lagrangian simulations and interannual variability of anchovy egg and larva dispersal in the sicily channel the interannual variability in the transport of anchovy eggs and larvae in the sicily channel relatively to the period 1999 2012 is studied by means of numerical simulations of the mediterranean forecasting system mfs circulation model provided by ingv subgrid scale dynamics not resolved by the mfs model is parameterized in terms of kinematic fields the latter affect small scale tracer relative dispersion while leaving the mean large scale advection substantially unchanged a lagrangian transport index lti can be defined to characterize the efficiency of the main currents e g the atlantic ionian stream in connecting spawning and nursery areas to each other in our case this indicator comes from the first arrival time statistics of tracers traveling from a spawning area near sciacca to a nursery area in proximity of cape passero we observe on the basis of lti values that there are years when the lagrangian connectivity is very efficient 2004 2008 2012 and years when it is weak 2000 2001 2003 2010 lagrangian indicators like the lti concur to explain observed fluctuations of larval density and also can be employed more in general in multivariate models of population dynamics

estimation of seismic hazard parameters for the himalayas and its vicinity from complete data files the maximum likelihood estimation of earthquake hazard parameters has been made in the himalayas and its surrounding areas on the basis of a procedure which utilizes data containing complete files of the most recent earthquakes the entire earthquake catalogue used covers the period from 1900 1990 the maximum regional magnitude m max the activity rate of the seismic event the mean return period r of earthquakes with a certain lower magnitude m max m along with their probability of occurrence as well as the parameter b of of gutenberg richter magnitude frequency relationship have been determined for six different seismic zones of the himalayas and its vicinity it is shown that in general the hazard is higher in the zone nei and ban than the other four zones the high difference of the b parameter and the hazard level from zone to zone reflect the high seismotectonic complexity and crustal heterogeneity

transverse tectonics in the sikkim himalaya evidence from seismicity and focal mechanism data abstract in the present study about 356 local earthquakes in the region of the sikkim himalaya have been accurately located and analyzed using 2181 p travel times and 2161 s travel times from a network of 11 broadband seismic stations operated by the national geophysical research institute during january 2006 to november 2007 further refinement of the hypocentral parameters using the hypodd relocation program resulted in 198 well constrained locations interestingly this study reveals several characteristic features that distinguish sikkim from the rest of the himalaya the seismicity distribution is found to be confined mostly between the main boundary thrust mbt and the main central thrust mct but not quite associated with either while the entire himalayan front is generally characterized by shallow angle thrust faulting focal mechanisms in this region are predominantly of strike slip type in conformity with a right lateral strike slip mechanism along the northwest trending tista and gangtok lineaments the p axis trends of earthquake focal mechanisms are clearly oriented north northwest marking a clear transition from the ambient north northeast trending direction of indian plate motion with respect to the eurasian plate all along the himalayan front moderate sized earthquakes occur down to 70 km depth in this region compared to an average focal depth of 15 20 km in the rest of the himalaya also a high average crustal p velocity of 6 66 km sec and a fairly low b value of 0 83 0 04 are obtained indicating the probability of occurrence of a higher magnitude earthquake in the future a north south section in the sikkim region shows a relatively flat topography unlike in the rest of the himalayan mountain chain and suggestive of lower rates of convergence in the recent geologic past it is proposed that crustal shortening in the sikkim himalaya has been substantially accommodated by transverse tectonics rather than underthrusting in recent times

transverse tectonics in the sikkim himalaya a magnetotelluric study abstract the tectonics of seismically active sikkim himalaya as inferred by numerous seismological studies is distinct from the conventional thrust tectonics proposed for the himalayan collision belt here focal mechanisms of several moderate magnitude earthquakes and composite fault plane solutions of microearthquakes have revealed strike slip motion along faults transverse to the northward convergence direction of the indian plate in the present study we analyze broadband magnetotelluric data of 12 sites located along an approximately n s profile cutting across major geological sub domains of sikkim to test whether magnetotelluric strikes also support such transverse tectonic nature of the region we have performed strike analysis of the data by two decomposition approaches as well as by phase tensor method the study has revealed local variations in the strike directions within the region consistent with the geological and tectonic setup and the presence of transverse tectonic features in the region of main central thrust zone mctz where major axis of phase ellipses align in nnw sse to nw se direction this trend coincides with the one obtained by microseismic data recorded after the september 18 2011 earthquake mw 6 9 magnetotelluric strike analysis thus supports the presence of nnw to nw trending transverse tectonic zone in mctz

seismotectonic model of the sikkim himalaya constraint from microearthquake surveys the seismotectonic model in the sikkim himalaya does not fit well with the proposed steady state or evolutionary models the main boundary thrust mbt is seismogenic and is a mantle reaching fault the earthquakes are not confined to shallower depths 25 km above the plane of detachment as proposed in the models the seismic activity continues from surface to the lower crust 0 45 km to the north of mbt and earthquakes are produced by a thrust mechanism the earthquakes to the east of sikkim in the bhutan himalaya on the other hand are produced along a 200 km long northwest southeast trending lineament by transverse tectonics the seismogenic lineament cuts across the himalayan major thrusts and extends to the goalpara wedge in the southeast the earthquakes occur by strike slip mechanism in the midcrust at a depth range of 10 25 km along this long active lineament

seismicity and one dimensional velocity structure of the himalayan collision zone earthquakes in the crust and upper mantle 1 earthquakes beneath the himalayan collision zone occur at depths between near surface and around 100 km below sea level after relocating earthquakes with two one dimensional 1 d velocity models we found a clear bimodal depth distribution for earthquakes in the himalayas of eastern nepal and the southern tibetan plateau and evidence that some earthquakes originate at upper mantle depths seismicity in nepal shows an accumulation of earthquakes along the front of the himalayan arc with a seismic gap between longitudes 87 3 e and 87 7 e although upper crustal seismicity along the topographic front of the high himalaya is consistent with a region of high strain accumulation associated with convergence on the main himalayan thrust fault microearthquakes do not necessarily occur on this fault instead they concentrate in the hanging wall seismic activity in the sub himalaya and the terai plains is almost exclusively limited to the vicinity of the location of the magnitude 6 5 20 august 1988 udayapur earthquake with most of the earthquakes in the lower crust and the upper mantle clusters of earthquakes in the lesser and high himalayas and south tibet tethyan himalayas mark very well defined zones of seismicity at depths between 50 and 100 km confirming the presence of earthquakes in the upper mantle in the region of continental collision the occurrence of earthquakes at sub moho depths favors the idea that the continental upper mantle deforms by brittle processes

field documentation and genesis of back structures in ductile and brittle regimes from the foreland part of a collisional orogen examples from the darjeeling sikkim lesser himalaya india in the foreland side of an orogen thrust related structures develop that verge towards the foreland fore thrusts although much less abundant structures with opposite vergence i e towards hinterland named back structures also exist we report back structures exposure scale back thrusts and associated folds from the darjeeling sikkim lesser himalaya india these structures occur mainly in three back structure zones bsz a b and c back structures probably originated in the ductile regime and continued in the brittle domain tectonic setting of the study area such as critical taper duplexing etc indicates a good potential for the presence of back structures in this region along with the previous work on back structures in collisional orogens himalaya in particular these structures seem to be ubiquitous the correlation of field observations with tectonics indicate that mechanisms e g critical taper sub surface barriers and passive roof duplex played roles in forming back structures in this part of the sikkim lesser himalaya

gravity anomalies flexure and deformation of the converging indian lithosphere in nepal and sikkim darjeeling himalayas researchers ubiquitously noted that the common processes of partitioning oblique convergence in response to drag from the trench hanging plate simultaneously produce radial slips along strike translation and extension parallel to the deformation front here we focus on the area between nepal and sikkim darjeeling himalayas and carry out gravity and finite element stress modeling of the strike orthogonal converging indian lithosphere we delineate the geometries of different layers and their interfaces through gravity modeling the optimum model parameters along with rheological parameters of different layers are used for finite element modeling finite element modeling is done with boundary conditions of keeping the upper surface free and rigidly fixing the section of the northern boundary below the main himalayan thrust we impart on its frontal section an amount of 6 1012 n m force equivalent to resistive force of the himalayan tibet system and analyze the maximum and minimum compressive stress fields evolved in the lithosphere we testify our observations with earthquake database and other geophysical and geological studies we note that an increasing flexing of the indian lithosphere beyond the main boundary thrust becomes maxima between the main central thrust and south tibetan detachment in both the areas however more steepening of the moho boundary is identified in the sikkim darjeeling himalaya this abrupt change in lithospheric geometry beneath the greater himalaya is likely correlated with the sharp elevation changes in the topography although the highest seismicity concentration is dominant in this zone the lesser and the tethys himalayas in sikkim darjeeling area also record relatively fair seismic activity more compressive stress field in different layers right within the sharp bending zone supports this observation we thus propose that the sharp bending zone beneath the greater himalaya is suffering maximum deformation and the deformation is continued in the mantle too we also identify both right lateral shear and radial vergence slip which are presumably associated with the general dynamics and kinematics of the himalaya

seismic activity at the mct in sikkim himalaya abstract a microearthquake survey in the sikkim himalaya raised a question whether the north south segment of the main central thrust mct in this part of the himalaya is seismically active fault plane solution of a cluster of events occurred below this segment of the mct shows right lateral strike slip motion the seismic observations and the geological evidences suggest that a nne ssw trending strike slip fault beneath this segment caused right lateral movement on the mct and is seismically active

microearthquake activity in some parts of the himalaya and the tectonic model abstract microearthquake data from temporary permanent networks in different parts of the himalaya shed new light on understanding the earthquake generating processes and their relation to tectonic models of the region the microearthquake activity in arunachal pradesh northeastern himalaya is found to be pronounced at the main boundary thrust mbt and to its south the subcrustal earthquakes depth 50 80 km occur much below the plane of detachment of the tectonic models proposed by seeber et al 1981 ni and barazangi 1984 the mbt is not the seismogenic fault the earthquakes are generated by strike slip movement on deep seated hidden faults transverse to the mbt the high seismic activity in the shillong plateau about 200 km south of the mbt in the northeast region is due to the influence of himalayan collision tectonics to the north and burmese arc subduction tectonics to the east the activity in the plateau is not directly related to the himalayan thrust belt or seismic belt these are mostly crustal earthquakes depth 10 30 km and are caused by local active faults lineaments in the eastern himalaya in the sikkim and darjeeling area the seismic activity is found to be clustered mostly to the north of the mbt the earthquakes occur at a depth range 0 50 km the majority of them occur below the detachment plane by thrust faulting in the central part in the nepal himalaya lateral variations of the seismic activity are observed which represent lateral segmentation of the mbt by transverse tectonic features in the western himalaya however the tectonic models fit well with the microearthquake data in the himachal pradesh of the western himalaya the microearthquakes are mostly recorded in the mbt zone and the hypocentres depth 0 20 km are confined above the plane of detachment or on the basement thrust the earthquakes mostly occur to the south of the main central thrust mct which suggests that the mct is not seismogenic it is rather a dormant fault no single tectonic model explains the himalayan earthquakes

parameterization of mixed layer eddies part i theory and diagnosis ageostrophic baroclinic instabilities develop within the surface mixed layer of the ocean at horizontal fronts and efficiently restratify the upper ocean in this paper a parameterization for the restratification driven by finite amplitude baroclinic instabilities of the mixed layer is proposed in terms of an overturning streamfunction that tilts isopycnals from the vertical to the horizontal the streamfunction is proportional to the product of the horizontal density gradient the mixed layer depth squared and the inertial period hence restratification proceeds faster at strong fronts in deep mixed layers with a weak latitude dependence in this paper the parameterization is theoretically motivated confirmed to perform well for a wide range of mixed layer depths rotation rates and vertical and horizontal stratifications it is shown to be superior to alternative extant parameterizations of baroclinic instability for the problem of mixed layer restratification two companion papers discuss the numerical implementation and the climate impacts of this parameterization

earthquake processes of the himalayan collision zone in eastern nepal and the southern tibetan plateau summary focal mechanisms determined from moment tensor inversion and first motion polarities of the himalayan nepal tibet seismic experiment himnt coupled with previously published solutions show the himalayan continental collision zone near eastern nepal is deforming by a variety of styles of deformation these styles include strike slip thrust and normal faulting in the upper and lower crust but mostly strike slip faulting near or below the crust mantle boundary moho one normal faulting earthquake from this experiment accommodates east west extension beneath the main himalayan thrust of the lesser himalaya while three upper crustal normal events on the southern tibetan plateau are consistent with east west extension of the tibetan crust strike slip earthquakes near the himalayan moho at depths 60 km also absorb this continental collision shallow plunging p axes and shallow plunging ew trending t axes proxies for the predominant strain orientations show active shearing at focal depths 60 90 km beneath the high himalaya and southern tibetan plateau beneath the southern tibetan plateau the plunge of the p axes shift from vertical in the upper crust to mostly horizontal near the crust mantle boundary indicating that body forces may play larger role at shallower depths than at deeper depths where plate boundary forces may dominate

late pleistocene holocene development of the tista megafan west bengal india 10 be cosmogenic and irsl age constraints abstract the himalayan proximal foreland is characterized by quaternary megafans of which the formational mechanisms remain debated the tista megafan spreads over more than 16 000 km2 from the mountain front where it is strongly incised to the confluence of the tista river with the jamuna brahmaputra river and stores sediments produced in the sikkim himalaya we propose a scenario for the late pleistocene holocene development of the tista megafan based on new 10be cosmogenic and infra red stimulated luminescence irsl age constraints and discuss the main potential controls on its evolution we suggest that two distal lobes developed successively downstream from a common proximal lobe deposition in the proximal lobe took place since at least 135 ka and incision began at 3 7 0 7 1 0 ka the western distal lobe of the megafan was deposited early in the history of the megafan when the sikkim himalaya catchment was drained by a tributary of the ganga river and was abandoned in the early holocene 10 11 ka the eastern recent

the 1987 aegean dense water formation a streamtube investigation by comparing theoretical model results satellite field and numerical data with contourite distribution abstract we here discuss a detailed investigation of the dense water formation evolution and spreading in the aegean sea during the year 1987 immediately prior to the onset of the eastern mediterranean transient emt we use hydrologic data collected during the lia cruise satellite images for sst sea surface temperature and protheus data a coupled ocean atmosphere numeric model along with theoretical streamtube models these hydrological analyses are related to late quaternary sedimentary drifts in the cyclades plateau and in the myrtoon basin our analysis shows that streamtube dynamics provide a novel model of dense water evolution and spreading in the aegean basin applying this model to dense water masses observed in winter and spring 1987 near samothrace and over the limnos lesbos plateau results in a geostrophic flow of this dense cold water towards the limnos sporades channel in the north aegean sea there it mixes with dense water from the limnos lesbos plateau and finally both move geostrophically towards the cyclades plateau these results indicate that most of the dense water observed near the cyclades formed initially about 3 months earlier at samothrace and limnos shelves during its long pathway it partially mixed with adjacent water masses although our analysis concerns only one year of dense water analyses these results are thought to reflect a more general and recurrent phenomenon in the aegean basin indeed high resolution airgun 10 in seismic reflection data from the cyclades plateau reveal the presence of late quaternary sediment drifts these observations are concordant with results from our theoretical model this suggests a direct link between such a dense water cascading and contourite dynamics the continuation of sediment drifts into the deep basin floor 900 m deep of the myrtoon basin moreover indicates a cascading character of such bottom currents at the flanks of the basin a feature that set further investigations

a simple kinematic mechanism for mixing fluid parcels across a meandering jet abstract recent observations of fluid parcel pathways in the gulf stream using isopycnal rafos floats revealed a striking pattern of cross stream and vertical motion associated with meanders bower and rossby 1989 in an attempt to explain the observed pattern a two dimensional kinematic model of a meandering jet has been developed which enables examination of the relationship between streamfunction patterns and fluid parcel trajectories the streamfunction fields are displayed in a reference frame moving with the wave pattern so motions of fluid parcels relative to the jet can be seen more easily the results suggest that the observed pattern of cross stream motion results primarily from the downstream phase propagation of meanders the model successfully reproduces several of the most distinctive features of the float observations 1 entrainment of fluid into the gulf stream occurs at the leading edges of meander extrema while detrainment takes place at the trailing edges 2 exchange between the gu

determination of the crustal structure in southern tibet by dispersion and amplitude analysis of rayleigh waves summary surface waves recorded by the nine broad band stations of the indepth ii experiment are analysed to study the crustal structure of southern tibet their frequency range is between approximately 0 015 and 0 050 hz i e between 20 and 60 s period phase velocity dispersion curves are calculated for the regions north and south of the tsangpo suture using wiener filtering of fundamental mode rayleigh waves incident upon the array with different backazimuths the two dispersion curves are inverted to obtain the s wave crustal models north and south of the suture they show that a low velocity layer is present in the lower crust north but not south of the tsangpo suture to confirm these findings variations in the amplitudes of the rayleigh waves across the suture are interpreted by numerical simulation the strong amplitude variations at a 30 s period are reproduced using a model with a low velocity layer in the lower crust north of the suture a normal high velocity layer to the south and a sharp transition between these layers

modeling the baroclinic circulation in the area of the sicily channel the role of stratification and energy diagnostics 1 aspects of the circulation of the sicily channel region are studied with a high resolution primitive equation sigma coordinate model this work is an attempt to study the process governing the purely baroclinic dynamics and its sensitivity to seasonal stratification thus no atmospheric forcing is used two numerical experiments are analyzed using as initial conditions diagnostic velocity fields derived from the winter and summer climatological hydrologies the quasi steady state is characterized by circulation patterns in the depth range of the modified atlantic water maw and the levantine intermediate water liw strongly controlled by mesoscale eddies and topography seasonal difference is found in the surface current which exhibits the major variability on the african side downstream of adventure bank and the ionian slope where the absolute maximum occurs the intermediate circulation instead does not show relevant seasonal differences liw enters through the two passages south of malta plateau and preferentially flows along the sicilian shelf edge exiting over the northern sill its pathway is strongly controlled by subsurface cyclonic and anticyclonic cells the results are in good agreement with observations an energy diagnostics is applied to model results and sheds important light on dynamical characteristics of the mesoscale eddy field and indicates seasonal differences in the energetic exchange with the mean flow the analysis of the mean mke and eddy eke kinetic energy the transfer terms between energy compartments and the eddy momentum flux divergence indicates how eddies are strongly energetic in summer and exchange energy more efficiently with the mean flow in the quasi steady state maw volume transport and mke and eke fluctuations are strongly correlated this result suggests that mesoscale motions can control up to 40 of volume transport variability

parameterization of mixed layer eddies part ii prognosis and impact abstract the authors propose a parameterization for restratification by mixed layer eddies that develop from baroclinic instabilities of ocean fronts the parameterization is cast as an overturning streamfunction that is proportional to the product of horizontal buoyancy gradient mixed layer depth and inertial period the parameterization has remarkable skill for an extremely wide range of mixed layer depths rotation rates and vertical and horizontal stratifications in this paper a coarse resolution prognostic model of the parameterization is compared with submesoscale mixed layer eddy resolving simulations the parameterization proves accurate in predicting changes to the buoyancy the climate implications of the proposed parameterization are estimated by applying the restratification scaling to observations the mixed layer depth is estimated from climatology and the buoyancy gradients are from satellite altimetry the vertical fluxes are comparable to monthly mean air sea fluxes in large areas of

arcuate pyroclastic conduits ring faults and coherent floor at kumano caldera southwest honshu japan abstract at the 41 23 km miocene kumano caldera in southwestern japan a large arcuate pyroclastic breccia unit is interpreted as the dissected conduit for voluminous explosive eruptions the pyroclastic breccia and associated granite porphyry occur along the southern margin of the caldera these rocks collectively as much as 22 km long and 800 m wide intrude the arcuate fault bounding the southern caldera margin the breccia is interpreted as the vent facies of ash flow tuff adjacent to the caldera based on similar lithologies phenocryst modes of juvenile clasts and matrix character cataclasites along the major faults include both country rocks and pyroclastic breccia yet some cataclasite blocks are contained within the pyroclastic breccia these geometric and textural relations suggest that the faulting took place during caldera forming eruption prevolcanic sedimentary rocks enclosed by the arcuate faults are interpreted as the dissected coherent floor of the caldera which were subsided several hundreds to a thousand meters no large scale piecemeal disruption of the caldera floor is evident orientations of striations with the cataclasites and altitudes of the base of the tuff suggest the asymmetric trap door subsidence of this caldera the overall caldera geometry is the nested trap door piston cylinder subsidence each 21 15 and 25 23 km in diameter in contrast to previous interpretation of a funnel shape

effects of changing stress states on the development of caldera bounding faults geological evidence from kumano caldera japan abstract collapse of a large caldera can cause spatial and temporal perturbations of stress and formation of caldera faults the stress variations influence the direction of slip vectors on the fault planes hence stress estimation is important for the study of caldera forming processes in our paleostress estimation the stress variations in the collapse of the ca 14 ma kumano caldera in japan have been revealed a stress inversion method based on the wallace bott hypothesis was used to compute the orientation of the principal stress axes 1 2 3 and the stress ratio 2 3 1 3 where 0 1 the caldera faults formed simultaneously with the caldera forming ash flow tuff eruption therefore paleostress solutions obtained from slip data measured on such faults show the spatial and temporal changes of the stress at the time of the caldera collapse the computed stress ratio characterizes a pair of stress fields in the early stage the stress field with 1 0 shows a semi radial trajectory of stress 2 and an eastern concentric trajectory of stress 3 this stress regime resulting from pre collapse tumescence counteracts the gravitational force and thus produces smaller net vertical stress the regional tumescence above an inflated magma chamber is the most plausible source of the stress field and it is consistent with the timing of the caldera formation in the late stage the stress field with 0 5 shows the semi radial trajectory of stress 2 and the west convex and concentric trajectory of stress 3 change of the stress ratio from 1 0 to 0 5 implies that increase in the relative magnitude of the stress 1 caused the deeper subsidence of the caldera floor stress variations may be of significant value for reconstructing the structural history of the caldera

erratum to effects of changing stress states on the development of caldera bounding faults geological evidence from kumano caldera japan j volcanol geotherm res 144 2005 89 103 abstract a paper published in the journal of volcanology and geothermal research miura d 2005 effects of changing stress states on the development of caldera bounding faults geological evidence from kumano caldera japan j volcanol geotherm res 144 89 103 contains an erroneous result in the stress tensor calculation for fault slip data and thus is incorrect more adequate and reliable solutions of stress tensor have been provided the revised analysis shows some changes in the orientations of stresses 2 and 3 and the stress ratio being smaller than the original one no other contents of the original paper however will be modified by this correction the important conclusions of the paper remain the same

seismicity in the kingdom of bhutan 1937 2003 evidence for crustal transcurrent deformation we investigate moderate sized historic to recent earthquakes in the bhutan himalaya spanning the years from 1937 to 2003 we find that few moderate sized earthquakes occurred in the region during this time period in order to better characterize the seismicity we relocate all earthquakes and estimate focal mechanisms for events for which we have adequate data we use first motion data for older events and waveform model digital seismograms for three earthquakes that occurred in 1980 m w 6 4 1995 m w 5 4 and 2003 m w 5 4 for the modern events we utilize three techniques for focal mechanism and depth determination regional full waveform time domain modeling of the two moderate m w 5 4 events and surface wave spectral method and body wave depth modeling approach for the m w 6 4 event we find that the first motion and digital data focal mechanisms are mostly strike slip with midcrustal to deep crustal depths although no recent great event has occurred along the main himalayan thrust the indian plate is undergoing significant midcrustal to deep crustal transcurrent deformation likely due to oblique convergence of the indian asian collision in this region unlike oceanic continent oblique subduction strike slip and thrust partitioning occurs throughout the crust not in distinct zones the geological and geophysical nature of the bhutan himalaya appears significantly different than other himalayan regions due to the strike slip nature of many of the events an out of sequence thrust fault and the implications of deformation in the shillong plateau

estimation of scattering and intrinsic attenuation based on multiple lapse time window analysis in sikkim himalayan region india abstract attenuation of seismic wave energy was estimated in and around the source region of the sikkim earthquake of 18 september 2011 using aftershocks the main shock had a moment magnitude 6 9 and after this main shock approximately 283 aftershocks with a magnitude distribution ranging from 1 02 to 5 0 were recorded by 8 temporary broad band seismometers in the present study the relative contributions of scattering attenuation and intrinsic absorption are estimated by multiple lapse time window analysis under the hypothesis of isotropic scattering and a uniform distribution of scatterers in the crustal part of the study area the coda wave attenuation is also estimated using single backscattering method all of the attenuation parameters are estimated as a function of frequency in the range 1 16 hz the results show that scattering attenuation is greater than intrinsic absorption for all of the frequencies the relative contribution of scattering attenuation decreases with increasing frequency around the 1 4 hz frequency band scattering attenuation primarily contributes to seismic wave attenuation in the sikkim region the estimated values of seismic albedo ranges from 0 65 to 0 79 as seismic albedo is higher than 0 5 for all frequencies it is concluded that the medium in the sikkim himalayas is highly heterogeneous and tectonically active our knowledge of the attenuation mechanism of the sikkim region is enhanced by the application of the multiple lapse time window analysis method and results can be useful for the hazard assessment

lagrangian motion and fluid exchange in a barotropic meandering jet kinematic models predict that a coherent structure such as a jet or an eddy in an unsteady flow can exchange fluid with its surroundings the authors consider the significance of this effect for a fully nonlinear dynamically consistent barotropic model of a meandering jet the calculated volume transport associated with this fluid exchange is comparable to that of fluid crossing the gulf stream through the detachment of rings although the model is barotropic and idealized in other ways the transport calculations suggest that this exchange mechanism may be important in lateral transport or potential vorticity budget analyses for the gulf stream and other oceanic jets the numerically simulated meandering jet is obtained by allowing a small amplitude unstable meander to grow until a saturated state occurs the resulting flow is characterized by finite amplitude meanders propagating with nearly constant speed and the results clearly illustrate the stretching and stirring of fluid particles along the edges of the recirculation regions south of the meander crests and north of the troughs the fluid exchange and resulting transport across boundaries separating regions of predominantly prograde retrograde and recirculating motion is quantified using a dynamical systems analysis the geometrical structures that result from the analysis are shown to be closely correlated with regions of the flow that are susceptible to high potential vorticity dissipation moreover in a related study this analysis has been used to effectively predict the entrainment and detrainment of particles to and from the jet