a scaling law for slow earthquakes with the availability of the global positioning system and other technical advances a growing number of unusual earthquake phenomena occurring at relatively long periods have been recognized they include deep episodic tremor low frequency earthquakes slow slip events and silent earthquakes based on data chiefly from western japan ide et al report that these slow seismic events follow a unified scaling relationship that clearly differentiates their behaviour from that of regular earthquakes a diverse array of unusual earthquake phenomena occurring at relatively long periods slow events follow a unified scaling relationship that clearly differentiates their behaviour from that of regular earthquakes indicating that they comprise a new earthquake category recently a series of unusual earthquake phenomena have been discovered including deep episodic tremor1 low frequency earthquakes2 very low frequency earthquakes3 slow slip events4 and silent earthquakes5 6 7 8 9 each of these has been demonstrated to arise from shear slip just as do regular earthquakes but with longer characteristic durations and radiating much less seismic energy here we show that these slow events follow a simple unified scaling relationship that clearly differentiates their behaviour from that of regular earthquakes we find that their seismic moment is proportional to the characteristic duration and their moment rate function is constant with a spectral high frequency decay of f 1 this scaling and spectral behaviour demonstrates that they can be thought of as different manifestations of the same phenomena and that they comprise a new earthquake category the observed scale dependence of rupture velocity for these events can be explained by either a constant low stress drop model or a diffusional constant slip model this new scaling law unifies a diverse class of slow seismic events and may lead to a better understanding of the plate subduction process and large earthquake generation

itrf2008 plate motion model 1 the itrf2008 velocity field is demonstrated to be of higher quality and more precise than past itrf solutions we estimated an absolute tectonic plate motion model made up of 14 major plates using velocities of 206 sites of high geodetic quality far from plate boundaries deformation zones and glacial isostatic adjustment gia regions derived from and consistent with itrf2008 the precision of the estimated model is evaluated to be at the level of 0 3 mm a wrms no gia corrections were applied to site velocities prior to estimating plate rotation poles as our selected sites are outside the fennoscandia regions where the gia models we tested are performing reasonably well and far from gia areas where the models would degrade the fit antarctica and north america our selected velocity field has small origin rate bias components following the three axis x y z respectively 0 41 0 54 0 22 0 64 and 0 41 0 60 95 per cent confidence limits comparing our model to nnr nuvel 1a and the newly available nnr morvel56 we found better agreement with nnr morvel56 than with nnr nuvel 1a for all plates except for australia where we observe an average residual rotation rate of 4 mm a using our selection of sites we found large global x rotation rates between the two models 0 016 ma and between our model and nnr morvel56 of 0 023 ma equivalent to 2 5 mm a at the earth surface

propagation of slow slip leading up to the 2011 mw 9 0 tohoku oki earthquake many large earthquakes are preceded by one or more foreshocks but it is unclear how these foreshocks relate to the nucleation process of the mainshock on the basis of an earthquake catalog created using a waveform correlation technique we identified two distinct sequences of foreshocks migrating at rates of 2 to 10 kilometers per day along the trench axis toward the epicenter of the 2011 moment magnitude mw 9 0 tohoku oki earthquake in japan the time history of quasi static slip along the plate interface based on small repeating earthquakes that were part of the migrating seismicity suggests that two sequences involved slow slip transients propagating toward the initial rupture point the second sequence which involved large slip rates may have caused substantial stress loading prompting the unstable dynamic rupture of the mainshock

interseismic strain accumulation measured by gps in the seismic gap between constitucion and concepcion in chile the concepcion constitucion area 35 37 s in south central chile is very likely a mature seismic gap since no large subduction earthquake has occurred there since 1835 three campaigns of global positioning system gps measurements were carried out in this area in 1996 1999 and 2002 we observed a network of about 40 sites including two east west transects ranging from the coastal area to the argentina border and one north south profile along the coast our measurements are consistent with the nazca south america relative angular velocity 55 9 n 95 2 w 0 610 ma discussed by vigny et al 2008 this issue which predicts a convergence of 68 mm year oriented 79 n at the chilean trench near

nonvolcanic tremor observed in the mexican subduction zone nonvolcanic tremor nvt activity is revealed as episodes of higher spectral amplitude at 1 8 hz in daily spectrograms from the continuous seismological records in guerrero mexico the analyzed data cover a period of 2001 2007 when in 2001 2002 a large slow slip event sse had occurred in the guerrero oaxaca region and then a new large sse occurred in 2006 the tremor burst is dominated by s waves more than 100 strong nvt bursts were recorded in the narrow band of 40 150 km 2 to the south of iguala city and parallel to the coastline depths of nvt hypocenters are mostly scattered in the continental crust between 5 and 40 km depth tremor activity is higher during the 2001 2002 and 2006 sse compared with that for the quiet period of 2003 2005 while resistivity pattern in guerrero does not correlate directly with the nvt distribution gravity and magnetic anomaly modeling favors a hypothesis that the nvt is apparently related to the dehydration and serpentinization processes

short and long term effects of gps measured crustal deformation rates along the south central andes in this study we present the contemporary crustal deformation field along the central and southern andes 17 42 s estimated from four global positioning sys tem gps campaigns conducted in 1994 97 we find that the majority of the observed crustal deformation field is relatively homogenous roughly parallel to the plate conver gence direction with decreasing velocities away from the trench we attribute this type of deformation pattern to the inter seismic phase of an earthquake deformation cycle caused by 100 locking of the thrust interface between the subducting nazca and the overrid ing south american plates we have also detected a strong post seismic deformation sig nal in the vicinity of the 1995 mw8 0 antofagasta 22 26 s and 1960 mw9 5 chile 38 43 s earthquakes this type of deformation can be described as short term in nature compared to geological timescales the above conclusions are based on the results of the 3 d andean elastic dislocation model aedm by subtracting the aedm predicted deformation rates from the observations we obtained a residual velocity field that high lights the post seismic as well as more long term deformation eects for example we find a strong evidence for the continuing crustal shortening across the back arc reach ing its maximum 4 mm yr in the very north of our study area in addition between latitudes 29 34 s there is an indication of e w oriented extension within the fore arc in accordance with the recent geologic findings for the n s oriented normal faulting

the use of gps horizontals for loading studies with applications to northern california and southeast greenland received 23 august 2012 revised 15 january 2013 accepted 20 january 2013 published 25 april 2013 1 we describe how gps measurements of horizontal crustal motion can be used to augment vertical crustal motion measurements to improve and extend gps studies of surface loading we show that the ratio of the vertical displacement to the horizontal displacement combined with the direction of the horizontal motion can help determine whether nearby loading is concentrated in a small region for example in a single lake or glacier and where that region is we illustrate this method by applying it to two specific cases an analysis of gps data from northern california to monitor the level of lake shasta and the analysis of data from a single gps site in southeast greenland to determine mass variability of two large nearby outletglaciers helheim glacier and midgaard glacier the californiaexampleserves largely as a proof of concept where the results can be assessed by comparing with independent observations lake shasta tide gauge data in this case our greenland results show that both helheim and midgaard have experienced notable interannual variations in mass loss rate over the last decade helheim sm ass loss accelerated rapidly in mid 2003 decelerated in late 2005 and increased again in 2008 2009 before returning to about its pre 2003 rate in late 2010 midgaard s mass loss accelerated in mid 2004 and remained more or less constant before returning to its pre 2003 rate in late 2008

intense foreshocks and a slow slip event preceded the 2014 iquique mw 8 1 earthquake the subduction zone in northern chile is a well identified seismic gap that last ruptured in 1877 the moment magnitude mw 8 1 iquique earthquake of 1 april 2014 broke a highly coupled portion of this gap to understand the seismicity preceding this event we studied the location and mechanisms of the foreshocks and computed global positioning system gps time series at stations located on shore seismicity off the coast of iquique started to increase in january 2014 after 16 march several mw 6 events occurred near the low coupled zone these events migrated northward for 50 kilometers until the 1 april earthquake occurred on 16 march on shore continuous gps stations detected a westward motion that we model as a slow slip event situated in the same area where the mainshock occurred

low frequency earthquakes in the mexican sweet spot 1 we use data from the meso america subduction experiment to detect and locate low frequency earthquakes lfes in the mexican subduction zone we use visually identified templates to perform a network waveform correlation search that produced 17 000 robustly detected lfes that form 15 distinct families stacking an lfe family s corresponding detections results in seismograms with high signal to noise ratios and clear p and s wave arrivals we use these travel times to locate the sources the resulting locations superpose a previously identified region of permanent non volcanic tremor nvt activity husker et al 2012 called this region a sweet spot suggesting that the local conditions are adequate to continuously generate nvt the lfe hypocenters have been located at a depth of 40 45 km in an area that is surrounding the upper slab plate interface we characterize their focal mechanisms by comparing their stacked seismograms to synthetic seismograms this analysis reveals a common low dipping focal mechanism

aseismic slip and seismogenic coupling along the central san andreas fault we use high resolution synthetic aperture radar and gps derived observations of surface displacements to derive the first probabilistic estimates of fault coupling along the creeping section of the san andreas fault in between the terminations of the 1857 and 1906 magnitude 7 9 earthquakes using a fully bayesian approach enables unequaled resolution and allows us to infer a high probability of significant fault locking along the creeping section the inferred discreet locked asperities are consistent with evidence for magnitude 6 earthquakes over the past century in this area and may be associated with the initiation phase of the 1857 earthquake as creeping segments may be related to the initiation and termination of seismic ruptures such distribution of locked and creeping asperities highlights the central role of the creeping section on the occurrence of major earthquakes along the san andreas fault

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

upper plate deformation measured by gps in the coquimbo gap chile abstract since the mw 7 3 punitaqui earthquake in 1997 the area between 30 s and 32 s coquimbo illapel section of the chilean subduction has been the locus of a decennial seismic swarm a dense network of 30 benchmarks have been installed in this area and surveyed six times with high precision gps over the last 3 years surface deformation here is compatible with elastic loading due to partial locking on the subduction interface at depth here we show that in this area only 40 45 of the total convergence rate between nazca and south america plates gives way to accumulation of elastic deformation in the upper plate the remaining 60 55 being dissipated by free or aseismic slip the cumulative slip due to the seismic swarm explaining no more than 1 3rd to 1 4th of it we also find that the accumulation decreases northward to reach almost zero around 30 s la serena tongoy whether this is a steady state or only a transient pattern a steady decrease of coupling is not clear since our measurements span only 3 years and since early measurements 10 years ago were sparse and differ only marginally from ours

slow earthquakes and nonvolcanic tremor nonvolcanic tremor is observed in close association with geodetically observed slow slip events in subduction zones accumulating evidence points to these events as members of a family of slow earthquakes that occur as shear slip on the downdip extensions of fault zones in a regime that is transitional between a frictionally locked region above and a freely slipping region below by virtue of their locations and their properties slow earthquakes are certain to provide new insights into the behavior of earthquakes and faulting and into the hazard they embody

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

interseismic coupling segmentation and mechanical behavior of the central chile subduction zone global positioning system gps measurements carried out in chile over the last two decades showed that an entire portion of the nazca south america subduction zone 38 s 24 s was locked over this period of time the induced accumulation of elastic deformation in the upper plate was not released until the recent maule earthquake of 27 february 2010 mw 8 8 that ruptured the southern part of this section locking or coupling between the two plates varies both with depth and along strike here we use our own gps data an updated solution of our extended network in central chile combined with other published data sets to quantify the spatial variations of the coupling that prevailed before the maule earthquake using a simple elastic model based on the back slip assumption we show that coupling variations on the subduction plane are sufficient to explain the observed surface deformation with no need of a sliver in central chile we identify four segments characterized by higher coupling and separated by narrow areas of lower coupling this segmentation is in good agreement with historical and recent seismicity in chile in particular the narrow zones of lower coupling seem to have stopped most large seismic ruptures including maule s these zones are often associated with irregular bathymetric or coastal features fracture zones or peninsulas finally coseismic and early post seismic slip distribution of the maule earthquake occurring either in previously highly or weakly coupled zones map a complex distribution of velocity weakening and velocity strengthening patches on the subduction interface

antarctica greenland and gulf of alaska land ice evolution from an iterated grace global mascon solution we have determined the ice mass evolution of the antarctica and greenland ice sheets ais and gis and gulf of alaska goa glaciers from a new grace global solution of equal area surface mass concentration parcels mascons in equivalent height of water the mascons were estimated directly from the reduction of the inter satellite k band range rate kbrr observations taking into account the full noise covariance and formally iterating the solution the new solution increases signal recovery while reducing the grace kbrr observation residuals the mascons were estimated with 10 day and 1 arc degree equal area sampling applying anisotropic constraints an ensemble empirical mode decomposition adaptive filter was applied to the mascon time series to compute annual mass balances the details and causes of the spatial and temporal variability of the land ice regions studied are discussed the estimated mass trend over the total gis ais and goa glaciers for the time period 1 december 2003 to 1 december 2010 is 380 plus or minus 31 gt a exp 1 equivalent to 1 05 plus or minus 0 09 mma exp 1 sea level rise over the same time period we estimate the mass acceleration to be 41 plus or minus 27 gt a exp 2 equivalent to a 0 11 plus or minus 0 08 mm a exp 2 rate of change in sea level the trends and accelerations are dependent on significant seasonal and annual balance anomalies

the 2006 slow slip event and nonvolcanic tremor in the mexican subduction zone the last decade featured an explosive sequence of discoveries of slow slip events sse and nonvolcanic tremor nvt in different subduction zones and continental faults many observations show that sse is usually associated with an increased nvt activity but it is not clear yet if those events are the result of the same process or are independent expressions of a common underlying seismotectonic source a large sse in central mexico occurred in 2006 during the meso american subduction experiment mase which provided continuous observations of the nvt for the years 2005 2007 gps and abundant seismic data show that although the nvt energy increased notably during the 2006 sse the two phenomena were separated spatially and not completely synchronized in time significant nvt episodes occur during the period between sses suggesting again that large slow slip events and nvt observed in the mexican subduction zone are of different origins the results presented here contribute to uncovering the nature of these two separate phenomena that have been indistinguishable in some other regions

triggering of tremors and slow slip event in guerrero mexico by the 2010 mw 8 8 maule chile earthquake 1 we investigate the triggering of seismic tremor and slow slip event in guerrero mexico by the february 27 2010 maule earthquake mw 8 8 triggered tremors start with the arrival of s wave generated by the maule earthquake and keep occurring during the passing of scs ss love and rayleigh waves the rayleigh wave dispersion curve footprints the high frequency energy envelope of the triggered tremor indicating a strong modulation of the source of tremors by the passing surface wave this correlation and modulation by the passing waves is progressively lost with time over a few hours the tremor activity continues during the weeks months after the earthquake gps time series suggest that the second sub event of the 2009 2010 sse in guerrero is actually triggered by the maule earthquake the southward displacement of the gps stations starts coincidently with the earthquake and tremors the long duration of tremors indicate a continuing deformation process at depth which we propose to be the second sub event of the 2009 2010 sse we show a quasi systematic correlation between surface displacement rate measured by gps and tremor activity suggesting that the nvt are controlled by the variations in the slip history of the sse this study shows that two types of tremors emerge 1 those directly triggered by the passing waves and 2 those triggered by the stress variations associated with slow slip this indicates the prominent role of aseismic creep in the mexican subduction zone response to a large teleseismic earthquake possibly leading to large scale stress redistribution

an aseismic slip transient on the north anatolian fault constellations of synthetic aperture radar sar satellites with short repeat time acquisitions allow exploration of active faults behavior with unprecedented temporal resolution along the north anatolian fault naf in turkey an 80 km long section has been creeping at least since the 1944 m w 7 3 earthquake near ismetpasa with a current interferometric synthetic aperture radar insar derived average creep rate of 8 3 mm yr i e a third of the naf long term slip rate we use a dense set of sar images acquired by the cosmo skymed constellation to quantify the spatial distribution and temporal evolution of creep over 1 year we identify a major burst of aseismic slip spanning 31 days with a maximum slip of 2 cm between the surface and 4 km depth this result shows that fault creep along this section of the naf does not occur at a steady rate as previously thought highlighting a need to revise our understanding of the underlying fault mechanics

slow slip events and strain accumulation in the guerrero gap mexico 1 global positioning system gps time series in guerrero mexico reveal the existence of large slow slip events sses at the boundary between the cocos and north american plates in this study we examined the last three sses that occurred in 2001 2002 2006 and 2009 2010 and their impact on the strain accumulation along the guerrero subduction margin gps displacements were inverted to retrieve the slip distribution during each sse and the inter sse coupling of the subduction interface the three analyzed sses have equivalent moment magnitudes of between 7 50 and 7 65 their lateral extents are variable and they all show significant slip in the guerrero seismic gap during the inter sse epochs the interplate coupling is high in the area where slow slip subsequently occurs in the guerrero gap the shallow portion of the plate interface from the trench to the coast is weakly coupled the average slip deficit accumulated in the guerrero gap over a period of 12 years which corresponds to three cycles of sse is only 1 4 of the slip deficit accumulated on both sides of the gap moreover the regions of large slip deficit coincide with the rupture areas of recent large earthquakes we conclude that the sses in the guerrero gap release a significant part of the strain accumulated during the inter sse period if large subduction thrust earthquakes occur in the guerrero gap their recurrence time is probably increased compared to adjacent regions

study of the atmospheric pressure loading signal in very long baseline interferometry observations 1 redistribution of air masses due to atmospheric circulation causes loading deformation of the earth s crust which can be as large as 20 mm for the vertical component and 3 mm for horizontal components rigorous computation of site displacements caused by pressure loading requires knowledge of the surface pressure field over the entire earth surface a procedure for computing three dimensional displacements of geodetic sites of interest using a 6 hourly pressure field from the national centers for environmental prediction numerical weather models and the ponte and ray 2002 model of atmospheric tides is presented we investigated possible error sources and found that the errors of our pressure loading time series are below the 15 level we validated our model by estimating the admittance factors of the pressure loading time series using a data set of 3 5 million very long baseline interferometry observations from 1980 to 2002 the admittance factors averaged over all sites are 0 95 0 02 for the vertical displacement and 1 00 0 07 for the horizontal displacements for the first time horizontal displacements caused by atmospheric pressure loading have been detected the closeness of these admittance factors to unity allows us to conclude that on average our model quantitatively agrees with the observations within the error budget of the model at the same time we found that the model is not accurate for several stations that are near a coast or in mountain regions we conclude that our model is suitable for routine data reduction of space geodesy observations

slip weakening as a mechanism for slow earthquakes slow earthquakes form part of a spectrum of fault behaviour between steady creep and fast rupture during a normal earthquake laboratory simulations of slow slip in rock samples taken from the nankai subduction zone japan reveal similar characteristics to fast earthquakes implying that some slow slip events could be prematurely arrested earthquakes

deep transient slow slip detected by survey gps in the region of atacama chile we detected a long term transient deformation signal between 2014 and 2016 in the atacama region chile using survey global positioning system gps observations over an 150 km along strike region survey gps measurements in 2014 and 2016 deviate significantly from the interseismic trend estimated using previous observations this deviation from steady state deformation is spatially coherent and reveals a horizontal westward diverging motion of several centimeters along with a significant uplift it is confirmed by continuous measurements of recently installed gps stations we discard instrumental hydrological oceanic or atmospheric loading effects and show that the transient is likely due to deep slow slip in the transition zone of the subduction interface 40 to 60 km depth in addition daily observations recorded by a continuous gps station operating between 2002 and 2015 highlight similar transient signals in 2005 and 2009 suggesting a recurrent pattern

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

afterslip and viscoelastic relaxation model inferred from the large scale post seismic deformation following the 2010 mw 8 8 maule earthquake chile

revisiting the north chile seismic gap segmentation using gps derived interseismic coupling no major earthquake occurred in north chile since the 1877 m w 8 6 subduction earthquake that produced a huge tsunami however geodetic measurements conducted over the last decade in this area show that the upper plate is actually deforming which reveals some degree of locking on the subduction interface this accumulation of elastic deformation is likely to be released in a future earthquake because of the long elapsed time since 1877 and the rapid accumulation of deformation thought to be 6 7 cm yr many consider this area is a mature seismic gap where a major earthquake is due and seismic hazard is high we present a new global positioning system gps velocity field acquired between 2008 and 2012 that describes in some detail the interseismic deformation between 18 s and 24 s we invert for coupling distribution on the nazca south america subduction interface using elastic modelling our measurements require that at these latitudes 10 to 12 mm yr 1 i e 15 per cent of the whole convergence rate are accommodated by the clockwise rotation of an andean block bounded to the east by the subandean fold and thrust belt this reduces the accumulation rate on the subduction interface to 56 mm yr 1 in this area coupling variations on the subduction interface both along strike and along dip are described we find that the north chile seismic gap is segmented in at least two highly locked segments bounded by narrow areas of weak coupling this coupling segmentation is consistent with our knowledge of the historical ruptures and of the instrumental seismicity of the region intersegment zones iquique mejillones correlate with high background seismic rate and local tectonic complexities on the upper or downgoing plates the rupture of either the paranal or the loa segment alone could easily produce a mw 8 0 8 3 rupture and we propose that the loa segment from 22 5 s to 20 8 s may be the one that ruptured in 1877

dilatant strengthening as a mechanism for slow slip events 1 the mechanics of slow slip events sse in subduction zones remain unresolved we suggest that sse nucleate in areas of unstable friction under drained conditions but as slip accelerates dilatancy reduces pore pressure p quenching instability competition between dilatant strengthening and thermal pressurization may control whether slip is slow or fast we model sse with 2 d elasticity rate state friction and a dilatancy law where porosity evolves toward steady state ss over distance dc and ss 0 ln v v0 v is slip speed we consider two diffusion models membrane diffusion md is approximated by p p tf where p and p are shear zone and remote pore pressure and tf is a characteristic diffusion time homogeneous diffusion hd accurately models fault normal flow with diffusivity chyd for md linearized analysis defines a boundary 1 a b between slow and fast slip where f0e b p f0 a and b are friction parameters and is compressibility when 1 a b slip speeds remain quasi static for hd ep eh p defines dilatancy efficiency where h is shear zone thickness and v is plate velocity sse are favored by large eh and low effective stress the ratio ep to thermal pressurization efficiency scales with 1 p so high p favors sse consistent with seismic observations for ep 10 3 transient slip rates repeat times average slip and stress drops are comparable to field observations model updip propagation speeds are comparable to those observed along strike many simulations exhibit slow phases driven by steady downdip slip and faster phases that relax the accumulated stress model sse accommodate only a fraction of plate motion the remaining deficit must be accommodated during coseismic or postseismic slip

crustal motion in the southern andes 26 36 s do the andes behave like a microplate 1 a new global positioning system gps derived velocity field for the andes mountains 26 36 s allows analysis of instantaneous partitioning between elastic and anelastic deformation at the orogen s opposing sides adding an andes microplate to the traditional description of nazca south america plate convergence provides the kinematic framework for nearly complete explanation of the observed velocity field the results suggest the oceanic nazca boundary is fully locked while the continental backarc boundary creeps continuously at 4 5 mm yr the excellent fit of model to data 1 7 mm yr rms velocity misfit and the relative aseismicity of the upper crust in the interior andean region in comparison with its boundaries supports the notion that the mountains are not currently accruing significant permanent strains additionally the model implies permanent deformation is not accumulating throughout the backarc contractional wedge but rather that the deformation is accommodated only within a narrow deformational zone in the backarc

the 2010 mw 8 8 maule megathrust earthquake of central chile monitored by gps large earthquakes produce crustal deformation that can be quantified by geodetic measurements allowing for the determination of the slip distribution on the fault we used data from global positioning system gps networks in central chile to infer the static deformation and the kinematics of the 2010 moment magnitude m w 8 8 maule megathrust earthquake from elastic modeling we found a total rupture length of 500 kilometers where slip up to 15 meters concentrated on two main asperities situated on both sides of the epicenter we found that rupture reached shallow depths probably extending up to the trench resolvable afterslip occurred in regions of low coseismic slip the low frequency hypocenter is relocated 40 kilometers southwest of initial estimates rupture propagated bilaterally at about 3 1 kilometers per second with possible but not fully resolved velocity variations

periodic slow earthquakes from the cascadia subduction zone continuous geodetic measurements from convergent margins have shown that deep transient creep events can release large amounts of strain energy without detectable seismic shaking and they are thus known as slow or silent earthquakes because subduction zones generate the largest earthquakes

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

ongoing drought induced uplift in the western united states the western united states has been experiencing severe drought since 2013 the solid earth response to the accompanying loss of surface and near surface water mass should be a broad region of uplift we use seasonally adjusted time series from continuously operating gps stations to measure this uplift which we invert to estimate mass loss the median uplift is 4 mm with values up to 15 mm in california s mountains the associated pattern of mass loss which ranges up to 50 cm of water equivalent is consistent with observed decreases in precipitation and streamflow we estimate the total deficit to be about 240 gt equivalent to a 10 cm layer of water over the entire region or the annual mass loss from the greenland ice sheet

gps derived deformation of the central andes including the 1995 antofagasta mw 8 0 earthquake in order to study both the interplate seismic loading cycle and the distribution of intraplate deformation of the andes a 215 site gps network covering chile and the western part of argentina was selected monumented and observed in 1993 and 1994 a dense part of the network in northern chile and northwest argentina comprising some 70 sites was re observed after two years in october november 1995 the m w 8 0 antofagasta north chile earthquake of 30th july 1995 took place between the two observations the city of antofagasta shifted 80 cm westwards by this event and the displacement still reached 10 cm at locations 300 km from the trench three different deformation processes have been considered for modeling the measured displacements 1 interseismic accumulation of elastic strain due to subduction coupling 2 coseismic strain release during the antofagasta earthquake and 3 crustal shortening in the sub andes eastward displacement of the sites to the north and to the south of the area affected by the earthquake is due to the interseismic accumulation of elastic deformation assuming a uniform slip model of interseismic coupling the observed displacements at the coast require a fully locked subduction interface and a depth of seismic coupling of 50 km the geodetically derived fault plane parameters of the antofagasta earthquake are consistent with results derived from wave form modeling of seismolog ical data the coseismic slip predicted by the variable slip model reaches values of 3 2 m in the dip slip and 1 4 m in the strike slip directions the derived rake is 66 our geodetic results suggest that the oblique nazca south american plate convergence is accommodated by oblique earthquake slip with no slip partitioning the observed displacements in the back arc indicate a present day crustal shortening rate of 3 4 mm year which is significantly slower than the average of 10 mm year experienced during the evolution of the andean plateau

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

slow slip events and seismic tremor at circum pacific subduction zones 1 it has been known for a long time that slip accompanying earthquakes accounts for only a fraction of plate tectonic displacements however only recently has a fuller spectrum of strain release processes including normal slow and silent earthquakes or slow slip events and continuous and episodic slip been observed and generated by numerical simulations of the earthquake cycle despite a profusion of observations and modeling studies the physical mechanism of slow slip events remains elusive the concurrence of seismic tremor with slow slip episodes in cascadia and southwestern japan provides insight into the process of slow slip a perceived similarity between subduction zone and volcanic tremor has led to suggestions that slow slip involves fluid migration on or near the plate interface alternatively evidence is accumulating to support the notion that tremor results from shear failure during slow slip global observations of the location spatial extent magnitude duration slip rate and periodicity of these aseismic slip transients indicate significant variation that may be exploited to better understand their generation most slow slip events occur just downdip of the seismogenic zone consistent with rate and state dependent frictional modeling that requires unstable to stable transitional properties for slow slip generation at a few convergent margins the occurrence of slow slip events within the seismogenic zone makes it highly likely that transitions in frictional properties exist there and are the loci of slow slip nucleation slow slip events perturb the surrounding stress field and may either increase or relieve stress on a fault bringing it closer to or farther from earthquake failure respectively this paper presents a review of slow slip events and related seismic tremor observed at plate boundaries worldwide with a focus on circum pacific subduction zones trends in global observations of slow slip events suggest that 1 slow slip is a common phenomena observed at almost all subduction zones with instrumentation capable of recording it 2 different frictional properties likely control fast versus slow slip 3 the depth range of slow slip may be related to the thermal properties of the plate interface and 4 the equivalent seismic moment of slow slip events is proportional to their duration mo different from the mo 3 scaling observed for 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

the iquique earthquake sequence of april 2014 bayesian modeling accounting for prediction uncertainty the subduction zone in northern chile is a well identified seismic gap that last ruptured in 1877 on 1 april 2014 this region was struck by a large earthquake following a two week long series of foreshocks this study combines a wide range of observations including geodetic tsunami and seismic data to produce a reliable kinematic slip model of the mw 8 1 main shock and a static slip model of the mw 7 7 aftershock we use a novel bayesian modeling approach that accounts for uncertainty in the green s functions both static and dynamic while avoiding nonphysical regularization the results reveal a sharp slip zone more compact than previously thought located downdip of the foreshock sequence and updip of high frequency sources inferred by back projection analysis both the main shock and the mw 7 7 aftershock did not rupture to the trench and left most of the seismic gap unbroken leaving the possibility of a future large earthquake in the region

a seismodynamical model of lithosphere deformation development of continental and oceanic rift networks seismicity and lithosphere extension on the scale of a tectonic plate are investigated in two horizontal dimensions and time using a dynamical model for a thin plate overlying a viscoelastic channel the plate consists of two layers a brittle elastic plastic crust that deforms as a result of earthquakes along faults and a strong viscoelastic layer representing the aseismic creeping lower lithosphere numerical experiments of lithosphere rifting are performed for one and two layer lithosphere models using two different rupture criteria in all the calculations earthquakes and faults of various sizes may form anywhere in the numerical domain as a result of the constitutive formulation the differences between the one and two layer model results suggest a mechanical explanation for the difference between continental and oceanic rifting when the lower lithosphere is absent a small number of faults dominate the deformation and a relatively simple narrow rift zone develops corresponding to oceanic rifting when a highly viscous lower lithosphere is included a complex distributed network of faults develops similar to continental rifting the complexity of the fault system also depends on the yield criterion in the crustal layer in our simulations complexity is greater for a yield criterion with strong shear stress dependence than for one with mainly extensional stress dependence whether a result of lower lithosphere stretching crustal heterogeneity or the yield criterion higher complexity increases the timescale for fault development increases self similarity in fault system geometry and stress and strain time series and results in power law moment frequency earthquake size scaling

delivery of upper basin sediment to the lower neuse river north carolina u s a extensive storage of upper basin piedmont sediment and apparent low sediment supply to streams in lower basin coastal plain areas generates questions as to the source of alluvium in lower reaches of rivers of the u s atlantic drainage this was investigated on the neuse river north carolina using a mineralogical indicator of sediment source areas the utility of mica flakes for discriminating between piedmont and non piedmont sources of sediment in the lower coastal plain reaches of the neuse was established on the basis of an examination of the u s national soils database and of 26 soil surveys of the north carolina coastal plain from the neuse river estuary to 48 km upstream there are no mica flakes in floodplain soils or in river bank and channel shelf sediments mica flakes become more common upstream this suggests that a very small proportion of the sediment eroded in the piedmont portion of the watershed is delivered to the river mouth the small amounts which presumably do reach the lower coastal plain are so diluted by coastal plain derived alluvium that no piedmont origin can be discerned this demonstrates a dominantly coastal plain source and underscores the importance of storage and discontinuous transport in fluvial sediment systems more importantly results suggest that upper and lower basin sediment dynamics are not only non linearly related but may be virtually decoupled

an integrated perspective of the continuum between earthquakes and slow slip phenomena slow slip a mechanism by which faults can relieve stress was thought to be distinct from earthquakes however a global review of slow slip phenomena suggests that instead there is a continuum between the two types of event