eastern mediterranean gravity potential and the hellenic subduction process tornographic images of the mediterranean upper mantle p wave velocity structure have been used to analyse the gravity potential in the vicinity of the hellenic subduction zone the velocity anomalies are assumed to be proportional to density variations according to birch s law the effect of the topography on the geoid in the region is also calculated the results indicate that the upper mantle geoid signal probably has significant amplitudes of several metres but it correlates poorly with the observed geoid the geoid calculated from topography correlates well but has an amplitude that is too large in comparison with the observed geoid the results show that an improved understanding of the hellenic subduction zone geoid requires refinement of the moho topography so that the effect of this topography can be separated from the upper mantle signature

the 2006 2007 kuril islands great earthquake sequence the southwestern half of a 500 km long seismic gap in the central kuril island arc subduction zone experienced two great earthquakes with extensive preshock and aftershock sequences in late 2006 to early 2007 the nature of seismic coupling in the gap had been uncertain due to the limited historical record of prior large events and the presence of distinctive upper plate trench and outer rise structures relative to adjacent regions along the arc that have experienced repeated great interplate earthquakes in the last few centuries the intraplate region seaward of the seismic gap had several shallow compressional events during the preceding decades notably an m s 7 2 event on 16 march 1963 leading to speculation that the interplate fault was seismically coupled this issue was partly resolved by failure of the shallow portion of the interplate megathrust in an m w 8 3 thrust event on 15 november 2006 this event ruptured 250 km along the seismic gap just northeast of the great 1963 kuril island m w 8 5 earthquake rupture zone within minutes of the thrust event intense earthquake activity commenced beneath the outer wall of the trench seaward of the interplate rupture with the larger events having normal faulting mechanisms an unusual double band of interplate and intraplate aftershocks developed on 13 january 2007 an m w 8 1 extensional earthquake ruptured within the pacific plate beneath the seaward edge of the kuril trench this event is the third largest normal faulting earthquake seaward of a subduction zone on record and its rupture zone extended to at least 33 km depth and paralleled most of the length of the 2006 rupture the 13 january 2007 event produced stronger shaking in japan than the larger thrust event as a consequence of higher short period energy radiation from the source the great event aftershock sequences were dominated by the expected faulting geometries thrust faulting for the 2006 rupture zone and normal faulting for the 2007 rupture zone a large intraplate compressional event occurred on 15 january 2009 m w 7 4 near 45 km depth below the rupture zone of the 2007 event and in the vicinity of the 16 march 1963 compressional event the fault geometry rupture process and slip distributions of the two great events are estimated using very broadband teleseismic body and surface wave observations the occurrence of the thrust event in the shallowest portion of the interplate fault in a region with a paucity of large thrust events at greater depths suggests that the event removed most of the slip deficit on this portion of the interplate fault this great earthquake doublet demonstrates the heightened seismic hazard posed by induced intraplate faulting following large interplate thrust events future seismic failure of the remainder of the seismic gap appears viable with the northeastern region that has also experienced compressional activity seaward of the megathrust warranting particular attention

reply to comment on attenuation in west bohemia evidence of high attenuation in the nový kostel focal zone and temporal change consistent with co2 degassing by m wcislo l eisner j malek t fischer j vlcek and g kletetschka by morozovreply

inversion of complex body waves we have developed a method that inverts seismic body waves to determine the mechanism and rupture pattern of earthquakes the rupture pattern is represented as a sequence of subevents distributed on the fault plane this method is an extension of our earlier method in which the subevent mechanisms were fixed in the new method the subevent mechanisms are determined from the data and are allowed to vary during the sequence when subevent mechanisms are allowed to vary however the inversion often becomes unstable because of the complex trade offs between the mechanism the timing and the location of the subevents many different subevent sequences can explain the same data equally well and it is important to determine the range of allowable solutions some constraints must be imposed on the solution to stabilize the inversion we have developed a procedure to explore the range of allowable solutions and appropriate constraints in this procedure a network of grid points is constructed on the i plane where and i are respectively the onset time and the distance from the epicenter of a subevent the best fit subevent is determined at all grid points then the correlation is computed between the synthetic waveform for each subevent and the observed waveform the correlation as a function of and i and the best fit mechanisms computed at each i grid point depict the character of allowable solutions and facilitate a decision on the appropriate constraints to be imposed on the solution the method is illustrated using the data for the 1976 guatemala earthquake

tsunamigenic potential of outer rise normal faults at the middle america trench in central america the middle america trench is formed by the subduction of the cocos and rivera plates under the caribbean and north american plates the subduction interface presents low coupling in central america showing its seismicity a high frequency of outer rise normal fault earthquakes these outer rise earthquakes are generated on the inherited structures of the seafloor spreading fabric during the subducting plate bending we analyze focal mechanism data in combination with the available structural data of the outer rise normal faults in order to constrain the rupture characteristics of the outer rise normal earthquakes a new empirical scaling relationship is developed to define earthquake magnitudes from normal fault dimensions in the outer rise context we numerically model the tsunami wave propagation due to the worst outer rise tsunamigenic source in the area to estimate its damaging potential wave elevations higher than 2 m are common at the coast in front of the fault extent with maximum wave elevations of 8 m the capability of these faults to generate ocean wide tsunamis is low however they can produce significant tsunamis locally

influence of host rock texture on the morphology of carbonate concretions in a meteoric diagenetic environment abstract the integrated stratigraphic petrographic geochemical study of quaternary marine terraces that have undergone well constrained sea level and water table oscillation s over geologically short time periods can provide important clues on diagenetic processes at the marine continental interface the punta di i cani marine terrace quaternary saint florent corsica unconformably overlies the well cemented low permeability arenites of the miocene monte s angelo formation and is erosively overlain by unlithified high permeability holocene continental sediments the terrace is composed of a retrogradational fining upward succession from fluvial pebbly sandstone to beach and shoreface deposits the entire thickness of the terrace hosts concretions made of low mg calcite concretion geometry is linked to the sedimentological facies of the host sediment i massive fluvial pebbly sandstone at the base of the terrace contains knobby subhorizontal concretions somewhat resembling turbidite flute casts ii very low angle cross bedded well sorted beach deposits contain pipy subhorizontal concretions iii trough crossbedded upper shoreface deposits in the upper part of the terrace contain a subtle diagenetic lineation on the laminae locally obliterated by a patchy isotropic cementation overall the degree of cementation decreases from the bottom to the top of the terrace cement chemistry and morphology as well as stable carbon and oxygen isotopic signatures indicate that the concretions formed by precipitation of meteoric phreatic water flowing toward the coast elongate concretions are invariably parallel to the topographic gradient consistent with the notion that the growth of concretions was controlled by advection smectitic vadose cement is locally present its crosscutting relationships with calcite cement point to periodic oscillations of the water table the results of this study i show that elongate concretions can be used as interstitial paleoflow indicators and ii suggest that concretion geometry in an advection dominated diagenetic environment can depend on the small scale permeability distribution as suggested by the fact that each type of concretion is invariably associated with a specific sedimentary facies

hypocenter locations in finite source rupture models we use a database of more than 80 finite source rupture models for more than 50 earthquakes m w 4 1 8 1 with different faulting styles occurring in both tectonic and subduction environments to analyze the location of the hypocenter within the fault and to consider the correlation between hypocenter location and regions of large slip rupture in strike slip and crustal dip slip earthquakes tends to nucleate in the deeper sections of the fault subduction earthquakes do not show this tendency ratios of the hypocentral slip to either the average or the maximum slip show that rupture can nucleate at locations with any level of relative displacement rupture nucleates in regions of very large slip d 2 3 d max in only 16 of the events in regions of large slip 1 3 d max d d max in 35 of the events and in regions of low slip d 1 3 d max in 48 of the events these percentages significantly exceed the percentages of fault area with very large 7 and large 28 slip ruptures that nucleate in regions of low slip however tend to nucleate close to regions of large slip and encounter a zone of very large slip within half the total rupture length applying several statistical tests we conclude that hypocenters are not randomly located on a fault but are located either within or close to regions of large slip

seismological monitoring on the 2003 tokachi oki earthquake derived from off kushiro permanent cabled obss and land based observations abstract japan marine science and technology center installed a cabled geophysical observatory system off kushiro hokkaido island in july 1999 this observatory system comprises three ocean bottom seismographs obss two tsunami gauges and a geophysical geochemical monitoring system 4 years and 2 months after the installation a megathrust earthquake the 2003 tokachi oki earthquake 26th september in japan standard time jst mjma 8 0 occurred along a plate boundary underneath a forearc basin where the system is located the system recorded clear unsaturated seismograms just at 28 6 km from the epicenter this paper demonstrates advantages brought by the cabled observatory to record the megathrust earthquake showing how earthquake detectability is improved dramatically combining permanent obs and land based observations around the region and importance of the in situ monitoring on the seismogenic zone in the present study processing obss and land based network together and comparing magnitudes of common observed earthquakes with national authorized network event detection level improved down to m 1 5 which is much lower than the previously designed as down to m 2 comparing detection level before and after installing obss we found dramatic improvement of the earthquake detection level in the interesting region real time continuous observations of microearthquakes since 1999 have brought us tremendous findings first a seismic quiescence started about 10 days before the 2003 tokachi oki earthquake second aftershock distribution is not uniform over the focal area and can be divided into several sub regions which might indicate an existence of several asperities we think that the geophysical observations helped to understand the initiation process of the rupture of the 2003 tokachi oki earthquake and that observations including seismological geodynamic hydrogeological and the other multidisciplinary observations would provide a clue to future understanding of seismogenic processes at subduction zones

influence of fore arc structure on the extent of great subduction zone earthquakes 1 structural features associated with fore arc basins appear to strongly influence the rupture processes of large subduction zone earthquakes recent studies demonstrated that a significant percentage of the global seismic moment release on subduction zone thrust faults is concentrated beneath the gravity lows resulting from fore arc basins to better determine the nature of this correlation and to examine its effect on rupture directivity and termination we estimated the rupture areas of a set of mw 7 5 8 7 earthquakes that occurred in circum pacific subduction zones we compare synthetic and observed seismograms by measuring frequency dependent amplitude and arrival time differences of the first orbit rayleigh waves at low frequencies the amplitude anomalies primarily result from the spatial and temporal extent of the rupture we then invert the amplitude and arrival time measurements to estimate the second moments of the slip distribution which describe the rupture length width duration and propagation velocity of each earthquake comparing the rupture areas to the trench parallel gravity anomaly tpga above each rupture we find that in 11 of the 15 events considered in this study the tpga increases between the centroid and the limits of the rupture thus local increases in tpga appear to be related to the physical conditions along the plate interface that favor rupture termination owing to the inherently long timescales required for forearc basin formation the correlation between the tpga field and rupture termination regions indicates that long lived material heterogeneity rather than short timescale stress heterogeneities are responsible for arresting most great subduction zone ruptures

seismicity and deformation at convergent margins due to heterogeneous coupling studies of the mechanics of subduction as inferred from earthquake cycle observations suggest that the distribution and style of seismicity in the seafloor between the trench and the outer rise and in the slab at intermediate depth can in some cases serve to identify asperity locations along the thrust interface dmowska and lovison 1992 such asperities identified from seismic wavefield modeling are the zones of highest seismic moment release in large underthrusting events to the extent that asperity locations are relatively stationary from one event to the next their locations provide the zones of highest expected moment release in future large earthquakes and rupture often nucleates at the border of an asperity the region of the thrust interface outside such asperities is apparently less well coupled and releases moment throughout the great earthquake cycle in some combination of aseismic creep and moderate seismicity thus it is reasonable that stress and deformation rates associated with the earthquake cycle should be most pronounced near asperities and that this should have seismic and geodetic consequences three dimensional finite element modeling is used here to understand such stress and deformation patterns and their variation in time in relation to heterogeneity of coupling along thrust interfaces the stress field helps to explain the observed clustering of seafloor seismicity along the strike of the convergent margin in cases of convergence at approximately normal incidence like for the region of the valparaiso chile 1985 thrust event the modeling is consistent with the observation that areas of large earthquakes in the seafloor toward the outer rise and in the slab tend to lie within corridors through thrust zone asperities running perpendicular to the line of the trench we seek to learn if such model stress fields are consistent with observations for the strongly oblique subduction margin of the rat islands western aleutians 1965 event that active areas of the outer rise and slab at intermediate depth are offset along strike from asperity locations modeling results here for the stress in the seafloor raise the possibility that to explain this offset the asperity zones along the thrust interface may have to be strung out along the direction of oblique slip perhaps reflecting the contact path of subducting seamounts or geometric irregularities along the interface shear stress patterns created in the upper plate when there is oblique subduction suggest that favorable areas for back arc strike slip activity following underthrusting as in the adak island central aleutians region of the 1986 andreanof island earthquake ekstrom and engdahl 1989 will also be shifted along strike from asperity locations our analyses show how deformation patterns on the earth s surface above asperities differ from patterns above nonasperities and hence provide tools to identify inhomogeneous coupling from geodetic observations we discuss possible bathymetric topographic and structural signals of strength of coupling and of asperities particularly noting that the density and extent from the trench of seafloor normal faults correlates with seismically inferred zones of strongest coupling in the central aleutians

incoming plate faulting in the northern and western pacific and implications for subduction zone water budgets abstract the greatest uncertainty in the amount of water input into the earth at subduction zones results from poor constraints on the degree of mantle serpentinization in the incoming plate recent studies suggest that the depth of serpentinization within the incoming plate mantle is likely controlled by the depth of extensional faulting caused by lithospheric bending at the outer rise and trench we explore the maximum depth of extension within the incoming plate at northwestern pacific subduction zones in order to estimate the depth limit of serpentinization and to identify any significant variation between subduction zone segments we relocate trench earthquakes to identify which events occurred within the incoming plate and determine accurate depths for 63 incoming plate earthquakes occurring during 1988 2011 by inverting teleseismic broadband p and sh waveforms we observe that the top 10 15 km of the incoming plate mantle experiences extensional faulting at all of the subduction zones with a reasonable sample of earthquakes 60 of the total number of extensional earthquakes occur at crustal depths or within the top 5 km of the incoming plate mantle 80 occur above 10 km within the mantle and 95 occur above 15 km there is evidence for variation throughout the different regions of study for example extensional earthquakes occur down to 20 km below the crust in the western aleutians and izu bonin we propose that the incoming plate mantle is most strongly hydrated in the upper 5 km and that partial serpentinization exists regionally within the incoming plate mantle to 15 km making reasonable assumptions about the degree of serpentinization and incorporating previous estimates of crustal water we calculate that the total water carried into the northern and western pacific subduction zones is generally higher than previous estimates and is approximately 4 6 10 8 tg myr or 45 70 10 3 tg myr per kilometer of subduction zone

the internal structure of carbonate concretions in mudrocks a critical evaluation of the conventional concentric model of concretion growth abstract carbonate concretions have traditionally been viewed as forming concentrically through the progressive addition of carbonate to the outer edge of the growing concretion this conventional model of concretion growth is based mainly upon center to edge textural and geochemical trends that are consistent with concentric growth however a number of recent studies of concretions in mudrocks have documented complex zonation that is not compatible with the conventional concentric model in some cases complexly zoned concretions contain late stage cements that precipitated throughout the concretion body none of the center to edge relationships used to support the conventional concentric model exclude more complex modes of origin as concretions that fit the conventional model may be the exception rather than the rule high resolution petrographic analysis of concretions should always be used to characterize internal structure and mode of growth prior to interpretation of geochemical and textural data

structural factors controlling the coseismic rupture zone of the 1973 nemuro oki earthquake the southern kuril trench seismogenic zone 1 the kuril trench is an active seismogenic zone where historic great earthquakes have occurred repeatedly with temporal and spatial regularities this paper presents the results of a wide angle ocean bottom seismographic obs survey across the coseismic rupture zone of the 1973 nemuro oki earthquake mw 7 8 together with thermal modeling the main purpose of this study is to understand the crustal and thermal controls on the kuril seismogenic zone revealing structures that can be controlling factors of a megathrust earthquake helps in estimating earthquake hazards we focus specifically on the precise structure of the seismogenic interface our imaged subduction structure clearly indicates that the coseismic rupture of the 1973 event occurred between the subducting oceanic crust and the kuril island arc crust at 15 30 km depth a thermally determined updip limit of the seismic rupture 100 c corresponds to the seismically determined updip limit 15 km depth an analysis of amplitude variations of wide angle reflections demonstrated a highly reflective plate interface immediately trenchward of the coseismic rupture zone shallower than 15 km depth while a weakly reflective interface is observed at the coseismic rupture zone from the observed amplitude variation with offsets a thin low velocity layer 4 5 km s is observed at the top of the highly reflective interface this suggests the presence of fluid which would indicate weak coupling updip of the rupture zone we also deduced from these observations that a weakly reflective interface in the coseismic slip zone represents a strongly coupled zone pending the next megathrust earthquake

microearthquakes and tectonics around an outer rise the zenisu ridge japan abstract to investigate the activity and tectonic implications of intraplate microearthquakes occurring within the deflecting oceanic plate along the nankai suruga trough japan we deployed eight ocean bottom seismometers obs s on the zenisu ridge for a period of 25 days in 1985 hypocenters of approximately 40 microearthquakes were identified around the zenisu ridge using the obs data the obs located hypocenters were distributed mainly on the southern half flank of the ridge there are no earthquakes located by the obs data within the upper layer of the philippine sea plate the focal depths range from 18 to 35 km indicating that the earthquakes occurred within the lower layer of the mechanically strong part of the lithosphere the composite focal plane solution of the microearthquakes that occurred on the zenisu ridge was a strike slip or reverse fault type having p axis in the wnw the tectonic origin of the earthquakes located on the ridge was demonstrated to be found in the bending with a regional compression of the philippine sea plate along the eastern nankai suruga through

source complexity of the 1988 armenian earthquake evidence for a slow after slip event we analyzed teleseismic p and s waves using a multiple event deconvolution method to investigate the source process of the spitak armenia earthquake of december 7 1988 teleseismic long period body waves exhibit complex waveforms significantly more complex than those normally seen for an event of this size we identified two groups of subevents one is a group of strike slip events during the first 20 s the other is a dip slip event initiating at about 30 s after the initial rupture the tensor sum of all the subevents is essentially strike slip strike 302 dip 59 rake 143 with a scalar moment of 1 47 10 19 n m the seismic moment of the dip slip event strike 89 dip 60 rake 88 is 5 6 10 18 n m nearly 40 of the total and the moment release rate is slower than the other subevents with a strike slip mechanism we call this event a slow after slip event the mechanism of the after sup event is consistent with the present day deformation pattern in the caucasus where north south compression is predominant due to the continental collision between the arabian plate and the russian platform this result suggests that in a region where both strike slip motion and crustal shortening are taking place like southern california a large strike slip event may accompany large thrust events and vice versa in order to determine the total coseismic deformation pattern it is essential to resolve these multiple events in time space and mechanism

intraplate and interplate faulting interactions during the august 31 2012 philippine trench earthquake mw 7 6 sequence on august 31 2012 a large m w 7 6 thrust earthquake occurred within the subducting philippine sea plate seaward of a low seismicity region of the plate boundary 9 5 n 11 5 n possibly as a result of horizontal compressional stress accumulation offshore of a locked megathrust the mainshock ruptured from 30 50 km depth with high radiated energy seismic moment ratio and enriched short period p wave radiation the nine largest aftershocks with global centroid moment tensor solutions m w 5 2 5 6 were shallow 10 13 km normal faulting outer rise events and a waveform template analysis using regional broadband data indicates many 48 110 similar normal faulting events m b 4 0 5 5 and a few 8 110 likely shallow thrust faulting events on the megathrust with additional very small unidentified events coulomb stress perturbations may contribute to the mix of intraplate and interplate faulting geodetic assessment of any slip deficit on the megathrust is essential for quantifying the potential for a future large interplate rupture in this region

source process of the great 1977 sumba earthquake in order to investigate the applicability of the asperity model to intraplate earthquakes we have studied the rupture process of the great 1977 sumba normal faulting earthquake mw 8 2 8 3 one of the largest earthquakes since 1963 this event has been variously interpreted as a plate detachment event i e rupture through the entire lithosphere or a shallow plate bending event we have analyzed long period body waves in order to determine the spatiotemporal rupture characteristics including the depth extent of the rupture area visible depth phases in the initial stage of weak radiation beginning about 15 s before the main pulse suggest that the earthquake nucleated near 29 km depth which corresponds to the maximum depth of the aftershock sequence the excitation of a strong tsunami implies that rupture extends to the surface while deconvolutions of long period p waves suggest a relatively shallow 50 km maximum depth extent however the existence of slip below this depth cannot be ruled out particularly if it preferentially radiates frequencies below the passband of the body waves used 0 02 hz for undiffracted phases the source time function of the principal rupture which initiated 30 km west of the epicenter of the precursor comprises a dominant initial short duration 24 s triangular pulse followed by several smaller pulses however slightly diffracted phases indicate a simple basic underlying character for the rupture consisting of the initial 24 s triangle superimposed on a longer duration 42 44 s trapezoid the absence of observable directivity in the deconvolved source time functions suggests a bilateral rupture mode although the body waves do not require a fault length greater than 80 km the aftershock area and surface wave results of zhang and kanamori 1988 imply a total length of at least 200 km the body wave source functions are well modeled by a 200 km long fault extending to 30 50 km depth on which slip nucleates at the center of the fault and has variable displacement along strike the peak moment release of the deconvolved source functions indicates higher displacement in the hypocentral area than in other areas of the fault the spatial relationship of the precursor and the main pulse is suggestive of rupture initiating at and propagating along the edge of an asperity prior to the rupture of the asperity itself the large size of the event may be due to an unusual stress environment arising from strong lateral gradients in seismic interplate coupling along the java timor arc

on the deformation cycle of a strongly coupled plate interface the triple earthquakes of 16 march 1963 15 november 2006 and 13 january 2007 along the kurile subduction zone 1 the great plate interface kurile earthquake of 15 november 2006 mw 8 3 was immediately followed by normal aftershocks in the outer rise of the central kurile subduction zone two months later at a distance 50 km from this event the 13 january 2007 mw 8 1 earthquake with a pure normal mechanism occurred in the outer rise of the central kurile the 15 november 2006 earthquake ruptured an area of 280 150 km2 with maximum slip of almost 7 m while the 13 january 2007 earthquake ruptured an area of 240 40 km2 with a maximum slip of almost 14 m these two significant events were preceded by a major reverse earthquake on 16 march 1963 mw 7 7 that took place close to the location of the 13 january 2007 earthquake these very different earthquakes demonstrate the different stages of the deformation cycle along strongly coupled plates at the central kurile arc and present a rare case of stress regime reversal over a short time span in order to understand the details of these three earthquakes we inverted for the source rupture processes of the earthquakes and delineated the location and dimension of asperities the role of gravity and topography anomalies and their correlation to the asperity distribution as well as the long term seismicity is studied in detail using trench parallel bouguer anomaly we have identified the differences in the asperities and the location of larger normal outer rise aftershocks as well as the location of 13 january 2007 earthquake we also show that the long term seismicity of the central kurile arc is confined to the intraslab and not the plate interface the static stress transfer for these earthquakes showed that the stress on optimally oriented thrust faults is increased in the northeastern part of the rupture area of the 15 november 2006 earthquake absence of major and great earthquakes to the northeastern immediate vicinity of the rupture area of the 15 november 2006 earthquake supports the hypothesis that this area is mature for the next strong earthquake along the kurile arc

faulting within the pacific plate at the mariana trench implications for plate interface coupling and subduction of hydrous minerals we investigate faulting within the incoming pacific plate at the mariana subduction trench to understand stresses within the bending plate regional stresses acting upon the plate interface and the extent of possible faulting induced mantle serpentinization we determine accurate depths by inverting teleseismic p and sh waveforms for earthquakes occurring during 1990 2011 with global centroid moment tensor gcmt solutions for earthquakes with mw 5 0 we determine centroid depths and source time functions and refine the fault parameters results from central mariana indicate that all earthquakes are extensional and occur at centroid depths down to 11 km below the moho at the southern mariana trench extensional earthquakes continue to 5 km below the moho one compressional earthquake at 34 km below the seafloor suggests stronger plate interface coupling here in addition we model the stress distribution within the pacific plate along two bathymetric profiles extending seaward from the mariana subduction trench axis to better understand whether our earthquake depth solutions match modeled scenarios for plate bending under applied external forces results from our flexure models match the locations of extensional and compressional earthquakes and suggest that the pacific plate at southern mariana is experiencing larger compressional stresses possibly due to greater interplate coupling additionally we conclude that if extensional faulting promotes the infiltration of water into the subducting plate mantle then the top 5 15 km of the pacific plate mantle are partially serpentinized and a higher percentage of serpentinization is located near the central mariana trench where extensional events extend deeper

stress triggering in thrust and subduction earthquakes and stress interaction between the southern san andreas and nearby thrust and strike slip faults 1 we argue that key features of thrust earthquake triggering inhibition and clustering can be explained by coulomb stress changes which we illustrate by a suite of representative models and by detailed examples whereas slip on surface cutting thrust faults drops the stress in most of the adjacent crust slip on blind thrust faults increases the stress on some nearby zones particularly above the source fault blind thrusts can thus trigger slip on secondary faults at shallow depth and typically produce broadly distributed aftershocks short thrust ruptures are particularly efficient at triggering earthquakes of similar size on adjacent thrust faults we calculate that during a progressive thrust sequence in central california the 1983 mw 6 7 coalinga earthquake brought the subsequent 1983 mw 6 0 nunez and 1985 mw 6 0 kettleman hills ruptures 10 bars and 1 bar closer to coulomb failure the idealized stress change calculations also reconcile the distribution of seismicity accompanying large subduction events in agreement with findings of prior investigations subduction zone ruptures are calculated to promote normal faulting events in the outer rise and to promote thrust faulting events on the periphery of the seismic rupture and its downdip extension these features are evident in aftershocks of the 1957 mw 9 1 aleutian and other large subduction earthquakes we further examine stress changes on the rupture surface imparted by the 1960 mw 9 5 and 1995 mw 8 1 chile earthquakes for which detailed slip models are available calculated coulomb stress increases of 2 20 bars correspond closely to sites of aftershocks and postseismic slip whereas aftershocks are absent where the stress drops by more than 10 bars we also argue that slip on major strike slip systems modulates the stress acting on nearby thrust and strike slip faults we calculate that the 1857 mw 7 9 fort tejon earthquake on the san andreas fault and subsequent interseismic slip brought the coalinga fault 1 bar closer to failure but inhibited failure elsewhere on the coast ranges thrust faults the 1857 earthquake also promoted failure on the white wolf reverse fault by 8 bars which ruptured in the 1952 mw 7 3 kern county shock but inhibited slip on the left lateral garlock fault which has not ruptured since 1857 we thus contend that stress transfer exerts a control on the seismicity of thrust faults across a broad spectrum of spatial and temporal scales

the great 2006 and 2007 kuril earthquakes forearc segmentation and seismic activity of the central kuril islands region we present a structural study of the central kuril islands forearc region where the great megathrust tsunamigenic earthquake m w 8 3 occurred on november 15 2006 based on new bathymetry and seismic profiles obtained during two research cruises of r v akademik lavrentiev in 2005 and 2006 ten crustal segments with along arc length ranging from 30 to 100 km separated by ns and nw trending transcurrent faults were identified within the forearc region the transcurrent faults may serve as barriers impeding stress transfer between the neighboring segments so that stress accumulated within separate forearc segments is usually released by earthquakes of moderate to strong magnitudes however the great november 15 2006 earthquake ruptured seven of the crustal segments probably following a 226 year gap since the last great earthquake in 1780 the geographic extent of earthquake rupture zones aftershock areas and earthquake clusters correlate well with forearc crustal segments identified using the geophysical data based on segmented structure of the central kuril islands forearc region we consider and discuss three scenarios of a great earthquake occurrence within this area although the margin is segmented we suggest that a rupture could occupy the entire seismic gap with a total length of about 500 km in such a case the earthquake magnitude m w might exceed 8 5 and such an event might generate tsunami waves significantly exceeding in height to those produced by the great 2006 2007 kuril earthquakes

application of the trace element and isotope geochemistry of strontium to studies of carbonate diagenesis carbonate rocks and natural waters exhibit a wide range in the concentration and isotopic composition of strontium this wide range and the quantifiable covariation of these parameters can provide diagnostic tools for understanding processes of fluid rock interaction careful consideration of the uncertainties associated with trace element partitioning sample heterogeneity and fluid rock interaction mechanisms is required to advance the application of the trace element and isotope geochemistry of strontium to studies of diagenesis goundwater evolution ancient seawater chemistry and isotope stratigraphy a principal uncertainty involved in the application of sr concentration variations to carbonate systems is the large range of experimental and empirical results for trace element partitioning of sr between mineral and solution this variation may be a function of precipitation rate mineral stoichiometry crystal growth mechanism fluid composition and temperature calcite and dolomite in ancient limestones commonly have significantly lower sr concentrations 20 70 p p m than would be expected from published trace element distribution coefficient values and sr ca ratios of most modern sedimentary pore waters this discrepancy probably reflects the uncertainties associated with determining distribution coefficient values as techniques improve for the analytical measurement and theoretical modelling of sr concentration and isotopic variations the petrological analysis of carbonate samples becomes increasingly important the presence of even small percentages of non carbonate phases with high rb concentrations and high 87 sr86 sr values such as clay minerals can have significant effects on the measured 87 sr 86 sr values of carbonate rocks due to the decay of 87rb to 87 sr for example a permian marine limestone with 50 p p m sr and 1 p p m rb will have a present day 87 sr 86 sr value that is 2 10 4 higher than its original value this difference is an order of magnitude greater than the analytical uncertainty and illustrates the importance of assessing the need for and accuracy of such corrections a quantitative evaluation of the effects of water rock interaction on sr concentrations and isotope compositions in carbonates strengthens the application of these geochemical tracers geochemical modelling that combines the use of trace elements and isotopes can be used to distinguish between different mechanisms of water rock interaction including diffusive and advective transport of diagenetic constituents in meteoric pore fluids during the recrystallization of carbonate minerals quantitative modelling may also be used to construct diagnostic fluid rock interaction trends that are independent of distribution coefficient values and to distinguish between mixing of mineral end members and fluid rock interaction

outer slope faulting associated with the western kuril and japan trenches summary elongated fault escarpments on the outer slopes of the western kuril and japan trenches have been investigated through detailed swath bathymetric mapping numerous horsts and grabens formed by these escarpments were identified distinct n70 e linear alignment of the escarpments parallel to the magnetic anomaly lineations was revealed on the outer slope of the western kuril trench in the japan trench north of 39 00aen most of the escarpments are parallel to the trench axis and oblique to the magnetic lineations a zig zag pattern of faulting exists south of 39 00aen each topographic profile was decomposed by computer analysis into two curves representing 1 the smoothed long wavelength slope of the subducting ocean crust surface and 2 the short wavelength 10 km roughness of plateaus and valleys edged by outwardand inward facing fault escarpments throughout the surveyed areas escarpment heights increase from the crest of the trench outer swell down to a depth of about 6000 m on the slope of the outer trench wall but with no distinct increase below that depth no significant diverence is recognized in fault throws towards and away from the trench it can be concluded that these elongated escarpments originate from normal faults on the upper layer of the oceanic crust under extensional stress in a direction perpendicular to the trench axis which is caused by downward bending of the subducting lithosphere the relationship of escarpment height to escarpment length is similar to that obtained from normal fault escarpments in the east pacific rise crest the maximum length and height of escarpments are small in the kuril trench compared with those in the japan trench implying a diverence in mechanical strength depending on the fault orientation the crust is weakest along the inherited spreading fabric second weakest probably along the non transform ovset direction and strongest in directions very oblique to these orientations seamounts appear to be more rigid than normal ocean crust with no particular weak orientations resulting in fewer but larger faults along the axis of plate bending as most clearly represented in the subducting daiichi kashima seamount

a reassessment of outer rise seismicity and its implications for the mechanics of oceanic lithosphere we use body waveform modelling to constrain the source parameters of earthquakes occurring globally in oceanic lithosphere beneath the subduction zone outer rise and outer trench slope these data are then used to map the stress state in the lithosphere of the downgoing plate as it bends into the subduction zone our results provide new constraints on the faulting of oceanic lithosphere at the outer rise which is important for understanding the transmission of plate driving forces through the subduction system in all cases shallow normal faulting earthquakes are observed at the top of the plate and are separated in depth from any deeper thrust faulting earthquakes no temporal variation associated with large thrust faulting earthquakes on the subduction interface is seen in the depth extent of each type of faulting at the outer rise the transition depth from trench normal extension to compression is found to vary in agreement with models in which deformation is driven by the combination of in plane stresses and bending stresses resulting principally from slab pull combining the seismologically derived constraints on the thickness of the elastic core of the plate with estimates of the plate curvature we place upper bounds on the strength of the lithosphere at the outer rise which is required to be 300 mpa for a constant yield stress model or governed by an effective coefficient of friction of 0 3

large trench parallel gravity variations predict seismogenic behavior in subduction zones we demonstrate that great earthquakes occur predominantly in regions with a strongly negative trench parallel gravity anomaly tpga whereas regions with strongly positive tpga are relatively aseismic these observations suggest that over time scales up to at least 1 million years spatial variations of seismogenic behavior within a given subduction zone are stationary and linked to the geological structure of the fore arc the correlations we observe are consistent with a model in which spatial variations in frictional properties on the plate interface control trench parellel variations in fore arc topography gravity and seismogenic behavior

topography and gravity across subduction zones topographic and free air gravimetric profiles across subduction zones show two distinct signatures average low topography 1250 m and pronounced gravimetric anomalies characterize west directed subduction zones average elevated topography 1200 m and smoother gravimetric waves are peculiar to east or northeast directed subduction zones these differences are particularly evident along the pacific margins but they persist also along the other subduction zones of the world in the atlantic mediterranean himalayas and indonesia regions therefore topography and gravimetry confirm the existence of two separate classes of subduction zones which appear to be independent of the age and nature of the subducting slab it is suggested that these differences might be linked to the westward drift of the lithosphere relative to the underlying upper mantle

lithospheric bending at subduction zones based on depth soundings and satellite gravity a global study of trench flexure was performed by simultaneously modeling 117 bathymetric profiles original depth soundings and satellite derived gravity profiles a thin elastic plate flexure model was fit to each bathymetry gravity profile by minimization of the l norm the six model parameters were regional depth regional gravity trench axis location flexural wavelength flexural amplitude and lithospheric density a regional tilt parameter was not required after correcting for age related trend using a new high resolution age map estimates of the density parameter confirm that most outer rises are uncompensated we find that flexural wavelength is not an accurate estimate of plate thickness because of the high curvatures observed at a majority of trenches as in previous studies we find that the gravity data favor a longer wavelength flexure than the bathymetry data a joint topography gravity modeling scheme and fit criteria are used to limit acceptable parameter values to models for which topography and gravity yield consistent results even after the elastic thicknesses are converted to mechanical thicknesses using the yield strength envelope model residual scatter obscures the systematic increase of mechanical thickness with age perhaps this reflects the combination of uncertainties inherent in estimating flexural wavelength such as extreme inelastic bending and accumulated thermoelastic stress the bending moment needed to support the trench and outer rise topography increases by a factor of 10 as lithospheric age increases from 20 to 150 ma this reflects the increase in saturation bending moment that the lithosphere can maintain using a stiff dry olivine rheology we find that the lithosphere of the gdh1 thermal model stein and stein 1992 is too hot and thin to maintain the observed bending moments moreover the regional depth seaward of the oldest trenches 150 ma exceeds the gdh1 model depths by about 400 m

changes in planview geometry and erosion deposition patterns along a channel levee complex in the southern corner of the kurile basin okhotsk sea abstract high resolution seismic profiles reveal the changes in planform and erosion deposition pattern in the abashiri oki trough aot the southwestern corner of the kurile basin the aot originated from a syncline in the late miocene early pliocene and is characterised by plio pleistocene channel levee complexes and debris flows mainly composed of hummocky chaotic and convergent reflectors the channel planform was changed by eustacy tectonics climate and hinterland volcanism regressive surfaces probably occur as the two reflectors of erosional surface and debris flow deposits the erosional depositional pattern suggests that the channel profile tends to evolve towards an exponential like form in the upper trough channels are incised probably inland volcanism induced to increase sedimentary supply consequently the slope progradation and steepened gradient volcanism also caused an additional channel in the middle trough channels show braided pattern related to subsidence and mildened gradient of the trough floor which lead to accommodation in the lower trough channels anastomose and in the lowermost trough finally the merged channel incises and cut offs the anticline dividing the aot from the kurile basin

neogene to quaternary rifting and inversion in corsica retreat and collision in the western mediterranean 1 stratigraphic structural and fission track data have been integrated in order to unravel the neogene to quaternary tectonic evolution of northeastern corsica results indicate that during early to middle miocene the study area was affected by a rapid cooling at low temperatures accompanied by exhumation and rifting basin inversion occurred during the tortonian again followed by extension in the messinian to early pliocene compressional deformations are finally recorded by early pliocene to quaternary deposits alternating rifting and inversion events are recorded not only in northeastern corsica but also in many peri tyrrhenian regions this alternation can be explained in terms of intraplate propagation of the compressional stress related to the africa europe convergence and to a discontinuous slab retreat along the apennine subduction system a pause in the slab retreat implies a break of the back arc extension in the upper plate and it allows a temporary propagation of africa europe compression

gravity modelling of the hellenic subduction zone a regional study abstract the hellenic subduction zone is clearly expressed in the arc shaped distribution of earthquake epicenters and gravity anomalies which connect the peloponnesos with crete and anatolia in this region oceanic crust of the african plate collides northward with continental crust of the aegean microplate which itself is pushed apart to the south west by the anatolian plate and at the same time is characterised by crustal extension the result is an overall collision rate of up to 4 cm year and a retreating subduction process recent passive and active seismic studies on and around crete gave first but not in all details consistent structural results useful for supporting gravity modelling this was undertaken with the aim of presenting the first 3d density structure of the entire subduction zone gravity interpretation was based on a bouguer map newly compiled using data from land marine and satellite sources the anomalies range from 170 mgal cretan sea to 10 mgal mediterranean ridge 3d gravity modelling was done applying the modelling software igmas the computed bouguer map fits the low frequency part of the observed one which is controlled by variations in moho depth less than 20 km below the cretan sea and extending 30 km below crete and the extremely thick sedimentary cover partly up to 18 km of the mediterranean ridge the southernmost edge of the eurasian plate with its more triangular shaped backstop area was traced south off crete only 50 to 100 km further to the south the edge of the african continent was traced as well in between these boundaries there is african oceanic crust which has a clear arc shaped detachment line situated at the eurasian continental edge the subduction arc is open towards the north its slab separates hotter mantle material lower density below the updoming moho of the cretan sea from colder one higher density in the south subjacent to the upper continental crust of crete is a thickened layer of lower crust followed by the subducted oceanic crust with some mantle material as intermediate layer the depth of the oceanic moho below crete is 50 km the presence and structure of subducted or underplated sediments remains uncertain

a great earthquake doublet and seismic stress transfer cycle in the central kuril islands temporal variations of the frictional resistance on subduction zone plate boundary faults associated with the stick slip cycle of large interplate earthquakes are thought to modulate the stress regime and earthquake activity within the subducting oceanic plate here we report on two great earthquakes that occurred near the kuril islands which shed light on this process and demonstrate the enhanced seismic hazard accompanying triggered faulting on 15 november 2006 an event of moment magnitude 8 3 ruptured the shallow dipping plate boundary along which the pacific plate descends beneath the central kuril arc the thrust ruptured a seismic gap that previously had uncertain seismogenic potential although the earlier occurrence of outer rise compressional events had suggested the presence of frictional resistance within minutes of this large underthrusting event intraplate extensional earthquakes commenced in the outer rise region seaward of the kuril trench and on 13 january 2007 an event of moment magnitude 8 1 ruptured a normal fault extending through the upper portion of the pacific plate producing one of the largest recorded shallow extensional earthquakes this energetic earthquake sequence demonstrates the stress transfer process within the subducting lithosphere and the distinct rupture characteristics of these great earthquakes illuminate differences in seismogenic properties and seismic hazard of such interplate and intraplate faults

towards understanding the lithospheric structure of the southern chilean subduction zone 36 s 42 s and its role in the gravity field summary the southern andes differ significantly from the central andes with respect to topography and crustal structures and are from a geophysical point of view less well known in order to provide insight into the along strike segmentation of the andean mountain belt an integrated 3 d density model was developed for the area between latitudes 36 s and 42 s the model is based on geophysical and geological data acquired in the region over the past years and was constructed using forward density modelling in general the gravity field of the south american margin is characterized by a relatively continuous positive anomaly along the coastline and the forearc region and by negative anomalies along the trench and the volcanic arc however in the forearc region of the central part of the study area located just to the south of the epicentre of the largest ever recorded earthquake valdivia 1960 the trench parallel positive anomaly is disrupted the forearc gravity anomaly differences thus allow the study area to be

macrofracturing of oceanic lithosphere in complex large earthquake sequences major earthquakes in oceanic lithosphere seaward of the subduction zone outer trench slope are relatively uncommon but several recent occurrences have involved very complex sequences rupturing multiple nonaligned faults and or having high aftershock productivity with diffuse distribution this includes the 21 december 2010 m w 7 4 ogasawara bonin 11 april 2012 m w 8 6 indo australia 23 january 2018 m w 7 9 off kodiak island and 20 december 2018 m w 7 3 nikol skoye northwest pacific earthquakes major oceanic intraplate event sequences farther from plate boundaries do not tend to be as complex in faulting or aftershocks outer trench slope extensional faulting can involve complex distributed sequences particularly when activated by great megathrust ruptures such as 11 march 2011 m w 9 1 tohoku and 15 november 2006 m w 8 3 kuril islands intense faulting sequences also occur near subduction zone corners with many fault geometries being activated including some in nearby oceanic lithosphere as for the 29 september 2009 m w 8 1 samoa 6 february 2013 m w 8 0 santa cruz islands and 16 november 2000 m w 8 0 new ireland earthquakes the laterally varying plate boundary stresses from heterogeneous locking recent earthquakes or boundary geometry influence the specific faulting geometries activated in nearby major intraplate ruptures in oceanic lithosphere preexisting lithospheric structures and fabrics exert secondary influences on the faulting intraplate stress release in oceanic lithosphere near subduction zones favors distributed macrofracturing of near critical fault systems rather than localized single fault failures both under transient loading induced by plate boundary ruptures and under slow loading by tectonic motions and slab pull

the 1977 sumba earthquake series evidence for slab pull force acting at a subduction zone the great 1977 sumba earthquake occurred at the eastern sunda trench just west of the collision of australian continental lithosphere with the island arc the length of the aftershock zone of this normal faulting earthquake is about 200 km aftershocks are concentrated 65 115 km east of the main shock epicenter with very few aftershocks in a 50 km long segment that spans the main shock epicenter relocated hypocenters and focal mechanism data are consistent with normal faulting throughout the upper 28 km of the oceanic lithosphere there is no evidence for thrust faulting of the deeper aftershocks these data imply that the neutral bending surface must be at least 35 40 km deep a second aftershock zone about 180 km northwest of the main shock became active immediately following the main shock but events were concentrated during days 50 52 this zone is a 70 km long lineation that trends toward the main shock epicenter and reflects right lateral strike slip faulting within the subducted oceanic plate seismicity exists to a depth of about 650 km in the very old plate beneath the sunda banda arc and that plate s negative buoyancy causes very large slab pull forces great interface thrust earthquakes are absent at the sumba region and slab pull forces are inferred to have partially decoupled the subducted plate from the overriding plate this decoupling permits slab pull stresses to be guided updip to the region of the sumba main shock such shallow acting slab pull provides a bending moment at the trench and explains the deformation and timing observed for the entire sumba earthquake series in this model slab pull forces stretch the subducted plate until the increasing stresses at the shallow subduction zone lead to a subduction zone earthquake postseismically the released oceanic plate undergoes a pulse of downdip strain returning the plate to a less extended state the moment of this downdip plate motion could exceed the seismic moment of the main shock

concretions in glacial sediments at seglvatnet norway abstract concretions in pleistocene glacial sediments at seglvatnet norway include a wide variety of forms the simplest of which apparently reflects relatively uniform growth rates in different directions the preferred orientation of others may be associated with water movement through the sediments concretion shape generally is influenced by the grain size and bedding of the enveloping sediments some concretions may have formed during or soon after deposition of the sediments others are forming at present

forecasting the evolution of seismicity in southern california animations built on earthquake stress transfer 1 we develop a forecast model to reproduce the distribution of main shocks aftershocks and surrounding seismicity observed during 1986 2003 in a 300 310 km area centered on the 1992 m 7 3 landers earthquake to parse the catalog into frames with equal numbers of aftershocks we animate seismicity in log time increments that lengthen after each main shock this reveals aftershock zone migration expansion and densification we implement a rate state algorithm that incorporates the static stress transferred by each m 6 shock and then evolves coulomb stress changes amplify the background seismicity so small stress changes produce large changes in seismicity rate in areas of high background seismicity similarly seismicity rate declines in the stress shadows are evident only in areas with previously high seismicity rates thus a key constituent of the model is the background seismicity rate which we smooth from 1981 to 1986 seismicity the mean correlation coefficient between observed and predicted m 1 4 shocks the minimum magnitude of completeness is 0 52 for 1986 2003 and 0 63 for 1992 2003 a control standard aftershock model yields 0 54 and 0 52 for the same periods four m 6 0 shocks struck during the test period three are located at sites where the expected seismicity rate falls above the 92 percentile and one is located above the 75 percentile the model thus reproduces much but certainly not all of the observed spatial and temporal seismicity from which we infer that the decaying effect of stress transferred by successive main shocks influences seismicity for decades finally we offer a m 5 earthquake forecast for 2005 2015 assigning probabilities to 324 10 10 km cells

an experiment in systematic study of global seismicity centroid moment tensor solutions for 201 moderate and large earthquakes of 1981 data from the global digital seismograph network were used to obtain centroid moment tensor solutions using the method of dziewonski et al 1981 results were obtained for 201 earthquakes ranging in seismic moment from 7 1023 to 3 1027 dyne cm the wide dynamic range of the sro asro stations allows us to investigate using the same algorithm series of events among which the smallest and the largest may differ in moment by a factor as large as 1000 among the events studied is a particularly interesting series in january 1981 off the island of honshu the main shock was preceded by three foreshocks and followed by four aftershocks all falling within the range of our analysis there is an indication that the source mechanism changes with the size of the event statistical analysis of the results for all earthquakes reveals that the half duration of shallow and intermediate events is approximated by 1 6 10 8 m01 3 the shifts in origin time for deep focus earthquakes are indicative of the general complexity of these events which depends only weakly on the seismic moment the extreme departures from a double couple mechanism seem to depend both on the moment and on the focal depth while for shallow earthquakes these departures decrease from a maximum at about 1025 dyne cm with increasing moment the reverse appears to be true with respect to deep focus earthquakes shallow earthquakes north of new guinea and along the solomon islands show systematic and substantial departures from the double couple mechanism

3 d simulation of steady plate subduction with tectonic erosion current crustal uplift and free air gravity anomaly in northeast japan free air gravity anomaly in plate subduction zones characterized by island arc high trench low and outer rise gentle high reflects the cumulative effects of long term crustal uplift and subsidence in northeast japan the island arc high of observed free air gravity anomaly takes its maximum about the eastern coastline on the other hand the current vertical crustal motion estimated from geological and geomorphological observations shows a gentle uplift in the land area and steep subsidence in the sea area with the neutral point near the eastern coastline such a discrepancy in spatial patterns between the free air gravity anomaly and current vertical crustal motion can be ascribed to a change in the mode of crustal uplift and subsidence associated with the initiation of tectonic erosion at the north american pacific plate interface we developed a realistic 3 d simulation model of steady plate subduction with tectonic erosion in northeast japan on the basis of elastic viscoelastic dislocation theory through numerical simulations with this model we found that simple steady plate subduction brings about the crustal uplift characterized by island arc high with its maximum about the eastern coastline while steady plate subduction with tectonic erosion which is represented by the landward retreat of the plate interface brings about gentle uplift in the land area and steep subsidence in the sea area with the neutral point near the eastern coastline therefore if we suppose that tectonic erosion started 3 4 million years ago after the long duration of simple steady plate subduction we can consistently explain both patterns of free air gravity anomaly and current crustal uplift in northeast japan

seismic coupling and outer rise earthquakes variation of interplate seismic coupling at subduction zones is a major factor controlling the size of the largest underthrusting events this variation also has a profound effect on the regional intraplate stresses in the vicinity of the subduction zone outer rise seismicity is strongly correlated with variations in interplate coupling reflecting the stress state of the interplate coupled zone over 200 outer rise earthquakes with known focal mechanisms are used to investigate the relationship between stresses in the outer rise and interplate seismic coupling these events occur within the downgoing i e oceanic plate near the bathymetric trench axes and generally fall into the categories of tensional normal or compressional thrust with their tensional or compressional stress axes oriented approximately horizontal and perpendicular to the trench in uncoupled subduction zones only tensional outer rise earthquakes occur which indicates that the outer rise is dominated by tensional stresses associated with plate bending and or slab pull forces in strongly coupled subduction zones both tensional and compressional outer rise events are found these events are related both spatially and temporally to the distribution of large underthrusting earthquakes and are thus an integral part of the earthquake cycle in the strongly coupled regions tensional outer rise events follow large underthrusting events as the outer rise is temporarily in tension due to the underthrusting motion compressional outer rise events take place as compressional stress slowly accumulates oceanward of locked sections of the interplate zone in four instances compressional outer rise earthquakes have been followed by large underthrusting events which have occurred 2 4 7 and 19 years after the associated outer rise event the remaining compressional outer rise events are located in regions that are either known seismic gaps or in regions where the seismic potential is unknown the occurrence of compressional outer rise earthquakes suggests that compressional stress is accumulating in the adjacent interplate region and that there is the potential for a future large underthrusting event in the region thirty compressional outer rise events have been located in trench segments of middle and south america the kurile islands the tonga and kermadec islands the new hebrides arc and the solomon islands regions in both the southern kamchatka and northern new hebrides regions the outer rise seismicity indicates that the stress regimes in the outer rise have changed with time from tensional following a previous large underthrusting event to compressional at present thus three stages of the cycle from underthrusting to tensional outer rise regime to compressional outer rise regime are present requiring only the occurrence of the next underthrusting event to complete the cycle the occurrence of compressional outer rise events is useful for assessing the seismic potential of a region on an intermediate time scale

strain partitioning and interplate friction in oblique subduction zones constraints provided by experimental modeling physical modeling of oblique subduction is performed to study the mechanism of strain partitioning the model is two layer and includes the elasto plastic lithosphere the overriding and subducting plates and the low viscosity liquid asthenosphere the subduction is driven by a push force from a piston and a pull force when the density contrast ap between the subducting plate and the asthenosphere is positive we vary both ap and the interplate friction frictional stresses slip partitioning is obtained only in the models with high interplate friction and only when the overrid ing plate contains a weak zone this zone in the models corresponds either to locally thinned litho sphere or to cut fault the horizontal trench normal component of the interplate friction force ffh can be comparable with the absolute value of the horizontal component of the nonhydrostatic interplate pressure force fph in the subduction zone ffh is always negative compression while fph can be either negative compressional subduction regime or positive extensional regime high friction which promotes partitioning can completely cancel the extensional suction force fph back arc tension and strike slip faulting appear thus as conflicting processes although they can coexist in the same subduction zone depending on the relative values of relevant forces it ap pears that high friction can exist only in compressional subduction zones where partitioning should develop more easily this conclusion is supported by the comparison of two oblique subduction zones having similar geometry the compressional southern kurile zone strong partitioning and extensional southern ryukyu zone no lithospheric scale partitioning other factors controlling the strain partitioning are the length of the oblique subductlon zone the boundary conditions at the transverse limits of the forearc sliver and of course the obliquity of subduction

assessing historical rate changes in global tsunami occurrence summary the global catalogue of tsunami events is examined to determine if transient variations in tsunami rates are consistent with a poisson process commonly assumed for tsunami hazard assessments the primary data analyzed are tsunamis with maximum sizes 1m the record of these tsunamis appears to be complete since approximately 1890 a secondary data set of tsunamis 0 1m is also analyzed that appears to be complete since approximately 1960 various kernel density estimates used to determine the rate distribution with time indicate a prominent rate change in global tsunamis during the mid 1990s less prominent rate changes occur in the early and mid 20th century to determine whether these rate fluctuations are anomalous the distribution of annual event numbers for the tsunami catalogue is compared to poisson and negative binomial distributions the latter of which includes the effects of temporal clustering compared to a poisson distribution the negative binomial distribution model provides a consistent fit to tsunami event numbers for the 1m data set but the poisson null hypothesis cannot be falsified for the shorter duration 0 1m data set temporal clustering of tsunami sources is also indicated by the distribution of interevent times for both data sets tsunami event clusters consist only of two to four events in contrast to protracted sequences of earthquakes that make up foreshock main shock aftershock sequences from past studies of seismicity it is likely that there is a physical triggering mechanism responsible for events within the tsunami source mini clusters in conclusion prominent transient rate increases in the occurrence of global tsunamis appear to be caused by temporal grouping of geographically distinct mini clusters in addition to the random preferential location of global m 7 earthquakes along offshore fault zones

mudrock hosted carbonate concretions a review of growth mechanisms and their influence on chemical and isotopic composition existing interpretations of cement textures and isotopic compositions may significantly under estimate the depth and duration of concretionary growth minus cement porosities can commonly under estimate depths of concretionary growth for some or all of the following reasons i cements might not passively replace host sediment porosity ii non cement carbonate phases such as replaced bioclastic carbonate can be significant iii sediment compaction models over estimate rates of porosity loss at shallow carbon isotope data from modern sediments show that dissolved carbonate in the methanogenic zone has a continuum of values from 30 to 15 and thus overlaps 13 c depleted values normally considered characteristic of sulphate reduction many concretions previously thought to have grown entirely during sulphate reduction may therefore have continued cementation during methanogenesis indicating a deeper and more prolonged cementation history the necessary carbonate supersaturation for concretionary growth could either occur throughout the porewaters the equilibrium model or be generated in situ by organic matter decay the local equilibrium model or created where external fluids are introduced the fluid mixing model

gravity constraints on the dynamics of the crust mantle system during calabrian subduction summary the thermomechanic evolution of the lithosphere upper mantle system during calabrian subduction is analysed using a 2 d finite element approach in which the lithosphere is compositionally stratified into crust and mantle gravity and topography predictions are cross checked with observed gravity and topography patterns of the calabrian region modelling results indicate that the gravity pattern in the arc trench region is shaped by the sinking of light material belonging to both the overriding and subduction plates the sinking of light crustal material up to depths of the order of 100 150 km is the ultimate responsible for the peculiar gravity signature of subduction characterized by a minimum of gravity anomaly located at the trench bounded by two highs located on the overriding and subducting plates with a variation in magnitude of the order of 200 mgal along a wavelength of 200 km in agreement with the isostatically compensated component of gravity anomaly observed along a transect crossing the calabrian arc from the tyrrhenian to the ionian seas the striking agreement between the geodetic retrieved profiles and the modelled ones in the trench region confirms the crucial role of compositional stratification of the lithosphere in the subduction process and the correctness of the kinematic hypotheses considered in our modelling that the present day configuration of crust mantle system below the calabrian arc results from trench s retreat at a rate of about 3 cm yr 1 followed by gravitational sinking of the subducted slab in the last 5 myr

intermediate term seismic precursors for some coupled subduction zones the paper discusses model results and then reviews observational data concerning some aspects of the mechanics of mature seismic gaps in coupled subduction zones the concern is with space and time varying stresses as signalled by the presence and mechanisms of earthquakes in the outer rise zones adjacent to main thrust areas of large subduction events and down dip from such areas in the downgoing slab observations are shown to be consistent with the expectation that in mature seismic gaps as a result of interplate boundary locking in presence of sustained gravitational driving forces at least the deeper portions of the ocean plate in the outer rise zones are under increased compression and the downgoing slab is under increased tension the observational data cover two cases of closed seismic gaps namely the region of the chilean valparaiso earthquake of march 3 1985 and the earthquake of october 4 1983 four other cases concern still to be closed gaps in northern chile and along the coast of guatemala and also the kurile islands trench gap and the northern new hebrides gap it is concluded that the intermediate term precursor consisting of a combination of compressional outer rise earthquake s and tensional intermediate depth intra plate events in the downgoing slab which mechanically signals the latter part of the earthquake cycle could be useful in evaluating the maturity and hence great earthquake potential of a seismic gap

kuril islands arc two seismic cycles of great earthquakes during which the complete history of seismicity ms 6 is observed two adjacent segments of pacific eurasia plate boundary along the kuril islands arc were broken during two great shallow thrust earthquakes that occurred in 1963 moment magnitude m w 8 5 and 1969 m w 8 2 respectively in 1994 a great shock m w 8 3 rebroke the 200 km long plate boundary segment previously broken by the 1969 event and a series of shocks in 1991 m w 7 6 1995 m w 7 9 and 1996 m w 7 2 rebroke major portions of the 300 km long segment previously ruptured by the 1963 event due to the heterogeneities and incompleteness of the instrumental seismicity catalog for shallow focal depth h m s 6 particularly for the first half of the century this is one of the first times that a complete history of instrumental seismicity at an energy level as low as m s 6 occurring in a focal region of great earthquakes during a full seismic cycle has been observed my findings indicate that significant activity at the m s 6 and m s 7 levels took place both within and as well as along the downdip edges of the forthcoming 19909s ruptures during most of the seismic cycle whereas the adjacent regions of the plate boundary were relatively less active the average displacements and repeat times 28 5 yr 3 5 observed for these great earthquakes along this section of the plate boundary as a whole are consistent with the strain energy accumulated during that time by subduction of the pacific plate under the eurasian plate at a rate of 10 cm yr

asperity distribution of the 1952 great kamchatka earthquake and its relation to future earthquake potential in kamchatka the 1952 kamchatka earthquake is among the largest earthquakes of this century with an estimated magnitude of m w 9 0 we inverted tide gauge records from japan north america the aleutians and hawaii for the asperity distribution the results show two areas of high slip the average slip is over 3 m giving a seismic moment estimate of 155 x 102onm or m w 8 8 the 20th century seismicity of the 1952 rupture zone shows a strong correlation to the asperity distribution which suggests that the large earthquakes m 7 are controlled by the locations of the asperities and that future large earthquakes will also recur in the asperity regions

oriented carbonate concretions in a paleoaquifer insights into geologic controls on fluid flow oriented carbonate concretions appear to provide a powerful new tool in the evaluation of flow through heterogeneous aquifers calcite cement forms elongate bodies of indurated rock that have distinct and mappable spatial orientations we have mapped 200 of these concretion orientations as well as the hydrogeologic characteristics of the host sediments in outcrops of the pliocene pleistocene sierra ladrones formation in central new mexico the average azimuthal concretion orientations is 150 which is consistent with the southeasterly groundwater flow suggested by past and present basin geometry using a first order approximation the dimensionless transverse velocity is estimated from the orientation data the spatial correlation structure of the dimensionless transverse velocity is distinctly different in the two units investigated however both are consistent with existing stochastic models the differences between the units and the similarities with theoretical models suggest that concretion orientations can be used to study how fluids flow through heterogeneous systems over scales ranging from centimeters to tens of kilometers

slab pull slab weakening and their relation to deep intra slab seismicity received 8 march 2005 revised 3 june 2005 accepted 21 june 2005 published 21 july 2005 1 subduction zone seismicity is highly variable great earthquakes occur at few subduction zones around the world with significant variation in size and frequency of deep events interactions between overriding and subducting plates and slab pull strength for individual plates provide a framework for understanding these variations previous work suggests an inverse correlation between great earthquake moment release and the degree to which the subducted slab is connected to the surface plate we find positive correlations between degree of plate slab attachment and moment release from intermediate and deep earthquakes this implies that shallow slab weakening that occurs at trenches where compressive stresses and great earthquakes dominate not only detaches slabs from plates but is maintained as the slab descends discouraging deep seismicity regions of low shallow moment release are consistent with extensional shallow stress regimes and undamaged slabs such slabs maintain mechanical strength during descent and deform seismogenically at depth citation bilek s l c p conrad and c lithgowbertelloni 2005 slab pull slab weakening and their relation to deep intra slab seismicity geophys res lett 32 l14305