subsurface energetics of the gulf stream near the charleston bump abstract the energy budgets of the eddies and the mean flow in the gulf stream near a topographic feature known as the charleston bump are computed first we consider these results in the context of the amplification hypothesis for the development of gulf stream meanders according to this hypothesis the finite amplitude gulf stream fluctuations observed offshore of onslow bay are the result of the destabilizing effect of the bump on the stream the present dataset was obtained both immediately upstream and downstream of the bump and the results of our analysis suggest 1 immediately south of the charleston bump the eddies perform net work on the gulf stream at a rate of 1 02 66 10 2 ergs cm 3 s 1 by transporting momentum offshore 2 the net work performed by the eddies south of the bump is not used locally to accelerate the mean rather it is exported to the rest of the ocean at a rate of 1 58 1 39 10 2 ergs cm 3 s 1 3 in spite of the net work performed by the eddies south of the bu

compressive and tensile failure of inclined well bores and determination of in situ stress and rock strength in this paper we investigate the occurrence of compressive and tensile failures of arbitrarily inclined well bores under a wide variety of stress conditions the principal assumptions in this analysis are that the rock is isotropic and that it deforms elastically to the point of failure as has been shown by previous investigators for a given stress state and well bore orientation it is straightforward to predict the orientation of the failures around the well bore as well as whether failure is likely to occur depending on such parameters as rock strength and borehole fluid pressure however as the stress state is almost never known in situ we demonstrate how observations of compressive and tensile wall failures in inclined holes can be used to constrain in situ stress orientations and magnitudes if there are independent data on the magnitude of the least principal stress from either leak off or microfrac tests and on the formation pore pressure we further demonstrate how once the stress state is determined it is possible to assess both an upper bound on the effective in situ rock strength and the degree to which increasing the borehole fluid pressure or mud weight can reduce the likelihood of borehole failure through application of this methodology to an inclined well bore in an area of complex faulting in the gulf of mexico we illustrate how it is possible to utilize observations of borehole failures to determine the magnitude and orientation of the stress tensor in areas such as offshore sedimentary basins where drilling inclined well bores is quite common

h v spectral ratios and array techniques applied to ambient noise recorded in the colfiorito basin central italy the colfiorito basin is a small intramountain depression in the southern section of the northern apennine chain that is filled with quaternary alluvial deposits the presence of soft alluvial deposits has significantly influenced the level of local damage that was caused by two major earthquakes m l 5 6 and 5 8 belonging to the swarm that started in september 1997 to verify the effects of the basin structure on the predominant frequency of seismic motion ambient noise measurements were carried out in the colfiorito basin during two experiments in may and july of 2002 the horizontal to vertical spectral ratios hvsrs were calculated for data collected at four profiles in the basin array techniques were applied to determine the wave types that composed the noise to estimate their apparent velocity and azimuth of propagation and to calculate a velocity dispersion curve from which a velocity depth structure was derived the data analysis shows a high amplification in the hvsr at low frequency this feature is common to most of the sites including the reference site and it is interpreted as being due to weather disturbances the peak frequencies of the spectral ratio calculated at the sites located in the center of the basin coincide with the theoretically estimated resonance frequencies the array averaged hvsr calculated for the array located in the middle of the plain has a pronounced peak at 0 9 hz this corresponds to the peak of the amplification function calculated on the basis of the velocity model deduced from the dispersion analysis the hvsr method is instead unsuitable for the prediction of the resonance frequencies of sediments in the sites where strong lateral variations of basement topography are present we measured apparent velocities in the range of 0 3 0 8 km sec by applying f k methods to array recordings these values are compatible with the predominance of surface waves in the noise as also confirmed by polarization analysis both rayleigh and love waves are present in the background seismic noise the results obtained by applying the spatial autocorrelation method to the vertical component of the ground motion recorded at a 240 m wide circular array deployed in the middle of the basin revealed the presence of rayleigh waves and f k methods combined with polarization techniques revealed the presence of polarized love waves the wave field analysis indicates two main propagation directions the first is around n100 e in the frequency band of 1 0 2 0 hz this radiation can be interpreted as being generated at the east southeast step borders of the basin the second main direction is around n300 e in the frequency band of 2 0 3 0 hz its source may be a 180 m deep depression located at the southwest corner of the basin

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

seismic property characterization of lithotypes cropping out in the siracusa urban area italy the town of siracusa is located in the south eastern coast of sicily southern italy in a wide inlet engraved into a limestone formation this lithotype which is overlaid by soft sediments such as sandy clays and detritus can be considered as the local bedrock present study aims to investigate on the dynamic properties of main lithotypes outcropping in the study area and their relationships with the local seismic response non invasive seismic prospecting techniques using the vertical component of surface waves masw and remi were adopted as well as ambient noise measurements processed through the nakamura technique the best solution for the experimental dispersion curves was selected using the neighbourhood algorithm and information about the deeper part of the estimated shear wave profiles was obtained by considering the ellipticity of the fundamental peak moreover a cluster analysis was performed to subdivide into homogeneous groups the experimental noise spectral ratios results obtained pointed out that the use of combined different methods provides a robust way to characterize the investigated soils and to reduce the problems linked to the non uniqueness of solutions during the interpretation of geophysical data

deep ventilation in the okinawa trough induced by kerama gap overflow near bottom water flowing over the kerama gap s sills is thought to ventilate the deep water below 1100 m depth in the okinawa trough and then upwell with 5 10 years residence time the present study follows up on this phenomenon using comprehensive profile data of temperature salinity dissolved oxygen currents and turbulence obtained by intensive shipboard observations performed in june 2013 and june 2014 in the region strong near bottom sub tidal flow with speeds exceeding 0 5 m s 1 was observed within a layer of about 100 m thickness over the western side of the peak of the main sill temperature and salinity sections along the kerama gap indicated some depressions and overturns of the deep water downstream of the strong overflow suggesting the existence of breaking internal gravity waves and hydraulic jumps associated vertical diffusivities estimated using the thorpe scale and the buoyancy frequency were three to four orders of magnitude larger than typical values observed in the thermocline of the open ocean 10 5 m2 s 1 the dissolved oxygen section also indicated strong vertical mixing and associated upwelling with the entrainment of the near bottom overflow water into the lower thermocline beneath the kuroshio in the okinawa trough the present study not only supports the previous conceptual model but also provides new evidence that the okinawa trough is an upwelling location where nutrient rich philippine sea intermediate water is sucked up into the lower thermocline below the kuroshio this article is protected by copyright all rights reserved

amplification of ground motion in fault and fracture zones observations from the tremestieri fault mt etna italy abstract a series of ambient noise measurements have been performed to evaluate their use in detecting the possible influence of tectonic structures on local amplification of seismic waves the area studied is located on the southeastern flank of mt etna a few kilometres north of the town of catania using a mobile station data were collected along three profiles which cross both a fault and an eruptive fracture in addition ambient noise was sampled at two permanent stations installed in close proximity to the fault and at another station located within the city limits of catania and considered to be a reference site analysis using spectral ratio techniques shows there is a tendency towards amplification at the sites located near the fault in h v spectral ratios such amplification is observed in the frequency range 4 0 8 0 hz and the amplitudes of the dominant spectral peaks decrease rapidly over the first few tens of meters from the discontinuity a similar tendency was observed for the sites located on the eruptive fracture zone dominant spectral peaks at 1 8 hz are also common in the study area the theoretical transfer function obtained through 1 d modelling indicates that such peaks can be related to the local stratigraphy the mean h h standard spectral ratio of microtremor evaluated at the permanent station located on the fault also shows an amplification peak at 4 0 hz azimuthal analysis shows that the resonance at 4 0 hz is directional with the maximum in the azimuth range n30 e n80 e

comment on current system east of the ryukyu islands by a nagano et al 1 in a recent paper nagano et al 2007 hereafter n2007 discussed the variation of current structure and volume transport of the ryukyu current system rcs east of the ryukyu islands using an inverse technique with hydrographic section data collected from three cruises their paper appears to be important for understanding this western boundary current since it is based on repeated hydrographic surveys in the region east of the ryukyu islands but acquiring meaningful results from inverse calculations requires great care fiadeiro and veronis 1982 p 160 say because inverse analysis always supplies a solution it appeared that the assumed reference level matters less in inverse theory than in the hydrographer s level of no motion approach actual computations have shown that is not true a bad assumption leads to bad results the advantage of inverse theory is that one sees how bad the results are the inverse technique minimizes the velocity at the reference level and that point is indeed raised in the final paragraph of n2007 which used the reference level of 100 dbar to determine whether this shallow reference level is an appropriate condition or not one should investigate the effect of choosing other reference levels in particular deeper levels in this note we perform two inverse calculations to calculate the current east of the ryukyu islands from the same data as one of the n2007 cruises but using a reference level of 2000 dbar the resulting rcs circulation field is we believe more realistic than that of n2007 2 three hydrographic surveys were carried out during may june september and october 2002 along three lines ae e os east of the ryukyu islands figure 1 may june and september cruises used xctd xbt casts along the e line but the october cruise collected ctd casts along all three lines surprisingly absolute geostrophic velocity sections determined by n2007 with a 100 dbar reference level revealed large values up to 30 40 cm s 1 at 1000 dbar the deepest level shown figures 2 3b and 4c in n2007 we have calculated full depth absolute geostrophic velocity sections using the inverse results of n2007 and plotted them to 3000 dbar figures 2a 2b 3a 3b 4a and 4b figures 2b 3b and 4b show strong deep currents with maximum speeds of 20 50 cm s 1 on each line in each case note the contour lines of velocity are nearly vertical and strong currents extend to the bottom for example a current velocity of 57 cm s 1 touches the bottom near 3100 dbar in the ae section is the computed strong deepcurrent field real or is it an artifact of the shallow reference level we address this question by carrying out the inverse calculation using a reference level of 2000 dbar instead of 100 dbar and compare results using the two reference levels we present results for the october cruise data only because the xbt xctd casts reached only 1000 dbar also the ctd measurements provide more accuracy in the inverse calculations

second mode internal tides in the east china sea deduced from historical hydrocasts and a model during the two year deployment period to obtain temperature t and specific volume anomaly d profiles from t and sea surface temperature sst observed respectively by pies and satellite we constructed multi index gravest empirical mode mi gem fields park et al 2005 using historical hydrocasts however comparison between the mi gem fields and the historical hydrocasts reveals that the mi gem fields fail to capture 44 and 52 of the t and d variance respectively in the p 100 200 dbar layer this may be caused by 2nd or higher mode variations of vertical structure since t is insensitive to all but the lowest baroclinic mode watts and rossby 1977 4 in this study we demonstrate that 2nd mode its in the ecs are responsible for failure of the mi gem fields to captureadequatelytand dvariationsinthep 100 200 dbar layer as seen in historical hydrographic measurements we verify our observations with a numerical simulation of its

kuroshio meanders in the east china sea abstract an array of seven inverted echo sounders was moored along and across the kuroshio in the east china sea for more than one year the data from this array show evidence of energetic meanders with periods of 7 11 and 16 days the respective phase velocities of these meanders are 28 20 and 17 km day 1 downstream the 7 and 16 day waves are intermittent but the 11 day waves are present throughout the deployment the instability responsible for these waves is investigated with a spectral numerical model applied to a background state representing the kuroshio in this region the fastest growing instability from the model has e folding growth time of 2 days period of 12 days and phase velocity of 18 km day 1 downstream it appears to be a close representation of the 11 day wave seen in the observational data such a model has been previously used to represent meanders in the gulf stream at similar latitudes off the east coast of the united states the kuroshio meanders have approximately half the

stress induced borehole elongation a comparison between the four arm dipmeter and the borehole televiewer in the auburn geothermal well the nature and origin of borehole elongation recorded by the four arm dipmeter calipers is studied utilizing information obtained from hydraulic fracturing stress measurements and borehole televiewer data taken in a well located in auburn new york a preferred orientation n10 w s10 e 10 and a less prominant e w orientation of borehole elongation was observed on two runs of the dipmeter comparisons of borehole geometry determined using the televiewer and the dipmeter show that both tools give the same orientation of borehole elongtion provided that the zone of elongation is longer than 30 cm comparisons of dipmeter caliper data with orientation of in situ stress and natural fractures obtained from hydrofracturing tests and televiewer data show that the n10 w s10 e borehole elongations 1 are axisymmetric 2 are aligned with the minimum horizontal stress sh and 3 are not associated with natural fractures intersecting the well these elongations are interpreted as stress induced well bore breakouts the e w elongation direction is characterized by an asymmetric borehole cross section in thinly bedded rocks and is not caused by breakouts this asymmetric geometry can be discriminated from breakouts using the oriented electric measurements provided by the dipmeter this study demonstrates that the dipmeter can be used to determine the orientation of sh by mapping breakouts confirming the results of earlier less detailed studies and provides a firm basis for mapping regional stress patterns using existing dipmeter data

kuroshio temporal and spatial variations south of japan determined from inverted echo sounder measurements 1 the affiliated surveys of the kuroshio off ashizuri misaki asuka project is a collaboration between scientists in japan and the united states to improve our understanding of the structure and dynamics of the kuroshio off the coast of southwest japan in this project an array of nine inverted echo sounders and nine current meter moorings were deployed for 2 years 1993 1995 along a line extending 1000 km from shikoku numerous hydrographic profiles along this section were used to determine the regional gravest empirical modes gems which relate vertical profiles of temperature and specific volume anomaly to vertical acoustic echo time these gems were used in conjunction with the inverted echo sounder data to calculate 2 year time series of entire sections of relative geostrophic velocity and temperature current meter data provided absolute velocity references for the geostrophic velocity sections in addition a time series of kuroshio position was determined from the gem temperature sections it shows three big 80 km displacement and three little offshore meanders of the kuroshio occurring in february may june and october of both years this suggests a 4 month periodicity possibly phase locked to the annual cycle the meanders may be caused by mesoscale eddies arriving from the east the observed meanders were preceded by low kuroshio volume transport and were followed by high kuroshio volume transport the kuroshio volume and temperature transports were highly variable with respective means of 65 4 sv and 3 7 0 2 pw and standard deviations of 20 sv and 0 9 pw

deep countercurrent beneath the kuroshio in the okinawa trough 1 the okinawa trough is geographically separated into the northern and southern parts by the kerama gap and the northern part is composed of the northern central and southern subbasins formed by bights of the continental slope previous observations have indicated that a deep countercurrent is present beneath the kuroshio on the continental slope in the northern okinawa trough however its persistence over time and its spatial structure over the entire basin have not been clarified to date the present study examines moored current meter data on the continental slope in the southern and central subbasins of the northern okinawa trough for november 2004 to november 2006 deep flows on the continental slope have a clear seasonality in the southern subbasin eddy motions due to kuroshio meanders are organized into a persistent countercurrent below the kuroshio in the winter spring period during this time high frequency kuroshio meanders with periods near 10 d are likely to diminish in the southern subbasin while low frequency kuroshio meanders with periods of 1 3 months tend to dominate in the northern subbasin in addition a high resolution ocean general circulation model is used to explore the deep flow field over the entire okinawa trough the model indicates that the deep flow field is stable in the southern okinawa trough over the year whereas it is unstable in the northern okinawa trough particularly in the winter spring period this results in a persistent countercurrent driven by cyclonic eddies on the continental slope in the northern okinawa trough

estimation of maximum horizontal principal stress magnitude from stress induced well bore breakouts in the cajon pass scientific research borehole in this paper we utilize the mechanical properties of core samples detailed observations of stress induced well bore breakouts and estimates of the magnitude of shmin from hydraulic fracturing experiments to construct a vertical profile of the maximum horizontal principal stress shmax to 3 5 km depth in the cajon pass borehole as in essentially all other boreholes the hydraulic fracturing stress measurements in the cajon pass borehole yielded appreciably more and more reliable data on the magnitude of the least principal horizontal stress shmin than the maximum principal horizontal stress shmax to utilize the breakout observations to constrain the magnitude of shmax a brittle failure criterion was used that is based on the effective strain energy concept this failure criterion also allows us to account for the polyaxial stress around the borehole and to incorporate the role of pore fluid pressure on rock strength in various ways a comparison of the shmax profile estimated from the breakouts with estimates of shmax obtained from the hydraulic fracturing tests indicates that they compare fairly well for the case when the effect of pore pressure on hydraulic fracture initiation is negligible the overall stress state to a depth of 3 5 km in the well corresponds to a normal strike slip faulting regime the shmax profile indicates several marked decreases in stress magnitude associated with major fault zones an observation consistent with the shmin profile obtained from hydraulic fracturing tests

observations of flow variability through the kerama gap between the east china sea and the northwestern pacific the kerama gap near the middle of the ryukyu island chain is the deepest channel with a sill depth of 1050 m connecting the east china sea ecs to the northwestern pacific we measured the flow through the kerama gap from june 2009 to june 2011 the 2 year mean transport 2 0 0 7 sv is into the ecs from the northwestern pacific it contributes about 11 of the mean kuroshio transport in the ecs at the pn line subtidal standard deviation of the transport through the kerama gap is 3 2 sv comparable to that of the pn line kuroshio transport 4 0 sv suggesting a significant effect of kerama gap transport on temporal variability of the kuroshio transport in the ecs comparison with time series of satellite measured sea surface height maps reveals that temporal variability of the kerama gap transport is related to the arrival of mesoscale eddies from the east high low transport into the ecs is associated with the presence of a cyclonic anticyclonic eddy south of the kerama gap

high frequency analysis of seismic background noise as a function of wind speed and shallow depth we used a deep 1500 m cased borehole near the town of datil in west central new mexico to study high frequency 1 hz seismic noise characteristics the remote site had very low levels of cultural noise but strong winds winter and spring made the site an excellent candidate to study the effects of wind noise on seismograms along with a three component set of surface sensors teledyne geotech gs 13 a vertical borehole seismometer gs 28 was deployed at a variety of depths 5 43 and 85 m to investigate signal and noise variations wind speed was measured with an anemometer event triggered and time triggered data streams were recorded on a reftek 72 02 data acquisition system located at the site our data show little cultural noise and a strong correlation between wind speed and seismic background noise the minimum wind speed at which the seismic background noise appears to be influenced varies with depth 3 m sec at the surface 3 5 m sec at 43 m in depth and 4 m sec at 85 m in depth for wind speed below 3 to 4 m sec we observe omni directional background noise that is coherent at frequencies below 15 hz this coherence is destroyed when wind speeds exceed 3 to 4 m sec we use a test event md 1 6 and superimposed noise to investigate signal to noise ratio snr improvement with sensor depth for the low q valley fill of the datil borehole dbh site we have found that snr can be improved by as much as 20 to 40 db between 23 and 55 hz and 10 to 20 db between 10 and 20 hz by deploying at a 43 m depth rather than at the surface at the surface there is little signal above noise in the 23 to 55 hz frequency band for wind speeds greater than 8 m sec thus high frequency signal information that is lost at the surface can be recorded by deploying at the relatively shallow depth of 40 m because we observe only minor further reductions in seismic background noise sbn at deeper depths 40 m is likely to be a reasonable deployment depth for other high frequency monitoring sites in similar environmental and geologic conditions

wind induced ground motion wind noise is a problem in seismic surveys and can mask the seismic signals at low frequency this research investigates ground motions caused by wind pressure and shear stress perturbations on the ground surface a prediction of the ground displacement spectra using the measured ground properties and predicted pressure and shear stress at the ground surface is developed field measurements are conducted at a site having a flat terrain and low ambient seismic noise triaxial geophones are deployed at different depths to study the wind induced ground vibrations as a function of depth and wind velocity comparison of the predicted to the measured wind induced ground displacement spectra shows good agreement for the vertical component but significant underprediction for the horizontal components to validate the theoretical model a test experiment is designed to exert controlled normal pressure and shear stress on the ground using a vertical and a horizontal mass spring apparatus this experiment verifies the linear elastic rheology and the quasi static displacements assumptions of the model the results indicate that the existing surface shear stress models significantly underestimate the wind shear stress at the ground surface and the amplitude of the fluctuation shear stress must be of the same order of magnitude as the normal pressure measurement results show that mounting the geophones flush with the ground provides a significant reduction in wind noise on all three components of the geophone further reduction in wind noise with depth of burial is small for depths up to 40 cm

glacial isostatic adjustment and earth rotation refined constraints on the viscosity of the deepest mantle we explore the extent to which two properties of earth s present day rotational state may be applied to constrain the viscosity of the lower regions of the lower mantle the analysis builds upon recent advances in understanding the radial resolving power of the relative sea level data of postglacial rebound which have demonstrated anew that no significant increase of viscosity across the 660 km seismic discontinuity appears to be allowed by these data such observations do not constrain the viscosity of the mantle below about 1400 km depth however and here we estimate the average viscosity in this deepest region by invoking observations of the present day rate and direction of polar wander and the present day magnitude of the nontidal acceleration of the rate of planetary rotation since the rotational response to the glaciation cycle depends only upon the degree 2 spherical harmonic components of the induced deformation this response is expected to provide the most specific sampling possible of deep mantle properties our analysis is based upon the use of glacial excitation functions calculated from complete gravitationally self consistent solutions of the sea level equation for the most recent refinement of the history of ice sheet thickness variations across the last glacial interglacial transition namely the ice 4g model this analysis shows that when earth rotation observations are combined with relative sea level constraints the viscosity of the deepest mantle is required to be 1 order of magnitude higher than the viscosity of the upper part of the lower mantle such significant elevation of viscosity in the lowermost region of the lower mantle is also in accord with recent inferences based upon analysis of the nonhydrostatic geoid the analyses presented herein therefore suffice to effect a reconciliation between the requirements of these distinct geophysical observations

observations of kuroshio flow variations in the east china sea 1 kuroshio velocity structure and transport in the east china sea ecs were investigated as part of a 23 month study using inverted echo sounders and acoustic doppler current profilers adcps along the regularly sampled pn line flow toward the northeast is concentrated near the continental shelf with the mean surface velocity maximum located 30 km offshore from the shelf break taken as the 170 m isobath there are two regions of southwestward flow a deep countercurrent over the continental slope beneath the kuroshio axis and a recirculation offshore which extends throughout the whole water column there is a bimodal distribution to the depth of maximum velocity with occurrence peaks at the surface and 210 dbar when the maximum velocity is located within the top 80 m of the water column it ranges between 0 36 m s and 2 02 m s when the maximum velocity is deeper than 80 m it ranges between 0 31 m s and 1 11 m s the 13 month mean net absolute transport of the kuroshio in the ecs is 18 5 0 8 sv standard deviation 4 0 sv the mean positive and negative portions of this net flow are 24 0 0 9 sv and 5 4 0 3 sv respectively

the influence of wind on measurements of seismic noise summary the horizontal to vertical spectral ratio hvsr technique of microtremor measurement is widely applied in microzonation and site response studies given the small amplitude of the measured signal unwanted disturbances may adversely affect the results we analysed the influence of local wind on microtremor measurements as follows first we studied variation in hvsr at a permanent three component seismological station under various wind patterns second we conducted an experiment under controlled condition in a wind room equipped with a laser particle image velocimeter analysing the effect of increasing wind speed on various sensor digitizer configurations third we undertook numerical modelling to explain the observed data our main conclusions are that wind increases the amplitude of all components of the microtremor wavefield but does not affect hvsr however certain sensor digitizer configurations can be adversely affected by instrumental noise due to turbulence at the air instrument ground interface

a study on seismic noise variations at colfiorito central italy implications for the use of h v spectral ratios 1 seismic noise recorded by broad band stations in the middle of and around the colfiorito plain is analyzed in the frequency band 0 1 to 10 hz small daily variations in noise amplitude are found on the order of 2 for f 1 hz in contrast long term amplitude variations due to weather conditions are significant throughout the analyzed frequency band for f 1 hz the amplitude increase can be as large as a factor of 50 in the low frequency band horizontal components vary much more than the vertical at both firm and soft sites however these noise variations at low frequencies do not contaminate significantly the 0 9 hz peak of the h v spectral ratio that fits the fundamental eigenfrequency of the sedimentary fill of the basin resonating during earthquakes correlating the long term variations of noise with different meteorological parameters we find that wind speed best matches the low frequency noise disturbances

an improved method for determining the regional stress tensor using earthquake focal mechanism data application to the san fernando earthquake sequence the orientations of fault planes and slip directions indicated by a population of earthquake focal mechanisms can be used to determine best fit regional principal stress directions and r 2 1 3 1 a measure of relative stress magnitudes under the assumption of uniform stress in the source region this analysis allows for the possibility that failure occurs on preexisting zones of weakness of any orientation in the inversion we perform a grid search of stress models to find the one which requires the smallest total rotation of all the fault planes that is needed to match the observed and predicted slip directions the method allows for errors in orientations of both the fault planes and slip directions we have an objective means for identifying the more likely of the two possible fault planes from each focal mechanism relative to a given stress model thus we do not face the problem of ambiguity of nodal planes which plagues other analyses of this kind by using a grid search of stress models rather than a linearization scheme we are able to perform a realistic error analysis and thus establish confidence limits for the preferred regional stresses the method can be used to investigate possible stress inhomogeneities during earthquake sequences by analyzing subsets of the data population the technique has been applied to 76 events from the san fernando earthquake sequence for which we have found best fit stresses plunge and azimuth 1 7 187 2 27 281 3 62 84 and r 0 65 the average misfit between this stress model and all the data is about 8 and all but eight of the aftershocks have misfits of less than 20 these values are considerably less than the uncertainty of the focal mechanism determinations therefore significant stress inhomogeneities are not required by the data our analysis does not support the suggestion of a change in stresses during the aftershock sequence as proposed by others on the basis of an apparent change in focal mechanisms

current system east of the ryukyu islands 1 the ryukyu current system rcs is a northeastward current southeast of the ryukyu islands the variation of current structure in the rcs region was investigated on the basis of the absolute geostrophic velocity estimated by inverse calculation using hydrographic data three realizations of the rcs are examined from cruises in may september and october 2002 it was found that the current structure in the rcs region is divided into upper and lower layers by an isopycnal surface of 26 the currents in both layers proceed northeastward along the eastern slope east of the ryukyu islands the current in the upper layer merges with the inflow from the interior region resulting in larger northeastward volume transport southeast of amami oshima island than southeast of okinawa island the volume transport from the east reaches more than 40 of that southeast of amami oshima island on the other hand the current in the lower layer is not affected by inflow from the east it is also found that the upper rcs gains heat mainly through the advection of warm water from the east resulting in an increase in the downstream temperature by about 0 5 c on average

site effect evaluation using spectral ratios with only one station the spectral ratio technique is a common useful way to estimate empirical transfer function to evaluate site effects in regions of moderate to high seismicity the purpose of this paper is to show that it is possible to estimate empirical transfer function using spectral ratios between horizontal and vertical components of motion without a reference station the technique originally proposed by nakamura to analyze rayleigh waves in the microtremor records is presented briefly and it is discussed why it may be applicable to study the intense s wave part in earthquake records results are presented for three different cities in mexico oaxaca oax acapulco gro and mexico city these cities are very different by their geological and tectonic contexts and also by the very different epicentral distances to the main seismogenic zones affecting each city each time we compare the results of nakamura s technique with standard spectral ratios in all three cases the results are very encouraging we conclude that if site effects are caused by simple geology a first estimate of dominant period and local amplification level can be obtained using records of only one station

deriving wavefield characteristics and shear velocity profiles from two dimensional small aperture arrays analysis of ambient vibrations in a small size alluvial basin colfiorito italy we analyze the dispersion characteristics of ambient noise vibrations for this purpose two dimensional 2d seismic array data were acquired in four different sites in the colfiorito plain an alluvial intramountain basin that exhibits strong site effects assuming seismic noise being mainly composed of surface waves we derive one dimensional 1d shallow shear velocity profiles through the inversion of dispersion curves measured by frequency wavenumber f k methods the inverted shear wave velocity profiles are consistent with a priori information for those sites that can be approximated by 1d simple models in these cases the use of passive records of seismic vibrations can be a valuable tool for determining the shallow velocity profile if a detailed depiction of velocity structure is not required the theoretical dispersion curves for rayleigh and love waves were compared with the measured dispersion curves for vertical and horizontal components respectively this allows us to discuss qualitatively the composition of ambient vibrations outlining a large proportion of love waves in the noise wave field and the effects of higher modes we also use the single station method for investigating the origin of the horizontal to vertical h v peak in the plain of colfiorito in terms of ellipticity of the fundamental rayleigh mode

tidal and residual currents across the northern ryukyu island chain observed by ferryboat adcp ferryboat acoustic doppler current profiler adcp data from 2003 to 2012 are used to estimate the tidal and residual currents across the northern ryukyu island chain ric between the islands of okinawa and amamioshima in this region the m2 tide current is the strongest tidal component and the k1 tide current is the strongest diurnal tidal component the corresponding maximum amplitudes are 40 and 34 cm s 1 respectively after removal of the tidal currents the mean volume transport 1 5 2 7 sv flows into the east china sea ecs from the western north pacific through four channels in this area in an empirical orthogonal function eof analysis performed to clarify the temporal and spatial variability of currents through the four channels the first two eof modes account for 71 and 18 of the total variance respectively the eof1 mode shows a clear bottom intensified mode through the deep channel which is likely to be formed by the propagation of bottom trapped long topographic rossby wave caused by the impingement of westward propagating mesoscale eddies upon the eastern slope of the northern ric the eof2 mode has significant seasonal variability and may be driven by the wind stress prevailing over the kuroshio flow region around the northern ric in october to november this study provides observational evidence of the water exchanges across the northern ric which is essential for constructing a circulation scheme in the north pacific subtropical western boundary region

interaction between the east china sea kuroshio and the ryukyu current as revealed by the self organizing map 1 the self organizing map som is used to study the linkage between the two western boundary currents the kuroshio current and the ryukyu current through the kerama gap four coherent ocean current patterns extracted from a numerical model output for the kerama gap area are used to describe the variability of the kuroshio current axis and the mesoscale eddies in the ryukyu current system the temporal evolution of these four patterns shows a robust cycle with an average period of 120 days the shift of the kuroshio current axis is found to be a dominant factor in determining the water exchange in the kerama gap and the eddies associated with the ryukyu current are also important in affecting the strength of eddies in the kerama gap the interaction between the kuroshio current and the ryukyu current through the kerama gap as revealed by the som provides new insights in understanding the water exchange between the east china sea and the northwest pacific

the current system east of the ryukyu islands as revealed by a global ocean reanalysis abstract the structure and variability of the ryukyu current system rcs which forms the western boundary current along the eastern slope of the ryukyu islands are studied using results from a 32 layer 1 12 5 global hybrid coordinate ocean model hycom and navy coupled ocean data assimilation ncoda reanalysis for the period 1993 2012 it is confirmed that the reanalysis realistically reproduces salient features of the observed currents at three sections southeast of miyakojima okinawa and amami ohshima the mean velocity sections show well developed subsurface velocity maxima between 700 and 900 m the current core southeast of amami ohshima shows year to year variations with cyclonic anticyclonic circulation east of amami ohshima generating weak strong velocity cores interaction of the rcs with an anticyclonic eddy often produces a two core velocity structure with a surface core in the upper 300 m and a deeper core near 700 900 m the horizontal structure of the rcs at 15 m depth shows a well developed northeastward current northeast of okinawa which is partly fed by the southwestward extension of the anticyclonic recirculation gyre the rcs forms a continuous northeastward current from miyakojima to amami ohshima below 500 m with shoreward intensification the circulation at 2000 m shows a seasonal flow reversal which is northeastward from december to june and southwestward from august to october with july and november being the transition months the volume transports across these three sections have respective mean values of 0 6 6 2 and 12 4 sv 1 sv 106 m3 s 1 and standard deviations of 10 2 7 1 and 11 3 sv they have dominant seasonal variations with the maximum in winter and spring and the minimum in summer the interannual variation of the transport anomaly which co varies with the rcs core results from westward propagating mesoscale eddies arriving from the pacific interior

microtremor measurements in the city of palermo italy analysis of the correlation between local geology and damage abstract this study presents the results of 90 seismic ambient noise measurements in palermo the main city of sicily italy the dataset has been processed using the horizontal to vertical spectral ratio hvnsr technique and interpreted in terms of local geology which is characterized by the presence of alluvial sediments of two riverbeds masked by urbanization since the seventeenth century hvnsrs show significant variations in the study area when the transition stiff to soft is crossed a typical spectral peak appears in the hvnsrs mostly in the frequency band 1 2 hz and exceeding a factor of 3 in amplitude using available information on subsurface geological structure we compute theoretical 1d and 2d transfer functions the resonance frequencies of soft soils obtained by hvnsr are well reproduced by the fundamental frequencies from numerical modeling the distribution of frequency peaks of hvnsr and their amplitudes are also compared with the local damage caused by historical earthquakes previous studies demonstrated that damage variations in palermo were controlled more by near surface geology than building vulnerability a uniform vulnerability is an ideal condition to test statistical methods and their capability in seeking correlation between hvnsr and potential damage due to local geological conditions we apply two well established multivariate statistical methodologies factor analysis and canonical correlation to the hvnsr dataset and macroseismic data damage grades of the european macroseismic scale through these analyses we quantify the significance of the correlation between the hvnsr peak in the low medium frequency range 0 5 3 hz and the occurrence of the highest damage grades this approach allows us 1 to estimate the threshold value in the resulting linear combination of the hvnsr amplitudes which separates zones of light damage from zones of significant damage and therefore 2 to improve the spatial definition of potentially high hazard zones through a denser grid of microtremor measurements

local seismic response in catania italy a test area in the northern part of the town abstract site effects were studied in an area located in the northern part of catania town using ambient noise measurements the study zone is particularly suitable for investigating local seismic response both because most of the terrains characterizing the urban area are here outcropping and a considerable amount of field measurements of their elastic properties is available the recorded ambient noise was processed through the nakamura h v spectral ratios technique the results set into evidence significant differences in the amplification of the horizontal component versus the vertical one in the litho types outcropping in the study area no amplifications were observed in the h v spectral ratios of sites located on the clayey basement as well as in those located on massive lavas by contrast a tendency towards significant h v spectral peaks in the frequency band 2 5 7 0 hz was observed in terrains formed by sandy clays gravelly sands detritus and altered lavas results of ambient noise spectral ratios were compared with preliminary findings from earthquake recordings at two stations located in the investigated area finally we computed the theoretical transfer functions using 1d numerical modelling the results pointed out that the observed h v peaks can be interpreted as the resonance effect due to the impedance contrast between the soft sediments and the basement quaternary clays found out at a depth ranging from 20 to 50 m

effect of borehole deviation on breakout orientations well bore breakouts are zones of spalling and fracture that form on opposite sides of a well bore and tend to change the cross sectional shape of the borehole from circular to roughly elliptical in vertical holes drilled in areas where one principal stress sv is vertical breakouts tend to form at opposite ends of the borehole diameter parallel to the least compressive horizontal principal stress direction sh this paper uses an analytical elastic solution for stress at the wall of a borehole to analyze the rotation of breakout orientations away from the direction of sh as the borehole deviates from the direction of the vertical principal stress the calculated orientations of breakouts in deviated boreholes depend on the type of faulting regime in which the well was drilled i e normal strike slip or thrust on the deviation angle o of the borehole axis from vertical on the angle between the horizontal projection of the borehole axis and the direction of sh and on the relative magnitudes of the three principal stresses sh sh the greatest compressive horizontal stress and sv in the strike slip faulting regime regardless of the values of sv sh and sh a borehole must deviate at least 35 from vertical before the horizontal projection of the breakout orientation differs by more than 10 from sh in the normal and thrust faulting regimes however the borehole deviation angle ocrit required to rotate projected breakout orientations by 10 from sh approaches zero as the value of sh approaches that of sh in the thrust faulting regime only about 3 of all combinations of sv sh and sh will produce ocrit values less than 10 while about 12 of all such combinations will yield ocrit 10 in the normal faulting regime about 12 and 33 of such combinations will yield ocrit 20 in the thrust and normal faulting regimes respectively careful study of changes in breakout orientation as a function of borehole deviation may improve the resolution of inferred stress directions when studying breakouts in deviated boreholes in these two faulting regimes

using borehole breakouts to constrain the complete stress tensor results from the sijan deep drilling project and offshore santa maria basin california we use borehole breakouts in nonvertical drill holes to constrain the directions of the three principal stresses and their relative magnitudes in this paper we start by modifying previously published breakout selection criteria to work with highly deviated borehole data we present a forward modeling technique using genetic algorithms and a nongradient n dimensional optimizer to find the best fitting stress state for a set of breakout data the stress state is parameterized by three euler angles and the stress state ratio o a technique is developed to determine the 95 confidence weighted misfit between a model and the data we then map out the 95 misfit confidence limits on the best fitting stress state this technique is applied to data published by qian and pedersen 1991 removing their constraint of a vertical principal stress direction reduces the misfit between the stress state and the breakout data we find that the best fitting stress state they report with a vertical principal stress direction lies outside our 95 confidence limits we also invert breakouts in the offshore santa maria basin california these data show a thrust faulting stress state with the maximum principal stress s 1 at n148 5 e plunging 31 5 the 95 confidence range for the azimuth of s 1 ranges from n143 0 e to n198 1 e the stress ratio o was found to be 0 82l 1 0 584

the kuroshio east of taiwan moored transport observations from the woce pcm 1 array observations from the woce pcm 1 moored current meter array east of taiwan for the period september 1994 to may 1996 are used to derive estimates of the kuroshio transport at the entrance to the east china sea three different methods of calculating the kuroshio transport are employed and compared these methods include 1 a direct method that uses conventional interpolation of the measured currents and extrapolation to the surface and bottom to estimate the current structure 2 a dynamic height method in which moored temperature measurements from moorings on opposite sides of the channel are used to estimate dynamic height differences across the current and spatially averaged baroclinic transport profiles and 3 an adjusted geostrophic method in which all moored temperature measurements within the array are used to estimate a relative geostrophic velocity field that is referenced and adjusted by the available direct current measurements the first two methods are largely independent and are shown to produce very similar transport results the latter two methods are particularly useful in situations where direct current measurements may have marginal resolution for accurate transport estimates these methods should be generally applicable in other settings and illustrate the benefits of including a dynamic height measuring capability as a backup for conventional direct transport calculations the mean transport of the kuroshio over the 20 month duration of the experiment ranges from 20 7 to 22 1 sv 1 sv 106 m3 s 1 for the three methods or within 1 3 sv of each other the overall mean transport for the kuroshio is estimated to be 21 5 sv with an uncertainty of 2 5 sv all methods show a similar range of variability of 10 sv with dominant timescales of several months fluctuations in the transport are shown to have a robust vertical structure with over 90 of the transport variance explained by a single vertical mode the moored transports are used to determine the relationship between kuroshio transport and sea level difference between taiwan and the southern ryukyu islands allowing for long term monitoring of the kuroshio inflow to the east china sea

vertical structure and transport on a transect across the north atlantic current near 42 n time series and mean a new method is presented for combining historical hydrography with the acoustic travel time measurements from an inverted echo sounder ies to obtain time series of full water column profiles of temperature t and specific volume anomaly hydrography is used to demonstrate that profiles constructed from the ies measurement account for more than 90 of the t and variance through the main thermocline range horizontal gradients between neighboring pairs of instruments when combined with measurements from bottom pressure sensors and deep current meters provide accurate estimates of absolute geostrophic velocity profiles a section of iess and current meters across the north atlantic current nac along world ocean circulation experiment line acm6 near 42 5 n is analyzed using these methods and the eulerian mean temperature and absolute velocity sections are calculated the mean transport for the combined nac and northward flow within the inshore portion of the mann eddy is 146 13 106 m3 s 1 the temporal standard deviation of the northward transport is 41 106 m3 s 1 arising not only from changes in the transport of the nac but also from lateral shifts of the currents and eddies captured by the fixed span of moorings assumption of a level of no motion at the bottom and at 2000 dbar underestimates the true absolute transport by 33 or 60 respectively historical measurements indicate that 50 60 106 m3 s 1 circulates within the mann eddy adjacent to the north atlantic current thus 86 96 106 m3 s 1 appears to be throughput at the acm6 line because the throughput observed on the acm6 line considerably exceeds the combined historical estimates of northward and eastward outflow from the newfoundland basin of 30 106 m3 s 1 these measurements suggest a substantial 50 106 m3 s 1 recirculation or southward flow within the newfoundland basin in addition to the historical recirculation within the mann eddy

the northeastward current southeast of okinawa island observed during november 2000 to august 2001 1 in order to estimate the variability of current structure and mean geostrophic volume transport in the southeast of okinawa island the round trip acoustic travel times between sea bottom and surface at nine sites were measured by inverted echo sounder with pressure gauge pies from november 2000 to august 2001 vertical sections of geostrophic velocity are calculated by using vertical profiles of specific volume anomaly derived by the gravest empirical mode method from the pies data in the upper 500 m layer over a slope shallower than 1000 m depth the northeastward current reached up to 60 cm s 1 during the occupation of an anticyclonic eddy and decreased to 15 cm s 1 during the occupation of a cyclonic eddy around the mean of 20 cm s 1 the temporal mean geostrophic volume transport relative to the 2000 dbar level was estimated to be 6 1 sv 1 sv 106 m3 s 1 northeastward in the west of 128 85 e

predominant period site classification for response spectra prediction equations in italy we propose a site classification scheme based on the predominant period of the site as determined from the average horizontal to vertical h v spectral ratios of ground motion our scheme extends zhao et al 2006 classifications by adding two classes the most important of which is defined by flat h v ratios with amplitudes less than 2 the proposed classification is investigated by using 5 damped response spectra from italian earthquake records we select a dataset of 602 three component analog and digital recordings from 120 earthquakes recorded at 214 seismic stations within a hypocentral distance of 200 km selected events are in the moment magnitude range 4 0 mw 6 8 and focal depths from a few kilometers to 46 km we computed h v ratios for these data and used them to classify each site into one of six classes we then investigate the impact of this classification scheme on empirical ground motion prediction equations gmpes by comparing its performance with that of the conventional rock soil classification although the adopted approach results in only a small reduction of the overall standard deviation the use of h v spectral ratios in site classification does capture the signature of sites with flat frequency response as well as deep and shallow soil profiles characterized by long and short period reso nance respectively in addition the classification scheme is relatively quick and inexpensive which is an advantage over schemes based on measurements of shear wave velocity online material tablesofparametersdefiningthegroundmotion predictionequa tions and figures of h v spectral ratios intraevent residuals and spectral amplitudes

long duration asynchronous ground motions in the colfiorito plain central italy observed on a two dimensional dense array 1 in winter 1998 a small aperture 200 m four station array was operating in the middle of the colfiorito plain waveforms of seven small magnitude 2 1 m 3 7 local earthquakes are analyzed in this study the peculiarity of the array seismograms is a 2 min long duration of the horizontal ground motion the predominant frequency in the plain is around 1 hz in this frequency band earthquake induced ground shaking is synchronous for a few seconds during direct s waves after this time window wave trains show an increasingly chaotic behavior within the array the energy variation of the horizontal ground shaking between the array and a nearby rock outcrop exceeds a factor of 500 at 1 hz in order to help understanding of observations and construct models for future numerical simulations the buried structure of the colfiorito plain has been investigated through seismic refraction profiles and geoelectric measurements a three dimensional reconstruction of the basin structure reveals an extremely complex bedrock topography which is probably a recurrent feature for intermontane basins in tectonically active regions apparent velocities and backazimuths in the frequency band 0 5 1 5 hz indicate that a 180 m deep depression nw of the array is responsible for the generation of edge diffracted surface love waves their arrival to the array breaks the synchronism of vertically reverberating waves which predominate in the first seconds of the s wave window