a continuum of stress strength and slip in the cascadia subduction zone movement of the down going oceanic plate in subduction zones is accommodated by earthquakes slow slip and free slip with increasing depth analysis of accompanying tremor reveals a continuum of slow slip events in the cascadia subduction zone which suggests that deep free slip of the subducted plate may cause stress to be gradually transferred up the plate interface towards the seismogenic zone

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

rupture area and displacement of past cascadia great earthquakes from coastal coseismic subsidence coastal marshes record a 6500 yr history of coseismic displacements in great earthquakes at the cascadia subduction zone we compiled estimates of coseismic displacement for past megathrust events based on correlations with megathrust triggered turbidites and estimated megathrust slip based on comparisons of marsh displacements with dislocation model predictions age correlated marsh data are compatible with event rupture extents defi ned by the published turbidite record and a 6500 yr mean recurrence interval that increases northward from 230 to 480 yr within the constraints of the marsh data the width of the coseismic rupture zone generally agrees with the downdip width of the interseismic locked zone inferred from geodetic and thermal data in southernmost cascadia where the model does not include the complex deformation near the mendocino triple junction the coastal data may be better fi t by a model with an 25 narrower rupture than that inferred from regional geophysical data at each coastal marsh site coseismic displacements are roughly similar from event to event independent of the time since the previous event slip in the a d 1700 earthquake was consistent with the preceding interval of strain accumulation 200 yr only at the northern and southern ends of the margin but it was apparently much higher in southern washington and northern oregon possibly indicating postseismic contamination and or catch up coseismic slip to make up for a defi cit in the preceding event overall agreement between the dislocation models and the marsh data for most of the margin implies that such models can be usefully applied to rupture and ground shaking predictions

seismicity variations associated with aseismic transients in guerrero mexico 1995 2006 primarily aseismic deformation transients in subduction zones sometimes associated with tremors and low frequency earthquakes are a newly recognized mode of deformation stressing in the up dip seismogenic zone is increased episodically due to down dip transientslips andeacheventmaymakeitmorepronetofailureinalargethrustearthquake itisimportantforseismichazardassessment to search and identify patterns of seismicity variation associated with transients the guerrero mexico region is chosen for this study because of long term continuous geodetic observations and abundant seismicity in the shallow subduction zone we search the gcmt and neic catalogs for earthquakeswithdepths lessthan100kmbetween1995and2006withintheareacoveringthe regionaffected by major transients since 1996 a completeness magnitude of mc 4 5 is determined for the neic catalog used in this study based on the maximum likelihood method three large transients in 1998 2001 2002 and 2006 are all temporally correlated with high seismic rates in the studied area in particular transients are either preceded by a cluster of extensional earthquakes relatively far inland from the trench or followed by shallow thrustearthquakes closetothe trench in somecases such asthe 2001 2002 transient both typesofactivityare foundbordering the transient the assembled evidence suggests that transients may serve as a mechanism of stress communication between distant seismicity clusters in shallow subduction zones 2007 elsevier b v all rights reserved

modeling of slow slip events along the deep subduction zone in the kii peninsula and tokai regions southwest japan 1 in the subduction zone of southwest japan short term slow slip events sses occur with low frequency tremors lfts at intervals of several months recently lfts have been located with high resolution and their activities have been examined in detail by setting the generation zones of sses such that these zones contain the lft hypocenters we simulate sses on a 3d plate interface beneath the kii peninsula and tokai regions by using a rate and state dependent friction law with a small cut off velocity for the evolution effect our numerical results show that recurrence intervals of sses in the southern and central kii peninsula in the northern kii peninsula and in the tokai region are 2 5 3 0 4 8 5 6 and 3 5 4 5 months respectively which are consistent with observed sse activity our simulation also produces a multisegment event that propagates from the kii to tokai segments at a speed of 10 km day which is consistent with observations the results suggest that generation zones of lfts coincide with sse regions and that these two events are different manifestations of the same slip process along the subduction zone we also perform 3d modeling of faster events accompanied by short term sses by considering local circular patches with a smaller critical displacement surrounded by sse zones with a larger critical displacement local circular patches are set at the observed lft locations the simulation reproduces fast events that propagate at a speed of 100 200 km day during a single sse event

volatile emission during the eruption of baitoushan volcano china north korea ca 969 ad magma volume dre 24 5 km3 the main phase ca 95 vol is represented by comenditic tephra deposited dominantly as widespread fallout blankets and proximal ignimbrites the eruption column is estimated to have reached ca 25 km and thus entered the stratosphere a late phase 5 vol is represented by trachyte emplaced chiefly as moderately welded ignimbrites the comendites contain 3 and the trachytes 10 20 vol phenocrysts mainly anorthoclase hedenbergite and fayalite primary glassy melt inclusions with no signs of leakage were found only in phenocrysts in the comenditic tephra whereas those in phenocrysts in the trachytes are devitrified the comendite magma is interpreted to have been generated by fractional crystallization from a trachyte magma represented by melt inclusions in the phenocrysts in the comendite tephra the mass of volatiles emitted to the atmosphere during the eruption was estimated using the petrologic method the average h2o concentration of the comenditic matrix glass is 1 5 wt probably largely secondary and of the corresponding melt inclusions 5 2 wt melt inclusions in feldspar and quartz present the highest halogen concentrations with a calculated average for chlorine of 4762 ppm and for fluorine of 4294 ppm the comenditic matrix glasses are represented by a fluorine rich 3992 ppm f and fluorine poor group 2431 ppm f averaging 3853 ppm for chlorine only 20 of all sulfur analyses of the comenditic matrix glasses and melt inclusions are above the detection limit of 250 ppm s the difference between pre and post eruptive concentration of h2o is at least 3 7 0 6 wt h2o taking into consideration re hydration of the matrix glass and possible leakage of melt inclusions the difference between pre and post eruptive concentrations of the halogens amounts to 909 90 ppm cl and 1863 280 ppm and 302 40 ppm f the difference for s was estimated based on the average of the maximum s concentrations in the melt inclusions 455 ppm s and the detection limit resulting in 205 40 ppm s the calculated mass of volatiles injected into the atmosphere based on the erupted magma volume and volatile data is 1796 453 megatons for h2o 45 10 megatons for chlorine 42 11 megatons for fluorine and 2 0 6 megatons for sulfur the 969 20 ad eruption of baitoushan volcano one of the largest eruptions of the past 2000 years is thought to have had a substantial but possibly short lived effect on climate

source parameters and time dependent slip distributions of slow slip events on the cascadia subduction zone from 1998 to 2008 1 we invert for the time dependent slip history of slow slip events on the cascadia subduction zone using gps data from 1998 to 2008 the 16 slip transients have sufficient station coverage to solve for the slip distribution on the plate interface gps time series are inverted for fault slip using the extended network inversion filter limited station coverage south of portland 45 5 n latitude restricts our analysis to events on the northern half of the subduction zone slip is resolved at the base of the seismogenic zone and the slip distributions suggest a potential segment boundary near seattle 47 6 n that correlates roughly with geologic and tectonic boundaries events that initiate to the north and south tend to overlap at about this latitude we compile statistics on source parameters such as propagation rate recurrence interval and stress drop which can be used to constrain proposed models of the source mechanics over a 10 year period total strain release from slow slip events is nonuniform along strike with the greatest cumulative slip 27 cm centered beneath port angeles 48 1 n this slip patch also exhibits the most regular recurrence of mw 6 events relative to other locations along strike the spatial extent of the slip patch beneath port angeles correlates with the along strike bend of the cascadia subduction zone in northwestern washington suggesting that plate geometry plays an important role in controlling the along strike characteristics of slow slip

role of fault gouge dilatancy on aseismic deformation transients 1 in the vicinity of episodic aseismic transients in several subduction zones the presence of interstitial fluids and near lithostatic pore pressure has been proposed to interpret seismic observations of high p to s wave speed ratio and high poisson s ratio under such conditions fault stabilization by dilatancy induced suction during increased shear strain rates becomes very efficient we analyze the frictional and hydraulic conditions for spontaneous transients on a fluid infiltrated fault including dilatancy and pore compaction in the framework of rate and state friction with a membrane diffusion approximation in both a simplified spectral model and a 2 d cascadia like subduction fault model the fault response is mainly controlled by three nondimensional parameters 1 w h the along dip width of the high pore pressure velocity weakening fault relative to a characteristic nucleation size 2 a drainage parameter u the relative time scales for fluid diffusion and friction evolution and 3 a dilatancy parameter e the relative contributions to stress drop from dilatancy and friction evolution the incorporation of dilatancy enables aseismic transients at much larger values of w h than is possible under conditions of constant pore pressure an analytic estimate of the maximum slip velocity as a function of w h e and u is derived and agrees reasonably well with the simulation results the dependence of the properties of modeled transients on the drainage parameter u is similar to that on the dilatancy parameter e for u e less than 1 maximum velocity decreases while recurrence period remains relatively constant for u e greater than 1 maximum velocity approaches the steady state velocity and recurrence period approaches the period at neutral stability in the subduction fault model using gabbro gouge friction properties the slip per episode and the recurrence period increase with w h generally following the trend defined without dilatancy the maximum velocity with dilatancy can be several orders of magnitude smaller than that without in particular for larger values of e and values of w h near the no dilatancy stability limit

basin centered asperities in great subduction zone earthquakes a link between slip subsidence and subduction erosion 1 published areas of high coseismic slip or asperities for 29 of the largest circum pacific megathrust earthquakes are compared to forearc structure revealed by satellite free air gravity bathymetry and seismic profiling on average 71 of an earthquake s seismic moment and 79 of its asperity area occur beneath the prominent gravity low outlining the deep sea terrace 57 of an earthquake s asperity area on average occurs beneath the forearc basins that lie within the deep sea terrace in sw japan slip in the 1923 1944 1946 and 1968 earthquakes was largely centered beneath five forearc basins whose landward edge overlies the 350 c isotherm on the plate boundary the inferred downdip limit of the locked zone basin centered coseismic slip also occurred along the aleutian mexico peru and chile subduction zones but was ambiguous for the great 1964 alaska earthquake beneath intrabasin structural highs seismic slip tends to be lower possibly due to higher temperatures and fluid pressures kilometers of late cenozoic subsidence and crustal thinning above some of the source zones are indicated by seismic profiling and drilling and are thought to be caused by basal subduction erosion the deep sea terraces and basins may evolve not just by growth of the outer arc high but also by interseismic subsidence not recovered during earthquakes basin centered asperities could indicate a link between subsidence subduction erosion and seismogenesis whatever the cause forearc basins may be useful indicators of long term seismic moment release the source zone for cascadia s 1700 a d earthquake contains five large basin centered gravity lows that may indicate potential asperities at depth the gravity gradient marking the inferred downdip limit to large coseismic slip lies offshore except in northwestern washington where the low extends landward beneath the coast transverse gravity highs between the basins suggest that the margin is seismically segmented and could produce a variety of large earthquakes

numerical simulations on megathrust rupture stabilized under strong dilatancy strengthening in slow slip region 1 episodic slow slip events sses typically involve a few millimeters to centimeters of slip over several days to months at depths near or further downdip of megathrust seismogenic zones despite its widespread presence in subduction margins it remains unknown how sses interact with the seismogenic zone and affect megathrust ruptures here i construct a 2 d thrust fault model governed by rate state friction to investigate how fault dilatancy influences the amplitude and spatial distribution of coseismic slip afterslip and sses model results illustrate that under strong dilatancy and high pore pressure around the friction stability transition coseismic rupture stops at the onset of sses modeled sses have lower velocities longer recurrence intervals and durations and larger slip amounts as dilatancy becomes stronger demonstrating a transition from short term to long term type of sse behavior these results qualitatively explain the range of spatial distributions of sses and megathrust ruptures observed or inferred in natural subduction zones furthermore the relative depths of sses and megathrust afterslip may serve as an indicator of dilatancy effectiveness

episodic slow slip events accompanied by non volcanic tremors in southwest japan subduction zone 1 episodic slow slip events have been recognized by means of tilt changes in the western shikoku area southwest japan the crustal tilt deformation was observed repeatedly with a recurrence interval of approximately six months coincident with the occurrences of major non volcanic deep tremor activities in this area observed tilt changes can be explained by slow slip events occurring around the source area of tremors in each episode the source of the slow slip event and tremor migrate simultaneously the spatial and temporal coincidence of tremors and slow slip events indicates that they both may be coupling phenomena reflecting the stress accumulation process at the subducting plate

comprehensive model of short and long term slow slip events in the shikoku region of japan incorporating a realistic plate configuration 1 we numerically simulate slow slip events sses in the shikoku region of japan incorporating the configuration of the subducting plate we adopt a rate and state dependent friction law with cutoff velocities assuming a frictional parameter distribution based on observed long term sses and nonvolcanic tremors that reflects the slip of short term sses our model reproduces recurrences of long and short term sses and segments of short term sses in our simulation short term sses transition from episodic to continuous slip is reproduced this feature is consistent with tremor activity recently reported in both shikoku and cascadia in addition to the long term sses in the bungo channel our model also reproduces newly found long term sses in central shikoku and predicts that these sses recur during the interseismic period between megathrust earthquakes our model comprehensively reproduces various sses and their characteristics as reported in the shikoku region

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

the frictional hydrologic metamorphic and thermal habitat of shallow slow earthquakes slow earthquakes have recently been discovered on the shallow parts of some subduction zones a review of the conditions under which these quakes form reveals that they could be common in most subduction zones globally

multi proxy dating the millennium eruption of changbaishan to late 946 ce ranking among the largest volcanic eruptions of the common era ce the millennium eruption of changbaishan produced a widely dispersed tephra layer known as the b tm ash which represents an important tie point for palaeoenvironmental studies in east asia hitherto there has been no consensus on its age with estimates spanning at least the tenth century ce here we identify the cosmogenic radiocarbon signal of 775 ce in a subfossil larch engulfed and killed by pyroclastic currents emplaced during the initial rhyolitic phase of the explosive eruption combined with glaciochemical evidence from greenland this enables us to date the eruption to late 946 ce this secure date rules out the possibility that the millennium eruption contributed to the collapse of the bohai kingdom manchuria korea in 926 ce as has previously been hypothesised further despite the magnitude of the eruption we do not see a consequent cooling signal in tree ring based reconstructions of northern hemisphere summer temperatures a tightly constrained date for the millennium eruption improves the prospect for further investigations of historical sources that may shed light on the eruption s impacts and enhances the value of the b tm ash as a chronostratigraphic marker

wetland soil formation in the rapidly subsiding mississippi river deltaic plain mineral and organic matter relationships abstract the elevation of submerging coastal marshes is maintained by vertical accretion of mineral and organic matter submergence rates currently exceed 1 0 cm year 1 in the mississippi deltaic plain and are expected to increase mineral matter organic matter relationships were examined in surface profiles of mississippi deltaic plain soil from both active delta zone marsh which receives freshwater and mineral sediment from the atchafalaya or mississippi rivers and inactive delta zone marsh which relies on rainfall for freshwater and on reworked sediments for mineral matter to gain insights into marsh soil structure and formation mineral and organic matter accounted for 4 14 of soil volume the remainder was pore space and was occupied by water and entrapped gases organic matter occupied more volume than mineral matter in all but saline marsh soil the regular influx of mineral matter to active fresh marsh resulted in active fresh marsh soil containing twice as much mineral and organic matter as inactive fresh marsh soil within the inactive delta zone the volume of mineral and organic matter increased from fresh inland to saline seaward marshes saline marsh soil required 1 7 times as much mineral matter as brackish marsh soil to vertically accrete at similar rates possibly as a result of soil bulk density requirements of the dominant saline marsh plant spartina alterniflora vertical accretion rates were highest in the active delta zone probably as a result of increased mineral matter availability and delivery current best estimates of the combination of mineral and organic matter required g m 2 year 1 to maintain marsh surface water level relationship are fresh marsh organic matter 1700 269 x mineral matter 424 x brackish marsh organic matter 553 583 x mineral matter 1052 x saline marsh organic matter 923 601 x mineral matter 1798 x where x the rate of submergence cm year 1

obsidian characterization by laser ablation icp ms and its application to prehistoric trade in the mediterranean and the near east sources and distribution of obsidian within the aegean and anatolia for geological studies interest in mass spectrometry with an inductively coupled plasma as an ion source and its association with laser ablation as a sample introduction technique la icp ms has steadily increased during the past few years and is now being developed in other fields such as archaeology after a description of the analytical procedure and the calculation method we show the potential of this technique to characterize almost non destructively archaeological artefacts among the 70 elements that could be routinely analysed by la icp ms with detection limits below the ppm level we choose to determine the more critical ones in order to evaluate the geochemical models of the magmatic process major elements rare earths and some transition elements a detailed survey of cappadocian obsidian flows is given and includes the characterization of nine different sources evidence of complex trade activities is clearly shown by the obsidian tools found at different prehistoric sites from neolithic to bronze age levels in the mediterranean and the near east new results obtained on some archaeological sites located in turkey syria and cyprus are presented they show the importance of cappadocian sources in obsidian trade our results show that la icp ms allows a non destructive analysis of archaeological objects and that it combines the advantage of the different classical methods used to characterize obsidian sources mainly xrf and inaa with high sensitivity and rapidity thus la icp ms appears to be a very powerful analytical tool and at this time this technique is the only one which can non destructively determine such an important number of elements with such low detection limits

segmentation and supercycles a catalog of earthquake rupture patterns from the sumatran sunda megathrust and other well studied faults worldwide abstract after more than 100 years of earthquake research earthquake forecasting which relies on knowledge of past fault rupture patterns has become the foundation for societal defense against seismic natural disasters a concept that has come into focus more recently is that rupture segmentation and cyclicity can be complex and that a characteristic earthquake model is too simple to adequately describe much of fault behavior nevertheless recognizable patterns in earthquake recurrence emerge from long high resolution spatially distributed chronologies researchers now seek to discover the maximum minimum and typical rupture areas the distribution variability and spatial applicability of recurrence intervals and patterns of earthquake clustering in space and time the term supercycle has been used to describe repeating longer periods of elastic strain accumulation and release that involve multiple fault ruptures however this term has become very broadly applied lumping together several distinct phenomena that likely have disparate underlying causes we divide earthquake cycle behavior into four major classes that have different implications for seismic hazard and fault mechanics 1 quasi periodic similar ruptures 2 clustered similar ruptures 3 clustered complementary ruptures rupture cascades and 4 superimposed cycles segmentation is likewise an ambiguous term we identify master segments and asperities as defined by barriers to fault rupture these barriers may be persistent rarely or never traversed frequent occasionally traversed or ephemeral changing location from cycle to cycle we compile a catalog of the historical and paleoseismic evidence that currently exists for each of these types of behavior on major well studied faults worldwide due to the unique level of paleoseismic and paleogeodetic detail provided by the coral microatoll technique the sumatran sunda megathrust provides one of the most complete records over multiple earthquake rupture cycles long historical records of earthquakes along the south american and japanese subduction zones are also vital contributors to our catalog along with additional data compiled from subduction zones in cascadia alaska and middle america as well as the north anatolian and dead sea strike slip faults in the middle east we find that persistent and frequent barriers rupture cascades superimposed cycles and quasi periodic similar ruptures are common features of most major faults clustered similar ruptures do not appear to be common but broad overlap zones between neighboring segments do occur barrier regions accommodate slip through reduced interseismic coupling slow slip events and or smaller more localized ruptures and are frequently associated with structural features such as subducting seafloor relief or fault trace discontinuities this catalog of observations provides a basis for exploring and modeling root causes of rupture segmentation and cycle behavior we expect that researchers will recognize similar behavior styles on other major faults around the world

time dependent modeling of slow slip events and associated seismicity and tremor at the hikurangi subduction zone new zealand we present a time dependent slip model of 12 slow slip events sses occurring in the hikurangi margin of new zealand during 2010 and 2011 this model is obtained by inverting daily gps solutions from geonet s continuous gps network on the north island and northern south island we compare the properties of these sses to observations in japan cascadia and mexico and find that hikurangi sses have comparatively large amounts of slip up to 27 cm high slip rates up to 1 4 cm d and a large range of depths 10 40 km durations 7 270 days and sizes mw 5 9 6 9 we further investigate the relationship between the cape turnagain sse and an associated seismic swarm and find that observations are consistent with stress triggering outside the slowly slipping region however other explanations cannot be ruled out we also compare slip during the long term manawatu sse with the tremor epicenters found by ide 2012 and note that tremor locations are offset in the downdip direction relative to the slipping region similar to observations in the bungo channel of japan and guerrero mexico

slow slip transients along the oaxaca subduction segment from 1993 to 2007 summary we use data from 12 continuous gps stations in southern mexico including eight new stations to better characterize transient slip episodes along the mexican subduction zone continuous gps recording in oaxaca that began 14 years ago constituting the longest continuous gps record in southern mexico defines nine distinct episodes of transient slip from 1993 to 2007 including previously unreported transient slip episodes in early 1995 and 2006 all transient slip episodes recorded in oaxaca city were also recorded at a gps site 400 km away in the state of guerrero after measurements began there in early 1997 demonstrating that transient slip affects widespread areas of southern mexico well recorded transients in 2004 and 2006 appear to have originated along the oaxaca trench segment hundreds of kilometres from the potentially hazardous guerrero seismic gap during the 2004 slip transient displacements of more than 20 mm were recorded at stations in the oaxaca gps array a factor of 2 3 larger than at sites in guerrero elastic half space modelling of the 2004 displacements at sites throughout southern mexico indicates that most slip was focused beneath oaxaca in deeper areas of the subduction interface immediately downdip from previous megathrust rupture zones but that slip also may have extended significantly updip into a seismic gap along the oaxaca coast the best fitting model is also able to explain transient vertical offsets of up to 30 mm observed during this event shortly before the onset of transient slip in 2004 a pair of moderate m w 5 1 5 5 earthquakes ruptured the downdip end of the seismogenic zone immediately east of the oaxaca seismic gap suggesting a possible relationship between the two in 2006 transient slip began 1 3 months earlier in oaxaca than in other areas offering the clearest evidence to date for the existence of one or more source regions for transient slip outside the guerrero seismic gap where large amplitude transient slip originated in 2002 the still limited data indicate that transient slip that originates elsewhere in mexico may trigger aseismic slip in guerrero and further indicate that transient slip beneath oaxaca is limited to areas of the subduction interface that surround the rupture zones of previous large shallow thrust earthquakes

slow slip predictions based on granite and gabbro friction data compared to gps measurements in northern cascadia received 7 october 2008 revised 17 april 2009 accepted 12 june 2009 published 29 september 2009 1 for episodic slow slip transients in subduction zones a large uncertainty in comparing surface deformations predicted by forward modeling based on rate and state friction to gps measurements lies in our limited knowledge of the frictional properties and fluid pore pressure along shallow subduction faults in this study we apply the laboratory rate and state friction data of granite and gabbro gouges under hydrothermal conditions to a cascadia like 2 d model to produce spontaneous aseismic transients and we compare the resulting intertransient and transient surface deformations to gps observations along the northern cascadia margin an inferred region along dip of elevated fluid pressure is constrained by seismological observations where available and by thermal and petrological models for the cascadia and sw japan subduction zones for the assumed

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

towards inferring earthquake patterns from geodetic observations of interseismic coupling ultimately seismotectonic studies seek to provide ways of assessing the timing magnitude and spatial extent of future earthquakes ample observations document the spatial variability in interseismic coupling defined as a degree of locking of a fault during the period of stress build up between seismic events fully or nearly locked fault patches are often surrounded by aseismically creeping areas however it is unclear how these observations could help assess future earthquakes here we simulate spontaneous seismic and aseismic fault slip with a fully dynamic numerical model our simulations establish the dependence of earthquake rupture patterns and interseismic coupling on spatial variations of fault friction we consider the long term evolution of slip on a model fault where two seismogenic locked segments are separated by an aseismically slipping patch where rupture is impeded we find that the probability for a large earthquake to break through the rupture impeding patch is correlated with the interseismic coupling averaged over this patch in addition the probability that an earthquake breaks through the rupture impeding patch and interseismic coupling are both related to fault friction properties through a single non dimensional parameter our study opens the possibility of predicting seismic rupture patterns that a fault system can produce on the basis of observations of its interseismic coupling and suggests that regions of low interseismic coupling may reveal permanent barriers to large earthquakes

scaling relationships of source parameters for slow slip events to better understand the physical mechanisms of slow slip events sses detected worldwide we explore the scaling relationships of various source parameters and compare them with similar scaling laws for earthquakes these scaling relationships highlight differences and similarities between slow slip events and earthquakes and hold implications for the degree of heterogeneity and fault healing characteristics the static stress drop remains constant for different sized events as is observed for earthquakes however the static stress drop of slow slip events is within a range of 0 01 1 0 mpa 1 2 orders of magnitude lower than that found for earthquakes which could be related to the low stress state on the fault the average rupture velocity ranging from kilometers per second to kilometers per day decreases linearly with increasing seismic moment in log log space unlike earthquakes that are nearly constant this inverse relationship of rupture velocity with seismic moment could be related to the heterogeneity of fault properties slow slip events typically have ratios of event duration over dislocation rise time less than 3 while earthquakes have ratios greater than 3 this indicates that slow slip events are less pulselike than earthquakes in their mode of propagation and suggests that the healing behind the rupture front is delayed the recurrence statistics of slow slip events on the northern cascadia subduction zone are weakly time predictable and moderately antislip predictable that is the event size and preevent recurrence interval are anticorrelated which may indicate that healing between events strengthens the fault with time online material table of source parameters and data sources

phenomenology of deep slow earthquake family in southwest japan spatiotemporal characteristics and segmentation 1 the phenomenology of deep slow earthquakes including low frequency tremors very low frequency earthquakes and short term slow slip events on the subducting plate interface in southwest japan is investigated on the basis of their spatiotemporal characteristics the belt like distribution of tremors is divided into segments bounded by gaps the repetition of tremor episode depends on the magnitude of the episode which is defined by the number of detected tremors within each episode major tremor episodes with a large number of detected tremors recur at an interval of approximately 6 months accompanying the short term slow slip events in large segments in small segments tremor episodes with small numbers of tremors have recurrence intervals of a few months some of them occasionally accompany the slight ground tilting caused by a small size slow slip event even in the same segment there exist different recurrence intervals according to the magnitude of the tremor episode the migration pattern varies greatly in initiation termination direction and speed however the migration direction has a general tendency for each segment on both sides of the gap the tremor starts next to the gap and propagates to the other side assuming all tremor episodes are caused by slow slip events the equivalent moment and slip are estimated from the number of detected tremor counts and the area of each tremor episode the equivalent slip history estimated from all tremor episodes is almost constant in each segment this indicates that tremor activity is a good proxy for slow slips

possible relationship between nonvolcanic tremor and the 1998 2001 slow slip event south central alaska 1 we document the occurrence of nonvolcanic tremor nvt in south central alaska for 3 months of each year between 1999 and 2001 to provide a first order attempt to understand the relationship between nvt and a large slow slip event that occurred over a 2 to 3 year period between 1998 and 2001 the majority of the nvt signals observed after the onset of the slow slip event are bursts lasting between 10 and 15 min with frequencies ranging from 1 to 6 hz by the summer of 2001 the quantity of nvt has decreased dramatically from the previous summers and episodes rarely last up to 10 min the decrease in nvt activity in the summer of 2001 is coincident with the end of the slow slip event there is a clear spatial correlation between the observed nvt and the slow slip event with most of the nvt events located on the downdip edge of the region of highest slip depth estimates range widely over the region with approximately half concentrated near the interpreted north america yakutat pacific plate interface and the remainder located above the plate interface however owing to inadequate station coverage and poor knowledge of the local structure determining accurate depths is difficult and thus the relationship between the nvt and the plate interface is problematic this is the first study giving evidence that the relationship between slow slip events and nvt seen in cascadia and southwest japan may also exist in alaska

earthquake nucleation on rate and state faults aging and slip laws we compare 2 d quasi static earthquake nucleation on rate and state faults under both aging and slip versions of the state evolution law for both versions mature nucleation zones exhibit 2 primary regimes of growth well above and slightly above steady state corresponding respectively to larger and smaller fault weakening rates well above steady state aging law nucleation takes the form of accelerating slip on a patch of fixed length this length is proportional to b 1 and independent of a where a and b are the constitutive parameters relating changes in slip speed and state to frictional strength under the slip law the nucleation zone is smaller and continually shrinks as slip accelerates the nucleation zone is guaranteed to remain well above steady state only for values of a b that are low by laboratory standards near steady state for both laws the nucleation zone expands the propagating front remains well above steady state giving rise to a simple expression for its effective fracture energy g c this fracture energy controls the propagation style for the aging law g c increases approximately as the square of the logarithm of the velocity jump this causes the nucleation zone to undergo quasi static crack like expansion to a size asymptotically proportional to b b a 2 for the slip law g c increases only as the logarithm of the velocity jump and crack like expansion is not an option instead the nucleation zone grows as an accelerating unidirectional slip pulse under both laws the nucleation front propagates at a velocity larger than the slip speed by roughly b divided by the logarithm of the velocity jump where is the effective elastic shear modulus for this prediction to be consistent with observed propagation speeds of slow slip events in subduction zones appears to require effective normal stresses as low as 1 mpa

along fault pore pressure evolution during a slow slip event in guerrero mexico abstract slow earthquakes are important constituents of the seismic cycle and are involved in the stress transfer between the viscously slipping portion of the plate interface and the seismogenic zone their occurrence is likely associated with the near lithostatic pore pressure in the slow earthquake source region where fluids might modify fault friction and whose presence is indicated by high ratios of compressional p wave velocity to shear s wave velocity observed at the interface between the subducting plate and the overlying crust here we compare two slow earthquake phenomena observed in the guerrero region of the mexican subduction zone low frequency earthquakes lfes and a slow slip event sse recorded by gps we observe variations of the lfe occurrence rates over month long time scales during a large sse that we interpret as a manifestation of transient changes in the fault shear strength we argue that these transient changes are caused by a pore pressure fluctuation that migrates updip along the subduction interface this mechanism suggests that fluids do not only passively weaken the plate interface but also play an active role in slow earthquake source regions

provenance of obsidian artifacts from the wolseongdong paleolithic site korea and its archaeological implications abstract the provenance of obsidian artifacts from the wolseongdong paleolithic site in korea has hitherto been uncertain a previous study was unable to identify the source despite the availability of major minor element concentrations strontium isotopic composition and k ar age we have revisited the problem and obtained geochemical data for 100 obsidian artifacts from wolseongdong using laser ablation inductive coupled plasma mass spectrometry la icp ms it was found that all lithics originated from a single source located around 700 km away at the paektusan volcano on the dpr korea chinese border our findings highlight the necessity of reliable data analysis and quality assurance for obsidian characterization studies

vertical accretion in microtidal regularly and irregularly flooded estuarine marshes abstract vertical accretion rates were measured in microtidal tidal amplitude less than 0 3 m regularly flooded twice daily by the astronomical tides and irregularly flooded inundated only during spring and storm tides estuarine marshes in north carolina to determine whether these marshes are keeping pace with rising sea level and to quantify the relative contribution of organic matter and mineral sediment to vertical growth accretion rates in streamside and backmarsh locations of each marsh were determined by measuring the cesium 137 137 cs activity in 2 cm soil depth increments soil bulk density organic carbon c total nitrogen n and particle density also were measured to estimate rates of accumulation of organic matter om mineral sediment and nutrients with the exception of the backmarsh location of the regularly flooded marsh vertical accretion rates in the marshes studied matched or exceeded the recent 1940 80 rate of sea level rise 1 9 mm year 1 along the north carolina coast accretion rates in the irregularly flooded marsh averaged 3 6 0 5 mm year 1 along the streamside and 2 4 0 2 mm year 1 in the backmarsh the regularly flooded marsh had lower accretion rates averaging 2 7 0 3 mm year 1 along the streamside and 0 9 0 2 mm year 1 in the backmarsh vertical accretion in the irregularly flooded marsh occurred via in situ production and accumulation of organic matter rates of soil om 196 280 g m 2 year 1 organic c 106 146 g m 2 year 1 and total n 6 9 10 3 g m 2 year 1 accumulation were much higher in the irregularly flooded marsh as compared to the regularly flooded marsh om 51 137 g m 2 year 1 c 21 59 g m 2 year 1 n 1 3 4 1 g m 2 year 1 in contrast vertical accretion in the regularly flooded marsh was sustained by allochthonous inputs of mineral sediment inorganic sediment deposition contributed 677 1139 g m 2 year 1 mineral matter to the regularly flooded marsh as compared to only 147 311 g m 2 year 1 to the irregularly flooded marsh the irregularly flooded marsh exhibited an accretionary balance vertical accretion rate minus local apparent sea level rise of 0 5 1 7 mm year 1 suggesting that these microtidal marshes would be capable of maintaining their elevation if the rate of sea level rise increased in the regularly flooded marsh the streamside zone had an accretionary balance of 0 8 mm year 1 while the backmarsh had a deficit of 1 0 mm year 1 our results suggest that microtidal regularly flooded marshes would be susceptible to submergence by an increase in the rate of sea level rise unless accompanied by an increase in mineral sediment deposition

seismic structure and tectonics of the continental wedge overlying the source region of the iquique mw8 1 2014 earthquake abstract on april 1 2014 a large earthquake mw 8 1 ruptured the central part of a historic seismic gap in northern chile in order to study the relationship between the co seismic rupture characteristics and the crustal structure of the subduction zone we processed a trench perpendicular seismic reflection profile acquired across the zone of maximum slip and generated a p wave velocity model the results show a frontal prism in the continental wedge characterized by low velocities that increase rapidly towards the shore and acted as a barrier for trench ward propagation of aftershocks landward a transition zone with increasing upper crust velocity 4 5 km s concentrates most of the aftershocks in addition a trench ward dipping set of fault zones is observed along the continental wedge associated to the iquique forearc basin formation 1 5 km thick at the depocenter on this profile we identify three stratigraphic units within the basin a landward tilt and thickness increase is detected in each stratigraphic unit along with growth strata and domino structures suggesting landward migration of syn extensional deformation in response to basal subduction erosion by extrapolating our results to the plate boundary and based on published focal mechanisms of intra crustal seismicity we find a strong spatial correlation between the iquique basin and the highest slip area for the 2014 earthquake suggesting long term extensional deformation due to coseismic tensional stresses

complex characteristics of slow slip events in subduction zones reproduced in multi cycle simulations 1 since the discovery of slow slip events along subduction zone interfaces worldwide dense geodetic and seismic networks have illuminated detailed characteristics of these events and associated tremor high resolution observations of tremor where the spatial temporal evolution is presumed to reflect that of the underlying slow slip events show highly complex patterns in which the origins remain poorly understood we present a new computationally efficient modeling technique that reproduces many features of observed slow slip events including slow initiation coalescence of separate events and rapid back propagation of renewed slip over previously slipped regions rapid back propagation speeds are explained as a consequence of rate and state dependent frictional healing consistent with analytical solutions developed in support of the simulations

central cascadia subduction zone creep central cascadia between 43 n and 46 n has reduced interseismic uplift observed in geodetic data and coseismic subsidence seen in multiple thrust earthquakes suggesting elevated persistent fault creep in this section of the subduction zone we estimate subduction thrust decade scale locking and crustal block rotations from three component continuous global positioning system gps time series from 1997 to 2013 as well as 80 year tide gauge and leveling derived uplift rates geodetic observations indicate coastal central oregon is rising at a slower rate than coastal washington southern oregon and northern california modeled locking distributions suggest a wide locking transition zone that extends inland under central oregon paleoseismic records of multiple great earthquakes along cascadia indicate less subsidence in central oregon the cascade thrust under central oregon may be partially creeping for at least 6500 years the length of the paleoseismic record reducing interseismic uplift and resulting in reduced coseismic subsidence large accretions of eocene age basalt siletzia terrane between 43 n and 46 n may be less permeable compared to surrounding terranes potentially increasing pore fluid pressures along the fault interface resulting in a wide zone of persistent fault creep in a separate inversion three component gps time series from 1 july 2005 to 1 january 2011 are used to estimate upper plate deformation locking between slow slip events sses slip from 16 sses and an earthquake mechanism cumulative sses and tectonic tremor are weakest between 43 n and 46 n where partial fault creep is increased and siletzia terrane is thick suggesting that surrounding rock properties may influence the mode of slip

sources of archaeological obsidian on sakhalin island russian far east abstract instrumental neutron activation analysis was performed on 79 obsidian tools and flakes from 35 sites on sakhalin island dating from upper paleolithic c 19 000 bp to early iron age c 2000 800 bp due to the absence of volcanic glass on sakhalin island raw materials from the nearest obsidian sources on hokkaido island such as oketo shirataki tokachi mitsumata and akaigawa were also analysed a strong correlation between the chemical compositions of obsidian artefacts from sakhalin and volcanic glass sources from hokkaido was discovered in particular the oketo and shirataki sources were used for tool manufacturing throughout all of sakhalin island s prehistory the distances between sources and archaeological sites range from 200 1000 km the intensive exchange of raw materials continued and even intensified after the appearance of the la perouse soya strait between hokkaido and sakhalin about 10 000 8000 bp the sakhalin island populations were deeply involved in the obsidian exchange network centered on hokkaido

slip rate and tremor genesis in cascadia at many plate boundaries conditions in the transition zone between seismogenic and stable slip produce slow earthquakes in the cascadia subduction zone these events are consistently observed as slow aseismic slip on the plate interface accompanied by persistent tectonic tremor however not all slow slip at other plate boundaries coincides spatially and temporally with tremor leaving the physics of tremor genesis poorly understood here we analyze seismic geodetic and strainmeter data in cascadia to observe for the first time a large tremor generating slow earthquake change from tremor genic to silent and back again the tremor falls silent at reduced slip speeds when the migrating slip front pauses as it loads the stronger adjacent fault segment to failure the finding suggests that rheology and slip speed regulated stressing rate control tremor genesis and the same section of fault can slip both with and without detectable tremor limiting tremor s use as a proxy for slip

diverse slow slip behavior at the hikurangi subduction margin new zealand 1 the installation of a continuous gps cgps network in new zealand since 2002 has enabled the discovery of 15 slow slip events at the hikurangi subduction margin our analysis and interpretation of the cgps data reveal a marked diversity in characteristics of slow slip events sses in the north island with durations varying from 6 days to 1 5 years equivalent moment release between mw 6 3 7 2 and recurrence intervals of repeating sses on the order of 2 years to more than 5 years the duration and magnitude characteristics of hikurangi sses appear to be related to the depth where they occur the deepest longest duration and largest sses occur at the southern hikurangi margin near the downdip limit of deep down to 40 km depth strong interseismic coupling the shallowest shortest duration smallest and most frequent sses occur at the northern and central hikurangi margin near the downdip limit of unusually shallow 10 15 km depth interseismic coupling the direction of slip on the interface in the hikurangi sses is consistent with slip partitioning at the hikurangi subduction margin we also show that moment accumulation rates on the interface for the time periods between sses are 40 higher than for the period of more than a decade averaging through the sses indicating that sses compose a major portion of the overall moment release budget of the hikurangi subduction interface

global sea level trend in the past century data derived from tide gauge stations throughout the world indicate that the mean sea level rose by about 12 centimeters in the past century the sea level change has a high correlation with the trend of global surface air temperature a large part of the sea level rise can be accounted for in terms of the thermal expansion of the upper layers of the ocean the results also represent weak indirect evidence for a net melting of the continental ice sheets

cascadia subducting plate fluids channelled to fore arc mantle corner ets and silica deposition in this study we first summarize the constraints that on the cascadia subduction thrust there is a 70 km gap downdip between the megathrust seismogenic zone and the episodic tremor and slip ets that lies further landward there is not a continuous transition from unstable to conditionally stable sliding seismic rupture occurs mainly offshore for this hot subduction zone ets lies onshore we then suggest what does control the downdip position of ets we conclude that fluids from dehydration of the downgoing plate focused to rise above the fore arc mantle corner are responsible for ets there is a remarkable correspondence between the position of ets and this corner along the whole margin hydrated mineral assemblages in the subducting oceanic crust and uppermost mantle are dehydrated with downdip increasing temperature and seismic tomography data indicate that these fluids have strongly serpentinized the overlying fore arc mantle laboratory data show that such fore arc mantle serpentinite has low permeability and likely blocks vertical expulsion and restricts flow updip within the underlying permeable oceanic crust and subduction shear zone at the fore arc mantle corner these fluids are released upward into the more permeable overlying fore arc crust an indication of this fluid flux comes from low poisson s ratios and vp vs found above the corner that may be explained by a concentration of quartz which has exceptionally low poisson s ratio the rising fluids should be silica saturated and precipitate quartz with decreasing temperature and pressure as they rise above the corner

episodic slow slip events and rate and state friction 1 there are several ways of generating episodic slow slip events in models of rate and state friction here i explore the possibility that they arise on velocity weakening faults whose length is tuned in some sense unlike spring block sliders which have a unique critical stiffness for instability elastically deformable faults have multiple length scales stiffnesses relevant to nucleation slow slip events occur when the fault is large enough to initiate an event but too small for that event to reach dynamic instability the available window of lengths depends upon the effective fracture energy of the growing nucleation zone for the aging evolution law this fracture energy increases rapidly with slip speed and the range of permissible lengths increases nearly as b b a where a and b are the coefficients of the velocity and state dependence of the frictional strength this range becomes very large for faults that are near velocity neutral a b however existing lab data firmly favor the slip law as a predictor of nucleation style and for this law the effective fracture energy increases much less rapidly with slip speed the range of fault lengths capable of hosting slow slip events in this case seems too small to explain why they are common to so many subduction zones slow slip can be stabilized over an exceedingly large range of fault lengths if the fracture energy increases with slip speed much more rapidly than for the aging law an appealing mechanism is inelastic dilation of the fault zone coupled with pore pressure reduction and diffusive recovery

source scaling relations and along strike segmentation of slow slip events in a 3 d subduction fault model scaling between slip event duration and equivalent moment is diagnostic of the underlying physics of rupture process for episodic slow slip events sses in subduction zones their moment duration relation is not clearly defined and shows considerable variation among individual margins where multiple episodes of sses are geodetically detected here i set up a 3 d planar thrust fault model within the framework of rate state friction to study the spatiotemporal evolution of slip and stress during sses sse source properties including along strike length duration equivalent moment and stress drop are quantified and their scaling relations are compared to observations modeled sses have nearly constant stress drops of 0 001 to 0 01 mpa due to near lithostatic pore pressure at the sse depths the modeled moment duration scaling is between 1 linear and 2 squared when multiple sses appear simultaneously along the strike the stress interaction between approaching slip fronts results in higher average propagation speeds for longer lengths which leads to a scaling close to 2 when sses are well offset in space and time stress interaction is negligible and the scaling is close to 1 two types of sse along strike segmentation gaps are identified from model results the primary gaps are persistent segmentation boundaries due to along strike variation of effective normal stress while the secondary gaps evolve through sse cycles and reflect the stress condition within a primary segment this implies that some geodetically inferred sse segmentation boundaries may result from slower slip velocities below the resolution limits of geodetic inversion models

slow slip slow earthquakes period two cycles full and partial ruptures and deterministic chaos in a single asperity fault abstract the assimilation of geological geophysical and laboratory data in physics based models of fault dynamics promises increasingly realistic simulations of the seismic cycle to assist this effort i explore the dynamics of a single velocity weakening asperity to delineate the relationship between a fault physical properties and the style of faulting during the seismic cycle based on a micro physical model of rate and state friction from a dimensional analysis four non dimensional parameters control the characteristics of slip events and the behavior during the interseismic period including the dieterich ruina rice number ru which is proportional to the ratio of asperity to critical nucleation size w h and rb b a b where a and b control the direct and local evolutionary effects respectively for sufficiently large rb the ru number controls the spectrum of fault slip from periodic slow slip events to aperiodic fast ruptures in finite faults but not in semi infinite faults the transition between these end members includes a bifurcation that involves period two period four period six cycles and deterministic chaos with increasing ru macroscopic fault slip is stabilized as rb vanishes even as ru 1 for finite faults but not for semi infinite faults the transition between slow and fast ruptures for increasing rb includes another type of bifurcation with period two and period four cycles of slow and fast ruptures for 0

gps constraints on 34 slow slip events within the cascadia subduction zone 1997 2005 1 refinements to gps analyses in which we factor geodetic time series to better estimate both reference frames and transient deformation resolve 34 slow slip events located throughout the cascadia subduction zone from 1997 through 2005 timing of transient onset is determined with wavelet transformation of geodetic time series thirty continuous stations are included in this study ranging from northern california to southwestern british columbia our improvements in analysis better resolve the largest creep events and also identify many smaller events at 48 5 n latitude a 14 month average recurrence interval has been observed over eight events since 1997 farther north along vancouver island a host of smaller events with a distinct 14 month periodicity also occurs in southern washington state some of the largest transient displacements are observed but lack any obvious periodicity in their recurrence along central oregon an 18 month recurrence is evident while in northern california an 11 month periodicity continues through 2005 we invert gps offsets of the 12 best recorded events for thrust slip along the plate interface using a cross validation scheme to derive optimal smoothing parameters these 12 events have equivalent moment magnitudes between 6 3 and 6 8 and have 2 3 cm of slip unlike other subduction zones no long duration events are observed and cumulative surface deformation is consistently less than 0 6 cm the many newly resolved smaller transient events in cascadia show that slow slip events occur frequently with gps best capturing only the largest events it is likely that slow slip events occur more frequently at levels not detectable with gps

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

teleseismic constraints on the geological environment of deep episodic slow earthquakes in subduction zone forearcs a review abstract more than a decade after the discovery of deep episodic slow slip and tremor or slow earthquakes at subduction zones much research has been carried out to investigate the structural and seismic properties of the environment in which they occur slow earthquakes generally occur on the megathrust fault some distance downdip of the great earthquake seismogenic zone in the vicinity of the mantle wedge corner where three major structural elements are in contact the subducting oceanic crust the overriding forearc crust and the continental mantle in this region thermo petrological models predict significant fluid production from the dehydrating oceanic crust and mantle due to prograde metamorphic reactions and their consumption by hydrating the mantle wedge these fluids are expected to affect the dynamic stability of the megathrust fault and enable slow slip by increasing pore fluid pressure and or reducing friction in fault gouges resolving the fine scale structure of the deep megathrust fault and the in situ distribution of fluids where slow earthquakes occur is challenging and most advances have been made using teleseismic scattering techniques e g receiver functions in this paper we review the teleseismic structure of six well studied subduction zones three hot i e cascadia southwest japan central mexico and three cool i e costa rica alaska and hikurangi that exhibit slow earthquake processes and discuss the evidence of structural and geological controls on the slow earthquake behavior we conclude that changes in the mechanical properties of geological materials downdip of the seismogenic zone play a dominant role in controlling slow earthquake behavior and that near lithostatic pore fluid pressures near the megathrust fault may be a necessary but insufficient condition for their occurrence

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

relationship between the cascadia fore arc mantle wedge nonvolcanic tremor and the downdip limit of seismogenic rupture great earthquakes anticipated on the cascadia subduction fault can potentially rupture beyond the geodetically and thermally inferred locked zone to the depths of episodic tremor and slip ets or to the even deeper fore arc mantle corner fmc to evaluate these extreme rupture limits we map the fmc from southern vancouver island to central oregon by combining published seismic velocity structures with a model of the juan de fuca plate these data indicate that the fmc is somewhat shallower beneath vancouver island 36 38 km and oregon 35 40 km and deeper beneath washington 41 43 km the updip edge of tremor follows the same general pattern overlying a slightly shallower juan de fuca plate beneath vancouver island and oregon 30 km and a deeper plate beneath washington 35 km similar to the nankai subduction zone the best constrained fmc depths correlate with the center of the tremor band suggesting that ets is controlled by conditions near the fmc rather than directly by temperature or pressure unlike nankai a gap as wide as 70 km exists between the downdip limit of the inferred locked zone and the fmc this gap also encompasses a 50 km wide gap between the inferred locked zones and the updip limit of tremor the separation of these features offers a natural laboratory for determining the key controls on downdip rupture limits

the puzzle of the primary obsidian source in the region of paektusan china dpr korea abstract since the 1990s a characteristic obsidian geochemistry has linked widespread archaeological assemblages spanning the russian far east korean peninsula and northeast china referred to as pnk1 the source of this material has yet to be identified as a contribution to solving this enduring puzzle we report here analyses of a commercial specimen of obsidian exported from chongjin in dpr north korea a combination of neutron activation analysis naa and potassium argon dating enable us to compare this piece with a large obsidian database for northeast asia we find that the chongjin sample is identical to pnk1 lithics from archaeological collections while the exact source of the chongjin sample remains unknown we can more confidently locate the primary source for pnk1 lithics in dpr korea based on an exhaustive literature review of the geology and geochemistry of volcanic glasses and other volcanic rocks in the northern part of the korean peninsula and drawing on our own unpublished data we suggest that the pnk1 source is most likely located south of paektusan volcano this corroborates the existing evidence for the long range transport of the material

aseismic slip transients emerge spontaneously in three dimensional rate and state modeling of subduction earthquake sequences 1 to investigate the possible physical mechanisms of recently observed aseismic slip events in the cascadia japan and mexico subduction zones we apply a dieterich ruina rate and state friction law to a three dimensional model of a shallow subduction fault that is loaded by imposed steady plate slip rate far downdip along the thrust interface friction properties are temperature and hence depth dependent such that sliding is stable at depths below about 30 km the system is perturbed into a significantly nonuniform slip mode along strike by introducing small along strike variations in the constitutive parameters a and a b in addition to large heterogeneous earthquake slip at seismogenic depths and associated postseismic transients we found that slip events which have clearly aseismic slip rates emerge spontaneously around the downdip end of the seismogenic zone both transients which start well after a seismic event and those which are triggered by other transients are observed from the simulations the slip velocity depth range and sometimes along strike migration speed of simulated transients are similar to the observations from natural subduction zones unstable stable transitional friction properties near the downdip end of the seismogenic zone are suggested to be an ingredient allowing such transients simulated transients can weaken the locking intensity of the updip seismogenic zone while enhancing that of the transition zone spatial temporal correlation of aseismic transients and nearby seismicity in the guerrero mexico area suggests that transients may signal a period of increased probability for nucleating their high frequency counterparts as damaging subduction thrust events

automated detection and location of tectonic tremor along the entire cascadia margin from 2005 to 2011 abstract we have constructed an automated routine to identify prominent bursts of tectonic tremor and locate their source region during time periods of raised amplitude in the tremor passband this approach characterizes 62 episodes of tectonic tremor between 2005 and 2011 with tremor epicenters forming a narrow band spanning the entire length of the cascadia subduction zone we find a range of along strike lengths in individual episodes but the length appears proportional to both duration and geodetic moment consistent with proposed scaling laws for slow earthquake phenomena examination of individual episodes in detail reveals intriguing updip downdip migration patterns including slow updip migration during initiation and repetitive downdip migration between different episodes the broader catalog of tremor episodes refines the inferences from earlier work that episodic tremor and slip are segmented along strike and correlated with apparent seismogenic zone segmentation in most cases the overall band of tremor is offset 50 km from the downdip edge of interseismic coupling along the central and northern parts of the subduction zone along the southern part of the subduction zone it is adjacent to this boundary suggesting that the locked and transition zones may be more closely linked in southern cascadia

seismic and geodetic constraints on cascadia slow slip 1 automatically detected and located tremor epicenters from episodic tremor and slip ets episodes in northern cascadia provide a high resolution map of washington s slow slip region thousands of epicenters from the past four ets events from 2004 to 2008 provide detailed map view constraints that correlate with geodetic estimates of the simultaneous slow slip each of these ets events exhibits remarkable similarity in the timing and geographic distribution of tremor density and geodetically inferred slip analysis of the latest 15 month inter ets period also reveals ageodetic tremor activity similar both in duration and extent to ets tremor epicenters from both ets and inter ets tremor are bounded between the 30 and 45 km plate interface depth contours and locate approximately 75 km east of previous estimates of the locked portion of the subducting juan de fuca plate inter ets tremor overlaps but is generally downdip of ets tremor and does not yet correlate with geodetically observed slip but this is likely because the slip is below current gps detection levels based on the tremor and slip correlation and the tremor duration and slip magnitude relationship we suggest that the well resolved sharp updip edge of tremor epicenters reflects a change in plate interface coupling properties the region updip of this boundary may accumulate stress with the potential for coseismic shear failure during a megathrust earthquake alternatively plate convergence in this region could be accommodated by continuous slow slip with no detectable tremor or by slow slip events with sufficiently long recurrence intervals that none have been detected during the past 10 years of gps observations

earthquakes triggered by silent slip events on kīlauea volcano hawaii silent earthquakes or slow slip events happen so slowly that they cannot be detected by conventional seismographs but now the availability of gps data means that they can be followed in detail segall et al report on a series of small earthquakes on k lauea volcano hawaii the earthquakes at depths of 7 to 8 km appear to be triggered by otherwise silent slow slips though small triggered earthquakes of this type can be used to help quantify the increased hazard due to slow slip events slow slip events or silent earthquakes have recently been discovered in a number of subduction zones including the nankai trough1 2 3 in japan cascadia4 5 and guerrero6 in mexico but the depths of these events have been difficult to determine from surface deformation measurements although it is assumed that these silent earthquakes are located along the plate megathrust this has not been proved slow slip in some subduction zones is associated with non volcanic tremor7 8 but tremor is difficult to locate and may be distributed over a broad depth range9 except for some events on the san andreas fault10 slow slip events have not yet been associated with high frequency earthquakes which are easily located here we report on swarms of high frequency earthquakes that accompany otherwise silent slips on k lauea volcano hawaii for the most energetic event in january 2005 the slow slip began before the increase in seismicity the temporal evolution of earthquakes is well explained by increased stressing caused by slow slip implying that the earthquakes are triggered the earthquakes located at depths of 7 8 km constrain the slow slip to be at comparable depths because they must fall in zones of positive coulomb stress change triggered earthquakes accompanying slow slip events elsewhere might go undetected if background seismicity rates are low detection of such events would help constrain the depth of slow slip and could lead to a method for quantifying the increased hazard during slow slip events because triggered events have the potential to grow into destructive earthquakes

recent volumetric changes in salt marsh soils salt marsh sediment volume decreases from organic decomposition compaction of solids and de watering and each of these processes may change with age variability in the vertical accretion rate within the upper 2 m was determined by assembling results from concurrent application of the 137 cs and 210 pb dating techniques used to estimate sediment age since 1963 1964 and 0 to ca 100 years before present ybp respectively the relationship between 210 pb and the 137 cs dated accretion rates sed 210 and sed 137 respectively was linear for 45 salt marsh and mangrove environments sed 210 averaged 75 of sed 137 suggesting that vertical accretion over the last 100 years is driven by soil organic matter accumulation as shown for the pre 137 cs dated horizon the ratio of sed 210 sed 137 declines with increasing mineral content a linear multiple regression equation that includes bulk density and sed 137 to predict sed 210 described 97 of the variance in sed 210 sediments from connecticut delaware and louisiana coastal environments dated with 14 c indicate a relatively constant sediment accretion rate of 0 13 cm year 1 for 1000 7000 ybp which occurs within 2 m of today s marsh surface and equals modern sea level rise rates soil subsidence is not shown to be distinctly different in these vastly different coastal settings the major reason why the sed 137 measurements indicate higher accretion rates than do the sed 210 measurements is because the former apply to younger sediments where the effects of root growth and decomposition are greater than in the latter the most intense rates of change in soil volume in organic rich salt marshes sediments is therefore neither in deep or old sediments 4 m 1000 years but within the first several hundreds of years after accumulation the average changes in organic and inorganic constituents downcore are nearly equal for 58 dated sediment cores from the northern gulf of mexico these parallel changes downcore are best described as resulting from compaction rather than from organic matter decomposition thus most of the volumetric changes in these salt marsh sediments occurs in the upper 2 m and declines quickly with depth extrapolation forwards or backwards using results from the 210 pb and the 137 cs dating technique appear to be warranted for the types of samples from the environments described here

contributions of mineral and organic components to tidal freshwater marsh accretion abstract vertical accretion in tidal marshes is necessary to prevent submergence due to rising sea levels mineral materials may be more important in driving vertical accretion in tidal freshwater marshes which are found near the heads of estuaries than has been reported for salt marshes accretion rates for tidal freshwater marshes in north america and europe n 76 data points were compiled from the literature simple and multiple linear regression analyses revealed that both organic and mineral accumulations played a role in driving tidal freshwater marsh vertical accretion rates although a unit mass of organic material contributed 4 times more to marsh volume than the same mass input of mineral material despite the higher mineral content of tidal freshwater marsh soils this ability of organic matter to effectively hold water and air in interstitial spaces suggests that organic matter is responsible for 62 of marsh accretion with the remaining 38 from mineral contributions the organic material that helps to build marsh elevation is likely a combination of in situ production and organic materials that are deposited in association with mineral sediment particles regional differences between tidal freshwater marshes in the importance of organic vs mineral contributions may reflect differences in sediment availability climate tidal range rates of sea level rise and local scale factors such as site elevation and distance to tidal creeks differences in the importance of organic and mineral accumulations between tidal freshwater and salt marshes are likely due to a combination of factors including sediment availability e g proximity to upland sources and estuarine turbidity maxima and the lability of freshwater vs salt marsh plant production

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

juan de fuca slab geometry and its relation to wadati benioff zone seismicity 1 a new model of the subducted juan de fuca plate beneath western north america allows first order correlations between the occurrence of wadati benioff zone earthquakes and slab geometry temperature and hydration state the geo referenced 3d model constructed from weighted control points integrates depth information from earthquake locations and regional seismic velocity studies we use the model to separate earthquakes that occur in the cascadia forearc from those that occur within the underlying juan de fuca plate and thereby reveal previously obscured details regarding the spatial distribution of earthquakes seismicity within the slab is most prevalent where the slab is warped beneath northwestern california and western washington suggesting that slab flexure in addition to expected metamorphic dehydration processes promotes earthquake occurrence within the subducted oceanic plate earthquake patterns beneath western vancouver island are consistent with slab dehydration processes conversely the lack of slab earthquakes beneath western oregon is consistent with an anhydrous slab double differenced relocated seismicity resolves a double seismic zone within the slab beneath northwestern california that strongly constrains the location of the plate interface and delineates a cluster of seismicity 10 km above the surface that includes the 1992 m7 1 mendocino earthquake we infer that this earthquake ruptured a surface within the cascadia accretionary margin above the juan de fuca plate we further speculate that this earthquake is associated with a detached fragment of former farallon plate other subsurface tectonic elements within the forearc may have the potential to generate similar damaging earthquakes

late holocene rupture of the northern san andreas fault and possible stress linkage to the cascadia subduction zone we relate the late holocene northern san andreas fault nsaf paleo seismic history developed using marine sediment cores along the northern california continental margin to a similar dataset of cores collected along the cascadia margin including channels from barclay canyon off vancouver island to just north of mon terey bay stratigraphic correlation and evidence of synchronous triggering imply earthquake origin and both temporal records are compatible with onshore paleoseis mic data in order to make comparisons between the temporal earthquake records from the nsaf and cascadia we refine correlations of southern cascadia great earth quakes including the land paleoseismic record along the nsaf during the last 2800 yr 15 turbidites including one likely from the great 1906 earthquake establish an average repeat time of 200 yr similar to the onshore value of 240 yr the combined land and marine paleoseismic record from the southern cascadia subduction zone includes a similar number of events during the same period while the average recurrence interval for full margin cascadia events is 520 yr the southern cascadia margin has a repeat time of 220 yr similar to that of the nsaf thirteen of the 15 nsaf events were preceded by cascadia events by 0 80 yr averaging 25 45 yr as compared to 80 400 yr by which cascadia events follow the nsaf based on the temporal association we model the coseismic and cumulative post seismic deformation from great cascadia megathrust events and compute related stress changes along the nsaf in order to test the possibility that cascadia earth quakes triggered the penultimate and perhaps other nsaf events the coulomb fail ure stress cfs resulting from viscous deformation related to a cascadia earthquake over 60 yr does not contribute significantly to the total cfs on the nsaf however the coseismic deformation increases cfs on the northern san andreas fault nsaf b y up to about 9 bars offshore of point delgada most likely enough to trigger that fault to fail in north to south propagating ruptures

dehydration induced porosity waves and episodic tremor and slip episodic tremor and slip ets along the subduction interface takes place where there is abundant evidence for elevated near lithostatic pore pressures at sufficiently great depths 30 45 km that chemical dehydration reactions must act as their dominant source we simulate fluid and heat flow while tracking the location of a vertically oriented one dimensional column of material as it subducts through the slow slip and tremor zone the material in the column is transformed through a pressure dependent and temperature dependent dehydration reaction that we describe with a generalized nonlinear kinetic rate law column deformation is largely dominated by viscous creep with a closure rate that depends linearly on porosity this behavior causes the dehydration reaction to generate traveling porosity waves that transport increased fluid pressures within the slow slip region to explore the possibility that the observed periodicity of slow slip and tremor in subduction zones can be explained by the migration of such porosity waves we derive a dispersion relation that accurately describes our numerical results we also obtain an expression for how the thickness of the dehydrating layer is expected to vary as a function of the parameters in the reaction rate law although the amplitudes of pore pressure perturbations rival those that are produced by known external forcings e g tides or passing surface waves our analysis suggests that given reasonable estimates of rock viscosity permeabilities in the range 6 5 10 15 to 5 10 10 m2 are required for porosity wave trains to form at periods comparable to those of slow slip and tremor

on the provenance of prehistoric obsidian artifacts in south korea abstract using a series of geochemical data from obsidian samples taken from unmodified rocks and prehistoric sites we investigated the provenance of some obsidian artifacts found in south korea by using la icp ms and shrimp methods we analyzed rare earth elements rees and lead pb isotopic ratios of obsidian samples from the north korean side of the baekdusan mountain nk and artifacts from a neolithic site in gadeokdo southeast coast of south korea bg published accounts on the elemental correlation of previously analyzed samples were re examined in consideration of their geological compatibility it appears that the prehistoric artifacts from the middle to northern part of south korea have a genetic relationship with obsidians from the baekdusan area whereas those of the southern part are related to kyushu japan ree patterns of the bg and the nk samples demonstrate a prominent contrast between them suggesting their different provenances presumably the bg obsidians are related to the volcanic rocks of kyushu given that pb isotopic ratios are indicative of the relative contribution of crust versus mantle component to the volcanic magma they indicate the addition of a crustal component to the volcanic magma for the baekdusan volcanic rocks and the nk obsidians the kyushu volcanics and the bg obsidians have a relative affinity to the mantle component the geochemical approach adopted in the current research may be regarded as an accurate and effective means to discriminate and isolate obsidian sources helpful for provenance and other archaeological study of obsidian artifacts

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

a silent slip event on the deeper cascadia subduction interface continuous global positioning system sites in southwestern british columbia canada and northwestern washington state usa have been moving landward as a result of the locked state of the cascadia subduction fault offshore in the summer of 1999 a cluster of seven sites briefly reversed their direction of motion no seismicity was associated with this event the sudden displacements are best explained by 2 centimeters of aseismic slip over a 50 kilometer by 300 kilometer area on the subduction interface downdip from the seismogenic zone a rupture equivalent to an earthquake of moment magnitude 6 7 this provides evidence that slip of the hotter plastic part of the subduction interface and hence stress loading of the megathrust earthquake zone can occur in discrete pulses

nucleation and early seismic propagation of small and large events in a crustal earthquake model 1 earthquake nucleation and early seismic propagation are studied in a two dimensional strike slip fault model with depth variable properties the fault is governed by the dieterich ruina rate and state friction law we use an efficient and rigorous numerical procedure for elastodynamic analysis of earthquake sequences on slowly loaded faults developed by lapusta et al 2000 we find that for decreasing values of the characteristic slip distance of the friction law small events appear at the transition from the locked to creeping behavior toward the bottom of the seismogenic zone small and large events have very similar nucleation phases in our simulations here by nucleation phase we mean gradually accelerating aseismic slip in a small slowly expanding zone before the breakout of the dynamic seismically detectable event moment acceleration to which velocity seismograms are proportional in early stages of seismic propagation exhibits irregular fluctuations in the form of speedups and slowdowns in the moment release rate consistently with observations as reported by ellsworth and beroza 1995 our simulations show that such irregular moment acceleration can at least in part be due to the heterogeneous stress distribution imprinted on the fault by the arrest of previous small events and by stress concentrations at the borders of creeping regions and to partial arrest of the rupture in velocity strengthening fault regions which inhibit seismic slip index terms 7209 seismology earthquake dynamics and mechanics 7260 seismology theory and modeling 3220 mathematical geophysics nonlinear dynamics 7230 seismology seismicity and seismotectonics 3230 mathematical geophysics numerical solutions 8164 tectonophysics stresses crust and lithosphere keywords earthquake nucleation phase event clustering irregular moment release stress concentrations rate and state friction earthquake sequences

episodic fault creep events in california controlled by shallow frictional heterogeneity stable fault slip or creep is thought to occur in unconsolidated sediments that form shallow parts of continental strike slip faults numerical simulations show that creep events observed on faults in california also require the presence of a shallow unstable layer of rock the thickness of which influences the duration of the creep event

slow slip hidden in the noise the intermittence of tectonic release referred to as slow slip events the transient aseismic slip that occurs along plate boundaries can be indirectly characterized through colocated seismicity such as tectonic tremor and low frequency earthquakes lfes using the timing of cataloged lfe and tremor activity in guerrero mexico and northern cascadia i decompose the inter aseismic gps displacement defined as the surface deformation between previously detected slow slip events into separate regimes of tectonic loading and release in such a way previously undetected slow slip events that produce less than a millimeter of surface deformation are extracted from the geodetic noise these new observations demonstrate that the inter aseismic period is not quiescent and that slow slip occurs much more often than previously thought this suggests that the plate interface where slow slip and tremor occur is in fact strongly coupled and that slow aseismic release occurs over a wide spectrum of time scales

space time correlation of slip and tremor during the 2009 cascadia slow slip event 1 episodic tremor and slip ets involving transient deformations accompanied by emergent low frequency tremor occurs in subduction zones around the world ets events increase the shear stress on locked megathrusts and may potentially trigger damaging earthquakes despite the clear association of tremor and slip the physical relationship between them is unresolved tremor appears to result from slip on small asperities on the plate interface due to either creep on the surrounding fault or stress increases ahead of the propagating slow slip front previous studies of migrating slow slip events have not had sufficient spatial and temporal resolution to differentiate between these two models to address this we invert gps data from the august 2009 ets event in central cascadia for the space time evolution of fault slip rate we find a correlation in both space and time between tremor epicenters and the independently determined position of high fault slip rate this supports the first hypothesis that tremor asperities are loaded directly by slow slip rather than by stress increases ahead of the slip front and provides new insights into the mechanics of ets

elastodynamic analysis for slow tectonic loading with spontaneous rupture episodes on faults with rate and state dependent friction we present an efficient and rigorous numerical procedure for calculating the elastodynamic response of a fault subjected to slow tectonic loading processes of long duration within which there are episodes of rapid earthquake failure this is done for a general class of rate and state dependent friction laws with positive direct velocity effect the algorithm allows us to treat accurately within a single computational procedure loading intervals of thousands of years and to calculate for each earthquake episode initially aseismic accelerating slip prior to dynamic rupture the rupture propagation itself rapid post seismic deformation which follows and also ongoing creep slippage throughout the loading period in velocity strengthening fault regions the methodology is presented using the two dimensional 2 d antiplane spectral formulation and can be readily extended to the 2 d in plane and 3 d spectral formulations and with certain modifications to the space time boundary integral formulations as well as to their discretized development using finite difference or finite element methods the methodology can be used to address a number of important issues such as fault operation under low overall stress interaction of dynamic rupture propagation with pore pressure development patterns of rupture propagation in events nucleated naturally as a part of a sequence the earthquake nucleation process earthquake sequences on faults with heterogeneous frictional properties and or normal stress and others the procedure is illustrated for a 2 d crustal strike slip fault model with depth variable properties for lower values of the state evolution distance of the friction law small events appear the nucleation phases of the small and large events are very similar suggesting that the size of an event is determined by the conditions on the fault segments the event is propagating into rather than by the nucleation process itself we demonstrate the importance of incorporating slow tectonic loading with elastodynamics by evaluating two simplified approaches one with the slow tectonic loading but no wave effects and the other with all dynamic effects included but much higher loading rate

spatiotemporal evolution of slow slip events in a nonplanar fault model for northern cascadia subduction zone slow slip events sses are identified as the quasi stable fault deformation in the deep transition zone from locked to continuous sliding in many subduction zones in the well instrumented cascadia margin a class of mw6 0 slow slip events arise beneath port angeles every 14 months as inferred from two decades of continuous geodetic monitoring the along strike bending of the incoming oceanic plate beneath north washington is a unique geometric feature whose influence on slow slip processes is still unknown here we incorporate a realistic fault geometry of northern cascadia in the framework of rate and state dependent friction law to simulate the spatiotemporal evolution of slow slip events on a nonplanar subduction fault the modeled sses capture the major characteristics revealed by gps observations the central 150 km long fault segment beneath port angeles acts as a repetitive slip patch where sses appear every 1 5 years with a maximum slip of 2 5 cm two minor slip patches with smaller areas and cumulative slips straddle this central slip patch the along strike segmentation of slow slip is inversely related to the local fault dip and strike angles of the slow slip zone suggesting strong geometrical control on the slow slip process this correlation holds even after removing the effect of w h ratio between velocity weakening sse fault width and characteristic nucleation size besides the gps detectable fast spreading phase we find that each sse cycle consists of deep pre sse preparation and post sse relaxation phases which may be the driving mechanism for the deep tremor activity between major sse episodes discovered in cascadia

modeling the activity of short term slow slip events along deep subduction interfaces beneath shikoku southwest japan 1 we developed a model of short term slow slip events sses on the 3 d subduction interface beneath shikoku southwest japan considering a rate and state dependent friction law with a small cutoff velocity for the evolution effect we assume low effective normal stress and small critical displacement at the sse zone on the basis of the hypocentral distribution of low frequency tremors we set three sse generation segments a large segment beneath western shikoku and two smaller segments beneath central and eastern shikoku using this model we reproduce events beneath western shikoku with longer lengths in the along strike direction and with longer recurrence times compared with events beneath central and eastern shikoku the numerical results are consistent with observations in that the events at longer segments have longer recurrence intervals the activity of sses is determined by nonuniform frictional properties at the transition zone we also attempt to model the very low frequency vlf earthquakes that accompany short term sses on a 2 d thrust fault we consider a local patch in which the friction parameters are varied in the case that critical displacement is very small at the patch fast multiple slips occur at the patch in the case that the effective normal stress is high at the patch the patch acts as a barrier to sses when it ruptures however rapid slip occurs because the source time functions of these cases are somewhat different it would be possible in the future to assess if either case is an appropriate model for vlf earthquakes

pole tide modulation of slow slip events at circum pacific subduction zones episodic slow slip ess events have been detected at several circum pacific subduction zones such as cascadia japan and mexico notably at least eight ess events along the northern cascadia subduction zone recurred with a period of 13 16 months we study the relationship between pole tide associated with chan dler wobble with a period of 14 months induced stress and the occurrence of the ess events our quantitative analysis shows that 14 of the 20 documented ess events occurred during the ascension phase prior to the maximum of a pole tide induced coulomb failure stress change and three events occurred at the stress change peak the pole tides modulate the stress field at the downdip edge of the transition zone along the plate interface and may trigger ess events when conditions are favorable the phase advance of the triggered events with respect to the induced coulomb failure stress change may reflect that the fault slip is dictated by a rate and state dependent friction law inferred from laboratory experiments

stressing of the new madrid seismic zone by a lower crust detachment fault a new mechanical model for the cause of the new madrid seismic zone in the central united states is analyzed the model contains a subhorizontal detachment fault which is assumed to be near the domed top surface of locally thickened anomalous lower crust rift pillow regional horizontal compression induces slip on the fault and the slip creates a stress concentration in the upper crust above the rift pillow dome in the coseismic stage of the model earthquake cycle where the three largest magnitude 7 8 earthquakes in 1811 1812 are represented by a single model mainshock on a vertical northeast trending fault the model mainshock has a moment equivalent to a magnitude 8 event during the interseismic stage corresponding to the present time slip on the detachment fault exerts a right lateral shear stress on the locked vertical fault whose failure produces the model mainshock the sense of shear is generally consistent with the overall sense of slip of 1811 1812 and later earthquakes predicted rates of horizontal strain at the ground surface are about 10 7 year 1 and are comparable to some observed rates the model implies that rift pillow geometry is a significant influence on the maximum possible earthquake magnitude

three dimensional boundary integral modeling of spontaneous earthquake sequences and aseismic slip 1 fault processes involve complex patterns of seismic events and aseismic slip this work develops a three dimensional 3 d methodology for simulating long term history of spontaneous seismic and aseismic slip on a vertical planar strike slip fault subjected to slow tectonic loading our approach reproduces all stages of earthquake cycles from accelerating slip before dynamic instability to rapid dynamic propagation of earthquake rupture to postseismic slip and to interseismic creep including aseismic transients we use the developed 3 d methodology to study interaction of fault slip with a small patch of higher normal stress over long term slip history for uniform initial prestress dynamic rupture is significantly affected by the stronger patch in the first simulated event but not in subsequent ones the change in behavior is due to redistribution of shear stress by prior slip which demonstrates that distributions of fault strength and stress are related and illustrates the importance of simulating long slip histories even in studies of dynamic rupture despite no long term effect on dynamic rupture the small patch of higher normal stress influences nucleation processes and hence long term slip patterns in the model comparison of the fully dynamic simulations and a widely used quasi dynamic approach shows that the quasi dynamic approach modifies long term slip patterns in addition to resulting in much smaller slip velocities and rupture speeds during dynamic events we show that the response of quasi dynamic formulations with reduced radiation damping terms can be scaled to match the results of the standard quasi dynamic formulation and hence cannot improve the comparison