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

seismic evidence for overpressured subducted oceanic crust and megathrust fault sealing water and hydrous minerals play a key role in geodynamic processes at subduction zones however there are few seismological constraints on the presence of water within the subducting plate audet et al model converted teleseismic waves to constrain the seismological properties of subducted oceanic crust from the cascadia continental margin to its intersection with the forearc mantle their observations suggest that water is pervasively present in fluid form at high pore pressures indicating that the megathrust is a low permeability boundary these results may hold important implications for our understanding of seismogenesis subduction zone structure and the mechanism of episodic tremor and slip this study models converted teleseismic waves to constrain the seismological properties of subducted oceanic crust from the cascadia continental margin to its intersection with the forearc mantle the observations suggest that water is pervasively present in fluid form at high pore pressures indicating that the megathrust is a low permeability boundary these results may hold important implications for our understanding of seismogenesis subduction zone structure and the mechanism of episodic tremor and slip water and hydrous minerals play a key part in geodynamic processes at subduction zones1 2 3 by weakening the plate boundary aiding slip and permitting subduction and indeed plate tectonics to occur4 the seismological signature of water within the forearc mantle wedge is evident in anomalies with low seismic shear velocity marking serpentinization5 6 7 however seismological observations bearing on the presence of water within the subducting plate itself are less well documented here we use converted teleseismic waves to obtain observations of anomalously high poisson s ratios within the subducted oceanic crust from the cascadia continental margin to its intersection with forearc mantle on the basis of pressure temperature and compositional considerations the elevated poisson s ratios indicate that water is pervasively present in fluid form at pore pressures near lithostatic values combined with observations of a strong negative velocity contrast at the top of the oceanic crust our results imply that the megathrust is a low permeability boundary the transition from a low to high permeability plate interface downdip into the mantle wedge is explained by hydrofracturing of the seal by volume changes across the interface caused by the onset of crustal eclogitization and mantle serpentinization these results may have important implications for our understanding of seismogenesis subduction zone structure and the mechanism of episodic tremor and slip

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

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

potential of surface to tunnel seismic tomography to detect vertical faults application to the tournemire underground research laboratory france the tournemire underground research laboratory aveyron france developed by the french institute for radiological protection and nuclear safety is composed of a tunnel excavated in an argillaceous geological layer belonging to a limestone argillite limestone sub horizontal sedimentary sequence sub vertical fault zones are intercepted by drifts and boreholes excavated from the tunnel in the argillaceous layer at a depth of about 250 m these fault zones are characterized by velocities lower than those of the embedding rocks in this study we assess the capacity of first arrival traveltime tomography to detect and characterize such fault zones in a surface to depth transmission configuration with a limited angle aperture the source at the surface is a sledgehammer and turns out to be very repetitive the source trigger is transmitted to the acquisition bay via a vhf transmitter receivers are located at depth in underground works first arrivals are clear and traveltime picking is straightforward before inverting real data we conduct synthetic tests with the real acquisition geometry to assess limits and validity of first arrival traveltime tomography to detect a lower velocity fault zone using different initial configurations and inversion constraints during the inversion we show that introducing a priori information on velocities in the shallow subsurface limestones and argillaceous layers and constraints on maximum velocities greatly helps improving results and subsequent interpretation velocities obtained from the real data display a main lower velocity zone that extends from the galleries in the argillaceous layer right up to the surface in limestones the location and extension of this lower velocity zone are consistent with fault and fracture zones mapped from geological observations

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

a tremor and slip event on the cocos caribbean subduction zone as measured by a global positioning system gps and seismic network on the nicoya peninsula costa rica in may 2007 a network of global positioning systems gps and seismic stations on the nicoya peninsula of northern costa rica recorded a slow slip event accompanied by seismic tremor the close proximity of the nicoya peninsula to the seismogenic part of the cocos caribbean subduction plate boundary makes it a good location to study such events several centimeters of southwest motion were recorded by the gps stations over a period of several days to several weeks and the seismic stations recorded three distinct episodes of tremor during the same time span inversion of the surface displacement data for the depth and pattern of slip on the plate interface shows peak slip at a depth of 25 30 km downdip of the main seismogenic zone estimated temperatures here are 250 300 c lower than in other subduction zones where events of this nature have been previously identified there may also be a shallower patch of slip at 6 km depth these results are significant in that they are the first to suggest that slow slip can occur at the updip transition from stick slip to stable sliding and that a critical temperature threshold is not required for slow slip tremor and low frequency earthquake locations are more difficult to determine our results suggest they occur on or near the plate interface at the same depth range as the deep slow slip but not spatially colocated

time dependent inversion of three component continuous gps for steady and transient sources in northern cascadia 1 an approach to invert gps time series to estimate crustal block rotations fault locking and strain rates while simultaneously solving for transient slow slip events is described and applied to the northern cascadia subduction zone the method can use continuous or survey mode gps time series or both i invert 5 6 years of 3 component continuous gps time series at 53 sites from cascadia to estimate simultaneously the block motions and strains locking on the subduction zone and source parameters of the four most recent slow slip events over the time period and section of the cascadia margin sampled the strain released in slow slip was 7 to 10 of the accumulated subduction strain but at the base of and immediately downdip of the locked zone beneath the olympic peninsula

the giant ruatoria debris avalanche on the northern hikurangi margin new zealand result of oblique seamount subduction despite convergent margins being unstable systems most reports of huge submarine slope failure have come from oceanic volcanoes and passive margins swath bathymetry and seismic profiles of the northern hikurangi subduction system new zealand show a tapering 65 30 km wide by 65 km deep margin indentation with a giant 3150 630 km3 blocky debris avalanche deposit projecting 40 km out across horizontal trench fill and a debris flow deposit projecting over 100 km slide blocks are well bedded up to 18 km across and 1 2 km high the largest being at the avalanche deposit s leading edge samples dredged from them are mainly miocene shelf calc mudstones similar to those outcropping around the indentation cores from cover beds suggest that failure occurred 170 40 ka possibly synchronously with a major extension collapse in the upper indentation however the northern part of the indentation is much older the steep straight northern wall is close to the direction of plate convergence and probably formed around 2 0 0 16 ma as a large seamount subducted leaving in its wake a deep groove obliquely across the margin and an unstable triangle of fractured rock in the 60 angle between groove and oversteepened margin front the triangle collapsed as a blocky avalanche leaving a scalloped southern wall and probably causing a large tsunami tentative calculations of compacted volumes suggest that the indentation is over 600 km3 larger than the avalanche supporting a two stage origin that includes subduction erosion since failure convergence has carried the deposits 9 km back toward the margin causing internal compression the eventual subduction accretion of the ruatoria avalanche explains the scarcity of such features on active margins and perhaps the nature of olistostromes in fold belts

very low frequency earthquakes within accretionary prisms are very low stress drop earthquakes 1 we report characteristic p wave spectra and stress drops of very low frequency vlf earthquakes that occurred within the accretionary prism along the nankai trough southwestern japan although many vlf earthquakes showed no distinct phases on a raw seismogram a few showed slightly distinct phases the arrival times of some phases were consistent with the calculated p wave arrival times the corner frequencies of the vlf earthquakes were calculated using the stacked p wave spectra assuming an omega square spectrum stress drops were very low i e in the range of 0 1 10 kpa which corresponds to 0 1 1 of those of ordinary earthquakes such extremely low stress drops of the vlf earthquakes suggest that the fault strength within the accretionary prism may have weakened due to the existence of a fluid within the thrust fault system of the accretionary prism

modelling of short interval silent slip events in deeper subduction interfaces considering the frictional properties at the unstable stable transition regime summary recent high resolution observations of crustal movements have revealed silent slip events sses with propagation velocities of around 10 15 km d 1 and with intervals of 3 14 months along the deeper parts of the cascadia and nankai subduction zones this study develops 2 d and 3 d models of these short interval sses considering the frictional behaviour that was confirmed experimentally by shimamoto for the unstable stable transition regime to represent this frictional behaviour a small cut off velocity to an evolution effect is introduced in a rate and state dependent friction law when the cut off velocity to the evolution effect is significantly smaller than that to a direct effect steady state friction exhibits velocity weakening at low slip velocities and velocity strengthening at high slip velocities at the deeper cascadia and nankai subduction interfaces the pore pressure is inferred to be high because of the dehydration of materials in the descending plate under conditions where the pore fluid pressure is nearly equal to the lithostatic pressure and the critical weakening displacement is very small short interval sses with propagation velocities and slip velocities of 4 8 km d 1 and 2 4 10 7 m s 1 respectively can be reproduced the propagation velocity of short interval sses is in proportion to the slip velocity the results also show that during the nucleation process of large earthquakes the occurrence of short interval sses becomes irregular because of the accelerated slips that occur at the bottom of the seismogenic zone our results suggest that monitoring of short interval sses might be useful for forecasting the main earthquakes

shallow morphology of the subducted pacific plate along the hikurangi margin new zealand abstract along the east coast of the north island new zealand the pacific plate is subducted beneath the australian plate the seismicity associated with this subduction has been determined using the results from a number of temporary and permanent microearthquake networks a synthesis of the microearthquake seismicity the depths of thrust events the depth of s to p conversions and deep reflection seismic studies leads to a coherent picture of the subducting slab both in terms of its mechanical structure and in terms of the general morphology the slab is initially subducted at a low angle of a few degrees is bent through a circular arc of few hundred kilometre radius and then becomes planar again below 120 km depth the radius of curvature varies along strike from about 280 km just north of wellington to 240 km north of hawke bay the slab shape between depths of 15 45 km is thus approximately conical it also approximates within the errors of hypocentre location a surface of constant gaussian curvature as would be geometrically expected from the simple bending of a thin spherical lithospheric shell observed seismicity is primarily concentrated within what is interpreted as the subducted crust of the pacific plate with a lower level of activity within the subducted mantle normal fault mechanisms at the top of the plate probably reflect tensional stress associated with the plate bending whereas thrust events observed at the lower bound of the observed seismicity probably reflect compression below the neutral plane

electrical imaging of the groundwater aquifer at banting selangor malaysia a geophysical study was carried out in the banting area of malaysia to delineate groundwater aquifer and marine clay layer of the alluvial quaternary deposits of beruas and gula formations the beruas formation is formed by peat and clayey materials as well as silt and sands whereas the gula formation consists of clay silt sand and gravels both formations were deposited on top of the carboniferous shale of the kenny hill formation a 2 d geoelectrical resistivity technique was used resistivity measurement was carried out using an abem sas 4000 terrameter the 2 d resistivity data of subsurface material for each survey line was calculated through inverse modelling and then compared with borehole data the resistivity images of all the subsurface material below the survey lines show similar pattern of continuous structure of layering or layers with some lenses with resistivity ranging from 0 1 to 50 m the upper layer shows resistivity values ranging from 0 1 to 10 m representing a clay horizon with a thickness up to 45 m the second layer with depth varies from 45 to 70 m below surface and has resistivity values ranging from 10 to 30 m borehole data indicate coarse sand with some gravels for this layer which is also the groundwater aquifer in the study area the lowermost layer at a depth of 70 m below ground level shows resistivity values ranging from 30 50 m and can be correlated with metasedimentary rocks consisting of shale and metaquartzite

subducting slab ultra slow velocity layer coincident with silent earthquakes in southern mexico great earthquakes have repeatedly occurred on the plate interface in a few shallow dipping subduction zones where the subducting and overriding plates are strongly locked silent earthquakes or slow slip events were recently discovered at the down dip extension of the locked zone and interact with the earthquake cycle here we show that locally observed converted sp arrivals and teleseismic underside reflections that sample the top of the subducting plate in southern mexico reveal that the ultra slow velocity layer usl varies spatially 3 to 5 kilometers with an s wave velocity of 2 0 to 2 7 kilometers per second most slow slip patches coincide with the presence of the usl and they are bounded by the absence of the usl the extent of the usl delineates the zone of transitional frictional behavior

on the mechanical role of smectite in subduction zones smectites a group of hydrated phyllosilicate minerals are often a main component of sediments entering a subduction zone they are common in hemipelagic sediments and consist of an authigenetic component that arises from the alteration of volcanic ash intercalated in the sediment and a detrital component smectite rich strata are structurally weak retain water and are highly porous a review of sediment lithology in subduction zones around the world suggests that decollement zones may preferentially form in smectite rich horizons one consequence of this observation is that the assignment of high frictional resistance to materials in a decollement may be unwarranted at deeper structural levels smectite is transformed to illite a mechanically stronger mineral estimates of the depth of this transition coincide with the depth at which earthquakes are first detected along plate interfaces i speculate that the smectite illite transition in subduction zones may be an important component of sediment consolidation processes that trigger interplate seismicity

a numerical comparison of 2d resistivity imaging with 10 electrode arrays numerical simulations are used to compare the resolution and efficiency of 2d resistivity imaging surveys for 10 electrode arrays the arrays analysed include polepole pp pole dipole pd half wenner hw wenner wn schlumberger sc dipole dipole dd wenner wb array gm multiple or moving gradient array gd and midpoint potential referred measurement mpr arrays five synthetic geological models simulating a buried channel a narrow conductive dike a narrow resistive dike dipping blocks and covered waste ponds were used to examine the surveying efficiency anomaly effects signal to noise ratios and the imaging capabilities of these arrays the responses to variations in the data density and noise sensitivities of these electrode configurations were also investigated using robust l1 norm inversion and smoothness constrained least squares l2 norm inversion for the five synthetic models the results show the following i gm and wn are less contaminated by noise than the other electrode arrays ii the relative anomaly effects for the different arrays vary with the geological models however the relatively high anomaly effects of pp gm and wb surveys do not always give a high resolution image pd dd and gd can yield better resolution images than gm pp wn and wb although they are more susceptible to noise contamination sc is also a strong candidate but is expected to give more edge effects iii the imaging quality of these arrays is relatively robust with respect to reductions in the data density of a multi electrode layout within the tested ranges iv the robust inversion generally gives better imaging results than the l2 norm inversion especially with noisy data except for the dipping block structure presented here v gd and mpr are well suited to multichannel surveying and gd may produce images that are comparable to those obtained with dd and pd accordingly the gd pd dd and sc arrays are strongly recommended for 2d resistivity imaging where the final choice will be determined by the expected geology the purpose of the survey and logistical considerations

evidence for episodic aseismic slip across the subduction seismogenic zone off costa rica cork borehole pressure observations at the subduction prism toe abstract slow slip events or silent earthquakes may relieve a significant amount of stress at many subduction plate boundaries both downdip of the limit of seismogenesis and within the seismogenic zone itself in cases where seismic energy release accounts for only a fraction of the plate tectonic displacement rate schwartz and rokosky 2007 slow slip has been identified in several instances downdip of the landward limit of the seismogenic zone and is often accompanied by seismic tremor or low frequency earthquake activity along and above the plate interface referred to as episodic tremor and slip or ets little is known however about the spatial distribution and history of slip between great earthquakes along the seismogenic thrust interface itself which lies mostly offshore in this article we present formation pressure transients observed in two deep sea boreholes near the toe of the subduction prism off nicoya peninsula costa rica which followed ets events observed on shore by 1 2 weeks the signatures of the transients are consistent with local slip on the shallow part of the thrust interface with the underthrusting plate experiencing relaxation and the outer prism experiencing contraction the delay between the tremor activity and the pressure transients observed c 100 km seaward at the prism toe suggests either slow propagation across the seismogenic zone or delayed deformation at the outer part of the prism triggered by the slip beneath nicoya such slip may serve generally to relieve stress at subduction zones but also to increase stress in parts of the plate boundary where interseismic slip does not occur

crustal deformation measurements in guerrero mexico 1 gps measurements of crustal deformation in guerrero southern mexico include surveys collected between 1992 and 2001 as well as continuous gps measurements at a few sites these geodetic observations are used to calculate interseismic deformation rates and assess the presence and possible location of transient deformation during the period encompassing 1992 25 to 2001 75 the data are used to examine transient deformation in 1998 previously described from data at a single site by lowry et al 2001 survey measurements and continuous data from a site near popocatepetl volcano confirm the 1998 transient and survey data also suggest another transient occurred following the 14 september 1995 mw 7 3 copala earthquake all of the available gps position estimates have been inverted for a combined model of slip during each event plus the steady state slip on the plate interface modeling of the steady state deformation rates confirms that the guerrero seismic gap is partially frictionally locked at depths shallower than about 25 km and accumulating strain that may eventually be released in a great earthquake the data also suggest that there is frictional coupling to much greater 40 km depths which releases more frequently in aseismic slip events the locations and sizes of the transient events are only partially constrained by the available data however the transient models which best fit the gps coordinate time series suggest that aseismic slip was centered downdip of the seismogenic portion of the plate bounding thrust in both events and the moment release had equivalent magnitudes mw 7 1 1 3 1 0 in 1995 1996 and 7 1 0 4 0 1 in 1998

temporal evolution of an episodic tremor and slip event along the northern cascadia margin 1 episodic tremor and slip ets have now been observed along the northern cascadia margin for over 15 years recent densification of gps coverage and the introduction of gladwin borehole strainmeters bsms under the plate boundary observatory have enabled the derivation of improved slip models and have allowed more detailed monitoring of the migration of the slip surface during prolonged ets events for this study we examine the along strike migration of the may 2008 ets as determined from the gps and bsm observations gps sites overlying the 30 km depth contour of the subducting plate interface show that the slip initiates west of northern puget sound and propagates bidirectionally shear strain time series at regional bsm sites confirm this bidirectional expansion of the slip zone in a simple model of along strike propagation constrained by the gps and bsm time series the speed of the northwest propagation varies from 8 then to 2 and then to 15 km d but the speed of the south propagation stays at 6 km d the tremors observed for this ets episode show a similar bidirectional migration pattern and similar changes in northwest migration velocity but the migration front is slightly ahead of the slip propagation front these results provide important information for understanding the mechanics of ets

modeling short and long term slow slip events in the seismic cycles of large subduction earthquakes 1 slow slip events sses occur in the deeper extents of areas where large interplate earthquakes are expected in subduction zones such as the nankai region of japan and the cascadia region of north america in the nankai region sses are divided into long and short term sses depending on their duration and recurrence interval we modeled and examined the occurrence of long and short term sses and changes in their behavior during the seismic cycles of large interplate earthquakes in these numerical simulations we adopted a rate and state dependent friction law with cutoff velocities and assumed that the distribution of pore fluid controls the recurrence interval of both long and short term sses the recurrence intervals of reproduced short term sses decrease during a long term sse as observed in western shikoku in the nankai region the recurrence intervals of both types of sses become shorter in the later stages of interseismic periods large interplate earthquakes nucleate between the region where sses occur and the locked region of the large earthquakes as suggested from observations of the 1944 tonankai earthquake our numerical results suggest that the stress buildup process in a seismic cycle affects the recurrence behavior of sses

reexamination of the interplate coupling in the tokai region central japan based on the gps data in 1997 2002 1 we re examined the interplate coupling in terms of backslip rate at the nankai suruga trough beneath the tokai region with a 3 dimensional gps time series and a refined plate boundary model we reanalyzed the gps data and reconstructed plate boundary configuration then we inverted gps velocities to infer the interplate coupling during april 1997 to april 2000 our results show that a maximum back slip rate of 2 cm yr was found at the depth of 15 25 km around 137 42e 34 32n we also estimated interplate coupling for the period from january 2001 to december 2002 this time period coincides with a slow slip event found by ozawa et al 2002 forward slip up to 3 cm yr was inferred beneath western region of lake hamana and we found that the epicenters of low frequency tremors are located there suggestive of a close connection between the occurrences of the slow slip event sse and low frequency tremors

detecting young slow slipping active faults by geologic and multidisciplinary high resolution geophysical investigations a case study from the apennine seismic belt italy 1 the southern apennines range of italy presents significant challenges for active fault detection due to the complex structural setting inherited from previous contractional tectonics coupled to very recent middle pleistocene onset and slow slip rates of active normal faults as shown by the irpinia fault source of a m6 9 earthquake in 1980 major faults might have small cumulative deformation and subtle geomorphic expression a multidisciplinary study including morphological tectonic paleoseismological and geophysical investigations has been carried out across the extensional monte aquila fault a poorly known structure that similarly to the irpinia fault runs across a ridge and is weakly expressed at the surface by small scarps warps the joint application of shallow reflection profiling seismic and electrical resistivity tomography and physical logging of cored sediments has proved crucial for proper fault detection because performance of each technique was markedly different and very dependent on local geologic conditions geophysical data clearly 1 image a fault zone beneath suspected warps 2 constrain the cumulative vertical slip to only 25 30 m 3 delineate colluvial packages suggesting coseismic surface faulting episodes paleoseismological investigations document at least three deformation events during the very late pleistocene 20 ka and holocene the clue to surface rupturing episodes together with the fault dimension inferred by geological mapping and microseismicity distribution suggest a seismogenic potential of m6 3 our study provides the second documentation of a major active fault in southern italy that as the irpinia fault does not bound a large intermontane basin but it is nested within the mountain range weakly modifying the landscape this demonstrates that standard geomorphological approaches are insufficient to define a proper framework of active faults in this region more in general our applications have wide methodological implications for shallow imaging in complex terrains because they clearly illustrate the benefits of combining electrical resistivity and seismic techniques the proposed multidisciplinary methodology can be effective in regions characterized by young and or slow slipping active faults

rapid continuous streaking of tremor in cascadia nonvolcanic tremor is a recently discovered weak seismic signal associated with slow slip on a fault plane and has potential to answer many questions about how faults move its spatiotemporal distribution however is complex and varies over different time scales and the causal physical mechanisms remain unclear here we use a beam backprojection method to show rapid continuous slip parallel streaking of tremor over time scales of several minutes to an hour during the may 2008 episodic tremor and slip event in the cascadia subduction zone the streaks propagate across distances up to 65 km primarily parallel to the slip direction of the subduction zone both updip and downdip at velocities ranging from 30 to 200 km h we explore mainly two models that may explain such continuous tremor streaking the first involves interaction of slowly migrating creep front with slip parallel linear structures on the fault the second is pressure driven fluid flow through structurally controlled conduits on the fault both can be consistent with the observed propagation velocities and geometries although the second one requires unlikely condition in addition we put this new observation in the context of the overall variability of tremor behavior observed over different time scales

a new statistical test for static stress triggering application to the 1987 superstition hills earthquake sequence over the past several years many investigators have argued that static stress changes caused by large earthquakes influence the spatial and temporal distributions of subsequent regional seismicity with earthquakes occurring preferentially in areas of stress increase and reduced seismicity where stress decreases some workers have developed quantitative methods to test for the existence of such static stress triggering but no firm consensus has yet been reached as to the significance of these effects we have developed a new test for static stress triggering in which we compute the change in coulomb stress on the focal mechanism nodal planes of a set of events spanning the occurrence of a large earthquake we compare the statistical distributions of these stress changes for events before and after the mainshock to decide if we can reject the hypothesis that these distributions are the same such rejection would be evidence for stress triggering we have applied this test to the november 24 1987 elmore ranch superstition hills earthquake sequence and find that those post mainshock events that experienced stress increases of at least 0 01 0 03 mpa 0 1 0 3 bar or that occurred from 1 4 to 2 8 years after the mainshocks are consistent with having been triggered by mainshock generated static stress changes

analysis of the physical integrity of earth dams from electrical resistivity tomography ert in brazil dams are structures that barrier rivers and streams for a variety of purposes the constant maintenance of these structures is essential since a possible accident can lead to damage of catastrophic proportions in november 2015 in the city of mariana minas gerais mg brazil a tailings dam burst and spilled 56 million cubic meters of tailings in addition to victimize 19 people the event caused material economic and environmental damage it is considered the largest environmental disaster of brazil this research presents a cheap and quickly applied alternative for investigation of seepage of water in earth dams built with distinct embankment materials one dam composed of predominantly silt and clay soil and the other predominantly composed of sandy soil the research methods used were geotechnical tests as gradation test permeability test with the guelph permeameter method and the application of the dc resistivity geophysical method from the electrical resistivity tomography ert technique in wenner array three ert lines were positioned parallel to the longitudinal axis at each dam the data are presented in 2d and 3d geophysical images with electrical resistivity values modeled based on the physical principle of electrolytic conduction i e decrease in electrical resistance in materials or siliceous minerals in moisture conditions compared to the material in the dry state the results revealed low resistivity zones restricted to some points associated with water infiltration in the transverse direction the results indicate saturation restricted to some points and low permeability at the present time an installation of piping processes

noise properties of continuous gps data from concrete pillar geodetic monuments in new zealand and comparison with data from u s deep drilled braced monuments 1 reducing noise levels in geodetic data is critical for the interpretation and modeling of geophysically interesting signals in this paper i estimate noise properties of continuous gps time series collected on concrete pillar monuments and compare them with similar data from deep drilled braced monuments that are considered the most stable three dimensional monuments available i show that the time series noise properties are very similar between the monument types at least for time series up to 4 5 years duration differences between the monument types are therefore not a dominant influence on these time series implying that the less expensive concrete pillar monuments are a valid choice for recording many signals of geophysical interest

high pore fluid pressure may cause silent slip in the nankai trough silent slip events have been detected at several subduction zones but the cause of these events is unknown using seismic imaging we detected a cause of the tokai silent slip which occurred at a presumed fault zone of a great earthquake the seismic image that we obtained shows a zone of high pore fluid pressure in the subducted oceanic crust located down dip of a subducted ridge we propose that these structures effectively extend a region of conditionally stable slips and consequently generate the silent slip

tsunami earthquakes possibly widespread manifestations of frictional conditional stability 1 tsunami earthquakes shallow events that produce larger tsunamis than expected given their surface wave magnitudes ms typically have long durations and a source spectrum depleted in short period energy seven cases of underthrusting tsunami earthquakes provide information on the rupture processes but little constraint on geographic distribution or frequency we compare their rupture characteristics with smaller magnitude earthquakes on circum pacific interplate thrust faults comparable moment release time histories are found for large tsunami earthquakes and for many smaller shallow subduction zone earthquakes with significantly longer durations and additional source complexity than for events deeper than 15 km thus very shallow interplate earthquake ruptures are scale invariant with variable frictional properties on the plate interface controlling the depth dependent rupture process widespread occurrence of small shallow interplate earthquakes with long durations suggests that many subduction faults have frictional properties that may enable large tsunami generating earthquakes to occur fortunately large shallow ruptures are infrequent

a discrete episode of seismic and aseismic deformation of the nankai trough subduction zone accretionary prism and incoming philippine sea plate new insights into episodic deformation at the nankai trough subduction zone are provided by data from two ocean drilling program borehole hydrologic observatories drilled into the philippine sea plate site 1173 and the seaward part of the nankai accretionary prism off southwestern japan site 808 and from an array of high sensitivity borehole accelerometer and velocity seismometers on shikoku island hi net fluid pressures monitored at multiple levels in each of the offshore boreholes document steady secular trends that indicate contraction of the crust and sedimentary section at the incoming plate site and relaxation of the accretionary prism toe the rate of strain ca 10 6 yr 1 inferred from the rates of pressure rise at site 1173 up to 5 kpa yr 1 is similar to that which would be produced by plate convergence if convergent elastic strain were distributed over a region a few tens of km wide opposing these trends are transient pressure anomalies observed in late june early july 2003 that indicate an episode of rapid relaxation of the incoming plate and contraction of the outer prism concurrent with these transients a swarm of very low frequency earthquakes occurred farther landward in the prism above the estimated seaward limit of the currently locked seismogenic portion of the subduction thrust reverse fault mechanisms determined for one event of this swarm and several of another also indicate transient contraction of the prism we suggest that both the earthquakes and the pressure transients are the consequences of an aseismic slip dislocation that initiated on about june 26 2003 at or near the up dip limit of the locked portion of the subduction thrust and propagated seaward over the course of about 10 days to the accretionary prism toe along the decollement separating the prism and underthrust section deformational events like this may serve incrementally to relieve stress locally along the subduction thrust and to load neighboring areas in addition to demonstrating that the prism is far from inactive during interseismic intervals the observations may also provide a small amplitude analog for strain and hydrologic response at the time of great subduction earthquakes

rapid least squares inversion of apparent resistivity pseudosections by a quasi newton method1 a fast inversion technique for the interpretation of data from resistivity tomography surveys has been developed for operation on a microcomputer this technique is based on the smoothness constrained least squares method and it produces a two dimensional subsurface model from the apparent resistivity pseudosection in the first iteration a homogeneous earth model is used as the starting model for which the apparent resistivity partial derivative values can be calculated analytically for subsequent iterations a quasi newton method is used to estimate the partial derivatives which reduces the computer time and memory space required by about eight and twelve times respectively compared to the conventional least squares method tests with a variety of computer models and data from field surveys show that this technique is insensitive to random noise and converges rapidly this technique takes about one minute to invert a single data set on an 80486dx microcomputer

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

electrical resistivity tomography to investigate geological structures of the earth s upper crust it is important to have detailed knowledge of the electrical properties of the earth s crust in order to recognize geological structures and to understand tectonic processes in the area surrounding the german continental deep drilling project ktb we have used dc dipole dipole soundings to investigate the electrical conductivity distribution down to a depth of several kilometres we have adapted the electrical resistivity tomography ert technique a well established near surface method to large scale experiments independent transmitting and receiving units were used to realize the concept of simultaneous multichannel registration of the scalar electrical potential at 44 dipoles the measured data yielded apparent resistivities which were inverted to a 2d resistivity model ranging from the surface down to a depth of 4 km two highly conductive structures with steep inclination were detected they are expected to be major fault zones embedded in a metamorphic body the rather low resistivity 10 m can be explained by the existence of graphitic minerals and or electrolytic fluids

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

episodic slow slip events in the japan subduction zone before the 2011 tohoku oki earthquake abstract we describe two transient slow slip events that occurred before the 2011 tohoku oki earthquake the first transient crustal deformation which occurred over a period of a week in november 2008 was recorded simultaneously using ocean bottom pressure gauges and an on shore volumetric strainmeter this deformation has been interpreted as being an m6 8 episodic slow slip event the second had a duration exceeding 1 month and was observed in february 2011 just before the 2011 tohoku oki earthquake the moment magnitude of this event reached 7 0 the two events preceded interplate earthquakes of magnitudes m6 1 december 2008 and m7 3 march 9 2011 respectively the latter is the largest foreshock of the 2011 tohoku oki earthquake our findings indicate that these slow slip events induced increases in shear stress which in turn triggered the interplate earthquakes the slow slip event source area on the fault is also located within the downdip portion of the huge coseismic slip area of the 2011 earthquake this demonstrates episodic slow slip and seismic behavior occurring on the same portions of the megathrust fault suggesting that the faults undergo slip in slow slip events can also rupture seismically

hornblende alteration and fluid inclusions in kardla impact crater estonia evidence for impact induced hydrothermal activity the well preserved krdla impact crater on hiiumaa island estonia is a 4 km diameter structure formed in a shallow ordovician sea about 455 ma ago into a target composed of thin 150 m unconsolidated sedimentary layer above a crystalline basement composed of migmatite granites amphibolites and gneisses the fractured and crushed amphibolites in the crater area are strongly altered and replaced with secondary chloritic minerals the most intensive chloritization is found in permeable breccias and heavily shattered basement around and above the central uplift alteration is believed to have resulted from convective flow of hydrothermal fluids through the central areas of the crater chloritic mineral associations suggest formation temperatures of 100 300 c in agreement with the most frequent quartz fluid inclusion homogenization temperatures of 150 300 c in allochthonous breccia the rather low salinity of fluids in krdla crater 13 wt nacleq suggests that the hydrothermal system was recharged either by infiltration of meteoric waters from the cater rim walls raised above sea level after the impact or by invasion of sea water through the disturbed sedimentary cover and fractured crystalline basement the well developed hydrothermal system in krdla crater shows that the thermal history of the shock heated and uplifted rocks in the central crater area rather than cooling of impact melt or suevite sheets controlled the distribution and intensity of the impact induced hydrothermal processes

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

ability of high resolution resistivity tomography to detect fault and fracture zones application to the tournemire experimental platform france the experimental platform of tournemire aveyron france developed by irsn french institute for radiological protection and nuclear safety is composed of a tunnel excavated in an argillite formation belonging to a limestone argillite limestone subhorizontal sedimentary sequence subvertical secondary fault zones were intercepted in argillite using drifts and boreholes in the tunnel excavated at a depth of about 250 m located under the larzac plateau a 2d 2 5 km baseline large scale electrical resistivity survey conducted in 2007 allowed detecting in the upper limestones several significantly low electrical resistivity subvertical zones gelis et al appl geophys 167 11 1405 1418 2010 one of these discontinuities is consistent with the extension towards the surface of the secondary fault zones identified in the argillite formation from the tunnel in an attempt to better characterize this zone irsn and mines paristech conducted a high resolution electrical resistivity survey located transversally to the fault and fracture zones a 760 m long profile was acquired using two array geometries and take outs of 2 4 and 8 m requiring several roll alongs these data were first inverted independently for each take out and then using all take outs together for a given array geometry different inverted 2d electrical resistivity models display the same global features with high higher than 5000 m to low lower than 100 m electrical resistivity zones these electrical resistivity models are finally compared with a geological cross section based on independent data the subvertical conductive zones are in agreement with the fault and fracture locations inferred from the geological cross section moreover the top of a more conductive zone below a high electrical conductive zone and between two subvertical fault zones is located in a more sandy and argillaceous layer this conductive zone is interpreted as the presence of a more scattered fracture zone located at depth between two fault zones this zone could be correlated with the fractured zones identified at 250 m depth in underground works this study highlights the interest of multi scale approaches to image complex heterogeneous near subsurface layers finally this study shows that the electrical resistivity tomography is a useful and powerful tool to detect fault and fracture zones in upper limestones such a method is complementary to other geophysical and geological data

remote triggering of tremor along the san andreas fault in central california received 30 august 2008 accepted 16 april 2009 published 18 july 2009 1 we perform a systematic survey of triggered tremor along the san andreas fault in central california for the 31 teleseismic earthquakes with mw 7 5 since 2001 we identify 10 teleseismic events associated with clear triggered tremor about 52 of the tremor is concentrated south of parkfield near cholame where ambient tremor has been identified previously and the rest is widely distributed in the creeping section of the san andreas fault north of parkfield tremor is generally initiated and is in phase with the love wave particle velocity however the pattern becomes complicated with the arrival of the rayleigh waves and sometimes tremor continues after the passage of the surface waves we identify two cases in which tremor is triggered during the teleseismic pkp phase these results suggest that while shear stress from the passage of the love waves plays the most important role in triggering tremor in central california other factors such as dilatational stresses from the rayleigh and p waves also contribute we also examine the ambient tremor occurrence rate before and after the teleseismic events and find a transient increase of stacked tremor rate during the passage of the teleseismic surface waves this observation implies that the occurrence time of tremor is temporally advanced by the dynamic stresses of the teleseismic waves the amplitude of the teleseismic waves correlates with the occurrence of triggered tremor and the inferred tremor triggering threshold is 2 3 kpa the relatively low triggering threshold indicates that the effective stress at the tremor source region is very low most likely due to near lithostatic fluid pressure

plate boundary deformation associated with the great sumatra andaman earthquake the sumatra andaman earthquake of 26 december 2004 is the first giant earthquake moment magnitude m w 9 0 to have occurred since the advent of modern space based geodesy and broadband seismology it therefore provides an unprecedented opportunity to investigate the characteristics of one of these enormous and rare events here we report estimates of the ground displacement associated with this event using near field global positioning system gps surveys in northwestern sumatra combined with in situ and remote observations of the vertical motion of coral reefs these data show that the earthquake was generated by rupture of the sunda subduction megathrust over a distance of 1 500 kilometres and a width of 150 kilometres megathrust slip exceeded 20 metres offshore northern sumatra mostly at depths shallower than 30 kilometres comparison of the geodetically and seismically inferred slip distribution indicates that 30 per cent additional fault slip accrued in the 1 5 months following the 500 second long seismic rupture both seismic and aseismic slip before our re occupation of gps sites occurred on the shallow portion of the megathrust where the large aceh tsunami originated slip tapers off abruptly along strike beneath simeulue island at the southeastern edge of the rupture where the earthquake nucleated and where an m w 7 2 earthquake occurred in late 2002 this edge also abuts the northern limit of slip in the 28 march 2005 m w 8 7 nias simeulue earthquake

preliminary non intrusive geophysical electrical resistivity tomography surveys of a mock up scale monitoring of an engineered barrier system at url tournemire

frontal wedge deformation near the source region of the 2011 tohoku oki earthquake 1 we report an uplift of 5 m with a horizontal displacement of more than 60 m due to the 2011 tohoku oki earthquake the uplift was measured by an ocean bottom pressure gauge installed before the earthquake on a frontal wedge which formed an uplift system near the japan trench horizontal displacements of the frontal wedge were measured using local benchmark displacements obtained by acoustic ranging before and after the earthquake the average displacements at the frontal wedge were 58 m east and 74 m east southeast these results strongly suggest a huge coseismic slip beneath the frontal wedge on the plate boundary the estimated magnitude of the slip along the main fault was 80 m near the trench our results suggest that the horizontal and vertical deformations of the frontal wedge due to the slip generated the tremendous tsunami that struck the coastal area of northeastern japan

potential of electrical resistivity tomography to detect fault zones in limestone and argillaceous formations in the experimental platform of tournemire france the experimental platform of tournemire aveyron france developed by irsn french institute for radiological protection and nuclear safety is located in a tunnel excavated in a clay rock formation interbedded between two limestone formations a well identified regional fault crosscuts this subhorizontal sedimentary succession and a subvertical secondary fault zone is intercepted in the clay rock by drifts and boreholes in the tunnel at a depth of about 250 m a 2d electrical resistivity survey was carried out along a 2 5 km baseline and a takeout of 40 m was used to assess the potential of this method to detect faults from the ground surface in the 300 m thick zone investigated by the survey electrical resistivity images reveal several subvertical low resistivity discontinuities one of these discontinuities corresponds to the position of the cernon fault a major regional fault one of the subvertical conductive discontinuities crossing the upper limestone formation is consistent with the prolongation towards the ground surface of the secondary fault zone identified in the clay rock formation from the tunnel moreover this secondary fault zone corresponds to the upward prolongation of a subvertical fault identified in the lower limestone using a 3d high resolution seismic reflection survey this type of large scale electrical resistivity survey is therefore a useful tool for identifying faults in superficial layers from the ground surface and is complementary to 3d seismic reflection surveys

a large slow slip event on the central hikurangi subduction interface beneath the manawatu region north island new zealand 1 we present continuous gps observations of a surface deformation episode in the manawatu region of the north island new zealand lasting 18 months from january 2004 to june 2005 we invert vertical and horizontal displacements of gps sites during the event for slow slip on the hikurangi subduction thrust we find that up to 350 mm of slip occurred on the thrust in the transition zone between strong interseismic coupling and aseismic creep if the entire slip in the manawatu slow slip event had occurred instantaneously it would have resulted in an mw 7 0 earthquake given the large amount of slip we expect that the recurrence interval for similar slow slip events may be ten years or more

do subducting seamounts generate or stop large earthquakes seamount subduction is a common process in subduction zone tectonics contradicting a widely held expectation that subducting seamounts generate large earthquakes seamounts subduct largely aseismically producing numerous small earthquakes on rare occasions when they do produce relatively large events the ruptures tend to be complex suggesting multiple rupture patches or faults we explain that the seismogenic behavior of these seamounts is controlled by the development and evolution of an adjacent fracture network during subduction and cannot be described using the frictional behavior of a single fault the complex structure and heterogeneous stresses of this network provide a favorable condition for aseismic creep and small earthquakes but an unfavorable condition for the generation and propagation of large ruptures

loci and maximum size of thrust earthquakes and the mechanics of the shallow region of subduction zones earthquakes do not extend updip along the plate interface at most subduction zones all of the way to the plate boundary at the trench axis or deformation front rather the shallowest part of that interface moves mainly through stable aseismic slip that part of the plate boundary referred to here as the aseismic zone occurs along the base of an accreted wedge of young sediments the probable primary cause for the existence of this aseismic zone is the stable slip properties of the unconsolidated and semiconsolidated sediments in that zone subducted sediment is progressively dewatered and underplated to the base of the overriding plate through this process more consolidated rocks eventually come into contact at depth across both sides of the plate boundary from the point where sufficiently hard rock is found across the plate interface that interface will change its slip behavior to unstable stick slip sliding which is characteristic of consolidated material under most conditions this type of motion is accommodated seismically as episodic slip in large earthquakes the location of this transition to seismic behavior referred to as the seismic front marks the deep end of the aseismic zone and the top of the seismogenic zone i e that part of the plate interface that moves primarily in thrust earthquakes several convergent plate margins are discussed to illustrate the seismic front and the aseismic zone we find that the seismic front defined by smaller earthquakes that occur during the interval between large events is nearly the same as that for large events as inferred from the locations of their aftershocks the location of the seismic front is important for making estimates of the maximum possible size of thrust earthquakes along the plate boundary because it delimits the trenchward limit of the potential rupture area of these events the size of large thrust earthquakes is proportional to rupture area and to at least the cube of the downdip width w of that area thus by defining the location of the seismic front for convergent margins it is possible to make better estimates of w and hence to deduce the maximum size of future interplate earthquakes the average repeat time of such events is also related to w and so better estimates of average repeat time are possible from improved knowledge of w the hypothesis that the location of the seismic front is related to the maximum depth of subduction of unconsolidated sediment has implications for forearc mechanics we use a mechanical analysis laboratory modeling and multichannel seismic information to develop a simple model explaining the growth of forearcs the outer arc high or trench slope break that occurs arcward of most accretionary wedges represents an abrupt change in the critical taper of the accretionary wedge we argue that that change is caused by a large arcward increase in the strength of the material within the overriding plate that stronger material is called the backstop our laboratory modeling experiments indicate that a backstop with a trenchward dipping upper surface results in the development of an overlying structure that includes all of the primary morphologic features observed in modern forearcs in our modeling an accretionary wedge develops trenchward of the backstop an outer arc high develops above the trenchward toe of the backstop and farther arcward a passive forearc basin forms above the stronger material of the backstop this model is consistent with the observation that earthquakes do not extend updip along the plate interface all the way to the trench axis we hypothesize that plate motion is accommodated seismically along the base of the consolidated backstop and mostly or entirely aseismically trenchward of the toe of the backstop along the base of the accretionary wedge at several margins the seismic front is approximately coincident with the outer arc high supporting this interpretation

migration characteristics of seismic tremors in the northern cascadia margin 1 seismic waveforms from a dense regional array were analyzed to study episodic tremor and slip ets events in northern cascadia the april 2005 episode occurred mostly in northern vancouver island vi where the explorer plate subducts beneath the north america plate while the may 2005 episode was mainly in middle vi all tremor occurrences are positively correlated with the presence of subducted slabs besides the steady along strike migration and halting behavior found in previous ets events a new pattern jumping is found this time visual inspection of previous seismic records suggests that the jumping behavior is probably common to ets tremors in all regions of vi the majority of tremors occurred between 25 and 45 km depth in places where local seismicity is sparse or absent our observations are compatible with the interpretation that fluids released from dehydration of subducted materials are involved in tremor generation

application of geophysical methods for the investigation of the large gravitational mass movement of sechilienne france several geophysical techniques electromagnetic profiling electrical tomography seismic refraction tomogra phy and spontaneous potential and seismic noise measurement were applied in the investigation of the large gravita tional mass movement of sechilienne france the aim of this study was to test the ability of these methods to characterize and delineate the rock mass affected by this complex movement in mica schists whose lateral and vertical limits are still uncertain a major observation of this study is that all the zones strongly deformed previously and at present by the movement are characterized by high electrical resistivity values 3 k m in contrast to the undis turbed mass which exhibits resistivity values between a few hundred and 1 k m as shown by the surface observa tions and the seismic results this resistivity increase is due to a high degree of fracturing associated with the creation of air filled voids inside the mass other geophysical techniques were tested along a horizontal transect through the movement and an outstanding coherency appeared between the geophysical anomalies and the displacement rate curve these preliminary results illustrate the benefits of combined geophysical techniques for characterizing the rock mass in volved in the movement results also suggest that monitoring the evolution of the rock mass movement with time lapse geophysical surveys could be beneficial resume plusieurs techniques geophysiques profil electromagnetique tomographie electrique tomographie sismique et potentiel spontane et bruit de fond sismique ont ete appliquees pour la reconnaissance du grand mouvement de ter rain de sechilienne france situe dans des micaschistes l objectif de cette etude etait de tester ces methodes geophy siques afin de caracteriser et de delimiter la masse de roche affectee par ce mouvement complexe dont la limite laterale reste incertaine l etude a montre que toutes les zones tres deformees encore actuellement et dans le passe par le mouvement sont caracterisees par de fortes valeurs de resistivite electrique superieur ea3k m tandis que dans la zone non perturbee les valeurs de resistivite sont de quelques centaines de m a1k m comme le montrent les observations de surface et les profils de tomographie sismique cette augmentation de resistivite est due a une frac turation importante associee a la creation de vides remplis d air au sein du massif les techniques electromagnetiques ps et de mesure de bruit ont ete testees le long d un profil transversal recoupant le mouvement une correlation remar quable est obtenue entre les anomalies geophysiques et le taux de deplacement ces resultats preliminaires soulignent l interet de combiner les methodes geophysiques pour caracteriser la masse de roche impliquee dans le mouvement et pour determiner l evolution du mouvement par un suivi temporel des parametres geophysiques mots cles mouvement gravitaire methodes geophysiques sechilienne meric et al 1115

magmatically triggered slow slip at kilauea volcano hawaii we demonstrate that a recent dike intrusion probably triggered a slow fault slip event sse on kilauea volcano9s mobile south flank our analysis combined models of advanced land observing satellite interferometric dike intrusion displacement maps with continuous global positioning system gps displacement vectors to show that deformation nearly identical to four previous sses at kilauea occurred at far field sites shortly after the intrusion we model stress changes because of both secular deformation and the intrusion and find that both would increase the coulomb failure stress on possible sse slip surfaces by roughly the same amount these results in concert with the observation that none of the previous sses at kilauea was directly preceded by intrusions but rather occurred during times of normal background deformation suggest that both extrinsic intrusion triggering and intrinsic secular fault creep fault processes can lead to sses

simultaneous long term and short term slow slip events at the hikurangi subduction margin new zealand implications for processes that control slow slip event occurrence duration and migration 1 we document a sequence of simultaneous short term and long term slow slip events sses at the hikurangi subduction zone during the 2010 2011 period the sequence of short term events each 2 3 weeks in duration ruptured much of the shallow plate interface 15 km at central and northern hikurangi over a 6 month period was accompanied by microseismicity and involved patchy irregular migration of sse slip we suggest that the patchy migration of the short term sse is due to large scale 100 3500 km heterogeneities on the plate interface related to seamount subduction and sediment subduction and or underplating this is in contrast to a 2010 2011 long term sse at the central hikurangi margin which evolved steadily over 1 5 years and ruptured much of the plate interface between 20 and 70 km depth we suggest that the occurrence of long term versus short term sses at hikurangi is related to differences in effective normal stresses and relative heterogeneity of the subduction interface the long term sse sequence began 1 year before the short term sequence coulomb stress change models suggest that the long term sse may have triggered initiation of the subsequent short term sse sequence initiation of the short term sequence occurred in a region just updip of or within an interseismically locked portion of the plate interface and may be located within the updip transition from seismic to aseismic behavior alternatively it could be characteristic of a region undergoing partial interseismic coupling this is in contrast to sses observed elsewhere in the world that typically occur within the downdip transition from seismic to aseismic behavior

evaluation of landfill disposal boundary by means of electrical resistivity imaging this paper deals with an employment of electrical resistivity imaging eri for survey of leachate content on the waste disposal site in northern israel the research consisted of conducting ten eri lines and drilling investigation wells data simulation used a 2d earthimager inversion program analysis of 2d eri interpretation results shows that determination of the boundary between the landfill body bottom intensively saturated with leachates and underlying layers of highly water saturated fat nonconsolidated clays presents a challenge however statistical analysis of eri data indicates that standard deviation and confidence interval of a set of resistivity data measured in the landfill body are significantly larger than those in underlying clays moreover maximum changes of these parameters are found on the boundary between landfill body and underlying soil thus reflecting natural differences in scattering of resistivity data measured in these two objects

deep tremor in new zealand triggered by the 2010 mw8 8 chile earthquake 1 deep non volcanic tremor nvt is usually associated with episodic slow slip events new zealand is one notable exception where numerous slow slip events have been identified yet nvt has remained undetected here we present the first known case of triggered nvt at new zealand s hikurangi subduction margin following the mw8 8 chilean earthquake of february 27 2010 we identify coherent high frequency tremor signals that are in phase with and modulated by the passing rayleigh waves this is consistent with the surface wave triggering potential for strike normal incidence on a low angle thrust fault after constraining the tremor depth on the plate interface we locate the tremor source within 20 km of the source area of episodic slow slip the tremor location is also near the edge of a region with high seismic attenuation that marks the boundary between dehydrated subducted slab and inferred hydrated underplated sediment we speculate that reduced interface friction and high fluid pressures provided by fluid rich underplated sediment facilitates the tremor generation

case studies of electrical and electromagnetic methods applied to mapping active faults beneath the thick quaternary it is of considerable importance to explore the geological structure around active faults especially near surface unconsolidated layers to estimate the faults activity there are numerous case studies to investigate active faults using geophysical exploration methods however only a few cases have been verified in detail by comparison with other geological information we have applied electric and electromagnetic methods which can be effective for exploring to several hundred meters depth to reveal geological structures covered by thick quaternary formations at four active fault sites in japan in this paper we used the controlled source audio frequency magnetotelluric csamt method the direct current dc resistivity method and the resistivity tomography method the resistivity profiles were analyzed by two dimensional inversion techniques and the resulting models were verified by comparison with geological evidence obtained by drilling or trenching our results are as follows 1 csamt is an effective method for defining an outline of geological structures around a fault to several hundred meters deep it enables us to define a resistivity boundary between different kinds of bedrock with a fault contact 2 the dc resistivity method distinguishes each sedimentary unit as a different resistivity zone and detects the vertical displacement in the quaternary formations 3 the resistivity tomography method is useful to determine in more detail the flexure structure produced by faulting using these latter two methods we can select drilling positions and trenching locations in addition it is verified from the data measured along trench walls and electrical logging that the resistivity of soft sedimentary layers and clayey cataclastic bedrock conforms to the relationship established between the resistivity and the clay content these resistivity methods have the advantages of detecting clayey layers as very low resistivity zones the overall conclusion is that the combination of these resistivity methods provides us with more detailed and accurate information for estimating fault activity

slow slip and frictional transition at low temperature at the hikurangi subduction zone temperature changes with depth do not appear to be a primary control for either slow slip or fault locking processes at the hikurangi margin north island new zealand both slow slip events and the geodetically observed transition from fault locking to free slip at depth occur at temperatures as low as 100 c shallow portions of faults exhibit brittle stick slip behaviour that gives way to more stable sliding with increasing depth limiting the depths to which earthquake inducing slip can occur the increase of temperature with depth is often assumed to transform friction in the fault from velocity weakening unstable to velocity strengthening stable and to change conditions from brittle to ductile1 2 3 4 5 a temperature of 350 c has been suggested to mark the base of the frictionally unstable portion of the fault which becomes free slipping at depth where temperatures rise above 450 c refs 2 4 6 here we show that both slow slip events and the geodetically observed transition from fault locking to free slip at the hikurangi subduction zone east of the north island new zealand occur at temperatures as low as 100 c suggesting that temperature is not a primary control on either slow slip or fault locking processes at the hikurangi margin although globally shallow slow slip events are rare five out of seven events observed so far at the hikurangi margin are less than 15 km deep

the updip and downdip limits to great subduction earthquakes thermal and structural models of cascadia south alaska sw japan and chile this study examines thermal and structural controls of the updip and downdip rupture limits of great subduction thrust earthquakes data on past great earthquake seismic limits have been compiled for four continental subduction zones cascadia sw japan south alaska and chile these limits have then been compared to the predictions of several models for what constrains great earthquake rupture temperatures on the subduction thrusts have been estimated by finite element numerical models the landward limits of the observed updip aseismic zones correspond to the position where the thrust temperature reaches about 100 c that is depths of about 2 to 10 km for the subduction zones studied this temperature agrees with the dehydration of stable sliding smectite clays to illite chlorite the temperatures in this region are controlled mainly by the thickness of sediment on the incoming crust and by the crustal age and thus heat flow the downdip limits correspond to the depth on the thrust where either 1 the temperature reaches about 350 c which corresponds to thermally activated stable sliding behavior for crustal rocks with a transition to 450 c or 2 about 40 km depth if 350 c is reached at greater depth depths of about 40 km approximately correspond to the intersection of the thrust with the continental forearc moho and this downdip limit may be a consequence of stable sliding serpentinite or talc and other hydrated forearc mantle rocks the primary temperature controls on the downdip region are the age of the subducting oceanic plate and the thrust dip profile secondary control comes from the thickness of incoming sediment the convergence rate and the radioactive heat generation in the overlying forearc the 100 c updip limit occurs near the trench for young subducting plates with a thick sediment section such as cascadia 6 8 ma and up to 80 km landward for older oceanic crust such as south alaska 50 ma the 350 c downdip thermal limit is applicable for young oceanic plates e g cascadia and nankai whereas the forearc mantle limit applies for older plates e g south alaska and chile except near the chile rise for the margins studied that have experienced great earthquakes there is generally good agreement between the postulated thermal and moho limits and the rupture or seismogenic zone as defined by the distribution of aftershocks and by waveform tsunami and dislocation modeling the downdip limit of the interseismic locked zone from dislocation modeling is also in agreement with these limits

southern california permanent gps geodetic array spatial filtering of daily positions for estimating coseismic and postseismic displacements induced by the 1992 landers earthquake the june 28 1992 m w 7 3 landers california earthquake was the first earthquake to be surveyed by a continuously operating global positioning system gps array the coordinate time series of seven sites are evaluated for station displacements during an interval of 100 days centered on the day of the earthquake we employ a new spatial filtering technique that removes common mode errors from the coordinate time series this approach provides precise estimates of site specific displacements compared to the cumbersome method of analyzing baselines between pairs of stations all sites indicate significant coseismic horizontal displacements of 5 65 mm with uncertainties of 1 2 mm horizontal displacements are in general agreement with elastic dislocation models in particular for sites closer to the epicenter vertical displacements range from 13 to 7 mm with uncertainties of 2 4 mm the observed vertical displacements in all cases show 5 10 mm more subsidence than expected from geodetic and seismic geologic models significant postseismic horizontal displacements totaling 6 2 mm 10 20 of the coseismic displacement are detected at the three sites closest to the epicenter these displacements are modeled as a short term exponential relaxation with a decay time of 22 10 days superimposed on a longer term linear interseismic trend scaling the observed coseismic and postseismic displacements at one of the sites with the distance to the epicenter provides a measure of site strain which agrees well with the direction and magnitude determined from more precise laser strain meter data the time series do not show any detectable preseismic displacements

hydrologic detection and finite element modeling of a slow slip event in the costa rica prism toe 1 we investigate transient fluid flux through the seafloor recorded near the costa rica trench during the 2000 costa rica seismogenic zone experiment using a 2 d fully coupled poroelastic finite element model we demonstrate that the observed hydrologic anomalies are consistent with a model of propagating slow slip at the subduction interface between the frontal prism and downgoing plate there are two sources of volumetric strain that drive fluid flux at the seafloor in response to fault slip at depth 1 compression and dilation in the vicinity of the tips of a slipping patch and 2 extension and compression due to flexure of the seafloor the superposition of these two effects results in distinctive spatial and temporal patterns of fluid flow through the seafloor in a forward modeling approach time series from shear ruptures with a range of fault length to depth ratios in a heterogeneous crust are generated and compared with flow rate observations assuming a constant propagation rate and an elliptical profile for the distribution of slip along the decollement the set of model predictions enables us to infer the probable rupture location extent propagation velocity and duration from a single flow rate time series the best fit model suggests that the slow slip event initiated within the toe at a depth of less than 4 km and propagated bilaterally at an average rate of 0 5 km d 1 this interpretation implies that stress in the shallow subduction zone is relieved episodically furthermore the costa rica data suggest that episodic slow slip events may initiate in the prism toe without being triggered by a seismic event further downdip

seafloor structural geomorphic evolution of the accretionary frontal wedge in response to seamount subduction poverty indentation new zealand abstract high quality swath bathymetry and seismic reflection data reveal that the steep forearc slope along the northern sector of the obliquely convergent hikurangi subduction zone is characteristic of non accretionary and tectonically eroding continental margins with reduced sediment supply in the trench relative to further south and the presence of subducting seamount relief on the hikurangi plateau these seamounts influence the subduction process and the structurally driven geomorphic development of the over riding margin of the australian plate frontal wedge the origin of the poverty indentation on the inboard trench slope is attributed to multiple seamount impacts over the last c 1 myr period accompanied by canyon incision thrust fault propagation into the trench fill and numerous large scale gravitational collapse structures with multiple debris flow and avalanche deposits ranging in downslope length from a few hundred metres to more than 40 km the indentation is directly offshore of the waipaoa river which is currently estimated to have a high sediment yield into the marine system the poverty canyon stretches 70 km from the continental shelf edge directly offshore from the waipaoa to the trench floor incising into the axis of the indentation the sediment delivered to the margin from the waipaoa catchment and elsewhere during sea level high stands including the holocene has remained largely trapped in a large depocentre on the poverty shelf while during low stand cycles sediment bypassed the shelf to develop a prograding clinoform sequence out onto the upper slope the formation of the indentation and the development of the upper branches of the poverty canyon system has led to the progressive removal of a substantial part of this prograding wedge by mass movements and gully incision sediment has also accumulated in the head of the poverty canyon and episodic mass flows contribute significantly to continued modification of the indentation by driving canyon incision and triggering instability in the adjacent slopes prograding clinoforms lying seaward of active faults beneath the shelf and overlying a buried inactive thrust system beneath the upper slope reveal a history of deformation accompanied by the creation of accommodation space the middle to lower poverty canyon represents a structural transition zone within the indentation coincident with the indentation axis the lower to mid slope south of the canyon conforms more closely to a classic accretionary slope deformation style with a series of east facing thrust propagated asymmetric anticlines separated by early stage slope basins north of the canyon system seamount impact has resulted in frontal tectonic erosion associated with the development of an over steepened lower to mid slope margin fault reactivation and structural inversion and over printing

tectonic and geological framework for gas hydrates and cold seeps on the hikurangi subduction margin new zealand the imbricated frontal wedge of the central hikurangi subduction margin is characteristic of wide ca 150 km poorly drained and over pressured low taper not vert similar 4 thrust systems associated with a relatively smooth subducting plate a thick trench sedimentary sequence not vert similar 3 4 km weak basal decollement and moderate convergence rate not vert similar 40 mm yr new seismic reflection and multibeam bathymetric data are used to interpret the regional tectonic structures and to establish the geological framework for gas hydrates and fluid seeps we discuss the stratigraphy of the subducting and accreting sequences characterize stratigraphically the location of the interplate decollement and describe the deformation of the upper plate thrust wedge together with its cover sequence of miocene to recent shelf and slope basin sediments we identify approximately the contact between an inner foundation of deforming late cretaceous and paleogene rocks in which widespread out of sequence thrusting occurs and a 65 70 km wide outer wedge of late cenozoic accreted turbidites although part of a seamount ridge is presently subducting beneath the deformation front at the widest part of the margin the morphology of the accretionary wedge indicates that frontal accretion there has been largely uninhibited for at least 1 2 myr this differs from the offshore hawkes bay sector of the margin to the north where a substantial seamount with up to 3 km of relief has been subducted beneath the lower margin resulting in uplift and complex deformation of the lower slope and a narrow 10 20 km active frontal wedge five areas with multiple fluid seep sites referred to informally as wairarapa uruti ridge omakere ridge rock garden and builders pencil typically lie in 700 1200 m water depth on the crests of thrust faulted anticlinal ridges along the mid slope uruti ridge sites also lie in close proximity to the eastern end of a major strike slip fault rock garden sites lie directly above a subducting seamount structural permeability is inferred to be important at all levels of the thrust system there is a clear relationship between the seeps and major seaward vergent thrust faults near the outer edge of the deforming cretaceous and paleogene inner foundation rocks this indicates that thrust faults are primary fluid conduits and that poor permeability of the cretaceous and paleogene inner foundation focuses fluid flow to its outer edge the sources of fluids expelling at active seep sites along the middle slope may include the inner parts of the thrust wedge and subducting sediments below the decollement within anticlinal ridges beneath the active seep sites there is a conspicuous break in the bottom simulating reflector bsr and commonly a seismically resolvable shallow fault network through which fluids and gas percolate to the seafloor no active fluid venting has yet been recognized over the frontal accretionary wedge but the presence of a widespread bsr an extensive protothrust zone 200 km by 20 km in the hikurangi trough and two unconfirmed sites of possible previous fluid expulsion suggest that the frontal wedge could be actively dewatering there are presently no constraints on the relative fluid flux between the frontal wedge and the active mid slope fluid seeps article outline

pseudo 3d imaging of a low slip rate active normal fault using shallow geophysical methods the geleen fault in the belgian maas river valley in a detailed site survey for paleoseismic trenching we applied shallow geophysical prospecting techniques including ground penetrating radar gpr electric resistivity tomography ert and resistivity mapping to identify locate and visualize in 3d the geleen fault an active normal fault bordering the roer valley graben in northeast belgium because of a low slip rate the geomorphic expression of this fault is very faint in the relatively young deposits of the maas river valley ert profiles show the fault as a broad near vertical anomaly characterized by sharp lateral resistivity contrasts with an associated vertical offset of sediment layers we observed offsets of 15 m and 5 m for the base and top respectively of a middle late pleistocene fluvial gravel layer shallow ert and gpr profiles indicate that younger sediments are also affected by faulting but the amount and sense of offset appear to be conflicting ert profiles show a near surface high resistivity layer with an apparent rever

stress transferred by the 1995 mw 6 9 kobe japan shock effect on aftershocks and future earthquake probabilities the kobe earthquake struck at the edge of the densely populated osaka kyoto corridor in southwest japan we investigate how the earthquake transferred stress to nearby faults altering their proximity to failure and thus changing earthquake probabilities we find that relative to the pre kobe seismicity kobe aftershocks were concentrated in regions of calculated coulomb stress increase and less common in regions of stress decrease we quantify this relationship by forming the spatial correlation between the seismicity rate change and the coulomb stress change the correlation is significant for stress changes greater than 0 2 1 0 bars 0 02 0 1 mpa and the nonlinear dependence of seismicity rate change on stress change is compatible with a state and rate dependent formulation for earthquake occurrence we extend this analysis to future mainshocks by resolving the stress changes on major faults within 100 km of kobe and calculating the change in probability caused by these stress changes transient effects of the stress changes are incorporated by the state dependent constitutive relation which amplifies the permanent stress changes during the aftershock period earthquake probability framed in this manner is highly time dependent much more so than is assumed in current practice because the probabilities depend on several poorly known parameters of the major faults we estimate uncertainties of the probabilities by monte carlo simulation this enables us to include uncertainties on the elapsed time since the last earthquake the repeat time and its variability and the period of aftershock decay we estimate that a calculated 3 bar 0 3 mpa stress increase on the eastern section of the arima takatsuki tectonic line attl near kyoto causes fivefold increase in the 30 year probability of a subsequent large earthquake near kyoto a 2 bar 0 2 mpa stress decrease on the western section of the attl results in a reduction in probability by a factor of 140 to 2000 the probability of a mw 6 9 earthquake within 50 km of osaka during 1997 2007 is estimated to have risen from 5 6 before the kobe earthquake to 7 11 afterward during 1997 2027 it is estimated to have risen from 14 16 before kobe to 16 22

detection of triggered deep low frequency events from the 2003 tokachi oki earthquake 1 we show the level of increased decreased seismicity mapped across japan immediately following the 2003 tokachi oki earthquake mw 8 1 of september 25 2003 ut by use of the statistic significant dynamic triggering of events is found near the nankai subduction zone 900 1400 km from the earthquake the events are inferred to be dynamically triggered deep low frequency earthquakes of a type that often occur in this region the triggering appears to be caused by the long period oscillations of the surface waves which may be effective in triggering fluid related events the region that showed the highest level of triggered events was an area of elevated activity in the bungo strait where a slow slip event was in progress

the kinematics of a transition from subduction to strike slip an example from the central new zealand plate boundary 1 we develop a kinematic model for the transition from subduction beneath the north island new zealand to strike slip in the south island constrained by gps velocities and active fault slip data to interpret these data we use an approach that inverts the kinematic data for poles of rotation of tectonic blocks and the degree of interseismic coupling on faults in the region convergence related to the hikurangi subduction margin becomes very low offshore of the northern south island indicating that in this region the majority of the relative plate motion has been transferred onto faults within the upper plate as suggested by previous studies this result has implications for understanding the likely extent of subduction interface earthquake rupture in central new zealand easterly trending strike slip faults such as the boo boo fault are the key features that facilitate the transfer of strike slip motion from the northern south island faults further north into the southern north island and onto the hikurangi subduction thrust our results also indicate that the transition from rapid forearc rotation adjacent to the hikurangi subduction margin to a strike slip dominated plate boundary with negligible vertical axis rotation in the south island occurs via a crustal scale hinge or kink in the upper plate compatible with paleomagnetic and structural geological data despite the ongoing tectonic evolution of the central new zealand region our study highlights a remarkable consistency between data sets spanning decades gps thousands of years active faulting data and millions of years paleomagnetic data and bedrock structure

microseismicity but no tremor accompanying slow slip in the hikurangi subduction zone new zealand abstract geodetically detected episodes of slow slip appear in several subduction zones to be accompanied by bursts of low frequency coherent noise known as seismic tremor but whether a single physical process governs this association or even whether slow slip is invariably accompanied by tremor remains unresolved detailed analysis of broadband seismic data spanning a slow slip episode in the hikurangi subduction zone new zealand reveals that slow slip was accompanied by distinct reverse faulting microearthquakes rather than tremor the timing location and faulting style of these earthquakes are consistent with stress triggering down dip of the slow slip patch either on the subduction interface or just below it these results indicate that tremor is not ubiquitous during subduction zone slow slip and that slow slip in subduction zone environments is capable of triggering high frequency earthquakes near the base of the locked subduction thrust in this and other locations hawaii boso peninsula where slow slip is accompanied by triggered microseismicity the estimated upper extent of the slow slip is shallower less than 20 km than in those locations from which tremor has been reported this suggests that ambient temperature or pressure dependent factors govern the character of the seismic response to slow slip on subduction thrusts and other large faults with rheological or lithological conditions at shallow depths triggering high frequency microearthquakes and those at greater depths triggering seismic tremor

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