an algorithm for automated tsunami warning in french polynesia based on mantle magnitudes we have developed a new magnitude scale mm based on the measurement of mantle rayleigh wave energy in the 50 to 300 sec period range and directly related to the seismic moment through mm log10 m 20 measurements are taken on the first passage of rayleigh waves recorded on scale on broadband instruments with adequate dynamical range this allows estimation of the moment of an event within minutes of the arrival of the rayleigh wave and with a standard deviation of 0 2 magnitude units in turn the knowledge of the seismic moment allows computation of an estimate of the high seas amplitude of a range of expectable tsunami heights the latter combined with complementary data from t wave duration and historical references have been integrated into an automated procedure of tsunami warning by the centre polynesien de prevention des tsunamis cppt in papeete tahiti

t phase spectra seismic moments and tsunamigenesis t phase spectrograms and spectra derived from deep ocean hydrophones for tsunamigenic and non tsunamigenic earthquakes in the pacific reveal the following 1 substantial amounts of t phase energy at high frequencies i e 1 hz to at least 35 hz 2 strong correlations of spectral strengths in the 10 hz to 35 hz frequency range to seismic moments and 3 large spectral strengths at high frequencies for tsunamigenic earthquakes these findings are consistent with the low attenuation of the so und fixing and ranging sofar channel which permits efficient propagation of high frequencies to great distances and with the perception that large earthquakes may generate high frequency signals at the water sediment interface which can best be observed by hydroacoustic sensors in the low noise environment of the deep oceans in addition these studies confirm that 1 source bathymetry can strongly influence the character of t phases 2 islands or seamounts near the source area can act as secondary radiators of energy which add to the complexity and duration of the coda 3 there appears to be no significant dependence of t phase strength on earthquake source mechanism and 4 the strength of the t phase is dependent on the purity of its oceanic travel path the strong correlation of t phase spectral strengths to seismic moments suggests that substantial improvements in the reliability of tsunami warnings may be possible by using t phases as an additional independent single station method for estimating seismic moments finally the high frequencies observed in the t phase may be associated with important alternate mechanisms for tsunamigenesis other than faulting i e slumpage compaction or liquefaction

comment on source of the great tsunami of 1 april 1946 a landslide in the upper aleutian forearc by g j fryer et al mar geol 203 2004 201 218

palaeoenvironment of the eocene eckfeld maar lake germany implications from geochemical analysis of the oil shale sequence abstract drill core samples from the depth interval between 19 4 and 32 0 m of the laminated central lake facies of the eocene eckfeld maar were investigated for biomarker and stable isotope composition bulk organic geochemical parameters c n hi and the molecular composition of the soluble organic matter indicate a dominance of particulate organic matter from land plants and microbially derived lipids in the lower part of the sedimentary succession an angiosperm dominated vegetation is indicated from the terpenoid biomarker composition abundant 4 methylsteroids in the 25 6 30 8 m section of the oil shale sequence reflect a contribution of algal derived biomass samples with high concentrations of methylsteroids are characterized by low amounts of triterpenoids related to the arborane skeleton and vice versa this pattern is interpreted as reflecting differences in autochthonous organic matter production vs microbial activity in the lowermost section 32 0 30 6 m a trend towards heavier 18 o and 13 c values indicates the evolution of permanently meromictic conditions in the lake and an increase in methanogenesis high 13 c values of siderites 10 throughout most of the sequence are consistent with permanently anoxic conditions at the sediment water interface the lighter 18 o values of siderites from turbidites relative to siderites from biogenic laminites are postulated to have been caused by temporary phases of increased precipitation followed by landslides and improved circulation within the lake depletion of the organic matter in 13 c average 13 c 29 4 in comparison with the fossil wood ranging from 23 1 to 26 6 is explained by the dominance of waxy lipid rich land plant material e g leaf waxes resins bark over wood supplied to the lake carbon cycling during anoxic decomposition of organic matter is assumed to further affect the 13 c values through the activity of anaerobic e g methanogenic bacteria resulting in a depletion of the biomass in 13 c the overall trend in the isotopic composition of organic carbon towards heavier values in the depth interval between 26 0 and 3 2 m is accompanied by decreasing c n ratios indicating an increase in aquatic organic matter production the geochemistry of the oil shale succession points towards a highly productive eutrophic ecosystem with intense microbial activity under meromictic conditions in the maar lake beside the high input of land plants to the biomass major contributions from bacteria and phytoplankton are indicated by the biomarker composition

t phase data and regional tsunamigenesis in japan abstract good correlations are found between t phase spectral strengths and seismic moments for large earthquakes off the coasts of northern and central honshu japan also earthquakes from these areas which generated regional tsunamis in japan have larger seismic moments and t phase spectral strengths over the frequency range of 10 to 35 hz than nontsunamigenic earthquakes with similar source locations these findings are consistent with earlier observations of t phases from tsunamigenic and nontsunamigenic earthquakes near alaska and the aleutian islands walker et al 1992 and suggest that t phase data may be useful in improving the reliability of tsunami warning systems

t waves from the 1998 papua new guinea earthquake and its aftershocks timing the tsunamigenic slump t waves recorded at hydrophone and seismic stations following the papua new guinea earthquake of 17 july 1998 and its aftershocks show that a small event at 09 02 gmt featured source properties incompatible with an elastic dislocation of appropriate body wave magnitude m b 4 4 these include an exceptional duration 47 s at the wake island hydrophone station wk31 a spectrum rich in high frequencies 7 to 12 hz and a generally low spectral amplitude these characteristics can be explained by the model of an underwater slump accelerating from a standstill and eventually slowing down the relocation of the 09 02 event is compatible with its location within an amphitheater inside which shipboard cruises in 1998 and 1999 documented the presence of a 4 c km3 geologically fresh slump we propose that the slump took place at 09 02 on 17 july 1998 i e 13 minutes after the mainshock and that it generated the locally catastrophic tsunami whose properties amplitude and distribution of runup timing could not be explained by a dislocation model

the earthquake and tsunami of 1865 november 17 evidence for far field tsunami hazard from tonga summary historical reports of an earthquake in tonga in 1865 november identify it as the only event from that subduction zone which generated a far field tsunami observable without instruments run up heights reached 2 m in rarotonga and 80 cm in the marquesas islands hydrodynamic simulations require a moment of 4 1028 dyn cm a value significantly larger than previous estimates of the maximum size of earthquake to be expected at the tonga subduction zone this warrants an upwards re evaluation of the tsunami risk from tonga to the cook islands and the various polynesian chains which had hitherto been regarded as minor

on the mechanism of conversion of seismic waves to and from t waves in the vicinity of island shores high frequency seismic records from the polynesian seismic network are used to investigate in detail the processes of conversion of acoustic t wave energy from and to seismic waves at island shores on the source side we study the seismic to acoustic conversion based on t phases from hawaiian events recorded at polynesian stations located on the coral platter on the receiver side we study the acoustic to seismic conversion based on t phases from marine sources recorded across the polynesian islands in both instances our results underline the importance of steep slopes typically 50 in allowing an efficient conversion between p waves in the island structure and t waves in the water column these slopes can be coral reefs or the heads of young presumably unconsolidated basalt flows under this geometry modeling based on raytracing indicates that the seismic record of the t phase consists of a p wave at distances from the conversion point greater than 9 km at shorter distances s waves and surface waves are generated in the absence of a steep slope only surface waves are present these models can be used to compute precise and predictable travel time station corrections allowing the use of seismometers located inland to exploit the superb detection and location capabilities of t waves

a seismological reassessment of the source of the 1946 aleutian tsunami earthquake summary we present a re evaluation of the seismological properties of the aleutian tsunami earthquake of 1946 april 1 characterized by a deceptively low conventional magnitude 7 4 in view of its catastrophic tsunami both in the near and far fields relocation of 40 aftershocks show that the fault zone extends a minimum of 181 km along the aleutian trench in a geometry requiring a bilateral rupture from the original nucleation at the epicentre their spatial and temporal distribution are typical of the aftershock patterns of a large earthquake and rule out the model of a landslide source exclusive of a dislocation the analysis of the spectra of mantle waves favours the model of a large seismic source with a static moment of 8 5 10 28 dyn cm making the event one of the ten largest earthquakes ever recorded hence the destructive tsunami in the far field and of a slow bilateral rupture at an average velocity of only 1 12 km s 1 hence the destructive interference in all azimuths for all but the longest mantle waves the exceptionally slow character of the earthquake is confirmed by a deficiency in radiated seismic energy expressed by the lowest value measured to date of the energy tomoment ratio the earthquake appears as an end member in the family of tsunami earthquakes resulting from the combination of anomalous but not unprecedented parameters such as low stress drop and rupture velocity

calibration of the hglp seismograph network and centroid moment tensor analysis of significant earthquakes of 1976 abstract a methodology is developed for determining accurate instrument response functions for seismographs of the high gain long period hglp network recordings of daily transient calibration pulses provide a detailed history of the time varying responses of the hglp stations when the instrument displacement transfer function is available knowledge of the seismometer mass calibration coil constant and calibration current allows for the prediction of the shape and amplitude of the calibration signal by simple integration of the transfer function in theory the inverse of this statement is also true but in practice noise in the recordings contaminates the instrument response function recovered through direct differentiation of the calibration pulse the unknown transfer function of the seismograph system is instead first described by the product of the nominal responses of its mechanical and electromagnetic components specific values of the characteristic parameters for each seismograph component are subsequently determined by iterative least squares minimization of the misfit between observed and model transient calibration pulses by application of this method to daily calibration pulses recorded on the ten stations of the hglp network refined instrument response functions for 1976 and part of 1975 are determined the results agree well with single frequency amplitude calibration data recovered from station maintenance records and produce synthetic waveforms which are consistent with data from other well calibrated stations we use the recalibrated hglp data together with long period data from early international deployment of accelerometers ida and seismic research observatory sro digital stations to determine 108 centroid moment tensor cmt solutions for moderate and large earthquakes of 1976 the new cmt results for several major earthquakes including the tangshan guatemala and friuli events are compared with those of previous studies

detached deep earthquakes are they really abstract we use primarily the generation of acoustic t waves into the ocean by deep seismic sources to investigate the propagation of high frequency seismic energy from the bottom of subduction zones to the shoreline at the earth s surface conversion from shear waves to oceanic acoustic waves can be used as a proxy for the existence of a continuous slab featuring low anelastic attenuation with the help of other techniques such as the estimation of q from s to p spectral amplitude ratios we examine systematically a number of regions where earthquakes have been described as detached we establish the mechanical continuity of the slab to the hypocenters of the 1990 sakhalin and 1982 bonin events which occurred several hundred kilometers in front of the mainstream seismic zone the study of the 1989 paraguay shock is inconclusive probably due to its much smaller size the vertical continuity of the south american slab through its aseismic depth range is verified and a similar situation probably exists in java attenuation data suggests that the deep spanish earthquakes occur within a vertically large segment of colder material and a similar situation may exist in colombia the only clearly detached deep events with no mechanical connection to the surface make up the vityaz cluster under the north fiji basin based on a variety of geophysical evidence the small deep earthquakes under new zealand are likely to take place in a detached blob at least 350 km below the termination of mainstream seismicity these results support a model integrating buoyancy forces over a long continuous slab as the source of the down dip compressional stresses observed in large earthquakes at the bottom of the transition zone

the energy release in earthquakes energy calculations are generally made through an empirical application of the familiar gutenberg richter energy magnitude relationships the precise physical significance of these relationships is somewhat uncertain we make use here of the recent improvements in knowledge about the earthquake source to place energy measurements on a sounder physical basis for a simple trapezoidal far field displacement source time function with a ratio x of rise time to total duration t 0 the seismic energy e is proportional to 1 x 1 x 2 m 0 2 t 0 3 where m 0 is seismic moment as long as x is greater than 0 1 or so the effect of rise time is not important the dynamic energies thus calculated for shallow events are in reasonable agreement with the estimate e 5 10 5 m 0 based on elastostatic considerations deep events despite their possibly different seismological character yield dynamic energies which are compatible with a static prediction similar to that for shallow events studies of strong motion velocity traces obtained near the sources of the 1971 san fernando 1966 parkfield and 1979 imperial valley earthquakes suggest that even in the distance range of 1 to 5 km most of the radiated energy is below 1 to 2 hz in frequency far field energy determinations using long period wwssn instruments are probably not in gross error despite their band limited nature the strong motion record for the intermediate depth bucharest earthquake of 1977 also suggests little teleseismic energy outside the pass band of a long period wwssn instrument

teleseismic estimates of the energy radiated by shallow earthquakes the energy flux contained in the p wave groups p pp sp or the s wave groups s ps ss radiated by a shallow earthquake is modeled assuming that the energy flux in the direct and depth phases adds incoherently by defining generalized radiation patterns which incorporate this neutral interference the wave groups are analyzed as though they were comprised of a single phase measurements of the energy flux in the wave groups are corrected in the frequency domain for both the body wave attenuation and the frequency band of the recording the corrected measurements are then used to estimate the seismic energy radiated by the earthquake this analysis is applied to digital recordings of the teleseismic wave groups radiated by the may 2 1983 coalinga california earthquake and the october 28 1983 borah peak idaho earthquake for the coalinga earthquake an estimate of es 1 6 0 4 1021 dyn cm was determined from six p wave groups while the sh wave group recorded at station col returned an estimate of es 1 2 1021 dyn cm for the borah peak earthquake an estimate ofes 3 2 0 5 1021 dyn cm was determined from seven p wave groups the distribution of the isoseismals for the borah peak earthquake indicate that the energy radiated by this event was focussed to the northwest in the direction of rupture propagation correcting the teleseismic estimate for this focussing gives es 3 6 0 5 1021 dyn cm combining these estimates of the radiated energy with broad band estimates of the seismic moment yields estimates of the apparent stress of 17 and 7 bars for the coalinga and the borah peak earthquakes respectively

the 1996 peru tsunamigenic earthquake broadband source process we investigate the spatio temporal complexity of moment release of the february 21 1996 peru earthquake mw 7 5 we use a non linear source tomographic technique based on simulated annealing to invert surface wave source spectra for the slip distribution on a gently dipping fault plane the spectra 5 65 mhz are obtained using an empirical green s function egf method applied to first and second orbit fundamental mode rayleigh waves spectra are well fit by a 110 km bilateral rupture subparallel to the trench updip of the hypocenter with a total moment of 2 0 1020 nm the non linear inversion reveals a 30 30 km major slip patch south the onset where rupture velocities attain 1 5 2 0 km s inversions of teleseismic broadband p and sh waves 10 500 mhz indicate little or no directivity consistent with the surface wave data the average source time functions for both the surface and body wave data are similar in shape and in duration 50 s part of the slip during the 1996 peru event occurred in a region of reduced background seismicity as was the case for the 1992 nicaragua slow event suggesting that the seismogenic potential of low seismicity regions near the trench should be globally reassessed

constraining shallow slip and tsunami excitation in megathrust ruptures using seismic and ocean acoustic waves recorded on ocean bottom sensor networks abstract great earthquakes along subduction zone plate boundaries like the 2011 magnitude 9 0 tohoku oki japan event deform the seafloor to generate massive tsunamis tsunami wave heights near shore are greatest when excitation occurs far offshore near the trench where water depths are greatest and fault slip is shallow the tohoku event featuring over 30 m of slip near the trench exemplifies this hazard unfortunately the rupture process that far offshore is poorly constrained with land based geodetic and even most seafloor deformation measurements and seismic inferences of shallow slip are often nonunique here we demonstrate through dynamic rupture simulations of the tohoku event that long period guided waves in the ocean specifically leaking oceanic p wave modes known as pl waves can resolve the shallow rupture process and tsunami excitation near the trench with predicted pressure changes of 0 1 1 mpa along most of the seafloor landward of the trench and periods of several seconds these pl waves should be observable with ocean bottom pressure sensors and or seismometers with cabled sensor networks like those being deployed offshore japan and in other subduction zones these waves could be used to rapidly quantify shallow slip and near trench seafloor uplift and improve local tsunami early warning systems

comparison of t phase spectra and tsunami amplitudes for tsunamigenic and other earthquakes t phase spectral strengths and seismic moments from earlier studies for tsunamigenic and nontsunamigenic earthquakes off alaska the aleutians northern honshu and central honshu are compared to tsunami height recordings from coastal tide gauges and deep ocean pressure recorders tsunamigenic earthquakes have larger seismic moments and t phase spectral strengths than nontsunamigenic earthquakes pacific wide tsunamigenic earthquakes had well recorded water waves on the deep ocean pressure gauges while water waves for the regional tsunamis could be found only on coastal tide gauges in close proximity to the earthquake epicenters thresholds of t phase spectral strengths required for tsunamigenesis are estimated for each of the areas investigated on comparing tsunami heights seismic moments and spectral strengths for two pacific wide tsunamis generated by earthquakes with similar source locations we note that the earthquake with the larger tsunami has the larger t phase spectral strength but smaller seismic moment we conclude that t phase spectral strengths may be useful in estimating tsunami energy

the deficient t waves of tsunami earthquakes summary we develop an algorithm quantifying the energy flux of t phases recorded at island stations following major teleseismic events which we further scale by the seismic moment m0 of the earthquake to define a t phase efficiency we apply this concept to a set of six recognized tsunami earthquakes which generated tsunamis larger than expected from their conventional seismic waves through comparison with nearby reference events the t waves of which were recorded at the same sites we find that the tsunami earthquakes exhibit a deficiency in ranging from 1 5 to 2 5 orders of magnitude this result settles a 50 yr old controversy on the possible correlation between t wave generation and tsunami genesis the deficient character of the t waves from tsunami earthquakes readily supports the proposed model of an exceedingly slow rupture velocity for this class of events and the close examination of t wave trains supports the concept of a jerky rupture in at least two cases the computation of is straightforward in real time and could become a valuable contribution to real time tsunami warning in the far field

tsunami earthquakes the quest for a regional signal using the technique developed by newman and okal j geophys res 103 1998 26885 a dataset of digital records from 84 earthquakes is analyzed to investigate their source slowness in the quest for a possible regional signal in three subduction zones which experienced recent tsunami earthquakes nicaragua 1992 java 1994 peru 1996 the dataset is augmented by analog seismograms from historical events including major tsunamigenic earthquakes of the past 65 years we fail to detect a regional trend for slowness which suggests that the latter may be controlled on a more local scale by morphological structures of the subducting plate no correlation is found between slowness and either depth focal mechanism or seismic moment in nicaragua we document two slow historical earthquakes located on the slab down dip from the 1992 shock the most interesting results are in peru where a local area of slowness is tentatively defined around the source of the 1960 tsunami earthquake and where both the 1996 and 1960 tsunami earthquakes occur at the intersection of the trench with major topographic features on the nazca plate the mendana fracture zone and the trujillo trough respectively 2001 elsevier science b v all rights reserved

seismic and hydroacoustic effects of the may 29 2010 submarine south sarigan volcanic explosion energy release and interpretation abstract the may 2010 submarine volcanic crisis of the shallow south sarigan seamount marianas arc ended on may 29 by a violent explosion that emitted a 12 km high atmospheric plume and created a crater 350 m in diameter the application of the multiphase localization method to the pg p t phases of this explosion allows us to refine considerably mainly based on the intense and impulsive t phases the location of their source that fits the position of the newly formed south sarigan crater we highlight the numerous similarities of this final explosion with artificial underwater explosions conventional or nuclear tests of known energy especially the explosive nature of the source in the volcanic basement is confirmed by the similarity of the p phases with those of underground nuclear tests and the application of discriminating criteria ms mb the explosive nature of the source in the water is also confirmedby the application of the identification criteria for hydroacoustic sources and the t phases exceptionally impulsive and of short durations these similarities allow us to provide a rough evaluation of the energy released by the south sarigan final explosion using the methods commonly applied to man generated explosions we estimate a minimal released energy of 1 kt 4 2 1012 j for the seismic effects of the shock and ca 1 t of equivalent tnt i e 4 2 109 j for the hydroacoustic effects of the explosive source in the water the processes leading to this final explosion are discussed on the basis of the sequence of the earlier seismic and eruptive events within the comprehensive nuclear test ban treaty framework this explosion that affected concomitantly the solid liquid and subaerial media is the first well documented one having generated intense waves p hydroacoustic t acoustic infrasounds and tsunamis

field survey of the east java earthquake and tsunami of june 3 1994 a field survey of the june 3 1994 east java earthquake tsunami was conducted within three weeks and the distributions of the seismic intensities tsunami heights and human and house damages were surveyed the seismic intensities on the south coasts of java and bali islands were small for an earthquake with magnitude m 7 6 the earthquake caused no land damage about 40 minutes after the main shock a huge tsunami attacked the coasts several villages in east java province were damaged severely and 223 persons perished at pancer village about 70 percent of the houses were swept away and 121 persons were killed by the tsunami the relationship between tsunami heights and distances from the source shows that the hatori s tsunami magnitude was m 3 which seems to be larger for the earthquake magnitude but we should not consider this an extraordinary event because it was pointed out by hatori 1994 that the magnitudes of tsunamis in the indonesia philippine region generally exceed 1 2 grade larger than those of other regions

tsunamigenic earthquakes past and present milestones we review a number of events which taken individually have significantly affected our understanding of the generation of tsunamis by earthquake sources and our efforts at mitigating their hazards notably through the development of warning algorithms starting with the 1700 cascadia earthquake we examine how significant tsunamis have changed our views in fields as diverse as seismotectonics the diversity of earthquake cycles the development of warning algorithms the response of communities at risk to warnings and their education the latter being either formal or rooted in ancestral heritage we discuss in detail lessons from the 2004 sumatra disasters and review the performance of warning centers and the response of affected populations during the nine significant tsunamis which have taken place since 2004

extreme runup from the 17 july 2006 java tsunami 1 the 17 july 2006 magnitude mw 7 8 earthquake off the south coast of western java indonesia generated a tsunami that effected over 300 km of coastline and killed more than 600 people with locally focused runup heights exceeding 20 m this slow earthquake was hardly felt on java and wind waves breaking masked any preceding withdrawal of the water from the shoreline making this tsunami difficult to detect before impact an international tsunami survey team was deployed within one week and the investigation covered more than 600 km of coastline measured tsunami heights and run up distributions were uniform at 5 to 7 m along 200 km of coast however there was a pronounced peak on the south coast of nusa kambangan where the tsunami impact carved a sharp trimline in a forest at elevations up to 21 m and 1 km inland local flow depth exceeded 8 m along the elevated coastal plain between the beach and the hill slope we infer that the focused tsunami and runup heights on the island suggest a possible local submarine slump or mass movement

teleseismic estimates of radiated seismic energy the e m 0 discriminant for tsunami earthquakes we adapt the formalism of boatwright and choy for the computation of radiated seismic energy from broadband records at teleseismic distances to the real time situation when neither the depth nor the focal geometry of the source is known accurately the analysis of a large data set of more than 500 records from 52 large recent earthquakes shows that this procedure yields values of the estimated energy ee in good agreement with values computed from available source parameters for example as published by the national earthquake information center neic the average logarithmic residual being only 0 26 units we analyze the energy to moment ratio by defining log10 ee m0 for regular earthquakes this parameter agrees well with values expected from theoretical models and from the worldwide neic catalogue there is a one to one correspondence between values of that are deficient by one full unit or more and the so called tsunami earthquakes previously identified in the literature as having exceedingly slow sources and believed due to the presence of sedimentary structures in the fault zone our formalism can be applied to single station measurements and its coupling to automated real time measurements of the seismic moment using the mantle magnitude mm should significantly improve real time tsunami warning

long range detection of hydroacoustic signals from large icebergs in the ross sea antarctica abstract hydroacoustic signals detected in late 2000 by seismic stations in polynesia are shown to originate from huge icebergs which at the time were drifting in the ross sea after calving off the ross ice shelf the signals present a broad variety of spectral characteristics most of them featuring prominent eigenfrequencies in the 4 7 hz range often complemented by overtones most epicenters obtained by combining observations of distant hydroacoustic and regional seismic records follow the spatio temporal evolution of the drift of iceberg b 15b most of the signals are generated during a 36 day time window when it is speculated that b 15b collided with smaller icebergs or was scraping the ocean floor on the shallow continental shelf we speculate on the possible physical nature of the resonator generating the signals which could correspond to an elastic mode of the iceberg or to the oscillation of fluid filled cracks in the ice

estimation of seismic moment and slip distribution of the april 1 1946 aleutian tsunami earthquake the 1946 aleutian earthquake produced a tsunami of tsunami magnitude mt 9 3 but the surface wave magnitude is only ms 7 4 making it a tsunami earthquake the discrepancy between the apparent size of the earthquake based on the seismic data and the size of the tsunami has been explained by several mechanisms including a landslide and a slow earthquake but there are few seismic data available to determine the correct mechanism we study the generating mechanism of the tsunami using tsunami waveforms recorded on tide gauges we have modeled the source of the 1946 aleutian tsunami as the result of an underthrusting earthquake we performed both forward and inverse modeling of the data using a finite difference calculation to compute synthetic tsunamis we include both vertical and horizontal deformation of the ocean bottom due to faulting in the computation the results of the inversion of the tsunami waveforms show that the slip on the fault is mainly concentrated in the shallow section of the fault near the epicenter there is little slip in the area of the aftershocks indicating that the aftershocks may represent an area of afterslip or triggered seismicity the moment estimate of the earthquake is 23 1020 n m or mw 8 2 the majority of the waveforms are well explained by this fault model and slip distribution including the honolulu waveform but the hawaiian data also suggest that other effects such as a landslide may be necessary for explaining the abnormal tsunami amplitudes in hawaii the 1946 earthquake is similar to other tsunami earthquakes such as the 1896 sanriku and 1992 nicaragua earthquakes indicating that slow shallow rupture may explain the disproportionally large tsunamis

correction to t waves from the great 1994 bolivian deep earthquake in relation to channeling of s waves energy up the slab by emile a okal and jacques talandier

t waves from the great 1994 bolivian deep earthquake in relation to channeling of s wave energy up the slab we report the observation of t phases recorded at a number of pacific island sites following the great bolivian deep earthquake of june 9 1994 by studying their arrival times at the various stations we unravel the process of conversion from seismic to acoustic energy at the south american coastline we find that the maxima of amplitude of the phase are incompatible with propagation along the great circle from source to receiver but rather require the generation of the acoustic wave at a common point at the arica bight for all stations in the south pacific and even farther south for stations in hawaii and the bonin islands the timing of these conversions corresponds to the arrival of regional s waves at the conversion points the high frequency nature of the t phase requires the channeling of the s wave from the seismic source to conversion point through low attenuation material which in turns adds supportive evidence for the mechanical continuity of the downgoing slab under that section of south america despite the observed gap in seismicity between 300 and 600 km

the 1992 nicaragua earthquake a slow tsunami earthquake associated with subducted sediments the 1992 nicaragua earthquake was a tsunami earthquake that is it generated tsunamis disproportionately large for its surface wave magnitude m s the moment magnitude m w determined from long period 250 s surface waves was 7 6 significantly larger than the 20 s m s of 7 this m s m w disparity is also characteristic of tsunami earthquakes the nicaragua earthquake is the first tsunami earthquake to be captured by modern broadband seismic networks allowing us to present here seismograms of sufficiently high quality to make inferences about the rupture mechanisms we conclude that the nicaragua earthquake was a slow thrust earthquake which occurred on the subduction interface between the cocos and north american plates and because of the absence of sediments on the trench floor offshore of nicaragua the slip propagated up dip all the way to the ocean bottom exciting large tsunamis the occurrence of slip on a plate interface filled with soft subducted sediments caused the rupture process to be slower than in ordinary subduction zone thrust earthquakes our results reinforce the idea that tsunami warning systems using long period 100 s waves are necessary to reduce the hazard from this type of earthquake

the mw 8 1 antofagasta north chile earthquake of july 30 1995 first results from teleseismic and geodetic data a strong mw 8 1 subduction earthquake occurred on july 30 1995 in antofagasta northern chile this is one of the largest events during this century in the region it ruptured the southernmost portion of a seismic gap between 18 s and 25 s in 1992 we had used gps to survey a network with about 50 benchmarks covering a region nearly 500 km long n s and 200 km wide e w part of these marks were re surveyed with gps after the 1995 earthquake comparison with 1992 positions indicate relative horizontal displacement towards the trench reaching 0 7 m the inland subsided several decimeters the mejillones peninsula was uplifted by more than 15 cm teleseismic body wave modelling of vbb records gives a subduction focal mechanism and source time function with three distinct episodes of moment release and southward directivity modelling the displacement field using a dislocation with uniform slip in elastic half space suggests a rupture zone with 19 24 eastward dip extending to a depth no greater than 50 km with n s length of 180 km and an average slip of about 5 m the component of right lateral slip inferred both from the teleseismic and geodetic data does not require slip partitioning at the plate boundary that the well constrained northern end of the 1995 rupture zone lies under the southern part of the mejillones peninsula increases the probability for a next rupture in the gap north of it

rapid forecast of tsunami wave heights from a database of pre computed simulations and application during the 2011 tohoku tsunami in french polynesia 1 we present a method for the rapid estimation of tsunami wave heights either in the deep pacific basin or at specific shore locations it uses a database of 260 pre computed scenarios of generic sources distributed along the pacific trenches and can provide an estimate of wave heights within minutes of the location of the earthquake and the estimation of its moment the method is tested against a set of dart data and of 51 maregraph records in tahiti and the marquesas islands it was used in real time to successfully predict tsunami amplitudes in polynesia during the 2011 tohoku alert

controls on the t phase energy fluxes recorded on juan fernandez island by continental seismic wave paths and nazca bathymetry conicyt pcha doctorado nacional 2017 21171480 prs programa de riesgo sismico universidad de chile fondecyt 1170430

lateral asthenospheric viscosity variations and postglacial rebound a case study for the barents sea the effect of lateral asthenospheric viscosity variations on observable signatures related to postglacial rebound in the barents sea is studied using a finite element approach to discretize the problem a comparison between a laterally homogeneous reference earth model and a laterally heterogeneous earth model is performed the results indicate that a change in asthenospheric viscosity of about three orders of magnitude influences predictions of land uplift up to 10 20 m present day velocities up to 0 5 1 5 mm a and present day gravity anomalies up to 0 4 0 8 mgal in the northwestern part of the barents sea region

source characteristics of the 1992 nicaragua tsunami earthquake inferred from teleseismic body waves we analyzed the broadband body waves of the 1992 nicaragua earthquake to determine the nature of rupture the rupture propagation was represented by the distribution of point sources with moment rate functions at 9 grid points with uniform spacing of 20 km along the fault strike the moment rate functions were then parameterized and the parameters were determined with the least squares method with some constraints the centroid times of the individual moment rate functions indicate slow and smooth rupture propagation at a velocity of 1 5 km s toward nw and 1 0 km s toward se including a small initial break which precedes the main rupture by about 10 s we obtained a total source duration of 110 s the total seismic moment is m o 3 4 1020 nm which is consistent with the value determined from long period surface waves m o 3 7 1020 nm the average rise time of dislocation is determined to be 10s the major moment release occurred along a fault length of 160 km with the assumption of a fault width w 50 km we obtained the dislocation d 1 3 m from and d the dislocation velocity is d d 0 1 m s significantly smaller than the typical value for ordinary earthquakes the stress drop 1 1 mpa is also less than the typical value for subduction zone earthquakes by a factor of 2 3 on the other hand the apparent stress defined by 2 e s m o where and e s are respectively the rigidity and the seismic wave energy is 0 037 mpa more than an order of magnitude smaller than the nicaragua tsunami earthquake is characterized by the following three properties 1 slow rupture propagation 2 smooth rupture 3 slow dislocation motion

shallow subduction zone earthquakes and their tsunamigenic potential summary we have examined the source spectra of all shallow subduction zone earthquakes from 1992 to 1996 with moment magnitude 7 0 or greater as well as some other interesting events in the period range 1 20 s by computing moment rate functions of teleseismic p waves after comparing the source spectral characteristics of tsunami earthquakes earthquakes that are followed by tsunamis greater than would be expected from their moment magnitude with regular events we identified a subclass of this group slow tsunami earthquakes this subclass consists of the 1992 nicaragua the 1994 java and the february 1996 peru earthquakes we found that these events have an anomalously low energy release in the 1 20 s frequency band with respect to their moment magnitude although their spectral drop ov is comparable to those of the other earthquakes from an investigation of the centroid and body wave locations it appears that most earthquakes in this study conformed to a simple model in which the earthquake nucleates in a zone of compacted and dehydrated sediments and ruptures up dip until the stable sliding friction regime of unconsolidated sediments stops the propagation sedimentstarved trenches e g near jalisco can produce very shallow slip because the fault material supports unstable sliding the slow tsunami earthquakes also ruptured up dip however their centroid is located unusually close to the trench axis the subduction zones in which these events occurred all have a small accretionary prism and a thin layer of subducting sediment ocean surveys show that in these regions the ocean floor close to the trench is highly faulted we suggest that the horst and graben structure of a rough subducting oceanic plate will cause contact zones with the overriding plate making shallow earthquake nucleation and up dip propagation to the ocean floor possible the rupture partly propagates in sediments making the earthquake source process slow two factors have to be considered in the high tsunami generating potential of these events first the slip propagates to shallow depths in low rigidity material causing great deformation and displacement of a large volume of water second the measured seismic moment may not represent the true earthquake displacement because the elastic constants of the source region are not taken into account in the standard cmt determination

modeling of the february 1996 peruvian tsunami the february 1996 peruvian earthquake generated a larger tsunami than expected from its surface magnitude this discrepancy as well as the long rupture duration indicate that this event is a tsunami earthquake the associated tsunami was strong locally with runup heights of 1 to 5 meters along a coastline of 400 km it is shown that this tsunami can be modeled for a seismic moment of 2 1020 nm using a rigidity of 2 1010 n m the tsunami propagation is modeled solving long wave equations by a finite difference method the maximum run up heights in the region of chimbote can be simulated using a grid increment of 10 meters the propagation of this small tsunami across the pacific ocean is modeled taking into account frequency dispersion the only notable amplification occurred in the marquesas islands where wave heights of 2 meters were observed and are simulated

near field survey of the 1946 aleutian tsunami on unimak and sanak islands the 1946 aleutian earthquake stands out among tsunamigenic events because it generated both very high run up near the earthquake source region and a destructive trans pacific tsunami we obtained new data on the distribution of its tsunami in the near field along south facing coasts between unimak pass on the west and sanak island on the east by measuring the height of driftwood and beach materials that were deposited by the tsunami above the extreme storm tide level our data indicate that 1 the highest measured run up which is at the scotch cap light house was 42 m above tide level or about 37 m above present storm tide elevation 2 run up along the rugged coast from scotch cap for 12 km northwest to sennett point is 12 18 m and for 30 km east of scotch cap to cape lutke it is 24 42 m 3 run up along the broad lowlands bordering unimak bight is 10 20 m and inundation is locally more than 2 km 5 run up diminishes to 8 m or less at the southeast corner of unimak island 6 no evidence was found for run up above present storm tides about 4 5 m above mllw on the ikatan peninsula or areas along the coast to the west and 7 run up above storm tide level in the sanak island group is restricted to southwest facing coasts of sanak long and clifford islands where it is continuous and locally up to 24 m high generation of the tsunami by one or more major earthquake triggered submarine landslides near the shelf edge south of unimak island seems to be the only viable mechanism to account for the data on wave arrival time run up heights and distribution as well as for unconfirmed anecdotal reports of local postquake increases in water depth and diminished bottom fisheries productivity a preliminary hydrodynamic simulation of the local tsunami propagation and run up using a dipolar model of a possible landslide off davidson bank provides an acceptable fit to the characteristics of the distribution of local run up with a value at 34 m at the scotch cap lighthouse

automatic detection location and quantification of earthquakes application to tsunami warning we describe a fully automated seismic event detection and location system providing for real time estimates of the epicentral parameters of both local and distant earthquakes the system uses 12 telemetered short period stations with a regional aperture of 350 km as well as two 3 component broad band stations detection and location of teleseismic events is achieved independently and concurrently on the short period and long period channels the long period data is then used to obtain an estimate of the seismic momentm0 of the earthquake through the mantle magnitudemm as introduced byokal andtalandier 1989 in turn this estimate ofm0 is used to infer the expected tsunami amplitude at papeete within 15 minutes of the recording of rayleigh waves the performance of the method is discussed in terms of the accuracy of the epicentral parameters and seismic moment obtained in real time as compared to the values later published by the reporting agencies our estimates are usually within 3 degrees of the reported epicenter and the standard deviation on the seismic moment only 0 19 unit of magnitude for a population of 154 teleseismic events

modeling of the hydroacoustic signal and tsunami wave generated by seafloor motion including a porous seabed 1 within the framework of a 2 d compressible tsunami generation model with a flat porous seabed acoustic waves are generated and travel outward from the source area the effects of the porous seabed during tsunami generation and propagation processes include wave amplitude attenuation and low pass filtering of both the hydroacoustic signal and tsunami wave the period of the acoustic wave generated by the seafloor motion depends on water depth over the source area and is given by four times the period of time required for sound to travel from the seabed to the surface these waves carry information about seafloor motion the semianalytical solution of the 2 d compressible water layer model overlying a porous seabed is presented and discussed furthermore to include the effects generated by the coupling between compressible porous sedimentary and water layers a simplified two layer model with the sediment modeled as a compressible viscous fluid is presented