teleseismic waveform complexities caused by near trench structures and their impacts on earthquake source study application to the 2015 illapel aftershocks central chile

neotectonic deformation of the central chile margin deepwater forearc basin formation in response to hot spot ridge and seamount subduction 1 underlying the midslope valparaiso terrace the valparaiso basin constitutes a unique and prominent deepwater forearc basin on the central chile margin the basin contains a 3 3 5 km thick sediment fill of late cenozoic age the seismic stratigraphic architecture of the valparaiso basin fill shows that margin wide subsidence above the underthrusting juan fernandez ridge an aseismic volcanic swell crested with seamounts on the nazca plate characterized the basin evolution contemporaneously with margin subsidence and seaward rotation of the upper slope and shelf the outer part of the forearc was deformed by thrust faulting above the leading flank of underthrusting seamounts that rotated the middle slope to a more horizontal attitude and formed seaward vergent outer forearc highs subsidence of the margin above the underthrusting juan fernandez ridge is ascribed to processes of subduction erosion enhanced by factors related to subduction of the ridge that caused dismemberment of upper plate material along the shallow aseismic part of the plate interface and transfer of material to the downgoing nazca plate accelerated midslope subsidence 55 75 km landward of the trench coincides with the seaward limit of interplate seismicity suggesting that enhanced basal erosion is related to the transition from aseismic to stick slip subduction behavior since subduction of the juan fernandez ridge began near 33 s 10 ma ago the chile trench north of 33 s is inferred to have retreated 3 km myr and the midslope valparaiso basin subsided 0 3 0 5 km myr approximating analogous neogene rates for the peruvian margin

effects of subducted seamounts on megathrust earthquake nucleation and rupture propagation 1 subducted seamounts have been linked to interplate earthquakes but their specific effects on earthquake mechanism remain controversial a key question is under what conditions a subducted seamount will generate or stop megathrust earthquakes here we show results from numerical experiments in the framework of rate and state dependent friction law in which a seamount is characterized as a patch of elevated effective normal stress on the thrust interface we find that whether subducted seamounts generate or impede megathrust earthquakes depends critically on their relative locations to the earthquake nucleation zone defined by depth variable friction parameters a seamount may act as a rupture barrier and such barrier effect is most prominent when the seamount sits at an intermediate range of the seamount to trench distances 20 100 of the nucleation zone to trench distance moreover we observe that seamount induced barriers can turn into asperities on which megathrust earthquakes can nucleate at shallow depths and rupture the entire seismogenic zone these results suggest that a strong barrier patch may not necessarily reduce the maximum size of earthquakes instead the barrier could experience large coseismic slip when it is ruptured

coseismic radiation and stress drop during the 2015 mw 8 3 illapel chile megathrust earthquake on 16 september 2015 an mw 8 3 earthquake struck middle chile due to the subduction of the nazca plate beneath the south america plate this earthquake is the consequence of 72 years of strain accumulation in the region since the 1943 m 8 3 event in this study we apply the compressive sensing method cs to invert for the spatiotemporal distribution of the coseismic radiation at different frequencies of this event the results show clear frequency dependent feature of earthquake rupture with low frequency lf radiation located in the updip region while high frequency hf radiation concentrated in the downdip region of the megathrust we also compare the cs results with three coseismic slip models as well as the stress drop distributions inferred from these slip models the comparison confirms our understanding of coseismic radiation that energy sources are mostly located in the margin of large coseismic slip regions furthermore we find that the lf radiation sources are mainly within the stress decreasing releasing regions while the hf radiation sources are mainly located in the stress increasing loading regions due to rupturing of relatively large asperities nearby stress decreasing and releasing these results help to better understand the physics of the rupture process during megathrust earthquakes moreover our results do not show radiation sources south of the epicenter suggesting that the subducting juan fernandez ridge probably stopped the rupture of this earthquake toward the south

modeling tsunami observations to evaluate a proposed late tsunami earthquake stage for the 16 september 2015 illapel chile mw 8 3 earthquake resolving seaward extent of slip during great subduction zone interplate ruptures using land based seismological and geodetic observations is challenging modeling of tsunami recordings from ocean bottom pressure sensors of the deep ocean assessment and reporting of tsunami dart network has added valuable constraints on near trench slip for recent events we use dart and tide gauge recordings to evaluate a proposed seismological scenario involving a late mw 8 08 tsunami earthquake following the 95 s long main rupture stage of the 16 september 2015 illapel chile mw 8 3 earthquake tsunami observations constrain the spatial extent of any late tsunami earthquake slip to locate north of the mainshock hypocenter the proposed late shallow slip predicts tsunami signals with considerable amplitudes but shorter wavelengths compared to those of the main stage slip constrained by joint seismic and tsunami modeling yielding over prediction of first arrival amplitudes at dart and tide gauge stations when the two stages are combined

double pincer movement encircling rupture splitting during the 2015 mw 8 3 illapel earthquake abstract the 2015 moment magnitude mw 8 3 illapel earthquake that ruptured the central section of the chilean subduction zone is among the largest megathrust events in recent years the coseismic rupture processes of the illapel earthquake are imaged by the back projection bp method in previous studies but these models differ significantly in the extent of high frequency radiations in the along dip direction here we conduct a refined high resolution music bp imaging analysis of the illapel earthquake based on teleseismic recordings in continental us in contrast to conventional bp imaging we add a slowness ray parameter error term calculated based on aftershock locations to effectively mitigate the spatial biases of bp this correction accounts for the p wave travel time errors at each receiver as a result of approximating the 3d earth structure with 1d models the calibrated bp images of aftershocks indicate that the root mean square location error was reduced from 24 17 km to 8 11 km our refined bp of the mainshock reveals geometrical rupture complexity with unprecedented details involving stages of diverse rupture speeds and simultaneous up dip and down dip high frequency bursts the earthquake starts with a slow initiation phase propagating northward at a speed of 1 km s in the first 13 s between 14 s to 34 s the rupture diverges into two simultaneous fronts seemingly unzipping the rim of a circular patch of large slip at a speed of 3 5 km s the two fronts reemerge as a single front between 35 s and 45 s the rupture splitting repeats in a second episode from 46 s to 60 s the two episodes of encircling rupture involve intermittent high frequency radiations both up dip and down dip which reconcile the discrepancy of the extent of along dip ruptures reported in previous bp studies key features of the rupture process correlate with the prominent pulses recorded by local strong motion network in one possible scenario the rupture initially encounters and splits around a barrier of higher strength or an asperity of higher prestress but eventually breaks into the asperity barrier and produces large slip in the center another scenario is the cascade up growth model in which the nucleation process initiates inside a small weak patch and tends to grow into large scale rupture surrounding the rim of a larger and stronger patch such degree of complexity is previously only reproduced in dynamic simulations but is directly observed with sufficient level of details for the first time this case study demonstrates the capability of the bp method enhanced by aftershock calibrations to observe and probe the geometrical complexity of dynamic ruptures

supercycle at the ecuadorian subduction zone revealed after the 2016 pedernales earthquake large earthquakes are usually assumed to release all of the strain accumulated since the previous event implying a reduced seismic hazard after them however long records of seismic history at several subduction zones suggest supercycle behaviour where centuries long accumulated strain is released through clustered large earthquakes resulting in an extended period of enhanced seismic hazard here we combine historical seismology results present day geodesy data and dense local observations of the recent mw 7 8 2016 pedernales earthquake to reconstruct the strain budget at the ecuador subduction zone since the great 1906 earthquake we show that the pedernales earthquake involved the successive rupture of two patches on the plate interface that were locked prior to the earthquake and most probably overlaps the area already ruptured in 1942 by a similar earthquake however we find that coseismic slip in 2016 exceeds the deficit accumulated since 1942 the seismic moment of every large earthquake during the twentieth century further exceeds the moment deficit accumulated since 1906 these results together with the seismic quiescence before 1906 highlighted by historical records and marine palaeoseismology argue for an earthquake supercycle at the ecuador colombia margin this behaviour which has led to an enhanced seismic hazard for 110 years is possibly still going on and may apply to other subduction zones that recently experienced a great earthquake large earthquakes are often assumed to reset the seismic hazard of a region analysis of recent and historical seismicity in ecuador suggests that this region may experience clusters of large earthquakes and extended periods of high seismic hazard

initiation of the great mw 9 0 tohoku oki earthquake abstract we determined the location size mechanism and the frequency content of the first 4 0 s of the 2011 tohoku oki earthquake since the beginning of this earthquake is very small we develop a comparative approach against a near by reference earthquake the master event we first determined the water depth near the master event using the differential timing between the water phase pwp reflected from the air water interface and the depth phase pp reflected from the water crust interface then we located the master event using the well known ocean bathymetry in the area after calibrating teleseismic arrays 30 to 90 at short periods for timing and amplitude with respect to the master event we were able to determine the initiation of the main event it began as a small m w 4 9 thrust event located at 38 19 n 142 68 e at a depth of 21 km and a few seconds later evolved into a slower extremely large slip event up dip

equilibrium pool dimensions and sediment sorting patterns in coarse grained new england channels abstract pools and riffles are natural bedforms that produce variations in width and depth along channels deemed critical for aquatic habitat an understanding of this morphology is necessary for the successful design of a reconstructed or restored channel to better understand pool geometry and sorting characteristics of new england channels characterizations of pool geometry were performed on 145 different pools strongly influenced by channel constrictions characterizations of channel bed sediments were also performed at 34 of these locations data from 120 pools were used in least squares multiple regression analysis with 19 different independent variables to develop prediction equations for pool depth length and exit slope gradient these equations were then tested using the 25 remaining pools eighteen different geometric variables were then used to predict sediment 50 values in pool centers pool exit slopes and riffles for the subset of 34 samples the regression analyses for pool geometry indicate that pool depth is significantly influenced to a decreasing degree by pool exit slope width constriction gradient constriction width drainage area upstream channel width and the exit slope expansion ratio with an r 2 value of 0 53 similarly pool length is influenced by channel gradient location of the channel constriction pool width drainage area and constriction length with an r 2 value of 0 72 the gradient of pool exit slope is influenced by drainage area channel gradient and constriction gradient with an r 2 value of 0 34 however r 2 values for exit slope increased to 0 65 when sediment d 50 data were utilized using the resulting regression equations to predict dimensions for the 25 verification pools yields average residuals near zero although moderate variations do exist a tukey kramer hsd comparison of the means for sediment 50 values indicates pool sediments are significantly coarser than pool exit slope and riffle sediments for the subset of 34 pools regression analyses also suggest significant relations between the size of sediments in pools and riffles and a combination of geometric variables with r 2 values that range from 0 45 to 0 62 the results suggest that pool dimensions are related to basin wide variability and local hydraulic conditions the findings also suggest that the characteristics of constrictions and the downstream section of pools provide an important control on scouring and sorting characteristics throughout the pool riffle morphology

pool spacing in forest channels field surveys of stream channels in forested mountain drainage basins in southeast alaska and washington reveal that pool spacing depends on large woody debris lwd loading and channel type slope and width mean pool spacing in pool riffle plane bed and forced pool riffle channels systematically decreases from greater than 13 channel widths per pool to less than 1 channel width with increasing lwd loading whereas pool spacing in generally steeper step pool channels is independent of lwd loading although plane bed and pool riffle channels occur at similar low lwd loading they exhibit typical pool spacings of greater than 9 and 2 4 channel widths respectively forced pool riffle channels have high lwd loading typical pool spacing of 2 channel widths and slopes that overlap the ranges of free formed pool riffle and plane bed channel types while a forced pool riffle morphology may mask either of these low lwd loading morphologies channel slope provides an indicator of probable morphologic response to wood loss in forced pool riffle reaches at all study sites less than 40 of the lwd pieces force the formation of a pool we also find that channel width strongly influences pool spacing in forest streams with similar debris loading and that reaches flowing through previously clear cut forests have lower lwd loading and hence fewer pools than reaches in pristine forests

post seismic viscoelastic deformation and stress transfer after the 1960 m9 5 valdivia chile earthquake effects on the 2010 m8 8 maule chile earthquake author posting the authors 2014 this article is posted here by permission of the royal astronomical society for personal use not for redistribution the definitive version was published in geophysical journal international 197 2014 697 704 doi 10 1093 gji ggu048

joint modeling of teleseismic and tsunami wave observations to constrain the 16 september 2015 illapel chile mw 8 3 earthquake rupture process the 16 september 2015 illapel chile m w 8 3 earthquake ruptured 170 km along the plate boundary megathrust fault from 30 0 s to 31 6 s a patch of offshore slip of up to 10 m extended to near the trench and a patch of 3 m slip occurred downdip below the coast aftershocks fringe the large slip zone extending along the coast from 29 5 s to 32 5 s between the 1922 and 1971 1985 ruptures the coseismic slip distribution is determined by iterative modeling of teleseismic body waves as well as tsunami signals recorded at three regional dart stations and tide gauges immediately north and south of the rupture the tsunami observations tightly delimit the rupture length suppressing bilateral southward extension of slip found in unconstrained teleseismic wave inversions the spatially concentrated rupture area with a stress drop of 3 2 mpa is validated by modeling dart and tide gauge observations in hawaii which also prove sensitive to the along strike length of the rupture

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

controls on pool characteristics along a resistant boundary channel abstract the north fork poudre river in phantom canyon has a pool riffle sequence formed in granitic bedrock we address two questions what controls downstream pool spacing within a pool what factors control pool dimensions we hypothesize that both pool spacing and pool geometry could be governed by available flow energy or by substrate characteristics these hypotheses were addressed using channel bed and water surface gradients surveyed under moderate flow selby rock mass strength at vertical outcrops forming lateral pool constrictions and at other vertical outcrops and joint density measured from high resolution digital images of the bedrock outcrop along each of 10 pools the downstream length between pools is quite variable documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usepackage portland xspace usepackage amsmath amsxtra usepackage ot2 ot1 fonten

the seawater neodymium and lead isotope record of the final stages of central american seaway closure the shoaling and final closure of the central american seaway cas resulted in a major change of the global ocean circulation and has been suggested as an essential driver for strengthening of atlantic meridional overturning circulation amoc the exact timing of cas closure is key to interpreting its importance here we present a reconstruction of deep and intermediate water nd and pb isotope compositions obtained from fossil fish teeth and the authigenic coatings of planktonic foraminifera in the eastern equatorial pacific ocean drilling program odp site 1241 and the caribbean odp sites 998 999 and 1000 covering the final stages of cas closure between 5 6 and 2 2 ma the data for the pacific site indicate no significant atlantic caribbean influence over this entire period the caribbean sites show a continuous trend to less radiogenic nd isotope compositions during the pliocene consistent with an enhancement of upper north atlantic deep water unadw inflow and a strengthening of the amoc superimposed onto this long term trend shorter term changes of intermediate caribbean nd isotope signatures approached more unadw like values during intervals when published reconstructions of seawater salinity suggested complete closure of the cas the data imply that significant deep water exchange with the pacific essentially stopped by 7 ma and that shallow exchange which still occurred at least periodically until approximately 2 5 ma may have been linked to the strength of the amoc but did not have any direct effect on the intermediate and deep caribbean nd isotope signatures through mixing with pacific waters

compressive sensing of the tohoku oki mw 9 0 earthquake frequency dependent rupture modes 1 compressive sensing cs is a technique for finding sparse signal representations to underdetermined linear measurement equations we use cs to locate seismic sources during the rupture of the 2011 tohoku oki mw9 0 earthquake in japan from teleseismic p waves recorded by an array of stations in the united states the seismic sources are located by minimizing the l2 norm of the difference between the observed and modeled waveforms penalized by the l1 norm of the seismic source vector the resulting minimization problem is convex and can be solved efficiently our results show clear frequency dependent rupture modes with high frequency energy radiation dominant in the down dip region and low frequency radiation in the updip region which may be caused by differences in rupture behavior more intermittent or continuous at the slab interface due to heterogeneous frictional properties

earthquake rupture dependence on hypocentral location along the nicoya peninsula subduction megathrust abstract although interseismic locking distributions have been used in qualitatively evaluating the future earthquake potential quantitatively estimating how an earthquake may rupture through the locked interface is a more useful tool for quantifying both seismic and tsunami hazards here we investigate rupture scenarios from interseismic locking models along the megathrust interface below nicoya peninsula costa rica using spontaneous rupture simulations we first estimate initial stress from locking then initiate spontaneous ruptures at different nucleation points and observe the eventual earthquake magnitudes and slip distribution we find that 40 of nucleations tested develop into large earthquakes of m w 7 2 based on present interseismic locking models of these events those nucleated from deeper depths have a tendency for larger amplitude shallow slip suggesting increased tsunami potential furthermore irrespective of the input locking models we do not observe rupture scenarios of earthquakes with intermediate magnitudes between 6 and 7 a result consistent with observations in nicoya the results of hypocentre dependent earthquake magnitudes and tsunamigenic potential not only pose challenges in estimating rupture extents from locking models but also underscore the significance of quantitatively evaluating seismic and tsunami hazard in subduction zones

early aftershocks and afterslip surrounding the 2015 mw 8 4 illapel rupture abstract on 16 september 2015 the mw 8 4 illapel earthquake ruptured a section of the subduction thrust on the west coast of central chile the mainshock was followed by numerous aftershocks including some normal faulting events near the trench we apply a template matching approach to improve the completeness of early aftershocks within one month of the mainshock to constrain the distribution of afterslip we utilize repeating earthquakes among the aftershocks and perform a joint slip inversion of postseismic gps and insar data the results show that the aftershock zone abruptly expands to the south 14 h after the mainshock while growing relatively continuously to the north within the first day the repeating earthquakes accompanying the early expansion suggest that aseismic afterslip on the subduction thrust surrounding the coseismic rupture is an important triggering mechanism of aftershocks in addition to stress transfer or poroelastic effects an energetic earthquake sequence near the trench initiated with a m 4 6 event 3 5 h after the mainshock suggesting delayed triggering by the static or dynamic stress changes induced by the mainshock the spatial distribution of repeating earthquakes and the geodetic inverted afterslip are consistent and appear to wrap around the large coseismic slip patch both data sets suggest that the largest cumulative afterslip is located at 30 5 s to the north of the mainshock rupture zone the estimated postseismic moment released in the first 24 days of afterslip is equivalent to an earthquake of mw 7 5 the afterslip illuminates the velocity strengthening sections of the plate interface that surround the mainshock rupture consistent with plate coupling models inferred from interseismic gps velocities

geometric adjustment of pools to changes in slope and discharge a flume experiment abstract to characterize the factors controlling pool shape 30 different forced pools were created utilizing a 50 triangular constriction in a 0 5 m wide 6 m long recirculating flume pools were scoured from an initial plane bed of sand with a d50 of 0 25 mm pool depth and length were measured and used as dependent variables in least squares multiple regression analyses discharge channel bed gradient and energy slope were the independent variables additional linear regression analyses were conducted with either pool depth or length and stream power results indicate that both pool depth and length are primarily a function of discharge channel bed and energy slopes are also significantly related to pool length but are not significantly related to pool depth stream power is significantly related to both pool depth and length but r2 values for pool depth versus discharge indicate stronger relations than those between pool depth and stream power observations on the type of geometric adjustment indicate that pools may minimize their rate of energy expenditure primarily through elongation in contrast pool depth appears to be more sensitive to the characteristics of the constrictions that create the forced pools the results suggest that many field studies may suffer from cross correlation problems in particular channel erodibility may exert a more dominant influence on pool geometry than hydraulic controls in many constriction influenced channels

random controls on semi rhythmic spacing of pools and riffles in constriction dominated rivers average pool spacing between five and seven bankfull widths has been documented in environments throughout the world but has limited theoretical justification in coarse bedded and bedrock environments pool formation in coarse bedded and bedrock channels has been attributed to bedrock and boulder constrictions because the spacing of these constrictions may be irregular in nature it is difficult to reconcile pool formation processes with the supposedly rhythmic spacing of pools and riffles to address these issues a simulation model for pool and riffle formation is used to demonstrate that semi rhythmic spacing of pools with an approximate spacing of five to seven bankfull widths can be recreated from a random distribution of obstructions and minimum pool and riffle length criteria it is assumed that a pool riffle couplet will achieve a minimum length based on dominant discharge conditions values for the minimum length assumption are based on field data collected in new england and california while the theoretical basis relies on the demonstrated hydraulic response of individual pools to elongation results from the simulations show that the location of pools can be primarily random in character but still assume an average spacing between four and eight bankfull widths for a variety of conditions field verification data generally support the model but highlight a highly skewed distribution of pool forming elements and pool spacing the relation between pool spacing and bankfull widths is attributed to the common geometric response of these features to dominant discharge conditions copyright 2001 john wiley sons ltd

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

gps derived interseismic coupling on the subduction and seismic hazards in the atacama region chile the atacama region between 29 s and 25 s is located in the north central area of chile a tectonically complex transition area between north and central chile deformation in atacama is due mainly to elastic loading on the subduction interface but also to diffuse shortening in the sierras pampeanas argentina the seismicity of the subduction is complex in this region seismic swarms often occur moderate mw 6 to large mw 7 earthquakes occur repeatedly and finally megathrust earthquakes of magnitudes significantly larger than 8 occur once in a while the last one being in 1922 almost a century ago we use new gps data we collected in the atacama region between 2008 and 2012 to complete and densify existing data we acquired since 2004 in north central chile these new data allow to quantify the motion of the andean sliver and assess the kinematic coupling on the subduction interface at these latitudes we find that only 7 per cent of the whole convergence motion is taken up by an eastward rotation of the rigid sliver a large part of the remaining 93 per cent approximately 6 cm yr gives way to accumulation of elastic deformation in the upper plate due to locking on the plate interface this accumulation shows important along strike and along dip variations interpreted in terms of variable coupling which we correlate with seismicity we identify two areas of low coupling near the la serena 30 s and baranquilla 27 5 s bays both are correlated with the subduction of singular bathymetric features and seem to stop the propagation of large seismic ruptures these zones are also seismic swarm prone areas which seem to occur rather on their edges these low coupling areas separate two seismic segments where coupling is high the atacama segment 100 km long between 29 s and 28 s and the cha naral segment 200 km long between 27 s and 25 s should they rupture alone these segments are sufficiently coupled and apparently since long enough to produce mw 8 events however a collective failure of both segments could generate a megathrust earthquake of magnitude close to 8 5 similar to the 1819 and 1922 complex events which produced important tsunamis such giant events may occur in the area once a century

recirculating flow and sedimentation in the colorado river in grand canyon arizona debris fans debouching into the bottom of grand canyon create rapids and flow separation in the colorado river the patterns of flow and the behavior of recirculation zones formed by flow separation are consistent throughout the canyon s length zones of recirculating flow occur along the margin of channel expansions recirculation zones are comprised of one primary eddy secondary eddies and areas of unorganized low velocity may exist upstream from the primary eddy the longest recirculation zones are formed by channel constrictions of low width to depth ratio recirculation zones increase in length with increasing discharge sand bars form beneath recirculation zones especially near separation and reattachment points reattachment bars project upstream from the reattachment point and underlie primary eddies separation bars mantle the downstream parts of the debris fans and form beneath secondary eddies and low velocity areas sediment that forms reattachment bars is dominated by sizes characteristic o

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

insights into the kinematic rupture of the 2015 m w 8 3 illapel chile earthquake from joint analysis of geodetic seismological tsunami and superconductive gravimeter observations

global variations of stress drop for moderate to large earthquakes 1 we investigate the global variation of earthquake stress drops using spectra of about 2000 events of mb 5 5 between 1990 and 2007 we use an iterative least squares method to isolate source displacement spectra from travel path and receiver contributions based on a convolutional model the observed p wave source spectra are corrected with a globally averaged empirical correction spectrum and estimates of near source attenuation assuming a brune type source model we estimate corner frequencies and compute stress drops stress drop estimates for individual earthquakes range from about 0 3 to 50 mpa but the median stress drop of about 4 mpa does not vary with moment implying earthquake self similarity over the mw 5 2 to 8 3 range of our data a comparison of our results with previous studies confirms this observation over most of the instrumentally observable magnitude range while the absolute values of our estimated stress drops depend upon the assumed source model we identify relative regional variations of stress drop that are robust with respect to the processing parameters and modeling assumptions which includes an inherent assumption of constant rupture velocity we find a dependence of median stress drop on focal mechanism with a factor of 3 5 times higher stress drops for strike slip earthquakes and also find a factor of 2 times higher stress drops for intraplate earthquakes compared to interplate earthquakes

barrier induced supershear ruptures on a slip weakening fault here we investigate the effects of a patch with elevated effective normal stress barrier on two dimensional in plane supershear rupture propagation on a planar fault from numerical experiments our results confirm that the barrier may slow down or stop coseismic ruptures but may also induce supershear ruptures we demonstrate that the supershear rupture may emerge in a region that is delineated by two approximate linear boundaries if the barrier size is below the lower boundary ruptures can overcome the barrier and propagate at subshear speeds if the barrier size is larger than the upper boundary ruptures are always stopped by the barrier furthermore we find that the barrier induced supershear ruptures may eventually slow down into subshear speed depending on the size and the location of the barrier the duration of supershear ruptures increases as the barrier sizes grow from the lower to the upper boundary which are proportional to the reduction in rupture speeds caused by the barrier these results indicate that a barrier on the fault may not stop coseismic ruptures rather the barrier may induce ruptures propagating at supershear speeds that play important roles in near field ground shaking and damage

source models of the 2012 haida gwaii canada and 2015 illapel chile earthquakes and numerical simulations of related tsunamis seismological observations provide essential input parameters for numerical tsunami simulations here we present source mechanism parameters finite fault source rupture models and numerical tsunami simulation results for the destructive october 28 2012 haida gwaii canada mw 7 7 and september 16 2015 illapel chile mw 8 3 earthquakes and resulting tsunamis these two earthquakes were controlled by active tectonic features along the subduction zones that had developed in response to the convergent movements of lithospheric plates the faulting geometry strike dip and rake angles focal depth fault dimensions average and maximum slip values on the fault planes and seismic moments of the earthquakes are estimated by analyzing teleseismic long period p and sh waves and broadband p waveforms and using waveform inversion and hybrid back projection methods the obtained slip models of the earthquakes reveal heterogeneous slip distributions on fault planes with long source durations 80 s and 150 s and low stress drop values 10 15 bars numerical simulations of tsunami wave propagation are further performed using the uniform and non uniform slip models and nonlinear long wave equations in spherical coordinates the shape and arrival times of leading tsunami waves are adequately constrained particularly with the heterogeneous slip distribution models the general characteristics of synthetic tsunami waveforms e g amplitude shape arrival time calculated using the non uniform slip model are more consistent with the observed tsunami records than those of a uniform slip model it is further seen that simulation results using preliminary and fast slip models for both earthquakes give only approximate early tsunami estimates tsunami wave heights and arrival times to the coasts are mostly not well simulated the results indicate that tsunami simulations based on finite fault source slip models likely contribute to the determination of tsunamigenic coastal regions by revealing locations arrival times amplitudes and directions of tsunami waves within a close approximation to observed records off shore and far from the source region they provide sufficient information to facilitate tsunami warning and mitigation challenges after the destructive earthquakes we further suggest that joint inversions of gps tsunami teleseismic and strong ground motion records and higher resolution bathymetry data are needed in order to obtain better correlations between observed and synthetic tsunami data especially for the later arriving waves

slip distribution of the february 27 2010 mw 8 8 maule earthquake central chile from static and high rate gps insar and broadband teleseismic data 1 the shallow depth underthrust earthquake of february 27 2010 mw 8 8 ruptured the subduction plate interface in central chile between 34 s and 38 s we retrieve the spatial and temporal distribution of slip during this mega earthquake through a joint inversion of teleseismic records insar and high rate gps hrgps data additionally our model is shown to agree with broadband surface waves rupture initiated at about 32 km depth and propagated bilaterally resulting in two main slip zones located ssw and nne of the hypocenter nucleation did not take place within or at the edge of one of these main asperities but in between during the first 30s slip propagated predominantly southwards later on the rupture evolved more slowly and more symmetrically eventually the northern asperity became predominant with maximum slip reaching about 20 m most of the seismic moment was released within 110s a relatively short time explained by the bilateral propagation the overall average rupture velocity is 2 6 km s but propagation occurred initially faster towards the south 3 2 km s large slip did not reach the trench a result consistent with the moderate size of the tsunami down dip rupture stopped at about 50 km depth in agreement with the lower limit of the locked zone inferred by ruegg et al 2009 from pre seismic gps data

the morphologic structure of step pools in mountain streams abstract step pool sequences in streams in the santa monica mountains of southern california impart a characteristic morphologic structure that varies with slope but despite the strong association with slope that suggests a direct process control analysis of 464 step pools in 13 study reaches reveals the relationship to reflect correlation but not necessarily causality the direct control on step height is particle size whereas discharge is the probable causal process determining step wavelength because both particle size and discharge generally change with channel slope downstream a slope variation with step wavelength and height is the apparent indirect geometric result a conceptual model of process form linkages is proposed based on these results whereby the step pool morphology is produced by positive relationships between wavelength and discharge and between height and particle size the model offers new insights for explaining the step pool morphology and it is potentially useful in channeling future efforts toward the appropriate scales and variables

rapidly estimated seismic source parameters for the 16 september 2015 illapel chile m w 8 3 earthquake on 16 september 2015 a great m w 8 3 interplate thrust earthquake ruptured offshore illapel chile producing a 4 7 m local tsunami the last major rupture in the region was a 1943m s 7 9 event seismic methods for rapidly characterizing the source process of value for tsunami warning were applied the source moment tensor could be obtained robustly by w phase inversion both within minutes chilean researchers had a good solution using regional data within 5 min and within an hour using broadband seismic data short period teleseismic p wave back projections indicate northward rupture expansion from the hypocenter at a modest rupture expansion velocity of 1 5 2 0 km s finite fault inversions of teleseismic p and sh waves using that range of rupture velocities and a range of dips from 16 consistent with the local slab geometry and some moment tensor solutions to 22 consistent with long period moment tensor inversions indicate a 180 to 240 km bilateral along strike rupture zone with larger slip northwest to north of the epicenter with peak slip of 7 10 m using a shallower fault model dip shifts slip seaward toward the trench while a steeper dip moves it closer to the coastline slip separates into two patches as assumed rupture velocity increases in all cases localized 5 m slip extends down dip below the coast north of the epicenter the seismic moment estimates for the range of faulting parameters considered vary from 3 7 1021nm dip 16 to 2 7 1021 nm dip 22 the static stress drop estimates range from 2 6 to 3 5 mpa and the radiated seismic energy up to 1 hz is about 2 2 3 15 1016 j

compressive sensing of frequency dependent seismic radiation from subduction zone megathrust ruptures megathrust earthquakes rupture a broad zone of the subducting plate interface in both along strike and along dip directions the along dip rupture characteristics of megathrust events e g their slip and energy radiation distribution reflect depth varying frictional properties of the slab interface here we report high resolution frequency dependent seismic radiation of the four largest megathrust earthquakes in the past 10 y using a compressive sensing sparse source recovery technique resolving generally low frequency radiation closer to the trench at shallower depths and high frequency radiation farther from the trench at greater depths together with coseismic slip models and early aftershock locations our results suggest depth varying frictional properties at the subducting plate interfaces the shallower portion of the slab interface above 15 km is frictionally stable or conditionally stable and is the source region for tsunami earthquakes with large coseismic slip deficient high frequency radiation and few early aftershocks the slab interface at intermediate depths 15 35 km is the main unstable seismogenic zone for the nucleation of megathrust quakes typically with large coseismic slip abundant early aftershocks and intermediate to high frequency radiation the deeper portion of the slab interface 35 45 km is seismically unstable however with small coseismic slip dominant high frequency radiation and relatively fewer aftershocks

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

relationships between land use and forced pool characteristics in the colorado front range abstract land use practices in colorado during the last two centuries altered the supply of sediment and water to many channels in the upper south platte basin as a result of increased supply of sediment and mobility and reduced peak flows the characteristics of pools associated with channel constrictions referred to as forced pools may have been altered increased supply of sediment and reduced transport capacity of high flows could lead to aggradation in forced pools channel confined by road corridors could lead to high velocities at normal flows increased energy dissipation from riprap or even increased pool frequency resulting from failed riprap to assess potential alterations four hypotheses were tested 1 impacted streams will show significantly different mean volume of pools than a control stream 2 mean volume of pools on streams where land use activities increased the supply of sediment will be significantly different from streams solely affected by flow regulation 3 the strongest change in characteristics of pools of impacted streams will be a reduced volume of pools 4 streams affected by road corridors will show statistically lower spacing of pools than streams unaffected by roads the downstream spacing and residual volume of twenty consecutive forced pools were surveyed on five streams in the colorado front range that varied from no contemporary impact to multiple historical and contemporary impacts ancova with stepwise model selection indicated that degree of land use categorical bankfull spacing of pools upstream riffle slope and expansion ratio were all significant 0 1 predictors of volume of pools r 2 0 73 simple linear regression of mean volume of pools and stream specific variables gradient drainage area and discharge and least square means comparison of mean volume of pools indicated a need to standardize volumes of pools by slope and discharge so that the volumes of pools could be compared among different levels of land use significant correlations between drainage area and volume of pools allowed volume of pools to be standardized by drainage area and thereby discharge this dimensionless variable was also significantly correlated with channel slope which permitted the construction of a new variable pv qs volume of pools standardized by discharge and slope least square means comparison of mean pv qs revealed that the control reach was significantly different from road impacted reaches mean volume of pools was significantly larger in the control reach compared to all but one road impacted stream this was likely a function of higher wood loading in the control reach and the competence of high flows in the road impacted reach streams affected by road corridors did not have significantly different bankfull spacing of pools from streams not impacted by roads the multiple interactions among control and response variables explored in this study indicate the need to identify the most constrained and sensitive response variables when attempting to assess channel response to land use

frequency dependent energy radiation and fault coupling for the 2010 mw8 8 maule chile and 2011 mw9 0 tohoku japan earthquakes 1 we carried out back projections of teleseismic data filtered in different frequency bands for the 2010 maule chile and the 2011 tohoku japan earthquakes for the maule earthquake there were differences along strike of the fault with the high frequency energy mainly originating from an area 200 km northeast of the epicenter whereas low frequency energy came from a location closer to the epicenter the tohoku earthquake shows strong frequency dependence in the dip direction high frequency sources were located about 100 km west of the epicenter while low frequency sources were around epicenter near the japan trench we compare the spatial distributions of energy with estimates of seismic coupling before the earthquakes areas of high frequency radiation seem correlated with regions that were strongly coupled before the earthquakes areas of high coupling may be associated with fault properties that are more heterogeneous and or have overall higher stress producing higher frequency seismic waves

source model of the 16 september 2015 illapel chile m w 8 4 earthquake based on teleseismic and tsunami data teleseismic data were provided by the incorporated research institutions for seismology http www iris edu wilber3 find event tide gauge data can be found at the intergovernmental oceanographic commission website http www ioc sealevelmonitoring org dart records were provided by noaa http nctr pmel noaa gov dart earthquake catalogs by the usgs national earthquake information center http earthquake usgs gov earthquakes search and global instrumental earthquake catalogue 1900 2009 of international seismological centre global earthquake model http www globalquakemodel org what seismic hazard instrumental catalogue were used in this study we used the gmt software for drawing the figures wessel and smith 1998 this article benefited from constructive review comments by costas e synolakis university of southern california usa and yuichiro tanioka hokkaido university japan for which we are grateful we acknowledge financial supports from the japan society for the promotion of science

along dip seismic radiation segmentation during the 2007 mw 8 0 pisco peru earthquake 1 the short period 0 5 2 s seismic radiation properties of the august 15 23 40 57 utc 2007 mw 8 0 pisco peru earthquake are imaged by back projecting p waves recorded at 374 elements of usarray deployed in western north america at distances of 54 74 from the source region the coherent short period seismic energy release has two main intervals similar to moment rate functions determined by inversion of longer period teleseismic body waves however the spatial locations of the coherent bursts of short period energyrelease are located northanddown dip of the region of major slip the contrast between short and long period seismic radiation properties of the pisco earthquake is more subtle than for the 2011 mw 9 0 tohoku earthquake but provides further support for the idea of depth dependent changes in sliding behavior during megathrust ruptures citation sufri o k d koper and t lay 2012 along dip seismic radiation segmentation during the 2007 mw 8 0 pisco peru earthquake geophys res lett 39 l08311 doi 10 1029 2012gl051316

imaging rupture process of the 2015 mw 8 3 illapel earthquake using the us seismic array we study the rupture process of the mw 8 3 illapel chile earthquake that occurred on 16 september 2015 using the us seismic network as a large aperture array we apply the back projection technique using two frequency bands 0 1 0 5 and 0 25 1 hz both frequency bands reveal that this event is characterized by rupture of three patches the higher frequency band shows an earlier burst of seismic radiation and illuminates a relatively down dip patch of energy radiation on the other hand the lower frequency band shows a more up dip rupture and matches well with the slip inversion model in other studies the illapel earthquake ruptures about 100 km along strike and shows 40 km up dip and 40 km down dip movement along the subduction megathrust fault the earthquake first ruptures around the epicenter with a relatively low level of seismic radiation then it propagates northeast along the juan femandez ridge jfr to rupture a patch down dip accompanied by strong higher frequency seismic radiation finally it ruptures to the northwest of the epicenter and terminates south of the challenger fracture zone cfz releasing a burst of strong lower frequency seismic radiation most of the aftershocks are either within or at the edge of the rupture patch a region characterized by high coupling in central chile the rupture is bounded along strike by two fractures zones to the north and south the jfr to the south of the rupture zone may have acted as a barrier along strike leaving the area south of the mainshock vulnerable for a large damaging earthquake in the near future

geometrical effects of a subducted seamount on stopping megathrust ruptures 1 we have numerically simulated dynamic ruptures along a slip weakening megathrust fault with a subducted seamount of realistic geometry demonstrating that seamounts can act as a barrier to earthquake ruptures such barrier effect is calculated to be stronger for increased seamount normal stress relative to the ambient level for larger seamount height to width ratio and for shorter seamount to nucleation distance as the seamount height increases from 0 to 40 of its basal width the required increase in the effective normal stress on the seamount to stop ruptures drops by as much as 20 we further demonstrate that when a seamount is subducted adjacent to the earthquake nucleation zone coseismic ruptures can be stopped even if the seamount has a lower effective normal stress than the ambient level these results indicate that subducted seamounts may stop earthquake ruptures for a wide range of seamount normal stress conditions including the case of the thrust fault being lubricated by seamount top fluid rich sediments as suggested from observations in the japan and sunda trenches

modeling earthquake sequences along the manila subduction zone effects of three dimensional fault geometry abstract to assess the potential of catastrophic megathrust earthquakes m w 8 along the manila trench the eastern boundary of the south china sea we incorporate a 3d non planar fault geometry in the framework of rate state friction to simulate earthquake rupture sequences along the fault segment between 15 n 19 n of northern luzon our simulation results demonstrate that the first order fault geometry heterogeneity the transitional segment possibly related to the subducting scarborough seamount chain connecting the steeper south segment and the flatter north segment controls earthquake rupture behaviors the strong along strike curvature at the transitional segment typically leads to partial ruptures of m w 8 3 and m w 7 8 along the southern and northern segments respectively the entire fault occasionally ruptures in m w 8 8 events when the cumulative stress in the transitional segment is sufficiently high to overcome the geometrical inhibition fault shear stress evolution represented by the s ratio is clearly modulated by the width of seismogenic zone w at a constant plate convergence rate a larger w indicates on average lower interseismic stress loading rate and longer rupture recurrence period and could slow down or sometimes stop ruptures that initiated from a narrower portion moreover the modeled interseismic slip rate before whole fault rupture events is comparable with the coupling state that was inferred from the interplate seismicity distribution suggesting the manila trench could potentially rupture in a m8 earthquake

coarse sediment transport in mountain streams in colorado and wyoming usa since the early 1990s us forest service researchers have made thousands of bedload measurements in steep coarse grained channels in colorado and wyoming usa in this paper we use data from 19 of those sites to characterize patterns and rates of coarse sediment transport for a range of channel types and sizes including step pool plane bed pool riffle and near braided channels this effort builds upon previous work where we applied a piecewise regression model to 1 relate flow to rates of bedload transport and 2 define phases of transport in coarse grained channels earlier the model was tested using bedload data from eight sites on the fraser experimental forest near fraser colorado the analysis showed good application to those data and to data from four supplementary channels to which the procedure was applied the earlier results were however derived from data collected at sites that for the most part have quite similar geology and runoff regimes in this paper we evaluate further the application of piecewise regression to data from channels with a wider range of geomorphic conditions the results corroborate with those from the earlier work in that there is a relatively narrow range of discharges at which a substantial change in the nature of bedload transport occurs the transition from primarily low rates of sand transport phase i to higher rates of sand and coarse gravel transport phase ii occurs on average at about 80 per cent of the bankfull 1 5 year return interval discharge a comparison of grain sizes moved during the two phases showed that coarse gravel is rarely trapped in the samplers during phase i transport moreover the movement and capture of the d16 to d25 grain size of the bed surface seems to correspond with the onset of phase ii transport particularly in systems with largely static channel surfaces however while there were many similarities in observed patterns of bedload transport at the 19 studied sites each had its own bedload signal in that the rate and size of materials transported largely reflected the nature of flow and sediment particular to that system published in 2005 by john wiley sons ltd

chile2015 levy flight and long range correlation analysis of earthquake magnitudes in chile the stochastic truncated levy flight model and detrended fluctuation analysis dfa are used to investigate the temporal distribution of earthquake magnitudes in chile we show that levy flight is appropriated for modeling the time series of the magnitudes of the earthquakes furthermore dfa shows that these events present memory effects suggesting that the magnitude of impeding earthquakes depends on the magnitude of previous earthquakes based on this dependency we use a non linear regression to estimate the magnitude of the 2015 m8 3 illapel earthquake based on the magnitudes of the previous events