alignment of near surface inclusions and appropriate crack geometries for geothermal hot dry rock experiments ubiquitous splitting of seismic shear waves indicates that most rocks in the upper half of the crust are pervaded by stress aligned fluid filled inclusions called eda cracks these inclusions are expected to be aligned perpendicular to the minimum compressional stress by stress relationships similar to those aligning industrial hydraulic fractures at depths where the overburden stress is sufficiently large typically below a few hundred metres this minimum stress is usually horizontal so that the eda cracks and hydraulic fractures are typically aligned vertically striking parallel or subparallel to the direction of maximum compression this is confirmed by the polarizations of the split shear waves along raypaths at depth in the crust at the free surface however the vertical stress is zero or approximately zero and cracks and hydraulic fractures at shallow depths in intact rock tend to be horizontal thus the directions of minimum stress and the orientations of hydraulic fractures are likely to swing through 90 near the surface of the earth since the behaviour of cracks and stress is often crucial to drilling operations the rotation of the crack and stress geometry near surface has important implications particularly for optimizing hydrocarbon production and geothermal reservoir management consequently evidence gained from experiments for example in hot dry rock geothermal heat extraction in inappropriate crack geometries at shallow depths may not be valid when applied to other crack and stress geometries at depth in hot rock

temporal variation of seismic b values beneath northeastern japan island arc 1 analysis of a high quality seismic catalog reveals that the average of seismic b values in the crust beneath most part of northeastern japan island arc decreased from 0 86 between 1984 and 1990 to 0 73 between 1991 and 1995 the two areas with the largest decrease are found to be in the same areas where the coupling between the north american and the pacific plates is the highest as suggested by a recent geodetic study in the same time period the annual seismic moment release increased by 10 times in addition there seems to be a corresponding increase in volcanic activities in the same area one of the most likely interpretations for the observations is an increase in the subduction rate starting from 1991 the timing of this possible increase in subduction rate is consistent with an apparent increase in global seismic activity

cycling of calcite in hard water lakes of different trophic states based on oxygen o2 ph calcium ca2 and carbonate co 22 3 sediment pore water concentration profiles we compare the benthic dissolution of autochthonous calcite in oligotrophic lake lucerne and eutrophic lake sempach despite their difference in trophic state the two lakes have similar benthic o2 regimes because l sempach is artificially oxygenated this peculiarity enabled the study of the direct effect of trophic state on benthic calcite dissolution although areal benthic o2 fluxes did not differ o2 penetrated deeper into the sediment of the oligotrophic l lucerne where most organic matter om 96 was degraded aerobically whereas in l sempach aerobic and anaerobic decomposition contributed about equal amounts to the biogenic carbon dioxide production release rates of bicarbonate from l sempach sediments exceeded those of l lucerne nearly twofold the hco 2 c a2 ratio of benthic fluxes was 3 7 in l lucerne compared to 10 3 in l sempach suggesting that in l sempach most of the released hco 2 did not originate from calcite dissolution furthermore benthic calcite dissolution in l lucerne exceeded that in l sempach by two fold despite lower ph values in the pore water of l sempach differences in benthic microbial decomposition of om and redissolution of calcite crystals are explained by the longer residence time of om and calcite in the oxic sediment layer of the oligotrophic lake and the larger weight specific surface area of its smaller autochthonous calcite crystals we suggest that trophic state and o2 supply to the sediment are key parameters controlling the cycling of calcite and organic carbon in lakes the cycling of calcium ca 2 and carbonate species hco 2 22 3 is a prominent seasonal process in hard water lakes it is driven by biogenic calcite precipitation and its redissolution related to aerobic decomposition of organic matter although the processes controlling calcite precipitation are relatively well understood the factors controlling redissolution of calcite are not the goal of this study was to help elucidate those factors and thus better understand the cycling of two biogeochemically important elements calcium ca and carbon c in freshwater systems most calcite formed in hard water lakes precipitates during the early algal bloom in spring and mid summer when nutrient enriched surface waters stimulate intense carbon dioxide co2 assimilation the consequent increase in ph shifts the hco 2 co 22

dynamic seismic response of a stable intraplate region to a megathrust earthquake abstract the 2011 m9 0 tohoku oki megathrust earthquake produced strong ground motions with a peak ground acceleration of 1 52 cm s 2 in the korean peninsula inducing large dynamic stress changes in the crust sixty one triggered earthquakes with magnitudes of 0 5 2 5 including 17 unusual spatially clustered events were identified from continuous seismic record sections of dense seismic networks for 18 h following the megathrust earthquake the triggered earthquakes occurred in regions of high seismicity the earthquake occurrence frequency increased after the megathrust earthquake keeping the gutenberg richter b value invariant the seismic occurrence rates decreased with time following a modified omori law the focal mechanism solutions of triggered earthquakes are consistent with those observed before the megathrust earthquake an unusual earthquake swarm displays apparent migration with a speed of 28 6 4 4 m h the changes in pore fluid pressure induced by strong seismic waves may have caused the triggering of earthquakes the duration and strength of dynamic triggering may be highly dependent on the magnitude and distance of megathrust earthquake

auto correlation analysis of coda waves from local earthquakes for detecting temporal changes in shallow subsurface structures the 2011 tohoku oki japan earthquake for monitoring temporal changes in subsurface structures i propose to use auto correlation functions of coda waves from local earthquakes recorded at surface receivers which probably contain more body waves than surface waves use of coda waves requires earthquakes resulting in decreased time resolution for monitoring nonetheless it may be possible to monitor subsurface structures in sufficient time resolutions in regions with high seismicity in studying the 2011 tohoku oki japan earthquake mw 9 0 for which velocity changes have been previously reported i try to validate the method kik net stations in northern honshu are used in this analysis for each moderate earthquake normalized auto correlation functions of surface records are stacked with respect to time windows in the s wave coda aligning the stacked normalized auto correlation functions with time i search for changes in phases arrival times the phases at lag times of 1 s are studied because changes at shallow depths are focused temporal variations in the arrival times are measured at the stations based on the stretching method clear phase delays are found to be associated with the mainshock and to gradually recover with time the amounts of the phase delays are 10 on average with the maximum of about 50 at some stations the deconvolution analysis using surface and subsurface records at the same stations is conducted for validation the results show the phase delays from the deconvolution analysis are slightly smaller than those from the auto correlation analysis which implies that the phases on the auto correlations are caused by larger velocity changes at shallower depths the auto correlation analysis seems to have an accuracy of about several percent which is much larger than methods using earthquake doublets and borehole array data so this analysis might be applicable in detecting larger changes in spite of these disadvantages this analysis is still attractive because it can be applied to many records on the surface in regions where no boreholes are available

three dimensional structure of vp vs and vp vs beneath northeastern japan implications for arc magmatism and fluids we estimated both p v p and s wave velocity v s structures beneath northeastern japan by applying a tomographic method to 169 712 p and 103 993 s wave arrival time data from 4338 local events the average value of v p v s ratio is 1 69 in the upper crust 1 75 in the lower crust and 1 77 in the uppermost mantle these differences in v p v s ratio may mainly reflect the lithological variations with depth low v p low v s and high v p v s zones are extensively distributed along the volcanic front in the uppermost mantle and are downward to the back arc side in the mantle wedge here the low v p low v s and high v p v s values are interpreted because of partial melting materials which imply the presence of a vast amount of melt in the uppermost mantle in the lower crust low v p low v s and high v p v s zones are not continuously visible along the volcanic front but are confined to individual volcanic areas which suggests that melting of lower crustal materials occurs just beneath each active volcano in contrast the upper crust beneath active volcanoes exhibits low v p low v s and low v p v s these results suggest that the partial melting zones under northeastern japan spread out from the uppermost mantle along the volcanic front up to the midcrust right beneath active volcanoes the low v p low v s and low v p v s features in the upper crust suggest the existence of h 2 o rather than melt right beneath active volcanoes

changes of mesozoic vegetation and the extinction of dinosaurs abstract the structure of mesozoic vegetation is outlined as consisting of evergreen brachyphyllous forests deciduous forests dominated by phoenicopsis and then by parataxodium cycadophyte sclerophyllous shrublands and fern marshes warm warm temperate and temperate zones are indicated for successive periods dinosaur localities are situated mostly in the warm and warm temperate zones but a few of them fall in the temperate zone feeding habits of dinosaurs are inferred from combined evidence of depositional environments surrounding vegetation and stomach contents it is suggested that dinosaurs were associated mainly with open vegetation such as shrublands and marshes capable of supporting large populations of herbivores the shrubland and marsh dinosaur communities are provisionally indicated the latter comprising diplodocids stegosaurs and hadrosaurids replacements of dinosaur communities were concomitant with major vegetational changes forestation at the end of cretaceous time might have played an important role in the final extinction

seismic evidence of partial melt within a possibly ubiquitous low velocity layer at the base of the mantle three source regions show evidence of a low velocity layer that is less than 15 kilometers thick on top of the core mantle boundary and require about a 3 1 ratio of shear to compressional velocity reduction which is consistent with partial melt layer thickness is correlated with travel time residuals of the seismic phases that are most sensitive to the lowermost mantle velocity these observations suggest that the layer is thinned beneath downwellings but is present everywhere along the core mantle boundary low viscosity accompanying partial melt can localize the upwelling of warmed mantle making the low velocity layer a plausible source of mantle plumes

local deformations around volcanoes associated with the 2011 off the pacific coast of tohoku earthquake 1 an mw 9 0 great earthquake struck northeast japan on 11 march 2011 causing crustal deformation of 1 to 2 m in volcanic areas we applied synthetic aperture radar interferometry using phased array type l band synthetic aperture radar on the alos satellite to investigate local deformation around volcanoes associated with the earthquake we estimated the fault slip distribution along the trough based on obtained interferograms and crustal deformation from geonet and the estimated fault model explained the observed coseismic deformations well the residual suggested local deformation around the akita komagatake kurikoma zao azuma and nasu volcanoes their deformations were obtained from independent synthetic aperture radar pairs additionally deformations in the kurikoma zao and azuma volcanoes were confirmed by geonet data no geonet stations are located in the deformation areas of other volcanoes these facts indicate that the obtained local deformations must be actual deformations rather than noise our hypothesis is that coseismic extensional deformation concentrates in the soft medium under a volcano e g magma and its surrounding rock and that this deformation has caused local deformation with subsidence to validate this hypothesis we carried out numerical experiments using the finite element method for a soft medium under a volcano distributions of observed local deformations stretch in the direction of the minor principal axis of strain and such distributions were obtained in this experiment indicating that the hypothesis is plausible conceivably such a concentration of coseismic deformation in a magma chamber may induce a volcanic eruption

vp vs ratios in the upper crust of the southern korean peninsula and their correlations with seismic and geophysical properties abstract the p and s velocity ratio v p v s is a seismic property that is convertible to poisson s ratio a widely analyzed physical property of elastic materials the lateral variation in the v p v s ratios of the upper crust of the southern korean peninsula is investigated based on the travel times of p and s waves of local events with epicentral distances of 50 km or less and focal depths of 25 km or less the dense seismic networks in the korean peninsula allow us to investigate the regional variation of v p v s ratios these v p v s ratios are estimated to be 1 60 1 91 with an average of 1 69 the v p v s ratios are as high as 1 73 1 91 in the gyeongsang basin jeju island and offshore region of the eastern okcheon belt but have relatively low values of 1 64 1 72 in precambrian massif regions the stability of the v p v s ratios is tested with randomly resampled travel time data the results of which suggest nearly constant v p v s ratios with increasing depth in the upper crust the influences of plausible errors on origin times and arrival times are quantified to verify the v p v s estimates the v p v s ratios are correlated with geological and tectonic structures comparisons with known seismic and geophysical properties suggest that structural features observed on the surface may extend at least to the mantle lid

seismic waveform attributes before and after the loma prieta earthquake scattering change near the earthquake and temporal recovery during 1987 1995 several clusters of nearly identical seismic events multiplets occurred near the loma prieta source region these multiplets allow us to investigate and demonstrate spatial and temporal changes in seismic wave character associated with the 1989 loma prieta main shock for seismogram pairs we use a moving window technique to compute coherencies depending on lapse time and frequency post loma prieta events have reduced coherencies with pre loma prieta events in a spatially limited region close to the loma prieta hypocenter while other paths remain nearly unaffected these changes gradually recover within a time interval of 5 years after the loma prieta earthquake a possible explanation for the time dependence is coseismically opened cracks which cause scattering increase for wavefields after the loma prieta event postseismic relaxation processes such as crack healing fluid diffusion or after deformations lead to progressive closure of these cracks with time after the main shock thus the scattering properties of the local crust approach the pre main shock state

randomness of megathrust earthquakes implied by rapid stress recovery after the japan earthquake the 2011 tohoku oki earthquake released stress within a subduction zone analysis of seismic data shows that stresses returned to pre quake levels within a few years implying that large quakes could occur more often than previously thought

continuous monitoring of propagation velocity of seismic wave using across 1 temporal variations in the p and s wave travel times were continuously monitored using across which is a newly developed system for utilizing accurately controlled continuous sinusoids for seismic exploration we made an experiment lasting for 15 months at a site near the nojima fault which ruptured during the 1995 kobe earthquake m7 2 the elastic waves emitted from the across vibrators located at the surface were observed with seismometers at 800 m and 1700 m depth the long term variations of about 2 ms for both the p and s waves were observed during the 15 month experiment the major cause of these variations is identified to be that of a near surface property which changes the near source vibration the variations in the deeper structures estimated after the reduction of the near source variation were about 0 5 ms an s wave delay of about 1 ms was detected due to the 2000 western tottori earthquake m6 6

prevalence of viscoelastic relaxation after the 2011 tohoku oki earthquake seafloor global positioning system observations immediately after the great 2011 tohoku oki earthquake provide unambiguous evidence for the dominant role of viscoelastic relaxation in short term postseismic deformation rather than just afterslip on the fault as is commonly assumed this paper presents revised estimates of the afterslip following the 2011 tohoku oki earthquake based on seafloor gps observations made immediately after the earthquake tianhaozhe sun et al obtain unambiguous evidence for the dominant role of viscoelastic relaxation in short term postseismic deformation rather than elastic afterslip on the fault as is commonly assumed they conclude that models which erroneously assume an elastic earth substantially overestimate afterslip downdip of the rupture zone and underestimate afterslip updip after a large subduction earthquake crustal deformation continues to occur with a complex pattern of evolution1 this postseismic deformation is due primarily to viscoelastic relaxation of stresses induced by the earthquake rupture and continuing slip afterslip or relocking of different parts of the fault2 3 4 5 6 when postseismic geodetic observations are used to study earth s rheology and fault behaviour it is commonly assumed that short term a few years deformation near the rupture zone is caused mainly by afterslip and that viscoelasticity is important only for longer term deformation6 7 however it is difficult to test the validity of this assumption against conventional geodetic data here we show that new seafloor gps global positioning system observations immediately after the great tohoku oki earthquake provide unambiguous evidence for the dominant role of viscoelastic relaxation in short term postseismic deformation these data reveal fast landward motion of the trench area opposing the seaward motion of gps sites on land using numerical models of transient viscoelastic mantle rheology we demonstrate that the landward motion is a consequence of relaxation of stresses induced by the asymmetric rupture of the thrust earthquake a process previously unknown because of the lack of near field observations our findings indicate that previous models assuming an elastic earth will have substantially overestimated afterslip downdip of the rupture zone and underestimated afterslip updip of the rupture zone our knowledge of fault friction based on these estimates therefore needs to be revised

high vp vs ratio saturated cracks or anisotropy effects 1 we measured vp vs ratios of thermally cracked westerly granite thermally cracked carrara marble and 4 porosity fontainebleau sandstone for an effective mean pressure ranging from 2 to 95 mpa samples were fluidsaturated alternatively with argon gas and water 5 mpa constant pore pressure the experimental results show that at ultrasonic frequencies vp vs ratio of water saturated specimen never exceeded 2 15 even at effective mean pressure as low as 2 mpa or for a lithology for which the poisson s ratio of minerals is as high as 0 3 calcite in order to check these results against theoretical models we examine first a randomly oriented cracked medium with dispersion but without anisotropy and second a medium with horizontally aligned cracks with anisotropy but without dispersion the numerical results show that experimental data agree well with the first model at high frequency vp vs ratios range from 1 6 to 1 8 in the dry case and from 1 6 to 2 2 in the saturated case the second model predicts both vp sv and vp sh to vary from 1 2 to 3 5 depending on the raypath angle relative to the crack fabric in addition perpendicular to the crack fabric a high vp vs ratio is predicted in the absence of shear wave splitting from these results we argue the possibility that high vp vs ratio 2 2 as recently imaged by seismic tomography in subduction zones may come from zones presenting important crack anisotropy the cumulative effects of crack anisotropy and high pore fluid pressure are required to get vp vs ratios above 2 2 citation wang x q a schubnel j fortin e c david y gueguen and h k ge 2012 high vp vs ratio saturated cracks or anisotropy effects geophys res lett 39 l11307 doi 10 1029 2012gl051742

tomographic inversion for three dimensional velocity structure at mount st helens using earthquake data tomographic inversion is applied to 17 659 p phase observations at 21 stations from 2023 earthquakes in the vicinity of mount st helens to study the three dimensional velocity structure block size for the inversion is 2 km horizontally and 2 km or more vertically locations of hypocenters are assumed known and are based on a reference one dimensional layered velocity structure a conjugate gradient technique lsqr is used to invert the large sparse system of equations augmented by regularization with a laplacian roughening matrix resolution is estimated by computing the impulse response of the inversion for various critical locations and uncertainties of the estimates are determined by a jackknife approach the results of the inversion show a remarkable correlation with known geological and geophysical features the spirit lake and spud mt plutons are characterized by high velocity regions extending to approximately 9 km depth the st helens seismic zone a band of diffuse seismicity extending nnw from the volcano is evident as a prominent low velocity lineation the change in character of the velocity anomalies south of st helens corresponds well with the near cessation of seismic activity there a low velocity anomaly beneath the crater from 6 to 16 km depths may represent modern magma accumulations

damage and recovery of calcite rocks deformed in the cataclastic regime compressional and shear wave velocities have been measured during the experimental deformation of carrara marble and solnhofen limestone in the cataclastic regime both in dry and wet conditions at room temperature measurements were performed under hydrostatic conditions up to 260 mpa confining pressure and 10 mpa pore pressure during triaxial loading at the constant strain rate of 10 s as well as during differential stress relaxation during a full cycle our results show that the seismic velocities first increase as effective mean stress increases however when the stress onset of cataclastic deformation was reached elastic velocities showed rapid decrease due to stress induced damage in the rock during stress relaxation tests we observed an increase of elastic velocities with time which suggested a fast recovery of the microstructure a substantial and rapid drop in the velocities occurred when reloading suggesting that the previous recovery was only transient subsequent relaxation tests showed other marked increases in velocities these experimental results suggest that during the deformation of low porosity calcite rich rocks dilatant crack opening and frictional sliding and compaction micromechanism pore closure compete evolutions of elastic properties mainly sensitive to crack density and macroscopic volumetric strain more sensitive to porosity are therefore not systematically correlated and depend on the strain rate the solid stress conditions and the

azimuthal anisotropy of rayleigh waves in the crust in southern tohoku area japan to reveal seismic anisotropy within the crust in the southern tohoku area japan we analyze the azimuthal anisotropy of rayleigh waves in the frequency range of 40 65 mhz rayleigh wave anisotropy is estimated by array analysis of 102 teleseismic events that occurred between 2007 and 2014 the frequency variation of the estimated azimuthal anisotropy indicates depth variation of the seismic anisotropy within the crust 1 north south fast velocity direction around the upper crust and 2 trench normal fast velocity direction in the deeper crust we also conduct a time lapse analysis of rayleigh wave anisotropy to demonstrate the stability of the estimated anisotropy in time and to estimate possible changes in seismic anisotropy associated with the 2011 tohoku oki earthquake we demonstrate that the azimuthal location of teleseismic events influences the accuracy of time lapse analysis moreover a decrease of azimuthal anisotropic ratio in time lapse results might be related to changes in the velocity structure associated with release of crustal stress during the tohoku oki earthquake

cracked media poisson s ratio and the structure of the upper oceanic crust summary theoretical models of water filled cracks within a solid are in general agreement and indicate that the poisson s ratio of the composite material will typically increase for thin cracks with aspect ratios less than a but will decrease for thick cracks with aspect ratios between and i near spherical pores cause little change in poisson s ratio this is true both for randomly oriented isotropic crack models and at certain directions for aligned crack models which predict seismic anisotropy observed anomalous values of poisson s ratio in oceanic layer 2 can often be explained using these models as an effect of cracks and do not necessarily require the presence of rocks of unusual composition in particular the low poisson s ratios reported by spudich orcutt 1980 and au clowes 1984 can approximately but not always exactly be fitted with a model consisting of thick cracks within higher poisson s ratio rock more typical of the upper oceanic crust however this interpretation is near the limit of existing theories of cracked material so other explanations for the anomalous observations must also be considered

stress before and after the 2011 great tohoku oki earthquake and induced earthquakes in inland areas of eastern japan 1 stress fields in inland areas of eastern japan before and after the tohoku oki earthquake were estimated by inverting focal mechanism data before the earthquake s1 axis was oriented ew in tohoku but nw se in kanto chubu the stress fields changed after the earthquake in northern tohoku and in southeastern tohoku near iwaki city where the orientations of the principal stresses became approximately the same as the orientations of the static stress change associated with the earthquake this indicates that differential stress magnitudes in these areas before the earthquake were smaller than 1 mpa the stress field did not change in central tohoku even though the stresses loaded after the earthquake had nearly reversed orientations which indicates that the differential stress magnitudes there were significantly larger than 1 mpa in kanto chubu stresses having nearly the same orientations as the background stresses were loaded after the earthquake and the stress fields did not change as expected this may have caused very high induced seismicities in kanto chubu citation yoshida k a hasegawa t okada t iinuma y ito and y asano 2012 stress before and after the 2011 great tohoku oki earthquake and induced earthquakes in inland areas of eastern japan geophys res lett 39 l03302

fluid driven seismicity activation in northern nagano region after the 2011 m9 0 tohoku oki earthquake the dynamic triggering of earthquakes is well documented however the underlying physical mechanisms remain obscure here we analyze the seismicity in northern nagano central japan following the tohoku oki quake until the occurrence 13 h later of an mw6 2 local earthquake we use waveform detection techniques to identify 17 times more earthquakes than those in the japan meteorological agency catalog the activation of seismicity in the epicentral region of the mw6 2 event is weak and delayed culminating with the occurrence of the moderate shock preceded by two small foreshocks the seismicity activation to the south is shallower abundant and starts during the passage of tohoku oki surface waves of high dynamic stresses the early activation occurs in areas of relatively high near surface fluid temperature indicating that the dynamic triggering is likely caused by excitation of geothermal crustal fluids the mw6 2 northern nagano earthquake might have been delay triggered by fluid migration from a deep source

trench parallel crustal anisotropy along the trench in the fore arc region of japan in northeastern japan the pacific plate is descending beneath the north american plate it is generally understood that trench normal principal stress is dominant in the crust along the japanese island arc because the stress field is controlled by the force of the subducting slab observations of shear wave splitting using crustal earthquakes reveal a marked lateral variation in fast polarization direction with distance from the trench trench normal and trench parallel fast polarization directions are observed on the back arc and fore arc sides respectively in this study two dimensional finite element modeling with subducting slab was conducted to investigate the interseismic stress field during earthquake cycles taking into account linear viscoelasticity in the model trench normal compression is found to dominate in the island arc region however an extensional field appears in the shallow upper crust of the fore arc region during earthquake cycles the trench parallel crustal anisotropy can be explained by this extensional field

minimum magnitude of completeness in earthquake catalogs examples from alaska the western united states and japan we mapped the minimum magnitude of complete reporting m c for alaska the western united states and for the junec earthquake catalog of japan mc was estimated based on its departure from the linear frequency magnitude relation of the 250 closest earthquakes to grid nodes spaced 10 km apart in all catalogs studied mc was strongly heterogeneous in offshore areas the mc was typically one unit of magnitude higher than onshore on land also mc can vary by one order of magnitude over distance less than 50 km we recommend that seismicity studies that depend on complete sets of small earthquakes should be limited to areas with similar mc or the minimum magnitude for the analysis has to be raised to the highest com mon value of mc we believe that the data quality as reflected by the mc level should be used to define the spatial extent of seismicity studies where mc plays a role the method we use calculates the goodness of fit between a power law fit to the data and the observed frequency magnitude distribution as a function of a lower cutoff of the magnitude data mc is defined as the magnitude at which 90 of the data can be modeled by a power law fit mc in the 1990s is approximately 1 2 0 4 in most parts of california 1 8 0 4 in most of alaska aleutians and panhandle excluded and at a higher level in the junec catalog for japan various sources such as ex plosions and earthquake families beneath volcanoes can lead to distributions that cannot be fit well by power laws for the hokkaido region we demonstrate how neglecting the spatial variability of m c can lead to erroneous assumptions about deviations from self similarity of earthquake scaling

evidence from shear wave splitting for the restriction of seismic anisotropy to the upper crust the existence of anistropy in the propagation speed of seismic waves through the earth s crust has been attributed to the non random alignment of microcracks in the crust1 for sparsely distributed parallel vertical cracks perturbation theory predicts the splitting of a shear wave into two orthogonally polarized waves2 4 here we present extremely clear evidence for shear wave splitting in three component seismograms from crustal and sub crustal microearthquakes recorded in the shikoku district of japan quantitative analysis of travel time differences between split shear waves leads to the conclusion that the observed anisotropy is limited to the upper crust shallower than 10 15 km this model is consistent with recent results from reflection seismology5 and implies that microcrack density or orientation changes from the upper to the lower crust

temporal changes of surface wave velocity associated with major sumatra earthquakes from ambient noise correlation abstract detecting temporal changes of the medium associated with major earthquakes has implications for understanding earthquake genesis here we report temporal changes of surface wave velocity over a large area associated with 3 major sumatra earthquakes in 2004 2005 and 2007 we use ambient noise correlation to retrieve empirical green s function egf of surface waves between stations because the process is completely repeatable the technique is powerful in detecting possible temporal change of medium we find that 1 excellent station pair psi in indonesia and chto in thailand shows significant time shifts up to 1 44 s after the 2004 and 2005 events in the rayleigh waves at 10 20 s but not in the love waves suggesting that the rayleigh time shifts are not from clock error the time shifts are frequency dependent with the largest shifts at the period band of 11 16 s we also observe an unusual excursion 1 month before the 2004 event we obtain a total of 17 pairs for june 2007 to june 2008 which allow us to examine the temporal and spatial variation of the time shifts we observed strong anomalies up to 0 68 s near the epicenter after the 2007 event but not in the region further away from the source or before the event or 3 months after the event the observations are interpreted as stress changes and subsequent relaxation in upper mid crust in the immediate vicinity of the rupture and the broad area near the fault zone

the 2011 magnitude 9 0 tohoku oki earthquake mosaicking the megathrust from seconds to centuries geophysical observations from the 2011 moment magnitude m w 9 0 tohoku oki japan earthquake allow exploration of a rare large event along a subduction megathrust models for this event indicate that the distribution of coseismic fault slip exceeded 50 meters in places sources of high frequency seismic waves delineate the edges of the deepest portions of coseismic slip and do not simply correlate with the locations of peak slip relative to the m w 8 8 2010 maule chile earthquake the tohoku oki earthquake was deficient in high frequency seismic radiation a difference that we attribute to its relatively shallow depth estimates of total fault slip and surface secular strain accumulation on millennial time scales suggest the need to consider the potential for a future large earthquake just south of this event

healing microstructures of experimental and natural fault gouge 1 the healing of fault gouge was studied by examining microstructures of naturally and experimentally produced granitoid fault rock we performed deformation experiments on intact granitoid rock samples at t 300 500 c pc 500 mpa and 1 2 10 4 1 3 10 7 s 1 with 0 2 wt h2o added healing experiments were carried out on deformed samples at t 200 500 c pc 500 mpa for 4 h to 14 days under hydrostatic and nonhydrostatic conditions the grain size distributions gsd of the deformed samples were quantified using the d value slope of log frequency log radius of the gsd for quartz and feldspar fault gouge healing causes a decrease in the d value from 2 0 to 1 5 the time dependence of the d decrease is described by a hydrostatic healing law of the form d d t df a e t the results of the laboratory experiments were compared to three natural fault systems 1 nojima fault zone japan 2 fault zones in the black forest germany and 3 orobic thrust italian alps natural and experimental gouges have similar d values healing is only observed in monomineralic aggregates polymineralic i e mixed fault gouges retain their high d value after extended healing times because grain growth is inhibited healing under nonhydrostatic conditions is more rapid than hydrostatic healing the low strain rates which were measured during nonhydrostatic healing are temperature dependent and suggest that diffusive mass transfer processes take place during deformation thus fault rocks at upper to midcrustal depth may deform by combined cataclasis and diffusive mass transfer

changes in seismic activity following the 2011 tohoku oki earthquake effects of pore fluid pressure abstract we examined the effects of pore fluid pressure on seismicity changes following the 2011 off the pacific coast of tohoku tohoku oki earthquake through the analysis of aftershocks based on the coulomb failure criterion background tectonic stress fields in northeast japan are generally characterized by e w compression after the tohoku oki earthquake as expected from decrease in the coulomb failure function shear stress 0 4 normal compressive stress seismicity in the upper crust of northeast japan decreased except some restricted regions where we observed many aftershocks with unfavourable focal mechanisms to the background stress fields by mapping the focal mechanisms of aftershocks on the 3 d mohr diagram region by region we confirmed that the aftershocks occurred on optimally oriented faults in some regions but on misoriented faults in other regions the aftershocks on optimally oriented faults indicate the increase in regional ambient fluid pressure caused by the flow of over pressurized fluid from a deep reservoir on the other hand the aftershocks on misoriented faults which cannot be attributed to coseismic stress rotation indicate the increase in fault confined fluid pressure relative to the ambient fluid pressure

damage to the shallow landers fault from the nearby hector mine earthquake crustal faults have long been identified as sites where localized sliding motion occurs during earthquakes which allows for the relative motion between adjacent crustal blocks although there is a growing awareness that we must understand the evolution of fault systems on many timescales to relate present day crustal stresses and fault motions to geological structures formed in the past fault zone damage and healing have been documented quantitatively in only a few cases we have been monitoring the healing of damage on the shallow johnson valley fault after its rupture in the 1992 magnitude 7 3 landers earthquake and here we report that this healing was interrupted in 1999 by the magnitude 7 1 hector mine earthquake rupture which occurred 20 30 km away the hector mine earthquake both strongly shook and permanently strained the johnson valley fault adding damage discernible as a temporary reversal of the healing process the fault has since resumed the trend of strength recovery that it showed after the landers earthquake these observations lead us to speculate that fault damage caused by strong seismic waves may help to explain earthquake clustering and seismicity triggering by shaking and may be involved in friction reduction during faulting

rupture process of the 2011 tohoku oki earthquake and absolute elastic strain release 1 on 11 march 2011 the tohoku oki earthquake in eastern japan and the devastating tsunami that followed it caused severe damage and numerous deaths to clarify the rupture process of the earthquake we inverted teleseismic p wave data applying a novel formulation that takes into account the uncertainty of green s function which has been a major error source in waveform inversion the estimated seismic moment is 5 7 1022 nm mw 9 1 associated with a fault rupture 440 km long and 180 km wide along the plate interface the source process is characterized by asymmetric bilateral rupture propagation but we also found continuous slips up dip from the hypocenter which led to a large maximum slip 50 m long slip duration 90 s and a large stress drop 20 mpa the long slip duration large stress drop extensional normal faulting aftershocks in a previously compressional stress regime and low angle normal slips at approximately the depth of the plate interface suggest that the earthquake released roughly all of the accumulated elastic strain on the plate interface owing to exceptional weakening of the fault the stress accumulated on the plate interface was about 20 mpa near the trench and 0 10 mpa in the down dip source region

long term evolution of intraplate seismicity in stress shadows after a megathrust abstract megathrusts produce large permanent lithospheric displacements as well as strong transient ground shaking up to regional distances the influence of the 2011 m9 0 tohoku oki earthquake on the seismicity in stable intraplate regions around the korean peninsula is investigated the differential lateral displacements by the megathrust build transient radial tension field over the backarc lithosphere constructing stress shadows for all types of faults in optimal orientation over the wide backarc region including the southern korean peninsula a characteristic seismic velocity decrease after the megathrust supports the medium relaxation the number of earthquakes with magnitudes greater than or equal to 2 5 was increased by 61 after the megathrust the earthquakes occurred episodically a series of unusual earthquake swarms and a temporal cluster of moderate size earthquakes were observed in the yellow sea region the significant seismicity increase since the megathrust may be due to the fluid diffusion during the transient tension field and the pore fluid pressure increase during the ambient compressional stress field recovery by tectonic loading the induced seismicity may continue until the ambient stress field is fully recovered

remote triggered seismicity caused by the 2011 m9 0 tohoku oki japan earthquake 1 seismic waves from large earthquakes have been shown to trigger seismicity large distances from a mainshock and this is termed remotely or dynamically triggered seismicity we performed a global search for seismicity potentially triggered by the seismic waves from the 2011 m9 0 tohoku oki japan earthquake using seismograms from global seismic networks and an event catalog we search for earthquakes and tremors instantaneously triggered during the passing of the seismic waves as well as for statistically significant changes in local and global seismic rates after the passing of the waves for earthquakes we find potential cases of instantaneous triggering in the united states russia china ecuador and mexico while for tremors we find evidence for triggering in taiwan armenia cuba and the united states in addition we observed a potential case of delayed triggering of larger magnitude earthquakes including a m5 2 in baja california mexico

propagation of an earthquake triggering front from the 2011 tohoku oki earthquake 1 increases in seismicity have been widely observed at varying distances from the source area following large earthquakes the increased number of earthquakes are usually called aftershocks if the area is within a rupture length of the mainshock and called remotely triggered events if they are well beyond that distance these earthquakes can be explained as being induced by static and or dynamic stress changes due to the mainshock however clear observations of dynamic triggering have been inadequate to differentiate between the two mechanisms this study shows that early post seismic events triggered by the 2011 mw 9 0 tohoku oki earthquake systematically propagated over japan in a southwestern direction associated with the strong seismic waves from the source the propagation front was consistent with the arrivals of large amplitude surface waves traveling at 3 1 to 3 3 km s and extending to a distance of 1 350 km there were no observations of triggered earthquakes in the northern direction dynamic stress changes toward the north were comparable to or smaller than those necessary for triggering in the southwestern direction static stress changes were one to two orders smaller than dynamic stress changes at remote distance indicating that static stress was not the main mechanism of the triggering furthermore the dynamic stress strain changes play an important role for remote triggering if the value is more than 500 kpa in stress or 10 6 in strain

time dependent recovery of microcrack damage and seismic wave speeds in deformed limestone limestone samples were deformed up to 5 inelastic axial strain at an effective confining pressure peff 50 mpa in the cataclastic flow regime and subsequently maintained under constant static stress conditions either isostatic of triaxial for extended periods of time while elastic wave speeds and permeability were continuously monitored during deformation both seismic wave speeds and permeability decrease with increasing strain due to the growth of subvertical microcracks and inelastic porosity reduction during the static hold period under water saturated conditions the seismic wave speeds recovered gradually typically by around 5 relative to their initial value after 2 days while permeability remained constant the recovery in wave speed increases with increasing confining pressure but decreases with increasing applied differential stress the recovery is markedly lower when the samples are saturated with an inert fluid as opposed to water the evolution in wave speed is interpreted quantitatively in terms of microcrack density which shows that the post deformation recovery is associated with a decrease in effective microcrack length typically of the order to 10 after 2 days the proposed mechanism for the observed damage recovery is microcrack closure due to a combination of backsliding on wing cracks driven by time dependent friction and closure due to pressure solution at contacts between propping particles or asperities and microcrack walls the recovery rates observed in the experiments and the proposed underlying mechanisms are compatible with seismological observations of seismic wave speed recovery along faults following earthquakes

ambient noise based monitoring of seismic velocity changes associated with the 2014 mw 6 0 south napa earthquake we perform an ambient noise based monitoring to explore temporal variations of crustal seismic velocities before during and after the 24 august 2014 mw 6 0 south napa earthquake a velocity drop of about 0 08 is observed immediately after the south napa earthquake spatial variability of the velocity reduction is most correlated with the pattern of the peak ground velocity of the south napa mainshock which suggests that fracture damage in rocks induced by the dynamic strain is likely responsible for the coseismic velocity change about 50 of the velocity reduction is recovered at the first 50 days following the south napa mainshock this postseismic velocity recovery may suggest a healing process of damaged rocks

mapping pressurized volcanic fluids from induced crustal seismic velocity drops volcanic eruptions are caused by the release of pressure that has accumulated due to hot volcanic fluids at depth here we show that the extent of the regions affected by pressurized fluids can be imaged through the measurement of their response to transient stress perturbations we used records of seismic noise from the japanese hi net seismic network to measure the crustal seismic velocity changes below volcanic regions caused by the 2011 moment magnitude m w 9 0 tohoku oki earthquake we interpret coseismic crustal seismic velocity reductions as related to the mechanical weakening of the pressurized crust by the dynamic stress associated with the seismic waves we suggest therefore that mapping seismic velocity susceptibility to dynamic stress perturbations can be used for the imaging and characterization of volcanic systems

time lapse changes of p and s wave velocities and shear wave splitting in the first year after the 2011 tohoku earthquake japan shallow subsurface

trench normal variation in observed seafloor displacements associated with the 2011 tohoku oki earthquake 1 seafloor geodetic measurements using the gps acoustic technique just above the rupture area of the 2011 tohoku oki earthquake revealed strong trench normal variation in the horizontal crustal displacement associated with the earthquake one set of observations at a site only 50 km away from the trench yielded the most trench ward data ever reported with an accuracy better than 1 m it showed a coseismic displacement of up to 31 m whereas another set of observations 100 km away from the trench showed a 15 m displacement these horizontal data as well as vertical data from pressure gauges and tsunami observations strongly indicate that the seismic slip reached the trench they are also likely to contribute quantitatively to further investigations that reveal the coseismic behavior of the frontal wedge of the overriding plate in the source region along the japan trench

afterslip and viscoelastic relaxation following the 2011 tohoku oki earthquake mw9 0 inferred from inland gps and seafloor gps acoustic data we simultaneously estimate 2 5 years of afterslip and viscoelastic relaxation as well as coseismic slip for the 2011 tohoku oki earthquake displacements at inland gps and seafloor gps acoustic stations are inverted using viscoelastic green s functions for a model with an upper elastic layer and lower viscoelastic substrate the result shows that afterslip is isolated from the rupture area and possibly asperities of historical earthquakes and has almost decayed by 10 september 2013 2 5 years after the main shock the inversion result also suggests that observed landward postseismic displacements at the seafloor gps acoustic stations are caused by the viscoelastic relaxation whereas trenchward displacements at inland stations are mainly an elastic response to afterslip

azimuthal seismic anisotropy in the upper crust of the japanese islands induced by the 2011 tohoku oki megathrust earthquake

monitoring seismic velocity change caused by the 2011 tohoku oki earthquake using ambient noise records 1 we estimated the changes in seismic velocity in the southern tohoku district of japan during the six month period centered on the 11 march 2011 tohoku oki earthquake using scattered waves retrieved by autocorrelation of ambient seismic noise the estimated velocity decrease after the earthquake and after two large aftershocks in the study area was as great as 1 5 in the area nearest to the mainshock the velocity changes displayed gradual healing the spatial distribution of the velocity change showed a correlation with both the changes in static strain derived from gps records and the peak particle velocity experienced during the three earthquakes derived from strong motion records therefore our results show that velocity changes possibly contain information from deep in the crust bearing on coseismic stress release in addition to shallower effects due to strong ground motion

time lapse change in anisotropy in japan s near surface after the 2011 tohoku oki earthquake 1 we apply seismic interferometry to strong motion records to detect the near surface i e an upper few hundred meters deep change in anisotropy caused by the mw9 0 tohoku oki earthquake on 11 march 2011 we show that the earthquake increased the difference between fast and slow shear wave velocities arising from shear wave splitting in most parts of northeastern japan but it did not significantly change fast shear wave polarization directions in the near surface through monitoring of anisotropy and shear wave velocity we find that the changes in anisotropy and velocity partially recover with time they are however still different from the pre event values after nine months the comparison of the spatial distribution between changes in anisotropy and velocity indicates the changes in anisotropy and velocity are generally correlated especially in the northeastern honshu the main island in japan the change in the largest principal stress direction weakly correlates with the change in anisotropy

imaging laterally varying regional heterogeneities from seismic coda using a source array analysis abstract seismic coda is composed of scattered waves originated from various kinds of heterogeneities whose locations are not confined in the great circle ray path direction between the source and receiver we devise a technique to image laterally varying regional heterogeneities using single station seismograms for clustered events we analyze regional seismic records of the borovoye seismic station for the balapan nuclear explosions in kazakhstan scattered waves that arrive coherently over the source arrays are extracted by directional beamformings the locations of scatterers responsible for the scattered waves are mapped from the beamforming direction travel time and slowness equivalently phase velocity the illuminated locations of heterogeneities are highly correlated with the structural variations in surface topography crustal thickness and sedimentary thickness the influence of the structural variations on seismic waves is quantified in terms of scattering intensity and quality factor the scattering properties are observed to vary with phase due to the difference in frequency content and phase velocity the proposed technique appears to be useful for a study of active tectonic regions with limited monitoring stations

near surface weakening in japan after the 2011 tohoku oki earthquake 1 the magnitude mw 9 0 tohoku oki earthquake on 11 march 2011 was one of the largest in recent history ground motion caused by the seismicity around the time of the main shock was recorded by kik net the strong motion network that covers most of japan by deconvolving waveforms generated by earthquakes that are recorded at the surface and in a borehole at kik net station fksh18 we detect a reduction of shear wave velocity in the upper 100 m of about 10 and a subsequent healing that varies logarithmically with time using all available borehole and surface records of more than 300 earthquakes that occurred between 1 january 2011 and 26 may 2011 we observe a reduction in the shear wave velocity of about 5 in the upper few hundred meters after the tohoku oki earthquake throughout northeastern japan the area of the velocity reduction is about 1 200 km wide which is much wider than earlier studies reporting velocity reductions following other larger earthquakes the reduction of the shear wave velocity is an indication that the shear modulus and hence the shear strength is reduced over a large part of japan

dynamic lithospheric response to megathrust and precursory seismicity features of megathrust abstract temporal variations of seismic properties in inner trench regions before and after three megathrusts with magnitudes greater than or equal to 8 8 since 2004 are investigated to understand the nature of megathrust earthquakes the seismicity was increased significantly and the fault type compositions changed after megathrusts the seismicity displays characteristic fault type dependent distribution on rupture planes the postseismic thrustal events were populated around the down dip rupture margins due to the concentration of shear stress after coseismic ruptures normal faulting earthquakes increased after the megathrusts particularly in shallow depth regions with large slips which may be associated with lithospheric rebound and development of splay faults the earthquake occurrence rate b value displays a characteristic slip dependent feature the earthquake occurrence rates decrease with the slip amount of forthcoming megathrust which may be caused by continuous accumulation of plate driven stress and tectonic loading around the future rupture planes on the slab surface the slip dependency of earthquake occurrence rates is enhanced with time until the occurrence of megathrust the level of seismicity after megathrust is inversely proportional to that before megathrust yielding comparable average seismicity over the rupture zone it was also observed that the dynamic lithospheric response is highly correlated with slip distribution on the rupture plane the tension axes of the normal faulting earthquakes for 100 days after the tohoku oki earthquake focus to an apparent pole suggesting a radial viscoelastic deformation of lithosphere the temporal changes of slip dependent b values fit well with an exponential function suggesting an exponential increase of normal stress on the locked region with time until the occurrence of the megathrust this observation suggests that the temporal variation of slip dependent b values may be useful for prediction of forthcoming megathrusts at least several tens years beforehand

volcanic subsidence triggered by the 2011 tohoku earthquake in japan the 2011 tohoku earthquake caused high levels of crustal deformation in japan analysis of satellite radar and gps data show that the earthquake caused nearby volcanic regions to subside instantaneously creating elliptical depressions that are parallel to the direction of quake induced crustal extension

crustal stress field perturbations in the continental margin around the korean peninsula and japanese islands abstract seismic activity and focal mechanisms are governed by the effective stress field that is a combined result of regional tectonic processes and local stress perturbation this study investigates the regional variation in the stress field in the eastern continental margin of the eurasian plate around the korean peninsula and japanese islands using a damped stress inversion technique based on the focal mechanism solutions of regional earthquakes the dominant compressional stress is directed ene wsw around the korean peninsula and eastern china e w at the central east sea and northern and southern japan nw se at central japan and n s around the northern nankai trough the dominant compression direction changes rapidly in the east sea and japanese islands which may be due to the combined effects of tectonic loading in the subduction zones off the japanese islands and the india eurasia plate boundary the crustal stress fields around the subduction zones off the japanese islands present characteristic depth dependent orientations the orientations of the largest horizontal stress components h in the subduction zones are subparallel with the plate convergence directions at shallow depths the h orientations are observed to rotate clockwise with the depth owing to slab subduction and lithospheric deformation the regional stress field around the japanese islands was perturbed temporally by the 2011 m9 0 tohoku oki megathrust earthquake the regional stress field was recovered in a couple of years the stress field and tectonic structures are mutually affected causing stress field distortion and a localized mixture of earthquakes in different faulting types

a review of shear wave splitting in the crack critical crust summary over the last 15 years it has become established that crack induced stress aligned shear wave splitting with azimuthal anisotropy is an inherent characteristic of almost all rocks in the crust this means that most in situ rocks are pervaded by fluid saturated microcracks and consequently are highly compliant the evolution of such stress aligned fluid saturated grain boundary cracks and pore throats in response to changing conditions can be calculated in some cases with great accuracy using anisotropic poro elasticity ape ape is tightly constrained with no free parameters yet dynamic modelling with ape currently matches a wide range of phenomena concerning anisotropy stress shear waves and cracks in particular ape has allowed the anisotropic response of a reservoir to injection to be calculated predicted with hindsight and the time and magnitude of an earthquake to be correctly stress forecast the reason for this calculability and predictability is that the microcracks in the crust are so closely spaced that they form critical systems this crack critical crust leads to a new style of geophysics that has profound implications for almost all aspects of pre fracturing deformation of the crust and for solid earth geophysics and geology we review past present and speculate about the future of shear wave splitting in the crack critical crust shear wave splitting is seen to be a dynamic measure of the deformation of the rock mass there is some good news and some bad news for conventional geophysics many accepted phenomena are no longer valid at high spatial and temporal resolution a major effect is that the detailed crack geometry changes with time and varies from place to place in response to very small previously negligible changes however at least in some circumstances the behaviour of the rock in the highly complex inhomogeneous earth may be calculated and the response predicted opening the way to possible control by feedback the need is to devise ways to exploit these new opportunities in the crack critical crust recent observations from the smsites project at husavik in northern iceland gathered while this review was being written display the extraordinarily sensitivity of in situ rock to small changes at great distances the effects are far too large to occur in a conventional elastic brittle crust and their presence confirms the highly compliant nature of the crack critical crust