structural analysis and metamorphism of the barlow fault zone chibougamau area neoarchean abitibi subprovince implications for gold mineralization faults and deformation zones are important features of archean terranes because of their significance for structural evolution and the formation of large gold districts in the chibougamau area no

deep lithospheric structures along the southern central chile margin from wide angle p wave modelling p crustal and upper mantle structures of the subduction zone in south central chile between 42 degrees s and 46 degrees s are determined from seismic wide angle reflection and refraction data using the seismic ray tracing method to calculate minimum parameter models three profiles along differently aged segments of the subducting nazca plate were analysed in order to study subduction zone structure dependencies related to the age that is thermal state of the incoming plate the age of the oceanic crust at the trench ranges from 3 ma on the southernmost profile immediately north of the chile triple junction to 6 5 ma old about 100 km to the north and to 14 5 ma old another 200 km further north off the island of chiloe remarkable similarities appear in the structures of both the incoming as well as the overriding plate the oceanic nazca plate is around 5 km thick with a slightly increasing thickness northward reflecting temperature changes at the time of crustal generation the trench basin is about 2 km thick except in the south where the chile ridge is close to the deformation front and only a small 800 m thick trench infill could develop in south central chile typically three quarters 1 5 km of the trench sediments subduct below the decollement in the subduction channel to the north and south of the study area only about one quarter to one third of the sediments subducts the rest is accreted above similarities in the overriding plate are the width of the active accretionary prism 35 50 km and a strong lateral crustal velocity gradient zone about 75 80 km landward from the deformation front where landward upper crustal velocities of over 5 0 5 4 km s su 1 su decrease seaward to around 4 5 km s su 1 su within about 10 km which possibly represents a palaeo backstop this zone is also accompanied by strong intraplate seismicity differences in the subduction zone structures exist in the outer rise region where the northern profile exhibits a clear bulge of uplifted oceanic lithosphere prior to subduction whereas the younger structures have a less developed outer rise this plate bending is accompanied by strongly reduced rock velocities on the northern profile due to fracturing and possible hydration of the crust and upper mantle the southern profiles do not exhibit such a strong alteration of the lithosphere although this effect may be counteracted by plate cooling effects which are reflected in increasing rock velocities away from the spreading centre overall there appears little influence of incoming plate age on the subduction zone structure which may explain why the m w 9 5 great chile earthquake from 1960 ruptured through all these differing age segments the rupture area however appears to coincide with a relatively thick subduction channel

the 1960 chile earthquake inversion for slip distribution from surface deformation summary a total of 166 observations of sea level change 130 measurements of elevation difference and 16 determinations of horizontal strain provide an excellent view of the quasi static source process of the great 1960 chilean earthquake these surface deformation data were employed in classical uniform slip fault models as well as more recently developed models that allow spatial variability of slip the best uniform slip planar usp model is 850km long 130km wide and dips 20 seventeen metres of fault displacement contributed to a usp moment of 9 4 times 1022 n m the variable slip planar vsp model concentrates slip on a 900 km long 150 km wide band parallel to the coast several peaks of slip with dimensions of 50 100 km appear in this band and are thought to represent major subduction zone asperities important fractures of the oceanic lithosphere bound the 1960 rupture and are offered as a potential source of fault segmentation within the chilean subduction zone the vsp moment for 1960 earthquake totals 9 5 times 1022 n m about one fifth of the value estimated for the foreshock mainshock sequence from seismic methods except for areas out to sea geodetic resolution on the fault is fairly uniform thus it is unlikely that slip missed by the network could increase the vsp moment much beyond 1 8 times 1023 n m several patches of moment isolated from the main body at 80 110 km depth are found down dip in the vsp model and are presumably indicative of aseismic slip one patch at the northern end of the rupture is probably associated with the initiation phase of the mainshock although the time sequence of the relationship is unknown tide gauge records suggest that another patch between 40 and 43 s responsible for the observed strain and uplifts inland at those latitudes is not of coseismic origin but derives from in place post seismic creep over several years apparently great 1960 type events are not typical members of the 128 yr earthquake cycle in south central chile the nazca south america boundary here is characterized by a variable rupture mode in which major asperities are completely broken by great earthquakes only once in four or five earthquake cycles the more frequent large earthquakes that geographically overlap the great events fill in between the locked zones

low frequency source characteristics of the great 1960 chilean earthquake the low frequency nature of the great 1960 chilean earthquake the earth s largest recorded event is characterized and a source model composed of three events with a combined seismic moment of 5 5 1023 n m and a duration of 1500 s is presented the results show conclusively that large scale slip which is only observed at low frequencies preceded the main shock complex amplitude measurements of normal mode data in the band 1 0 5 0 mhz recorded at eight vertical component stations comprise the data set in this band the earthquake source is assumed to be described by a line source propagating at a constant rupture velocity the data set is the basis for a sequence of least squares inversions to determine the seismic moment rupture velocity spatial slip distribution and the temporal slip function the data are best explained by a source model that begins 1150 s before the main shock with an event of moment 1 9 1023 n m and rise time of 300 s a main shock with moment of 3 2 1023 n m and for which most of the low frequency energy was released beginning about 50 s after the short period origin time and an event 350 s later with moment of 0 4 1023 n m the uncertainty in the moment estimate of the great 1960 chilean earthquake is about 50 and is due primarily to the probable range of fault plane dip which is not well constrained at this time

contrasting nature of deformation along an intra arc shear zone the liquine ofqui fault zone southern chilean andes abstract the liquine ofquifault zone lofz cuts the patagonian batholith and the modern volcanic arc of southern chile for ca 1000 km the rock fabric along three transects of the lofz combined with new and published geochronological data suggest marked differences in the nature and timing of deformation along strike in the liquine transect 39 s a 1 km wide northeast striking subvertical mylonitic zone shows north plunging stretching lineations this mylonitic zone has been juxtaposed by high angle reverse faulting against a nearly undeformed miocene granitoid metamorphic assemblages and microstructures in the mylonites indicate greenschist facies conditions and sinistral reverse displacement deformation pre dates a 100 2 ma undeformed porphyritic dike hornblende 40ar 39ar mean age in the reloncavi transect 41 42 s deformation in cretaceous and miocene plutons is predominantly brittle kinematic analysis of two fault populations yields compressional and dextral strike slip stress regimes interpreted as late miocene in age in the hornopiren transect 42 43 s a 4 km wide mylonitic zone developed in plutons and wallrocks shows subhorizontal stretching lineations and dextral displacement a single fault population overprinting the mylonites supports a dextral strike slip stress regime available u pb k ar and 40ar 39ar dates on deformed cenozoic plutons and wallrock range from 9 to 13 ma on hornblende and from 6 to 3 ma on biotite microstructures and mineral assemblages indicate that the youngest ductile fabrics in the plutons formed at greenschist facies similar to the biotite ar closure temperature subparallel magmatic and solid state fabrics combined with geochronology suggest that dextral displacement was continuous during emplacement and cooling of the plutons dextral oblique subduction of the nazca plate beneath western south america has driven long term intra arc deformation at the southern andes plate boundary zone ridge collision in turn has favored dextral displacement at the leading edge of the continent since the pliocene

the chiloe mw 7 6 earthquake of 25 december 2016in southern chile and its relation tothe mw 9 5 1960 valdivia earthquake on 25 december 2016 a mw 7 6 earthquake broke a portion of the southern chilean subduction zone south of chiloe island located in the central part of the mw 9 5 1960 valdivia earthquake this region is characterized by repeated earthquakes in 1960 and historical times with very sparse interseismic activity due to the subduction of a young 15 ma and therefore hot oceanic plate we estimate the co seismic slip distribution based on a kinematic finite fault source model and through joint inversion of teleseismic body waves and strong motion data the coseismic slip model yields a total seismic moment of 3 94 1020 nm that occurred over 30 s with the rupture propagating mainly downdip reaching a peak slip of 4 2 m regional moment tensor inversion of stronger aftershocks reveals thrust type faulting at depths of the plate interface the fore and aftershock seismicity is mostly related to the subduction interface with sparse seismicity in the overriding crust the 2016 chiloe event broke a region with increased locking and most likely broke an asperity of the 1960 earthquake the updip limit of the main event aftershocks foreshocks and interseismic activity are spatially similar located 15 km offshore and parallel to chiloe islands west coast the coseismic slip model of the 2016 chiloe earthquake suggests a peak slip of 4 2 m that locally exceeds the 3 38 m slip deficit that has accumulated since 1960 therefore the 2016 chiloe earthquake possibly released strain that has built up prior to the 1960 valdivia earthquake

prevalence of viscoelastic relaxation after the 2011 tohoku oki earthquake seafloor global positioning system observations immediately after the great 2011 tohoku oki earthquake provide unambiguous evidence for the dominant role of viscoelastic relaxation in short term postseismic deformation rather than just afterslip on the fault as is commonly assumed this paper presents revised estimates of the afterslip following the 2011 tohoku oki earthquake based on seafloor gps observations made immediately after the earthquake tianhaozhe sun et al obtain unambiguous evidence for the dominant role of viscoelastic relaxation in short term postseismic deformation rather than elastic afterslip on the fault as is commonly assumed they conclude that models which erroneously assume an elastic earth substantially overestimate afterslip downdip of the rupture zone and underestimate afterslip updip after a large subduction earthquake crustal deformation continues to occur with a complex pattern of evolution1 this postseismic deformation is due primarily to viscoelastic relaxation of stresses induced by the earthquake rupture and continuing slip afterslip or relocking of different parts of the fault2 3 4 5 6 when postseismic geodetic observations are used to study earth s rheology and fault behaviour it is commonly assumed that short term a few years deformation near the rupture zone is caused mainly by afterslip and that viscoelasticity is important only for longer term deformation6 7 however it is difficult to test the validity of this assumption against conventional geodetic data here we show that new seafloor gps global positioning system observations immediately after the great tohoku oki earthquake provide unambiguous evidence for the dominant role of viscoelastic relaxation in short term postseismic deformation these data reveal fast landward motion of the trench area opposing the seaward motion of gps sites on land using numerical models of transient viscoelastic mantle rheology we demonstrate that the landward motion is a consequence of relaxation of stresses induced by the asymmetric rupture of the thrust earthquake a process previously unknown because of the lack of near field observations our findings indicate that previous models assuming an elastic earth will have substantially overestimated afterslip downdip of the rupture zone and underestimated afterslip updip of the rupture zone our knowledge of fault friction based on these estimates therefore needs to be revised

the liquine ofqui fault zone a long lived intra arc fault system in southern chile abstract plate reconstructions for the cenozoic document relatively steady right oblique subduction of the farallon nazca plate beneath the chilean continental margin the kinematic signature recorded along the intra arc liquine ofqui fault zone lofz a major feature of the southern andes may help to understand the way in which the nazca south america slip vector has been partitioned into strain and displacement along and across the continental margin the lofz consists of two nne trending right stepping straight lineaments a strike slip duplex at the right step and curved features which splay off the straight lineaments toward the northwest the lofz runs mostly through heterogeneously deformed cenozoic plutonic rock of the north patagonian batholith and patchy metamorphic wall rock early cenozoic volcano sedimentary rocks and dyke swarms found in close spatial association with the strike slip duplex are believed to have developed in strike slip related basins quaternary volcanoes are aligned parallel to the lofz both ductile and brittle kinematic indicators within centimeter to meter wide high strain zones document late cenozoic dextral shear deformation contrasting left lateral deformation recorded on older and wider mylonitic zones suggests that the lofz may be a long lived shear zone that accommodated continental scale deformation arising from the farallon nazca south america plate convergence a block rotation pattern as indicated by paleomagnetic data is consistent with the geometry and cenozoic kinematics of the lofz

earthquake cycle dominates contemporary crustal deformation in central and southern andes with the advent of global positioning system gps technology and its applications to high precision geodesy earth scientists have gained an unprecedented opportunity to study the kinematics and dynamics of present day deformation processes along plate boundary zones however until now our knowledge of the deformation processes associated with the andean subduction along the western coast of south america has been limited here we present first estimates of present day crustal deformation rates in the central and southern sections of the andes between latitudes 22 s and 42 s we find that the deformation in the central section of our study area is dominated by the interseismic phase of an earthquake deformation cycle caused by 100 coupling of the thrust interface between the subducting nazca and the overriding south america plates the estimated depth of coupling is not uniform along strike north of 30 s it is v33 km deep while south of 35 s it reaches 50 km depth in addition we observed postseismic relaxation effects in the northern part of our network in the area of the 1995 mw8 0 antofagasta earthquake south of 38 s we detected a similar deformation pattern as in the antofagasta area which we attribute to postseismic relaxation effects of the 1960 mw9 5 valdivia earthquake fl 2001 elsevier science b v all rights reserved

heterogeneous plate locking in the south central chile subduction zone building up the next great earthquake abstract we use global positioning system gps velocities and kinematic finite element models fe models to infer the state of locking between the converging nazca and south america plates in south central chile 36 s 46 s and to evaluate its spatial and temporal variability gps velocities provide information on earthquake cycle deformation over the last decade in areas affected by the megathrust events of 1960 m w 9 5 and 2010 m w 8 8 our data confirm that a change in surface velocity patterns of these two seismotectonic segments can be related to their different stages in the seismic cycle accordingly the northern 2010 segment was in a final stage of interseismic loading whereas the southern 1960 segment is still in a postseismic stage and undergoes a prolonged viscoelastic mantle relaxation after correcting the signals for mantle relaxation the residual gps velocity pattern suggests that the plate interface accumulates slip deficit in a spatially and presumably temporally variable way towards the next great event though some similarity exist between locking and 1960 coseismic slip extrapolating the current decadal scale slip deficit accumulation towards the 300 yr recurrence times of giant events here does neither yield the slip distribution nor the moment magnitude of the 1960 earthquake this suggests that either the locking pattern is evolving in time to reconcile a slip deficit distribution similar to the 1960 earthquake or that some asperities are not persistent over multiple events the accumulated moment deficit since 1960 suggests that highly locked patches in the 1960 segment are already capable of producing a m 8 event if triggered to fail by stress transfer from the 2010 event

space geodetic estimation of the nazca south america euler vector abstract gps data from four sites in the nazca plate easter island galapagos robinson crusoe and san felix islands and from five sites in the stable core of the south american plate enabled us to estimate the euler vector of the nazca plate with respect to south america the observed velocities of easter island 6 6 cm yr at 102 3 galapagos 5 1 cm yr at 90 0 robinson crusoe 6 6 cm yr at 80 1 and san felix 6 0 cm yr at 82 1 are significantly slower than the global plate model nuvel 1a velocites for those four sites our estimated euler pole is located at 48 8 n 91 7 w with a rate of 0 59 m y the nuvel 1a and earlier space geodetic studies give rotation rates that are 20 faster

impact of megathrust geometry on inversion of coseismic slip from geodetic data application to the 1960 chile earthquake 1 we analyze the role of megathrust geometry on slip estimation using the 1960 chile earthquake mw 9 5 as an example a variable slip distribution for this earthquake has been derived by barrientos and ward 1990 applying an elastic dislocation model with a planar fault geometry their model shows slip patches at 80 110 km depth isolated from the seismogenic zone interpreted as aseismic slip we invert the same geodetic data set using a finite element model fem with precise geometry derived from geophysical data isoparametric fem is implemented to constrain the slip distribution of curve shaped elements slip resolved by our precise geometry model is limited to the shallow region of the plate interface suggesting that the deep patches of moment were most likely an artifact of the planar geometry our study emphasizes the importance of fault geometry on slip estimation of large earthquakes

structure of the seismogenic zone of the southcentral chilean margin revealed by local earthquake traveltime tomography we use traveltime data of local earthquakes and controlled sources observed by a large temporary amphibious seismic network to reveal the anatomy of the southcentral chilean subduction zone 37 39 s between the trench and the magmatic arc at this location the giant 1960 earthquake m 9 5 nucleated and ruptured almost 1000 km of the subduction megathrust for the three dimensional tomographic inversion we used 17 148 p wave and 10 049 s wave arrival time readings from 439 local earthquakes and 94 shots the resolution of the tomographic images was explored by analyzing the model resolution matrix and conducting extensive numerical tests the downgoing lithosphere is delineated by high seismic p wave velocities high vp vs ratio in the subducting slab reflects hydrated oceanic crust and serpentinized uppermost oceanic mantle the subducting oceanic crust can be traced down to a depth of 80 km as indicated by a low velocity channel the continental crust extends to approximately a 50 km depth near the intersection with the subducting plate this suggests a wide contact zone between continental and oceanic crust of about 150 km potentially supporting the development of large asperities eastward the crustal thickness decreases again to a minimum of about a 30 km depth relatively low vp vs at the base of the forearc does not support a large scale serpentinization of the mantle wedge offshore low vp and high vp vs reflect young fluid saturated sediments of forearc basins and the accretionary prism

first seismic record for intra arc strike slip tectonics along the liquine ofqui fault zone at the obliquely convergent plate margin of the southern andes a temporal seismic network recorded local seismicity along a 130 km long segment of the transpressional dextral strike slip liquine ofqui fault zone lofz in southern chile seventy five shallow crustal events with magnitudes up to m tief w 3 8 and depths shallower than 25 km were observed in an 11 month period mainly occurring in different clusters those clusters are spatially related to the lofz to the volcanoes chaiten michinmahuida and corcovado and to active faulting on secondary faults further activity along the lofz is indicated by individual events located in direct vicinity of the surface expression of the lofz focal mechanisms were calculated using deviatoric moment tensor inversion of body wave amplitude spectra which mostly yield strike slip mechanisms indicating a ne sw direction of the p axis for the lofz at this latitude the seismic activity reveals the present day activity of the fault zone the recent m tief w 6 2 event near puerto aysen southern chile at 45 4 s on april 21 2007 shows that the lofz is also capable of producing large magnitude earthquakes and therefore imposing significant seismic hazard to this region

seismo tectonic structure of the aysen region southern chile inferred from the 2007 mw 6 2 aysen earthquake sequence summary on 2007 april 21 a mw 6 2 earthquake shook the aysen fjord southern chile in an unprecedented episode for this region characterized by low seismicity the area is intersected by the liquine ofqui fault system lofs a 1000 km long strike slip fault that absorbs part of the oblique convergence motion between nazca and south america plates to study the aftershock sequence of this main event we installed a seismic network of 15 stations in the area for a period of nearly 7 months we characterized the seismogenic structure of the zone by calculating a minimum 1 d local velocity model and obtaining precise hypocentral coordinates and uncertainty estimates by using a non linear probabilistic approach we also obtained fault plane solutions based on first motion polarities and sv p amplitude ratios the velocity model shows an average vp vs ratio of 1 76 for the area and low shear wave velocity values for the upper 3 km of crust the aftershock seismicity was located mainly between 4 and 10 km depth and disposed in 1 an n s trending alignment that follows the trace of the lofs and 2 an e w alignment at the east of the main fault furthermore we re analysed the previously published foreshock and early aftershock activity of the sequence including four of its largest events improving considerably previous location estimates selected focal mechanisms show a strong strike slip component that coincides with the nature of the lofs based on our new analysis we conclude that the 2007 aysen seismic sequence had a tectonic origin related to activity on the southern end of the lofs however not discarding the presence and potential action of fluids on the aftershock activity

fallout and distribution of volcanic ash over argentina following the may 2008 explosive eruption of chaiten chile 1 the major explosive eruption of chaiten volcano chile in may 2008 provided a rare opportunity to track the long range dispersal and deposition of fine volcanic ash the eruption followed 10 000 years of quiescence was the largest explosive eruption globally since hudson chile in 1991 and was the first explosive rhyolitic eruption since novarupta alaska in 1912 field examination of distal ashfall indicates that 1 6 1011 kg of ash dense rock equivalent volume of 0 07 km3 was deposited over 2 105 km2 of argentina during the first week of eruption the minimum eruption magnitude estimated from the mass of the tephra deposit is 4 2 several discrete ashfall units are identifiable from their distribution and grain size characteristics with more energetic phases showing a bimodal size distribution and evidence of cloud aggregation processes ash chemistry was uniform throughout the early stages of eruption and is consistent with magma storage prior to eruption at depths of 3 6 km deposition of ash over a continental region allowed the tracking of eruption development and demonstrates the potential complexity of tephra dispersal from a single eruption which in this case comprised several phases over a week long period of intense activity

radiated seismic energy and earthquake source duration variations from teleseismic source time functions for shallow subduction zone thrust earthquakes 1 earthquake source time functions deconvolved from teleseismic broadband p wave recordings are used to examine rupture variations for 417 underthrusting earthquakes located on the interplate interface in circum pacific subduction zones moment scaled duration of significant moment release varies with depth with longer duration events occurring in the shallowest 20 km of the megathrusts the source time functions are also used to estimate radiated seismic energy two estimates are obtained a simple scaled triangle substitution for the moment release history provides a minimum estimate while integration of the time function shape provides an estimate limited only by the bandwidth of the teleseismic deconvolutions while these energy calculations underestimate total energy they enable systematic comparisons of rupture process within and between subduction zones we do not find significant depth dependence for radiated energy overall but some regions do show mild trends of increasing energy seismic moment ratios e mo with increasing source depth that correspond to rupture duration variations in those regions the observations of longer rupture duration at shallow depth with moderate e mo may be due to heterogeneous friction and structural features on the shallow plate interface index terms 7215 seismology earthquake parameters 7230 seismology seismicity and seismotectonics 8164 tectonophysics stresses crust and lithosphere keywords radiated energy shallow subduction source parameters

age spreading rates and spreading asymmetry of the world s ocean crust we present four companion digital models of the age age uncertainty spreading rates and spreading asymmetries of the world s ocean basins as geographic and mercator grids with 2 arc min resolution the grids include data from all the major ocean basins as well as detailed reconstructions of back arc basins the age spreading rate and asymmetry at each grid node are determined by linear interpolation between adjacent seafloor isochrons in the direction of spreading ages for ocean floor between the oldest identified magnetic anomalies and continental crust are interpolated by geological estimates of the ages of passive continental margin segments the age uncertainties for grid cells coinciding with marine magnetic anomaly identifications observed or rotated to their conjugate ridge flanks are based on the difference between gridded age and observed age the uncertainties are also a function of the distance of a given grid cell to the nearest age observation and the proximity to fracture zones or other age discontinuities asymmetries in crustal accretion appear to be frequently related to asthenospheric flow from mantle plumes to spreading ridges resulting in ridge jumps toward hot spots we also use the new age grid to compute global residual basement depth grids from the difference between observed oceanic basement depth and predicted depth using three alternative age depth relationships the new set of grids helps to investigate prominent negative depth anomalies which may be alternatively related to subducted slab material descending in the mantle or to asthenospheric flow a combination of our digital grids and the associated relative and absolute plate motion model with seismic tomography and mantle convection model outputs represents a valuable set of tools to investigate geodynamic problems

monitoring the earthquake source process in north america with the implementation of the usgs national earthquake information center prompt assessment of global earthquakes for response system pager rapid determination of earthquake moment magnitude is essential especially for earthquakes that are felt within the contiguous united states we report an implementation of moment tensor processing for application to broad seismically active areas of north america this effort focuses on the selection of regional crustal velocity models codification of data quality tests and the development of procedures for rapid computation of the seismic moment tensor we systematically apply these techniques to earthquakes with reported magnitude greater than 3 5 in continental north america that are not associated with a tectonic plate boundary using the 0 02 0 10 hz passband we can usually determine with few exceptions moment tensor solutions for earthquakes with m w as small as 3 7 the threshold is significantly influenced by the density of stations the location of the earthquake relative to the seismic stations and of course the signal to noise ratio with the existing permanent broadband stations in north america operated for rapid earthquake response the seismic moment tensor of most earthquakes that are m w 4 or larger can be routinely computed as expected the nonuniform spatial pattern of these solutions reflects the seismicity pattern however the orientation of the direction of maximum compressive stress and the predominant style of faulting is spatially coherent across large regions of the continent

2010 maule earthquake slip correlates with pre seismic locking of andean subduction zone analysis of seismic data and global positioning system gps observations from the region around the site of the recent magnitude 8 8 maule earthquake in chile have been combined with modelling of the andean subduction zone to build up a detailed image of the event the earthquake occurred at a seismic gap part of the fault that has not experienced a major earthquake since 1835 and it seems to have released most of the stress accumulated since that time the observations suggest that coseismic slip heterogeneity at the scale of single asperities and therefore the seismic potential of future great earthquakes might be anticipated by geodetic observations these authors show evidence for a high coherence between the slip distribution inferred from the 2010 maule earthquake chile and the patchwork of interseismic locking distribution derived from global positioning system observations during the previous decade their work suggests that coseismic slip heterogeneity at the scale of single asperities should indicate the seismic potential of future earthquakes which thus might be anticipated by geodetic observations the magnitude 8 8 maule chile earthquake of 27 february 2010 ruptured a segment of the andean subduction zone megathrust that has been suspected to be of high seismic potential1 2 3 4 5 6 it is the largest earthquake to rupture a mature seismic gap in a subduction zone that has been monitored with a dense space geodetic network before the event this provides an image of the pre seismically locked state of the plate interface of unprecedentedly high resolution allowing for an assessment of the spatial correlation of interseismic locking with coseismic slip pre seismic locking might be used to anticipate future ruptures in many seismic gaps6 7 8 9 10 11 12 given the fundamental assumption that locking and slip are similar this hypothesis however could not be tested without the occurrence of the first gap filling earthquake here we show evidence that the 2010 maule earthquake slip distribution correlates closely with the patchwork of interseismic locking distribution as derived by inversion of global positioning system gps observations during the previous decade the earthquake nucleated in a region of high locking gradient and released most of the stresses accumulated in the area since the last major event in 1835 two regions of high seismic slip asperities appeared to be nearly fully locked before the earthquake between these asperities the rupture bridged a zone that was creeping interseismically with consistently low coseismic slip the rupture stopped in areas that were highly locked before the earthquake but where pre stress had been significantly reduced by overlapping twentieth century earthquakes our work suggests that coseismic slip heterogeneity at the scale of single asperities should indicate the seismic potential of future great earthquakes which thus might be anticipated by geodetic observations

systematic changes of earthquake rupture with depth a case study from the 2010mw 8 8 maule chile earthquake aftershock sequence the very shallow part of subduction megathrusts occasionally hosts tsunami earthquakes with unusually slow rupture propagation the aftershock sequence of the 2010 mw 8 8 maule earthquake offshore chile provides us with the opportunity to study systematic changes in source properties for smaller earthquakes within a single segment of a subduction zone we invert amplitude spectra for double couple moment tensors and centroid depths of 71 aftershocks of the maule earthquake down to magnitudes mw 4 0 in addition we also derive average source durations we find that shallower earthquakes tend to have longer normalized source durations on average similar to the pattern observed previously for larger magnitude events this depth dependence is observable for thrust and normal earthquakes the normalized source durations of normal faulting earthquakes are at the lower end of those for thrust earthquakes probably because of the higher stress drops of intraplate earthquakes compared to interplate earthquakes we suggest from the similarity of the depth dependence of normal and thrust events and between smaller and larger magnitude earthquakes that the depth dependent variation of rigidity rather than frictional conditional stability at the plate interface is primarily responsible for the observed pattern tsunami earthquakes probably require both low rigidity and conditionally stable frictional conditions the presence of longduration moderate magnitude events is therefore a helpful but not sufficient indicator for areas at risk of tsunami earthquakes

slab1 0 a three dimensional model of global subduction zone geometries 1 we describe and present a new model of global subduction zone geometries called slab1 0 an extension of previous efforts to constrain the two dimensional non planar geometry of subduction zones around the focus of large earthquakes slab1 0 describes the detailed non planar three dimensional geometry of approximately 85 of subduction zones worldwide while the model focuses on the detailed form of each slab from their trenches through the seismogenic zone where it combines data sets from active source and passive seismology it also continues to the limits of their seismic extent in the upper mid mantle providing a uniform approach to the definition of the entire seismically active slab geometry examples are shown for two well constrained global locations models for many other regions are available and can be freely downloaded in several formats from our new slab1 0 website http on doi gov d9arbs we describe improvements in our two dimensional geometry constraint inversion including the use of average active source seismic data profiles in the shallow trench regions where data are otherwise lacking derived from the interpolation between other active source seismic data along strike in the same subduction zone we include several analyses of the uncertainty and robustness of our three dimensional interpolation methods in addition we use the filtered subduction related earthquake data sets compiled to build slab1 0 in a reassessment of previous analyses of the deep limit of the thrust interface seismogenic zone for all subduction zones included in our global model thus far concluding that the width of these seismogenic zones is on average 30 larger than previous studies have suggested

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

compressional and transpressional stress pattern for pliocene and quaternary brittle deformation in fore arc and intra arc zones andes of central and southern chile kinematic analysis of fault slip data for stress determination was carried out on late miocene to quaternary rocks from the fore arc and intra arc regions of the chilean andes between 33 and 46 south latitudes studies of neogene and quaternary infilling the central depression as well as plutonic rocks of the north patagonian batholith along the liquine ofqui fault zone have revealed various compressional and or transpressional states of stress in the pliocene the maximum compressional stress 1 was generally oriented east west during the quaternary the deformation was partitioned into two coeval distinctive states of stress in the fore arc zone the state of stress was compressional with 1 oriented in a n s to nne ssw direction in the intra arc zone the state of stress was transpressional with 1 striking ne sw along the coast in one site 37 30 s the quaternary strain deformation is extensional with an e w direction which can be explained by a co seismic crustal bending readjustment

prolonged post seismic deformation of the 1960 great chile earthquake and implications for mantle rheology 1 contemporary crustal deformation of the southern andean margin shows an interesting feature while nearly all coastal gps sites move landward consistent with inter seismic deformation near a locked subduction fault sites 300 400 km landward of the rupture region of the mw9 5 1960 chile earthquake are moving in the opposite direction we attribute the seaward motion of these inland sites to a prolonged crustal deformation due to mantle stress relaxation following the 1960 great earthquake in order to reproduce the observed seaward motion using a three dimensional finite element model we need to incorporate a mantle viscosity of about 3 1019 pa s the possibility that the seaward motion is caused by a silent slip event on the plate interface at large depths cannot be completely excluded and our analysis provides a working model for future field tests

crustal motion in the zone of the 1960 chile earthquake detangling earthquake cycle deformation and forearc sliver translation temporary deformation in great earthquake cycles and permanent shear deformation associated with oblique plate convergence both provide critical clues for understanding geodynamics and earthquake hazard at subduction zones in the region affected by the mw 9 5 great chile earthquake of 1960 we have obtained gps observations that provide information on both types of deformation our velocity solutions for the first time span the entire latitudinal range of the 1960 earthquake the new observations revealed a pattern of opposing roughly arc normal motion of coastal and inland sites consistent with what was reported earlier for the northern part of this region this finding supports the model of prolonged postseismic deformation as a result of viscoelastic stress relaxation in the mantle the new observations also provide the first geodetic evidence for the dextral motion of an intravolcanic arc fault system and the consequent northward translation of a forearc sliver the sliver motion can be modeled using a rate of 6 5 mm a accommodating about 75 of the margin parallel component of nazca south america relative plate motion with the rate diminishing to the north furthermore the new gps observations show a southward decrease in margin normal velocities of the coastal area we prefer explaining the southward decrease in terms of changes in the width or frictional properties of the megathrust seismogenic zone because of the much younger age of the subducting plate and warmer thermal regime in the south the currently locked portion of the plate interface may be narrower using a three dimensional viscoelastic finite element model of postseismic and interseismic deformation following the 1960 earthquake we demonstrate that this explanation although not unique is consistent with the gps observations to the first order

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

seismicity and geometry of the south chilean subduction zone 41 5 s 43 5 s implications for controlling parameters in 2005 an amphibious seismic network was deployed on the chilean forearc between 41 75 s and 43 25 s 364 local events were observed in a 11 month period a subset of the p and s arrival times were inverted for hypocentral coordinates 1 d velocity structure and station delays main seismic activity occurred predominantly in a belt parallel to the coast of chiloe island in a depth range of 12 30 km presumably related to the plate interface the 30 inclination of the shallow part of the wadati benioff zone is similar to observations further north indicating that oceanic plate age is not controlling the subduction angle of the shallower part for the chilean subduction zone the down dip termination of abundant intermediate depth seismicity at approximately 70 km depth seems to be related to the young age and high temperature of the oceanic plate crustal seismicity is associated with the liquine ofqui fault zone and active volcanoes

the 1960 chilean earthquakes an unusual foreshock sequence that began with an earthquake of moment 2 0 1021 n m and rupture length of about 150 km preceded the great 1960 chilean earthquake earthquake relocations of the sequence show a progression of seismic activity toward the initiation of the main shock the rupture length of the great 1960 chilean earthquake is estimated from the distribution of aftershocks and crustal deformation to be 920 100 km the source mechanisms of a foreshock and two aftershocks are determined and used to constrain the source mechanism of the main shock the first event in the sequence ruptured the segment of the peru chile trench between 37 03 s and 38 74 s whereas the great 1960 chilean main shock ruptured the adjoining segment to the south the great 1960 chilean main shock initiated within the rupture area of the first event and terminated near the intersection of the chile ridge with the peru chile trench 46 5 s

characterization of the paleoproterozoic hottah terrane wopmay orogen using multi isotopic u pb hf and o detrital zircon analyses an evaluation of linkages to northwest laurentian paleoproterozoic domains abstract the paleoproterozoic wopmay orogen is modeled as a simple arc continent collision involving the archean slave craton and an enigmatic continental arc terrane termed the hottah terrane hottah is a composite terrane that includes a juvenile 2 6 2 1 ga basement and a younger 1 93 1 90 ga continental arc the extent and crustal age structure of the terrane is poorly known which limits interpretations as to its origin and eventual role in the development of the orogen multi isotopic u pb hf o analyses of detrital zircon from rocks of the hottah terrane and its cover sequence are used to indirectly evaluate its age and crustal characteristics the data confirm that ca 2 6 2 1 ga crust is an important component of the terrane but hf isotopic data indicate mostly non juvenile compositions consistent with recycled neoarchean crust sources ages of detrital zircon are distinct from those expected of the slave craton but are similar to adjacent 2 0 1 90 ga paleoproterozoic terranes of northwestern laurentia the similarity to terranes such as the ksituan buffalo head and taltson thelon magmatic zones south and east of the wopmay orogen indicate that hottah could represent a terrane that initially evolved adjacent to the earliest assembled parts of the nuna continent between 2 0 and 1 9 ga and was rifted prior to the collision with the slave margin that produced the calderian orogeny

determination of constitutive relations of fault slip based on seismic wave analysis constitutive laws define the boundary conditions on fault plane and govern many aspects of earthquake failure although several constitutive laws have been formulated based on laboratory rock experiments and applied to theoretical studies in various fields no actual relation during a natural earthquake has been determined the 1995 kobe earthquake is suitable for detailed kinematic analysis and this enables the first evaluation of constitutive relations for a natural earthquake in this study we determine spatiotemporal slip distribution on an assumed fault plane of the 1995 kobe earthquake by waveform inversion and then solve elastodynamic equations using a finite difference method to determine the stress distribution and constitutive relations on the fault plane an inversion method based on bayes theorem is employed to obtain a spatiotemporal slip distribution and enables us to ensure the objective uniqueness of the solution with numerous parameters and smoothing constraints this slip distribution is then used as part of the boundary condition in the finite difference calculation the time histories of slip and shear stress obtained then provide a constitutive relation at each point on the fault plane they show slip weakening relations almost everywhere on the fault plane while slip rate dependency is not clear the slip weakening behavior has a clear depth dependency indicating that the slip weakening rate d du is smaller in the shallow crust than that in the deep crust this may be associated with the paucity of shallow seismicity observed in the source region of this earthquake as reported for many mature fault systems

the updip seismic aseismic transition of the sumatra megathrust illuminated by aftershocks of the 2004 aceh andaman and 2005 nias events great subduction earthquakes exhibit segmentation both within the rupture of individual events and in the long term history of the margin the 2004 december 26 aceh andaman and 2005 march 28 nias event in northern sumatra are two of the largest earthquakes in recent years with both co and post seismic displacements constrained in unprecedented detail using aftershock locations from a temporary seismic array in the boundary region between both events and waveform modelling of large aftershocks we demonstrate that the vast majority of aftershocks in the study region occur on the plate interface within a narrow band 20 km seaward of the outer arc high comparing the seismicity distribution to the co and post seismic displacements we infer that the seismic band marks the transition between the seismogenic zone and stable sliding the location of the band and therefore the transition appears to be correlated with the 500 m bathymetry contour this close correspondence is disrupted at the boundary between the two great earthquakes where the transition to seismogenic behaviour occurs further landward by 25 km to the west of simeulue where seafloor bathymetry throughout the forearc is deeper than 500 m the seismic band terminates abruptly and the focus of aftershock activity is found near the trench the seismic efficiency of afterslip varies dramatically along strike the segment below the banyak islands in the gap between the two main asperities of the nias earthquake accommodates a much larger proportion of afterslip seismically