form drag due to flow separation at a headland observational and model estimates of the form drag on three tree point a headland located in a tidal channel of puget sound washington are presented subsurface three tree point is a sloping ridge tidal flow over this ridge gives rise to internal lee waves that lead to wave drag and enhanced mixing at the same time horizontal flow separation produces a headland eddy that distorts the surface height field in the lee of the point two observational methods for estimating the portion of the form drag associated with deformation of the surface height field referred to here as the external form drag are also introduced drogued drifters and ship mounted acoustic current profiles from different days are used to indirectly map the flood tide surface height field data are derived from a depth shallow enough that baroclinic pressure gradient forcing may be neglected and yet deep enough that wind stress may also be ignored this leaves an approximate balance between the acceleration and surface height pressure gradient permitting in this case two independent estimates of the surface height to within a constant these fields are used to calculate the external form drag at the headland drag estimates from both observational datasets agree well external form drag decreases offshore of the headland as expected and is highly dependent on tidal phase with maximum drag leading peak flood currents by 1 2 h at this location form drag is much larger than model estimates of the frictional drag implying that it is the dominant mechanism extracting energy from the barotropic tide a kinematic argument is also presented to show why the external form drag should increase in importance relative to the frictional drag as the topographic slope and tidal excursion increase

source mechanism of the luzon philippines earthquake of july 16 1990 the luzon philippines earthquake of july 16 1990 with ms 7 8 was generated by left lateral faulting in the central luzon island ground breakage was observed along a linear trace extending 110 km the maximum horizontal offset as measured on the fault was as much as 6 m a fault area of 120 20 km2 was inferred from a field study and aftershock data this event is one of the largest strike slip earthquakes ever recorded in the world for long period surface waveform analysis we used very broadband records from 14 stations of the gdsn geoscope iris and erios networks the centroid moment tensor cmt solution from surface waves represents almost pure left lateral strike slip faulting on a steep fault with strike 155 dip 88 and rake 7 the seismic moment is 3 9 1020 nm 1027 dyn cm which gives mw 7 7 the average dislocation on the fault is 5 4 m and the stress drop is 5 2 mpa 52 bars teleseismic p and sh waves from 14 stations are used to model the spatiotemporal distribution of subevents five subevents are detected in an interval of 44 sec their sequence indicates a bilateral rupture the mean velocity of rupture toward the north is 2 7 km sec the total seismic moment of the subevents is 3 6 1020 nm the largest aftershock ms 6 6 occurred on july 17 near the recognized northern end of the main fault the cmt solution for the aftershock represents a reverse faulting with moment of 6 4 1019 nm mw 6 5 this aftershock was probably caused by compression produced by block motion of the eastern block of the main fault

earthquake processes in the rainbow mountain fairview peak dixie valley nevada region 1954 1959 the 1954 rainbow mountain fairview peak dixie valley nevada sequence produced the most extensive pattern of surface faults in the intermountain region in historic time five earthquakes of m 6 0 occurred during the first 6 months of the sequence including the december 16 1954 fairview peak m 7 1 and dixie valley m 6 8 earthquakes three 5 5 m 6 5 earthquakes occurred in the region in 1959 but none exhibited surface faulting the results of the modeling suggest that the m 6 5 earthquakes of this sequence are complex events best fit by multiple source time functions although the observed surface displacements for the july and august 1954 events showed only dip slip motion the fault plane solutions and waveform modeling suggest the earthquakes had significant components of right lateral strike slip motion rakes of 135 to 145 all of the earthquakes occurred along high angle faults with dips of 40 to 70 seismic moments for individual subevents of the sequence range from 8 0 1017 to 2 5 1019 n m stress drops for the subevents including the fairview peak subevents were between 0 7 and 6 0 mpa

on the influence of stratification and continental shelf and slope topography on the dispersion of subinertial coastally trapped waves abstract the behavior of subinertial coastally trapped free waves in a continuously stratified ocean is examined using a two slope topography in which the continental shelf and slope are each represented by a single uniform slope surface intensified stratification is assumed in which the squared buoyancy frequency profile is of the form n2e z where n is the buoyancy frequency at the surface z 0 and the vertical decay scale normalized by the deep sea depth the continental slope is typically assumed to be steeper than the shelf two qualitatively different types of dispersive behavior are distinguished when n f a2 e h 2 where f is the coriolis parameter a2 the bottom slope of the continental slope and h the shelf break depth normalized by the deep sea depth then free waves may occur at any subinertial frequency and each dispersion curve rises to f at some finite alongshore wavenumber as in the case of baroclinic kelvin waves if n f a2 e h 2 then all of the free wave dispersion curves a

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

rupture process of a multiple main shock sequence analysis of teleseismic local and field observations of the tennant creek australia earthquakes of january 22 1988 on january 22 1988 three large intraplate earthquakes with ms 6 3 6 4 and 6 7 occurred within a 12 hour period near tennant creek australia these earthquakes which occurred over a small interval of time and within a small volume of space present a unique opportunity to study the rupture process of the class of intraplate earthquakes that occur as multiple main shocks broadband displacement and velocity records of body waves from teleseismically recorded data are analyzed to determine source mechanisms depths and complexity of rupture of each of the three main shocks hypocenters of an additional 150 foreshocks and aftershocks constrained by local arrival time data and field observations of surface rupture are used to complement the source characteristics of the main shocks in order to derive as complete a description of the rupture process as possible the interpretation of the combined data sets suggests that the overall rupture process involved unusually complicated stress release as locations of the main shock hypocenters progressively moved from west to east we infer that the first and third main shocks denoted as ms1 and ms3 produced the southeast northwest trending scarps observed at the western end the kunayungku fault and at the eastern end the east end of the lake surprise fault respectively of the rupture zone the epicenter of the only immediate foreshock was located in the gap between these two fault scarps ms1 nucleated near this epicenter and ruptured upward and to the northwest from a depth of 6 5 km ms3 ruptured predominantly to the se at a depth of 4 5 km the second main shock ms2 is inferred to have produced the deformation of the southwest trending central scarp segment the western end of the lake surprise fault from the sense of thrusting seen at the surface and from the distribution of aftershock hypocenters the south dipping nodal planes derived from waveform modeling are identified as the fault planes for earthquakes ms1 and ms3 in contrast the dip of the central fault scarp is reversed relative to the dips of the western and eastern fault scarps the rupture process of ms2 turns out to be commensurately complex and sufficiently explains the geological complexity ms2 consisted of three subevents the southeast dipping nodal plane of the first two subevents is coplanar with a southeast dipping plane implied by locations of aftershocks which did not break the surface choice of the north dipping plane as the rupture plane of the third subevent consistent with the surface deformation and coplanar with a second plane delineated by aftershocks would imply conjugate faulting the majority of the aftershocks are concentrated near the edges of the fault planes and there is an absence of activity in the center of the planes the areas of absent activity may represent the failed asperities of the main shocks in which substantial stress relief occurred the rupture process of each main shock is characterized by the rapid release of energy followed by a much slower release of moment and by aftershock zones whose dimensions exceed the inferred dimensions of the rupture these characteristics suggest that substantial slow slip occurred on each of the three fault interfaces that was not accompanied by major energy release the first main shock nucleated at the deepest part of its aftershock zone and ruptured upward in contrast ms2 and ms3 nucleated at depths that were one third to one half of the maximum depth of their aftershock zones this variation of focal depth and the strong increase of moment and radiated energy with each main shock imply that lateral variations of strength were more important than vertical gradients of shear stress in controlling the progression of rupture

finite source modeling of the 1999 taiwan chi chi earthquake derived from a dense strong motion network the 1999 chi chi earthquake m w 7 6 20 september 1999 17 47 15 9 utc located at 23 853 n 120 816 e and depth of 7 5 km inicted severe re gional scale damage to taiwan the strong motion waveeld was captured by a dense network of stations with average station spacing of 5 km which represents the most complete strong motion dataset to date to use to study the kinematic source process of an earthquake we inverted velocity waveforms recorded by 21 stations for the spatial variation in slip on a planar fault model composed of 416 subfaults each with a dimension of 3 5 km by 3 5 km the planar model has a strike of n5 e and a dip of 30 e and the inversion solves for the direction and magnitude of the slip to account for possible temporal source complexity we allowed each subfault to slip within 10 overlapping time windows each with a duration of 3 sec the results show that the source is composed primarily of three major asperities the rst of which is mainly dip slip extending from the hypocenter to the northern end of the surface rupture in this asperity slip occurred in two pulses separated in time by 5 sec the dislocation rise time for each pulse is short 3n4 sec yielding an approximate av erage slip velocity of 80 cm sec the second asperity is located at shallow depth near the northern end of the rupture where very large ground velocities were observed this asperity is on average oblique and shows a temporal rake rotation from pure dip slip to strike slip the rotating rake suggests a low initial shear stress on the northern end of the fault slip in this asperity is dominated by a large pulse with a dislocation rise time of 8 sec a station near the northern end of the surface rupture recorded a peak velocity of 390 cm sec which we nd to be due to the constructive interference of energy radiated from the rst two asperities the third asperity is located south of the epicenter the total moment from the three asperities is 4 1 10 27 dyne cm which was released over a period of 30n35 sec within an area of 900 km 2 synthetics calculated from the three asperity model explain 85 of the data and represent 98 of the total variance reduction our results indicate that slip is conned to the shallow region of the fault deep slip patches are less constrained and that the slip distribution may be representative of fault segmentation along the chelungpu fault system

moment tensor solutions for the 24 november 1987 superstition hills california earthquakes the teleseismic long period waveforms recorded by the global digital seismograph network from the two largest superstition hills earthquakes are inverted using an algorithm based on optimal filter theory these solutions differ slightly from those published in the preliminary determination of epicenters monthly listing because a somewhat different improved data set was used in the inversions and a time dependent moment tensor algorithm was used to investigate the complexity of the main shock the foreshock origin time 01 54 14 5 m b 5 7 m s 6 2 had a scalar moment of 2 3 1025 dyne cm a depth of 8 km and a mechanism of strike 217 dip 79 rake 4 the main shock origin time 13 15 56 4 m b 6 0 m s 6 6 was a complex event consisting of at least two subevents with a combined scalar moment of 1 0 1026 dyne cm a depth of 10 km and a mechanism of strike 303 dip 89 rake 180

a rupture model for the 1967 mudurnu valley turkey earthquake and its implication for seismotectonics in the western part of the north anatolian fault zone six destructive earthquakes had successively occurred from 1939 to 1967 along the north anatolian fault zone the july 22 1967 mudurnu valley earthquake ms 7 1 was the last of this series with its western neighbour remaining as a seismic gap surface ruptures associated with this earthquake appeared within a broad shear zone extending to a distance of 80 km the generated teleseismic body waves were so complex that they were different even at stations in the same azimuth in this study we inverted the observed teleseismic body waves to investigate such a presumably complicated rupture process of the mudurnu valley earthquake we could identify six subevents within 2 minutes with their total seismic moment amounting to 1 1 1020 nm although right lateral strike slip faulting was found to be dominant two minor subevents had a dip slip mechanism one showed a reverse faulting mechanism and the other a normal faulting mechanism

a separating coastal upwelling jet at cape blanco oregon and its connection to the california current system the coastal upwelling region near cape blanco oregon 433n o the west coast of the united states was studied using a towed ctd on seasoar a shipboard acoustic doppler current pro ler adcp satellite sea surface temperature maps and surface drifters during august 1995 the equatorward upwelling jet was inshore of the shelfbreak north of cape blanco meandered gently o shore around the cape and then veered sharply o shore just to the south of the cape analysis of vertical sections of density velocity and spicinessa con rmed the separation of an upwelling jet and front the jet was followed from over the shelfbreak north of the cape to 100 km o shore downstream of the cape the separating jet originates from the coastal upwelling jet leaving the shelf but is augmented by an o shore branching of the poleward undercurrent by combining information from adcp streamfunction maps with analysis of hydrographic data including distributions of the tracer like quantity spicinessa a conceptual model of the three dimensional circulation near the cape emerges a mid shelf upwelling jet encounters a coastal promontory then turns o shore stretching and deepening as it crosses the continental margin the jet then turns back shoreward cyclonically where the deepened equatorward ow encounters the top of the poleward undercurrent owing along the continental slope this causes a portion of the undercurrent to turn o shore to join and strengthen the equatorward transport in the separated jet throughout the separation process the coastal upwelling front and jet are continuous robust features separation of a coastal upwelling jet is an important mechanism for cross shelf transport from the coast to the deep ocean cape blanco appears to be the northernmost point where an equatorward jet regularly separates from the coast to become an oceanic jet and thus serves as the northern boundary of the region where an intense meandering current characteristic of the california current system

evidence for self similar triangular slip distributions on earthquakes implications for earthquake and fault mechanics we characterize average slip distributions on earthquakes beyond their individual heterogeneity for that we analyze a large number of seismic slip distributions both measured at the surface after earthquakes 44 profiles and derived from slip inversion models 76 models investigating the overall shape of these slip profiles we find that they are roughly triangular both along strike and dip and most of them 70 80 are asymmetric long linear slopes and high slip gradients therefore are the key ingredients to describe earthquake slip profiles the scaling relations between maximum displacement and length or width suggest furthermore that the triangular slip profiles are self similar such slip patterns make earthquakes dominated by one major zone of maximum slip hence one major asperity analyzing the position of hypocenters with respect to these asperities we find that earthquakes nucleate at a distance from them that averages 20 30 of their total length compiling observations on 56 earthquakes we show that this distance i e the asperity size is structurally defined we then compare the earthquake slip profiles to cumulative slip profiles measured on long term faults of various ages and sizes and find that all profiles have a similar shape triangular and asymmetric hence combining data for a large number of earthquakes leads to point out average generic characteristics of the coseismic slip that are similar to those that emerge from the accumulation of events with time on a single fault this suggests that these characteristics result from robust physical properties

coseismic deformation of the 2001 mw 7 8 kokoxili earthquake in tibet measured by synthetic aperture radar interferometry the 14 november 2001 m w 7 8 kokoxili earthquake ruptured more than 400 km of the westernmost stretch of the left lateral kunlun fault in northern tibet interferometric synthetic aperture radar data from descending orbits along four adjacent tracks covering almost the entire rupture and 1 m pixel ikonos satellite images are used to map the rupture geometry and the surface displacements produced by the event interferograms are then inverted to solve for coseismic slip on the fault at depth the radar data show that the rupture connected the heituo fault where the earthquake initiated to the main kunlun fault cutting across a pull apart trough in between the two strike slip faults the fault model includes two vertical sections extending to a depth of 20 km and discretized into 5 km 5 km patches using a nonnegative least squares method that includes an appropriate degree of smoothing we solve for the left lateral slip on each fault patch our solution shows that the largest slip occurred at depths between 0 and 5 km reaching 8 m in two areas 200 and 250 km east of the earthquake epicenter significant slip took place below 10 km at both ends of the rupture slip appears to have been highly variable along the fault defining six sections of major moment release these sections correspond to six subsegments of the kunlun fault system defined from the surface morphology of the fault this suggests that fault geometry exerted a predominant influence on controlling the rupture propagation

on the spatial structure of coastal circulation off newport oregon during spring and summer 2001 in a region of varying shelf width 1 a time series of hourly surface current maps in the shelf waters off newport oregon was made during april september 2001 using five seasonde hf current mappers during coastal advances in shelf transport coast the surface currents responded rapidly to the changing winds in repeated patterns that were strongly affected by bottom topography an equatorward current jet repeatedly formed in response to upwelling winds its strength but not its trajectory covarying with the meridional wind stress near cape foulweather 44 8 n where the shelf begins to widen the jet rotates weakens and trends offshore to the south first along then across the isobaths below cape foulweather inshore of the jet a lee region of generally weak currents was commonly observed the equatorward jet core was most commonly observed near the 80 m isobath between 45 0 n and 44 4 n but transited offshore between spring and summer over heceta bank at newport 44 6 n it was rarely observed less than 8 km from the coast a second inshore equatorward jet previously unknown was observed repeatedly south of waldport 44 4 n sustained downwelling wind episodes produced poleward currents though less responsively north of cape foulweather strongest poleward flow was generally trapped near the coast surface currents were correlated with the northward wind except regionally far from shore over heceta bank responding within half a day response to the wind varies spatially being intensified in the narrow shelf northern region the equatorward jet persists through periods of zero wind forcing coastal sea level covaries with the meridional wind and the primary mode of ocean current response

heterogeneous fault stresses from previous earthquakes and the effect on dynamics of parallel strike slip faults 1 we combine a viscoelastic model for the interseismic process and an elastodynamic model for the coseismic process to explore the dynamics over multiple earthquake cycles of two parallel strike slip faults embedded in a two dimensional full space the step over fault geometry results in a buildup of heterogeneous fault stress near the step over this heterogeneous stress accumulates at the early stage of the evolution of the fault system and finally stabilizes after a number of earthquake cycles the heterogeneity in fault stress varies with the geometrical parameters e g width and along strike overlap gap of the step over as well as the rupture history of the fault system this heterogeneous fault stress from previous earthquakes has significant effects on earthquake rupture initiation propagation and termination the locations with a low normal stress level near a step over are favorable points for earthquake initiation rupture can jump a 4 km wide compressional step over and a 8 km or wider dilational step over if the fault system has historically experienced many earthquakes a young step over with less induced heterogeneity allows rupture to jump only smaller step over widths these results may have important implications for seismic hazard analysis in areas where segmented strikeslip faults predominate particularly for estimating maximum earthquake potential citation duan b and d d oglesby 2006 heterogeneous fault stresses from previous earthquakes and the effect on dynamics of parallel strike slip faults j geophys res 111 b05309 doi 10 1029 2005jb004138

intensified diurnal tides along the oregon coast abstractintensified diurnal tides are found along portions of the oregon shelf u s west coast based on analyses of high frequency hf radar surface current data and outputs of a 1 km resolution ocean circulation model the k1 tidal currents with magnitudes near 0 07 m s 1 over a wider part of the shelf heceta bank complex 44 44 5 n previously predicted by erofeeva et al are confirmed here by newly available hf radar data intensified diurnal tides are also found along the narrow shelf south of heceta bank in the close vicinity of cape blanco 42 8 n diurnal tidal currents k1 and o1 constituents combined may reach 0 3 m s 1 appreciable differences in diurnal tide intensity are found depending on whether the model is forced with tides and winds tw or only tides also diurnal variability in wind forcing is found to affect diurnal surface velocities for the case forced by tides alone results strongly depend on whether the model ocean is stratified tides only stratified tos or not t

global positioning system measurements of deformations associated with the 1987 superstition hills earthquake evidence for conjugate faulting large station displacements observed from imperial valley global positioning system gps campaigns are attributed to the november 24 1987 superstition hills earthquake sequence thirty sites from a 42 station gps network established in 1986 have been reoccupied during 1988 and or 1990 displacements at three sites within 3 km of the surface rupture approach 0 5 m eight additional stations within 20 km of the seismic zone are displaced at least 10 cm this is the first occurrence of a large earthquake ms 6 6 within a preexisting gps network best fitting uniform slip models of rectangular dislocations in an elastic half space indicate 130 8 cm right lateral displacement along the northwest trending superstition hills fault and 30 10 cm left lateral displacement along the conjugate northeast trending elmore ranch fault the geodetic moments are 9 4 1025 dyn cm and 2 3 1025 dyn cm for the superstition hills and elmore ranch faults respectively consistent with teleseismic source parameters the data also suggest that postseismic slip along the superstition hills fault is concentrated at shallow depths distributed slip solutions using singular value decomposition indicate near uniform displacement along the elmore ranch fault and concentrated slip to the northwest and southeast along the superstition hills fault a significant component of nonseismic secular displacement is observed across the imperial valley which is attributed to interseismic plate boundary deformation

primary surface rupture associated with the mw 7 1 16 october 1999 hector mine earthquake san bernardino county california the m w 7 1 hector mine earthquake occurred within the mojave desert portion of the eastern california shear zone and was accompanied by 48 km of dextral surface rupture complex northward rupture began on two branches of the lavic lake fault in the northern bullion mountains and also propagated southward onto the bullion fault lesser amounts of rupture occurred across two right steps to the south surface rupture was mapped using postearthquake 1 10 000 scale aerial photography field mapping provided additional detail and more than 400 fault rupture observations of these approximately 300 measurements were used to characterize the slip distribution en echelon surface rupture predominated in areas of thick alluvium whereas in the bedrock areas rupture was more continuous and focused within a narrower zone measured dextral offsets were relatively symmetrical about the epicentral region with a maximum displacement of 5 25 0 85 m 1 vertical slip was a secondary component and was variable with minor west side down displacements predominating in the bullion mountains field and aerial photographic evidence indicates that most of the faults that ruptured in 1999 had had prior late quaternary displacement although only limited sections of the rupture show evidence for prior holocene displacement 1 fn 1

diurnal period continental shelf waves along vancouver island a comparison of observations with theoretical models abstract current and sea level data from the coastal oceanic dynamics experiment conducted of vancouver island from may 1979 to september 1980 reveal shelf waves of diurnal period whose motions dominate the flow over the continental shelf in this paper current meter data from mooring lines off brooks peninsula estevan point and carmanah point are compared with theoretical solutions for a combination of free shelf waves and barotropic kelvin waves over uniform alongshore topography use of brink s scheme for baroclinic shelf waves gives close agreement between the modeled and observed k1 period horizontal currents over the continental margin off central vancouver island and accurately predicts vertical velocities and sea levels the shelf waves am shown to be entirely dominated by the first baroclinic mode wavelength derived from the model closely approximate wavelenghts computed from the alongshore change in phase of the observed diurnal current ellipses the baroclinic model successfully predicts the

source parameters of earthquakes in the nevada seismic zone 1915 1943 the nevada seismic zone has historically been one of the most active seismic regions of the intermountain west although all large m 7 0 earthquakes located within this zone occurred prior to the establishment of a worldwide seismograph network most have been well recorded instrumentally this study uses available instrumental data to determine the source parameters for some of the earliest earthquakes occurring within the region namely the 1915 m 7 6 pleasant valley and 1932 m 7 2 cedar mountain earthquakes and several smaller events of 5 5 m 6 5 occurring within the cedar mountain region between 1934 and 1943 results of body waveform inversions suggest that the pleasant valley earthquake at the northern end of the nevada seismic zone is a complex event best fit by a multiple source time function waveform and first motion information for the cedar mountain earthquake located within the walker lane suggest the earthquake was composed of two events each having significant components of right lateral strike slip motion rakes of 176 to 179 waveforms of the m 6 5 excelsior mountain earthquake located only 40 km southwest of cedar mountain suggest the earthquake was a simple rupture along a normal fault rake of 90 20 although surface faulting indicates that the event had a component of left lateral strike slip motion

estimates of sea surface height and near surface alongshore coastal currents from combinations of altimeters and tide gauges 1 present methods used to retrieve altimeter data do not provide reliable estimates of sea surface height ssh in the nearshore region resulting in a measurement gap of 25 50 km next to the coast in the present work gridded ssh fields produced by archiving validation and interpretation of satellite oceanographic data aviso in the offshore region are combined with coastal tide gauge time series of ssh to improve estimation in that gap along the west coast of the united states in the northern california current system between 40 and 45n and 123 8 and 126w to assess the increase in skill provided by this procedure the geostrophic alongshore currents calculated from the new ssh fields in the gap region are compared to three in situ nearshore current measurements resulting in correlation coefficients of 0 73 0 83 and standard deviations of the differences of 11 6 12 6 cm s substantially improved from the aviso only results when the ekman current components are estimated and added to the geostrophic currents comparisons to the 10 m deep acoustic doppler current profiler velocities are only slightly improved the ekman components make a more significant contribution when compared to hf radar surface current measurements providing correlations of 0 94 and standard deviations of the differences of 6 4 9 5 cm s these results represent a dramatic improvement in the quality of the ssh fields and estimated alongshore currents when additional realistic ssh data from the coastal region are added here we use coastal tide gauges to provide the additional ssh data but also discuss more general approaches for altimeter ssh retrievals in coastal regions where tide gauge data are not available

dynamic 3d simulations of earthquakes on en echelon faults one of the mysteries of earthquake mechanics is why earthquakes stop this process determines the difference between small and devastating ruptures one possibility is that fault geometry controls earthquake size we test this hypothesis using a numerical algorithm that simulates spontaneous rupture propagation in a three dimensional medium and apply our knowledge to two california fault zones we find that the size difference between the 1934 and 1966 parkfield california earthquakes may be the product of a stepover at the southern end of the 1934 earthquake and show how the 1992 landers california earthquake followed physically reasonable expectations when it jumped across en echelon faults to become a large event if there are no linking structures such as transfer faults then strike slip earthquakes are unlikely to propagate through stepover s 5 km wide

surface faulting accompanying the borah peak earthquake and segmentation of the lost river fault central idaho on the morning of 28 october 1983 the ms 7 3 borah peak earthquake struck central idaho and formed a y shaped zone of surface faults that is divided into a southern a western and a northern section the total length of the surface faults is 36 4 3 1 km and the maximum net throw is 2 5 to 2 7 m the near surface net slip direction determined from the rakes of striations in colluvium averaged 0 17 m of sinistral slip for 1 00 m of dip slip the 20 8 km long southern section is the main zone of surface faulting and coincides with the thousand springs segment of the lost river fault it has the largest amount of net throw most complex rupture patterns and best evidence of sinistral slip the surface faults include zones of ground breakage as much as 140 m wide en echelon scarps with synthetic and antithetic displacements and individual scarps that are nearly 5 m high the 14 2 km long western section diverges away from the lost river fault near the northern end of the southern section the net throw on this section is generally less than 0 5 m but locally is as much as 1 6 m the new ruptures are poorly developed across the crest and north flank of the willow creek hills they are mostly downhill facing arcuate scars perhaps incipient landslides that may overlie a deeper zone of tectonic movement the northern section at least 7 9 km long is on the warm spring segment of the lost river fault and has a maximum net throw of about 1 m the pattern of surface faulting on this section is simple compared to the other sections a 4 7 km long gap in 1983 surface faults separates the northern and southern sections but contains an older scarp of late pleistocene age geologic seismologic and geodetic data from the earthquake suggest that barriers confined the primary coseismic rupture to the thousand springs segment of the fault the rupture propagated unilaterally to the northwest from a hypocenter near the southeastern end of the segment the southeastern boundary of the segment is marked by an abrupt bend in the range front a 4 km long gap in late quaternary scarps and transverse faults of eocene age that intersect the lost river fault the northwestern boundary of the thousand springs segment is at the junction of the willow creek hills and the lost river fault here the southern and western sections of surface faults diverge and there is a gap in the 1983 scarps during the first few weeks after the main shock the large magnitude and large stress drop aftershocks clustered near this barrier later aftershocks were mainly northwest of the barrier on the warm spring and challis segments and showed that strain adjustments eventually affected the entire northern part of the lost river fault fault scarp morphology and the bedrock geology suggest that the boundary between the thousand springs and warm spring segments has probably ruptured less frequently and had less net slip during much of the late cenozoic than the interior of the adjacent segments the 1983 faulting shows that although segment boundaries can stop or deflect primary ruptures secondary surface faulting can occur on adjacent segments of the main fault a late pleistocene scarp in the 1983 gap suggests that infrequent earthquakes perhaps larger than the 1983 event might break through a segment boundary and thus release strain on two adjacent segments

transient eddy formation around headlands eddies with length scales of 1 10 km are commonly observed in coastal waters and play an important role in the dispersion of water borne materials the generation and evolution of these eddies by oscillatory tidal flow around coastal headlands is investigated with analytical and numerical models using shallow water depth averaged vorticity dynamics eddies are shown to form when flow separation occurs near the tip of the headland causing intense vorticity generated along the headland to be injected into the interior an analytic boundary layer model demonstrates that flow separation occurs when the pressure gradient along the boundary switches from favoring accelerating to adverse decelerating and its occurrence depends principally on three parameters the aspect ratio b a where b and a are characteristic width and length scales of the headland h cda where h is the water depth cd is the depth averaged drag coefficient and uo a where uo and are the magnitude and frequency of the far field tidal flow simulations with a depth averaged numerical model show a wide range of responses to changes in these parameters including cases where no separation occurs cases where only one eddy exists at a given time and cases where bottom friction is weak enough that eddies produced during successive tidal cycles coexist interacting strongly with each other these simulations also demonstrate that in unsteady flow a strong start up vortex forms after the flow separates leading to a much more intense patch of vorticity and stronger recirculation than found in steady flow

deformation during the 12 november 1999 duzce turkey earthquake from gps and insar data only 87 days after the mw 7 5 17 august 1999 izmit earthquake the duzce earthquake ruptured a ca 40 km long adjoining strand of the north anatolian fault naf system to the east we used displacements of 50 global positioning system gps sites together with interferometric synthetic aperture radar insar range change data spanning the event to estimate the geometry and slip distribution of the coseismic rupture postseismic deformation transients from the duzce earth quake and the preceding i zmit event that are included in some of the measurements are corrected for using dislocation models fit to gps data spanning the various time periods nonlinear inversions for fault geometry indicate that the rupture occurred on a ca 54 north dipping oblique normal right lateral fault distributed slip inver sions indicate maximum strike slip near the center of the duzce fault close to the earthquake hypocenter slip magnitude and depth of faulting decrease to the west and east of the hypocenter both gps and insar data suggest that normal slip is restricted to the shallow portion of the rupture the duzce earthquake had the highest slip to rupture length ratio of any historic earthquake along the naf

stratification and mean flow effects on diurnal tidal currents off vancouver island abstract a series of numerical experiments with a three dimensional baroclinic model were conducted to study the influences of density stratification and wind driven currents on the k1 tide over the continental shelf off vancouver island the region is one of anomalously large diurnal tidal currents due to the generation of coastally trapped waves at the entrance to juan de fuca strait model results are compared with data obtained from a number of moorings deployed over the shelf including a line extending for over 300 km in the alongshore direction the results show that inclusion of stratification significantly improves the representation of k1 currents in the model particularly with respect to the alongshore phase propagation of the clockwise and counterclockwise rotary components with homogeneous water the coastally trapped waves propagate relatively slowly and are dissipated before reaching brooks peninsula in contrast the ambient stratification permits coastally trapped motions to propagate

influence of varying upper ocean stratification on coastal near inertial currents the influence of varying horizontal and vertical stratification in the upper layer o 10 m associated with riverine waters and seasonal atmospheric fluxes on coastal near inertial currents is investigated with remotely sensed and in situ observations of surface and subsurface currents and realistic numerical model outputs off the coast of oregon based on numerical simulations with and without the columbia river cr during summer the directly wind forced near inertial surface currents are enhanced by 30 60 when the near surface layer has a stratified condition due to riverine water inputs from the cr comparing model results without the cr for summer and winter conditions indicates that the directly wind forced near inertial surface current response to a unit wind forcing during summer are 20 70 stronger than those during winter depending on the cross shore location which is in contrast to the seasonal patterns of both mixed layer depth and amplitudes of near inertial currents the model simulations are used to examine aspects of coastal inhibition of near inertial currents manifested in their spatial coherence in the cross shore direction where the phase propagates upward over the continental shelf bounces at the coast and continues increasing upward offshore toward surface and then downward offshore at the surface with magnitudes and length scales in the near surface layer increasing offshore this pattern exhibits a particularly well organized structure during winter similarly the raypaths of clockwise near inertial internal waves are consistent with the phase propagation of coherence showing the influence of upper layer stratification and coastal inhibition

near surface dynamics of a separated jet in the coastal transition zone off oregon 1 three dimensional circulation in the coastal transition zone ctz off oregon is studied using a 3 km resolution model based on the regional ocean modeling system the study period is spring and summer 2002 when extensive observations were available from the northeastern pacific component of the global ocean ecosystems dynamics project our main focus is on near surface transports particularly in an area off cape blanco where an energetic coastal current is separated in the ctz comparisons with available observations velocities from midshelf moorings surface velocities from high frequency radars satellite sea surface temperature maps along track sea surface height altimetry and seasoar hydrography show that the model reproduces qualitatively correctly the flow structure and variability in the study area the near surface flow behavior during 26 july to 21 august a late summer time period of strong time variable southward winds is examined during that period the coastal jet separates from the continental shelf around cape blanco 43 n the energetic separated jet continues to flow southward in a near coastal region between 42 2 n and 43 n it subsequently turns around 42 n to flow westward offshore past 127 w relatively vigorous up and downwelling is found concentrated in the region of the separated jet frontogenesis secondary circulation nonlinear effects of the relative vorticity on the ageostrophic ekman transport and submesoscale instabilities contribute to the vertical circulation within the jet vertical velocities are found to reach 50 m d 1 in the offshore part of the jet and 100 m d 1 in the near coastal part where the jet is aligned with the wind direction

rupture process of the ms 6 6 superstition hills california earthquake determined from strong motion recordings application of tomographic source inversion abstract we analyze strong motion recordings of the m s 6 6 superstition hills earthquake to determine the timing location spatial extent and rupture velocity of the subevents that produced the bulk of the high frequency 0 5 to 4 hz seismic energy radiated by this shock the earthquake can be characterized by three principal subevents the largest ones occurring about 3 and 10 sec after initiation of rupture timing relationships between pulses on the seismograms indicate that the three subevents are located within 8 km of each other along the northern portion of the superstition hills fault the two largest subevents display different directivity effects we apply a tomographic source inversion to the integrated accelerograms to determine the slip acceleration on the fault as a function of time and distance based on a one dimensional fault model the azimuthal distribution of amplitudes for the second subevent can be largely explained by a rupture that propagated about 2 km to the southeast along the superstition hills fault at a velocity about equal to the p wave velocity an alternative model with rupture propagating to the northeast along a conjugate fault plane can also account for the observed directivity of this subevent but it is not supported by the aftershock distribution the third subevent ruptured to the southeast along an 8 km long portion of the superstition hills fault at about the shear wave velocity this rupture propagation caused the relatively large accelerations and velocities observed in strong motion records for stations southeast of the hypocenter the long time intervals between the subevents and their relative proximity to each other indicate a very slow component to the rupture development the southern half of the superstition hills fault did not generate significant high frequency strong ground motion although it showed substantial co seismic surface displacement the subevents are situated along the same northern portion of the fault where most of the aftershocks are located the locations of the subevents appear to be controlled by bends in the fault mapped at the surface and by changes in basement structure at depth

geometry of the 1954 fairview peak dixie valley earthquake sequence from a joint inversion of leveling and triangulation data in 1954 four earthquakes greater than ms 6 0 occurred within a 30 km radius and in a period of 6 months elevation and angle changes calculated from repeated leveling and triangulation surveys which span the coseismic period provide constraints on the fault geometries and coseismic slip of the faults which were activated the quality of the coseismic geodetic data is assessed corrections are applied to the leveling data for subsidence due to groundwater withdrawal in the fallon area and a rod miscalibration error of 150 30 ppm is isolated in leveling surveys made in 1967 the leveling and triangulation observations are then simultaneously inverted using the single value decomposition svd inversion method to determine fault geometries and coseismic slip using svd it is possible to determine on which faults slip is resolvable given the data distribution the faults are found to dip between 50 and 80 and extend to depths of 5 to 14 km the geodetically derived slip values are generally equal to or greater than the maximum observed displacement along the surface scarps where slip is resolvable the geodetic data indicates the 1954 sequence contained a significant component of right lateral slip this is consistent with the n15 w trending shear zone which geodetic surveys have detected in western nevada

dynamics of fault interaction parallel strike slip faults we use a two dimensional finite difference computer program to study the effect of fault steps on dynamic ruptures our results indicate that a strike slip earthquake is unlikely to jump a fault step wider than 5 km in correlation with field observations of moderate to great sized earthquakes we also find that dynamically propagating ruptures can jump both compressional and dilational fault steps although wider dilational fault steps can be jumped dilational steps tend to delay the rupture for a longer time than compressional steps do this delay leads to a slower apparent rupture velocity in the vicinity of dilational steps these dry cases assumed hydrostatic or greater pore pressures but did not include the effects of changing pore pressures in an additional study we simulated the dynamic effects of a fault rupture on undrained pore fluids to test sibson s 1985 1986 suggestion that wet dilational steps are a barrier to rupture propagation our numerical results validate sibson s hypothesis by demonstrating that the effect of the rupture on the undrained pore fluids is to inhibit the rupture from jumping dilational stepovers the basis of our result differs from sibson s hypothesis in that our model is purely elastic and does not necessitate the opening of extension fractures between the fault segments

evidence for an earthquake barrier model from mw 7 8 kokoxili tibet earthquake slip distribution abstract the slip distribution of the mw 7 8 kokoxili tibet 2001 earthquake has been measured at high resolution using optical correlation of satellite images and provides both the parallel and perpendicular components of the horizontal co seismic slip this reveals a variation of the horizontal slip at a scale of 20 km along strike anti correlation of slip parallel and perpendicular to the fault indicates transfer of slip from the horizontal to the vertical component at the ends of segments these features suggest a rupture model with segments separated by strong persistent geometric barriers the unexpected ending of the rupture south of the main fault can be explain by such a structure but bears important implications for the initiation and rupture directivity of the next earthquake

earthquakes quaternary faults and seismic hazard in california data describing the locations slip rates and lengths of quaternary faults are the primary basis in this work for constructing maps that characterize seismic hazard in california the expected seismic moment m0e and the strength of ground shaking resulting from the entire rupture of each mapped fault or fault segment are estimated using empirical relations between seismic moment m0 rupture length source to site distance and strong ground motions assuming a fault model whereby the repeat time t of earthquakes on each fault equals m0e m0g where the moment rate m0g is proportional to fault slip rate it is observed that the moment frequency distribution of earthquakes predicted from the geologic data agrees well with the distribution determined from a 150 year historical record the agreement is consistent with the argument that the geologic record of quaternary fault offsets contains information sufficient to predict the average spatial and size distribution of earthquakes through time in california the estimates of t for each fault are the foundation for constructing maps that depict the average return period of 0 1g peak horizontal ground accelerations and the horizontal components of peak acceleration peak velocity and the pseudovelocity response at 1 period and 5 damping expected to occur at the level of 0 1 probability during a 50 year period of time a map is also formulated to show the probability that 0 1g horizontal ground accelerations will occur during the next 50 years the maps serve to illustrate the potential value of quaternary fault studies for assessing seismic hazard interpretation of available slip rates indicates that the largest and most frequent occurrence of potentially destructive strong ground motions are associated principally with the san andreas san jacinto calaveras hayward and ventura basin fault zones other regions of similarly high hazard may yet remain unrecognized this inadequacy results primarily from an incomplete data set numerous faults for example are mapped along the coastal region of northern california and within the modoc plateau but relatively few studies relating to fault slip rate are reported a similar problem exists for other stretches of coastal california where marine reflection studies provide evidence of active faulting offshore yet yield little or no information of fault slip rate geological and geophysical field studies can work to remove these deficiencies a concerted effort to locate and define rates of activity on all faults in california is the most promising means to further quantify present levels of seismic hazard in california

tidal currents on the central oregon shelf models data and assimilation 1 measurements of tidal currents on the central oregon shelf are available from several sources including recent high frequency hf coastal radar and acoustic doppler profiler adp deployments and historical current moorings in this paper we use a generalized inverse gi approach to compare these data to and then assimilate them into numerical models for the barotropic tides harmonic analysis of the data in short time windows using a modified admittance approach reveals that tidal currents on the oregon shelf are highly variable in time and can contain significant baroclinic components data from the winter months when waters on the shelf are only weakly stratified are found to be most nearly barotropic and thus most reasonable for assimilation into the shallow water equations model the various data sources are used in several different combinations for assimilation and validation forcing the prior forward model with normal flow open boundary conditions obtained from a regional barotropic inverse model results in semidiurnal barotropic currents that are consistent within estimated error limits with all available data in contrast diurnal currents on the shelf are very sensitive to details of the model configuration and are significantly improved by data assimilation very similar solutions result from assimilation of either the hf radar or adp data sets the high sensitivity of the diurnal band currents can be understood dynamically in terms of trapped shelf waves a short 85 km long section of shelf off the central oregon coast is wide enough to allow first mode barotropic shelf waves at the subinertial diurnal frequencies this results in locally resonant large amplitude diurnal tidal currents that are very sensitive to details in the local forcing and hence quite variable in time

teleseismic source parameters and rupture characteristics of the 24 november 1987 superstition hills earthquake long period body waves from the 24 november 1987 superstition hills earthquake are studied to determine the focal mechanism and spatial extent of the seismic source the earthquake is a complex event consisting of two spatially distinct subevents with different focal mechanisms two consistent models of rupture are developed for both models the second subevent begins 8 sec after the initiation of the first subevent and the preferred centroid depth lies between 4 to 8 km model 1 consists of two point sources separated by 15 to 20 km along strike of the superstition hills fault model 2 consists of one point source and one line source with a rupture velocity of 2 5 km sec with moment release distributed along strike of the focal plane at a distance of 10 to 22 km from the epicenter these moment release patterns show that a significant amount of long period energy is radiated from the southern segment of the fault total moment release for both models is approximately 8 10 25 dyne cm both models also suggest a change of dip from near vertical near the epicenter to steeply southwesterly dipping along the southern segment of the fault the difference in rupture characteristics and fault dips seen teleseismically is also reflected in aftershock and afterslip data and crustal structure underlying the two fault segments the northern segment had more aftershocks and a smaller proportion of afterslip than the southern segment the boundary between the two segments lies at a step in the basement that separates a deeper metasedimentary basement to the south from a shallower crystalline basement to the north

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

complex source process of the 17 august 1999 izmit turkey earthquake broadband teleseismic p wave data at epicentral distances of 30 90 are inverted to retrieve the complex source process of the 17 august 1999 izmit earthquake a comparison of the waveforms of the mainshock with those of the aftershocks suggests a spatially complex rupture process having a duration of more than 45 sec inversion and modeling of broadband p waveforms are performed in this time window incorporating a priori field observations of coseismic displacements both single point and multiple point source representations are determined we found that the rupture process can be divided into at least three steps in the first step rupture initiated from the hypocenter and extended bilaterally along the e w striking fault with an almost pure right lateral strike slip motion the eastern portion of the rupture front passed through the sapanca lake and stopped around akyazi whereas the western portion stopped near hersek this step lasted for 22 23 sec releasing a total moment of 1 43 1020 n m the dislocation was concentrated briefly at two areas one near golcuk and the other between the sapanca lake and akyazi slip in these two areas was concentrated in the upper 10 km of the crust after 1 2 sec a second source started possibly initiating on an underwater fault west of hersek although its rupture lasted for almost 20 sec its moment release was very low just 0 17 1020 n m another 8 9 sec later the easternmost fault segment between akyazi and the area west of duzce was triggered with a rupture lasting for more than 15 sec producing little energy in the short period band with slip concentrated in a zone extending vertically 25 km to the surface and with a moment of 0 61 1020 n m manuscript received 22 september 2000

three dimensional tidal flow around headlands field measurements of tidal flow around a headland indicate secondary circulation induced by flow curvature the secondary flow defined to be the flow in the plane normal to the direction of the vertically averaged current is directed toward the headland near the bottom and seaward near the surface consistent with theoretical predictions the strength of the secondary flow varies from 5 to 15 of the streamwise flow it is strongest when the water column is stratified because of both the enhanced shear of the streamwise flow and the reduced frictional damping of the secondary flow the transverse exchange accomplished by the secondary flow significantly influences the structure of the streamwise flow causing a broadening of the transverse shear and changing the horizontal and vertical distributions of momentum it may also have a significant influence on horizontal dispersion in the vicinity of headlands

the 1971 san fernando earthquake a double event evidence is presented which suggest that the 1971 san fernando earthquake may have been a double event that occurred on two separate subparallel thrust faults it is postulated that the initial event took place at depth on the sierra madre fault zone which runs along the base of the san gabriel mountains rupture is postulated to have occurred from a depth of about 15 km to a depth of about 3 km a second event is thought to have initiated about 4 sec later on another steeply dipping thrust fault which is located about 4 km south of the sierra madre fault zone the surface trace of this fault coincides with the san fernando fault zone which was the principal fault associated with surface rupture it is postulated that rupture propagated from a depth of 8 km to the free surface the moments of the first and second events are approximately 0 7 10 26 dyne cm and 1 0 10 26 dyne cm respectively this model is found to explain the combined data sets of strong ground motions teleseismic p and s waveforms and static offsets better than previous models which consist of either a single fault plane or a plane having a dip angle which shallows with decreasing depth nevertheless many features of the observed motions remain unexplained and considerable uncertainty still exists regarding the faulting history of the san fernando earthquake

depth of faulting during the 1968 meckering australia earthquake sequence determined from waveform analysis of local seismograms waveforms for 11 foreshocks and 48 aftershocks of the ms 6 8 meckering earthquake recorded at the world wide standard seismograph network station mundaring are analyzed to determine the depth distribtion of faulting during this unusual intraplate earthquake sequence clear depth phases including sp and rg are seen in the local seismograms at distances of 60 95 km and are studied using synthetic seismograms computed using generalized ray theory and wave number integration techniques large rg s ratios seen on the vertical component short period data for many events imply source depths less than 2 km the short period p waveform contains the best depth estimator in the form of sp so that depth can be estimated to within an uncertainty of about 1 km for most events the foreshocks cluster at less than 2 km depth and most aftershocks occur within 1 km of the surface a few aftershocks occur as deep as 7 km these results are consistent with a previous teleseismic waveform study in which faulting was inferred to start near the surface at 1 5 km depth with rupture proceeding downward and not exceeding 6 km depth these results coupled with previous stress studies in the australian shield and models of crustal strength show that faulting in a cold shield area is a near surface phenomenon and implies that most of the crust is too strong to be fractured

a simple method for orienting conventional core using microresistivity fms images and a mechanical goniometer to measure directional structures on cores orienting core and gathering downhole orientation data such as paleocurrents or fractures has always been a challenge in the petroleum industry and academia downhole core orientation while drilling is expensive time consuming and not always accurate nowadays microresistivity logs are run in many boreholes and can easily be used for orienting conventional core of all sizes and many shapes whole slabbed or plugged the only requirement is a facies or lithologic change with a sharp contact visible in both core and microresistivity log downhole logging tools can thus provide a quick and inexpensive way to orient conventional core a simple mechanical goniometer can then be used to measure foresets of cross stratification for paleocurrent analysis mechanical goniometers have the advantage of being more robust than their electronic counterparts and measurement errors are within a reasonable margin using this setup paleocurrents from core were commonly found to be more precise than those generated digitally from microresistivity logs

connectivity and larval dispersal along the oregon coast estimated by numerical simulations 1 connectivity and larval dispersal is explored off the oregon coast during the summer upwelling season of 2001 using numerical ocean circulation simulations the study region with strong wind driven currents and variable topography is modeled using the regional ocean modeling system roms forced by the coupled ocean atmosphere mesoscale prediction system a large number of passive particles as models of planktonic larvae are released daily for 120 days from 1 may to 28 august at depths of 1 7 15 20 50 and 75 m at every grid point shoreward of the 200 m isobath on average 32 km offshore the particles are transported by the three dimensional currents of the model simulation the competency time window for larval settlement is assumed to be in between days 15 and 35 after larvae are released larval settlement occurs at the shallowest location during the competency time window connectivity matrices reveal that some of the places of highest retention are similar to the proposed oregon marine reserve sites especially cape perpetua the heceta bank region has high probabilities as both a source and a destination for settled larvae larvae released in the heceta bank region often settle at higher latitudes than their release location there are strong correlations between the number of settled larvae shallower than the 50 m isobath and a 6 to 8 day running mean of the alongshore wind stress larvae are retained near the shore when the winds averaged over the previous 6 to 8 days are relaxed or downwelling favorable

spatial and temporal distribution of slip for the 1992 landers california earthquake we have determined a source rupture model for the 1992 landers earthquake m w 7 2 compatible with multiple data sets spanning a frequency range from zero to 0 5 hz geodetic survey displacements near field and regional strong motions broadband teleseismic waveforms and surface offset measurements have been used explicitly to constrain both the spatial and temporal slip variations along the model fault surface our fault parameterization involves a variable slip multiple segment finite fault model which treats the diverse data sets in a self consistent manner allowing them to be inverted both independently and in unison the high quality data available for the landers earthquake provide an unprecedented opportunity for direct comparison of rupture models determined from independent data sets that sample both a wide frequency range and a diverse spatial station orientation with respect to the earthquake slip and radiation pattern in all models consistent features include the following 1 similar overall dislocation patterns and amplitudes with seismic moments of 7 to 8 10 26 dyne cm seismic potency of 2 3 to 2 7 km 3 2 very heterogeneous unilateral strike slip distributed over a fault length of 65 km and over a width of at least 15 km though slip is limited to shallower regions in some areas 3 a total rupture duration of 24 sec and an average rupture velocity of 2 7 km sec and 4 substantial variations of slip with depth relative to measured surface offsets the extended rupture length and duration of the landers earthquake also allowed imaging of the propagating rupture front with better resolution than for those of prior shorter duration strike slip events our imaging allows visualization of the rupture evolution including local differences in slip durations and variations in rupture velocity rupture velocity decreases markedly at shallow depths as well as near regions of slip transfer from one fault segment to the next as rupture propagates northwestward along the multiply segmented fault length the rupture front slows as it reaches the northern limit of the johnson valley landers faults where slip is transferred to the southern homestead valley fault an abrupt acceleration is apparent following the transfer this process is repeated and is more pronounced as slip is again passed from the northern homestead valley fault to the emerson fault although the largest surface offsets were observed at the northern end of the rupture our modeling indicates that substantial rupture was also relatively shallow less than 10 km in this region

co seismic strike slip and rupture length produced by the 2001 ms 8 1 central kunlun earthquake field investigations show that the surface wave magnitude ms 8 1 central kunlun earthquake tibetan plateau of 14 november 2001 produced a nearly 400 kilometer long surface rupture zone with as much as 16 3 meters of left lateral strike slip along the active kunlun fault in northern tibet the rupture length and maximum displacement are the largest among the co seismic surface rupture zones reported on so far the strike slip motion and the large rupture length generated by the earthquake indicate that the kunlun fault partitions its deformation into an eastward extrusion of tibet to accommodate the continuing penetration of the indian plate into the eurasian plate

source parameters of the 28 october 1983 borah peak idaho earthquake from body wave analysis modeling of long period body waves of the m s 7 3 borah peak idaho earthquake suggests that the earthquake was a simple rupture that nucleated at a depth of about 16 km and propagated unilaterally northwestward toward the surface the seismic moment tensor obtained from the inversion of teleseismic body wave amplitude data agrees well with the fault plane solution obtained from short period first motion data strike 138 3 dip 45 3 rake 60 5 and the observed surface faulting the scalar double couple moment of 2 1 10 26 dyne cm obtained from the inversion is comparable to a moment of 1 4 10 26 dyne cm estimated from the observed surface faulting estimates of stress drop based on these values for the moment are 17 to 12 bars respectively

variational assimilation of satellite observations in a coastal ocean model off oregon 1 satellite along track sea surface height ssh and multisatellite sea surface temperature sst maps are assimilated in a coastal ocean circulation model off oregon the study period is june october 2005 featuring intensive separation of the coastal upwelling jets in the eddy dominated coastal transition zone ctz the data assimilation da system combines the nonlinear regional ocean modeling system roms and the advanced variational regional ocean representer analyzer avrora tangent linear and adjoint codes developed by our group the variational representer da method is implemented in a series of 6 day time windows with initial conditions corrected at the beginning of each window to avoid the problem of matching the model and observed ssh mean levels the observed ssh slope has been assimilated location timing and intensity of jets and eddies in the ctz are constrained to improve accuracy of nonlinear model analyses and forecasts in the case assimilating ssh alone the geometry of the sst front is improved ssh assimilation results in the cross shore transport more uniformly distributed along the coast than in the free run model an outer front is identified in the da analyses at a distance of 200 km from the coast a strong subsurface horizontal temperature gradient across this front influences the depth of the thermocline in an area between the front and the continental slope the da correction term is comparable in magnitude to dominant terms in the volume integrated heat equation the time averaged da correction term in the volume integrated heat balance is closer to 0 in the combined ssh sst assimilation case than in the case assimilating ssh alone

fault rupture process of the 20 september 1999 chi chi taiwan earthquake we modeled the source rupture process of the 20 september 1999 chi chi taiwan earthquake mw 7 6 using an integrated dataset of near field strong ground motion and global positioning system observations this large inland thrust earthquake produced a surface break more than 80 km long along the chelungpu fault the event triggered over 700 strong motion instruments on the island of tai wan this large ground motion dataset provides the best opportunity to date to un derstand earthquake source processes in a major earthquake first we develop a 3d curved fault model consistent with the surface rupture data and aftershock distribu tion the subsurface fault plane has an average dip of 30 to the east and measures 96 km along strike and 40 km down dip next we applied a genetic algorithm to reconstruct the source rupture process the inversion results indicate a complex slip distribution with a generally broad triangular shaped slip zone that points down dip most of the displacement occurred over a 15 km depth range in the northern segment of the fault with the maximum slip exceeding 20 m the average slip is 3 8 m and the average rupture velocity is 2 6 km sec the mainshock slip distribution clearly complements the aftershock location distribution slip rise times range from 8 to 6 sec over most of the primary slip area and decrease slightly as rupture propagates south to north this relatively long rise time resulted in a low dynamic stress drop and low peak ground accelerations observed at surface stations the rake angle rotates across the rupture plane from predominantly dip slip in the southern segment to mostly left lateral oblique slip in the north we find that geometrical irregularities over the fault plane played an important role in controlling the temporal rupture behavior at fault bends rupture tends to decelerate the rake angle rotates to a near dip slip orientation and the shear stress increases as rupture tries to overcome the bending barriers the total seismic moment from our inversion is 2 9 10 27 dyne cm in good agreement with the harvard and the u s geological survey moment estimation

slip along the san andreas fault associated with the great 1857 earthquake historical records indicate that several meters of lateral slip along the san andreas fault accompanied the great 1857 earthquake in central and southern california these records together with dendrochronological evidence suggest that the rupture occurred along 360 to 400 km of the fault including several tens of kilometers of the currently creeping reach in central california geomorphic expressions of late holocene right lateral offsets are abundant along the 1857 rupture along 300 kilometers of the 1857 rupture between cholame and wrightwood the youngest discernible offset ranges from 3 to 9 1 2 meters dormancy of the fault since 1857 almost certainly indicates that this latest offset was created in 1857 fault slip apparently associated with the 1857 earthquake varies in a broadly systematic way along the trace of the fault it is relatively uniform along each of several long segments but changes rather abruptly in value between these segments this nonuniform displacement pattern may imply that some segments of the fault rupture more frequently or experience a slower long term slip rate than others the 1857 offsets indicate a seismic moment m o between 5 3 and 8 7 10 27 dyne cm assuming a 10 to 15 km depth of rupture and relatively uniform slip as a function of depth a comparison with the rupture length average slip value and tectonic setting of the california earthquake of 1906 m s 8 1 4 indicates a value of m 8 1 4 for the 1857 event

active tectonics of northeastern sonora mexico southern basin and range province and the 3 may 1887 mw 7 4 earthquake north south striking and west dipping basin and range province normal faults form the western edge of the sierra madre occidental plateau in northeastern sonora these faults and associated half grabens extend over a distance of more than 300 km between the san bernardino basin in the north and the sahuaripa basin in the south an earthquake in 1887 ruptured three neighboring segments of this major fault zone our field mapping in this region indicates that the surface rupture of the 1887 earthquake extends farther to the south and is considerably longer 101 4 km end to end length than previously reported a compilation of the seismicity in the epicentral region of the 1887 earthquake shows the epicenters to be distributed in well defined clusters at the northern end of the 1887 surface rupture in the step overs between the three rupture segments on a neighboring fault in the west fronteras fault and on fault segments farther south along the same fault zone granados region the distribution of seismicity correlates well with calculated changes in coulomb failure stress resulting from the 1887 earthquake

co seismic displacements folding and shortening structures along the chelungpu surface rupture zone occurred during the 1999 chi chi taiwan earthquake abstract a nearly 100 km long surface rupture zone called chelungpu surface rupture zone occurred mostly along the pre existing chelungpu fault on the northwestern side of taiwan accompanying the 1999 chi chi ms 7 6 earthquake the chelungpu surface rupture zone can be divided into four segments based on the characteristics of co seismic displacements geometry of the surface ruptures and geological structures these segments generally show a right step en echelon form and strike ne sw to n s and dip to the east with angles ranging from 50 to 85 the co seismic flexural slip folding structures commonly occurred in or near the surface rupture zone from a few meters to a few hundreds of meters in width which have an orientation in fold axes parallel or oblique to the surface rupture zone the displacements measured in the southern three segments are approximately 1 0 3 0 m horizontally and 2 0 4 0 m vertically the largest displacements were measured in the northern segment 11 1 m horizontally and 7 5 m vertically respectively the amount of co seismic horizontal shortening caused by flexural slip folding and reverse faulting in the surface rupture zone is generally less than 3 m it is evident that the co seismic displacements of the surface rupture zone are a quantitative surface indicator of the faulting process in the earthquake source fault the relations between the geometry and geomorphology of the surface rupture zone dips of the co seismic faulting planes and the striations on the main fault planes generated during the co seismic displacement show that the chelungpu surface rupture zone is a reverse fault zone with a large left lateral component

a comparison of long coastal trapped wave theory with observations off peru abstract the agreement between coastal trapped wave theory and observation is studied for the case of observations made off peru during the 1977 cuea joint ii experiment wave properties are calculated using a numerical model with realistic horizontally uniform stratification and realistic bottom topography these properties are then explored as a function of the ratio of the first internal rossby radius of deformation to the shelf slope width the agreement of observed and calculated first mode free wave phase speeds 230 cm s 1 is excellent while modal structures agree more poorly a forced wave calculation using observed winds and currents as input is used to hindcast alongshore currents and sea level in the frequency band where smith 1978 observed free coastal trapped waves during 1977 the model suggests that most of the observed sea level and alongshore velocity fluctuations in the 5 10 day period band are due to free waves originating equatorward of 5 deg s while winds between 5 deg s and

complexity of rupture in large strike slip earthquakes in turkey complexity of rupture propagation has an important bearing on the state of stress along the earthquake fault plane and on the prediction of strong ground motion in the near field by studying far field body waveforms recorded by wwssn long period seismograms it has been possible to investigate the degree of complexity of several turkish earthquakes the results which are obtained by matching synthetic p waveforms to observed data indicate that the july 22 1967 mudurnu valley earthquake m s 7 1 is a complex event which can be explained by the superposition of elementary sources with variable amplitudes and source time sequence history in this regard it is very similar to the february 4 1976 guatemala earthquake m s 7 5 a comparison of these two events indicates that their source time series ranges from 5 to ca 20 s and regardless of the total moment of the earthquake the moment of the individual events is bounded at around 5 10 26 dyn cm the november 24 1976 e turkey earthquake m s 7 3 on the other hand has a complexity which cannot be explained by such a simple model in this respect it may be more similar to the tangshan china earthquake and as such may involve significant thrust normal or other complications to its faulting mechanism than the strike slip mechanism of the p wave first motion data the source time history for the 1967 mudurnu valley event is used to illustrate its significance in modeling strong ground motion in the near field the complex source time series of the 1967 event predicts greater amplitudes 2 5 larger in strong ground motion than a uniform model scaled to the same size for a station 20 km from the fault such complexity is clearly important in understanding what strong ground motion to expect in the near field of these and other continental strike slip faults such as the san andreas

evidence of diurnal shelf waves in satellite tracked drifter trajectories off the kuril islands abstract satellite tracked surface drifters deployed in september 1993 in the vicinity of the kuril kamchatka trench were advected onto the pacific continental shelf of the kuril islands where they encountered strong 40 50 cm s 1 diurnal tidal currents one of the drifters subsequently passed through friz strait into the sea of okhotsk experiencing intense 100 cm s 1 diurnal currents in the strait and strong 35 40 cm s 1 diurnal currents over the okhotsk shelf of the kuril islands the across shelf structure of the diurnal tidal currents is shown to be consistent with that of free topographically trapped subinertial waves propagating along the continental margin of the islands of the three continental shelf wave models considered a barotropic model with zero mean flow a barotropic model with nonzero alongshore mean flow and a baroclinic model based on the observed density structure only the baroclinic model accurately explains the main features of the diurnal currents for the pacific and ok

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

spatial and temporal variability of the m2 internal tide generation and propagation on the oregon shelf abstracta 1 km horizontal resolution model based on the regional ocean modeling system is implemented along the oregon coast to study average characteristics and intermittency of the m2 internal tide during summer upwelling wind driven and tidally driven flows are simulated in combination using realistic bathymetry atmospheric forcing and boundary conditions the study period is april through august 2002 when mooring velocities are available for comparison modeled subtidal and tidal variability on the shelf are in good quantitative agreement with moored velocity time series observations depth integrated baroclinic tidal energy flux ef its divergence and topographic energy conversion tec from the barotropic to baroclinic tide are computed from high pass filtered harmonically analyzed model results in a series of 16 day time windows model results reveal several hot spots of intensive tec on the slope at these locations tec is well balanced by ef divergence changes in background stratific

high resolution satellite imagery mapping of the surface rupture and slip distribution of the mw 7 8 14 november 2001 kokoxili earthquake kunlun fault northern tibet china the mw 7 8 kokoxili earthquake of 14 november 2001 which ruptured a 450 km long stretch of the sinistral kunlun strike slip fault at the northeastern edge of the tibet plateau china ranks as the largest strike slip event ever recorded instrumentally in asia newly available high resolution satellite hrs images pixel size 1 m acquired in the months following the earthquake proved a powerful tool to complement field investigations and to produce the most accurate map to date of the coseismic displacements along the central kusai hu segment of the rupture the coseismic rupture geometry south and west of buka daban feng near the earthquake epicenter was also investigated in detail along the kusai hu segment slip parti tioning is for the first time observed to occur simultaneously during a single event with two parallel strands 2 km apart localizing almost pure strike slip and normal faulting in all 83 new hrs coseismic offset measurements some of which calibrated by field work show large well constrained variations 100 of the slip function over distances of only25 km tension cracks opening ahead of the shear dislocation and later offset by the upward propagating strike slip rupture were observed dem onstrating that the rupture front propagated faster at depth than near the surface the triple junction between the central kusai hu segment the kunlun pass fault where the rupture ended and the xidatan dongdatan segment which could be the next segment to fail along the main kunlun fault acted as a strong barrier implying that direct triggering of earthquake rupture on the xidatan dongdatan segment by kokoxili type earthquakes may not be the rule

displacement and geometrical characteristics of earthquake surface ruptures issues and implications for seismic hazard analysis and the process of earthquake rupture there now exist about three dozen historical earthquakes for which in vestigators have constructed maps of earthquake rupture traces accompanied by de scriptions of the coseismic slip observed along the fault strike the maps and slip distributions are compiled here to place observational bounds on aspects of seismic hazard analysis and fault mechanics analysis leads to an initial statistical basis to predict the end points of rupture and the amount of surface slip expected at sites along the strike during earthquakes on mapped faults the observations also give support to the ideas that there exists a process zone or volume of about 3 4 km in dimension at the fronts of large laterally propagating earthquake ruptures within which stress changes may be sufficient to trigger slip on adjacent faults and that the ultimate length of earthquake ruptures is controlled primarily by the geometrical complexity of fault traces and variations in accumulated stress levels along faults that arise due to the location of past earthquakes to this may be added the observation that the form of earthquake surface slip distributions is better described by asymmetric rather than symmetric curve forms and that earthquake epicenters do not appear to correlate in any systematic manner to regions of maximum surface slip observed along strike online material maps of surface ruptures digitized values and curve fits to surface slip distributions and notes and references for tables 1 and 2

large slip velocity of the surface rupture associated with the 1990 luzon earthquake we found more than fifty people who provided important information on coseismic fault motion of the 1990 luzon the philippines earthquake about thirty of them witnessed coseismic fault motion close to less than 30 m the surface rupture the average slip duration reported was about 1 s and some reported much less than 1 s which is surprisingly short compared with the predicted value of about 10 s for its size e g fault length 120 km slip 5 m according to scaling laws obtained from teleseismic studies teleseismic studies only obtain spatially and temporally averaged values of fault motion but actual coseismic fault slip has a high degree of spatial heterogeneity the large slip velocity over 10 m s obtained by our study suggests a very high local stress drop 100 mpa other important information from the eyewitness accounts is that the slip velocity seems to have been nearly constant implying that the fault slip is well described by a ramp function proposed by haskell

near field investigations of the landers earthquake sequence april to july 1992 the landers earthquake which had a moment magnitude m w of 7 3 was the largest earthquake to strike the contiguous united states in 40 years this earthquake resulted from the rupture of five major and many minor right lateral faults near the southern end of the eastern california shear zone just north of the san andreas fault its m w 6 1 preshock and m w 6 2 aftershock had their own aftershocks and foreshocks surficial geological observations are consistent with local and far field seismologic observations of the earthquake large surficial offsets as great as 6 meters and a relatively short rupture length 85 kilometers are consistent with seismological calculations of a high stress drop 200 bars which is in turn consistent with an apparently long recurrence interval for these faults