paleoseismic evidence from trench investigation along hajipur fault himalayan frontal thrust nw himalaya implications of the faulting pattern on landscape evolution and seismic hazard abstract the study area falls within the mesoseismal zone of 1905 kangra earthquake mw 7 8 two parallel nnw sse striking active fault scarps named as hajipur faults hf1 and hf2 along the northwestern end of the janauri anticline in the foothill zone have displaced floodplain sediments of the beas river the hf1 and hf2 represent the imbricate faults of the himalayan frontal thrust hft and are the result of lateral propagation of deformation from two fold segments i e jf1 and jf2 respectively in northwest direction along the strike ground penetrating radar gpr profiles and trenching across the hf2 reveal two low angle thrust fault strands f1 and f2 displacements of 7 5 m on f2 and 1 5 m on the associated branching faults f a f b and f c were observed total four stratigraphic units unit a gravel with a lens of medium sand unit a is the oldest overlain by units b medium to coarse sand unit c with fine to medium sand and unit d fine to medium sand with scattered gravel were observed in trench radiocarbon ages of the charcoal samples from unit b and unit d optical ages of sediments from units a b and c gpr data and trench log suggest two major events along f1 and f2 strands event i along f1 occurred during 2600 800 yr bp and event ii along f2 around 400 yr bp and before 300 yr bp given the uncertainty in dates it is suggested that the latest event occurred during 1500 1600 ad considering the oldest unit unit a exposed in trench with vertical displacement of 7 5 8 m age of 2600 500 yr bp and net displacement of 9 m during single event along low angle fault 25 implies slip rate 7 6 1 7 mm yr uplift rate 3 2 0 6 mm yr shortening rate 6 9 1 4 mm yr and recurrence interval 1160 250 yr for large magnitude event with mw 7 0 with the recurrence of 1100 yr the penultimate event probably occurred at around 1400 1500 yr bp given the recent gps based slip rate of 14 1 mm yr in kangra reentrant baneerjee and burgman 2002 the present study suggests that about half of this slip is consumed along the hft and that this fault is more active compared to those in the hinterland

numerical modeling of crustal block and fault dynamics earthquakes and slip rates in the tibet himalayan region the tibetan plateau and himalayans have resulted from the continuous indian and eurasian plate convergence following their initial collision about 55 million years ago earthquakes in the region occur mainly in response to the crustal motion and stress localization associated with this convergence to understand the basic features of the crustal motion and seismicity in the tibet himalayan region we develop a numerical model of block and fault dynamics the model structure is composed of six major upper crustal blocks separated by fault planes these blocks are assumed to be perfectly rigid and move as a consequence of the indian plate push and of a flow of the lower crust deformations take place along the fault planes separating the blocks the interaction of the blocks along the fault planes is visco elastic as long as the ratio of the shear stress to the difference between the pore pressure and normal stress remains below a critical strength level when the critical level is exceeded in some part of a fault plane an earthquake stress drop occurs causing also failures in adjacent parts of the fault plane the stress drop affected parts of the fault plane enter in a state of creep immediately after the earthquake and the creep lasts until the stress falls below a certain level we develop several sets of numerical experiments to analyze the earthquake clustering frequency to magnitude relationships earthquake focal mechanisms and fault slip rates in the model large events in the numerical experiments cluster on the fault segments associated with the himalayan frontal thrust as well as at some internal faults of the tibetan plateau the clustering of earthquakes on a given fault is a consequence of the dynamics of the regional fault system rather than that of the fault only we show that variations in the relationship of magnitude to frequency of the events are associated with changes in the motion of the upper crustal blocks and depend on the rheological properties of fault plane zones the focal mechanisms of model events are found to be consistent with that of earthquakes in the region the synthetic moment rate captures the observed rate of seismic moment release we demonstrate in the model that the present crustal motion in the region is indeed governed by the north northeastern movement of india toward eurasia and the movement of the lower crust variations in the rheological properties of fault plane zones and or in the motion of the lower crust influence rates of the crustal block displacements and slips at the faults separating the blocks this can explain the discrepancies in estimates of slip rates over short and long time scales at major faults in the region

a comparison of extended and quasigeostrophic dynamics for a case of small rossby number extratropical cyclone development abstract this note compares the extended ext and quasigeostrophic qg dynamics of a small rossby number extratropical cyclone using the zwack okossi zo equation applied to a cyclone that occurred on 8 9 november 1985 over the north atlantic ocean results show that although differences exist both the ext and qg forms of the zo equation provide very adequate estimates of the large scale forcing processes associated with this case

a modified approach to initialize an idealized extratropical cyclone within a mesoscale model abstract a technique for initializing realistic idealized extratropical cyclones for short term 0 72 h numerical simulations is described the approach modifies select methods from two previous studies to provide more control over the initial cyclone structure additional features added to the technique include 1 deformation functions to initialize more realistic low level fronts tropopause structure and enhanced jet maximum at upper levels 2 a barotropic shear function to help develop different cyclone and frontal geometries and 3 damping functions to create an isolated baroclinic wave in the horizontal therefore the initialized cyclone is not influenced by the domain boundaries for relatively short simulations since this procedure allows for control of the initialized cyclone structures it may be useful for studies of frontal and cyclone interaction with topography and mesoscale predictability the initialization system produces a variety of basic states and synoptic disturbances ranging f

clockwise rotation of the brahmaputra valley relative to india tectonic convergence in the eastern himalaya naga hills and shillong plateau gps data reveal that the brahmaputra valley has broken from the indian plate and rotates clockwise relative to india about a point a few hundred kilometers west of the shillong plateau the gps velocity vectors define two distinct blocks separated by the kopili fault upon which 2 3 mm yr of dextral slip is observed the shillong block between longitudes 89 and 93 e rotating clockwise at 1 15 myr and the assam block from 93 5 e to 97 e rotating at 1 13 myr these two blocks are more than 120 km wide in a north south sense but they extend locally a similar distance beneath the himalaya and tibet a result of these rotations is that convergence across the himalaya east of sikkim decreases in velocity eastward from 18 to 12 mm yr and convergence between the shillong plateau and bangladesh across the dauki fault increases from 3 mm yr in the west to 8 mm yr in the east this fast convergence rate is inconsistent with inferred geological uplift rates on the plateau if a 45 n dip is assumed for the dauki fault unless clockwise rotation of the shillong block has increased substantially in the past 4 8 myr such acceleration is consistent with the reported recent slowing in the convergence rate across the bhutan himalaya the current slip potential near bhutan based on present day convergence rates and assuming no great earthquake since 1713 a d is now 5 4 m similar to the slip reported from alluvial terraces that offsets across the main himalayan thrust and sufficient to sustain a mw 8 0 earthquake in this area

structural interpretation of the great earthquakes of the last millennium in the central himalaya abstract a major question about the himalaya remains open does a great earthquake like the mw 8 1 1934 earthquake release all the strain stored by the tibet india convergence during the preceding interseismic period and only that strain or can it also release a background store of energy that remained unreleased through one or more earlier earthquakes and so potentially engender giant events or a relatively random sequence of events to consider this question the history of the great earthquakes of the last millennium is investigated here by combining data provided by the historical archives of kathmandu trenches through surface ruptures isoseismal damage mapping seismites and the instrumental record in the kathmandu basin the location of the epicenter of the 1934 earthquake was determined from the arrival of high energy p waves that caused sedimentary dikes and ground fractures perpendicular to the epicenter azimuth the epicenter of the mw 7 6 1833 earthquake can therefore be determined analogously from dike orientation and its location to the ne of kathmandu indicates an overlap with the mw 8 1 1934 rupture the 1934 earthquake released strain not released by the 1833 earthquake comparison of the historical records of earthquakes in kathmandu with 14c ages from paleo seismic trenches along the himalayan front suggests that 1 the 1344 kathmandu event ruptured the surface as far away as kumaon and was therefore a giant mw 8 6 earthquake and 2 the 1255 event that destroyed kathmandu is attested by surface ruptures in central and western nepal and by seismites in soft sediment as far away as kumaon geometric and rheologic controls for the different types of ruptures during the medium mw 7 great mw 8 and giant mw 8 4 earthquakes are illustrated in structural cross sections it is found that the epicenters of great himalayan earthquakes are located on the basal thrust farther north or close to the locked zone which is defined from geodetic measurements of regional deformation during the interseismic period this suggests that great earthquakes initiate in a wide transition zone between exclusively brittle and exclusively creeping regimes the extent of which depends on the dip of the main himalayan thrust the succession of the great earthquakes during the last millennium has released all the 20 m millennial himalayan convergence even in the central seismic gap which has been locked since 1505 the millennial seismic release rate is close to the convergence rate nonetheless no evidence of a succession of characteristic earthquakes has been found the 1100 1833 and 1934 earthquakes in the eastern himalaya are characterized neither by constant displacement nor by constant recurrence furthermore some great earthquakes do not release all the strain elastically stored by the himalayan and tibetan upper crust after the 1255 event there was still the potential for a slip of several meters for the mw 8 1 1505 event this suggests a rather random release of seismic energy great earthquakes could occur anytime and in any part of the central himalaya furthermore a future giant earthquake of mw 8 6 cannot be excluded

seismology raising kathmandu on 25 april 2015 northern nepal shifted up to 7 m southward and kathmandu was raised by 1 m the causal earthquake failed to fully rupture the main fault beneath the himalaya and hence a large earthquake appears to be inevitable in nepal s future

plateau pop up in the great 1897 assam earthquake the great assam earthquake of 12 june 1897 reduced to rubble all masonry buildings within a region of northeastern india roughly the size of england and was felt over an area exceeding that of the great 1755 lisbon earthquake1 hitherto it was believed that rupture occurred on a north dipping himalayan thrust fault propagating south of bhutan2 3 4 5 but here we show that the northern edge of the shillong plateau rose violently by at least 11 m during the assam earthquake and that this was due to the rupture of a buried reverse fault approximately 110 km in length and dipping steeply away from the himalaya the stress drop implied by the rupture geometry and the prodigious fault slip of 18 7 m explains epicentral accelerations observed to exceed 1g vertically and surface velocities exceeding 3 m s 1 ref 1 this quantitative observation of active deformation of a pop up structure confirms that faults bounding such structures can penetrate the whole crust plateau uplift in the past 2 5 million years has caused the indian plate to contract locally by 4 2 mm yr 1 reducing seismic risk in bhutan but increasing the risk in northern bangladesh

numerical modelling of earthquake flow in the southeastern carpathians vrancea effect of a sinking slab abstract the earthquake prone vrancea region is modelled as a system of perfectly rigid blocks separated by infinitely thin plane faults the interaction of the blocks along the fault planes and with the surrounding medium is assumed to be a viscous elastic the displacements of the block system are caused by motions of boundary blocks the velocities of the motions are found from a model of mantle flows induced by a sinking slab beneath the vrancea region when a ratio of stress to pressure for some portion of a fault plane exceeds a certain strength level a stress drop earthquake occurs as a result of the numerical simulation a catalog of synthetic earthquakes is produced several numerical experiments for various model parameters show that the spatial distribution of synthetic events is significantly sensitive to the directions of the block movements small variations in a slab rotation control the pattern of the synthetic seismicity the results of the analysis show that the catalogs obtained by the simulation of the block structure dynamics have certain features similar to those of the real earthquake catalog of the vrancea region

the impact of the prevailing synoptic situation on the lake aggregate effect abstract the effects of a group aggregate of relatively warm circular meso scale lakes on different flow regimes were investigated by conducting a series of idealized numerical experiments this investigation was motivated by the observed behavior of synoptic scale cyclones moving through the great lakes region during winter three with lake wl and three corresponding no lake nl simulations were initialized with 1 zonal flow 2 a solitary trough and 3 continuous sinusoidal waves respectively the wl experiments were intercompared to examine the importance of a preexisting disturbance and preconditioning the nl simulations were compared to the corresponding wl simulations to study the contributions of the lake aggregate the simulation results suggest that the lake aggregate induced or enhanced warm fronts when there were preexisting disturbances they also suggest that a perturbation mesoscale aggregate vortex was generated in each of the three different flow scenarios even though the lake a

predicting the lithospheric stress field and plate motions by joint modeling of lithosphere and mantle dynamics the way in which basal tractions associated with mantle convection couples with the lithosphere is a fundamental problem in geodynamics a successful lithosphere mantle coupling model for the earth will satisfy observations of plate motions intraplate stresses and the plate boundary zone deformation we solve the depth integrated three dimensional force balance equations in a global finite element model that takes into account effects of both topography and shallow lithosphere structure as well as tractions originating from deeper mantle convection the contribution from topography and lithosphere structure is estimated by calculating gravitational potential energy differences the basal tractions are derived from a fully dynamic flow model with both radial and lateral viscosity variations we simultaneously fit stresses and plate motions in order to delineate a best fit lithosphere mantle coupling model we use both the world stress map and the global strain rate model to constrain the models we find that a strongly coupled model with a stiff lithosphere and 3 4 orders of lateral viscosity variations in the lithosphere are best able to match the observational constraints our predicted deviatoric stresses which are dominated by contribution from mantle tractions range between 20 70 mpa the best fitting coupled models predict strain rates that are consistent with observations that is the intraplate areas are nearly rigid whereas plate boundaries and some other continental deformation zones display high strain rates comparison of mantle tractions and surface velocities indicate that in most areas tractions are driving although in a few regions including western north america tractions are resistive citation ghosh a w e holt and l m wen 2013 predicting the lithospheric stress field and plate motions by joint modeling of lithosphere and mantle dynamics

block and fault dynamics modelling of the himalayan frontal arc implications for seismic cycle slip deficit and great earthquakes abstract a numerical block and fault dynamics model bafd of the himalayan frontal arc india is developed to understand the long term patterns of strain accumulation and occurrences of great earthquakes in the himalaya the morphostructural scheme outlines twelve major crustal blocks and external driving motions are prescribed using gps data the bafd model reproduces essential features of the geodynamics and seismicity of the himalayan frontal arc the locations of the large synthetic earthquakes and their maximum magnitudes are consistent with the information available from the instrumental and historical earthquake catalogues we model the evolution of the slip deficit and seismic cycles for different sections across the himalaya frontal arc the modelled seismic cycles are found to be varying from 700 to 2100 years and are in good agreement with the return periods estimates from the recent paleoseismological studies we notice that the accumulation of the slip deficit depends not only on the rate of shortening rheology and structure but also on the dynamics of the confining crustal blocks further we observe that tectonic motions of the shillong plateau and assam basin microplates play a significant role in controlling the seismicity patterns of the bhutan block which resulted in the decreased seismic activity and increased rate of aseismic displacement thus we infer that the regional seismicity patterns are a consequence of dynamics of the entire regional fault and block system rather than dynamics of individual fault our bafd modelling predicts the maximum earthquake hazard associated with future large great earthquakes for the central himalayan gap region which lies between the 1905 kangra and the 2015 gorkha earthquake ruptures but relatively less hazard in kashmir and assam

a proposed method of surface map analysis present surface frontal analyses suffer from the defect that frontal positions are typically not collocated with zones of intense temperature contrast further individuals typically do not agree as to the existence type and location of fronts the author argues that the lack of a surface temperature analysis is mainly responsible for these flaws and it is proposed that such analysis preferably of potential temperature in regions of variable terrain elevation become part of routine procedure such an analysis will reveal nonfrontal baroclinic zones of considerable intensity most cold fronts except the strongest ones are denoted as baroclinic troughs propagating eastward in the prevailing westerly flow it is argued that when a meridional cold front exists in the presence of even a small meridional temperature gradient the wind shift should propagate away from the intense surface temperature gradient which then weakens an explanation is provided based on quasigeostrophic theory it follows that fronts are short lived phenomena

fluvial incision and tectonic uplift across the himalayas of central nepal the pattern of fluvial incision across the himalayas of central nepal is estimated from the distribution of holocene and pleistocene terraces and from the geometry of modern channels along major rivers draining across the range the terraces provide good constraints on incision rates across the himalayan frontal folds sub himalaya or siwaliks hills where rivers are forced to cut down into rising anticlines and have abandoned numerous strath terraces farther north and upstream in the lesser himalaya prominent fill terraces were deposited probably during the late pleistocene and were subsequently incised the amount of bedrock incision beneath the fill deposits is generally small suggesting a slow rate of fluvial incision in the lesser himalaya the terrace record is lost in the high range where the rivers are cutting steep gorges to complement the terrace study fluvial incision was also estimated from the modern channel geometries using an estimate of the shear stress exerted by the flowing water at the bottom of the channel as a proxy for river incision rate this approach allows quantification of the effect of variations in channel slope width and discharge on the incision rate of a river the determination of incision rates requires an additional lithological calibration the two approaches are shown to yield consistent results when applied to the same reach or if incision profiles along nearby parallel reaches are compared in the sub himalaya river incision is rapid with values up to 10 15 mm yr it does not exceed a few millimeters per year in the lesser himalaya and rises abruptly at the front of the high range to reach values of 4 8 mm yr within a 50 km wide zone that coincides with the position of the highest himalayan peaks sediment yield derived from the measurement of suspended load in himalayan rivers suggests that fluvial incision drives hillslope denudation of the landscape at the scale of the whole range the observed pattern of erosion is found to closely mimic uplift as predicted by a mechanical model taking into account erosion and slip along the flat ramp flat geometry of the main himalayan thrust fault the morphology of the range reflects a dynamic equilibrium between present day tectonics and surface processes the sharp relief together with the high uplift rates in the higher himalaya reflects thrusting over the midcrustal ramp rather than the isostatic response to reincision of the tibetan plateau driven by late cenozoic climate change or late miocene reactivation of the main central thrust

simulation of seismicity in the block structure model of italy and its surroundings the numerical block model of the lithosphere dynamics is used to simulate seismicity in italy and its surroundings based on the available structural and geodynamics information the purpose of the study is to understand which are the tectonic processes that control the main features of the observed seismicity and the kinematics of the region the influence of the rheology of the fault systems is studied as well the model we use differs from other modeling approaches in that it simulates earthquakes and hence it possibly relates to seismicity and geodynamics the model provides an effective capability to include the set of documented constraints supplied by widely available earthquake catalogs this is done by means of the comparison of the gr relation of the focal mechanisms and of the space distribution for observed and computed seismicity the region is modeled as a system of perfectly rigid blocks separated by infinitely thin fault planes in viscoelastic interaction between themselves and with the underlying medium the movement of the boundary blocks and of the underlying medium determines the motion of the blocks the synthetic seismicity obtained with the defined block model is similar to the observed one for the most seismically active areas a linear frequency magnitude fm relation gutenberg richter law is obtained for synthetic earthquakes the slope b value of the fm plot appears larger for the synthetic seismicity than for the observed one nevertheless the b value is essentially larger in northern and central italy than that in southern italy both in the model and in the observations the analysis of the source mechanisms of the synthetic earthquakes shows a good agreement with the observations in the model normal faulting is typical for the apennines the eastern edge of sicily and the calabrian arc while reverse faulting takes place at the northwestern boundary of the adriatic sea in the southern alps and along the eastern edge of the adria along the dinarides the model correctly reproduces the extension zone along the apennines and the contraction zone along the northwestern boundary of the adriatic sea the counter clockwise rotation of the adria is mimed the resulting movements of the blocks are in overall agreement with gps global positioning system observations the results of the modeling experiments suggest that the main features of dynamics and seismicity in the central mediterranean region cannot be satisfactorily explained as a consequence of africa and eurasia convergence only the passive subduction in the calabrian arc and the different rheology of faults are essential as well

age of initiation of collision between india and asia a review of stratigraphic data abstract the collision of india with asia is perhaps the most profound tectonic event to have occurred in past 100 ma it is responsible for the uplift of the himalayas and tibetan plateau and has been argued to have been responsible for geological geochemical and climatological consequences of global extent yet the age of initiation of this collision remains poorly constrained the literature is replete with estimates that range from the late cretaceous 65 ma to latest eocene

lake aggregate mesoscale disturbances part iii description of a mesoscale aggregate vortex abstract the structure of a meso scale vortex that developed over the great lakes in late autumn is described understanding the structure of this particular vortex is important because 1 it altered local and regional scale precipitation 2 it developed in a complicated fashion and 3 it represents a class of vortices that develop frequently during cold air outbreaks over the great lakes and whose development is not yet understood detailed perturbation analyses of the synoptic scale and mesoscale conditions over the great lakes that led to the vortex development are presented using model output from previous numerical simulations that included all of the great lakes wl and none of the great lakes nl the initial thermal perturbation was characterized by an elongated warm plume near the surface that advanced southeastward toward the mid atlantic coast as cold air overspread the entire lakes region the plume then became more circular and deepened as it rotated toward the northeast in response to

a study of the early winter effects of the great lakes i comparison of very fine scale numerical simulations with observed data abstract development of a framework for study of the great lakes effects on late fall early winter cyclones andarctic air masses has been initiated the central theoretical component is a three dimensional numericalprimitive equations model the 40 45 km horizontal grid point spacing provides for resolution of the shapeand dimension of each lake and 15 levels in the vertical resolve interaction of boundary layer and midtropospheric processes over land locally computed vertical diffusion coefficients depending on static stabilityand richardson number are used to parameterize subgrid scale turbulent processes throughout the depthof the atmosphere at over lake grid points the businger et al 1971 formulation of the monin obukhov 1954 similarity equations is used in the constant flux layer and the combined o brien 1971 k profileand deardorff 1974 boundary layer depth prediction equation are used for turbulence parameterizationin the rest of the boundary layer the prognostic variables pressure

himalayan seismic hazard the devastating earthquake in bhuj on 26 january 2001 highlighted the high earthquake risk in the indian region of gujarat in their perspective bilham et al warn that major earthquakes may be expected in another part of india the himalayan arc an analysis of historic earthquakes suggests that several major earthquakes are overdue in this region but that recent low activity has focused attention away from the himalayan arc projections from earlier earthquakes suggest that just one of the possibly overdue himalayan earthquakes may lead to 200 000 predictable fatalities

a technique for generating idealized initial and boundary conditions for the psu ncar model mm5 abstract a new idealized initialization technique has been developed for the mesoscale model version 5 modeling system the technique allows the specification of baroclinic disturbances that feature vertical variations of the height temperature and wind fields in terms of phase lag wavelength and phase speed the technique involves specifying a sounding profile at some reference point generating the desired height fields using an analytic formulation constructing the wind fields to be in geostrophic balance and generating temperature fields using the hydrostatic relationship a distinct advantage of this technique over existing ones is that the boundary conditions are not restricted to being specified as periodic the flexibility means that 1 users do not have to specify a domain whose size is equal to an integer number of wavelengths of the specified flow 2 users can specify a flow that consists of different wavelengths at different heights as is typically observed and 3 any responses that a

interseismic coupling on the main himalayan thrust we determine the slip rate and pattern of interseismic coupling on the main himalayan thrust along the entire himalayan arc based on a compilation of geodetic interferometric synthetic aperture radar and microseismicity data we show that convergence is perpendicular to the arc and increases eastwards from 13 3 1 7 mm yr to 21 2 2 0 mm yr these rates are comparable to geological and geomorphic estimates indicating an essentially elastic geodetic surface strain the interseismic uplift rate predicted from the coupling model closely mimics the topography suggesting that a small percentage of the interseismic strain is permanent we find that the fault is fully locked along its complete length over about 100 km width we don t find any resolvable aseismic barrier that could affect the seismic segmentation of the arc and limit the along strike propagation of seismic ruptures the moment deficit builds up at a rate of 15 1 1 10 19 n m yr for the entire length of the himalaya