active deformation near the nicoya peninsula northwestern costa rica between 1996 and 2010 interseismic megathrust coupling 1 we use campaign and continuous gps measurements at 49 sites between 1996 and 2010 to describe the long term active deformation in and near the nicoya peninsula northwestern costa rica the observed deformation reveals partial partitioning of the cocos caribbean oblique convergence into trench parallel forearc sliver motion and less oblique thrusting on the subduction interface the northern costa rican forearc translates northwestward as a whole ridge block at 11 1 mm yr relative to the stable caribbean the transition from the forearc to the stable caribbean occurs in a narrow deforming zone of 16 km wide subduction thrust earthquakes take 2 3 of the trench parallel component of the plate convergence however surface deformation caused by interseismic megathrust coupling is primarily trench normal two fully coupled patches one located offshore nicoya centered at 15 km depth and the other located inland centered at 24 km depth are identified in nicoya with the potential to generate an mw 7 8 1950 type earthquake another fully coupled patch se of nicoya coincides with the rupture region of the 1990 nicoya gulf earthquake interface microearthquakes non volcanic tremor low frequency earthquakes and transient slow slip events generally occur in the intermediately to weakly coupled regions

observation of the seismic nucleation phase in the ridgecrest california earthquake sequence near source observations of five m 3 8 5 2 earthquakes near ridgecrest california are consistent with the presence of a seismic nucleation phase these earthquakes start abruptly but then slow or stop before rapidly growing again toward their maximum rate of moment release deconvolution of instrument and path effects by empirical green s functions demonstrates that the initial complexity at the start of the earthquake is a source effect the rapid growth of the p wave arrival at the start of the seismic nucleation phase supports the conclusion of mori and kanamori 1996 that these earthquakes begin without a magnitude scaled slow initial phase of the type observed by iio 1992 1995

moment release rate of cascadia tremor constrained by gps 1 a comparison of gps and seismic analyses of 23 distinct episodic tremor and slip events located throughout the cascadia subduction zone over an 11 year period yields a highly linear relationship between moment release as estimated from gps and total duration of nonvolcanic tremor as summed from regional seismic arrays the events last 1 5 weeks typically produce 5 mm of static forearc deformation and show cumulative totals of tremor that range from 40 to 280 h moment released by each event is estimated by inverting gps measured deformation which is sensitive to all rates of tremor synchronous faulting including aseismic creep for total slip along the north american juan de fuca plate interface tremor which is shown to be largely invariant in amplitude and frequency content both between events and with respect to its duration is quantified using several different parameterizations that agree to within 10 all known cascadia events detected since 1997 which collectively span the cascadia arc from northern california to vancouver island canada release moment during tremor at a rate of 5 2 0 4 1016 n m per hour of recorded tremor this relationship enables estimation of moment dissipation via seismic monitoring of tremor along the deeper cascadia subduction zone that poses the greatest threat to its major metropolitan centers

source scaling of microearthquakes at mt etna volcano and in the calabrian arc southern italy microearthquake data recorded at mt etna volcano and in the calabrian arc southern italy have been used to study the scaling of the main source parameters after correction of the p wave displacement spectra for both path attenuation and the site amplification effects an inverse method has been applied to compute spectral parameters low frequency spectral level corner frequency and high frequency roll off results show that seismic moments m0 range from ca 1016 to 1021 dyne cm at mt etna and from ca 1017 to 1020 dyne cm in southern calabria corner frequencies range from ca 3 to 15 hz in both areas we found that the stress drop decreases from ca 100 to few bars with decreasing seismic moment a simple brune source model is not able to explain the source scaling because the typical fall off observed at higher frequencies 3 as an average is larger than that of brune s theory furthermore the relation between the seismic moment and the corner frequency points to a scaling law behaving as m0 c 4 5 and m0 c 3 6 on average at mt etna and in southern calabria respectively and higher for smaller events in both areas therefore the cube law m0 3 generally accepted for large earthquakes does not hold true for the analysed microearthquakes neither for those which occur along the tectonic structures of southern calabria or along those hosting the roots of the feeding system of the largest european volcano

cosmogenic nuclides and the dating of lateglacial and early holocene glacier variations the alpine perspective abstract based on cosmogenic 10 be data from four sites in the alps we discuss geological uncertainties associated with the dating of former cirque and small valley glacier margins at the early lateglacial gschnitz site trins austria a 3000 yr spread in 10 be exposure ages points to prolonged boulder instability three out of seven ages are not included in the mean age calculation which yielded 15 400 1000 yr indistinguishable from the oldest boulder age of 16 130 1040 yr as a result of the distinctive morphology at julier pass switzerland site we are able to exposure date the early 12 300 1300 yr and the late 11 300 600 yr egesen stadial glacier advances younger dryas equivalent not just final retreat at the kromer site austria 10 be exposure ages from five clast supported boulders are indistinguishable within the analytical uncertainties mean age 8400 500 yr in addition to moraine age key factors that may lead to too young ages include degree of matrix vs clast support of the boulders post depositional periglacial activity and tree coverage at the nagelisgratli bedrock site near grimsel pass switzerland exposure ages of 10 760 11 720 yr are consistent with early holocene cirque glacier retreat and underline the marked lack of nuclide inheritance in bedrock exposures in the alps

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

geodetic and seismic constraints on some seismogenic zone processes in costa rica new seismic and geodetic data from costa rica provide insight into seismogenic zone processes in central america where the cocos and caribbean plates converge seismic data are from combined land and ocean bottom deployments in the nicoya peninsula in northern costa rica and near the osa peninsula in southern costa rica in nicoya inversion of gps data suggests two locked patches centered at 14 2 and 39 6 km depth interplate microseismicity is concentrated in the more freely slipping intermediate zone suggesting that small interseismic earthquakes may not accurately outline the updip limit of the seismogenic zone the rupture zone for future large earthquakes at least over the short 1 year observation period we also estimate northwest motion of a coastal sliver block at 8 3 mm yr probably related to oblique convergence in the osa region to the south convergence is orthogonal to the trench cocos caribbean relative motion is partitioned here with 8 cm yr on the cocos panama block boundary including a component of permanent shortening across the fila costena fold and thrust belt and 1 cm yr on the panama block caribbean boundary the gps data suggest that the cocos plate panama block boundary is completely locked from 10 50 km depth this large locked zone as well as associated forearc and back arc deformation may be related to subduction of the shallow cocos ridge and or younger lithosphere compared to nicoya with consequent higher coupling and compressive stress in the direction of plate convergence

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

initial rupture of earthquakes in the 1995 ridgecrest california sequence close examination of the p waves from earthquakes ranging in size across several orders of magnitude shows that the shape of the initiation of the velocity waveforms is independent of the magnitude of the earthquake a model in which earthquakes of all sizes have similar rupture initiation can explain the data this suggests that it is difficult to estimate the eventual size of an earthquake from the initial portion of the waveform previously reported curvature seen in the beginning of some velocity waveforms can be largely explained as the effect of anelastic attenuation thus there is little evidence for a departure from models of simple rupture initiation that grow dynamically from a small region the results of this study indicate that any precursory radiation at seismic frequencies must emanate from a source region no larger than the equivalent of a m0 5 event i e a characteristic length of 10 m the size of the nucleation region for magnitude 0 to 5 earthquakes thus is not resolvable with the standard seismic instrumentation deployed in california

the rupture extent of low frequency earthquakes near parkfield ca the low frequency earthquakes lfes that constitute tectonic tremor are often inferred to be slow to have durations of 0 2 to 0 5 s a factor of 10 to 100 longer than those of typical m w 1 2 earthquakes here we examine lfes near parkfield ca in order to assess several proposed explanations for lfes long durations we determine lfe rupture areas and location distributions using a new approach similar to directivity analysis where we examine how signals coming from various locations within lfes finite rupture extents create differences in the apparent source time functions recorded at various stations we use synthetic ruptures to determine how much the lfe signals recorded at each station would be modified by spatial variations of the source station travel time within the rupture area given various possible rupture diameters and then compare those synthetics with the data our synthetics show that the methodology can identify inter station variations created by heterogeneous slip distributions or complex rupture edges and thus lets us estimate lfe rupture extents for unilateral or bilateral ruptures to obtain robust estimates of the sources similarity across stations we stack signals from thousands of lfes using an empirical green s function approach to isolate the lfes apparent source time functions from the path effects our analysis of lfes in parkfield implies that lfes apparent source time functions are similar across stations at frequencies up to 8 to 16 hz depending on the family the inter station coherence observed at these relatively high frequencies or short wave lengths down to 0 2 to 0 5 km suggest that lfes in each of the 7 families examined occur on asperities they are clustered in patches with sub 1 km diameters the individual lfes rupture diameters are estimated to be smaller than 1 1 km for all families and smaller than 0 5 km and 1 km for the two shallowest families which were previously found to have 0 2 s durations coupling the diameters with the durations suggests that it is possible to model these m w 1 2 lfes with earthquake like rupture speeds around 70 of the shear wave speed however that rupture speed matches the data only at the edge of our uncertainty estimates for the family with highest coherence the data for that family are better matched if lfes have rupture velocities smaller than 40 of the shear wave speed or if lfes have different rupture dynamics they could have long rise times contain composite sub ruptures or have slip distributions that persist from event to event

non volcanic tremor resulting from the combined effect of earth tides and slow slip events swarms of non volcanic tremor in southeastern japan are associated with slow slip events and tend to occur with a periodicity of 12 or 24 h this periodicity can be reproduced by a combination of stresses due to earth tides and transient stress changes caused by slow slip events non volcanic tremors may therefore be useful for understanding stress relaxation at the subduction zone interface slow slip events1 are accompanied by swarms of non volcanic tremor2 3 along the subduction zone of the philippine sea plate in southwest japan the swarms often occur with a periodicity of about 12 or 24 h refs 4 5 these episodic events are considered to be a manifestation of stress relaxation at the subducting plate interface1 6 7 here we analyse seismic data to record the locations and durations of non volcanic tremor swarms that occurred in may 2005 and february 2006 we evaluate the magnitude of stress changes produced by slow slip events as well as the effective normal stress on the plate interface where slow slip events occur we find that the observed periodicity in tremor occurrence originates from a combined effect of the periodic stress due to earth tides and the transient stress due to slow slip events our calculations show that non volcanic tremor is sensitive to stress change this phenomenon can therefore be effective in monitoring the process of stress relaxation at subducting plate interfaces

non volcanic tremor associated with the march 2010 gisborne slow slip event at the hikurangi subduction margin new zealand 1 non volcanic tremor accompanies slow slip events at most circum pacific subduction zones previously the hikurangi subduction margin new zealand and the boso peninsula of japan have been noted as exceptions where slow slip which occurs at shallow depth compared to other subduction zones does not generate seismic tremor the lack of tremor observations raises questions whether tremor and slow slip are manifestations of the same process and whether different temperature and pressure conditions influence the physical mechanism of tremor production analysis of seismic data during the march 2010 gisborne slow slip event new zealand reveals that this slow slip event at the northern hikurangi margin is accompanied by tremor with distinctive characteristics compared to local microearthquakes both the gisborne area of new zealand and the boso peninsula of japan are underlain by thick accumulations of sedimentary rocks that likely inhibit the observation of low amplitude tremor due to high attenuation discovery of tremor in new zealand suggests that tremor may always accompany slow slip and that its apparent absence at the boso peninsula the hikurangi margin prior to this study and any future regions discovered to experience slow slip without concurrent tremor may be the effect of highly attenuating sediments

fore arc motion and cocos ridge collision in central america 1 we present the first regional surface velocity field for central america showing crustal response to interaction of the cocos and caribbean plates elastic half space models for interseismic strain accumulation on the dipping subduction plate boundary fit the gps data well and show strain accumulation offshore and beneath the nicoya and osa peninsulas in costa rica but not in nicaragua since large subduction zone earthquakes occur in nicaragua we suggest that interseismic locking in nicaragua and some other parts of central america occurs but is mainly shallow 20 km depth too far offshore to be detected by our on land gps measurements our data also show significant trench parallel motion for most of the region generally interpreted as due to oblique convergence and strong mechanical coupling between subducting and overriding plates however trench parallel motion is also observed in central costa rica where plate convergence is normal to the trench and in the nicaraguan fore arc where trench parallel motion is fast up to 9 mm a 1 but mechanical coupling is low a finite element model of collision as opposed to subduction involving the aseismic cocos ridge also fits the gps surface velocity field most significantly reproducing the pattern of trench parallel motion we infer that buoyant thickened cns 2 cocos ridge crust resists normal subduction and instead acts as an indenter to the caribbean plate driving crustal shortening in southern costa rica and contributing to trench parallel fore arc motion in costa rica and perhaps nicaragua as a type of tectonic escape

rupture processes of the 2012 september 5 mw 7 6 nicoya costa rica earthquake constrained by improved geodetic and seismological observations

large and primarily updip afterslip following the 2012 mw 7 6 nicoya costa rica earthquake we present detailed surface measurements of the first 3 5 years of postseismic deformation following the 5 september 2012 moment magnitude mw 7 6 nicoya costa rica earthquake the dominant signal in the first 2 5 years is uniform horizontal trenchward motion totaling 7 26 cm across 40 stations trenchward velocity is strongly diminished by mid 2014 and appears by 2016 to have begun reversing we invert the first 2 5 years to determine the corresponding afterslip on a detailed 3d interface results show significant afterslip both up and down dip of the main coseismic rupture zone with as much as 1 7 m of offset in two patches at 15 20 km depth and immediately up dip of the maximum coseismic slip this updip slip represents an important mechanism to address unrelieved interseismic locking although sufficient strain energy remains to generate up to a mw 7 1 event near the coastline the afterslip patches are anticorrelated with strongly clustered aftershocks at the same depth which is indicative of varying frictional behavior along strike an additional patch of slip is colocated with reoccurring slow slip events beneath the gulf of nicoya the magnitude of the observed slip however cannot be sufficiently explained by the known slow slip events ongoing measurements will be crucial to understanding the relocking process in nicoya

future cascadia megathrust rupture delineated by episodic tremor and slip 1 a suite of 15 episodic tremor and slip events imaged between 1997 and 2008 along the northern cascadia subduction zone suggests future coseismic rupture will extend to 25 km depth or 60 km inland of the pacific coast rather than stopping offshore at 15 km depth an ets derived coupling profile accurately predicts gps measured interseismic deformation of the overlying north american plate as measured by 50 continuous gps stations across western washington state when extrapolated over the 550 year average recurrence interval of cascadia megathrust events the coupling model also replicates the pattern and amplitude of coseismic coastal subsidence inferred from previous megathrust earthquakes here for only the washington state segment of the cascadia margin this translates into an mw 8 9 earthquake with significant moment release close to its metropolitan centers

persistent tremor within the northern costa rica seismogenic zone 1 we identify tremor using a spectral detection method and characterize its occurrence over a period of four years 2006 2009 in the vicinity of the nicoya peninsula costa rica although a few major tremor events accompanied by geodetic slow slip occur much of the tremor record consists of minor episodes with short duration and no detectable geodetic slip its persistent occurrence suggests that some portion of the interface is experiencing slow slip nearly continuously driving small patches to fail in accelerated slip locations indicate that much of the tremor occurs at shallow depth in freely slipping regions of the seismogenic zone this result is significant in that locations of slow slip and tremor at other subduction zones are largely limited to the downdip frictional transition tremor locations may help to refine the heterogeneous distribution of locked and freely slipping patches within the costa rica seismogenic zone

nicoya earthquake rupture anticipated by geodetic measurement of the locked plate interface part of the subduction zone plate interface beneath costa rica was previously locked which allowed strain to accumulate analyses using gps and geomorphic data show that almost the entire locked region ruptured during a megathrust quake in 2012 implying that plate interface mapping towards the end of the earthquake cycle can aid seismic hazard assessments

hydrologic control of forearc strength and seismicity in the costa rican subduction zone the subduction zone beneath costa rica experiences infrequent large earthquakes in its northwestern part whereas slow slip dominates in the southeast seismic data reveal a disparity in fluid accumulation in the overriding continental crust that correlates with this change in seismic behaviour implying that spatial gradients in fluid content may control subduction zone seismicity

remotely triggered nonvolcanic tremor in sumbawa indonesia we present for the first time evidence for triggered tremor beneath the island of sumbawa indonesia we show triggered tremor in response to three teleseismic earthquakes the mw9 0 2011 tohoku earthquake and two oceanic strike slip earthquakes mw 8 6 and mw8 2 offshore of sumatra in 2012 we constrain an apparent triggering threshold of 1 mm s ground velocity that corresponds to about 8 kpa dynamic stress peak tremor amplitudes of about 180 nm s are observed and scale with the ground velocity induced by the remote earthquakes triggered tremor responds to 45 65 s period surface waves and predominantly correlates with rayleigh waves even though the 2012 oceanic events have stronger love wave amplitudes we could not locate the tremor because of minimal station coverage but data indicate several potential source volumes including the flores thrust the java subduction zone or tambora volcano

a mixed seismic aseismic stress release episode in the andean subduction zone in subduction zones stress is released by earthquakes and transient aseismic slip the latter falls into two categories slow slip and afterslip slow slip events emerge spontaneously during the interseismic phase and show a progressive acceleration of slip with a negligible contribution of synchronous tremors or microseismicity to the energy or moment release1 2 3 4 5 6 7 8 9 10 11 12 in contrast afterslip occurs immediately after large and moderate earthquakes decelerates over time and releases between 20 and 400 of the moment released by the preceding earthquake13 14 15 16 17 18 here we use seismic and gps data to identify transient aseismic slip that does not fit into either of these categories we document a seismic aseismic slip sequence which occurred at shallow depths along a weakly coupled part of the andean subduction zone19 in northern peru and lasted seven months the sequence generated several moderate earthquakes that together account for about 25 of the total moment released during the full sequence equivalent to magnitude 6 7 transient slip immediately followed two of the earthquakes with slip slowing at a logarithmic rate considered separately the moment released by transient slip following the second earthquake was more than 1 000 of the moment released during the earthquake itself a value incompatible with classical models of afterslip synchronous seismic swarms and aseismic slip may therefore define a stress release process that is distinct from slow slip events and afterslip

slow slip and tremor search at kilauea volcano hawaii 1 kilauea volcano hawaii has hosted a long series of slow slip events observed since the installation of the continuous gps network in 1996 kilauea s slow slip events are inferred to occur on the decollement fault at 8 km depth beneath its south flank with a location updip of the epicenters of large regular earthquakes fault slip typically lasts about two days and the events have magnitudes equivalent to mw 5 3 6 0 while slow slip events in subduction zones are commonly accompanied by tectonic tremor also called nonvolcanic tremor no tremor has yet been reported in association with kilauea s slow slip events instead there are swarms of small triggered earthquakes which is a characteristic only seen at select subduction zones e g boso and hikurangi a temporary array of seismometers was installed at kilauea in 2007 in anticipation of a slow slip event here we use several established methods to perform a systematic search for tectonic tremor during geodetically defined slow slip events as well as searching for tremor triggered by teleseismic surface waves we do not detect tectonic tremor using any of these methods although we are able to detect episodes of previously identified deep offshore volcanic tremor at 15 20 km depth and volcanic tremor from kilauea although kilauea s seismic network may not be adequate to observe tectonic tremor because hawaii is seismically noisy and its crust is highly attenuating it is also possible that the specific fault conditions on kilauea s decollement are not conducive to such tremor generation

detailed spatiotemporal evolution of microseismicity and repeating earthquakes following the 2012 mw 7 6 nicoya earthquake we apply a waveform matching technique to obtain a detailed earthquake catalog around the rupture zone of the 5 september 2012 moment magnitude 7 6 nicoya earthquake with emphasis on its aftershock sequence starting from a preliminary catalog we relocate 7900 events using tomodd to better quantify their spatiotemporal behavior relocated aftershocks are mostly clustered in two groups the first is immediately above the major coseismic slip patch partially overlapping with shallow afterslip the second one is 50 km se to the main shock nucleation point and near the terminus of coseismic rupture in a zone that exhibited little resolvable afterslip using the relocated events as templates we scan through the continuous recording from 29 june 2012 to 30 december 2012 detecting approximately 17 times more than template events we find 190 aftershocks in the first half hour following the main shock mostly along the plate interface later events become more scattered in location showing moderate expansion in both along trench and downdip directions from the detected catalog we identify 53 repeating aftershock clusters with mean cross correlation values larger than 0 9 and indistinguishably intracluster event locations suggesting slip on the same fault patch most repeating clusters occurred within the first major aftershock group very few repeating clusters were found in the aftershock grouping along the southern edge of the peninsula which is not associated with substantial afterslip our observations suggest that loading from nearby afterslip along the plate interface drives spatiotemporal evolution of aftershocks just above the main shock rupture patch while aftershocks in the se group are to the se of the observed updip afterslip and poorly constrained

correlation of tremor activity with tidal stress in the northern cascadia subduction zone 1 we analyze hourly data from five tremor episodes in the northern cascadia subduction zone over the period 2003 2005 provided by the tremor activity monitoring system tams all five tremor episodes correspond to slow slip events observed by gps fourier decomposition is used to separate the hourly tremor counts for each episode into long period 0 2 2 cpd components the tidal component of the observations is compared with theoretical stress variations at depths of 20 30 and 40 km with 40 km being the depth of the interpreted subduction thrust interface the stress variations are predicted by a 2 d ocean tide loading model combined with estimates of stress variations from earth tides we find that the shear stress in the thrust direction and the compressive normal stress on shallow dipping surfaces correlates with the data significantly better than the confining stress over the range of depths investigated the relative amplitudes of tidal shear stress and compressive normal stress result in positive coulomb stress favoring slip peak tremor activity occurs at times of maximum tidal shear stress in the thrust direction which would assist slow slip and would suggest that tidal tremor and slip are colocated the response of the tremor to tidal shear stress is roughly proportional to the mean activity level controlled by tectonic conditions of stress and pore pressure a significant nontidal daily variation in tremor activity of unknown origin is identified

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

implications of a composite source model and seismic wave attenuation for the observed simplicity of small earthquakes and reported duration of earthquake initiation phase an examination of p waves recorded on near source velocity seismograms generally shows that most small earthquakes mw 2 to 3 are simple on the other hand larger earthquakes mw 4 are most often complex the simplicity of the seismograms of mw 2 to 3 events may reflect the simplicity of the source and hence may imply that smaller and larger earthquakes are not self similar or may be a consequence of attenuation of seismic waves to test whether the attenuation is the cause we generated synthetic p wave seismograms from a composite circular source model in which subevent rupture areas are assumed to follow a power law distribution the rupture of an event is assumed to initiate at a random point on the fault and to propagate with a uniform speed as the rupture front reaches the center of a subevent patch all of which are circular a p pulse is radiated that is calculated from the kinematic source model of sato and hirasawa 1973 synthetic p wave seismograms which are all complex are then convolved with an attenuation operator for different values of t the results show that the observed simplicity of small events mw 2 to 3 may be entirely explained by attenuation if t 0 02 sec the composite source model predicts that the average time delay between the initiation of the rupture and the rupture of the largest patch scales as m 1 3 such that log 1 3 log m 8 462 this relation is very similar to that reported by umeda et al 1996 between m and the observed time difference between the initiation of the rupture and the rupture of the bright spot it roughly agrees with the relation between m and the duration of the initiation phase reported by ellsworth and beroza 1995 and beroza and ellsworth 1996 the relation also fits surprisingly well the data on duration of slow initial phase t sip and m reported by iio 1995 one possible explanation of this agreement may be that the composite source model which is essentially the cascade model successfully captures the evolution of the earthquake source process and that the rupture initiation and the abrupt increase in the velocity amplitude observed on seismograms by previous researchers roughly corresponds to the rupture of the first subevent and the breaking of the largest subevent in the composite source model

nucleation phase and high speed rupture propagation of faulting at mt etna volcano southern italy a detailed analysis of microearthquake waveforms recorded at mt etna shows with some exceptions that first pulse of events with magnitude m 2 5 is consistent with the presence of a slow initial phase which precedes a phase of high speed rupture propagation this is in agreement with experimental results theoretical models and laboratory experiments which considered gradually increasing rupture velocity or slip in order to investigate the dependence of the pulse shapes on the azimuth we analyze recordings for six earthquakes m 2 7 3 7 with well constrained focal mechanisms computed by a high number of observations 21 27 for each earthquake we observe that the values of the slow phase duration tsip and those of the high speed rupture duration tris compared over the focal sphere exhibit a spatial distribution which seem to depend strictly on the type of rupture mechanism moreover waveforms of very closely located earthquakes do not exhibit similar characteristics in the pulse shapes which would exclude that the waveforms of analyzed earthquakes are influenced drastically by attenuation effects and that the slow initial phase is the result of the propagation path these and other evidence suggest that i the nucleation phases are mainly a source effect and ii directivity effects must be adequately considered on pulse width measurements

a global search for triggered tremor following the 2011 mw 9 0 tohoku earthquake abstract the 2011 m w 9 0 tohoku japan earthquake triggered deep tectonic tremor and shallow microearthquakes in numerous places worldwide here we conduct a systematic survey of triggered tremor in regions where ambient or triggered tremor has been previously identified tremor was triggered in the following regions south central alaska the aleutian arc shikoku in southwest japan the north island of new zealand southern oregon the parkfield cholame section of the san andreas fault in central california the san jacinto fault in southern california taiwan and vancouver island we find no evidence of triggered tremor in the calaveras fault in northern california one of the most important factors in controlling the triggering potential is the amplitude of the surface waves data examined in this study suggest that the threshold amplitude for triggering tremor is 0 1 cm s which is equivalent to a dynamic stress threshold of 10 kilopascals the incidence angles of the teleseismic surface waves also affect the triggering potentials of love and rayleigh waves the results of this study confirm that both love and rayleigh waves contribute to triggering tremor in many regions in regions where both ambient and triggered tremor are known to occur tremor triggered by the tohoku event generally occurred at similar locations with previously identified ambient and or triggered tremor further supporting the notion that although the driving forces of triggered and ambient tremor differ they share similar mechanisms we find a positive relationship between the amplitudes of the triggering waves and those of the triggered tremor which is consistent with the prediction of the clock advance model online material table of measured parameters and other information related to triggering nontriggering information and figures of observed seismograms

circum pacific seismic potential 1989 1999 the seismic potential for 96 segments of simple plate boundaries around the circum pacific region is presented in terms of the conditional probability for the occurrence of either large or great interplate earthquakes during the next 5 10 and 20 years i e 1989 1994 1989 1999 and 1989 2009 this study represents the first probabilistic summary of seismic potential on this scale and involves the comparison of plate boundary segments that exhibit varying recurrence times magnitudes and tectonic regimes presenting these data in a probabilistic framework provides a basis for the uniform comparison of seismic hazard between these differing fault segments as well as accounting for individual variations in recurrence time along a specific fault segment and uncertainties in the determination of the average recurrence time

seismic and aseismic slip on the central peru megathrust slip on a subduction megathrust can be seismic or aseismic with the two modes of slip complementing each other in time and space to accommodate the long term plate motions although slip is almost purely aseismic at depths greater than about 40 km heterogeneous surface strain suggests that both modes of slip occur at shallower depths with aseismic slip resulting from steady or transient creep in the interseismic and postseismic periods thus active faults seem to comprise areas that slip mostly during earthquakes and areas that mostly slip aseismically the size location and frequency of earthquakes that a megathrust can generate thus depend on where and when aseismic creep is taking place and what fraction of the long term slip rate it accounts for here we address this issue by focusing on the central peru megathrust we show that the pisco earthquake with moment magnitude m w 8 0 ruptured two asperities within a patch that had remained locked in the interseismic period and triggered aseismic frictional afterslip on two adjacent patches the most prominent patch of afterslip coincides with the subducting nazca ridge an area also characterized by low interseismic coupling which seems to have repeatedly acted as a barrier to seismic rupture propagation in the past the seismogenic portion of the megathrust thus appears to be composed of interfingering rate weakening and rate strengthening patches the rate strengthening patches contribute to a high proportion of aseismic slip and determine the extent and frequency of large interplate earthquakes aseismic slip accounts for as much as 50 70 of the slip budget on the seismogenic portion of the megathrust in central peru and the return period of earthquakes with m w 8 0 in the pisco area is estimated to be 250 years

seismogenic zone structure beneath the nicoya peninsula costa rica from three dimensional local earthquake p and s wave tomography the subduction plate interface along the nicoya peninsula costa rica generates damaging large mw 7 5 earthquakes we present hypocenters and 3 d seismic velocity models vp and vp vs calculated using simultaneous inversion of p and s wave arrival time data recorded from small magnitude local earthquakes to elucidate seismogenic zone structure in this region interseismic cycle microseismicity does not uniquely define the potential rupture extent of large earthquakes plate interface microseismicity extends from 12 to 26 and from 17 to 28 km below sea level beneath the southern and northern nicoya peninsula respectively microseismicity offset across the plate suture of east pacific rise derived and cocos nazca spreading center derived oceanic lithosphere is 5 km revising earlier estimates suggesting 10 km of offset interplate seismicity begins downdip of increased locking along the plate interface imaged using gps and a region of low vp along the plate interface the downdip edge of plate interface microseismicity occurs updip of the oceanic slab and continental moho intersection possibly due to the onset of ductile behaviour slow forearc mantle wedge p wave velocities suggest 20 30 per cent serpentinization across the nicoya peninsula region while calculated vp vs values suggest 0 10 per cent serpentinization interpretation of vp vs resolution at depth is complicated however due to ray path distribution we posit that the forearc mantle wedge is regionally serpentinized but may still be able to sustain rupture during the largest seismogenic zone earthquakes

automated detection and location of cascadia tremor 1 a new autonomous seismic location and detection methodology enables real time opportunities for high resolution spatio temporal monitoring of non volcanic tremor combining a unique cross correlation technique with epicenter clustering analysis in northern cascadia automatically yields thousands of tremor epicenters from the may 2008 episodic tremor and slip ets event while routinely detecting and locating inconspicuous inter ets tremor bursts although ets events in this area produce about two weeks of continuous tremor we find a nearly equal amount of tremor during the last 15 month inter ets period the resulting ets and inter ets epicenters occur in the slow slip region where the plate interface is 30 45 km deep and have a sharp well resolved updip boundary about 75 km east of the downdip edge of the seismogenic megathrust zone this ability to track tremor with high spatio temporal resolution facilitates automatic tremor monitoring and the mapping of the transition zone and regions of locked zone stress accumulation

an automatic monitoring system for nonvolcanic tremors in southwest japan 1 the recent development of a system for exchanging and distributing seismic waveform data over high speed networks enables seismic events to be monitored in real time throughout japan in the present study we have developed an automatic real time monitoring system for deep nonvolcanic tremors in southwest japan the system automatically detects the occurrence of nonvolcanic tremors and determines their hypocenters in real time in addition the system creates image files for the detected tremor activities and makes them accessible via the world wide web to detect tremors we carry out a two step numerical hypothesis test in which the first step is to test whether two given envelope seismograms are correlated and the second step is to test whether an event occurs using the results of the first test this two step test is applied to real time data every 2 min once an event is detected we can regard time lags that generate maximum cross correlations as the travel time differences which we use for hypocenter determination although this procedure detects nontremor signals most of them can be rejected using several criteria since the start of monitoring in 2006 the system has worked well for detecting a wide variety of tremor activities results from the present system will contribute to understanding the stress relaxation process in the transition zone between the locked and stable slip zones of the subducting philippine sea plate interface

quaternary uplift and seismic cycle deformation peninsula de nicoya costa rica differing rates and styles of quaternary deformation along the costa rican fore arc reflect segmentation of the trench corresponding with three contrasting domains of subducting sea floor offshore rapid upward flexure of the southern fore arc segment results from the subduction of the buoyant cocos ridge whereas moderate deformation along the central fore arc segment reflects the subduction of buoyant seamounts in contrast the northern costa rican fore arc deforms in response to the subduction of relatively dense sea floor devoid of major bathymetric anomalies quaternary geomorphic evidence and earthquake oral histories from the peninsula de nicoya within the northern costa rican fore arc demonstrate arcward tilting of the fore arc crust with discrete uplift events occurring during large subduction earthquakes uplift rates calculated from the late holocene cabuya terrace along the peninsula s trench perpendicular southeastern coast decrease systematically toward the arc from 4 5 m k y at cabuya to 1 7 m k y at montezuma 8 km to the northeast an uplifted carbonate beachrock horizon radiocarbon age 4500 5200 yr b p correlated between cabuya and montezuma is tilted 0 1 downward toward the arc although quaternary uplift is evident as far arcward as tambor 10 km northeast of montezuma uplifted terraces are absent between tambor and the golfo de nicoya a submerged archaeological site radiocarbon age 2500 yr b p located along the golfo de nicoya coast 30 km northeast of montezuma demonstrates late holocene subsidence of 0 5 m k y these data indicate net late holocene arcward tilting of the peninsula at an angular rotation rate of between 0 01 and 0 02 k y oral histories describing the m 7 7 nicoya subduction earthquake of 5 october 1950 provide evidence of seismic cycle deformation along the peninsula s southwestern coast between puerto carrillo and nosara interviews with 48 residents show that coseismic uplift of at least 1 m affected this coastline and that a significant fraction of this uplift has subsequently been reversed during four decades of gradual subsidence the coseismic deformation pattern estimated from a uniform slip dislocation model for the 1950 earthquake is consistent with both geomorphic and oral history evidence these observations suggest that seismic cycle deformation functions as an important mechanism of vertical tectonism within the costa rican fore arc arcward rotation and doming of the peninsula de nicoya during the quaternary may reflect repeated cycles of sudden coseismic deformation followed by gradual postseismic and or interseismic crustal movement

far field triggering of foreshocks near the nucleation zone of the 5 september 2012 m w 7 6 nicoya peninsula costa rica earthquake abstract on 5 september 2012 a moment magnitude mw 7 6 earthquake occurred directly beneath the nicoya peninsula an area with dense seismic and geodetic network coverage the mainshock ruptured a portion of a previously identified locked patch that was recognized due to a decade long effort to delineate the megathrust seismic and aseismic processes in this area here we conduct a comprehensive study of the seismicity prior to this event utilizing a matched filter analysis that allows us to decrease the magnitude of catalog completeness by 1 unit we observe a statistically significant increase in seismicity rate below the nicoya peninsula following the 27 august 2012 mw 7 3 el salvador earthquake about 450 km to the northwest and 9 days prior to the nicoya earthquake additionally we identify a cluster of small magnitude

tidal modulation of nonvolcanic tremor episodes of nonvolcanic tremor and accompanying slow slip recently have been observed in the subduction zones of japan and cascadia in cascadia such episodes typically last a few weeks and differ from normal earthquakes in their source location and moment duration scaling the three most recent episodes in the puget sound southern vancouver island portion of the cascadia subduction zone were exceptionally well recorded in each episode we saw clear pulsing of tremor activity with periods of 12 4 and 24 to 25 hours the same as the principal lunar and lunisolar tides this indicates that the small stresses associated with the solid earth and ocean tides influence the genesis of tremor much more effectively than they do the genesis of normal earthquakes because the lithostatic stresses are 10 5 times larger than those associated with the tides we argue that tremor occurs on very weak faults