tectonics and slumping in the source region of the 1998 papua new guinea tsunami from seismic reflection images in september 1999 we collected seven high resolution seismic reflection profiles along the northern continental margin of papua new guinea which targeted the source region of the 1998 tsunami that inundated sissano lagoon we utilized swath bathymetry collected by the jamstec sopac groups in january 1999 the seismic profiles image several faults bottom simulating reflectors and a large rotational slump the slump has a head scarp of 100 m vertical extent coinciding with the headwall and tension cracks observed previously by submersible at the southern edge of the amphitheater the central back rotated part of the slump is coherent with parallel reflections the interpreted basal failure plane has a maximum depth of 760 m below the seafloor and it crops out at a steep escarpment about 100 meters high located 4 5 km north of the head scarp this escarpment separates the slide toe from a series of seafloor parallel coherent reflections that are top lapped by basin deposits at the foot of the amphitheater to the north the cross sectional area of the displaced mass is 2 3 km2 from the bathymetry the width is approximately 2 5 3 km yielding a total volume assuming parabolic shape of 3 8 4 6 km3 based on these interpretations the slump was restored to its undeformed position this technique yields a center of mass vertical drop of 380 m horizontal movement of 840 m and slip of 980 m along the slide plane

size distributions and failure initiation of submarine and subaerial landslides abstract landslides are often viewed together with other natural hazards such as earthquakes and fires as phenomena whose size distribution obeys an inverse power law inverse power law distributions are the result of additive avalanche processes in which the final size cannot be predicted at the onset of the disturbance volume and area distributions of submarine landslides along the u s atlantic continental slope follow a lognormal distribution and not an inverse power law using monte carlo simulations we generated area distributions of submarine landslides that show a characteristic size and with few smaller and larger areas which can be described well by a lognormal distribution to generate these distributions we assumed that the area of slope failure depends on earthquake magnitude i e that failure occurs simultaneously over the area affected by horizontal ground shaking and does not cascade from nucleating points furthermore the downslope movement of displaced sediments does not entrain significant amounts of additional material our simulations fit well the area distribution of landslide sources along the atlantic continental margin if we assume that the slope has been subjected to earthquakes of magnitude 6 3 regions of submarine landslides whose area distributions obey inverse power laws may be controlled by different generation mechanisms such as the gradual development of fractures in the headwalls of cliffs the observation of a large number of small subaerial landslides being triggered by a single earthquake is also compatible with the hypothesis that failure occurs simultaneously in many locations within the area affected by ground shaking unlike submarine landslides which are found on large uniformly dipping slopes a single large landslide scarp cannot form on land because of the heterogeneous morphology and short slope distances of tectonically active subaerial regions however for a given earthquake magnitude the total area affected by subaerial landslides is comparable to that calculated by slope stability analysis for submarine landslides the area distribution of subaerial landslides from a single event may be determined by the size distribution of the morphology of the affected area not by the initiation process

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

centroid moment tensor solutions for july september 1998 abstract centroid moment tensor solutions are presented for 214 earthquakes that occurred during the third quarter of 1998 the solutions are obtained using corrections for aspherical earth structure represented by a whole mantle shear velocity model sh8 u4l8 of dziewonski and woodward dziewonski a m woodward r l 1992 acoustic imaging at the planetary scale in emert h harjes h p eds acoustical imaging plenum new york 19 785 797 a new model of anelastic attenuation of durek and ekstrom durek j j ekstrom g 1996 a radial model of anelasticity consistent with long period surface wave attenuation bull seism soc am 86 144 158 is used to predict the decay of the waveforms

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

an energy duration procedure for rapid determination of earthquake magnitude and tsunamigenic potential summary we introduce a rapid and robust energy duration procedure based on the haskell extended source model to obtain an earthquake moment and a moment magnitude med using seismograms at teleseismic distances 30 90 this procedure combines radiated seismic energy measures on the p to s interval of broadband signals and source duration measures on high frequency p wave signals the med energy duration magnitude is scaled to correspond to the global centroid moment tensor cmt moment magnitude mcmtw and can be calculated within about 20 min or less after origin time ot the measured energy and duration values also provide the energy to moment ratio used for identification of tsunami earthquakes the med magnitudes for a set of recent large earthquakes match closely mcmtw even for the largest great earthquakes these results imply that the med measure is accurate and does not saturate after the 2004 december 26 sumatra andaman mega thrust earthquake magnitude estimates available within 1 hr of ot ranged from m 8 0 to 8 5 the cmt magnitude available about 3 hr after ot was mcmtw 9 0 and several months after the event mw 9 1 9 3 was obtained from analysis of the earth normal modes the energy duration magnitude for this event is med 9 2 a measure that is potentially available within 20 min after ot after the 2006 july 17 java earthquake the magnitude was evaluated at m 7 2 at 17 min after ot the cmt magnitude available about 1 hr after ot was mcmtw 7 7 the energy duration results for this event give med 7 8 with a very long source duration of about 160 s and a very low value indicating a possible tsunami earthquake

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

localization of t wave energy on land revealed by a dense seismic network in japan summary we have investigated the wave propagation characteristics of a seismic t wave on land in northeastern japan using the seismograms recorded by a dense seismic network the analysed t wave is a unique one that was generated by a large intermediate depth earthquake beneath the network that backpropagated from the emperor seamount chain in the northern pacific the t wave has a predominant frequency of 1 5 hz which is lower than the previously reported values spatiotemporal variation of an rms envelope bandpass filtered with a passband of 1 2 hz demonstrates multiple arrivals of the t wave and inhomogeneous distribution of amplitude judging from the spatial pattern of first arrival times and the polarization characteristics such as the relatively large dip angle and high planarity we regard the seismic t wave as a rayleigh wave a possible conversion area estimated by a method similar to the source scanning algorithm is located to the northeast of honshu island and may have a dimension of 100 km the most prominent feature of the spatiotemporal variation of the rms amplitude is the localization of t wave energy in the northeastern part of honshu island this localization can be attributed either to the close proximity of the conversion area to land or to the large extent of the area however these factors are only supplementary because they cannot explain a sharp contrast in amplitude between the two areas with comparable distance but different azimuth from the conversion point an additional and essential factor in explaining the observation is the non isotropic radiation from the conversion points since the conversion occurred on the continental slope the maximum amplitude of converted energy is expected to appear either in the propagation direction of incoming acoustic waves or in the steepest direction of the local topography these factors in particular a convex shape of bathymetry probably caused the focusing of converted energy into the northeastern part of honshu island

intraplate seismicity of the pacific basin 1913 1988 we establish here a comprehensive database of intraplate seismicity in the pacific basin relocation and analysis of 894 earthquakes yield 403 reliable intraplate earthquakes during 1913 1988 these numbers do not include earthquake swarms which account for another 838 events most of the remainder 304 events are actually plate boundary earthquakes that have been erroneously located in intraplate regions a significant number occur in recent years when location capabilities should have guarded against this situation relocations involve a careful linear inversion of p and s arrivals accompanied by a monte carlo statistical analysis we have also attentively removed the high number of clerical errors and nuclear tests that exist in epicenter bulletins

hydroacoustic detection of submarine landslides on kilauea volcano landslides produced at the site where lava flows intothe o cean at kilauea vo lcanohave been detected hy droacoustically up to 10 landslides per day were detected by a hydrophone on the hawaii undersea geo observatory hugo located 50 km south of the entry site the largest of these landslides partly subaerial events known as bench collapses were detected by a network of hydrophones in the eastern pacific 5000 7000 km away from the source the landslides display a characteristic spectral signature eas ily recognizable among other signals such as earthquake t phases and anthropogenic noises the fact that signals are detected at great distances suggests that hydroacoustic de tection of landslides could be a powerful tool in tsunami monitoring and modeling efforts

the 1956 greek tsunami recorded at yafo israel and its numerical modeling floating type tidal gauge installed in the port of yafo israel the tsunami was triggered by an earthquake in the aegean sea on 9 july 1956 this paper presents a retrieval of tsunami waves from the record at the first stage of the study an attempt had been undertaken to reproduce the 1956 tsunami assuming a coseismic nature of its generation source although these simulations resulted in tsunami waves with their amplitude close to that obtained from the record measured at yafo they did not contain significant spectral energy components with periods of 15 min as appear in the spectra of 1956 tide gauge records when landslide movement triggered by the main shock and or by the largest aftershock is suggested as a source of these tsunami waves the spectra of the resulted marigram obtained in the proximity to yafo contain harmonics with frequencies very close to those measured this corroborates the landslide nature of the tsunamigenic source responsible for generation of higher frequency relative to the tidal waves energy components the peak periods determined via spectral analysis of the recent tide gauge records 1 year and longer in the absence of tsunami events vary from 50 to 60 min similar periods have been revealed in a special numerical study dealing with longwave propagation toward the coast of israel thus confirming that their origin is related to continental shelf resonance these resonance periods differ significantly from those found for the 1956 tsunami

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

the 1998 papua new guinea earthquake and its fault plane estimated from relocated aftershocks the 1998 papua new guinea earthquake of m w 7 0 occurred near the wewak trench where the north bismarck plate is subducting beneath the australian plate its mechanism is thrust type and one of the nodal planes is almost parallel to the plate interface to determine which of the two nodal planes of the main shock is the fault plane we relocated the main shock and aftershocks using a method of modified joint hypocenter determination we combined and employed two types of data in this study firstly we used data reported by the national earthquake information center neic of the u s geological survey usgs which includes three stations at the northeastern edge of irian jaya and one station in northern papua new guinea from which the epicentral distances are less than 2 degrees secondly in addition to the above permanent station data we used data from temporary aftershock observations near the epicentral area around the sissano lagoon carried out by tsuji et al 1998 using three component seismometers they carried out observations from august 2 to october 2 1998 at three sites although the network did not record the main shock and immediate aftershocks the data obtained by temporary observation sites can clearly assist in identifying their absolute locations since it is possible to apply the joint hypocenter determination jhd method hypocenters were relocated between the coastline and the wewak trench distributed along a nodal plane dipping shallowly to the southwest therefore we can conclude that this nodal plane is the main shock fault and that the 1998 papua new guinea earthquake was an interplate earthquake between the north bismarck and australian plates

hydroacoustic investigation of submarine landslides at west mata volcano lau basin submarine landslides are an important process in volcano growth yet are rarely observed and poorly understood we show that landslides occur frequently in association with the eruption of west mata volcano in the ne lau basin these events are identifiable in hydroacoustic data recorded between 5 and 20 km from the volcano and may be recognized in spectrograms by the weak and strong powers at specific frequencies generated by multipathing of sound waves the summation of direct and surface reflected arrivals causes interference patterns in the spectrum that change with time as the landslide propagates observed frequencies are consistent with propagation down the volcano s north flank in an area known to have experienced mass wasting in the past these data allow us to estimate the distance traveled by west mata landslides and show that they travel at average speeds of 10 25 m s

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

numerical modeling of the june 17 2017 landslide and tsunami events in karrat fjord west greenland on june 17 2017 the western coast of greenland was the site of a tsunami which flooded several villages killing 4 people and destroying 11 houses in the village of nuugaatsiaq this tsunami was triggered by a subaerial landslide which occurred in a fjord 32 km ene of nuugaatsiaq this paper presents the numerical modeling of this landslide of sim 50 million hbox m 3 and of the tsunami propagation from its source to nuugaatsiaq the landslide is considered as a granular flow under gravity forces and the water waves generated are related to the displacement of the sea bottom the results obtained are similar in amplitude to our inferences from videos i e three water waves between 1 and 1 5 m arriving at nuugaatsiaq with a period of roughly 3 min and are also in general agreement with the amplitude 1 m resulting from deconvolution of oscillations recorded on a horizontal seismogram operating at nuugaatsiaq nuug according to the field survey performed by fritz et al egu general assembly conference abstracts vol 20 of egu general assembly conference abstracts p 18345 2018a on july 2017 a second mass next to the landslide is threatening karrat fjord a sensitivity study is realized on its volume with 2 7 14 and 38 million hbox m 3 reaching the sea the shape of the water waves is found to be independent of volume and linearity is observed between the volume and the water wave heights finally the orientation of the slide does not seem to influence either the period or the shape of the generated water waves

seismic and acoustic signatures of surficial mass movements at volcanoes abstract surficial mass movements such as debris avalanches rock falls lahars pyroclastic flows and outburst floods are a dominant hazard at many volcanoes worldwide understanding these processes cataloging their spatio temporal occurrence and detecting tracking and characterizing these events would advance the science of volcano monitoring and help mitigate hazards seismic and acoustic methods show promise for achieving these objectives many surficial mass movements generate observable seismic and acoustic signals and many volcanoes are already monitored significant progress has been made toward understanding modeling and extracting quantitative information from seismic and infrasonic signals generated by surficial mass movements however much work remains in this paper we review the state of the art of the topic covering a range of scales and event types from individual rock falls to sector collapses we consider a full variety of volcanic settings from submarine to subaerial shield volcano to stratovolcano finally we discuss future directions toward operational seismo acoustic monitoring of surficial mass movements at volcanoes

the tsunami induced by the 2003 zemmouri earthquake mw 6 9 algeria modelling and results summary a strong tsunami with sea disturbances observed along the algerian coast but with significant damage mainly in the balearic islands spain harbours affected the western mediterranean following the 2003 zemmouri earthquake m w 6 9 algeria an average regional uplift of 0 55 m was measured along the shoreline in the epicentral area field observations main shock and aftershocks characteristics are consistent with thrust along a 55 km long rupture trending ne sw dipping se the seismotectonic parameters indicate a hypocentre 7 8 km deep and a possible fault break between 5 and 15 km offshore several tide gauges located in the western mediterranean coast indicated an average of 0 4 m of sea level change with a maximum of 2 m in the balearic islands we generated high resolution bathymetry grids from the algerian coasts to the balearic islands coasts in order to test different seismic sources with different fault rupture location strike and dip and model the tsunami initiation and propagation for the modelling we employed the crank nicolson numerical schema with a finite difference method and the okada elastic dislocation theory for the fault rupture we also highlight the different factors responsible for waves amplification around the balearic coast the best fit between synthetic and real data tide gauges gps levelling and coastal uplift as compared to run up values are obtained for a thrust rupture comparable with the earthquake fault inferred from seismotectonic studies and located within 15 km offshore an analysis of t waves reinforces the earthquake rupture origin for the tsunami this study presents the results and modelling of a major tsunami recorded in the western mediterranean sea

mm a variable period mantle magnitude this paper lays the theoretical groundwork for a variable period mantle magnitude mm based on the measurement of the spectral amplitude x of very long period rayleigh waves we retain the concept of magnitude by restricting ourselves to single station measurements ignoring the focal mechanism and the exact depth of the shallow earthquakes considered our measurements are made at a series of periods in all cases greater than 40 s and the largest value is retained this procedure effectively avoids the well known interference effects leading to saturation of magnitude scales defined at a fixed period two corrections are used a period dependent distance correction cd and a source correction cs also period dependent compensating for the variation of the excitation of rayleigh waves with period both of these corrections are fully predictable on the basis of standard surface wave excitation and dispersion theory the result is a formula of the type mm log10 x cd cs c0 in which all coefficients including the constant c0 are justifiable on sound theoretical grounds the analysis of a data set of 256 records from the broadband seismograph at papeete tahiti the ultra long period system at pasadena and stations of the geoscope network shows that the mean error in the estimation of the seismic moment is on the order of 0 1 0 2 units of magnitude with the standard deviation at each station also on the order of 0 2 units of magnitude no significant trend with either distance period or station can be identified the method can also be transposed to the time domain under some simple assumptions which are justifiable theoretically for typical teleseismic distances across the pacific basin both versions of the method lend themselves well to automation thus by providing a real time estimate of the seismic moment of distant earthquakes mm has considerable potential for tsunami warning purposes its concept can easily be extended to love waves and also to intermediate and deep earthquakes

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

twenty five years of progress in the science of geological tsunamis following the 1992 nicaragua and flores events we review a set of 47 tsunamis of geological origin triggered by earthquakes landslides or volcanoes which have occurred over the past 25 years and provided significant new insight into theoretical experimental field or societal aspects of tsunami science among the principal developments in our command of various aspects of tsunamis we earmark the development of the w phase inversion for the low frequency moment tensor of the parent earthquake the abandonment of the concept of a maximum earthquake magnitude for a given subduction zone controlled by simple plate properties the development and implementation of computer codes simulating the interaction of tsunamis with initially dry land at beaches thus introducing a quantitative component to realistic tsunami warning procedures and the recent in situ investigation of current velocities in addition to the field of surface displacements during the interaction of tsunamis with harbors continued research remains warranted notably in the field of the real time identification of tsunami earthquakes whose tsunamis are larger than expected from their seismic magnitudes especially conventional ones the recent tragedy during the 2018 krakatau flank collapse along a scenario which had been quantitatively forecast also emphasizes the need for a continued effort in the education of the populations at risk

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

thermocline control on coccolith diversity and abundance in recent sediments from the celtic sea and english channel abstract the first systematic record of the abundance and species diversity of coccolith assemblages in the recent shelf sediments of the celtic sea and english channel is presented eighteen coccolith species occur in the sediments although the assemblages are dominated by emiliania huxleyi which frequently forms over 90 of the total flora highest coccolith numbers occur in sediments from the celtic sea 10 9 coccoliths g 10 of the fine fractions coccoliths are either scarce 10 6 g kn assemblages deposited beneath a pronounced thermocline contain high numbers of coccoliths a sparse nannoflora limited to six or fewer species occurs in assemblages deposited from a tidally mixed water column similar controls on coccolith distribution are likely to have occurred in the past the abundance and mode of preservation of coccoliths may therefore provide information on the degree of turbulence in ancient shelf environments

sediment instability and slumping in the southern aegean sea and the case history of the 1956 tsunami the aegean and ionian seas in greece and adjacent regions constitute the most tsunamigenic areas in europe the most recent large tsunami was a 20 m high wave that generated on 9 july 1956 in the amorgos basin south aegean sea in association with a ms 7 5 earthquake we first present new evidence for sea floor sediment instability from bathymetric shallow and intermediate penetration seismic profiles and a number of gravity cores second we investigate the generation mechanism of the 1956 large tsunami the determination of the mean repeat time of the minimum seismic ground acceleration required for slump triggering of sediment masses showed that in particular south aegean basins like the argolikos and amorgos ones the mean recurrence of massive sediment slumping ranges between 50 and 100 years in other basins however it is around or more than 500 years in the southern amorgos basin a large scale sediment slump has been identified this was probably triggered by the 1956 mainshock and or its aftershock of ms 7 2 that occurred in the slump source area 13 min after the mainshock the generation of the 1956 tsunami is attributed to the combined action of a reactivated large normal fault to the south of the amorgos island and to the occurrence of the large sediment slump

source mechanism of the magnitude 7 2 grand banks earthquake of november 1929 double couple or submarine landslide we have examined p s and surface waves derived from seismograms that we collected for the 1929 grand banks canada earthquake this event is noteworthy for the sediment slide and turbidity current that broke the trans atlantic cables and for its destructive tsunami both the surface wave magnitude m s and the body wave magnitude m b calculated from these seismograms are 7 2 fault mechanisms previously suggested for this event include a nw se striking strike slip mechanism and an approximately e w striking thrust mechanism in addition because of the presence of an extensive area of slump and turbidity current there exists the possibility that sediment slumping could also be a primary causative factor of this event we tested these fault models and a horizontal single force oriented n5 w model representing a sediment slide against our data among these models only the single force model is consistent with the p s and surface wave data our data however do not preclude fault models which were not tested from the spectral data of love waves at a 50 sec period we estimated the magnitude of the single force to be about 1 4 10 20 dynes from this value we estimated the total volume of sedimentary slumping to be about 5 5 10 11 m 3 which is approximately 5 times larger than a recent estimate of volume from in situ measurements the difference in estimates of overall volume is likely due to a combination of the inherent difficulty in estimating accurately the displaced sediments from in situ measurements and of inadequacy of the seismic model or perhaps because not only the slump but also a tectonic earthquake could have been the cause of this event and contributed significantly to the waveforms studied

reply to comment of emile okal on source of the great tsunami of 1 april 1946 a landslide in the upper aleutian forearc

on the influence of slopes source seabed and water column properties on t waves generation at shore the term t waves is generally associated with acoustic waves generated by seismic events that subsequently travel horizontally in the ocean at the speed of sound in this paper we use a time domain spectral element method to perform a parametric study of the influence of seafloor slope source position and media properties for a typical downslope t wave generation scenario we find that the energy and duration of these waves are particularly sensitive to the environment in particular the slopes and physical characteristics of the seabed play a crucial role for both the generation and the conversion of these waves likewise the depth and position of the earthquake relative to the slope is of great importance with the presence of privileged areas for the generation of t waves which we map

a theoretical comparison of tsunamis from dislocations and landslides we use simple physical models to evaluate and compare the orders of magnitude of the energy generated into a tsunami wave by seismic dislocations and underwater slumps we conclude that the two sources can generate tsunamis of comparable total energy however the slumping source is shown to be fundamentally dipolar in nature which results in a low frequency deficiency in the far field these simple conclusions corroborate the interpretation of the 1998 papua new guinea tsunami as being generated by an underwater slump

a single force model for the 1975 kalapana hawaii earthquake a single force mechanism is investigated as the source of long period seismic radiation from the 1975 kalapana hawaii earthquake m s 7 1 the observed love wave radiation pattern determined from the spectra of world wide standard seismograph network and high gain long period records at 100 s is two lobed with azimuth consistent with a near horizontal single force acting opposite strike 330 to the observed displacement direction of the earthquake this pattern is inconsistent with the expected double couple pattern assuming a form of the force time history of a one cycle sinusoid the total duration of the event estimated from rayleigh waves at two international deployment of accelerometers stations is approximately 180 s the peak amplitude f o of the time function is 1 10 15 n from amplitudes of love and rayleigh waves the interpretation is that the bulk of the seismic radiation was produced by large scale slumping of a large area of the south flank of kilauea volcano the single force is a crude representation of the effect on the earth of the motion of a partially decoupled large slide mass using the mass estimated from the tsunami generation area 10 15 10 16 kg the peak acceleration of the slide block 0 1 1 m s 2 inferred from the seismic force is comparable with the acceleration due to gravity on a gently inclined plane the slump model for the kalapana earthquake is also more qualitatively consistent with the large horizontal deformation 8 m on land and tsunami associated with the earthquake which are difficult to explain with the conventional double couple source model the single force source has been used previously to model the long period seismic waves from the landslide accompanying the eruption of mount st helens volcano and may explain other anomalous seismic events as being due to massive slumping of sediments or unconsolidated material and not to elastic dislocation

converted t phases recorded on hawaii from polynesian nuclear tests a preliminary report we present a preliminary study of twaves from polynesian nuclear tests at mururoa recorded on digital stations of the hawaii volcano observatory network following their conversion to seismic waves at the southern shore of the island of hawaii and subsequent propagation to the recording stations we show that seismograms are composed of several packets which can be interpreted as resulting fromt p and t sconversions and which feature distinct spectral characteristics as the distance from the shoreline to the station increases the relative importance of the several wave packets changes a prominent shadow for t p is found at 8 12 km from the shore this pattern is affected by the local crustal structure in a favorable case propagation in deep low attenuation layers resulted in a clear record as far as 76 km from the shoreline while these results are generally robust they can be moderately affected by a change of location of the source inside mururoa atoll

near field modeling of the july 17 1998 tsunami in papua new guinea modest earthquakes may trigger large submarine landslides responsible for disastrous tsunami waves as demonstrated by the papua new guinea event of july 17 1998 the relatively small earthquake was followed by unexpectedly high waves up to 15 m wiping out 3 villages and killing more than 2200 people numerical simulations show that seismic dislocation sources are not energetic enough to reproduce the observed tsunami along the coast tsunami generation by a submarine landslide has been simulated by a finite difference model assimilating the landslide to a flow of granular material long wave approximation is adopted for both water waves and the slide numerical results show that observed inundation heights are well reproduced for a volume of 4 km located 20 km offshore sliding downslope with a coulomb type friction

analysis of seismic body waves excited by the mount st helens eruption of may 18 1980 seismic body waves which were excited by the may 18 1980 eruption of mount st helens and recorded by the global digital seismographic network stations are analyzed to determine the nature and the time sequence of the events associated with the eruption the polarity of teleseismic p waves period 20s is identical at six stations which are distributed over a wide azimuthal range this observation together with a very small s to p amplitude ratio at 20 s suggests that the source is a nearly vertical single force a simple model shows that for seismic radiation a volcanic eruption can be represented by a single force applied in the direction opposite to the blast direction the time history of the vertical force suggests two distinct groups of events about 2 min apart each consisting of several subevents with a duration of about 25 s the magnitude of the force is approximately 2 6 10 12 n this vertical force is in contrast with the long period 150 s southward horizontal single force which has been determined by a previous study and interpreted to be due to the massive landslide an m s 5 2 earthquake initiated the eruption sequence the direction of the p wave first motion of this event observed at two nearby stations is consistent with the radiation pattern expected for the landslide and suggests that it represents the onset of the landslide the ground motions observed at station lon 67 km are dominated by rayleigh waves i e lamb pulse and provide tight constraints on the time sequence of the events

dikes emplaced into fractured basement timna igneous complex israel dikes are usually envisioned as arrays of parallel segments dilated perpendicular to the direction of the least compressive stress we describe here four dikes of highly irregular shape intruded in the fractured basement in the timna igneous complex southern israel the dikes include a doleritic dike 2 3 km long and 1 6 m to 32 m thick and three andesitic dikes up to 1 5 km long and 8 m thick the dikes each display significant variations of dip up to 60 strike up to 160 and thickness the thickness variations correlate better with the segment attitude than with the position along the dikes we show that the irregular shapes of the timna dikes are the result of emplacement into fractured host rock under different paleostress states and driving pressures three dilation styles that differ by the geometry of the initial cracks are analyzed an array of randomly oriented cracks style a a single linear crack style b and an array of interconnected nonparallel cracks style c the analysis of style a provides the stress state during dike emplacement including the orientations of the three principal stresses 1 2 3 the stress ratio 2 3 1 3 and the normalized driving pressure r pm 3 1 3 the stress ratio indicates the shape of the stress ellipsoid and it ranges from 0 for 2 3 prolate ellipsoid to 1 for 1 2 oblate ellipsoid the normalized driving pressure r indicates the relative magnitude of the internal magma pressure pm with respect to the tectonic stresses and it ranges from r 0 for pm 3 to r 1 for pm 1 we found that for three dikes in timna 0 25 indicating small differences between the two horizontal principal stresses and for one dike 0 9 indicating a large difference between the two horizontal principal stresses the normalized driving pressure r is about 0 08 in two horizontally propagating dikes and about 0 25 in two vertically propagating dikes style b predicts an elliptical thickness profile along the dike due to dilation of a linear crack this prediction agrees with the profile of one of the dikes the predicted thicknesses due to dilation of the interconnected array of cracks style c are in good agreement with the thickness variations of the doleritic dike and in fair agreement with two of the andesitic dikes deviations from the ideal geometry suggest separate stages of propagation and dilation in some of the dike segments

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