surface climate variations over the north atlantic ocean during winter 1900 1989 abstract the low frequency variability of the surface climate over the north atlantic during winter is described using 90 years of weather observations from the comprehensive ocean atmosphere data set results are based on empirical orthogonal function analysis of four components of the climate system sea surface temperature sst air temperature wind and sea level pressure an important mode of variability of the wintertime surface climate over the north atlantic during this century is characterized by a dipole pattern in ssts and surface air temperatures with anomalies of one sign cast of newfoundland and anomalies of the opposite polarity off the southeast coast of the united states wind fluctuations occur locally over the regions of large surface temperature anomalies with stronger than normal winds overlying cooler than normal ssts this mode exhibits variability on quasi decadal and biennial time scales the decadal fluctuations are irregular in length averaging 9 years before 1945 and 1

ground motion relations for eastern north america predictive relations are developed for ground motions from eastern north american earthquakes of 4 0 m 7 25 at distances of 10 r 500 km the predicted parameters are response spectra at frequencies of 0 5 to 20 hz and peak ground acceleration and velocity the predictions are derived from an empirically based stochastic ground motion model the relations differ from previous work in the improved empirical definition of input parameters and em pirical validation of results the relations are in demonstrable agreement with ground motions from earthquakes of m 4 to 5 there are insufficient data to adequately judge the relations at larger magnitudes although they are consistent with data from the saguenay m 5 8 and nahanni m 6 8 earthquakes the underlying model parameters are constrained by empirical data for events as large as m 6 8

high frequency site effects at two parkfield downhole and surface stations abstract using stacked ratios of microearthquake source spectra recorded at the surface and 200 m downhole we have established the p and s wave site effect at two locations in parkfield california the frequency responses of both sites are bimodal being completely dominated by multiples and amplification below 10 hz and by attenuation above 30 hz the low frequency amplification factors show roughly three to five times more uphole motion compared to that downhole the multiples produce peaks with a maximum of nearly 10 times more uphole motion above 50 hz the downhole motion is always larger approaching a factor of 5 at the high frequency limits of our study when fit with a linear attenuation model the high frequency ratios yield compressional and shear q values between 6 and 19 the data were divided into subsets based on event location and time of year statistical comparison of these subsets shows no systematic variation with azimuth or season the results of our study accounts for the lack of high frequency surface reflections in the parkfield downhole data but not for the lack of source scaling of parkfield microearthquakes

assessment of coherency for bidirectional horizontal ground motions and its application for simulating records at multiple stations estimation of the coherency of ground motion records in two horizontal orthogonal directions at single or multiple stations is carried out using records from smart 1 array for several seismic events in taiwan empirical coherency function is suggested for the components of records in two horizontal orthogonal directions at single and multiple recording stations it was also found that the coherency for the records along the major and minor principal axes at a recording station is similar to that for two randomly oriented orthogonal directions the spatial coherency and the spatial correlation of the records are used to establish a procedure for simulating bidirectional horizontal ground motions at multiple stations considering that the stochastic point source method or the stochastic finite fault method can be used to define the reference fourier amplitude spectra for scenario events use of the proposed procedure to simulate records is illustrated for a scenario seismic event the adequacy of the simulated records in approximating the target spatial correlation and coherency is presented

the relationship between u s east coast sea level and the atlantic meridional overturning circulation a review scientific and societal interest in the relationship between the atlantic meridional overturning circulation amoc and u s east coast sea level has intensified over the past decade largely due to 1 projected and potentially ongoing enhancement of sea level rise associated with amoc weakening and 2 the potential for observations of u s east coast sea level to inform reconstructions of north atlantic circulation and climate these implications have inspired a wealth of model and observation based analyses here we review this research finding consistent support in numerical models for an antiphase relationship between amoc strength and dynamic sea level however simulations exhibit substantial along coast and intermodel differences in the amplitude of amoc associated dynamic sea level variability observational analyses focusing on shorter generally less than decadal timescales show robust relationships between some components of the north atlantic large scale circulation and coastal sea level variability but the causal relationships between different observational metrics amoc and sea level are often unclear we highlight the importance of existing and future research seeking to understand relationships between amoc and its component currents the role of ageostrophic processes near the coast and the interplay of local and remote forcing such research will help reconcile the results of different numerical simulations with each other and with observations inform the physical origins of covariability and reveal the sensitivity of scaling relationships to forcing timescale and model representation this information will in turn provide a more complete characterization of uncertainty in relevant relationships leading to more robust reconstructions and projections

dependency of near field ground motions on the structural maturity of the ruptured faults little work has been undertaken to examine the role of specific long term fault properties on earthquake ground motions here we empirically examine the influence of the structural maturity of faults on the strong ground motions generated by the rupture of these faults and we compare the influence of fault maturity to that of other source properties slip mode and blind versus surface rupturing we analyze the near field ground motions recorded at rock sites for 28 large mw 5 6 7 8 crustal earthquakes of various slip modes the structural maturity of the faults broken by those earthquakes is classified into three classes mature intermediate and immature based on the combined knowledge of the age slip rate cumulative slip and length of the faults we compare the recorded ground motions to the empirical prediction equation of boore et al 1997 at all frequencies earthquakes on immature faults produce ground motions 1 5 times larger than those generated by earthquakes on mature faults the fault maturity appears to be associated with larger differences in ground motion amplitude than the style of faulting factor of 1 35 between reverse and strike slip earthquakes and the surface rupture occurrence factor of 1 2 between blind and surface rupturing earthquakes however the slip mode and the fault maturity are dependent parameters and we suggest that the effect of slip mode may only be apparent actually resulting from the maturity control we conclude that the structural maturity of faults is an important parameter that should be considered in seismic hazard assessment

changes in vp vs with depth implications for appropriate velocity models improved earthquake locations and material properties of the upper crust properties associated with the arrival times of shallow microearthquakes are determined for three tectonically different sites soviet central asia the central united states and southern california simple graphical presentations of the earthquake data including wadati and riznichenko diagrams are used to resolve the trade off in origin time and focal depth estimates of the average half space velocities for p and s waves and of the travel time ratio ts tp are also obtained that are relatively free of any model constraints used to initially locate the earthquake in all cases p and s arrivals exhibit a systematic decrease in ts tp with depth in the upper few kilometers this decrease is significant and matches similar variations observed in situ for the velocity ratio vp vs based on laboratory and theoretical studies such observations are consistent with the closing of saturated microcracks with increasing confining pressure independent determinations of velocity structure and rock properties from both refraction studies and borehole experiments show analogous results by specifying separate velocity models for both p and s waves that reflect this variation rather than assuming a constant value of vp vs we find improved stability in hypocenter determination and increased resolution of shallow seismicity patterns

site amplifications for generic rock sites seismic shear wave velocity as a function of depth for generic rock sites has been estimated from borehole data and studies of crustal velocities and these velocities have been used to compute frequency dependent amplifications for zero attenuation for use in simulations of strong ground motion we define a genetic rock site as one whose velocity at shallow depths equals the average of those from the rock sites sampled by the borehole data most of the boreholes are in populated areas for that reason the rock sites sampled are of particular engineering significance we consider two genetic rock sites rock corresponding to the bulk of the borehole data and very hard rock such as is found in glaciated regions in large areas of eastern north america or in portions of western north america the amplifications on rock sites can be in excess of 3 5 at high frequencies in contrast to the amplifications of less than 1 2 on very hard rock sites the consideration of unattenuated amplification alone is computationally convenient but what matters for ground motion estimation is the combined effect of amplification and attenuation for reasonable values of the attenuation parameter k 0 the combined effect of attenuation and amplification for rock sites peaks between about 2 and 5 hz with a maximum level of less than 1 8 the combined effect is about a factor of 1 5 at 1 hz and is less than unity for frequencies in the range of 10 to 20 hz depending on t using these amplifications we find provisional values of about ao 70 bars and k 0 0 035 sec for rock sites in western north america by fitting our empirically determined response spectra for an m 6 5 event to simulated values the borehole data yield shear velocities 033o of 618 and 306 rrdsec for rock and soil sites respectively when averaged over the upper 30 m from this we recommend that v30 equals 620 and 310 m sec for applications requiring the average velocity for rock and soil sites in western north america by combining the amplifications for rock sites and the site factors obtained from our analysis of strong motion data we derive amplifications for sites with 17 3o 520 m sec nehrp class c corresponding to a mix of rock and soil sites and v3o 310 and 255 m sec average soil and nehrp class d sites respectively for the average soil site the combined effect of amplification and attenuation exceeds a factor of 2 0 for frequencies between 0 4 and about 4 hz with a peak site effect of 2 4 the peak of the nehrp class d site effect is 2 7

variability along the atlantic water pathway in the forced norwegian earth system model the growing attention on mechanisms that can provide predictability on interannual to decadal time scales makes it necessary to identify how well climate models represent such mechanisms in this study we use a high 0 25 horizontal grid and a medium 1 resolution version of a forced global ocean sea ice model utilising the norwegian earth system model to assess the impact of increased ocean resolution our target is the simulation of temperature and salinity anomalies along the pathway of warm atlantic water in the subpolar north atlantic and the nordic seas although the high resolution version has larger biases in general at the ocean surface the poleward propagation of thermohaline anomalies is better resolved in this version i e the time for an anomaly to travel northward is more similar to observation based estimates the extent of these anomalies can be rather large in both model versions as also seen in observations e g stretching from scotland to northern norway the easternmost branch into the nordic and barents seas carrying warm atlantic water is also improved by higher resolution both in terms of mean heat transport and variability in thermohaline properties a more detailed assessment of the link between the north atlantic ocean circulation and the thermohaline anomalies at the entrance of the nordic seas reveals that the high resolution is more consistent with mechanisms that are previously published this suggests better dynamics and variability in the subpolar region and the nordic seas in the high resolution compared to the medium resolution this is most likely due a better representation of the mean circulation in the studied region when using higher resolution as the poleward propagation of ocean heat anomalies is considered to be a key source of climate predictability we recommend that similar methodology presented herein should be performed on coupled climate models that are used for climate prediction

on the interpretation of the north atlantic averaged sea surface temperature abstractthe north atlantic na basin averaged sea surface temperature nasst is often used as an index to study climate variability in the na sector however there is still some debate on what d

near surface attenuation and site effects from comparison of surface and deep borehole recordings abstract near surface attenuation and site effects are investigated using the seismograms of 17 local earthquakes recorded at depths of 0 0 3 1 5 2 5 and 2 9 km in the cajon pass borehole southern california the borehole penetrates 500 m of miocene sandstone and then crystalline granitic basement rock previous estimates of site response have been limited to shallower holes where the surface reflection interferes with the upgoing direct wave and the deepest sensor is not below the severe near surface effects in bedrock spectral ratios of the direct p and s waves for each earthquake between the different recording levels are well modeled with frequency independent q and amplification at the borehole q p 27 8 and q s 21 7 in the upper 2 9 km increasing from q p 26 and q s 15 in the upper 300 m to q p 133 and q s 47 between 1 5 and 3 km one event was also recorded at a surface granite site less than 1 5 km from the wellhead comparison of the 2 9 km recording with that at this granite site gives q p 50 and q s 23 the similarity of these values with those of previous studies at a wide range of sites suggests that q is very low in the near surface independent of rock type near surface amplification appears considerably more site dependent at the wellhead the amplifications at 1 hz of the direct p and s waves are 12 7 and 13 7 respectively these values include the free surface effect and are in reasonable agreement with the impedance contrast from the borehole logs at the granite site amplification of both p and s waves is less than four direct wave amplification at the wellhead is therefore at least three times that of the granite site the spectra of the direct and coda waves of the one earthquake recorded at both the wellhead and granite sites are compared with the corresponding 2 9 km recording coda wave amplification is in good agreement with the direct wave at the rock site but at the borehole the coda wave amplification factor overestimates the direct wave amplification by a factor of 3

a new ground motion prediction model for northeastern india nei crustal earthquakes in this study a stochastic point source model is used to develop a ground motion prediction model for northeastern india nei crustal earthquakes calibrated using region specific source path and site parameters the nei strong ground motion database is too limited to derive an empirical ground motion prediction model valid for all magnitudes and distances in the present study we simulated 30 000 ground motions to develop the horizontal ground motion prediction model for nei these simulations are for 1000 earthquakes of moment magnitudes m w 4 8 5 and epicentral distances of 1 300 km in simulating ground motions quality factor stress drop and kappa derived from available nei strong motion records have been used the model has been validated by comparing it with the available but sparse database of recorded events the best fit between the model and observed strong ground motion records indicate that the new model is consistent with the available data and can be used in seismic hazard analyses until more data are collected and the model is improved

on the drivers of decadal variability of the gulf stream north wall abstractthe gulf stream is bounded to the north by a strong temperature front known as the north wall the north wall is subject to variability on a wide range of temporal and spatial scales on int

direct observations of formation and propagation of subpolar eddies into the subtropical north atlantic abstract subsurface float and moored observations are presented to show for the first time the formation and propagation of anticyclonic submesoscale coherent vortices that transport relatively cold fresh subpolar water to the interior subtropical north atlantic acoustically tracked rafos floats released in the southward flowing western boundary current at the exit of the labrador sea reveal the formation of three of these eddies at the southern tip of the grand banks 42 n 50 w using a recently developed method to detect eddies in float trajectories and estimate their kinematic properties it was found that the eddies had average rotation periods of 5 7 day at radii of 10 25 km with mean rotation speeds of up to 0 3 m s 1 one especially long lived 5 1 months eddy crossed under the gulf stream path and translated southwestward in the subtropical recirculation to at least 35 n where it hit one of the corner rise seamounts velocity temperature and salinity measurements from a nine month deployment of two moorings south of the gulf stream at 38 n 50 w reveal the passage of at least two eddies with similar hydrographic and kinematic properties the core temperature and salinity properties of the eddies imply their formation at intermediate levels of the labrador current south of the tail of the grand banks these observations confirm earlier speculation that eddies form in this region and transport anomalously cold low salinity water directly into the subtropical interior possible formation mechanisms and potential importance of these eddies to interior ventilation and the equatorward spreading of labrador sea water are discussed

observations inferences and mechanisms of the atlantic meridional overturning circulation a review this is a review about the atlantic meridional overturning circulation amoc its mean structure temporal variability controlling mechanisms and role in the coupled climate system the amoc plays a central role in climate through its heat and freshwater transports northward ocean heat transport achieved by the amoc is responsible for the relative warmth of the northern hemisphere compared to the southern hemisphere and is thought to play a role in setting the mean position of the intertropical convergence zone north of the equator the amoc is a key means by which heat anomalies are sequestered into the ocean s interior and thus modulates the trajectory of climate change fluctuations in the amoc have been linked to low frequency variability of atlantic sea surface temperatures with a host of implications for climate variability over surrounding landmasses on intra annual timescales variability in amoc is large and primarily reflects the response to local wind forcing meridional coherence of anomalies is limited to that of the wind field on interannual to decadal timescales amoc changes are primarily geostrophic and related to buoyancy anomalies on the western boundary a pacemaker region for decadal amoc changes is located in a western transition zone along the boundary between the subtropical and subpolar gyres decadal amoc anomalies are communicated meridionally from this region amoc observations as well as the expanded ocean observational network provided by the argo array and satellite altimetry are inspiring efforts to develop decadal predictability systems using coupled atmosphere ocean models initialized by ocean data

global linkages originating from decadal oceanic variability in the subpolar north atlantic the anomalous decadal warming of the subpolar north atlantic ocean spna and the northward spreading of this warm water has been linked to rapid arctic sea ice loss and more frequent cold europe

rock and stiff soil site amplification dependency on vs30 and kappa κ0 abstract a ground motion prediction equation gmpe specific to rock and stiff soil sites is derived using seismic motion recorded on high v s 30 sites in japan this gmpe applies to events with 4 5 m w 6 9 and v s 30 ranging from 500 to 1500 m s stiff soil to rock sites the empirical site coefficients obtained and the comparison with the simulated site functions show that seismic motion on rock and stiff soil sites does not depend only on v s 30 but also on the high frequency attenuation site properties 0 the effects of the site specific 0 on site amplification are analyzed using stochastic simulations with the need to take into account both of these parameters for rock site adjustments adding the site specific 0 into the gmpes thus appears to be essential in future work the rock site stochastic ground motion simulations show that the site specific 0 controls the frequency corresponding to the maximum response spectral acceleration f amp 1 this observation is used to link the peak of the response spectral shape to 0 in this specific japanese dataset and then to add the effects of high frequency attenuation into the previous gmpe from the peak ground acceleration and up to periods of 0 2 s the inclusion of 0 allows the observed bias to be corrected for the intraevent residuals and thus reduces sigma however this 0 determination is limited to a minimum number of rock site records with m w 4 5 and to distances of less than 50 km

on the emergence of the atlantic multidecadal sst signal a key role of the mixed layer depth variability driven by north atlantic oscillation abstractdespite its wide ranging potential impacts the exact cause of the atlantic multidecadal oscillation variability amo amv is far from settled while the emergence of the amo sea surface te

on multidecadal and quasi decadal north atlantic variability observed sea surface temperatures ssts in the north atlantic from 1958 through 2000 as well as data from an ocean model simulation driven with the atmospheric variability observed during the same period are examined using multichannel singular spectrum analysis the two leading oscillatory modes are associated with a multidecadal and a quasi decadal period the former is connected to a basinwide uniform sst pattern and changes in the deep north atlantic meridional overturning circulation the quasi decadal mode involves a tripolar sst anomaly pattern forced by atmospheric variability with a spatial structure resembling that of the north atlantic oscillation nao the upper ocean s dynamical response to this nao variability provides an instantaneous positive feedback to the sst pattern while a delayed negative feedback is due to shallow overturning circulation anomalies

mechanisms of decadal north atlantic climate variability and implications for the recent cold anomaly decadal sea surface temperature sst fluctuations in the north atlantic ocean influence climate over adjacent land areas and are a major source of skill in climate predictions however the mechanisms underlying decadal sst variability remain to be fully understood this study isolates the mechanisms driving north atlantic sst variability on decadal time scales using low frequency component analysis which identifies the spatial and temporal structure of low frequency variability based on observations large ensemble historical simulations and pre industrial control simulations we identify a decadal mode of atmosphere ocean variability in the north atlantic with a dominant time scale of 13 18 years large scale atmospheric circulation anomalies drive sst anomalies both through contemporaneous air sea heat fluxes and through delayed ocean circulation changes the latter involving both the meridional overturning circulation and the horizontal gyre circulation the decadal sst anomalies alter the atmospheric meridional temperature gradient leading to a reversal of the initial atmospheric circulation anomaly the time scale of variability is consistent with westward propagation of baroclinic rossby waves across the subtropical north atlantic the temporal development and spatial pattern of observed decadal sst variability are consistent with the recent observed cooling in the subpolar north atlantic this suggests that the recent cold anomaly in the subpolar north atlantic is in part a result of decadal sst variability

interdecadal variations of the thermohaline circulation in a coupled ocean atmosphere model abstract a fully coupled ocean atmosphere model is shown to have irregular oscillations of the thermohaline circulation in the north atlantic ocean with a time scale of approximately 50 years the irregular oscillation appears to be driven by density anomalies in the sinking region of the thermohaline circulation approximately 52 n to 72 n combined with much smaller density anomalies of opposite sign in the broad rising region the spatial pattern of see surface temperature anomalies associated with this irregular oscillation bears an encouraging resemblance to a pattern of observed interdecadal variability in the north atlantic the anomalies of sea surface temperature induce model surface air temperature anomalies over the northern north atlantic arctic and northwestern europe

unified structural representation of the southern california crust and upper mantle we present a new 3d description of crust and upper mantle velocity structure in southern california implemented as a unified structural representation usr the usr is comprised of detailed basin velocity descriptions that are based on tens of thousands of direct velocity vp vs measurements and incorporates the locations and displacement of major fault zones that influence basin structure these basin descriptions were used to developed tomographic models of crust and upper mantle velocity and density structure which were subsequently iterated and improved using 3d waveform adjoint tomography a geotechnical layer gtl based on vs30 measurements and consistent with the underlying velocity descriptions was also developed as an optional model component the resulting model provides a detailed description of the structure of the southern california crust and upper mantle that reflects the complex tectonic history of the region the crust thickens eastward as moho depth varies from 10 to 40 km reflecting the transition from oceanic to continental crust deep sedimentary basins and underlying areas of thin crust reflect neogene extensional tectonics overprinted by transpressional deformation and rapid sediment deposition since the late pliocene to illustrate the impact of this complex structure on strong ground motion forecasting we simulate rupture of a proposed m 7 9 earthquake source in the western transverse ranges the results show distinct basin amplification and focusing of energy that reflects crustal structure described by the usr that is not captured by simpler velocity descriptions we anticipate that the usr will be useful for a broad range of simulation and modeling efforts including strong ground motion forecasting dynamic rupture simulations and fault system modeling the usr is available through the southern california earthquake center scec website http www scec org

seismotectonics of the newport inglewood fault zone in the los angeles basin southern california the newport inglewood fault zone nif strikes northwest along the western margin of the los angeles basin in southern california the seismicity 1973 to 1985 of m l 2 5 that occurred within a 20 km wide rectangle centered on the nif extending from the santa monica fault in the north to newport beach in the south is analyzed a simultaneous full inversion scheme velest is used to invert for hypocentral parameters two velocity models and a set of station delays arrival time data from three quarry blasts are included to stabilize the inversion the first velocity model applies to stations located along the rim and outside the los angeles basin and is well resolved it is almost identical to the starting model which is the model routinely used by the cit usgs southern california seismic network for locating local earthquakes the second velocity model applies to stations located within the los angeles basin it shows significantly lower velocities down to depths of 12 to 16 km which is consistent with basement of catalina schist below the sediments in the western los angeles basin the distribution of relocated hypocenters shows an improved correspondence to mapped surface traces of late quaternary fault segments of the nif a diffuse trend of seismicity is observed along the inglewood fault from the dominguez hills across the baldwin hills to the santa monica fault in the north the seismicity adjacent to long beach however is offset 4 to 5 km to the east near the trace of the subsurface los alamitos fault the depth distribution of earthquakes along the nif shows clustering from 6 to 11 km depth which is similar to average seismogenic depths in southern california thirty nine single event focal mechanisms of small earthquakes 1977 to 1985 show mostly strike slip faulting with some reverse faulting along the north segment north of dominguez hills and some normal faulting along the south segment south of dominguez hills to newport beach the results of an inversion of the focal mechanism data for orientations of the principal stress axes and their relative magnitudes indicate that the minimum principal stress is vertical along the north segment while the intermediate stress is vertical along the south segment the maximum principal stress axis is oriented 10 to 25 east of north reverse faulting along the north segment indicates that a transition zone of mostly compressive deformation exists between the los angeles block and the central transverse ranges

repeatable process for seismic microzonation using 1 d site specific response spectra assessment approaches application to the city of nice france abstract we are testing three different approaches to assess the site effects based on 1d soil column data the first method follows the eurocodes 8 ec8 approach based on the determination of vs30 soil classes the second one is based on an empirical relationship between vs30 and the fundamental resonance frequency of the site f0 with a response spectra amplification function proposed by cadet et al 2013 and the last one is the application of a 1 d equivalent linear simulation then we propose a repeatable methodology to define the zonation and the associated surface response spectrum from individual results this methodology uses a shape recognition algorithm to build homogeneous response spectra zones and the definition of a specific ec8 like response spectrum adjusted to the distribution of the response spectra in each zone this has been applied to downtown nice a city located on the french riviera that faces the highest seismic hazard in the french mainland area the city is built on two different sedimentary valleys that are prone to lithological site effects the ground acceleration around 1 8 hz can be 20 times higher in the valleys than the one recorded on the surrounding jurassic rock outcrop we defined a 3d geotechnical model composed of 9 homogenous soil layers the surface elastic response spectra in pseudo acceleration obtained with the three methods are compared on the whole city the results indicate that the amplification functions methodology proposed by cadet et al 2012b provides results closer to the numerical simulations compared to ec8 in addition in five sites of the french permanent accelerometric network rap resif located in the valley of nice the site to reference response spectra ratio from the numerical simulations and the spectra amplification function proposed by cadet et al 2012b were compared to earthquake recordings data although the spectra amplification functions are closer to the observations both evaluations underestimate the amplification as they could not capture complex site geometry using the repeatable zonation process on the response spectra from the amplification function three different zones are defined the associated specific response spectra are significantly different from the recommended ec8 response spectra

the mw 6 3 2009 l aquila earthquake source path and site effects from spectral analysis of strong motion data summary the strong motion data of 2009 april 6 l aquila central italy earthquake mw 6 3 and of 12 aftershocks 4 1 mw 5 6 recorded by 56 stations of the italian strong motion network are spectrally analysed to estimate the source parameters the seismic attenuation and the site amplification effects the obtained source spectra for s wave have stress drop values ranging from 2 4 to 16 8 mpa being the stress drop of the main shock equal to 9 2 mpa the spectral curves describing the attenuation with distance show the presence of shoulders and bumps mainly around 50 and 150 km as consequence of significant reflected and refracted arrivals from crustal interfaces the attenuation in the first 50 km is well described by a quality factor equal to q f 59f0 56 obtained by fixing the geometrical spreading exponent to 1 finally the horizontal to vertical spectral ratio provides unreliable estimates of local site effects for those stations showing large amplifications over the vertical component of motion

a study of site response and regional attenuation in the longmen shan region eastern tibetan plateau sw china from seismic recordings using the generalized inversion method abstract in this study more than 1600 seismic recordings from 88 small to moderate earthquakes during 2009 and 2013 which were recorded at 36 seismic stations were used to calculate the high frequency attenuation parameter 0 by comparing the 0 of six seismic stations with neighboring strong motion stations we observed that the surficial soil layers have aggravated the high frequency attenuation phenomenon besides we found that stations located in crustal low velocity anomaly areas maintained higher 0 and those located in high velocity anomaly areas tended to have lower 0 the correlation between 0 and s wave velocity anomaly showed that at the 0 10 km depth range the 0 values clearly decrease as the velocity anomaly increases the generalized inversion technique git was adopted to estimate the q f model of the sichuan basin sb and songpan garze orogen sgo in accompaniment with the site responses of 28 seismic stations the derived q f model were similar to those obtained from previous studies analyses of site responses revealed that the amplification curves and levels of sb and sgo were significantly different then site responses estimated from the genetic algorithm and git were compared the site response curves of most stations are similar for stations having significantly different site responses we investigated by comparing with the results obtained from accelerograms recorded at nearby strong motion stations by applying the horizontal to vertical spectral ratio hvsr method the results showed that site responses obtained from the git were closer to those of hvsr than those of the genetic algorithm

near surface velocities and attenuation at two boreholes near anza california from logging data to investigate near surface site effects in granite rock we drilled 300 m deep boreholes at two sites which are collocated with stations from the digital array at anza california the first borehole was sited at station knw keenwild fire station which is located along a ridge line about 8 7 km east of the san jacinto fault zone station pfo pinon flat observatory chosen for the second site is another 6 km further to the east of station knw and is located on a gently sloping hillside we logged each borehole for p and s wave velocities as well as for crack density and orientation p waves were generated by striking a plate with a hammer at the surface a tool consisting of weighted anvils driven by compressed air against end plates along a 3 5 m beam was used to generate shear waves signals were recorded downhole with a three component sensor package at 2 5 m intervals from the surface to 50 m depth and at 5 m intervals from 50 m depth to the bottom of the hole velocities were determined by differencing the measured arrival times of first arrivals or peaks over each interval in depth travel times were computed for the first breaks at shallow depths however below about 100 m depth times were computed for the first peaks rather than for first breaks since the first arrival was no longer clearly distinguishable the knw site yielded a shear velocity of 1 9 km sec by only 30 m in depth and reached close to 2 6 km sec at the bottom of the hole p wave velocities at knw were also high at 5 4 km sec starting at 120 m depth the pfo site had similar but slightly higher shear wave velocities the bottom hole shear wave velocity reached 3 0 km sec and the p wave velocity was 5 4 km sec shear wave attenuation was computed using both the pulse rise time and spectral ratio methods at station knw attenuation was significant only in an interval between 17 5 and approximately 40 m in depth over the top 50 m attenuation corresponding to a q of about 8 was obtained a total t of 0 004 sec was measured for this interval pulse rise times also increased rapidly in this zone the spectral ratio data for station pfo yields two peaks in attenuation above 50 m similar to the attenuation found for station knw the peak in attenuation corresponds to a q of about 11 averaged over the top 50 m spectra of the seismic pulses produced by the hammer give good signal between 20 to 80 hz significant motion perpendicular to the polarizations of the first shear wave arrival was recorded within a few meters of the surface apparently the rock structure is sufficiently complicated that body waves are being converted sh to sv at oblique incidence very close to the surface the presence of these elliptical particle motions within a mere few m of the pure shear wave source suggests that the detection of polarizations perpendicular to the main shear arrival at a single location at the surface is not by itself a good method for detecting shearwave splitting within the upper few tens of kilometers of the earth s crust crack densities and orientations were determined from televiewer records these records showed cracks with a preferred direction at station knw and of a greater density than at station pfo at station pfo crack densities were smaller and more diffuse in orientation

regional correlations of vs30 and velocities averaged over depths less than and greater than 30 meters using velocity profiles from sites in japan california turkey and europe we find that the time averaged shear wave velocity to 30 m vs30 used as a proxy for site amplification in recent ground motion prediction equations gmpes and building codes is strongly correlated with average velocities to depths less than 30 m vsz with z being the averaging depth the correlations for sites in japan corresponding to the kik net network show that vs30 is systematically larger for ag ivenvsz than for profiles from the other regions the difference largely results from the placement of the kik net station locations on rock and rocklike sites whereas stations in the other regions are generally placed in urban areas underlain by sediments using the kik net velocity profiles we provide equations relating vs30 to vsz for z ranging from 5 to 29 m in 1 m increments these equations and those for california velocity profiles given in boore 2004b can be used to estimate vs30 from vsz for sites in which velocity profiles do not extend to 30 m the scatter of the residuals decreases with depth but even for an averaging depth of 5 m a variation in logvs30 of 1 standard deviation maps into less than a 20 uncertainty in ground motions given by recent gmpes at short periods the sensitivity of the ground motions to vs30 uncertainty is considerably larger at long periods but is less than a factor of 1 2 for averaging depths greater than about 20 m we also find that vs30 is correlated with vsz for z as great as 400 m for sites of the kik net network providing some justification for using vs30 as a site response variable for predicting ground motions at periods for which the wavelengths far exceed 30 m online material estimates of vs30 at k net stations

subannual to interannual variabilities of sst in the north atlantic ocean abstractbased on observational data this work examines the multi time scale feature of the sea surface temperature sst variability averaged in the whole north atlantic ocean to be referred to a

structure of interannual to decadal climate variability in the tropical atlantic sector abstract a search for coupled modes of atmosphere ocean interaction in the tropical atlantic sector is presented previous studies have provided conflicting indications of the existence of coupled modes in this region the subject is revisited through a rotated principal component analysis performed on datasets spanning the 36 yr period 1958 93 the analysis includes four variables sea surface temperature oceanic heat content wind stress and atmospheric diabatic heating the authors find that the first rotated principal component is associated with fluctuations in the subtropical wind system and correlates with the north atlantic oscillation nao while the second and third modes which are the focus of interest are related to tropical variability the second mode is the atlantic nino mode with anomalous sea surface temperature and anomalous heat content in the eastern equatorial basin wind stress weakens to the west of anomalously warm water while convection is shifted south and eastward surface

the central role of ocean dynamics in connecting the north atlantic oscillation to the extratropical component of the atlantic multidecadal oscillation abstractthe relationship between the north atlantic oscillation nao and atlantic sea surface temperature sst variability is investigated using models and observations coupled climate models are used in which the ocean component is either a fully dynamic ocean or a slab ocean with no resolved ocean heat transport on time scales less than 10 yr nao variations drive a tripole pattern of sst anomalies in both observations and models this sst pattern is a direct response of the ocean mixed layer to turbulent surface heat flux anomalies associated with the nao on time scales longer than 10 yr a similar relationship exists between the nao and the tripole pattern of sst anomalies in models with a slab ocean a different relationship exists both for the observations and for models with a dynamic ocean in these models a positive negative nao anomaly leads after a decadal scale lag to a monopole pattern of warming cooling that resembles the atlantic multidecadal oscillation amo although with sma

analysis of atlantic sst variability factoring interbasin links and the secular trend clarified structure of the atlantic multidecadal oscillation abstract atlantic sst variability in the twentieth century is analyzed factoring the influence of natural sst variability in the pacific basin and the secular change in global ssts the tropical and northern extratropical basins are analyzed together using the extended eof technique which permits extraction of the interannual and multidecadal modes in the pan atlantic basin in a single step the leading mode of pacific uninfluenced sst variability is a multidecadal oscillation focused in the extratropical basin with a period of 70 yr the mode differs from the conventional atlantic multidecadal oscillation amo in the near quiescence of the tropical subtropical basin highlighting the significant influence of the pacific basin on this region in conventional analysis as much as 45 of the regional variance resulting from the conventional amo is due to this influence the second and third modes capture the growth east to west development and decay near simultaneous loss of amplitudes of interannual

on the path of the gulf stream and the atlantic meridional overturning circulation abstract the atlantic meridional overturning circulation amoc simulated in various ocean only and coupled atmosphere ocean numerical models often varies in time because of either forced or internal variability the path of the gulf stream gs is one diagnostic variable that seems to be sensitive to the amplitude of the amoc yet previous modeling studies show a diametrically opposed relationship between the two variables in this note this issue is revisited bringing together ocean observations and comparisons with the gfdl climate model version 2 1 cm2 1 both of which suggest a more southerly northerly gs path when the amoc is relatively strong weak also shown are some examples of possible diagnostics to compare various models and observations on the relationship between shifts in gs path and changes in amoc strength in future studies

the icelandic low as a predictor of the gulf stream north wall position abstractthe gulf stream s north wall east of cape hatteras marks the abrupt change in velocity and water properties between the slope sea to the north and the gulf stream itself an index of the north wall position constructed by taylor and stephens called gulf stream north wall gsnw is analyzed in terms of interannual changes in the icelandic low il pressure anomaly and longitudinal displacement sea surface temperature sst composites suggest that when il pressure is anomalously low there are lower temperatures in the labrador sea and south of the grand banks two years later warm sst anomalies are seen over the northern recirculation gyre and a northward shift in the gsnw occurs similar changes in ssts occur during winters in which the il is anomalously west resulting in a northward displacement of the gsnw 3 years later although time lags of 2 and 3 years between the il and the gsnw are used in the calculations it is shown that lags with respect to each atmospheric variable are statistica

observed impact of atlantic sst anomalies on the north atlantic oscillation the large scale patterns of covariability between monthly sea surface temperature sst and 500 mb height anomalies z500 in the atlantic sector are investigated as a function of time lag in the ncep ncar reanalysis 1958 97 in agreement with previous studies the dominant signal is the atmospheric forcing of sst anomalies but statistically significant covariances are also found when sst leads z500 by several months in winter a panatlantic sst pattern precedes the north atlantic oscillation nao by up to 6 months such long lead time covariance is interpreted in the framework of the stochastic climate model reflecting the forcing of the nao by persistent atlantic sst anomalies a separate analysis of midlatitudes 208 708n and tropical 208s 208n sst anomalies reveals that the bulk of the nao signal comes from the midlatitudes a dipolar anomaly with warm sst southeast of newfoundland and cold sst to the northeast and southeast precedes a positive phase of the nao and it should provide a prediction of up to 15 of its monthly variance several months in advance since the forcing sst pattern projects significantly onto the tripole pattern generated by the nao these results indicate a positive feedback between the sst tripole and the nao with a strength of up to 25 mk 21 at 500 mb or 2 3 mb k21 at sea level additionally a warming of the tropical atlantic 208s 208n roughly symmetric about the equator induces a negative nao phase in early winter this tropical forcing of the nao is nearly uncorrelated with and weaker than that resulting from the midlatitudes and is associated with shorter lead times and reduced predictive skill

stochastic prediction of ground motion and spectral response parameters at hard rock sites in eastern north america empirical predictions of ground motions from large eastern north american earthquakes are hampered by a lack of data for such events for this reason most prediction techniques have been based at least in part on data from the seismically active and well instrumented western north america concentrating on the prediction of response spectra on hard rock sites we have used a relatively new theoretical technique that does not require western data to make ground motion predictions for eastern north america this method often referred to as the stochastic model has its origins in the work of hanks and mcguire who treat high frequency motions as filtered random gaussian noise for which the filter parameters are determined by a seismological model of both the source and the wave propagation the model has been successfully applied to the predictions of ground motions in the western united states and to short period magnitudes from large to great earthquakes worldwide for our application the essential parameters of the model are estimated by using existing data from small to moderate eastern north american earthquakes a crucial part of the model is the relation between seismic moment and corner frequency the relation proposed in 1983 by nuttli for mid plate earthquakes leads to predictions of ground motions that are lower than available data by a factor of about 4 on the other hand a constant stress parameter of 100 bars gives model predictions in good accord with the data to aid in applications the ground motion predictions are given in the form of regression equations for earthquakes of magnitude 4 5 to 7 5 at distances within 100 km of the source the explanatory variables are hypocentral distance and moment magnitude m because predictions are often required in terms of m g rather than m we have used the theoretical model to establish a relation between the two magnitudes the predicted relation agrees with the sparse data available although the large uncertainties in the observed magnitudes for the larger events as well as the sensitivity of the theoretical magnitude to the attenuation model make it difficult to discriminate between various source scaling models

estimation of ground motion at deep soil sites in eastern north america the stochastic model used previously to estimate motions at hard rock sites in eastern north america has been modified to include the effect of deep soils we simulated motions for a number of distances and magnitudes for a representative soil column and used these motions to derive equations giving ground motion as a simple function of magnitude and distance these new equations are intended for use in building codes and those engineering applications that do not require detailed site evaluations the ground motions for which we derived equations include 5 damped response spectra at 13 periods ranging from 0 05 to 4 sec peak acceleration and the maximum pseudovelocity and maximum pseudoacceleration responses the latter two quantities are introduced here for the first time they represent the maxima over the period range 0 1 to 4 sec for a given magnitude and distance and they may be useful as a basis for determining the seismic coefficient in building codes

modeling strong motion recordings of the 2010 mw 8 8 maule chile earthquake with high stress drop subevents and background slip strong motion recordings of the m w 8 8 maule earthquake were modeled using a compound rupture model consisting of 1 a background slip distribution with large correlation lengths relatively low slip velocity and long peak rise time of slip of about 10 s and 2 high stress drop subevents asperities on the deeper portion of the rupture with moment magnitudes 7 9 8 2 high slip velocity and rise times of slip of about 2 s in this model the high frequency energy is not produced in the same location as the peak coseismic slip but is generated in the deeper part of the rupture zone using synthetic seismograms generated for a plane layered velocity model i find that the high stress drop subevents explain the observed fourier spectral amplitude from about 0 1 to 1 0 hz broadband synthetics 0 10 hz were calculated by combining deterministic synthetics derived from the background slip and asperities 1 hz with stochastic synthetics generated only at the asperities 1 hz the broadband synthetics produced response spectral accelerations with low bias compared to the data for periods of 0 1 10 s a subevent stress drop of 200 350 bars for the high frequency stochastic synthetics was found to bracket the observed spectral accelerations at frequencies greater than 1 hz for most of the stations the synthetics had durations of the arias intensity similar to the observed records

atlantic pacific links in observed multidecadal sst variability is the atlantic multidecadal oscillation s phase reversal orchestrated by the pacific decadal oscillation abstractthe atlantic and pacific basin are found linked in the context of multidecadal sst variability from analyses of 118 years of observational data recurrent spatiotemporal variability includ

ground motion modeling of hayward fault scenario earthquakes part ii simulation of long period and broadband ground motions abstract we simulate long period t 1 0 2 0 s and broadband t 0 1 s ground motions for 39 scenario earthquakes m w 6 7 7 2 involving the hayward calaveras and rodgers creek faults for rupture on the hayward fault we consider the effects of creep on coseismic slip using two different approaches both of which reduce the ground motions compared with neglecting the influence of creep nevertheless the scenario earthquakes generate strong shaking throughout the san francisco bay area with about 50 of the urban area experiencing modified mercalli intensity vii or greater for the magnitude 7 0 scenario events long period simulations of the 2007 m w 4 18 oakland earthquake and the 2007 m w 5 45 alum rock earthquake show that the u s geological survey s bay area velocity model version 08 3 0 permits simulation of the amplitude and duration of shaking throughout the san francisco bay area for hayward fault earthquakes with the greatest accuracy in the santa clara valley san jose area the ground motions for the suite of scenarios exhibit a strong sensitivity to the rupture length or magnitude hypocenter or rupture directivity and slip distribution the ground motions display a much weaker sensitivity to the rise time and rupture speed peak velocities peak accelerations and spectral accelerations from the synthetic broadband ground motions are on average slightly higher than the next generation attenuation nga ground motion prediction equations we attribute much of this difference to the seismic velocity structure in the san francisco bay area and how the nga models account for basin amplification the nga relations may underpredict amplification in shallow sedimentary basins the simulations also suggest that the spudich and chiou 2008 directivity corrections to the nga relations could be improved by increasing the areal extent of rupture directivity with period

influence of the north atlantic sst variability on the atmospheric circulation during the twentieth century the ocean atmosphere coupling in the north atlantic is investigated during the twentieth century using maximum covariance analysis of sea surface temperature sst and 500 hpa geopotential height analyses and performing regressions on dynamical diagnostics such as eady growth rate wave activity flux and velocity potential the north atlantic oscillation nao generates the so called sst anomaly tripole a rather similar sst anomaly tripole with the subpolar anomaly displaced to the east and a more contracted subtropical anomaly which is referred to as the north atlantic horseshoe pattern in turn influences the atmosphere in the fall and early winter the response is nao like and primarily results from subpolar forcing centered over the labrador sea and off newfoundland in summer the largest atmospheric response to sst resembles the east atlantic pattern and results from a combination of subpolar and tropical forcing to emphasize the interannual to multidecadal variability the same analysis is repeated after low pass filtering the sst influence is dominated by the atlantic multidecadal oscillation amo which also has a horseshoe shape but with larger amplitude in the subpolar basin a warm amo phase leads to an atmospheric warming limited to the lower troposphere in summer while it leads to a negative phase of the nao in winter the winter influence of the amo is suggested to be primarily forced by the atlantic ssts in the northern sub tropics such influence of the amo is found in winter instead of early winter because the winter sst anomalies have a larger persistence presumably because of sst reemergence

shear wave anisotropy in the parkfield varian well vsp abstract a vertical seismic profile vsp survey was run to 1334 m depth in the instrumented varian well 1 4 km from the san andreas fault trace at parkfield california to test the sensor string shortly after its permanent installation the cable subsequently failed near the 1000 m level so the test survey represents the deepest data acquired in the study a shear wave vibrator source was used at three ofsets and two orthogonal orientations and the data have been processed for p and s wave velocities and for s wave velocity anisotropy velocities are well determined 3 3 and 1 9 km sec respectively at the deeper levels and the s waves are seen clearly to be split by anisotropy below about 400 m some 8 per cent velocity difference is apparent between polarizations parallel to and perpendicular to the san andreas fault faster and slower respectively and the difference seems to decrease with distance from the fault suggesting that the cause may be the fabric of the fault zone repeated surveys at the 1000 m depth are being conducted as part of the parkfield monitoring program

a geology based 3d velocity model of the los angeles basin sediments abstract seismic hazard studies of the los angeles basin area require a realistic seismic velocity model we use geologic information about depth to crystalline basement depths to sedimentary horizons uplift of sediments and surface geology in a velocity depth age function to construct a three dimensional velocity model in earthquake location tests the model predicts travel times satisfactorily and in earthquake ground motion simulations the model correctly determines the timing and amplitude of late arriving waves

vertical seismic profiling of oroville microearthquakes velocity spectra and particle motion as a function of depth direct evidence of site distortion of p and s wave microearthquake source spectra at oroville california is presented the data were gathered by placing vertical and three component seismometers at 90 m intervals in a 500 m borehole through the cleveland hill normal fault on which the 1975 ml 5 7 oroville earthquake took place high pressure hydraulic locking mechanisms were used to firmly lock the seismometer packages against the borehole wall digital event triggering geos recorders were used to receive the data some 30 seismic events including 12 microearthquakes were recorded during the 4 months the seismometers were deployed by comparing the velocity spectra of microearthquake waves at the different depths it can be seen that scattering and attenuation in the shallow crust around the borehole dominantly affect high frequency s waves above 15 hz the value of the apparent s wave quality factor qas for the upper 500 m of crust at this site is 9 one feature of this low qas is a gross difference between s wave corner frequencies observed at ground level and 500 m downhole for example the uphole and downhole s wave corner frequencies for the mcoda 0 4 microearthquake of julian day 259 differ by a factor of 2 or more low quality factors and depth dependent corner frequencies were also observed for p waves but these data are less definitive due to lower signal to noise ratios based on their three component particle motions and polarizations the direct s waves of the microearthquakes appear to be composed of two phases which have similar amplitudes but different apparent velocities it is possible that the velocity differences are a result of anisotropy in the underlying rock

is there a north south phase shift in the surface labrador current transport on the interannual to decadal scale 1 the transport of the labrador current has substantial interannual to decadal variability that may significantly impact the ocean climate and marine ecosystem off atlantic canada and northeast united states nevertheless the alongshore coherence of the labrador current on the interannual to decadal scales has been a long standing question here we have used satellite altimetry data to study interannual to decadal variability of the unit depth surface labrador current in the past two decades in the context of the subpolar gyre of the north atlantic the study for the first time reveals that the transport over the labrador and northeastern newfoundland slope is out of phase with that over the scotian slope the surface labrador current transport is positively and negatively correlated with the winter north atlantic oscillation nao index with the transport lagging by about 1 year in the north the labrador and northeastern newfoundland slope and in the south the scotian slope respectively in addition the surface labrador current transport declines over the labrador slope and northeastern newfoundland slope and increases over the scotian slope the north south phase shift suggests two distinct regimes which warrants further studies of underlying dynamic mechanisms and may have important implications for regional ecosystems and climate

numerical simulation of the atmospheric signature of artificial and natural seismic events the mechanical coupling between solid planets and their atmospheres enables seismically induced acoustic waves to propagate in the atmosphere we numerically simulate this coupled system for two application cases active seismic experiments ases and passive seismic experiments a recent ase krishnamoorthy et al 2018 https doi org 10 1002 2018gl077481 observed the infrasonic signals produced by a seismic hammer to measure the sensitivity of observations to seismic parameters we attempt to reproduce the results from this experiment at short range by considering a realistic unconsolidated subsurface and an idealized rock solid subsurface at long range we investigate the influence of the source by using two focal mechanisms we found surface waves generate an infrasonic plane head wave in the ase case of the rock solid material for the passive seismic experiments the amplitude of atmospheric infrasound generated by seismic surface waves is investigated in detail despite some limitations the simulations suggest that balloon measurement of seismically induced infrasound might help to constrain ground properties

on the persistence and coherence of subpolar sea surface temperature and salinity anomalies associated with the atlantic multidecadal variability this study identifies key features associated with the atlantic multidecadal variability amv in both observations and a fully coupled climate model e g decadal persistence of monthly mean subpolar north atlantic na sea surface temperature sst and salinity sss anomalies and high coherence at low frequency among subpolar na sst sss upper ocean heat salt content and the atlantic meridional overturning circulation amoc fingerprint these key amv features which can be used to distinguish the amv mechanism cannot be explained by the slab ocean model results or the red noise process but are consistent with the ocean dynamics mechanism this study also shows that at low frequency the correlation and regression between net surface heat flux and sst anomalies are key indicators of the relative roles of oceanic versus atmospheric forcing in sst anomalies the oceanic forcing plays a dominant role in the subpolar na sst anomalies associated with the amv

gulf stream variability and ocean atmosphere interactions abstract time series of gulf stream position derived from the topex poseidon altimeter from october 1992 to november 1998 are used to investigate the lead and lag relation between the gulf stream path as it leaves the continental shelf and the changes in sea level pressure surface wind stress and sea surface temperature sst as given by the ncep reanalysis the dominant signal is a northward southward displacement of gulf stream axis 11 to 18 months after the north atlantic oscillation nao reaches positive negative extrema a sst warming cooling peaking north of the gulf stream is also seen to precede the latitudinal shifts but it is a part of the large scale sst anomaly tripole that is generated by the nao fluctuations there is no evidence that the gulf stream shifts have a direct impact onto the large scale atmospheric circulation a fast passive response of the gulf stream to nao forcing is also suggested by a corresponding analysis of the yearly mean gulf stream position estimated from

an empirical study of earthquake source spectra for california earthquakes we generalize source path and site effects for california earthquakes as functions of magnitude and distance based on regression analysis of 1000 fourier acceleration spectra from 43 california earthquakes in the moment magnitude range from 4 4 to 7 4 recorded at rupture distances from 1 to 200 km empirically derived source spectra for california earthquakes are generally inconsistent with the spectral shape implied by a brune omega squared point source model this is manifested by magnitude and frequency dependence of the brune model parameters for ex ample the brune stress parameter that best matches the data at high frequencies decreases from a value of about 120 bars at m5 5 to a value near 50 bars at m7 5 at frequencies below 1 hz though source spectra have much lower spectral ampli tudes than predicted by the brune point source model for these values of stress this discrepancy grows with increasing magnitude finite fault simulations indicate that this is a consequence of the breakdown of the validity of the point source approxi mation for large ruptures a stochastic finite fault model in which the fault is dis cretized as a number of subfaults each of which is represented by a brune omega squared point source correctly matches the observed spectral shapes and amplitudes the spectral decay parameter kappa representing average near surface attenuation of high frequency motion at rock sites increases with increasing magnitude from values near 0 035 sec at m5 5 to 0 050 sec at m7 5 magnitude dependence of kappa may be interpreted as evidence of nonlinearity for typical california sites subjected to strong ground motion comparisons of our empirical source spectra for california to corresponding spec tra for eastern north america suggest that the spectral amplitudes are similar in the two regions for low frequency motions f 2 hz for m5 5 f 0 5 hz for m7 5 for equivalent crustal conditions the eastern events appear to have enhanced high frequency near source amplitudes relative to the california events this is particularly pronounced for large magnitude earthquakes

the july 1986 oceanside ml 5 3 earthquake sequence in the continental borderland southern california an earthquake of m l 5 3 occurred at 32 58 7 n 117 51 5 w southwest of oceanside in san diego county at 13 47 13 july 1986 ut this main shock was followed by an extensive aftershock sequence with 55 events of m l 3 0 during july 1986 the epicenters of the main shock and aftershocks are located at the northern end of the san diego trough bahia soledad fault zone sdt bs where it changes strike from northwest to a more westerly direction through a left offset or a bend in the fault the northwest striking sdt bs is one of three strike slip fault systems that constitute the offshore agua blanca fault system the spatial distribution of the aftershocks indicates a unilateral 7 to 9 km long rupture to the east southeast away from the epicenter of the main shock the focal mechanism of the main shock also has an east southeast striking and south dipping plane with mostly reverse movement on it focal mechanisms of the m l 3 0 aftershocks show both reverse and strike slip movement the reverse focal mechanisms indicate that this sequence may have occurred on a thrust fault that provides for a left stepping offset or a bend in the san diego trough fault as movement is transferred to the west along the santa cruz catalina island escarpment some of the aftershocks that are located to the southeast of the main shock and have strike slip focal mechanisms suggest activation of the northwest trending san diego trough fault a stress inversion of the focal mechanism data shows that the maximum principal stress determined from the focal mechanisms of the main shock and 22 aftershocks that occurred within 36 hours of the main shock has an azimuth of s30 w plunging 18 the maximum principal stress determined from 30 aftershocks that occurred from 15 july to 2 october 1986 has an azimuth of s20 w plunging 18 the values the measure of the relative sizes of the principal stresses are approximately 0 07 and 0 1 respectively indicating that the intermediate and minimum principal stress are of similar magnitude the results of the stress inversion and the focal mechanisms that showed reverse faulting suggest that the inner continental borderland offshore from oceanside is not currently a pure strike slip tectonic regime but rather a strike slip mixed with reverse faulting regime when the 52 aftershock focal mechanisms are divided into four groups and the stress inversion is repeated the change in stress can be described as a progressive counter clockwise rotation of 14 of the orientation of the maximum principal stress to a more southerly direction with the greatest change in stress orientation observed shortly after the main shock the abundance of aftershocks may be related to the large temporal variation in stress orientation that in turn may have resulted from the small stress drop of the main shock

relationships between instrumental ground motion parameters and modified mercalli intensity in eastern north america a new relationship between modified mercalli intensity mmi and peak ground velocity pgv is developed by comparing instrumentally recorded and inferred historical pgv values to observed mmi for 18 significant earthquakes from eastern north america ena of moment magnitude 3 6 7 25 this pgv mmi relationship is implemented in shakemaps in ontario to estimate ground shaking intensity instrumentally derived mmi given instrumental recordings of pgv corresponding relationships for 5 damped pseudoacceleration psa at frequencies of 1 5 and 10 hz are also developed we compare the results with previous relationships between mmi and ground motion parameters developed for california by wald et al 1999a and atkinson and sonley 2000 we conclude that empirical relationships between mmi and ground motion are significantly different in eastern north america than in california thus such relationships should be assessed for each region where shakemaps are implemented manuscript received 24 october 2003

what is a reference site many methods for estimating site response compare ground motions at sites of interest to a nearby rock site that is considered a reference motion the critical assumption in these methods is that the surface rock site record reference is equivalent to the input motion at the base of the soil layers data collected in this study show that surface rock sites can have a site response of their own which could lead to an underestimation of the seismic hazard when these sites are used as reference sites data were collected from local and regional earthquakes on digital recorders both at the surface and in boreholes at two rock sites and one basin site in the san jacinto mountains southern california the two rock sites keenwild and pinon flat are located on granitic bedrock of the southern california peninsular ranges batholith the basin site garner valley is an ancestral lake bed with watersaturated sediments on top of a section of decomposed granite which overlies the competent bedrock ground motion is recorded simultaneously at the surface and in the bedrock at all three sites when the surface rock sites are used as the reference site i e the surface rock motion is used as the input to the basin the computed amplification underestimates the actual amplification at the basin site for frequencies above 2 to 5 hz this underestimation by a factor of 2 to 4 depending on frequency and site results from the rock sites having a site response of their own above the 2 to 5 hz frequencies the near surface weathering and cracking of the bedrock affects the recorded ground motions at frequencies of engineering interest even at sites that appear to be located on competent crystalline rock the bedrock borehole ground motion can be used as the reference motion but the effect of the downgoing wave field and the resulting destructive interference must be considered this destructive interference may produce pseudo resonances in the spectral amplification estimates if one is careful the bedrock borehole ground motion can be considered a good reference site for seismic hazard analysis even at distances as large as 20 km from the soil site

a stochastic earthquake ground motion prediction model for the united kingdom low seismicity regions such as the united kingdom uk pose a challenge for seismic hazard analysis in view of the limited amount of locally recorded data available in particular ground motion prediction is faced with the problem that most of the instrumental observations available have been recorded at large distances from small earthquakes direct extrapolation of the results of regression on these data to the range of magnitudes and distances relevant for the seismic hazard analysis of engineered structures generally leads to unsatisfactory predictions the present study presents a new ground motion prediction equation gmpe for the uk in terms of peak ground acceleration pga peak ground velocity pgv and 5 damped pseudospectral acceleration psa based on the results of numerical simulations using a stochastic point source model calibrated with parameters derived from local weak motion data the predictions from this model are compared with those of previous gmpes based on uk data other gmpes derived for stable continental regions scrs as well as recent gmpes developed for the wider european area

two modes of gulf stream variability revealed in the last two decades of satellite altimeter data monthly mapped sea level anomalies mslas of the nw atlantic in the region immediately downstream ofthegulfstream gs separationpointrevealaleadingmodeinwhichthepathshiftsapproximately 100km meridionally about a nominal latitude of 398n producing coherent sea level anomaly sla variability from 728 to 508w this mode can be captured by use of a simple 16 point index based on sla data taken along the maximum of the observed variability in the region 338 468n and 458 758w the gs shifts between 2010 and 2012 are the largest of the last decade and equal to the largest of the entire record the second group of eof modesofvariabilitydescribesgsmeanders whichpropagatemainlywestwardinterruptedbybriefperiodsof eastwardorstationarymeanders thesemeandershavewavelengthsofapproximately400kmandcanbeseen in standard eofs by spatial phase shifting of a standing meander pattern in the sla data the spectral properties of these modes indicate strong variability at interannual and longer periods for the first mode and periods of a few to several months for the meanders while the former is quite similar to a previous use of the altimeter for gs path the simple index is a useful measure of the large scale shifts in the gs path that is quickly estimatedand updatedwithoutchangesin previous estimates thetime scaleseparationallows alowpass filtered 16 point index to be reflective of large scale coherent shifts in the gs path

the great salinity anomaly in the northern north atlantic 1968 1982 the widespread freshening of the upper 500 800m layer of the northern north atlantic which this paper describes represents one of the most persistent and extreme variations in global ocean climate yet observed in this century though a range of explanations have been advanced to explain this event including in situ changes in the surface moisture flux this paper describes the great salinity anomaly as largely though not entirely an advective event traceable around the atlantic subpolar gyre for over 14 years from its origins north of iceland in the mid to late 1960s until its return to the greenland sea in 1981 1982 the overall propagation speed around this subpolar gyre is estimated at about 3cm s 1 of the total salt deficit associated with the anomaly as it passed south along the labrador coast in 1971 1973 about 72 109 tonnes a deficit equivalent to about two thirds of this figure 47 109 tonnes ultimately passed through the faroe shetland channel to the barents sea arctic ocean and greenland sea during the mid 1970s possible effects on deep water formation and on the representativeness of historical section data are discussed

influence of the atlantic subpolar gyre on the thermohaline circulation during the past decade record high salinities have been observed in the atlantic inflow to the nordic seas and the arctic ocean which feeds the north atlantic thermohaline circulation thc this may counteract the observed long term increase in freshwater supply to the area and tend to stabilize the north atlantic thc here we show that the salinity of the atlantic inflow is tightly linked to the dynamics of the north atlantic subpolar gyre circulation therefore when assessing the future of the north atlantic thc it is essential that the dynamics of the subpolar gyre and its influence on the salinity are taken into account

coherent surface subsurface fingerprint of the atlantic meridional overturning circulation 1 satellite altimeter data shows a weakening of the north atlantic subpolar gyre during the 1990s which is thought as an indicator of a slowdown of the atlantic meridional overturning circulation amoc however whether the recent slowing subpolar gyre is a decadal variation or a long term trend remains unclear here i show that altimeter data is highly correlated with instrumental subsurface ocean temperature data in the north atlantic and both show opposite signs between the subpolar gyre and the gulf stream path such a dipole pattern is a distinctive fingerprint of amoc variability as shown for the first time by a 1000 year coupled ocean atmosphere model simulation the results suggest that contrary to previous interpretations the recent slowdown of the subpolar gyre is a part of a multidecadal variation and suggests a strengthening of the amoc the ongoing satellite and subsurface temperature measurements could be used to monitor future amoc variations sensitively

atlantic multidecadal variability in a model with an improved north atlantic current we examine the simulated atlantic multidecadal variability amv in a model that includes a correction for a longstanding problem with climate models namely the misplacement of the north atlantic current the corrected model shows that in the warm amv phase heat is lost by the ocean in the northwestern part of the basin and gained by the ocean to the east suggesting an advective transfer of heat by the mid latitude westerlies the basin wide response is consistent with a role for cloud feedback and is in broad agreement with estimates from observations but is poorly represented in the uncorrected model the corrected model is then used to show that the ocean atmosphere heat transfer is influenced by low frequency variability in the overlying atmosphere we also argue that changing ocean heat transport is an essential feature of our results

was the midcontinent rift part of a successful seafloor spreading episode the 1 1 ga midcontinent rift mcr the 3000 km long largely buried feature causing the largest gravity and magnetic anomaly within the north american craton is traditionally considered a failed rift formed by isolated midplate volcanism and extension we propose instead that the mcr formed as part of the rifting of amazonia precambrian northeast south america from laurentia precambrian north america and became inactive once seafloor spreading was established a cusp in laurentia s apparent polar wander path near the onset of mcr volcanism recorded by the mcr s volcanic rocks likely reflects the rifting this scenario is suggested by analogy with younger rifts elsewhere and consistent with the mcr s extension to northwest alabama along the east continent gravity high southern appalachian rocks having amazonian affinities and recent identification of contemporaneous large igneous provinces in amazonia

gulf stream excursions and sectional detachments generate the decadal pulses in the atlantic multidecadal oscillation abstractdecadal pulses within the lower frequency atlantic multidecadal oscillation amo are a prominent but underappreciated amo feature representing decadal variability of the subpolar gyre e g the great salinity anomaly of the 1970s and wielding notable influence on the hydroclimate of the african and american continents here clues are sought into their origin in the spatiotemporal development of the gulf stream s gs meridional excursions and sectional detachments apparent in the 1954 2012 record of ocean surface and subsurface salinity and temperature observations the gs excursions are tracked via meridional displacement of the 15 c isotherm at 200 m depth the gs index whereas the amo s decadal pulses are targeted through the amo tendency which implicitly highlights the shorter time scales of the amo index the gs s northward shift is shown to be preceded by the positive phase of the low frequency north atlantic oscillation lf nao and followed by a positive amo tendency by 1 25 and 2 5 yea

the effect of quaternary alluvium on strong ground motion in the coyote lake california earthquake of 1979 abstract the effect of alluvium on strong ground motion can be seen by comparing two strong motion records of the coyote lake california earthquake of 6 august 1979 m l 5 9 one record at a site on franciscan bedrock had a peak horizontal acceleration of 0 13 g and a peak horizontal velocity of 10 cm sec the other at a site 2 km distant on 180 meters of quaternary alluvium overlying franciscan had values of 0 26 g and 32 cm sec amplifications by factors of 2 and 3 horizontal motions computed at the alluvial site for a linear plane layered model based on measured p and s velocities show reasonably good agreement in shape with the observed motions but the observed peak amplitudes are greater by a factor of about 1 25 in acceleration and 1 8 in velocity about 15 per cent of the discrepancy in acceleration and 20 per cent in velocity can be attributed to the difference in source distance the remainder may represent focusing by refraction at a bedrock surface concave upward there is no clear evidence of nonlinear soil response fourier spectral ratios between motions observed on bedrock and alluvium show good agreement with ratios predicted from the linear model in particular the observed frequency of the fundamental peak in the amplification spectrum agrees with the computed value indicating that no significant nonlinearity occurs in the secant shear modulus computations show that nonlinear models are compatible with the data if values of the coefficient of dynamic shear strength in terms of vertical effective stress are in the range of 0 5 to 1 0 or greater the data illustrate that site amplification may be less a matter of resonance involving reinforcing multiple reflections and more the simple effect of the low near surface velocity application of traditional seismological theory leads to the conclusion that the site amplification for peak horizontal velocity is approximately proportional to the reciprocal of the square root of the product of density and shear wave velocity

on the existence of storm tracks abstract given that middle latitude weather systems transport heat in a manner such as to weaken the baroclinicity that is thought to be crucial to their growth it is perhaps surprising that concentrated regions of such eddy activity i e storm tracks are found in the northern hemisphere winter the existence and possible self maintenance of storm tracks is investigated using a linear stationary wave model with storm track region forcings taken from data averaged over a number of winters it is found that the direct thermal effect of the eddies does indeed act against the existence of the storm track their vorticity fluxes lead to some reduction of this effect it is argued that the mean diabatic heating in the storm track region is an indirect eddy effect this heating is found to maintain the mean maximum in baroclinicity in the region further the mean low level flow induced by the eddy effects is such as to enhance the warm western oceanic boundary currents that are crucial to the existence of t

gulf stream variability in five oceanic general circulation models five non eddy resolving oceanic general circulation models driven by atmospheric fluxes derived from the ncep reanalysis are used to investigate the link between the gulf stream gs variability the atmospheric circulation and the atlantic meridional overturning circulation amoc despite the limited model resolution the temperature at the 200 m depth along the mean gs axis behaves similarly in most models to that observed and it is also well correlated with the north atlantic oscillation nao indicating that a northward southward gs shift lags a positive negative nao phase by 0 2 yr the northward shift is accompanied by an increase in the gs transport and conversely the southward shift with a decrease in the gs transport two dominant time scales appear in the response of the gs transport to the nao forcing a fast time scale less than 1 month for the barotropic component and a slower one about 2 yr for the baroclinic component in addition the two components are weakly coupled the gs response seems broadly consistent with a linear adjustment to the changes in the wind stress curl and evidence for baroclinic rossby wave propagation is found in the southern part of the subtropical gyre however the gs shifts are also affected by basin scale changes in the oceanic conditions and they are well correlated in most models with the changes in the amoc a larger amoc is found when the gs is stronger and displaced northward and a higher correlation is found when the observed changes of the gs position are used in the comparison the relation between the gs and the amoc could be explained by the inherent coupling between the thermohaline and the wind driven circulation or by the nao variability driving them on similar time scales in the models

comment on the atlantic multidecadal oscillation without a role for ocean circulation clement et al reports 16 october 2015 p 320 claim that the atlantic multidecadal oscillation amo is a thermodynamic response of the ocean mixed layer to stochastic atmospheric forcing and that ocean circulation changes have no role in causing the amo these claims are not justified we show that ocean dynamics play a central role in the amo

the dominant influence of the icelandic low on the position of the gulf stream northwall 1 the location where the gulf stream separates from the american coast and turns eastward is called its northwall the interannual fluctuations of the northwall are significantly correlated with the north atlantic oscillation with a lag of two years when the azores high and the icelandic low pressures are taken as independent variables the latter dominates the relationship with the northwall and the influence of the azores high pressure is insignificant this is consistent with the hypothesis that the major oceanic control of the northwall is in the southward flow of labrador sea water into the slope sea the alternative mechanism that the interaction of westward propagating rossby waves with the american coast is responsible for northwall fluctuations is considered less likely because its initiation requires perturbations of the eastward winds in the mid atlantic region and they are very likely dependent on the azores high the analysis suggests that the time lag between perturbations of the icelandic low and the northwall varies between one and three years

ocean atmosphere dynamical coupling fundamental to the atlantic multidecadal oscillation abstractthe north atlantic has shown large multidecadal temperature shifts during the twentieth century there is ongoing debate about whether this variability arises primarily through the influenc

a characteristic rupture model for the 2001 geiyo japan earthquake in this study we present a characteristic kinematic rupture model for an intraslab earthquake of the type of the 2001 geiyo earthquake the procedure for developing the characteristic rupture model follows the recipe developed by irikura and miyake proceedings of the 8th us national conference on earthquake engineering san francisco 2006 with a few modifications we used the functional form of nakamura and miyatake zisin j seism soc jpn 53 1 9 2000 to model the spatial and temporal variability of the slip rate function in our procedure the earthquake source is specified by the kinematic description of the fault model that incorporates spatial heterogeneity in slip and rise time and constant rupture velocity in the proposed characteristic model the asperity locations and rupture initiation point were the only parameters that were constrained by the available earthquake rupture models of the target earthquake the quality of the characteristic rupture model was assessed by comparing recorded and synthetic ground motion time histories from the 2001 geiyo earthquake calculated with a standard broadband 0 1 10 hz ground motion simulation technique our analyses show that the characteristic rupture model performs well in reproducing the recorded ground motion in spite of its simple representation of the fault geometry and kinematic rupture complexity the analyses of ground motion sensitivity to relative location of asperities and their stress drop contrast suggest that the overall ground motion goodness of fit remains the same at short periods but decreases slightly at periods longer than 1 s we suspect that due to the depth of the intraslab source 40 50 km the higher frequency ground motions are relatively insensitive to the details of the slip distribution and slip contrast on the other hand even for intraslab events the lower frequency motions are influenced by rupture directivity effects and slip distribution

the high frequency shape of the source spectrum for earthquakes in eastern and western canada abstract the high frequency shape of the earthquake spectrum strongly influences the amplitude of the peak ground acceleration and of the response spectrum at frequencies of 10 hz and greater a key parameter for the description of high frequency ground motions is kappa which is the decay slope of the fourier spectrum of acceleration at near source distances anderson and hough 1984 note anderson and hough originally referred to this parameter as kappa 0 kappa may be attributed to site effects f max hanks 1982 source processes papageorgiou and aki 1983 or both seismographic data place weak but significant constraints on kappa values on average there is no resolved kappa effect on spectra recorded at rock sites in eastern canada in the frequency range f 30 hz four firm soil sites in southwestern ontario also show no kappa effect an implied upper bound for kappa is 0 004 or lower bound of 30 hz for f max by contrast source spectra from earthquakes in the cascadia region recorded on hard rock sites in southwestern british columbia b c appear to be well described by a kappa of 0 011 0 002 the b c spectra are thus intermediate to the eastern case with zero apparent kappa and the typical california case for which kappa is about 0 04