the location and source parameters of the lompoc california earthquake of 4 november 1927 in this paper we address the relocation magnitudes and the style of faulting of the lompoc earthquake from a sparse assortment of teleseismic and regional seismograms the highest quality teleseismic waveform data come from a station at de bilt netherlands that remains in operation thus recordings of numerous modern events in central coastal california i e the 1969 santa lucia banks 1983 coalinga 1978 santa barbara and 1989 loma prieta earthquakes have been used for comparison with the 1927 records location constraints for the lompoc event were established from the de bilt recording by comparing s p and sss s waveform matches against the above master events to avoid the effect of unknown clock errors on locations that use absolute times these same seismograms were modeled to estimate the depth faulting parameters and source strength a similar approach using observational comparisons and numerical modeling was applied to the regional waveform data obtained from the stations at berkeley tucson and pasadena our results indicate a north northwesterly striking reverse event located about 40 km west of point conception which is in excellent agreement with the recent tsunami modeling results by satake and somerville 1992 this location is 25 km south of that proposed by hanks 1979 and well within his error bars we obtain a body wave moment of 1 10 26 dyne cm a trapezoidal time history of 2 2 2 sec and a source depth of 10 km the weak beginning of the pnl wavetrain at berkeley indicates some source complexity which is characteristic of many large events the fault parameters are strike n20 w dip 66 ne and rake 95 most seismicity catalogs report a m s 7 3 for this event after gutenberg and richter 1956 but this was a long period body wave magnitude and not a surface wave result their original worksheets indicate a smaller ms 7 0 the body waves of the loma prieta event m s 7 1 appear distinctly larger than those of the lompoc event at de bilt in agreement with our lower estimate of source strength

estimating locations and magnitudes of earthquakes in southern california from modified mercalli intensities modified mercalli intensity mmi assignments instrumental moment magnitudes m and epicenter locations of thirteen 5 6 m 7 1 training set events in southern california were used to obtain the attenuation relation mmi 1 64 1 41 m 0 00526 h 2 63 log h where h is the hypocentral distance in kilometers and m is moment magnitude intensity magnitudes m i and locations for five 5 9 m 7 3 independent test events were consistent with the instrumental source parameters fourteen historical earthquakes between 1890 and 1927 were then analyzed of particular interest are the m i 7 2 9 february 1890 and m i 6 6 28 may 1892 earthquakes which were previously assumed to have occurred near the southern san jacinto fault a more likely location is in the eastern california shear zone ecsz these events and the 1992 m 7 3 landers and 1999 m 7 1 hector mine events suggest that the ecsz has been seismically active since at least the end of the nineteenth century the earthquake catalog completeness level in the ecsz is m 6 5 at least until the early twentieth century online material figures and table of empirical mmi site corrections

orogen parallel flow during continental convergence numerical experiments and archean field examples using triaxial numerical experiments we investigated the evolution of the state of stress and that of the bulk instantaneous and fi nite strain during ongoing convergence and subsequent progressive tectonic unloading of a warm and buoyant continental lithosphere various unloading histories of the driving tectonic force were considered as the tectonic force progressively declines the instantaneous strain evolves from plane strain to horizontal constriction in a direction perpendicular to that of convergence and fi nally to horizontal fl attening during the progressive unloading of the tectonic force driving convergence bulk constrictional strain accommodates the release of accumulated gravitational stress the decline of the triaxial strain rates to low values reduces the potential for the orogen parallel linear fabric to be erased by horizontal fl attening this is confi rmed by the fi nite strain ellipsoid that evolves toward plane strain with a long axis parallel to the orogen in the ca 2 5 ga gawler and terre adelie cratons we have identifi ed a well preserved and widespread horizontal linear fabric as suggested by our numerical experiments we associate the development of this linear fabric with the waning stages of late archean convergence

continental crust composition constrained by measurements of crustal poisson s ratio deciphering the geological evolution of the earth s continental crust requires knowledge of its bulk composition and global variability the main uncertainties are associated with the composition of the lower crust seismic measurements probe the elastic properties of the crust at depth from which composition can be inferred of particular note is poisson s ratio this elastic parameter can be determined uniquely from the ratio of p to s wave seismic velocity and provides a better diagnostic of crustal composition than either p or s wave velocity alone1 previous attempts to measure have been limited by difficulties in obtaining coincident p and s wave data sampling the entire crust2 here we report 76 new estimates of crustal spanning all of the continents except antarctica we find that on average increases with the age of the crust our results strongly support the presence of a mafic lower crust beneath cratons and suggest either a uniformitarian craton formation process involving delamination of the lower crust during continental collisions followed by magmatic underplating or a model in which crust formation processes have changed since the precambrian era

mesozoic large scale lateral extrusion rotation and uplift of the tongbai dabie shan belt in east china the tectonic convergence between the south china block and qinling belt that occurred in mesozoic time was not homogeneous along strike it was mainly concentrated in the shengnongjia and hannan domes which formed a pair of indentors along which the south china block penetrated the qinling belt as a consequence the tongbai dabie shan belt the eastern part of the qinling orogenic belt may have undergone large scale eastward extrusion clockwise rotation and uplift as indicated by its boundary deformation features it was originally located beneath the narrowest part of the qinling belt where it underwent ultrahigh pressure metamorphism in the early triassic

constriction in a transpressive regime an example in the iberian branch of the ibero armorican arc abstract detailed strain analyses in the armorican quartzites have been performed in various places within the centro iberian zone of western europe the observed strain pattern shows that in the inner ibero armorican arc as well as near the hinge zone sinistral transpression produces constrictive ellipsoids in the outer arc away from the hinge zone the deformation regime produces plane strain to oblate strain ellipsoids some of these data clearly contradict existent kinematical models which associate constriction with transtension and consider transpression zones to generate oblate strain ellipsoids however newly developed models show that it is possible to obtain a wide range of finite strain ellipsoids in transpression zones if one takes account of lateral escape axial depression and volume change the geodynamic implications of the strain analyses suggest generation of constriction in a transpressive regime caused by lateral expulsion in front of the cantabrian indenter that produced the ibero armorican arc this mechanism was responsible for the variscan wrench component in western europe which was mainly sinistral in iberia and dextral in britanny in iberia the displacement by lateral escape was easily accommodated by subduction of the south portuguese terrane under the ossa morena zone of the iberian terrane

tracing the subducted oceanic crust beneath the central california continental margin results from ocean bottom seismometers deployed during the 1986 pacific gas and electric edge experiment large aperture seismic data were collected on several ocean bottom seismometers obs deployed along a deep crustal seismic profile that was shot across the central california continental margin the line of shots extends from the oceanic crust seaward of the santa lucia escarpment to the california coast near morro bay and crosses the santa lucia basin santa lucia bank santa maria basin and hosgri fault zone the obs data permit us to trace the subducted oceanic crust from seaward of the santa lucia escarpment to beneath the central part of the santa maria basin a complementary study using onshore recordings of the same shots extends the crustal model onshore just seaward of the santa lucia escarpment the oceanic crust is subhorizontal and covered by a thin layer of low velocity sediment the velocity 4 5 km s and gradient 1 20 1 25 km s km of the upper oceanic crust in this region are well determined and agree with earlier determinations of the crustal structure of the eastern pacific beneath the santa lucia escarpment and santa lucia basin the oceanic crust dips approximately 16 to the east it is overlain by material with a velocity that increases from 4 8 to 6 4 km s at a depth of 1 7 5 5 km below the seafloor beneath the santa lucia basin a low velocity zone may be sandwiched between the subducted crust and this shallow high velocity material which we interpret to represent obducted oceanic crustal material beneath the eastern edge of santa lucia basin the dip of the subducted oceanic crust decreases to less than 2 the configuration of the subducted crust in this region is consistent with imbrication of the subducted crust as suggested by others based on common midpoint reflection data beneath the central santa maria basin the top of the subducted oceanic crust is at a depth of about 14 16 km and the moho is at 19 21 km

exhumation of the ultrahigh pressure continental crust in east central china cretaceous and cenozoic unroofing and the tan lu fault the orogenic architecture of the world s largest ultrahigh pressure exposure the hong an dabie mountains of the triassic qinling dabie orogenic belt is dominated by cretaceous and cenozoic structures that contributed to its exhumation from 30 km depth cretaceous magmatic crustal recycling 50 for the entire dabie and heating 250 to 700 c were most prominent in dabie and exhumation magmatism and cooling were all controlled by cretaceous transtension exhumation was accomplished principally by an asymmetric cordilleran type extensional complex in the northern dabie northern orthogneiss unit between 140 and 120 ma at rates as fast as 2 mm yr and average horizontal stretching rates of up to 6 mm yr cretaceous reactivation occurred within a regional transtensional strain field as a result of far field collisions and pacific subduction the onset of crustal extension was preceded and possibly facilitated by a reheating of the hong an dabie crust 140 ma coeval with the onset of voluminous magmatism in eastern china 145 ma which resulted from a change in pacific subduction from highly oblique to orthogonal the tan lu continental scale fault was a normal fault zone in the mid cretaceous 110 90 ma and underwent 5 4 km dip slip and 4 km throw in the cenozoic during the india asia collision the qinling dabie belt acted as the structural discontinuity between the strike slip dominated escape tectonics south of the qilian qinling dabie belt and the rifting dominated tectonism north of it the most prominent cretaceous and cenozoic structures of the hong an dabie the xiaotian mozitang and the jinzhai fault zones respectively reactivated major lithospheric structures of the triassic orogen i e the huwan detachment zone and the suture

segmented african lithosphere beneath the anatolian region inferred from teleseismic p wave tomography summary lithospheric deformation throughout anatolia a part of the alpine himalayan orogenic belt is controlled mainly by collision related tectonic escape of the anatolian plate and subduction roll back along the aegean subduction zone we study the deeper lithosphere and mantle structure of anatolia using teleseismic finite frequency p wave traveltime tomography we use data from several temporary and permanent seismic networks deployed in the region approximately 34 000 p wave relative traveltime residuals measured in multiple frequency bands are inverted using approximate finite frequency sensitivity kernels our tomograms reveal segmented fast seismic anomalies beneath anatolia that corresponds to the subducted portion of the african lithosphere along the cyprean and the aegean trenches we identify these anomalies as the subducted aegean and the cyprus slabs that are separated from each other by a gap as wide as 300 km beneath western anatolia this gap is occupied by slow velocity perturbations that we interpret as hot upwelling asthenosphere the eastern termination of the subducting african lithosphere is located near the transition from central anatolia to the eastern anatolian plateau or arabian eurasian collision front that is underlain by large volumes of hot underplating asthenosphere marked by slow velocity perturbations our tomograms also show fast velocity perturbations at shallow depths beneath northwestern anatolia that sharply terminates towards the south at the north anatolian fault zone nafz the associated velocity contrast across the nafz persists down to a depth of 100 150 km hence our study is the first to investigate and interpret the vertical extent of deformation along this nascent transform plate boundary overall the resolved upper mantle structure of anatolia is directly related with the geology and tectonic features observed at the surface of the anatolian plate and suggest that the segmented nature of the subducted african lithosphere plays an important role in the evolution of anatolia and distribution of its tectonic provinces

processes controlling vertical coupling and decoupling between the upper and lower crust of orogens results from fiordland new zealand the pre cenozoic configuration of western new zealand allows determination of the effects of magmatism and a changing lower crustal rheology on the evolution of a cretaceous orogen from upper to lower crustal levels 10 50 km beginning at 126 ma a composite batholith dominated by diorite was emplaced into the lower crust during emplacement deformation was partitioned into zones weakened by magma and heat leading to the development of two layer parallel shear zones at the upper and lower contacts of the batholith transient vertical decoupling of the crust above and below the batholith occurred from 126 ma until 120 ma as magma was emplaced into and moved through a weak thick lower crust by 116 ma however much of the batholith had crystallized and the lowermost crust had cooled from 750 c t 850 c to t 650 700 c cooling was aided by the juxtaposition of pre existing crust against hot new crust and by the efficient extraction of partial melts out of the lower crust cooling together with dehydration of the lower crust and mafic compositions led to the development of a strong dry lower crustal root by 116 ma a strong lower crust resulted in high degrees of vertical coupling between the upper and lower crust during contraction from 116 to 105 ma even as magma continued to be emplaced into the mid upper crust a narrow focused orogenic style in the upper crust at this time reflected a highly viscous lower crust through which compressional stresses were transferred vertically the results imply that changes in plate boundary dynamics rather than the thermal weakening of thick lower crust during convergence controlled the onset of regional extension at 108 105 ma

deformation partitioning during transpression in response to early devonian oblique convergence northern appalachian orogen usa abstract transpressive deformation was distributed heterogeneously within the central maine belt shear zone system which formed in response to early devonian oblique convergence during the acadian orogeny in the northern appalachians straight belts are characterized by tight folds s l fabrics and sub parallel form lines and asymmetric structures that together indicate dextral se side up kinematics in contrast intervening zones between straight belts are characterized by open folds and l s fabrics within both types of zone metasedimentary rocks have fabrics defined by the same minerals at the same metamorphic grade including a penetrative moderately to steeply ne plunging mineral lineation thus we interpret accumulation of plastic deformation and regional metamorphic re crystallization to have been synchronous across the central maine belt shear zone system discordance between inclusion trails in regionally developed porphyroblasts of garnet and staurolite and matrix fabrics in straight belt rocks records shortening by tightening of folds and greater reorientation of matrix fabrics with respect to porphyroblasts kinematic partitioning of flow was responsible for the contrasting states of finite deformation recorded in the central maine belt shear zone system perturbations in the flow were caused by serially developed thrust ramp anticlines in the stratigraphic succession immediately above the avalon like basement at which decollement of the shear zone system was initially rooted general shear deformation at the ramps involved strain softening with an enhanced component of noncoaxial flow in contrast deformation during extrusion in the intervening zones involved strain hardening with a greater component of coaxial flow part of the thickening stratigraphic succession exceeded tsolidus reflected by the occurrence of migmatites and granites the latter were partly sourced from the underlying avalon like basement that was involved in the deformation and melting

structural architecture of the rhodes basin a deep depocentre that evolved since the pliocene at the junction of hellenic and cyprus arcs eastern mediterranean abstract interpretation of 1500 km of multi channel seismic reflection profiles shows that the rhodes basin evolved in two distinct tectonic stages a protracted miocene convergence episode p1 resulted in the development of a mainly sse verging fold thrust belt this period corresponds with the emplacement of the lycian nappes to the northeast and fold thrust complexes on the island of rhodes to the west this phase of deformation ceased in the late miocene the absence of evaporites in the rhodes basin suggests that this region must have remained above the depositional base of marine evaporite environment during the messinian the morphology of the m reflector and the architecture of the lowermost pliocene growth strata in the central portion of the rhodes basin demonstrate the existence of rugged paleo relief over the pre existing miocene fold thrust belt in early pliocene the middle pliocene quaternary phase of deformation is characterised by ne sw sinistral transpression p2 and rapid regional subsidence the p2 deformation occurred in response to an actively curving hellenic arc and the increasing obliquity of its eastern limb the pliny strabo trenches or fault zones to the convergence vector of the african plate during this time the p1 structures became re activated as transpressional faults further facilitating the rapid subsidence we envisage the evolution of the rhodes basin as the result of subsidence associated with loading of the large imbricate thrust panels that carry the western tauride mountains in the north at present the pliny strabo fault zones are delineated as a ne sw trending 30 50 km wide zone that continue into the western segment of the rhodes basin this fault zone is further correlated with the similar trending 50 km wide burdur fethiye fault zone in southwestern turkey

building and testing an a priori geophysical model for western eurasia and north africa we construct and evaluate a new three dimensional model of crust and upper mantle structure in western eurasia and north africa wena extending to 700 km depth and having 1 parameterization the model is compiled in an a priori fashion entirely from existing geophysical literature specifically combining two regionalized crustal models with a high resolution global sediment model and a global upper mantle model the resulting wena1 0 model consists of 24 layers water three sediment layers upper middle and lower crust uppermost mantle and 16 additional upper mantle layers each of the layers is specified by its depth compressional and shear velocity density and attenuation quality factors q p and q s the model is tested by comparing the model predictions with geophysical observations including crustal thickness surface wave group and phase velocities upper mantle n velocities receiver functions p wave travel times waveform characteristics regional 1 d velocities and bouguer gravity we find generally good agreement between wena1 0 model predictions and empirical observations for a wide variety of independent data sets we believe this model is representative of our current knowledge of crust and upper mantle structure in the wena region and can successfully be used to model the propagation characteristics of regional seismic waveform data the wena1 0 model will continue to evolve as new data are incorporated into future validations and any new deficiencies in the model are identified eventually this a priori model will serve as the initial starting model for a multiple data set tomographic inversion for structure of the eurasian continent

the 1978 earthquake sequence near thessaloniki northern greece summary this paper presents a detailed study of teleseismically and locally recorded foreshocks and aftershocks of the 1978 thessaloniki earthquake sequence and discusses the relations between the locations and mechanisms of these shocks and the three dimensional geometry of faulting in the source region sixteen teleseismically recorded events were relocated using a relative relocation method and positioned geographically using the accurate locally determined location of the largest aftershock all these shocks had depths shallower than 15 km the spatial distribution of the foreshocks showed that the activity was initiated at the central part of the epicentral region progressed westwards and for about 20 days clustered in the region of the imminent mainshock no teleseismically recorded foreshock was located west of the mainshock location in less than 1 hr after the mainshock large aftershocks occurred west of it and in later stages spanned the entire western part of the epicentral region no teleseismically recorded aftershocks were located east of the mainshock locally recorded aftershocks were accurately located and provided a more detailed picture of the seismic deformation they occurred at depths between 3 and 12 km and in three distinct clusters separated by well defined gaps the largest foreshock on may 23 had a moment of 5 6 1024dyne cm and a mean displacement of 31cm the mainshock on june 20 had a moment of 5 2 1025dyne cm a strain drop of 4 0 10 5 static stress drop of 12 bar and a mean displacement of 64 cm these values are for one of the two possible interpretations of the aftershock distribution which suggests that the largest earthquakes of the sequence occurred on two different but adjacent fault segments the first event 1 on may 23 occurred along the central fault segment and was followed 28 days later by the second event 2 on june 20 along a western fault segment finally 61 days later another smaller earthquake event 3 occurred along another fault east of event 1

structural geometry microstructural and strain analyses of l tectonites from paleoproterozoic orthogneiss insights into local transport parallel constrictional strain in the sikkim himalayan fold thrust belt paleoproterozoic lingtse orthogneiss shows three dominant structural associations in the sikkim himalayan fold thrust belt ftb a these rocks locally define the pelling thrust pt zone that lies in the footwall of the main central thrust mct b they occur as linear almost n s trending imbricates within the pt sheet and c they form a n s trending 13 5 km long 2 km wide discontinuous linear mylonitic klippen within the daling formation of the lower lesser himalayan sequence lhs that lie east of the n s trending teesta valley the klippe records n s trending strong l tectonites that are spatially associated with ls and sl tectonites the stretching lineations are oriented along the transport direction these rocks are exposed along three mylonite zones from north to south these are the phodong mylonite zone the tumin eingee mylonite zone and the rumtek mylonite zone all the three mylonite zones are overall folded along gently plunging transport parallel n s trending synform with the strongest l fabric developed along the hinge zone and its dominance decreases progressively toward the eastern and western structural contacts of the klippen the highest constrictional strain is recorded in phodong and tumin eingee mylonite zones and decreases south toward rumtek mylonite zone the long axes x of the quartz strain ellipsoids show n s trend and gentle plunge that agrees with the stretching lineations observed in the field additionally the xy plane of the generated ellipsoids overall agree with the observed variation of the mylonitic foliation planes in the field from all the three locations microstructural analysis from the mylonite klippe suggests that quartz and feldspar have undergone 35 and 76 grain size reduction with respect to the protolith dislocation creep and microfracturing are the dominant deformation mechanisms in quartz and feldspar respectively the grain size reduction is more prominent near the eastern and the western boundaries as they mark structural contacts between the l tectonites and the daling phyllites strain is partitioned between quartz and feldspar in the mylonite zones with quartz recording constrictional strain while feldspar records flattening strain we explain this variation due to their different deformation mechanisms shear sense analysis of feldspar porphyroclasts suggest dominantly transport parallel flow along with a component of transport perpendicular flow in the mylonite zones existing models on mechanism of l tectonite formation and transport parallel folds do not completely explain our observations we propose the possible existence of a lateral ramp beneath the pt sheet to explain the generation of l tectonites and transport parallel fold in the study area

strain patterns in archaean dome and basin structures the dharwar craton karnataka south india abstract models simulating the role of gravity in the earth s crust are the main source of criteria used for the field identification of diapirs after a short review of the distribution of finite strain in experimental diapir models we describe an example where differential erosion of a tilted craton has provided 3d geometrical information on patterns in a diapiric system at various depths from greenschist to granulitic facies conditions within the archaean continental crust of the dharwar craton south india diapirs and anti diapirs sagducted greenstones are observed at different levels structures and strain are consistent with all the field identification criteria inferred from experimental simulation but some peculiar structural features are also observed which are not predicted by the models these features such as strain trajectory triple junctions result from i the progressive deformation of diapiric domes or sagducted basins ii interferences between diapiric structures body forces and iii the superimposition of diapiric strain fields on regional horizontal shortening boundary forces

thermobaric structure of a traverse across western dabieshan implications for collision tectonics between the sino korean and yangtze cratons as the best preserved high and ultrahigh pressure hp and uhp metamorphic terrane in the qinling dabieshan sulu orogen western dabieshan is divided into six lithotectonic units along a traverse across the orogen i e from north to south the nanwan balifan huwan xinxian hong an and mulanshan units in this terrane five eclogite bearing zones i v are developed the garnet and clinopyroxene in eclogites from these zones exhibit chemical zoning suggesting that the rims record general peak temperature and pressure thermobarometric study indicates that the peak p t conditions of eclogite are 550 570 c and 21 kbar for zone i 470 500 c and 14 17 kbar for zone ii 620 670 c and 26 29 kbar for zone iii 530 560 c and 20 22 kbar for zone iv and 490 510 c and 19 20 kbar for zone v the symmetrical thermobaric pattern in conjunction with structural and geochronological data demonstrates that the huwan and hong an units belong to the same hp slice overlying the uhp slice this pattern together with the mulanshan lt hp blueschist greenschist belt in the south roughly constitutes a normal metamorphic zonation however clear metamorphic gaps occur between different slices it is inferred that the lt hp hp and uhp slices were broken up from the downgoing slab during subduction and reached different depths along different geothermal gradients the successive subduction of underlying slices leads to a nearly concomitant uplift of overlying slices whereas exhumation of the deepest uhp slice was effected by underthrusting of the lower crust of the yangtze craton

comments on the lompoc california earthquake november 4 1927 m 7 3 and its aftershocks by thomas c hanks

regional wave propagation in turkey and surrounding regions this paper was published by the american geophysical union agu copyright 2000 agu see also http www agu org journals gl gl0003 1999gl008375 pdf 1999gl008375 pdf http atlas geo cornell edu turkey publications gok et al 2000 htm

early cretaceous extensional reworking of the triassic hp uhp metamorphic orogen in eastern china corresponding to the early mesozoic continental subduction between the north china block ncb and the south china block scb the tongbaishan hong an dabieshan sulu massifs are famous for their hp uhp metamorphism more than 50 of the hp uhp orogenic belt was significantly reworked by early cretaceous extensional tectonics this early cretaceous event with a fast cooling period at 130 120 ma superimposed on the early mesozoic hp uhp orogenic belt and intensively changed the architecture of this orogen each individual segment documents different early cretaceous extensional structures namely the central tongbaishan domain is a metamorphic core complex mcc represented by an a type non cylindrical antiform the central dabieshan domain is a typical cordilleran type migmatite cored mcc the southern sulu uhp domain is a wedge shaped structure exhumed by a simple detachment fault these late stage extensional structures expose the previous hp uhp orogenic belt as fragments along the ncb scb boundary the geodynamic setting of this early cretaceous extensional tectonics along the hp uhp orogen is a part of a 1000km scale crustal extension belt that is widespread in eastern eurasia continent from trans baikal to the central part of scb convective erosion or delamination of the mantle lithosphere might be considered as a possible mechanism for mantle removal

thermochronologic constraints on deformation and cooling history of high and ultrahigh pressure rocks in the qinling dabie orogen eastern china the hong an block is the best place to study the exhumation of high pressure hp and ultrahigh pressure uhp metamorphic rocks in the qinling dabie orogen of eastern china because it lacks the extensive cretaceous tectonic and thermal overprint observed in the dabie shan we measured timing of deformation and rate of cooling of the hp uhp rocks by 40ar 39ar analyses of synkinematic minerals from tectonites of key structural zones in the hong an and tongbai shan normal sense shear along the north dipping huwan detachment at the northern edge of the hong an block occurred between 237 and 231 ma this detachment facilitated the bulk of the exhumation of the hp uhp rocks our new 40ar 39ar ages combined with u pb zircon and sm nd ages of 245 240 ma suggest that exhumation of uhp rocks from mantle depths occurred at rates of 5 25 mm yr from 245 to 230 ma the mountain range is a warped extensional footwall within which white mica cooled from 225 to 205 ma locally younger extension is recorded by white mica recrystallization at 198 194 ma after which the entire block had cooled to below 300 c early cretaceous 40ar 39ar ages from the tongbai shear zone indicate that dextral shear along the southwest boundary of the orogen was contemporaneous with normal to sinistral oblique slip along the xiaotian mozitan fault along the northern boundary coeval dextral and sinistral shear zones along the northern and southwestern margins of the hong an and dabie shan would have caused eastward lateral extrusion of these two blocks perhaps driven by collision of the lhasa block with eurasia

fold fault relationships in low angle detachment systems a close kinematic and timing relationship between low angle extensional faulting and upright to moderately inclined folding with fold axes parallel to the extension direction is established for two well exposed neogene detachment systems in the simplon region of the alps and in the death valley region of california fold amplitude is largest in the oldest mylonitic foliation of the footwall these folds are transected by younger mylonitic foliation s and cataclastic detachment faults which are themselves folded about similar axes in general the amplitude decreases and the wavelength increases for progressively younger fold structures consistent with a history of progressive folding during faulting the interplay between folding and faulting in the footwall reflects a component of shortening perpendicular to fold axial surfaces during extension parallel to fold axes this strain pattern can develop in regions with a transcurrent component or during lateral extrusion and does not necessarily require overall crustal thinning

constriction due to subduction evidence for slab pull in the marianske lazně complex central european variscides pervasive l and l s tectonites of the marianske lazn eclogites include pencil fabrics constrictional folds and mullions that result from the first deformation increment observed petrological and microstructural data suggest that these structures formed by constrictional flow at deep subduction levels after or even during the eclogite facies stage and before the subsequent high pressure granulite facies overprint constriction at mantle depths is explained by taking into account the geometry and seismic properties of recent subduction zones here constrictional strain and associated l s tectonites should be expected below the rheologycontrolled slab bend at about 40 km depth where dip parallel extension and a reduced viscosity of the downgoing slab are compatible with a coaxial flow regime

using along strike variation in strain and kinematics to define the movement direction of curved transpressional shear zones an example from northwestern superior province manitoba a review of current understanding of structures in shear zones reveals that correlating the orientation of stretching lineations with movement direction once a common practice based on the simple shear model is not generally applicable to transpressional zones it is difficult to determine the movement direction of a transpressional zone based on internal structures we show that the movement direction can be better defined by considering the variation in strain geometry and kinematics of differently oriented and kinematically related shear zones or different segments of a curved shear zone application of this method to a shear zone in the northwestern superior province of manitoba shows that the movement direction there is approximately north south in contrast to a commonly held view for similarly oriented shear zones in the superior province that the movement direction is approximately east west

tomographic pn velocity and anisotropy structure beneath the anatolian plateau eastern turkey and the surrounding regions an edited version of this paper was published by the american geophysical union agu copyright 2003 agu see also http www agu org pubs crossref 2003 2003gl017391 shtml http atlas geo cornell edu turkey publications al lazki et al 2003 htm

high pressure metamorphic rocks from tongbaishan central china u pb and 40ar 39ar age constraints on the provenance of protoliths and timing of metamorphism abstract the tongbaishan area is situated at the junction between the paleozoic north qinling orogen and the mesozoic south qinling dabie sulu orogen the area contains an important geological section for understanding the assembly of the sino korean and yangtze cratons two eclogite zones were recently recognized in this area the peak metamorphic conditions are estimated to be 530 610 c and 17 20 kbar for the northern eclogite zone and 460 560 c and 13 19 kbar for the southern eclogite zone shrimp u pb analyses on zircons of eclogite metagabbro and orthogneiss indicate that their protoliths were formed during the neoproterozoic and experienced high pressure hp recrystallization during the permian triassic period therefore the tongbaishan area belongs to the western extension of the dabieshan hp uhp terrane in addition u pb ages of detrital zircons from quartzite paragneiss and schist show three age populations of 2 49 ga 1 93 ga and 1 85 1 82 ga suggesting that extensive paleoproterozoic orogeny or tectonothermal events took place in the northern margin of the yangtze craton the shrimp dating and complementary 40ar 39ar dating of muscovite from quartzofeldspathic gneiss and quartzite reveal that the crustal rocks were subducted to great depths and underwent hp eclogite facies metamorphism at ca 255 ma slightly earlier than the timing of deep subduction of the uhp slice the hp rocks were later exhumed to mid to upper crustal levels and suffered from retrograde recrystallization at ca 238 ma the dating also discloses a still later phase of deformation and recrystallization at ca 215 ma the available age data throughout the tongbai dabie sulu orogen reflect diachronous exhumation from ca 238 ma for the hp slice to ca 213 ma for the uhp slice such a phenomenon could be explained by successive subduction and exhumation of the broken slices of the subducting yangtze slab

structural significance of l tectonites in the eastern central laramie mountains wyoming abstract the formation of l tectonites is little understood and scarcely studied however it is probably an important part of plastic deformation in the crust to improve our understanding of this strain phenomenon i present a detailed case study of a kilometer wide domain of l tectonites developed in and around the 2 05 ga boy scout camp granodiorite bscg in the laramie mountains wyoming detailed mapping and structural analyses allow for the reconstruction of the structural setting of this domain of apparent constrictional strain elongation lineations plunge moderately to the south southwest and lie parallel with both the local fold hinge lines and regional fold axes whereas poles to foliation generally cluster in the northwest quadrant roughly defining fold axial surfaces map scale folds are west northwest vergent but at the outcrop and thin section scales there is no evidence for a significant component of simple shear reconstruction of the orientation of contacts in and around the bscg i

mesozoic extensional tectonics in eastern asia the south liaodong peninsula metamorphic core complex ne china abstract in the north china block the south liaodong peninsula massif is an elliptical metamorphic core complex mcc with a long axis trending ne sw in cross section view it is asymmetric with a steeply dipping northwestern flank and a gently dipping southeastern flank it consists of three lithotectonic units a gneissic migmatite unit a paleo to meso proterozoic micaschist slate unit and a neoproterozoic to mesozoic sedimentary cover three deformation events related to extensional tectonics are distinguished in the study area d1 is a ductile deformation related to the exhumation of the mcc the following event d2 corresponds to the development of recumbent folds formed during the early exhumation of the mcc and the youngest event d3 corresponds to brittle normal faulting that controlled the opening of a cretaceous continental half graben basin a pre d1 event characterized as northward verging is interpreted as the result of n s shortening that occurred in the late triassic during the fin

tectonics of the dabieshan eastern china and possible exhumation mechanism of ultra high pressure rocks the dabieshan is divided into three tectonic domains the southern dabieshan is a stack of allochtons from top to bottom i unmetamorphosed cambrian early triassic series unconformably covered by jurassic sandstone ii weakly metamorphosed proterozoic slate iii hp rocks mostly retrogressed into greenschist facies iv uhp allochton v uhp free gneisses these units exhibit a nw se lineation and top to the nw shearing reworked by s verging folds the central dabieshan is a migmatitic dome superimposed on uhp metamorphism and bounded by a detachement fault responsible for the exhumation of the uhp unit during its retrogression into amphibolite facies in the northern dabieshan early foliation and n s trending compressional lineation are deformed by n verging folds coeval to the syn exhumation ductile structures of the central dabieshan a geodynamic model involving coeval thrusting and normal faulting is discussed

kinematic significance of l tectonites in the footwall of a major terrane bounding thrust fault klamath mountains california usa abstract detailed geologic mapping cross section reconstructions strain analyses and kinematic analyses enable the reconstruction of a one kilometer wide domain of l tectonites in the east west striking subhorizontal to gently south dipping pigeon point high strain zone pphsz associated with a major thrust fault separating oceanic and arc affinity terranes in the klamath mountains california l tectonites are associated with 1 a convex upward warp of the upper high strain zone boundary 2 a transition from mafic metavolcaniclastic rocks to micaceous quartzites 3 folds subparallel with mineral lineations 4 emplacement of synkinematic ultramafic mafic intrusive bodies and 5 a local temperature increase from greenschist to amphibolite facies conditions pure shear dominated deformation accommodated zone normal shortening and transport parallel elongation coupled with subordinate top to the west directed thrust style simple shear l tectonite formation was controlled by the shape of the high strain zone boundary driving lateral flow into the apex of the lens shaped zone in response to a favorable kinematic geometry and bulk strain in the constrictional field localized magmatic heating best explains the shape of the high strain zone boundary but l tectonites are not partitioned into a single rheological domain during terrane amalgamation strain path partitioning occurred with localized top to the west directed simple shear partitioned into a structurally overlying thrust zone and pure shear dominated subvertical shortening and transport parallel elongation partitioned into the pphsz

peculiarities of surface wave propagation across central eurasia abstract the recent installation of six broadband digital iris ida seismic stations in the ussr has provided new opportunities for studying surface wave propagation across eurasia group velocities of fundamental rayleigh and love modes between epicenters and these stations were determined for 35 events that occurred since april 1989 to the middle of july 1990 near eurasia differential phase velocities were found for the same arrivals along paths between several pairs of stations group and phase velocities were obtained in the period range from 15 to 300 sec frequency time polarization analysis was used for studying polarization properties of surface waves in some cases significant anomalies in the particle motion for periods up to 100 sec were observed they are attributed to surface wave refraction and scattering due to lateral inhomogeneities at the boundaries and inside the eurasia continent

orogen scale l tectonite domain in the tongbai orogenic belt central china geological setting and origin abstract l tectonite is well developed and widely distributed in the tongbai orogenic belt in central china the orogenic belt as a whole has an antiformal geometry and the hinge of the antiform is subhorizontal and trends nw se the l tectonite occurs in the core of the antiform in a zone that is 10 30 km wide and over 100 km long lineations in the l tectonite are sub horizontal parallel to the hinge of the antiform sheath folds are also well developed associated with the l tectonite with the hinges parallel to the lineations migmatite occurs in the core and structurally below the l tectonite and has a gradational relationship with the l tectonite the domain of l tectonite is bounded by three ductile shear zones on the north at the top and on the south respectively well developed shear sense indicators indicate that the southern the overlying and the northern shear zones have a dextral top to nw and sinistral sense of shear respectively these geometrical and kinematic data indicate that the three shear zones are likely part of a single shear zone that wraps around the l tectonite domain the l tectonite zone in the core moves southeast relative to the hanging wall the development of the tectonite is interpreted to be a result of this special geometry and kinematics and reflects a post collisional orogen parallel extension synchronous with migmatization and the continuing convergence between the yangtze block and the north china block in the early cretaceous

reply to w gawthrop s comments on the lompoc california earthquake november 4 1927 m 7 3 and its aftershocks

first paleomagnetic evidence for a post eocene clockwise rotation of the western taurides thrust belt east of the isparta reentrant southwestern turkey abstract a paleomagnetic study was carried out on 23 sites sampled in paleocene eocene and lower miocene sedimentary formations of the western taurides belt east of the isparta reentrant the paleomagnetic data based on twelve suitable sites record a coherent post eocene 40 clockwise rotation throughout the area studied we interpret this regional rotation as a semi rigid rotation of the whole western taurides belt above a major deep decollement level together with previously published data these new results suggest that the isparta reentrant would result from diachronous opposite rotations of the two branches first a late eocene oligocene clockwise rotation of the akseki beysehir taurides initiating the tauride arc and then anticlockwise rotation of the lycian taurides probably during middle miocene times

thermochronological constraints on two stage extrusion of hp uhp terranes in the dabie sulu orogen east central china along the qinling dabie sulu orogenic belt in china crops out the world s largest terrane composed of ultrahigh pressure uhp metamorphic rocks differences in the timing and mechanisms of oceanic and continental subductions are assumed to be responsible for different ages of high pressure hp and uhp slices in different parts of the belt the western part of the dabie orogen western dabie terrane holds a key to understanding of the transition from oceanic to continental subduction this paper reports geochronological results to test a two stage tectonic model for the exhumation of hp uhp rocks in western dabie this model involves two different stages and types of extrusion for exhumation of the hp uhp rocks in east central china mica ar ar ages ranging from 241 to 231 ma indicate a general middle triassic cooling probably driven by early upward extrusion during the collision between the north and south china blocks late triassic early jurassic cooling was associated with later eastward extrusion ranging from 200 to 184 ma the second event is recorded also in mica in the region that was not affected by later deformation and magmatism the lateral movement along lithosphere scale faults resulted in the eastward extrusion of the hp uhp metamorphic terrane which was followed in the late triassic early jurassic time by a major compressive event these two extrusion events are correlative with the two stages of triassic exhumation of the western dabie hp uhp rocks respectively wintin the framework of the qinling dabie sulu orogenic belt it is suggested for western dabie that the subduction exhumation of blueschist facies unit is related to the mianlue suture whereas the subduction exhumation of hp uhp eclogite facies units is related to the shangdan suture

the crustal structure of the east anatolian plateau turkey from receiver functions an edited version of this paper was published by the american geophysical union agu copyright 2003 agu see also http www agu org pubs crossref 2003 2003gl018192 shtml http atlas geo cornell edu turkey publications zor et al 2003 htm

devonian orogen parallel opposed extension in the central norwegian caledonides late orogenic early to middle devonian extension in the scandinavian caledonides was unidirectional in western norway new data from two detachment zones hoybakken and kollstraumen north of the more trondelag fault complex show that bidirectional opposed orogen parallel extension dominated in this region at this time the fault complex acted as a transfer zone for the hoybakken detachment extension and uplift in central norway triggered significant magmatic activity in contrast to the lack of granite intrusions during exhumation of western norway

three dimensional seismic model of the sierra nevada arc california and its implications for crustal and upper mantle composition a three dimensional p wave velocity model of south central california from the coast ranges to the sierra nevada shows that the crust under most of the southern sierra nevada batholith has seismic velocities 5 9 6 3 km s below the continental average the crust is not much thicker on average about 35 km than in the adjacent great valley and basin and range province apart from a small northward thickening crustal root under the western sierra nevada that reaches a depth of 42 km crustal velocities above the continental average are observed beneath much of the great valley due to a high velocity body underlying the sedimentary basin and the foothills metamorphic belt 6 4 7 0 km s upper mantle velocities are generally low 7 8 km s but span a wide range 7 4 8 2 km s we display the velocity model in several cross sections and maps of moho depth and average crustal velocity the measured velocities in the upper and mid crust of the sierra nevada batholith are in good agreement with laboratory measurements on sierra nevada tonalites after corrections for density and temperature peridotite xenoliths from the eastern sierra nevada suggest strong upper mantle anisotropy which could explain some of the velocity heterogeneity in the sierra nevada mantle by the time cretaceous subduction related magmatism ceased the sierra nevada arc must have had a thick mafic lower crust yet a principal result of our work is that today the batholith has a crust of mainly felsic composition throughout a subcrustal layer with velocities below normal pn velocities 7 6 km s may indicate the presence of lower crustal material in eclogite facies

sheath folds as discriminators of bulk strain type abstract nested elliptical closures defining eye folds represent classic y z cross sections through highly curvilinear sheath folds generated during intense ductile deformation in metamorphic rocks systematic analysis of 1425 such eye folds based on our own field observations and examples from the published literature reveals distinct and consistent differences in ellipticites measured from the outer r yz to the inner most r y z elliptical rings of individual sheaths the variation in overall aspect ratios from outer to inner rings is defined as r where r r yz r y z and may display a relative increase or decrease in ellipticity to define cats eye r bulls eye r 1 fold patterns respectively layer thicknesses may also be measured along the y axis parallel to the axial surface t y and at 90 to this along the z axis t z to define the ratio of t yz sheath folds generated during broadly simple shear deformation k 1 display mean r yz 4 61 t yz 3 31 and cats eye folds r 0 69 sheath folds generated during general shear also display cats eye folds with identical mean r 0 69 values but greater thickness variations and elliptical ratios t yz 4 35 r yz 5 76 thus within both simple and general shear dominated deformations the overall variation in layer thickness t yz and ellipticity of eye folds r yz increases with increasing deformation and a greater component of pure shear whilst the r value remains constant and reflects original fold patterns sheath folds formed during constrictional k 1 deformation display markedly lower aspect ratios r yz 2 42 and thickness variations t yz 2 94 together with distinctive bulls eye folds r 1 23 these empirical relationships suggest fundamental and universal constraints on curvilinear fold generation across this broad spectrum of deformation types and allow sheath folds to act as both effective 95 consistent and robust discriminators of bulk strain type

a laterally constricted shear zone system the nordre stromfjord steep belt nagssugtoqidian orogen w greenland many ductile shear zones are interpreted to operate by simple shear flow but some form under other flow regimes lineations and foliations in such shear zones can lie obliquely to those in simple shear zones which can lead to erroneous tectonic interpretations on the assumption of simple shear flow this paper describes a gently dipping shear zone system from the n central segment of the palaeoproterozoic nagssugtoqidian orogen of w greenland which operated with a lateral constriction component this resulted in the development of upright folds with axes parallel to the transport direction where the constriction component is weak where it is strong a linear fabric and even a subvertical foliation normal to the rotation axis of bulk flow developed this steep foliation is interpreted as the origin of the nordre stromfjord steep belt previously interpreted as a crustal scale sinistral transcurrent shear zone shear zones of this type may occur elsewhere and shear zone fabrics should therefore be carefully analysed before the direction of tectonic transpost can be determined

crustal thickness variations in the aegean region and implications for the extension of continental crust 1 we installed 5 broadband and 45 short period temporary seismic stations distributed partly as a dense 100 km long n s linear array and partly as a regional network throughout the menderes massif of western turkey in order to study crust upper mantle structure and seismicity in this study we have combined teleseismic waveform data from these stations with data from several permanent seismic stations to determine crustal thickness variations in the aegean region receiver function studies at seven broadband stations using the h stacking method have yielded crustal thicknesses and vp vs ratios over a broad region of the aegean a more detailed crustal image was obtained in the central menderes massif where we applied common conversion point stacking to receiver functions obtained from the n s linear array the results show a general trend of westward crustal thinning from 36 km in central anatolia to 28 30 km in the central menderes massif to 25 km beneath the aegean sea the results also indicate that crustal thinning in the aegean is not uniform in the n s extensional direction the crust is thinner in the central menderes massif 28 30 km of crustal thicknesses and the cycladic massif 25 26 km than in surrounding regions where crustal thicknesses are 32 34 km the long lived elevated moho under the metamorphic core complexes suggests that the lower crust in the aegean region is at least 3 times more viscous than that in the basin and range province where the moho is much flatter

what triggered the early to mid pleistocene tectonic transition across the entire eastern mediterranean abstract subduction plays a fundamental role in plate tectonics and when interrupted it may trigger a series of geodynamic and sedimentary responses synchronous structural modifications recorded across the entire eastern mediterranean region are dated to a relatively short period early to mid pleistocene these deformations are documented within plates e g arabian sinai and african plates along plate boundaries e g dead sea and north anatolian faults and cyprus arc and in the mediterranean basin during the same period the northward subduction of the sinai plate was interrupted when the eratosthenes seamount cyprus arc collision initiated subduction collision processes of the eastern mediterranean serve as a unique modern analogue for similar settings worldwide understanding their association with accompanying neo tectonic processes is therefore predominantly important by fostering a detailed and comprehensive approach this research provides a coherent tectonic picture for the eastern mediterranean early to mid pleistocene tectonic transition in order to explore its triggering mechanisms since the neogene convergence across the eastern mediterranean was accompanied by eurasian indentation by arabia northward motion westwards anatolia escape and southwards aegean propagation this semi counterclockwise plate motion was temporarily interrupted by the incipient seamount arc collision which is suggested here as a trigger of the early to mid pleistocene tectonic transition

lithosphere tearing at step faults response to edges of subduction zones abstract slab edges are a relatively common feature in plate tectonics two prominent examples are the northern end of the tonga subduction zone and the southern end of the new hebrides subduction zone near such horizontal terminations of subduction trenches ongoing tearing of oceanic lithosphere is a geometric consequence we refer to such kinks in the plate boundary as a subduction transform edge propagator or step other steps are the north and south ends of the lesser antilles trench the north end of the south sandwich trench the south end of the vrancea trench and both ends of the calabria trench volcanism near steps is distinct from typical arc volcanism in some cases slab edges appear to coincide with mantle plumes using 3d mechanical models we establish that step faults are stable plate tectonic features in most circumstances in the probably rare cases that the resistance to fault propagation is high slab break off will occur relative motion along the transform segment of the plate boundary often is non uniform and the step is not a transform plate boundary in the rigid plate tectonics sense of the phrase step propagation may result in substantial deformation rotation topography and sedimentary basins with a very specific time space evolution surface velocities are substantially affected by nearby steps

multi phased uplift of the southern margin of the central anatolian plateau turkey a record of tectonic and upper mantle processes abstract uplifted neogene marine sediments and quaternary fluvial terraces in the mut basin southern turkey reveal a detailed history of surface uplift along the southern margin of the central anatolian plateau from the late miocene to the present new surface exposure ages 10be 26al and 21ne of gravels capping fluvial strath terraces located between 28 and 135 m above the goksu river in the mut basin yield ages ranging from ca 25 to 130 ka corresponding to an average incision rate of 0 52 to 0 67 mm yr published biostratigraphic data combined with new interpretations of the fossil assemblages from uplifted marine sediments reveal average uplift rates of 0 25 to 0 37 mm yr since late miocene time starting between 8 and 5 45 ma and 0 72 to 0 74 mm yr after 1 66 to 1 62 ma together with the terrace abandonment ages the data imply 0 6 to 0 7 mm yr uplift rates from 1 6 ma to the present the different post late miocene and post 1 6 ma uplift rates can imply increasing uplift rates through time or multi phased uplift with slow uplift or subsidence in between longitudinal profiles of rivers in the upper catchment of the mut and ermenek basins show no apparent lithologic or fault control on some knickpoints that occur at 1 2 to 1 5 km elevation implying a transient response to a change in uplift rates projections of graded upper relict channel segments to the modern outlet together with constraints from uplifted marine sediments show that a slower incision uplift rate of 0 1 to 0 2 mm yr preceded the 0 7 mm yr uplift rate the river morphology and profile projections therefore reflect multi phased uplift of the plateau margin rather than steadily increasing uplift rates multi phased uplift can be explained by lithospheric slab break off and possibly also the arrival of the eratosthenes seamount at the collision zone south of cyprus

evidence for intracontinental thrust related exhumation of the ultra high pressure rocks in china coesite and diamond bearing ultra high pressure metamorphic rocks produced during the triassic continental collision between the sino korean and yangtze plates are offset by about 530 km along the sinistral tanlu fault in eastern china the tanlu fault terminates abruptly south of the ultra high pressure metamorphic terrain in dabie shan and does not extend into the foreland fold belt along the yangtze river this suggests that in this region the mesozoic major sinistral displacement along the tanlu fault was transferred to southward directed thrusting which led to the exhumation of the ultra high pressure metamorphic rocks formed earlier postcollisional himalayan type intracontinental thrusting and concomitant erosion appear to be the main agents in the exhumation of the very high pressure metamorphic rocks in china

strain distribution in a fold in the west norwegian caledonides abstract strain has been measured from clasts within a deformed conglomerate layer at 17 localities around an asymmetric fold in the rundemanen formation in the bergen arc system west norwegian caledonides strain is very high and a marked gradient in strain ellipsoid shape exists to either side of the fold strain within the conglomerate bed is of the extreme flattening type in the fold especially on the lower fold closure the strain is constrictional mathematical models of perturbations of flow in glacial ice have produced folds of the same geometry as this fold with a strikingly similar pattern of finite strain the fold geometry and strain pattern as well as other field observations suggest that the fold developed passively as the result of a perturbation of flow in a shear zone where the strain was accommodated by simple shear accompanied by extension along y

kinematic analyses of orogen parallel l tectonites from pelling munsiari thrust of sikkim himalayan fold thrust belt insights from multiple incremental strain markers abstract fault rocks associated with the pelling thrust pt in the sikkim himalayan fold thrust belt ftb change from sl tectonites to local transport parallel l tectonites that are exposed in discontinuous klippen south of the pt zone by estimating the incremental kinematic vorticity number wk from quartz c axes fabric oblique fabric and subgrains we reconstruct a first order kinematic path of these l tectonites quartz c axes fabric suggests that the deformation initiated as pure shear dominated 56 96 that progressively became simple shear dominated 29 54 as recorded by the oblique fabric and subgrains in the l tectonites these rocks record a non steady deformation where the kinematic vorticity varied spatially and temporally within the klippen the l tectonites record 30 greater pure shear than the pt fault rocks outside the klippen and the greatest pure shear dominated flow among the published vorticity data from major fault rocks of the himalayan ftb the relative decrease in the transport parallel simple shear component within the klippen and associated relative increase of transport perpendicular pure shear component support the presence of a sub pt lateral ramp in the sikkim himalayan ftb this study demonstrates the influence of structural architecture for fault systems for controlling spatial and temporal variations of deformation fabrics and kinematic path of deforming thrust wedges

structural and geochronological evidence for early cretaceous orogen parallel extension of the ductile lithosphere in the northern dabie orogenic belt east china abstract the wnw trending north dabie dome ndd in the northern dabie orogenic belt is bounded by the xiaotian mozitan ductile shear zone xmsz in the north and the wuhe shuihou shear zone wssz in the south fabric geometries and kinematics of both the xmsz and the wssz are similar they both show a top to nw or wnw sense of shear and display similar microstructures which indicate that the deformation temperature was about 600 650 c 40 ar 39 ar dating of hornblende and biotite from the mylonites of the xmsz suggests that the shear zone was developed prior to 142 ma u pb zircon la icpms dating of undeformed granite dikes that cut the xmsz suggests that the ductile shearing occurred before 130 ma the wssz was also developed in the early cretaceous the interior of the ndd is dominated by top to nw or wnw sense of shear in the migmatitic gneiss and deformed plutons of the earliest early cretaceous ages we suggest that the xmsz the wssz and the interior of the ndd were involved in the same early cretaceous deformation the xmsz and the wssz were originally a single connected more flat lying zone which we call the east dabie detachment zone eddz it developed at a crustal level of over 18 km in depth kinematics of the eddz suggest that the ductile crust and possibly part of the lithospheric mantle in the eastern dabie orogen underwent pervasive orogen parallel and ese ward extension at the beginning of the early cretaceous large scale magmatic intrusions following this deformation and the resultant increase in buoyancy led to the exhumation of the ndd and the warping of the eddz erosion separated the eddz into two zones the xmsz and the wssz as observed today many metamorphic core complexes of early cretaceous were developed in the eastern north china craton most showing top to nw or wnw sense of shear we suggest that such a widespread uniform shear sense reflects a uniform flow direction of the ductile lithosphere in the east china that has also been documented in the liaonan yiwulushan and yumenshan metamorphic core complexes in the northeastern part of the north china craton

location and size of the 1927 lompoc california earthquake from tsunami data abstract the lompoc earthquake of 4 november 1927 m s 7 0 was one of the largest offshore events in california and the associated tsunami was recorded in hawaii as well as on the california coast the epicenter of this event has long been debated one location is offshore where the ocean is about 1000 m deep whereas another location is very near shore beneath a water depth of less than 100 m we analyzed the tsunami records from this event from tsunami travel times the source location was estimated to be well offshore at about 34 2 n 120 75 w consistent with recent seismic waveform analysis waveform modeling of the tsunami also supports an outer continental shelf location the seismic moment is estimated to be 3 10 26 dyne cm corresponding to a moment magnitude of 7 0 the tsunami computation reproduced the large tsunami in hawaii indicating that the observed large tsunami was due to bathymetry effects particularly near hilo bay the tsunami magnitude of 7 6 obtained from the hawaiian recordings by abe thus appears to be an overestimate

continental subduction and exhumation of uhp rocks structural and geochronological insights from the dabieshan east china in the dabieshan the available models for exhumation of ultrahigh pressure uhp rocks are poorly constrained by structural data a comprehensive structural and kinematic map and a general cross section of the dabieshan including its foreland fold belt and the northern dabieshan domain foziling and luzenguang groups are presented here south dabieshan consists from bottom to top of stacked allochtons 1 an amphibolite facies gneissic unit devoid of uhp rocks interpreted here as the relative autochton 2 an uhp allochton 3 a hp rock unit susong group mostly retrogressed into greenschist facies micaschists 4 a weakly metamorphosed proterozoic slate and sandstone unit and 5 an unmetamorphosed cambrian to early triassic sedimentary sequence unconformably covered by jurassic sandstone all these units exhibit a polyphase ductile deformation characterized by i a nw se lineation with a top to the nw shearing and ii a southward refolding of early ductile fabrics the central dabieshan is a 100 km scale migmatitic dome newly discovered eclogite xenoliths in a cretaceous granitoid dated at 102 ma by the u pb method on titanite demonstrate that migmatization post dates hp uhp metamorphism ductile faults formed in the subsolidus state coeval to migmatization allow us to characterize the structural pattern of doming along the dome margins migmatite is gneissified under post solidus conditions and mylonitic ultramylonitic fabrics commonly develop the north and west boundaries of the central dabieshan metamorphics i e the xiaotian mozitan and macheng faults are ductile normal faults formed before late jurassic early cretaceous a cretaceous reworking is recorded by synkinematic plutons north of the xiaotian mozitan fault the north dabieshan domain consists of metasediments and orthogneiss foziling and luzenguang groups metamorphosed under greenschist to amphibolite facies which never experienced uhp metamorphism a rare n s trending lineation with top to the south shearing is dated at 260 ma by the 40ar 39ar method on muscovite this early structure related to compressional tectonics is reworked by top to the north extensional shear bands the main deformation of the dabieshan consists of a nw se stretching lineation which wraps around the migmatitic dome but exhibits a consistently top to the nw sense of shear the central dabieshan is interpreted as an extensional migmatitic dome bounded by an arched top to the nw detachment fault this structure may account for a part of the uhp rock exhumation however the abundance of amphibolite restites in the central dabieshan migmatites and the scarcity of eclogites found only in a few places argue for an early stage of exhumation and retrogression of uhp rocks before migmatization this event is coeval to the n s extensional structures described in the north dabieshan domain recent radiometric dates suggest that early exhumation and subsequent migmatization occurred in triassic liassic times the main foliation is deformed by north verging recumbent folds coeval to the south verging folds of the south dabieshan domain an intense cretaceous magmatism accounts for thermal resetting of most of the 40ar 39ar dates a lithosphere scale exhumation model involving continental subduction synconvergence extension with inversion of southward thrusts into nw ward normal faults and crustal melting is presented

constrictional strain in a non coaxial shear zone implications for fold and rock fabric development central mojave metamorphic core complex california finite strain and fold analyses of footwall mylonites in the central mojave metamorphic core complex cmmcc reveal two distinct deformation paths that generated non coaxial constrictional strain the first path recorded in the waterman hills accomplishes constrictional strain through the formation of l tectonites at the grain scale the second path recorded in the mitchel range involves a combination of plane strain at the grain scale and y axis shortening through syn mylonitic folding the ductile shear zone in the waterman hills is approximately 500 m thick and is developed entirely within a miocene syn kinematic granodiorite strain magnitude decreases structurally downward the mylonites contain abundant ne directed non coaxial microstructures yet are l tectonites rf o analysis of quartz ribbon grain shapes indicate prolate strains k 6 and bulk chemical data suggest that mylonitization was isochemical or involved volume loss therefore ductile shearing in the waterman hills involved true constrictional strain at the grain scale immediately to the southeast in the mitchel range the lateral continuation of the shear zone is more than 1000 m thick and primarily involves lithologically heterogeneous pre tertiary basement the mylonitic fabric comprises a well developed foliation and ne trending stretching lineation rf o strain analysis was applied to grain shapes of cataclasized and strongly altered garnet porphyroclasts in a peraluminous granite in contrast to the waterman hills finite strains in these l s tectonites approximate plane strain k 1 1 however the mylonitic fabric is strongly folded about axes uniformly oriented subparallel to the stretching lineation the coaxial folds range from open to isoclinal we interpret the folds to have nucleated with axes parallel to the stretching lineation during mylonitization and to have accomplished y axis shortening in the shear zone macroscopic folds of the brittle detachment spatially correspond to open folds in the ductile shear zone suggesting that y axis shortening continued after the fault zone had reached the brittle regime corrugations and folds oriented subparallel to the transport direction are characteristic features of fault zones in cordilleran metamorphic core complexes therefore constrictional strain may be common in core complexes strain compatibility with upper plate rocks in core complexes may be maintained by y axis shortening along conjugate strike slip faults a nearly uniaxial stress field 3 2 1 is consistent with most of the structures formed in basin and range extension and could generate the observed constrictional strain

upper mantle discontinuity structure beneath east anatolian plateau turkey from receiver functions abstract imaging of seismic velocity discontinuities with receiver functions suggests a complex mantle structure beneath the east anatolian plateau by stacking all the receiver functions as a function of ray parameter we examined the moveout characteristics of the data set and tested different velocity models to fit the arrival times of converted phases from the moho and the lithosphere asthenosphere boundary and their multiples the best fitting model shows anomalously thin crust 40 km and lithosphere 65 km and low uppermost mantle velocities causing systematic delays on later discontinuity arrivals these findings are consistent with the high plateau supported by partially molten and buoyant asthenosphere the upper mantle discontinuities are all visible in different frequencies 0 15 and 0 4 hz especially the 410 km discontinuity does not show frequency dependence in amplitude and suggests a sharpness of 10 km or less spatial variations of the 410 and 660 km discontinuities reveal anticorrelated topography and distinct zones of diminished amplitude associated with a detached slab and delaminated fragments of lithospheric mantle in the south the slab becomes deeper and horizontally deflected towards the east suggesting westward migration of slab detachment and resistance to slab penetration at the 660 km discontinuity in the north the mantle transition zone is characterized by two spatially limited lithospheric fragments with complex geometry at the center of the study area the transition zone is thin 230 km suggesting excess temperature of 120 c this warm mantle anomaly most likely is due to hot material trapped within the upper mantle between slab in the south and delaminated fragments in the north

high strain zones a unified model abstract where a shear zone is bounded by undeformed wall rocks and there is no volume change the deformation path within the zone on the bulk scale approximates a simple shear where the zone boundaries are stretched and the shear direction between the two boundaries is parallel to one of the principal stretching directions of the boundaries the deformation path within the zone is not a simple shear but still has monoclinic symmetry both simple shear and general monoclinic deformation paths should be regarded as special cases in nature because generally not only are the zone boundaries stretched but also the shear is oblique to the principal stretching directions of the boundaries in this general case the deformation path is triclinic we establish a model which includes this general case also taking into consideration volume change five independent parameters are required to characterize the rate of deformation of the flow four are sufficient to characterize the flow kinematics the model is generally triclinic and orthorhombic and monoclinic deformations are subgroups by varying the values of the characterizing parameters the various types of high strain zones can be represented the kinematics of flow within such zones and the accumulated finite deformation geometry are investigated many field observations such as for example lineations in transcurrent shear zones that vary between vertical and horizontal cleavage transected folds and the absence of sheath folds in some shear zones where folds have been significantly rotated can sometimes be better interpreted in the context of our general model

gps constraints on continental deformation in the africa arabia eurasia continental collision zone and implications for the dynamics of plate interactions 1 the gps derived velocity field 1988 2005 for the zone of interaction of the arabian african nubian somalian and eurasian plates indicates counterclockwise rotation of a broad area of the earth s surface including the arabian plate adjacent parts of the zagros and central iran turkey and the aegean peloponnesus relative to eurasia at rates in the range of 20 30 mm yr this relatively rapid motion occurs within the framework of the slow moving 5 mm yr relative motions eurasian nubian and somalian plates the circulatory pattern of motion increases in rate toward the hellenic trench system we develop an elastic block model to constrain present day plate motions relative euler vectors regional deformation within the interplate zone and slip rates for major faults substantial areas of continental lithosphere within the region of plate interaction show coherent motion with internal deformations below 1 2 mm yr including central and eastern anatolia turkey the southwestern aegean peloponnesus the lesser caucasus and central iran geodetic slip rates for major block bounding structures are mostly comparable to geologic rates estimated for the most recent geological period 3 5 myr we find that the convergence of arabia with eurasia is accommodated in large part by lateral transport within the interior part of the collision zone and lithospheric shortening along the caucasus and zagros mountain belts around the periphery of the collision zone in addition we find that the principal boundary between the westerly moving anatolian plate and arabia east anatolian fault is presently characterized by pure left lateral strike slip with no fault normal convergence this implies that extrusion is not presently inducing westward motion of anatolia on the basis of the observed kinematics we hypothesize that deformation in the africa arabia eurasia collision zone is driven in large part by rollback of the subducting african lithosphere beneath the hellenic and cyprus trenches aided by slab pull on the southeastern side of the subducting arabian plate along the makran subduction zone we further suggest that the separation of arabia from africa is a response to plate motions induced by active subduction

kinematic and thermochronological constraints on the xincheng huangpi fault and mesozoic two phase extrusion of the tongbai dabie orogen belt abstract the tongbai dabie orogenic belt dob is composed of several fault bounded terranes with different metamorphic and deformation intensities these tectonically stacked terranes were extruded along their boundary faults from depths of 120 km during the mesozoic systematic structural studies on these boundary faults can provide important information for the exhumation processes of the orogen in this paper we focus on the xincheng huangpi fault xhf which is located along the southern boundary of the central dob ultrahigh pressure complex unit uc comprehensive macro and micro structural u pb zircon and 40 ar 39 ar geochronological data are presented here to constraint the structural chronology of the xhf the xhf represents the lower detachment surface formed during extrusion of the uhp slab and experienced two episodes of ductile shearing the xhf experienced early southwestward thrusting around 234 ma and was exhumed to middle crustal levels during 234 195 ma with an average exhumation rates of ca 1 5 mm yr the uhp rocks then exhumed to the surface by erosion later nw se trending dextral strike slip shearing of the xhf occurred between 145 and 140 ma and was generally contemporaraneous with sinistral oblique slip of the xiaotian mozitan fault along the northern margin of the uc coeval dextral and sinistral oblique shearing along the southern and northern margins of the uc would have caused southeastern lateral extrusion this lateral extrusion has no relationship with the uhp exhumation

seismicity and rates of relative motion on the plate boundaries of western north america summary the consistency of earthquake data and plate tectonic models and other estimates of fault slip may be tested by estimating rates of motion from the earthquakes using the concept of seismic moment the contribution of individual events may simply be summed but a generally better estimate of long term average slip rate is obtained by integration over magnitudefrequency of occurrence relations estimates of fault motion rates associated with earthquakes are possible within about a factor of 2 using this approach if the major sources of uncertainty are given careful consideration e g incompleteness and inaccuracies in the earthquake data empirical moment magnitude relations and the effect of their stochasticity fault widths or depth extents the recurrence relations maximum magnitudes and the form of truncation at the maximum magnitude a formulation for the recommended magnitude density truncation is developed application of the latter method to the earthquake data of the offshore transform faults of the juan de fuca ridge system the queen charlotte fault zone and the northern vancouver island area in each case gives good agreement with rates from plate tectonic models for the southern san andreas fault and gulf of california area there is also good agreement with previous estimates obtained by summing the contributions of individual events however the displacement rate in the margin convergence zone of southern british columbia washington and oregon computed from the seismicity is at least a factor of 10 lower than from plate models and from other convergence estimates and primarily aseismic slip is suggested the fault motions as a function of time computed from the seismicity records have also been plotted and compared to the longterm average rates the plots permit estimates of the minimum present accumulated elastic strain and show if there are any temporal relations among earthquake displacements on different fault zones

m 6 earthquakes in southern california during the twentieth century no evidence for a seismicity or moment deficit abstract a broadly based report on seismic hazards in southern california wgcep 1995 concluded that the predicted seismicity exceeds that observed since 1850 a subsequent independent analysis argued that infrequent huge m 8 earthquakes are needed to explain the low rate of large earthquakes jackson 1996 frequency magnitude relationships and earthquake reporting suggest that the 1903 to 1997 catalog we present here with a b value of 1 0 and a rate of m 6 shocks of 0 42 to 0 49 yr 1 is nearly complete in contrast the 1850 to 1994 catalog used by wgcep is incomplete before the turn of the century and thus its reported seismicity rate of 0 32 m 6 shocks yr 1 is too low principally because the wgcep 1995 model results in b values of up to 4 0 for regions of lesser and blind faults the rate of m 6 shocks off the san andreas system predicted by the wgcep 1995 model is three times greater than that observed in this century because they obtained b 0 4 for m b 2 2 for m 7 3 on major faults their expected rate of m 7 san andreas shocks is twice as high as observed thus part of the seismicity and moment discrepancy identified by wgcep was caused by use of an incomplete catalog and part was caused by inappropriate b values we obtain a southern california moment release rate of 8 to 12 10 18 n m yr 1 which cannot be distinguished from the moment release estimated by fault slip or the moment accumulation inferred from plate motions or geodetically measured shear strain we thus find no evidence for a moment deficit significant aseismic moment release or for rare m 8 earthquakes off the san andreas fault system finally the number of m 6 earthquakes per decade does not depart significantly from a poisson process during this century and thus we find no evidence that the rate of seismicity is increasing now or at any other time since 1900

constrains on the origin and history of the eastern mediterranean basin abstract the basin formed along the northern passive margin of gondwanaland as a relict of the mesozoic neotethys in early mesozoic time though direct information from the basin itself is meagre the geology of its passive margins and the regional framework of the tethys evolution constrain the formation and history of the basin the eastern mediterranean and its passive margins are interpreted to have formed as a result of several faulting and continental breakup phases from early permian to middle jurassic times before pangaea s complete disintegration this led to the detachment of the eratosthenes and tauride blocks from the margins of the levant and herodotus basins respectively the latter merged in the northeast with the cyprus basin that extended along arabia s northern margin the main rifting probably occurred in the triassic leading to seafloor spreading in the herodotus and cyprus basins while along the levant margin important rifting also occurred in the jurassic during the initial rifting stages extension perpendicular to the levant margin was important but subsequently the tauride block drifted mainly northward the existence of the passive margins and slopes of the eastern mediterranean is documented at least from the end of the middle jurassic until then the basin was probably narrow 200 300 km but during the main phase of the africa laurasia separation it grew to twice its present width or more this scenario depends critically on the interpretation that the tauride block was originally located next to northeastern africa on the western side of the eratosthenes block plate convergence and consumption of the northern portion of the basin have taken place since mid cretaceous times but the active convergent boundary on its northern side formed only in the neogene by modification of earlier structures some intra plate deformation also took place especially in the neogene but it hardly changed the original configuration of the remaining portion of the basin

exhumation tectonics of the ultrahigh pressure metamorphic rocks in the qinling orogen in east china new petrological structural radiometric insights from the shandong peninsula 1 in eastern china the sulu area is recognized as the eastern extension of the qinling dabie belt which is famous for its ultrahigh pressure uhp metamorphism although numerous petrologic and geochemical works are available structural data are still rare this paper provides the first extensive study of bulk geometry and kinematic analysis of the shandong peninsula the study area is divided into three tectonic areas by cretaceous faults namely a southern uhp belt or sulu area a northern migmatite area and an eastern eclogite and migmatite area or weihai area conversely to the deeply entrenched idea that the later area belongs to the north china belt and the two others to the south china block scb we argue that all three areas are parts of the scb structural petrologic 40ar 39ar and u pb data comply with this new interpretation in the north shandong area mafic granulites enclosed as blocks within gneissic migmatites do not significantly differ from the sulu and weihai eclogites which also experienced a granulite facies overprint before migmatization the circa 210 200 ma age of the main ductile deformation is related to an extensional event during the triassic or indosinian orogeny this date corresponds to the temperature climax but the time of the pressure peak i e the real age of the uhp metamorphism is discussed

two stage triassic exhumation of hp uhp terranes in the western dabie orogen of china constraints from structural geology abundant exposures of widely distributed hp uhp metamorphic rocks in the western part of the dabie orogen enable us to study the tectonic evolution of hp uhp terranes associated with the world s largest preserved continental subduction zone previous tectonic models for the dabie orogen were based largely on metamorphic studies most of them lacking significant structural constraints we present a comprehensive structural analysis based on detailed structural geology the results suggest that syn uhp d0 at 241 231 ma and syn hp d1 at 225 215 ma southeast vergent thrusting formed a series of stacked structural slices this was followed by southeast vergent folding under amphibolite facies conditions d2 at 215 205 ma then a third generation of flexural folding occurred at shallow levels d3 at 200 184 ma this leads us to proposes a two stage triassic exhumation model in which initially rapid vertical extrusion d0 d1 from uhp to hp conditions to lower crustal levels is followed by slow southeastward extrusion d3 from lower crustal levels to the earth s surface the tectonic model combines the early southeastward vertical extrusion with the later southeastward lateral extrusion revealing two different stages and thus different types of triassic extrusion for the exhumation of hp uhp rocks in the dabie orogen the first stage extrusion occurred in the middle triassic whereas the second stage extrusion lasted from the late triassic to early jurassic these two extrusion episodes correlate with the two stages of triassic exhumation of the dabie hp uhp rocks respectively during continental collision