local site effects in atakoy istanbul turkey due to a future large earthquake in the marmara sea summary since the 1999 izmit and duzce earthquakes in northwest turkey many seismic hazard studies have focused on the city of istanbul an important issue in this respect is local site effects strong amplifications are expected at a number of locations due to the local geological conditions in this study we estimate the local site effects in the atakoy area southwestern istanbul by applying several techniques using synthetic data hybrid 3 d modelling and 1 d modelling and comparing to empirical data we apply a hybrid 3 d finite difference method that combines a complex source and wave propagation for a regional 1 d velocity model with site effects calculated for a local 3 d velocity structure the local velocity model is built from geological geotechnical and geomorphological data the results indicate that strongest spectral amplifi cations sa in the atakoy area occur around 1 hz and that amplification levels are largest for alluvial sites where sa reaching a factor of 1 5 2 can be expected in the case of a large earth quake we also compare our results to h v horizontal to vertical component of the recorded signal spectral ratios calculated for microtremor data recorded at 30 sites as well as to ambient noise synthetics simulated using a 1 d approach because the applied methods complement each other they provide comprehensive and reliable information about the local site effects in atakoy added to that our results have significant implications for the southwestern parts of istanbul built on similar geological formations for which therefore similar sa levels are expected

horizontal to vertical spectral ratio and geological conditions the case of garner valley downhole array in southern california the aim of the present article is to further check the use of the hori zontal to vertical h v spectral ratio which has been recently suggested as an indi cator of site effects the data set consists of 1 t0 three component high sensitivity accelerograms recorded at five different depths by the garner valley downhole array gvda in southern california with peak ground accelerations 0 0002 g ag 0 04 g magnitudes 3 0 ml 4 6 and hypocentral distances 16 km r 107 km first the stability of the h v spectral ratio is investigated by computing the mean for the whole data set in different depths the h v spectral ratio on the surface is compared with the surface to depth standard spectral ratio with theoretical s wave transfer functions derived from the vertical geotechnical profile as well as with the h v spectral ratio of synthetic accelerograms generated by the discrete wavenumber method both theoretical and experimental data show a good stability of the h v spectral ratio shape which is in good agreement with the local geological structure and is insensitive to the source location and mechanism however the absolute level of the h v spectral ratio depends on the wave field and is different from the surface to depth spectral ratio consequently the h v spectral ratio tech nique provides only partially the information that can be obtained from a downhole array but surface to depth ratios may also be misleading because they combine effects at surface and at depth

a pressure solution creep law for quartz from indentation experiments 1 indenter experiments have been performed on quartz crystals in order to establish a pressure solution creep law relevant at upper to middle crustal conditions this deformation mechanism contributes to earth s crust geodynamics controlling processes as different as fault permeability strength and stress evolution during interseismic periods or mechanochemical differentiation during diagenesis and metamorphism indenter experiments have been performed at 350 c and 20 120 mpa during months with differential stress varying from 25 to 350 mpa several experimental parameters were varied nature of quartz synthetic or natural nature of fluid manner in which the solid solution solid interface was filled and orientation of the indented surfaces versus quartz crystallographic c axis significant strain rates could only be obtained when using high solubility solutions naoh 1 mol l 1 displacement rates of the indenter were found activated by differential stress with exponential dependence as theoretically predicted the mean thickness of the trapped fluid phase below the indenter was estimated in the range 2 10 nm moreover the development of this trapped fluid phase was relatively fast and allowed fluid penetration into previously dry contact regions by marginal dissolution the indenter displacement rate was driven by differential stress and its kinetics was controlled by diffusion along the trapped fluid and the development of a morphological roughness along the interface conversely marginal strain energy driven dissolution was observed around the indenter and its kinetics was controlled by free surface reaction these experimental results are applied to model the interactions between pressure solution and brittle processes in fault zones providing characteristic time scales for postseismic transitory creep and sealing processes in quartz rich rocks

can broad band earthquake site responses be predicted by the ambient noise spectral ratio insight from observations at two sedimentary basins site effect assessments performed through earthquake based approaches such as the standard spectral ratio ssr require good quality records of numerous earthquakes in contrast the use of ambient noise appears to be an attractive solution for ease and rapid computation of site responses with sufficient spatial resolution microzonation especially in low seismicity areas two main approaches are tested here the horizontal to vertical spectral ratio hvsr and the noise based ssr ssrn the hvsr uses the relative amplitude of the horizontal and vertical components of the ambient noise instead the ssrn defines the spectral ratio between the seismic noise recorded simultaneously at a site and at a rock reference station similar to earthquake based ssr while the hvsr is currently used in hundreds of site specific studies the ssrn approach has been gradually abandoned since the 1990s in this study we compare the results obtain from these two approaches with those of earthquake based ssr this comparison is carried out for two sedimentary basins in provence southeastern france and in argostoli western greece in agreement with the literature the hvsr does not provide more than the fundamental resonance frequency of the site f0 the ssrn leads to overestimation of the ssr amplification factors for frequencies higher than the minimal f0 of the basin f0min this discrepancy between ssrn and ssr is discussed and appears to be mainly dependent on the local geological configuration we thus introduce the hybrid standard spectral ratio ssrh approach which aims to improve upon the ssrn by adding an intermediate station inside the basin for which the ssr is known this station is used in turn as a local reference inside the basin for the ssrn computation the ssrh provides site transfer functions very similar to those of the ssr in a broad frequency range based on these results the ssrn or ssrh should be further tested and should receive renewed attention for microzonation inside sedimentary basins

a comparison and test of various site response estimation techniques including three that are not reference site dependent abstract we compare various site response estimation techniques using after shock data of the 1989 loma prieta earthquake collected in oakland california because of recent interest in comparing results from weak and strong motion to infer any nonlinearity and between direct s and coda waves we pay particular attention to the uncertainties first sediment to bedrock spectral ratio estimates between pairs of sites are compared with those obtained from various generalized inversion approaches where the source and site effects of multiply recorded events are solved for simultaneously we find that the site amplification factors are very similar among these approaches but that the uncertainties can be significantly different depending on how the data are weighted we also examine and test three site response estimation techniques that do not rely on a reference site to estimate source and path effects the first involves a parameterized source and path effects inversion even when the bedrock data are excluded from consideration this approach is found to reveal the frequency dependence of site response at each of the sediment sites the second technique involves taking horizontal to vertical component spectral ratios receiver function type estimates of shear wave aftershock data these are also found to reveal the frequency dependence of site response at the sediment sites and the results for the bedrock site are relatively flat and near unity the third estimate is formed by taking horizontal to vertical component ratios of ambient seismic noise and these are shown to reveal the fundamental resonant frequency of the sediment sites unfortunately discrepancies exist among all of the site response estimates and with one dimensional predictions with respect to a frequency independent scaling factor nevertheless the highly frequency dependent character of site response is well constrained and the fact that non reference site dependent methods are capable of revealing this is promising for site specific hazard assessments in regions that lack adequate reference sites

microtremors as a geophysical exploration tool applications and limitations the usefulness of microtremors as a geophysical exploration tool has been analyzed this application is possible due to the relationship between the main resonance frequency of a given soil obtained from the h v spectral ratios of microtremors its thickness and average shear velocity we first measured the ambient noise at 33 sites and determined their main resonance frequency detailed geotechnical information was available for 23 of the sites thereby allowing us to establish a quantitative relationship between the resonance frequency and the thickness of the soil and indirectly between either of them and the shear velocity of the soil the practical application of this relationship has revealed its usefulness in determining the surface structure of a valley with excellent accuracy with an error of only 15 in the depths calculated these errors are due to the simplification of the problem that this method implies it requires that the shear velocity vary constantly with depth throughout the study region which is evidently not always so and that the input data themselves intrinsically have a certain degree of uncertainty this method is therefore not valid when there is no mechanical contrast between the study soil and the underlying layer or when the shear velocity varies irregularly with depth in the study area

an evaluation on h v ratio vs spectral ratio for site response estimation using the 1994 northridge earthquake sequences the applicability of the single station h v method based on the spectral ratio between the horizontal and the vertical components of strong ground motions is examined for site response estimation using the high quality data from the 1994 northridge earthquake sequence instead of using rayleigh wave data from microtremors the large amplitude wave part of the s wave data is used and based on the 1994 northridge mainshock and aftershock recordings we have found that upon averaging over a number of recordings for a given station the station site responses derived both from the single station h v ratio and from the standard spectral ratio with respect to a reference rock site station are sufficiently close for practical purposes we therefore conclude that the h v ratio can reasonably predict the resonant frequency and the amplification level of a site response especially for sites in the neighborhood of the epicenters in the absence of a reference rock site station the h v ratio provides a practical alternative to the standard site response estimation

advances in swash zone research small scale hydrodynamic and sediment transport processes abstract extensive research efforts in the last decade have improved knowledge of swash zone processes this paper reviews and synthesizes from 2004 onward the research advances of small scale hydrodynamics and sediment transport processes considering field laboratory and numerical modeling efforts swash zone hydrodynamics are examined by means of shoreline motions fluid velocities pressure gradients flow structure bed shear stress friction coefficients and turbulence subsequently advances related to sediment transport mechanisms and morphological changes are described detailed descriptions of measuring techniques novel findings and the strengths and weaknesses of the different approaches are discussed the review also acknowledges the major advances in the development of instrumentation to collect highly resolved flow and sediment concentration measurements in direct proximity of the bed and the experimental framework for analyzing local dynamics on a wave by wave time scale e g dam break

on the role of infiltration and exfiltration in swash zone boundary layer dynamics boundary layer dynamics are investigated using a 2 d numerical model that solves the volume averaged reynolds averaged navier stokes equations with a vof tracking scheme and a k turbulence closure the model is validated with highly resolved data of dam break driven swash flows over gravel impermeable and permeable beds the spatial gradients of the velocity bed shear stress and turbulence intensity terms are investigated with reference to bottom boundary layer bl dynamics numerical results show that the mean vorticity responds to flow divergence convergence at the surface that result from accelerating decelerating portions of the flow bed shear stress and sinking injection of turbulence due to infiltration exfiltration hence the zero up crossing of the vorticity is employed as a proxy of the bl thickness inside the shallow swash zone flows during the uprush phase the bl develops almost instantaneously with bore arrival and fluctuates below the surface due to flow instabilities and related horizontal straining in contrast during the backwash phase the bl grows quasi linearly with less influence of surface induced forces however the infiltration produces a reduction of the maximum excursion and duration of the swash event these effects have important implications for the bl development the numerical results suggest that the bl growth rate deviates rapidly from a quasi linear trend if the infiltration is dominant during the initial backwash phase and the flat plate boundary layer theory may no longer be applicable under these conditions

sand transport processes and bed level changes induced by two alternating laboratory swash events abstract sand transport processes and net transport rates are studied in a large scale laboratory swash zone bichromatic waves with a phase modulation were generated producing two continuously alternating swash events that have similar offshore wave statistics but which differ in terms of wave swash interactions measured sand suspension and sheet flow dynamics show strong temporal and spatial variability related to variations in flow velocity and locations of wave capture and wave backwash interactions suspended and sheet flow layer transport rates in the lower swash zone are generally of same magnitude but sheet flow exceeds the suspended load transport by up to a factor four during the early uprush the bed level near the inner surf zone is relatively steady during a swash cycle but changes of o cm s are measured near the mid swash zone where wave swash interactions lead to strongly non uniform flows the two alternating swash events produce a dynamic equilibrium with bed level changes up to a few mm induced by single swash events but with net morphodynamic change over multiple events that is two orders of magnitude lower most of the intra swash and the single event averaged bed level changes in the swash zone are caused by a redistribution of sediment within the swash the transport of sediment across the surf swash boundary is minor at intra swash time scale but becomes increasingly significant at swash averaged time scales or longer i e averaged over multiple swash events

direct bed shear stress measurements in bore driven swash direct measurements of bed shear in the swash zone are presented the data were obtained using a shear plate in medium and large scale laboratory bore driven swash and cover a wide range of bed roughness data were obtained across the full width of the swash zone and are contrasted with data from the inner surf zone estimates of the flow velocities through the full swash cycle were obtained through numerical modelling and calibrated against measured velocity data the measured stresses and calculated flow velocities were subsequently used to back calculate instantaneous local skin friction coefficients using the quadratic drag law the data show rapid temporal variation of the bed shear stress through the leading edge of the uprush which is typically two four times greater than the backwash shear stresses at corresponding flow velocity the measurements indicate strong temporal variation in the skin friction coefficient particularly in the backwash the general behaviour of the skin friction coefficient with reynolds number is consistent with classical theory for certain stages of the swash cycle a spatial variation in skin friction coefficient is also identified which is greatest across the surf swash boundary and likely related to variations in local turbulent intensities skin friction coefficients during the uprush are approximately twice those in the backwash at corresponding reynolds number and cross shore location it is suggested that this is a result of the no slip condition at the tip leading to a continually developing leading edge and boundary layer into which high velocity fluid and momentum are constantly injected from the flow behind and above the tip region finally the measured stress data are used to determine the asymmetry and cross shore variation in potential sediment transport predicted by three forms of sediment transport formulae crown copyright c 2009 published by elsevier b v all rights reserved

understanding of slip weakening and strengthening in a single framework of modeling and its seismological implications 1 we theoretically study dynamic fault slip taking account of thermoporoelastic effects including inelastic porosity change the porosity on the fault is assumed to increase inelastically with increasing fault slip we find in the analysis of a 1d fault model that qualitative nature of system behavior is controlled by a single nondimensional parameter su a quantity proportional to the increase rate of inelastic porosity divided by the thickness of shear heating zone the change of value of su is found to cause slip weakening as well as slip strengthening it is reported in some studies that the radiation efficiency estimated seismologically exceeds unity for some earthquakes which contradicts its definition this paradox can be solved if we assume a relatively large su value for these earthquakes

hydrodynamics and sediment transport in the swash zone a review and perspectives the dominant hydrodynamic forcing and resulting sediment transport mechanisms in the swash zone are reviewed combined with a discussion of future measurement and modelling requirements the importance of swash zone processes in the overall behaviour of the nearshore littoral zone are identified with the paper subsequently focusing on aspects that directly relate to sediment transport on beaches the review considers analytical and numerical modelling work and both field and laboratory data the hydrodynamics of the swash zone are first discussed with reference to the surf zone boundary swash characteristics forcing mechanisms and shoreline oscillations subsequent sections consider more micro scale processes such as the internal flow kinematics turbulence the bed boundary layer and infiltration exfiltration through permeable beds the second part of the paper outlines the fundamental mechanics of sediment transport in the swash zone followed by a more detailed discussion of sediment transport modes induced by the dominant hydrodynamic conditions modelling concepts are reviewed and the strengths and weaknesses of different approaches identified a final summary and future modelling perspectives conclude the paper

surface soil effects study using short period microtremor observations in almeria city southern spain in almeria city large earthquakes occurred and many buildings were completely destroyed in these historical earthquakes the actual population of almeria city is about 200 000 people this population is rapidly increasing and new urbanizing areas are growing to the eastern part of the city where they are located in softer soil conditions consequently the evaluation of surface soil conditions is very important from a standpoint of earthquake disaster mitigation we have obtained a landform classification map developed by analysing aerial photos large scale topographic maps and 80 borehole data eleven unit areas which have different soil conditions were inferred from this research also s wave velocity prospecting tests were carried out at several sites within the city the shear velocity values of the ground vary from 1689 m s in hard rock to 298 m s in soft soil these results are useful for understanding the uppermost soil characteristics and are used for soil classification finally short period microtremor observations were densely carried out in the research area and nakamura s method 1989 was applied for determining predominant periods microtremors were observed at about 173 sites with mainly 400 m interval in rock sites and 200 m interval in relatively soft soil sites from the result of these microtremor measurements the predominant period determined at rock site in the western part of the city and historic area is very short about 0 1 s and very stable however at soft soil sites in the center of the city near zapillo beach and in the newly developed urban area the predominant period is about 1 0 s and even larger in concordance with the geological conditions finally at medium soil sites in the eastern part of the city the predominant period is about 0 4 s and it appears very stable in the whole region the difference of predominant periods between hard rock and soft soil sites is very clear and it has been observed that the distribution of predominant periods depends heavily on the surface soil conditions

modeling fluid transfer along california faults when integrating pressure solution crack sealing and compaction processes 1 several models pertaining to earthquake cycles imply intermittent fluid flow through fault during the interseismic period increase in fluid pressure from hydrostatic to lithostatic values is a crucial parameter in mechanisms leading to earthquakes to achieve such pressures geodynamic processes gouge compaction fluid flow and changes in permeability are required previous models have postulated that changes in permeability by self healing are faster than the effects of geodynamic processes we consider the different mechanisms and rates of crack sealing near active fault on the examples of uplifted californian faults we find that natural crack sealing is normally not achieved by a rapid self healing process pressure solution with mass transfer from solution cleavage to cracks appears to be a more important mechanism for crack sealing and creep during postseismic deformation the geometry of transfer path and experimental data have been used to model crack sealing rates by pressure solution which are estimated to be rather slow similar to the recurrence time of some earthquakes such slow changes in permeability may be crucial factors in controlling the increase in fluid pressure and consequently the mechanism of critical failure in faults then numerical modeling of fluid pressure and transfer around active faults has been performed integrating a slow change in permeability by crack sealing gouge compaction and fluid flow from depth this modeling shows various location and evolution of fluid overpressure during the interseismic period depending on these processes and allows one to estimate the amount of fluid transferred from depth during interseismic periods

using microtremors to assess potential earthquake site response a case study in flushing meadows new york city abstract we have used portable 5 sec period seismometers to record ambient noise across a glacially cut valley filled with unconsolidated holocene sediments the valley located in flushing meadows new york city is surrounded by a densely populated urban environment microtremors were recorded at several sites on and adjacent to the valley while some raw spectra of valley site microtremors exhibit no predominant peaks spectral ratios taken with respect to recordings made at a reference station outside the valley show a sharp peak near 0 8 hz a secondary peak near 2 4 hz is also visible in some of the spectral ratios the frequency of the predominant peak remains constant across the valley width while the relative amplitude decreases systematically from a maximum at the valley center to background levels near the valley edge resonant frequencies predicted by one dimensional modeling of the valley center site response show excellent agreement with observations the 0 8 hz spectral ratio peak is interpreted as the fundamental resonance mode and the 2 4 hz peak is interpreted as the first harmonic of the region above the base of an organic clay layer observed in borehole data the amplification factors implied by the observed spectral ratios are unrealistically high up to 100 which can be attributed to the close proximity of microtremor sources an experiment involving the use of a pile driver source located outside the valley was also performed signals obtained at valley sites during times when the pile driver was in operation show a two fold increase in the amplitude of a spectral peak when compared to signals obtained when the pile driver was turned off this observation gives additional evidence that observed spectral peaks represent soil layer resonances in the valley based on the results of this and other previous studies we conclude that easily obtained microtremor measurements can contribute valuable microzonation and site response information to a study of regional earthquake hazard

interseismic pore compaction suppresses earthquake occurrence and causes faster apparent fault loading 1 physical and chemical processes operating on faults during interseismic periods are important for earthquake generation in this study we focus on pore compaction within fault zones driven by chemical kinetic effects one established model of compaction causes an increase of pore fluid pressure almost linearly with time if fluid diffusion is neglected we introduced it into a simple numerical model for earthquake cycles and found that this effect can drastically change the recurrence of earthquakes 1 it gradually stabilizes the fault and eventually suppresses earthquake occurrence 2 it surprisingly causes faster apparent fault loading furthermore we developed an expression for the apparent loading velocity and checked that it is consistent with the results of numerical calculations we also extended the expression for the apparent loading velocity to include the effect of pore dilatancy this apparent loading would not only appear in a simple elastic system with a single degree of freedom but also in complicated systems that involve simulations of realistic earthquake cycles

advances in numerical modelling of swash zone dynamics we present a comprehensive and critical review of work on the numerical modelling of swash zone processes between 2005 and 2015 a wide range of numerical models has been employed for the study of this region and hence only phase resolving approaches i e depth averaged and depth resolving models are analyzed the current advances in the modelling of swash zone processes are illustrated by comparing different numerical models against laboratory experiments of a dam break driven swash event depth averaged and depth resolving models describe well the swash flow for both coarse sand and gravel impermeable beach cases depth averaged models provides a practical tool for engineering use whereas depth resolving models improve the flow description especially for the backwash phase with a significantly higher computational cost the evolution and magnitude of bed shear stresses predicted by all models is reasonable when compared with laboratory estimates based on the log law however differences between modelling approaches cannot be rigorously evaluated owing to the uncertainty in shear stress estimates while employing such approximation furthermore small scale processes such as turbulence evolution are investigated with depth resolving models finding differences between the two dimensional and three dimensional approaches numerical models allow us to investigate other processes such as beach morphology changes the evolution of the turbulence coherent structures and the infiltration exfiltration effects on the swash flow a discussion on the advantages and limitations of each model is presented the future of swash zone modelling depends on the increase of the computational power and more importantly on the improvement of the current capability to obtain intra wave measurements for model validation calibration and greater resolution of physical processes

seismic microzonation in australia abstract since the 1980s seismic microzonation studies have been undertaken in australia to assess the likely effects of earthquakes on urban centres built on unconsolidated sediments presently the nakamura method is used for processing data so far parts of perth adelaide cairns gladstone rockhampton newcastle sydney and launceston have been zoned the launceston tasmania study was the pilot study for many of these as it refined the methodology used and the data obtained were incorporated into a gis database building heights and site factor zoning maps were produced for the launceston city council one of the major activities of the new initiative by the australian geological survey organisation agso popularly known as the cities project is coordinating seismic microzonation throughout australia microzonation data have been included in agso s geohazards gis database this is helping local councils zone land for seismic hazards state emergency services use the information to plan for emergencies resulting from the effects of earthquakes these practical applications of seismic microzonation data will help mitigate the destructive effects of any future large earthquakes occurring near major urban centres in the launceston case it was found that there is a variable risk dependant on epicentral distance and the nature of relatively unconsolidated sediments in various parts of the city disastrous amplification could occur at some sites

the swash of solitary waves on a plane beach flow evolution bed shear stress and run up the swash of solitary waves on a plane beach is studied using large scale experiments ten wave cases are examined which range from non breaking waves to plunging breakers the focus of this study is on the influence of breaker type on flow evolution spatiotemporal variations of bed shear stresses and run up measurements are made of the local water depths flow velocities and bed shear stresses using a shear plate sensor at various locations in the swash zone the bed shear stress is significant near the tip of the swash during uprush and in the shallow flow during the later stages of downrush in between the flow evolution is dominated by gravity and follows an explicit solution to the nonlinear shallow water equations i e the flow due to a dam break on a slope the controlling scale of the flow evolution is the initial velocity of the shoreline immediately following waveform collapse which can be predicted by measurements of wave height prior to breaking but also shows an additional dependence on breaker type the maximum onshore directed bed shear stress increases significantly onshore of the stillwater shoreline for non breaking waves and onshore of the waveform collapse point for breaking waves a new normalization for the bed shear stress which uses the initial shoreline velocity is presented under this normalization the variation of the maximum magnitudes of the bed shear stress with distance along the beach which is normalized using the run up follows the same trend for different breaker types for the uprush the maximum dimensionless bed shear stress is approximately 0 01 whereas for the downrush it is approximately 0 002

laboratory scale swash flows generated by a non breaking solitary wave on a steep slope the main goal of this paper is to provide insights into swash flow dynamics generated by a non breaking solitary wave on a steep slope both laboratory experiments and numerical simulations are conducted to investigate the details of runup and rundown processes special attention is given to the evolution of the bottom boundary layer over the slope in terms of flow separation vortex formation and the development of a hydraulic jump during the rundown phase laboratory experiments were performed to measure the flow velocity fields by means of high speed particle image velocimetry hspiv detailed pathline patterns of the swash flows and free surface profiles were also visualized highly resolved computational fluid dynamics cfd simulations were carried out numerical results are compared with laboratory measurements with a focus on the velocities inside the boundary layer the overall agreement is excellent during the initial stage of the runup process however discrepancies in the model data comparison grow as time advances because the numerical model does not simulate the shoreline dynamics accurately introducing small temporal and spatial shifts in the comparison yields adequate agreement during the entire rundown process highly resolved numerical solutions are used to study physical variables that are not measured in laboratory experiments e g pressure field and bottom shear stress it is shown that the main mechanism for vortex shedding is correlated with the large pressure gradient along the slope as the rundown flow transitions from supercritical to subcritical under the developing hydraulic jump furthermore the bottom shear stress analysis indicates that the largest values occur at the shoreline and that the relatively large bottom shear stress also takes place within the supercritical flow region being associated with the backwash vortex system rather than the plunging wave it is clearly demonstrated that the combination of laboratory observations and numerical simulations have indeed provided significant insights into the swash flow processes

site response evaluation using the h v ratio at the yan liau station in hualien taiwan four days after the december 13 1990 hualien taiwan earthquake m l 6 9 a temporary array of fifteen triaxial digital accelerographs was deployed in the epicenter area to monitor aftershocks approximately 600 earthquakes triggered this array during the three month deployment period the yan liau station s63 alone recorded 162 events most of the accelerograms at s63 exhibit resonance we have estimated site responses at the yan liau station using both the single station spectral ratio or h v ratio method and the traditional spectral ratio method that compares ratios at a soil site with those at a reference hard rock site based on site response analyses of s waves and coda waves of ground motion recordings both types of waves show that the h v ratio provide a good estimate at the resonant frequency although the site amplification factor is overestimated in addition the study of microtremor is also a good alternate for estimating the site predominant frequency while the ground acceleration or pga gradually increases the resonant frequency shifts to lower frequencies

distribution of ground motion intensity inferred from questionnaire survey earthquake recordings and microtremor measurements a case study in christchurch new zealand during the 1994 arthurs pass earthquake the areal distribution of seismic ground motion intensity in the city of christchurch new zealand during the 1994 arthurs pass earthquake ml 6 6 was evaluated using an intensity questionnaire together with local site amplifications inferred from seismic recordings and microtremors in order to estimate the intensity in parts of the city where no intensity data were available intensity data were compared to relative levels of shaking determined from both weak motion and microtremor recordings weak ground motion amplification factors were determined using ratios of ground accelerations at five sediment sites with respect to a rock site microtremor amplification factors were determined from horizontal to vertical spectral ratios at a 1 km spacing throughout the city a positive correlation between weak motion and microtremor amplification factors allowed extrapolation of microtremor amplification to estimated mm intensity emmi emmi ranged from 3 to 6 and was consistent with the questionnaire intensity and geological conditions and showed detailed information on the areal distribution of ground motion intensity in the city

assessment of seismic site conditions a case study from guwahati city northeast india the 1897 great shillong earthquake revealed considerable seismic susceptibility in guwahati city such as soil liquefaction landslides and surface fissures in an attempt to quantify the seismic vulnerability of the city based on geological seismological and geotechnical aspects concerning seismic site characterization in depth analysis was performed using a microtremor survey with recordings of five small to moderate magnitude 4 8 mb 5 4 earthquakes that occurred in 2006 and geotechnical investigations using the standard penetration test spt additionally the basement topography was established using vertical electrical resistivity sounding and selected drill hole information region specific relationships are derived by correlating the estimated values of predominant frequency shear wave velocity and basement depth indicating conformity with the predominant frequency distribution and the basin topography underlain by a hard granitic basement most parts of the city adhere to the predominant frequency range of 0 5 3 5 hz setting aside areas of deep sediment fills or hilly tracts suggesting that the existing moderate rise rc buildings in the territory are seismically vulnerable furthermore the geotechnical assessment of the soil liquefaction potential reveals widespread susceptibility across the terrain eventually a site classification map of the city is prepared following the national earthquake hazard program nehrp provision the average site amplification factor from geotechnical modeling for site class d is about 3 in the frequency range of 2 4 hz in addition earthquake data yield an average site amplification factor of 4 6 in the frequency range of 1 2 5 0 hz at the seismic stations located in site class e and f high site amplifications of around 5 5 and 7 5 at 2 hz respectively are observed at amtron and irrig seismic stations which are located in the proximity of precambrian rocks indicating probable basin edge effects scattering and diffraction of incident energy interplay of dispersed valleys surrounded by small hillocks in the study region is likely to induce micro basin effects where the sediment thickness depth vis a vis predominant frequency and basin geometry in conjunction play pivotal roles in the augmentation of site response

modeling swash zone hydrodynamics and shear stresses on planar slopes using reynolds averaged navier stokes equations 1 a numerical model solving the reynolds averaged navier stokes equations with a volume of fluid tracking scheme and turbulence closure is employed for estimating hydrodynamics in the swash zone model results for run up distance water depth and near bed velocity are highly correlated r2 0 97 with ensemble averaged dam break driven swash data moreover modeled bed shear stresses are within 20 of estimates derived from measured velocity profiles dam break driven swash simulations are conducted to determine the effect of foreshore characteristics bed roughness and foreshore slope on bore induced swash zone hydrodynamics and bed shear stresses numerical results revealed that the boundary layer vanishes during flow reversal grows during the backwash and becomes depth limited at the end of the swash cycle in general the uprush experiences larger shear stresses but for a shorter duration than the backwash some variability in this pattern is observed depending on the bed roughness foreshore slope and cross slope location in the swash zone implying that large spatial gradients in shear stresses can occur on the foreshore the mean tangential force per unit area supplied to the bed is offshore directed for the simulated cases with the exception of the mild slope 1 25 cases owing to the skewed nature of swash flows the temporal evolution of the momentum balance inside the swash zone shows an important contribution to the total force from turbulence and advection at the early final stage of the swash cycle whereas the local acceleration does not appear to be a significant contribution

site response for urban los angeles using aftershocks of the northridge earthquake ground motion records from aftershocks of the 1994 northridge earthquake are used to estimate site response in the urban los angeles area over 1300 shear wave records from 61 sources and 90 sites are used in a linear inversion for source and site response spectra the methodology makes no assumptions about the shape of the source spectrum to obtain a stable unique inverse a q model and geometrical spreading factor are assumed in addition the site response at a hard rock site is constrained to be approximately 1 0 with a kappa of 0 02 the site response spectra compare favorably with the results of previous and on going investigations in los angeles a couple of first order effects are lower site response in the surrounding mountains dominated by mesozoic and tertiary rocks and higher values in the san fernando and los angeles basins containing surficial pleistocene and holocene alluvial deposits results show good correlation of high site response spectral values with localized areas of severe damage interstate 10 collapse sherman oaks northridge interstate 5 14 collapse however widespread trends in site response across the sedimentary basins are not obvious the data suggest that site responses are lower near the southern margin of the san fernando valley for sources to the north due to north dipping sedimentary structures but the general pattern of site response is characterized by high variability on length scales less than a kilometer variations of a factor of 2 in site response are observed over the length scale of 200 m and for the same surficial geologic unit for some of the alluvial basin sites surface wave generation is a significant contributor to elevated site response at lower frequencies below 2 hz the total damage pattern for the northridge earthquake is influenced by strong source directivity to the north and strong local site effects the correlation of weak motion site response estimates with areas of significant damage demonstrates the value of these field measurements in future urban planning and in the reduction of seismic risk in urban areas

variability of site response in seattle washington ground motion from local earthquakes and the ships seismic hazards investigation in puget sound experiment is used to estimate site amplification factors in seattle earthquake and ships records are analyzed by two methods 1 spectral ratios relative to a nearby site on tertiary sandstone and 2 a source site spectral inversion technique our results show site amplifications between 3 and 4 below 5 hz for west seattle relative to tertiary rock these values are approximately 30 lower than amplification in the duwamish valley on artificial fill but significantly higher than the calculated range of 2 to 2 5 below 5 hz for the till covered hills east of downtown seattle although spectral amplitudes are only 30 higher in the duwamish valley compared to west seattle the duration of long period ground motion is significantly greater on the artificial fill sites using a three dimensional displacement response spectrum measure that includes the effects of ground motion duration values in the duwamish valley are 2 to 3 times greater than west seattle these calculations and estimates of site response as a function of receiver azimuth point out the importance of trapped surface wave energy within the shallow low velocity sedimentary layers of the duwamish valley one dimensional velocity models yield spectral amplification factors close to the observations for till sites east of downtown seattle and the duwamish valley but underpredict amplifications by a factor of 2 in west seattle a two dimensional finite difference model does equally well for the till sites and the duwamish valley and also yields duration estimates consistent with the observations for the duwamish valley the two dimensional model however still underpredicts amplification in west seattle by up to a factor of 2 this discrepancy is attributed to 3d effects including basin edge induced surface waves and basin geometry focusing effects caused by the proximity of the seattle thrust fault and the sediment filled seattle basin

laboratory observations of flow and sediment transport induced by plunging regular waves 1 two parallel experiments involving the evolution and runup induced by plunging regular waves near the shoreline of a sloping bed are considered 1 a rigid bed experiment allowing direct hot film measurements of bed shear stresses and 2 a sediment bed experiment allowing for the measurement of pore water pressures as well as observation of sediment suspension and bed morphological changes both experiments utilize the same initial bed profile and wave forcing the experiments show that the mean bed shear stresses experienced onshore of incipient breaking are amplified by nearly a factor of 2 relative to prebreaking conditions whereas their corresponding turbulent fluctuations are amplified even more strongly by a factor of 5 6 the plunging processes lead to a series of vortices whose formation may be explained as the result of shear layer instability measurements show that these vortices can significantly enhance peaks in the offshore directed bed shear stresses moreover near bed pore pressure measurements indicate that these vortices cause large upward directed pressure gradients which in turn produce a corresponding series of suspended sediment plumes shoreward of the initial breaking event these findings are related to the induced morphological changes over both short and long time scales the present results are also compared and contrasted with previous experiments utilizing a similar methodology but involving plunging solitary waves

simulating coastal engineering processes with openfoam abstract in the present work the openfoam newly developed wave generation and active absorption boundary condition presented in the companion paper higuera et al submitted for publication is validated in order to do so the simulation of some of the most interesting physical processes in coastal engineering is carried out and comparisons with relevant experimental benchmark cases presented water waves are found to be generated realistically and agreement between laboratory and numerical data is very high regarding wave breaking run up and undertow currents

microtremor survey in talchir india to ascertain its basin characteristics in terms of predominant frequency by nakamura s ratio technique abstract the talchir basin one of india s oldest basins has been a subject of interest because of its rich coal deposits the maximum thickness of the basin is about 1500 m beyond the basin is the hard metamorphic rocks of precambrian age the ambient noise survey data have been analyzed for the talchir basin using nakamura s technique of horizontal vertical spectral ratio hvsr to ascertain the basin structure in terms of the predominant frequency the predominant frequency varies from 0 25 hz to 7 8 hz but a major portion of the basin comes under the range of 0 3 hz 2 4 hz while on the metamorphic rocks it is as high as 7 8 hz the variation in predominant frequency shows a good correlation with the sediment thickness of the basin the results have been compared with the previous studies by other researchers and it shows consistency with the northerly dip of the basin the present study has also been compared with the results of the synthetic seismogram that was performed for the talchir basin the predominant frequency obtained from hvsr technique complements well with the frequency at which the peak response spectra ratio is observed the present study of the predominant frequency identifies quite well the characteristics of talchir basin and is in good agreement with the synthetic ground motion modeling of the region

investigation of breaking and non breaking solitary waves and measurements of swash zone dynamics on a 5 beach abstract this study presents an experimental investigation of plunging breakers on a sloping beach with an inclination of 5 1 the incident waves are solitary waves with various amplitudes from non breaking waves to plunging breakers and the area investigated is the swash zone piv particle image velocimetry is performed on images captured at four different field of views fov shoreline position and maximum runup are measured and are repeatable in both time and height although cross sectional variations of the shoreline shape are observed at maximum runup for non breaking waves the runup and fluid flow is computed by a boundary integral technique combined with a boundary layer model then there is excellent agreement between the experimental and the computed velocity profiles at the lower region of the beach while the boundary integral technique overpredicts the maximum runup height severely for breaking waves the experiments indicate that the motion becomes more irregular as we move further up the beach in addition there are more irregularities present for waves with larger amplitude length and velocity of air bubbles entrapped by the plunging breakers are extracted from an image series captured with a large fov the images showed that a large air bubble remains intact for a time period during runup for the breaking waves

explosion earthquake and ambient noise recordings in a pliocene sediment filled valley inferences on seismic response properties by reference and non reference site techniques abstract explosion earthquake and ambient noise recordings were collected at the eastern edge of a pliocene sediment filled valley nearby the town of san casciano dei bagni tuscany central italy the anomalous amplification of amplitudes as high as a factor of 20 between sediment and hard rock sites shown by classical spectral ratios were compared with results obtained by using non reference site techniques like that of nakamura 1989 and its receiver function like extension the explosion data were collected in june 1990 as part of a crustal refraction experiment carried out in the monti vulsini volcanic area a linear array of 13 digital stations was deployed orthogonally to the eastern border of the radicofani graben 2 stations were set up on a bedrock outcrop whereas the remaining 11 were deployed on soft sediments 100 m apart along a straight line toward the center of the valley during a second part of the study two stations were left in the field to record local and regional seismicity acquiring data from more than 150 events from a seismic swarm that occurred in the monti vulsini volcanic area in february 1992 with a maximum magnitude m d 3 8 spectral ratios were computed on the 41 strongest events showing a seismic response consistent with that computed using explosion data at least in the 0 5 to 4 hz frequency band non reference site techniques were employed to analyze earthquake and noise data although it is clear that the horizontal vertical h v spectral ratios describe some intrinsic properties of sites noise and earthquake data give equivalent results in our case they failed in recognizing both resonances and amplification levels large amplifications shown by classical spectral ratios were probably due to basin induced surface waves and 3d resonances seismic waves recorded by a small 50m radius 2d array deployed within the valley provided instrumental evidence for the existence of waves diffracted locally on lateral heterogeneities

the runup of solitary waves this is a study of the runup of solitary waves on plane beaches an approximate theory is presented for non breaking waves and an asymptotic result is derived for the maximum runup of solitary waves a series of laboratory experiments is described to support the theory it is shown that the linear theory predicts the maximum runup satisfactorily and that the nonlinear theory describes the climb of solitary waves equally well different runup regimes are found to exist for the runup of breaking and non breaking waves a breaking criterion is derived for determining whether a solitary wave will break as it climbs up a sloping beach and a different criterion is shown to apply for determining whether a wave will break during rundown these results are used to explain some of the existing empirical runup relationships

laboratory and numerical study of dambreak generated swash on impermeable slopes new laboratory experiments have produced detailed measurements of hydrodynamics within swash generated by bore collapse on a steep beach the experiments are based on a dambreak rig producing a highly repeatable large scale swash event enabling detailed measurements of depths and velocities at a number of locations across the swash zone experiments were conducted on two beaches differentiated by roughness results are presented for uprush shoreline motion flow depths depth averaged velocity velocity profiles and turbulence intensity estimates of the time and spatially varying bed shear stress are obtained via log law fitting to the velocity profiles and are compared with the shear plate measurements of barnes et al 2009 for similar experimental conditions experimental results are compared with model predictions based on a nlswe model with momentum loss parameterised using the simple quadratic stress law in terms of the depth averaged velocity predicted and measured flow depths and depth averaged velocities agree reasonably well for much of the swash period but agreement is not good at the time of bore arrival and towards the end of the backwash the parameterisation of total momentum loss via the quadratic stress law cannot adequately model the swash bed shear stress at these critical times

earthquake site response estimation a weak motion case study using weak motion recordings of aftershocks of the 1989 loma prieta earthquake recorded in oakland california near the failed nimitz freeway two methods have been applied to estimate the site response of an alluvium site and three mud over alluvium sites the first estimate is the traditional spectral ratio and the second utilizes the cross spectrum recordings obtained at a nearby bedrock site are used as estimates of the sediment site input motions while the two site response estimates produce similar peaks and troughs there is an approximate factor of 2 difference in amplitudes this discrepancy is evidence that there is a much greater level of noise than would be expected from the pre event ambient noise we interpret this as signal generated noise produced by scattering from heterogeneities which causes the true sediment site input to differ significantly from the bedrock site recording given this level of noise the cross spectrum estimate suffers a severe downward bias by a factor of 2 in this study and should probably not be used when the input motion is estimated from a bedrock site recording the spectral ratio estimates are relatively unbiased but the level of noise introduces a large degree of uncertainty therefore inferences about site response from individual spectral ratios should probably be avoided on the other hand ensemble averages of the estimates significantly reduce the scatter to reveal resonances that agree quite well in frequency and overall shape with those of one dimensional models whose parameters were determined independently a discrepancy of higher observed amplitudes than predicted by theory remains unexplained but most likely results from the effects of boundary layer topography which are not accounted for by the simple one dimensional models

array observations of microseismic noise and the nature of h v in the mississippi embayment abstract ambient ground motion data were collected using phased seismic arrays in fall 2002 and spring 2007 within the mississippi embayment and at a single station external to the embayment these data allowed us to determine the wave field composition of ambient noise for understanding wave propagation mechanisms giving rise to spectral peaks using nakamura s h v technique ambient ground motions in the frequency band of 0 1 0 33 hz 10 3 sec period were dominated by spatially localized rayleigh and love wave microseisms generated by high ocean waves along the north american seaboard in the time periods of analysis seismic waves important in forming the h v peak near 4 sec period are composed of relatively high phase velocity rayleigh and love waves that convert to propagating homogeneous shear waves in the thick unconsolidated sediments of the embayment the h v resonant period is controlled by both constructive and destructive interference of these shear waves a simple relationship for the h v peak is given using a propagator matrix formulation that predicts the resonance frequency of a layered medium for surface wave motion at the base of the system the amplitude of the observed h v peak however does not give an accurate estimate of shear wave amplification because it depends on the slowness of the incident wave the inconsistency in estimated average shear wave velocities using the h v method and differential travel times of local earthquake sp phases in the mississippi embayment may be explained by misidentification of sp wave conversion points from deeper interfaces

coseismic thermal pressurization can notably prolong earthquake recurrence intervals on weak rate and state friction faults numerical experiments using different constitutive equations 1 we add a new perspective to component factors of earthquake cyclicity namely coseismic thermal pressurization tp within fluid saturated fault zones which is pore fluid pressurization caused by frictional heating by using a single degree of freedom system with a rate and state dependent friction law we show that the short lived tp can prolong earthquake recurrence intervals this lengthening effect can operate even without any notable shear heating in weak faults moreover if the maximum increase in temperature is above a certain level the permeability rather than the maximum temperature becomes important for the lengthening effect lower permeability causes longer recurrence intervals by contrast narrower slip zones more pronounced heating do not simply prolong recurrence intervals although they entail higher dynamic undershoot and energy radiation these features do not depend on whether the assumed evolution law is the ruina law or the dieterich law however our results indicate that if the degree of tp changes for each earthquake the ideal time predictable model for earthquake cycles can be applicable only in the case of faults obeying the ruina law furthermore on the basis of the above mentioned dependence of the interval on the permeability we point out that it is necessary to measure the permeability rather than the slip zone thickness or the increase in temperature in order to estimate the tp effect on long term earthquake cycles although it is currently difficult to measure the permeability under ground measurements should be performed in the light of the importance of permeability in the prediction of future seismic hazards

microtremor measurements used to map thickness of soft sediments the observations about the behavior of microtremor spectra presented here show that noise measurements can be used as a powerful tool to determine the thickness of soft cover layers the most suitable method for this determination is nakamura s technique which is the ratio of the horizontal component noise spectrum and that of the vertical component i i v spectrum the frequency of the main peak in these spectral ratios correlates well with the sediment thickness at the site using an extensive database of microtremor measurements carried out in the western lower rhine embayment germany it was possible to show that this correlation is clearly valid for a wide range of thickness namely from tens of meters to more than 1000 m a simple formula was derived that for the sediments to be found in the area investigated directly calculates the cover thickness from the frequency of the main peak in the h v spectrum a comparison with calculated resonant frequencies sug gests the relation derived from the noise measurements depending on the velocity depth function of the shear wave classical spectral ratios are shown to be strongly influenced by the noise level and are therefore less reliable in determining the res onant frequency of the subsoil the practical relevance of the investigation is illus trated by means of cross sections constructed from results of the microtremor anal yses which provide a convincing image of the surficial structure of the areas investigated

flow and sediment transport induced by a plunging solitary wave 1 two parallel experiments involving the evolution and runup of plunging solitary waves on a sloping bed were conducted 1 a rigid bed experiment allowing direct hot film measurements of bed shear stresses and 2 a sediment bed experiment allowing for the measurement of pore water pressures and for observation of the morphological changes the two experimental conditions were kept as similar as possible the experiments showed that the complete sequence of the plunging solitary wave involves the following processes shoaling and wave breaking runup rundown and hydraulic jump and trailing wave the bed shear stress measurements showed that the mean bed shear stress increases tremendously with respect to that in the approaching wave boundary layer by as much as a factor of 8 in the runup and rundown stages and that the rms value of the fluctuating component of the bed shear stress is also affected by as much as a factor of 2 in the runup and hydraulic jump stages the pore water pressure measurements showed that the sediment at or near the surface of the bed experiences upward directed pressure gradient forces during the down rush phase the magnitude of this force can reach values as much as approximately 30 of the submerged weight of the sediment the experiments further showed that the sediment transport occurs in the sheet flow regime for a substantial portion of the beach covering the area where the entire sequence of the wave breaking takes place the bed morphology is explained qualitatively in terms of the measured bed shear stress and the pressure gradient forces

evolution of the turbulence structure in the surf and swash zones the velocity field and turbulence structure within the surf and swash zones forced by a laboratory generated plunging breaking wave were investigated using a particle image velocimetry measurement technique two dimensional velocity fields in the vertical plane from 200 consecutive monochromatic waves were measured at four cross shore locations shoreward of the breaker line the phase averaged mean flow fields indicate that a shear layer occurs when the uprush of the bore front interacts with the downwash flow the turbulence characteristics were examined via spectral analysis the larger scale turbulence structure is closely associated with the breaking wave and the bore generated turbulence in the surf zone then the large scale turbulence energy cascades to smaller scales as the turbulent kinetic energy tke evolves from the outer surf zone to the swash zone smaller scale energy injection during the latter stage of the downwash phase is associated with the bed generated turbulence yielding a 1 slope in the upper inertial range in the spatial spectra depth integrated tke budget components indicate that a local tke equilibrium exists during the bore front phases and the latter stage of the downwash phases in the outer surf zone the tke decay resembles the decay of grid turbulence during the latter stage of the uprush and the early stage of the downwash as the production rate is small because of the absence of strong mean shear during this stage of the wave cycle as well as the relatively short time available for the growth of the bed boundary layer

earthquake site response study in giumri formerly leninakan armenia using ambient noise observations we have tested whether ambient noise observations reveal useful information regarding site response at sediment sites in giumri formerly leninakan armenia this was done by comparing the noise observations with spectral ratio site response estimates based on aftershock data of the 7 december 1988 earthquake we show that neither the horizontal component noise spectra alone nor spectral ratios taken with respect to a nearby bedrock site reveal useful information regarding site response however spectral ratios of horizontal components taken with respect to vertical components nakamura s method exhibit a prominent peak that corresponds to the fundamental resonant frequency observed in the aftershock data based on this and other recent investigations we conclude that nakamura s method may be a reliable procedure for determining the fundamental resonant frequency of sedimentary deposits from ambient noise observations