short paper terrane rotations in the irish caledonides palaeozoic palaeomagnetic data from scotland and ireland have been compared on a terrane model and early caledonide clockwise rotation of a terrane through 65o 30 connemara massif and later anticlockwise rotation of up to 50 in the vicinity of clew bay have been deduced these are the firfirst estimates of terrane rotations in the european part of the caledonian appalachian orogen terrane analysis of orogenic belts is currently a major field of study to a large extent this has been stimulated by studies in the north american cordillera where large rotations and translations have been determined palaeomagnetically see beck et al 1986 and references therein terrane analysis may be applied to older orogenic belts such as the caledonides which have been particularly intensively studied previously published palaeomagnetic data from connemara morris tanner 1977 and nw galway morris et al 1973 had indicated local block rotations but furnished few constraints on either their age and magnitude or on the identities of the blocks this paper relates the currently available palaeomagnetic dataseto a terrane model of w ireland hutton dewey 1986 see fig 1 new data new palaeomagnetic data from the irish caledonides comprise the following connemara gabbro robertson 1988 the dalradian rocks of the connemara massif are unique in the british caledonides in lying to the south of a caledonian ophiolite and also south of a thick sequence of ordovician shales and volcanics of low metamorphic grade in clew bay and the south mayo trough respectively the structural

the metagabbros orthogneisses and paragneisses of the connemara complex western ireland although now largely disappeared within the 400 ma old galway granite the syntectonic connemara metagabbro gneiss complex which crystallized at 490 ma arenig is the largest intrusion into the dalradian rocks it is part of widespread cambro ordovician volcanism and plutonic injection into continental crust in the appalachian caledonide orogenic belt being synchronous in crystallization with the widely obducted 490 ma ophiolites within the orogeny the peridotites and hornblende gabbros were injected broken up and shouldered aside by quartz diorite granodiorite granite and trondhjemite gneisses and it is shown that these orthogneisses are not the in situ differentiation products of the gabbro magma the hornblende in the metagabbros is mainly igneous but is partly metamorphic and replaces olivine fo 75 92 orthopyroxene en 65 92 clinopyroxene wo 48 5 en 50 39 fs 5 14 and plagioclase typically an 80 92 range an 50 96 an aureole at least 10 km wide in the sillimanite zone was imposed and cordierite garnet sillimanite dalradian hornfelses were partially melted at temperatures up to 1000 o c near to the gabbros at 4 5 1 kbar corresponding to c 18 km depth this suggests that the complex forms part of the root of a now eroded batholith of calc alkaline affinities the gabbros corresponding to the transition zone to a basic bottom which is often supposed to underlie many batholiths within the orthogneisses are sheets of paragneiss formed from dalradian metasediments which have been folded up from the floor and down into sides of the magma chamber which process could be illustrative of the means by which basic magma can intimately interact with crustal material the 18 o 16 o d h nd and sr isotope evidence and the existence of inherited zircons in the gneisses indicate that the gabbro and gneiss magmas were significantly contaminated with crustal possibly dalradian material both before and after intrusion with the lowest initial 87 sr 86 sr at 490 ma being 0 708 even in samples far removed from metasediment the metagabbros are tholeiitic to high alumina basalt in character but the gneisses have distinct calc alkaline geochemistry the chemistry igneous hornblende and highly calcic plagioclase match many arc plutons in the western usa the syntectonic nature and the ubiquitous gneissic fabric in the quartz diorites trondhjemites and granites is a consequence of early movements which were probably in part connected with the separation of the connemara massif and which culminated in slicing off the largely inverted complex and carrying it southwards on the mannin thrust which underlies the whole of connemara the complex is thus a fragment of a now disrupted cambro ordovician continental magmatic arc or continent island arc environment which can be traced along the se edge of the laurentian continent

stress field constraints on intraplate seismicity in eastern north america focal mechanisms of 32 north american midplate earthquakes mo 3 8 6 5 were evaluated to determine if slip is compatible with a broad scale regional stress field derived from plate driving forces and if so under what conditions stress regime pore pressure and frictional coefficient using independent information on in situ stress orientations from well bore breakout and hydraulic fracturing data and assuming that the regional principal stresses are in approximately horizontal and vertical planes 10o the constraint that the slip vector represents the direction of maximum resolved shear stress on the fault plane was used to calculate relative stress magnitudes defined by the parameterb s2 s3 s s3 from the fault stress geometry as long as the focal mechanism has a component of oblique slip i e the b axis does not coincide with the intermediate principal stress direction this calculation identifies which of the two nodal planes is a geometrically possible slip plane gephart 1985 slip in a majority of the earthquakes 25 of 32 was found to be geometrically compatible with reactivation of favorably oriented preexisting fault planes in response to the broad scale uniform regional stress field slip in five events was clearly inconsistent with the regional stress field and appears to require a localized stress anomaly to explain the seismicity significantly all five of these events occurred prior to 1970 when many regional networks were installed and their focal mechanisms are inconsistent with more recent solutions of nearby smaller events the frictional likelihood of the geometrically possible slip on the selected fault planes was evaluated in the context of conventional frictional faulting theory the ratio of shear to normal stress on the fault planes at hypocentral depth was calculated relative to an assumed regional stress field regional stress magnitudes were determined from 1 s s3 ratios based on the frictional strength of optimally oriented faults the basis for the linear brittle portion of lithospheric strength profiles 2 the computed relative stress magnitude b values and 3 a vertical principal stress assumed equal to the lithostat two end member possibilities were examined to explain the observed slip in these less than optimally oriented fault planes first the frictional coefficient was held constant on all faults hydrostatic pore pressure was assumed regionally and the fault zone pore pressure was determined since pore pressure is a measurable quantity with real limits in the crust p0 s3 this end member case was used to determine which of the geometrically possible slip planes were frictionally likely slip planes alternately pore pressure was fixed at hydrostatic everywhere and the required relative lowered frictional coefficient of the fault zone was computed slip in 23 of the 25 geometrically compatible earthquakes was determined to also be frictionally likely in response to an approximately horizontal and vertical regional stress field derived from plate driving forces whose magnitudes are constrained by the frictional strength of optimally oriented faults assuming hydrostatic pore pressure regionally the conditions for slip on these 23 relatively well oriented earthquake faults were determined relative to this regional crustal strength model and require only moderate increases in pore pressure between about 0 4 0 8 of lithostatic hydrostatic is about 0 37 of lithostatic or alternately moderate lowering 50 of the frictional coefficient on the faults which slipped superlithostatic pore pressures are not required focal mechanisms for the two other earthquakes with slip vectors geometrically consistent with the regional stress field however did require pore pressures far exceeding the least principal stress or extremely low coefficients of friction these events may reflect either local stress rotations undetected with current sampling or poorly constrained focal mechanisms the analysis also confirmed a roughly north to south contrast in stress regime between the central eastern united states and southeastern canada previously inferred from a contrast in focal mecha nisms between the two areas most central eastern united states earthquakes occur in response to a strike slip stress regime whereas the southeastern canadian events require a thrust faulting stress regime this contrast in stress regime with a constant maximum horizontal stress orientation determined by far field plate driving forces requires a systematic lateral variation in relative stress magnitudes superposition of stresses due to simple flexural models of glacial rebound stresses are of the correct sense to explain the observed lateral variation but maximum computed rebound related stress magnitude changes are quite small about 10 mpa and do not appear large enough to account for the stress regime change if commonly assumed stress magnitudes determined from frictional strength apply to the crust at seismogenic depths

the geology of sw connemara ireland a fold and thrust dalradian and metagabbroic gneiss complex sillimanite grade dalradian schists composed of pelites impure psammites quartzites and calcite marbles all containing amphibolites were intruded and hornfelsed giving hornfels sillimanite garnet and cordierite by a plutonic basic to acid igneous rock series now metamorphosed and folded important folding denoted d 2 d 3 d 4 and d 5 as been recognized with a major southward facing d 2 anticline the cashel antiform being repeatedly folded by d 3 which was a very strong phase and accompanied and followed by d 3 d 4 major ductile slides and thrusting although the meta igneous suite includes rare peridotites olivine fo 75 87 and anorthosites it is mostly hornblende augite labradorite or bytownite metagabbro and later quartz diorite or trondhjemite gneiss which has injected the earlier more basic rocks variably preserved igneous layering in the basic rocks indicates that the whole intrusive basic sheet is flat lying and inverted lying on the inverted limb of the cashel antiform about 460 ma ago the d 3 d 4 mannin thrust carried the igneous complex including the largely crystallized gneisses and the cover of dalradian metasediment over a now largely mylonitized set of acid volcanic rocks rhyolites or ignimbrites which enclose a separate suite of massive amphibolites intruded or extruded into the acid volcanic rocks before the thrusting the base of the overthrust metagabbro sheet which had cooled to albite epidote amphibolite facies conditions was ground down into a fine grained nnw lineated amphibolite the volcanic rocks the mannin thrust and the overlying basic complex were folded by d 4 and d 5 into a domed structure about 400 ma the aplopegmatitic facies of the inish granite intruded and caused hornfelsing and folding while the galway granite was intruded in the south lamprophyric sills and dykes and porphyry dykes were followed by the final phase of the inish granite the southward facing folding and thrusting of the connemara dalradian block and the gabbro gneiss emplacement are major elements in the caledonide history of the british isles it is postulated that there was a tectonic and genetic connection between the gabbro gneiss intrusion into these dalradian rocks the unusually rapid decrease in metamorphic pressure already documented for connemara and the exceptionally southern position of the connemara block

basic magmatism in connemara ireland evidence for a volcanic arc it is found by the use of pearce cann diagrams that basic magmatism during dalradian sedimentation in connemara was of a fundamentally different type to that which led to later synorogenic basic intrusions the dalradian magmatism is of a transitional within plate to divergent plate margin type whereas the synorogenic intrusions are of volcanic arc type it is suggested that the synorogenic basic intrusions of connemara tyrone and ne scotland represent the roots of a volcanic arc that developed by arenig times over a northerly directed subduction zone

u pb isotopic dating of fluid infiltration and metasomatism during dalradian regional metamorphism in connemara western ireland a metasomatic diopside rock occurs at the top of the dolomitic connemara marble formation of western ireland and contains titanite and k feldspar in addition to around 90 diopside xmg 0 90 0 97 u pb isotopic measurements on this mineral assemblage show that the titanite is both unusually uranium rich and isotopically concordant with the result that a precise u pb age of 478 2 5 ma can be determined the age is identical within error to a less precise rb sr age of diopside k feldspar of 483 6 ma petrological evidence indicates that the assemblage crystallized at c 620 c close to or below the closure temperature of titanite the age thus provides a precise estimate of the time of metamorphism this age is 11 3 ma younger than the 490 ma age for nearby gabbroic plutons which has previously been used to constrain the peak metamorphic age this difference accords well with geological evidence that the gabbros were emplaced prior to the metamorphic peak analysis of minerals with high closure temperature from assemblages whose crystallization is unambiguously associated with a specific episode of fluid infiltration at the peak of metamorphism provides the basis for a new approach to dating metamorphism the success of this approach is demonstrated by the results from connemara

on the structure and dynamics of indian monsoon depressions abstractera interim reanalysis data from the past 35 years have been used with a newly developed feature tracking algorithm to identify indian monsoon depressions originating in or near the bay of bengal these were then rotated centralized and combined to give a fully three dimensional 106 depression composite structure a considerably larger sample than any previous detailed study on monsoon depressions and their structure many known features of depression structure are confirmed particularly the existence of a maximum to the southwest of the center in rainfall and other fields and a westward axial tilt in others additionally the depressions are found to have significant asymmetry owing to the presence of the himalayas a bimodal midtropospheric potential vorticity core a separation into thermally cold 1 5 k and neutral 0 k cores near the surface with distinct properties and the center has very large cape and very small cin variability as a function of background state has also been explo

low angle extensional faulting and the emplacement of the connemara dalradian ireland a breccia mapped at the contact of the connemara dalradian and the unconformably overlying silurian succession of north galway shows evidence of having formed from strains developed at the brittle ductile deformation transition this breccia was surficially exposed just prior to the onset of an upper llandovery marine transgression the geometry of the breccia outcrop is consistent with its having developed along a regional low angle extensional fault two possible regimes of formation are proposed in the first the breccia represents the remnant of a significant low angle strike slip extensional fault along which the connemara dalradian was laterally emplaced in the second the extensional faulting may be a slightly later event related to the rapid uplift of the connemara massif both models involve rapid footwall uplift an event already inferred from metamorphic criteria the fault may be compared to major extensional detachments such as those in the basin and range province of the united states however this is the first description of an early caledonian fault of this nature and may have important consequences for future tectonic studies in this and other orogen s

geochemistry of dalradian pelites from connemara ireland new constraints on kyanite genesis and conditions of metamorphism whole rock and mineral analyses of dalradian pelites from w connemara show that kyanite pelites are not unusually mg rich as previously supposed their chemistry is transitional especially in ca content between overlying fe rich staurolite pelites and underlying ca rich rocks the flysch basin in which they were deposited was established relatively early in the west its sediment fill including carbonate rich influxes derived from an adjacent swell to the east which later subsided to form an enlarged basin kyanite has a very restricted spatial distribution because its development was controlled by fe deficiency associated with the carbonate rich influxes which in turn led to relatively high x mg during metamorphism p t estimates for the metamorphic peak are 650 25 c and 8kbar about 50 c and 3kbar greater than for similar rocks in the east the difference can be related to structural level with respect to regional scale folds which may have developed as a huge backfolded complex during the emplacement of the connemara allochthon

westward propagating predecessors of monsoon depressions abstract by examining maps of 24 h change of sea level pressure during july and august over the 10 year period 1969 78 we find that 45 87 of the 52 lows and depressions that formed in the bay of bengal were associated with predecessor disturbances coming from the cast in 12 23 instances the predecessor was associated with a typhoon or named tropical storm in the south china sea while the remaining 33 64 were weaker systems originating over a broad region of land and sea from examination of time sections over the same period from eastern thailand to the burmese coast we identified 50 westward moving disturbances with consider able vertical extent of which 64 developed into lows or depressions on reaching the bay in 60 of the 50 instances the disturbance could be traced to the south china sea 32 being typhoons and named tropical storms and 28 weaker circulations the remaining 40 of the 50 disturbances appeared to originate over land for the three stations along the section line cr

the ordovician evolution of the south mayo trough western ireland the south mayo trough a broad synclinorium containing a 10 km sequence of early ordovician turbidites passing up into shallow water sandstones is interpreted as a forearc basin with an ophiolitic basement that formed a backstop to an accretionary prism on the northern edge of a north facing arc the arc collided with the laurentian margin in early llanvirn times to deform the dalradian supergroup rifted margin clastic sequence prior to the late llandovery sinistral transcurrent faulting transposed the connemara dalradian terrane to its present position on the outboard ocean ward side of the south mayo trough the south mayo trough was fed principally by arc and ophiolite derived elastics during the arenig with an increasing metamorphic component during the llanvirn the late ordovician transpressional docking of connemara provided the southerly source for high grade metamorphic clasts in the deny veeny formation

testing self organized criticality by induced seismicity we examine the hypothesis proposed in recent years by several authors that the crust is in a self organized critical soc state this hypothesis has been suggested on the basis of the observation of power law distributions such as the gutenberg richter law for earthquakes and the fault length distribution and of the fractal geometry of sets of earthquake epicenters and of fault patterns these self similar properties are shared by simplified models of the crust exhibiting a spontaneous organization toward a critical point characterized by similar scale invariant properties the term critical is here used in the sense of phase transitions such as the curie point in magnetism the usefulness of a hypothesis is measured by its predictive and explanatory power outside the range of observations that have helped defined it we thus explore how the soc concept can help in understanding the observed earthquake clustering on relatively narrow fault domains and the phenomenon of induced seismicity we review the major reported cases of induced seismicity in various parts of the world and find that both pore pressure changes p and mass transfers m leading to incremental deviatoric stresses of 1 mpa are sufficient to trigger seismic instabilities in the uppermost crust with magnitude ranging up to 7 0 in otherwise historically aseismic areas once triggered stress variations of at least 1 order of magnitude less but still larger than the 0 01 mpa tidal stress are enough to sustain seismic activity we argue that these observations are in accord with the soc hypothesis as they show that a significant fraction of the crust is not far from instability and can thus be made unstable by minute perturbations this property is shared by simplified models of soc not all perturbations however trigger seismic activity this is also compatible with the soc hypothesis which embodies naturally the existence of large heterogeneities in the stress field the induced seismicity is found to obey generally the gutenberg richter law up to a magnitude cutoff which correlates well with the width of the local seismogenic bed ranging in size from that of mine pillars for mining induced seismicity to the thickness of brittle sedimentary beds in the vicinity of dams or depleted hydrocarbon reservoirs in conclusion the properties of induced seismicity and their rationalization in terms of the soc concept provide further evidence that potential seismic hazards extend over a much larger area than that where earthquakes are frequent

monsoon depression amplification by moist barotropic instability in a vertically sheared environment author s diaz m boos wr abstract 2019 royal meteorological society this study makes the case that monsoon depressions over south asia can form from a variant of moist barotropic instability using an idealized numerical framework in which the atmosphere is partitioned into a basic state and a perturbation we simulate vortices resembling monsoon depressions that draw energy from the meridional shear of the monsoon trough and amplify when they interact with precipitating ascent the influence of the basic state vertical shear on the vortex induces upward velocity which couples precipitation with a rossby wave like mode arising from dry barotropic growth allowing the vortex to intensify sensitivity experiments reveal that both the sheared basic state and latent heating are necessary to achieve positive growth rates and that this process requires a sufficiently large initial perturbation trajectory analyses suggest that the combined flow of the vortex and the large scale monsoon transport diabatically generated potential vorticity from southwest of the vortex into the vortex center thus enabling growth in contrast with tropical cyclones this mechanism does not require a feedback between surface wind speed and surface heat and moisture fluxes though this feedback does ultimately result in a slightly stronger vortex

a geological and tectonic cross section of the caledonides of western ireland geological and geophysical criteria allow division of the caledonides of western ireland into four principal zones zone 1 in the north contains grenvillian basement with late proterozoic supra crustals zone 2 contains the westport complex the deer park complex and the south mayo trough connemara and the delany dome formation occupy zone 3 zone 4 contains the south connemara group and mid to late ordovician and silurian sediments and volcanic rocks the various tectonic models proposed for these zones are discussed and a minimum tectonic model is presented which involves early ordovician collision of the northern part of zone 2 with the laurentian margin zone 1 followed by subduction flip northern part of zone 4 the site of early collision between zones 1 and 2 subsequently underwent orogenic collapse and strike slip dismemberment leading to the sinistral transpressive emplacement of zone 3 assemblages in zone 4 were accreted to the now south facing arc northwards stress transfer consequent on suturing deformed the thinned crust and overlying silurian sequences in zones 2 and 3

barotropic growth of monsoon depressions author s diaz m boos wr abstract 2018 royal meteorological society although monsoon depressions are a principal synoptic scale element of the south asian monsoon producing extreme rainfall over india and surrounding regions there exists no widely accepted mechanism explaining their occurrence this study presents a hierarchy of numerical experiments aimed at finding such an explanation using a perturbation basic state decomposition we derive an anelastic system of equations that can represent disturbances growing in the complex three dimensional monsoon basic state we find that modal solutions to these equations linearized about this basic state can explain many features of observed monsoon depressions including their warm over cold core structure westward propagation and lower tropospheric wind maximum for the zonally symmetric case these modes are barotropically unstable drawing energy from the meridional shear of the monsoon trough for the zonally varying basic state modal solutions still derive energy from barotropic conversion but fail to achieve positive net growth rates when dissipative processes are included for the nonlinear equation set these modes can be excited by a heating impulse and their energy then remains roughly constant over several days as barotropic energy transfers oppose dissipative losses our results support the idea that the general concept of barotropic instability can explain the structure propagation and geographic distribution of monsoon depressions but not their rapid growth rates we speculate that condensational heating coupled to these waves is needed to obtain a positive growth rate

the cooling history of connemara western ireland from k ar and rb sr age studies k ar age determinations are reported on 26 hornblendes 17 coexisting muscovites and biotites nine muscovites and nine biotites from the dalradian connemara schists metagabbros and gneisses these are supplemented by 19 rb sr whole rock mica ages and four 40 ar 39 ar incremental heating ages on micas a long at least 75 ma and complex cooling history without a simple pattern of ages has been obtained the ages are not correlated with the grain sizes or the chemical compositions of the analysed minerals or the topographic elevation from which the samples came but there is an irregular increase of hornblende k ar ages to 480 10 ma with increase of metamorphic grade southwards towards the metagabbros and gneiss the preservation of the complex cooling pattern is ascribed to the action of syn and post metamorphic slides or faults which moved slices of the massif upwards by varying amounts closely spaced samples give results which rule out simple tilting of the massif rapid cooling c 30 ma 1 at 480 10 ma arenig llanvirn during the f3 fold phase was followed by slower cooling until 455 10 ma caradoc when renewed rapid uplift occurred possibly correlated with the southward thrusting of connemara and with synchronous renewed uplift in the scottish dalradian rocks widespread biotite k ar and rb sr ages of 440 5 ma end ordovician throughout connemara and the dalradian rocks of scotland are ascribed to the major taconic tectonic event which docked the dalradian rocks against the flanking folded ordovician successions of the midland valley and the south mayo trough biotites giving k ar ages of about 415 ma may have been reset during the late silurian folding of the cover rocks the importance of very close sampling integrated with structural studies is emphasized

influence of static stress changes on earthquake locations in southern california earthquakes induce changes in static stress on neighbouring faults that may delay hasten or even trigger subsequent earthquakes1 10 the length of time over which such effects persist has a bearing on the potential contribution of stress analyses to earthquake hazard assessment but is presently unknown here we use an elastic half space model11 to estimate the static stress changes generated by damaging magnitude m 5 earthquakes in southern california over the past 26 years and to investigate the influence of these changes on subsequent earthquake activity we find that in the 1 5 year period following a m 5 earthquake any subsequent nearby m 5 earthquake almost always ruptures a fault that is loaded towards failure by the first earthquake after this period damaging earthquakes are equally likely to rupture loaded and relaxed faults our results suggest that there is a short period of time following a damaging earthquake in southern california in which simple coulomb failure stress models could be used to identify regions of increased seismic hazard

role of barotropic mechanism in the development of a monsoon depression a monex study the role of barotropic processes in the development of a monsoon depression formed on 5 july 1979 during monex observational period is studied by considering it as a quasi geostrophic divergent barotropic instability problem of zonal flow of 3 july 1979 at 700 mb level numerical solutions are obtained by initial value approach the preferred wave has a wavelength of 2750 km an e folding time of 4 3 days a period of 6 5 days and an eastward phase speed of 4 9 ms 1 structure of preferred wave is found to be in good agreement with the observed horizontal structure of the depression at 700 mb poleward momentum transports are found to predominate over equatorward transports

perspectives on moist baroclinic instability implications for the growth of monsoon depressions abstractlittle is known about the genesis and growth mechanisms of monsoon depressions despite the great importance of these storms for the hydrological cycle of the asian australian monsoon region of the few theoretical studies that have examined this issue most have attributed the amplification of monsoon depressions to some form of baroclinic instability or stable baroclinic growth highly modified by the diabatic effects of moist convection here a simple criterion namely the upshear tilt of potential vorticity anomalies is argued be necessary for dry or moist baroclinic growth reanalysis data are then used to assess whether a large ensemble of south asian monsoon depressions has vertical structures consistent with this criterion the evolution of these monsoon depressions is compared with that of ensembles of hurricanes and diabatic rossby waves the latter being prototypical examples of moist baroclinic instability during their amplification phase monsoon depressions do not exhibit an upshea

a stable isotope study of retrograde alteration in sw connemara ireland dalradian metamorphic rocks lower ordovician meta igneous rocks mgs and caledonian granites of the connemara complex in sw connemara all show intense retrograde alteration alteration primarily involves sericitization and saussuritization of plagioclase the alteration of biotite and hornblende to chlorite and the formation of secondary epidote the alteration is associated with sealed microcracks in all rocks and planes of secondary fluid inclusions in quartz where it occurs and was the result of a phase of fluid influx into these rocks in hand specimen k feldspar becomes progressively reddened with increasing alteration mineralogical alteration in the mgs and caledonian granites took place at temperatures 275 15 c and in the mgs pfluid is estimated to be 1 5 kbar during alteration the d values of alteration phases are 18 to 29 fluid inclusions 47 to 61 chlorites and 11 to 31 epidotes chlorite 18o values are 0 2 to 4 3 while 18o values for quartz k feldspar pairs show both positively sloped mgs and highly unusual negatively sloped caledonian granites arrays diverging from the normal magmatic field on a plot the stable isotope data show that the fluid that caused retrogression continued to be present in most rocks until temperatures fell to 200 140 c the retrograde fluid had d 20 to 30 in all lithologies but the fluid 18o varied both spatially and temporally within the range 4 to 7 the fo2 of the fluid that deposited the epidotes in the mgs varied with its 18o value with the most 18o depleted fluid being the most oxidizing the d values together with low 0 18o values for the retrograde fluid in some lithologies indicate that this fluid was of meteoric origin this meteoric fluid was probably responsible for the alteration in all lithologies during a single phase of fluid infiltration the variation in retrograde fluid 18o values is attributed to the effects of variable oxygen isotope shifting of this meteoric fluid by fluid rock interaction infiltration of meteoric fluid into this area was most likely accomplished by convection of pore fluids around the heat anomaly of the galway granite soon after intrusion at 400 ma however convective circulation of meteoric water and mineralogical alteration could possible have occurred considerably later

structure and evolution of the large scale flow and an embedded upper tropospheric cyclonic vortex over northeast brazil horizontal structure and evolution of large scale flow and an embedded synoptic scale cyclonic vortex over northeast brazil as separate systems and dynamical interaction between them are studied at 200 hpa a quasistationary cyclonic vortex with its average position at 10 8s and 358w that formed and remained active during 5 10 january 1993 is selected for the investigation the evolution of large scale flow in the prevortex period 1 4 january is also explored an efficient and effective scale separation technique is developed and used to separate the large scale flow and embedded synoptic scale vortex it is shown that a strong positive shear zone developed in the latitude domain 17 58 7 58s within the south atlantic trough region before the vortex formation the shear zone has a characteristic meridional zonal scale of 1000 km 3000 km and satisfies strongly the necessary condition for barotropic instability it is identified that the development of a strong shear zone is associated with the intensification of a bolivian anticyclone and associated ridge and their eastward shift and intensification of the south atlantic trough east west orientation of the atlantic trough and the presence of a transient trough over the equatorial atlantic ocean the average structure of vortex including zonal and meridional characteristic scales is computed from the synoptic bandpass flow the vortex is identified as a nonlinear wave packet with an average zonal wavelength of 2750 km and it is confined to a latitude belt of about 17 58 the vortex shows a strong westward tilt with latitude the convergence zone is located to its southwest and it is a weak cold cored system maximum cyclonic vorticity of the vortex is 23 24 3 1025 s 21 which is comparable to the value for embedding flow the momentum transports due to the vortex large scale eddy and the vortex large scale eddy interaction are computed it is found that the vortex and vortex large scale eddy westerly momentum transports are southward down the gradient of embedding zonal flow and their divergence convergence is located over the latitudes of large scale westerlies easterlies the sensible heat transports are weak it is noted that the vortex large scale flow interaction leads to the weakening of the shear zone and restoration of the large circulation features to their january 1993 mean configuration which have undergone significant deviation during the prevortex period the signature of vortex large scale interaction is also seen in the evolution of dynamical parameters y and n2 q square of refractive index parameter

the southern uplands as an accretionary prism the importance of analogues in reconstructing palaeogeography fore arc regions whether accretionary erosional or composite vary greatly both along strike and through time in the geometries which they assume in response to subduction there is no well studied modern neogene margin which can be established as the 9type9 accretionary prism all are individual in some respect or other nor is there an example of a well studied modern neogene accretionary margin which can be compared closely to the southern uplands though there are several good analogues for particular stages of its history accretion took place along the southern uplands margin for c 50 million years the range of geometries on modern neogene accretionary active margins and the extent to which the behaviour of those margins can change during periods as long as 50 million years is reviewed emphasizing the accretionary prisms of mexico sw japan and the makran the interpretation of the southern uplands as an accretionary prism as presented in the late 1970s and early 1980s is reassessed in the light of advances made subsequently in understanding modern neogene prisms the recent alternative model of stone et al for the southern uplands envisages that the terrane evolved by the opening and closure by arc subduction of a marginal basin the new model draws heavily on arc type detritus derived from the oceanward side of the ancient southern uplands trough there are areas along the sw japan fore arc where oceanward derived tubidites are accumulating in a trench nankai trough and where active submarine arc type volcanism is occurring outboard of a currently growing accretionary prism such features in an ancient terrane like the southern uplands do not necessarily mean that an alternative model must be sought involving whole new arc systems furthermore analysis of the life spans and sedimentary fills of modern neogene marginal basins begs the conclusion that the southern uplands9 strata were not deposited in a marginal basin it is most unlikely that the c 50 ma history of pelagic sedimentation preserved there can be manifesting anything other than the closure of a sizeable ocean basin of a scale exceeding any known western pacific type marginal basin and with a different sedimentation history from any such marginal basin

metamorphic conditions in central connemara ireland metamorphic conditions have been estimated for an area in central connemara that includes cashel and lissoughter hill pressures lie in the range 3 0 6 0 kbar temperatures increase from 625 675 c on the n slopes of lissoughter hill to 650 700 c on the s slopes to 700 750 c in the migmatized metasediments n of the cashel ultrabasic intrusion before increasing sharply towards the contact away from the area adjacent to the intrusion a horizontal thermal gradient of between 30 c and 40 c km may be inferred differences in the relative spatial position with increasing temperature of the staurolite out muscovite and quartz out and beginning of partial melting isograds imply that the rocks exposed at the eastern end of the steep belt at maam cross were metamorphosed at a lower pressure than those farther w at recess similarly the stable co existence of muscovite and quartz in the recess area may indicate that the second sillimanite isograd dips towards the s a condition that would be consistent with sub vertical isotherms associated with a thermal anticline centred on the cashel volcanic arc

end silurian modifications of ordovician terranes in western ireland the ordovician elements in the caledonides of western ireland may be divided into the clew bay south mayo north connemara and south connemara sub zones evidence suggests the presence of a number of proximal suspect terranes and the remnants of one or possibly two arc complexes palaeontological and sedimentary evidence suggests an allochthonous relationship between the silurian rocks of croagh patrick and north galway these successions may therefore not represent a single sedimentary overlap to the ordovician suspect terranes end silurian deformation was the result of transpression which was responsible in part for the present configuration of the area s geology deep seated shear zones with fuchsite and gold mineralization were foci for lateral translation concomitant with southward directed thrusting northward directed back thrusts and variable degrees of metamorphism being of higher grade in the north the end silurian event is intermediate between the high grade metamorphism in parts of the appalachians and the non metamorphic silurian sequences of scotland

the gazli ussr 19 march 1984 earthquake the mechanism and tectonic implications the fault parameters of the gazli ussr earthquake of 19 march 1984 ms 7 0 were determined from the inversion of the gdsn long period p and sh and short period p seismograms the frequency of the short period seismograms was broadened by partially deconvolving the effect of the recording instruments the earthquake represents a thrust fault with a small amount of a left handed strike slip component on a ne sw trending fault dipping northwest the average depth is 9 km the rupture propagated essentially continuously while breaking several high stress asperities directivity of the observed waveforms indicates principal rupture direction from se to nw the total duration of rupture is about 13 sec the average scalar seismic moment found from the long period wave forms is 2 5 1019 n m in addition to the 1984 event the gazli region experienced two large ms 7 0 earthquakes in 1976 and one medium size earthquake ms 5 7 in 1978 the mechanisms of the 1976 events were studied by hartzell 1980 and kristy et al 1980 and are thrust events striking in the general e w direction we determined the mechanism of the 1978 earthquake and find it similar to those of the 1976 earthquakes an interesting feature of the gazli earthquake sequence is the migration of activity from east to west along an arc shaped fault zone prior to 1976 the region was relatively aseismic based on instrumental and historical seismicity data

u pb and rb sr geochronology of magmatism and metamorphism in the dalradian of connemara western ireland new geochronological data which clarify the timing of syn orogenic magmatism and regional metamorphism in the connemara dalradian are presented u pb zircon data on four intermediate to acid foliated magmatic rocks show important inherited components but the most concordant fractions demonstrate that major magmatism continued until 465 ma whereas the earliest basic magmatism has been dated previously at 490 ma a fine grained fabric cutting granite contains discordant zircons which also appear to be 465 ma old arc magmatism in connemara therefore spanned a period of at least 25 ma recent u pb data on titanite from central connemara which gave a peak metamorphic age of 478 ma are supplemented by u pb data on titanite and monazite from metamorphic veins in the east of connemara which indicate that low p high t regional metamorphism continued there to 465 ma i e at least 10 ma later than in the central region dated previously new rb sr data on muscovites from coarse grained segregations in different structural settings range from 475 to 435 ma in part this range probably also reflects differences in age from west to east with three ages close to 455 ma from the eastern area which is also the site of the lowest pressure metamorphism thermal modelling indicates that at any one locality the duration of metamorphism was probably as little as 1 2 ma the new dates emphasize the complexity in the spatial and temporal distribution of high level regional metamorphism caused by magmatic activity the relatively simple overall distribution of mineral appearance isograds revealed by regional mapping masks the complexity of a prolonged but punctuated metamorphic history related to multiple intrusions primarily in the southern part of connemara the later stages of magmatic activity followed progressive uplift and erosion after the onset of magmatism and were localized in the eastern part of the region

stress rotation during the coalinga aftershock sequence this study considers spatial and temporal changes of the stress regime during the 1983 coalinga aftershock sequence in both cases the observed changes manifest themselves as rotations of the most compressive stress axis inversion of 165 m 3 aftershocks shows that in the southern aftershock zone the azimuth of the most compressional stress axis is oriented 24 e of north while in the northern and central zones it is oriented 51 e of north statistical analysis by use of non parametric bootstrap resampling shows that this rotation is significant at above the 95 confidence level inverting the focal mechanisms of 122 m 3 aftershocks in the central and northern aftershock zones reveals a rotation of the principal stress axes during the first 500 days after the main shock the compressional axis rotates from an azimuth of 62 e of north to 47 e of north statistical analysis by use of nonparametric bootstrap resampling shows that this rotation is just significantly different from zero at the 95 confidence level subject to the assumption that 80 of the fault planes can be correctly picked from the two nodal planes as the number of fault planes picked correctly varies from 50 random choices to 100 the significance of the rotation varies from 87 to 98 further investigation fails to find the signature of the stress changes predicted by dislocation theory in the focal mechanisms of the aftershocks active folds in the area suggest that the pre main shock stress regime had a compressional axis with a ne sw orientation thus the rotation during the aftershock sequence is thought to be a rebound from a stress anomaly induced by the main shock this stress anomaly may be causally related to the occurrence of the aftershocks

scaling of ground motion parameters state of stress and focal depth the ground motion parametersrv and ra where r is hypocentral distance v is peak velocity is density and a is peak acceleration are found observationally to be strong functions of stress state and linearly related to focal depth z if the stress state and focal depth are properly taken into account then the ground motion parameters depend on the seismic moment m0 as expected from basic scaling principles that is rv m01 3 and ra is independent of earthquake size regression lines fitted to observations covering broad ranges in seismic moment and focal depth indicate that for extensional and compressional tectonic regimes corresponding to normal and thrust or reverse faulting earthquakes respectively peak acceleration is given by ra 1 08 mpa 3 06 mpa km z normal and ra 5 65 mpa 8 76 mpa km z thrust and for peak velocity rv m01 3 10 4 m2 s n m 1 3 3 00 0 69 km 1 z normal and rv m01 3 10 4 m2 s n m 1 3 4 63 1 82 km 1 z thrust for strike slip earthquakes the data currently are insufficient to define regression fits but such lines would definitely lie between those for the normal and thrust stress regimes these equations are appropriate for ground motion at small hypocentral distance as recorded in a whole space it follows that for comparable hypocentral depth peak acceleration in a compressional tectonic regime for example much of the eastern united states is a factor of about 3 greater than in an extensional regime such as nevada and for peak velocity a similar comparison yields a factor of 2 difference the similarity in behavior of the peak acceleration parameter to crustal strength estimated from byerlee s law of friction with respect to depth and stress state indicates that crustal strength is probably the factor governing the seismic source processes that give rise to the high frequency peak ground motion analysis of the peak acceleration data in the context of crustal strength suggests bounds on this ground motion parameter as recorded at a typical surface site that depend on stress state specifically a normal 0 5 g and a thrust 1 9 g thus the state of stress as well as the focal depth clearly is an important factor to be taken into account in the prediction of seismic ground motion

late ordovician to early silurian amalgamation of the dalradian and adjacent ordovician rocks in the british isles from detailed radiometric and pressure temperature estimates of the metamorphic history uplift and erosion of the dalradian rocks of the british isles we find that 15 25 km of erosion took place mainly in ordovician time none of this vast volume of material is apparently present in the ordovician sedimentary basins that now flank the dalradian block we conclude that the ordovician basins to the south of the dalradian block are exotic terranes and we document their emplacement into their present position during late ordovician to early silurian time i e taconic by using evidence mainly from western ireland

geochemical evolution of an ordovician island arc south mayo ireland early ordovician volcanic rocks exposed in the south mayo region of western ireland document the history of a volcanic arc complex produced following the initiation of south dipping subduction within the iapetus ocean in the late cambrian or early ordovician lavas of the lough nafooey group tremadoc arenig show an eruption history marked by an initial period of tholeiitic basaltic volcanism followed by a shift to increasing silica compositions of calc alkaline affinity subsequent volcanism of the tourmakeady group arenig shows a mixture of rhyolitic and andesitic compositions which are in turn succeeded by tuffs of the rosroe and mweelrea formations of the murrisk group llanvirn these are also rhyolitic and andesitic but are generally more siliceous the overall increase in silica contents may reflect increasing fractional crystallization due to crustal thickening trace element studies of the basaltic members of the lough nafooey group show a strong subduction zone influence while absolute levels of immobile trace and rare earth elements decrease upsection relative depletion of the most incompatible elements decreases over the same time period these trends suggest decreasing degrees of partial melting of a progressively more depleted source mantle upsection the basaltic bohaun volcanic formation tremadoc arenig shows greater depletion in its incompatible trace elements than the lough nafooey group so indicating a more depleted mantle source comparison with modern arc systems suggests that the bohaun volcanic formation was probably generated shortly after the initiation of subduction and was erupted in a more trenchward position than the lough nafooey group i e in the forearc this confirms a south dipping polarity to the subduction zone and suggests an age of initiation during the late cambrian or earliest ordovician

evidence for holocene palaeoseismicity along the basel reinach active normal fault switzerland a seismic source for the 1356 earthquake in the upper rhine graben summary we conducted a palaeoseismic study with geomorphologic mapping geophysical prospecting and trenching along an 8 km long nne ssw trending fault scarp south of basel the city as well as 40 castles within a 20 km radius were destroyed or heavily damaged by the earthquake of 1356 october 18 io ix x the largest historical seismic event in central europe active river incisions as well as late quaternary alluvial terraces are uplifted along the linear basel reinach br fault scarp the active normal fault is comprised of at least two main branches reaching the surface as evident by resistivity profiles reflection seismic data and direct observations in six trenches in trenches the normal fault rupture affects three colluvial wedge deposits up to the base of the modern soil radiocarbon as well as thermoluminescence tl age determinations from other trenches helped to reconstruct the holocene event chronology we identified three seismic events with an average coseismic movement of 0 5 0 8 m and a total vertical displacement of 1 8 m in the last 7800 yr and five events in the last 13 200 yr the most recent event occurred in the interval ad 500 1450 2 and may correspond to the 1356 earthquake furthermore the morphology suggests both a southern and northern fault extensions that may reach 20 km across the jura mountains and across the rhine valley taking this fault length and a 10 km thick seismogenic layer suggests a mw 6 5 or greater event as a possible scenario for the seismic hazard assessment of the basel region

on the evolution of planetary scale fields and genesis of monsoon depressions over the indian region daily composite fourier coefficients of height zonal meridional and vertical velocity temperature vorticity and divergence for zonal wavenumbers 0 to 4 during 7 days of pre and 4 days of post depression from 1000 to 200 hpa in the latitude belt 0 30n are obtained for 6 monsoon depressions formed over the bay of bengal in the years 2006 2008 the planetary scale fields zonally averaged over the indian region 75e 96e are examined consistent with the quasi geostrophic approximation in the northern sector 15n 30n the monsoon trough the low level westerlies and the vorticity are strongly intensified and progressively extended upward to 400 hpa preceding depressions wavenumber 1 is the dominant contributor towards the strengthening and vertical upward expansion of these entities linked to an increase of its amplitude in the lower and a large westward phase shift in the mid troposphere respectively the cyclonic shear zone in the lower troposphere is developed to the north of 15n due to the combined effect of intensification and sharp decrease of meridional scale of the westerlies different northward speeds of the zonal wind reversal and westerly maximum creates a strong cyclonic zone 2 days before depressions at 400 hpa the planetary scale zonal flow in the troposphere satisfies the necessary condition for barotropic instability the northward westward movement of wavenumber 1 at 400 hpa is 0 73 latitude 5 6 longitudes day 1 an intensification of direct thermal meridional circulation is associated with a southward and upward shift of the primary rising motion zone the planetary waves have captured the main characteristics of observed vertical and latitudinal profiles of unstable background zonal flow used earlier for instability studies it is concluded that wavenumber1is the main contributor to genesis of a depression the planetary fields weakened in the presence of depressions mainly due to wavenumbers 3 and 4

active tectonics of the alpine himalayan belt between western turkey and pakistan summary over 80 new fault plane solutions combined with satellite imagery as well as both modern and historical observations of earthquake faulting are used to investigate the active tectonics of the middle east between western turkey and pakistan the deformation of the western part of this region is dominated by the movement of continental material laterally away from the lake van region in eastern turkey this movement helps to avoid crustal thickening in the van region and allows some of the shortening between arabia and eurasia to be taken up by the thrusting of continental material over oceanic type basement in the southern caspian mediterranean makran and black sea thus central turkey bounded by the north and east anatolian strike slip faults is moving west from the van region and overrides the eastern mediterranean at two intermediate depth seismic zones one extending between antalya bay and southern cyprus and the other further west in the hellenic trench the motion of northern iran eastwards from the van region is achieved mainly by a conjugate system of strike slip faults and leads to the low angle thrusting of iran over the southern caspian sea the seismicity of the caucasus shows predominantly shortening perpendicular to the regional strike but there is also some minor elongation along the strike of the belt as the causcasus overrides the caspian and black seas the deformation of the eastern part of this region is dominated by the shortening of iran against the stable borders of turkmenistan and afghanistan the north east direction of compression seen in zagros is also seen in north east iran and the kopet dag where the shortening is taken up by a combination of strike slip and thrust faulting large structural as well as palaeomagnetic rotations are likely to have occurred in ne iran as a result of this style of deformation north south strike slip faults in southern iran allow some movement of material away from the collision zone in ne iran towards the makran subduction zone where genuinely intermediate depth seismicity is seen within this broad deforming belt large areas such as central turkey nw iran azerbaijan central iran and the southern caspian appear to be almost aseismic and therefore to behave as relatively rigid blocks surrounded by active belts 200 300 km wide the motion of these blocks can usefully be described by poles of rotation the poles presented in this paper predict motions consistent with those observed and also predict the opening of the gulf of iskenderun ne of cyprus the change within the zagros mountains from strike slip faulting in the nw to intense thrusting in the se and the relatively feeble seismicity in se iran baluchistan this description also explains why the north south structures along the iran afghanistan border do not cut the east west ranges of the makran within the active belts surrounding the relatively aseismic blocks a continuum approach is needed for a description of the deformation even though motions at the surface may be concentrated on faults the evolution of fault systems within the active zones is controlled by geometric constraints such as the requirement that simultaneously active faults do not in general intersect many of the active processes discussed in this paper particularly large scale rotations and lateral movement along the regional strike are likely to have caused substantial complexities in older mountain belts and should be accounted for in any reconstructions of them

a high precision u pb age for the ben vuirich granite implications for the evolution of the scottish dalradian supergroup high precision high accuracy u pb analyses of zircons from the ben vuirich granite in the scottish dalradian succession were performed on carefully picked high integrity abraded fractions of specific morphologies zircon needles which grew during crystallization give an age of 590 2 ma stubby prisms show inheritance with an upper concordia intercept of 1448 7 ma the age of intrusion at 590 ma contrasts strongly with a previous u pb zircon age of 514 6 7 ma determined on bulk fraction unabraded grains which it is argued must have suffered significant pb loss as the ben vuirich granite was emplaced between the regional d2 and d3 deformation events in the dalradian block the new data imply that all dalradian sedimentation was precambrian supposed lower cambrian fauna1 links between the dalradian succession and laurentia are thus discounted and the possibility that the dalradian supergroup has non laurentian affinities must be considered the early d1 d2 nappe forming grampian structures are also precambrian and may be associated with terrane docking along a tectonically active ocean margin later d3 structures and associated peak barrovian metamorphism suggest a subsequent thickening event possibly c 520 ma ago

structural and fluid chemical properties of seismogenic normal faults abstract structures in extensional fault zones can be classified using the configuration of fault branch lines and tip lines important classes include the segment bend segment termination segment branch cross fault intersection and segment offset the effect of these structures on rupture history is not necessarily consistent neither between individual earthquakes nor between different fault zones rupture behavior is dependent on several other factors including loading conditions regional and localized rupture tip stress fields fluid mechanical processes and chemical processes fracture toughness is partly controlled by the angular discordance between slip directions on adjacent fault segments greater discordance between slip directions and intersection lines of fault segments results in greater strain incompatibility an internal fracture network generally evolves within a segment boundary to maintain compatibility and transfer slip between the segments the dimensions and structure of this fracture network may also partly control rupture propagation presumably activation of a fault network with large angular discordances between slip directions and intersection lines will generate numerous asperities as the subsidiary faults mutually interact and offset each other the geometry of a segment boundary may change with depth and the three dimensional nature of the structure may be important in controlling rupture history fluids influence rupturing via fluid pressure effects and time dependent chemical processes fracture propagation by stress corrosion may favor instability and chemical alteration may produce minerals of lower strengths allowing time dependent creep sealing and healing of fractures however may remove damage and increase strength elementary computations indicate that representative times for sealing and chemical alteration are between 1 and 1000 years for reasonable physical conditions well within the recurrence intervals of most large earthquakes time to failure for stress corrosion cracking is more highly variable and strongly sensitive to applied stress and fluid pressure

conditions of high grade metamorphism in the dalradian of connemara ireland in e connemara ireland dalradian metasediments were initially metamorphosed to kyanite staurolite grade at pressures above 7kbar the subsequent emplacement of basic to intermediate magmas accompanied by uplift and erosion produce a steepening of the geothermal gradient and led to the formation of migmatitic garnet cordierite sillimanite gneisses in the highest grade regions in the s cation exchange equilibria between coexisting mineral pairs suggest that partial melting took place under high temperatures 750 c and moderate pressures 4 5 6 kbar fluid inclusion studies and andalusite occurrences from migmatite leucosomes suggest that crystallization of the melts occurred at lower pressures

divergent circulations on the 30 to 50 day time scale abstract a brief review of some of the recent results on the 30 to 50 day time scale is presented in this paper we have examined the divergent circulations on the time scale of 30 to 50 days during the fgge year the present study is based on two different data sets these are the fgge iiib analysis from the european center for medium range weather forecasts ecmwf and the florida state university s analysis over the monsoon region during the fgge year the analysis clearly identifies a planetary scale divergence wave that traverses around the globe eastward throughout the fgge year its speed of eastward propagation is around 8 longitude day 1 the amplitude of this wave is largest during the summer season over the monsoon region and the western pacific oceans the amplitude decreases somewhat as the wave traverses across the eastern pacific and atlantic oceans this wave appears to modulate the monsoon activity such that active inactive spells seem to bear a close relationship to the divergence on t

rupture kinematics of the three gazli major earthquakes from vertical and horizontal displacements data abstract an inversion of horizontal and vertical displacement data in the gazli region shows that the gazli earthquakes of april and may 1976 and march 1984 occurred on variously orientated fault planes dipping to the ese n and ese respectively the kinematics of the 1984 seismic rupture exhibits a pure thrust slip motion of 2 5 m common data for distinct events during the 1976 rupture sequence are not optimal to solve the rupture characteristics however the complexity of the faulting is highlighted by 1 well resolved different dips for the two shocks 2 strike slip components of motions on fault planes with thrust motion components close to the value of the 1984 event and 3 discrepancy between geodetic and seismic fault models for the april 1976 earthquake the results express the complex mechanics that drive compound intraplate earthquakes

stress analysis in the intraplate area of gazli uzbekistan from different sets of earthquake focal mechanisms occurrence of intraplate earthquakes have been related either to reactivation of preexisting zones of weakness in a uniformly oriented regional stress field or to local stress changes more recently buildup of pore pressure anomalies has been proposed to explain both the low recurrence rate and some misorientation of rupture planes in the prevailing regional stress field in this study we analyze local stress field orientation in the area of the three ms 7 0 gazli western uzbekistan earthquakes by using different sets of earthquakes focal mechanisms we show that stress tensor inversions from both seven 4 2 ms 7 0 forty five 0 1 ml 3 2 and twenty five 1 0 ml 3 2 earthquake focal mechanisms give constant maximum horizontal stress direction in agreement with the one deduced from the india asia collision the best model for the local stress tensor exhibits a significant 25 discrepancy from vertical for one of the principal stresses we note moreover that the common assumption that one principal stress axis is oriented vertically is not strictly supported by stress states derived from earthquake focal mechanisms available in the world stress database by evaluating each hypothesis of stress inversion methods from earthquake focal mechanisms it is shown that especially in intraplate settings the first motion focal solution should be the most appropriate one for a formal inversion and that the magnitude of the considered event may not be the only criterion to assess the quality of a stress inversion this is particularly timely because more and more focal mechanisms are moment tensor solutions instead of first motion solutions concerning the gazli sequence the slip conditions pore pressure and frictional coefficient are evaluated for each of the three mainshocks in terms of an independently determined local stress field because variations in orientations between local and regional stress field are not detected and because the three mainshock fault planes seem to be relatively well oriented for a frictional activation in the local stress field it is concluded that this seismic sequence is localized on preexisting weakness zones and is not due to local stress orientation anomalies

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

u pb zircon ages of basic rocks and gneisses intruded into the dalradian rocks of cashel connemara western ireland new isotopic ages are presented from the syntectonic cashel lough wheelaun basic intrusion and an associated k feldspar granite gneiss of the connemara gneiss complex from lettershinna hill the linear normally discordant distribution of data points from the cashel lough wheelaun metagabbro indicates that the zircons in this intrusion have no significant inherited radiogenic pb they yield an upper concordia intercept age of 477 25 6 ma and a more precise 207 pb 206 pb age of 490 1 ma in contrast zircons from the k feldspar granite gneiss show distinct reverse discordance the non magnetic fractions show a good linear arrangement yielding a lower intercept age of 454 6 14 ma and a very uncertain upper intercept age of 1807 646 570 ma the lower intercept age is younger than the 477 9 ma k ar age of hornblendes in gneisses from lettershinna hill elias et al 1988 and therefore reflects a pb loss episode younger than igneous crystallization the imprecise proterozoic upper intercept age indicates contamination by older inherited and only partially reset zircons

recent deformation in the turan and south kazakh platforms western central asia and its relation to arabia asia and india asia collisions in this study we investigate the recent and active tectonics of the turan and south kazakh platforms in western central asia this area which has been considered stable during the tertiary was struck in its eastern part gazli and kyzyl kum by three earthquakes of magnitude ms 7 0 between 1976 and 1984 from structural observations we show that in the kyzyl kum cenozoic deformation on structures oriented nw se is dominated by dextral strike slip motion on a flower structure involving reactivated late paleozoic faults this deformation is compatible with the stress pattern induced by the pamir tien shan collision zone at the scale of the turan south kazakh platform comparison of repeated leveling measurements gives mean uplift rates of 5 mm yr 1 for most of the area south of the 44 latitude including the kyzyl kum these observations indicate that the turan south kazakh platform has been actively deforming since recent times pleistocene in response to the collision of both india and arabia with asia earthquake data also reveal that propagation of deformation from the kopet dagh and the pamir tien shan collision zones into the turan south kazakh platform is accommodated aseismically except in the kyzyl kum this might reflect differences in the deformation style and nature of the upper crust in the kyzyl kum and north of the kopet dagh respectively we propose that the gazli earthquakes highlight the northwestward continuation within the turan south kazakh platform and along reactivated older structures of the deformation related to the pamir indentation and to a lesser degree to the arabia asia convergence

structural age of the connemara gabbros western ireland a d2 age of intrusion for the connemara gabbros is rejected the gabbros were intruded 490 ma ago probably just prior to the d3 deformation and together with younger members of the metagabbro and gneiss complex were responsible for a widespread sillimanite grade contact metamorphism which overprinted the regional d2 gamet staurolite kyanite metamorphism and the major d3 folds comparison with the ne scotland gabbros is thereby strengthened supporting the idea that they were both part of a coeval magmatic arc developed at the margin of the caledonian fold belt

the 1989 ms 6 3 ungava quebec earthquake a complex intraplate event on 25 december 1989 the largest earthquake ms 6 3 in northern quebec in at least 60 yr occurred in the ungava peninsula this earthquake was unique in that it marked the first time surface faulting could be confirmed for a historical eastern north american earthquake field observations indicated a combination of thrust and strike slip motion waveforms modeled in this study show that the earthquake consisted of two subevents a thrust subevent on a ne sw striking plane followed by a larger strike slip subevent on a nne ssw striking plane the surface waves give an equivalent double couple moment of 1 3 1025 dyne cm the sum of the subevent moments is greater than the simple source moment by almost a factor of 2 both subevents occurred at a depth of 3 km they were separated by 0 9 sec in time with the second subevent occurring 5 2 km southwest of the first the source parameters determined by modeling and those inferred from the ground observations generally agree but there are some differences with respect to the subevent offset these may be reconciled if the strike slip motion was distributed among the several small faults at the southwestern end of the rupture or if the complete surface rupture was not found the stress orientation nw compression inferred from the fault plane solution is consistent with the focal mechanisms of many other recent northeastern canadian events the ungava earthquake and many intraplate events from several continents share a number of characteristics including shallow hypocenters source complexity and occurrence on faults that showed no evidence for previous ruptures

short paper ophiolitic detritus in the ordovician sediments of south mayo ireland sandstones from ordovician sediments of the south mayo trough western irish caledonides show marked stratigraphic variation in their major and trace element geochemistry high cr ni and mg concentrations of ultramafic derivation succeed high ti and fe concentrations of mafic provenance this sequence is interpreted as the result of the progressive unroofing of an ophiolite a possible sedimentary linkage with ophiolite lithologies in the clew bay domain to the north would indicate minimal post arenig transcurrent displacement the south mayo flysch with its ophiolitic detritus is typical of caledonian flysch sequences which pre date the mid ordovician taconic deformation but differs in character from those of late ordovician age

palaeomagnetism of silurian sediments in w ireland evidence for block rotation in the caledonides summary a palaeomagnetic study of mid silurian wenlock sediments of the salrock formation in nw galway yields a reliable silurian palaeomagnetic pole position for w ireland at latitude 1 6 s longitude 287 7 e dp 2 5 dm 4 6 n 27 sites a further 12 sampling sites were located in silurian redbeds on clare island s mayo where a palaeomagnetic remanence of silurian age was also identified both remanences pre date local late caledonian folding however the clare island result has an anomalous azimuth when compared with the salrock result and with published silurian results for britain the two irish results can be reconciled by anticlockwise block rotation of the clare island region through 40 50 the rotation brings both palaeomagnetic and structural trends within the two sampling regions into alignment strike slip displacement across the clew bay fault zone producing a sinistral shear couple might have enabled such a rotation the timing and geographic extent of the proposed block rotation is as yet poorly defined however a younger age limit for rotation is provided by a late devonian or carboniferous partial magnetic overprint observed throughout both study areas and from geological evidence it seems likely that rotation is confined to the clew bay fault zone the dalradian rocks of the connemara massif located to the south of the salrock district have an e w structural grain some workers have proposed clockwise rotation of the connemara massif of ca 30 at between 500 and 390 ma which would bring the structural trends in w ireland into parallelism with caledonian trends in scotland because the silurian salrock succession which rests unconformably on the dalradian basement of connemara shows no such anomaly it provides a younger age limit for the possible rotation of connemara

stress tensor and fault plane solutions for a population of earthquakes an algorithm for the simultaneous estimation of the orientation and shape of the stress tensor and the individual fault plane solutions for a population of earthquakes is studied it corresponds to a synthesis of the methods used by brillinger et al 1980 to obtain focal mechanisms and by armijo and cisternas 1978 for stress tensor analysis in microtectonics the input data are the polarities of the p arrival and take off angles for the set of source station pairs the method distinguishes in general which one of the nodal planes corresponds to the fault and gives the direction of the slip the application to the aftershock sequence of the 1980 arudy earthquake western pyrenees shows that the observations may be explained by a single stress tensor producing a n32 e extension with a likelihood of 95 per cent

rupture planes of the gazli earthquakes deduced from local stress tensor calculation and geodetic data inversion geotectonic implications three major earthquakes with ms 7 were clustered in space and time 1976 1984 near gazli uzbekistan without reported evidence for fault scarps to constrain the kinematics of the seismic sequence we invert both focal mechanism solutions of the mainshocks and major aftershocks and vertical surface displacements associated with the three major shocks for seven m 4 earthquakes that occurred in the 1976 1984 period we find that all the focal mechanisms agree with a single stress tensor one of the mechanical implications of this mathematical solution is the choice of the seismic fault plane the 1976 earthquake fracture planes are well constrained by the stress tensor to be striking e w and ene wsw and dipping to the south and the nnw respectively from stress tensor inversion alone it is impossible to determine if the fracture plane of the 1984 event dips to the se or to the nw coseismic vertical surface displacements allow us to infer possible fault plane orientations of the 1976 and 1984 events the best fit to the surface displacement for the 1976 earthquakes is obtained from the geometries that are derived from the homogeneous stress tensor inversion the inversion of vertical surface displacements for the 1984 event constrains the associated fault plane to correspond to a ne ws striking and se dipping plane the inversions of complementary geophysical data argue for the complexity of the orientations of the faults activated by the 1976 1984 seismic sequence the 1984 earthquake fault plane is well orientated to allow failure to be activated by a horizontal 1 under a mohr coulomb failure criterion under the same failure criterion and stress conditions unlike the 1984 fracture plane the 1976 fault planes are misorientated and likely to correspond to preexisting discontinuities concerning the principle stress orientations the gazli region seems to be under control of the regional tectonic setting from a regional point of view the wnw ese strike of 1 and the nne ssw strike of 2 deduced from this study for the kyzylkum desert can be explained at once by the interaction of the regional plate boundary motions

present plate tectonics between turkey and tibet abstract by studying seismicity and active tectonics in the eastern part of the alpine belt we were able to identify microplates for which poles of rotation have been computed from focal mechanism solutions and directions of strike slip faults using these data and rates of movement along microplate boundaries we have compiled a reconstruction for the time of 10 m y b p the mosaic of microplates within the belt originated due to interactions of the main lithospheric plates of eurasia india and arabia the collision of which is responsible for the present active tectonics of the belt the northward movement of india and arabia accounts not only for large crustal shortening but also for changes in the motions of the assemblage of plates leading to the large strike slip faulting and rotation of individual blocks plate and microplate interactions in the region are analyzed on the assumption of their rigidity especially near plate boundaries reliable data however suggest that within some zones plate rigidity is not valid

major southward thrusting of the dalradian rocks of connemara western ireland the connemara schists are of dalradian late precambrian cambrian age and since the work of kilburn et al 1 it has been apparentthat they occupy an anomalous geographical position south southeast of the strike continuation of the dalradian rocks of scotland and ireland and south of the inferred position of the highland boundary fault fig 1 also the connemara schists are unusual in having reached a higher metamorphic grade and having had a different metamorphic history from most other parts of the dalradian the model which we propose here for the connemara dalradian that of an allochthonous thrust sheet offers an explanation for these anomalies and highlights hitherto unsuspected similarities between the tectonic histories of the south east margins of the metamorphic caledonides in the british isles and scandinavia

a pre d2 age for the 590 ma ben vuirich granite in the dalradian of scotland regional mapping demonstrates that s2 is the main fabric in the central highland dalradian and that it is this fabric not s3 as previously thought which overprints the 590 ma ben vuirich granite the granite appears to have been emplaced following a tectonic event d1 in the dalradian rocks for a finely spaced penetrative fabric seen in newly discovered hornfelses from the granite aureole is overgrown by contact metamorphic cordierite and andalusite porphyroblasts now both altered which predate the d2 metamorphism the ben vuirich granite cuts the neoproterozoic dalradian sequence of the central highlands of scotland fig 1 inset and was first recognized as an older foliated granite by barrow et al 1905 later workers bradbury et al 1976 bradbury 1978 concluded that the granite was intruded between d2 and d3 in the dalradian rocks harris et al 1976 and for many years an u pb zircon age of 514 7 ma from the intrusion pankhurst pidgeon 1976 provided a valuable datum point in the evolution of the scottish caledonides however dalradian chronology has recently undergone a radical revision following the determination of a precise u pb age of 590 2 ma for the emplacement of the ben vuirich granite rogers et al 1989 in accepting the interpretation of bradbury et al 1976 that the regional penetrative fabric which affects the country rocks and is continuous with that in the granite is of d3 age rogers et al were also guided by the conclusions of harte et al 1984 and dempster harte

interannual and intraseasonal variations in monsoon depressions and their westward propagating predecessors abstract the majority of monsoon depressions develop from the regenesis of westward propagating residual lows from the east most of these residual lows can be traced to weather disturbances in the south china sea including tropical cyclones and 12 24 day monsoon lows hypothetically any mechanism causing a variation in the occurrence frequency of these two types of weather disturbances in the western tropical pacific south china sea wtp scs region may result in a corresponding change in the formation frequency of monsoon depressions over the bay of bengal two such possible mechanisms are interannual and intraseasonal variations of large scale summer circulation in the wtp scs region induced by 1 the interannual variation of the sea surface temperature sst in the eastern tropical pacific and 2 the northward migration of the 30 60 day monsoon trough ridge the national centers for environmental prediction national center for atmospheric research reanalysis data and the 6 hourly tropical cyclone tr

the 30 50 day mode at 850 mb during monex abstract the analyzed wind field at 850 mb during the summer monsoon experiment monex is subjected to a time series analysis to confirm the existence of a peak in the time range of 30 50 days having established that this study presents a mapping of the motion field for this time scale in this short paper we illustrate the steady meridional propagation of a train of troughs and ridges that seem to form near the equator and dissipate near the himalayas the meridional scale of this mode is around 300 km and its meridional speed of propagation is 0 75 latitude per day the amplitude of the wind for this mode is around 3 6 m s 1 the salient contributions here are the mapping and the demonstration of a very regular behavior of this mode its existence is here noted from a period well before the onset of monsoon i e from early may to late july three major storms during monex were noted to form within the trough line of this system and the period of major cessation of rains over the indian subconti

caledonian transpressional terrane accretion along the laurentian margin in co mayo ireland the highland border fair head clew bay baie verte brompton suture clew bay suture on achill island western ireland is an e w trending zone of vertical ductile dextral transpression bounding the southern edge of the dalradian terrane the achill dalradian a sequence of coarse grained psammite overlain by conglomerate quartzite schist and limestone disposed in recumbent curvilinear folds represents laurentian continental margin deposits which were translated westward during deformation parallel to the suture trace studies of fabric development and albite porphyroblast growth indicate that e w dextral transpression and west directed recumbent folding were synchronous and are interpreted as separate expressions of the same nw directed terrane impingement event this process of terrane docking was marked by a c 4kbar phase of decompression within the suture four separate terrane slivers are recognized the presence of pyrope garnet and crossite amphibole within two imply the clew bay zone experienced sufficient displacement to exhume rocks from deep lithospheric levels in addition the extensive retrogression and destruction suffered by these remnant high pressure mineral assemblages during the albite generating transpressional phase implies that ductile deformation was enhanced by the introduction of fluid into and along the suture zone during impingement

evidence for a regional scale fluid loss event during mid crustal metamorphism how fluid is released from the deep crust during metamorphism remains controversial whereas some authors advocate large scale fluid fluxes due to convective circulation of metamorphic fluid1 others consider that only one way flow is possible2 3 furthermore some flow models imply that fluid moves across and largely independently of sedimentary layering1 2 whereas many fluid based studies find evidence for focusing of flow by particular lithologies2 4 7 here we report a study of metamorphic fluid flow on a regional rather than an outcrop scale using a combination of field geology petrology and theoretical and isotope geochemistry we identify metasomatic lithologies at the top of a dolomitic marble unit which must have drawn in water over a kilometre scale from adjacent pelitic formations we suggest that this flow was part of a single major fluid loss event near the metamorphic peak fluid followed the metasomatic layers to structural highs where it broke out into adjacent schists to form skarns this fluid loss may have changed the rheology of the rock involved and terminated regional folding

fluid disturbed hornblende k ar ages from the dalradian rocks of connemara western ireland the results of k ar age determinations and hydrogen and oxygen stable isotope measurements on hornblendes from the poly metamorphic dalradian schists of connemara western ireland indicate that the hornblende k ar systems have been significantly disturbed by low temperature fluid reaction correlations between k ar ages d values structural water contents and the occupancy of the hornblende structural a sites suggest that excess water as h 3 o occupies vacant a site positions during stable isotope exchange and displaces ar causing lowering of the k ar ages this process occurs below the normally accepted closure temperature for ar in hornblende and is not detectable by optical or x ray investigation of the mineral this process may not be unique to connemara hornblendes and so is of potential importance to geochronology in other metamorphic terranes

alpine metamorphism in the south east tauern window austria 2 rates of heating cooling and uplift existing geochronological data are reviewed and new rb sr k ar and 39ar 40ar ages are presented including a suite of 33 mica ages from a 20 km north south tunnel section these data are discussed in relation to the thermal history from the overthrusting of the autroalpine nappes c 65 myr ago to the present the earliest phase of metamorphism involving lawsonite crystallization is associated with emplacement of these nappes subsequently temperatures in the rocks beneath rose at a mean rate of 3 6 c myr until the climax of metamorphism at high structural levels published data indicate an age 35 myr for the metamorphic climax in contrast a new 39ar 40ar step heating age of 23 8 0 8 myr on amphibole from near the base of peripheral schieferhulle closely approximates the age of metamorphism and provides the first clear indication that the climax of metamorphism occurred later at deeper structure levels following the climax near isothermal uplift and erosion reduced pressure to c 1 kbar before white mica closure at 19 myr this implies uplift at 3 mm yr along the tunnel section white mica k ar ages vary systematically from 24 myr to 16 5 myr with position relative to a late 4 km amplitude dome whereas biotite rb sr ages are uniform at 16 5 myr across the whole profile doming is thus dated at 16 5 myr with transient uplift rates 5 mm yr at other times uplift rates were 1 mm yr

a note on fault reactivation reactivation of existing faults whose normal lies in the 1 3 plane of a stress field with effective principal compressive stresses 1 2 3 is considered for the simplest frictional failure criterion n n p where and n are respectively the shear and normal stresses to the existing fault p is the fluid pressure and is the static friction for a plane oriented at to 1 the stress ratio for reactivation is 1 3 1 cot 1 tan this ratio has a minimum positive value at the optimum angle for reactivation given by 12tan 1 1 but reaches infinity when 2 beyond which 3 0 is a necessary condition for reactivation an important consequence is that for typical rock friction coefficients it is unlikely that normal faults will be reactivated as high angle reverse faults or thrusts as low angle normal faults unless the effective least principal stress is tensile

comparison of centroid moment tensor and first motion solutions for western mediterranean earthquakes abstract comparison of centroid moment tensor and first motion solutions shows that the two different methods give compatible solutions for moderate sized earthquakes in the western mediterranean while the centroid moment tensor solution provides a good indication of the general style of deformation occurring in an area careful consideration of the first motion solution is still necessary for detailed study of source mechanics there is no obvious character of the centroid moment tensor solution such as small values of moment or large non double couple contribution that can be used as diagnostic of a significantly different first motion solution

global omori law decay of triggered earthquakes large aftershocks outside the classical aftershock zone 1 triggered earthquakes can be large damaging and lethal as evidenced by the1999 shocks in turkey and the 2001 earthquakes in el salvador in this study earthquakes with ms 7 0 from the harvard centroid moment tensor cmt catalog are modeled as dislocations to calculate shear stress changes on subsequent earthquake rupture planes near enough to be affected about 61 of earthquakes that occurred near defined as having shear stress change 0 01 mpa the ms 7 0 shocks are associated with calculated shear stress increases while 39 are associated with shear stress decreases if earthquakes associated with calculated shear stress increases are interpreted as triggered then such events make up at least 8 of the cmt catalog globally these triggered earthquakes obey an omori law rate decay that lasts between 7 11 years after the main shock earthquakes associated with calculated shear stress increases occur at higher rates than background up to 240 km away from the main shock centroid omori s law is one of the few time predictable patterns evident in the global occurrence of earthquakes if large triggered earthquakes habitually obey omori s law then their hazard can be more readily assessed the characteristic rate change with time and spatial distribution can be used to rapidly assess the likelihood of triggered earthquakes following events of ms 7 0 i show an example application to the m 7 7 13 january 2001 el salvador earthquake where use of global statistics appears to provide a better rapid hazard estimate than coulomb stress change calculations

a deep seismic reflection transect across the irish caledonides new reflection profiles recorded to 18s c 60km along a 600 km north south transect west of ireland wire lines provide a cross section of the irish caledonides from lewisian basement in the north to the variscan fold and thrust belt in the south and constrain the offshore extrapolations of major caledonide structures we interpret the profiles as showing the great glen fault and associated ne trending strike slip faults as near vertical structures which cut the whole crust and the uppermost mantle beneath the surface trace of the fair head clew bay line we image a north dipping zone which soles into horizontal layers just above the reflection moho the north dipping zone separates south dipping reflections above and to the north from north dipping reflections below and to the south from the fair head clew bay line as far south as the iapetus suture the lower crust contains north dipping packages of reflectors possibly related to acadian accretionary underplating the iapetus suture zone can be identified as a zone more than 50 km wide dipping north at 30 from 5 km depth offshore dingle peninsula to sole into the moho at c 30 km depth west of the shannon estuary in the upper crust the shallow part of the iapetus suture zone appears to be transported to the north by late caledonian retrocharriage or by variscan thrusting the iapetus suture does not penetrate through the present day reflection moho but there are scattered reflectors in the mantle not continuous with crustal reflectors perhaps relics of a subducted slab we recognize lower crustal reflectivity and the reflection moho along almost all the wire profiles regionally the travel time to the reflection moho varies from 9 s c 28 km offshore donegal northwest of ireland to 12 s c 35 km offshore kerry and cork southwest of ireland apparent moho offsets rapid lateral changes in the travel time to the reflection moho north of donegal and north of mayo are probably due to the great glen fault and associated faults the lower crustal reflectivity varies considerably in thickness and prevalent dip direction along the wire profiles in donegal bay this reflectivity is observed at depths less than 5 km c 1 5s whereas west of kerry prominent reflectivity is only observed beneath 6s c 17 km though the age of crustal reflectors cannot in general be determined beneath central ireland from donegal to dingle the lower crustal reflectors mimic in dip direction the structural vergence of the exposed dalradian and early palaeozoic rocks so that the lower crustal reflectivity patterns and probably much of the crust must be caledonian in age

reconciling short recurrence intervals with minor deformation in the new madrid seismic zone at least three great earthquakes occurred in the new madrid seismic zone in 1811 and 1812 estimates of present day strain rates suggest that such events may have a repeat time of 1000 years or less paleoseismological data also indicate that earthquakes large enough to cause soil liquefaction have occurred several times in the past 5000 years however pervasive crustal deformation expected from such a high frequency of large earthquakes is not observed this suggests that the seismic zone is a young feature possibly as young as several tens of thousands of years old and no more than a few million years old

dynamical response of the south asian monsoon trough to latent heating from stratiform and convective precipitation simulation experiments using a simplified atmospheric gcm and supplementary diagnostic analyses of observations are performed to understand how the south asian monsoon trough mt responds dynamically to latent heating from mesoscale convective systems mcss observations reveal that the mt during active monsoons is characterized by a deep cyclonic vorticity extending from the surface to 350 hpa and organized mcss covering over 3500 4000 km along the indo gangetic plains the mcss during active monsoons are composed of a relatively higher abundance of stratiform type precipitation mostly nimbostratus as compared to the convective type the results suggest that a stratiform type heating profile is very effective in promotingupward development of continental scale cyclonic circulation well above the midtroposphere over the mt region the vertical development involves a dynamical uplift of the layer of cyclonic circulation and is induced by midlevel 600 500 hpa convergence and vorticity stretching above 500 hpa by varying the population of stratiform and convective rain types in the simulation the horizontal scale of midlevel vorticity response is shown to increase significantly with stratiform population in contrast the midlevel response is more localized when the mcs is dominated by deep convective clouds for large stratiform populations the midlevel responseis found to extend far westward up to the northernflanks of the africanitcz indicativeof rossby wave dispersion of pv anomalies that are generated near the level of maximum heating gradient from the present findings one can conclude that the vertical deepening of mt during active monsoons is not merely a localized phenomenon instead it represents a large scale dynamical response to organized mcss that exert pivotal influence on the upward development of cyclonic circulation well above the midtroposphere