the q structure of the upper mantle constraints from rayleigh wave amplitudes 1 the three dimensional shear attenuation or q structure of the upper mantle is still poorly understood despite the increasing accuracy and sophistication of velocity models of the same part of the earth here we present a set of three dimensional q models of the upper mantle based on amplitude measurement of minor and major arc rayleigh waves in the period range 70 170 s the models show that areas of low attenuation underlie continents to a depth of around 300 km and areas of high attenuation are associated with oceans and plate boundaries particularly in the top 200 km below 350 km the sensitivity of the data to attenuation structure decreases rapidly it is well known that the amplitudes of surface waves can be strongly influenced by factors other than attenuation in particular focusing due to elastic structure and errors in source mechanisms we consider the effects of focusing by discussing the implications of the results of selby and woodhouse 2000 comparisons with focusing predictions using phase velocity maps allow us to identify features due to focusing in maps of attenuation distribution the influence of the source on the observed attenuation distribution is investigated by including a source term in the model inversion we find that successfully combining the data at each frequency into one three dimensional model requires that this source term must vary with frequency suggesting that a simple correction to the scalar moment of each event cannot explain the observations although the effects of focusing and the source can be significant we find that the observed attenuation pattern is robust up to degree 8 however shorter wavelength structure can be strongly influenced by other controls finally we use one of the models to predict the degree 2 attenuation pattern for 250 s rayleigh waves the observed pattern suggests that existing normal mode observations may be explainable in terms of structure above 350 km depth

analysis of landslide frequencies and characteristics in a natural system coastal british columbia two hundred and one debris slides and debris ows were analyzed in a 286 km2 study area on the west coast of vancouver island british columbia canada the study area remains essentially untouched by humans and therefore affords a natural setting in which to examine slope processes landslides were identi ed and characterized on aerial photographs from 1 15 000 to 1 31 680 and were then mapped and transferred to a gis for analysis based on detailed landslide surveys we propose a new method to accurately determine volume of landslides of this type by measured total area results indicate average denudation rates of 56 m3 y 1 km 2 and higher natural rates of failure than analogous regions in coastal british columbia in contrast the landslide rates are substantially less than those from forested watersheds landslide distribution is spatially clustered in air photograph epochs and we propose intense storm cells within regional events as the causal mechanism further failures occurred preferentially over the west coast crystalline complex by 1 4 times a metamorphic assemblage of gabbros schists and amphibolites but 1 5 times less often over the island plutonic suite a granitic intrusive formation the former result represents a new nding while the latter corroborates ndings of previous authors we examined magnitude frequency relationships of the data set and present for the rst time a strong argument that the rollover effect is not merely an artefact but is instead a consequence of the physical characteristics of the landslides themselves we subsequently analyzed magnitude frequency relationships from two other complete data sets from coastal british columbia and produced a family of curves corroborating this result copyright 2004 john wiley sons ltd

selection of earthquake scaling relationships for seismic hazard analysis a fundamentally important but typically abbreviated component of seismic hazard analysis is the selection of earthquake scaling relationships these are typically regressions of historical earthquake datasets in which magnitude is estimated from parameters such as fault rupture length and area the mix of historical data from different tectonic environments and the different forms of the regression equations can result in large differences in magnitude estimates for a given fault rupture length or area we compile a worldwide set of regressions and make a first order shortlisting of regressions according to their relevance to a range of tectonic regimes plate tectonic setting and fault slip type in existence around the world regression relevance is based largely on the geographical distribution age and quantity quality of earthquake data used to develop them our compilation is limited to regressions of magnitude or seismic moment on fault rupture area or length and our shortlisted regressions show a large magnitude range up to a full magnitude unit for a given rupture length or area across the various tectonic regimes these large differences in magnitude estimates underline the importance of choosing regressions carefully for seismic hazard application in different tectonic environments

characterization of the heterogeneous source model of intraslab earthquakes toward strong ground motion prediction we characterize the heterogeneous source slip model of intraslab earthquakes to compare source scaling properties with those of inland crustal and subduction zone plate boundary earthquakes we extracted rupture area s total area of asperity s a average slip d and average slip on asperity d a of eleven intraslab earthquakes following the procedure proposed by somerville et al seism res lett 70 59 80 1999 and proposed the empirical scaling relationship formula of s s a and d for intraslab earthquakes under the same seismic moment an intraslab earthquake has a smaller rupture area and total area of asperity and smaller average slip than an inland crustal earthquake the area ratio of asperity area and total rupture area of intraslab earthquakes are similar to those of inland crustal earthquakes the strong motion generation area smga scaling of intraslab earthquakes appears self similar and those results support the idea the characterized source model of intraslab earthquakes can be modeled in a manner similar to that of inland crustal earthquakes

inversion of complex body waves we have developed a method that inverts seismic body waves to determine the mechanism and rupture pattern of earthquakes the rupture pattern is represented as a sequence of subevents distributed on the fault plane this method is an extension of our earlier method in which the subevent mechanisms were fixed in the new method the subevent mechanisms are determined from the data and are allowed to vary during the sequence when subevent mechanisms are allowed to vary however the inversion often becomes unstable because of the complex trade offs between the mechanism the timing and the location of the subevents many different subevent sequences can explain the same data equally well and it is important to determine the range of allowable solutions some constraints must be imposed on the solution to stabilize the inversion we have developed a procedure to explore the range of allowable solutions and appropriate constraints in this procedure a network of grid points is constructed on the i plane where and i are respectively the onset time and the distance from the epicenter of a subevent the best fit subevent is determined at all grid points then the correlation is computed between the synthetic waveform for each subevent and the observed waveform the correlation as a function of and i and the best fit mechanisms computed at each i grid point depict the character of allowable solutions and facilitate a decision on the appropriate constraints to be imposed on the solution the method is illustrated using the data for the 1976 guatemala earthquake

the effects of logging on frequency and distribution of landslides in three watersheds on vancouver island british columbia abstract three hundred and sixty three landslides in three watersheds that totaled 382 km2 were identified from air photographs beginning at a date that preceded logging to the present the three watersheds all lie on vancouver island however they have different precipitation regimes topography and amounts logged landslide areas in the watersheds varied in size from 200 m2 to more than 1 ha nearly 80 of the landslides were debris slides 15 were debris flows and the remainder primarily rock falls following logging the number of landslides increased substantially in all watersheds although the amount of increase was variable approximately 11 3 and 16 times in macktush creek artlish river and nahwitti river respectively other analyses of changes in landslide density also produced highly variable results with the number of landslides increasing between 2 4 and 24 times further 2 12 times more landslides reached streams following logging activities densities for landslides impacting streams increased for the period of record from 1 5 to 10 times following logging activities the densities were substantially greater where only landslides that reached streams since development began in a watershed were considered roads had the greatest spatial impact in the watersheds compared to their total area with frequencies determined to have increased by 27 12 and 94 times for macktush artlish and nahwitti respectively the results highlight the relative impact of roads and their role in slope stability

empirical ground motion relations for subduction zone earthquakes and their application to cascadia and other regions ground motion relations for earthquakes that occur in subduction zones are an important input to seismic hazard analyses in many parts of the world in the cascadia region washington oregon northern california and british columbia for example there is a significant hazard from megathrust earthquakes along the subduction interface and from large events within the subducting slab these hazards are in addition to the hazard from shallow earthquakes in the overlying crust we have compiled a response spectra database from thousands of strong motion record ings from events of moment magnitude m 5 8 3 occurring in subduction zones around the world including both interface and in slab events the 2001 m 6 8 nis qually and 1999 m 5 9 satsop earthquakes are included in the database as are many records from subduction zones in japan kyoshin net data mexico guerrero data and central america the size of the database is four times larger than that available for previous empirical regressions to determine ground motion relations for subduc tion zone earthquakes the large dataset enables improved determination of attenu ation parameters and magnitude scaling for both interface and in slab events soil response parameters are also better determined by the data we use the database to develop global ground motion relations for interface and in slab earthquakes using a maximum likelihood regression method we analyze regional variability of ground motion amplitudes across the global database and find that there are significant regional differences in particular amplitudes in cascadia differ by more than a factor of 2 from those in japan for the same magnitude distance event type and national earthquake hazards reduction program nehrp soil class this is believed to be due to regional differences in the depth of the soil profile which are not captured by the nehrp site classification scheme regional correction factors to account for these differences are proposed for cascadia and japan the results of this study differ significantly from previous analyses based on more limited data and have important implications for seismic hazard analysis the ground motion relations predict that a great megathrust earthquake m 8 at a fault distance of about 100 km would produce pseudoacceleration psa 5 damped horizontal component on soil sites of about 110 cm sec 2 at 0 5 hz 660 cm sec 2 at 2 5 hz and 410 cm sec 2 at 5 hz with a peak ground acceleration of about 180 cm sec 2 these damaging levels of motion would be experienced over a very large area corresponding to a rectangular area about 300 km wide by 500 km long large in slab events m 7 5 would produce even higher psa values within 100 km of the fault but the in slab motions attenuate much more rapidly with distance thus the hazard posed by moderate to large in slab events such as the 2001 nisqually earth quake is modest compared to that of a cascadia megathrust earthquake of m 8 in terms of the area that would experience damaging levels of ground motion

source investigation and comparison of the 1939 1946 1949 and 1965 earthquakes cascadia subduction zone western washington over the past 65 years intraslab earthquakes have caused the most significant damage in the western washington region this study examines regional and teleseismic seismograms for four historic suspected intraslab events of m 5 5 occurring within the cascadia subduction zone in 1939 south seattle 1946 puget sound 1949 olympia and 1965 sea tac to better determine the source locations mechanisms and rupture histories of these events our study is aided by digital seismograms of post 1990 intraslab events with well determined focal depths and focal mechanisms that were recorded in the same locations as the historic events thus the recent events were used as empirical greens functions to study the historic events our results suggest that the 1946 earthquake is not an intraslab event that the 1939 event closely resembles the 1965 event and that the 1949 event is similar to the 2001 nisqually earthquake although the 1949 event appears to have ruptured toward the south causing significantly more damage than the nisqually event these results suggest that earthquakes periodically rupture along the same or similarly oriented faults within the subducting slab

normal modes and long period seismograms in a 3d anelastic elliptical rotating earth 1 we present results of a direct method to compute realistic long period 200 s in this example synthetic seismograms using higher order perturbation theory up to the 3rd order normal modes are computed for the earth taking into account rotation ellipticity 3d elastic lateral heterogeneities saw12d for the whole mantle and anelastic lateral variations in the upper mantle qr19 coupling between different modes and branches is included in the computation we study the sensitivity of the waveform to 3d anelasticity and the biases between 3d elastic and 3d anelastic variations the resulting seismograms can be computed to higher frequency and may then be used to perform whole mantle joint inversions for elastic and anelastic structure

basin shear wave velocities beneath seattle washington from noise correlation rayleigh waves tomography with short period rayleigh waves extracted using noise interferometry can refine s wave velocity v s models in urban areas with dense arrays of short period and broadband instruments we apply this technique to the seattle area to develop a new shallow v s model for use in seismic hazard assessment continuous data from the seismic hazards in puget sound ships array and local broadband stations have interstation distances of 90 km or less this spacing allows us to extract rayleigh waves with periods between 2 and 10 s that are sensitive to shallow basin structure this new v s model for the seattle basin is constructed using direct observations rather than using p wave velocity v p observations and a v p v s ratio as all previous 3d models at this scale have been constructed our results reveal greater detail in the upper 3 5 km than previous models earthquake simulations calculated using our new model better predict peak ground velocities pgv at periods between 1 and 2 s for two local earthquakes than the previous model used to calculate seattle s seismic hazard map frankel et al 2007 we collected data from two local earthquakes and ran finite difference simulations using our new velocity model as well as the previous velocity model used in development of the seattle seismic hazard maps to assess how well our model predicts ground motions relative to the previous model with a recent deployment of netquakes strong motion stations by the pacific northwest seismic network pnsn and the u s geological survey we are now able to make more comprehensive assessments of the predictions for recent events

rupture process of the 1964 prince william sound alaska earthquake from the combined inversion of seismic tsunami and geodetic data 1 four great earthquakes 1952 1960 1964 and 2004 have occurred since seismic monitoring began and only two since the installation of a global seismic network a reexamination of the 1964 m 9 2 prince william sound pws alaska earthquake is timely due to the 2004 sumatra earthquake because it adds constraints to the potential range of source parameters for these types of infrequent events and aids in the ability to predict the ground motions for other subduction zone including cascadia we first measured the durations of high frequency energy radiation from teleseismic p wave codas recorded by short period world wide standardized seismographic network wwssn sp instruments to put constraints on the earthquake rupture length the durations ranged between 250 and 600 s and are shorter in time between azimuths of 190 and 260 the fault length is estimated to range from 540 to 740 km rupturing at average speeds of 1 4 2 km s in a 220 238 direction we developed a multiple time window kinematic rupture model for the pws earthquake from the least squares inversion of teleseismic p waves tsunami tide gauge records and geodetic leveling survey observations based on the green s function technique we assume three major fault segments for the subduction zone dipping 6 12 based on geologic data the subfault size on the megathrust was set to 50 50 km the patton bay fault pbf imbricate thrust was assigned a 60 dip with a subfault size of 20 20 km we estimated a seismic moment of 5 52 1022 n m mw9 12 we identified three areas of major moment release on the pws segment near montague and middleton islands extending out to the trench beneath the portlock anticline on the cook segment between 58 n fracture zone and the kodiak bowie seamount chain and finally on the katmai segment off the coast of kodiak island extending to the trench our preferred rupture model has a peak slip of 14 9 m along the megathrust and 17 4 m along the pbf the addition of the pbf resulted in an 8 improvement in residuals and also had a significant effect on the overall slip distribution moment release occurred as deep as 50 km depth slab contour near the 350 c isotherm and mantle fore arc wedge which is about 10 20 km deeper than previous coupling depths

contemporary squamish river sediment flux to howe sound british columbia squamish river drains 3600 km2 in the southern coast mountains of british columbia to howe sound at squamish some 50 km north of vancouver this study uses differencing of digitized bathymetric surfaces based on the canadian hydrographic services surveys of 1930 1973 and 1984 at the head of howe sound to yield a long term sedimentation rate for squamish river delta the sediment flux from squamish river to howe sound is determined to be 1 29 106 m3 a 1 or 1 81 109 kg a 1 rates consistent with loads calculated from flow and sediment concentration regimes measured in the estuary in 1973 1975 and 1987 1988 the latter data indicate that the modal discharge effectiveness class is 600 700 m3 s 1 moving 13 of the annual suspended sediment load discharges up to 1400 m3 s 1 constitute 99 8 of all flows and are responsible for transporting 81 5 of the annual load a very significant 18 5 of the load is moved by large magnitude floods 1400 m3 s 1 which occur less than 0 2 of the time squam

a procedure for modelling shallow dislocation sources summary expressions for displacements on the surface of a layered half space due to an arbitrary oriented shear dislocation are given in terms of generalized ray expansions useful approximations of these expressions for shallow events as recorded at teleseismic distances for realistic earth models are presented the results of this procedure are used to generate synthetic p sv and sh waveforms for various assumptions of stress drop

studies of wadati benioff zone seismicity of the anchorage alaska region we have relocated over 8600 earthquakes occurring between 1964 and 1999 at depths 25 km within 100 km of anchorage alaska using the double difference technique the relocated seismicity reveals important details of the subducting pacific plate and yakutat blocks including clustering of seismicity within the pacific plate mantle northeast and northwest striking near vertical faults within the pacific plate crust and a region of intense deformation associated with the southwestern edge of the yakutat block stress analyses from the direct inversion of first motion data and from inversion of focal mechanisms for 713 events indicates a rotation of the maximum compressive stress direction from a trench parallel direction northeast in the southwestern portion of the study area to an east west direction near the southwestern edge of the yakutat block located just north of anchorage regions of the pacific plate mantle that produced m w 6 4 earthquakes in 1934 and 1954 continue to be seismically active

source characteristics and propagation effects of the puebla mexico earthquake of 15 june 1999 the analysis of arrival times indicates that the focus of the 15 june 1999 20 42 utc 6 3 m b 6 5 m s 7 0 m w puebla mexico earthquake is located at 18 15 n and 97 52 w and is 68 km deep in the contact region between the continental american and the cocos subducting plate first motion data and regional and teleseismic waveform modeling indicate that the main rupture occurred as normal faulting along a fault striking n64 w and dipping approximately 42 toward the north northeast the aftershock activity though scarce is concentrated mainly toward the west of the mainshock three successive subevents are necessary to fit observed and synthetic waveforms the location in space and time of subevents indicates that the rupture started as a small release at 76 km deep and then propagated toward the northwest releasing most of the seismic energy at 73 km deep teleseismic spectral analysis indicates that the total seismic moment release was 2 0 1019 n m and the mainshock fault length is of the order of 18 km with a stress drop of 15 bars the source time function consisted of three sources with a total duration of 10 sec recorded acceleration amplitudes of the mainshock show a clear enhancement that can be up to eight times higher toward the northwest of the epicenter in the frequency range from 0 06 hz to 6 0 hz compared with the opposite direction the distribution of reported seismic intensity also shows this feature the directivity effect cannot be fully explained by the orientation of the fault neither by the rupture propagation direction therefore we investigate the possibility that the directivity could be due to a regional propagation effect by analyzing the lg coda decay of the mainshock the average frequency dependent q lg quality factor for the vertical component in the frequency range from 0 2 hz to 2 hz was q lg f 200 12 f 0 60 0 17 and q lg f 202 7 f 0 53 0 09 for paths toward the northwest and southeast of the epicenter respectively the resulting average factor q o and do not show significant azimuthal fluctuations therefore variations of crustal attenuation properties cannot explain the notable extent of felt area and observed damage northwest of the epicenter probably the presence to the north of the transmexican volcanic belt has played an important role in the enhancement of low frequency seismic signals

subevent structure of large earthquakes a ground motion perspective our ability to predict ground motions from future earthquakes hinges on the accurate modeling of the radiation from the earthquake source a successful approach to modeling earthquake radiation has been to represent faults as a series of discrete independently rupturing subfaults although their physical interpretation has remained largely unclear our simulation of ground motions from twenty six well recorded moderate to large earthquakes substantiates the hypothesis that large ruptures are made up of a sequence of smaller subevents the size of a subevent follows a simple linear relationship with the size of the earthquake fault in an apparently deterministic manner the strength of the high frequency radiation is controlled by the maximum slip velocity which varies stochastically over a small range both the characteristic subevent size and the slip velocity appear to be region independent indicating a remarkable uniformity in earthquake source properties this observation helps to reduce the uncertainty in ground motion prediction by constraining its essential and previously ambiguous parameters

a multiple time window rupture model for the 1999 chi chi earthquake from a combined inversion of teleseismic surface wave strong motion and gps data 1 we present the results of a comprehensive analysis of the rupture process of the 1999 chi chi taiwan earthquake using a broad array of seismic as well as geodetic data spanning a very wide frequency band our results indicate that the rupture was quite smooth with the slip concentrated in a wide arcuate region north of the epicenter with very little slip to the east or south we found a moment of 3 3 1027 dyn cm which is consistent with the long period determinations for this earthquake the rupture velocity is approximately 2 25 km s and is quite uniform across the fault we have tested both a single fault plane model as well as a composite fault model with a second e w striking plane to the north of the rupture to improve the fit of the geodetic data overall the differences in slip distribution between the two models are negligible but the fit to the gps data is significantly better for the composite model which is thus our preferred solution this model is similar to other rupture models as far as the large scale features are concerned but differs for the smaller asperities that are present in other models but not as much in ours these are usually poorly constrained and with the use of the geodetic data we believe that there is little evidence for a significant amount of slip away from our main slip concentration

identifying the rupture plane of the 2001 nisqually washington earthquake the 2001 nisqually earthquake occurred within the subducting juan de fuca plate previous seismic and geodetic studies could not confidently identify its actual fault plane from the two nodal planes in this study we apply the recently developed source scanning algorithm to local seismic waveforms and show unambiguously that the steeply east dipping plane is the rupture plane the rupture began near the bottom of the subducting crust and propagated downward into the subducting uppermost mantle if intraslab earthquakes are assumed to be due to dehydration embrittlement the source dimension is unlikely to grow any larger because the warm thermal state of the subducting juan de fuca plate limits dehydration to a shallow depth below the slab surface numerical modeling of the thermal structure indicates that dehydration embrittlement can only take place in the top 10 km of the subducting mantle implying that the maximum size of an intraslab earthquake in northern cascadia would be m w 7 or less

evolution of the west andean escarpment at 18 s n chile during the last 25 ma uplift erosion and collapse through time abstract the geological record of the western andean escarpment warp reveals episodes of uplift erosion volcanism and sedimentation the lithological sequence at 18 s comprises a thick pile of azapa conglomerates 25 19 ma an overlying series of widespread rhyodacitic oxaya ignimbrites up to 900 m thick ca 19 ma which are in turn covered by a series of mafic andesite shield volcanoes between 19 and 12 ma the surface of the oxaya ignimbrites evolved into a large monocline on the western slope of the andes a giant antithetically rotated block oxaya block 80 km 20 km formed on this slope at about 10 12 ma and resulted in an easterly dip and a reversed drainage on the block s surface morphology topography and stratigraphic observations argue for a gravitational cause of this rotation a secondary gravitational collapse 50 km3 extending 25 km to the west occurred on the steep western front of the oxaya block alluvial and fluvial sediments 11 2 7 ma accumulated in a half graben to the east of the tilted block and were later thrust over by the rocks of the escarpment wall indicating further shortening between 8 and 6 ma flatlying upper miocene sediments

a global tomographic model of shear attenuation in the upper mantle we present a global three dimensional model of shear attenuation in the upper mantle based on the measurement of amplitudes of low frequency 100 300s rayleigh waves observed at stations of the geoscope and iris networks attenuation coefficients are measured on r1 and r2 paths using a method which minimizes the effects of focussing due to propagation in a three dimensional elastic earth through a series of tests which in particular involve the computation of synthetic models of attenuation and focussing we demonstrate that long wavelength lateral variations in attenuation in the first 400 500 km of the mantle can indeed be resolved the model is obtained in a two step procedure the first step consists in the computation of maps of rayleigh wave attenuation at different periods using an inversion method without a priori parametrisation which involves the introduction of a correlation length chosen here at 3000 km to optimize the trade off between resolution and variance in the model in the second step after corrections for shallow structure an inversion with depth is performed assuming lateral heterogeneity is confined to depths between 80 and 650 km the resulting model presents lateral variations in qp that are correlated with tectonic features in particular ridges and shields in the first 250 km of the upper mantle below that depth the pattern shifts and becomes correlated with the hotspot distribution particularly so if the buoyancy strength of hotspots is taken into account two major low velocity zones appear to be located in the central pacific and beneath northern africa in the depth range 300 500 km this pattern seems to continue at greater depth but resolution becomes insufficient below 500 km to draw definitive conclusions the smooth lateral variations retrieved are on the order of 50 down to 400 km we propose an interpretation in terms of plume lithosphere ridge interaction in the upper mantle arguing for deflection of the bulk of hot upwelling material from plumes towards ridges which may be occurring between 200 and 300 km depth

effects of metamorphic crustal densification on earthquake size in warm slabs 1 some recent damaging earthquakes occurred in the lower crust or mantle of warm subducting slabs they are consistent with a theoretical prediction that larger events tend to be deeper inside the slab as a result of mechanical damage to the crust caused by metamorphic rock densification the densification begins in a thin layer along the slab surface inducing a stretching force in it fracture spacing scales with layer thickness resulting in a shattered upper crust in which earthquake ruptures have limited propagation distance in contrast the more uniform untransformed substrata can host larger ruptures often the lack of compression in warm slab mantle is also consistent with a shattered crust

source parameters of the 1949 magnitude 7 1 south puget sound washington earthquake as determined from long period body waves and strong ground motions teleseismic p sh and sv first motions and sh to sv amplitude ratios recorded at eight teleseismic receivers from the 1949 magnitude 7 1 olympia washington earthquake in combination with data from three stations at regional distances were utilized in a grid testing routine to constrain focal mechanism identification of the pp phase places the event at 54 km depth distinct pulses assumed to be source effects are observed in the far field waveforms analysis of these pulses for directivity made possible discrimination between the fault and auxiliary planes the plane taken to represent the fault surface strikes east west 15 dips 45 15 to the north and has nearly pure left lateral slip the preferred source model has an eastward propagation of 40 km surface reflections of successive source pulses suggest an upward component of propagation of 5 km bounds on the earthquake location and rupture of the 13 april event were determined using depth and source mechanism constraints from the teleseismic study and characteristics of local strong ground motion recordings the 9 sec s instrument trigger time seen in the seattle acceleration recordings places the event at least 60 km from seattle strong motion velocity at the olympia highway test laboratory is characterized by an impulsive and rectilinear s wave the low amplitude of the vertical component of initial s motion suggests that either the epicenter is within 5 km of the olympia highway test laboratory for a pure incident sv wave or located along an azimuth of n159 if the wave is sh the combined constraint of minimum distance from seattle and the s polarization angle implied by the teleseismic data focal mechanism places the initiation of rupture 5 to 10 km north to north northwest of the olympia highway test laboratory at 47 13 n 122 95 w this is approximately 20 km west of previously determined epicenters the t axis gently dipping to the southeast supports other evidence that the juan de fuca plate dips to the southeast in a zone between segments of the plate north and south of the event s location the fault plane s slip is taken to indicate that subduction is still active beneath washington and that motion of the two segments is probably independent

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

source models of two large intraslab earthquakes from broadband strong ground motions we construct source models of two large intraslab earthquakes the 1993 kushiro oki and 1994 hokkaido toho oki earthquakes along the southern kurile hokkaido arc based on strong motion records the source models well explain observed broadband strong ground motions we assume a distribution of rectangular shaped asperities on a fault plane and apply the empirical green9s function method to the synthesis of strong ground motions from the asperities the asperity parameters area and stress drop are estimated by matching the synthetic waveforms displacement velocity and acceleration time histories and spectra to the observed ones our source models have the following characteristics compared with those of inland and plate boundary earthquakes having a comparable seismic moment 1 the total asperity area is much smaller and 2 the stress drop is extremely high about 200 400 mpa these indicate that the large intraslab earthquakes radiate seismic energies from a small area in a short time this rupture process results in extremely strong radiation of short period seismic waves finally we confirm a correlation between outer entire fault size seismic moment and short period level of the acceleration source spectrum and inner fault parameters areas and stress drops of asperities for the two intraslab earthquakes

earthquake ground motion and 3d georgia basin amplification in southwest british columbia shallow blind thrust scenario earthquakes abstract finite difference modeling of 3d long period 2 s ground motions for large m w 6 8 scenario earthquakes is conducted to investigate the effects of the georgia basin structure on ground shaking in greater vancouver british columbia canada scenario earthquakes include shallow blind thrust north america na plate earthquakes simulated in locations congruent with linear clusters of shallow seismicity that is potential active faults a slip distribution model of the m w 6 7 northridge california blind thrust earthquake with the hypocenter modified to 5 km depth is used to characterize the source rupture process two sets of simulations are performed for a given scenario earthquake using models with and without georgia basin sediments the ratio of predicted peak ground velocity pgv for the two simulations is applied here as a quantitative measure of amplification due to 3d basin structure a total of eight shallow blind thrust na plate scenario earthquakes are simulated within 100 km of greater vancouver overall predicted ground motions are higher in the down dip direction of each epicenter due to the source radiation pattern hence scenario earthquakes located south of vancouver produce the highest motions in the city the average maximum pgv at stiff soil sites across greater vancouver considering all eight scenario earthquakes is 17 8 cm s modified mercalli intensity vii the average increase in peak motion due to the presence of georgia basin sediments is a factor of 4 1 the effective duration of moderate level 3 4 cm s shaking within greater vancouver is an average of 22 s longer when georgia basin sediments are included in the 3d structure model online material snapshots and videos of wave propagation and peak ground velocity maps

the impacts of logging on landslide activity at clayoquot sound british columbia abstract the objective of this study was to investigate the impacts of logging on landslide activity in clayoquot sound on the west coast of vancouver island british columbia a total of 1004 landslides were documented in order to test the hypothesis that areas affected by logging activities show different density frequency and magnitude characteristics of landsliding than areas unaffected by logging the frequency of landslides in logged terrain was found to be nine times higher than in undisturbed forest an exponential increase in landslide frequency within the area logged was observed on a large watershed scale failures in logged terrain occur on gentler slopes than in natural terrain partly because fewer slopes steeper than 40 have been logged debris slides and debris flows are the most frequently occurring mass movements initiating mostly from road fill failures and from within cutblocks most landslides initiated on se facing slopes with the highest landslide frequency near the coast and diminishing exponentially further inland this pattern of activity most likely reflects the greater impact of severe storms arriving from the pacific with winds dominating from the southeast concave and straight slopes are most susceptible to landslide initiation a preliminary examination of geologic control on the frequency of landslides suggests that the quatsino formation the island plutonic suite and the sicker group are significantly above the average rate further work is needed to identify and quantify factors confounding the trends and correlations identified in this overview study results obtained in this study will be used to implement changes in forest management

work persistence and formative events the geomorphic impact of landslides abstract understanding the scale and frequency of physical processes that act upon and form the surface of the earth is a fundamental goal of earth science here we determine the magnitudes of landslides that impact the landscape in terms of work persistence and formative events a systematic analysis of rapid landsliding the analysis did not consider creep and other slow semi continuous processes indicates that moderate sized landslides do the most work transporting material on hillslopes the work peak defines the moderate magnitude and that magnitude varies based on local physiography and climate landslides that form the work peak are distinct from catastrophic landslides that are themselves formative and system resetting the persistence time for debris slides debris flows p ds and rock slides rock avalanches p rs is calculated over six orders of magnitude we consider an event catastrophic when it persists in the landscape as described by a persistence ratio p f an order of magnitude longer than the population of landslides that form the work peak

a source and wave propagation study of the copalillo mexico earthquake of 21 july 2000 mw 5 9 implications for seismic hazard in mexico city from inslab earthquakes the copalillo earthquake of 21 july 2000 m w 5 9 is the closest well located inslab event to mexico city ever to be recorded in this study we analyze local and regional broadband and accelerometric recordings to determine the source parameters of the earthquake and the attenuation of ground motion with distance and to obtain a preliminary estimate of the seismic hazard posed to the city by such events our results show that the earthquake occurred at a depth of about 50 km most probably in the subducted oceanic crust the waveform inversion discriminates between the two nodal planes the fault plane defined by the following strike 305 dip 32 and rake 80 the rupture propagated nearly unilaterally along the strike toward northwest with a small downdip component the observed source spectrum can be well explained by an 2 source model with m 0 6 0 10 25 dyne cm and a stress drop of 360 bar we find that high frequency ground motion f 3 hz which is related to a max during inslab earthquakes is not amplified at ciudad universitaria cu a hill zone site in the valley of mexico that is known to suffer amplification at low frequencies 0 1 f m w 7 0 event could give rise to an a max value of 30 40 gal the cu recordings indicate that the a max value of 30 gal could have a return period of about 40 yr about the same as from shallow dipping thrust earthquakes along the mexican subduction zone which have been regarded as posing the highest hazard for the city an inslab earthquake with an a max value of about 40 gal could cause heavy damage to small buildings at certain locations of the city we conclude that seismic hazard from inslab earthquakes to mexico city has so far been underestimated

moment tensor and rupture model for the 1949 olympia washington earthquake and scaling relations for cascadia and global intraslab earthquakes we reanalyzed the 13 april 1949 olympia washington earthquake by using digitized records and first motion polarities from long period seismograms the moment tensor mechanism is normal faulting with a down dip trending t axis similar in style to other cascadia intraslab earthquakes the total seismic moment is 1 3 1026 dyne cm m w 6 7 and the hypocenter depth is 60 km additional inverse modeling for the kinematic rupture process assuming the steeply east dipping fault plane from the moment tensor resulted in a slightly higher total moment of 1 9 1026 dyne cm m w 6 8 the earthquake ruptured to the south with at least two subevents the combined area of asperities and seismic moment for the 1949 earthquake was compiled with those from the 1965 seattle tacoma and the 2001 nisqually earthquakes and with those from japan and mexico to develop a source scaling relation separate from shallow global strike slip earthquakes we infer that deeper intraslab earthquakes have a significantly smaller combined area of asperities than those compiled for shallower strike slip earthquakes with the same seismic moment this difference in rupture area leads to a 3 to 5 fold increase in stress drop for earthquakes with seismic moments between 1024 and 1028 dyne cm

landslides earthquakes and erosion this paper relates landslide inventories to erosion rates and provides quantitative estimates of the landslide hazard associated with earthquakes we do this by utilizing a three parameter inverse gamma distribution which fits the frequency area statistics of three substantially dcompletet landslide event inventories a consequence of this general distribution is that a landslide event magnitude ml lognlt can be introduced where nlt is the total number of landslides associated with the landslide event using this general distribution landslide event magnitudes ml can be obtained from incomplete landslide inventories and the total area and volume of associated landslides as well as the area and volume of the maximum landslides can be directly related to the landslide event magnitude using estimated recurrence intervals for three landslide events and the time span for two historical inventories we estimate regional erosion rates associated with landslides as typically 0 1 2 5 mm year 1 we next give an empirical correlation between the earthquake magnitude associated landslideevent magnitude and the total volume of associated landslides using these correlations we estimate that the minimum earthquake magnitudes that will generate landslides is m 4 3f0 4 finally using gutenberg richter frequency magnitude statistics for regional seismicity we relate the intensity of seismicity in an area and the magnitude of the largest regional earthquakes to erosion rates we find that typical seismically induced erosion rates in active subduction zones are 0 2 7 mm year 1 and adjacent to plate boundary strike slip fault zones are 0 01 0 7 mm year 1

probabilistic landslide hazard assessment at the basin scale abstract we propose a probabilistic model to determine landslide hazard at the basin scale the model predicts where landslides will occur how frequently they will occur and how large they will be we test the model in the staffora river basin in the northern apennines italy for the study area we prepare a multi temporal inventory map through the interpretation of multiple sets of aerial photographs taken between 1955 and 1999 we partition the basin into 2243 geo morpho hydrological units and obtain the probability of spatial occurrence of landslides by discriminant analysis of thematic variables including morphological lithological structural and land use for each mapping unit we obtain the landslide recurrence by dividing the total number of landslide events inventoried in the unit by the time span of the investigated period assuming that landslide recurrence will remain the same in the future and adopting a poisson probability model we determine the exceedance probability of having one or more landslides in each mapping unit for different periods we obtain the probability of landslide size by analysing the frequency area statistics of landslides obtained from the multi temporal inventory map assuming independence we obtain a quantitative estimate of landslide hazard for each mapping unit as the joint probability of landslide size of landslide temporal occurrence and of landslide spatial occurrence

geometric effects of global lateral heterogeneity on long period surface wave propagation long period rayleigh waves from iranian earthquakes have large amplitude asymmetries between minor arc and major arc arrivals e g r 2 and r 3 at digital stations in the azimuth range n20 w to n60 e these asymmetries are as large as a factor of 2 at a period of 256 s and persist to periods greater than 300 s in some cases the entire rayleigh wave group arrival spanning periods from 100 to 300 s is either uniformly enhanced in amplitude or diminished to such a degree that the group arrival appears to be missing the amplitude anomalies are generally not accompanied by significant phase anomalies the irregular azimuthal distribution of the amplitude asymmetries and their occurrence for events with different focal mechanisms and epicentral separations of several hundred kilometers preclude an explanation of these observations by source complexity events in the mediterranean and nepal do not produce similar amplitude asymmetries at the same stations the anomalies are thus most likely due to focusing and defocusing propagation effects as a preliminary investigation of the effects of lateral heterogeneity of upper mantle velocity structure on long period surface wave amplitudes surface wave ray tracing calculations are performed using recently proposed global phase velocity distributions dramatic deviations from great circle paths are predicted for long propagation paths e g r 3 the particular spatial distribution of lateral velocity gradients around a given source location determines whether substantial amplitude asymmetries will be observed between minor arc and major arc arrivals and whether these will persist for sequential great circle orbits the 200 s period amplitude asymmetry observed at kip for the iranian source region r 2 4 r 3 is well predicted by the ray tracing results the absence of this anomaly for the other source regions is also predicted other observed anomalies are not all well predicted but it is clear that geometric effects can contribute significantly to the observed variations of rayleigh and love wave amplitudes this is the probable explanation for the instability of q estimates made from surface waves other source regions producing large surface wave amplitude anomalies include japan and southeastern alaska

rupture process of the 1944 tonankai earthquake ms 8 1 from the inversion of teleseismic and regional seismograms 1 we digitized teleseismic and regional records of the 1944 tonankai earthquake we used the multiple time window method to invert these records for the spatial and temporal distribution of slip and rake we assume a 220 140 km fault with a spacing of 20 20 km and a maximum rupture velocity of 2 5 km s the inversion resolved an asperity along the accretionary wedge and under the shima and atsumi peninsulas the rupture propagated from southwest to northeast and there was little slip near the hypocenter consistent with the absence of uplift in the overlying submarine forearc basin the peak slip is 2 3 m and the total seismic moment is 2 4 1028 dyn cm mw 8 2 we compared the predicted and observed vertical geodetic displacements and inferred that the limit of rupture is consistent with the change from subsidence to uplift west of the atsumi peninsula this suggested that the earthquake did not rupture the plate interface in the tokai gap we modeled the tsunami using sea bottom displacements generated from this slip model the tide gauge amplitudes and frequency content are consistent with those predicted resolution tests from inverting synthetic seismograms computed using a simplified slip model indicated that the combination of teleseismic and regional data sets best recovers the asperity locations and peak slips given similar station geometry and degrees of freedom an inversion of the synthetic regional data set indicates that slip artifacts can occur early in the rupture process due to many clipped records while the inversion of synthetic teleseismic data set had less resolution and recovered only 50 of the peak slip

the most cited works in geomorphology abstract we conducted a review and analysis of the references cited in articles published 1995 2004 in the journal geomorphology and also solicited comments from the authors of the most cited works on their major influences of the 31 696 unique works cited in the journal only 22 were referenced at least 20 times with the vast majority 92 cited only once or twice we divided the citations into the 10 most cited books i e complete volumes and 10 most cited papers i e journal articles book chapters reports a total of 23 different researchers were responsible for the 20 works with one wolman being an author or co author of a quarter of them seven of the ten most cited papers were based on work in the usgs in the mid twentieth century indicating a particularly fruitful time of geomorphic research and a particularly important cohort of scientists based on our citation analysis and author commentaries we suggest that classic works in geomorphology are most likely to be those that provide useful knowledge and those that incorporate interdisciplinary perspectives

rupture process and near source shaking of the 1965 seattle tacoma and 2001 nisqually intraslab earthquakes 1 we inverted teleseismic data for the 1965 seattle tacoma earthquake slip and rake the earthquake had 2 asperities of 12 and 16 km2 near the hypocenter with average slip of 2 and 2 8 m respectively mo 9 4 1025 dyne cm mw 6 6 we also inverted strong motion and teleseismic data for the 2001 nisqually earthquake this earthquake had 2 subevents with an asperity area of 45 km2 between 59 and 62 km depth with an average slip of 1 7 m mo 1 7 1026 dyne cm mw 6 8 shake maps of peak ground acceleration pga and spectral acceleration sa were generated using a time domain approach including slip model site and basin depth corrections based on california geology corrections reduced the residuals between observed and predicted pga and sa the simulated pattern of shaking from the 1965 earthquake was twice as high as in the 2001 earthquake due to the proximity of the 1965 epicenter to sedimentary basins

fragmentation energy in rock avalanches fragmentation is one of the mechanisms involved in rock avalanches quantifying the associated energy dur ing a rock avalanche can help to assess the influence of fragmentation on post failure mass movements in this paper in situ block size distributions of the intact rock mass and the debris deposits are presented and analyzed for nine rock avalanches five in the canadian rocky mountains and four in the european alps degrees of fragmentation are esti mated from these data two methods are examined to assess fragmentation energy one based on the comminution the ory and one on the blasting energy used in the mining industry the results show that for the studied rock avalanches there is a relationship between the reduction in diameter ratio rr d50 d50 where d50 and d50 are the mean diameter of the intact rock mass and the mean diameter of the debris respectively and the potential energy per unit volume normalized with respect to the point load strength of rock hg c where is the unit weight of the material hg is the vertical distance between the centres of gravity of the mass at the start and end positions and c is the point load strength for the cases studied fragmentation energy calculations average 20 of the potential energy an empirical relationship between rr and hg c has been established and is used in the definition of a disintegration index id this index seems to reflect the physics of the disintegration process since it accounts for the fact that the reduction in diameter ratio is a function of the dissipated energy and the strength of the rock these factors have long been known to affect fragmentation but have never been presented in a coherent manner for rock avalanches

rupture history of september 30 1999 intraplate earthquake of oaxaca mexico mw 7 5 from inversion of strong motion data near source strong motions are inverted to estimate the rupture history of intraslab normal faulting september 30 1999 oaxaca mexico earthquake two focal mechanisms harvard and neic cmt solutions are tested for the source geometry the inversion with the ne dipping fault plane of the harvard solution best matches the data strike 295 dip 50 rake 82 we estimated the slip distribution on the fault and the associated rupture front propagation as well as the rise time the inversion results show that the rupture mainly propagated from ese to wnw and slightly downdip with an average rupture velocity of about 3 km s the rise time ranges between 1 and 2 s the slip distribution on the fault is mainly concentrated in two interconnected patches with a maximum slip of 2 5 m located about 20 km and 40 km wnw of the hypocenter most of the slip is released at an average depth of 45 km a smaller area with a maximum slip of 1 5 m is also observed close to the hypocenter the total co seismic moment released is equal to 1 8 1020 nm

long period toroidal earth free oscillations from the great sumatra andaman earthquake observed by paired laser extensometers in gran sasso italy summary strain data recorded by two crossed laser extensometers operating in the gran sasso underground observatory recorded seismic free oscillations excited by the 2004 december 26 sumatra andaman earthquake the main source of instrumental noise can be mitigated by differencing data from the crossed strainmeter arms so that the resulting differential strain data set offers an unprecedented resolution of the seismic toroidal free oscillations with periods t 1000 s we reconstruct the time evolution of selected free oscillations for comparison with synthetic seismograms that include normal mode coupling effects from coriolis force attenuation and ellipticity envelopes estimated for the gran sasso differential data set for free oscillations with period t 1 mhz are approximated adequately by a composite centroid moment tensor cmt source with five subevents and an aggregate mw 9 3 moment magnitude envelopes for several toroidal free oscillations with t 1000 s are predicted less well the amplitude of the rarely observed mode 0t2 is overpredicted at gran sasso by roughly a factor of two and other modes are underpredicted the amplitude discrepancy for 0t2 is confirmed at selected exceptionally low noise seismic stations hypothetical explanations include a slow slip component of the seismic moment release errors in the composite cmt source model unmodelled coupling effects to earth s secular modes and feedback from the sumatra andaman tsunami on indian ocean coastlines of these hypotheses either an extended duration strain release or tsunami feedback seem most plausible the viability of the tsunami feedback mechansim deserves further investigation

inversion of strong ground motion and teleseismic waveform data for the fault rupture history of the 1979 imperial valley california earthquake a least squares point by point inversion of strong ground motion and teleseismic body waves is used to infer the fault rupture history of the 1979 imperial valley california earthquake the imperial fault is represented by a plane embedded in a half space where the elastic properties vary with depth the inversion yields both the spatial and temporal variations in dislocation on the fault plane for both right lateral strike slip and normal dip slip components of motion inversions are run for different fault dips and for both constant and variable rupture velocity models effects of different data sets are also investigated inversions are compared which use the strong ground motions alone the teleseismic body waves alone and simultaneously the strong ground motion and teleseismic records the inversions are stabilized by adding both smoothing and positivity constraints the moment is estimated to be 5 0 10 25 dyne cm and the fault dip 90 5 dislocation in the hypocentral region south of the united states mexican border is relatively small and almost dies out near the border dislocation then increases sharply north of the border to a maximum of about 2 m under interstate 8 dipslip motion is minor compared to strike slip motion and is concentrated in the sediments the best fitting constant rupture velocity is 80 per cent of the local shear wave velocity however there is a suggestion that the rupture front accelerated from the hypocenter northward the 1979 imperial valley earthquake can be characterized as a magnitude 5 earthquake at the hypocenter which then grew into or triggered a magnitude 6 earthquake north of the border

gigantic paleolandslide associated with active faulting along the bogd fault gobi altay mongolia on the basis of analyses of satellite imagery aerial photographs and field observations we describe the occurrence of one of the largest paleolandslides 50 km3 ever recognized in an intracontinental domain the slide occurred along the active bogd fault in the gobi altay mountain range in mongolia morphological and structural analyses of the relationships between the landslide and the area affected by active tectonics suggest that this gigantic mass movement was associated with surface faulting during a strong earthquake

the effect of forearc mantle serpentinization on ground motions from megathrust and intraslab events in the cascadia subduction zone we re examine large scale structural controls on ground motions from megathrust and intraslab events in the cascadia subduction zone in light of recent evidence pointing to a highly hydrated and serpentinized forearc mantle we employ 2d p sv pseudospectral synthetic seismograms double couple line sources and a structural model for cascadia based on the study of bostock et al 2002 that includes both serpentinized forearc mantle and eclogitized oceanic crust as in a previous study cohee et al 1991 we note that ground motions at greater epicentral distances are dominated by postcritical reflections from the moho however in our modeling of megathrust earthquakes we find that the presence or absence of serpentinized forearc mantle dictates whether maximum ground motions in the pacific northwest urban corridor portland seattle vancouver victoria result from postcritical reflection at the oceanic moho or continental moho respectively as well as their range dependence moreover serpentinization reduces the efficacy of the subducting oceanic crust as a wave guide by allowing energy to escape through the overlying wedge this effect is particularly important for intraslab wadati benioff events as it allows focusing of upward propagating energy toward the surface that would otherwise be redirected downward consequently ground motions from intraslab sources at lower frequencies 0 2 hz can be up to 5 times greater than those modeled in the absence of a serpentinized forearc mantle at higher frequencies the lower q of serpentine may act to reduce this amplification

global mantle shear velocity model developed using nonlinear asymptotic coupling theory we present a three dimensional shear velocity model of the whole mantle developed using s h waveform data the model is expressed horizontally in terms of spherical harmonics up to degree 12 and vertically in terms of legendre polynomials up to degrees 5 and 7 in the upper and lower mantle respectively what distinguishes this model from other tomographic models published to date is 1 the theoretical normal mode based wave propagation approach where we include across branch mode coupling terms in order to model the body wave sensitivity to structure along the path more accurately 2 the wave packet weighting scheme which allows to balance contributions from high amplitude and low amplitude phases increasing the resolution in some parts of the mantle we also relax the constraints on the moho depth which is allowed to vary in the inversion thus absorbing some uncertainties in crustal structure the resulting model is generally in good agreement with other recent global mantle s velocity models and with some regional models the rms profile with depth has more power than other models in the upper mantle lower mantle transition region and the zone of increased power and low degree structure near the base of the mantle is confined to the last 500 km in depth this model provides a particularly good fit to the non hydrostatic geoid through harmonic degree 12 79 variance reduction as well as good fits to observed splitting functions of s velocity sensitive mantle modes indicating that both large scale and small scale features are really well constrained