dispersal concentration and deposition of suspended matter in the north sea suspended matter comes into the north sea from the atlantic ocean from the channel rivers seafloor erosion coastal erosion the atmosphere and from primary production the contribution of the last source is temporarily large when phytoplankton growth is abundant but is soon decomposed mineralized or consumed so that over the year the net effect is small accumulation and deposition of suspended matter occurs predominantly in only a few areas the waddensea the german bight the skagerrak norwegian channel the remainder of the north sea floor consists of pleistocene and early holocene relict deposits and of reworked sands and gravels the mechanisms resulting in accumulation and deposition are discussed there are strong indications that the amount of suspended matter flowing out from the north sea into the norwegian sea along the norwegian coast is only little more or the same as the amount coming in from the north atlantic although its composition may be different

horizontal viscoelastic gravitational displacement due to a rectangular dipping thrust fault in a layered earth model calculations of horizontal displacements due to a rectangular finite thrust fault in a viscoelastic gravitational layered earth model are presented the earth model consists of a single elastic gravitational layer overlying a viscoelastic gravitational half space a review of the full three dimensional theoretical solutions is presented along with the explicit solutions for horizontal displacements several examples of computations for dipping faults with various angles and located at different depths are shown the results indicate that viscoelasticity introduces a long wavelength component into the interseismic deformation field which is not present in published elastic techniques and also that a proper consideration of gravity is necessary only for near field computations at longer periods of time a pattern is found in the cumulative displacement of cycled earthquakes which indicates that the viscoelastic displacements are visible for longer recurrence time events and that these may serve as a time index for the various stages between cycles

the effect of microstructural and rheological heterogeneity on porphyroblast kinematics and bulk strength in porphyroblastic schists abstract the kinematic record and bulk viscous strength of polyphase rocks depend in part upon the relative strengths and distributions of rheologically distinct fabric elements here we explore the effects of microstructural and rheological heterogeneity in porphyroblastic schists electron backscatter diffraction and petrographic analyses reveal asymmetric microboudinage of staurolite indicating relative rotation of staurolite porphyroblasts synchronous with bulk non coaxial strain boudinage and relative rotation both require porphyroblast matrix shear coupling based on 2d optical observations the extent of the coupling appears related to the initial and boudinaged staurolite grain shape and orientation as well as the geometry of heterogeneities such as mica domains or shear bands we designed 2d finite element numerical models to assess the role of microstructural variation and rheological heterogeneity on the degree of porphyroblast matrix shear coupling and bulk viscous strength model results indicate that the bulk strength of a three phase system comprising inclusion weak domain and matrix is sensitive to the relative proximity of weak and strong domains particularly at high viscosity contrasts i e matrix weak 10 the threshold for bulk weakening below the matrix strength occurs over a narrow range of weak domain viscosities matrix weak 2 6 5 5 regardless of the relative abundance and spatial distribution of weak domains kinematic decoupling of porphyroblasts occurs at low viscosity contrasts when weak domains are proximal matrix weak 2 5 but for all other spatial distributions and modal abundances investigated kinematic decoupling occurs at viscosity contrasts of matrix weak 15 20 these data indicate that bulk weakening due to rheological heterogeneity is not necessarily coincident with kinematic decoupling

global displacements caused by point dislocations in a realistic earth model we define dislocation love numbers h nm ij l nm ij k nm ij l nm t ij and green s functions to describe the elastic deformation of the earth caused by a point dislocation and study the coseismic displacements caused in a radially heterogeneous spherical earth model we derive spherical harmonic expressions for the shear and tensile dislocations which can be expressed by four independent solutions a vertical strike slip a vertical dip slip a tensile opening in a horizontal plane and a tensile opening in a vertical plane we carry out calculations with a radially heterogeneous earth model 1066a the results indicate that the dominating deformations appear in the near field and attenuate rapidly as the epicentral distance increases the shallower the point source the larger the displacements both the earth s curvature and vertical layering have considerable effects on the deformation fields especially the vertical layering can cause a 10 difference at the epicentral distance of 0 1 as an illustration we calculate the theoretical displacements caused by the 1964 alaska earthquake m w 9 2 and compare the results with the observed vertical displacements at 10 stations the results of the near field show that the vertical displacement can reach some meters the far field displacements are also significant for example the horizontal displacements u can be as large as 1 cm at the epicentral distance of 30 0 5 cm at about 40 magnitudes detectable by modern instrument such as satellite laser ranging slr very long baseline interferometry vlbi or global positioning system gps globally the displacement u r caused by the earthquake is larger than 0 25 mm

interpretation of porphyroblast inclusion trails limitations imposed by growth kinetics and strain rates porphyroblast inclusion trails provide important information about the tectonometamorphic evolution of a metamorphic rock however there remains considerable controversy over whether porphyroblasts rotate during bulk non coaxial deformation with reference to an area of the scandinavian caledonides and utilizing existing data from theoretical and experimental modelling this study demonstrates that both straight and s shaped inclusion trails are consistent with an interpretation in terms of syndeformational porphyroblast growth in a regime approximating to newtonian simple shear at crustal strain rates of 10 14 s 1 and porphyroblast growth times of 0 1 1 0 ma it is shown that a maximum of 5d 9d angular rotation would occur during growth at faster strain rates of 10 12 s 1 e g those in a shear zone porphyroblast angular rotations of 90d are shown to occur in 0 1 0 25 ma i e times comparable with or faster than porphyroblastesis in view of this s shaped inclusion trails are to be expected in porphyroblasts growing in active shear zones or other situations of high shear strain whereas straight inclusion trails can be interpreted as static overgrowth of an existing fabric or as syndeformational porphyroblastesis at low strain rates

shear zone vs folding origin for spiral inclusion trails in the canton schist the three dimensional geometry of spiral inclusion trails from the canton schist were measured to determine whether the spirals were a product of porphyroblast rotation within a shear zone or porphyroblast growth during a series of overprinting fold events the spiral inclusion trails are composed of three separate sub planar inclusion trail surfaces occupying texturally distinct parts of the porphyroblasts these surfaces are correlated across a 10 km2 area using textural criteria and relative timing measured patterns of inclusion trail orientation and asymmetry suggest they did not form by porphyroblast rotation within a non coaxial shear zone rather the porphyroblasts grew during three successive overprinting fold events f2 f4 and the spiral inclusion trails represent the accumulated curvature associated with folding of successive axial plane foliations the data show that spiral garnets are not peculiar to shear zones and can form by overprinting crenulations and folds this is consistent with the common occurrence of spiral garnets in multiply deformed regionally metamorphosed fold belts

x ray computed micro tomography of spiral garnets a new test of how they form abstract garnet porphyroblasts with spiral shaped inclusion trails of two micaschist samples have been investigated with x ray computed tomography for each garnet crystal the orientation of its internal foliation intersection inflexion axes fia was measured its volume and shape orientation the latter via calculation of best fit ellipsoids additionally image analysis of inclusion trails was performed in slices passing through garnet centres oriented normal to fia our data demonstrate subvertical and subhorizontal preferred orientations of the inclusion trails and of the porphyroblast crystals themselves in both samples this supports a genetic model in which garnets periodically overgrew a succession of vertical and horizontal foliations during alternating crustal shortening and gravitational collapse without significantly rotating the fact that both samples come from areas previously identified as regional shear zones supports the idea that porphyroblasts are able to maintain stable positions even in such environments our study exemplifies the strength of x ray computed micro tomography compared to previous techniques based on serial thin sections for distinguishing multiple fia sets present in single samples

lattice preferred orientation of quartz inclusions within garnet porphyroblasts from the imjingang belt south korea abstract quartz inclusions within intertectonic garnet porphyroblasts of metapelites from the southern imjingang belt have a lattice preferred orientation c axis fabrics of the quartz inclusions tend to show a single girdle pattern at a high angle to an earlier foliation together with a submaximum subparallel to an earlier lineation this lattice preferred orientation of the quartz inclusions might result from intracrystalline deformation together with solution creep prior to the garnet growth or from selective entrapment of quartz grains with a specific lattice orientation during the garnet growth

permo triassic changes in bulk crustal shortening direction during deformation and metamorphism of the taebaeksan basin south korea using foliation intersection inflection axes implications for tectonic movement at the eastern margin of eurasia during the songrim indosinian orogeny abstract the permo triassic songrim indosinian orogeny in south korea was a major tectonic event involving complicated continental collisions at the eastern margin of eurasia previous studies have examined the structural and metamorphic features of the songrim orogeny in each of the paleozoic terranes of the orogenic belt i e the taebaeksan basin the okcheon basin and the imjingang belt but correlations of these features among the terranes remain uncertain the aim of this paper is to reveal deformation history including bulk crustal shortening directions in the taebaeksan basin and to correlate the tectono metamorphic evolution of the taebaeksan basin with other phanerozoic mobile belts in eastern asia based on a combined analysis of foliation intersection inflection axes fia trends and metamorphic p t and t t time paths the orientations and relative timing of fia preserved as inclusion trails within porphyroblasts of andalusite chloritoid garnet and staurolite reveal two age groups of inclusion trails in the pyeongan supergroup at the northeastern margin of the taebaeksan basin these microstructures indicate the development of early nnw nne trending structures and fabrics followed by later e w trending ones these observations suggest a change in the orientation of bulk crustal shortening from e w to n s during the songrim orogeny based on the similar microstructures and temperature time paths of the three paleozoic terranes we interpret that the e w bulk crustal shortening influenced the eastern part of the korean peninsula during the early stages of the songrim orogeny presumably related to amalgamation between the proto japan terrane and the eastern margin of eurasia whereas the n s bulk crustal shortening was stronger in the western part of the peninsula during the later stages of the orogeny related to collision between the south and north china blocks

a viscoelastic coupling model for the cyclic deformation due to periodically repeated earthquakes at subduction zones vertical displacements due to periodic reverse faulting events in an elastic plate overlying a viscoelastic maxwell half space are obtained and compared with the observed deformation cycle coseismic strain release postseismic transients interseismic strain accumulation from japan the viscoelastic effects including the influence of buoyant restoring forces are obtained using the method developed by rundle and plate convergence and strain accumulation are incorporated following the procedure suggested by savage the resulting deformation cycle is compared with that of an analogous elastic half space dislocation model in which postearthquake effects are due to transient aseismic slip below the coseismic fault cyclic deformation is similar but not identical for the two models and observations from southwest japan suggest the superiority of the viscoelastic coupling model in particular inclusion of the effects of steady state flow in the asthenosphere overcomes a defect of the elastic half space model and results in agreement with the observed interseismic movement pattern several aspects of the postseismic deformation its landward migration and its transition to the interseismic phase of the cycle are explained as well but the short duration of near trench transients relative to those observed farther inland is not matched the success of a buried slip model in explaining early postseismic near trench movements and asthenospheric flow in accounting for cumulative postearthquake transient motions suggests the existence of a transition zone between lithosphere and asthenosphere whose behavior is brittle elastic in the short term and ductile for longer term deformation and such a modification may reconcile remaining discordant observations however reasonable variations in coupling model parameters cannot account for observed differences in the deformation cycle in other parts of japan and these regional differences remain unexplained

global postseismic deformation deep earthquakes we study the global viscoelastic deformations associated with a shear dislocation on a fault embedded in a viscoelastic mantle to address this problem we extend the theory of the quasi static deformations of a maxwell spherical n layer incompressible earth previously limited to the modeling of the effects of earthquakes occurring only within the elastic lithosphere permanent postseismic deformations which can be generated by lithospheric sources cannot be sustained if the source region is viscoelastic however the transient response of the mantle strongly depends on the viscosity of the source region we use the technique developed here to investigate thoroughly the quasi static surface deformations induced by seismic events of variable depth we show that owing to the combined effect of sphericity and viscoelastic mantle relaxation the surface displacements do not systematically decrease as the depth of the source increases instead with increasing source depth we predict an increasing efficiency of mantle relaxation in triggering postseismic deformations of large size most of our results are based on a simple four layer model with a 100 km thick lithosphere upper and lower mantle separated by the 670 km discontinuity and a fluid core the last part of this work is devoted to a study of the effects of a low viscosity asthenosphere on the rates of deformation detected at the earth s surface the findings reported here may be useful for the interpretation of the transient motions of the earth s surface in response to deep focus earthquakes

rotated staurolite porphyroblasts in the littleton schist at bolton connecticut usa staurolite porphyroblasts 1 5 8cm in length and 0 3 2cm in width in the littleton schist at bolton connecticut contain curved quartz inclusion trails which document synkinematic rotations of at least 135 the orientations of long axes of these staurolite crystals define a weak preferred orientation in a plane approximately parallel to the external foliation serial sections of four differently orientated crystals and u stage measurements of the orientations of their inclusion trails demonstrate that the inflection hinge line and the statistical symmetry axis characterizing the foliation within a porphyroblast are unrelated to the orientations of external crenulations and are in all cases parallel to the long axis of the porphyroblast the cumulative rotation reflected in the curvature of the inclusion trails is a maximum in a c axis section through the initial core of a crystal the amount of rotation about the c axis decreases linearly along the length of the crystal away from the nucleation site the sense and amount of rotation recorded by a porphyroblast is related to its orientation a tightly constrained transition from clockwise to anticlockwise rotation defines a slip direction that coincides with the preferred orientation of the staurolite c axes the total rotation reflected by the inclusion trails increases as a function of the angle between the c axes of the staurolite crystals and the slip direction initially random staurolite porphyroblasts rotated during growth as a consequence of laminar shear in the surrounding viscous matrix this interpretation is quantitatively consistent with the staurolite preferred orientation its coincidence with the apparent slip direction the correlation between both the sense and the amount of rotation and the orientation of the long axis of the porphyroblast and the twisted conical shape of the family of surfaces defined by the inclusion trails

fold mechanisms in the canton schist constraints on the contribution of flexural flow abstract fold mechanisms operating in the canton schist have been resolved using the geometric relationship between folds and spiral inclusion trail geometries of the four end member fold mechanisms tangential longitudinal strain folding and slip folding are unable to produce the observed inclusion trail and fold geometries but a combination of flexural flow and pure shear folding is consistent with the geometric constraints the maximum flexural flow component during each fold event was determined from the geometric data during f 3 and f 4 flexural flow produced 27 and 37 of measured limb rotation respectively which corresponds to a maximum of 24 limb rotation by flexural flow in each fold event to satisfy the geometric constraints the remainder of limb rotation must be a product of pure shear folding the maximum possible component of flexural flow folding during f 3 and f 4 increases with increased variation in vorticity between layers in the rock mass in the flexural flow pure shear model a maximum of 28 of inclusion trail curvature is produced by rotation of porphyroblasts relative to irrotational fold limbs with a minimum 72 curvature due to rotation of fold limbs relative to irrotational porphyroblasts all model solutions produce less than 8 syn folding porphyroblast rotation relative to geographic coordinates

spherical versus flat models of coseismic and postseismic deformations we perform an exhaustive study of coseismic and postseismic surface deformations induced by shear dislocations using flat and spherical earth models our aim is to examine the effects of the spherical geometry the vertical layering and the self gravitation on surface displacement field for a 100 km long fault spherical and flat models produce comparable coseismic deformations up to a distance of 300 km from the epicenter this distance is sensibly reduced in the postseismic regime and when infinitely long strike slip faults are considered the differences between predictions based on flat and spherical models are due both to their global geometry and the effect of the gravity forces self gravitation has a minor role with respect to that of sphericity for surface coseismic deformations while in the postseismic regime its effects increase considerably as a case study we consider the coseismic and postseismic deformations due to the great 1960 chilean earthquake the results of the spherical stratified model differ sensibly from those of a flat uniform model moreover within the framework of spherical earth models the rheological stratification plays a major role in determining the pattern of the displacement field we show that the present day rates of vertical and horizontal deformations are considerably large 10 2 m yr 1 for an asthenospheric viscosity ranging from 10 19 to 10 20 pa s these rates which could possibly be detected by geodetic investigations are found to be also sensitive to the rheological properties of the mantle beneath the asthenosphere

calculation of static deformation following the bolivia earthquake by summation of earth s normal modes the vertical ground displacement associated with the 9 june 1994 great bolivia earthquake is calculated by summation of earth s normal modes because of the great depth of the earthquake the contributions to the surface displacement field from modes of low radial and angular orders predominate convergence is fast and the truncated mode sum provides a good estimate of the total global displacement field the vertical displacement is calculated to be on the order of 1 cm within a few hundred kill of the epicenter and 1 mm at distances as great as 1500 km normal mode seismograms are calculated for a location near the epicenter and the static offset is seen to occur primarily between the p and s phases consistent with the effect of a near field term the predicted seismograms are in qualitative agreement with the recently reported observations of seismically recorded static displacements on the banjo broadband array jiao et al this issue the static offset calculated in this study is smaller than the observations and predictions reported by jiao et al probably owing to uncertainties in the observations and in their approximate calculations which are based on dislocation theory in an elastic halfspace

global post seismic deformation summary we quantify the effects of post seismic deformation on the radial and horizontal components of the displacement in the near and far field of strike and dip slip point dislocations these sources are embedded in the elastic top layer of a spherical self gravitating stratified viscoelastic earth within the scheme of the normal mode technique we derive the explicit analytical expression of the fundamental matrix for the toroidal component of the field equations this component is propagated together with its spheroidal counterpart from the core mantle boundary to the earth s surface viscosity stratification at 670km depth influences the radial and horizontal deformation accompanying viscoelastic relaxation in the mantle over time scales of 103 104 yr both in the near field ranging from 100 to 500 km and in the far field from 103 to 5 x 103 km if the upper mantle is differentiated into a low viscosity zone beneath the lithosphere and a normal upper mantle faster relaxation is obtained for an asthenospheric viscosity of 1020 pa s we obtain for a strike slip dislocation and a seismic moment of 1022 n m characteristic of an average large earthquake horizontal rates of 1 4 mm yr 1 in the near field and 0 05 0 4 mm yr 1 in the far field these values are maintained over time scales of 10 103 yr larger rates with shorter duration are obtained if the viscosity is reduced in the low viscosity channel as expected strike slip dislocations are the most effective in driving horizontal deformation in the far field in comparison with dip slip ones it is noteworthy that horizontal velocities are maintained longer in the far field in comparison with radial ones which is not surprising since momentum is propagated in far regions essentially in the horizontal direction radial deformation is generally lower in the far field vlbi techniques with a precision of a few parts per billion over distances of 103 km can detect global post seismic deformation induced by large earthquakes our results affect the interpretation of the transfer of stress and seismic activity among different plate boundaries

the interrelationship between deformation and metamorphismpapers presented at an international meeting held in granada spain 23 26 may 2011 celebrating the career contribution of t h bell the interrelationship between deformation and metamorphism is a topic of active research connecting such disciplines as structural geology metamorphic petrology geochronology material science and economic geology this special issue is dedicated to a notable scientist who is also our friend mentor and colleague prof tim h bell james cook university of north queensland australia the eight papers in this issue were presented at a conference last year in granada spain at the occasion of tim s retirement an additional set of 15 papers will appear in tectonophysics as fruit of the same conference

deformation partitioning and porphyroblast rotation in meta morphic rocks a radical reinterpretation abstract most porphyroblasts never rotate during ductile deformation provided they do not intern ally deform during subsequent events with the exception of relatively uncommon but spectacular examples of spiralling garnets instead the sur rounding foliation rotates and reactivates due to partitioning of the deformation around the porphyroblast consequently porphyroblasts commonly preserve the orientation of early foliations and stretching lineations within strain shadows or inclusion trails even where these structures have been rotated or obliterated in the matrix due to subsequent deformation these relationships can be readily used to help develop an understanding of the processes of foliation development and they demonstrate the prominent role of reactivation of old foliations during subse quent deformation they can also be used to determine the deformation history as porphyro blasts only rotate when the deformation cannot partition and involves progressive shearing with no combined bulk shortening component

dynamics diffusion and geomorphological significance of tidal residual eddies many shallow tidal areas show the occurrence of ebb and flood surplusses organized in cell like structures or tidal residual eddies they seem to arise from a nonlinear transfer of vorticity from the oscillating tidal field to the mean field the irregular structure of the bottom topography or the coastline acting as a catalyst to produce the necessary vorticity gradients the dynamical characteristics of the eddies assist our understanding of the geomorphology of the sea bed

effects on post glacial rebound from the hard rheology in the transition zone summary we analyse the influences of a viscosity increase in the transition zone between 420 and 670 km on the geophysical signatures induced by post glacial rebound ranging from the perturbations in the earth s rotation to the short wavelength features associated with the migration of the peripheral bulge a self gravitating model is adopted consisting of an elastic lithosphere a three layer viscoelastic mantle and an inviscid core the horizontal displacements and velocities and the stress pattern are extremely sensitive to the viscosity increase and to the chemical stratification of the transition zone the hardening of the upper and the chemical density jumps in mantle below the 420 discontinuity induces a channel effect which contaminates the horizontal deformation both in the near field and in the far field from the ice sheets these findings indicate that intraplate geodetic data can be used to put bounds on the viscosity increase in the transition zone and on the amount of chemical stratification in the mantle the stress field induced in the lithosphere by the pleistocenic ice sheet disintegration is a very sensitive function of mantle viscosity stratification the existence of seismic activity along passive continental margins of previously glaciated areas requires a substantial viscosity increase in the mantle with the viscosity of the transition zone acting as a controlling parameter a viscously stratified mantle is responsible for a delayed upward migration of stress in the lithosphere which can account for the seismicity today

large earthquakes and earth rotation the role of mantle relaxation by means of a radially stratified spherical model and using the available moment tensor solutions we evaluate the contribution of large earthquakes to polar drift in the last two decades in contrast to previous analyses which only considered the elastic response of the earth to the release of seismic moment we account for mantle rheology and thus for the time dependent postseismic inertia changes driven by global seismicity we confirm that during the last twenty years the global seismic activity has not significantly altered the rotational parameters of the earth however we find that for values of asthenospheric viscosity suggested by recent studies of postseismic stress diffusion the delayed relaxation of the mantle amplifies the average rate of polar drift by a factor of 1 2 to 1 7 depending on the width of the asthenosphere even on a decade time scale

correlating deformation in variscan nw iberia using porphyroblasts implications for the ibero armorican arc abstract 3 d microstructural analysis of 30 porphyroblastic samples from the variscan orogen in nw iberia has revealed four sets of inclusion trails with distinctive geographic trends and relative timing the chronological and orientational consistency of these microstructures provides a reference frame for the correlation of macroscopic structural successions the two younger inclusion trail sets correlate with the main map scale structures of middle to upper carboniferous age whereas the two older sets correspond to mesoscopic structures preserved locally in low strain pods and dating back as far as 365 ma upper devonian inclusion trail orientations appear uninfluenced by a major orocline in the study area ibero armorican arc outlined by late stage folds and thrusts with variable trends it is proposed that the orocline developed by wnw ese trending transpression superposed on originally n s to ne sw trending structures during a late stage of the orogeny upper carboniferous domains of low or zero strain e g porphyroblasts are inferred to have maintained relatively constant orientations in the zone of transpression presumably due to deformation partitioning effects consequently they preserve a succession of pre orocline structural trends the collected microstructural data also indicate moderate preferred vertical and horizontal orientations of inclusion trails in the analysed samples as reported earlier in other variscan regions this probably witnesses a dynamic equilibrium between tectonic forces and gravity during four periods of differently oriented crustal shortening that generated the four recognised sets of inclusion trails

deformation history of the otago schists new zealand from progressively developed porphyroblast matrix microstructures uplift collapse orogenesis and its implications abstract foliation overprinting relationships preserved in porphyroblasts and the surrounding matrix in the otago schists indicate development of up to six penetrative foliations during the late paleozoic mesozoic rangitata orogeny s1 s3 and s5 formed with steep dips and s2 s4 and s6 formed with gentle dips s1 and s2 are preserved only as inclusion trails in porphyroblasts because of matrix foliation reworking during progressive deformation s3 s6 are preserved in the matrix as well as in porphyroblasts and are generally correlatable from one to the other inclusion trail asymmetries define the location of the orogenic uplift core during the rangitata orogeny when the porphyroblasts grew the location of this core is consistent with macroscale geological and structural observations alternating steep and gently dipping foliations are inferred to indicate alternating horizontal compression and extension predictions made by an orogenic model compatible with continually alternating horizontal compression and extension compare favorably with geometries observed in the schists reconstruction of the gross geometry of the otago schists during the rangitata orogeny based on the three dimensional geometry of porphyroblast inclusion trails is similar to reconstructions based on regional geological considerations and plate tectonic calculations

effect of subductions and trends in seismically induced earth rotational variations in the past the influences of large earthquakes on earth rotation and on changes of the gravity field have been the subject of extensive investigations though it is now recognized that earthquakes cannot excite the chandler wobble and that they only drive a very modest secular drift of the earth s spin axis their rotational signatures present some intriguing peculiarities in fact they preferentially drive the rotation axis toward a well defined direction i e 0 140oe and systematically induce negative variations of the earth s oblateness in the first part of this work the static dislocation theory is employed to ascertain the origin of these two remarkable trends this task is accomplished by considering the effects of seismicity on earth rotation during the last two decades we find that the above tendencies are operating even on a yearly time scale and we explain their nature by means of simple geometrical and physical arguments we also find that the trend of the pole toward 140oe is essentially due to the seismicity which characterizes the western pacific subduction zones the seismic excitation function takes for shallow thrust earthquakes a direction roughly opposite to the excitation function associated with mass injection along active subduction zones this point highlights the potential effects of aseismic mass rearrangement at subduction zones on the secular drift of the pole our findings based on a simple model of steady state subduction show that in the last two decades this process substantially acts to counterbalance the polar drift due to global seismic activity we verify that this balance between earthquake and subduction induced rotational signatures also characterizes the time variations of the dynamic oblateness which is intrinsically independent of the inertia changes that drive polar motion from these results which may potentially have some impact on the interpretation of long term polar motion we conclude that the pole of rotation cannot be significantly perturbed by tectonic motions on a decade time scale

from adria to africa driven orogenesis evidence from porphyroblasts in the betic cordillera spain abstract in order to unravel the kinematic evolution of the betic rif orogen we investigated the geometry of porphyroblast inclusion trails in the nevado filabride complex a high pressure unit situated at the base of the betic nappe stack a large number of quantitative orientation data for these microstructures and their mutual overprinting relationships reveal two age groups of inclusion trails in the study area with distinctive geographic trends coupled to a comprehensive compilation of field data in the study area these microstructures are shown to coherently witness the development of early ne sw trending structures and fabrics followed by younger nw se trending ones whereby the former experienced clockwise reorientations a major change in the direction of bulk crustal shortening from nw se to ne sw is inferred from these data and tentatively linked to the plate tectonic history of the mediterranean region paleomagnetic data indicate that prior to about 35 ma nw se convergence between adria eurasia and iberia produced orogenesis along a belt bordering greater iberia including sardinian and corsica and probably continuous in the alps brianconnais domain the roughly ne sw trend of this precursor appears to be preserved within porphyroblasts that grew during this period presumably due to the partitioning of deformation around them africa iberia relative motion had been mainly transcurrent until 35 ma azores transform but then rapidly changed to head on nne ssw convergence this gave rise to a second set of nw se trending structures which accompanied deformation of the precursor orogen into several oroclines western alps gibraltar and calabria arcs orogenic collapse and crustal extension initiated shortly after this transition in tectonic regime suggesting a causal relationship we propose that the waning of compressive stresses transmitted by adria and their substitution by a near perpendicular maximum stress direction resulting from africa eurasia convergence could have enhanced the sinking of a thick lithospheric root or roll back of a subducted slab which in turn would have provoked crustal extension and basin formation

a broadband p wave analysis of the large deep fiji island and bolivia earthquakes of 1994 the complex broadband p wave displacement recordings of the 570 km deep march 9 1994 mw 7 6 fiji island and the 660 km deep june 9 1994 mw 8 2 bolivia earthquakes are analyzed to estimate the spatial and temporal characteristics of their ruptures we model relative arrival times and amplitudes of coherent subevents in p waveforms and perform waveform analyses we resolve 1 short rupture durations relative to their seismic moments 12 and 40 s for the fiji and bolivia earthquakes respectively 2 small areas of main moment release for both earthquakes 30 40 km 3 high stress drops compared to shallow earthquakes with the stress drop of the bolivia event 283 mpa being significantly higher than the stress drop of the fiji event 26 mpa 4 small changes in mechanism up to 10 changes in fault plane orientation and 5 a steeply dipping rupture plane for the fiji earthquake and a shallowly dipping rupture plane for the bolivia earthquake details of the ruptures are difficult to resolve using teleseismic p waveforms

de bugging the millipede porphyroblast microstructure a serial thin section study and 3 d computer animation abstract seventy five spatially orientated serial thin sections cut from a single rock containing millipede porphy roblast microstructure from the robertson river metamorphics australia reveal thc three dimensional 3 dj geometry of oppositely concave microfolds ocms that define the microstructurc electronic animations showing progressive scrial sections of thc 3 d microstructurc arc made available via the world wide web the ocm amplitudes decrease regularly from a maximum in near central sections to a minimum in near marginal scctions whereas the ocm interlimb angles increase regularly from a minimum in near ccntral sections to a maximum in near marginal sections these observations illustrate that the ocms are noncylindrical surfaces with culminations located in near central scctions because the porphyroblast cores appear to have been present before significant development of the syn ocm foliation all of the ocms were formed by heterogcncous cxtension around thcse cores the overall gcometry of the ocms described hcre reflects the strain state and cannot be used to constrain defor mation paths

porphyroblast inclusion trails the key to orogenesis detailed microstructural analysis of inclusion trails in hundreds of garnet porphyroblasts from rocks where spiral shaped inclusion trails are common indicates that spiral shaped trails did not form by rotation of the growing porphyroblasts relative to geographic coordinates they formed instead by progressive growth by porphyroblasts over several sets of near orthogonal foliations that successively overprint one another the orientations of these near orthogonal foliations are alternately near vertical and near horizontal in all porphyroblasts examined this provides very strong evidence for lack of porphyroblast rotation the deformation path recorded by these porphyroblasts indicates that the process of orogenesis involves a multiply repeated two stage cycle of 1 crustal shortening and thickening with the development of a near vertical foliation with a steep stretching lineation followed by 2 gravitational instability and collapse of this uplifted pile with the development of a near horizontal foliation gravitational spreading near coaxial vertical shortening and consequent thrusting on the orogen margins correlation of inclusion trail overprinting relationships and asymmetry in porphyroblasts with foliation overprinting relationships observed in the field allows determination of where the rocks studied lie and have moved within an orogen this information combined with information about chemical zoning in porphyroblasts provides details about the structural metamorphic p t t paths the rocks have followed the ductile deformation environment in which a porphyroblast can rotate relative to geographic coordinates during orogenesis is spatially restricted in continental crust to vertical ductile tear transcurrent faults across which there is no component of bulk shortening or transpression

microfabric reconstruction via quantitative digital petrographic image analysis for weakly foliated gneisses abstract detection and documentation of petro structural features such as alignment features of minerals grains and extraction of such spatial property data are two fundamental steps for structural geology such tasks were mostly carried out manually however manual analysis is laborious and potentially biased these drawbacks are less obvious when the foliation is well developed and the amount of platy mineral is higher for samples with weakly developed foliation and low platy mineral content automatic method is required for subjective interpretation a semi automatic computerized method of 3d foliation orientation reconstruction via two dimensional petrographic shape fabric analysis from serial oriented digital microphotograph has been developed and demonstrated in this study the foliation is reconstructed by fitting a best fitting plane to the maximum modal peaks of micro textural parameters spo for different mineral groups of platy and granular minerals from each thin section on a stereonet for four coarse grained biotite gneiss samples collected along the jialie fault se tibet china regardless of platy or granular mineral aggregates the reconstructed foliations showed similar orientation within 10 angular variation to the field measurement the 10 angular variation can be maintained if the foliations are reconstructed by consecutive thin section groupings 50 angular intervals and a horizontal thin section the angular spread increased to 30 for thin section groupings with 50 to 100 angular intervals with a horizontal thin section major advantages of the computerized photometric methods demonstrated by this study are the reduction of human prejudice and obtaining quantified and repeatable data sets

non rotation of garnet porphyroblasts and 3 d inclusion trail data an example from the imjingang belt south korea abstract we describe non rotation of garnet porphyroblasts in non coaxially deformed metapelites of the imjingang orogenic belt in the middle korean peninsula the three dimensional geometry of inclusion trails within 1 2 mm garnet porphyroblasts was analyzed by serial polishing and reflected light microscopy most of the garnet porphyroblasts have straight inclusion trails of quartz and some plagioclase s i oblique to an external foliation s e serial polishing of two samples normal to mineral elongation lineation a plane and normal to s e and parallel to the lineation b plane with twenty intervals of about 0 1 mm reveals that the straight s i is a planar structure measurement of the angles between s i and s e on both planes from samples of sixteen outcrops shows that s i orientation of individual garnets is fairly constant in each sample the attitude of s i in geographic space determined by using its pitch angles on the a and b planes is more or less constant throughout the area over 6 5 km traversing normal to the strike of regional foliation the sense of asymmetry of strain shadows at the margin of garnet porphyroblasts and the s i s e relationship indicate rotation of s e rather than garnet porphyroblasts with respect to the geographic reference frame rotation of s e is also supported by a sense of shear inferred from other shear criteria all indicating a top up to the south shearing

toroidal poloidal partitioning of global post seismic deformation an earth model subject to dislocations is studied in order to investigate the toroidal poloidal content of global post seismic deformation differently from previous analyses our approach allows us to deal with some of the main complexities of the real earth such as sphericity self gravitation and rheological stratification the time dependent ratio between toroidal and poloidal displacements is evaluated in the near and far field of both strike and dip slip lithospheric sources characterized by a finite length our findings show that post seismic deformation changes its nature from poloidal to toroidal and viceversa on time scales of several decades and over distances comparable with the dimensions of the lithospheric plates the effects on horizontal velocities in north america of both poloidal and toroidal components induced by the alaska 1964 earthquake is comparable with the signatures due to postglacial rebound these two geodynamical phenomena are currently detectable by variations along baselines connecting vlbi stations

possible eastward extension of chinese collision belt in south korea the imjingang belt structural petrological and geochronological data from the middle korean peninsula indicate that the qinling dabie sulu collisional belt of east central china crosses the yellow sea and extends into the imjingang belt the yeoncheon complex first identified as the western imjingang belt comprises primarily north dipping metamorphic sequences 1 the northern jingok unit consisting of barrovian type metapelites and 2 the southern samgot unit consisting of calc silicate and amphibolitic rocks south vergent structures with reverse sense shearing are dominant in the jingok unit whereas late normal sense shearing is pervasive in the samgot unit and the deformed granitoid to the south these structural patterns are interpreted to correspond to extensional deformation associated with uplift following compression in a collisional belt pressure temperature p t estimates from the amphibolites suggest a high p amphibolite facies metamorphism 8 13 kbar and 630 790 c possibly evolving from eclogite facies conditions along a clockwise p t path sm nd and rb sr geochronological data suggest that the amphibolites emplaced in late proterozoic time were metamorphosed during permian triassic time

stress transfer and nonlinear stress accumulation at the north anatolian fault turkey an analysis is presented of the accumulation of stress along the north anatolian fault the analysis is based on the time dependent reloading of the plate boundary by using a modified elsasser model of a coupled lithosphere asthenosphere system

porphyroblast rotation during crenulation cleavage development an example from the aureole of the mooselookmeguntic pluton maine usa in the low pressure high temperature metamorphic rocks of western maine usa staurolite porphyroblasts grew at c 400 ma very late during the regional orogenesis these porphyroblasts which preserve straight inclusion trails with small thin section scale variation in pitch were subsequently involved in the strain and metamorphic aureole of the c 370 ma mooselookmeguntic pluton the aureole shows a progressive fabric intensity gradient from effectively zero emplacement related deformation at the outer edge of the aureole 2900 m map distance from the pluton margin to the development of a pervasive emplacement related foliation adjacent to the pluton the development of this pervasive foliation spanned all stages of crenulation cleavage development which are preserved at different distances from the pluton the spread of inclusion trail pitches in the staurolite porphyroblasts as measured in two dimensional 2 d thin sections increases nonlinearly from 16 to 75 with increasing strain in the aureole these data provide clear evidence for rotation of the staurolite porphyroblasts relative to one another and to the developing crenulation cleavage the data spread is qualitatively modelled for both pure and simple shear and both solutions match the data reasonably well the spread of inclusion trail orientations 40 75 in the moderately to highly strained rocks is similar to the spread reported in several previous studies we consider it likely that the sample scale spread in these previous studies is also the result of porphyroblast rotation relative to one another however the average inclusion trail orientation for a single sample may in at least some instances reflect the original orientation of the overgrown foliation

on the significance of foliation patterns preserved around folds by mineral overgrowth abstract simple inclusion trail geometries in porphyroblasts that vary symmetrically around folds suggest the porphyroblasts have rotated during folding however they do not provide proof that the porphyroblasts have rotated as such geometries may also form by overgrowth during folding this uncertainty results from the difficulty in establishing the relative ages of the fold and the porphyroblasts when the latter contain simple trails simple inclusion trail geometries in porphyroblasts that do not change around a fold remaining orthogonal to the axial plane from limb to limb suggest that the porphyroblasts have not rotated during folding however they can be rationalized as having rotated by arguing that synthetic rotation due to buckling has been exactly counterbalanced by antithetic rotation due to flexural flow if the folds vary in tightness from open to isoclinal and the trails still remain perpendicular to the axial plane this can still be rationalized by arguing for rotation during buckling balancing that due to flexural flow followed by coaxial deformation with no subsequent rotation tests of porphyroblast behaviour are only useful if they conclusively demonstrate that inclusion trail geometries around a fold are incompatible with rotation or alternatively non rotation of the porphyroblasts simple inclusion trail geometries in porphyroblasts that uniquely indicate a fold mechanism involving no rotation are those which remain parallel from limb to limb but lie oblique to the axial plane independent of limb angle particularly powerful indicators of folding mechanisms involving no porphyroblast rotation are folds containing two different porphyroblastic phases that preserve contrasting geometries for example rocks containing porphyroblasts preserving parallel trails from limb to limb in the earlier phase and symmetrically varying trails for the later phase such folds demonstrate that simple trails that vary symmetrically around a fold cannot be used as proof of porphyroblast rotation where the rotation axes of such simple inclusion trail geometries lie at a high angle to the axial plane and vary around the fold proof of porphyroblast rotation may be possible however such proof can be more readily provided using complex inclusion trails with an orthogonal and or truncational character that vary in orientation from limb to limb

porphyroblast non rotation during crustal extension in the variscan lys caillaouas massif pyrenees abstract the dominant foliation s 2 in the variscan lys caillaouas massif central pyrenees france spain formed in a subvertical orientation during crustal thickening d 2 subsequent non coaxial crustal extension produced a subhorizontal crenulation cleavage s 3 whereby s 2 was folded and rotated andalusite staurolite cordierite and biotite porphyroblasts grew very early during this extension d 3 and included s 2 as straight curved and weakly crenulated inclusion trails these inclusion trails exhibit a strong subvertical preferred orientation which is independent of the local magnitude of d 3 strain the dip angle of the external main foliation s 2 or the aspect ratio and shape orientation of porphyroblasts this indicates that porphyroblasts did not rotate in the d 3 deformation field and hence preserve the orientation of s 2 at the time it was trapped in the porphyroblast relative to the bulk d 3 flow plane porphyroblasts could maintain a stable orientation in the d 3 flow due to complete accommodation of the bulk flow vorticity by heterogeneous shear strain the lack of vorticity of local volumes of zero shear strain such as porphyroblasts was balanced by concentration of shear strain in planar zones anastomosing around them it is likely that s 2 maintained a subhorizontal orientation throughout the d 3 crustal extension which would imply that porphyroblasts also remained stationary relative to the earth s surface during d 3 whereas s 2 in the deforming matrix experienced shear induced rotation a late brittle ductile folding event d 4 involving differential rigid block rotations dispersed the orientation of inclusion trails to some degree these late rotations could be corrected for by artificial unfolding of the f 4 folds

distribution of pre folding linear indicators of movement direction around the spring hill synform vermont significance for mechanism of folding in this portion of the appalachians abstract three distinctly oriented sets of pre folding and one set of syn folding axes of curved inclusion trails are preserved in garnet porphyroblasts in 50 samples around the doubly plunging spring hill synform in southeast vermont over one third of the samples contain consistent changes in the trend of these axes from the core to rim since the core grew before the rim this enabled the relative timing of each set of axes to be determined from the oldest to the youngest as ne sw e w nnw sse and nne ssw the youngest trend is parallel to the axial plane of the regional folds only those samples with the latter trend have their inclusion trails connected continuously to the matrix foliation the three pre folding sets of axes have the same orientation on both limbs this consistency in orientation has significant implications for the processes operating during folding and three mechanisms are presented that could potentially explain it these involve the classic card deck model of shear folding de sitter s model of clay bricks shortening as they shear past one another and the progressive bulk inhomogeneous shortening model the relative merits of each of these models are discussed

evidence for static displacements from the june 9 1994 deep bolivian earthquake the 1994 bolivian earthquake mw 8 3 was recorded on scale by 8 very broadband stations deployed approximately 600 km south of the epicenter when these seismograms are carefully converted to ground displacement there appears to be a static offset which is on order of 2 cm we have modeled the waveforms with a synthetic waveform method that contains near intermediate and far field terms although the synthetics are only calculated for an elastic half space they compare favorably with the observed waveform in terms of shape however the theoretical amplitude is 1 2 of the observed static offset which probably reflects the limitations of a homogeneous half space model and or the instabilities in deconvolution

the kinematic interpretation of obliquely transected porphyroblasts an example from the trois seigneurs massif france abstract obliquely transected porphyroblasts otps contain a straight inclusion pattern that is continuous with the external foliation but oblique in orientation otps are interpreted to form by porphyroblast growth between two phases of deformation the obliqueness of the inclusion pattern and external foliation is due to the second deformation phase and has been variously explained by porphyroblast rotation in the kinematic reference frame of bulk flow or by foliation rotation around a stationary porphyroblast the two models imply opposite sense of vorticity also loosely referred to as sense of shear to produce the same geometry and their relevance should be known if otps are to be used as sense of vorticity indicators andalusite otps in the trois seigneurs massif french pyrenees have a spool shape in three dimensions that is interpreted to result from passive overgrowth of andalusite on a spaced s 2 cleavage subsequent non coaxial d 3 flow led to development of an s 3 crenulation cleavage and the otp geometry although the porphyroblasts rotated rotation of the foliation in the kinematic reference frame of bulk flow was mainly responsible for the otp geometry this example shows that otps can indeed develop by foliation rotation in non coaxial flow similar looking otps can apparently develop in flows with opposite sense of vorticity depending on whether foliation or porphyroblast rotation is dominant the dominance of either development mechanism depends on the importance of flow partitioning and solution transfer during progressive deformation

the internal inclusion trail geometries preserved within a first phase of porphyroblast growth the inclusion trail geometry within a first phase of porphyroblast growth can differ significantly from that preserved by further enlargement because the porphyroblast forms a rigid mass up against which the rock preferentially strains during ensuing events the geometry of the first overgrown inclusion trails is affected by their primary orientation including any pre existing curvature combined with any heterogeneous rotation of this foliation about the developing stretching lineation this can impact the apparent timing of foliation intersection inflection axes preserved within porphyroblasts fias that nucleated during the development of a sub horizontal foliation but is readily resolved 3 d computer analysis of sigmoidal inclusion trails reveals that the asymmetry method for fia determinations is unaffected by the cut location relative to the porphyroblast core significantly perfect spiral inclusion trail geometries can be produced from a sigmoidal shape in cuts up 30 away from the fia therefore since fias in most porphyroblasts bear no relation to matrix structures there is a 17 chance that thin sections cut relative to the foliation lie within 30 of a fia and could contain such an apparent spiral fias maintain consistent trends for the first phase of porphyroblast growth accompanying horizontal bulk shortening but may vary in plunge fias have sub horizontal plunges for porphyroblasts nucleating during gravitational collapse but may vary in trend for all periods of porphyroblast regrowth the data available indicates that fias remain consistently trending and sub horizontal until the relative direction of plate motion causing orogenesis changes

conjugate shear folding a model for the relationships between foliations folds and shear zones abstract microstructural mapping of whole thin sections cut from two samples of micaschist containing cm scale folds plus garnet porphyroblasts has provided new insight in the relationships between folding shearing and foliation development the garnets exhibit coherent inclusion trail patterns that place important constraints on the kinematic development of both samples which are shown to be representative of coaxial versus non coaxial deformation in rocks containing a pre existing schistosity a comparison of crenulations cleavages geometries in both samples and a review of the geometry of natural and experimental multilayer folds leads to the conclusion that folding involves conjugate shearing at different scales at microscopic scales crenulation cleavages nucleate as conjugate kink or shear instabilities and develop further as a function of the macroscopic partitioning of deformation in fold hinge domains bulk coaxial deformation results in equal development of conjugate crenulations that progressively coalescence into symmetrical crenulation patterns so that macroscopically parallelism is achieved between foliation fold axial planes and long axes of strain ellipses fold limb domains represent a system of conjugate shear zones where single sets of crenulation instabilities with synthetic shearing component preferentially develop producing oblique relationships between the aforementioned elements cleavage fanning is inferred as a direct consequence of this conjugate shear origin of folds the model implies that crenulation cleavages and s c fabrics in shear zones form by analogous processes in both cases involving a component of shearing along foliation planes the development of conjugate sets of foliation planes surrounding porphyroblasts during early relatively coaxial stages of deformation explains continued gyrostatic behaviour during more advanced non coaxial stages as indicated by consistently oriented inclusion trails in the studied samples

an approach to modeling present day deformation in southern california this paper presents an approach to modeling the complete time dependent deformation in southern california we make use of a variety of techniques to include the far field plate motion stress relaxation in the asthenosphere aseismic fault slip within the elastic lithosphere and the complex three dimensional nature of the faults within the southern california region among the conclusions of the work here are the following 1 the data exhibit a marginal preference for a relatively thin lithosphere in southern california 2 the most sensitive determinant for lithospheric thickness and viscosity of the asthenosphere is the rotation rate of the motion vectors toward or away from major faults 3 the major faults in southern california are slipping at depth at or near their average holocene rates 4 a shallow active decollement beneath the transverse ranges is apparently needed to realistically model the strain changes observed there and 5 this modeling technique offers the best approach for understanding the complex deformation field in southern california

unravelling the spirals a serial thin section study and three dimensional computer aided reconstruction of spiral shaped inclusion trails in garnet porphyroblasts seventy seven spatially orientated serial thin sections cut from a single rock reveal changes in the geometry of spiral shaped inclusion trails sslts in garnet porphyroblasts the observed sits are doubly curved non cylindrical surfaces with total inclusion trail curvature decreasing systematically from the cores to the rims of porphyroblasts the three dimensional geometry of the ssits reconstructed with the aid of computer graphics shows that the orientations of spiral axes defined by the ssits are not related in any expected nor predictable way to the main foliation in the matrix this suggests continued deformation after or during the latest stages of porphyroblast growth which has important implications for the use of ssits as shear sense indicators whether the formation of ssits involves significant porphyroblast rotation with respect to a geographically fixed reference frame cannot be determined from the available data key wocds computer graphics garnet porphyroblasts serial thin sections spiral shaped inclusion trails three dimensional reconstruction

measurement of horizontal motions in alaska using very long baseline interferometry we have analyzed 6 years of very long baseline interferometry vlbi data beginning in 1984 from a network of sites in alaska the yukon and the conterminous united states the analysis of these 53 data sets includes constrained continuous piecewise linear estimation of the site atmospheres and clocks application of values and correlations from a self consistent earth orientation series derived from other vlbi data and simultaneous estimation of site positions and velocities from a solution that includes 21 007 observations with a fit of 40 ps in delay and 64 fs s in delay rate we have determined the horizontal velocities of seven sites with precisions of 0 5 2 mm yr 1 standard deviation the three vlbi sites within the alaska aleutian subduction boundary zone yakataga kodiak and sand point have higher instantaneous velocities relative to eastern north america than the interior sites of alaska fairbanks and sourdough the estimated velocity of yakataga relative to fairbanks is 37 8 1 3 mm yr at n27 w 2 modeling of the yakataga data suggests that the observed motion is the result of elastic straining of the overriding plate due to a locked main thrust zone with a component of oblique slip the estimated velocity of kodiak relative to fairbanks is 13 6 0 8 mm yr at n41 w 3 this result is lower than the rate predicted on the basis of simple elastic dislocation models the estimated velocity of sand point relative to fairbanks is 6 4 0 9 mm yr at n65 w 8 the component of this velocity in the plate direction 3 5 1 1 mm yr is not consistent with either an aseismic slip model i e no strain accumulation in the overriding plate or a model in which the site is undergoing compressional strain 10 9 mm yr at n28 w due to simple subduction at the predicted orientation of pacific plate convergence in a north america fixed reference frame the estimated velocities of fairbanks 1 5 0 5 mm yr at s12 e 20 and sourdough 3 9 1 0 mm yr at s13 w 13 are both southward these results may imply motion of this region relative to stable north america but more observations are required to reduce the uncertainties in the azimuths the time evolution of the estimated site positions from vlbi in alaska are in general consistent with constant velocity however in 1988 the yakataga site showed a significant departure from the position predicted from a constant velocity model obtained from the previously estimated position this departure may be static displacement associated with two major strike slip earthquakes that occurred in the gulf of alaska between the 1987 and 1988 measurement sessions

postseismic deformation in chile constraints on the asthenospheric viscosity by means of a spherical earth model with maxwell rheology an analysis of the postseismic deformation field due to the viscoelastic relaxation of the mantle and asthenosphere following the great 1960 chile earthquake is performed due to the exceptional energy release of that earthquake geomorphological evidences of postseismic deformation are available in a broad area surrounding the rupture zone the comparison of the synthetic results with the available data allows to put some constraints on the viscosity of the asthenosphere beneath the chilean region values between 8 1019 and 1020pa s are compatible with the available postseismic deformation field data

the mechanism of the deep bolivia earthquake of june 9 1994 we analyzed the iris broad band seismograms for the june 9 1994 bolivia earthquake the largest deep focus earthquake ever recorded we inverted the record sections with a duration of 330 sec which include p pp and sp phases and obtained a dip slip mechanism dip rake strike 13 4 1 or 89 103 95 with a scalar moment of mo 2 9 10 21 nm mw 8 2 this mechanism is similar to that obtained from long period 175 to 250 sec rayleigh and love waves 83 100 90 mo 3 0 10 21 nm mw 8 3 the main rupture was preceded by about 10 sec by a cluster of smaller events with a total moment of 1 2 10 20 nm mw 7 3 the main rupture starts at about 20 km east or northeast of the initial break and propagates horizontally in the east to northeast direction the source duration is 40 sec and the rupture dimension is about 40km if a fault area of 40 40km is assumed the stress drop is 110 mpa an inversion of body waves p pp and sp with 6 basis moment tensors yielded a best fit solution with a 10 implosive component this result is of marginal significance and its confirmation would require more detailed information on the structures near the source region pp bounce points and stations the observed amplitude of the radial mode 0s 0 1226 sec is consistent with a double couple model with less than 2 isotropic component

the effects of post seismic motions on the moment of inertia of a stratified viscoelastic earth with an asthenosphere summary we give the analytical formulation for calculating the transient displacement of fields produced by earthquakes in a stratified selfgravitating incompressible viscoelastic earth we have evaluated the potential of viscous creep in the asthenosphere in exciting the chandler wobble by a four layer model consisting of an elastic lithosphere a two layer maxwell viscoelastic mantle and an inviscid core the seismic source is modelled as an inhomogeneous boundary condition which involves a jump condition of the displacement fields across the fault in the lithosphere the response fields are derived from the solution of a two point boundary value problem using analytical propagator matrices in the laplace transformed domain transient flows produced by post seismic rebound are found to be confined within the asthenosphere for local viscosity values less than 1ozop the viscosity of the mantle below the low viscosity channel is kept at 1oz2p for low viscosity zones with widths greater than about 100 km and asthenospheric viscosities less than lo p we find that viscoelasticity can amplify the perturbations in the moment of inertia by a factor of 4 5 above the elastic contribution within the time span of the wobble period we have carried out a comparative study on the changes of the inertia tensor from forcings due to surface loading and to faulting in general the global responses from faulting are found to be much more sensitive to the viscosity structure of the asthenosphere than those produced from surface loading

global postseismic rebound of a viscoelastic earth theory for finite faults and application to the 1964 alaska earthquake a spherically symmetric earth model with viscoelastic rheology is used to study the postseismic rebound associated with finite lithospheric dislocations we perform a systematic study of surface deformations due to sources characterized by two and three dimensional faults modeled by a linear and planar distribution of point sources our approach is based on the normal mode technique for a layered earth with linear viscoelastic rheology and allows for a self consistent description of the time evolution of postseismic displacements due to strike and dip slip faults as a case study we compare the predicted horizontal displacements due to the 1964 alaska earthquake with very long baseline interferometry vlbi baselines changes observed in this region in the period 1984 1989 although subduction and postglacial isostatic adjustment are expected to contribute significantly to present day velocities our results show that the postseismic rebound due to the 1964 alaska earthquake plays a relevant role in the changes of several vlbi baselines the last section is devoted to the analysis of the evolution of other north american baselines as suggested by recent investigations based on forward approaches isostatic readjustment of the earth s crust in response to the melting of the last pleistocene ice sheets is a major contributor to baseline variations in this area our results indicate that a correct interpretation of vlbi baseline changes in north america should account also for the effects of postseismic deformation

porphyroblast inclusion trail orientation data eppure non son girate extensive examination of large numbers of spatially orientated thin sections of orientated samples from orogens of all ages around the world has demonstrated that porphyroblasts do not rotate relative to geographical coordinates during highly non coaxial ductile deformation of the matrix subsequent to their growth this has been demonstrated for all tectonic environments so far investigated the work also has provided new insights and data on metamorphic structural and tectonic processes including 1 the intimate control of deformation partitioning on metamorphic reactions 2 solutions to the lack of correlation between lineations that indicate the direction of movement within thrusts and shear zones and relative plate motion and 3 a possible technique for determining the direction of relative plate motion that caused orogenesis in ancient orogens

postseismic relaxation theory on the spherical earth abstract postseismic displacements and strains observed at the earth9s surface can be explained through the relaxation of a viscoelastic asthenosphere underlying a purely elastic crust a theory is presented for modeling the effects of postseismic relaxation on a spherically symmetric earth for an earthquake point source located in the upper elastic layer the displacement field is decomposed into its toroidal and spheroidal components a linear maxwell rheology in the viscoelastic layers is assumed enabling the use of the correspondence principle for the solutions of the equations of static equilibrium displacement and strain fields are then calculated using normal mode summation computational results are presented for two simple earthquake sources a strike slip fault and a uniaxial thrust fault the patterns of postseismic displacements and strains are found to depend strongly on both the earth model and earthquake source geometry in particular the elastic plate thickness asthenosphere thickness fault type and fault length each play a major role in determining the spatial pattern of postseismic relaxation effects asthenospheric viscosity controls the temporal pattern of relaxation

parageneses and th u distributions among allanite monazite and xenotime in barrovian type metapelites imjingang belt central korea the paragenetic relationships and th u distributions among allanite monazite and xenotime were investigated in a progressive sequence of garnet to kyanite zone metapelites of the imjingang belt korea allanite is predominant in the garnet and staurolite zones whereas monazite and xenotime predominate in the kyanite zone epidote grains in the lower garnet zone are commonly zoned from allanite core to relatively y rich rare earth element ree epidote to clinozoisite rim although both ree epidote and clinozoisite disappear in higher grade metapelites moreover allanite and ree epidote often contain minute inclusions of thorium silicate the isogradic distributions and similarity of ree patterns between allanite and monazite suggest that the latter has grown at the expense of the former in addition the discontinuous th zoning in monazite is apparently inherited from heterogeneous th distribution and thorium silicate inclusions in allanite thus thorium silicate possibly provided the additional th and u necessary for the monazite formation paragenetic relationships of allanite and monazite inclusions within various index minerals suggest that at amphibolite facies conditions allanite is stable at higher pressures than monazite xenotime grains in the staurolite zone are rarely produced by the breakdown of clinozoisite and ree epidote whereas those in the kyanite zone are grown primarily at the expense of garnet incorporation of th and u into monazite and xenotime is governed mainly by the brabantite and thorite substitutions respectively taken together our results suggest that the allanite to monazite transformation is primarily responsible for the distributions of rees th and u among metapelitic phases and that the xenotime formation was facilitated by the contribution from major silicates particularly garnet

sediment deposition in offshore deeps of the western north sea questions for models a three dimensional hydrodynamic model is used to investigate the potential for offshore bathymetric deeps in the north sea to act as fine sediment traps simple conditions are established representative of the observed conditions and the response of the model investigated two deeps are considered here inner silver pit and sole pit the model study suggests that in inner silver pit deposition of fine sediment is only possible under weak tidal neap flows under all other conditions the flow is too energetic to allow deposition a transport path for fine sediment across inner silver pit is established but does not significantly modify the sediment dynamics in the pit experiments including wave action show that 50 year return period waves induce bed shear velocities sufficiently large to remove coarse sediment for sole pit a cycle of deposition followed by erosion at spring tides will inhibit deposition in the pit long term accretion of fine sediment does not seem possible in either pit

preferred orientation of planar microstructures determined via statistical best fit of measured intersection lines the fitpitch computer program the fitpitch computer program allows characterisation of preferred orientation of planar microstructures in a rock from the orientations of their intersection lines on different sections measured pitch or strike angles of such intersection lines are fitted to the theoretical intersection lines of a single model plane or a combination of two or three model planes the degree of fit is quantified in terms of the deviation between natural and theoretical intersection lines normalised by uniform data a first application is described concerning porphyroblast inclusion trails whose orientation in 28 samples from the variscan iberian massif was measured analysis of these data illustrates how the method can be used to quantify preferred orientation of relict foliations contained in a group of porphyroblasts and how this complements existing techniques for determining foliation intersection axes fia in porphyroblasts a second described application deals with previously published orientation data for microfracture trace lines in quartz grains of a variscan granite in the rhine graben qualitatively established best fit planes derived originally from this data are compared with the numerically established planes using the fitpitch program and discussed in terms of the advantages and potential limitations of the method q 2002 published by elsevier science ltd

faulting associated with large earthquakes and the average rate of deformation in central and eastern asia we determine approximate average rates of deformation in portions of eastern and central asia for the last 80 years these rates are based on estimates of source dimensions average displacements seismic moments and orientations of faults of all large earthquakes m 7 5 and as many other major earthquakes m 7 0 as possible in asia since 1900 a major part of this study is the compilation of these data for separate parts of asia we combine seismic moment tensors to estimate the average rotational strain or deformation tensors for these regions for the last 80 years we estimate that shortening across the tien shan has occurred at 11 mm yr between 5 and 19 mm yr left lateral shear on easterly trending planes in mongolia in northwestern tibet gansu and ningxia and on the xianshuihe fault in western sichuan has been very rapid more than 10 mm yr in each region and apparently as rapid as 40 mm yr in northwestern tibet gansu and ningxia slower rates of a few to 10 mm yr appear to characterize east west extension and conjugate north south shortening of tibet the earthquake history of the himalaya is consistent with rates of underthrusting of more than 10 mm yr but is probably less than the convergence rate of india with eurasia of about 50 mm yr the overall strain field is consistent with a large part of india s penetration into eurasia being absorbed by the extrusion of material out of india s way as a result southeast china moved at about 21 mm yr east southeast with respect to eurasia in the last 80 years with an uncertainty of about a factor of 2 in this estimated rate

porphyroblast rotation eppur si muove in a number of recent papers the theory has been postulated that porphyroblasts as a rule do not rotate with respect to geographical coordinates and can be used to determine the original orientation of older foliations complex inclusion patterns in spiral garnets have even been used to advocate a new model of orogenesis involving several alternating phases of horizontal shortening and extension critical assessment of the assumptions and data used to support the theory of irrotational porphyroblasts reveals numerous flaws millipede structures used as proof for flow partitioning can also form by other flow geometries evidence quoted to support irrotational behaviour of porphyroblasts is unsound porphyrobl asts do occur in sets with a preferred orientation of the internal foliation trace but these cannot be shown to represent original orientations microstructures which resemble truncation planes in spiral garnets are used as evidence that these structures developed by several phases of deformation and as proof for periodic extension and horizontal shortening in orogenesis they can however also be explained by intermittent growth of a rotating porphyroblast during a single phase of deformation finally porphyroblast sets in which orientation is a function of aspect ratio indicate that porphyroblast rotation with respect to kinematic axes does occur in at least some situations

fine sediment sources and sinks around the east anglian coast uk the cliffs of norfolk and suffolk yield an average of 785 000 tonnes t of fine sediments to the coastal zone annually east anglian rivers yield very little 5500 t a 1 but those of the wash produce about 100 000 t a 1 by contrast the region is dominated by 1 4 l0 6 ta 1 input from cliff erosion in holderness accumulation in vertical accretion alone of the coastal marshes of east anglia the wash north lincolnshire and the humber requires 1 12 10 6 t a 1 of fines progradation around the wash probably accounts for another 1 1 10 6 t a 1 the east anglian area including the wash is thus sufficient to trap over half the regional mud input from flamborough head to the north side of the thames estuary and could take it all depending on assumptions involved in calculation

the 1994 bolivia and tonga events fundamentally different types of deep earthquakes the 1994 bolivia and tonga events show large differences in source and aftershock properties the bolivia earthquake characterized by high stress drop slow rupture propagation and a weak aftershock sequence appears similar to other large deep earthquakes that are isolated from active seismic zones including the 1970 colombia earthquake in contrast the 1994 tonga event showed stress drop rupture propagation velocities and an aftershock sequence similar to that found for shallow earthquakes the aftershock sequence of the 1994 tonga event is many times stronger than has been observed for any other deep earthquake a survey of deep earthquake aftershocks suggests that aftershock occurrence is correlated with the overall subduction zone magnitude frequency relation b value the largest deep events occur in isolated regions lacking smaller earthquakes or in subduction zones characterized by anomalously low b values the 1994 tonga event is an exception and is the largest deep earthquake to occur within an active subduction zone showing a large b value perhaps explaining the strong aftershock sequence the bolivia and tonga events may represent end members of a population of deep earthquakes showing exceptional diversity in source properties or they may represent two fundamentally different types of deep earthquakes perhaps resulting from different physical mechanisms

time dependent residual deformations associated with the june 9 1994 bolivia earthquake by means of a spherical earth model with maxwell rheology we compute the coseismic and the postseismic displacements associated with the june 9 1994 bolivia earthquake our results are compared with the coseismic uplift detected by an array of broadband seismic stations in southern bolivia and with previous theoretical predictions our solution method has been recently employed to study the global deformations due to large lithospheric earthquakes in contrast to purely elastic earth models our method includes the time dependent effects associated with mantle relaxation the results presented here show that the surface deformation due to a deep focus earthquake are sensibly magnified by the delayed viscoelastic mantle relaxation the time scales which characterize mantle relaxation and the time evolution of surface observables depend on the rheological profile of the upper mantle and particularly on the thickness of the viscoelastic asthenosphere

global postseismic gravity changes of a viscoelastic earth a spherically symmetric earth model with a viscoelastic mantle and an inviscid core is used to study the gravitational perturbation due to a lithospheric shear dislocation in the coseismic and postseismic regime our approach is based on a quasi static solution of the equilibrium equations taking advantage of the normal mode technique for a layered incompressible earth with linear viscoelastic rheology we perform a systematic study of space and time evolution of gravity changes associated with a wide selection of seismic sources investigating the effects of several different mantle viscosity profiles our results show that the gravitational signal is sensitive not only to the viscosity of the asthenosphere but also to that of the mantle including the portion below the 670 km discontinuity as a case study we compute the coseismic and postseismic gravity perturbation due to the 1964 alaska earthquake the last section is devoted to the analysis of the postseismic relaxation rates of the gravitational perturbation following that earthquake for several different viscosity profiles of the mantle our results show that experimental attempts to obtain reliable detection of static and quasi static gravitational perturbation associated with seismic events would be of great importance in understanding the dynamic and viscosity profile of both upper and lower mantle

partitioning of deformation along an orogen and its effects on porphyroblast growth during orogenesis an identical succession of foliation inflection intersection axis trends in porphyroblasts fias is present in three separate areas affected by acadian deformation and metamorphism along 130 kms of the appalachians from east central vermont to north central massachusetts the fias trend successively nw se sw ne w e nnw sse and ssw nne and appear to have formed during the same succession of deformations which have been dated in se vermont as follows not yet dated pre 425 ma 425 to 404 ma 404 to 385 ma and 385 to 360 ma respectively the two areas that are furthest apart in east central vermont and north central massachusetts have strikingly similar total distributions of fias in garnet porphyroblasts that show a somewhat inverse relationship to those observed in the chester athens dome area of se vermont that separates them that is the number of samples containing the first formed fia set is greatest for the two regions lying furthest apart and decreases in younger sets whereas the number of samples containing the first fia set is the least in the central region and increases for more recently developed sets partitioning of deformation into zones of progressive shearing and shortening has been demonstrated to control the sites of development of differentiated crenulation cleavage versus porphyroblast growth and sites of porphyroblast growth on one limb of a regional fold versus the other we argue that partitioning of the deformation around competent feldspathic gneiss bodies at an orogen scale produced the variation in the number of samples containing the various fia sets between the central and outer areas described above porphyroblasts most commonly grew during sw ne directed shortening to the north and south of the chester athens dome region of the appalachians but only rarely grew in the latter region this suggests that deformation at this time partitioned around an outlier of competent basement feldspathic gneiss that underlies the chester athens dome region and this protected the rocks above and in the strain shadow to the nw and se from the effects of the great bulk of the deformation that occurred over the period of time during which nw se trending fias formed we attribute the increase in the number of samples containing progressively younger fias in the chester athens dome area during subsequent periods of nw se n s wsw ene and wnw ese directed shortening to the rise in temperature and pressure recorded in the rocks above the chester athens dome with peak conditions occurring during the development of the nnw sse oriented fia set between 404 and 385 ma as the temperature and pressure increased the gneiss below would have become less competent allowing the deformation associated with the succession of fia sets to partition more pervasively through the dome core this provided more sites for porphyroblast nucleation and growth and hence the number of samples recording these fia sets increased the concomitant decrease in the number of samples in which porphyroblasts grew in the rock within the areas to the north and south with successive fias possibly resulted from a progressive increase in competency of these rocks as the number of porphyroblasts increased

lack of porphyroblast rotation in noncoaxially deformed schists from petrel cove south australia and its implications abstract inclusion trails representing an s 1 cleavage demonstrate the lack of porphyroblast rotation during subsequent highly non coaxial deformations the pelitic schists of the kanmantoo group at petrel cove south australia contain two generations of porphyroblasts the first one consists of cordierite porphyroblasts that formed early in d2 and contain straight to slightly sigmoidal inclusion trails of s 1 the second generation consists of andalusite porphyroblasts that overgrew crenulated s 2 late during d3 several hundred inclusion trail traces from cordierites measured from oriented specimens taken throughout a strongly folded area show a horizontal great circle distribution when plotted and contoured on a stereographic projection hence s 1 was planar and horizontal prior to d2 s 1 measurements on limbs and hinges of a mesoscale d2 foldpair show that folding had little effect on porphyroblast orientation as the s 1 orientation remained constant and subhorizontal around the fold hence porphyroblasts have not rotated during any of the non coaxial deformations accompanying and following their growth this is interpreted as a result of the partitioning of the deformation around them s 1 in the matrix has been totally destroyed by the formation of s 2 as a fully differentiated crenulation cleavage what has previously been regarded as inconsistent senses of shear recorded by porphyroblasts around folds is resolved by the fact that the matrix foliation rotated rather than the porphyroblasts due to the effects of deformation partitioning the presence of a subhorizontal s 1 foliation suggests horizontal movements e g thrusting or detachment faulting during the earliest phase of the adelaidian orogeny

a new method for the computation of global viscoelastic post seismic deformation in a realistic earth model i vertical displacement and gravity variation summary we introduce a new method by which to compute global post seismic deformation psd in a spherically symmetric self gravitating viscoelastic earth model previous methods are based on simplified earth models that neglect compressibility and or the continuous variation of the radial structure of earth this is because the previous mode summation technique cannot avoid intrinsic numerical difficulties caused by the innumerable poles that appear in a realistic earth model that considers such effects in contrast the proposed method enables both of these effects to be taken into account simultaneously we carry out numerical inverse laplace integration which allows evaluation of the contribution from all of the innumerable modes of the realistic earth model using this method a complete set of green s functions is obtained including functions of the time variation of the displacement gravity change and the geoid height change at the surface for strike slip dip slip horizontal and vertical tensile point dislocations as an earth model we employ the preliminary reference earth model prem and a convex viscosity profile further we investigate the effects of fine layering of the viscoelastic structure and compressibility on a time series of psd using the green s function for a dip slip fault the result indicates that the effect of increasing number of layers is saturated at several tens of layers even when compressibility is taken into account and that the effect of compressibility is detectable with modern observational techniques for a shallower large earthquake mw 8 as an application the psd due to the sumatra andaman islands earthquake mw 9 3 is estimated we show that the rate of post seismic vertical displacement and gravity change is possibly detected in the far field where the epicentral distance exceeds 400 km