precursory seismic quiescence before the 1994 kurile earthquake mw 8 3 revealed by three independent seismic catalogs we have found that the m w 8 3 kurile earthquake on october 4 1994 followed an outstanding seismic quiescence starting 5 6 years before the mainshock near the ruptured area we have analyzed three independent seismic catalogs institute of seismology and volcanology hokkaido university isv japan meteorological agency jma and international seismology center isc in spite of selecting different magnitude bands and time windows all three catalogs presented the common feature of the seismic quiescence this fact strongly suggests that the seismic quiescence should not be a man made change but actually occurred moreover we have confirmed that the seismic quiescence was the most significant and the earthquake was the largest in the past twenty five years in this region therefore we confidently interpret this seismic quiescence as an indication of a preparation process for the m w 8 3 kurile earthquake

spatio temporal evolution of coulomb stress in the pacific slab inverted from the seismicity rate change and its tectonic interpretation in hokkaido northern japan abstract we estimated spatio temporal evolution of coulomb stress within the subducted pacific slab in hokkaido from the analysis of seismicity rate change for this purpose we used earthquake catalog from the institute of seismology and volcanology isv hokkaido university for the period 1993 4 1 2006 12 31 after relocating to compensate location errors due to the heterogeneous p and s wave structure beneath hokkaido we found that spatial pattern of coulomb stress change inverted from the seismicity rate change is comparable with static change in coulomb stress estimated from dislocation models our results and analyses reveal important insights on spatio temporal pattern of deformation of the subducted pacific slab in terms of coulomb stress change we found that the 2003 tokachi oki earthquake mw 8 0 pervasively perturbed coulomb stress in a regional scale with a significant impact to trigger the 2004 kushiro oki earthquake the 2004 kushiro oki earthquake mw 7 0 is another significant stressing event that changed the pattern of coulomb stress in the area we found that stressing events with magnitude smaller than 7 0 has minimal impact on coulomb stress change in the pacific slab similarly comparatively deep focused large earthquakes could not change coulomb stress significantly further the pattern of coulomb stress change after the 2003 tokachi oki earthquake correlates the pattern of afterslip distribution in hokkaido

creep dike intrusion and magma chamber deflation model for the 2000 miyake eruption and the izu islands earthquakes 1 analysis of global positioning system data shows shrinkage of miyake island and the widening between nijima and kozu islands during the period of the miyake island volcanic activity and the ensuing izu islands earthquakes in 2000 the estimated time evolution of a model consisting of a dike creeping faults and a mogi source suggests that a crack opening on miyake island occurred immediately after the start of the seismic activities on 26 june and ended within several days at the west coast of miyake island after the seabed eruption on 27 june magma migrated from miyake island to kozu and nijima islands within several days the estimated volume of intruded magma totals around 1 2 109 m3 associated with the magma intrusion between miyake and kozu islands left lateral and right lateral creep motions occurred in regions off the west coast of miyake island and near kozu island the accumulated moment energy is equivalent to an earthquake of mw 6 6 and 6 6 for right lateral and left lateral creeping faults respectively the estimated magma chamber continued deflation beneath the southwestern part of miyake island from 26 june totaling around 0 12 109 m3 in volume change in addition to the collapse volume of 0 6 109 m3 at the summit of mount oyama on miyake island the volume change on miyake island can be compensated by the migrated magma toward kozu island from the deflation source beneath miyake island the deflation speed of the magma chamber beneath miyake island decreased and increased before and after the eruption of 14 15 july and 18 august suggesting a change in balance of mass influx and draining out rate of the magma chamber

an application of synthetic seismicity in earthquake statistics the middle america trench this paper demonstrates how synthetic seismicity calculations which are based on the concept of fault segmentation and incorporate the physics of faulting through static dislocation theory can improve earthquake recurrence statistics and hone the probabilities of hazard compared to forecasts constructed from a handful of earthquake recurrence intervals forecasts constructed from synthetic seismicity are more robust in that they embody regional seismicity information over several units of magnitude they can extrapolate seismicity to higher magnitudes than have actually been observed and they are formulated from a catalog which can be extended as long as needed to be statistically significant synthetic seismicity models can also be used to judge the stability of common rate estimates and the appropriateness of idealizations to the earthquake cycle i find that estimates of fault slip rate are unbiased regardless of sampling duration while estimates of earthquake recurrence time are strongly biased recurrence intervals estimated from seismicity samples less than about 10 times the actual recurrence interval will almost certainly be too short for the middle america trench mat it would take 200 and 400 years of monitoring to constrain slip and recurrence rates to 10 events m 6 have as much as a 60 probability of recurrence within 5 years due to the clustering of small earthquakes in foreshocks and aftershocks this probability drops to less than 15 for m 7 events increasing gap time generally increases conditional probability of earthquake occurrence but the effect is weak for the mat the spread parameters of the best fitting lognormal or weibull distributions 0 75 are much larger than the 0 21 intrinsic spread proposed in the nishenko buland hypothesis stress interaction between fault segments disrupts time or slip predictability and causes earthquake recurrence to be far more aperiodic than has been suggested

global positioning system gps and gps acoustic observations insight into slip along the subduction zones around japan the global positioning system gps is one of the most powerful tools available for observation of earth s surface deformation in particular coseismic postseismic slow transient and interseismic deformation have all been observed globally by gps over the past two decades especially in subduction zones moreover gps acoustic techniques have been developed for practical use in the past decade allowing observation of offshore deformation immediately above slip regions here we describe the application of gps and gps acoustic observations to the detection of deformation due to plate boundary slip for interplate earthquakes as well as afterslip and slow slip events in subduction zones around japan where geodetic data coverage is particularly dense the data demonstrate temporally variable strain accumulation in the source region of the 2011 mw 9 0 tohoku oki earthquake and observation of the huge slip of the tohoku oki earthquake near the trench using gps acoustic methods has considerably advanced o

observational constraints on the fracture energy of subduction zone earthquakes we relate seismologically observable parameters such as radiated energy seismic moment rupture area and rupture speed to the dynamics of faulting to achieve this objective we computed the radiated energy for 23 subduction zone earthquakes recorded between 1992 and 2001 most of these earthquakes have a magnitude m w 7 5 but we also included some smaller m w 6 7 well studied subduction zone earthquakes and six crustal earthquakes we compiled static stress drop estimates for these 29 earthquakes from literature and used a slip weakening model to determine the radiation efficiency of these earthquakes we also determined the rupture speed of these earthquakes from literature from fracture mechanics fracture energy and hence radiation efficiency can be related to the rupture speed the radiation efficiencies estimated from the partitioning of energy as given by the slip weakening model are consistent with the rupture speed estimated for these earthquakes most earthquakes have radiation efficiencies between 0 25 and 1 and are hence efficient in generating seismic waves but tsunami earthquakes and two deep earthquakes the 1994 bolivia and the 1999 russia china border earthquakes have very small radiation efficiencies 0 25 and hence dissipate a large amount of energy during faulting we suggest that differences in the radiation efficiencies of different types of earthquakes could be due to fundamental differences in their rupture mechanics in deep events the energy is probably dissipated in thermal processes in the fault zone while it is possible that the morphology of the trench causes large energy dissipation during the rupture process of tsunami earthquakes

geodetic inversion for the fault model of the 1994 shikotan earthquake the fault parameters of the 1994 shikotan earthquake were determined by inverting all available geodetic data using an iterative linearized least squares method a one fault inversion shows that a shallow dip fault plane model does not reproduce the minor deformation observed on shikotan island while a steep dip model can fit all the data well multifault inversion shows that a fault plane divided into two subfaults lengthwise is the best fitting model based on akaike s information criteria aic for shallow dip faulting mechanism this model yields a very high stress drop 40 mpa on the deeper subfault for a steep dip model a fault plane divided into two subfaults sideways gives the minimum aic all the computations for models consisting of two to eight subfaults show that the chi square values of the shallow dip models are about 10 higher than those of the steep dip models considering the high stress drop the larger chi square value and the requirements of a complex subfault system for the shallow dip model we reach the conclusion that the steep dip model is more suitable to explain the geodetic observations

sun ocean nuclear bombs and fossil fuels radiocarbon variations and implications for high resolution dating radiocarbon or 14c is a radiometric dating method ideally suited for providing a chronological framework in archaeology and geosciences for timescales spanning the last 50 000 years 14c is easily detectable in most common natural organic materials and has a half life 5 730 40 years relevant to these timescales 14c produced from large scale detonations of nuclear bombs between the 1950s and the early 1960s can be used for dating modern organic materials formed after the 1950s often these studies demand high resolution chronology to resolve ages within a few decades to less than a few years despite developments in modern high precision 14c analytical methods the applicability of 14c in high resolution chronology is limited by short term variations in atmospheric 14c in the past this article reviews the roles of the principal natural drivers e g solar magnetic activity and ocean circulation and the anthropogenic perturbations e g fossil fuel co2 and 14c from nuclear and thermonuclear bombs

far field simulation of tsunami propagation in the pacific ocean impact on the marquesas islands french polynesia the islands in the marquesas archipelago are most exposed to far field tsunamis in french polynesia four recent earthquakes located at the pacific rim kurile 1994 chile 1995 mexico 1995 and peru 1996 earthquakes generated trans pacific tsunamis and caused contrasting inundations in several inhabited marquesian bays the aim of this study is to better understand the amplification phenomena observed in the marquesas islands and to improve the risk assessment we present here numerical simulations of these four tsunamis by means of a finite difference model solving the equations of tsunami propagation at different scales the water heights computed in the bays are in excellent agreement with the available observations and thus validate our numerical method these numerical results allow us to determine 1 which propagation azimuths are dangerous for the whole marquesas archipelago and 2 the behavior of each studied bay amplitude frequency in response to tsunami waves we observe that the seismogenic subduction zone along south america is likely to define one of the most dangerous tsunami generation areas for the marquesas archipelago owing to the source geometries and to the trapping of the tsunami energy by bathymetric features in the southern pacific ocean fracture zones seamount chains

newly imaged shape of the deep seismic zone within the subducting pacific plate beneath the hokkaido corner japan kurile arc arc junction 1 the geometry of the deep seismic zone associated with the subducting pacific plate beneath the north american plate in the hokkaido corner japan kurile arc arc junction has been investigated based on the hypocenters accurately relocated by a dense local seismographic network with three dimensional p and s wave velocity structures the model suggests that the lateral changes in the dip of the subduction zone are more rapid than previously believed we found that the deep seismic zone in the pacific plate dips at 20 to 30 on the side of the japan arc the dip angle increased in a narrow region around 143 144 e by 10 to 20 and the dip was 40 to 50 on the side of the kurile arc in the transitional zone around 143 144 e an unusual distribution of microearthquakes has been discovered within the pacific plate which was located on a near vertical plane with an area of 50 100 km2 with strike that was perpendicular to the kurile trench axis this feature was named the tokachi oki slab cracking zone we suggest that this is a slab cracking zone torn by the extensional stress due to the rapid lateral changes in the dip of the subduction zone the slab cracking zone may possibly grow into the large disruption or tear of the slab in the future

visibility of fault strands in exploratory trenches and timing of rupture events many estimates of seismic risk depend crucially on how well the date of faulting events can be determined from the stratigraphic position of fault strands exposed in exploratory trenches however fault strands cut by trenches may seem to die out where they are in fact only poorly expressed or they may actually die out such ambiguity can lead to misinterpretation of the time of the most recent displacement and also of the recurrence interval between faulting events to investigate the frequency of occurrence and other characteristics of strands that falsely appear to die out or that actually do die out more than 1200 fault strands were analyzed for strands associated with individual faulting events 45 could not be visibly traced in the trench walls to the ground surface that existed at the time of faulting for reverse and strike slip faults the number exceeds 70 thus any apparent upward termination of a fault strand that is thought to indicate the date of a faulting event requires critical examination and corroboration from other evidence nonvisibility i e dieout upward obscure segments and dieout downward is more common on strike slip and reverse faults than on normal faults and is more common in soil horizonsmore than in clay and gravel nonvisibility occurs on strands that have had large 1m as well as small displacements less

the shikotan earthquake of october 4 1994 lithospheric earthquake a large m w 8 2 earthquake occurred off shikotan is one of the kurile is on october 4 1994 we inverted 32 body wave records to determine the rupture pattern using an iterative deconvolution method the mechanisms of the subevents were allowed to vary during rupture the source parameters obtained are the location of the initial break 43 48 n 147 40 e the centroid depth 56 km strike dip rake 49 75 125 for the total source the seismic moment m o 2 6 10 21 nm m w 8 2 source time duration t 42 s the average rupture velocity 2 5 km s we also determined the mechanism using long period love and rayleigh waves from 14 stations the solution for a finite source distributed over a depth range from 0 to 90 km is strike dip rake 54 76 129 with mo 2 3 10 21 nm in good agreement with that from body waves referring to the extent of the aftershock area and the subevent distribution we estimated the fault area s 120 60 km the average slip d 5 6m and the stress drop 11 mpa we computed synthetic waveforms as well as static displacements using either the steep or the low angle plane as the fault plane and found that the steep dip fault model fits the data better our result the mechanism large centroid depth high stress drop strongly suggests that the 1994 shikotan earthquake is a lithospheric earthquake an intra plate event that ruptures through a substantial part of the subducting oceanic lithosphere this type of lithospheric earthquake is relatively common

evidence for chaotic fault interactions in the seismicity of the san andreas fault and nankai trough interactions between fault segments are one of the main sources of complexity in the seismicity of active tectonic regions such interactions are likely to influence the spatial and temporal patterns of earthquakes here we examine the dynamical behaviour introduced by fault interactions using a simple spring loaded slider block model with velocity weakening friction the model consists of two slider blocks coupled to each other and to a constant velocity driver by elastic springs for an asymmetric system in which the frictional forces on the two blocks are not equal the solutions exhibit chaotic behaviour the system s behaviour over a range of parameter values seems to be generally analogous to that of weakly coupled segments of an active fault we see similarities between our model simulations and observed patterns of seismicity on the south central san andreas fault in california and in the nankai trough along the coast of southwestern japan

multicycle slip distribution along a laboratory fault slip distribution along a laboratory fault which consists of eight spring connected blocks that are elastically driven to slide on a frictional surface has been examined for a long sequence of slip events to test the applicability of some conceptual models proposed recently in the literature the distributions of large slip events are found to be quite variable and do not fit the uniform slip or characteristic earthquake models the rupture initiation points are usually not near the corresponding maximum slip points in contrast to observations by thatcher 1990 and by fukao and kikuchi 1987 that earthquake hypocenters are commonly near corresponding regions of maximum slip in the fault planes this contrast may suggest that either the present observations or theirs are not representative or the teleseismically determined hypocenters may not always be true rupture initiation points as usually assumed large slip events are also found to be a stress roughening process they are triggered by some small events after the stresses have been adjusted by some earlier small to moderate events to be near the critical levels at most locations along the fault this suggests that earthquake prediction monitoring efforts should not be limited to a small region near an asperity but should be spread out to cover the entire fault segment in a seismic gap in order to detect the condition of simultaneous strain buildup

forecast model for large and great earthquakes in southern california an earthquake instability model is used to compute theoretical fault slip and ground surface deformation before possible future earthquakes on the san andreas fault in southern california the quasistatic model represents the earth s crust by an elastic half space and the san andreas imperial cerro prieto and san jacinto faults by flat rectangular surfaces whose strikes approximate the actual local strikes the seismogenic zone of the san andreas fault is represented by a brittle strain softening patch extending from the ground surface to 11 km depth and from parkfield to the salton sea 500 km the strength of the patch varies along strike and unstable failures of parts of the patch are earthquake analogs failed areas heal immediately after instability for the model to reproduce the lengths slips and times of earthquakes since 1080 a d reported by k sieh and others the patch must be divided into five sections along strike the sections have alternately low and high strength with the two strongest sections being roughly coincident with the major bends of the san andreas fault ten to twenty years before unstable slippage of patch areas portions of the patch bottom begin to fail stably aseismically the stable failure causes accelerating fault slip at depth and at the fault trace as well as anomalous changes in lengthening rates of trilateration lines in the model simulation the next two sections to fail unstably in the future are just north of the salton sea and just south of parkfield rupture lengths are about 100 km and 40 km at favorable locations precursory anomalies of fault slip and trilateration line length become large enough to be detected in field data a few years before each earthquake

stratigraphic evidence for seven meters of dextral slip on the san andreas fault during the 1857 earthquake in the carrizo plain the smallest geomorphic offsets along a 35 km section of the san andreas fault in the carrizo plain vary from 7 to 10 m our three dimensional excavation of alluvial deposits a few km southeast of wallace creek confirms that at least 6 6 to 6 9 m of dextral slip occurred there during the latest large earthquake in 1857 dates on detrital charcoal suggest that the last event prior to the 1857 earthquake occurred before a date within the range a d 1305 to 1623 the 3 m range in smallest offsets along this portion of the fault may reflect either a 3 m variation in slip along the san andreas in 1857 or 2 to 3 m of slip during an event prior to 1857 observations made after the recent landers earthquake are compatible with the hypothesis of large local variations in slip during a single earthquake but do not explain the cause of such variations off fault dextral rotations would be one plausible explanation however paleoseismic data in the carrizo plain are too sparse to allow rejection of the alternative hypothesis that slip in the event prior to 1857 was only 2 to 3 m an amount of slip which would be several times too small to fit a time predictable model

dynamics of fault interaction parallel strike slip faults we use a two dimensional finite difference computer program to study the effect of fault steps on dynamic ruptures our results indicate that a strike slip earthquake is unlikely to jump a fault step wider than 5 km in correlation with field observations of moderate to great sized earthquakes we also find that dynamically propagating ruptures can jump both compressional and dilational fault steps although wider dilational fault steps can be jumped dilational steps tend to delay the rupture for a longer time than compressional steps do this delay leads to a slower apparent rupture velocity in the vicinity of dilational steps these dry cases assumed hydrostatic or greater pore pressures but did not include the effects of changing pore pressures in an additional study we simulated the dynamic effects of a fault rupture on undrained pore fluids to test sibson s 1985 1986 suggestion that wet dilational steps are a barrier to rupture propagation our numerical results validate sibson s hypothesis by demonstrating that the effect of the rupture on the undrained pore fluids is to inhibit the rupture from jumping dilational stepovers the basis of our result differs from sibson s hypothesis in that our model is purely elastic and does not necessitate the opening of extension fractures between the fault segments

paleomagnetic measurement of nonbrittle coseismic deformation across the san andreas fault at pallett creek paleomagnetic data have been obtained to address a problem at the pallett creek paleoseismological site the 9 mm yr slip rate determined from three dimensional mapping of late holocene offsets across discrete faults is only a quarter of the expected value we suspected that nonbrittle deformation adjacent to the faults might account for the 26 mm yr discrepancy in our search for the missing slip we collected and analyzed 264 paleomagnetic samples from a 53 m wide transect across the fault zone half the samples came from a unit deposited immediately after a large earthquake of about a d 1480 these samples were affected by two large earthquakes that involved rupture at the site in 1812 and 1857 we collected the other half of the samples from a slightly older bed one that was deposited before the earthquake of about a d 1480 relative to control groups composed of 10 samples and collected 50 m from the fault samples closer to the fault display clockwise rotations of 30 or less if interpreted as block rotations the data from the older unit imply that it has sustained a total of 14 0 2 9 m of dextral warp during the past three major earthquakes and that the younger unit has experienced a total of 8 5 1 0 m of warp during the most recent two combining these values with the amounts of dextral slip across the mapped fault planes yields dextral offsets of 5 5 6 25 and 6 25 m for the events of a d 1480 1812 and 1857 and a slip rate of 35 6 6 7 mm yr this slip rate averaged over the past three complete seismic cycles is consistent with published rates from other sites offsets associated with the past three events are remarkably similar these amounts however appear independent of the length of interseismic cycles these observations suggest 1 that this part of the san andreas fault has a characteristic strength and 2 that conventional concepts of strain accumulation and relief for example time and slip predictable models of earthquake occurrence are unrealistic

evidence for and implications of self healing pulses of slip in earthquake rupture dislocation time histories of models derived from waveforms of seven earthquakes are discussed in each model dislocation rise times the duration of slip for a given point on the fault are found to be short compared to the overall duration of the earthquake 10 however in many crack like numerical models of dynamic rupture the slip duration at a given point is comparable to the overall duration of the rupture i e slip at a given point continues until information is received that the rupture has stopped propagating alternative explanations for the discrepancy between the short slip durations used to model waveforms and the long slip durations inferred from dynamic crack models are 1 the dislocation models are unable to resolve the relatively slow parts of earthquake slip and have seriously underestimated the dislocations for these earthquakes 2 earthquakes are composed of a sequence of small dimension short duration events that are separated by locked regions barriers 3 rupture occurs in a narrow self healing pulse of slip that travels along the fault surface evidence is discussed that suggests that slip durations are indeed short and that the self healing slip pulse model is the most appropriate explanation a qualitative model is presented that produces self healing slip pulses the key feature of the model is the assumption that friction on the fault surface is inversely related to the local slip velocity the model has the following features high static strength of materials kilobar range low static stress drops in the range of tens of bars and relatively low frictional stress during slip less than several hundreds of bars it is suggested that the reason that the average dislocation scales with fault length is because large amplitude slip pulses are difficult to stop and hence tend to propagate large distances this model may explain why seismicity and ambient stress are low along fault segments that have experienced large earthquakes it also qualitatively explains why the recurrence time for large earthquakes may be irregular

discordant 14c ages from buried tidal marsh soils in the cascadia subduction zone southern oregon coast peaty tidal marsh soils interbedded with estuarine mud in late holocene stratigraphic sequences near coos bay oregon may have been submerged and buried during great m 8 subduction earthquakes smaller localized earthquakes or by nontectonic processes radiocarbon dating might help distinguish among these alternatives by showing that soils at different sites were submerged at different times along this part of the cascadia subduction zone but comparison of conventional 14c ages for different materials from the same buried soils shows that they contain materials that differ in age by many hundreds of years errors in calibrated soil ages represent about the same length of time as recurrence times for submergence events 150 500 yr this similarity precludes using conventional 14c ages to distinguish buried soils along the southern oregon coast accelerator mass spectrometer 14c ages of carefully selected macrofossils from the tops of peaty soils should provide more precise estimates of the times of submergence events

irregular recurrence of large earthquakes along the san andreas fault evidence from trees old trees growing along the san andreas fault near wrightwood california record in their annual ring width patterns the effects of a major earthquake in the fall or winter of 1812 to 1813 paleoseismic data and historical information indicate that this event was the san juan capistrano earthquake of 8 december 1812 with a magnitude of 7 5 the discovery that at least 12 kilometers of the mojave segment of the san andreas fault ruptured in 1812 only 44 years before the great january 1857 rupture demonstrates that intervals between large earthquakes on this part of the fault are highly variable this variability increases the uncertainty of forecasting destructive earthquakes on the basis of past behavior and accentuates the need for a more fundamental knowledge of san andreas fault dynamics

a more precise chronology of earthquakes produced by the san andreas fault in southern california improved methods of radiocarbon analysis have enabled us to date more precisely the earthquake ruptures of the san andreas fault that are recorded in the sediments at pallett creek previous dates of these events had 95 confidence errors of 50 100 calendar years new error limits are less than 23 calendar years for all but two of the dated events this greater precision is due to larger sample size longer counting time lower background noise levels more precise conversion of radiocarbon ages to calendric dates and better stratigraphic constraints and statistical techniques the new date ranges with one exception fall within the broader ranges estimated previously but our estimate of the average interval between the latest 10 episodes of faulting is now about 132 years variability about the mean interval is much greater than was suspected previously five of the nine intervals are shorter than a century three of the remaining four intervals are about two to three centuries long despite the wide range of these intervals a pattern in the occurrence of large earthquakes at pallett creek is apparent in the new data the past 10 earthquakes occur in four clusters each of which consists of two or three events earthquakes within the clusters are separated by periods of several decades but the clusters are separated by dormant periods of two to three centuries this pattern may reflect important mechanical aspects of the fault s behavior if this pattern continues into the future the current period of dormancy will probably be greater than two centuries this would mean that the section of the fault represented by the pallett creek site is currently in the middle of one of its longer periods of repose between clusters and sections of the fault farther to the southeast are much more likely to produce the next great earthquake in california the greater precision of dates now available for large earthquakes recorded at the pallett creek site enables speculative correlation of events between paleoseismic sites along the southern half of the san andreas fault a history of great earthquakes with overlapping rupture zones along the mojave section of the fault remains one of the more attractive possibilities

synthetic aperture radar interferogram of the 1995 kobe earthquake and its geodetic inversion crustal deformation from the mw 6 9 january 17 jst 1995 kobe japan earthquake was detected by synthetic aperture radar interferometry sar more than four fringes with ellipsoidal shape were observed surrounding the nojima fault on northern awaji island suggesting a shortening in the range of more than 11 75 4 cm on the east side of this fault the sar sensor shows ellipsoidal fringes with an uplift zone in the rokko mountain range and sharp subsidence around the kobe area in addition to sar interferometry leveling and gps surveys were conducted by the geographical survey institute of japan gsi the permanent gps observation sites of the gsi monitored ground displacements from this earthquake with daily updates based on these geodetic data we estimated the faulting mechanism of the earthquake the analytical procedure was an iterative linearized least squares method a multi fault system consisting of six subfaults was constructed the locations of the estimated model faults were close to those of the active faults in this area running from the nojima fault on awaji island to the rokko faults in the kobe area with a change in strike angle near the ohtsuki fault in the kobe area the slip vectors of the nojima fault on awaji island had a large component of reverse dip slip of about 2 m and strike slip of about 2 m in the kobe area the amount of slip ranged from 0 3 to 1 2 m and was small compared with the slip on the nojima fault the results of these slip vectors agreed well with the results of other seismic geodetic and field studies

coseismic crustal deformation from the 1994 hokkaido toho oki earthquake monitored by a nationwide continuous gps array in japan using a brand new nationwide continuous gps array we monitored coseismic displacements from the october 4 1994 hokkaido toho oki kurile islands earthquake mjma 8 1 based on 2 week time series of site coordinates of 21 gps stations we present a coseismic deformation field of whole hokkaido within 1 cm precision for example the station at nemuro 170 km west of the epicenter moved 44 cm to the east and subsided 10 cm even stations in southern hokkaido 600 km apart from the epicenter moved a few cm horizontally toward the epicenter we compare the gps result with displacements calculated from two preliminary models assuming fault planes parallel or perpendicular to the kurile trench since the observed were far field displacements on land both models can explain the gps result

aftershock distribution of the october 4 1994 mw8 3 kurile islands earthquake determined by a local seismic network in hokkaido japan on october 4 1994 an earthquake with magnitude mw8 3 occurred in the western part of kurile islands at 43 42 n 146 81 e and 33 km in depth the hypocenter parameters were determined by hokkaido university in japan aftershocks following this remarkable event were located using data from a local seismic network operated by hokkaido university we found that most of the aftershocks occurred 1 on the fault plane of the mainshock 2 in the subducting plate around the fault plane of the mainshock and 3 in the focal area of the largest aftershock which occurred on october 9 with mw7 3 both 2 and 3 were not active immediately after the mainshock considering the time sequence of the aftershock activity we identified one of the nodal planes of the harvard quick cmt solutions as the fault plane of the mainshock the strike is almost parallel to the trench axis and the dip angle is near vertical it is obvious that this event is different from a low angle thrust type interplate earthquake the distribution of aftershocks strongly suggests that it is an intraplate event

source depth dependence of micro tsunamis recorded with ocean bottom pressure gauges the january 28 2000 mw 6 8 earthquake off nemuro peninsula japan abstract micro tsunami waves with a maximum amplitude of 4 6 mm were detected with the ocean bottom pressure gauges on a cabled deep seafloor observatory south of hokkaido japan following the january 28 2000 earthquake m w 6 8 in the southern kuril subduction zone we model the observed micro tsunami and estimate the focal depth and other source parameters such as fault length and amount of slip using grid searching with the least squares method the source depth and stress drop for the january 2000 earthquake are estimated to be 50 km and 7 mpa respectively with possible ranges of 45 55 km and 4 13 mpa focal depth of typical inter plate earthquakes in this region ranges from 10 to 20 km and stress drop of inter plate earthquakes generally is around 3 mpa the source depth and stress drop estimates suggest that the earthquake was an intra slab event in the subducting pacific plate rather than an inter plate event in addition for a prescribed fault width of 30 km the fault length is estimated to be 15 km with possible ranges of 10 20 km which is the same as the previously determined aftershock distribution the corresponding estimate for seismic moment is 2 7 10 19 nm with possible ranges of 2 3 10 19 3 2 10 19 nm standard tide gauges along the nearby coast did not record any tsunami signal high precision ocean bottom pressure measurements offshore thus make it possible to determine fault parameters of moderate sized earthquakes in subduction zones using open ocean tsunami waveforms

a 100 year average recurrence interval for the san andreas fault at wrightwood california evidence for five large earthquakes during the past five centuries along the san andreas fault zone 70 kilometers northeast of los angeles california indicates that the average recurrence interval and the temporal variability are significantly smaller than previously thought rapid sedimentation during the past 5000 years in a 150 meter wide structural depression has produced a greater than 21 meter thick sequence of debris flow and stream deposits interbedded with more than 50 datable peat layers fault scarps colluvial wedges fissure infills upward termination of ruptures and tilted and folded deposits above listric faults provide evidence for large earthquakes that occurred in a d 1857 1812 and about 1700 1610 and 1470

a five years super slow aseismic precursor model for the 1994 m8 3 hokkaido toho oki lithospheric earthquake based on tide gauge data 1 here we present a super slow aseismic event model prior to the magnitude 8 3 kurile island hokkaido toho oki earthquake on 4 october 1994 based on data recorded by two tide gauges located 50 150 km from the earthquake epicenter both instruments recorded several cm of subsidence during a five year period prior to the earthquake the observed signals are consistent with a precursory quasi stable slip on the western half of the hokkaido toho oki fault plane when recognized such aseismic events can considerably improve our intermediate term several years prediction capability

the 2000 nemuro hanto oki earthquake off eastern hokkaido japan and the high intraslab seismic activity in the southwestern kuril trench 1 the 2000 nemuro hanto oki earthquake mw6 8 occurred in the southwestern part of the kuril trench the hypocenter was located close to the aftershock region of the great 1994 kuril earthquake mw8 3 named the 1994 hokkaido toho oki earthquake by the japan meteorological agency for which the fault plane is still in debate analysis of the 2000 event provides a clue to resolve the fault plane issue for the 1994 event the hypocenters of the 2000 main shock and aftershocks are determined using arrival times from a combination of nearby inland and submarine seismic networks with an improved azimuthal coverage they clearly show that the 2000 event was an intraslab event occurring on a shallow dipping fault plane between 55 and 65 km in depth the well focused aftershock distribution of the 2000 event the relative location of the 1994 event with respect to the 2000 event and the similarity between their focal mechanisms strongly suggest that the faulting of the great 1994 earthquake also occurred on a shallow dipping fault plane in the subducting slab the recent hypocenter distribution around the 1994 aftershock region also supports this result large intraslab earthquakes occurring to the southeast of hokkaido may occur due to a strong coupling on the plate boundary which generates relatively large stress field within the subducting pacific plate

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

quick aftershock relocation of the 1994 shikotan earthquake and its fault planes the 1994 shikotan earthquake of mw 8 2 occurred near the western kurile trench where the pacific plate is subducting beneath the north american plate although its mechanism is thrust type it is not a typical low angle thrust event with a nodal plane parallel to the plate boundary that occurs at the plate boundary in order to determine which of the two nodal planes of the main shock was the fault plane we relocated the main shock and all aftershocks with m 5 3 using a modified joint hypocenter determination method earthquakes on the northwestern side of the aftershock area including the main shock are located along a plane dipping east southeastward with a dip of 70 this plane is about 80 to 150 km long and 70 km wide the main shock occurred at the north northeastern bottom of this plane which is almost parallel to one of the two nodal planes of the main shock determined by harvard university which has a strike of n51 e and a dip of 76 thus we conclude that this plane is the fault plane that the fault broke at the northeastern bottom of the fault plane and that the rupture propagated to the surface and also to the southeast in addition to the aftershocks aligned with this fault plane there is a secondary alignment which is subparallel to the main fault plane and about 50 km east where the largest aftershock of mw 7 3 occurred on oct 9 since several aftershocks occurred on this secondary fault plane on the same day as the main shock it seems reasonable to suppose that this secondary fault plane was generated together with the main fault plane at the time of the main shock

fault behavior and characteristic earthquakes examples from the wasatch and san andreas fault zones paleoseismological data for the wasatch and san andreas fault zones have led to the formulation of the characteristic earthquake model which postulates that individual faults and fault segments tend to generate essentially same size or characteristic earthquakes having a relatively narrow range of magnitudes near the maximum analysis of scarp derived colluvium in trench exposures across the wasatch fault provides estimates of the timing and displacement associated with individual surface faulting earthquakes at all of the sites studied the displacement per event has been consistently large measured values range from 1 6 to 2 6 m and the average is about 2 m on the basis of variability in the timing of individual events as well as changes in scarp morphology and fault geometry six major segments are recognized along the wasatch fault on the basis of the most likely number of surface faulting events 18 that have occurred on segments of the wasatch fault zone during the past 8000 years an average recurrence interval of 400 666 years with a preferred average of 444 years is calculated for the entire zone geologic data on the distribution of slip associated with prehistoric earthquakes and slip rates along the south central segment of the san andreas fault suggest that the m 8 1857 earthquake is a characteristic earthquake for this segment comparisons of earthquake recurrence relationships on both the wasatch and san andreas faults based on historical seismicity data and geologic data show that a linear constant b value extrapolation of the cumulative recurrence curve from the smaller magnitudes leads to gross underestimates of the frequency of occurrence of the large or characteristic earthquakes only by assuming a low b value in the moderate magnitude range can the seismicity data on small earthquakes be reconciled with geologic data on large earthquakes the characteristic earthquake appears to be a fundamental aspect of the behavior of the wasatch and san andreas faults and may apply to many other faults as well

coseismic displacements of the mw 6 1 july 9 1998 faial earthquake azores north atlantic 1 on 9 july 1998 an earthquake occurred ne of faial island azores north atlantic the harvard cmt solution points to a sub vertical strike slip event corresponding to the strikes n241e and n151e here we use gps data to estimate the coseismic displacements and to constrain the geometry of the earthquake source gps observations collected between 1993 and 1999 are processed to separate the interseismic and coseismic movements additionally a displacement field is derived from a denser gps network of 30 stations we model the coseismic movements by a dislocation in a homogenous elastic half space the data do not allow to infer the fault strike direction which have helped to understand the relationships with the regional geodynamics however the models give consistent figures for the fault surface 40 km2 the coseismic slip 1 m and the depth of the upper and lower edges of the fault plane 2 and 6 km

paleoseismic evidence of clustered earthquakes on the san andreas fault in the carrizo plain california exposures we have excavated across the san andreas fault contradict the hypothesis that part of the fault in the carrizo plain is unusually strong and experiences relatively infrequent rupture the exposures record evidence of at least seven surface rupturing earthquakes which have been approximately dated by accelerated mass spectrometry radiocarbon analysis of detrital charcoal and buried in situ plants five large earthquakes have occurred since 1218 a d the most recent earthquake event a was the 1857 fort tejon earthquake which we have associated with 6 6 10 m of dextral slip along the main fault trace the penultimate earthquake event b most likely occurred within the period a d 1405 1510 slip from either events b and c combined or from event b alone totals 7 11 m three earthquakes events c d and e occurred in a temporal cluster prior to event b and after approximately a d 1218 the average recurrence interval within this cluster is 73 116 years depending on assumptions events f and g occurred after 200 years b c a depositional hiatus between events e and f may hide evidence of additional earthquakes events b and d within the carrizo cluster of a d 1218 1510 may correlate with events t a d 1329 1363 and v a d 1465 1495 at pallett creek on the mojave segment of the fault this suggests two fault ruptures similar in length to that of 1857 events c and e apparently did not rupture the mojave section which suggests that the carrizo segment has ruptured independently or in combination with segments to the north irregular repeat times of large earthquakes suggest a pattern of clustered events at the end of seismic supercycles

the great kurile earthquake of october 4 1994 tore the slab the fault geometry depth and slip distribution of the kurile earthquake of oct 4 1994 are estimated using seismic waveforms aftershock distribution geodetic measurements and tsunami waveforms previous large earthquakes in the kurile arc had typical underthrusting focal mechanisms due to the local subduction seismic wave inversions of the 1994 event indicate a thrust type mechanism with a large strike slip component this does not represent an underthrust event at the subduction interface the focal depth is estimated at 50 kin just beneath the previously estimated subduction interface we calculate crustal deformation and tsunami waveforms from the two possible fault planes of the focal mechanism solution and find that both fault planes explain the observations we choose the north south striking plane because of the occurrence of a large m w 7 8 intermediate depth earthquake on dec 6 1978 northwest of the 1994 rupture area the lineation of aftershock distributions of these two events suggests that both earthquakes were due to a tearing of the slab perpendicular to the trench the joint inversion of geodetic and tsunami data shows that the largest slip about 17 m occurred at the upper end of the slab

refined coseismic displacement modeling for the 1994 shikotan and sanriku oki earthquakes we consider refined modeling of gps measurements of coseismic displacement for two large earthquakes occurring in the japan and kurile trenches calculations are performed for a layered sphere and the homogeneous half space more commonly used to model such data using fault geometry and slip distributions from previously published studies we show that the difference between the layered sphere and homogeneous half space calculations can be significant as expected from previous theoretical studies however it does not appear large enough to seriously affect results from previously published studies of these earthquakes nevertheless the fact that the effects of sphericity and especially layering are measurable in coseismic observations of great earthquakes at moderate distances indicates that these effects should be taken into account in order to fully exploit the precision of modern gps measurements

the october 4 1994 shikotan kurile islands tsunamigenic earthquake an open problem on the source mechanism on october 4 1994 an earthquake of magnitude m w 8 2 occurred in the western part of the kurile islands generating a tsunami that has been well recorded along the entire coast of japan previous works have shown that this earthquake does not represent a low angle thrust event normally expected in a subduction zone rather an intra plate event rupturing through the slab on the basis of the accepted mechanism two fault models representative of the nodal plane ambiguity have been suggested the goal of this work is to verify whether the tsunami simulations are able to rule out one of the two proposed fault models taking into account both fault models together with a heterogeneous slip along the fault we have performed numerical simulations of the tsunami all source models produce tide gauge records in agreement with the observed ones the limit of resolution of the performed simulations estimated by means of a perturbed bathymetry does not allow us to distinguish the best source model

a physical model for earthquakes 2 application to southern california the purpose of this paper is to apply ideas developed in a previous paper to the construction of a detailed model for earthquake dynamics in southern california the basis upon which the approach is formulated is that earthquakes are perturbations on or more specifically fluctuations about the long term motions of the plates this concept is made mathematically precise by means of a fluctuation hypothesis which states that all physical quantities associated with earthquakes can be expressed as integral expansions in a fluctuating quantity called the offset phase while in general the frictional stick slip properties of the complex interacting faults should properly come out of the underlying physics a simplification is made here and a simple spatially varying friction law is assumed together with the complex geometry of the major active faults an assumed spatially varying earth rheology the average rates of long term offsets on all the major faults and the friction coefficients one can generate synthetic earthquake histories for comparison to the real data the result is a set of slip time histories for all of the major faults which are similar to data obtained by geologic trenching studies however the patterns of earthquake occurrence are evidently chaotic in the technical sense meaning that although there is an element of periodicity to the events the patterns shift change and evolve with time time scales for pattern evolution seem to be of the order of a thousand years for average recurrance intervals of a hundred years or so in the synthetic slip histories for the model faults a series of events on the big bend is identified which resembles the pattern of events leading up to the 1857 fort tejon earthquake one of the events is similar enough to the 1857 event that it is taken as a model of that earthquake the horizontal surface deformation 130 years after the model event is calculated for comparison to the data observed by various methods during the past decade in southern california for example horizontal surface rates of strain and velocities are calculated and compared to u s geological survey trilateration data to very long baseline interferometry line length changes and to laser ranging data on the san andreas fault experiment baseline with a few exceptions agreement is good

earthquake recurrence and risk assessment in circum pacific seismic gaps the development of the concept of seismic gaps regions of low earthquake activity where large events are expected has been one of the notable achievements of seismology and plate tectonics its application to long term earthquake hazard assessment continues to be an active field of seismological research here i have surveyed well documented case histories of repeated rupture of the same segment of circum pacific plate boundary and characterized their general features i find that variability in fault slip and spatial extent of great earthquakes rupturing the same plate boundary segment is typical rather than exceptional but sequences of major events fill identified seismic gaps with remarkable order earthquakes are concentrated late in the seismic cycle and occur with increasing size and magnitude furthermore earthquake rup ture starts near zones of concentrated moment release suggesting that high slip regions control the timing of recurrent events the absence of major earthquakes early in the seismic cycle indicates a more complex behaviour for lower slip regions which may explain the observed cycle to cycle diversity of gap filling sequences

near field investigations of the landers earthquake sequence april to july 1992 the landers earthquake which had a moment magnitude m w of 7 3 was the largest earthquake to strike the contiguous united states in 40 years this earthquake resulted from the rupture of five major and many minor right lateral faults near the southern end of the eastern california shear zone just north of the san andreas fault its m w 6 1 preshock and m w 6 2 aftershock had their own aftershocks and foreshocks surficial geological observations are consistent with local and far field seismologic observations of the earthquake large surficial offsets as great as 6 meters and a relatively short rupture length 85 kilometers are consistent with seismological calculations of a high stress drop 200 bars which is in turn consistent with an apparently long recurrence interval for these faults