rupture process of the 2011 tohoku oki mega thrust earthquake m9 0 inverted from strong motion data 1 we investigate the rupture process of the m9 0 tohoku oki mega thrust earthquake using the relatively low frequency strong motion records 0 01 0 125 hz observed at 36 k net and kik net stations the epicentral distances of which range from 120 km to 400 km the fault model is a rectangular plane the length and width of which are 510 km along the japan trench and 210 km along subducting direction of the pacific plate respectively we perform the multi time window inversion analysis with a 30 30 km2 subfault the derived slip model has one large slip area this area extends from the region around the hypocenter to the shallow part of the fault plane and further to the north and south along the trench axis located far off southern iwate miyagi and northern fukushima prefectures the seismic moment is 4 42 1022 nm mw 9 0 and the maximum slip is 48 m the slips near the coast are relatively small except off miyagi prefecture which experienced a slip greater than 5 m the shallow large slip area which continuously ruptured from 60 s to 100 s after the initial break radiated seismic waves rich in very low frequency content 0 02 hz the rupture after 100 s propagating to the southern fault area contributes to the distinct phases observed for fukushima and ibaraki prefectures the relationship between the proposed rupture model and the feature of the acceleration waveforms is not straightforward and suggests the frequency dependency of the seismic wave radiation

seismically active fold and thrust belt in the san joaquin valley central california structural analysis of late cenozoic folds along the western and southern margins of the san joaquin basin suggests that the folds are related to development of a fold and thrust belt rather than to wrench tectonics the folds have formed by the processes of fault bend folding and fault propagation folding which commonly occur in fold and thrust belts our structural interpretation attributes the seismically active coalinga and kettleman hills north dome anticlines to fault bend folding above a thrust fault s that steps up from a detachment within the franciscan assemblage to a detachment at the base of the great valley group this thrust does not reach the surface blind thrust and its slip is consumed in backthrusting and formation of subsurface folds under the san joaquin valley movement on the postulated thrust s would explain the cause of the may 2 1983 coalinga earthquake and the august 15 1985 avenal earthquake and would account for the lack of significant surface rupture or shallow subsurface faulting during both earthquakes well documented examples of fault bend and fault propagation folding also occur at wheeler ridge in the san emigdio mountains and at kettleman hills south dome deformation associated with fold and thrust belts can be extremely complicated considerable fault movement can occur without accompanying surface rupture or shallow level faulting conversely surface rupture can occur that has no direct relationship to fault slip at depth an example would be flexural slip folding wherein the slip planes reach the surface but do not root into any significant faults at depth consequently traditional geologic approaches to seismic risk evaluation which rely largely on surface data are subject to numerous pitfalls when applied to fold and thrust belts our interpretation of the structural style that developed in central california during the late cenozoic requires that the strain associated with the transpressive motion between the pacific and north american plates be resolved into normal and tangential components thrust faulting and folding normal to the plate boundary and strike slip faulting parallel to the plate boundary san andreas fault the thrust faults root in a deecollement at the brittle ductile transition zone above which shortening is associated with folding and thrust faulting and beneath which shortening in the lower crust is accommodated by ductile processes of tectonic thickening or incipient subduction

potential for larger earthquakes in the east san francisco bay area due to the direct connection between the hayward and calaveras faults the hayward and calaveras faults two strike slip faults of the san andreas system located in the east san francisco bay area are commonly considered independent structures for seismic hazard assessment we use interferometric synthetic aperture radar to show that surface creep on the hayward fault continues 15 km farther south than previously known revealing new potential for rupture and damage south of fremont the extended trace of the hayward fault also illuminated by shallow repeating micro earthquakes documents a surface connection with the calaveras fault at depths greater than 3 5 km repeating micro earthquakes located 10 km north of the surface connection highlight the 3 d wedge geometry of the junction our new model of the hayward and calaveras faults argues that they should be treated as a single system with potential for earthquake ruptures generating events with magnitudes greater than 7 posing a higher seismic hazard to the east san francisco bay area than previously considered

very low frequency earthquakes related to small asperities on the plate boundary interface at the locked to aseismic transition 1 very low frequency vlf seismic signals observed in southwestern japan are evidently radiated from shear slips on the upper surface of the subducting philippine sea plate we used grid moment tensor inversion and centroid moment tensor inversion to calculate 242 moment tensor solutions with moment magnitudes between 3 1 and 3 8 from continuous seismograms recorded over a 5 year period by using a very dense broadband seismic network at least 5 10 sequences of repetitive activity were observed during the 5 years the vlf events formed clustered distributions along the 35 km isodepth contour of the subducting plate surface the nodal planes which dip landward of moment tensor solutions of the vlf events reflected the configuration of the subducting plate interface the slip vectors were consistent with the direction of movement of the subducting plate the dip and strike of the slip vectors clearly reflected the configuration of the upper surface of the subducting plate we found that the rates of seismic moment release per unit area associated with five major vlf clusters were very similar although both the seismic magnitudes and sizes of the clusters varied considerably the rate of seismic moment released from detectable vlf sources was 0 1 of the rates of short term slow slip events suggesting that the source areas occupied only 0 1 of the fault segment on which the short term slow slip events occurred

block kinematics of the pacific north america plate boundary in the southwestern united states from inversion of gps seismological and geologic data 1 the active deformation of the southwestern united states 30 41 n is represented by a finite number of rotating elastic plastic spherical caps gps derived horizontal velocities geologic fault slip rates transform fault azimuths and earthquake derived fault slip vector azimuths are inverted for block angular velocities creep on block bounding faults permanent strain rates within the blocks and the rotations of 11 published gps velocity fields into to a common north american reference frame gps velocities are considered to be a combination of rigid block rotations recoverable elastic strain rates resulting from friction on block bounding faults and nonrecoverable strain rates resulting from slip on faults within the blocks the resulting pacific north america angular velocity is similar to some published estimates and satisfies transform azimuths and one spreading rate in the gulf of california earthquake slip vectors in the gulf of california and alaska and gps velocities along coastal california and within the pacific basin published fault slip rates are satisfied except in the southern mojave desert where the motion of the mohave block relative to north america is faster than can be explained by mapped faults the largest blocks the sierra nevada great valley and the eastern basin and range show permanent strain rates after removing elastic strain of only a few nanostrain per year demonstrating approximately rigid behavior observed horizontal strain rates correlate strongly with predicted strain rates from known faults suggesting that the short term strains evident in gps velocities are largely elastic in only about 20 of the region is distributed deformation needed to match the data indicating that a plate tectonic style description of the deformation of the western united states is plausible most blocks rotate about vertical axes at approximately the same rate as the pacific relative to north america suggesting that locally spin rates are communicated from block to block arguing against both floating block and ball bearing mechanisms of block rotation the similarities of the blocks spin rates to that of the pacific suggests that the pacific strongly influences their motions through edge tractions however it is shown that the blocks cannot rotate about the pacific north america pole without spinning counter to the sense of pacific north america shear unlike some other broad plate boundaries in the western united states vertical axis rotations take up very little of the slip rate budget across the region

recurring and triggered slow slip events near the trench at the nankai trough subduction megathrust the discovery of slow earthquakes has revolutionized the field of earthquake seismology defining the locations of these events and the conditions that favor their occurrence provides important insights into the slip behavior of tectonic faults we report on a family of recurring slow slip events sses on the plate interface immediately seaward of repeated historical moment magnitude mw 8 earthquake rupture areas offshore of japan the sses continue for days to several weeks include both spontaneous and triggered slip recur every 8 to 15 months and are accompanied by swarms of low frequency tremors we can explain the sses with 1 to 4 centimeters of slip along the megathrust centered 25 to 35 kilometers km from the trench 4 to 10 km depth the sses accommodate 30 to 55 of the plate motion indicating frequent release of accumulated strain near the trench

very low frequency earthquakes along the ryukyu subduction zone 1 a total of 1314 very low frequency earthquakes vlfes were identified along the ryukyu trench from seismograms recorded at broadband networks in japan f net and taiwan bats in 2007 the spectra of typical vlfes have peak frequencies between 0 02 to 0 1 hz among those waveforms from 120 vlfes were inverted to obtain their centoroid moment tensor cmt solutions and locations using an examination grid to minimize a residual between the observed and synthetic waveforms within an area of 11 14 in latitude and longitude and at depths of 0 to 60 km most of the vlfes occur on shallow thrust faults that are distributed along the ryukyu trench which are similar to those earthquakes found in honshu and hokkaido japan the locations and mechanisms of vlfes may be indicative of coupled regions within the accretionary prism or at the plate interface this study highlights the need for further investigation of the ryukyu trench to identify coupled regions within it

very low frequency earthquakes off the pacific coast of tohoku japan we found very low frequency earthquakes vlfes at a shallow subduction zone close to the japan trench off the pacific coast of tohoku japan centroid moment tensor solutions of vlfes showed reverse fault mechanisms with a compression axis in the east west direction a cross correlation analysis of seismograms with template events between 2005 and 2013 revealed three major vlfe clusters and their temporal evolution a vlfe cluster in the central off tohoku region located in the large slip area of the 2011 tohoku earthquake was detectable only before the tohoku earthquake however vlfes in the northern and southern off tohoku regions at the rim of the large slip area were activated after the tohoku earthquake the change in the activity may reflect the stress redistribution by the coseismic and or afterslip processes of the tohoku earthquake

nied seismic moment tensor catalogue for regional earthquakes around japan quality test and application abstract we have examined the quality of the national research institute for earth science and disaster prevention nied seismic moment tensor mt catalogue obtained using a regional broadband seismic network freesia first we examined using synthetic waveforms the robustness of the solutions with regard to data noise as well as to errors in the velocity structure and focal location then to estimate the reliability robustness and validity of the catalogue we compared it with the harvard centroid moment tensor cmt catalogue as well as the japan meteorological agency jma focal mechanism catalogue we found out that the nied catalogue is consistent with harvard and jma catalogues within the uncertainty of 0 1 in moment magnitude 10 km in depth and 15 in direction of the stress axes the nied mt catalogue succeeded in reducing to 3 5 the lower limit of moment magnitude above which the moment tensor could be reliably estimated finally we estimated the stress tensors in several different regions by using the nied mt catalogue this enables us to elucidate the stress deformation field in and around the japanese islands to understand the mode of deformation and applied stress moreover we identified a region of abnormal stress in a swarm area from stress tensor estimates

very low frequency earthquakes within accretionary prisms are very low stress drop earthquakes 1 we report characteristic p wave spectra and stress drops of very low frequency vlf earthquakes that occurred within the accretionary prism along the nankai trough southwestern japan although many vlf earthquakes showed no distinct phases on a raw seismogram a few showed slightly distinct phases the arrival times of some phases were consistent with the calculated p wave arrival times the corner frequencies of the vlf earthquakes were calculated using the stacked p wave spectra assuming an omega square spectrum stress drops were very low i e in the range of 0 1 10 kpa which corresponds to 0 1 1 of those of ordinary earthquakes such extremely low stress drops of the vlf earthquakes suggest that the fault strength within the accretionary prism may have weakened due to the existence of a fluid within the thrust fault system of the accretionary prism

coseismic slip distribution of the 2011 off the pacific coast of tohoku earthquake m9 0 refined by means of seafloor geodetic data 1 on 11 march 2011 the devastating m9 0 tohoku earthquake occurred on the interface of the subducting pacific plate and was followed by a huge tsunami that killed about 20 000 people several geophysical studies have already suggested that the very shallow portion of the plate interface might have played an important role in producing such a large earthquake and tsunami however the sparsity of seafloor observations leads to insufficient spatial resolution of the fault slip on such a shallow plate interface for this reason the location and degree of the slip has not yet been estimated accurately enough to assess future seismic risks thus we estimated the coseismic slip distribution based on terrestrial gps observations and all available seafloor geodetic data that significantly improve the spatial resolution at the shallow portion of the plate interface the results reveal that an extremely large greater than 50 m slip occurred in a small about 40 km in width and 120 km in length area near the japan trench and generated the huge tsunami the estimated slip distribution and a comparison of it with the coupling coefficient distribution deduced from the analysis of the small repeating earthquakes suggest that the 2011 tohoku earthquake released strain energy that had accumulated over the past 1000 years probably since the jogan earthquake in 869 the accurate assessments of seismic risks on very shallow plate interfaces in subduction zones throughout the world can be obtained by improving the quality and quantity of seafloor geodetic observations

along strike translation of a fossil slab abstract the isabella anomaly is a high seismic velocity anomaly beneath the southern central valley of california that has previously been interpreted to represent a lithospheric drip or delaminated sierra nevada root however recent work suggests that the anomaly is a remnant slab left over from cenozoic subduction attached to the pacific plate underneath the edge of the north american plate this hypothesis requires the slab to translate hundreds of kilometers along strike while remaining intact and attached to the pacific plate despite drag from the surrounding asthenosphere and overriding lithosphere we use 3 d finite element models to simulate this scenario and calculate the viscosity ratio between the slab and the surrounding asthenosphere required for the slab to translate undeformed the required viscosity ratio increases with increasing downdip extent of the slab and decreases with increasing slab dip for geometries approximating that of our proposed slab the required ratio ranges from 10 2 to 10 4 given the thermal and petrologic history of the slab mantle flow laws predict viscosity contrasts greater than or equal to these requirements as such we conclude that along strike translation of a remnant slab is feasible and serves as a possible explanation of the isabella anomaly the significance of this finding extends beyond our general understanding of subduction dynamics in that the presence of such a slab could have implications for the water budget of the san andreas fault and its role in aseismic slip

very low frequency earthquakes spatiotemporally asynchronous with strong tremor during the 2014 episodic tremor and slip event in cascadia we find very low frequency earthquakes vlfes in cascadia during the 2014 episodic tremor and slip event under washington and vancouver island using a grid search centroid moment tensor inversion method the very low frequency earthquakes occur when and where there is no strong tremor detected contrasting with previous findings where tremor and very low frequency earthquakes have a clear spatiotemporal relationship this challenges our current understanding of the dynamic relationship between the different types of slow earthquakes and their relationship to slow slip we interpret these findings to suggest that vlfes and tremor may have their own seismic cycles resulting from asperities of different sizes or characteristics that respond pseudo independently to stress loading we propose that very low frequency earthquakes and tremor are subject to asynchronous seismic cycles

palaeoredox conditions and sequence stratigraphy of the cretaceous storm dominated mixed siliciclastic carbonate ramp in the eastern cordillera basin colombia evidence from sedimentary geochemical proxies and facies analysis abstract the cretaceous black shales of colombia are among the most important successions in the north of south america and have attracted the attention of many geoscientists and exploration companies over the last few decades because of their high hydrocarbon potential and the presence of emerald deposits however many uncertainties still remain with regard to their tectonic setting sequence stratigraphy depositional environments palaeoxygenation conditions and organic matter preservation in order to develop a more integrated picture of these different processes and conditions we conducted a detailed sedimentological inorganic geochemical u v ni zn mn fe ti mo cu cr cd ba and sequence stratigraphic analysis of the cretaceous black shales in the magdalena tablazo sub basin eastern cordillera basin of colombia eleven lithofacies and five lithofacies associations of a storm dominated siliciclastic carbonate ramp were identified which range from basin to shallow inner ramp environments these facies were grouped into six third order stratigraphic sequences showing high order cycles of marine transgression with constrained regressive pulses during the late valanginian to early coniacian the black shales succession represents deposition under anoxic bottom water with some intervals representing dysoxic suboxic conditions the evolution of the sedimentary environments and their palaeoxygenation history reflect tectonic and eustatic sea level controls that 1 produced a variable orientation and position of the coastline throughout the cretaceous 2 conditioned the low gradient ramp geometry

the synchronous occurrence of shallow tremor and very low frequency earthquakes offshore of the nicoya peninsula costa rica 1 the occurrence of transient shallow slow slip at seismogenic zones has important implications for earthquake and tsunami hazards here we provide evidence that a tremor and slow slip event occurred at shallow depth offshore of the nicoya peninsula costa rica in august 2008 the temporal coincidence of offshore tremor very low frequency earthquakes vlfes motions consistent with slow slip on the plate interface on western coastal gps stations and a pressure transient in an iodp borehole all indicate slow slip occurring at shallow depths large ocean loading stresses on the shallow plate interface modulate tremor activity with the peak coulomb stress forced by semi diurnal ocean tides correlating with tremor productivity based on beamforming data we constrain that the vlfe activity occurs in the same region as the tremor and slow slip the presence of slow slip at shallow depth has important implications for the up dip extent of earthquake rupture the proximity of the 5 september 2012 mw 7 6 megathrust earthquake to slow slip tremor and vlfe activity in the 2008 event suggests abrupt frictional transitions from locked to conditionally stable behavior on the plate interface offshore of the nicoya peninsula

constraining the kinematics of metropolitan los angeles faults with a slip partitioning model due to the limited resolution at depth of geodetic and other geophysical data the geometry and the loading rate of the ramp decollement faults below the metropolitan los angeles are poorly understood here we complement these data by assuming conservation of motion across the big bend of the san andreas fault using a bayesian approach we constrain the geometry of the ramp decollement system from the mojave block to los angeles and propose a partitioning of the convergence with 25 5 0 5 mm yr and 3 1 0 6 mm yr of strike slip motion along the san andreas fault and the whittier fault with 2 7 0 9 mm yr and 2 5 1 0 mm yr of updip movement along the sierra madre and the puente hills thrusts incorporating conservation of motion in geodetic models of strain accumulation reduces the number of free parameters and constitutes a useful methodology to estimate the tectonic loading and seismic potential of buried fault networks

an elusive blind thrust fault beneath metropolitan los angeles seismic reflection profiles petroleum wells and relocated earthquakes reveal the presence of an active blind thrust fault beneath metropolitan los angeles a segment of this fault likely caused the 1987 whittier narrows magnitude 6 0 earthquake mapped sizes of other fault segments suggest that the system is capable of much larger magnitude 6 5 to 7 and more destructive earthquakes

evidence for large earthquakes in metropolitan los angeles the sierra madre fault along the southern flank of the san gabriel mountains in the los angeles region has failed in magnitude 7 2 to 7 6 events at least twice in the past 15 000 years restoration of slip on the fault indicated a minimum of about 4 0 meters of slip from the most recent earthquake and suggests a total cumulative slip of about 10 5 meters for the past two prehistoric earthquakes large surface displacements and strong ground motions resulting from greater than magnitude 7 earthquakes within the los angeles region are not yet considered in most seismic hazard and risk assessments

anomalous deepening of a seismic belt in the upper plane of the double seismic zone in the pacific slab beneath the hokkaido corner possible evidence for thermal shielding caused by subducted forearc crust materials abstract hypocenter relocations of earthquakes in the pacific slab have shown an anomalous deepening of a seismic belt in the upper plane of the double seismic zone at depths of 80 120 km beneath the hokkaido corner while it is located at depths of 70 90 km in the surrounding tohoku and eastern hokkaido areas seismic tomographic inversions performed beneath the hokkaido corner have shown that a low velocity zone having seismic velocities of crust materials exists in the mantle wedge just above the pacific slab and makes direct contact with the upper surface of the pacific slab these observations suggest that 1 the low velocity zone just above the pacific slab is part of the subducted kuril forearc sliver 2 the contact with the subducted and so relatively cold sliver materials prevents the mantle wedge from heating the pacific slab and causes a lower temperature condition in the pacific slab crust beneath the hokkaido corner than in the surrounding areas 3 as a result a delay of eclogite forming phase transformations occurs and enhances the local deepening of the seismic belt in the slab crust there

millimeter scale tsunami detected by a wide and dense observation array in the deep ocean fault modeling of an mw 6 0 interplate earthquake off sanriku ne japan

quasi static slip on the plate boundary associated with the 2003 m8 0 tokachi oki and 2004 m7 1 off kushiro earthquakes japan abstract we analyzed small repeating earthquakes recorded over a 13 year period and gps data recorded over an 8 month period to estimate interplate quasi static slip associated with the 2003 tokachi oki earthquake m8 0 and the 2004 off kushiro earthquake m7 1 the repeating earthquake analysis revealed that the slip rate near the source region of the tokachi oki earthquake was relatively low

seismotectonics beneath the tokyo metropolitan area japan effect of slab slab contact and overlap on seismicity 1 we first determine the configuration of the upper surface of the pacific pac slab beneath kanto japan from the distribution of interplate earthquakes relocated by an appropriate 1 d velocity model then traveltime tomography is carried out to estimate three dimensional seismic velocity structures around kanto using 735 520 p wave and 444 049 s wave arrival times from 6508 local earthquakes the obtained results suggest that the philippine sea phs slab is subducting to depths of 130 140 km without a gap even to the northwest of the izu collision zone we subsequently define the lateral extent of the contact zone between the bottom of the phs slab and the upper surface of the pac slab phs pac interface and reveal that the slab contact zone underlies a wider area beneath kanto in harmony with the kanto plain the downdip limit of interplate thrust type earthquakes on the pac slab is deepened by 30 km locally under the slab contact zone this deepening is probably caused by a lower temperature environment in the pac slab resulting from the overlap with the phs slab subducting above and consequent thermal shielding by the phs slab from the hot mantle wedge we detect an extremely low velocity anomaly in the easternmost portion of the phs slab which is probably attributable to serpentinization of mantle peridotite interplate earthquakes are almost absent along the phs pac interface overlain by the serpentinized mantle in the phs slab suggesting that ductile deformation takes place along the interface because of low viscosity of the serpentine

interseismic strain accumulation and anthropogenic motion in metropolitan los angeles 1 we use global positioning system gps geodesy and synthetic aperture radar sar interferometry to distinguish between interseismic strain accumulation and anthropogenic motion in metropolitan los angeles we establish a relationship between horizontal and vertical seasonal oscillations of the santa ana aquifer use this relationship to infer cumulative horizontal anthropogenic motions from cumulative vertical motions caused by water and oil resource management and estimate horizontal interseismic velocities corrected for anthropogenic effects vertical anthropogenic rates from 1992 to 1999 are slower than 3 mm yr 1 in the santa ana and san gabriel aquifers and faster than 5 mm yr 1 in the chino aquifer and in many oil fields inferred horizontal anthropogenic velocities are faster than 1 mm yr 1 at 18 of 46 gps sites northern metropolitan los angeles is contracting with the 25 km south of the san gabriel mountains shortening at 4 5 1 mm yr 1 95 confidence limits the thrust fault in an elastic edge dislocation model of the observed strain is creeping at 9 2 mm yr 1 beneath and north of a position 6 2 km deep and 8 8 km north of downtown los angeles the model fault is near the los angeles segment of the puente hills thrust but south of the sante fe springs segment of the thrust disagreement between the 6 km locking depth in the model and the 15 km seismogenic depth inferred from earthquakes suggests that the elastic continuum model may be unsatisfactory models with different stiffnesses of sedimentary basin and crystalline basement must be investigated

complexities of the san andreas fault near san gorgonio pass implications for large earthquakes 1 geologic relationships and patterns of crustal seismicity constrain the three dimensional geometry of the active portions of san andreas fault zone near san gorgonio pass southern california within a 20 km wide contractional stepover between two segments of the fault zone the san bernardino and coachella valley segments folds and dextral reverse and dextral normal faults form an east west belt of active structures the dominant active structure within the stepover is the san gorgonio pass garnet hill faults a dextral reverse fault system that dips moderately northward within the hanging wall block of the san gorgonio pass garnet hill fault system are subsidiary active dextral and dextral normal faults these faults relate in complex but understandable ways to the strike slip faults that bound the stepover the pattern of crustal seismicity beneath these structures includes a 5 8 km high east west striking step in the base of crustal seismicity which corresponds to the downdip limit of rupture of the 1986 north palm springs earthquake we infer that this step has been produced by slip on the linked san gorgonio pass garnet hill coachella valley banning sgp gh cvb fault this association enables us to construct a structure contour map of the fault plane the large step in the base of seismicity downdip from the sgp gh cvb fault system probably reflects a several kilometers offset of the midcrustal brittle plastic transition u th he thermochronometry supports our interpretation that this south under north thickening of the crust has created the region s 3 km of topographic relief we conclude that future large earthquakes generated along the san andreas fault in this region will have a multiplicity of mostly specifiable sources having dimensions of 1 20 km two tasks in seismic hazard evaluation may now be attempted with greater confidence first the construction of synthetic seismograms that make useful predictions of ground shaking and second theoretical investigations of the role of this complexity in retarding the propagation of future seismic ruptures

very low frequency earthquakes in cascadia migrate with tremor we find very low frequency earthquakes vlfes in cascadia under northern washington during 2011 episodic tremor and slip event vlfes are rich in low frequency energy 20 50 s and depleted in higher frequencies higher than 1 hz compared to local earthquakes based on a grid search centroid moment tensor inversion we find that vlfes are located near the plate interface in the zone where tremor and slow slip are observed in addition they migrate along strike with tremor activity their moment tensor solutions show double couple sources with shallow thrust mechanisms consistent with shear slip at the plate interface their magnitude ranges between mw 3 3 and 3 7 seismic moment released by a single vlfe is comparable to the total cumulative moment released by tremor activity during an entire episodic tremor and slip event the vlfes contribute more seismic moment to this episodic tremor and slip event than cumulative tremor activity and indicate a higher seismic efficiency of slow earthquakes in cascadia than previously thought spatiotemporal correlation of vlfe and tremor activity suggests that they are the results of the same physical processes governing slow earthquakes

fossil slabs attached to unsubducted fragments of the farallon plate as the pacific farallon spreading center approached north america the farallon plate fragmented into a number of small plates some of the microplate fragments ceased subducting before the spreading center reached the trench most tectonic models have assumed that the subducting oceanic slab detached from these microplates close to the trench but recent seismic tomography studies have revealed a high velocity anomaly beneath baja california that appears to be a fossil slab still attached to the guadalupe and magdalena microplates here using surface wave tomography we establish the lateral extent of this fossil slab and show that it is correlated with the distribution of high mg andesites thought to derive from partial melting of the subducted oceanic crust we also reinterpret the high seismic velocity anomaly beneath the southern central valley of california as another fossil slab extending to a depth of 200 km or more that is attached to the former monterey microplate the existence of these fossil slabs may force a reexamination of models of the tectonic evolution of western north america over the last 30 my

dynamic deformation of the accretionary prism excites very low frequency earthquakes 1 we have detected anomalous very low frequency earthquakes within the accretionary prism along the nankai trough southwestern japan centroid moment tensor inversion analysis reveals that the earthquake hypocenters are distributed at 10 km depth above the upper surface of the subducting philippine sea plate and within 50 70 km landward of the trough axis the focal mechanisms indicate reverse faulting their hypocenters are distributed beneath a deformation zone of an accretionary prism in sea floor topography these observations suggest that the occurrence of very low frequency earthquakes is related to numerous reverse fault systems within the accretionary prism and that the earthquakes reflect the dynamics of deformation within this accretionary prism

periodic slow slip triggers megathrust zone earthquakes in northeastern japan both aseismic and seismic slip accommodate relative motion across partially coupled plate boundary faults in northeastern japan aseismic slip occurs in the form of decelerating afterslip after large interplate earthquakes and as relatively steady slip on uncoupled areas of the subduction thrust here we report on a previously unrecognized quasi periodic slow slip behavior that is widespread in the megathrust zone the repeat intervals of the slow slip range from 1 to 6 years and often coincide with or precede clusters of large magnitude m 5 earthquakes including the 2011 m 9 tohoku oki earthquake these results suggest that inherently periodic slow slip events result in periodic stress perturbations and modulate the occurrence time of larger earthquakes the periodicity in the slow slip rate has the potential to help refine time dependent earthquake forecasts

possible shallow slow slip events in hyuga nada nankai subduction zone inferred from migration of very low frequency earthquakes we investigated the spatiotemporal evolution of a shallow very low frequency earthquake svlfe swarm linked to the 2009 2010 long term slow slip event sse in the bungo channel southwestern japan broadband seismograms were analyzed using a cross correlation technique to detect svlfes having similar waveforms to template svlfes and their relative locations were estimated the svlfes exhibit clear migration over a distance of 150 km along the nankai trough similar to nonvolcanic tremors and deep very low frequency earthquakes dvlfes accompanied by short term sses on the downward extension of the seismogenic zone this similarity between svlfes and dvlfes suggests that sses occur in both deeper and shallower extensions of the seismogenic zone the analyzed svlfes were likely caused by a shallow sse that occurred from january to march 2010 following the initiation and acceleration of the long term sse this temporal evolution may be caused by stress interaction between the shallow sse and the long term sse

escape tectonics in the los angeles metropolitan region and implications for seismic risk recent damaging earthquakes in california including the 1971 san fernando1 1983 coalinga2 1987 whittier narrows3 and 1994 northridge4 events have drawn attention to thrust faults as both potentially hazardous seismic sources and as a mechanism for accommodating shortening in many regions of southern california consequently many geological studies5 6 have concluded that thrust faults in southern california pose the greatest seismic hazard and also account for most of the estimated 5 7 mm yr 1 of contraction across the greater los angeles metropolitan area7 8 indicated by global positioning system geodetic measurements9 our study demonstrates however that less than 50 of the geodetically observed contraction is accommodated on the principal thrust systems across the los angeles region we integrate the most recent geological geodetic and seismological data to assess the spatial distribution of strain across the los angeles metropolitan region we then demonstrate that a significant component of seismic moment release and shortening in this region is accommodated by east west crustal escape extrusion along known strike slip and oblique slip faults

pre and postseismic slow slip surrounding the 2011 tohoku oki earthquake rupture abstract slow aseismic slip that accommodates part of the long term plate motion on subduction megathrusts is thought to be strongly related to the occurrence of large earthquakes on the same fault zone however the temporal evolution and spatial distribution of the aseismic slip before major earthquakes and of accelerated postseismic afterslip are largely unconstrained we estimate cumulative offsets of small repeating earthquakes that are interpreted to reflect the in situ aseismic slip history on the subduction zone offshore northeastern japan these data reveal contrasting aseismic slip patterns between the coseismic rupture area of the mw 9 0 tohoku oki earthquake and surrounding portions of the subduction thrust the rupture area is characterised by low and variable slip rates before 2008 and the slip stopped almost completely after the earthquake the region surrounding the rupture area exhibited higher aseismic fault slip rates before the earthquake and clear postseismic slip of up to 1 6 m within 9 months following the main shock the frictional fault properties and complete relief of ambient stress in the central rupture zone of the main shock probably control the observed distribution the postseismic slip shows a more abrupt increase in the region closer to the source suggesting outwards propagation of afterslip small but distinct increases in the slip rate in the 3 yr before the earthquake near the area of large coseismic slip suggests preseismic unfastening of the locked area in the last stage of the earthquake cycle

slow earthquakes coincident with episodic tremors and slow slip events we report on the very low frequency earthquakes occurring in the transition zone of the subducting plate interface along the nankai subduction zone in southwest japan seismic waves generated by very low frequency earthquakes with seismic moment magnitudes of 3 1 to 3 5 predominantly show a long period of about 20 seconds the seismicity of very low frequency earthquakes accompanies and migrates with the activity of deep low frequency tremors and slow slip events the coincidence of these three phenomena improves the detection and characterization of slow earthquakes which are thought to increase the stress on updip megathrust earthquake rupture zones

is there a discrepancy between geological and geodetic slip rates along the san andreas fault system previous inversions for slip rate along the san andreas fault system safs based on elastic half space models show a discrepancy between the geologic and geodetic slip rates along a few major fault segments in this study we use an earthquake cycle model representing an elastic plate over a viscoelastic half space to demonstrate that there is no significant discrepancy between long term geologic and geodetic slip rates the california statewide model includes 41 major fault segments having steady slip from the base of the locked zone to the base of the elastic plate and episodic shallow slip based on known historical ruptures and geologic recurrence intervals the slip rates are constrained by 1981 secular velocity measurements from gps and l band intereferometric synthetic aperture radar a model with a thick elastic layer 60 km and half space viscosity of 1019pa s is preferred because it produces the smallest misfit to both the geologic and the geodetic data we find that the geodetic slip rates from the thick plate model agrees to within the bounds of the geologic slip rates while the rates from the elastic half space model disagree on specific important fault segments such as the mojave and the north coast segment of the san andreas fault the viscoelastic earthquake cycle models have generally higher slip rates than the half space model because most of the faults along the safs are late in the earthquake cycle so today they are moving slower than the long term cycle averaged velocity as governed by the viscoelastic relaxation process

activation of very low frequency earthquakes by slow slip events in the ryukyu trench long term activity of shallow very low frequency earthquakes vlfes in the ryukyu trench unassociated with recent large thrust earthquakes was analyzed using a broadband seismometer network the distribution of shallow vlfes was divided into three large clusters the activity of the vlfes is modulated by repetitive slow slip events and the activity of these vlfes increases to 2 3 times its ordinary rate at 10 20 days after the onset of the slow slip events the activation of vlfes could be generated by small increases on the order of approximately 0 1 0 5 kpa in coulomb failure stress suggesting that stress in the plate interface where the vlfes occur is frequently released in small amounts moreover the distribution of vlfes is complementary to the historical tsunami source area and locked area the distribution of the vlfes indicates heterogeneity in interplate coupling along the trench

high resolution interseismic velocity data along the san andreas fault from gps and insar 1 we compared four interseismic velocity models of the san andreas fault based on gps observations the standard deviations of the predicted secular velocity from the four models are larger north of the san francisco bay area near the creeping segment in central california and along the san jacinto fault and the east california shear zone in southern california a coherence spectrum analysis of the secular velocity fields indicates relatively high correlation among the four models at longer wavelengths 15 40 km with lower correlation at shorter wavelengths to improve the short wavelength accuracy of the interseismic velocity model we integrated interferometric synthetic aperture radar insar observations initially from advanced land observing satellite alos ascending data spanning from the middle of 2006 to the end of 2010 totaling more than 1100 interferograms with gps observations using a sum remove filter restore approach the final insar line of sight data match the point gps observations with a mean absolute deviation of 1 5 mm yr we systematically evaluated the fault creep rates along major faults of the san andreas fault and compared them with creepmeters and alignment array data compiled in uniform california earthquake rupture forecast version 2 ucerf2 moreover this insar line of sight dataset can constrain rapid velocity gradients near the faults which are critical for understanding the along strike variations in stress accumulation rate and associated earthquake hazard

slip along the san andreas fault associated with the great 1857 earthquake historical records indicate that several meters of lateral slip along the san andreas fault accompanied the great 1857 earthquake in central and southern california these records together with dendrochronological evidence suggest that the rupture occurred along 360 to 400 km of the fault including several tens of kilometers of the currently creeping reach in central california geomorphic expressions of late holocene right lateral offsets are abundant along the 1857 rupture along 300 kilometers of the 1857 rupture between cholame and wrightwood the youngest discernible offset ranges from 3 to 9 1 2 meters dormancy of the fault since 1857 almost certainly indicates that this latest offset was created in 1857 fault slip apparently associated with the 1857 earthquake varies in a broadly systematic way along the trace of the fault it is relatively uniform along each of several long segments but changes rather abruptly in value between these segments this nonuniform displacement pattern may imply that some segments of the fault rupture more frequently or experience a slower long term slip rate than others the 1857 offsets indicate a seismic moment m o between 5 3 and 8 7 10 27 dyne cm assuming a 10 to 15 km depth of rupture and relatively uniform slip as a function of depth a comparison with the rupture length average slip value and tectonic setting of the california earthquake of 1906 m s 8 1 4 indicates a value of m 8 1 4 for the 1857 event

fault slip rates at depth from recurrence intervals of repeating microearthquakes unique attributes in sequences of recurring similar microearthquakes at parkfield california provide a means for inferring slip rate at depth throughout the active fault surface from the time intervals between sequence events application of the method using an 11 year microseismicity record revealed systematic spatial and temporal changes in the slip rate that were synchronous with earthquake activity and other independent measures of fault zone slip if this phenomenon is found to be generally common behavior in active faults it forms the basis for a method to monitor the changing strain field throughout a seismogenic fault zone

a cross section of the los angeles area seismically active fold and thrust belt the 1987 whittier narrows earthquake and earthquake hazard retrodeformable cross sections across the los angeles area interpret the pliocene to quaternary deformation to be a developing basement involved fold and thrust belt the fold and thrust belt is seismically active as evidenced by the 1987 whittier narrows earthquake ml 5 9 and the 1971 san fernando earthquake mw 6 6 the structural geology of the los angeles area is dominated by three major compressional uplift trends 1 the palos verdes anticlinorium and western shelf 2 the santa monica mountains anticlinorium and 3 the verdugo mountains san rafael hills and the san gabriel mountains these trends result from major thrust ramps off a detachment s at 10 15 km depth thrusts of the verdugo mountains san rafael hills and the san gabriel mountains reach the surface the other two uplifts are associated with blind thrusts compressional seismicity is concentrated along these thrust ramps the 1987 whittier narrows earthquake probably occurred on the elysian park thrust which underlies the santa monica mountains anticlinorium the thrust interpretation accounts for the geometry of the anticlinorium the seismological characteristics of the earthquake and the geometry of coseismic uplift the earthquake and aftershocks occurred within a structurally complex narrow zone of miocene and pliocene northwest trending faults that cross the anticlinorium at a high angle these northwest trending faults are interpreted to be reactivated faults now behaving as tears in the elysian park thrust and not the result of active right lateral deformation extending into the whittier narrows area our analysis suggests the whittier narrows earthquake sequence occurred within a structurally weakened zone along the elysian park thrust we also suggest that the whittier fault is not an important quaternary structure and may not be seismogenic the regional cross section is a nonunique solution and other possible solutions are considered multiple solutions arise from the presence of two intersecting compressional belts in the los angeles area the transverse ranges and the northern peninsular ranges the belts may be due to one or more regional detachments and the northern peninsular ranges may be northeast or southwest vergent the deformed top of the crystalline basement along the regional cross section requires a minimum of 15 0 km of north south convergence between the palos verdes hills and the san andreas fault regardless of the structural solution restoration of our cross section solution requires 21 4 km of north south convergence on top of the crystalline basement including 6 4 km of slip continuing offshore to make structures of the continental borderland and 29 7 km of convergence on the basal detachment geologic relationships suggest major shortening started between early and late pliocene time 2 2 4 0 ma which yields a minimum convergence rate of 3 8 6 8 mm yr between the palos verdes hills and the san andreas fault convergence rates for our solution range from 5 4 to 13 5 mm yr between the edge of the continental borderland and the san andreas fault slip rate estimates for the elysian park thrust along the eastern portion of the santa monica mountains anticlinorium are 2 5 5 2 mm yr if the 1987 whittier narrows earthquake is the characteristic earthquake along the 170 km long anticlinorium then recurrence intervals are estimated to be 5 6 12 1 years this recurrence is higher than the historic seismic record along the santa monica mountains anticlinorium and suggests that 1 our slip rates are too high 2 some crustal shortening is taken up aseismically and or 3 earthquakes larger than the 1987 whittier narrows earthquake will occur along the anticlinorium but less frequently

migrating tremor off southern kyushu as evidence for slow slip of a shallow subduction interface detection of shallow slow earthquakes offers insight into the near trench part of the subduction interface an important region in the development of great earthquake ruptures and tsunami generation ocean bottom monitoring of offshore seismicity off southern kyushu japan recorded a complete episode of low frequency tremor lasting for 1 month that was associated with very low frequency earthquake vlfe activity in the shallow plate interface the shallow tremor episode exhibited two migration modes reminiscent of deep tremor down dip of the seismogenic zone in some other subduction zones a large scale slower propagation mode and a rapid reversal mode these similarities in migration properties and the association with vlfes strongly suggest that both the shallow and deep tremor and vlfe may be triggered by the migration of episodic slow slip events

episodic slow slip events in the japan subduction zone before the 2011 tohoku oki earthquake abstract we describe two transient slow slip events that occurred before the 2011 tohoku oki earthquake the first transient crustal deformation which occurred over a period of a week in november 2008 was recorded simultaneously using ocean bottom pressure gauges and an on shore volumetric strainmeter this deformation has been interpreted as being an m6 8 episodic slow slip event the second had a duration exceeding 1 month and was observed in february 2011 just before the 2011 tohoku oki earthquake the moment magnitude of this event reached 7 0 the two events preceded interplate earthquakes of magnitudes m6 1 december 2008 and m7 3 march 9 2011 respectively the latter is the largest foreshock of the 2011 tohoku oki earthquake our findings indicate that these slow slip events induced increases in shear stress which in turn triggered the interplate earthquakes the slow slip event source area on the fault is also located within the downdip portion of the huge coseismic slip area of the 2011 earthquake this demonstrates episodic slow slip and seismic behavior occurring on the same portions of the megathrust fault suggesting that the faults undergo slip in slow slip events can also rupture seismically

anomalous low velocity zone and linear alignment of seismicity along it in the subducted pacific slab beneath kanto japan reactivation of subducted fracture zone 1 a detailed investigation of the hypocenter distribution beneath kanto japan reveals a nw se trending linear alignment of seismicity within the subducted pacific slab we estimate the 3d seismic velocity structure in the pacific slab to understand the factors controlling the genesis of such intraslab earthquakes a narrow low velocity zone is imaged within the subducted slab over a length of 150 km which partly penetrates into the mantle portion of the slab the low velocity zone correlates in space with the nw se trending earthquake cluster a reactivation of hydrated fracture zone formed prior to subduction is probably related to the low velocity anomaly dehydration reactions of the hydrated oceanic mantle as well as the oceanic crust might lower the seismic velocity along the fossil fracture zone accompanied by intraslab earthquakes these observations support the hypothesis of dehydration embrittlement as the most viable mechanism for generating intraslab earthquakes

the velocity field along the san andreas fault in central and southern california the velocity field within a 100 km broad zone centered on the san andreas fault between the mexican border and san francisco bay has been inferred from repeated surveys of trilateration networks in the 1973 1989 interval the velocity field has the appearance of a shear flow that remains parallel to the local strike of the fault even through such major deflections as the big bend of the san andreas fault in the transverse ranges of southern california across strike profiles of the fault parallel component of velocity exhibit the expected sigmoidal shape whereas across strike profiles of the fault normal component of velocity are flat and featureless no significant convergence upon the fault is observed even along the big bend sector of the fault simple dislocation models can explain most of the features of the observed velocity field but those explanations are not unique about 35 mm yr of relative plate motion is accounted for within the span of the trilateration networks geologic studies indicate that the secular slip rate on the san andreas fault is about 35 mm yr the agreement between these two estimates implies that most of the strain accumulation is elastic and will be recovered in subsequent earthquakes the relative motion observed across the san andreas fault 35 mm yr plus that observed across the eastern california shear zone 8 mm yr accounts for most 43 mm yr of the observed north america pacific relative plate motion 47 mm yr