spatial distribution of focal mechanisms for interplate and intraplate earthquakes associated with the subducting pacific plate beneath the northeastern japan arc a triple planed deep seismic zone the northeastern japan arc is located in one of the most seismically active subduction zones in the world in this study we relocated hypocenters and determined focal mechanisms of small earthquakes m 5 beneath the arc in order to investigate in detail the stress distribution in and around the descending oceanic plate in the hypocenter relocation we adopted a source region station correction method in which station corrections vary with hypocenter locations we have developed a new focal mechanism determination technique named master solution method which is analogous to the master event method in hypocenter determination we applied the method to p and sh wave amplitude data to obtain 1106 focal mechanism solutions from the new mechanism solutions and relocated hypocenters we found that there occur both low angle thrust fault lt type and downdip compression dc type earthquakes at depths from 40 to 70 km near the aseismic front the dc type events are underlying the lt type events almost all the earthquake clusters are composed of lt type events the western limit of the region where lt type events have occurred is subparallel to the trench axis although it undulates considerably it delineates the westernend of the active region of interplate seismicity furthermore we found that normal fault nf type events also occur at depths from 70 km in the upper plane of the double planed deep seismic zone which is characterized mainly by dc type event these nf type events are distributed only in a thin uppermost portion of the slab close to the plate boundary below these in the lower plane are downdip extension de type events this result indicates that the deep seismic zone in the northeastern japan arc is not double planed but triple planed even beneath the land area which cannot be explained by any simple models

tomographic imaging outside a seismic network application to the northeast japan arc the conventional local tomography can determine the 3d seismic velocity structure right beneath a seismic network but it cannot determine the 3d structure outside a seismic network in this study we show that such a limitation of tomography can be overcome if many earthquakes occur outside a seismic network in the northeast japan arc earthquakes occur actively from the japan trench to the pacific coast we detected and used sp depth phase to relocate the suboceanic earthquakes accurately and then used p and s wave arrival times from the relocated suboceanic events and the earthquakes under the northeast japan land area to determine the 3d p and s wave velocity and poisson s ratio structures of the entire northeast japan arc from the japan trench to the japan sea coast our results exhibit strong lateral heterogeneities under the forearc region the mainshock hypocenters of large interplate earthquakes m 7 0 8 2 mainly cluster near the boundaries of high and low velocity and poisson s ratio above the subducting pacific slab a few large earthquakes are located in areas with high velocity and low poisson s ratio these results suggest that lateral heterogeneities on the slab boundary can affect the rupture nucleation of large thrust earthquakes and the degree of interplate seismic coupling

rock surface modeling as a tool to assess the morphology of inland notches mount carmel israel abstract inland notches are elongated c shape indentations carved into hard dense carbonate rocks of the mediterranean climate zone in recent years these unique features became of particular interest as geoindicators of denudation and slope erosion processes the study goals are to learn the processes acting upon the notches cavity by 1 examining the micromorphology of the backwall 2 identifying and classifying zones of erosion 3 learning the surface flow pattern and 4 proposing an erosion mechanism induced by exfoliation to this end a machine learning algorithm was designed using the microstructure texture streamlines formation and potential focal flow the workflow uses data from terrestrial laser scanning applies high resolution textural and curvature analyses and trains an artificial neural network to the different segments of the notch the reconstructed surface model shows division into three distinct belts within the cavity surface 1 the spalled belt sb 2 the transition zone belt tz and 3 the deposition belt db each belt owes its distinct microtopography implying on different geomorphic processes the newly developed methodology improves the recognition of streamline networks along the cavity backwall which mimic alluvial networks the organization of the reconstructed micro channels is similar to drainage basin systems where first order channels developed upstream converge into larger ones and diverge as distributaries as the gradient decreases depositing tufa along the notches base

three dimensional seismic velocity structure around the focal area of the 1978 miyagi oki earthquake 1 we performed a 3d seismic tomography around the rupture area of the 1978 miyagi oki earthquake m 7 4 using both onshore and offshore seismic station data in our results the subducting oceanic crust and the mantle wedge of the overriding plate were imaged as the landward dipping low p wave velocity 7 0 km s layer and the high velocity 8 0 km s layer above it respectively most of the earthquakes were relocated along the plate boundary including the mainshock and the aftershocks of 16 august 2005 miyagi oki earthquake m 7 2 the relationship between spatial extents of the rupture areas of the 1978 and 2005 earthquakes and the velocity variation in the mantle wedge suggests that the heterogeneity of the upper plate delimits the extent of the rupture area of large m 7 interplate earthquakes

development and applications of double difference seismic tomography double difference dd tomography is a generalization of dd location it simultaneously solves for the three dimensional velocity structure and seismic event locations dd tomography uses a combination of absolute and more accurate differential arrival times and hierarchically determines the velocity structure from larger scale to smaller scale this method is able to produce more accurate event locations and velocity structure near the source region than standard tomography which uses only absolute arrival times we conduct a stability and uncertainty analysis of dd tomography based on a synthetic data set currently three versions of the dd tomography algorithms exist tomodd tomofdd and tomoadd tomodd assumes a flat earth model and uses a pseudo bending ray tracing algorithm to find rays between events and stations while tomofdd uses a finite difference travel time algorithm and the curvature of the earth is considered both codes are based on a regularly distributed inversion grid with the former for a local scale and the latter for a regional scale in contrast tomoadd adapts the inversion mesh to match with the data distribution based on tetrahedral and voronoi diagrams we discuss examples of applying dd tomography to characterize fault zone structure image high resolution structure of subduction zones and determine the velocity structure of volcanoes

the 2005 m7 2 miyagi oki earthquake ne japan possible rerupturing of one of asperities that caused the previous m7 4 earthquake 1 a large m7 2 interplate earthquake occurred on 16 august 2005 in the miyagi oki region where large interplate earthquakes with magnitude of 7 5 have occurred repeatedly at a recurrence interval of 37 yrs ne japan we compared aftershock distribution of the 2005 miyagi oki earthquake with that of the previous 1978 miyagi oki earthquake m7 4 using double difference hypocenter locations the aftershock area of the 2005 miyagi oki earthquake is partly overlapped with the southern southeastern part of that of the 1978 event locations of aftershock clusters of the 2005 event correspond with those of the 1978 event and those of the background seismicity coseismic slip area of the 2005 event estimated by seismic waveform inversion is also partly overlapped with that of the 1978 event these observations suggest that spatial seismicity pattern on the plate boundary in subduction zone persists and the 2005 event possibly ruptured a part of the source area of the 1978 event

the role of metasomatic alteration on frictional properties of subduction thrusts an example from a serpentinite body in the franciscan complex california abstract fluid rock interaction within accretionary prisms drastically changes the frictional strength and slip stability of the fault zone in order to understand the effect of ultramafic components on the degree of interplate coupling we present data on frictional properties of a reaction zone between serpentinite and argillite in a tectonic melange of the franciscan complex central california field and petrographic observations indicate that the argillite and serpentinite along the lithological boundary are metasomatized to tremolite and talc schists respectively forming a ductile shear zone simulated gouges made from fault and wall rock samples collected are sheared at effective normal stresses n eff of 60 180 mpa and temperatures t of 20 400 c using a hydrothermal ring shear machine the serpentinite is frictionally strong steady state friction coefficient ss 0 5 0 6 and exhibits both velocity weakening and velocity strengthening behavior the ss of the argillite and tremolite schist increases up to 0 7 and 0 6 respectively with increasing n eff and t while a b transitions from positive to negative with increasing t at a given experimental condition and a b values are lower and higher for the tremolite schist than for the argillite in contrast the talc schist exhibits very low friction ss 0 1 0 2 and velocity strengthening behavior at all experimental conditions tested our results demonstrate that si metasomatism along the argillite serpentinite contact results in reduced friction and stabilized slip forming frictionally weak velocity strengthening regions in the megathrust zone

venus gravity anomalies and their correlations with topography this report provides a summary of the high resolution gravity data obtained from the pioneer venus orbiter radio tracking data gravity maps covering a 70 latitude band through 360 of longitude are displayed as line of sight and vertical gravity topography converted to gravity and bouguer gravity maps are also shown in both systems topography to gravity ratios are made over several regions of the planet there are markedly different ratios for the aphrodite area as compared to the beta and atla areas

envelope inversion analysis for high frequency seismic energy radiation from the 2011 mw 9 0 off the pacific coast of tohoku earthquake abstract i study s wave energy radiation in higher frequencies of 1 8 hz from the 2011 m w 9 0 off the pacific coast of tohoku japan earthquake hereafter called the tohoku oki earthquake based on a seismogram envelope inversion method i first evaluate two medium parameters of scattering attenuation and intrinsic absorption for s waves using spatial and temporal distributions of seismic energy from aftershock records which are necessary for calculating green s functions next applying the envelope inversion method to 27 near field strong motion records from the mainshock i estimate the s wave energy radiation from 40 subfaults on the fault of 500 km 250 km each subfault is allowed to rupture for eight consecutive source time windows rupture velocity and the duration of energy radiation for each time window are determined by a grid search to be 2 5 km s and 8 0 s respectively energy radiated from the entire fault is 5 8 10 16 j for 1 2 hz 4 5 10 16 j for 2 4 hz 1 5 10 16 j for 4 8 hz and totaling 1 2 10 17 j in the 1 8 hz range strong energy emanated twice from greater depths of the off miyagi region corresponding to two peaks seen at the northern stations and energy radiation at greater depths off the fukushima ibaraki border is compatible with a single peak found at the southern stations strong high frequency radiations at greater depths strikingly contrast with large slips at shallower depths estimated in lower frequencies this frequency dependent rupture may accord with structural changes along the dip direction online material snapshots of high frequency energy radiation from the fault plane and results of estimating scattering parameters by the multiple lapse time window analysis in 1 2 and 2 4 hz

forearc structure beneath southwestern british columbia a three dimensional tomographic velocity model 1 this paper presents a three dimensional compressional wave velocity model of the forearc crust and upper mantle and the subducting juan de fuca plate beneath southwestern british columbia and the adjoining straits of georgia and juan de fuca the velocity model was constructed through joint tomographic inversion of 50 000 first arrival times from earthquakes and active seismic sources wrangellia rocks of the accreted paleozoic and mesozoic island arc assemblage underlying southern vancouver island in the cascadia forearc are imaged at some locations with higher than average lower crustal velocities of 6 5 7 2 km s similar to observations at other island arc terranes the mafic eocene crescent terrane thrust landward beneath southern vancouver island exhibits crustal velocities in the range of 6 0 6 7 km s and is inferred to extend to a depth of more than 20 km the cenozoic olympic subduction complex an accretionary prism thrust beneath the crescent terrane in the olympic peninsula is imaged as a low velocity wedge to depths of at least 20 km three zones with velocities of 7 0 7 5 km s inferred to be mafic and or ultramafic units lie above the subducting juan de fuca plate at depths of 25 35 km the forearc upper mantle wedge beneath southeastern vancouver island and the strait of georgia exhibits low velocities of 7 2 7 5 km s inferred to correspond to 20 serpentinization of mantle peridotites and consistent with similar observations in other warm subduction zones estimated dip of the juan de fuca plate beneath southern vancouver island is 11 16 and 27 at depths of 30 40 and 50 km respectively

spatial heterogeneity of the mantle wedge structure and interplate coupling in the ne japan forearc region 1 we performed 3 d seismic tomography in the forearc region of the northeastern japan subduction zone using both onshore and offshore seismic station data we obtained the vp vs and vp vs structures around the plate boundary with high spatial resolution the position of the plate boundary as defined by relocated hypocenters coincides with the sharp velocity boundary between the oceanic crust and the mantle wedge the mantle wedge above the coseismic slip area of the 1978 and 2005 off miyagi interplate earthquakes m 7 is characterized by high vp and vs but low vp vs off fukushima however where large earthquakes rarely occur we found a high vp vs anomaly at the tip of the mantle wedge the spatial distribution of serpentinized mantle wedge limits the spatial extent of the strongly coupled area on the plate boundary and thus can explain the difference in seismic activity between the off miyagi and off fukushima regions

venus limited extension and volcanism along zones of lithospheric weakness three global scale zones of possible tectonic origin are described as occurring along broad low rises within the equatorial highlands on venus lat 50 n to 50 s long 60 to 310 the two longest of these tectonic zones the aphrodite beta and themis atla zones extend for 21 000 and 14 000 km respectively several lines of evidence indicate that beta and atla regiones located at the only two intersections of the three major tectonic zones are dynamically supported volcanic terranes associated with currently active volcanism rift valleys south of aphrodite terra and between beta and phoebe regiones are characterized by 75 to 100 km widths raised rims and extensions of only a few tens of kilometers about the same magnitudes as in continental rifts on the earth horizontal extension on venus was probably restricted by an early choking off of plate motion by high crustal and upper mantle temperatures and the subsequent loss of water and an asthenosphere

mantle wedge structure in the miyagi prefecture forearc region central northeastern japan arc and its relation to corner flow pattern and interplate coupling 1 we applied three dimensional 3 d seismic tomography to both active source data and local earthquake data recorded at onshore and offshore seismic stations in the miyagi prefecture forearc region of central northeastern japan to obtain a detailed seismic velocity model of the mantle wedge the velocity model showed a clear boundary that divides the mantle wedge into an oceanward high velocity toe and a landward low velocity region that extends trenchward from beneath currently active arc volcanoes the top of the seaward dipping boundary is about 20 30 km landward from the coastline and its bottom is approximately beneath the coastline we consider that this velocity boundary represents the trenchward limit of corner flow and the high velocity toe represents a stagnant mantle wedge the high spatial resolution of the tomographic image we produced allowed us to identify a spatial correlation between velocity variations in the mantle wedge immediately above the plate boundary and the spatial extent of the rupture areas of the large interplate earthquakes that occur repeatedly in the region our results suggest that variations of the volume fraction of serpentinization in the mantle wedge cause the irregularity of rupture patterns of megathrust earthquake sequences we also identified a swarm of active microseismicity in the mantle wedge well above the seismogenic plate boundary this activity may be related to dehydration of a detached seamount

seismogenic characteristics of the northern mariana shallow thrust zone from local array data 1 the northern mariana seismogenic zone has no shallow thrust earthquakes larger than ms 7 4 in the historical seismological record and is traditionally considered decoupled or aseismic during the 2003 2004 mariana subduction factory imaging experiment we recorded local shallow earthquakes throughout the central and northern regions of the mariana forearc using an array of terrestrial broadband and ocean bottom seismographs accurate locations for both the 2003 2004 local seismicity as well as earthquakes with global centroid moment tensor gcmt solutions from 1976 to 2008 were obtained using the hypocentroidal decomposition relocation method and a local velocity model additionally focal mechanisms for the largest 2003 2004 earthquakes were determined using regional waveform inversion thrust faulting earthquakes occur along the mariana megathrust between depths of 20 60 km showing that the lack of great shallow thrust earthquakes does not result from a narrow seismogenic zone and that most seismicity occurs where the downgoing plate contacts the overriding mantle wedge clusters of small plate interface earthquakes with ml 1 6 4 7 occur within patches 100 120 km west of the trench at depths of 30 45 km furthermore the larger gcmt earthquakes mw 4 9 5 8 occur mostly updip and downdip of the patches of smaller earthquakes recorded by our local array and is suggestive of changes in the fault properties with depth clusters of small forearc earthquakes occur discontinuously along the length of the mariana subduction zone showing that northern mariana is variable both along the strike of the margin and with depth along the seismogenic zone we propose that the lack of great mw 8 thrust faulting earthquakes is due in part to the variable frictional heterogeneity along the megathrust

strength of slightly serpentinized peridotites implications for the tectonics of oceanic lithosphere we deformed cores of peridotite with 10 15 lizardite and chrysotile serpentine to determine the influence of serpentine content on the strength and the style of deformation the strength the pressure dependence of strength and the nominally nondilatant mode of brittle deformation of slightly serpentinized peridotites are comparable to those of pure serpentinites these results indicate that deformation is accommodated primarily by serpentine while olivine despite being the more abundant component remains nominally undeformed on the basis of these data and previous work we determine that the transition from a strong dilatant dunite rheology to a weak nondilatant serpentinite rheology is not a linear function of the degree of serpentinization instead an abrupt transition in strength is observed at low degrees of serpentinization the pressure of the transition from localized to distributed deformation also decreases abruptly from 1000 mpa to 150 350 mpa the change in rheological behavior occurs at a serpentine content of 10 15 or less which corresponds to published compressional seismic velocity of 7 8 7 5 km s at a pressure of 200 mpa the seismic velocity of the oceanic lithosphere particularly of that formed at slow spreading ridges can thus provide constraints on its mechanical properties at depth because slightly serpentinized peridotites have a rheology similar to that of pure serpentinite significant lithospheric weakening may occur after the onset of alteration near or at the ridge axis

pāhoehoe flow cooling discharge and coverage rates from thermal image chronometry 1 theoretically and empirically derived cooling rates for active p hoehoe lava flows show that surface cooling is controlled by conductive heat loss through a crust that is thickening with the square root of time the model is based on a linear relationship that links log time with surface cooling this predictable cooling behavior can be used assess the age of recently emplaced sheet flows from their surface temperatures using a single thermal image or image mosaic this allows quantification of the variation in areal coverage rates and lava discharge rates over 48 hour periods prior to image capture for p hoehoe sheet flow at k lauea hawai i this gives coverage rates of 1 5 m2 min at discharge rates of 0 01 0 05 m3 s increasing to 40 m2 min at 0 4 0 5 m3 s our thermal chronometry approach represents a quick and easy method of tracking flow advance over a three day period using a single thermal snap shot

along arc structural variation of the plate boundary at the japan trench margin implication of interplate coupling 1 at the japan trench convergent margin many large interplate earthquakes of greater than m7 5 frequently occur their epicenters have uneven distribution mostly located in the northern area to investigate the relationship between this distribution and tectonic structures we have conducted multichannel seismic surveys since 1996 our data show two kinds of interplate sedimentary units a wedge shaped unit and a channel like unit both units have a lower p wave velocity than the basal part of the overriding island arc crust the wedge shaped unit having a velocity of 2 3 km s is widely distributed over the forearc region in the northern area its thickness decreases with depth becoming several hundred meters at a depth of 12 km the channel like unit having a velocity of 3 4 km s is observed in the southern area extending in the downdip direction its thickness reaches 2 km at a depth of 12 km if the low velocity of these units results from the existence of fluid as many authors assume the units being thick implies higher fluid content assuming constant porosity considering that fluid reduces basal friction and with an assumption that fluid available at a specific interface is proportional to the total fluid content in the sediment the thickness variation of the units would cause different degrees of coupling at the plate boundary along the arc this may provide one explanation for the regional disparity in the interplate earthquake occurrence in the margin furthermore we attempt to call attention to the possibility that the channel like sediment works as a shear stress releaser

supraslab earthquake clusters above the subduction plate boundary offshore sanriku northeastern japan seismogenesis in a graveyard of detached seamounts 1 thousands of offshore repeating earthquakes with low angle thrust focal mechanisms occur along the subduction plate boundary of ne japan double difference relocation methods using p and s wave arrivals reveal clusters of events above these repeating events to assure good depth control we restrict our study to events that are close to seismic stations these supraslab earthquake clusters are regional features at depths of 25 to 50 km and most of these clusters are below the depth of the forearc moho which we determined from converted waves seismicity over this depth range does not occur under the inland area of ne japan except just below the vicinity of the arc volcanoes re entrants in the inner trench slope indicate that repeated collisions of seamounts have occurred in the past our preliminary interpretation of supraslab clusters is that they represent seismicity in seamounts detached from the pacific plate during slab descent driven by the resistance of seamounts to subduction detachment during slab descent probably occurs on the sedimented and hydrothermally altered seafloor on which seamounts were originally constructed since these are known as zones of weakness during active island growth high fluid pressure produced during dehydration of clay minerals and other low temperature hydrous minerals could enable detachment at depths seamount crust is thus accreted to forearcs possibly leading to a long term component of near coastal uplift supraslab earthquake clusters may be our most direct evidence of the fates of seamounts and suggest that tectonic underplating is actively occurring in this subduction system

evidence for serpentinization of the forearc mantle wedge along the nicoya peninsula costa rica 1 characterizing the hydration state of the forearc mantle wedge yields valuable information on frictional stability at the downdip edge of subduction megathrusts simultaneous inversion of p and s wave arrival times collected as part of the costa rica seismogenic zone experiment yields 1d and 3d p and s wave velocity models vp and vs for the nicoya peninsula segment of the middle america trench nicoya peninsula 1d velocity models show similar velocity gradients to country wide 1d velocity models from 5 30 km depth but diverge at expected moho depths due to proximity to the subducting cocos plate 3d vp values range from 7 2 7 6 km sec in the forearc mantle wedge receiver functions computed at global seismic network station jts in northwestern costa rica confirm these vp values yield vp vs of 1 85 and place the continental moho at 36 4 km depth vp and vp vs are consistent with 15 25 serpentinization of the forearc mantle wedge

the great 1933 sanriku oki earthquake reappraisal of the main shock and its aftershocks and implications for its tsunami using regional tsunami and seismic data

thermal evolution of venus abstract the theory of three dimensional and finite amplitude convection in a viscous spherical shell with temperature and pressure dependent physical parameters is developed on the basis of a modified boussinesq fluid assumption the lateral dependences of the variables are resolved through their spherical harmonic representations whereas their radial and time dependences are determined by numerical procedures the theory is then applied to produce thermal evolution models for venus the emphasis is on illustrating the effects of certain physical parameters on the thermal evolution rather than proposing a specific thermal history for the planet the main conclusions achieved in this paper are 1 a significant portion of the present temperature in the mantle and heat flux at the surface of venus is probably owing to the decay of a high temperature established in the planet at the completion of its core formation 2 the effective rayleigh number of the mantle is so high that even the lower order modes of convection cool the planet sufficiently and maintain an almost adiabatic temperature gradient in the convecting region and high temperature gradients in the thermal boundary layers 3 the convection is oscillatory with avalanche type properties which induces oscillatory features to the surface heat flux and the thickness of the crustal layer and 4 a planetary model with a recycling crust cools much faster than those with a permanently buoyant crust the models presented in this paper suggest that venus has been highly convective during its history until 0 5 ga ago the vigorous convection was bringing hot and fresh material from the deep interior to the surface and dragging down the crustal slags floating on the surface in to the mantle the rate of cooling of the planet was so high that its core has solidified in the last 0 5 ga the vigour of convection diminished considerably and the crustal slags developed into a global and permanently buoyant crustal layer the tectonic style on venus has consequently changed from the recycling of crustal plates to hot spot volcanics at the present time the planet is completely solid except in the upper part of its mantle where partial melting may occur