mechanisms governing the development of the north atlantic warming hole in the cesm le future climate simulations abstracta warming deficit in north atlantic sea surface temperatures is a striking feature in global climate model future projections this north atlantic warming hole has been related to a slowing

global adjustment of the thermocline in response to deepwater formation the global adjustment of the thermocline in response to deepwater formation is studied in a single mode model on a beta plane the signal is carried from ocean to ocean by kelvin waves which travel equatorward along western boundaries eastward across the equator poleward at the eastern boundaries and then eastward around the southern tip of continents into the next ocean basin the interior is filled by rossby waves emanating from eastern boundaries stronger weaker deepwater formation induces an upward downward motion of the main thermocline in the world oceans the adjustment is completed on centennial time scales

test of source parameter inversion of the intensities of a 54 000 death shock of the seventeenth century in southeast sicily we inverted the macroseismic intensity data set felt reports of the m 5 4 earthquake of 1990 in se sicily and retrieved source parameters that were compatible with those obtained independently by other authors who treated instrumental observations our technique uses voronoi polygons and our kinematic function kf after this validation we attempted the inversion of the macroseismic intensity data set of one of the strongest earthquakes that has ever struck the mediterranean basin in 1693 in southeast sicily 54 000 casualties it was possible to invert the regional intensity patterns of these two earthquakes because their data sets are sufficiently uncontaminated by local site responses and retain regional traces of source effects the 1693 source constrained by our inversion is a nne oriented fault approximately 60 km long dipping from 90 to 54 80 with positive error of 10 and negative error of 26 toward ese 50 strike slip and 50 dip slip which crosses se sicily from the hyblean plateau to the coast of the ionian sea south of the city of catania the nucleation is 37 08 n 14 93 e this source best fits the regional distribution of damage observed in the field at the limit of the negative error of the dip angle a value of 54 makes our line source at depth compatible with the trace of the scicli active transcurrent fault which is 12 14 km to the west the retrieved source is also compatible with the orientation of the maximum horizontal geodynamical compressive stress confidently measured in the area as well as with an authoritative tectonic interpretation independent from this study the combined use of tessellation and of our kf model is promising for inverting intensity data sets of preinstrumental earthquakes

nonlinearity liquefaction and velocity variation of soft soil layers in port island kobe during the hyogo ken nanbu earthquake clear nonlinear behavior is analyzed from the acceleration records of the 1995 hyogo ken nanbu earthquake at port island kobe from four triaxial in struments placed at four different depths the surficial effects during strong ground motions were compared with those during weak motions before and after the main shock we used a spectral ratio technique and a nonlinear inversion for velocity structure to analyze the data from the spectral analysis we observed a large variation of the spectral ratios between the surface and different depths during the strong ground motions and during the liquefied state the spectral ratios after the mainshock i e after the liquefied state are different from those before the mainshock the peak frequencies in the spectral ratios after the mainshock are shifted to lower fre quencies with respect to those in the spectral ratios before the mainshock we in verted the s wave velocities using a genetic algorithm technique to determine the velocity structure before during and after the mainshock the s wave velocity struc ture before and after the mainshock was found to be different specifically the s wave velocity of the second layer 5 m to 16 m depth after the mainshock was 20 lower than before our analysis shows that the liquefied state remains at least 3 hr after the mainshock but no more than 24 hr the rigidity of the soil decreased close to zero when liquefaction happened and later increases gradually following a trend that resembles a consolidation curve the strong influence of nonlinearity during the mainshock yielded a big reduction of the horizontal surface ground motions so that the observed horizontal peak acceleration was only about 25 of the peak acceler ation expected from the linear theory however the nonlinear effects in the vertical peak acceleration were not significant

observed fingerprint of a weakening atlantic ocean overturning circulation the atlantic meridional overturning circulation amoc a system of ocean currents in the north atlantic has a major impact on climate yet its evolution during the industrial era is poorly known owing to a lack of direct current measurements here we provide evidence for a weakening of the amoc by about 3 1 sverdrups around 15 per cent since the mid twentieth century this weakening is revealed by a characteristic spatial and seasonal sea surface temperature fingerprint consisting of a pattern of cooling in the subpolar atlantic ocean and warming in the gulf stream region and is calibrated through an ensemble of model simulations from the cmip5 project we find this fingerprint both in a high resolution climate model in response to increasing atmospheric carbon dioxide concentrations and in the temperature trends observed since the late nineteenth century the pattern can be explained by a slowdown in the amoc and reduced northward heat transport as well as an associated northward shift of the gulf stream comparisons with recent direct measurements from the rapid project and several other studies provide a consistent depiction of record low amoc values in recent years

impact of great salinity anomalies on the low frequency variability of the north atlantic climate abstract in this paper it is shown that coherent large scale low frequency variabilities in the north atlantic ocean that is the variations of thermohaline circulation deep western boundary current northern recirculation gyre and gulf stream path are associated with high latitude oceanic great salinity anomaly events in particular a dipolar sea surface temperature anomaly warming off the u s east coast and cooling south of greenland can be triggered by the great salinity anomaly events several years in advance thus providing a degree of long term predictability to the system diagnosed phase relationships among an observed proxy for great salinity anomaly events the labrador sea sea surface temperature anomaly and the north atlantic oscillation are also discussed

differences between site characteristics obtained from microtremors s waves p waves and codas we examine differences of empirical site characteristics among s waves p waves coda and microtremors using records at 20 sites in and around the sendai basin japan and interpret the differences theoretically at soft soil sites the horizontal to vertical spectral ratios hvrs for early p coda become different from hvrs for a p wave with increasing time and eventually converge on hvrs for microtremors the hvrs for an s coda become similar to hvrs for microtremors with increasing time in the frequency range lower than 3 hz at soft soil sites by contrast at a rock site and two hard soil sites hvrs for s coda agree well with hvrs for an s wave the soil to rock spectral ratios for horizontal hhrs and vertical vvrs components for early s coda are larger than those for an s wave at soft soil sites when we use the deep sedimentary structures above the bedrock before tertiary age theoretical hvr for the fundamental mode of rayleigh waves is consistent with observed hvr for microtremors and theoretical hvr for an obliquely incident sv wave is consistent with observed hvr for an s wave theoretical s wave site amplification factor explains well observed hhr for s wave but does not coincide with hvr for microtremors in general the frequencies of maximum peaks of hvrs for microtremors do not coincide with those of hvrs and hhrs for s wave however if we select hvrs with peak frequencies lower than 1 hz and peak amplitudes larger than three the peak frequencies of hvrs for microtremors roughly coincide with those of hvrs and hhrs for s wave even under these constraints their amplitudes do not coincide with each other concerning coda we conclude that the rayleigh wave contamination in coda is significant in the frequency range lower than 3 hz at soft soil sites

multidecadal climate variability in the greenland sea and surrounding regions a coupled model simulation pronounced oscillations of ocean temperature and salinity occur in the greenland sea in a 2000 year integration of a coupled ocean atmosphere model the oscillations involving both the surface and subsurface ocean layers have a timescale of approximately 40 80 years and are associated with fluctuations in the inten sity of the east greenland current the greenland sea temperature and salinity variations are preceded by large scale changes in near surface salinity in the arctic which appear to propagate out of the arctic through the east greenland current these anomalies then propagate around the subpolar gyre into the labrador sea and the central north atlantic these oscillations are coherent with previously identified multi decadal fluctuations in the intensity of the north atlantic thermohaline circula tion the oscillations in the g eenland sea are related to atmospheric variability negative cold anomalies of surface air temperature are associated with negative cold sea surface temperature sst anomalies in the greenland sea with amplitudes up to 2oc near green land declining to several tenths of a degree c over north western europe the c01d sst anomalies and intensified east greenland current are also associated with enhanced northerly winds over the greenland sea

characteristics of observed peak amplitude for strong ground motion from the 1995 hyogoken nanbu kobe earthquake over 200 peak amplitudes of strong motion were observed at distances of less than 250 km from the fault during the 1995 hyogo ken nanbu kobe earth quake we analyzed the attenuation of the peak ground acceleration and velocity as a function of distance and geological site conditions the observed peak amplitudes agree well with those predicted by an empirical attenuation relation that was devel oped for japanese earthquakes this demonstrates that on average the peak amplitude of the ground motion generated by this damaging earthquake did not exceed the level predicted by the empirical attenuation relation we found a significant effect of the surface geology on the observed ground motion peak amplitude in particular for soft soil sites located near the fault the peak horizontal acceleration decreases rap idly with distance as a result of the nonlinear response of soils in order to take into account the effect of the site conditions we introduced correction factors to the ex isting attenuation relation this resulted in a significant reduction of the residuals between the predicted and observed peak amplitudes based on the attenuation re lation corrected for the site condition effect we generated a map of horizontal peak ground acceleration in the kobe and osaka area for the kobe earthquake the area of simulated large ground motion agrees well with the severe damage zone of inten sity vii jma scale

impact of the atlantic meridional overturning circulation amoc on arctic surface air temperature and sea ice variability abstractthe simulated impact of the atlantic meridional overturning circulation amoc on the low frequency variability of the arctic surface air temperature sat and sea ice extent is studied with a 1000 year long segment of a control simulation of the geophysical fluid dynamics laboratory climate model version 2 1 the simulated amoc variations in the control simulation are found to be significantly anticorrelated with the arctic sea ice extent anomalies and significantly correlated with the arctic sat anomalies on decadal time scales in the atlantic sector of the arctic the maximum anticorrelation with the arctic sea ice extent and the maximum correlation with the arctic sat occur when the amoc index leads by one year an intensification of the amoc is associated with a sea ice decline in the labrador greenland and barents seas in the control simulation with the largest change occurring in winter the recent declining trend in the satellite observed sea ice extent also shows a similar pattern in t

a microtremor survey to define the subsoil structure in a mud volcanoes area the case study of salinelle mt etna italy a microtremor survey aiming to obtain information on subsoil structure was performed in the lower southwestern etnean flank sicily italy the area is characterized by emissions of muddy and salty water which create specific pseudo volcanic edifices recording sites were both randomly selected in the area and along two profiles horizontal to vertical noise spectral ratio polarization and surface wave prospecting techniques were used the spectral ratios results set into evidence different frequency ranges that appear interesting to infer information on the subsoil structure the depth of the hydrocarbon reservoir was inferred through 1d modeling by using the information coming from the literature and experimental surveys moreover a strongly directional effect suggests the existence of a nnw sse oriented mud feeding dike

a diagnostic indicator of the stability of the atlantic meridional overturning circulation in ccsm3 a diagnostic indicator dmov is proposed in this paper to monitor the stability of the atlantic meridional overturning circulation amoc the dmov is a diagnostic for a basinwide salt advection feedback and defined as the difference between the freshwater transport induced by the amoc across the southern border of the atlantic ocean and the overturning liquid freshwater transport from the arctic ocean to the north atlantic as validated in the community climate system model version 3 ccsm3 for an amoc in the conveyor state a positive dmov freshwater convergence in the atlantic basin indicates a monostable amoc and a negative dmov freshwater divergence indicates a bistable amoc based on dmov the authors investigate the amoc stability in the last glacial maximum lgm and analyze the modulation of the amoc stability by an open closed bering strait moreover the authors estimate that the real amoc is likely to be bistable in the present day since some observations suggest a negative dmov freshwater divergence is currently in the atlantic basin however this estimation is very sensitive to the choice of the observational data

a simulation of thermohaline effects of a great salinity anomaly abstract model simulations of an idealistic great salinity anomaly gsa demonstrate that variability in the sea ice export from the arctic when concentrated to short pulses can have a large influence on the meridional heat transport and can lead to an altered overturning state one single freshwater disturbance resulting from excess ice export as in 1968 can disrupt the deep mixing process the critical condition for a large oceanic response is defined by the intensity duration and timing of the ice pulse in particular as it exits through the denmark strait a recovery from this event takes several years for advection and diffusion to remove the salinity anomaly concurrently the influence of the gsa propagates to the subtropics via the boundary currents and baroclinic adjustment as a result of this adjustment there are large up to 20 changes in the strength of the overturning cell and in the meridional heat transport in the subtropics and subpolar areas simulations show a temperature sali

the role of ocean atmosphere coupling in the zonal mean atmospheric response to arctic sea ice loss abstractthe role of ocean atmosphere coupling in the zonal mean climate response to projected late twenty first century arctic sea ice loss is investigated using community climate system model version 4 ccsm4 at 1 spatial resolution parallel experiments with different ocean model configurations full depth slab and no interactive ocean allow the roles of dynamical and thermodynamic ocean feedbacks to be isolated in the absence of ocean coupling the atmospheric response to arctic sea ice loss is confined to north of 30 n consisting of a weakening and equatorward shift of the westerlies accompanied by lower tropospheric warming and enhanced precipitation at high latitudes with ocean feedbacks the response expands to cover the whole globe and exhibits a high degree of equatorial symmetry the entire troposphere warms the global hydrological cycle strengthens and the intertropical convergence zones shift equatorward ocean dynamics are fundamental to producing this equatorially symmetric pattern

imaging the rupture of the mw 6 3 april 6 2009 l aquila italy earthquake using back projection of teleseismic p waves 1 we present rupture details of the mw 6 3 april 6 2009 l aquila earthquake derived by back projecting teleseismic p waves this technique has previously been applied to large magnitude earthquakes but this is the first application to a moderate size event we processed vertical component seismograms for 60 broadband stations obtained from the incorporated research institutions for seismology iris data center the traces were aligned and normalized using a multi channel cross correlation algorithm and 4th root stacking was used to image the rupture we found that the l aquila earthquake ruptured towards the south and that a second discrete pulse of energy occurred 20 25 km east of the epicenter about 17 18 s after the nominal origin time the spatial extent of the rupture image correlates well with a post seismic survey of damage in the region because the technique is potentially very fast images can be produced within 20 30 minutes of the origin time it may be useful to governmental agencies tasked with emergency response and rescue

source of the 1693 catania earthquake and tsunami southern italy new evidence from tsunami modeling of a locked subduction fault plane 1 the 1693 catania earthquake which caused 60000 deaths in eastern sicily and generated a 5 10 m high tsunami is investigated gps data indicate ese wnw convergence in the calabrian arc at 4 5 mm yr new high resolution seismic data image active compression at the toe of the accretionary wedge the lack of instrumentally recorded thrust earthquakes suggests the presence of a locked subduction fault plane thermal modeling is applied to calculate the limits of the seismogenic zone tsunami modeling is performed to test the hypothesis that the 1693 earthquake occurred on the subduction fault plane 160 120 km in size with 2 m of mean co seismic slip this source successfully reproduces historical observations with regard to polarity and predicts 1 3 m high amplitudes it is likely that only the sw segment of the subduction fault plane ruptured in 1693 and 1169 implying a recurrence interval of roughly 500 years for similar events

optimal excitation of amoc decadal variability links to the subpolar ocean this study describes the excitation of variability of the atlantic meridional overturning circulation amoc by optimal perturbations in surface temperature and salinity our approach is based on a generalized stability analysis within a realistic ocean general circulation model which extends the conventional linear stability analysis to transient growth unlike methods based on singular value decomposition our analysis invokes an optimization procedure using lagrangian multipliers which is a more general approach allowing us to impose relevant constraints on the perturbations and use linear measures of the amoc meridional volume and heat transports we find that the structure of the optimal perturbations is characterized by anomalies in surface temperature or salinity centered in the subpolar regions of the north atlantic off the east coasts of greenland and canada south of the denmark strait the maximum impact of such perturbations on the amoc is reached after 7 9 yr this is a robust result independent of the perturbations type the optimization measures the model surface boundary conditions or other constraints the transient growth involves the following mechanism after the initial positive surface density perturbation reaches the deep ocean it generates a cyclonic geostrophic flow that extracts a zonally varying temperature anomaly from the mean temperature field in the upper ocean in turn the anomalous zonal temperature gradient induces by thermal wind balance a northward flow in the upper ocean and a southward flow in the deep ocean thus strengthening the amoc subsequently the transient growth gives way to a decaying oscillation corresponding to a damped oceanic eigenmode with a period of about 24 yr this mode is controlled by westward propagating large scale thermal rossby waves modifying the density field in the north atlantic and hence the amoc simple estimates show that realistic changes in salinity or temperature in the upper ocean such as those due to the great salinity anomaly can induce amoc variations of several sverdups via this mechanism or 10 20 of the mean overturning an idealized model is formulated to investigate the transient growth and highlight the role of mean convection in communicating surface density anomalies to the deep ocean 2014 published by elsevier ltd

permian age from radiolarites of the hawasina nappes oman mountains the hawasina napper of the oman mountains yielded permian radiolarians from cherts stratigraphically overlying a thick volcanic basement al jil formation at the base of the hamrat duru group this fauna represents the first permian radiolarians and radiolarites in the central and western tethyan realm a permain age for pelagic sequences within the hawasina complex of oman has major significance for regional paleogeographic reconstruction a clear differentiation between platform reefal sediments and basin radiolarites from the base of the late permian 255 ma is implied it suggests a flexure of the platform during permian time the present data implies that a zone of rifting was already developed adjacent to the northeast gondwana platform margin during the late permian the hamrat duru basin corresponds to an opening intracontinental rift area sphenochasm between arabia and northeast gondwana a reentrant of the paleo tethys

middle permian plume related magmatism of the hawasina nappes and the arabian platform implications on the evolution of the neotethyan margin in oman 1 permian pillow basalts are commonly found in oman either at the base of the hawasina nappes or within the arabian platform successions exposed in the saih hatat tectonic window there is an ongoing debate on whether these lavas include normal mid oceanic ridge basalts nmorb witnessing the permian opening of the neotethys or if they are plume related magmas that are emplaced either on the arabian platform or on its thinned continental margin we sampled these lavas from several paleontologically dated middle permian sites four of them buday ah rustaq al ajal and wadi wasit are located within the hawasina nappes and are exposed as thrust slices overlain by the samail nappe and one wadi aday is within the arabian platform units and is exposed in the saih hatat window these lavas are associated with marine sediments deposited in environments ranging from proximal saih hatat wadi wasit and base of the thrust pile of al ajal to distal buday ah rustaq and top of the al ajal pile with respect to the arabian platform major and trace element features of the basalts allow two groups to be recognized enriched high ti basalts similar to alkali basalts from intracontinental traps rifted continental zones and oceanic islands are exposed in wadi aday wadi wasit and at the structural base of the al ajal pile moderately enriched to slightly depleted low ti tholeiitic basalt magmas resembling the low ti flood basalts and those from seaward dipping reflector sequences are represented in wadi al hulw in saih hatat buday ah rustaq and at the top of the al ajal thrust pile both groups show distinct plume related trace element signatures and they do not include typical nmorb although emplaced in shallow to deep submarine environments these basalts provide no direct evidence for a neotethyan seafloor spreading event in the hawasina basin instead they were likely erupted through the crust of the already rifted and drowned arabian continental margin thus despite their characteristic plume related geochemical signatures the middle permian basalts from oman were not likely emplaced during the evolution of a typical volcanic rifted margin we suggest that they originated from a mantle plume which ascended beneath the arabian passive margin well after the initiation of seafloor spreading of the neotethys

ambient vibration measurements to support morphometric analysis of a pyroclastic cone pyroclastic cones are a typical feature on volcanoes characterized by flank activity their distribution and orientation are important markers to obtain information on the maximum horizontal compressional stress acting on a volcano a geophysical survey was performed on the pyroclastic cone of mt vetore mt etna volcano southern italy to obtain information on its internal structural setting and to support the standard morphometric analysis results highlighted evident frequency peaks at 1 0 hz inside the cone which are attenuated away from it the random decrement method was applied to this peak to compute damping and then to exclude links with anthropogenic sources moreover time frequency polarization analysis revealed that ambient vibrations are strongly polarized in a narrow frequency band centered at a frequency of 1 0 hz with a preferred oscillation azimuth of 70 90 n array measurement of ambient vibrations was also used to obtain a shear wave velocity profile and then to retrieve the main interfaces with high seismic impedance results suggest a cone structure having a feeder dike consisting of fractured rocks with thickness of about 50 m surrounded by pyroclastic material lying on a high velocity substrate finally a 3d model of mt vetore cone was built employing the finite element method to reproduce an experimental modal frequency of the cone itself the numerical results successfully reproduced the experimental ones collected by the geophysical survey

latitudinal dependence of atlantic meridional overturning circulation amoc variations 1 amoc variations are often thought to propagate with the kelvin wave speed resulting in a short time lead between high and low latitudes amoc variations however as shown in this paper using a coupled climate model gfdl cm2 1 with the existence of interior pathways of north atlantic deep water nadw from flemish cap to cape hatteras as that observed recently amoc variations estimated in density space propagate with the advection speed in this region resulting in a much longer time lead several years between subpolar and subtropical amoc variations and providing a more useful predictability the results suggest that amoc variations have significant meridional coherence in density space and monitoring amoc variations in density space at higher latitudes might reveal a stronger signal with a several year time lead

the mechanisms of the atlantic meridional overturning circulation slowdown induced by arctic sea ice decline abstractwe explore the mechanisms by which arctic sea ice decline affects the atlantic meridional overturning circulation amoc in a suite of numerical experiments perturbing the arctic sea ice ra

space time patterns of magmatism along the tethysides a preliminary study five maps showing spatio temporal evolution of magmatism along the tethysides for the following time intervals late carboniferous and permian 320 248 ma triassic and early jurassic 247 188 ma

site frequency response characterisation of the maltese islands based on ambient noise h v ratios abstract the maltese islands in the central mediterranean are composed of a simple 4 layer sedimentary sequence of oligocene miocene limestones and clays highly disturbed by synsedimentary to recent tectonic activity so that the surface outcrops present a variety of lithologies as well as complex geomorphology the seismic history of the islands includes a number of damaging earthquakes the largest intensity since 1500 being ems 98 vii viii in 1693 in this study a first seismic site response survey was undertaken over the whole archipelago by recording ambient noise and applying the h v horizontal to vertical spectral ratio technique the results show a clear correlation between site response and outcrop geology in general where the two oldest layers the lower coralline limestone and the globigerina limestone outcrop the h v is flat above 0 5 hz a thick layer of clays and marls blue clay deposited originally on top of the globigerina limestone is preserved in the western half of the archipelago and this strongly influences the site response where the clay outcrops at the surface it produces the highest amplitudes and peak frequencies ranging between 2 and 5 hz whereas all sites on the hard upper coralline limestone which overlies the clay in many regions still exhibit h v peaks at a consistent frequency between 1 and 2 hz which we attribute to the presence of the underlying clay results were validated by a second measurement survey and numerical modelling the site effect induced by the clay layer has implications for the assessment of seismic risk as well as for the validity of using v s30 as a proxy for site class and site amplification

response of thermohaline circulation to freshwater forcing under present day and lgm conditions responses of the thermohaline circulation thc to freshwater forcing hosing in the subpolar north atlantic ocean under present day and the last glacial maximum lgm conditions are investigated using the national center for atmospheric research community climate system model versions 2 and 3 three sets of simulations are analyzed with each set including a control run and a freshwater hosing run the first two sets are under present day conditions with an open and closed bering strait the third one is under lgm conditions which has a closed bering strait results show that the thc nearly collapses in all three hosing runs when the freshwater forcing is turned on the full recovery of the thc however is at least a century earlier in the open bering strait run than the closed bering strait and lgm runs this is because the excessive freshwater is diverged almost equally toward north and south from the subpolar north atlantic when the bering strait is open a significant portion of the freshwater flowing northward into the arctic exits into the north pacific via a reversed bering strait throughflow which accelerates the thc recovery when the bering strait is closed this arctic to pacific transport is absent and freshwater can only be removed through the southern end of the north atlantic together with the surface freshwater excess due to precipitation evaporation river runoff and melting ice in the closed bering strait experiments after the hosing the removal of the excessive freshwater takes longer and this slows the recovery of the thc although the background conditions are quite different between the present day closed bering strait run and the lgm run the thc responds to the freshwater forcing added in the north atlantic in a very similar manner

lusi hydrothermal structure inferred through ambient vibration measurements abstract the spectacular lusi mud eruption started in northeast java indonesia the 29th of may 2006 following a m6 3 strike slip seismic event after the earthquake several mud pools aligned along a ne sw direction appeared in the sidoarjo district the most prominent eruption site was named lusi lusi is located 10 km to the ne of the northernmost cone of the arjuno welirang volcanic complex with which it is connected by the watukosek fault system in this study we applied the hvsr method which is a common tool used for site effect investigations as well as to infer buried structures and reconstruct sub surface geology the method is based on the ratio of the horizontal to vertical components of ground motion and it generally exhibits a peak corresponding to the fundamental frequency of the site spectral ratio results highlight a fundamental frequency band between 0 4 and 1 0 hz in the lusi neighborhood we interpret these peaks as related to the velocity lithological contrast at depth between alluvial deposits and bluish grey clay our analysis also highlights the presence of a depocenter characterized by fundamental frequency up to 0 3 hz which is interpreted as the subsidence caused by withdrawal of mud and fluids from depth as also shown by the comparison of the hvsr results with gravimetry data moreover in the area of the lusi vent a broad band frequency range is related to the lusi conduit in this paper we show that detailed microtremor surveys could be used as a preliminary and fast approach to locate mud conduits with sufficient precision

consistent changes in the sea ice seasonal cycle in response to global warming the northern hemisphere sea ice cover has diminished rapidly in recent years and is projected to continue to diminish in the future the year to year retreat of northern hemisphere sea ice extent is faster in summer thanwinter whichhasbeenidentifiedasoneofthemoststrikingfeaturesof satellite observations aswellasof state of the art climate model projections this is typically understood to imply that the sea ice cover is most sensitive to climate forcing in summertime and previous studies have explained this by calling on factors such as the surface albedo feedback in the southern hemisphere however it is the wintertime sea ice extent that retreats fastest in climate model projections here it is shown that the interhemispheric differences in the model projections can be attributed to differences in coastline geometry which constrain where sea ice can occur after accounting for coastline geometry it is found that the sea ice changes simulated in both hemispheres in most climate models are consistent with sea ice retreat being fastest in winter in the absence of landmasses these results demonstrate that despite the widely differing rates of ice retreat among climate model projections the seasonal structure of the sea ice retreat is robust among the models and is uniform in both hemispheres

impact of north atlantic freshwater forcing on the pacific meridional overturning circulation under glacial and interglacial conditions abstractthe pacific meridional overturning circulation pmoc is not well known compared to the atlantic meridional overturning circulation amoc due to its absence today however considering pm

mimoc a global monthly isopycnal upper ocean climatology with mixed layers a monthly isopycnal mixed layer ocean climatology mimoc global from 0 to 1950 dbar is compared with other monthly ocean climatologies all available quality controlled profiles of temperature t and salinity s versus pressure p collected by conductivity temperature depth ctd instruments from the argo program ice tethered profilers and archived in the world ocean database are used mimoc provides maps of mixed layer properties conservative temperature absolute salinity sa and maximum p as well as maps of interior ocean properties sa and p to 1950 dbar on isopycnal surfaces a third product merges the two onto a pressure grid spanning the upper 1950 dbar adding more familiar potential temperature and practical salinity s maps all maps are at monthly 0 5 0 5 resolution spanning from 80 s to 90 n objective mapping routines used and described here incorporate an isobath following component using a fast marching algorithm as well as front sharpening components in both the mixed layer and on interior isopycnals recent data are emphasized in the mapping the goal is to compute a climatology that looks as much as possible like synoptic surveys sampled circa 2007 2011 during all phases of the seasonal cycle minimizing transient eddy and wave signatures mimoc preserves a surface mixed layer minimizes both diapycnal and isopycnal smoothing of s as well as preserves density structure in the vertical pycnoclines and pycnostads and the horizontal fronts and their associated currents it is statically stable and resolves water mass features fronts and currents with a high level of detail and fidelity

the north atlantic ocean is in a state of reduced overturning the atlantic meridional overturning circulation amoc is responsible for a variable and climatically important northward transport of heat using data from an array of instruments that span the atlantic at 26 n we show that the amoc has been in a state of reduced overturning since 2008 as compared to 2004 2008 this change of amoc state is concurrent with other changes in the north atlantic such as a northward shift and broadening of the gulf stream and altered patterns of heat content and sea surface temperature these changes resemble the response to a declining amoc predicted by coupled climate models concurrent changes in air sea fluxes close to the western boundary reveal that the changes in ocean heat transport and sst have altered the pattern of ocean atmosphere heat exchange over the north atlantic these results provide strong observational evidence that the amoc is a major factor in decadal scale variability of north atlantic climate

malta escarpment fault zone offshore eastern sicily pliocene quaternary tectonic evolution based on new multichannel seismic data 1 the malta escarpment represents the dominant morphological feature offshore eastern sicily linking the deep ionian basin to the east with the hyblean carbonate platform to the west interpretation of purposely acquired multichannel seismic data allows division of the malta escarpment into two portions characterized by different tectonic structures along the segment south of siracusa the malta escarpment is not affected by recent faulting and appears as a steep surface that flattens out toward the ionian basin a recent deformation characterized by a broad area of uplift occurs 20 30 km east from the slope along a nnw sse trend the segment of the malta escarpment extending north of siracusa on the other hand is characterized by the presence of nnw sse east dipping recent extensional faults and related sedimentary basins the observed structural features support the occurrence of a lithospheric tear between the ionian oceanic basin and the hyblean plateau

graben formation the maltese islands a case history abstract the structural setting of the maltese islands is governed by two rift systems of different ages and trends and the interference of both accompanying faults are exposed at many places along cliffs and belong to the most spectacular phenomena of rift faulting of the world malta is part of a wide shelf bridge that connects the ragusa platform of southern sicily and the tripolitanian platform of northern libya the archipelago is underlain by a continental crust of african provenance the older rift generation traversing the islands strikes about 50 to 70 to create a basin and range structure on western malta comino and eastern gozo this micro province is framed by two master faults at an average distance of 14 km crustal extension started during the early miocene as observed by growth faulting and sedimentary dikes parallel to the future rift a syndepositional uparching of about 200 m has preceded the physiographical rifting in post middle miocene times discrete dip slip faulting created an external wedge block split by internal tilt blocks of antithetic character both compensating an average 15 crustal spreading normal to the rift axis shoulder upwarping of approximately 120 m has evolved synchronously with the rifting structures of the first generation are crosscut by still active second generation rift faults which on malta strike about 120 but on gozo between 80 and 90 these faults are associated with the pantelleria rift whose deep trough sets immediately south of the islands rifting was mainly originated during late miocene early pliocene time to continue in parts up to the present a set of transform faults runs through the straits on both sides of comino to form a complicated en echelon or riedel shear structure on easternmost gozo and westernmost malta shoulder upwarping related to the pantelleria rift has considerably tilted the block of malta nne ward and caused the inundated river valleys of the natural harbour of valletta the superimposition of two rift structures of different trends has been caused principally by a rotation of the controlling stress regime about 10 m y ago the active afro eurasian collision front is located about 200 km north and northwest of the islands a contemporary change of plate tectonic stresses is discussed to explain the intraplate rift pattern on malta as foreland specific reactions to plate tectonic processes

deep structure of the southern apennines italy thin skinned or thick skinned 1 the deep structure of the southern apennines sa accretionary wedge is still debated since industrial seismic reflection and well data provide reliable constraints only to a depth of about 10 km as a consequence two directly linked questions regard 1 the shortening in the accretionary prism particularly within the buried apulian thrust units and 2 the degree of involvement of the lower plate basement i e the apulian crystalline basement to address these issues we have constructed a regional section along a recently released deep seismic reflection profile crop 04 which intersects the entire sa the resulting cross section adequately constrained to a depth of about 15 km has been framed in a geodynamic scenario characterized by the eastward roll back of the westward subducting apulo adriatic lithosphere on the basis of this section we speculate on the deep structure building both thin and thick skinned thrust models a cross check of these end members models against documented tectonic geophysical and geochemical features shows that the thin skinned model is generally more consistent with the available data the development of basement slices with thicknesses of tens of kilometers is unlikely while it remains possible that the apulian basement could have been involved with its upper few kilometers in the thin skinned model the total shortening of the allochthonous units i e apennine and apulian carbonate platforms and lagonegro basin is estimated to be greater than 280 300 km some 90 km of shortening can be attributed to the apulian thrust units

numerical modeling of seismic site effects in a shallow estuarine bay suai bay shantou china abstract this paper presents the results of numerical modeling of seismic site effects in a shallow estuarine bay suai bay shantou china which is meaning for seismic hazard assessment and mitigation of estuarine and coastal structures such as immersed tunnels pipelines caissons and breakwaters the subsurface stratum and soil properties in the study area are obtained from geological and geotechnical surveys large scale 2d finite element refined nonlinear modeling is used to simulate ground motion for near field and far filed input motions with different design earthquake levels the results show that for the study area 1 the spatial distribution of pga amplification factor presents obvious vertical and horizontal variations and is strongly affected by the overall geometry of interfaces of different materials 2 the attenuation in soft sediments have significant influences on surface ground motion which leads to a deamplification of the acceleration amplitude a prolongation of the significant duration and a filtration of the high frequency spectral content 3 the pga alone cannot be regarded as an adequate parameter to quantify nonlinear site effects while the energy content expressed by arias intensity is more closely related to transfer functions patterns 4 the seismic intensity at surface is greater than the intensity of input motion during weak motions while the seismic intensity at surface is smaller than the intensity of input motion during strong motions suggesting that isolation effects may be expected in the areas having thick soft soils with a low plasticity index during strong motions

the leading interdecadal eigenmode of the atlantic meridional overturning circulation in a realistic ocean model abstractvariations in the strength of the atlantic meridional overturning circulation amoc are a major potential source of decadal and longer climate variability in the atlantic this study analyzes continuous integrations of tangent linear and adjoint versions of an ocean general circulation model ocean parallelise opa and rigorously shows the existence of a weakly damped oscillatory eigenmode of the amoc centered in the north atlantic ocean and controlled solely by linearized ocean dynamics in this particular gcm the mode period is roughly 24 years its e folding decay time scale is 40 years and it is the least damped oscillatory mode in the system its mechanism is related to the westward propagation of large scale temperature anomalies in the northern atlantic in the latitudinal band between 30 and 60 n the westward propagation results from a competition among mean eastward zonal advection equivalent anomalous westward advection caused by the mean meridional temperature gradient and westw

transient response of the moc and climate to potential melting of the greenland ice sheet in the 21st century 1 the potential effects of greenland ice sheet gris melting on the atlantic meridional overturning circulation moc and global climate in the 21st century are assessed using the community climate system model version 3 with prescribed rates of gris melting only when gris melting flux is strong enough to be able to produce net freshwater gain in upper subpolar north atlantic does the moc weaken further in the 21st century otherwise this additional melting flux does not alter the moc much relative to the simulation without this added flux the weakened moc doesn t make the late 21st century global climate cooler than the late 20th century but does reduce the magnitude of the warming in the northern high latitudes by a few degrees moreover the additional dynamic sea level rise due to this weakened moc could potentially aggravate the sea level problem near the northeast north america coast

lateral heterogeneities and microtremors limitations of hvsr and spac based studies for site response abstract we report a site effect study carried out in a small alluvial valley nari basin in ulleung island republic of korea in that small valley a permanent broad band array of five stations records ground motion continuously in addition we performed microtremor measurements using two arrays of stations a small aperture array 60 m and a medium aperture one 500 m ambient vibration was also recorded at 38 points inside the basin the records were analyzed using horizontal to vertical spectral ratios hvsr to estimate dominant frequency and maximum amplification and the spatial autocorrelation spac method to estimate the subsoil structure via phase velocity dispersion curves nari basin is clearly a 3d structure but it was expected that a laterally irregular model might be built from the interpolation of several 1d models dominant frequency maps based on results from hvsr suggest a simple sedimentary structure with mostly smooth lateral variations in contrast maximum amplification distribution is very irregular and shows no correlation with dominant frequency in the case of nari it seems that the complexity of the basin structure cancels the usefulness of hvsr we could estimate a phase velocity dispersion curve for 81 of the station pairs recording simultaneously ambient vibration in our arrays in all the cases the resulting dispersion curve had a simple shape suggesting that the subsoil structure consists of a single layer over a half space however the dispersion curves are incompatible among them even for different station pairs covering the same path something impossible if the subsoil structure were 1d it seems that the passive methods we have used in nari basin are not adapted to its structure this makes a tomography unfeasible and we are unable to propose a subsoil structure for nari basin our results show that surface wave dispersion may be estimated using the spac method even when the medium is far from 1d we believe that this problem is enhanced by the small size of this basin which amplifies the effect of lateral heterogeneities

isolating the atmospheric circulation response to arctic sea ice loss in the coupled climate system abstractin this study coupled ocean atmosphere land sea ice earth system model esm simulations driven separately by sea ice albedo reduction and by projected greenhouse dominated radiative forcing are combined to cleanly isolate the sea ice loss response of the atmospheric circulation a pattern scaling approach is proposed in which the local multidecadal mean atmospheric response is assumed to be separately proportional to the total sea ice loss and to the total low latitude ocean surface warming the proposed approach estimates the response to arctic sea ice loss with low latitude ocean temperatures fixed and vice versa the sea ice response includes a high northern latitude easterly zonal wind response an equatorward shift of the eddy driven jet a weakening of the stratospheric polar vortex an anticyclonic sea level pressure anomaly over coastal eurasia a cyclonic sea level pressure anomaly over the north pacific and increased wintertime precipitation over the west coast of north america many

pantelleria rift crustal extension in a convergent intraplate setting the pantelleria rift system is a wide zone of post miocene northwest trending grabens and horsts beneath the sicily strait the central grabens host volcanics of predominantly alkalic composition which are exposed on the islands of pantelleria and linosa on the maltese islands along the northeastern shoulder of the rift an oligocene miocene carbonate succession exposed above sea level allows structural analysis and determination of shallow crustal stresses within the otherwise largely submarine rift system an older northeast trending set of normal faults is probably the expression of an oligocene miocene crustal extension event which produced continental rifts in western europe and led to passive margin formation in the western mediterranean younger northwest trending grabens of the pantelleria rift system cut the older faults almost at right angles and define a zone of lithospheric stretching between tunisia and sicily the northwest trending grabens which subsided dramatically since the beginning of pliocene time appear to be connected by east trending dextral and more rarely north trending sinistral transforms displacement along the transforms is probably in the order of a few kilometres in situ stress measurements carried out on the maltese islands show maximum horizontal compression sh parallel to the rift this suggests that in general 1 vertical and 2 horizontal and parallel to the rift are of about the same magnitude both exceed 3 sh which trends northeasterly slight intraplate convergence in a nw se direction seems to be more than balanced by extension in a ne sw direction neotectonics of the region possibly reflects an asthenospheric flow pattern which became established during the messinian salinity crisis the mechanism of recent intraplate deformation of the pelagian shelf has relevance for the understanding of more anciently subsided platforms of the apulian plate

the freshening of surface waters in high latitudes effects on the thermohaline and wind driven circulations abstract the impacts of a freshening of surface waters in high latitudes on the deep slow thermohaline circulation have received enormous attention especially the possibility of a shutdown in the meridional overturning that involves sinking of surface waters in the northern atlantic ocean a recent study by fedorov et al has drawn attention to the effects of a freshening on the other main component of the oceanic circulation the swift shallow wind driven circulation that varies on decadal time scales and is closely associated with the ventilated thermocline that circulation too involves meridional overturning but its variations and critical transitions affect mainly the tropics a surface freshening in mid to high latitudes can deepen the equatorial thermocline to such a degree that temperatures along the equator become as warm in the eastern part of the basin as they are in the west the tropical zonal sea surface temperature gradient virtually disappears and permanently warm conditions prevail

inversion of surface wave data for subsurface shear wave velocity profiles characterized by a thick buried low velocity layer the study formed part of the simit project integrated italy malta cross border system of civil protection b1 2 19 11 part financed by the european union under the italiamalta cross border cooperation programme 2007 2013

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

on the role of stiff soil deposits on seismic ground shaking in western liguria italy evidences from past earthquakes and site response abstract in this work we analyze the macroseismic fields of the main historical earthquakes occurred in western liguria northwestern italy in order to identify possible relations between the isoseismal patterns and the local geological setting anomalies in the spatial distribution of macroseismic intensities are often attributed to site effects we observed that in the region of study such anomalies are mainly located in areas characterized by outcropping pliocene soil deposits mainly made up of stiff silty and marly clays to investigate the influence of such deposits on ground response both horizontal to vertical spectral ratio measurements and numerical site response analyses were carried out for all sites analyzed the spectral ratio curves show marked amplification peaks between 2 and 5 hz following such empirical evidence equivalent linear ground response analyses were performed in order to examine the relation between the measured resonance frequencies and the response of a set of soil columns presenting pliocene marly clayey deposits at their top to this end a database of geotechnical and geophysical properties including 50 reference soil profiles was compiled this database was used to define alternative numerical models considering three different ranges of thickness of the pliocene marly clayey deposits between 5 and 35 m 30 and 65 m 60 and 105 m results show marked amplification effects in the ranges 1 3 hz 2 5 hz and 3 10 hz depending on the thickness of the investigated soil deposits these frequency ranges are in agreement with those observed from the experimental measurements which are therefore proved adequately representative of the resonance frequencies of the pliocene marly clayey deposits therefore based on our findings such deposits can be considered an essential factor in producing the anomalies observed in the isoseismal patterns of the macroseismic fields of the historical earthquakes occurred in western liguria

implications of arctic sea ice changes for north atlantic deep convection and the meridional overturning circulation in ccsm4 cmip5 simulations 1 using ccsm4 climate simulations for 1850 2300 with four different future forcing scenarios we show that the maximum strength of the atlantic meridional overturning circulation moc decreases proportionally to the applied co2 forcing this weakening of the overturning is caused by a reduction or shut down of north atlantic na deep convection due to a surface freshening in the labrador sea the surface freshening is caused by strongly increased liquid freshwater exports from the arctic which are largely due to the decrease in the arctic sea ice cover in the strongest forcing scenario rcp8 5 the arctic becomes summer ice free by the end of the 21st century and year round ice free by the end of the 23rd century as a result of the associated freshening all na deep convection ceases by 2145 which leads to a 72 18 sv decrease of the moc strength by the end of the simulation in 2300

nonlinear site response in kushiro during the 1994 hokkaido toho oki earthquake the 1994 hokkaido toho oki earthquake of m w 8 2 and its aftershocks were used to estimate nonlinear site response in kushiro hokkaido japan the records from the mainshock and 10 aftershocks observed at 14 sediment sites in kushiro and aks a reference rock site were used in this study the sediment sites were located in a limited area within a radius of 3 km and some of them were located in the areas where liquefaction damage was observed at backfilled or reclaimed land amplification factors of peak ground acceleration and spectral ratios between sediment and rock sites for strong motion were compared with those for weak motions to investigate nonlinear site response at several sites the sediment to rock ratios of peak ground acceleration for strong motion differed by more than 50 from those for weak motions the fundamental peak frequencies of the spectral ratios became 10 to 20 percent lower during the mainshock at tbs and kkp sites on the reclaimed ground the strong to weak spectral amplification ratios at the high frequency range 2 to 20 hz significantly decreased to 0 4 during the mainshock however those on the natural ground were 0 6 to 0 9 using a moving time window we observed the drop in the strong to weak amplification ratios during the s wave main shaking the ratios tended to rise gradually in the later part of the records both the extent of the falling and the time for recovery in spectral amplification ratios depended on the degree of nonlinearity our analyses showed that nonlinearity was observed at the sites in kushiro during the mainshock and that the degree of nonlinearity varied greatly from site to site even in a limited area this variation indicated that the soil response at each site was greatly affected by the surface geology in the kushiro area

is the wind stress forcing essential for the meridional overturning circulation 1 we use a global couple d atm osphere ocean sea ice model of interm ediate complexity to demonstrate that wind forcing i s a crucial element to sustain meridional overturning flow i n t he atlantic neglecting wind stress in our multi century lon g simulations leads to a complete shutdown of the conveyor belt ci r culation this r esult may have tremendous impacts f or an assessment of the sensitivity of 2 d clima t e models which typicall y do not capture wind driven gyres it is argued that wind effects may be a key element in determining the f ate and length of a collapsed thc state possible paleo implications will be discussed

shallow high resolution geophysical investigation along the western segment of the victoria lines fault island of malta abstract the victoria lines fault island of malta is a 15 km long and n260 striking segmented normal fault system which is probably inactive since the late pliocene in the westernmost part the fomm ir rih segment displays comparable geologic throw and escarpment height 150 170 m moreover its hangingwall hosts thin patches of middle pleistocene clastic continental deposits red beds which are poorly preserved elsewhere we acquired two seismic transects by collecting ambient vibration recordings processed by using horizontal to vertical spectral ratios complemented by one high resolution 2 d refraction tomography survey crossing this fault where it is locally covered by red beds and recent colluvial deposits we found a resonance peak at 1 0 hz in the hangingwall block whereas clear peaks in the range 5 0 10 0 hz appear when approaching the subsurface fault and we relate them to the fractured bedrock within the fault zone the best fit tomographic model shows a relatively high vp shallow body vp 2200 2400 m s that we relate to the weathered top of the miocene upper coralline limestone fm bounded on both sides by low vp regions 230 m s above the weathered top bedrock our results depict a clear seismic signature of the victoria lines fault characterized by low seismic velocity and high amplification of ground motion we hypothesize that during the middle pleistocene faulting may have affected the basal part of the red beds so that this part of the investigated complex fault system may be considered inactive since 0 6 myr ago

optimal surface salinity perturbations of the meridional overturning and heat transport in a global ocean general circulation model abstract recent observations and modeling studies have stressed the influence of surface salinity perturbations on the north atlantic circulation over the past few decades as a step toward the estimation of the sensitivity of the thermohaline circulation to salinity anomalies optimal initial surface salinity perturbations are computed and described for a realistic mean state of a global ocean general circulation model ocean parallelise opa optimality is defined successively with respect to the meridional overturning circulation intensity and the meridional heat transport maximum although the system is asymptotically stable the nonnormality of the dynamics is able to produce a transient growth through an initial stimulation optimal perturbations are calculated subject to three constraints the perturbation applies to surface salinity the perturbation conserves the global salt content and the perturbation is normalized to remove the degeneracy in the linear maximization problem maximization us

evidence of the amoc interdecadal mode related to westward propagation of temperature anomalies in cmip5 models climate models show a broad diversity in the simulations of the atlantic meridional overturning circulation amoc with its leading modes of variability having different amplitudes periods and driving mechanisms theoretical considerations and computations using ocean gcms suggest that on interdecadal timescales this variability can be controlled by an internal weakly damped oceanic mode associated with westward propagation of large scale density anomalies in the north atlantic ocean these anomalies are dominated by temperature with some compensation from salinity the quadrature phases of this mode include the strengthening of the amoc followed a quarter period later by the development of a broad warm temperature anomaly in the northern atlantic extending to about 1000 m then followed by the weakening of the amoc and then the upper ocean cooling here we investigate whether this mode is present in the simulations of coupled model intercomparison project 5 cmip5 out of the 25 models investigated we find that more than half of the models exhibit variability consistent with this mode some of the relevant modal features includes statistically significant spectral peaks in the band between 15 and 35 years the westward propagation of density anomalies in the 40 circ n 60 circ n latitudinal band which sets the period of the mode the existence of the distinct quadrature phases of the amoc variability and the predominant effect of temperature on density anomalies

are microtremors useful in site response evaluation we have reviewed the applicability of microtremor measurements to evaluate site response of soft soils to this end we evaluated three different techniques commonly used to estimate site effects from microtremor measurements interpretation of fourier amplitude spectra computation of spectral ratios relative to a firm reference station and finally computation of spectral ratios of horizontal components relative to the vertical component of ground motion nakamura s technique these techniques are applied to microtremor records obtained in three cities in mexico mexico city oaxaca and acapulco these cities differ in their local geological conditions and in their seismotectonic environment in order to evaluate the results obtained from microtremor measurements we compare them with standard spectral ratios of the intense s wave part of weak or strong motion records obtained at the same sites our results showed that microtremor measurements can be used to estimate the dominant period of a site with very acceptable reliability in the range 0 3 to 5 hz the best results were obtained with nakamura s technique which also gives a rough estimate of amplification of seismic waves when the local geology is relatively simple simple numerical simulations indicate that the underlying assumptions of nakamura s technique are consistent with the propagation of rayleigh waves these simple numerical simulations also explain why different researchers have been able to successfully characterize 1d site effects using microtremor records regardless of whether they consider microtremors to consist of surface or body waves our results strongly suggest that the technique by nakamura effectively compensates for source effects in microtremor measurements which eliminates a major limitation to their application in earthquake engineering

a theory for the surface atlantic response to thermohaline variability abstract the response of the upper warm limb of the thermohaline circulation in the north atlantic to a rapid change in deep water formation at high latitudes is investigated using a reduced gravity ocean model changes in deep water formation rate initiate kelvin waves that propagate along the western boundary to the equator on a timescale of months the response in the north atlantic is therefore rapid the southern hemisphere response is much slower limited by a mechanism here termed the ldquo uatorial buffer since to leading order the flow is in geostrophic balance the pressure anomaly decreases in magnitude as the kelvin wave moves equatorward where the coriolis parameter is lower together with the lack of sustained pressure gradients along the eastern boundary this limits the size of the pressure field response in the southern hemisphere interior adjustment is by the westward propagation of rossby waves but only a small fraction of the change in thermohaline circulation strength is commun

comparison of site response characteristics inferred from microtremors and earthquake shear waves we investigated the validity of seismic site response characteristics es timated from microtremors by comparing them with those of earthquake motions for this purpose we observed microtremors as well as earthquake motions using large 5 km diameter and small 0 5 km diameter arrays deployed on soft sedi ments specifically we examined four estimates from microtremors relative site amplification factors to incident shear waves site amplification factors by the naka mura method resonance frequency in horizontal to vertical spectral ratios and horizontal to vertical spectral ratios as a result of the comparisons we obtained the following conclusions the relative amplification factors can be inferred from horizontal component ratios of microtremors to a reference site within a small area of several hundred meters the horizontal to vertical spectral ratios inferred by the nakamura method partly reflect site amplification factors but do not agree with site amplification factors a sharp peak frequency in the horizontal to vertical spectral ratios is possibly the resonance frequency the horizontal to vertical spectral ratios of microtremors either agree with those of earthquake motions at some array sites or are slightly smaller at the other sites

will greenland melting halt the thermohaline circulation 1 climate projections for the 21st century indicate a gradual decrease of the atlantic meridional overturning circulation amoc the weakening could be accelerated substantially by meltwater input from the greenland ice sheet gis here we repeat recent experiments conducted for the intergovernmental panel of climate change providing an idealized additional source of freshwater along greenland s coast for conservative and high melting estimates the amoc reduction is 35 and 42 respectively compared to a weakening of 30 for the original a1b scenario even for the high meltwater estimate the amoc recovers in the 22nd century the impact of the additional fresh water is limited to further enhancing the static stability in the irminger and labrador seas whereas the backbone of the overturning is maintained by the overflows across the greenland scotland ridge our results suggest that abrupt climate change initiated by gis melting is not a realistic scenario for the 21st century citation jungclaus j h h haak m esch e roeckner and j marotzke 2006 will greenland melting halt the thermohaline circulation geophys res lett 33 l17708 doi 10 1029 2006gl026815

the met office hadley centre sea ice and sea surface temperature data set version 2 1 sea ice concentrations we present a new version of the sea ice concentration component of the met office hadley centre sea ice and sea surface temperature data set hadisst 2 1 0 0 passive microwave data are combined with historical sources such as sea ice charts to create global analyses on a 1 grid from 1850 to 2007 climatology was used when no information about the sea ice was available our main aim was to create a homogenous data set by calculating and applying bias adjustments using periods of overlaps between the different data sources used national ice center charts from 1995 to 2007 have been used as a reference to achieve this in particular large bias adjustments have been applied to the passive microwave data in both the antarctic and arctic summers overall hadisst 2 1 0 0 contains more ice than hadisst1 1 with higher concentrations shorter marginal ice zones and larger extents and areas in some regions and periods a new method for estimating the concentrations within the ice pack using the distance from the ice edge has been developed and evaluated this was used when only the extents were known or the original concentration fields were heterogeneous a number of discontinuities in the hadisst1 1 record are no longer found in hadisst 2 1 0 0

shallow structure of the tangshan fault zone unveiled by dense seismic array and horizontal to vertical spectral ratio method abstract the tangshan fault zone has been considered to be a potential seismogenic fault from the devastating 1976 ms 7 8 tangshan earthquake based on the dense seismic array with interstation distance of 1 km and length of 40 km hvsr horizontal to vertical spectral ratio curves at 37 stations are obtained with the micro tremor seismic waveforms and the two dimensional quaternary sedimentary structures cross the tangshan fault zone are imaged by frequency to depth conversion results suggest that two significant seismic impedance interfaces at 100 m and 300 800 m depth are clearly revealed respectively the interface at 100 m depth can be attributed to the strong contrasts between the unconsolidated sand clay and semi consolidated silt which suggests very small variations and is well consistent with the seismic reflection interface from shallow seismic reflection exploration while the deeper interface at 300 800 m depth can be attributed to the quaternary sedimentary basement which increases from 300 to 800 m from the west to the east and is also consistent with the results in previous studies rapid variations 200 m of the quaternary sedimentary basement depth just beneath the fault zone well agrees with spatial characteristics of the fault revealed by deep seismic reflection profiling our work suggests that the tangshan fault zone has been significantly ruptured and modified by strong earthquake activities since quaternary this study also suggests that the hvsr method with dense seismic array is an efficient effective non invasive and low cost method for investigating active faults in shallow sediments it is useful for probing the active faults buried by thick sediments in the densely populated urban settings where seismic investigation with explosive sources are too hazardous to carry out

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

the influence of sea ice on ocean heat uptake in response to increasing co2 two significant changes in ocean heat uptake that occur in the vicinity of sea ice cover in response to increasing co2 are investigated with community climate system model version 3 ccsm3 a deep warming below 500 m and extending down several kilometers in the southern ocean and warming in a 200 m layer just below the surface in the arctic ocean ocean heat uptake caused by sea ice retreat is isolated by running the model with the sea ice albedo reduced artificially alone this integration has a climate response with strong ocean heat uptake in the southern ocean and modest ocean heat uptake in the subsurface arctic ocean the arctic ocean warming results from enhanced ocean heat transport from the northern north atlantic at the time of co2 doubling about 1 3 of the heat transport anomaly results from advection of anomalously warm water and 2 3 results from strengthened inflow at the same time the overturning circulation is strengthened in the northern north atlantic and arctic oceans wind stress changes cannot explain the circulation changes which instead appear related to strengthened convection along the siberian shelves deep ocean warming in the southern ocean is initiated by weakened convection which is mainly a result of surface freshening through altered sea ice and ocean freshwater transport below about 500 m changes in convection reduce the vertical and meridional temperature gradients in the southern ocean which significantly reduce isopycnal diffusion of heat upward around antarctica the geometry of the sea ice cover and its influence on convection have a strong influence on ocean temperature gradients making sea ice an important player in deep ocean heat uptake in the southern ocean

investigating the reliability of h v spectral ratio and image entropy for quantifying the degree of disintegration of weak rocks abstract characterization and quantification of disintegration behavior of weak rocks such as shales claystones mudstones and siltstones are usually a difficult task because of their extremely diverse nature these rocks present numerous stability problems along cut slopes around the world because they can change rapidly from rock like to soil like materials upon exposure to natural climatic conditions engineers often overestimate the design parameters for cut slopes in these rocks when laboratory tests are performed on fresh samples adjusting the design parameters for the anticipated amount of disintegration can be problematic because of the complex and time dependent nature of disintegration behavior in this study we investigate the reliability of using microtremor h v spectral ratio derived from microtremor signals and image entropy obtained from image analysis techniques for quantifying the varying degrees of disintegration during 2011 2014 both techniques were used to study disintegration of slopes cut through claystones mudstones and limestones along the 80 km stretch of a highway between bogota and tunja in central colombia for image analysis a new algorithm was developed to discriminate between varying degrees of disintegration across the complete color structure of the image avoiding the gray scale transformation that is usually time consuming the results indicate significant correlations between the degree of disintegration of the cut face the dominant frequency estimated from the microtremor h v ratio and the image entropy values suggesting that h v ratio and image entropy can be reliable techniques for quantifying the degree of disintegration

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