evidence for postseismic viscoelastic relaxation following the 1959 m 7 5 hebgen lake montana earthquake a 1983 releveling survey conducted by the national geodetic survey combined with previous surveys in 1923 1960 1967 and 1975 provides evidence for ongoing vertical deformation of a broad region diameter of 150 km surrounding the site of the 1959 hebgen lake earthquake deformation consists of relative uplift centered roughly on the coseismic fault and a smaller amplitude zone of relative subsidence south of the fault maximum observed elevation change during the postseismic period 1960 1983 exceeds 30 cm assuming that the entire uplift i e 1923 1983 occurred following the 1959 earthquake i e uplift measured between 1923 and 1960 was entirely postseismic the rate of vertical deformation appears to have decreased exponentially with a characteristic decay time of about 10 years the spatial pattern and time behavior of the observed movements are consistent with simple models of postseismic deformation following normal faulting in an elastic layer thickness of 30 40 km overlying a viscoelastic half space viscosity of 1019 pa s this model may also account for the anomalously large horizontal strain around the hebgen lake region measured by repeated trilateration surveys during the period 1973 1984 the releveling measurements in the hebgen lake region appear to provide the first observations of viscoelastic relaxation in the asthenosphere following an intraplate earthquake in the united states

a new attenuation relation for strong ground motion in japan based on recorded data following the 1995 hyogo ken nanbu kobe earthquake the japanese government in an effort to prevent future earthquake disasters installed networks consisting of a large number of strong motion observation stations further national seismic hazard maps were made available to the public on an internet website in march 2005 by the headquarters for earthquake research promotion however these maps indicate only the local seismic intensity for japan as empirically con verted from predicted peak velocity in consolidated soils for various applications other strong motion indexes such as the response spectral acceleration are required in this study a database of whole japanese strong ground motion records between 1963 and 2003 is established in order to identify a new standard attenuation relation for japan for response acceleration as well as peak value it is usually very difficult to determine a suitable model form due to the large variability of strong motion data and correlation among the model variables because the strong coupling of variables in an attenuation model and the statistical power of the data is often not large enough to determine the necessity of these parameters therefore in this study our model has only three variables earthquake magnitude shortest distance to the seismic fault plane and focal depth to improve predictions given by the model site correction terms are adopted and additional terms for correcting regional anomalous seismic intensity with respect to the base model are determined the good fit between the model and observed strong motion records suggests that the new model is reasonably robust

identification of the fortnightly wave observed along the northern coast of the gulf of guinea abstract numerical calculations of coastally trapped wave modes along the northern coast of the gulf of guinea using representative bottom topography and continuous stratification on a plane were carried out to identify the observed fortnightly propagating coastal wave results showed that the propagation speed of the observed wave approximately 53 cm s 1 for sea level and 54 cm s 1 for sea surface temperature is close to that of the second mode 64 cm s 1 and no other off the shelf this mode has a baroclinic structure having considerable amplitude at 2 km depth ray theory calculations indicate that if as is likely the observed wave were generated on the shelf a vertically standing modal structure with large amplitude at 2 km depth is not possible therefore no coastally trapped vertically standing wave modes are consistent with the observed wave consequently it is most likely that the wave is a vertically propagating coastally trapped wave as has been observed recently in other contexts th

on the connection between benguela and equatorial atlantic ninos and the role of the south atlantic anticyclone for the eastern tropical atlantic two recurring el nino like phenomena with high interannual sst anomalies have been described one centered in the equatorial region as part of the atlantic zonal mode and one off angola referred to as benguela nino both events are supposed to be generated not locally but by a relaxation of the trade winds in the western equatorial atlantic here the connection between sst variations in the two regions is investigated with observational data sets as well as ocean model simulations they are correlated to such an extent that joint events should rather be viewed as one atlantic nino an intriguing feature counterintuitive in view of the remote forcing mechanism is that sst anomalies off angola precede those in the equatorial atlantic we show this behavior to be related to the difference in thermocline depths and a different seasonality of interannual sst variability in the two regions while benguela ninos peak in austral fall due to the angola benguela front being located furthest to the south and high interannual variability in coastal kelvin wave activity warm events at the equator are phase locked to austral winter when the thermocline is shallow perturbation experiments confirm the importance of remote forcing from the equator for sst variability off angola and demonstrate the leading role of wind stress in the generation of sst anomalies in the eastern tropical atlantic these wind stress variations are shown to be linked to fluctuations in the strength of the south atlantic anticyclone a connection that might be important with respect to the predictability of atlantic ninos

brunt vaisala frequency and rossby radii in the south atlantic abstract brunt vaisala frequency profiles have been calculated in the south atlantic and neighboring regions on a 5 5 grid between 30 n and 70 s 70 w and 70 e using the annual mean temperature and salinity profiles computed by levitus from data available from the national oceanographic data center nodc these brunt vaisala frequency profiles are used in the computation of the first and second internal rossby deformation radii the external rossby radius is computed for reference these results compare very well with those of emery et at for the equatorial atlantic very small values of the radii are evidenced in the extreme south less than 10 km in the antarctic circumpolar current for the first internal mode high vertical variability in brunt vaisala frequency profiles is also observed at the center of the subtropical gyre this behavior is probably due to the lack of deep data in this region

the source of benguela ninos in the south atlantic ocean 1 the intermittent occurrence of anomalous warm events in the upwelling regions of the pacific el ninos has been intensively studied pacific ninos have striking effects on the local ecosystem hence on the fisheries and on rainfall similar dramatic events have been observed in the south atlantic off the coasts of angola and namibia and named benguela ninos they tend not to occur in unison with their pacific counterpart and may thus have unrelated forcing mechanisms using an ocean general circulation model forced by real winds and verified with satellite data it is shown that benguela ninos are generated by specific wind stress events in the west central equatorial atlantic and progress from there as subsurface temperature anomalies that eventually outcropped only at the south west african coast these results suggest that it now may be possible to predict the occurrence of these disruptive events with a lead time of 2 months

source rupture process of the 2004 chuetsu mid niigata prefecture japan earthquake inferred from waveform inversion with dense strong motion data abstract the kinematic source rupture process of the 2004 chuetsu mid niigata prefecture japan earthquake is estimated from strong motion data by the linear waveform inversion method in order to develop appropriate green s functions one dimensional velocity structure models for each station are constructed by modeling the aftershock waveforms the estimated top of the bedrock is deeper at the western side of the fault and relatively shallow at the eastern side this tendency coincides with other investigations of seismic tomography and microtremor array observations the obtained source model shows large slips in the vicinity of the hypocenter the reverse slipping rupture originated from the deeper part of the fault and propagated toward the up dip and southwest directions the near surface slip is small two tests are demonstrated to check the stability of the obtained source model the first test examines the effects of the number of available stations on the solution and the second test examines how the difference in the target waveform type affects the solution the number of stations affects the variation of slip amount and more than 12 stations appear to be sufficient to obtain a stable solution in this case the difference in the target wave type in the data set does not significantly affect the solution if the number of stations is sufficient and the green s functions are well calibrated the model obtained using calibrated velocity structure models shows clear image of high slip area compared to the model obtained using a single velocity structure model

variability of near field ground motion from dynamic earthquake rupture simulations this study investigates near field ground motion variability due to dynamic rupture models with heterogeneity in the initial shear stress ground velocity seismograms are synthesized by convolving the time histories of slip velocity obtained from spontaneous dynamic rupture models with green s functions of the medium calculated with a discrete wavenumber finite element method peak ground velocity pgv estimated on the synthetics generally matches well with an empirically derived attenuation relation whereas spectral acceleration sa shows only an acceptable match at periods longer than 1 sec using the geometric mean to average the two orthogonal components leads to a systematic bias for the synthetics in particular at the stations closest to the fault this bias is avoided by using measures of ground motion that are independent of the sensor orientation the contribution from stress heterogeneity to the overall ground motion variability is found to be strongest close to the fault and in the backward directivity region of unilaterally propagating ruptures in general the intraevent variability originating from the radiation pattern and the effect of directivity is on the same order or larger than the interevent variability the interevent ground motion variability itself is dominated by the hypocenter station configuration and is influenced only to a lesser extent by the differences in the dynamic rupture process due to the stress heterogeneity in our modeling approach the hypocenter location is not picked arbitrarily but is determined to be mechanically consistent with the stress heterogeneity through a procedure emulating tectonic stress loading of the fault and nucleation compared to the peak ground motion recorded during the 2004 parkfield california earthquake our simulated seismograms show enhanced spatial correlation that may be attributed to the simplicity of the assumed crustal model or to an incomplete representation of the spatial heterogeneity of dynamic rupture parameters nevertheless the intraevent pgv variability in the near fault region determined for the parkfield dataset is of the same order of magnitude as for our simulations

distance and azimuthal dependence of ground motion variability for unilateral strike slip ruptures abstract we investigate near field ground motion variability by computing the seismic wavefield for five kinematic unilateral rupture models of the 1992 m w 7 3 landers earthquake eight simplified unilateral rupture models based on the landers event and a large m w 7 8 shakeout scenario we include the geometrical fault complexity and consider different 1d velocity density profiles for the landers simulations and a 3d heterogeneous earth structure for the shakeout scenario for the landers earthquake the computed waveforms are validated using strong motion recordings we analyze the simulated ground motion data set in terms of distance and azimuth dependence of peak ground velocity pgv our simulations reveal that intraevent ground motion variability is higher in close distances to the fault ln pgv is well described by a cauchy lorentz function that provides a novel empirical quantification to model the spatial dependency of ground motion online material figures of slip distributions residuals to ground motion prediction equations gmpes distance and azimuthal dependence and directivity predictor of ground motion variability for different source models

atmosphere ocean mechanisms of climate anomalies in the angola tropical atlantic sector abstract interannual variations in the large scale atmospheric and oceanic fields over the tropical atlantic are studied in relation to rainfall anomalies on the angola coast departure patterns are constructed by stratification with respect to extremely dry and wet years and by correlation with rainfall in angola which is concentrated in march april the analysis suggests a causality chain of atmospheric oceanic anomalies variations of westward wind stress on the western equatorial atlantic constitute an early link in this chain the annual cycle is characterized by a relaxation of the wind stress from september november to february march anomalous seasonal relaxation of easterly wind stress over the western equatorial atlantic remotely forces the sea surface temperature sst departures in the eastern south atlantic a large relaxation being followed by positive sst departures sea surface temperature modulates the rainfall over downstream angola by controlling the atmospheric moisture and stability

source mechanism of very long period signals accompanying dome growth activity at merapi volcano indonesia 1 very long period vlp pulses with period of 6 7s displaying similar waveforms were identified in 1998 from broadband seismographs around the summit crater these pulses accompanied most of multiphase mp earthquakes a type of long period event locally defined at merapi volcano source mechanisms for several vlp pulses were examined by applying moment tensor inversion to the waveform data solutions were consistent with a crack striking 70 and dipping 50 sw 100m under the active dome suggest pressurized gas transport involving accumulation and sudden release of 10 60 m3 of gas in the crack over a 6s interval

coastal trapped wave propagation along the southwest african shelf as revealed by moored observations abstractcoastal trapped waves ctws that propagate poleward along the southwest african shelf potentially leak energy from lower latitudes into the benguela upwelling system bus thus in additi

oceanic kelvin waves and tropical atlantic intraseasonal variability 1 kelvin wave characterization 1 oceanic kelvin waves from the equator to the west african coast are investigated in the framework of tropical atlantic intraseasonal variability in order to better highlight the wave propagations a 25 95 day band pass filter was applied to the sea surface height ssh product derived from the topex poseidon altimeter and an ocean general circulation model simulation for the 1993 2000 period in addition to equatorial eastward propagations our analysis reveals recurrent and continuous propagations distinguishable over thousands of kilometers poleward along the coasts as far as about 10 15 latitude a novel result with altimeter data the variance of the filtered ssh signal goes from 1 cm at the equator to 2 cm at the african coast estimates of the phase speed range from 1 5 to 2 1 m s along the equator and the west african coastline such values are very close to those of equatorial kelvin wave propagations likely dominated by the first two baroclinic modes supporting the fact that the coastal propagations are coastally trapped kelvin waves in order to simplify the description of these kelvin waves we present an intraseasonal climatology which reveals regular boreal autumn winter equator to coast propagations an improved description is achieved thanks to the computation of an extended empirical orthogonal function for the boreal autumn winter propagations lag correlation of ssh signals allows for a twofold quantification the phase speed and the importance of remote forcing along the coast the remote forcing effect of intraseasonal kelvin waves is clearly evidenced over coastal upwelling regions as far as 10 15 latitude the physical mechanism associated with the forcing of the kelvin waves and its impacts will be investigated in a future paper

new empirical relationships among magnitude rupture length rupture width rupture area and surface displacement source parameters for historical earthquakes worldwide are compiled to develop a series of empirical relationships among moment magnitude m surface rupture length subsurface rupture length downdip rupture width rupture area and maximum and average displacement per event the resulting data base is a significant update of previous compilations and includes the additional source parameters of seismic moment moment magnitude subsurface rupture length downdip rupture width and average surface displacement each source parameter is classified as reliable or unreliable based on our evaluation of the accuracy of individual values only the reliable source parameters are used in the final analyses in comparing source parameters we note the following trends 1 generally the length of rupture at the surface is equal to 75 of the subsurface rupture length however the ratio of surface rupture length to subsurface rupture length increases with magnitude 2 the average surface displacement per event is about one half the maximum surface displacement per event and 3 the average subsurface displacement on the fault plane is less than the maximum surface displacement but more than the average surface displacement thus for most earthquakes in this data base slip on the fault plane at seismogenic depths is manifested by similar displacements at the surface log linear regressions between earthquake magnitude and surface rupture length subsurface rupture length and rupture area are especially well correlated showing standard deviations of 0 25 to 0 35 magnitude units most relationships are not statistically different at a 95 significance level as a function of the style of faulting thus we consider the regressions for all slip types to be appropriate for most applications regressions between magnitude and displacement magnitude and rupture width and between displacement and rupture length are less well correlated and have larger standard deviation than regressions between magnitude and length or area the large number of data points in most of these regressions and their statistical stability suggest that they are unlikely to change significantly in response to additional data separating the data according to extensional and compressional tectonic environments neither provides statistically different results nor improves the statistical significance of the regressions regressions for cases in which earthquake magnitude is either the independent or the dependent parameter can be used to estimate maximum earthquake magnitudes both for surface faults and for subsurface seismic sources such as blind faults and to estimate the expected surface displacement along a fault for a given size earthquake

validation of the recipe for broadband ground motion simulations of japanese crustal earthquakes the robustness of broadband ground motion simulation can promote seismic hazard assessment a broadband ground motion simulation technique called the recipe is used in the scenario earthquake shaking maps of the national seismic hazard maps for japan the recipe represents a fault rupture based on a multiple asperity model referred to as the characterized source model broadband ground motion time histories on the engineering bedrock are computed by a hybrid approach of the 3d finite difference method and the stochastic green s function method for the long 1 s and short period 70 km such conditions are outside of the target range of the recipe simulations using a 1d velocity structure model were also examined the simulation results for the 1d and 3d velocity structure models indicated that the 3d velocity structure models are important in reproducing pgv and the later phases with long duration especially on deep sediment sites

recipe for predicting strong ground motion from crustal earthquake scenarios we developed a recipe for predicting strong ground motions based on a characterization of the source model for future crustal earthquakes from recent developments of waveform inversion of strong motion data used to estimate the rupture process we have inferred that strong ground motion is primarily related to the slip heterogeneity inside the source rather than average slip in the entire rupture area asperities are characterized as regions that have large slip relative to the average slip on the rupture area the asperity areas as well as the total rupture area scale with seismic moment we determined that the areas of strong motion generation approximately coincide with the asperity areas based on the scaling relationships the deductive source model for the prediction of strong ground motions is characterized by three kinds of parameters outer inner and extra fault parameters the outer fault parameters are defined as entire rupture area and total seismic moment the inner fault parameters are defined as slip heterogeneity inside the source area of asperities and stress drop on each asperity based on the multiple asperity model the pattern of rupture nucleation and termination are the extra fault parameters that are related to geomorphology of active faults we have examined the validity of the earthquake sources constructed by our recipe by comparing simulated and observed ground motions from recent inland crustal earthquakes such as the 1995 kobe and 2005 fukuoka earthquakes

low frequency sea level fluctuations along the coasts of namibia and south africa summary sea level records at nine ports along the coasts of namibia and south africa are used to establish the existence of coastal trapped disturbances in sea level as a response to the passage of synoptic weather systems using spectral analysis the characteristics and spatial variability of the sea level fluctuations are identified the results of cross correlation analyses performed on sea level data at adjacent ports for two periods during 1982 are discussed in detail to examine the propagation of coastal trapped waves round the coast sea level records from coastal areas in southern africa exhibit extra tidal fluctuations on several different time scales associated with local or remotely forced atmospheric phenomena these scales include the synoptic or event scale of period 2 20 day the seasonal scale of period 3 6 month and the interannual or long term scale with a period of a few years the seasonal and long term components of sea level variability along the west coast of southern africa have been discussed by brundrit 1984 he concluded that there is a clear difference between the seasonal response at the northern and southern ports associated with the difference in winds affecting these two regions the long term component was found to be similar at all ports suggesting large scale non local forcing the theoretical response of sea level to pressure changes at the low frequencies associated with the passage of weather systems is that of an inverted baromei er robinson 1964 records should show a decrease in sea level of 1 01 cm for an increase in atmospheric pressure of 1 mb this assumes an ocean such that the total pressure at any fxed point on the bottom is constant in coastal areas over continental shelves this is rarely valid changes in atmospheric pressure are accompanied by changes in the velocity and direction of the wind and hence wind stress and these also contribute to fluctuations in sea level robinson

geographical variability of the first baroclinic rossby radius of deformation global 1 83 18 climatologies of the first baroclinic gravity wave phase speed c1 and the rossby radius of deformation l1 are computed from climatological average temperature and salinity profiles these new atlases are compared with previously published 5 83 58 coarse resolution maps of l1 for the northern hemisphere and the south atlantic and with a 1 83 18 fine resolution map of c1 for the tropical pacific it is concluded that the methods used in these earlier estimates yield values that are biased systematically low by 5 15 owing to seemingly minor computational errors geographical variations in the new high resolution maps of c1 and l1 are discussed in terms of a wkb approximation that elucidates the effects of earth rotation stratification and water depth on these quantities it is shown that the effects of temporal variations of the stratification can be neglected in the estimation of c1 and l1 at any particular location in the world ocean this is rationalized from consideration of the wkb approximation

vertical deformation associated with normal fault systems evolved over coseismic postseismic and multiseismic periods vertical deformation of extensional provinces varies significantly and in seemingly contradictory ways sparse but robust geodetic seismic and geologic observations in the basin and range province of the western united states indicate that immediately after an earthquake vertical change primarily occurs as subsidence of the normal fault hanging wall a few decades later a 100 km wide zone is symmetrically uplifted the preserved topography of long term rifting shows bent and tilted footwall flanks rising high above deep basins we develop finite element models subjected to extensional and gravitational forces to study time varying deformation associated with normal faulting we replicate observations with a model that has a weak upper mantle overlain by a stronger lower crust and a breakable elastic upper crust a 60 dipping normal fault cuts through the upper crust and extends through the lower crust to simulate an underlying shear zone stretching the model under gravity demonstrates that asymmetric slip via collapse of the hanging wall is a natural consequence of coseismic deformation focused flow in the upper mantle imposed by deformation of the lower crust localizes uplift under the footwall the breakable upper crust is a necessary model feature to replicate footwall bending over the observed width 10 km which is predicted to take place within 1 2 decades after each large earthquake thus the best preserved topographic signature of rifting is expected to occur early in the postseismic period the relatively stronger lower crust in our models is necessary to replicate broader postseismic uplift that is observed geodetically in subsequent decades

rupture processes of the 2004 chuetsu mid niigata prefecture earthquake japan a series of events in a complex fault system 1 we relocated the hypocenters of the 2004 chuetsu earthquake sequence niigata japan using the double difference method the distribution of aftershocks reveals a complex fault system consisting of five different fault planes inversions of strong motion records for the five major events within the sequence indicate that the mainshock mw 6 6 and the largest aftershock mw 6 3 occurred on parallel wnw dipping fault planes the zones of large slip asperities of these two events are located near the hypocenters in contrast the three other large earthquakes mw 5 9 5 7 and 5 9 occurred on east dipping fault planes oriented perpendicular to the fault plane of the mainshock we used slip distributions deduced from waveform inversions to estimate the coulomb failure stress changes that occurred immediately prior to each event cff values were positive at the hypocenters and within the asperities of the major aftershocks these results suggest that stress changes resulting from individual earthquakes led directly to the occurrence of subsequent earthquakes within the complex fault system

atmospheric effects in the angola benguela frontal zone the angola benguela front is the generic border between on the one hand the benguela current and the coastal upwelling regime along the southwest african coastline and on the other hand the warm southward flowing angola current this frontal zone has a variable morphology geographic location and thermal characteristics it has been suggested that this variability may be related to changing wind patterns we have studied the thermal characteristics of the surface expression of the frontal zone for a 74 day period using daily thermal infrared images and compared these to wind patterns from synoptic weather maps there is little correlation between the location of the northern and the southern front that form the envelope for this frontal zone the location of the southern front largely determines the thermal gradient across the entire frontal zone large short term displacements in the geographic location of the frontal zone as well as short term variations in its thermal characteristics are shown to be strongly correlated to the atmospheric pressure gradient of the south atlantic anticyclone with a 1 day lag period this is true irrespective of the latitude changes of the center of the south atlantic anticyclone

fault kinematics and surface deformation across a releasing bend during the 2010 mw 7 1 darfield new zealand earthquake revealed by differential lidar and cadastral surveying dextral slip at the western end of the east west striking greendale fault during the 2010 m w 7 1 darfield earthquake transferred onto a northwest trending segment across an apparent transtensional zone here named the waterford releasing bend we used detailed surface mapping differential analysis of pre and postearthquake light detection and ranging lidar and property boundary cadastral resurveying to produce high resolution centimeter scale estimates of coseismic ground surface displacements across the waterford releasing bend our results indicate that the change in orientation on the greendale fault incorporates elements of a large scale releasing bend from the viewpoint of westward motion on the south side of the fault as well as a smaller scale restraining stepover from the viewpoint of southeastward motion on the north side of the fault these factors result in the waterford releasing bend exhibiting a decrease in displacement to near zero at the change in strike and the presence within the overall releasing bend of a nested localized restraining stepover with contractional bulging the exceptional detail of surface deformation and kinematics obtained from this contemporary surface rupture event illustrates the value of multimethod investigations our data provide insights into strike slip fault bend kinematics and into the potentially subtle but important structures that may be present at bends on historic and prehistoric rupture traces

the angola current flow and hydrographic characteristics as observed at 11 s the eastern boundary circulation off the coast of angola has been described only sparsely to date although it is a key element in the understanding of the highly productive tropical marine ecosystem off angola here we report for the first time direct velocity observations of the angola current ac at 11 s collected between july 2013 and october 2015 in the depth range from 45 to 450 m the measurements reveal an alongshore flow that is dominated by intraseasonal to seasonal variability with periodically alternating southward and northward velocities in the range of 40 cm s during the observation period a weak southward mean flow of 5 8 cm s at 50 m depth is observed with the southward current extending down to about 200 m depth corresponding mean southward transport of the ac is estimated to be 0 32 0 046 sv an extensive set of hydrographic measurements is used to investigate the thermal structure and seasonality in the hydrography of the eastern boundary circulation within the depth range of the ac the superposition of annual and semiannual harmonics explains a significant part of the total variability although salinity in the near surface layer appears to be also impacted by year to year variability and or short term freshening events in the central water layer temperature and salinity on isopycnals vary only weakly on seasonal to annual time scales the available data set is further used to evaluate different reanalysis products particularly emphasizing the ocean s role in coupled climate model sst biases in the eastern tropical atlantic

bi annual intrusion of tropical water in the northern benguela upwelling 1 the benguela current is one of the most productive marine ecosystems in the world a difference from other eastern boundary currents is a thermal front at its northern border the angola benguela front abf separating warm tropical water from cold upwelled water there is an annual net modelled transport of 0 45 sverdrup of near surface tropical water flowing poleward across the abf into the northern benguela current upwelling system this transport follows a bi annual harmonic quasi synchronized to the annual cycle of sea level anomaly in the eastern tropical atlantic with maxima in october and february and minima in june and december the bi annual advection of warm angolan water in the northern benguela across the abf is a key element in the development of benguela ninos warmer than normal oceanic events that have an impact on fisheries hypoxia and rainfall of the region

theory of the benguela upwelling system the paper gives a theoretical study of the benguela upwelling system by means of a relatively simple conceptual model that allows an analytical treatment the model consists of a stratified flat bottomed coastal ocean the coast is idealized by a straight wall the model ocean is forced by an alongshore wind band extending from the area near cape town to the border of angola and namibia the wind varies alongshore and cross shore wind stress curl and changes periodically in time the response of the coastal ocean is governed by coastal jets upwelling and kelvin waves as well as by a current system driven by the wind stress curl the model is able to reproduce several observed features such as the poleward undercurrent the northward coastal currents in most of the wind band and a southward coastal current near the northern edge of the wind band export of coastal jets out of the forcing area by coastal kelvin waves provide a mechanism to guide energy into the area off cape town the southward propagating kelvin waves may bend around the southern tip of africa and provide a dynamic linkage between the benguela coastal current and the agulhas current

effects of lithospheric viscoelastic relaxation on the contemporary deformation following the 1959 mw 7 3 hebgen lake montana earthquake and other areas of the intermountain seismic belt 1 the 1959 mw 7 3 hebgen lake mt normal faulting earthquake occurred in an extensional stress regime near the yellowstone volcanic field time dependent crustal deformation data following this major earthquake were acquired by precise trilateration and gps surveys from 1973 to 2000 around the hebgen lake fault zone modeling the changes of baseline lengths across and near the fault reveals a lateral variation of transient rheology in which the lithosphere is stronger near the hebgen lake fault zone than in the vicinity of the yellowstone volcano system the models also imply that the lower crust is stronger than the upper mantle in agreement with results from studies of postseismic and post lake filling relaxations 100 years in addition evaluations of the postseismic motion produced by the hebgen lake and the 1983 mw 6 9 borah peak id earthquakes indicate that horizontal transient motion of up to 1 mm yr contribute significantly to the contemporary regional crustal deformation near the epicentral areas for the eastern basin and range 500 km south of the hebgen lake fault similar rheologic models were derived from the observed uplift associated with the lake bonneville rebound and were used to evaluate the postseismic deformation associated with six most recent paleoearthquakes of the wasatch fault zone and three m 5 6 historic earthquakes of northern utah the results show 0 1 mm yr of horizontal postseismic motion at present time that are within the horizontal uncertainties of continuous gps velocity from the basin and range and significantly smaller than the contemporary extension of 1 3 mm yr in the wasatch front

remotely forced biweekly deep oscillations on the continental slope of the gulf of guinea current meter measurements on the continental slope of the gulf of guinea at 7 20 s and 1300 m depth have revealed biweekly oscillations of the currents bottom intensified and oriented along the bathymetry we develop a three dimensional primitive equation model of the gulf of guinea to study the oscillations and their forcing mechanism the high resolution 1 12 regional model reproduces remarkably well the main characteristics of the deep currents on the continental slope experiments with different forcings demonstrate that the biweekly variability at 1300 m depth is remotely forced by equatorial winds deep yanai waves generated by the wind propagate eastward along the equator upon reaching the african coast the energy propagates poleward in both directions as coastal trapped waves the selection of the dominant biweekly period is explained by the absence of equatorial waves with westward group velocities in that frequency band contrary to a previous hypothesis involving tidal forcing our interpretation is coherent with the significant interannual variability of the biweekly energy

variability in satellite winds over the benguela upwelling system during 1999 2000 1 wind stress variability over the benguela upwelling system is considered using 16 months 01 august 1999 to 29 november 2000 of satellite derived quikscat wind data variability is investigated using a type of artificial neural network the self organizing map som and a wavelet analysis the som and wavelet analysis are applied to an extracted data set to find that the system may be divided into six discrete wind regimes the wavelet power spectra for these wind regions span a range of frequencies from 4 to 64 days with each region appearing to contain distinct periodicities to the north 10 23 5 s the majority of the power occurs during austral winter with a 4 16 day periodicity further investigation of national centers for environmental prediction reanalysis outgoing longwave radiation data indicates that the winter intensification of wind stress off the angolan coast is linked with convective activity over equatorial west africa the summer activity appears to be linked with the intensification of the angolan heat low convective activity over the congo basin appears to impact upon wind stress variability off the angolan coast throughout the year farther south 24 35 s the majority of the power occurs in the summer here a bimodal distribution occurs with peaks of 4 12 and 25 50 days the southernmost regions appear to be forced at higher frequencies by both midlatitude cyclones austral winter and mesoscale coastal lows austral summer at lower frequencies eastward propagating periodic wind events that originate over eastern south america appear to be important to the forcing of wind stress over the southern benguela

models of crustal deformation this review is principally concerned with theoretical models of crustal deformation developed during this quadrennium observational data as well as topics in lithospheric flexure and isostasy are covered in companion reviews in this volume progress has been made toward constructing both new inelastic and inhomogeneous elastic models of earthquake induced crustal deformation most of the inelastic models involve dislocations or green s functions in an elastic or anelastic lithosphere which overlies a maxwell viscoelastic asthenosphere

an elastic rebound model for normal fault earthquakes a viscoelastic finite element method is used to formulate an elastic rebound model for normal fault earthquake cycles model generated displacements correlate well with geodetic survey data collected before and after the 1954 m 7 1 fairview peak nevada and the 1959 m 7 1 hebgen lake montana earthquakes model coseismic deformation results in an uplift of the footwall block and a depression of the hanging wall block as has been reported by savage and hastie 1966 the interseismic phase of the deformation is characterized by a regional doming of the crust in the vicinity of the modeled normal faults doming observed before and after and adjacent to the faults which ruptured during the hebgen lake earthquake indicate that areas which are experiencing doming may be the future sites of normal fault earthquakes two areas which are presently experiencing crustal doming and are in the vicinity of a normal fault are the socorro new mexico and diablo plateau texas brown et al 1978 regions the interseismic doming will not occur if the modeled fault ruptures through the entire lithosphere if a single normal fault is active then model generated coseismic and interseismic deformations result in sum to a tilt block topography if two normal faults are active one master fault and a minor fault which dips toward the master fault then the resultant deformation is a horst and graben type of topography the rate at which the doming proceeds is primarily a function of the seismic stress drop and the effective viscosity of the asthenosphere doming rates following the hebgen lake earthquake indicate an asthenospheric viscosity of about 2 1021 p model recurrence intervals for the fairview peak and hebgen lake earthquakes are on the order of 103 yr

analysis of tilting near normal faults using calculus of variations implications for upper crustal stress and rheology abstract an initially horizontal surface in the surroundings to a normal fault will after extension tilt towards the fault if in the hanging wall or away from it if in the footwall coseismic deformation of these surroundings can be validly modelled as flexure cumulative deformation on geological time scales has been regarded as flexure also but this has led to the apparent paradox that many observed structures require the effective elastic thickness of the brittle upper crust to be much smaller than its seismogenic thickness this article presents a possible alternative that cumulative deformation of the upper crust near some active normal faults may be regarded instead as partitioned into separation of the blocks that comprise their surroundings through the horizontal component of dip slip on the fault and distributed vertical simple shear in their surroundings which causes them to tilt and takes up the vertical slip on the fault a generalized profile of tilting near a normal fault which approximates a parabola can be derived following two assumptions first the brittle layer retains an elastic term in its rheology on geological time scales such that it resists arbitrary length changes second the brittle layer minimizes its overall vertical deflection thus minimizing the buoyancy force acting on it maximum stress and total strain energy associated with observed profiles of tilting are typically smaller for distributed vertical simple shear favouring this mechanism over flexure

performance of irikura recipe rupture model generator in earthquake ground motion simulations with graves and pitarka hybrid approach we analyzed the performance of the irikura and miyake pure and applied geophysics 168 2011 85 104 2011 im2011 asperity based kinematic rupture model generator as implemented in the hybrid broadband ground motion simulation methodology of graves and pitarka bulletin of the seismological society of america 100 5a 2095 2123 2010 for simulating ground motion from crustal earthquakes of intermediate size the primary objective of our study is to investigate the transportability of im2011 into the framework used by the southern california earthquake center broadband simulation platform in our analysis we performed broadband 0 20 hz ground motion simulations for a suite of m6 7 crustal scenario earthquakes in a hard rock seismic velocity structure using rupture models produced with both im2011 and the rupture generation method of graves and pitarka bulletin of the seismological society of america 2016 gp2016 the level of simulated ground motions for the two approaches compare favorably with median estimates obtained from the 2014 next generation attenuation west2 project nga west2 ground motion prediction equations gmpes over the frequency band 0 1 10 hz and for distances out to 22 km from the fault we also found that compared to gp2016 im2011 generates ground motion with larger variability particularly at near fault distances 1 s for this specific scenario the largest systematic difference in ground motion level for the two approaches occurs in the period band 1 3 s where the im2011 motions are about 20 30 lower than those for gp2016 we found that increasing the rupture speed by 20 on the asperities in im2011 produced ground motions in the 1 3 s bandwidth that are in much closer agreement with the gmpe medians and similar to those obtained with gp2016 the potential implications of this modification for other rupture mechanisms and magnitudes are not yet fully understood and this topic is the subject of ongoing study we concluded that im2011 rupture generator performs well in ground motion simulations using graves and pitarka hybrid method therefore we recommend it to be considered for inclusion into the framework used by the southern california earthquake center broadband simulation platform

a model for the 1908 messina straits italy earthquake by inversion of levelling data abstract the 28 december 1908 messina earthquake was a normal faulting event which produced considerable vertical displacements three levelling surveys having an overall extension of 125 km in calabria and sicily were performed by the igmi italian military geographical institute shortly before the occurrence of the main event and during the first months of 1909 vertical subsidence up to 70 cm was measured at bench marks located close of messina the inversion of the observed displacements has been performed by using a model consisting of uniform dislocation on one or more rectangular faults and the mathematical formalism developed by matsu9ura and hirata 1982 results indicate that the observed displacements are well modeled by a normal fault oriented about ns with a dislocation of 1 5 m dipping 39 e this fault is located beneath the messina straits with the upper end at 1 km depth and crossing to the city of messina this model gives a seismic moment m o 4 9 0 8 10 26 dyne cm and shows a good agreement with the fault plane solution derived from the long period p wave first arrivals

postseismic deformation due to subcrustal viscoelastic relaxation following dip slip earthquakes the deformation of the earth following a dip slip earthquake is calculated by using a three layer rheological model and finite element techniques the three layers are an elastic upper lithosphere a standard linear solid lower lithosphere and a maxwell viscoelastic asthenosphere attention is focused on the magnitude of the postseismic subsidence and the width of the subsidence zone that develops due to the viscoelastic response to coseismic reverse slip detailed analysis for a fault extending from the surface to 15 km with a 45 dip reveals that postseismic subsidence is sensitive to the depth to the asthenosphere but is only weakly dependent on lower lithosphere depth the greatest subsidence occurs when the elastic lithosphere is about 30 km thick and the asthenosphere lies just below this layer asthenosphere depth 2 times the fault depth the extremum in the subsidence pattern occurs at about 5 km from the surface break of the fault and lies over the slip plane at this location the subsidence reaches 60 of the coseismic uplift after about 30 maxwell times unlike the horizontal deformation following a strike slip earthquake significant vertical deformation due to asthenosphere flow persists for many times the maxwell time of the asthenosphere as a consequence the relaxation of the lower lithosphere has only a secondary effect on uplift and subsidence it does however substantially increase horizontal straining the width of the postseismic subsidence zone also depends strongly on the depth to the asthenosphere and shows little sensitivity to the presence of a slowly relaxing lower lithosphere parametric adjustment of the lithosphere thickness and fault dip angle over a considerable range of values in a simple model of an elastic lithosphere and viscoelastic asthenosphere reveals that the postseismic subsidence is greatest when the fault penetrates through about one half the lithosphere previous estimates of the asthenosphere viscosity 1019 pa s and lithosphere thickness 30 40 km for the region of japan affected by the 1896 riku u earthquake are confirmed by model calculations

coastal trapped waves off the coast of south africa generation propagation and current structures abstract coastal sea level variations from six sites around south africa are used to establish the characteristics of coastal trapped wave ctw propagation substantial amplitudes 50 cm are found along the south coast but further propagation on the east coast against the agulhas current is inhibited current measurements over the shelf in this region show barotropic reversals during the passage of the peak of a ctw with essentially geostrophic flow occurring comparisons are made with theoretically calculated first mode ctw characteristics along various sections of the coast these calculated speeds fall within the range of speeds determined from observation though an admixture of a mode 2 ctw is possible it is found that the speeds of wind systems moving along the coast also fall in the same range probably leading to a resonance condition and an explanation for the large ctw amplitudes

from coseismic offsets to fault block mountains in the basin and range extensional province of the western united states coseismic offsets under the influence of gravity display predominantly subsidence of the basin side fault hanging wall with comparatively little or no uplift of the mountainside fault footwall a few decades later geodetic measurements gps and interferometric synthetic aperture radar insar show broad 100 km aseismic uplift symmetrically spanning the fault zone finally after millions of years and hundreds of fault offsets the mountain blocks display large uplift and tilting over a breadth of only about 10 km these sparse but robust observations pose a problem in that the coesismic uplifts of the footwall are small and inadequate to raise the mountain blocks to address this paradox we develop finite element models subjected to extensional and gravitational forces to study time varying deformation associated with normal faulting stretching the model under gravity demonstrates that asymmetric slip via collapse of the hanging wall is a natural consequence of coseismic deformation focused flow in the upper mantle imposed by deformation of the lower crust localizes uplift which is predicted to take place within one to two decades after each large earthquake thus the best preserved topographic signature of earthquakes is expected to occur early in the postseismic period

crustal versus asthenospheric relaxation and post seismic deformation for shallow normal faulting earthquakes the umbria marche central italy case summary following a normal mode approach for a strati ed viscoelastic earth we investigate the eiects induced by shallow normal faulting earthquakes on surface post seismic vertical displacement and velocity at the surface when stress relaxation occurs in the crust or in the asthenosphere the modelled earthquake is a moderate one characteristic of some slowly deforming plate boundaries in the central mediterranean region we focus on the umbria marche central italy region where deep seismic re ection studies crop03 and the 1997 earthquake sequence clearly show a seismogenic layer decoupled from the lower crust by a sizeable transition zone accordingly the crust is subdivided into three layers an elastic upper crust a transition zone and a low viscosity lower crust the fault is embedded in the upper crust the layered viscoelastic structure of the crust and mantle imposes a pattern and scale on the modelled coseismic and post seismic deformation with a major contribution from the transition crustal zone and low viscosity lower crust stress relaxation in the mantle being negligible we show that signi cant vertical deformation rates of the order of 1 mm yr 1 could be expected for a shallow and moderate event such as the recent umbria marche earthquake for viscosity values of 10 19 and 10 18 pa s in the crustal transition zone and lower crust respectively