great thrust earthquakes and aseismic slip along the plate boundary of the makran subduction zone the makran subduction zone of iran and pakistan exhibits strong variation in seismicity between its eastern and western segments and has one of the world s largest forearcs we determine the source parameters for 14 earthquakes at makran including the great mw 8 1 earthquake of 1945 the only instrumentally recorded great earthquake at makran we determine the loci of seismic and aseismic slip along the plate boundary and we assess the effects of the large forearc and accretionary wedge on the style of plate boundary slip we apply body waveform inversions and for small magnitude events use first motions of p waves to estimate earthquake source parameters for the 1945 event we also employ dislocation modeling of uplift data we find that the earthquake of 1945 in eastern makran is an interplate thrust event that ruptured approximately one fifth the length of the subduction zone nine smaller events in eastern makran that are also located at or close to the plate interface have thrust mechanisms similar to that of the 1945 shock seaward of these thrust earthquakes lies the shallowest 70 80 km of the plate boundary we find that this segment and the overlying accretionary wedge remain aseismic both during and between great earthquakes this aseismic zone as in other subduction zones lies within that part of the accretionary wedge that consists of largely uconsolidated sediments seismic velocities less than 4 0 km s the existence of thrust earthquakes indicates that either the sediments along the plate boundary in eastern makran become sufficiently well consolidated and de watered about 70 km from the deformation front or older lithified rocks are present within the forearc so that stick slip sliding behavior becomes possible this study shows that a large quantity of unconsolidated sediment does not necessarily indicate a low potential for great thrust earthquakes in contrast to the east the plate boundary in western makran has no clear record of historic great events nor has modem instrumentation detected any shallow thrust events for at least the past 25 years most earthquakes in western makran occur within the downgoing plate at intermediate depths the large change in seismicity between eastern and western makran along with two shallow events that exhibit right lateral strike slip motion in central makran suggest segmentation of the subduction zone two paleozoic continental blocks dominate the overriding plate the boundary between them is approximately coincident with the transition in seismicity although relative motion between these blocks may account for some of the differing seismic behavior the continuity of the deformation front and of other tectonic features along the subduction zone suggests that the rate of subduction does not change appreciably from east to west the absence of plate boundary events in western makran indicates either that entirely aseismic subduction occurs or that the plate boundary is currently locked and experiences great earthquakes with long repeat times evidence is presently inconclusive concerning which of these two hypotheses is most correct the presence of well defined late holocene marine terraces along portions of the coasts of eastern and western makran could be interpreted as evidence that both sections of the arc are capable of generating large plate boundary earthquakes if that hypothesis is correct then western makran could produce a great earthquake or it could rupture as a number of segments in somewhat smaller magnitude events alternatively it is possible that western makran is significantly different from eastern makran and experiences largely aseismic slip at all times a knowledge of the velocity structure and nature of the state of consolidation or lithification of rocks at depth in the interior portion of the forearc of western makran should help to ascertain whether that portion of the plate boundary moves aseismically or ruptures in large to great earthquakes a resolution of this question has important implications for seismic hazard not only for western makran but also for other margins such as the cascadia subduction zone of western north america where historical thrust events have not occurred

probabilistic tsunami hazard in the mediterranean sea 1 estimating the occurrence probability of natural disasters is critical for setting construction standards and more generally prioritizing risk mitigation efforts tsunami hazard in the mediterranean region has traditionally been estimated by considering so called most credible scenarios of tsunami impact for limited geographical regions but little attention has been paid to the probability of any given scenario we present here the first probabilistic estimate of earthquake generated tsunami hazard for the entire mediterranean sea we estimate the annual probability of exceeding a given tsunami amplitude at any coastal location in the region by applying a monte carlo based technique earthquake activity rates are estimated from the observed seismicity and tsunami impact is derived from deterministic tsunami wave propagation scenarios the highest hazard is in the eastern mediterranean owing to earthquakes along the hellenic arc but most of the mediterranean coastline is prone to tsunami impact our method allows us to identify the main sources of tsunami hazard at any given location and to investigate the potential for issuing timely tsunami warnings we find that the probability of a tsunami wave exceeding 1 m somewhere in the mediterranean in the next 30 years is close to 100 this underlines the urgent need for a tsunami warning system in the region

tsunami hazard assessment of coastal south africa based on mega earthquakes of remote subduction zones the nuclear structural engineering pty and the national research foundation through the technology and human resources for industry programme project thrip tp2011061400009

three dimensional finite difference viscoelastic wave modelling including surface topography summary i have undertaken 3 d finite difference fd modelling of seismic scattering fromfree surface topography exact free surface boundary conditions for arbitrary 3 d topographies have been derived for the particle velocities the boundary conditions are combined with a velocity stress formulation of the full viscoelastic wave equations a curved grid represents the physical medium and its upper boundary represents the free surface topography the wave equations are numerically discretized by an eighth order fd method on a staggered grid in space and a leap frog technique and the crank nicholson method in time i simulate scattering from teleseismic p waves by using plane incident wave fronts and real topography from a 60 60 km area that includes the noress array of seismic receiver stations in southeastern norway synthetic snapshots and seismograms of the wavefield show clear conversion from p to rg short period fundamental mode rayleigh waves in areas of rough topography which is consistent with numerous observations by parallelization on fast supercomputers it is possible to model higher frequencies and or larger areas than before

numerical modeling of the 26 november 1999 vanuatu tsunami 1 on 26 november 1999 at 1321 ut central vanuatu was struck by a large offshore earthquake mw 7 5 followed by a tsunami that killed five people and caused significant damage to nearshore structures mainly at martelli bay south pentecost island the tsunami is simulated using the geowave model the tsunami open and progressive initial conditions system topics source component of the model simulates the initial water column deformation and the propagation and runup are simulated with the funwave fully nonlinear boussinesq and dispersive model a special effort was made on the construction of the computational grid through comprehensive bathymetry data sets obtained especially from two multibeam bathymetric surveys performed after the earthquake and tsunami three different tsunami sources have been considered the first one is the fault rupture itself the second is a landslide located east of ambrym island and the third source is a submarine structure within the selwyn strait that will be considered as a landslide however with a large uncertainty because it could be a result of lava deposit as well it is found that the earthquake derived tsunami source fits most of the postsurvey observations in particular the overall wave amplitudes up to 6 7 m observed and simulated the timing of the tsunami is also satisfactory when objective interpretation of the eyewitnesses is processed thus it is found that the hypothetical landslide derived tsunami contributions are not necessary to predict the tsunami this is because they do not help in the tsunami timing but also because their wave amplitude contributions are one order of magnitude lower than that of the earthquake source

theoretical analysis of tsunami generation by pyroclastic flows 1 pyroclastic flows are a common product of explosive volcanism and have the potential to initiate tsunamis whenever thick dense flows encounter bodies of water we evaluate the process of tsunami generation by pyroclastic flow by decomposing the pyroclastic flow into two components the dense underflow portion which we term the pyroclastic debris flow and the plume which includes the surge and coignimbrite ash cloud parts of the flow we consider five possible wave generation mechanisms these mechanisms consist of steam explosion pyroclastic debris flow plume pressure plume shear and pressure impulse wave generation our theoretical analysis of tsunami generation by these mechanisms provides an estimate of tsunami features such as a characteristic wave amplitude and wavelength we find that in most situations tsunami generation is dominated by the pyroclastic debris flow component of a pyroclastic flow this work presents information sufficient to construct tsunami sources for an arbitrary pyroclastic flow interacting with most bodies of water

boulder emplacement on a tectonically stable wave dominated coastline mission rocks northern kwazulu natal south africa abstract the presence of large boulders along rocky coastlines is a useful indicator as to the occurrence and nature of past storms and or tsunami field observations from mission rocks northern kwazulu natal south africa allowed for the assessment of historical high magnitude wave events in the area a total of 143 anomalously large boulders were assessed in terms of their dimensions morphologies and distribution along a regionally developed 3 m raised shore platform based on long intermediate and short axes relationships we calculate boulder masses of up to 9 03 t that were found to have been transported horizontally shoreward for up to 65 m based on geomorphological evidence we infer that the majority of boulders encountered were from a joint bound pre transport setting additionally overturning of the boulders was apparent we assess the boulder field numerically via the numerical model of pignatelli et al 2009 which we deemed most applicable for slab like boulders such as those encountered here results yielded a maximum breaking storm wave height of 11 36 m or a maximum tsunami height of 2 84 m an analysis of swell data revealed that the modelled storm wave heights fell within the range defined by the storm wave records for the area within the past 32 years boulder alignments were likewise compatible with the wave regime of the northern kwazulu natal coastline additional review of offshore seismic records and landslide hazards on the tectonically stable passive margin show that the tsunami hazard for landslides within the area is negligible the findings suggest a storm provenance as the causal mechanism for boulder emplacement at mission rocks

global frequency of magnitude 9 earthquakes for decades seismologists have sought causal relationships between maximum earthquake sizes and other properties of subduction zones with the underlying notion that some subduction zones may never produce a magnitude 9 or larger event the 2004 andaman m w 9 2 earthquake called into question such ideas given multicentury return times of the greatest earthquakes ignorance of those return times and our very limited observation span i suggest that we cannot yet make such determinations present evidence cannot rule out that any subduction zone may produce a magnitude 9 or larger earthquake based on theoretical recurrence times i estimate that one to three m9 earthquakes should occur globally per century and the past half century with five m9 events reflects temporal clustering and not the long term average

far field tsunami hazard from mega thrust earthquakes in the indian ocean summary we evaluate far field tsunami hazard in the indian ocean basin based on hydrodynamic simulations of ten case studies of possible mega earthquakes at the major seismic zones surrounding the basin they represent worst case scenarios of seismic rupture along the full extent of seismogenic faults having supported large earthquakes in the historical record in a series of numerical experiments in which the source parameters of the 2004 sumatra tsunami are allowed to vary one by one while keeping the seismic moment and the fault orientation unchanged we document that the main patterns of far field tsunami amplitudes are remarkably robust with respect to nominal variations in such parameters as hypocentral depth exact centroid location and slip distribution on the fault plane these results validate the concept of modelling case scenarios of potential future earthquakes whose source is by definition imprecise we consider seismic sources located at the extremities of the 2004 sumatra andaman rupture namely along the southern coast of sumatra and in the andaman myanmar province along the makran coast of pakistan and iran and also along the southern coast of java where the possibility of a large interplate thrust earthquake cannot be entirely dismissed the results of our hydrodynamic simulations indicate that the distribution of maximum amplitudes in the indian ocean basin is primarily controlled by the classical effect of source directivity and additionally by refraction and focusing along bathymetric features as a result many provinces in the basin could be threatened by higher tsunami amplitudes than in 2004 this pattern is particularly important along the coast of east africa from somalia to and including south africa in madagascar and the mascarene islands especially under a south sumatra scenario involving an earthquake comparable to or even possibly larger than the 1833 event whose epicentral area is widely believed to be under enhanced seismic risk as a result of stress transfer from the 2004 and 2005 ruptures to the northwest possibly even in the wake of the 2007 bengkulu earthquakes

humidity changes in southern tunisia during the late pleistocene inferred from u th dating of mollusc shells abstract calcareous deposits mainly consisting of mollusc shell accumulations which have been dated by the u th disequilibrium method mark the shorelines of paleolake highstands in the great chotts area of southern tunisia the 5 sites studied consist of discontinuous accumulations of fossils of marine like organisms e g cerastoderma glaucum melania tuberculata melanopsis praemorsa cerithium rupestre u th isochron plots and age frequency histograms for 39 shell samples are reported here limited variations for u content and 234u 238u activity ratios ar of shells support the hypothesis of closure of the geochemical system with respect to this element it is remarkable that 234u 238u ar of shells collected in chott fejej or chott jerid are clustered around different values reflecting probably different groundwater recharge from the continental intercalaire ci or complexe terminal ct aquifers furthermore waters collected near wadi el akarit show 234u 238u ar values comparable to those observed for shells 14c determinations made on aliquots of some of these samples suggested an age distribution between 18 and 34 ka bp the u th data of these 39 shell samples imply that 4 distinct flood episodes of these lakes occurred at about 30 95 100 130 150 and 180 200 ka for the episode centred around 30 ka the frequency histogram of ages shows a multimodal age group that could represent the existence of several humid pulses rather than a unique event moreover the comparison of 13c and 18o with those of older humid pleistocene phases when very large palaeolakes have been recorded suggests that these young carbonate shells are not related to a true highstand lake it is suggested that they represent a period of less humid climatic conditions with carbonate accumulation in minor water ponds in which intensive biological activity could have taken place it should be noted that this period was less arid than the present

estimation of tsunami hazard in new zealand due to south american earthquakes we develop a probabilistic model for estimating the tsunami hazard along the coast of new zealand due to plate interface earthquakes along the south american subduction zone to do this we develop statistical and physical models for several stages in the process of tsunami generation and propagation and develop a method for combining these models to produce hazard estimates using a monte carlo technique this process is largely analogous to that used for seismic hazard modelling but is distinguished from it by the use of a physical model to represent the tsunami propagation as opposed to the use of empirical attenuation models for probabilistic seismic hazard analysis

introduction to global tsunami science past and future volume ii twenty two papers on the study of tsunamis are included in volume ii of the pageoph topical issue global tsunami science past and future volume i of this topical issue was published as pageoph vol 173 no 12 2016 eds e l geist h m fritz a b rabinovich and y tanioka three papers in volume ii focus on details of the 2011 and 2016 tsunami generating earthquakes offshore of tohoku japan the next six papers describe important case studies and observations of recent and historical events four papers related to tsunami hazard assessment are followed by three papers on tsunami hydrodynamics and numerical modelling three papers discuss problems of tsunami warning and real time forecasting the final set of three papers importantly investigates tsunamis generated by non seismic sources volcanic explosions landslides and meteorological disturbances collectively this volume highlights contemporary trends in global tsunami research both fundamental and applied toward hazard assessment and mitigation

beam stack imaging using a small aperture array we seek to gain a fuller understanding of seismic coda generation in the continental crust by identifying secondary scattering sources illuminated by a distant primary source we have developed a migration technique to scan seismic coda recorded by a small aperture seismic array for phases generated locally by scattering from large heterogeneities or topographic undulations we use a widely distributed suite of seismic events to illuminate the local crustal volume from different directions and produce an image of the local crust stable apparent secondary seismic sources are observed and interpreted as scatterers excited by the primary events

mechanical models of the 1975 kalapana hawaii earthquake and tsunami abstract our objective is to produce a mechanically realistic model for the 1975 kalapana event that explains the overall deformation and geological evolution of the south flank of kilauea and reproduces most known earthquake and tsunami observations to do this we present a new structural interpretation of geological data from kilauea along with modeling of the tsunami using recent seismic analyses in so doing we hypothesize an offshore north facing normal fault that we call the kalapana fault because of its limited onshore expression near kalapana we argue that several different interpretations of seismic data are simultaneously true each coinciding with a specific geological structure we perform a direct numerical simulation of the 1975 kalapana tsunami and we report results for the near field and the far field simultaneously our interpretation of geological structures provides sufficient constraints to derive three tsunami sources the kalapana fault a slump and a thrust fault these three tsunami sources are mechanically coupled according to our model of kilauea evolution although their contributions to tsunami generation remain relatively distinct slump displacement predicts a small shear stress beneath kilauea volcano we find that our geological interpretation and tsunami sources are sufficiently robust to reproduce almost all tsunami observations repeated earthquakes like the 1975 kalapana event will produce extension and subsidence in the upper flank of kilauea as well as compression and uplift of the toe region accompanied by limited slump movement these deformations appear to stabilize kilauea and make catastrophic failure of the volcano flank less likely at this time

travel times and attenuation relations for regional phases in the barents sea region a database containing 45 events in the barents sea region has been compiled and analyzed with the aim of evaluating crustal models travel times and attenuation relations in the context of performing regional detection threshold monitoring of this region the 45 events are mostly located around the circumference of the study area due to the virtually aseismic nature of the barents sea itself regional p n and s n phases were observable for most events in the database while p g and l g phases were only observable for events with raypaths that do not cross the tectonic structures in the barents sea this corroborates a number of previous observations of l g wave blockage within the barents sea three existing velocity models were evaluated with a model having slightly lower s velocities than earlier assumed in the upper mantle giving the overall best fit to the observed arrivals in order to estimate magnitudes short term average sta and spectral amplitude values were calculated in several frequency bands for all phase arrivals in the database there were no significant differences between spectral and sta amplitudes so the latter were used as this parameter is more efficient to calculate in real time processing an inversion was performed in order to determine an attenuation relation specific for this region the resulting magnitudes based on p n p g s n and l g phases gave an internally consistent reasonably stable set of values which can be calibrated towards any existing global or regional scale

modelling of tsunami generated by the giant late bronze age eruption of thera south aegean sea greece summary tsunami generated by the late bronze age lba eruption of thera were simulated using synthetic tide records produced for selected nearshore 20 m depths sites of northern crete the cyclades islands sw turkey and sicily inundation distances inland were also calculated along northern crete modelling was performed by incorporating fully non linear boussinesq wave theory with two tsunamigenic mechanisms the first involved the entry of pyroclastic flows into the sea assuming a thick 55 m 30 km3 flow entering the sea along the south coast of thera in three different directions all directed towards northern crete then a thin pyroclastic flow 1 m 1 2 km3 entering the sea along the north coast of thera directed towards the cyclades islands flows were modelled as a solid block that slowly decelerates along a horizontal surface the second mechanism assumed caldera collapse of 19 km3 and 34 km3 modelled as a dynamic landslide producing rapid vertical displacements calculated nearshore wave amplitudes varied from a few metres to 28 m along northern crete from pyroclastic flows and up to 19 m from caldera collapse 34 km3 volume inundation distances on crete were 250 450 m waves produced by pyroclastic flows were highly focused however as a function of sea entry direction smaller volume pyroclastic flows produced nearshore wave amplitudes up to 4 m in the cyclades islands north of thera wave amplitudes in the cyclades from smaller volume caldera collapse 19 km3 were up to 24 m whereas in sw turkey were as low as 2 1 and 0 8 m didim and fethye where lba tsunami deposits have been found wave amplitudes for the larger volume caldera collapse 34 km3 were generally 2 5 3 times larger than those generated by the smaller volume collapse 19 km3 these results provide estimates for understanding possible consequences of tsunami impact in lba coastal zones thus providing criteria at archaeological sites for detecting inundation damage as well as for contemporary hazard assessment they also provide additional criteria for deciphering homogenite layers in the abyssal stratigraphy of the ionian and eastern mediterranean seas

rg observations from four continents inverse and forward modelling experiments summary using short period recordings of fundamental mode rayleigh waves rg from seven arrays on four continents we have explored structural properties in the respective siting areas through inversion of rg phase velocity dispersion characteristics the arrays studied were noress and arcess in norway geress in germany eskdalemuir in scotland yellowknife in canada gauribidanur in india and alice springs in australia the simplest model used consists of one layer over a half space with shear velocities and layer thickness as unknowns densities were held fixed while p velocities were constrained by a constant poisson ratio of 0 25 with one exception eskdalemuir the estimated s velocities were remarkably consistent between the arrays with an average value of 2 9 0 1 kms 1 in the upper layer and 3 55 0 1 kms 1 in the half space however estimated layer thicknesses varied considerably ranging from 0 12 km yellowknife to 1 6 km alice springs inversions were also performed with a simulated gradient layer near the surface model results and the ability to fit the observed velocity dispersion were very similar with the two types of models thus revealing a resolution problem with the limited frequency range available and the lack of higher modes to examine the effect of lateral inhomogeneities in terms of von karman velocity variations and topography on rg propagation 2 d finite difference synthetics were computed in both cases scattering was most pronounced for frequencies above 1 hz and thus explain the lack of rg phase velocity estimates for periods shorter than 0 6 s

bayesian analysis of extreme earthquake occurrences part i probabilistic hazard model bayesian probability theory in conjunction with the model of extremes is used to develop a bayesian distribution of extreme earthquake occurrences by assuming that earthquakes represent a poisson process with exponential distribution of magnitudes the bayesian distribution represents the probability that m max the largest earthquake expected to occur within a period of t years will exceed some specified magnitude m and may be computed from the relationship p m max m t 1 t t t 1 f m n where n and t represent updated posterior bayesian estimates of the number of earthquakes and the time period of observation respectively and f m is the bayesian distribution of magnitudes each updated from prior estimates of seismicity using historical observations of earthquake occurrences through the application of bayesian probability theory the above distribution contains two features that make it more powerful and reliable than the conventional extreme value distribution first it incorporates statistical uncertainty in the estimation of seismicity in addition to the inherent uncertainty associated with the random nature of earthquake occurrences second it provides a rigorous means of combining prior information on seismicity such as geologica data with available historical observations of earthquake occurrences the last feature represents a major step toward the ability of earthquake engineers to systematically use information from geologists and seismologists regarding the seismic potential of faults and small regions in the probabilistic assessment of seismic hazards and provides a means of periodically updating estimates of earthquake occurrence probabilities as new seismicity data become available

3 d versus 2 d finite difference seismic synthetics including real surface topography abstract we have pursued and compared two dimensional 2 d and three dimensional 3 d finite difference f d modeling of scattering from free surface topography a velocity stress formulation of the full elastic wave equations are combined with exact boundary conditions for the surface topography and numerically discretized by an eighth order f d method on a staggered grid we have simulated scattering in 2 d and 3 d from teleseismic p waves using a plane vertically incident p wave and real topography from a 60 60 km2 area including the noress array in southeastern norway many field observations that are not easily explained by simpler 2 d cases are shown to better match qualitative effects from 3 d surface topography modeling these include strong amplifications at hills complex wave pattern caused by scattering and directivity of scattered waves snapshots and seismograms show clear conversion from p to rg short period fundamental mode rayleigh waves in an area of rough topography in the vicinity of the array site all results are consistent with numerous observations by parallellization of the original software possibilities have been opened for modeling with higher resolution and or larger areas than before

probabilistic tsunami hazard assessment at seaside oregon for near and far field seismic sources 1 the first probabilistic tsunami flooding maps have been developed the methodology called probabilistic tsunami hazard assessment ptha integrates tsunami inundation modeling with methods of probabilistic seismic hazard assessment psha application of the methodology to seaside oregon has yielded estimates of the spatial distribution of 100 and 500 year maximum tsunami amplitudes i e amplitudes with 1 and 0 2 annual probability of exceedance the 100 year tsunami is generated most frequently by far field sources in the alaska aleutian subduction zone and is characterized by maximum amplitudes that do not exceed 4 m with an inland extent of less than 500 m in contrast the 500 year tsunami is dominated by local sources in the cascadia subduction zone and is characterized by maximum amplitudes in excess of 10 m and an inland extent of more than 1 km the primary sources of uncertainty in these results include those associated with interevent time estimates modeling of background sea level and accounting for temporal changes in bathymetry and topography nonetheless ptha represents an important contribution to tsunami hazard assessment techniques viewed in the broader context of risk analysis ptha provides a method for quantifying estimates of the likelihood and severity of the tsunami hazard which can then be combined with vulnerability and exposure to yield estimates of tsunami risk

gas hydrate and mud volcanoes on the southwest african continental margin off south africa widespread occurrence of bottom simulating reflectors bsrs has been detected in multichannel seismic profiles on the upper continental slope in the southern periphery of the orange river delta probably indicating the presence of large quantities of gas hydrate in this area this report is the first to show the presence of bsrs on seismic records on the southwest african continental margin south of the walvis ridge another remarkable feature in the area is the occurrence of a large number of mud volcanoes the distribution of the bsrs and the location of the mud volcanoes are controlled by the locations of active faults the gas hydrate in this region may consist of a mixture of microbial and thermogenic gas whereas much of the gas flowing through the mud volcanoes probably originated from deep seated aptian source shales

2d finite difference elastic wave modelling including surface topography1 a 2d numerical finite difference algorithm accounting for surface topography is presented higher order dispersion bounded cost optimized finite difference operators are used in the interior of the numerical grid while non reflecting absorbing boundary conditions are used along the edges transformation from a curved to a rectangular grid achieves the modelling of the surface topography we use free surface boundary conditions along the surface in order to obtain complete modelling of the effects of wave propagation it is important to account for the surface topography otherwise near surface effects such as scattering are not modelled adequately even if other properties of the medium for instance randomization can improve numerical simulations inclusion of the surface topography makes them more realistic

evaluation of topographic effects on p and s waves of explosions at the northern novaya zemlya test site using 3 d numerical simulations using a 3 d finite difference simulation we calculated the effects of surface topography on the amplitudes and waveforms of seismic waves generated by a hypothetical nuclear explosion at the northern novaya zemlya test site matochkin shar the simulation shows substantial azimuthal variations in the amplitude of the downgoing p waveform at shallow depths beneath the source caused by variations in the amplitude of pp however these azimuthal amplitude variations diminish as the wavefront propagates deeper in the crust based on these results we estimate that the topographic scarp considered here produces a maximum azimuthal variation of 0 05 magnitude units for mb determined from teleseismic p waves the sloping topography causes substantial sh motion for azimuths along the strike of the scarp

bayesian analysis of extreme earthquake occurrences part ii application to the san jacinto fault zone of southern california abstract the bayesian extreme value distribution of earthquake occurrences developed in the first part of this study is tested and applied to the estimation of seismic hazards for the san jacinto fault zone of southern california prior estimates of seismicity are developed from seismotectonic data based on standard seismological relationships among seismic moment slip rate earthquake recurrence rate and magnitude these estimates are then updated using bayes9 theorem and historical estimates of seismicity associated with the san jacinto fault zone bayesian extreme value distributions available from the literature are found either to overestimate exceedance probabilities of earthquake occurrences or require more complex computations as compared to the distribution proposed in this study on the other hand the conventional extremevalue distribution of earthquake occurrences first proposed by epstein and lomnitz 1966 was found to give results consistent with the bayesian distribution of this study if updated estimates of the seismicity parameters are used and the standard deviations of these parameters are restricted to be less than about 25 per cent of their mean values the bayesian analysis of extreme earthquake occurrences for the 300 km long san jacinto fault zone indicated a rather large sensitivity to the uncertainty associated with the prior seismotectonic estimate of seismicity using moderate estimates of this uncertainty magnitudes of 6 2 6 9 7 1 7 4 and 7 5 are found to be associated with return periods at 10 50 100 500 and 1000 yr for an upper bound magnitude of 7 5 m s on the fault zone these estimates lie approximately midway between those based on historical and seismotectonic estimates of seismicity estimated magnitudes are reduced significantly for return periods of 50 to 1000 yr if upper bound magnitude is restricted to a value of 7 0 m s closer to the largest historical earthquake observed on the zone in this case for example the 100 and 1000 yr earthquakes have magnitudes of 6 8 and 7 0 respectively

estimation of earthquake hazard parameters from incomplete data files part iii incorporation of uncertainty of earthquake occurrence model most probabilistic seismic hazard analysis procedures require that at least three seismic source parameters be known namely the mean seismic activity rate the gutenberg richter b value and the area characteristic seismogenic source maximum possible earthquake magnitude m max in almost all currently used seismic hazard assessment procedures that utilize these three parameters it is explicitly assumed that all three remain constant over time and space however closer examination of most earthquake catalogs has indicated that significant spatial and temporal variations existed in the seismic activity rate as well as in the gutenberg richter b value in this study the maximum likelihood estimation of these earthquake hazard parameters considers the incompleteness of the catalogs the uncertainty in the earthquake magnitude determination as well as the uncertainty associated with the applied earthquake occurrence models the uncertainty in the earthquake occurrence models is introduced by assuming that both the mean seismic activity rate and the gutenberg richter b value are random variables each described by the gamma distribution this approach results in the extension of the classic frequency magnitude gutenberg richter relation and the poisson distribution of the number of earthquakes with their compounded counterparts benjamin 1968 campbell 1982 1983 the proposed procedure was applied in the estimation of the seismicity parameters in an area that had experienced the strongest and most devastating earthquake in contemporary south african history namely the 29 september 1969 m w 6 3 ceres tulbagh event in this example it was shown that the introduction of uncertainty in the earthquake occurrence model reduced the mean return periods leading to an increase of the estimated seismic hazard additionally this study confirmed that accounting for magnitude uncertainties had the opposite effect that is it brought about increases in the return periods or equivalently a reduction of the estimated seismic hazard