a scaling law for slow earthquakes with the availability of the global positioning system and other technical advances a growing number of unusual earthquake phenomena occurring at relatively long periods have been recognized they include deep episodic tremor low frequency earthquakes slow slip events and silent earthquakes based on data chiefly from western japan ide et al report that these slow seismic events follow a unified scaling relationship that clearly differentiates their behaviour from that of regular earthquakes a diverse array of unusual earthquake phenomena occurring at relatively long periods slow events follow a unified scaling relationship that clearly differentiates their behaviour from that of regular earthquakes indicating that they comprise a new earthquake category recently a series of unusual earthquake phenomena have been discovered including deep episodic tremor1 low frequency earthquakes2 very low frequency earthquakes3 slow slip events4 and silent earthquakes5 6 7 8 9 each of these has been demonstrated to arise from shear slip just as do regular earthquakes but with longer characteristic durations and radiating much less seismic energy here we show that these slow events follow a simple unified scaling relationship that clearly differentiates their behaviour from that of regular earthquakes we find that their seismic moment is proportional to the characteristic duration and their moment rate function is constant with a spectral high frequency decay of f 1 this scaling and spectral behaviour demonstrates that they can be thought of as different manifestations of the same phenomena and that they comprise a new earthquake category the observed scale dependence of rupture velocity for these events can be explained by either a constant low stress drop model or a diffusional constant slip model this new scaling law unifies a diverse class of slow seismic events and may lead to a better understanding of the plate subduction process and large earthquake generation

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

slow slip near the trench at the hikurangi subduction zone new zealand the range of fault slip behaviors near the trench at subduction plate boundaries is critical to know as this is where the world s largest most damaging tsunamis are generated our knowledge of these behaviors has remained largely incomplete partially due to the challenging nature of crustal deformation measurements at offshore plate boundaries here we present detailed seafloor deformation observations made during an offshore slow slip event sse in september and october 2014 using a network of absolute pressure gauges deployed at the hikurangi subduction margin offshore new zealand these data show the distribution of vertical seafloor deformation during the sse and reveal direct evidence for sses occurring close to the trench within 2 kilometers of the seafloor where very low temperatures and pressures exist

propagation of slow slip leading up to the 2011 mw 9 0 tohoku oki earthquake many large earthquakes are preceded by one or more foreshocks but it is unclear how these foreshocks relate to the nucleation process of the mainshock on the basis of an earthquake catalog created using a waveform correlation technique we identified two distinct sequences of foreshocks migrating at rates of 2 to 10 kilometers per day along the trench axis toward the epicenter of the 2011 moment magnitude mw 9 0 tohoku oki earthquake in japan the time history of quasi static slip along the plate interface based on small repeating earthquakes that were part of the migrating seismicity suggests that two sequences involved slow slip transients propagating toward the initial rupture point the second sequence which involved large slip rates may have caused substantial stress loading prompting the unstable dynamic rupture of the mainshock

characterization of nucleation during laboratory earthquakes 1 we observe the nucleation phase of in plane ruptures in the laboratory we show that the nucleation is composed of two distinct phases a quasi static and an acceleration stage followed by dynamic propagation we propose an empirical model which describes the rupture length evolution the quasi static phase is described by an exponential growth while the acceleration phase is described by an inverse power law of time the transition from quasi static to accelerating rupture is related to the critical nucleation length which scales inversely with normal stress in accordance with theoretical predictions and to a critical surfacic power which may be an intrinsic property of the interface finally we discuss these results in the frame of previous studies and propose a scaling up to natural earthquake dimensions

quantitative measure of the variation in fault rheology due to fluid rock interactions we analyze friction data from two published suites of laboratory tests on granite in order to explore and quantify the effects of temperature t and pore water pressure pp on the sliding behavior of faults rate stepping sliding tests were performed on laboratory faults in granite containing gouge granite powder both dry at 23 to 845 c lockner et al 1986 and wet pp 100 mpa at 23 to 600 c blanpied et al 1991 1995 imposed slip velocities v ranged from 0 01 to 5 5 m s and effective normal stresses were near 400 mpa for dried granite at all temperatures and wet granite below 300 c the coefficient of friction shows low sensitivity to v t and pp for wet granite above 350 drops rapidly with increasing t and shows a strong positive rate dependence and protracted strength transients following steps in v presumably reflecting the activity of a water aided deformation process by inverting strength data from velocity stepping tests we determined values for parameters in three formulations of a rate and state dependent constitutive law one or two state variables were used to represent slip history effects each velocity step yielded an independent set of values for the nominal friction level five constitutive parameters transient parameters a b1 and b2 and characteristic displacements dc1 and dc2 and the velocity dependence of steady state friction ss ln v a b1 b2 below 250 data from dry and most wet tests are adequately modeled by using the slip law ruina 1983 and one state variable a 0 003 to 0 018 b 0 001 to 0 018 dc 1 to 20 m dried tests above 250 can also be fitted with one state variable in contrast wet tests above 350 require higher direct rate dependence a 0 03 to 0 12 plus a second state variable with large negative amplitude b2 0 03 to 0 14 and large characteristic displacement dc2 300 to 4000 m thus the parameters a b1 and b2 for wet granite show a pronounced change in their temperature dependence in the range 270 to 350 c which may reflect a change in underlying deformation mechanism we quantify the trends in parameter values from 25 to 600 c by piecewise linear regressions which provide a straightforward means to incorporate the full constitutive response of granite into numerical models of fault slip the modeling results suggest that the succeptibility for unstable stick slip sliding is maximized between 90 and 360 c in agreement with laboratory observations and consistent with the depth range of earthquakes on mature faults in the continental crust

physical and transport property variations within carbonate bearing fault zones insights from the monte maggio fault central italy the physical characterization of carbonate bearing normal faults is fundamental for resource development and seismic hazard here we report laboratory measurements of density porosity vp vs elastic moduli and permeability for a range of effective confining pressures 0 1 100 mpa conducted on samples representing different structural domains of a carbonate bearing fault we find a reduction in porosity from the fault breccia 11 7 total and 6 2 connected to the main fault plane 9 total and 3 5 connected with both domains showing higher porosity compared to the protolith 6 8 total and 1 1 connected with increasing confining pressure p wave velocity evolves from 4 5 km s to 5 9 km s in the fault breccia is constant at 5 9 km s approaching the fault plane and is low 4 9 km s in clay rich fault domains we find that while the fault breccia shows pressure sensitive behaviour a reduction in permeability from 2 10 16 m2 to 2 10 17 m2 the cemented cataclasite close to the fault plane is characterized by pressure independent behaviour permeability 4 10 17 m2 our results indicate that the deformation processes occurring within the different fault structural domains influence the physical and transport properties of the fault zone in situ vp profiles match well the laboratory measurements demonstrating that laboratory data are valuable for implications at larger scale combining the experimental values of elastic moduli and frictional properties it results that at shallow crustal levels m 1 earthquakes are less favoured in agreement with earthquake depth distribution during the l aquila 2009 seismic sequence that occurred on carbonates

the long precursory phase of most large interplate earthquakes many earthquakes are preceded by foreshocks however the mechanisms that generate foreshocks and the reason why they occur before some earthquakes and not others are unknown here we use seismic catalogues from the best instrumented areas of the north pacific to analyse the foreshock sequences preceding all earthquakes there between 1999 and 2011 of magnitude larger than 6 5 and at depths shallower than 50 km the data set comprises 31 earthquakes at plate boundaries and 31 in plate interiors we find that there is a remarkable contrast between the foreshock sequences of interplate compared with intraplate earthquakes most large earthquakes at plate interfaces in the north pacific were preceded by accelerating seismic activity in the months to days leading up to the mainshock in contrast foreshocks are much less frequent in intraplate settings we suggest that at plate boundaries the interface between the two plates begins to slowly slip before the interface ruptures in a large earthquake this relatively long precursory phase could help mitigate earthquake risk at plate boundaries

seismic evidence of nonlinear crustal deformation during a large slow slip event in mexico repeated cross correlations of ambient seismic noise indicate a long term seismic velocity change associated with the 2006 m7 5 slow slip event sse in the guerrero region mexico because the sse does not radiate seismic waves the measured velocity change cannot be associated with the response of superficial soil layers to strong shaking as observed for regular earthquakes the perturbation observed maximized at periods between 7 s and 17 s which correspond to surface waves with sensitivity to the upper and middle crust the amplitude of the relative velocity change 10 3 was much larger than the volumetric deformation 10 6 at the depths probed 5 20 km moreover the time dependence of the velocity perturbation indicated that it was related to the strain rate rather than the strain itself this suggests that during strong slow slip events the deformation of the overlying crust shows significant nonlinear elastic behavior

a laboratory experiment to monitor the contact state of a fault by transmission waves abstract we performed a series of laboratory experiments in which elastic waves were transmitted across a simulated fault two types of experiments were carried out 1 normal stress holding test nsht normal stress was kept constant for about 3 h without shear stress and transmission waves were observed 2 shear stress increasing test ssit shear stress was gradually increased until a stick slip event occurred transmission waves were continuously observed throughout the process of stress accumulation we focused on the change in transmission waves during the application of shear stress and especially during precursory slips it was found in nsht that the amplitude of transmission waves linearly increased with the logarithm of stationary contact time the increase amounted to a few percent after about 3 h creep at asperity contacts is responsible for this phenomenon from a theoretical consideration it was concluded that the real contact area increased with the logarithm of stationary contact time we observed in ssit a significant increase in wave amplitude with shear stress application this phenomenon cannot be attributed to the time effect observed in nsht instead it can be explained by the mechanism of junction growth proposed by tabor junction growth yields an increase in real contact area it is required for junction growth to occur that the material in contact is already plastic under a purely normal loading condition a computer simulation confirmed that this requirement was satisfied in our experiments we also found that the rate at which the amplitude increased was slightly reduced prior to a stick slip event the onset time of the reduction well coincides with the onset of precursory slip the cause of the reduction is attributed to the reset of stationary contact time due to displacement this interpretation is supported by the result of nsht taking the time of stationary contact in ssit into account we may expect the change in wave amplitude to be at most only a few percent the observed slight reduction in increasing rate is in this sense reasonable the static stiffness of the fault also decreases with precursory slip it was also found that low frequency waves are a better indicator of precursory slip than high frequency waves this might suggest that low frequency waves with longer wavelength are a better indicator of average behavior of faults the problem however merits a further investigation the shifts in phase were also found to be a good indicator of the change in contact state of the fault the changes in both amplitude and phase of transmission waves are unifyingly understood through the theory of transmission coefficient presented by pyrak nolte et al rough surfaces have a tendency to give larger stick slips than smooth surfaces the amount of precursory slip is larger for rough surfaces than for smooth surfaces although it was confirmed by a computer simulation that rough surfaces have larger contact diameters than smooth surfaces the rigorous relationship between the surface roughness contact diameter and the amount of precursory slips was not established

distribution of seismic wave speed changes associated with the 12 may 2008 mw 7 9 wenchuan earthquake 1 we used continuous recordings in sichuan china to track the temporal change of the seismic wave speed at a regional scale for 2 years including the wenchuan mw 7 9 earthquake the data are recorded by a temporary network of 156 broad band seismographs in a region that covers the southern 2 3 of the fault activated during the earthquake a doublet analysis applied on the codas of seismic noise cross correlation functions is used to detect temporal velocity changes we found clear evidence that the seismic velocity drops by up to 0 08 in the fault region just after the earthquake with fluctuations within 0 02 before the earthquake we compared the measurements in different sub arrays to get a spatial distribution of the velocity changes this distribution is consistent with the volumetric strain change during the wenchuan earthquake and shows that the co seismic velocity change is not controlled by the response of sediments

high salinity facilitates dolomite precipitation mediated by haloferax volcanii ds52 abstract although most modern dolomites occur in hypersaline environments the effects of elevated salinity on the microbial mediation of dolomite precipitation have not been fully evaluated here we report results of dolomite precipitation in association with a batch culture of haloferax volcanii ds52 a halophilic archaeon under various salinities from 120 to 360 and the impact of salinity on microbe mediated dolomite formation the mineral phases morphology and atomic arrangement of the precipitates were analyzed by xrd sem and tem respectively the amount of amino acids on the archaeal cell surface was quantified by hplc ms the xrd analysis indicated that disordered dolomite formed successfully with the facilitation of cells harvested from cultures with relatively high salinities 200 and 280 but was not observed in association with cells harvested from cultures with lower salinity 120 or the lysates of cells harvested from extremely high salinity 360 the tem analysis demonstrated that the crystals from cultures with a salinity of 200 closely matched that of dolomite importantly we found that more carboxyl groups were presented on the cell surface under high salinity conditions to resist the high osmotic pressure which may result in the subsequent promotion of dolomite formation our finding suggests a link between variations in the hydro chemical conditions and the formation of dolomite via microbial metabolic activity and enhances our understanding about the mechanism of microbially mediated dolomite formation under high salinity conditions

the feni drift the importance and meaning of slump deposits on the eastern slope of the rockall bank abstract sedimentary facies of cores from the eastern side of the rockall bank and the feni drift 55 58 n have been studied they confirm the existence of slumping which contributes only in small part to drift build up these slumps occurred at different episodes during last glacial and early post glacial periods they are sandwiched in between more important turbidites and are found in places where the drift lies against the slope and so is acted upon by continental rise sedimentary processes the sea level rise periods with ice melting seems to favour gravity flow release

dilatant strengthening as a mechanism for slow slip events 1 the mechanics of slow slip events sse in subduction zones remain unresolved we suggest that sse nucleate in areas of unstable friction under drained conditions but as slip accelerates dilatancy reduces pore pressure p quenching instability competition between dilatant strengthening and thermal pressurization may control whether slip is slow or fast we model sse with 2 d elasticity rate state friction and a dilatancy law where porosity evolves toward steady state ss over distance dc and ss 0 ln v v0 v is slip speed we consider two diffusion models membrane diffusion md is approximated by p p tf where p and p are shear zone and remote pore pressure and tf is a characteristic diffusion time homogeneous diffusion hd accurately models fault normal flow with diffusivity chyd for md linearized analysis defines a boundary 1 a b between slow and fast slip where f0e b p f0 a and b are friction parameters and is compressibility when 1 a b slip speeds remain quasi static for hd ep eh p defines dilatancy efficiency where h is shear zone thickness and v is plate velocity sse are favored by large eh and low effective stress the ratio ep to thermal pressurization efficiency scales with 1 p so high p favors sse consistent with seismic observations for ep 10 3 transient slip rates repeat times average slip and stress drops are comparable to field observations model updip propagation speeds are comparable to those observed along strike many simulations exhibit slow phases driven by steady downdip slip and faster phases that relax the accumulated stress model sse accommodate only a fraction of plate motion the remaining deficit must be accommodated during coseismic or postseismic slip

on the evolution of elastic properties during laboratory stick slip experiments spanning the transition from slow slip to dynamic rupture the physical mechanisms governing slow earthquakes remain unknown as does the relationship between slow and regular earthquakes to investigate the mechanism s of slow earthquakes and related quasi dynamic modes of fault slip we performed laboratory experiments on simulated fault gouge in the double direct shear configuration we reproduced the full spectrum of slip behavior from slow to fast stick slip by altering the elastic stiffness of the loading apparatus k to match the critical rheologic stiffness of fault gouge kc our experiments show an evolution from stable sliding when k kc to quasi dynamic transients when k kc to dynamic instabilities when k kc to evaluate the microphysical processes of fault weakening we monitored variations of elastic properties we find systematic changes in p wave velocity vp for laboratory seismic cycles during the coseismic stress drop seismic velocity drops abruptly consistent with observations on natural faults in the preparatory phase preceding failure we find that accelerated fault creep causes a vp reduction for the complete spectrum of slip behaviors our results suggest that the mechanics of slow and fast ruptures share key features and that they can occur on same faults depending on frictional properties in agreement with seismic surveys on tectonic faults our data show that their state of stress can be monitored by vp changes during the seismic cycle the observed reduction in vp during the earthquake preparatory phase suggests that if similar mechanisms are confirmed in nature high resolution monitoring of fault zone properties may be a promising avenue for reliable detection of earthquake precursors

the parkfield tremors reveal slow and fast ruptures on the same asperity a tremor source on the san andreas fault produced an unusual sequence of low frequency earthquakes until it was disrupted by the 2004 parkfield earthquake the peculiar recurrence pattern has now been modelled showing that such slip behaviour occurs when the tremor asperity size is close to the critical nucleation size of earthquakes an isolated tremor source on the san andreas fault near parkfield california produces an unusual sequence of low frequency earthquakes which regularly oscillated between recurrence intervals of three and six days until it was disrupted by the 2004 magnitude 6 0 parkfield earthquake after that event the source ruptured every three days only gradually returning to its initial alternating recurrence pattern after two years deepa mele veedu and sylvain barbot have now modelled the mechanism driving the tremor source to form this peculiar recurrence pattern they demonstrate that such slip behaviour can occur when the tremor asperity size is close to the critical nucleation size of earthquakes they also show that changes in pore pressure following the 2004 parkfield earthquake can explain the sudden change and gradual recovery of the recurrence intervals the deep extension of the san andreas fault is believed to be creeping but the recent observations of tectonic tremors from these depths indicate a complex deformation style1 in particular an isolated tremor source near parkfield has been producing a sequence of low frequency earthquakes2 that indicates an uncommon mechanism of stress accumulation and release the tremor pattern regularly oscillated between three and six days from mid 2003 until it was disrupted by the 2004 magnitude 6 0 parkfield earthquake after that event the tremor source ruptured only about every three days but over the next two years it gradually returned to its initial alternating recurrence pattern the mechanism that drives this recurrence pattern is unknown here we use physics based models to show that the same tremor asperity the region from which the low frequency earthquakes radiate can regularly slip in slow and fast ruptures naturally resulting in recurrence intervals alternating between three and six days this unusual slip behaviour occurs when the tremor asperity size is close to the critical nucleation size of earthquakes we also show that changes in pore pressure following the parkfield earthquake can explain the sudden change and gradual recovery of the recurrence intervals our findings suggest a framework for fault deformation in which the same asperity can release tectonic stress through both slow and fast ruptures

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

spontaneous and triggered aseismic deformation transients in a subduction fault model 1 aseismic deformation transients can emerge as a natural outcome of the rate and state friction processes revealed in laboratory fault sliding experiments when that constitutive formulation is applied to model subduction earthquake sequences transients can arise spontaneously for certain effective stress variations with depth we show that if interstitial fluids are present and pore pressure is near lithostatic around and downdip from the frictional stability transition transients with recurrence intervals of 1 year are predicted on the basis of laboratory friction parameters and their temperature hence depth variations the recurrence interval decreases with and reaches 14 months when is 2 3 mpa dimensional analysis and numerical studies show that the fault response primarily depends on a parameter w h here the high pore pressure zone extends distance w updip from the stability transition and h is the stable patch size for steady sliding evidence that such fluid conditions may actually be present is independently provided by the occurrence of nonvolcanic tremors as apparent responses to extremely small stress changes and by petrological constraints on expected regions of dehydration for the shallow dipping subduction zones where transients are observed transient sequences can also be triggered by a modest one time step like interseismic stress perturbation on the subduction fault due to nearby earthquakes or to pore pressure changes e g during episodes of metamorphic fluid release properties of triggered transients and future thrust earthquakes depend on the interseismic time when the perturbation is introduced its relative location along the subduction fault and its magnitude

precursory changes in seismic velocity for the spectrum of earthquake failure modes temporal changes in seismic velocity during the earthquake cycle have the potential to illuminate physical processes associated with fault weakening and connections between the range of fault slip behaviors including slow earthquakes tremor and low frequency earthquakes1 laboratory and theoretical studies predict changes in seismic velocity prior to earthquake failure2 however tectonic faults fail in a spectrum of modes and little is known about precursors for those modes3 here we show that precursory changes of wave speed occur in laboratory faults for the complete spectrum of failure modes observed for tectonic faults we systematically altered the stiffness of the loading system to reproduce the transition from slow to fast stick slip and monitored ultrasonic wave speed during frictional sliding we find systematic variations of elastic properties during the seismic cycle for both slow and fast earthquakes indicating similar physical mechanisms during rupture nucleation our data show that accelerated fault creep causes reduction of seismic velocity and elastic moduli during the preparatory phase preceding failure which suggests that real time monitoring of active faults may be a means to detect earthquake precursors

an integrated perspective of the continuum between earthquakes and slow slip phenomena slow slip a mechanism by which faults can relieve stress was thought to be distinct from earthquakes however a global review of slow slip phenomena suggests that instead there is a continuum between the two types of event