waveform retrieval and phase identification for seismic data from the cass experiment the little destruction to the deployment site and high repeatability of the controlled accurate seismic source cass shows its potential for investigating seismic wave velocities in the earth s crust however the difficulty in retrieving impulsive seismic waveforms from the cass data and identifying the seismic phases substantially prevents its wide applications for example identification of the seismic phases and accurate measurement of travel times are essential for resolving the spatial distribution of seismic velocities in the crust until now it still remains a challenging task to estimate the accurate travel times of different seismic phases from the cass data which features extended wave trains unlike processing of the waveforms from impulsive events such as earthquakes or explosive sources in this study we introduce a time frequency analysis method to process the cass data and try to retrieve the seismic waveforms and identify the major seismic phases traveling through the crust we adopt the wigner ville distribution wvd approach which has been used in signal detection and parameter estimation for linear frequency modulation lfm signals and proves to feature the best time frequency convergence capability the wigner hough transform wht is applied to retrieve the impulsive waveforms from multi component lfm signals which comprise seismic phases with different arrival times we processed the seismic data of the 40 ton cass in the field experiment around the xinfengjiang reservoir with the wvd and wht methods the results demonstrate that these methods are effective in waveform retrieval and phase identification especially for high frequency seismic phases such as pmp and sms with strong amplitudes in large epicenter distance of 80 120 km further studies are still needed to improve the accuracy on travel time estimation so as to further promote applicability of the cass for and imaging the seismic velocity structure

effects of prestress state and rupture velocity on dynamic fault branching 1 we consider a mode ii rupture which propagates along a planar main fault and encounters an intersection with a branching fault using an elastodynamic boundary integral equation formulation allowing the failure path to be dynamically self chosen we study the following questions does the rupture initiate along the branch does it continue is the extensional or compressional side most favored for branching does rupture continue on the main fault too failure is described by a slip weakening law for which the strength at any amount of slip is proportional to normal stress our results show that dynamic stresses around the rupture tip which increase with rupture velocity at locations off the main fault plane relative to those on it could initiate rupture on a branching fault as suggested by prior work whether branched rupture can be continued to a larger scale depends on principal stress directions in the prestress state and on rupture velocity the most favored side for branching rupture switches from the extensional to the compressional side as we consider progressively shallower angles of the direction of maximum compressive prestress with the main fault simultaneous rupturing on both faults can be activated when the branching angle is wide but is usually difficult for a narrow branching angle due to strong stress interactions between faults however it can be also be activated by enhanced dynamic stressing when the rupture velocity is very near the rayleigh velocity natural examples seem consistent with the simulations that we present

microtremor measurement to evaluate site characteristics by horizontal to vertical spectral ratio technique in sikkim northeast himalayas india abstract the measurement of site amplification of microtremors is an important tool for evaluating seismic hazard at local and regional level the h v spectral ratio hvsr method is applied to estimate the amplification of ground motion at resonance frequency the fundamental resonance frequency is estimated at 8 different sites in study region and shows the maximum vulnerability of the site to the earthquakes this frequency ranges between a minimum of 2 8 hz to a maximum of 9 3 hz the thickness of the sediments below the surface of recording sites is calculated using the empirical relationship that comes out to be in a particular range of 9 5 m 33 1 m above the bed rock the sedimentary thickness and the resonance frequency clearly matched with geological setting of the study area the observation shows a slow reduction in the thickness of the sediments and increase in the resonance frequency from south western part to north eastern part of the study region the results show that most of the sites are highly vulnerable to seismic risks with high amplification of seismic waves in the area thus current study provides a deep insight in to the seismic hazard of the sikkim region with a clear emphasis on the site amplification and the sedimentary cover for the region

observations of nearshore circulation alongshore uniformity 1 nearshore circulation observed for 4 months on a 200 m long stretch of natural beach during the sandyduck field experiment is shown to be alongshore uniform an alongshore momentum balance between wind and wave forcing and bottom stress cross shore integrated between the shoreline and approximately 4 m water depth holds on each of five instrumented cross shore transects skill 0 87 the corresponding five best fit drag coefficients are similar consistent with the assumption that terms in the momentum balance associated with alongshore nonuniformity are negligible in addition the alongshore nonuniformity of the circulation and bathymetry were examined at five cross shore locations except near the shoreline the circulation and bathymetry were rarely strongly alongshore nonuniform and the circulation nonuniformities were usually no larger than expected from current meter noise alone near the shoreline the bathymetry was more irregular and the circulation was often detectably nonuniform although no relationship between bathymetric and circulation nonuniformities was found the closure of the alongshore momentum balances on cross shore transects and the observed alongshore uniformity of the circulation on four of five alongshore transects demonstrates that the simplified dynamics of alongshore uniform circulation are valid during the experiment

the frictional behavior of lizardite and antigorite serpentinites experiments constitutive models and implications for natural faults laboratory studies of the frictional behavior of rocks can provide important information about the strength and sliding stability of natural faults we have conducted friction experiments on antigorite and lizardite serpentinites rocks common to both continental and oceanic crustal faults we conducted both velocity step tests and timed hold tests on bare surfaces and gouge layers of serpentinite at room temperature we find that the coefficient of friction of lizardite serpentinite is quite low 0 15 0 35 and could explain the apparent low stresses observed on crustal transform faults while that of antigorite serpentinite is comparable to other crustal rocks 0 50 0 85 the frictional behavior of both types of serpentinite is well described by a two mechanism model combining state variable dominated behavior at high slip velocities and flow dominated behavior at low velocities the two mechanism model is supported by data from velocity step tests and timed hold tests the low velocity behavior of serpentinite is strongly rate strengthening and should result in stable fault creep on natural faults containing either antigorite or lizardite serpentinite

the 2002 denali fault earthquake alaska a large magnitude slip partitioned event the mw moment magnitude 7 9 denali fault earthquake on 3 november 2002 was associated with 340 kilometers of surface rupture and was the largest strike slip earthquake in north america in almost 150 years it illuminates earthquake mechanics and hazards of large strike slip faults it began with thrusting on the previously unrecognized susitna glacier fault continued with right slip on the denali fault then took a right step and continued with right slip on the totschunda fault there is good correlation between geologically observed and geophysically inferred moment release the earthquake produced unusually strong distal effects in the rupture propagation direction including triggered seismicity

boussinesq modeling of longshore currents 1 a time domain boussinesq model for nearshore hydrodynamics is improved to obtain the conservation of vertical vorticity correct to second order and extended for use on an open coast using longshore periodic boundary conditions the model is utilized to simulate surface waves and longshore currents under laboratory and field conditions satisfactory agreement is found between numerical results and measurements including root mean square wave height mean water level and longshore current one striking result of the simulations is the prediction of the strong longshore current in the trough shoreward of the bar as observed during the duck experiment on low frequency and incident band longshore and across shore hydrodynamics field campaign the model results give insight into the spatial and temporal variability of wave driven longshore currents and the associated vertical vorticity field under the phase resolving random wave forcing with wave current interaction numerical experiments are carried out to examine the response of the modeled longshore currents to the randomness of surface waves and the cross shore distributions of bed shear stress coefficient we find that both regular and irregular waves lead to very similar mean longshore currents while the input of monochromatic unidirectional waves results in much more energetic shear waves than does the input of random waves the model results favor whitford and thornton s 1996 finding that the bed shear stress coefficient for the area offshore the bar is larger than that in the trough as better agreement with the field data for both regular and irregular waves is found if such coefficients are used in the boussinesq model

a self similar scaling for cross shelf exchange driven by transient rip currents transient rip currents episodic offshore flows from the surf zone to the inner shelf present a recreational beach hazard and exchange material across the nearshore ocean the magnitude and offshore extent of transient rip current induced exchange and its relative importance to other inner shelf exchange processes are poorly understood here 120 model simulations with random normally incident directionally spread waves spanning a range of beach slopes and wave conditions show that the transient rip current exchange velocity is self similar the nondimensional exchange velocity surf zone flushing time and cross shore decay length scale are scaled by beach slope and wave properties depending strongly on wave directional spread transient rip current driven exchange can be compared to other cross shelf exchange processes for example transient rip current driven exchange is stronger than wave induced stokes drift driven exchange up to six surf zone widths from shore

why the 2002 denali fault rupture propagated onto the totschunda fault implications for fault branching and seismic hazards 1 the propagation of the rupture of the mw7 9 denali fault earthquake from the central denali fault onto the totschunda fault has provided a basis for dynamic models of fault branching in which the angle of the regional or local prestress relative to the orientation of the main fault and branch plays a principal role in determining which fault branch is taken geoearthscope lidar and paleoseismic data allow us to map the structure of the denali totschunda fault intersection and evaluate controls of fault branching from a geological perspective lidar data reveal the denali totschunda fault intersection is structurally simple with the two faults directly connected at the branch point 227 2 km east of the 2002 epicenter the 2002 rupture diverges southeast to become the totschunda fault we use paleoseismic data to propose that differences in the accumulated strain on each fault segment which express differences in the elapsed time since the most recent event was one important control of the branching direction we suggest that data on event history slip rate paleo offsets fault geometry and structure and connectivity especially on high slip rate short recurrence interval faults can be used to assess the likelihood of branching and its direction analysis of the denali totschunda fault intersection has implications for evaluating the potential for a rupture to propagate across other types of fault intersections and for characterizing sources of future large earthquakes

on the nature of an unusual wave train observed in the northern tien shan region we describe an unusual wave group that propagates in the northern tien shan region along the border between mountain ranges and the chu and ili depressions to the north this wave group which we call s l stands out against the short period coda on the recordings of local earthquakes and quarry explosions at distances up to 100 km the time t m needed for the s l group to reach maximum amplitude varies between 98 and 131 sec and at the same time the t m value does not depend on epicentral distance at distances up to 30 km the s l group has a very narrow spectrum t 1 5 1 8 sec but when the epicentral distance increases the predominant period also increases up to approximately 2 3 sec at 100 km characteristics of the wave group are significantly different for the zaili fault zone than for the regions to the west of 76 e and to the east of 79 e in the zaili fault region the s l group is characterized by great variability of velocity amplitude and polarization parameters even for nearby paths the s l group maintains an amplitude within 0 7 of its maximum for 4 36 sec depending on the path the polarization of the s l group is in the vertical plane in the zaili fault zone region and in the horizontal plane in other regions particle motion is elliptical or almost circular we suggest that the s l group consists of shear waves propagating in a subvertical wave guide and reflected from a thin upper mantle layer

ground based measurements and dual doppler analysis of 3 d wind fields and atmospheric circulations induced by a meso γ scale inland lake 1 this paper presents a high resolution dual doppler analysis of lake breeze mesoscale circulation induced by an elongated reservoir with a mean width of 2 km and an area of 125 km2 compared to previous meso scale lake breeze studies based on point measurements or aircraft observations the present study provides both a unique quantification and a high resolution spatial and temporal 3 d visualization several hundred meters and 5 min respectively of the kinematic structure of the lake breeze initiation and evolution visible satellite images show a cloud free zone over the lake and adjacent land areas that was promoted by subsidence associated with the lake breeze circulation the background synoptic scale wind flow was almost parallel to the major axis of the lake and distinct lake breeze frontal zones formed along both shorelines spanning the length of the lake dual doppler analyses showed updrafts in the frontal zones perturbation horizontal velocities of 1 5 m s 1 on both sides of the lake and maximum downdrafts of 2 m s 1 centered over the lake vertical vorticity in the boundary layer was produced by differential friction between the smooth lake and adjacent land the circulations are robust and are maintained during the day against a minor change in background wind direction the study shows that the circulations produced by a small lake can generate significant mesoscale circulations that influence local climatology and identifies the importance of including such small mesoscale processes in global forecast models

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

shortening within underplated oceanic crust beneath the central california margin structures within a tectonically underplated layer of early miocene age oceanic crust indicate that the lower crust of offshore central california has been deformed under compression prior to the inception of the san andreas transform system along the continental margin shortening in the lower crust is inferred from the geometry of two structures the santa lucia monocline and the santa maria antiform delineated by an integrated interpretation of multichannel and wide angle seismic reflection data in conjunction with regional gravity data and teleseismic receiver functions the 700 km of multichannel seismic data and 300 km of wide angle seismic data from the 1986 pacific gas and electric edge seismic experiment form the primary data base used to establish the northwesterly trend and extent of the monocline and the wnw trend of the antiform in cross sectional view the santa lucia monocline is a 30 kink in the oceanic crust while the santa maria antiform is characterized by local thickening of the oceanic crust these structures are probably the result of convergence between the monterey and arguello microplates that took place as subduction along the margin waned the multichannel seismic reflection data image two miocene age shelf basins the santa lucia and offshore santa maria basins that formed within a transtensional stress regime the offshore santa maria basin directly overlies the santa maria antiform suggesting that either the upper and lower crustal stress regimes were completely decoupled in miocene time or that the two features formed in different places differential slip between the upper crust and lower crust may have been accommodated along a detachment zone located above oceanic crust convergence within the oceanic crust and apparent differential motion between upper and lower crust are indicative of the processes that can affect the transition from subduction to an oceanic continental transform zone

automatic reconstruction of fault networks from seismicity catalogs three dimensional optimal anisotropic dynamic clustering 1 we propose a new pattern recognition method that is able to reconstruct the three dimensional structure of the active part of a fault network using the spatial location of earthquakes the method is a generalization of the so called dynamic clustering or k means method that partitions a set of data points into clusters using a global minimization criterion of the variance of the hypocenters locations about their center of mass the new method improves on the original k means method by taking into account the full spatial covariance tensor of each cluster in order to partition the data set into fault like anisotropic clusters given a catalog of seismic events the output is the optimal set of plane segments that fits the spatial structure of the data each plane segment is fully characterized by its location size and orientation the main tunable parameter is the accuracy of the earthquake locations which fixes the resolution i e the residual variance of the fit the resolution determines the number of fault segments needed to describe the earthquake catalog the better the resolution the finer the structure of the reconstructed fault segments the algorithm successfully reconstructs the fault segments of synthetic earthquake catalogs applied to the real catalog constituted of a subset of the aftershock sequence of the 28 june 1992 landers earthquake in southern california the reconstructed plane segments fully agree with faults already known on geological maps or with blind faults that appear quite obvious in longer term catalogs future improvements of the method are discussed as well as its potential use in the multiscale study of the inner structure of fault zones

observed and modeled drifters at a tidal inlet material transport and dispersion near the mouth of a tidal inlet new river inlet nc are investigated using gps tracked drifters and numerical models for ebb tide releases velocities are largest 1 m s 1 in two approximately 30 m wide channels that bisect the 1 3 m deep ebb shoal in the channels drifter and subsurface current meter velocities are similar consistent with strong vertical mixing and 2 d hydrodynamics drifters were preferentially entrained in the channelized jets where drifter cluster lateral spreading rates in were small in 0 5 m2 s 1 at the seaward edge of the ebb shoal jet velocities decrease linearly with distance to 0 2 m s 1 about 1 km from shore and cluster spreading rates are larger with out 3 m2 s 1 although the models coawst and nearcom generally reproduce the observed trajectory directions certain observed drifter properties are poorly modeled for example modeled mean drifter velocities are smaller than observed and upon exiting the inlet observed drifters turn north more than modeled drifters the model simulations do reproduce qualitatively the spreading rates observed in the inner inlet the flow deceleration and the increase in out observed in the outer inlet however model spreading rates increase only to out 1 m2 s 1 smaller modeled than observed out may result from using unstratified models noncoincident in space observations show evidence of a buoyant plume 1 kg m 3 in the outer inlet likely affecting drifter lateral spreading generally drifter based model performance is good within the inlet channels where tidal currents are strongest whereas model data differences are significant farther offshore

liquefaction at oceano california during the 2003 san simeon earthquake the 2003 m 6 5 san simeon california earthquake caused liquefaction induced lateral spreading at oceano at an unexpectedly large distance from the seismogenic rupture we conclude that the liquefaction was caused by ground motion that was enhanced by both rupture directivity in the mainshock and local site amplification by unconsolidated fine grained deposits liquefaction occurred in sandy artificial fill and undisturbed eolian sand and fluvial deposits the largest and most damaging lateral spread was caused by liquefaction of artificial fill the head of this lateral spread coincided with the boundary between the artificial fill and undisturbed eolian sand deposits values of the liquefaction potential index in general were greater than 5 at liquefaction sites the threshold value that has been proposed for liquefaction hazard mapping although the mainshock ground motion at oceano was not recorded peak ground acceleration was estimated to range from 0 25 and 0 28 g on the basis of the liquefaction potential index and aftershock recordings the estimates fall within the range of peak ground acceleration values associated with the modified mercalli intensity vii reported at the u s geological survey usgs did you feel it web site

observing surf zone dispersion with drifters abstract surf zone dispersion is studied using drifter observations collected within about 200 m of the shoreline at depths of less than about 5 m on a beach with approximately alongshore uniform bathymetry and waves there were about 70 individual drifter releases each 10 20 min in duration on two consecutive days on the first day the sea swell significant wave height hs was equal to 0 5 m and mean alongshore currents were moderate 0 1 m s 1 on the second day the obliquely incident waves were larger with hs equal to 1 4 m and at some surf zone locations was greater than 0 5 m s 1 the one particle diffusivity was larger with larger waves and stronger currents on both days the one particle diffusivity tensor is nonisotropic and time dependent the major axis is initially parallel to the cross shore direction but after a few wave periods it is aligned with the alongshore direction in both the along and cross shore directions the asymptotic diffusivity is reached sooner within r

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

double difference tomography the method and its application to the hayward fault california we have developed a double difference dd seismic tomography method that makes use of both absolute and relative arrival times by reducing systematic errors using the more accurate relative arrival times the method produces an improved velocity model simultaneously it yields event locations of a quality equivalent to those of the dd location method while avoiding simplifying assumptions of that method we test this method on a synthetic dataset and find that it produces a more accurate velocity model and event locations than standard tomography we also test this method on a hayward fault california earthquake dataset spanning 1984 1998 the earthquakes relocated by this method collapse to a thin line along the fault trace consistent with previous results the dd velocity model has sharper velocity contrasts near the source region than the standard tomography model

influence of the synoptic scale flow on sea breezes observed during cape abstract mean sea breeze characteristics were determined by analyzing a number of sea breeze events during offshore parallel and onshore flow regimes during the convection and precipitation electrification experiment cape it was observed that offshore flow cases exhibited the widest and relatively strongest radar detected thin lines the thin line reflectivity values steadily increased during the day in contrast a thin line was detected only during late afternoon on parallel flow days while no easily identifiable thin line was observed during onshore flow days the gradients of temperature and moisture as measured by a surface meteorological station during sea breeze passage were strongest and weakest during offshore and onshore flow days respectively in addition the moisture and temperature gradients across the leading edge of the sea breeze steadily increased during the day and were strongest during late afternoon using dual doppler techniques the detailed kinematic structure of the sea

controls on sediment distribution in the coastal zone of the central california transform continental margin usa abstract we use 10 000 km of high resolution seismic reflection data together with multibeam bathymetry to document complex and highly variable post last glacial maximum lgm sediment distribution and thickness in the coastal zone 10 m isobath to 5 6 km offshore along a 800 km section of central california s transform continental margin sediment thickness ranges from 0 seafloor bedrock to 64 m with a mean of 8 7 m we delineate 25 coastal zone sediment domains and group them based on common geomorphology and sediment occurrence thickest sediment occurs in mountain front and large river domains which comprise 14 5 and 7 9 of the coastal zone and contain 30 1 and 18 2 of coastal zone sediment respectively in contrast small river domains and sediment poor shelf domains comprise 50 7 and 15 7 of the coastal zone and contain 18 4 and 12 7 of its sediment the distribution and thickness of post lgm sediment in the coastal zone is controlled by a combination of tectonics sediment supply and eustasy sediment is derived from a tectonically controlled coastal landscape of rapidly uplifting mountain fronts more slowly uplifting marine terraces and fault bounded headlands and alluvial estuarine troughs sediment supply is maximized along steep landslide prone mountain fronts and at the mouths of large watersheds and minimized along lower relief terraced coastal landscape drained by smaller rivers and creeks in the offshore coastal zone tectonics generates local uplifts and basins and influences shelf width and gradient as well as the locations of some shelf incised submarine canyons sea level rise raises base level drowns estuaries creates accommodation space on the shelf amount based on gradient and isolates the heads of many submarine canyons at or near the shelfbreak comparison of shelf sediment volumes with estimates of unaltered watershed sediment supply reveals that a relatively small proportion of post lgm sediment supply is preserved on the shelf offshore of some of the largest rivers sediments deposited in shoreline and shelf environments have limited preservation potential and the most complete long term geologic record of the post lgm transgression and highstand is likely represented in slope and submarine fan deposits

source and site characteristics of earthquakes that have caused exceptional ground accelerations and velocities abstract this study investigates the characteristics of the free field strong motion records that have yielded the 100 largest peak accelerations and the 100 largest peak velocities in a relatively complete database of accelerograms recorded through the summer of 2007 the peak is defined as the maximum zero to peak amplitude of the acceleration or velocity vector during the strong shaking this compilation includes 35 records with peak acceleration greater than 1 g 980 cm sec 2 and 40 records with peak velocities greater than 100 cm sec the results sample an estimated 150 000 instrument years of strong motion recordings the geometric mean of the two horizontal components of acceleration or velocity as used in many ground motion prediction equations is typically 0 76 times the magnitude of this vector peak accelerations in the top 100 come from earthquakes as small as magnitude 4 8 while velocities in the top 100 all come from earthquakes with magnitude 5 7 or larger these records are dominated by crustal earthquakes with thrust oblique thrust or strike slip mechanisms normal faulting mechanisms in crustal earthquakes constitute under 5 of the records in the databases searched and an even smaller percentage of the 100 largest acceleration or velocity records all national earthquake hazard reduction program site categories have contributed exceptional records in proportions similar to the extent that they are represented in larger databases

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

surf zone diffusivity on a rip channeled beach absolute and relative diffusivity are measured on a rip channeled beach using 30 position tracking drifters released in clusters 4 12 drifters deployed on 7 days with different wave forcing and tidal elevations at sand city monterey bay california diffusivity and dispersion were found to be larger on days with rip current flow patterns and larger waves rip currents cause material to diffuse quickly for t 0 9 two independent methods are used to measure the small scale turbulent diffusion contribution kxy which are found significantly correlated r2 0 95 with each other and calculated surf zone wave breaking induced turbulent eddy viscosity here kxy is small relative to the total dispersion ke kxy 3 30 indicating that the shear flow is the primary mechanism responsible for dispersion in a rip current system

connecting wind driven upwelling and offshore stratification to nearshore internal bores and oxygen variability this study utilizes field observations in southern monterey bay ca to examine how regional scale upwelling and changing offshore shelf conditions influence nearshore internal bores we show that the low frequency wind forcing e g upwelling relaxation time scales modifies the offshore stratification and thermocline depth this in turn alters the strength and structure of observed internal bores in the near shore an internal bore strength index is defined using the high pass filtered potential energy density anomaly in the nearshore during weak upwelling favorable conditions and wind relaxations the offshore thermocline deepens in this case both the amplitude of the offshore internal tide and the strength of the nearshore internal bores increase in contrast during strong upwelling conditions the offshore thermocline shoals toward the surface resulting in a decrease in the offshore internal tide amplitude as a result cold water accumulates in the nearshore nearshore pooling and the internal bore strength index decreases empirical orthogonal functions are utilized to support the claim that the bore events contribute to the majority of the variance in cross shelf exchange and transport in the nearshore observed individual bores can drive shock like drops in dissolved oxygen do with rapid onset times while extended upwelling peri ods with reduced bore activity produce longer duration low do events

effect of wave frequency and directional spread on shoreline runup 1 wave breaking across the surf zone elevates the mean water level at the shoreline setup and drives fluctuations about the mean runup runup often is divided into sea swell 0 04 0 3 hz and lower frequency infragravity 0 00 0 04 hz components with energetic incident waves runup is dominated by infragravity frequencies and total water levels combined setup and runup can exceed 3 m significantly contributing to coastal flooding and erosion setup and runup observations on sandy beaches are scattered about empirical parameterizations based on near shoreline beach slope and deep water wave height and wavelength accurate parameterizations are needed to determine flooding and erosion risk to coastal ecosystems and communities here numerical simulations with the boussinesq wave model funwavec are shown to statistically reproduce typical empirical setup and runup parameterizations furthermore the model infragravity runuprs ig strongly depends on the incident wave directional and frequency spread about the mean direction and peak frequency realistic directional spread variations change rs ig equivalent to a factor of two variation in incident wave height the modeled rs ig is shown to vary systematically with a new non dimensional spreading parameter that involves peak frequency frequency spread and directional spread this suggests a new parameterization forrs ig potentially useful to predict coastal flooding and erosion

radar observations of mesoscale circulations induced by a small lake under varying synoptic scale flows 1 this paper examines doppler radar observations of springtime lake breeze lb circulations produced by a small reservoir mean width of 2 km wheeler lake on the tennessee river in northern alabama the analysis allows for the formation of a general understanding of the flow structures as a composite of many lb circulation events it is found that lb circulation once formed is robust and persistent over a range of background or synoptic scale wind flows despite the small size of wheeler lake and the relatively small differences between land and lake temperature often a few degrees celsius that drive the lb circulation the formation location strength and inland penetration of the wheeler lake breeze are highly sensitive to the background wind speed and direction with respect to the lakeshore resulting in complex spatial and temporal variations in the lb characteristics the lb front is most prominent as a radar fine line when the ambient flow is offshore opposing the lb background wind and perpendicular to the orientation 120 300 of the lake for wind speeds 4 5 m s 1 a radar detectable thin line delineating the lb front appears primarily on the upwind side of the lake either to the north or south while synoptic scale winds stronger than 5 m s 1 tend to destroy the breeze front entirely if the background wind is parallel to lake orientation and the wind is 4 m s 1 the lb circulations often develop on both sides of the lake the radar fine line often appears patchy and broad for low wind conditions near 2 m s 1 overall the findings of this study show that small lakes can generate persistent local circulations that follow similar patterns of behavior and respond to the synoptic flow as large lakes or sea breezes

observations and a model of undertow over the inner continental shelf abstract onshore volume transport stokes drift due to surface gravity waves propagating toward the beach can result in a compensating eulerian offshore flow in the surf zone referred to as undertow observed offshore flows indicate that wave driven undertow extends well offshore of the surf zone over the inner shelves of martha s vineyard massachusetts and north carolina theoretical estimates of the wave driven offshore transport from linear wave theory and observed wave characteristics account for 50 or more of the observed offshore transport variance in water depths between 5 and 12 m and reproduce the observed dependence on wave height and water depth during weak winds wave driven cross shelf velocity profiles over the inner shelf have maximum offshore flow 1 6 cm s 1 and vertical shear near the surface and weak flow and shear in the lower half of the water column the observed offshore flow profiles do not resemble the parabolic profiles with maximum flow at middepth observed within the su

direct estimate of lateral eddy diffusivity upstream of drake passage abstractthe first direct estimate of the rate at which geostrophic turbulence mixes tracers across the antarctic circumpolar current is presented the estimate is computed from the spreading of a tracer released upstream of drake passage as part of the diapycnal and isopycnal mixing experiment in the southern ocean dimes the meridional eddy diffusivity a measure of the rate at which the area of the tracer spreads along an isopycnal across the antarctic circumpolar current is 710 260 m2 s 1 at 1500 m depth the estimate is based on an extrapolation of the tracer based diffusivity using output from numerical tracers released in a one twentieth of a degree model simulation of the circulation and turbulence in the drake passage region the model is shown to reproduce the observed spreading rate of the dimes tracer and suggests that the meridional eddy diffusivity is weak in the upper kilometer of the water column with values below 500 m2 s 1 and peaks at the steering level near 2 km where the eddy ph

powerful low frequency vibrators for active seismology in the past two decades active seismology studies in russia have made use of powerful 40 and 100 ton low frequency vibrators these sources create a force amplitude of up to 100 tons and function in the 1 5 3 3 6 and 5 10 hz frequency bands the mobile versions of the vibrator have a force amplitude of 40 tons and a 6 12 hz frequency band recording distances for the 100 ton vibrator are as large as 350 km enabling the refracted waves to penetrate down to 50 km depths vibrator operation sessions are highly repeatable having distinct summer or winter spectral patterns a long profile of seismic records allows estimation of fault zone depths using changes in recorded spectra other applications include deep seismic profiling seismic hazard mapping structural testing stress induced anisotropy studies seismic station calibration and large structure integrity testing the theoretical description of the low frequency vibrator is given in the appendices which contain numerical examples

modeling surf zone tracer plumes 2 transport and dispersion 1 five surf zone dye tracer releases from the hb06 experiment are simulated with a tracer advection diffusion model coupled to a boussinesq surf zone model funwavec model tracer is transported and stirred by currents and eddies and diffused with a breaking wave eddy diffusivity set equal to the breaking wave eddy viscosity and a small 0 01 m2 s 1 background diffusivity observed and modeled alongshore parallel tracer plumes transported by the wave driven alongshore current have qualitatively similar cross shore structures although the model skill for mean tracer concentration is variable from negative to 0 73 depending upon release cross shore integrated tracer moments normalized by the cross shore tracer integral have consistently high skills 0 9 modeled and observed bulk surf zone cross shore diffusivity estimates are also similar with 0 72 squared correlation and skill of 0 4 similar to the observations the model bulk absolute cross shore diffusivity is consistent with a mixing length parameterization based on low frequency 0 001 0 03 hz eddies the model absolute cross shore dispersion is dominated by stirring from surf zone eddies and does not depend upon the presence of the breaking wave eddy diffusivity given only the bathymetry and incident wave field the coupled boussinesq tracer model qualitatively reproduces the observed cross shore absolute tracer dispersion suggesting that the model can be used to study surf zone tracer dispersion mechanisms

observations of the sea breeze front during cape part ii dual doppler and aircraft analysis abstract the three dimensional kinematic structures of offshore and onshore flow sea breeze fronts observed during the cape experiment are shown using high resolution dual doppler and aircraft data the fronts interact with horizontal convective rolls hcrs that develop within the convective boundary layer nearly perpendicular intersections between the hcrs and sea breeze front were observed during the offshore flow case close to the front the hcr axes were tilted upward and lifted by the frontal updrafts consequently a deeper updraft was created at the intersection points providing additional impetus for cloud development furthermore clouds forming at periodic intervals along the ncrs intensified as they propagated over the front during the onshore flow case the hcr orientation was nearly parallel to the front extended sections of the front merged with the hcrs this process strengthened the front and is explained as the merger of like sign vortices associated with both the front and hcrs

strengths of serpentinite gouges at elevated temperatures serpentinite has been proposed as a cause of both low strength and aseismic creep of fault zones to test these hypotheses we have measured the strength of chrysotile lizardite and antigorite rich serpentinite gouges under hydrothermal conditions with emphasis on chrysotile which has thus far received little attention at 25 c the coefficient of friction of chrysotile gouge is roughly 0 2 whereas the lizardite and antigorite rich gouges are at least twice as strong the very low room temperature strength of chrysotile is a consequence of its unusually high adsorbed water content when the adsorbed water is removed chrysotile is as strong as pure antigorite gouge at room temperature heating to 200 c causes the frictional strengths of all three gouges to increase limited data suggest that different polytypes of a given serpentine mineral have similar strengths thus deformation induced changes in polytype should not affect fault strength at 25 c the chrysotile gouge has a transition from velocity strengthening at low velocities to velocity weakening at high velocities consistent with previous studies at temperatures up to 200 c however chrysotile strength is essentially independent of velocity at low velocities overall chrysotile has a restricted range of velocity strengthening behavior that migrates to higher velocities with increasing temperature less information on velocity dependence is available for the lizardite and antigorite gouges but their behavior is consistent with that outlined for chrysotile the marked changes in velocity dependence and strength of chrysotile with heating underscore the hazards of using room temperature data to predict fault behavior at depth the velocity behavior at elevated temperatures does not rule out serpentinite as a cause of aseismic slip but in the presence of a hydrostatic fluid pressure gradient all varieties of serpentine are too strong to explain the apparent weakness of faults such as the san andreas

mechanisms of mid to outer shelf transport of shoreline released tracers abstracttransport of shoreline released tracer from the surfzone across the shelf can be affected by a variety of physical processes from wind driven to submesoscale with implications for shorelin

breaking wave induced cross shore tracer dispersion in the surf zone model results and scalings 1 the dispersion of surf zone tracers including pollutants and bacteria is determined by many processes acting over a range of timescales and space scales breaking waves bores are clearly important to cross shore tracer dispersion in the surf zone but little is known about the dispersal effects of bores here a simple model for bore induced cross shore dispersion are developed based upon the diffusion equation with an eddy diffusivity that propagates with the bores depth uniform tracer and bore induced mixing along with alongshore uniformity are assumed the bores are assumed well developed and the dispersion results are for a self similar constant wave height to water depth ratio surf zone four nondimensional parameters are identified and solution space is explored the tracer center of mass is approximately constant and tracer width grows with the square root of time tracer distribution becomes initially skewed after the passage of the first bore but becomes symmetric after multiple bores have passed the nondimensional tracer patch growth and dilution rates depend strongly upon the nondimensional phase speed and wave period the simple model results are consistent with the a boussinesq wave model where the breaking wave eddy viscosity is used for the bore eddy diffusivity the scaling of the dimensional parameters regarding the bore eddy diffusivity and the ranges of the nondimensional parameters are examined covariation of the nondimensional phase speed and wave period suggest that nondimensional tracer dispersion is largely cross shore independent

geometry and earthquake potential of the shoreline fault central california abstract the shoreline fault is a vertical strike slip fault running along the coastline near san luis obispo california much is unknown about the shoreline fault including its slip rate and the details of its geometry here i study the geometry of the shoreline fault at seismogenic depth as well as the adjacent section of the offshore hosgri fault using seismicity relocations and earthquake focal mechanisms the optimal anisotropic dynamic clustering oadc algorithm ouillon et al 2008 is used to objectively identify the simplest planar fault geometry that fits all of the earthquakes to within their location uncertainty the oadc results show that the shoreline fault is a single continuous structure that connects to the hosgri fault discontinuities smaller than about 1 km may be undetected but would be too small to be barriers to earthquake rupture the hosgri fault dips steeply to the east while the shoreline fault is essentially vertical so the hosgri fault dips towards and under the shoreline fault as the two faults approach their intersection the focal mechanisms generally agree with pure right lateral strike slip on the oadc planes but suggest a non planar hosgri fault or another structure underlying the northern shoreline fault the shoreline fault most likely transfers strike slip motion between the hosgri fault and other faults of the pacific north america plate boundary system to the east a hypothetical earthquake rupturing the entire known length of the shoreline fault would have a moment magnitude of 6 4 6 8 a hypothetical earthquake rupturing the shoreline fault and the section of the hosgri fault north of the hosgri shoreline junction would have a moment magnitude of 7 2 7 5

seismicity of south central coastal california october 1987 through january 1997 earthquakes recorded along south central coastal california from october 1987 through january 1997 by the pacific gas and electric company9s 20 station central coast seismic network and the u s geological survey9s northern and southern california networks are used to study their relation to previous seismicity mapped quaternary faults and regional tectonic features we developed p and s wave velocity models station corrections and duration magnitude calibrations to process 1184 reliable earthquake locations and 212 well constrained focal mechanisms seismicity generally coincides with mapped quaternary faults and areas of tectonic uplift including the southern offshore santa maria basin and areas to the west and the uplifted blocks within the los osos tectonic domain comparison of our data to previous microearthquake locations 1969 1987 and larger m 5 historical earthquakes shows that these patterns have been persistent seismically quiescent areas have few or no mapped quaternary faults and typically are structural lows the base of the seismogenic zone is about 12 km in depth above the relic oceanic crust microearthquake locations and strike slip focal mechanisms document the strike slip nature of the hosgri fault zone and its step over to the san simeon fault along the western boundary of the los osos domain uplifting blocks within the los osos domain are most seismically active toward their western ends along the hosgri fault zone and they exhibit reverse and oblique faulting consistent with block uplift and interaction with the hosgri fault zone the observed patterns and character of microseismicity and macroseismicity clearly show transpressional deformation associated with the hosgri fault zone overprinted by rotation and westward migration of the western transverse ranges within this tectonic setting clockwise rotation of the western transverse ranges causes internal deformation of the los osos domain and westward migration of the ranges appears to deflect the hosgri fault zone westward and causes east west directed crustal shortening in the southern offshore santa maria basin

seismotectonics and fault structure of the california central coast abstract i present and interpret new earthquake relocations and focal mechanisms for the california central coast the relocations improve upon catalog locations by using 3d seismic velocity models to account for lateral variations in structure and by using relative arrival times from waveform cross correlation and double difference methods to image seismicity features more sharply focal mechanisms are computed using ray tracing in the 3d velocity models seismicity alignments on the hosgri fault confirm that it is vertical down to at least 12 km depth and the focal mechanisms are consistent with right lateral strike slip motion on a vertical fault a prominent newly observed feature is an 25 km long linear trend of seismicity running just offshore and parallel to the coastline in the region of point buchon informally named the shoreline fault this seismicity trend is accompanied by a linear magnetic anomaly and both the seismicity and the magnetic anomaly end where they obliquely meet the hosgri fault focal mechanisms indicate that the shoreline fault is a vertical strike slip fault several seismicity lineations with vertical strike slip mechanisms are observed in estero bay events greater than about 10 km depth in estero bay however exhibit reverse faulting mechanisms perhaps reflecting slip at the top of the remnant subducted slab strike slip mechanisms are observed offshore along the hosgri san simeon fault system and onshore along the west huasna and rinconada faults while reverse mechanisms are generally confined to the region between these two systems this suggests a model in which the reverse faulting is primarily due to restraining left transfer of right lateral slip

fault behavior and characteristic earthquakes examples from the wasatch and san andreas fault zones paleoseismological data for the wasatch and san andreas fault zones have led to the formulation of the characteristic earthquake model which postulates that individual faults and fault segments tend to generate essentially same size or characteristic earthquakes having a relatively narrow range of magnitudes near the maximum analysis of scarp derived colluvium in trench exposures across the wasatch fault provides estimates of the timing and displacement associated with individual surface faulting earthquakes at all of the sites studied the displacement per event has been consistently large measured values range from 1 6 to 2 6 m and the average is about 2 m on the basis of variability in the timing of individual events as well as changes in scarp morphology and fault geometry six major segments are recognized along the wasatch fault on the basis of the most likely number of surface faulting events 18 that have occurred on segments of the wasatch fault zone during the past 8000 years an average recurrence interval of 400 666 years with a preferred average of 444 years is calculated for the entire zone geologic data on the distribution of slip associated with prehistoric earthquakes and slip rates along the south central segment of the san andreas fault suggest that the m 8 1857 earthquake is a characteristic earthquake for this segment comparisons of earthquake recurrence relationships on both the wasatch and san andreas faults based on historical seismicity data and geologic data show that a linear constant b value extrapolation of the cumulative recurrence curve from the smaller magnitudes leads to gross underestimates of the frequency of occurrence of the large or characteristic earthquakes only by assuming a low b value in the moderate magnitude range can the seismicity data on small earthquakes be reconciled with geologic data on large earthquakes the characteristic earthquake appears to be a fundamental aspect of the behavior of the wasatch and san andreas faults and may apply to many other faults as well

a new offshore transport mechanism for shoreline released tracer induced by transient rip currents and stratification offshore transport from the shoreline across the inner shelf of early stage larvae and pathogens is poorly understood yet is critical for understanding larval fate and dilution of polluted shoreline water with a novel coupling of a transient rip current trc generating surf zone model and an ocean circulation model we show that transient rip currents ejected onto a stratified inner shelf induce a new previously unconsidered offshore transport pathway for incident waves and stratification typical for southern california in the fall this mechanism subducts surf zone origin tracers and transports them at least 800 m offshore at 1 2 km d analogous to subduction at ocean fronts this mechanism requires both trcs and stratification as trcs are ubiquitous and the inner shelf is often stratified this mechanism may have an important role in exporting early stage larvae pathogens or other tracers onto the shelf

field observations of surf zone inner shelf exchange on a rip channeled beach cross shore exchange between the surf zone and the inner shelf is investigated using lagrangian and eulerian field measurements of rip current flows on a rip channeled beach in sand city california surface drifters released on the inner shelf during weak wind conditions moved seaward due to rip current pulses and then returned shoreward in an arcing pattern reentering the surf zone over shoals the cross shore velocities of the seaward and shoreward moving drifters were approximately equal in magnitude and decreased as a function of distance offshore the drifters carried seaward by the rip current had maximum cross shore velocities as they exited the surf zone and then decelerated as they moved offshore the drifters moving shoreward accelerated as they approached the surfzone boundary with maximum cross shore velocities as they reentered the surf zone over shoals it was found that stokes drift was not solely responsible for the onshore transport across the surfzone boundary the cross shore diffusivity on the inner shelf was greatest during observations of locally contained cross shore exchange these field observations provide evidence that the cross shore exchange between the surf zone and inner shelf on a rip channeled beach is due to wave driven rip current circulations and results in surface material being contained within the nearshore region

scaling surf zone turbulence 1 turbulence in the surf zone the shallow region adjacent to the shoreline has a key role in beach erosion fertilization dispersal and larval settlement of marine invertebrates and microbial contamination dilution in beach waters breaking wave generated the dominant source surf zone turbulence is understood poorly a new surf zone turbulent dissipation rate scaling is derived that collapses new field surf zone observations with relatively high skill compared to other scalings the vertically uniform length scale is 1 6 the water depth and 15 of the wave energy flux gradient is dissipated below the mean surface field and laboratory surf zone turbulence observations are shown to be consistent using the scaling the non dimensional surf zone diffusivity and suspended sediment profile can be applied to sediment transport and a range of biological processes including microbial pathogen contamination of beach waters

the generation of surfzone eddies in a strong alongshore current abstractthe surfzone contains energetic two dimensional horizontal eddies with length scale larger than the water depth yet the dominant eddy generation mechanism is not understood the wave resolving model funwavec is used to simulate surfzone eddies in four case examples from the sandyduck field experiment that had alongshore uniform bathymetry the funwavec model is initialized with the observed bathymetry and the incident wave field in 8 m depth and reproduces the observed cross shore structure of significant wave height and mean alongshore current within the surfzone the wave resolving funwavec modeled e f ky spectra and the bulk frequency and ky integrated rotational velocities are consistent with the observations below the sea swell band 0 05 hz demonstrating that the model can be used to diagnose surfzone eddy generation mechanisms in the mean squared perturbation vorticity budget the breaking wave vorticity forcing term is orders of magnitude larger than the shear instability gene

the sea breeze and gravity current frontogenesis the development of a sea breeze circulation into a sea breeze front in often observed late in the afternoon measurements of horizontal temperature and humidity profiles in a number of sea breeze circulation made using an instrumented light aircraft are presented on each of the four days for which data are presented an initial weak horizontal temperature gradient extending over a distance of 5 to 10 kilometres developed later in the into a sharp front only a few hundred metres across the data are discussed in terms of simple gravity current frontogenesis models applied to the development of sharp sea breeze front from an initial diffuse transition between the air over the land sea examination of the equations for frontogenesis and the result of some previous laboratory experiments on gravity current frontogenesis lead to the proposal that given sufficient contrast between land and sea temperatures the formation of a sea breeze front depends on the balance between convergent horizontal winds which act to generate a front and turbulent convective mixing over the land which tends to prevent its formation the differences in driving force wind convergence and turbulent intensity are discussed for each day on which data are available and are shown to be consistent with the theory proposed

nonuniform prestress from prior earthquakes and the effect on dynamics of branched fault systems 1 to examine the effects of branched fault geometry on the dynamics of fault systems in the long term we perform multicycle simulations on generic faulting models an explicit finite element algorithm is used to simulate spontaneous dynamic rupture of earthquakes the fault stress during the interseismic period is evaluated by an analytical viscoelastic model we find that the fault prestress field becomes highly nonuniform near the branch point and on the two branch segments over multiple earthquake cycles owing to the branched fault geometry and stress interaction between the two segments the principal prestress on faults rotates over multiple earthquake cycles and departs from the regional stress field significantly near the branch point after a number of earthquake cycles the branched fault systems evolve to a steady state in which several patterns of the fault prestress and earthquake rupture repeat the nonuniform prestress developed from previous earthquakes has large effects on the rupture and slip patterns several different rupture scenarios can occur on a given branched fault system in addition backward branching can occur in the nonuniform prestress field either driven by slip on the stem of the fault system or through a triggering mechanism these modeling results may have important implications for understanding fault branching behavior observed in the 1992 landers the 1999 hector mine and the 2002 denali fault earthquakes and for seismic hazard analysis in the areas where branched fault systems exist

mean lagrangian flow behavior on an open coast rip channeled beach a new perspective article i nfo the accepted view of rip currents is that they are an efficient mechanism for transporting material out of the surf zone previous rip current campaigns on natural beaches have focused on eulerian measurements with sparse in situ pressure and current meter arrays here for the first time spatially synoptic estimates of rip current flow patterns vorticity and lagrangian transport behavior are measured in the field using a fleet of 30 position tracking surfzone drifters during multiple rip current occurrences on an open coast beach in monterey ca contrary to the classic view shepard et al 1941 the rip current flow field consisted of semi enclosed large scale vortices that retained the drifters and resulted in a high number of lagrangian observations that are temporally and spatially repeated approximately 19 of the drifters deployed in the rip currents exited the surf zone per hour on average during the experiments the observed surf zone retention of drifters is consistent with measurements from different open coast beach rip current systems 14 at meso macrotidal truc vert france and 16 at macrotidal perranporth united kingdom the three hour average cross shore rip current velocity at monterey was 30 cm s with peak time averaged velocities of 40 60 cm s depending on wave and tidal conditions drifters that episodically exited the surf zone were transported approximately 2 surf zone widths offshore at 20 cm s published by elsevier b v

cross shore surfzone tracer dispersion in an alongshore current 1 cross shore surfzone tracer dispersion in a wave driven alongshore current is examined over a range of wave and current conditions with 6 continuous dye releases each roughly 1 2 hours in duration at huntington beach california fluorescent dye tracer released near the shoreline formed shore parallel plumes that were sampled on repeated cross shore transects with a jet ski mounted fluorometer ensemble averaged cross shore tracer concentration profiles are generally shoreline attached maximum at or near the shoreline with increasing cross shore widths and decreasing peak values with downstream distance more than a few 100 m from the source tracer is often well mixed across the surfzone i e saturated with decreasing tracer concentrations farther seaward for each release cross shore surfzone absolute diffusivities are estimated using a simple fickian diffusion solution with a no flux boundary at the shoreline and range from 0 5 2 5 m2 s 1 surfzone diffusivity scalings based on cross shore bore dispersion surfzone eddy mixing length and undertow driven shear dispersion are examined the mixing length scaling has correlation r2 0 59 and the expected best fit slope 1 indicating that horizontal rotational motions are important for cross shore tracer dispersion in the surfzone

surf zone flushing on embayed beaches 1 using a numerical model we show that the surf zone of embayed beaches systematically flushes out more floating material simulated using passive tracers than on open beaches with most exits occurring through the headland rips for obliquely incident waves a headland rip acts as a persistent conduit for transporting floating material out of the surf zone and into the inner shelf region wave angle and embayment size determine which headland rip upwave or downwave flushes out more the surf zone material for narrow embayed beaches passive drifters exit the surf zone through the upwave headland rip for wider embayed beaches the longshore current has enough room to develop and is further deflected against the downwave headland where most drifters exit the surf zone our results indicate that wave exposed rugged coasts strongly enhance exchange of floating matter e g pollutants and nutrients at the ocean continent interface

observations of basin ground motions from a dense seismic array in san jose california we installed a dense array of 41 digital seismographs in san jose california to evaluate in detail the effects of a deep sedimentary basin and shallow sedimentary deposits on earthquake ground motions this urban array is located near the eastern edge of the santa clara valley and spans the evergreen sedimentary basin identified by gravity data average station spacing is 1 km with three stations initially spaced 110 m apart despite the high noise urban environment the stations of the array successfully triggered on and recorded small local earthquakes m 2 5 2 8 at 10 25 km distance and larger regional events such as the m 5 0 bolinas earthquake 90 km distance m 4 6 5 6 earthquakes near mammoth lakes 270 km distance m 4 9 5 6 events in western nevada 420 km distance and the m 7 1 hector mine earthquake 590 km distance maps of spectral ratios across the array show that the highest amplitudes in all frequency bands studied 0 125 8 hz are generally observed at stations farther from the eastern edge of the santa clara valley larger spectral amplitudes are often observed above the western edge of the evergreen basin snapshots of the recorded wavefield crossing the array for regional events to the east reveal that large low frequency 0 125 0 5 hz arrivals after the s wave travel from south to north across the array a moving window cross correlation analysis finds that these later arrivals are surface waves traveling from the south the timing and propagation direction of these arrivals indicates that they were likely produced by scattering of incident s waves at the border of the santa clara valley to the south of the array it is remarkable that the largest low frequency phases at many of the valley sites for regional events to the east are basin surface waves coming from a direction about 70 degrees different from that of the epicenters basin surface waves emanating from the eastern edge of the valley are also identified by the cross correlation analysis

the effect of stokes drift and transient rip currents on the inner shelf part i no stratification abstractthis is part ii of a two part study focused on stokes drift and transient rip current trc effects on the unstratified part i and stratified this paper inner shelf part i focuses on funwavec coupled ocean atmosphere wave sediment transport coawst coupling and trc effects on mixing and exchange on an unstratified inner shelf here two simulations r3 and r4 are performed on a stratified inner shelf and surfzone with typical bathymetry stratification and wave conditions r3 is a coawst only simulation no trcs while r4 has funwavec coawst coupling with trcs in r4 trcs lead to patchy near surface cooling vertical isotherm displacement and increased water column mixing for both r3 and r4 the mean lagrangian circulation has two nearly isolated surfzones and inner shelf overturning circulation cells with a stronger r4 inner shelf circulation cell the r4 inner shelf vertical velocity variability is 2 3 times stronger than a simulation with trcs and no stratification relative

subsurface structure and kinematics of the calaveras hayward fault stepover from three dimensional vp and seismicity san francisco bay region california the calaveras and hayward faults are major components of the san andreas fault system in the san francisco bay region dextral slip is presumed to transfer from the calaveras fault to the hayward fault in the mission hills region an area of uplift in the contractional stepover between the two faults here the estimated deep slip rates drop from 15 to 6 mm yr on the calaveras fault and slip begins on the hayward fault at an estimated 9 mm yr a lineament of microseismicity near the mission fault links the seismicity on the calaveras and hayward faults and is presumed to be related directly to this slip transfer however geologic and seismologic evidence suggest that the mission fault may not be the source of the seismicity and that the mission fault is not playing a major role in the slip transfer we perform a joint inversion for hypocenters and the 3d p wave velocity structure of the stepover region using 477 earthquakes we find strong velocity contrasts across the calaveras and hayward faults corroborated by geologic gravity and aeromagnetic data detailed examination of two seismic lineaments in conjunction with the velocity model and independent geologic and geophysical evidence suggests that they represent the southern extension of a northeasterly dipping hayward fault that splays off the calaveras fault directly accounting for the deep slip transfer the mission fault appears to be accommodating deformation within the block between the hayward and calaveras faults thus the calaveras and hayward faults need to be considered as a single system for developing rupture scenarios for seismic hazard assessments online material 3d interactive visualizations of the mission and alum rock hypocenters

alongshore momentum balances in the nearshore the one dimensional time averaged over many wave periods along shore momentum balance between forcing by wind and breaking waves and the bottom stress is examined with field observations spanning a wide range of con ditions on a barred beach near bottom horizontal currents were measured for 2 months at 15 locations along a cross shore transect extending 750 m from the shoreline to 8 m water depth the hourly averaged bottom stress was estimated from observed currents using a quadratic drag law the wave radiation stress was estimated in 8 m depth from an array of pressure sensors and the wind stress was estimated from an anemometer at the seaward end of a nearby pier the combined wind and wave forcing integrated over the entire cross shore transect is balanced by the integrated bottom stress the wind stress contributes about one third of the forcing over the transect analysis of the momentum balances in different cross shore regions shows that in the surf zone wave forcing is much larger than wind forcing and that the bottom drag coefficient is larger in the surf zone than farther seaward consistent with earlier studies

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

modeling surf zone tracer plumes 1 waves mean currents and low frequency eddies 1 a model that accurately simulates surf zone waves mean currents and low frequency eddies is required to diagnose the mechanisms of surf zone tracer transport and dispersion in this paper a wave resolving time dependent boussinesq model is compared with waves and currents observed during five surf zone dye release experiments in a companion paper clark et al 2011 compare a coupled tracer model to the dye plume observations the boussinesq model uses observed bathymetry and incident random directionally spread waves for all five releases the model generally reproduces the observed cross shore evolution of significant wave height mean wave angle bulk directional spread mean alongshore current and the frequency dependent sea surface elevation spectra and directional moments the largest errors are near the shoreline where the bathymetry is most uncertain the model also reproduces the observed cross shore structure of rotational velocities in the infragravity 0 004 f 0 03 hz and very low frequency vlf 0 001 f 0 004 hz bands although the modeled vlf energy is 2 3 times too large similar to the observations the dominant contributions to the modeled eddy induced momentum flux are in the vlf band these eddies are elliptical near the shoreline and circular in the mid surf zone the model data agreement for sea swell waves low frequency eddies and mean currents suggests that the model is appropriate for simulating surf zone tracer transport and dispersion

active thrusting as a possible seismogenic source in sicily southern italy some insights from integrated structural kinematic and seismological data abstract this paper proposes a new seismogenic interpretation of mainland and central southern sicily based on an integrated structural kinematic seismological approach through analysis of available structural and geophysical data the tectonic setting the major kinematic units and the crust geometry of the sicilian southward verging fold and thrust belt system are schematized in sections and in map form the depth contour lines of the outermost basal thrust plane which dates back to plio pleistocene times with some evidence of holocene activity are reconstructed this plane here named sicilian basal thrust sbt emerges along the southward convex sciacca gela catania front and reaches the base of the crust at a depth of about 30 km beneath northern sicily additionally an important regional upper crust splay with the same arched shape has been identified some kilometres northward in order to detect any possible indication of seismogenic activity linked to ongoing deformation of the sbt and its splay we analyzed the distribution and kinematics of the instrumental seismicity in the period between 1981 and 2006 particular attention was given to the background seismicity ml up to 4 6 located beneath the sedimentary cover at mt etna as it allows individuating a northward deepening seismogenic volume undergoing an average n s compression which corresponds well with the sbt geometry in section view a merged dataset of all the known major historical and instrumental events moment magnitude 4 5 that occurred above the sbt 0 to 30 km depth contour lines from 217 b c to 2006 was compiled and analyzed based on information from instrumental data and or on speculations on the shape and extent of the historical earthquake macroseismic fields two major ranges of hypocentral depths have been schematically identified within the merged dataset an upper crust range in average