deep seated gravitational slope deformations related landslides and tectonics abstract deep seated gravitational slope deformations and their relationships with tectonic deformation of rocks is considered to examine the viewpoint of tectonics as a causative factor in slope deformation first a distinction is made between the different types of deep seated gravitational slope deformation then the geomorphological and structural effects of the different macrostructural deformations induced by tectonics on the scale of the whole deforming ridge is briefly discussed finally some case studies that represent either verified or possible cases of gravity deformation in response to tectonic activity are used as illustration

thickening and partial melting of the northern qinling orogen china insights from zircon u pb geochronology and hf isotopic composition of migmatites the widespread migmatites in the precambrian basement of the north qinling belt are products of partial melting of the earth9s crust and record the tectono thermal response to late paleozoic collision along the shangdan suture the morphology and trace element geochemistry of zircons from the migmatites suggest a metamorphic origin related to partial melting the zircons from leucosome melanosome and banded migmatites yield u pb weighted mean ages of 408 2 403 2 and 400 2 ma respectively constraining the timing of migmatization the granitic dyke intruded into the migmatites gives a zircon u pb weighted mean age of 396 2 ma constraining the minimum time of migmatization zircons from the melanosome and banded migmatite yield upper intercept ages of 1088 1061 ma representing the protolith ages of the basement of the north qinling belt the zircon rims of the melanosome and banded migmatite predominantly display negative and positive ehf t values respectively suggesting the variable input of mantle material together with the regional geology and previous geochronological data we propose that the thickening and partial melting in the north qinling belt was induced by the collision along the shangdan suture between the north and south china blocks from c 408 to 400 ma supplementary material la icp ms u pb data lu hf isotopic compositions and trace element geochemistry data of the zircons and ti in zircon thermometry are available at https doi org 10 6084 m9 figshare c 4521389

landslides and climate change in the italian dolomites since the late glacial abstract the paper deals with the relationship between the temporal occurrence of landslides and climatic changes in the italian dolomites since the late glacial after an introduction on the state of the art with particular reference to the alpine region the results of recent investigations in the two study sites are illustrated at cortina d ampezzo several landslides were dated mainly by the radiocarbon method the most ancient landslide event there involved large rock slides which affected the dolomitic slopes following the withdrawal of glaciers after the last glacial maximum lgm and also slides and flows mainly occurring in pelitic materials of the valley floors from 13 000 to 10 000 cal bp a later series of flows occurred between 5500 and 2500 cal bp in the upper badia valley alta badia the most ancient events go back to 10 000 and 9000 cal bp and correspond with earth flows that followed vast rotational slides affecting the bedrock up to a depth of about 50 m more recent earth flows involving more modest amounts of material took place between 6500 and 2300 cal bp by analysing the dates from the two study areas it was possible to correlate the recorded increase of landslide activity with the climatic changes occurring at the boundary between the late glacial and the holocene and between the atlantic and the subboreal and to compare the results with those derived from other european regions the types and causes of landslides taking place in these two periods were substantially different reflecting the different morphoclimatic conditions that existed in the two areas when these mass movements were triggered finally notwithstanding the importance of non climatic causes such as geological structural factors and possible human influences it is concluded that many of the dated landslides can be considered as indicators of climatic change

three different downstream fates of the boreal summer mjos on their passages over the maritime continent the boreal summer mjos exhibit three distinctive downstream evolutions on their passages over the maritime continent mc i smoothly transitioning from indian ocean io to western pacific type i ii rapidly decayed over the mc type ii and iii significantly intensified over the mc type iii during the life cycles of type i and iii mjos basin wide overturning circulations connect the convective dipoles between western and eastern north pacific for type ii mjo regional overturning circulations connect the convective dipoles between the io and western north pacific wnp for type i and iii mjos the associated convection over eastern io is able to generate strong kevin wave responses and significant positive sst anomalies over the mc and western pacific on the other hand for type ii mjo in the io a persistent convection lingers around the wnp it intensifies westerly monsoon flows thus preventing the generation of coherent positive sst anomalies ahead of the io mjo convection it also blocks the formation of a robust kelvin wave response over the mc and western pacific by delaying the northeastward migrations of the dry phase the convection of type i and iii mjos at eastern io is able to generate positive boundary layer moisture anomalies along with positive column integrated moisture tendencies over the mc and western pacific thus allowing them to propagate eastward smoothly on the other hand the type ii mjo convection in eastern io is associated with a very dry troposphere and negative column integrated moisture tendency over western pacific which result in the rapid decay of convection over the mc these results emphasize the important roles of robust kelvin wave responses and positive sst anomalies on the eastward propagation of boreal summer mjos over the mc through moistening the troposphere ahead of the convection

tectonic controls on a large landslide complex williams fork mountains near dillon colorado abstract an extensive 25 km2 landslide complex covers a large area on the west side of the williams fork mountains in central colorado the complex is deeply weathered and incised and in most places geomorphic evidence of sliding breakaways hummocky topography transverse ridges and lobate distal zones are no longer visible indicating that the main mass of the slide has long been inactive however localized holocene reactivation of the landslide deposits is common above the timberline at about 3300 m and locally at lower elevations clasts within the complex as long as several tens of meters are entirely of crystalline basement proterozoic gneiss and granitic rocks from the hanging wall of the laramide late cretaceous to early tertiary west directed williams range thrust which forms the western structural boundary of the colorado front range late cretaceous shale and sandstone compose most footwall rocks the crystalline hanging wall rocks are pervasively fractured or shattered and alteration to clay minerals is locally well developed sackung structures trenches or small scale grabens and upslope facing scarps are common near the rounded crest of the range suggesting gravitational spreading of the fractured rocks and oversteepening of the mountain flanks late tertiary and quaternary incision of the blue river valley just west of the williams fork mountains contributed to the oversteepening major landslide movement is suspected during periods of deglaciation when abundant meltwater increased pore water pressure in bedrock fractures a fault flexure model for the development of the widespread fracturing and weakening of the proterozoic basement proposes that the surface of the williams range thrust contains a concave downward flexure the axis of which coincides approximately with the contact in the footwall between proterozoic basement and mostly cretaceous rocks movement of brittle hanging wall rocks through the flexure during laramide deformation pervasively fractured the hanging wall rocks

natural deformation fabrics of plagioclase implications for slip systems and seismic anisotropy abstract the optical and tem microstructures and fabrics of twelve naturally deformed plagioclase containing rocks of compositions from an0 an80 have been studied with a view to determining the deformation mechanisms the optical indicatrix fabrics have been recorded in all samples with respect to the foliation and lineation in general and form a girdle in the foliation plane with a high concentration of normal to the foliation in some cases the orientation of 010 and 001 cleavages or albite and pericline twins has allowed the construction of pole figures in all cases 010 has been shown to be the dominant slip plane with either 001 or 100 the dominant slip direction tem shows that the dominant slip system is 010 001 with secondary 010 100 the seismic p wave anisotropy has been calculated for the first time from the lpo data of plagioclase the anisotropy coefficient is high at around 15 the minimum p velocity is normal to the lineation in the foliation plane and the maximum is sub parallel to the foliation normal the combined information on deformation kinematics and seismic anisotropy is valuable for interpretations of deep crustal seismic sections

microstructure development in an experimentally sheared orthopyroxene granulite abstract rheologies of the lower continental crust and overall contrast with the underlying upper mantle likely control the evolution of first order structures stress and strain partitioning between natural shear zones and wall rock s foliation development flow mechanism s and constitutive relations of rocks that make up the lower crust are poorly known we have undertaken an experimental study in which an orthopyroxene granulite is deformed in simple shear the starting material is a three phase plagioclase orthopyroxene amphibole equigranular granulite previously used in coaxial experiments wafers cut at 45 to the long axis of cores were placed between zircoa forcing blocks that have been cut obliquely at 45 at one end all experiments were run at 1 2 gpa pc and temperatures of 650 950 c specimens have been strained up to a maximum of 2 6 at shear strain rates of 7 10 5 to 7 10 7 s 1 most shear stress shear strain curves have a similar form they are characterised by an initial linear response that is followed by a work hardening region that leads to a level of quasi steady state the quasi steady state behaviour is followed by a gradual decrease in flow stress to a second quasi steady state stress level that very gradually decreases with increasing strain optical and tem examination of deformed samples indicates that an amphibole foliation develops during the first quasi steady state stress level by fragmentation and alignment of amphibole plagioclase and orthopyroxene undergo minimal crystal plastic strain at the onset of the second quasi steady state stress level plagioclase develops neoblasts orthopyroxene develops clinopyroxene lamellae and the amphibole foliation is better developed with increasing strain compositional lamination develops as in natural mylonites with extensive neoblast development in plagioclase and orthopyroxene and cataclastic grain refinement in amphibole strength data measured at the onset of the second quasi steady state level fit a power law with q 203 kj mole and n 2 3 these q and n values are significantly lower than those determined under similar conditions in previous coaxial experiments with increasing shear strain as under natural conditions there is a significant grain size reduction that may lead to a switch in flow mechanism from grain size insensitive flow at low strain to grain size sensitive flow at higher natural strains

evidence for syntectonic intrusion of plutons in the bear mountains fault zone california in the foothills terrane western metamorphic belt california the bear mountains fault zone bmfz a zone of complex multiple deformation has deformed composite maficfelsic granitoids of the guadalupe igneous complex gic and the hornitos pluton at magmatic to upper amphibolite facies temperatures evidence for high temperature deformation includes the occurrence of orthopyroxene clinopyroxene and brown hornblende in syndeformationally recrystallized aggregates in deformed rocks of the gic and the occurrence of melt leucosomes in the axial surfaces of folds in cordierite k feldspar migmatites in contact metamorphic country rocks in the bmfz away from the bmfz composite granitoids of the gic show no evidence of magmatic flow so that deformation of the gic granitoids in the bmfz was entirely by solid state flow this suggests that the gic was intruded before this mylonitic deformation in the bmfz however other evidence suggests some deformation in the bmfz before intrusion of the pluton in the hornitos pluton components of composite granitoids showing relatively weak solid state deformation are strongly elongate suggesting a component of magmatic flow although later subsolidus deformation also occurred in most places supporting evidence of magmatic flow in the hornitos pluton also includes dimensional alignment of plagioclase laths and prismatic hornblende grains as well as preferred orientation of twins in recrystallized aggregates of elongate grains of plagioclase away from the bmfz the regional metamorphic grade is low suggesting that heat for the high temperature deformation and metamorphism was supplied by the intrusions u pb zircon ages are consistent with emplacement of the gic and the hornitos pluton as well as their deformation in the bmfz around 150 ma 40 ar 39 ar ages of hornblende in foliations in the deformed granitoids and of biotite in foliations in the contact aureole rocks suggest that the plutons and the country rocks in the bmfz remained hot enough for amphibolite to upper greenschist facies conditions to persist for 5 to 15 ma after emplacement of the plutons

the puglia uplift se italy an anomaly in the foreland of the apenninic subduction due to buckling of a thick continental lithosphere the apenninic foreland shows two distinct structural signatures comparing the central adriatic sea and the puglia region during the pliocene pleistocene the central adriatic underwent high subsidence rates due to the eastward rollback of the hinge of the west dipping apenninic subduction the puglia region and the bradanic foredeep are located southward along strike in the same foreland but in contrast with the central adriatic after pliocene early pleistocene subsidence they underwent uplift since the middle pleistocene the geometry and the kinematics of the frontal accretionary wedge and related foreland changed from that moment on between the two areas at the front of the central northern apennines off scraping and subsidence continued whereas the foredeep and foreland of the southern apennines were buckled those differences are interpreted as being due to the larger subduction hinge rollback rate since middle pleistocene of the central adriatic lithosphere 70 km thick with respect to the thicker puglia 110 km the different thicknesses of the continental crust and lithosphere were inherited from the mesozoic rifting that disrupted the adriatic plate the different thicknesses appear to have controlled the variable degree of flexure of the lithosphere and its asthenospheric penetration rate the tremiti e w alignment is the right lateral lithospheric transfer zone of those different tectonic regimes the consequent different dip of the subduction in the two sections steeper west of puglia could also explain the lower elevation of the southern apennines compared to their central northern sector

deformation resulting from regional extension during pluton ascent and emplacement central sierra nevada california solid state foliation lineation small scale folds and domainal shear zones have developed in preexisting granitic and minor metasedimentary wallrock during a combined deformation involving a regional extensional strain and ascent and emplacement of the mt givens pluton mgp mylonite is common throughout much of the 1 2 km wide 10 km long shear zone with ultramylonite best developed near the contact with the mgp which itself lacks significant solid state deformation migmatization accompanies ultramylonite formation in the northern half of the zone but both these features are poorly developed or absent in its southern half where the shear zone is distributed over a wider area strain estimates across the shear zone using microgranitic enclaves as markers show a positive gradient and an increasing ratio of simple shear pure shear towards the mgp microprobe analyses on hornblende and plagioclase yield pressure and temperature estimates of 3 5 kb and 680 c respectively during shear zone formation at least at its late stages of development zircon pb u and 40 ar 39 ar ages constrain timing of the high temperature movement on the shear zone to 90 ma essentially the age of the mgp although movement immediately prior to that time appears likely we speculate that a regional extensional shear zone was developing prior to the emplacement of the mgp which as it ascended heated the wallrock facilitating both further strain in the zone as well as buoyant rise of the pluton along the zone the mgp was near its critical melt fraction during the last several kilometers of its ascent and could have possessed sufficient viscosity strength to impose a weak shear strain on the shear zone rocks although most of the foliation and extensional features in the zone are probably related to the regional strain field late stage folding of the foliation is attributed to shouldering aside of the wallrock by the mgp during the last increment of its ascent and final emplacement

ductile deformation of k feldspar in dry eclogite facies shear zones in the bergen arcs norway abstract the deformation microstructures of k feldspar of dry eclogite facies shear zones in syenitic granulites are studied in detail the eclogite facies overprint occurred syntectonically the pyroxenes feldspars quartz and apatite in the shear zones recrystallized dynamically during shearing partially changing their chemical composition the metamorphic paragenesis is represented by omphacitic clinopyroxene k feldspar plagioclase rutile ilmenite and quartz during dry eclogite facies shearing k feldspar deformation was predominantly plastic the dominant microstructures are undulatory extinction kink bands 010 deformation bands and micro shear zones 100 and 010 although rare intra and intercrystalline microfractures are observed stress induced flame perthites and replacement bands are present but uncommon grain size reduction via dynamic recrystallization occurred by two different mechanisms the recrystallization mechanism switches from subgrain rotation in the wall rocks to low temperature grain boundary migration in the shear zones due to an increase in strain rate similarities of the lattices of k feldspar and plagioclase lead to the suggestion that both minerals deform in a similar style under dry eclogite facies conditions therefore we assume that the proven style of deformation is a dominant feature of high pressure deformation in continental root zones where fluid activity is low

kinematic stratification in the hinterland of the central scandinavian caledonides abstract a transect through west central norway illustrates the changing geometry and kinematics of collision in the hinterland of the central scandinavian caledonides a depth section through the crust is exposed on fosen peninsula comprising three tectonic units separated by two shear zones the lowest unit exposed in the roan window is a modestly deformed caledonian granulite complex framed by a subhorizontal decollement with nw se oriented lineations and kinematic indicators showing top to the northwest transport the middle unit the vestranden gneiss complex contains relict granulites but was penetratively deformed at amphibolite facies to produce an orogen parallel family of structures during translation on the decollement shallow plunging lineations on steep schistosities are subparallel to fold axes of the dominant upright non cylindrical folds a small component of sinistral strike slip is also recorded in contrast southernmost fosen peninsula contains an abundance of cover rocks infolded with proterozoic basement in a fold nappe with shallow e dipping schistosities down dip lineations and orogen oblique top to the west shear sense indicators a ne striking sinistral shear zone separates the gneisses from southern fosen deformation in the scandian hinterland was partitioned both in space and time with orogen parallel extension and shear at middle structural levels and orogen oblique transport at shallower levels

characteristics of the tropical intraseasonal oscillation in the ncar community climate model summary the structure of the intraseasonal oscillation in a perpetual january integration of the ncar community climate model ccm is analysed and compared with observations the simulated oscillation is identified as an eastward moving perturbation in the equatorial velocity potential field with predominantly zonal wavenumber 1 structure analysis of its vertical and horizontal structure based on composites shows good agreement with the observed oscillation from station data and from numerical weather prediction model analyses the simulated intraseasonal oscillation is evident in the wind fields at all longitudes but its appearance in the precipitation and outgoing long wave radiation is confined to the eastern hemisphere the perturbation to the zonal wind component is characterized by an out of phase behaviour between the lower and upper troposphere which is most coherent in the convective regions of the indian ocean and west pacific the streamfunction anomalies in these regions are suggestive of a coupled rossby kelvin wave whilst in the western hemisphere the oscillation is more characteristic of a kelvin wave the role of cloud radiation interaction was studied using a parallel integration in which the cloud longwave forcing in the atmosphere was removed this was found to influence the strength of the oscillation but had no significant impact on the period in common with other model simulations of the intraseasonal oscillation the period was found to be too short near 25 days reasons for this are discussed in the context of a similar analysis of a perpetual july integration in which a much slower period near 54 days and less coherent oscillation was identified

new empirical relationships among magnitude rupture length rupture width rupture area and surface displacement source parameters for historical earthquakes worldwide are compiled to develop a series of empirical relationships among moment magnitude m surface rupture length subsurface rupture length downdip rupture width rupture area and maximum and average displacement per event the resulting data base is a significant update of previous compilations and includes the additional source parameters of seismic moment moment magnitude subsurface rupture length downdip rupture width and average surface displacement each source parameter is classified as reliable or unreliable based on our evaluation of the accuracy of individual values only the reliable source parameters are used in the final analyses in comparing source parameters we note the following trends 1 generally the length of rupture at the surface is equal to 75 of the subsurface rupture length however the ratio of surface rupture length to subsurface rupture length increases with magnitude 2 the average surface displacement per event is about one half the maximum surface displacement per event and 3 the average subsurface displacement on the fault plane is less than the maximum surface displacement but more than the average surface displacement thus for most earthquakes in this data base slip on the fault plane at seismogenic depths is manifested by similar displacements at the surface log linear regressions between earthquake magnitude and surface rupture length subsurface rupture length and rupture area are especially well correlated showing standard deviations of 0 25 to 0 35 magnitude units most relationships are not statistically different at a 95 significance level as a function of the style of faulting thus we consider the regressions for all slip types to be appropriate for most applications regressions between magnitude and displacement magnitude and rupture width and between displacement and rupture length are less well correlated and have larger standard deviation than regressions between magnitude and length or area the large number of data points in most of these regressions and their statistical stability suggest that they are unlikely to change significantly in response to additional data separating the data according to extensional and compressional tectonic environments neither provides statistically different results nor improves the statistical significance of the regressions regressions for cases in which earthquake magnitude is either the independent or the dependent parameter can be used to estimate maximum earthquake magnitudes both for surface faults and for subsurface seismic sources such as blind faults and to estimate the expected surface displacement along a fault for a given size earthquake

principal oscillation pattern analysis of the 30 to 60 day oscillation in general circulation model equatorial troposphere a new technique is described for identifying time dependent patterns i e principal oscillation patterns or pops in a set of geophysical time series pops are defined as the normal modes of a linear dynamical representation of the data in terms of a first order autoregressive vector process with residual noise forcing pops associated with real eigenvalues represent nonpropagating nonoscillatory patterns which decay exponentially pops associated with complex eigenvalues occur in complex conjugate pairs and can represent standing wave structures if one pattern is much stronger than the other propagating waves if both patterns are periodic and have the same structure except for a quarter wavelength shift or in general an arbitrary amphidromal oscillation after the pops have been defined for a selected set of primary variables associated correlation or composite patterns may be derived for additional secondary fields to gain further insight into the structure of the interaction mechanisms the method is illustrated by analyzing the tropical variability structure of a 10 year numerical simulation with the t21 general circulation model gcm of the european centre for medium range weather forecasts reading england the pop analysis is applied to the 200 hpa horizontal divergence field along the equator for time scales shorter than 10 weeks the associated patterns are determined for a number of additional fields in the tropical belt between 30 s and 30 n one dominant pop pair is found its spatial scale corresponds to zonal wave number 1 the patterns travel eastward with an average period of 24 days and an e folding decay time of 10 days the maximum variance occurs in the area with maximum tropical precipitation between 100 e and the dateline these features correspond rather closely to the characteristics of the observed tropical 30 to 60 day wave except for the smaller period a frequency wave number analysis confirms that this 30 to 60 day wave is the most dominant regular oscillation in the tropical gcm troposphere the associated patterns of sea level pressure precipitation and other quantities exhibit a number of intriguing aspects namely 1 the phase velocity of the 30 to 60 day wave varies with longitude from 6 m s 1 in the indonesian area to more than 30 m s 1 over the eastern pacific small phase speeds being associated with large amplitudes and high phase speeds with small amplitudes 2 in the high amplitude regions rainfall and upper air velocity potential are in phase while in the low amplitude regions rainfall and velocity potential appear uncorrelated 3 at the surface a pattern strongly resembling gill s theoretical response to an equatorial heating source is found with a trough to the east and two off equatorial cyclones to the west of the heating the lack of meridional winds is probably related to the disregard of the seasonal asymmetries

natural deformation and recrystallization of some intermediate plagioclase feldspars abstract intermediate an25 an48 plagioclase feldspars from the nordre stromfjord shear zone central west greenland have undergone extensive ductile deformation by intracrystalline slip and by twinning the plagioclases were deformed under low granulite facies conditions optical substructures include undulatory extinction deformation bands subgrains and deformational twins mainly on the albite law dynamic recrystallization occurred primarily by subgrain rotation with bulge nucleation migration of a high angle boundary as a secondary mechanism in some cases recrystallization is accompanied by a small decrease in the an content which is thought to indicate prograde metamorphic conditions the plagioclases exhibit a good crystallographic preferred orientation which is compatible with 010 001 being the principal slip system quartz has in the same rocks undergone more plastic deformation and more extensive recovery than plagioclase this is at least in part due to the fact that most dislocations in plagioclase are dissociated

considerations on the significance of some post glacial fault scarps in the abruzzo apennines central italy abstract in this paper the tectonic and palaeoseismological significance of the fault scarps present in the massifs of the velino and of mount greco and in the plains adjacent to these massifs forming part of the abruzzo apennines is discussed the basic features of post glacial fault scarps already mentioned in the literature are illustrated found in the fucino plain in the ovindoli piani di pezza area on the mount magnola in the valle majelama alluvial fan and in the piano di aremogna others not previously mentioned surveyed by the author in the mount ocre cefalone area in the piana di corvaro and on the mount greco toppe del tesoro are also discussed on the basis of the characteristics of these scarps and of the chronological framework of the last phases of activity of the faults which gave rise to the scarps described the reliability of the assumptions made for palaeoseismological studies in other places is discussed for the abruzzo area the studies performed in the area of the velino and greco massifs suggest that to establish the possible co seismical activity of the faults the use of morphological indices and also of the results obtained with the excavation of trenches has to be very cautiously applied it is considered that the following can be stated it is probable that the majority of the mentioned fault scarps are co seismic in view of the height of some fault scarps it cannot be excluded that they were formed during the course of earthquake sequences lasting not more that 2 3000 years it is possible that some of the above mentioned scarps were produced during seismic events of great magnitude it does not seem possible at present to calculate a precise slip rate the amount of the offset often changes along the same fault even over short distances moreover there are many horst and graben type structures produced by local effects which contribute towards making an assessment of the fault offsets complicated it is also clear that erosion can change the aspect of the scarps an evaluation of the displacements caused by the faults producing them must therefore be made extremely cautiously caution is needed in assessing the magnitude of past earthquakes and in assuming recurrence intervals the dating of the phases of fault activity is approximate and there is great difficulty in recognizing with any certainty the duration the sort of activity and the length of the fault segment concerned in the activity moreover the existence in the past of aseismic creep and of movements linked to post glacial isostatic rebound cannot be excluded with any certainty these considerations must be regarded for the two massifs examined since there have been the epicentres of rare earthquakes of low intensity the only large earthquake known in history which caused surface ruptures occurred in the fucino area in 1915 the fault scarps reported in this paper seem however interpretable in general as indications of post glacial tectonic activity the intensity of which was unsuspected until a few years ago

landslides triggered by earthquakes and their relations with faults and mountain slope geometry an example from ecuador abstract a large number of landslides occurred during two seismic events respectively 6 9 and 6 1 msw on 5 march 1987 in the ecuadorian andes these landslides have been mapped digitized and coregistered with topography at 1 50 000 scale geometry of coseismic and holocene faulting has been assessed integrating field and geophysical data landslide distribution and holocene tectonic features have been compared with earthquake foci geological deposits slope area inclination and orientation and vegetation cover the macro seismic field deduced by landslide distribution is ellipse shaped with the major axis striking nne and coinciding with the trend of the coseismic and holocene faults landslide distribution also shows a correlation with respect to the dip direction of these faults and the orientation of mountain slopes slopes parallel to the coseismic fault planes sloping towards wnw are almost unaffected by landsliding while this increases on the slopes at high angle to the fault plane and lying along its strike if these results could be confirmed in other areas a method of reconstruction of geometry of seismogenetic faults from topographic effects appears feasible

pyroxene orientation within the upper mantle petrofabric analyses of orthopyroxene and olivine for a suite of rocks from the bay of islands ophiolite newfoundland show systematic relationships between the minerals9 fabrics the plane of the mohorovicic discontinuity determined from the contact of the gabbro and ultramafic sections and the spreading direction inferred from the attitude of the sheeted dikes the orthopyroxene c crystallographic axes maxima which are aligned subparallel to the spreading direction coincide with olivine a axes maxima the orthopyroxene b axes and olivine c axes also lie approximately within the plane of the mohorovicic discontinuity but parallel the ridge whereas the orthopyroxene a axes maxima and olivine b axes maxima are approximately perpendicular to the mohorovicic discontinuity using olivine and orthopyroxene elastic constants and their pressure derivatives velocities have been calculated from composite petrofabric data and contoured for varying proportions of olivine and pyroxene the results of these calculations show that within a vertical direction compressional wave velocities change only slightly with increasing pyroxene content whereas parallel to the mohorovicic discontinuity velocities decrease with increasing pyroxene content anisotropy decreases from 4 for a rock with 100 olivine to 2 6 for a rock with 50 olivine and 50 orthopyroxene also within the plane of mohorovicic discontinuity the maximum and minumum velocities occur at approximately the same azimuth for differing percentages of orthopyroxene a comparison of the calculated anisotropy and the observed seismic anisotropy off the coast of california shows a striking agreement from this comparison it is estimated that the percentage of orthopyroxene within the upper mantle of this region varies between 0 and 30

the contribution of landslides to landscape evolution in europe abstract after a review of some analytical and conceptual models of slope evolution with the intervention of mass movements a proposal is made of a series of indicators for the quantitative description of landscape evolution in relation to mass movements the ratio between landslide mobilisation rate and downwearing rate is proposed as a quantitative measure of the significance of mass movements in landscape evolution a subdivision of european regions with respect to their susceptibility to landsliding as a process of landscape evolution is proposed the role of landsliding for the evolution of landscape in some regions is described the data presented show that landsliding may in some cases be the main contributor to landscape change

effect of dry large scale vertical motions on initial mjo convective onset anomalies of eastward propagating large scale vertical motion with 30 day variability at addu city maldives move into the indian ocean from the west and are implicated in madden julian oscillation mjo convective onset using ground based radar and large scale forcing data derived from a sounding array typical profiles of environmental heating moisture sink vertical motion moisture advection and eulerian moisture tendency are computed for periods prior to those during which deep convection is prevalent and those during which moderately deep cumulonimbi do not form into deep clouds convection with 3 7 km tops is ubiquitous but present in greater numbers when tropospheric moistening occurs below 600 hpa vertical eddy convergence of moisture in shallow to moderately deep clouds is likely responsible for moistening during a 3 7 day long transition period between suppressed and active mjo conditions although moistening via evaporation of cloud condensate detrained into the environment of such clouds may also be important reduction in large scale subsidence associated with a vertical velocity structure that travels with a dry eastward propagating zonal wavenumbers 1 1 5 structure in zonal wind drives a steepening of the lapse rate below 700 hpa which supports an increase in moderately deep moist convection as the moderately deep cumulonimbi moisten the lower troposphere more deep convection develops which itself moistens the upper troposphere reduction in large scale subsidence associated with the eastward propagating feature reinforces the upper tropospheric moistening helping to then rapidly make the environment conducive to formation of large stratiform precipitation regions whose heating is critical for mjo maintenance

antecedents and self induction of active break south asian monsoon unraveled by satellites 1 understanding the origin and perpetuation of the monsoon cycle has eluded scientists for decades using a suite of unprecedented satellite measurements we show that the antecedents of the active break monsoon emerge in the western equatorial indian ocean eio the initiation of a new rainy phase in the western eio is preceded by in situ surface wind convergence and central eio warming both are induced by the subdued condition over the eastern eio set up in the previous cycle thus a self induction mechanism appears to be operating in maintenance of the indian monsoon intraseasonal oscillation the finding here offers a focus for prediction of the active break indian monsoon with potential predictability about four weeks in advance

a methodological approach for the analysis of the temporal occurrence and triggering factors of landslides the temporal occurrence of landslides in an area of the cantabrian range during the last 120 000 years is analyzed an initial relative chronology was established on the basis of aging degree and spatial relationships between landslides and glacial and fluvial features ten landslide classes were thus identified and their chronological limits defined on the basis of 19 14c age determinations on fluvial and glacial deposits including eight new ones the chronology was tested with 14c dates obtained on landslide deposits 10 from previous work and nine new ones the chronological classes identified were compared with existing climate models for the region the type and spatial distribution of landslides in each class were also analyzed the approach made it possible to identify periods during which landslides were triggered mainly by channel incision seismic activity and rainfall increase human activity played a significant role after 5000 bp and especially in the last few centuries mobilization of materials by slope movements has increased in the region by a factor of 10 compared to pre neolithic rates

when did the northern apennine become a mountain chain abstract the purpose of the present paper is to bracket the age of the initial uplift of the northern apennine chain by means of all the available evidence the collected data show that the age of the lacustrine or fluvio lacustrine units which have aggraded in the intramontane basins is late pliocene in the northwestern tip of the northern apennine and mostly early pleistocene elsewhere the age of the oldest terraced fluvial deposits showing the initiation of incision is mostly middle pleistocene the uplift of the summit areas of low relief most likely took place during the middle pleistocene it is concluded that the uplift occurring during middle and upper pleistocene caused an area of rather low relief to become the northern apennine mountain chain an eastward shift of the uplift through time is likely

the holocene paleoearthquakes on the 1915 avezzano earthquake faults central italy implications for active tectonics in the central apennines abstract extensive paleoseismological research was conducted in the fucino plain central italy in order to better understand the seismogenic characteristics of the fault responsible for the 1915 avezzano earthquake ms 7 0 and improve the general knowledge regarding active tectonics in the central apennines evidence for late pleistocene holocene surface faulting events was obtained through the study of thirteen sites across four different fault branches the paleoseismological analysis outlined the occurrence of ten surface faulting events in the past 33 000 years seven of which occurred during the holocene radiocarbon thermoluminescence and archaeological dating permitted the definition of an event chronology and the estimation of a recurrence interval for surface faulting events ranging between 1400 and 2600 years on the basis of the observed offsets it was possible to calculate vertical slip rates for the individual fault branches ranging between 0 24 mm yr 1 and 0 5 mm yr 1 and an extension rate across the fucino plain ranging between 0 6 and 1 mm yr 1 the chronology of surface faulting events appears linearly distributed in time and the observed recurrence times are similar to those inferred by other paleoseismological studies along different active apennine faults the general consequence of the large time span between strong earthquakes is that even a 2000 year long historical record such as the italian earthquake catalogue does not cover the entire seismic cycle of all the active apennine faults a comparison of the extension rate across the fucino plain with that across the entire central apennines as inferred from the sum of seismic moments of earthquakes which occurred in the interval 1000 1992 shows a seismicity deficit in the period indicated this confirms that a number of seismogenic faults were not active during the past 1000 years

interpretation of sks waves using samples from the subcontinental lithosphere abstract the seismic properties of five south african kimberlite nodules have been calculated from petrofabric measurements these garnet lherzolite and harzburgite composition nodules 56 80 olivine are known from previous studies to have originated at depths of 120 170 km in the subcontinental lithosphere their in situ seismic properties have been calculated by extrapolating the elastic constants to the appropriate temperature 900 1050 c and pressure 3 0 3 5 gpa conditions the average of the five samples has a maximum s wave anisotropy v s of 3 7 which is sufficiently high to explain previously reported teleseismic sks delay times t in continental shield areas of up to 1 7 s the biggest delay time is observed when the foliation is vertical the lineation horizontal and the fastest s wave polarized parallel to the lineation i e an orientation for transcurrent motion delay times of over 1 s can only be generated by this orientation a strong mantle crust mechanical coupling is suggested for such situations the potential use of seismic anisotropy as an indicator of strain in the lithosphere has been investigated using experimental and simulated fabric data for olivine the most abundant phase 70 in the upper mantle the v p and v s seismic anisotropy increases with fabric strength and finite strain recrystallization tends to reduce fabric strength and seismic anisotropy resulting in saturation values for experimental and simulated fabrics which correspond to approximately 50 60 strain or 8 9 v s for pure olivine aggregates a survey of 25 naturally deformed peridotites of oceanic origin suggests an average maximum s wave anisotropy for the olivine component of 9 or about 8 for a lherzolite or harzburgite rock composition when the orthopyroxene component is taken into account the ophiolite samples are twice as anisotropic as the kimberlite nodules if an average anisotropy value is representative of the lithosphere then the sks delay times represent variations in anisotropic layer thickness for delay times over 1 s as the orientation is constrained to be foliation vertical and lineation horizontal the magnitude of s wave anisotropy is less sensitive than v p to variations in olivine volume fraction in range 50 100 and to deformation or fabric intensity further suggesting that s wave anisotropy is particularly apt for the determination of the anisotropic lithosphere thickness for smaller delay times there is some trade off between structural orientation and thickness

networking of shear zones at the brittle to viscous transition cap de creus ne spain a crustal scale shear zone network at the fossil brittle to viscous transition exposed at cap de creus ne spain evolved by coeval fracturing and viscous mylonitic overprinting of an existing foliation initial fracturing led to mylonitic shearing as rock softened in ductilely deformed zones surrounding the fractures mylonitic shear zones widened by lateral branching of fractures from these shear zones and by synthetic rotation of the existing foliation between the fractures and shear zones shear zones lengthened by a combination of fracturing and mylonitic shearing in front of the shear zone tips shear zones interconnected along and across their shearing planes separating rhomb shaped lozenges of less deformed rock lozenges were subsequently incorporated into the mylonitic shear zones by widening in the manner described above in this way deformation became homogeneous on the scale of initial fracturing metre to decametre scale in contrast the shear zone network represents localisation of strain on a decametre length scale the strength of the continental crust at the time of coeval fracturing and viscous shearing is inferred to have decreased with time and strain as fracturing evolved to mylonitic shearing and as the shear zones coalesced to form a through going network subparallel to the shearing plane crustal strength must therefore be considered as strain and scale dependent

image processing and roughness analysis of exposed bedrock fault planes as a tool for paleoseismological analysis results from the campo felice fault central apennines italy abstract morphologic investigations along the campo felice cf fault central apennines italy have been made in order to develop a procedure for the paleoseismological analysis of bedrock fault scarps the cf fault has been responsible for the formation of an impressive limestone fault scarp geomorphologic work on the cf basin and related fault indicated that the scarp originated from tectonic fault displacements three morphologic units have been distinguished along the fault scarp and defined as morphosome m1 lowest part of the scarp m2 and m3 the uppermost part these units display different karstic features which are the result of their different duration of exposure to weathering micromorphologic analyses focused on the morphosome m1 along which the cf fault plane is exposed for a height ranging between 4 and 7 m these analyses were aimed at defining differently weathered bands located at various heights and parallel to the fault scarp top and base the presence of these bands suggests repeated fault movements the exposed fault surface displays a low grade biokarstic weathering due to the action of epilithic and endolithic organisms the biokarst distribution is however inhomogeneous and conditioned by the presence of nourishing elements moisture and by light intensity an area preferentially affected by the biokarstic processes develops as a band at the bedrock soil contact at the base of the scarp roughness and colour analyses were made to identify uplifted bands which previously formed at the bedrock soil contact the roughness analysis was made using a microroughness meter along 20 cm long horizontal transects repeated each 20 cm of fault height for the entire morphosome m1 at various sites along the scarp the roughness variance data plotted vs the fault height failed to identify differently weathered bands of paleoseismological interest this result is probably due to the complex distribution of biokarst along the investigated fault plane more reliable results have been obtained by areal analysis of the variation of the colour rendering of the rocks exposed along the fault plane at different sites photographic images of large portions of fault surfaces have been processed with standard graphic computer programs the variations of colour indicated the presence of bands at various heights along the fault plane two uplifted bands have been recognised at all the investigated sites suggesting two displacement events e1 and e2 a preliminary chronological framework for these two events the youngest of which affected the cf fault can be derived from the paleoseismological data available for the southernmost branch of the regional fault system that includes the cf fault according to these data e1 may have occurred between 860 and 1300 ad while e2 may have occurred at about 1900 bc work is in progress to define surface exposure ages of different parts of the fault plane by means of in situ produced cosmogenic 36 cl this procedure will give further chronological constraints for the age of e1 and e2 and will also permit to test the validity of the micromorphologic analysis of bedrock fault scarps for paleoseismological aims

structure and petrology of peridotites clues to their geodynamic environment the first part of this paper is a review on the main mineralogical petrological and structural criteria which can be used to unravel the history of the various types of mantle peridotites met at the earth s surface these criteria are applied in the second part to show that most peridotites share a common history which is that of an asthenospheric uprise followed by specific fates corresponding to their lithospheric history the unifying concept is that of adiabatic ascent rate related to rifting and spreading rates rates lower than 0 5 cm yr in continental graben correspond to departure from adiabatic conditions at depths greater than 30 km this inhibits further melt extraction with as consequences a limited melt extraction and comparatively fertile spinel lherzolites as residue higher rates probably not exceeding 1 cm yr correspond to oceanic rifts with the main melt extraction completed around 15 km generating a thin oceanic crust and plagioclase lherzolites as residue finally rates greater than 1 2 cm yr correspond to oceanic ridges with melt being extracted at moho depth thus generating a 6 km thick crust and leaving depleted harzburgites as residue thus examination of the peridotite type and associated crustal formations give some clue to trace back the environment of origin this conclusion must however be tempered by the fact that the spreading rate envisioned here as the principal controlling parameter can change with space and time in a given environment mantle diapirism rifting seafloor spreading crust generation

direct observation of deformation processes in crystal mushes isothermal microstructural development in deforming melt bearing crystal mushes is studied using synkinematic microscopy and a polyphase thiocyanate system the aim of the work is to contribute to the basis for understanding the origin of microstructures in rocks which have undergone melt present deformation during high strain rate pure shearing experiments microstructures indicating crystal plasticity and dynamic recrystallization are observed during low strain rate pure shearing experiments a pressure solution like process called contact melting is active resulting in optically strain free crystals crystal boundary sliding is active in both regimes framework scale processes such as filter pressing grain flow and development of a micro shear zone are illustrated some of these processes are cryptic microstructurally and may be difficult or impossible to recognize in rocks the validity of the experimental system as an analog for magmatic systems is discussed we conclude that the experiments can serve as a source of ideas to test against the evidence from rocks but that no direct analogy to the behavior of natural crystal mushes has been or will readily be established

a proposal for the kinematic modelling of w dipping subductions possible applications to the tyrrhenian apennines system in w dipping subduction zones there is a general eastward progression of the back arc basin accretionary wedge foredeep complex with the forward progression early stages of the complex are revealed by slices of upper crust and sedimentary cover abandoned to the west left floating above a new section of mantle a major shear zone should form at the new moho separating upper crust slices of earlier accretionary stages and the eastward flowing mantle the mantle wedging at the top of the subduction plane could be responsible for the uplift of the central parts of the belt the retreating of the subduction hinge is interpreted as due to the push generated by the eastward mantle flow detected in the hot spot reference frame the foredeep depth is mainly a function of the radius of curvature of the subduction hinge the frontal wedge is constructed from the stacking of the upper layers of the subducting plate and the syntectonic clastics that fill the foredeep which are progressively involved in thrusting and later by extension in order to preserve volume balance the lithosphere of the eastern plate before subduction has to be the same size as that which has been subducted due to the longer length of the arc with respect to the original length of the linear margin between the two converging plates laterally stretched subducted lithosphere is predicted at depth w dipping subductions usually have a short life probably due to their inherent capability to produce new lateral heterogeneities of the lithosphere the thin back arc which are a key factor in controlling and generating new subductions both e and w dipping this model is applied to the apennines tyrrhenian sea system

ultra high temperature and subsolidus shear zones examples from the poe mountain anorthosite wyoming abstract ultra high temperature shear zones formed with interstitial melts present during the emplacement of the poe mountain anorthosite wyoming the shear zones are characterized by coarse grained plagioclase with flat extinction and rare deformation microstructures dissected grain microstructures suggest that plagioclase underwent recrystallization by fast grain boundary migration orthopyroxene crystallized from interstitial melts as strain free foliation parallel tablet grains plagioclase has a magmatic petrofabric characterized by poles to 010 normal to the shear foliation and 100 parallel to the foliation and movement direction poles to 001 have a broad distribution with a point maximum roughly parallel to the foliation and normal to the movement direction orthopyroxene petrofabrics result from oriented growth parallel to the shear foliation 100 defines a point maximum perpendicular to the shear foliation and 010 and 001 have great circle distributions approximately parallel to the shear foliation microstructures of the ultra high temperature shear zones contrast with those of granulite grade shear zones cutting across the intrusion the granulite grade shear zones initiated as fractures which evolved into shear zones by dynamic recrystallization deformed primary plagioclase and orthopyroxene recrystallized by grain boundary rotation into smaller polygonal grains

emplacement related deformation of granitoid magmas southern adamello massif italy the lago della vacca suite in the tertiary adamello massif italian alps is a small 10 km 2 crudely zoned granitoid pluton emplaced at a pressure of 3 5 kbar into folded mesozoic sediments and precursor intrusive rocks field relations and detailed mapping reveal a temporal evolution in the style of emplacement from early passive stoping by the mafic to intermediate composition marginal units to later forceful emplacement of the more silicic core marginal units of the pluton have highly discordant stoped outer contacts against folded triassic carbonates and precursor mafic ultramafic rocks in contrast the core units have steeply inward dipping contacts against these marginal units magmatic foliations defined by the planar alignment of plagioclase amphibole and biotite and by mafic enclaves are well developed in all units they describe steeply inward dipping concentric trajectories that approximately parallel unit contacts and in general increase in intensity toward the pluton margin lineations are rarely present the most intensely foliated rocks occur in the marginal units as anastomosing sinuous bands that wrap around lenses of less intensely foliated granitoid three dimensional strain analysis using mafic enclaves from throughout the pluton indicates that these bands represent zones of very high strain strain ellipsoids are weakly prolate within the core of the pluton becoming increasingly oblate as strain increases toward the pluton margin the short axis z of the strain ellipsoid is uniformly subnormal to the foliation suggestive of radial flattening textures of the marginal rocks which record high strain coupled with amphibole plagioclase thermometry indicate that deformation occurred in the magmatic or submagmatic state 650 780 c and was accompanied by significant migration of interstitial melt the documented transition from passive to forceful emplacement and final geometry of the suite resulted from temporal changes in the rheology of both the magma and adjacent country rocks pulses of low density hydrous magma were initially emplaced by stoping denser country rocks on cooling and solidification these magmas contracted by 15 20 creating an unpressured volume which allowed subsequent magma pulses to be emplaced into the pluton core these pulses distended and flattened their partially molten carapace and those parts of the aureole that had been thermally softened by intrusion of earlier magmas emplacement of the lago della vacca suite was therefore the product of several internal or magma related processes an interaction between stoping radial expansion and volume contraction on solidification of the hydrous magmas the heterogeneous distribution of strain in the marginal units reflects local variations in temperature and most importantly in the distribution of interstitial melt during emplacement

quaternary mass movements controlled by a structurally complex setting in the central apennines italy abstract the paper discusses the results of an engineering geology study of an area in central italy affected by complex gravity induced slope instability a finite difference analysis was implemented to demonstrate that stratigraphy and recent tectonics have had a crucial impact on the gravitational processes that have occurred in a built up area of the central apennines italy the creation of a reliable geological evolutionary model proved to be a key tool for subsequent development of a numerical model capable of elucidating the main factors and parameters controlling slope instabilities the study area in the vicinity of the small mountain village of micigliano central apennines displays extensive outcrops of carbonate platform lithotypes hemipelagic marly clayey deposits and arenaceous pelitic turbidites its tectonic setting is very complex with intense faulting thrusts normal faults and complex kinematic faults and folding a geological evolutionary model of the instability processes in the various sectors of the study area was formulated and fine tuned on the basis of detailed geological and engineering geology surveys assumptions on the mechanical and hydraulic characters of the local geological bodies and observation of the morpho evolutionary processes subsequently a stress strain analysis was applied to the model using the finite difference method in order to reconstruct the complex mechanisms governing evolution of the various sectors of the investigated slopes and the effects of gravity caused instability on the exposed lithotypes the numerical model also helped to validate the consistency of the stress strain assumptions with the deformation mechanisms observed in the various investigated sectors of the study area yielding a kinematic picture of the causal factors of the local gravity caused instability in space and time

quaternary tectonics and large scale gravitational deformations with evidence of rock slide displacements in the central apennines central italy eight cases of large scale gravitational movements with evidence of rock slide type displacements evolving close to quaternary faults have been analysed in the central apennines geomorphological and structural surveys have defined the relationship between the gravitational displacements and the tectonically controlled modifications of the landscape the evolution of all the investigated cases has been conditioned by the presence of fault planes located along the mountain slopes in most cases mt cefalone cima della fossa villavallelonga casali d aschi gioia dei marsi the faults played or are playing a primary role in increasing the local relief and their activity represents the main geomorphic factor conditioning the gravitational movements this kind of relationship has been observed along mountain slopes bordering depressions which have not been drained for most of their geomorphic history or have been characterised by an evolution of the hydrographic network that has been conditioned only by the local tectonic subsidence in such cases the gravitational movements develop in the footwalls of the faults in other cases fiamignano pescasseroli the faults have played a passive role since they only bound the sliding masses and coincide with the surficial expressions of the sliding planes therefore the gravitational displacements develop in the hangingwall of the faults the evolution is conditioned by the incision of the hydrographic network in response to regional quaternary uplift the illustrated case studies provide a wide range of examples of the gravitational response of slopes to the modifications of the landscape due to linear and areal tectonics the identification of the geomorphic traces of the large scale gravitational movements along fault controlled mountain fronts has implications for hazard particularly for the evolution of the displacement the quantitative analysis of the vertical displacements and data on the characteristics of the surface breaking during historical earthquakes demonstrate that along fault offsets strongly increases where the unstable large scale rock masses are located therefore the large coseismic vertical offset may represent a major problem for the displacement of utilities and may represent a potential cause for the sudden and catastrophic evolution of the gravitational movement

deformation mechanism maps for feldspar rocks abstract deformation mechanism maps for feldspar rocks were constructed based on recently published constitutive laws for dislocation and grain boundary diffusion creep of wet and dry plagioclase aggregates the maps display constant temperature contours in stress grain size space for strain rates ranging from 10 16 to 10 12 s 1 two fields of dominance of grain boundary diffusion controlled creep and dislocation creep are separated by a strongly grain size sensitive transition zone for wet rocks diffusion controlled creep dominates below a grain size of about 0 1 1 mm depending on temperature stress strain rate and feldspar composition plagioclase aggregates containing up to 0 3 wt water as often found in natural feldspars are more than 2 orders of magnitude weaker than dry rocks the strength of water bearing feldspar rocks is moderately dependent on composition and water fugacity for a grain size range of about 10 50 m commonly observed in natural ultramylonites the deformation maps predict that diffusion controlled creep is dominant at greenschist to granulite facies conditions low viscosity estimates of 10 18 10 19 pa s from modeling postseismic stress relaxation and channel flow of the continental lower crust can only be reconciled with laboratory experiments assuming dislocation creep at high temperatures 900 c or at lower temperatures diffusion creep of fine grained rocks possibly localized in abundant high strain shear zones for similar thermodynamic conditions and grain size lower crustal rocks are predicted to be less than order of magnitude weaker than upper mantle rocks

fast and slow kelvin waves in the madden julian oscillation of a gcm the structure of the madden julian oscillation mjo in an 1800 day integration of the hadley centre unified model was analysed and interpreted within a kelvin wave framework the model was forced with constant equinoctial march boundary conditions so that a clean mjo signal could be separated from the effects of the seasonal cycle and forced interannual variability the simulated mjo was fairly realistic in terms of its large scale spatial structure and propagation characteristics although its period of 30 days corresponding to an average phase speed of 15 mps was shorter than that observed the signal in deep convection was less coherent than in observations and appeared to move eastward as a sequence of discrete convective anomalies rather than by a smooth eastward propagation both fast and slow equatorial kelvin waves appeared to play an important role in the eastward propagation of the simulated mjo enhanced convection over the indian ocean was associated with a fast equatorial kelvin wave that propagated eastward at 55 m s 1 over the pacific on reaching the west coast of south america a component of this kelvin wave propagated northward and southward as a trapped wave along the mountain ranges of central america and the andes in agreement with observations the anomalous surface easterlies over the tropical eastern pacific associated with this fast kelvin wave enhanced the climatological mean easterlies and led to positive convective anomalies over the eastern pacific consistent with the wishe mechanism however wishe was not able to account for the eastward development of the convective anomalies over the indian ocean western pacific region by splitting the equatorial divergence anomalies of the simulated mjo into their du dx and dv dy components the role of kelvin wave dynamics in the slow 15 m s 1 average eastward propagation of the simulated mjo was examined although the two components were of comparable magnitude the dudx component exhibited a pronounced eastward propagation which tended to be disrupted by the dvdy component thus supporting the paradigm of an underlying but strongly modified kelvin wave mechanism

intraseasonal variability of the south china sea summer monsoon the objective of this study is to explore based on the national centers for environmental prediction national center for atmospheric research ncep ncar reanalysis data the intraseasonal variability of the south china sea scs summer monsoon sm in terms of its structure and propagation as well as interannual variations a possible mechanism that is responsible for the origin of the 10 20 day oscillation of the scs sm is also proposed the 30 60 day hereafter the 3 6 mode and 10 20 day hereafter the 1 2 mode oscillations are found to be the two intraseasonal modes that control the behavior of the scssm activities for most of the years both the 3 6 and 1 2 modes are distinct but may not always exist simultaneously in a particular year and their contributions to the overall variations differ among different years thus the interannual variability in the intraseasonal oscillation activity of the scs sm may be categorized as follows the 3 6 category in which the 3 6 mode is more significant in terms of the percentage of variance explained than the 1 2 mode the 1 2 category in which the 1 2 mode is dominant and the dual category in which both the 3 6 and 1 2 modes are pronounced composite analyses of the 3 6 category cases indicate that the 30 60 day oscillation of the scs sm exhibits a trough ridge seesaw in which the monsoon trough and subtropical ridge exist alternatively over the scs with anomalous cyclones anticyclones along with enhanced suppressed convection migrating northward from the equator to the midlatitudes the northward migrating 3 6 mode monsoon trough ridge in the lower troposphere is coupled with the eastward propagating 3 6 mode divergence convergence in the upper troposphere it is also found that for the years in the dual category the scs sm activities are basically controlled by the 3 6 mode but modified by the 1 2 mode composite results of the 1 2 mode category cases show that the 10 20 day oscillation is manifest as an anticyclone cyclone system over the western tropical pacific propagating northwestward into the scs a close coupling also exists between the upper level convergence divergence and the low level anticyclone cyclone it is found that the 1 2 mode of the scs sm mainly originates from the equatorial central pacific although a disturbance from the northeast of the scs also contributes to this mode the flow patterns from an inactive to an active period resemble those associated with a mixed rossby gravity wave observed in previous studies

fabric development in a middle devonian intraoceanic subduction regime the careon ophiolite northwest spain abstract a middle devonian suprasubduction zone ophiolite the careon unit northwest spain displays amphibolite facies ductile deformation fabrics related to the onset of the rheic ocean closure two different fabrics an early high t foliation and a subsequent lower t foliation each of which characterized by distinct deformation mechanisms have been identified in two distinct crustal scale shear zones of the same ophiolitic thrust sheet combined quantitative texture analysis by electron backscattered diffraction and time of flight neutron diffraction were carried out on the shear zones and correlated with micro and macrostructural data the results indicate that the regional lineation and shear zone kinematics east west top to the east represent fabrics developed essentially during the intraoceanic subduction of the rheic ocean and their orientation may be considered a reference vector for convergence models in this part of the variscan belt

structures and mechanisms of the northward propagating boreal summer intraseasonal oscillation abstract the spatial and temporal structures of the northward propagating boreal summer intraseasonal oscillation bsiso are revealed based on the analysis of both the echam4 model simulation and the ncep ncar reanalysis the bsiso structure and evolution characteristics simulated by the model bear many similarities to those derived from the ncep ncar reanalysis the most notable features are the remarkable meridional asymmetries relative to the bsiso convection in the vorticity and specific humidity fields a positive vorticity perturbation with an equivalent barotropic structure appears a few latitude degrees north of the convection center the maximum specific humidity also shows a clear northward shift in the lower troposphere two internal atmospheric dynamics mechanisms are proposed to understand the cause of the northward propagation of the bsiso the first is the vertical shear mechanism the key process associated with this mechanism is the generation of barotropic vorticity due to the couplin

preferred lattice orientations of plagioclase from amphibolite and greenschist facies rocks near the insubric line western alps abstract preferred lattice orientations of plagioclase measured by the universal stage from deformed amphibolite and greenschist facies rocks near the insubric line western alps reflect the type and orientation of the strain system either 001 or 010 are oriented parallel or subparallel to the schistosity and form more or less complete girdles around the stretching direction by the preferred orientation patterns dominant 010 001 slip is indicated and additionally slip on 001 parallel to the a direction possibly at somewhat higher temperatures and or at a higher an content of the plagioclase it is suggested that obliquities of the symmetry planes of the orientation patterns against the principle axes of strain are related to the sense of shearing

plagioclase fabric development in a high grade shear zone jotunheimen norway abstract shear zones of precambrian age transform meta anorthositic rocks to mylonites of high metamorphic grade in jotunheimen norway a plagioclase microfabric study is presented for one of these shear zones the shear zone is heterogeneously and asymmetrically developed regarding the degree of recrystallization and this is inferred as reflecting strain variations pre shear zone plagioclase is preserved in the deformed rocks as porphyroclasts which display large variations in grain elongation in the plane of mylonitic foliation with aspect ratios long dimension average short dimension as large as 25 1 the preferred orientation of lattice and optical directions in the plagioclase porphyroclasts indicates that they are preferentially oriented with the pole to 010 at a moderate angle to the foliation pole in such a way that they are unfavorably oriented for mechanical twinning on the albite and pericline laws in a flattening strain across the plane of the mylonitic foliation this is taken to indicate that the porphyroclasts represent those pre shear zone plagioclase grains which were oriented in order to accommodate such a flattening strain by mechanical twinning while grains otherwise oriented accommodated the strain by kinking with an axis of external rotation at 100 and glide which accumulated lattice strain and eventually led to recrystallization the plagioclase porphyroclasts with large aspect ratios are preferentially oriented with 100 at a large angle to the inferred translation direction of simple shear strain they are the products of preferential recrystallization of zones of large lattice strain in grains which were strongly kinked due to their special orientation this implies that grain elongation is not applicable as a measure of strain the microstructures indicate that the recrystallization was dynamic the produced neoblasts display a preferred orientation which is weak although with a preference for 010 to have a low angle to the foliation plane which mimics the preferred orientation of the porphyroclasts there is a slight indication that the orientation of neoblasts is controlled by the plagioclase host such that 100 of the neoblasts prefer intermediate rather than large angles against 100 of the porphyroclast these features and microstructural observations indicate that rotation recrystallization is a basic recrystallization mechanism under high grade metamorphic conditions

the evolution of planetary scale 200 mb divergent flow during the fgge year a descriptive study of the large scale horizontally divergent wind field during the fgge year is presented using empirical orthogonal functions eofs of the 200 mb velocity potential the mean flow and annual cycle are shown to be realistically related to climatological features these and large scale patterns represented by the eofs are consistent with very similar patterns of opposite sign seen at 850 mb the main result of this work is the clear description of an eastward propagating wave in the 200 mb divergences with zonal wavenumber 1 and period 30 50 days this mode has been deduced in other studies and related to variability in the asian summer monsoon these results show it to exist throughout the fgge year and imply that a relationship exists between the planetary scale eastward propagating mode and smaller scale divergence bands apparently propagating northward over the monsoon region

zonally symmetric and asymmetric features of the tropospheric madden julian oscillation the evolving intraseasonal is modes of the zonally symmetric zs part the latitudinal profile of the 200 hpa stream function have been determined by performing extended empirical orthogonal function eeof analyses for the northern hemisphere nh summer and winter in each analysis the first eeof mode describes an oscillation with a period of about 50 days the prominent feature of the upper tropospheric stream function latitudinal profiles for both seasons is the propagation of the largest loadings in both hemispheres from near the equator toward higher latitudes this propagation is more evident during the nh winter and throughout the year in the southern hemisphere sh in the nh the poleward propagation of the loadings is more conspicuous within the equator and the 30 n latitudinal band the associated patterns for the zonally asymmetric za part of the sea level pressure and the 850 and 200 hpa zonal winds have also been determined these patterns feature in general the largest correlations in the tropics and a large scale zonal wavenumber one structure propagating continuously eastward around the globe with a 50 day period the za patterns for certain variables show strong seasonal dependence the 850 hpa za zonal wind patterns feature the largest correlations approximately along the climatological position of the intertropical convergence zone whereas the largest correlations for the upper level za zonal wind patterns are found near the equator mainly in the winter hemisphere

syn emplacement recrystallization and deformation microstructures in the poe mountain anorthosite wyoming plagioclase recrystallization microstructures and petrofabrics in the unmetamorphosed 1 43 ga poe mountain anorthosite wyoming are indicative of very high temperature deformation and recrystallization during the emplacement of the anorthosite body the poe mountain anorthosite consists of a core of recrystallized massive anorthosite transitional with a series of layered anorthositic cumulates at the margin of the intrusion irregular grain boundaries and dissected grain microstructures in the massive core and transitional anorthosites suggest that the anorthositic rocks recrystallized by fast grain boundary migration and possibly subgrain rotation recrystallization at very high temperatures 1050 c during emplacement of the intrusion in the mid crust 3 kbar the deformation and recrystallization of the poe mountain anorthosite was continuous from subliquidus to subsolidus temperature conditions during the emplacement of the intrusion anorthosites with the lowest modal percentages of ferromagnesian minerals and fe ti oxides are always the most recrystallized this suggests that melt interstitial to the plagioclase crystal framework was removed during deformation and recrystallization of the intrusion bulging of plagioclase grain boundaries around fe ti oxides together with deformed oikocrystic ferromagnesian minerals and plagioclase chadacrysts indicate that the deformation and recrystallization of the intrusion continued after the crystallization of the interstitial melt minerals

a diagnostic study of recurrent meteorological anomalies appearing in a 15 year simulation with a gfdl general circulation model abstract the spatial structure and temporal characteristics of prominent anomalies occurring in a 15 year simulation with a gfdl spectral general circulation model are examined using empirical orthogonal functions teleconnection patterns composite charts lagged correlation functions and frequency spectra despite the absence of any nonseasonal perturbation in the prescribed forcing such as sea surface temperature insolation and cloud cover the simulated circulation exhibits an appreciable degree of temporal variability on monthly time scales the standing oscillation in the northern hemisphere winter which accounts for the largest fraction of this variance has a coherent three dimensional structure in the middle and upper troposphere this preferred mode of oscillation is characterized by a wavelike pattern with multiple centers of action the corresponding anomaly pattern at the sea level is dominated by north south pressure seesaws over the north atlantic and north pacific the flow patterns assoc

depth and modes of pliocene pleistocene crustal extension of the apennines italy since early pliocene times the apenninic chain has been dissected by normal faults propagating towards the adriatic foreland in the tyrrhenian sea extension involved deep crustal sections whereas in the central apennines downfaulted area it affected the shallow crust the tyrrhenian back arc domain is connected to the overall flexural retreat of the adriatic apulia plate in front of the apenninic collisional wedge in the outer apenninic belt thin skinned delamination and gravitational collapse occurred in the hanging wall of a thickened wedge overthrusting the uplifted buoyant crust of the apulia foreland differential sinking velocity of the foreland plate results from the inherited competence contrast between the rigid gargano apulia carbonate platform to the south and the low competence lithology of the pelagic sequence of the adriatic basin to the north during late messinian early pliocene times this palaeogeographical boundary acted as a lithospheric tear separating segments of the apulia plate subjected to different subduction modes

how extensive are subsolidus grain shape changes in cooling granites abstract the hypothesis that granites sensu lato commonly undergo extensive grain shape changes recrystallization during cooling is not supported by microstructural evidence especially the abundance of non truncated zoning patterns in mineral grains regional metamorphic felsic gneisses that have undergone extensive neocrystallization recrystallization at amphibolite facies conditions which some have suggested are equivalent to those in slowly cooling granites typically lose igneous microstructures including oscillatory zoning and are characterized by polygonal to irregularly xenoblastic grains of quartz and feldspar as well as by rounded inclusions of quartz in feldspar and vice versa in contrast granites typically show oscillatory zoning especially in plagioclase elongate euhedral to subhedral feldspar grains and euhedral plagioclase inclusions in quartz and k feldspar the contrast between these two situations is probably the result of felsic gneisses undergoing chemical reactions and regional deformation especially in the presence of water released pervasively from dehydration reactions which are strong driving forces for the production of new grains whereas the minerals in cooling granites are chemically compatible without strong deformation and so do not react with each other or recrystallize therefore massive granites without solid state foliations generally do not undergo grain shape changes owing to inadequate driving forces as well as to decreasing temperature an important implication of this conclusion is that internal structures formed during chamber construction and magmatic flow in granite plutons are not likely to be removed by subsolidus intergranular microstructural changes

the 40 to 50 day oscillation in a perpetual january simulation with a general circulation model a 1200 day record from a perpetual january simulation with a general circulation model is analyzed for the presence of an oscillation resembling the 40 to 50 day oscillation observed in the atmosphere representation of the global velocity potential at 200 mbar by empirical orthogonal functions eofs reveals an eastward propagating disturbance having a principally zonal wave number 1 character it is determined from power spectra of the velocity potential at points around the equator that the period of the oscillation is in the range of 28 31 days time series of the coefficients of the first two eofs are used to define epochs for the compositing in equatorial latitudes of anomalies in zonal winds in 500 mbar convective heating and in precipitation time longitude diagrams of the zonal wind anomalies indicate the presence of an eastward propagating disturbance characterized by two longitudinal scales the principal anomalies in convective heating and precipitation appear as two stationary oscillations one situated in a zone extending from 120 e to the dateline and the other in a relatively narrow zone near 60 w

on the measurement of plagioclase lattice preferred orientations abstract there are two major difficulties in measuring plagioclase lattice preferred orientations lpos by u stage the first which is caused by dependence of the lpo determination on anorthite content cannot be overcome using the u stage method at present the second difficulty which is caused by the dependence on orientation of thin sections can be overcome by measuring all twinned grains in any two orthogonal sections compared with previous methods published in the literature the present method using two rather than three orthogonal sections is more statistically meaningful and time saving in practice this method was used for measuring lpos of plagioclase an 50 from a typical anorthosite mylonite deformed under the granulite facies conditions in the morin ductile shear zone within the canadian grenville tectonic province

deformation of granitic rocks experimental studies and natural examples crustal deformation is inherently complex because the crust is inhomogeneous and anisotropic on a wide variety of scales advances in our understanding have come from a combination of field observations laboratory experiments and theoretical models what necessarily links all these investigations is a focus on process crystal plasticity dislocation creep is one of several grain scale deformation processes or mechanisms each process is dominant over a certain range of conditions in the crust has a particular form of the flow law and produces a characteristic set of microstructures characterizing the deformation mechanisms for different minerals over a range of conditions allows one to link the mechanical behavior or flow law associated with that process to the microstructures it produces the information on microstructures can be used to help interpret the thermomechanical history of naturally deformed rocks and flow laws can be used to create more realistic models predicting crustal behavior in different tectonic settings iterations among field theoretical and experimental approaches are critical for making progress in our understanding the deformation process of crystal plasticity is the main focus of this volume crystal plastic deformation of the crust is in many ways more complex than that of the mantle because most crustal rocks are polyphase aggregates and the strengths of common crustal silicates such as quartz feldspar and mica are very different at a given set of conditions yield strength envelopes for the crust as shown schematically in figure 1 are commonly plotted using the dislocation creep flow law for quartz which inherently assumes that quartz is the controlling phase and undergoes steady state flow but is the flow law for dislocation creep of quartz a good approximation for the deformation of a granite let alone a crustal plum pudding of regions and layers of different lithologies the crust

early uplift history of the abruzzi apennines central italy available geomorphological constraints abstract remants of a flat paleolandscape of erosional origin top paleolandscape tpl have been detected in the abruzzi apennines central italy at high elevations 1350 1500 m a s l according to current views the tpl formation occurred at an elevation close to sea level and probably marks the first significant geomorphic event in the investigated sector since this erosional paleolandscape affects an already deformed pre pliocene marine substratum and different structural units its formation occurred after the thrust faulting phase which affected the investigated area the present elevation of the tpl remnants indicates a significant uplift following the formation of this geomorphic feature this uplift began during the pliocene age of the first post thrusting continental deposits subsequent or sub contemporaneous to the tpl and related to the formation of intermontane basins pliocene deposits have been found in the turano salto and fucino basins the origin of these basins was conditioned by the activity of normal faults which affected and displaced the tpl during the pliocene considering 1 that the tpl experienced uplift since the pliocene and 2 that after the beginning of the uplift phase it was displaced during the pliocene by the faults responsible for the evolution of the mentioned basins uplift of the apennine chain and normal faulting are closely related the analysis of the mentioned basins permitted to hypothesise a succession of pliocene early pleistocene geomorphic and tectonic events 1 pliocene formation of the tpl at low elevation a s l 2 beginning of the uplift and displacement of the tpl due to the activity of normal faults 3 formation of the turano salto and fucino pliocene basins 4 fault activity responsible for the displacement of the pliocene deposits 5 erosional phase affecting all the investigated basins 6 deposition of the early pleistocene units

the geotectonic stress field and crustal movements abstract it is shown that there is a direct connection between the geotectonic stress field and crustal displacements the determination of the stress field is based on in situ measurements and on observations of orientations of joints the knowledge of the crustal displacements stems from geodetic measurements as well as from geological geomorphological considerations in this fashion it was possible to correlate plate tectonic motions as well as vertical motions with the neotectonic stress field in various parts of the world such as the alps the himalaya and north america in all these areas a good conformity between the indicated phenomena was found

azimuth dependent amplification of weak and strong ground motions within a fault zone nocera umbra central italy 1 during three moderate magnitude earthquakes occurred in september october 1997 in the central apennines italy accelerations larger than 0 5 g were recorded in the town of nocera umbra 10 to 15 km n nw of the epicenters the accelerograph is sited in a fault zone close to a n30 e tectonic contact six temporary seismological stations installed across the fault recorded 82 aftershocks occurred in two seismogenic zones the colfiorito sellano area s se of the array and the gualdo tadino area to the north the array data reveal large variations in terms of both peak ground motions and spectral amplitudes within the fault zone amplifications show a strong dependence on the source azimuth at the accelerograph site the effects are particularly large for events from s se peak ground motions are a factor of 14 larger than those of a reference site and conventional spectral ratios attain amplitudes as large as 50 at 7 hz along the n30 e direction of motion parallel to the strike of the fault nineteen strong motion accelerograms were then used to compare ground motion properties between weak and strong events up to m 0 1 2 x 10 25 dyn cm a particle motion analysis shows that the directional effect is also present in the strongest motions even though the amplification of peak ground motion decreases when m 0 increases results from stochastic simulations indicate that such a behavior is not due to nonlinearity applying the empirical weak motion transfer functions in a purely linear model the observed peak ground motions of the largest events are fit satisfactorily

three dimensional structure and evolution of the mjo and its relation to the mean flow abstractthe two leading principal components of the daily 850 minus 150 hpa global velocity potential in the interim european centre for medium range weather forecasts ecmwf re analysis era interim 1979 2011 data are used as time varying madden julian oscillation mjo indices regression maps and meridional cross sections based on these indices are used to document the structure and evolution of the zonal wind u and geopotential height z anomalies in the mjo cycle the data are daily and they are not separated by season at upper tropospheric levels the mjo signature is dominated by eastward propagating planetary wave packets consisting of equatorial kelvin waves flanked by rossby waves centered along 28 n s for which the westerly jet streams serve as waveguides at lower tropospheric levels the pattern more closely resembles the response to a pulsating heat source over the maritime continent where the andes block the eastward propagating kelvin wave pulse the contrasting upper and lower

dynamic recrystallization of feldspar a mechanism for ductile shear zone formation feldspar aggregates experimentally deformed in the dislocation creep regime undergo dynamic recrystallization because recovery is difficult due to the limited climb of dislocations recrystallizing aggregates have a lower strength because of the cyclic production of small strain free grains and they develop a strong preferred orientation consistent with that observed in mylonites thus recrystallization accommodated dislocation creep may be responsible for the grain size reduction and strain softening that lead to the formation of many mylonites and ductile shear zones

preferred orientation of anorthite deformed experimentally in newtonian creep abstract synthetic anorthite aggregates were deformed in a paterson gas deformation apparatus at confining pressures up to 400 mpa in torsion and axial compression at temperatures between 950 c and 1200 c samples deformed in torsion under newtonian creep display development of texture or crystallographic preferred orientation as documented with synchrotron x ray diffraction measurements complex diffraction patterns were deconvoluted with the rietveld method to obtain quantitative texture information torsion samples deformed up to shear strains of 4 and samples deformed in compression at higher stresses to total strains of 0 3 develop clear textures texture and shape preferred orientation spo of torsion samples display a monoclinic pattern with an asymmetry inclined against the sense of shear consistent with polycrystal plasticity simulations that assume the deformation is accomplished by dislocation glide these results show that a material deforming in linear viscous creep can develop a strong texture in striking contrast to the paradigm that the presence of a texture precludes low stress newtonian behavior our observations show that the presence or absence of crystallographic preferred orientation is not sufficient to uniquely infer the dominant rheological mechanical regime as sometimes applied for interpretation of seismic anisotropy in the earth

microstructure and micromotion in recrystallization flow of octachloropropane a first look advance of the genetic theory of metamorphic fabric depends in part on improved understanding of dynamic recrystallization processes and the effects of these processes upon various fabric elements this paper describes aspects of the microstructural evolution and associated small scale motion in a dynamically recrystallizing sheet of octachloropropane the material was deformed in progressive pure shear at 2 10 3 sec 1 with interruptions for photography and u stage measurement at 70 of its absolute melting temperature the dominant recrystallization process is migration of grain boundaries with consequent major adjustment of the shapes and sizes of grains but no marked change in the average grain size and no creation of new grains typical grains in the fully deformed material 30 bulk shortening have a composite structure with primitive high strain regions inherited directly from the undeformed state rimmed by successively younger regions of lower strain accreted behind outwardmoving boundaries an array of second phase marker particles permits distinction between grain boundary motion with and through the material and reveals an unexpected ability of grains as a whole to migrate short distances up a bulk strain gradient the markers also show that the only important deformation process is intragranular deformation and that it is proceeding at somewhat different rates in different grains the central problem posed by the observations is to explain the direction and speed of each migrating boundary two hypotheses were tested neither with outstanding success one of these hypotheses is that grain boundary migration is part of a strain accomodation process that operates between grains stretching or shortening at different rates parallel to their mutual boundary

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

global equatorial variability of 850 and 200 hpa zonal winds from rawinsondes between 1963 and 1989 the longitude height time variability of 3 month averaged zonal wind anomalies at 850 and 200 hpa over the equatorial area 5 degrees n 5 degrees s is analyzed using a three dimensional dataset constructed from rawinsonde data 1963 1989 the first mode closely related to the southern oscillation index suggests a strong vertical coupling associated with a horizontal out of phase pattern between the central western pacific and the remainder of the equatorial belt the vertical coupling appears to be phase locked to the annual cycle with strongest intensities found over south america and near the maritime continent early in the calendar year and over the pacific basin and africa during the second half of the year this mode of variability can be viewed as a standing pattern superimposed with an eastward migrating component coherent with the annual cycle this westerly moving mode originates near the maritime continent during the northern autumn and tends to precede el nino southern oscillation events in the central and eastern pacific ocean variance is mainly concentrated in the 3 8 year low frequency time scale throughout the tropics and in the 2 3 year quasi biennal band from 110 degrees 120 degrees e to 180 degrees 24 refs 4 figs

the south to north progression of rainfall anomalies across india during the summer monsoon season the low frequency spatio temporal intraseasonal evolution of monsoon rainfall over india is studied by considering the pentad rainfall averages taken over 2 5 wide and 5 0 long blocks lying across the central longitudinal and latitudinal transacts the time latitude cross sections show south to north progressions of rainfall anomalies with a recurrence period of about 40 days the progressions show considerable inter annual and intra seasonal variation in frequency amplitude and rate of progression the extended empirical orthogonal function analysis shows that the first two most important functions correspond to this northward progression of rain anomalies recurring after an interval of about 40 days the rate of progression of anomalies is about 0 5 lat day the time longitude cross sections show the movement of rainfall anomalies towards both directions east and the west with slight preference towards the east the importance of these signals in rainfall forecasting is foreseen

recrystallization and fabric development in plagioclase the microstructures and fabrics of naturally deformed intermediate composition plagioclase feldspars from the amphibolite granulitic gneisses from the lower crust have been studied special interest in the effects of dynamic recrystallization and deformation fabrics has been taken the plagioclase feldspars an40 50 have undergone extensive ductile deformation by intracrystalline slip and twinning they show strong crystallographic preferred orientation which was produced by dominant 010 001 slip dynamic recrystallization is indicated by fine grained new grains neoblasts interspersed with deformed relicts porphyroclasts the neoblasts have formed preferentially along grain boundaries kink band boundaries kbbs intracrystalline shear zones and around solid inclusions such as garnet and pyroxene optical microstructural evidence suggests that dynamic recrystallization occurred primarily by grain boundary migration with subsidiary subgrain rotation which appears to have occurred only at low st

evaluation of upper mantle microstructures in the table mountain massif bay of islands ophiolite within the undisrupted 6 km thick mantle section of the table mountain massif bay of islands ophiolite newfoundland several distinct peridotite microstructures are recognized in the uppermost mantle section very high temperature t 1200 high strain microstructures with evidence for syntectonic melt infiltration are preserved remarkable among these is an orthopyroxene impregnated dunite at an intermediate level of the mantle section peridotites have been affected by a weak lower temperature t 1000 1100 c overprint they are underlain by a thin sliver of low strain high temperature peridotites all these peridotites are interpreted to have formed during spreading related strain lower temperature t 1000 c high stress microstructures with high accumulated strain are locally preserved at intermediate levels of the mantle section and are regionally present at its base they culminate in metasomatic ultramafic ultramylonites and are related to detachment of the ophiolite with the exception of the basal ultramylonitic peridotites the activated olivine slip system was 0kl 100 in the highest temperature peridotites a weak preference for the activation of distinct slip planes 010 001 011 was noted based on piezometry and olivine flow laws strain rate estimates for the basal detachment fabrics are 10 12 s 1 this strain rate is consistent with the observed width of detachment overprint in the ophiolite and reasonable plate tectonic convergence rates strain rate estimates for the very high temperature peridotites are even higher recent data about grain growth rates in olivine indicate that in order to preserve the peridotite microstructures olivine grain growth must have been highly impeded olivine flow law data suggest that even peridotites with lower temperature microstructures t 900 950 c could form within the rheological asthenosphere the detachment or spreading related origin of peridotites with a lower temperature overprint may thus only be concluded from the regional geological context

proterozoic massif type anorthosites as the archetypes of long lived 100 myr magmatic systems new evidence from the kunene anorthosite complex angola abstract proterozoic massif type anorthosites are voluminous plagioclase dominated plutonic suites with characteristic intermediate compositions an50 10 that represent mantle derived magmas ponded at moho depths and crystallized polybarically until emplacement at mid crustal levels we present new id tims and la icpms u pb ages as well as detailed field observations from the kunene anorthosite complex kac of sw angola our main objective in this work is to contextualize a variety of important petrographic and geochronological features of the kac that have implications for proterozoic anorthosite petrogenesis and the geological evolution of the sw congo craton high precision u pb zircon and baddeleyite ages for anorthositic rocks from across the complex n 11 range between 1376 and 1438 ma a period of 60 myr showing that such systems may be remarkably long lived dating of magmatic zircons from a comagmatic pegmatoidal enclave in the kac which also contains high al orthopyroxene megacrysts haom gives an age of 1500 ma indicating as much as 120 myr between some of the earliest and latest crystallization products of the system these enclaves provide a snapshot of the liquid line of descent of the anorthosites and are compelling evidence for the comagmatic nature of the haom field evidence for block structure magma mingling and extreme textural heterogeneity in the kac supports emplacement as multiple influxes of magma of various volumes carrying variable proportions of crystals and autoliths from below we infer that the kac represents a long lived mushy magmatic system that was likely emplaced in distinct pulses these observations refine our understanding of proterozoic anorthosite petrogenesis they also provide evidence for an array of magmatic processes operating at various levels of crystallinity that may create textural and chemical heterogeneity in evolving magma products at lower to mid crustal levels

enso regulation of mjo teleconnection the extratropical teleconnections associated with madden julian oscillation mjo are shown to have an action center in the north pacific where the pressure anomalies have opposite polarities between the phase 3 convective indian ocean and phase 7 convective western pacific of the mjo the teleconnection in the same phase of mjo may induce opposite anomalies over east asia and north america between el nino and la nina years during mjo phase 3 a gigantic north pacific anticyclonic anomaly occurs during la nina making coastal northeast asia warmer wetter than normal but the west us colder drier whereas during el nino the anticyclonic anomaly is confined to the central north pacific hence the northwest us experiences warmer than normal weather under influence of a downstream cyclonic anomaly during phase 7 an extratropical cyclonic anomaly forms over the northwest pacific during la nina due to convective enhancement over the philippine sea causing bitter winter monsoon over japan whereas during el nino the corresponding cyclonic anomaly shifts to the northeast pacific due to enhanced convection over the equatorial central pacific which causes warm and wet conditions along the west coast of us and canada further the presence of enso induced seasonal anomalies can significantly modify mjo teleconnection but the aforementioned mjo teleconnection can still be well identified during phase 3 the mjo teleconnection pattern over north pacific will be counterbalanced enhanced by el nino la nina induced seasonal mean anomalies during phase 7 on the other hand the mjo teleconnection anomalies in the northeastern pacific will be enhanced during el nino but reduced during la nina thereby the impacts of mjo teleconnection on the north america is expected to be stronger during el nino than during la nina

planetary scale characteristics of the atmospheric circulation during january and february 1979 abstract the vertical and temporal structure of the global scale flow in the goddard laboratory for atmospheric sciences analyses of data from the first garp global experiment are presented the fields are represented in terms of spherical harmonic expansions of the streamfunction velocity potential and geopotential the global scale patterns are obtained from triangular truncations of such series neglecting terms past the fourth degree some modes display prominent high frequency oscillations in the velocity potential and geopotential height that may be related to diurnal cycles of cumulus convection such oscillations are not apparent in the streamfunction low order harmonics with nodes only along latitude circles are nearly equivalent barotropic however those harmonics that have no nodes between the poles reverse phase with height the following conclusions are drawn regarding the global scale patterns 1 since the divergent component of the meridional flow is not much smaller than the rotational

pre collisional anastomosing shear zones in the kohistan arc nw pakistan ductile strain localisation commonly forms a pattern of shear zones anastomosing around lenses of less deformed rock initiation and development history of anastomosing shear zones which are little documented are studied through the description of the structures and the deformation history of plutonic rocks that form the lower crust of the kohistan complex structures and textures developed in these rocks result from primary magmatic to solid state regional strain overprinted by anastomosing shear zones the primary strain was mainly acquired during magmatic emplacement at 100 90 ma strain localisation took place continuously from magmatic emplacement to solid state deformation during cooling of the plutons and formed 3 successive sets of shear zones set 1 is composed of associated discrete riedel and thrust shear zones developed above solidus conditions during sw ward thrusting continuous deformation from solidus to amphibolite facies conditions between 100 and 83 ma formed the second set of shear zones the lower amphibolite facies set 3 shear zones are differentiated by larger strain recorded in the thicker mylonitic zones and enlargement of the spacing between shear zones during cooling the anastomosing pattern of shear zones described here probably represents arc related deformation during subduction of the tethys oceanic lithosphere below the kohistan arc complex

dislocation creep regimes in quartz aggregates abstract using optical and tem microscopy we have determined that three regimes of dislocation creep occur in experimentally deformed quartz aggregates depending on the relative rates of grain boundary migration dislocation climb and dislocation production within each regime a distinctive microstructure is produced due primarily to the operation of different mechanisms of dynamic recrystallization at lower temperatures and faster strain rates the rate of dislocation production is too great for diffusion controlled dislocation climb to be an effective recovery mechanism in this regime recovery is accommodated by strain induced grain boundary migration recrystallization with an increase in temperature or decrease in strain rate the rate of dislocation climb becomes sufficiently rapid to accommodate recovery in this regime dynamic recrystallization occurs by progressive subgrain rotation with a further increase in temperature or decrease in strain rate dislocation climb remains sufficiently rapid to accommodate recovery however in this regime grain boundary migration is rapid thus recrystallization occurs by both grain boundary migration and progressive subgrain rotation the identification of the three regimes of dislocation creep may have important implications for the determination of flow law parameters and the calibration of recrystallized grain size piezometers in addition the identification of a particular dislocation creep regime could be useful in helping to constrain the conditions at which a given natural deformation has occurred

spatial and temporal variations in growth rates along active normal fault systems an example from the lazio abruzzo apennines central italy abstract the geometry kinematics and rates of active extension in lazio abruzzo italian apennines have been measured in order to gain a better understanding of the spatial and temporal variations in fault growth rates and seismic hazards associated with active normal fault systems we present fault map traces throws throw rates and slip directions for 17 parallel en echelon or end on active normal faults whose 20 40 km lengths combine to form a soft linked fault array ca 155 km in length and ca 55 km across strike throw rates derived from observations of faulted late glacial features and holocene soils show that both maximum throw rates and throw rate gradients are greater on centrally located faults along the strike of the array total throws and throw gradients show similar spatial variations but with weaker relationships with distance along strike when summed across strike throw rates are increasingly high towards the centre of the array relative to summed throws we interpret the above to suggest that throw rates have changed in the recent past ca 0 7 ma from spatially random fault growth rates initiating at 2 5 3 3 ma to growth rates that are greater on centrally located faults we interpret this as evidence for fault interaction producing throw rate variations that drive throw profile readjustment on these crustal scale soft linked faults the results are used to discuss seismic hazards in the region which are quantified in a second paper in this issue

evolution of the hongzhen metamorphic core complex evidence for early cretaceous extension in the eastern yangtze craton eastern china we conducted structural and geochronological studies on the hongzhen metamorphic core complex in the eastern yangtze craton the hanging wall of the hongzhen metamorphic core complex consists of neoproterozoic to permian unmetamorphosed strata which were folded during nw se shortening in the middle triassic and cretaceous terrestrial basins the exposed paleoproterozoic dongling complex in the footwall is widely overprinted by a detachment ductile shear zone which has consistent sw plunging mineral elongation lineations and top to the sw shear indicators analysis of the mesostructures microstructures and quartz c axis fabrics indicates that they formed within a low angled sw dipping extensional shear zone at midcrustal levels four muscovite grains separated from mylonites within the shear zone yielded 40 ar 39 ar plateau ages ranging from 128 5 1 0 ma to 126 1 1 1 ma they are interpreted as cooling ages of the shear zone associated with the hongzhen metamorphic core complex we propose that the hongzhen metamorphic core complex was initiated as a midcrustal low angle extensional shear zone with top to the sw shear sense at ca 145 ma and the shear zone was then warped and uplifted by the emplacement of the hongzhen granite at 122 ma brittle normal faulting and basin rifting in the hanging wall also developed during the formation of the hongzhen metamorphic core complex but these processes continued until the late cretaceous this study of the hongzhen metamorphic core complex demonstrates that the eastern yangtze craton was also involved in the early cretaceous extension widely occurring in the eastern china continent a ne sw extensional direction during the early cretaceous is indicated by the hongzhen metamorphic core complex