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

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

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

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

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

impact of near field deep ocean tsunami observations on forecasting the 7 december 2012 japanese tsunami following the devastating 11 march 2011 tsunami two deep ocean assessment and reporting of tsunamis dart dart and the dart logo are registered trademarks of the national oceanic and atmospheric administration used with permission stations were deployed in japanese waters by the japanese meteorological agency two weeks after deployment on 7 december 2012 a mw 7 3 earthquake off japan s pacific coastline generated a tsunami the tsunami was recorded at the two japanese darts as early as 11 min after the earthquake origin time which set a record as the fastest tsunami detecting time at a dart station these data along with those recorded at other darts were used to derive a tsunami source using the national oceanic and atmospheric administration tsunami forecast system the results of our analysis show that data provided by the two near field japanese darts can not only improve the forecast speed but also the forecast accuracy at the japanese tide gauge stations this study provides important guidelines for early detection and forecasting of local tsunamis

tsunami forecast analysis for the may 2006 tonga tsunami 1 this study applies tsunami forecast models developed for noaa s tsunami warning and forecast system to investigate the may 2006 tonga tsunami inversion of the deep ocean assessment and reporting of tsunamis dart measurements estimates a tsunami magnitude equivalent to an earthquake moment magnitude of 8 0 the dart constrained modeling forecasts show good agreement with observations at eight coastal tide stations in hawaii u s west coast and alaska including first arrival times wave periods wave amplitudes and decay during the day following the earthquake the forecast system correctly reproduces the reflected waves from north america and the scattered waves by the bottom topography in the south pacific which arrived in the hawaiian islands 16 and 18 5 h after the earthquake respectively wavelet analysis of the tsunami waves suggests that harbor and local shelf resonances may be predominantly responsible for the late occurrence of the maximum wave observed in some coastal areas these results suggest expanding the operational use of the real time forecast models and demonstrate the applicability of the forecast results for all clear evaluations search and rescue operations as well as event and postevent planning this research highlights the value of high resolution inundation models in real time forecasts during a long duration hazard for coastal communities it also provides a rigorous and successful test of the performance and accuracy of the forecast models when run in real time mode

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

sr isotope disequilibrium in columbia river flood basalts evidence for rapid shallow level open system processes geochemical variability among columbia river basalt group flood lavas has been attributed to two different origins derivation from heterogeneous mantle and modification of mantle derived magmas by open system processes involving continental crust we present in situ analyses of sr isotopes from core to rim transects of plagioclase phenocrysts and groundmass from each major columbia river basalt group formation and show that plagioclase crystals are usually internally zoned in 87 sr 86 sr and are in 87 sr 86 sr disequilibrium with their host groundmass these data unequivocally demonstrate that columbia river basalt magmas regardless of the nature of mantle sources were modified by opensystem processes operating at crustal depths one dimensional diffusion modeling indicates that observed isotopic heterogeneities cannot have existed at magmatic temperatures for more than a few years or decades in general results indicate that these flood basalt magmas were erupted while still in the process of assembly a typical columbia river flood basalt magma melt plus phenocrysts therefore only attains its final geochemical identity just before or during eruption a fact that is generally obscured when evaluating conventional whole rock isotope analyses

defining the source region of the indian ocean tsunami from gps altimeters tide gauges and tsunami models abstract to understand the role of the co seismic moment magnitude mw 9 1 9 3 sumatra andaman earthquake rupture mechanism on the severity of the indian ocean tsunami we used permanent global positioning system gps data and carried out an analysis of co seismic displacement and tsunami models tsunami modelling validated against independent jason 1 altimetry data and tsunami arrival time data as determined from tide gauges was used to analyse the results of five co seismic slip inversions using gps seismicity and or uplift data in this way we determined the most likely slip distribution characterized by slip maxima of 20 m in the south and 20 m in the north we used both the distribution and temporal evolution of the co seismic slip as derived from the gps data we show that the 9 min propagation time of the rupture led to constructive interference of waves radiating first from the south and minutes later from the north strengthening the tsunami in southern india sri lanka and thailand we conclude that the incorporation of permanent real time gps stations would represent a valuable component of future tsunami warning systems

formation of undular bores and solitary waves in the strait of malacca caused by the 26 december 2004 indian ocean tsunami 1 deformation of the indian ocean tsunami moving into the shallow strait of malacca and formation of undular bores and solitary waves in the strait are simulated in a model study using the fully nonlinear dispersive method fndm and the korteweg devries kdv equation two different versions of the incoming wave are studied where the waveshape is the same but the amplitude is varied full amplitude and half amplitude while moving across three shallow bottom ridges the back face of the leading depression wave steepens until the wave slope reaches a level of 0 0036 0 0038 when short waves form resembling an undular bore for both full and half amplitude the group of short waves has very small amplitude in the beginning behaving like a linear dispersive wave train the front moving with the shallow water speed and the tail moving with the linear group velocity energy transfer from long to short modes is similar for the two input waves indicating the fundamental role of the bottom topography to the formation of short waves the dominant period becomes about 20 s in both cases the train of short waves emerging earlier for the larger input wave than for the smaller one eventually develops into a sequence of rank ordered solitary waves moving faster than the leading depression wave and resembles a fission of the mother wave the kdv equation has limited capacity in resolving dispersion compared to fndm

hydrodynamic modeling of tsunamis from the currituck landslide article i nfo article history accepted 24 september 2008 tsunami generation fromthe currituck landslide offshore northcarolina and propagation of waves towardthe u s coastline are modeled based on recent geotechnical analysis of slide movement a long and intermediate wave modeling package coulwave based on the non linear boussinesq equations are used to simulate the tsunami this model includes procedures to incorporate bottom friction wave breaking and overland flow during runup potential tsunamis generated from the currituck landslide are analyzed using four approaches 1 tsunami wave history is calculated from several different scenarios indicated by geotechnical stability and mobility analyses 2 a sensitivity analysis is conducted to determine the effects of both landslide failure duration during generation and bottom friction along the continental shelf during propagation 3 wave history is calculated over a regional area to determine the propagation of energy oblique to the slide axis and 4 a high resolution 1d model isdeveloped to accuratelymodel wavebreakingand the combined influence of nonlinearity and dispersion during nearshore propagation and runup the primary source parameter that affects tsunami severity for this case study is landslide volume with failure duration having a secondary influence bottom friction during propagation across the continental shelf has a strong influence on the attenuation of the tsunami during propagation the high resolution 1d model also indicates that the tsunami undergoes nonlinear fission prior to wave breaking generating independent short period waves wave breaking occurs approximately 40 50 km offshore where a tsunami bore is formed that persists during runup these analyses illustrate the complex nature of landslide tsunamis necessitating the use of detailed landslide stability mobility models and higher order hydrodynamic models to determine their hazard published by elsevier b v

shelf resonance and impact of near field tsunami generated by the 2010 chile earthquake 1 the 2010 chile earthquake of mw 8 8 generated a destructive tsunami in the near field that resulted in warnings across the pacific numerical modeling shows trapping and amplification of the energy over the continental shelf and slope a spectral analysis of the computed surface elevation reveals resonance oscillations with periods up to 129 min along the central chile coast the temporal and spectral data provides an explanation for the long period waves recorded by dart buoys and the prolonged wave activities and belated impacts reported by residents and survey teams the present study of the 2010 chile tsunami together with those of the 2006 kuril and 2009 samoa tsunamis has directly associated shelf resonance with impacts on insular and continental coasts and provided a tool to identify at risk localities in tsunami hazard assessment

modeling of the 2011 japan tsunami lessons for near field forecast during the devastating 11 march 2011 japanese tsunami data from two tsunami detectors were used to determine the tsunami source within 1 5 h of earthquake origin time for the first time multiple near field tsunami measurements of the 2011 japanese tsunami were used to demonstrate the accuracy of the national oceanic and atmospheric administration noaa real time flooding forecast system in the far field to test the accuracy of the same forecast system in the near field a total of 11 numerical models with grids telescoped to 2 arcsec 60 m were developed to hindcast the propagation and coastal inundation of the 2011 japanese tsunami along the entire east coastline of japan using the noaa tsunami source computed in near real time the model results of tsunami propagation are validated with tsunami time series measured at different water depths offshore and near shore along japan s coastline the computed tsunami runup height and spatial distribution are highly consistent with post tsunami survey data collected along the japanese coastline the computed inundation penetration also agrees well with survey data giving a modeling accuracy of 85 5 for the inundation areas along 800 km of coastline between ibaraki prefecture north of kashima and aomori prefecture south of rokkasho the inundation model results highlighted the variability of tsunami impact in response to different offshore bathymetry and flooded terrain comparison of tsunami sources inferred from different indirect methods shows the crucial importance of deep ocean tsunami measurements for real time tsunami forecasts the agreement between model results and observations along japan s coastline demonstrate the ability and potential of noaa s methodology for real time near field tsunami flooding forecasts an accurate tsunami flooding forecast within 30 min may now be possible using the noaa forecast methodology with carefully placed tsunameters and large scale high resolution inundation models with powerful computing capabilities

development testing and applications of site specific tsunami inundation models for real time forecasting 1 the study describes the development testing and applications of site specific tsunami inundation models forecast models for use in noaa s tsunami forecast and warning system the model development process includes sensitivity studies of tsunami wave characteristics in the nearshore and inundation for a range of model grid setups resolutions and parameters to demonstrate the process four forecast models in hawaii at hilo kahului honolulu and nawiliwili are described the models were validated with fourteen historical tsunamis and compared with numerical results from reference inundation models of higher resolution the accuracy of the modeled maximum wave height is greater than 80 when the observation is greater than 0 5 m when the observation is below 0 5 m the error is less than 0 3 m the error of the modeled arrival time of the first peak is within 3 of the travel time the developed forecast models were further applied to hazard assessment from simulated magnitude 7 5 8 2 8 7 and 9 3 tsunamis based on subduction zone earthquakes in the pacific the tsunami hazard assessment study indicates that use of a seismic magnitude alone for a tsunami source assessment is inadequate to achieve such accuracy for tsunami amplitude forecasts the forecast models apply local bathymetric and topographic information and utilize dynamic boundary conditions from the tsunami source function database to provide site and event specific coastal predictions only by combining a deep ocean assessment and reporting of tsunami constrained tsunami magnitude with site specific high resolution models can the forecasts completely cover the evolution of earthquake generated tsunami waves generation deep ocean propagation and coastal inundation wavelet analysis of the tsunami waves suggests the coastal tsunami frequency responses at different sites are dominated by the local bathymetry yet they can be partially related to the locations of the tsunami sources the study also demonstrates the nonlinearity between offshore and nearshore maximum wave amplitudes

the july 15 2009 fiordland new zealand tsunami real time assessment on 15 july 2009 a mw 7 8 earthquake occurred off the new zealand coast which by serendipitous coincidence occurred while the international tsunami symposium was in session in novosibirsk russia the earthquake generated a tsunami that propagated across the tasman sea and was detected in new zealand australia and as far away as the us west coast small boats close to the epicenter were placed in jeopardy but no significant damage was observed despite a measured run up height of 2 3 m in one of the sounds in close proximity to the source wilson in gns science report 46 62 2009 peak to trough tsunami heights of 55 cm were measured at southport tasmania and a height of 1 m was measured in jackson bay new zealand the international tsunami symposium provided an ideal venue for illustration of the value of immediate real time assessment and provided an opportunity to further validate the real time forecasting capabilities with the scientific community in attendance a number of agencies with responsibility for tsunami forecast and or warning such as the noaa center for tsunami research the pacific tsunami warning center gns science in new zealand the australian bureau of meteorology and the european commission joint research centre were all represented at the meeting and were able to demonstrate the use of state of the art numerical models to assess the tsunami potential and provide warning as appropriate

the 2009 samoa tonga great earthquake triggered doublet great earthquakes having seismic magnitudes of at least 8 usually involve abrupt sliding of rock masses at a boundary between tectonic plates such interplate ruptures produce dynamic and static stress changes that can activate nearby intraplate aftershocks as is commonly observed in the trench slope region seaward of a great subduction zone thrust event1 the earthquake sequence addressed here involves a rare instance in which a great trench slope intraplate earthquake triggered extensive interplate faulting reversing the typical pattern and broadly expanding the seismic and tsunami hazard on 29 september 2009 within two minutes of the initiation of a normal faulting event with moment magnitude 8 1 in the outer trench slope at the northern end of the tonga subduction zone two major interplate underthrusting subevents both with moment magnitude 7 8 with total moment equal to a second great earthquake of moment magnitude 8 0 ruptured the nearby subduction zone megathrust the collective faulting produced tsunami waves with localized regions of about 12 metres run up that claimed 192 lives in samoa american samoa and tonga overlap of the seismic signals obscured the fact that distinct faults separated by more than 50 km had ruptured with different geometries with the triggered thrust faulting only being revealed by detailed seismic wave analyses extensive interplate and intraplate aftershock activity was activated over a large region of the northern tonga subduction zone

tsunami sources of the november 2006 and january 2007 great kuril earthquakes abstract along the northern kuril trench a great interplate earthquake occurred in november 2006 followed by an outer rise normal fault event in january 2007 surface wave magnitudes m s 7 8 and 8 2 indicate that the 2007 event was larger while the global cmt solutions m w 8 3 and 8 1 indicate that the 2006 event was larger tsunamis from both events were recorded at tide gauge stations in japan russia and the united states as well as deep ocean assessment and reporting of tsunamis dart systems and cabled tsunami sensors installed on deep ocean bottom inversion of 52 tsunami waveforms indicates that the 2006 tsunami source was about 200 km long extending from the epicenter to northeast the largest slips of 4 7 m are estimated on the northeastern subfaults for the 2007 event inversion of 32 waveforms shows that the tsunami source was about 120 km long with the largest slip of 3 5 m on the northeastern subfault the agreements between the observed and synthetic tsunami waveforms are generally good for both events not only within the inversion time windows but also for the later phases which were not used in inversions the slip distributions yield the seismic moment of m w 8 1 for the 2006 event and m w 7 9 for the 2007 event the seismic moment of the 2006 event was larger than the 2007 event from comparison of tsunami data regardless of fault model

tsunami scattering provinces in the pacific ocean we use a scattering index to identify the regions in the pacific ocean where topographic features scatter significant tsunami energy based on linear wave theory the index is computed from the smith sandwell topography consistent with numerical simulations it shows that there is a narrow band of strong scatterers running across the ocean from the northwest emperor seamount chain to the southeast easter island fracture zone the eastern pacific is nearly devoid of scatterers except for this band and isolated features along the eastern margin to the west of the band lies a region with moderate scattering the strongest scattering occurs in the southwestern pacific the pacific is rimmed by island arcs and shallow continental shelves that also trap and scatter tsunamis these results show that numerical models of trans pacific tsunamis must resolve the effects of the small scale topography in order to accurately simulate their wave patterns and amplitudes

near simultaneous great earthquakes at tongan megathrust and outer rise in september 2009 the tsunami that struck the samoan and northern tongan islands in september 2009 was preceded by a magnitude 8 earthquake on the outer slope of the oceanic trench where the pacific plate bends as it enters the subduction zone this was initially thought to be the sole source of the tsunami but a more complex picture is emerging two groups report the occurrence of two earthquakes a triggered doublet at nearly the same time and place what is not clear is which triggered the other beavan et al use an analysis of global positioning system station displacements and tsunami models to show that the outer rise earthquake was accompanied possibly triggered by a near simultaneous mega thrust earthquake in the adjacent tonga subduction zone lay et al analyse the available seismic data and their model suggests that the outer rise event triggered megathrust faulting either way this dual strike suggests a mechanism for the occasional large tsunamis generated at the tonga subduction zone on 29 september 2009 a tsunami devastated the samoan and northern tongan islands it is shown here that an unusual earthquake sequence preceded this tsunami a magnitude 8 earthquake in the outer rise intraplate region occurred almost simultaneously with rupture of the shallow subduction interplate interface equivalent to a magnitude 8 earthquake the findings provide information on strain release mechanisms at subduction zones and a possible mechanism for the occasional large tsunamis generated at the tonga subduction zone the earth s largest earthquakes and tsunamis are usually caused by thrust faulting earthquakes on the shallow part of the subduction interface between two tectonic plates where stored elastic energy due to convergence between the plates is rapidly released1 2 the tsunami that devastated the samoan and northern tongan islands on 29 september 2009 was preceded by a globally recorded magnitude 8 normal faulting earthquake in the outer rise region where the pacific plate bends before entering the subduction zone preliminary interpretation suggested that this earthquake was the source of the tsunami3 here we show that the outer rise earthquake was accompanied by a nearly simultaneous rupture of the shallow subduction interface equivalent to a magnitude 8 earthquake that also contributed significantly to the tsunami the subduction interface event was probably a slow earthquake with a rise time of several minutes that triggered the outer rise event several minutes later however we cannot rule out the possibility that the normal fault ruptured first and dynamically triggered the subduction interface event our evidence comes from displacements of global positioning system stations and modelling of tsunami waves recorded by ocean bottom pressure sensors with support from seismic data and tsunami field observations evidence of the subduction earthquake in global seismic data is largely hidden because of the earthquake s slow rise time or because its ground motion is disguised by that of the normal faulting event earthquake doublets where subduction interface events trigger large outer rise earthquakes have been recorded previously4 but this is the first well documented example where the two events occur so closely in time and the triggering event might be a slow earthquake as well as providing information on strain release mechanisms at subduction zones earthquakes such as this provide a possible mechanism for the occasional large tsunamis generated at the tonga subduction zone5 where slip between the plates is predominantly aseismic6

the 2011 magnitude 9 0 tohoku oki earthquake mosaicking the megathrust from seconds to centuries geophysical observations from the 2011 moment magnitude m w 9 0 tohoku oki japan earthquake allow exploration of a rare large event along a subduction megathrust models for this event indicate that the distribution of coseismic fault slip exceeded 50 meters in places sources of high frequency seismic waves delineate the edges of the deepest portions of coseismic slip and do not simply correlate with the locations of peak slip relative to the m w 8 8 2010 maule chile earthquake the tohoku oki earthquake was deficient in high frequency seismic radiation a difference that we attribute to its relatively shallow depth estimates of total fault slip and surface secular strain accumulation on millennial time scales suggest the need to consider the potential for a future large earthquake just south of this event

w phase inversion and tsunami inundation modeling for tsunami early warning case study for the 2011 tohoku event centroid moment tensor solutions for the 2011 tohoku earthquake are determined by w phase inversions using 5 and 10 min data recorded by the full range seismograph network of japan f net by a scaling relation of moment magnitude to rupture area and an assumption of rigidity of 4 1010 n m 2 simple rectangular earthquake fault models are estimated from the solutions tsunami inundations in the sendai plain minamisanriku rikuzentakata and taro are simulated using the estimated fault models then the simulated tsunami inundation area and heights are compared with the observations even the simulated tsunami heights and inundations from the w phase solution that used only 5 min data are considerably similar to the observations the results are improved when using 10 min of w phase data these show that the w phase solutions are reliable to be used for tsunami inundation modeling furthermore the technique that combines w phase inversion and tsunami inundation modeling can produce results that have sufficient accuracy for tsunami early warning purposes

near field tsunami forecasting from cabled ocean bottom pressure data 1 we propose a method for near field tsunami forecasting from data acquired by cabled offshore ocean bottom tsunami meters obtms in real time we first invert tsunami waveforms recorded at obtms to estimate the spatial distribution of initial sea surface displacements in the tsunami source region without making any assumptions about fault geometry and earthquake magnitude then we synthesize the coastal tsunami waveforms from the estimated sea surface displacement distribution to improve the reliability of the tsunami forecasting we use updated obtm data to repeat the forecast calculation at 1 min intervals we tested our method by simulating the 1896 sanriku tsunami earthquake which caused a devastating tsunami with maximum runup height of 38 m along the pacific coast of northeastern japan instead of real obtm records proxies were used the simulation demonstrated that our method provided accurate estimations of coastal arrival times and amplitudes of the first peak of the tsunami more than 20 min before the maximum amplitude wave reached the coastal site nearest to the source we also applied the method to real data of a small tsunami that was caused by a local earthquake and successfully forecasted the tsunami at coastal tide stations we found that accuracy of our estimated coastal tsunami amplitudes can be affected by the spatial relationship between the tsunami source and the offshore observation stations our numerical simulation showed that even more accurate tsunami amplitude forecasts would be achieved by deployment of additional offshore stations separated by a distance comparable to the trench parallel length of the tsunami source

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

real time experimental forecast of the peruvian tsunami of august 2007 for u s coastlines 1 at 23 41 utc on 15 august 2007 an offshore earthquake of magnitude 8 0 severely damaged central peru and generated a tsunami severe shaking by the earthquake collapsed buildings throughout the region and caused 514 fatalities the tsunami resulted in three casualties and a representative maximum runup height of 7 m in the near field the first real time tsunami data available came from a deep ocean tsunami detection buoy within 1 hour of tsunami generation these tsunami data were used to produce initial experimental forecasts within 2 hours of tsunami generation the far field forecasts indicated that the tsunami would not flood any of the 14 u s communities comparison with real time tide gage data showed very accurate forecasts

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

dispersive modeling of the 2009 samoa tsunami 1 in this study we investigate the dispersive effects in the 2009 samoa tsunami through numerical simulations the wave propagation is first simulated with a weakly nonlinear and dispersive boussinesq model and a non dispersive shallow water equations model comparison of the numerical results between these models indicates that tsunami propagation is significantly affected by the frequency dispersion east of tonga trench neglecting dispersive effects results in larger wave heights and speeds the strong frequency dispersion is primarily attributed to the dramatic variation of water surface elevations generated by the earthquake doublet and enhanced by the uneven bathymetry in tonga trench tsunami propagation is also simulated with most method of splitting tsunamis which is based on the shallow water equations but uses numerical dispersion to mimic physical frequency dispersion at operational resolutions a good agreement is observed between most and the boussinesq model as well as the field measurements in the leading wave in the shorter trailing waves agreement becomes poorer due to the mismatch between numerical and physical dispersions

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

survey of 2011 tohoku earthquake tsunami inundation and run up 1 at 14 46 local time on march 11 2011 a magnitude 9 0 earthquake occurred off the coast of northeast japan this earthquake generated a tsunami that struck japan as well as various locations around the pacific ocean with the participation of researchers from throughout japan joint research groups conducted a tsunami survey along a 2000 km stretch of the japanese coast more than 5300 locations have been surveyed to date generating the largest tsunami survey dataset in the world on the sendai plain the maximum inundation height was 19 5 m and the tsunami bore propagated more than 5 km inland along the ria coast from about 50 to 200 km north of sendai the narrow bays focused the tsunami waves generating the largest inundation heights and run ups the survey data clearly show a regional dependence of tsunami characteristics

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 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

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

displacement above the hypocenter of the 2011 tohoku oki earthquake the moment magnitude m w 9 0 2011 tohoku oki mega thrust earthquake occurred off the coast of northeastern japan combining global positioning system gps and acoustic data we detected very large sea floor movements associated with this event directly above the focal region an area with more than 20 meters of horizontal displacement that is four times larger than those detected on land stretches several tens of kilometers long along the trench the largest amount reaches about 24 meters toward east southeast just above the hypocenter furthermore nearly 3 meters of vertical uplift occurred contrary to observed terrestrial subsidence

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

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

tsunamigenic sea floor deformations in addition to the primary damage they do earthquakes can cause tsunamis massive ocean swells that can inundate coastal regions in their perspective synolakis et al describe results presented at a workshop on the interface between seismology and tsunami hydrodynamics held in santa monica in may 1997 the authors discuss the highlights of the meeting and summarize future directions for research

direct energy estimation of the 2011 japan tsunami using deep ocean pressure measurements 1 we have developed a method to compute the total energy transmitted by tsunami waves to the case where the earthquake source is unknown by using deep ocean pressure measurements and numerical models tsunami source functions based on the first wave recorded at the two closest tsunameters deep ocean assessment and reporting of tsunamis dart our analysis suggests that the march 11 2011 tohoku oki tsunami generated off japan originated from a 300 400 km long and 100 km wide area and the total propagated energy is 3 1015j with 6 uncertainty measurements from 30 tsunameters and 32 coastal tide stations show excellent agreement with the forecasts obtained in real time our study indicates that the propagated energy and the source location are the most important source characteristics for predicting tsunami impacts interactions of tsunami waves with seafloor topography delay and redirect the energy flux posing hazards from delayed and amplified waves with long duration seafloor topography also gives its spectral imprint to tsunami waves travel time forecast errors are path specific and correlated to the major wave scatterers in the pacific numerical dissipation in the propagation modeling highlights the need of high resolution inundation models for accurate coastal predictions on the other hand it also can be used to account for physical dissipation to achieve efficiency our results provide guidelines for the earliest reliable tsunami forecast warnings of long duration tsunami waves signals and enhancement of the experimental tsunami forecast system we apply the method to quantify the energy of 15 past tsunamis independently from earthquake magnitudes the small tsunami to seismic radiation energy ratios and their variability 0 01 0 8 reinforce the importance of using deep ocean tsunami data the direct measures of tsunamis for estimates of tsunami energy and accurate forecasting

rapid determination of earthquake magnitude using gps for tsunami warning systems 1 the 26 december 2004 sumatra earthquake mw 9 2 9 3 generated the most deadly tsunami in history yet within the first hour the true danger of a major oceanwide tsunami was not indicated by seismic magnitude estimates which were far too low mw 8 0 8 5 this problem relates to the inherent saturation of early seismic wave methods here we show that the earthquake s true size and tsunami potential can be determined using global positioning system gps data up to only 15 min after earthquake initiation by tracking the mean displacement of the earth s surface associated with the arrival of seismic waves within minutes displacements of 10 mm are detectable as far away as india consistent with results using weeks of data after the event these displacements imply mw 9 0 0 1 indicating a high tsunami potential this suggests existing gps infrastructure could be developed into an effective component of tsunami warning systems

source discriminants for near field tsunamis summary we present numerical simulations of tsunami run up in the near field for a data set of 72 models of sources involving both seismic dislocations and landslides by varying one by one the parameters describing the source and the receiving beach we are able to separate their individual influence on the amplitude and distribution of run up which we characterize by forming several dimensionless parameters principally the ratio i 2 of its maximum amplitude to its lateral extent along the beach we find that i 2 remains less than 10 4 for seismic dislocation sources but is greater than this threshold for all physically realistic models of underwater landslides thus it can be used as a discriminant for the nature of the source of a near field tsunami for seismic dislocations we also consider the ratio i 1 of maximum run up to seismic slip on the fault plane and validate numerically the previously suggested rule of thumb that this ratio cannot be much greater than 1 in the case of underwater landslides we show that the distribution of near field run up is primarily controlled by the 2 d wall of water displaced on the ocean surface as an initial condition to the simulation and is practically independent of its extension in the third dimension perpendicular to the beach we apply this approach to nine profiles of tsunami run up obtained experimentally during recent field surveys and show that our method successfully identifies the 1998 papua new guinea tsunami as having been generated by an underwater landslide thus confirming the results of shipboard and hydroacoustic investigations it also strongly suggests a similar mechanism for the generation of the near field aleutian tsunami of 1946 april 1