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

imaging the nonvolcanic tremor zone beneath the san andreas fault at cholame california using station pair double difference tomography abstract nonvolcanic tremors have been detected deep beneath the san andreas fault saf near cholame california the tremors are modulated by small stress changes induced by earth tides and regional and teleseismic earthquakes implying elevated pore fluid pressure in the tremor zone in this area tremors lie beneath the seismogenic zone limiting the usefulness of local earthquakes for resolving seismic velocity properties in the tremor zone station pair double difference tomography that uses differential tremor arrival times is used for the first time to provide new detailed information about the complexity of the lower crust and upper mantle transition and the occurrence of deep tremors in zones of localized low shear wave velocity anomalies the anomalies may represent zones containing high pore pressure fluids that migrate into the tremor zone episodically from the southwest and that are ultimately derived from dehydration of deep serpentinized mantle wedge material these results improve our understanding of the tremor process why tremors are concentrated in specific zones along the saf and possible relationships between tremors and large historic earthquakes

duplex like structures in submarine fan channels ouachita mountains arkansas submarine fan channel sequences of the jackfork formation lower pennsylvanian at degray dam section in the ouachita mountains arkansas contain discrete units 10 75 cm thick with moderately dipping 25 40 sigmoidal imbricate slices adjacent units with opposing imbricate slices are common the sigmoidal structures are similar in geometry to a tectonic feature known as a duplex a tectonic origin of sigmoidal structures however seems unlikely because opposing directions of imbrication in adjacent units would require an unrealistic tectonic movement history for the area we propose that the jackfork sigmoidal structures were formed by a process kinematically similar to that responsible for generating duplex structures unlike tectonic duplexes however the sigmoidal structures were formed by soft sediment deformation of sand and mud layers as high energy sediment gravity flows glided over these layers sediment gravity flows responsible for forming the sigmoidal deformation were probably generated by slumping of adjacent channel walls dip direction of sigmoidal slices is perpendicular to channel axes thus recognition of sigmoidal deformation structures may be useful in inferring the trend of channels in ancient submarine fan complexes

α β phase transition in quartz monitored using acoustic emissions summary it is usually suggested that thermal cracking in a quartz bearing rock results from the anomalously high volumetric expansion coefficients of quartz e g simmons cooper 1978 it has also been recognized that thermal expansion mismatch and mineral anisotropy contribute to thermal cracking in materials that consist of a polycrystalline aggregate composed of several anisotropic minerals even in the absence of a temperature gradient friedrich wong 1986 experiments investigating thermal cracking in rocks commonly involve imaging and quantitative stereology of crack populations induced in rocks treated to various peak temperatures e g friedrich johnson 1978 homand etienne troalan 1984 atkinson mcdonald meredith 1984 meredith atkinson 1985 here we report on acoustic emission experiments that monitor the process of thermal cracking as it occurs during heating supported by measurements of crack surface area pore fluid permeability porosity and surface conductivity carried out on rock samples treated to various peak temperatures the acoustic emission measurements show a strong peak of microcracking at the phase transition temperature for quartz 573 c superimposed upon a background of microcracking due to thermal expansion there is also a clear peak of microcracking at higher temperatures 800 c that can be attributed to oxidation dehydroxylation reactions of hornblende and chlorite measurements of fluid permeability pore surface area porosity and electrical conductivity made on samples that have been heat treated to various maximum temperatures show increases associated with a major episode of cracking in the 500 600 c temperature range indicating that the new cracks form a well interconnected network this has been confirmed by sem and optical microscopy these results have implications for the electrical conductivity of the continental crust providing a mechanism enabling the high pore fluid connectivity needed to explain zones of high electrical conductivity at depth providing that cracks opened in this way remain open at the high pressures existing at depth it should be recognized however that th se measurements are limited in their direct application since they were obtained under initially dry conditions at laboratory pressures

stress and fluid driven failure during fracture array growth implications for coupled deformation and fluid flow in the crust brittle experimental deformation on dolomite rocks shows for the fi rst time the differ ence in growth of fracture networks by ordinary percolation and invasion percolation processes stress driven fracture growth in the absence of fl uid pressure is an ordinary percolation process characterized by distributed nucleation and growth of microfractures which coalesce with increasing strain to form a connected fracture network fluid pres sure driven fracture growth is more akin to an invasion percolation process characterized by preferential fracture growth occurring initially at the high fl uid pressure part of the rock with progressive deformation the network propagates rapidly through the sample and away from the high fl uid pressure reservoir x ray microtomography analysis suggests that the fracture network in three dimensions 3 d is probably a fully connected network at peak stress conditions whereas conventional 2 d analysis suggests that connectivity only occurs at shear failure the development of 3 d fracture connectivity prior to shear failure has important implications for fl uid fl ow and fl uid pressure changes immediately prior to rupture nucleation in active fault zones for fl uid migration in ore producing hydrothermal systems and for reservoir integrity in hydrocarbon systems

seismic tremor in subduction zones rock physics evidence 1 episodic tremor and slip ets have been correlated with rupture phenomena in subducting oceanic lithosphere at 30 45 km depth where high vp vs ratios which suggest high fluid pressures have been observed ets by accommodating slip in the down dip portion of the subduction zone may trigger megathrust earthquakes up dip in the locked section during dehydration experiments on serpentinite typical rock of the oceanic lithosphere at temperatures found in nature at 30 45 km depth 400 550 c we observe seismic signals in the form of acoustic emissions that closely resemble low frequency earthquakes seismic tremor and regular earthquakes our findings support the concept that water released during dehydration reactions increases the pore pressures and can trigger ets and regular earthquakes by reducing slip resistance

thermo poro mechanics of chemically active creeping faults 3 the role of serpentinite in episodic tremor and slip sequences and transition to chaos during the last decade knowledge over episodic tremor and slip ets events has increased dramatically owing to the widespread installation of gps and seismic networks the most puzzling observations are i the periodic nature of slow seismic events ii their localization at intermediate depths estimated 15 40 km and iii the origin of the nonvolcanic fluids that are responsible for the tremor activity we reconcile these observations using a first principles approach relying on physics continuum mechanics and chemistry of serpentinite in the megathrust interface the approach reproduces the gps sequences of 17 years of recording in cascadia north america as well as over 10 years in the hikurangi trench of new zealand we show that strongly endothermic reactions such as serpentinite dehydration are required for ets events we report that in this tectonic setting it is its chemical reaction kinetics not the low friction that marks serpentinite as a key mineral for stable self sustained oscillations we find that the subduction zone instabilities are driven from the ductile realm rather than the brittle cover even when earthquakes in the cover perturb the oscillator it relaxes to its fundamental mode such a transition from stable oscillations to chaos is witnessed in the ets signal of nz following the m6 8 2007 seismic event which triggered a secondary mode of oscillations lasting for a few years we consequently suggest that the rich dynamics of ductile modes of failure may be used to decipher the chaotic time sequences underpinning seismic events

withdrawn source duration of stress and water induced seismicity as derived from experimental analysis of p wave pulse width in granite we used analyses of pulse widths of p waves in granite measured during a laboratory experiment to investigate source durations of rupture processes for water induced and stress induced microseismicity water was injected into a dry granite sample under constant axial stress of about 70 of fracture strength and a confining pressure of 40 mpa after elimination of the effects of event size and hypocentral distance from observed pulse widths we obtained scaled source durations of 0 50 s and 0 26 s for stress induced and water induced microseismicity respectively this difference suggests that the rupture velocity of water induced microseismicity is greater than that of stress induced microseismicity or that fault geometry is more equidimensional in the wet state than in the dry state our results suggest that pulse width analysis of p waveforms can be used to distinguish water induced events from those induced by regional stress and to characterize the faulting process

syndeformational antigorite dehydration produces stable fault slip we conducted deformation experiments in which temperature was increased above the thermal stability of antigorite to directly test the dehydration embrittlement hypothesis and its potential link to intermediate depth earthquakes the experiments were designed to maximize the possibility for instability pore pressure was undrained pre dehydration stress was high and deformation was localized prior to initiation of reaction however stick slip instabilities or unstable fault behavior did not develop rather we find that weakening occurs stably at a rate that depends on the ratio of the temperature ramp rate to the strain rate resulting in laboratory slow slip or stress relaxation events

high vp vs zone accompanying non volcanic tremors and slow slip events beneath southwestern japan abstract in southwestern japan the philippine sea plate subducts beneath the eurasian plate non volcanic tremors and slow slow slip events are observed beneath southwestern japan seismic tomography based on the data obtained from the dense seismic network revealed the velocity structure in and around the subducting philippine sea plate the oceanic crust of the philippine sea plate subducting from the suruga and nankai troughs can be imaged clearly beneath the tokai region and the kii peninsula non volcanic tremors and short term slow slip events may occur in the high vp vs zones owing to the fluid dehydrated from the subducting plate where the oceanic crust of the philippine sea plate encounters the serpentinized wedge mantle of the eurasian plate these tremors and short term slow slip events occur in the high vp vs zone at depths of 30 40 km beneath the tokai region the landward edge of the high vp vs zone beneath the kii peninsula and eastern shikoku region and the seaward edge of the high vp vs zone beneath the western shikoku region long term slow slip events were observed beneath the tokai region and the bungo channel and both these events are located on the seaward side of a high vp vs zone these long term slow slip events are considered to be caused at the plate boundary between the oceanic crust of the philippine sea plate and the lower crust of the eurasian plate by the high pore fluid pressure caused by the fluid dehydrated from the subducting plate the existence of the high vp vs lower crust of the eurasian plate may control the occurrence of the long term slow slip events

slow earthquakes coincident with episodic tremors and slow slip events we report on the very low frequency earthquakes occurring in the transition zone of the subducting plate interface along the nankai subduction zone in southwest japan seismic waves generated by very low frequency earthquakes with seismic moment magnitudes of 3 1 to 3 5 predominantly show a long period of about 20 seconds the seismicity of very low frequency earthquakes accompanies and migrates with the activity of deep low frequency tremors and slow slip events the coincidence of these three phenomena improves the detection and characterization of slow earthquakes which are thought to increase the stress on updip megathrust earthquake rupture zones

dynamic control on serpentine crystallization in veins constraints on hydration processes in oceanic peridotites deformation and hydration processes are intimately linked in the oceanic lithosphere but the feedbacks between them are still poorly understood especially in ultramafic rocks where serpentinization results in a decrease of rock density that implies a volume increase and or mass transfer serpentinization is accompanied by abundant veining marked by different generations of vein filling serpentines with a high variety of morphologies and textures that correspond to different mechanisms and conditions of formation we use these veins to constrain the role of deformation and mass transfer processes during hydration of oceanic peridotites at slow spreading ridges we have selected a representative set of veins from ocean floor serpentinites of the mid atlantic ridge near kane transform fault 23 n and characterized these in detail for their microstructures and chemistry by coupling optical and electron microscopy sem tem with electron microprobe analyses four main veining episodes v1 to v4 accompany the serpentinization the first episode identified as vein generation v1 is interpreted as the tectonically controlled penetration of early seawater dominated fluid within peridotites enhancing thermal cracking and mesh texture initiation at 3 4 km up to 8 km depth and at t 300 350 c the two following vein stages v2 and v3 formed in a closed diffusive system and accommodate volume expansion required to reach almost 50 serpentinization of the protolith the cracks exploited by these veins were caused by the progressive unroofing at depths of 4 to 2 km along a detachment fault degree and rate of serpentinization seem to be controlled by the capacity of the system to create space and to drive the mass transfer needed for ongoing serpentinization and this capacity is in turn linked to the exhumation rate and local tectonics during this period water consumed by hydration may prevent the establishment of convective hydrothermal cells the onset of an open hydrothermal system in the shallow lithosphere 2 km where brittle fracturing and advective transfer dominate and enable the completion of serpentinization is marked by the last vein generation v4 these results show a complete history of alteration with the crystallization of different types of serpentine recording different tectonic events chemical conditions and modes of hydrothermal alteration of the lithosphere

slow slip events and seismic tremor at circum pacific subduction zones 1 it has been known for a long time that slip accompanying earthquakes accounts for only a fraction of plate tectonic displacements however only recently has a fuller spectrum of strain release processes including normal slow and silent earthquakes or slow slip events and continuous and episodic slip been observed and generated by numerical simulations of the earthquake cycle despite a profusion of observations and modeling studies the physical mechanism of slow slip events remains elusive the concurrence of seismic tremor with slow slip episodes in cascadia and southwestern japan provides insight into the process of slow slip a perceived similarity between subduction zone and volcanic tremor has led to suggestions that slow slip involves fluid migration on or near the plate interface alternatively evidence is accumulating to support the notion that tremor results from shear failure during slow slip global observations of the location spatial extent magnitude duration slip rate and periodicity of these aseismic slip transients indicate significant variation that may be exploited to better understand their generation most slow slip events occur just downdip of the seismogenic zone consistent with rate and state dependent frictional modeling that requires unstable to stable transitional properties for slow slip generation at a few convergent margins the occurrence of slow slip events within the seismogenic zone makes it highly likely that transitions in frictional properties exist there and are the loci of slow slip nucleation slow slip events perturb the surrounding stress field and may either increase or relieve stress on a fault bringing it closer to or farther from earthquake failure respectively this paper presents a review of slow slip events and related seismic tremor observed at plate boundaries worldwide with a focus on circum pacific subduction zones trends in global observations of slow slip events suggest that 1 slow slip is a common phenomena observed at almost all subduction zones with instrumentation capable of recording it 2 different frictional properties likely control fast versus slow slip 3 the depth range of slow slip may be related to the thermal properties of the plate interface and 4 the equivalent seismic moment of slow slip events is proportional to their duration mo different from the mo 3 scaling observed for earthquakes

a multi proxy approach to reconstructing sedimentary environments from the sperchios delta greece this paper presents an integrated approach to assess holocene environmental changes in the sperchios delta sperchios rift central greece a multidisciplinary study was carried out applying established analytical methods as well as exploring new techniques to detect past environmental conditions in a fluvio deltaic depositional system a series of six deep boreholes up to 50 m long and four shallow cores up to 6 m long from across the delta plain were studied in detail sedimentary facies were defined by changes in grain size and macro and microfaunal composition variability in mineral magnetic composition documented by changes in bulk magnetic susceptibility and 77k 293k and remanence parameters s 300 and arm sirm ratios as well as down core elemental variations obtained by scanning micro x ray fluorescence xrf provide constraints on the depositional changes related to the evolution of the sperchios delta correlations between elemental data derived by xrf analyses and grain siz

newly observed deep slow slip events at the central hikurangi margin new zealand implications for downdip variability of slow slip and tremor and relationship to seismic structure 1 we present previously undocumented deep 25 45 km depth moderate duration 2 3 months slow slip events sses directly downdip of known shallow 15 km depth short term 2 3 weeks sses at the central hikurangi margin new zealand the moderate duration sses produce 2 6 mm of horizontal displacement at continuous global positioning system stations in 2006 and 2008 similar to cascadia sses they involve 2 5 cm of slip over 5000 km2 of the subduction interface tremor occurs just downdip of the deep sse source area we also present results from a large shallow 12 km sse in 2013 just updip of the 2006 2008 sses the location of deep sses between shallow short term sses and tremor indicates strong downdip variation of subduction interface slip behavior at central hikurangi the deep sses occur where qp and vp vs data suggest an accumulation of fluid rich underplated sediment at the interface consistent with the idea that sses occur under high fluid pressure

quartz vein formation by local dehydration embrittlement along the deep tremorgenic subduction thrust interface hydrothermal quartz veins are ubiquitous in exhumed accretionary complexes including the namibian damara belt here subduction related deformation occurred at temperatures 550 c and vein geometry is consistent with plate interface shear low effective normal stresses and mixed mode deformation quartz vein 18o values relative to standard mean ocean water smow range from 9 4 to 17 9 n 30 consistent with precipitation from metamorphic fluids a dominant subset of quartz veins away from long lived high strain zones and basaltic slivers have 18o values in a smaller range of 14 9 1 requiring precipitation from a fluid with 18o of 12 1 at 470 550 c this uniform fluid isotope value is consistent with progressive local breakdown of chlorite allowing extensive hydrofracture at temperatures typical of the plastic regime in active subduction zones brittle deformation within the plastic regime is inferred from observations of tectonic tremor a noise like seismic signal including overlapping low and very low frequency earthquakes which occurs below the seismogenic zone both tremor and hydrothermal veins correlate with zones of inferred high fluid pressure could represent a mixture of shear and dilatant failure and may therefore be controlled by episodic hydrofracturing within a dominantly plastic and aseismic regime

seismicity preceding volcanic eruptions new experimental insights a variety of seismic signals representing different physical mechanisms precedes volcanic eruptions the most meaningful signals are high and low frequency earthquakes and volcanic tremor that have tentatively been related to fracturing and magma transport in the volcanic edifice we provide experimental support for this association by reproducing magma migration while recording seismic signals opening fractures emit high frequency acoustic events while the switch to low frequency and harmonic tremor accompanies the flow of the melt in the fractures discerning between these seismic signals in nature can significantly refine volcanic hazard evaluation

laboratory simulation of volcano seismicity the physical processes generating seismicity within volcanic edifices are highly complex and not fully understood we report results from a laboratory experiment in which basalt from mount etna volcano italy was deformed and fractured the experiment was monitored with an array of transducers around the sample to permit full waveform capture location and analysis of microseismic events rapid post failure decompression of the water filled pore volume and damage zone triggered many low frequency events analogous to volcanic long period seismicity the low frequencies were associated with pore fluid decompression and were located in the damage zone in the fractured sample these events exhibited a weak component of shear double couple slip consistent with fluid driven events occurring beneath active volcanoes

seismic consequences of warm versus cool subduction metamorphism examples from southwest and northeast japan warm and cool subduction zones exhibit differences in seismicity seismic structure and arc magmatism which reflect differences in metamorphic reactions occurring in subducting oceanic crust in southwest japan arc volcanism is sparse and intraslab earthquakes extend to 65 kilometers depth in northeast japan arc volcanism is more common and intraslab earthquakes reach 200 kilometers depth thermal petrologic models predict that oceanic crust subducting beneath southwest japan is 300 to 500 c warmer than beneath northeast japan resulting in shallower eclogite transformation and slab dehydration reactions and possible slab melting

tidal modulation of nonvolcanic tremor episodes of nonvolcanic tremor and accompanying slow slip recently have been observed in the subduction zones of japan and cascadia in cascadia such episodes typically last a few weeks and differ from normal earthquakes in their source location and moment duration scaling the three most recent episodes in the puget sound southern vancouver island portion of the cascadia subduction zone were exceptionally well recorded in each episode we saw clear pulsing of tremor activity with periods of 12 4 and 24 to 25 hours the same as the principal lunar and lunisolar tides this indicates that the small stresses associated with the solid earth and ocean tides influence the genesis of tremor much more effectively than they do the genesis of normal earthquakes because the lithostatic stresses are 10 5 times larger than those associated with the tides we argue that tremor occurs on very weak faults