecture that the intermittent and erratic occurrences of em signals are a consequence of the progressive build up of the battery charges in the earth crust and of their release when crack networks percolate through the stressed rock volumes providing a conductive pathway for the battery currents to discharge em signals are thus expected close to the rupture either slightly before or after that is when percolation is most favored the proposed mechanism should be relevant for the broader understanding of fractoemissions

laboratory micro seismic signature of shear faulting and fault slip in shale this article reports the results of a triaxial deformation experiment conducted on a transversely isotropic shale specimen this specimen was instrumented with ultrasonic transducers to monitor the evolution of the micro seismic activity induced by shear faulting triaxial failure and subsequent fault slip at two different rates the strain data demonstrate the anisotropy of the mechanical quasi static compliance of the shale the p wave velocity data demonstrate the anisotropy of the elastic dynamic compliance of the shale the spatio temporal evolution of the micro seismic activity suggests the development of two distinct but overlapping shear faults a feature similar to relay ramps observed in large scale structural geology the shear faulting of the shale specimen appears quasi aseismic at least in the 0 5 mhz range of sensitivity of the ultrasonic transducers used in the experiment concomitantly the rate of micro seismic activity is strongly correlated with the imposed slip rate and the evolution of the axial stress the moment tensor inversion of the focal mechanism of the high quality micro seismic events recorded suggests a transition from a non shear dominated to a shear dominated micro seismic activity when the rock evolves from initial failure to larger and faster slip along the fault the frictional behaviour of the shear faults highlights the possible interactions between small asperities and slow slip of a velocity strengthening fault which could be considered as a realistic experimental analogue of natural observations of non volcanic tremors and very low frequency earthquakes triggered by slow slip events

immediate foreshocks time variation of the b value abstract we compare b values in the frequency magnitude law for the foreshocks and long term seismicity foreshocks are considered in two non overlapping time intervals preceding a main shock i last hours ii last days statistical analysis of the regional and global earthquake catalogs shows that in either of these intervals b value drops by a half compared to long term seismicity this extends the previous results by molchan and dmitrieva molchan g dmitrieva o 1990 dynamics of the magnitude frequency relation for foreshocks phys earth planet inter 61 99 112 who have found such a drop a few hours before a mainshock our results concern a statistical regularity not necessarily seen for each individual sequence of foreshocks

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

effects of physical fault properties on frictional instabilities produced on simulated faults laboratory studies of large scale simulated faults show that physical properties of the fault specifically normal stress and fault roughness significantly influence the unstable shear failure behavior of the fault in addition the experiments provide insights into important length scaling effects that are useful for assessing concepts such as critical crack length or rupture nucleation dimension stick slip shear failures have been generated along a 2 m long simulated fault in a block of sierra white granite experiments were conducted at normal stresses between 0 6 and 4 mpa with two different prepared roughnesses of the simulated fault a smooth fault with a profilometer measured roughness of 0 2 m and a rough fault with a measured roughness of 80 m high speed records of shear strains and slip velocities clearly show both the propagation of the stick slip failures and details of the local deformations and motions from which slip weakening of the fault at the onset of sliding can be resolved both the dynamic stress drops of the stick slip events and the apparent fracture energies of the events determined from the records of the fault slip weakening increase with increasing normal stress although critical slip weakening displacements are insensitive to normal stress they increase with increased fault roughness such that the apparent fracture energies are also larger on the rough fault than on the smooth fault slip velocities in these experiments are influenced by roughness and are proportional to stress drop although the onset of slip is sharply defined the termination of slip is more gradual without a clear stopping phase measured rupture velocities on the rough fault are lower than those on the smooth fault when a length scale based on rupture nucleation dimensions directly proportional to critical displacements is introduced the data suggest that at fault lengths close to the nucleation lengths rupture velocity and slip velocity increase with increasing fault length

a laboratory acoustic emission experiment under in situ conditions in this paper we revisit acoustic emission ae data from an in situ rock fracture experiment conducted at the underground research laboratory url in manitoba canada the mine by experiment a large scale excavation response test was undertaken at a depth of 420 m and involved the mechanical excavation of a cylindrical tunnel during the experiment a small array of 16 panametrics v103 ae sensors enclosed a 0 7 m 0 7 m 1 1 m rectangular prism of lac du bonnet granite located in the tunnel wall the v103 sensors were later calibrated in the laboratory and a source parameter analysis was undertaken using a spectral fitting method corner frequency and moment magnitude were found to be inside the ranges 250 khz fc 490 khz and 7 5 mw 6 8 respectively static stress drops ranged from 0 3 to 4 mpa which is consistent with large seismicity recorded at the url

observations of premonitory acoustic emission and slip nucleation during a stick slip experiment in smooth faulted westerly granite 1 to investigate laboratory earthquakes stick slip events were induced on a saw cut westerly granite sample by triaxial loading at 150 mpa confining pressure acoustic emissions ae were monitored using an innovative continuous waveform recorder the first motion of each stick slip was recorded as a large amplitude ae signal these events source locate onto the saw cut fault plane implying that they represent the nucleation sites of the dynamic failure stick slip events the precise location of nucleation varied between events and was probably controlled by heterogeneity of stress or surface conditions on the fault the initial nucleation diameter of each dynamic instability was inferred to be less than 3 mm a small number of ae were recorded prior to each macro slip event for the second and third slip events premonitory ae source mechanisms mimic the large scale fault plane geometry

seismic regime in the vicinity of the 2011 tohoku mega earthquake japan m w 9 the 2011 tohoku mega earthquake m w 9 is unique due to a combination of its large magnitude and the high level of detail of regional seismic data the authors analyzed the seismic regime in the vicinity of this event using data from the japan meteorological agency catalog and world databases it was shown that a regional decrease in b value and of the number of main shocks took place in the 6 7 years prior to the tohoku mega earthquake the space time area of such changes coincided with the development of precursor effects in this area as revealed by lyubushin geofiz prots biosfera 10 9 35 2011 from the analysis of microseisms recorded by the broadband seismic network f net in japan the combination of episodes of growth in the number of earthquakes accompanied by a corresponding decrease in the b value and average depth of the earthquakes was observed for the foreshock and aftershock sequences of the 2011 tohoku earthquake some of these anomalies were similar to those observed also post factum by katsumata earth planets space 63 709 712 2011 nanjo et al geophys res lett 39 2012 and huang and ding bull seismol soc am 102 1878 1883 2012 whereas others were not described before the correlation of the periods of growth in seismic activity with the decrease of the average depth of earthquakes can be explained by the growth of fluid activity and the tendency of a penetration of low density fluids into the upper horizons of the lithosphere the unexpectedly strong tohoku mega earthquake with a rather small rupture area caused an unexpectedly high tsunami wave from here it seems plausible that m9 earthquakes with a large tsunami could occur in other subduction zones where such cases were suggested before to be impossible

mainshocks are aftershocks of conditional foreshocks how do foreshock statistical properties emerge from aftershock laws 1 the inverse omori law for foreshocks discovered in the 1970s states that the rate of earthquakes prior to a mainshock increases on average as a power law 1 tc t p of the time to the mainshock occurring at tc here we show that this law results from the direct omori law for aftershocks describing the power law decay 1 t tc p of seismicity after an earthquake provided that any earthquake can trigger its suit of aftershocks in this picture the seismic activity at any time is the sum of the spontaneous tectonic loading and of the activity triggered by all preceding events weighted by their corresponding omori law the inverse omori law then emerges as the expected in a statistical sense trajectory of seismicity conditioned on the fact that it leads to the burst of seismic activity accompanying the mainshock in particular we predict and verify by numerical simulations on the epidemic type aftershock sequence etas model that p is always smaller than or equal to p and a function of p of the b value of the gutenberg richter law gr and of a parameter quantifying the number of direct aftershocks as a function of the magnitude of the mainshock the often documented apparent decrease of the b value of the gr law at the approach to the mainshock results straightforwardly from the conditioning of the path of seismic activity culminating at the mainshock however we predict that the gr law is not modified simply by a change of b value but that a more accurate statement is that the gr law gets an additive or deviatoric power law contribution with exponent smaller than b and with an amplitude growing as a power law of the time to the mainshock in the space domain we predict that the phenomenon of aftershock diffusion must have its mirror process reflected into an inward migration of foreshocks toward the mainshock in this model foreshock sequences are special aftershock sequences which are modified by the condition to end up in a burst of seismicity associated with the mainshock foreshocks are not just statistical creatures but are genuine forerunners of large shocks as shown by the large prediction gains obtained using several of their qualifiers

a review of climate reconstructions from terrestrial climate archives covering the first millennium ad in northwestern europe large changes in landscape vegetation and culture in northwestern nw europe during the first millennium ad seem concurrent with climatic shifts understanding of this relation requires high resolution palaeoclimate reconstructions therefore we compiled available climate reconstructions from sites across nw europe extent research area 10 w 20 e 45 60 n through review of literature and the underlying data to identify supraregional climatic changes in this region all reconstructions cover the period from ad 1 to 1000 and have a temporal resolution of 50 yr this resulted in 22 climate reconstructions proxy records based on different palaeoclimate archives chironomids 1 pollen 6 sphagnum mosses 1 stalagmites 8 testate amoebae 4 and tree rings 2 comparing all temperature reconstructions we conclude that summer temperatures between ad 1 and 250 were relatively high and the period between ad 250 and 700 was characterised by colder summer conditions the period from ad 700 to 1000 was again characterised by warmer summers these temperature shifts occurred in the whole of nw europe in contrast the compilation of precipitation reconstructions does not show a common pattern across nw europe either as a result of a heterogeneous precipitation pattern or the lack of suitable and consistent precipitation proxies

microfracture processes in the breakdown zone during dynamic shear rupture inferred from laboratory observation of near fault high frequency strong motion high frequency velocities are measured during stick slip motion in the immediate vicinity of a fault in a granite sample to reveal the microscopic process taking place in the breakdown zone defined in the slip weakening model it is found that 1 the onset time of the observed strong motion approximately coincides with the local rupture onset time 2 the observed near fault high frequency strong motion duration is approximately proportional to the local breakdown time and 3 the power spectra of strong motions exhibit significant amplitudes at frequencies above the value offmax wherefmax is a cut off frequency relevant to rupturing the breakdown zone these observations suggest that the high frequency motion would be due to the incoherent brittle microfracture whose characteristic scale is much shorter than the breakdown zone size we present a stochastic fault model to synthesize the near fault high frequency velocity waveforms in the model a number of small circular subfaults are distributed randomly on the fault and the rupture onset time of an individual subfault is assumed to be random the main features of the observed velocity waveforms are well explained by this numerical modeling it is concluded that approximately half of the total energy of high frequency elastic waves observed at a point is radiated from the propagating breakdown zone we emphasize the importance of the observation of near fault high frequency strong motions for large shallow earthquakes

damage formation associated with bending under a constant moment abstract deformation within the earth s lithosphere is largely controlled by the rheology of the rock fracture and faulting are characterized by elastic rheologies with brittle mechanisms while folding and flow are characterized by plastic and or viscous rheologies due to ductile mechanisms however it has been recognized that deformation that resembles ductile behavior can be produced within the confines of the brittle lithosphere specific examples are folds that form in the shallow crust steep hinges at subduction zones that are accompanied by seismicity and large scale deformation at plate boundaries in these cases the brittle lithosphere behaves elastically with fracture and faulting yet produces ductile behavior in this paper we attempt to simulate such ductile behavior in elastic materials using continuum damage mechanics engineers utilize damage mechanics to model the continuum deformation of brittle materials we utilize a modified form of damage mechanics that represents a reduction in frictional strength of preexisting fractures and faults we use this empirical approach to simulate the bending of the lithosphere under the application of a constant moment we use numerical simulations to obtain elastostatic solutions for plate bending and where the longitudinal stress at a particular node exceeds a yield stress we apply damage to reduce young s modulus at the node damage is calculated at each time step by a power law relationship of the ratio of the yield stress to the longitudinal stress and the yield strain to the longitudinal strain this results in the relaxation of the material due to increasing damage to test our method we apply our damage rheology to an infinite plate deforming under a constant bending moment we simulate a wide range of behaviors from slow relaxation to instantaneous failure over timescales that span six orders of magnitude using this method stress relaxation produces elastic perfectly plastic behavior in cases where failure does not occur for cases of failure we observe a rapid increase in damage leading to failure analogous to the acceleration of microcrack formation and acoustic emissions prior to failure the changes in the rate of damage accumulation in failure cases are similar to the changes in b values of acoustic emissions observed in triaxial compression tests of fractured rock and b value changes prior to some large earthquakes thus continuum damage mechanics can simulate the phenomenon of ductile behavior due to brittle mechanisms as well as observations of laboratory experiments and seismicity

the preparatory phase of the 2009 mw 6 3 l aquila earthquake by improving the detection capability of low magnitude foreshocks we explored the detection capability of low magnitude earthquakes before the 6 april 2009 mw 6 3 l aquila event by using a matched filter technique and 512 foreshocks as templates we analyzed continuous waveforms from 10 broadband seismic stations in a 60 km radius from the epicenter and for 3 months before the main shock more than 3000 new events mostly located on the main shock fault were detected to define the spatial temporal evolution of micro seismicity the foreshock sequence was active northwest of the mw 6 3 hypocenter in january then migrated toward it at a speed of 0 5 km day in middle of february at that time in a 4 km2 patch close to the main shock nucleation point the cumulative number of earthquakes gradually increased until the mw 6 3 event this patch characterized by a low b value played a key role in controlling the preparation stage to the 2009 l aquila main rupture

source distribution of acoustic emissions during an in situ direct shear test implications for an analog model of seismogenic faulting in an inhomogeneous rock mass abstract we monitored acoustic emission ae events during an in situ direct shear test on a specimen composed of a slate dominant alternation of slate and sandstone measuring 0 5 m long 0 5 m wide and 0 2 m high the test was conducted in a survey tunnel for an underground powerhouse in central japan the ae epicenters located on a fractured plane are compared with the locations of joints and a loosening seam the height distribution of the fractured plane and the horizontal movement of the test block prior to failure we conclude that an initially intact region of rock bounded by the joints and the seam is fractured generating the ae considering these results in connection with asperity models of seismogenic faulting for a subduction zone earthquake the significant contrast of stress conditions derived from the geological inhomogeneity and the uneven fractured plane is analogous to that due to subducted seamounts and horst graben structures on a subducted oceanic plate for an inland earthquake the intact regions on an expected shear plane can be considered to be a portion of the fault asperity that causes strong ground motion while the weakened portion can be considered to correspond to a region of aseismic creep consequently large scale inhomogeneous rock fracturing experiments such as the in situ direct shear test may provide useful insights as analog models of seismogenic faulting furthermore understanding of inhomogeneous rock mass fracturing obtained from such experiments will not only contribute to a better understanding of the mechanism of earthquakes but also provide valuable knowledge for ae monitoring applications in rock engineering such as the predictions of rockbursts in mines and the monitoring of fractures around large underground chambers

intermediate depth earthquakes linked to localized heating in dunite and harzburgite earthquakes can occur at great depths in the earth within subducting tectonic plates deformation experiments suggest these deep earthquakes can be triggered by localized heating of the slabs under high pressures

earthquake nucleation on faults with rate and state dependent strength abstract dieterich j h 1992 earthquake nucleation on faults with rate and state dependent strength in t mikumo k aki m ohnaka l j ruff and p k p spudich editors earthquake source physics and earthquake precursors tectonophysics 211 115 134 faults with rate and state dependent constitutive properties reproduce a range of observed fault slip phenomena including spontaneous nucleation of slip instabilities at stresses above some critical stress level and recovery of strength following slip instability calculations with a plane strain fault model with spatially varying properties demonstrate that accelerating slip precedes instability and becomes localized to a fault patch the dimensions of the fault patch follow scaling relations for the minimum critical length for unstable fault slip the critical length is a function of normal stress loading conditions and constitutive parameters which include dc the characteristic slip distance if slip starts on a patch that exceeds the critical size the length of the rapidly accelerating zone tends to shrink to the characteristic size as the time of instability approaches solutions have been obtained for a uniform fixed patch model that are in good agreement with results from the plane strain model over a wide range of conditions above the steady state stress the logarithm of the time to instability linearly decreases as the initial stress increases because nucleation patch length and premonitory displacement are proportional to dc the moment of premonitory slip scales by d3c the scaling of dc is currently an open question unless dc for earthquake faults is significantly greater than that observed on laboratory faults premonitory strain arising from the nucleation process for earthquakes may by too small to detect using current observation methods excluding the possibility that dc in the nucleation zone controls the magnitude of the subsequent earthquake then the source dimensions of the smallest earthquakes in a region provide an upper limit for the size of the nucleation patch

scaling of the shear rupture process from nucleation to dynamic propagation implications of geometric irregularity of the rupturing surfaces a series of systematic high resolution laboratory experiments have been performed on the nucleation of propagating slip failure on preexisting faults having different surface roughnesses to demonstrate how the size scale and duration of shear rupture nucleation are affected by geometric irregularity of the rupturing surfaces on the basis of the experimental results it has been discussed theoretically how consistently scale dependent physical quantities inherent in shear rupture are scaled the experiments led to conclusive results that the nucleation process consists of two phases phase i an initial quasi static phase and phase ii a subsequent accelerating phase and that the nucleation process is greatly affected by geometric irregularities on the rupturing surfaces in phase i the rupture grows at a slow steady speed which is independent of the rupture growth length l in contrast during phase ii the rupture develops at accelerating speeds v which increase with an increase in l obeying a power law v vs l c n where vs is the shear wave velocity c is the characteristic length representing the geometric irregularity of the fault surfaces and and n are constants 8 87 10 29 and n 7 31 scale dependency of scale dependent physical quantities including the nucleation zone size and its duration is commonly ascribed to scale dependency of the slip dependent constitutive law parameter dc which is in turn governed by c it has been discussed that a unified comprehension can be provided for shear rupture of any size scale if the constitutive law for shear rupture is formulated as a slip dependent law

effect of grain size on fractal structure of acoustic emission hypocenter distribution in granitic rock abstract triaxial compression tests were carried out on inada and oshima granodiorites under constant loading rate conditions at a confining pressure of 50 mpa acoustic emissions ae were monitored and recorded using a multichannel system and the spatial distributions of ae in the two samples were examined and compared as the experimental conditions were identical approximately 3000 and 1000 events were located in oshima fine grained and inada coarse grained granodiorites respectively and the fractal dimensions of their spatial distributions were estimated by grassberger s method the ae hypocenter distribution of the fine grained granodiorite showed a single fractal structure with a fractal dimension of 2 7 whereas that of the coarse grained granodiorite showed a band limited fractal structure the fractal dimension of the spatial distribution of inada granodiorite changed from 2 0 to 2 4 when the length scale r became nearly equal to the average grain size 5 mm of the rock these results imply that the spatial distribution of newly developed microcracks which are the sources of ae and the scatterers of elastic wave can be influenced by the grain of the rock

mapping the frequency magnitude distribution in asperities an improved technique to calculate recurrence times we hypothesize that highly stressed asperities may be defined by mapping anomalously low b values along the san andreas fault near parkfield the asperity under middle mountain with its b 0 46 can be distinguished from all other parts of the fault surface likewise along the calaveras fault the northern asperity of the morgan hill 1984 m6 2 rupture can be identified by its low b of 0 5 as a high stress patch along the fault we add further evidence to the observations that the b value of the frequency magnitude relationship of earthquakes is inversely proportional to stress by showing that it decreases with depth in the parkfield segment of the san andreas and along the calaveras fault in both of these areas b values above and below 5 km depth are 1 2 and 0 8 respectively we propose that probabilistic recurrence times tr based on the seismicity parameters a and b should be calculated from their values within asperities only instead of from the values of the entire rupture area of the maximum expected earthquake the strong patches on faults control the time of rupture because they are capable of accumulating larger stresses than the rest of the fault zone which slips along passively when an asperity breaks therefore no information on tr is contained in the passive fault segments only in the asperities at parkfield the probabilistic estimates of tr derived from the data in the whole rupture and in the asperity only are 72 18 24 and 23 12 18 years respectively compared to the historically observed repeat time of 22 years at morgan hill the tr estimates are 122 46 76 and 78 47 110 years respectively compared to the observed repeat time of 72 years

evolution of b value during the seismic cycle insights from laboratory experiments on simulated faults abstract we investigate the evolution of the frequency magnitude b value during stable and unstable frictional sliding experiments using a biaxial shear configuration we record broadband acoustic emissions ae while shearing layers of simulated granular fault gouge under normal stresses of 2 8 mpa and shearing velocity of 11 m s ae event amplitude ranges over 3 4 orders of magnitude and we find an inverse correlation between b and shear stress the reduction of b occurs systematically as shear stress rises prior to stick slip failure and indicates a greater proportion of large events when faults are more highly stressed for quasi periodic stick slip events the temporal evolution of b has a characteristic saw tooth pattern it slowly drops as shear stress increases and quickly jumps back up at the time of failure the rate of decrease during the inter seismic period is independent of normal stress but the average value of b decreases systematically with normal stress for stable sliding b is roughly constant during shear however it exhibits large variability during irregular stick slip we see a mix of both behaviors b decreases during the interseismic period between events and then remains constant when shear stress stabilizes until the next event where a co seismic increase is observed our results will help improve seismic hazard assessment and ultimately could aid earthquake prediction efforts by providing a process based understanding of temporal changes in b value during the seismic cycle

multifractal analysis of earthquakes multifractal properties of the epicenter and hypocenter distribution and also of the energy distribution of earthquakes are studied for california japan and greece the calculateddq q curves the generalized dimension indicate that the earthquake process is multifractal or heterogeneous in the fractal dimension japanese earthquakes are the most heterogeneous and californian earthquakes are the least since the earthquake process is multifractal a single value of the so called fractal dimension is not sufficient to characterize the earthquake process studies of multifractal models of earthquakes are recommended temporal changes of thedq q curve are also obtained for californian and japanese earthquakes thedq q curve shows two distinctly different types in each region the gentle type and the steep type the steeptype corresponds to a strongly heterogeneous multifractal which appears during seismically active periods when large earthquakes occur dq for smallq or negativeq is considerably more sensitive to the change in fractal structure of earthquakes thandq forq 2 we recommend use ofdq at smallq to detect the seismicity change in a local area

on the spatio temporal distribution of acoustic emissions in two granitic rocks under triaxial compression the role of pre existing cracks we used a new rapid data acquisition system to examine the role of pre existing crack density in determining the mechanical properties of crystalline rock two similar coarse grained samples tsukuba granite tg and granitic porphyry gp were used in triaxial compression tests the main difference between the two rocks is that tg contains main large pre existing cracks whereas gp is almost crack free in our tests the two rocks showed significantly different behaviors in gp before the fault nucleation ae activity was low and showed increasing b values with increasing stress but in tg a large number of aes were observed and showed short term b value anomalies mutual fluctuations on a decreasing background the short term fluctuations of b values are closely correlated with those of the spatio temporal clustering of ae locations our results demonstrate 1 pre existing cracks are the most dominant factor of all heterogeneities that govern the fault nucleation process in laboratory rock samples 2 failure predictability is dependent on the pre existing crack density

higher order interrelations between seismogenic structures and earthquake processes abstract aki k 1992 higher order interrelations between seismogenic structures and earthquake processes in t mikumo k aki m ohnaka l j ruff and p k p spudich guest editors earthquake source physics and earthquake precursors tectonophysics 211 1 12 to advance our understanding of higher order smaller scale interrelations between the fault zone structure and the earthquake process we start with the observation that the source parameters of major california earthquakes deviate systematically from the self similarity this departure from the self similarity is interpreted in terms of both the specific barrier model and the asperity model the asperity model however is found to be inconsistent with the following observations 1 sharp impulsive displacements waveform in the direction perpendicular to the fault trace 2 the complementary relationship between fault slip and aftershock and 3 existence of barriers in the creeping segment of the san andreas fault the application of the specific barrier model on the other hand leads to a predominant subevent crack size of a few hundred meters in the creeping segment this result is consistent with the negative correlation between coda q 1 and b value observed in the stone canyon area for 1 5 3 temporal increase in coda q 1 is sometimes accompanied by an increase in the rate of surface deformation but not always so this is attributed to the erratic coupling between the creeping brittle region and the overlying brittle region the applicability of the conclusions obtained from california earthquakes to other regions is investigated using the observed scaling laws of seismic source spectra and it is suggested that the crack size of the creeping brittle zone may vary regionally from a few hundred meters to a few kilometers as an alternative to the widely held view that the aseismic creep in the plate boundary may occur as a giant slow earthquake our result suggests that it may be occurring as small fractures with scale lengths from a few hundred meters to a few kilometers

aftershock patterns and main shock faulting we have compared aftershock patterns following several moderate to large earthquakes with the corresponding distributions of coseismic slip obtained from previous analyses of the recorded strong ground motion and teleseismic waveforms well located aftershock hypocenters are projected onto the main shock fault plane and their positions are examined relative to the zones of coseismic displacement indicated by the estimated distributions of main shock slip we also examine the aftershock focal mechanisms when these data are available in an attempt to identify possible patterns of secondary faulting within the aftershock zone our results are consistent with a hypothesis of aftershock occurrence that requires a secondary redistribution of stress following primary failure on the earthquake fault aftershocks following the earthquakes examined in this study occur mostly outside of or near the edges of the source areas indicated by the patterns of main shock slip the spatial distribution of aftershocks reflects either a continuation of slip in the outer regions of the areas of maximum coseismic displacement or the activation of subsidiary faults within the volume surrounding the boundaries of main shock rupture

mapping asperities by minima of local recurrence time san jacinto elsinore fault zones minima of the local recurrence time tl m are correlated with the locations of historical main shocks in the san jacinto sj elsinore e fault zones of southern california we define tl m as the recurrence time calculated from the local b and a values of the frequency magnitude distribution earthquakes within 6 and 10 km from each point in the sj and e fault zones respectively we propose that anomalously low tl m values map asperities out of six historic main shocks 1899 1968 five ruptured substantial parts of four asperities mapped by our method which uses solely the modern earthquake catalog m 1 2 1981 0 1998 8 we estimate the probability for this correlation to occur at random as 10 2 to 10 3 depending on the scenario chosen it appears that the minima in tl m are tied to minima in b values more than to maxima in a values thus locations of low b values can also be used as an indication where asperities may be located and where main shocks are most likely the anza gap a segment of the san jacinto fault with low a values is mapped as an asperity by our method the heterogeneity in b values is strong throughout the study area the b values range from 0 5 to 1 8 over distances of 10 km volumes with approximately constant b values have radii of r 8 6 km our results suggest that detailed mapping of b values and local recurrence times in volumes with a few kilometers radius reveals important information about the local seismic hazard hitherto untapped by conventional seismicity analyses