crustal versus mantle core complexes deep crustal and mantle rocks are exhumed in core complex mode of extension in three types of structures metamorphic core complexes oceanic core complexes and magma poor passive margins using available analogue and numerical models and their comparison with natural examples the present paper reviews the mechanical processes involved in these different types of extensional setting three main aspects are considered i the primary role of lithosphere rheology ii the lithosphere scale patterns of progressive deformation that lead to the exhumation of deep metamorphic or mantle rocks and iii the initiation and development of detachment zones crustal core complexes develop in continental lithospheres whose moho temperature is higher than 750 c with upper crust dominated strength profiles contrary to what is commonly believed it is argued from analogue and numerical models that detachments that accommodate exhumation of core complexes do not initiate at the onset of extension but in the course of progressive extension when the exhuming ductile crust reaches the surface in models convex upward detachments result from a rolling hinge process mantle core complexes develop in either the oceanic lithosphere at slow and ultra slow spreading ridges or in continental lithospheres whose initial moho temperature is lower than 750 c with sub moho mantle dominated strength profiles it is argued that the mechanism of mantle exhumation at passive margins is a nearly symmetrical necking process at lithosphere scale without major and permanent detachment except if strong strain localization could occur in the lithosphere mantle distributed crustal extension by upper crust faulting above a decollement along the ductile crust increases toward the rift axis up to crustal breakup mantle rocks exhume in the zone of crustal breakup accommodated by conjugate mantle shear zones that migrate with the rift axis during increasing extension

flow and fabric development during the diapiric rise of magma scaled isothermal experiments of the internal circulation induced by viscous drag at a diapir country rock interface are compared with published theoretical studies of flow induced finite deformation inside a rising sphere and new numerical results are presented for the incremental strain pattern developed in spherical diapirs the results predict a time dependent deformation history within rising diapirs that produces finite strains characterized by strong oblate flattening strains at the margin and strong vertical prolate strains in the center with an intervening zone of low plane strain finite strains are discussed in terms of the different sub fabrics expected to form in granitoids after considering the history of rheology and temperature distribution in rising magma strong rheological and temperature gradients are predicted for the margins of internally circulating diapirs that can lead to the formation of strong penetrative foliations at the margin and magmatic or even isotropic fabrics in the i

timing and duration of partial melting and magmatism in the variscan montagne noire gneiss dome french massif central unravelling the detailed pressure temperature time deformation p t t d evolution of magmatic and metamorphic rocks provides essential insights into the timing and duration of partial melting and related plutonism during crustal flow and migmatitic dome formation the montagne noire axial zone mnaz is a migmatitic dome located within the variscan orogen in the southern french massif central the timing of the main thermal event that was responsible for intense partial melting is still highly debated in this study we present new laser ablation inductively coupled plasma mass spectrometry la icp ms age data on micaschists migmatites and granites that clarify the p t t d evolution of the mnaz structurally controlled samples were collected in order to constrain the timing of metamorphism migmatization and plutonism regarding the main structural pattern d1 d2 and d3 d1 and d2 correspond to nappe stacking and dextral transpression respectively d3 is related to vertical shortening and coaxial thinning with a preferential ne sw to e w directed stretching la icp ms analyses on the syntectonic angles soulie and martys granites yielded u th pb monazite ages of 305 1 5 306 1 9 and 314 2 ma respectively five migmatitic rocks sampled in the eastern and central espinouse area yielded in situ ages ranging between 312 2 and 301 2 ma along the dome envelope two garnet staurolite bearing micaschists near saint pons de thomieres village gave in situ u th pb ages of 312 1 2 1 and 309 0 3 1 ma a fine grained gneiss with a d3 fabrics in the eastern dome envelope yield a 208pb 232th mean age at 305 7 3 9 ma all ages obtained in this study for the micaschists migmatites and granites range between 315 and 301 ma we interpret this time span as the record of the high thermal event responsible for intense crustal partial melting within the lower and middle crust the onset of partial melting occurred at ca 315 ma that marked the beginning of transpressional deformation d2 based on structural and petrological studies our new u th pb results suggest that 1 partial melting may have started at ca 315 ma and lasted 15 10 myr and 2 d2 et d3 developed between 315 and 300 ma and were synchronous d1 deformation ended at 315 ma the onset and duration of d1 related to nappe stacking and crustal thickening is still uncertain

variation of ti in quartz in gneiss domes exposing the world s youngest ultrahigh pressure rocks d entrecasteaux islands papua new guinea 1 the d entrecasteaux island gneiss domes papua new guinea expose the world s youngest ultrahigh pressure rocks 5 8 ma which were exhumed nearly isothermally to the mid crust at rates of cm yr 1 because quartz grains are internally distorted by deformation bands and have strongly interlobate grain boundary microstructures indicative of rapid grain boundary migration we infer that ti content in the quartz was frozen in by dynamic recrystallization that accompanied the continued deformation of the gneisses as they were exhumed through the crust toward the surface we infer that average ti content of an assemblage of quartz grains in a sample depends on the ratio of cooling rate to dynamic recrystallization rate an increase in the former preserves and captures a larger fraction of relatively high ti high temperature grains whereas an increase in the latter removes such relict grains and replaces them with a newer set of lower ti low temperature recrystallized grains based on this concept we use ti in quartz as a tool to infer domains of differing relative cooling rate across four d entrecasteaux island domes ti concentrations in quartz grains from 89 samples of quartzofeldspathic gneiss and eclogite increase inwardly away from the dome margins 2 5 20 ppm toward the center of the domes 20 100 ppm from this we infer that the most rapidly cooled rocks were exhumed near the center of the domes our data reinforces structurally based arguments that the symmetric domes were emplaced vertically into the crust as diapirs rather than laterally exhumed as a result of large magnitude slip on dome bounding detachment faults

application of stress release models to historical earthquakes from north china univariate and multivariate stress release models are fitted to historical earthquake data from north china it is shown that a better fit is obtained by treating separately the eastern part of the region including the north china plain and bohai sea and the western part of the region including the ordos plateau and its eastern boundary further improvement is obtained by fitting the large events m 7 6 and smaller events in the western region by different stress release models the comparisons are made by computing the likelihoods of the fitted models and discounting the number of parameters used by akaike s aic criterion the models are used to develop long term risk scenarios for the east and west regions

synthetic aperture radar observation of ocean roughness from rolls in an unstable marine boundary layer simultaneous synthetic aperture radar sar and cloud photographic observations of the atlantic ocean off the coast of florida were made from a high altitude aircraft when there was an unstable marine boundary layer the synthetic aperture radar images show unusual kilometer sized features on the ocean surface which are related to clouds the ocean near shore was cloud free and had no radar features while from 30 to 330 km offshore there were clouds and prominent kilometer sized features in the sar image these radar features are most prominent when the radar was looking upwind are less prominent when the radar was looking downwind and disappear entirely when the radar was looking crosswind since ocean radar echo strengths are believed to be controlled primarily by ocean waves satisfying the bragg relation these radar features most likely resulted from local enhancements of short gravity waves with 17 to 34 cm wavelengths which in turn are surface expressions of roll convections in a kilometer thick unstable marine boundary layer

long term earthquake prediction in the circum pacific convergent belt investigation of the time dependent seismicity in 274 seismogenic regions of the entire continental fracture system indicates that strong shallow earthquakes in each region exhibit short as well as intermediate term time clustering duration extending to several years which follow a power law time distribution mainshocks however interevent times of the order of decades show a quasiperiodic behaviour and follow the regional time and magnitude predictable seismicity model this model is expressed by the following formulas begin gathered log t t 0 19 m min 0 33 m p 0 39 log m 0 q hfill m f 0 73 m min 0 28 m p 0 40 log m 0 m hfill end gathered which relate the interevent time tt in years and the surface wave magnitude mf of the following mainshock with the magnitude mmin of the smallest mainshock considered the magnitude mp of the preceded mainshock and the moment rate m0 in dyn cm yr 1 in a seismogenic region the values of the parametersq andm vary from area to area the basic properties of this model are described and problems related to its physical significance are discussed

structure and kinematics of upper cenozoic extensional detachment on naxos and paros cyclades islands greece this paper presents a study of the ductile and brittle deformation on naxos and paros islands cyclades greece previous maps and studies of the two islands have shown that a major low angle fault zone separates surface rocks above the contact from an initially deep seated unit below showing a metamorphic evolution from high to low pressures structural analysis as well as available stratigraphical metamorphic and geochronological data taken together demonstrate that this fault zone is a major normal sense detachment zone dipping to the north rapid denudation of footwall rocks subsequent to high temperature metamorphism at an estimated rate of 1 8 9 5 mm yr attests for tectonic unroofing during regional scale top to the north ductile shearing the change from ductile to brittle behavior of the footwall rocks together with a progressive localization of high strain intensity deformations just below the hangingwall is explained by the progressive cooling of the uprisen footwall of the detachment mio pliocene clastic sediments in the hangingwall represent the infilling of half grabens opened in between major normal faults that are synthetic to the underlying ductile shear zone these sediments are as old as aquitanian 25 ma or younger than the earliest recognized evidence of ductile extension in the footwall this provides a minimum age for the onset of extension in the cyclades which appears significantly older than maximum ages reported up to now 13 5 ma structural data strongly suggest that the detachment fault was initially rather low dipping 35 an evolutionary model is proposed in which migmatite domes in the footwall correspond to the uprise of the lower ductile crust between two separating upper crustal blocks during a process of asymmetric boudinage of the crust this detachment model applies to a previously thickened continental lithosphere which then suffers thermal relaxation and weakening allowing extensional deformation to reach a climax during and subsequent to high temperature metamorphism in the cyclades crustal scale extension started after early cenozoic thrusting while the crust was still thick or less likely before late underthrusting below the present surface

the vaasa migmatitic complex svecofennian orogen finland buildup of a lp ht dome during nuna assembly tectonic evolution of the paleoproterozoic vaasa migmatitic complex vmc in the central part of the svecofennian accretionary orogen is deciphered using aeromagnetic and gravity maps deep seismic

a time predictable model for earthquake generation in greece 20th century data have been used to determine repeat times t of main shocks in seven of the most active seismogenic sources of shallow earthquakes in greece it is observed that t depends on magnitude mp of the preceding main shock and not on the magnitude mf of the following main shock this means that the time predictable model and not the slip predictable model is valid for the main shocks of these sources a relation of the form log t cmp a fits the data while the parameter a depends on the seismicity of each source and on the minimum cutoff magnitude of the main shocks considered a representative of all sources value equal to 0 3 is found for parameter c when mp is surface wave magnitude and t is measured in yr

long term earthquake prediction in central america and caribbean sea based on the time and magnitude predictable model abstract instrumental and historical information on strong mainshocks for 12 seismogenic sources in central america and caribbean sea has been used to show that the interevent time t t in years between two strong earthquakes and the magnitude m f of the following mainshock are given by the relations log t t 0 30 m m i n 0 48 m p 0 69 log m 0 13 70 m f 0 98 m m i n 0 31 m p 0 28 log m 0 4 55 where m min is the surface wave magnitude of the smallest mainshock considered m p the magnitude of the preceding mainshock and m 0 the moment rate per year in each source on the basis of these relations the probability of the occurrence of a mainshock during the decade 1993 to 2002 as well as the magnitude of this expected mainshock in each seismogenic source has been calculated the highest probability p 10 0 67 was estimated for the seismogenic source of el salvador a 1 for the occurrence of a large earthquake with expected magnitude m f 7 5 and high probabilities p 10 0 55 were estimated for the seismogenic sources of jamaica c 3 and puerto rico c 5 for earthquakes with expected magnitudes m f 7 5 in both sources

isostatic rebound due to tectonic denudation a viscous flow model of a layered lithosphere a four layer model of the upper 150 km of the earth is used to calculate the viscous response of continental crust and the underlying mantle to tectonic denudation the model comprises a strong upper crustal layer a weak lower crustal layer a very strong mantle lithosphere layer and a weak mantle asthenosphere layer which is in accord with experimental constraints on strength depth profiles for continental lithosphere the strength of each layer is represented by its effective viscosity flow in the crust and mantle is driven by buoyancy forces which arise from the unloading of an allochthon along a detachment fault by a series of instantaneous displacements earthquakes or rapid creep events numerical solutions obtained by using a finite element technique predict footwall uplift moho deflection and surface topography that are consistent with observations from the basin and range province of the western united states the calculated curvature of the footwall uplift is also similar to that observed and is sensitive to the geometry of the detachment fault such bending need not be elastically controlled hence the curvatures of footwall domes do not clearly place limits on the effective elastic thickness of the extending crust the upward deflection of the moho and the surface topography are sensitive to the viscosity structure and enable us to bound the range of the various viscosities by matching observations from the basin and range province which indicate no moho deflection and low magnitude of surface topography 3 5 km we estimate the upper crustal lower crustal and mantle lithospheric viscosities in the ranges 1021 1023 pa s 1019 1021 pa s and 1021 1023 pa s respectively

origin of a large scale fold nappe in the montagne noire variscan belt france abstract detailed structural analysis of a large recumbent fold in low grade palaeozoic sediments of the montagne noire and the previously established tectonometamorphic history of its crystalline substratum indicate a two stage development history first relatively homogeneous crustal thickening produced folds with steep axial planes associated with a regional cleavage s1 subsequently these structures became rotated and amplified in a subhorizontal flow with pure shear and simple shear components related to low angle thrusting the development of an associated horizontal crenulation cleavage s2 with a component of vertical shortening of s1 plus evidence for a synchronous decompression of autochthonous units allows this flow regime to be placed in the context of a thrust wedge undergoing gravitational spreading above a continuously contracting footwall decoupling of an extending thrust wedge from a contracting footwall by a basal thrust with low shear resistance explains bulk shortening uplift and exhumation of mid to lower crustal autochthonous basement during thrusting and recumbent folding at higher levels structural relationships in the southern montagne noire demonstrate that traditional tectonic units recognized in this area the so called nappes are in fact unrelated to the recumbent folding as inferred previously these nappes postdate not only the recumbent folding but also a later phase of refolding d3 associated with the formation of a gneiss dome the traditional nappe division can be simplified to a hanging wall and footwall domain of a major decollement that formed during a second syn collisional collapse d4 associated with the formation of intermontane stephanian basins the late timing of the nappes and simplified tectonic structure of the southern montagne noire imply a thinner d2 recumbent fold structure with only one major anticline syncline pair and is in better agreement with the low metamorphic grade of the area

two stage partial melting during the variscan extensional tectonics montagne noire france one of the striking features that characterise the late stages of the variscan orogeny is the development of gneiss and migmatite domes as well a s extensional late carboniferous and permian sedimentary basins it remains a matter of debate whether the formation of domes was related to the well documented late orogenic extension or to the contractional tectonics that preceded migmatization and magmatism are expected to predate extension if the domes are compression related regional anticlines but they must both precede and be contemporaneous with extension if they are extensional core complexes in the montagne noire area s outhern french massif central where migmatization magmatism and the deformation framework are well documented the age of the extensional event was unequivocally constrained to 300 0 ma therefore dating migmatization in this area is a key point for discriminating between the two hypotheses and understanding the late palaeozoic evolution of this part of the variscan belt for this purpose a migmatite and an associated anatectic granite from the montagne noire dome were dated by la icp ms u th pb on zircon and monazite and laser probe 40 ar 39 ar k ar on muscovite although zircon did not record any variscan age unequivocally related to compression 380 330ma two age groups were identified from the monazite crystals a first event at ca 319 ma u th pb on monazite is interpreted as a first stage of migmatization and as the emplacement age of the granite respectively a second event at ca 298 295 ma recorded by monazite u th pb and by the muscovite 40 ar 39 ar system in the migmatite and in th e granite could be interpreted as a fluid induced event probably related to a second melting event identified through the syn extensional emplacement of the nearby montalet leucogranite ca 295 ma ago the age s of these two events post date the variscan compression and agree with an overall extensional context for the development of the montagne noire dome shaped massif comparison of these results with published chemical epma dating of monazite from the same rocks demonstrates that the type of statistical treatment applied to epma data is crucial in order to resolve different monazite age populations

integration of geological and seismological data for the analysis of seismic hazard a case study of japan seismic hazard analyses are associated with large uncertainties when historical data are insufficient to define secular rates of seismicity such uncertainties may be decreased with geological data in areas where seismicity is shallow and produced by quaternary faulting to illustrate we examine intraplate japan large intraplate earthquakes in japan characteristically produce surface ruptures along mappable quaternary faults and show a systematic relation between seismic moment m 0 and rupture length i log m 0 23 5 1 94 log i it is observed that within the bounds placed by geologically assessed slip rates the mean regional moment release rate m 0 resulting from slip on mapped quaternary faults is in accord with estimates of m 0 determined with the 400 yr record of seismicity recent work also shows that when the repeat time t of earthquakes on quaternary faults in southwest japan is assumed to equal m 0 m 0 g where m 0 is estimated for rupture extended over the entire fault length and m 0 g is the geologically assessed moment release rate of each fault the moment frequency distribution of earthquakes predicted from the geologic record is virtually identical to that seen with the 400 yr record of seismicity these observations indicate that the geologic record of quaternary fault offsets contains sufficient information to predict both the spatial and size distribution of intraplate earthquakes in japan a contour map of the average recurrence time of ground shaking of jma intensity v is thus computed using an empirical relation between seismic moment and the areal distribution of seismic intensity and assuming that the repeat time t of earthquakes on each quaternary fault equals m 0 m 0 g the map demonstrates how quaternary fault data may be used to assess long term seismic hazard in areas of active faulting where historical records of seismicity are relatively short or absent another shortcoming of conventional seismic hazard analysis is that hazard is not considered a function of the time since each fault in a region last ruptured a simple procedure is used to demonstrate how the time dependent nature of the earthquake cycle affects the evaluation of seismic hazard the distribution of seismic shaking characteristic of large interplate earthquakes offshore of japan is estimated from published isoseismal maps the observed average repeat times of ruptures along specific segments of the plate boundaries then provide the basis to make probabilistic estimates of the next expected time of seismic shaking due to plate boundary earthquakes when data are too few to document the average repeat times of rupture the estimates of probability are calculated with data relating to the relative coseismic slip during past earthquakes and the rate of interseismic strain accumulation interpreted within the framework of the time predictable model of earthquake occurrence results are displayed as maps of instantaneous seismic hazard the probability that seismic shaking will occur conditional to knowledge of where in time each fault in a region presently resides with respect to the earthquake cycle

the late alpine evolution of an extensional shear zone naxos greece the mid miocene structural evolution of the metamorphic complex on naxos involved deformation in a kilometre scale low angle ductile shear zone the structures described are consistent with exhumation of the metamorphic complex during crustal extension after and possibly during localized high temperature barrovian style metamorphism non coaxial fabrics developed throughout the structural history indicate that upper levels were transported to the north during ductile extension this shear sense is opposite that inferred previously for the development cordilleran style metamophic core complexes in the cvclades ductile deformation was accompanied during its later stages by e w directed compression

an application of the time and magnitude predictable model for the long term prediction of strong shallow earthquakes in the japan area the country of japan and its surrounding area has been divided into 12 seismogenic sources on the basis of certain seismotectonic and geomorphological criteria in each of these sources interevent times between successive mainshocks with magnitudes equal to or larger than certain cutoff magnitudes were considered these interevent times as well as the magnitudes of the mainshocks have been used to determine the following relations log t t 0 30 m min 0 19 m p 0 18 log m 0 2 41 m f 0 88 m min 0 25 m p 0 46 log m 0 9 06 where tt is the interevent time measured in years m min is the surface wave magnitude of the smallest mainshock considered mp is the magnitude of the preceding mainshock mf is the magnitude of the following mainshock and m is the yearly released seismic moment in each source on the basis of these two relations and taking into account the time of occurrence and the magnitude of the last mainshock in each source time dependent conditional probabilities for the occurrence of the next large ms 7 5 shallow mainshocks in the 12 seismogenic sources during the next 10 yrs 1993 to 2002 and the magnitudes of the expected mainshocks are determined for seismogenic sources 5 fukushima 9 western honshu 7 southern hokkaido 1 ryukyu islands and 12 okushiri island relatively high probabilities p 10 0 5 were assigned it is of interest to note that in seismogenic source 12 okushiri for which an expected magnitude of 7 5 was calculated an earthquake with a magnitude of 7 6 national earthquake information center occurred on 12 july 1993

deep crustal source of gneiss dome revealed by eclogite in migmatite montagne noire french massif central in orogens worldwide and throughout geologic time large volumes of deep continental crust have been exhumed in domal structures extension driven ascent of bodies of deep hot crust is a very efficient mechanism for rapid heat and mass transfer from deep to shallow crustal levels and is therefore an important mechanism in the evolution of continents the dominant rock type in exhumed domes is quartzofeldspathic gneiss typically migmatitic that does not record its former high pressure hp conditions in its equilibrium mineral assemblage rather it records the conditions of emplacement and cooling in the mid shallow crust mafic rocks included in gneiss may however contain a fragmentary record of a hp history and are evidence that their host rocks were also deeply sourced an excellent example of exhumed deep crust that retains a partial hp record is in the montagne noire dome french massif central which contains well preserved eclogite garnet omphacite rutile quartz in migmatite in two locations one in the dome core and the other at the dome margin both eclogites record p 1 5 0 2 gpa at t 700 20 c but differ from each other in whole rock and mineral composition deformation features shape and crystallographic preferred orientation cpo extent of record of prograde metamorphism in garnet and zircon and degree of preservation of inherited zircon rim ages of zircon in both eclogites overlap with the oldest crystallization ages of host gneiss at c 310 ma interpreted based on zircon rare earth element abundance in eclogite zircon as the age of hp metamorphism dome margin eclogite zircon retains a widespread record of protolith age c 470 450 ma the same as host gneiss protolith age whereas dome core eclogite zircon has more scarce preservation of inherited zircon possible explanations for differences in the two eclogites relate to differences in the protolith mafic magma composition and history and or the duration of metamorphic heating and extent of interaction with aqueous fluid affecting zircon crystallization differences in hp deformation fabrics may relate to the position of the eclogite facies rocks relative to zones of transpression and transtension at an early stage of dome development regardless of differences both eclogites experienced hp metamorphism and deformation in the deep crust at c 310 ma and were exhumed by lithospheric extension with their host migmatite near the end of the variscan orogeny the deep crust in this region was rapidly exhumed from 50 to 10 km where it equilibrated under low p high t conditions leaving a sparse but compelling record of the deep origin of most of the crust now exposed in the dome

atmospheric boundary layer rolls observed by the synthetic aperture radar aboard the ers 1 satellite two synthetic aperture radar sar images acquired by the european remote sensing satellite ers 1 over the jade weser estuary in the german bight of the north sea on january 2 and 20 1992 are analyzed the images show sea surface manifestations of atmospheric boundary layer rolls this is inferred from the orientation of the quasi periodic sea surface patterns which are aligned approximately with the wind direction from the ratio of the wavelength of the patterns to the height of the boundary layer and from the conditions encountered in the atmospheric boundary layer as measured quasi simultaneously by radiosondes the atmospheric boundary layer rolls were generated by a dynamic instability on january 2 and by a thermal instability on january 20 for the first time quantitative estimates of variations of the wind velocity at the sea surface associated with the atmospheric rolls are extracted from a spaceborne radar sar image it is shown that wind velocities derived from sar image intensity variations are in agreement with theoretical estimates

mechanisms of seismic quiescences in the past decade there have been major advances in understanding the seismic cycle in terms of the recognition of characteristic patterns of seismicity over the entire tectonic loading cycle the most distinctive types of patterns are seismic quiescences of which three types can be recognized post seismic quiescence which occurs in the region of the rupture zone of an earthquake and persists for a substantial fraction of the recurrence time following the earthquake intermediate term quiescences which appear over a similar region and persist for several years prior to large plate rupturing earthquakes andshort term quiescences which are pronounced lulls in premonitory swarms that occur in the hypocentral region hours or days before an earthquake although the frequency with which intermediate term and short term quiescences precede earthquakes is not known and the statistical significance of some of the former has been challenged there is a need if this phenomena is to be considered a possibly real precursor to consider physical mechanisms that may be responsible for them the characteristic features of these quiescences are reviewed and possible mechanisms for their cause are discussed post seismic quiescence can be readily explained by any simple model of the tectonic loading cycle as due to the regional effect of the stress drop of the previous principal earthquake the other types of quiescence require significant modification to any such simple model of the possibilities considered only two seem viable in predicting the observed phenomena dilatancy hardening and slip weakening intermediate term quiescences typically occur over a region equal to or several times the size of the rupture zone of the later earthquake and exhibit a relationship between the quiescence duration and size of the earthquake they thus involve regional hardening or stress relaxation and agree with the predictions of the dilatancy diffusion theory short term quiescences on the other hand are more likely explained by fault zone dilatancy hardening and or slip weakening within a small nucleation zone because seismicity is a locally relaxing process seismicity should follow a behaviour known in rock mechanics as the kaiser effect in which only a very slight increase in strength due to dilatancy hardening or decrease in stress due to slip weakening is required to cause quiescence this is in contrast to other precursory phenomena predicted by dilatancy which require large dilatant strains and complete dilatancy hardening

viscous collision in channel explains double domes in metamorphic core complexes comment rey et al 2011 1 propose an appealing numerical model for the development of gneiss domes in an extending crust they suggest that extension in the upper brittle crust triggers oppositely verging ductile flows in the deep crust resulting in the rising of two domes of foliation separated by a

long term earthquake prediction along the north and east anatolian fault zones based on the time and magnitude predictable model summary the north and east anatolian fault zones have been separated into 10 seismogenic sources on the basis of certain seismological and geomorphological criteria in each of these sources the interevent times between successive main shocks with magnitudes equal to or larger than a certain magnitude threshold were considered these times and the magnitudes of the main shocks have been used to determine the following empirical relations log tt 0 27 mmin 0 19 mp a mf 0 76 mmin 0 48mp m where tt is the interevent time measured in years m min the surface wave magnitude of the smallest main shock considered mp is the magnitude of the preceding main shock and mf is the magnitude of the following main shock multiple correlation coefficients equal to 0 83 and 0 70 and standard deviations equal to 0 16 and 0 34 were calculated for the first and second of these relations respectively on the basis of these relations and taking into account the time of occurrence of the last main shock the probabilities of occurrence of main shocks in each seismogenic source during the next decade were determined

an l band ocean geophysical model function derived from palsar this paper examines l band normalized radar cross section nrcs dependence on ocean surface wind more than 90 000 match ups each consisting of the l band hh nrcs incidence angles wind speeds and wind directions were collected from the phased array l band synthetic aperture radar palsar and scatterometer wind vectors based on the match ups the l band hh nrcs dependence on incidence angle and wind vector is modeled for 0 20 m s wind speeds and 17deg 43deg incidence angles the derived relation indicates that the wind sensitivity of the l band nrcs is less than that of the c band at moderate winds and large incidence angles whereas comparable at stronger winds 10 m s and small incidence angles the upwind crosswind difference is amplified in the 10 15 m s range followed by an almost zero amplitude from 4 to 8 m s which represents a clear phase shift with the c band vv and ku band hh models wind speeds are then estimated from the match ups based on the derived model function a comparison with the reference scatterometer winds reveals a 0 05 m s bias and a 1 85 m s root mean square error where crosswind data give rise to large errors due to low wind sensitivity at wind speeds of around 10 m s particularly at large incidence angles the l band nrcs behavior in strong winds 20 m s at which the c band is saturated was not determined in the current model due to the limited number of the match ups

compressional metamorphic core complexes low angle normal faults and extensional fabrics in compressional tectonic settingscompressional core complexesm searle t lamont metamorphic core complexes mccs are interpreted as domal structures exposing ductile deformed high grade metamorphic rocks in the core underlying a ductile to brittle high strain detachment that experienced tens of kilometres of normal sense displacement in response to lithospheric extension extension is supposedly the driving force that has governed exhumation however numerous core complexes notably himalayan karakoram and pamir domes occur in wholly compressional environments and are not related to lithospheric extension we suggest that many mccs previously thought to form during extension are instead related to compressional tectonics pressures of kyanite and sillimanite grade rocks in the cores of many of these domes are c 10 14 kbar approximating to exhumation from depths of c 35 45 km too great to be accounted for solely by isostatic uplift the evolution of high grade metamorphic rocks is driven by crustal thickening shortening regional barrovian metamorphism isoclinal folding and ductile shear in a compressional tectonic setting prior to regional extension extensional fabrics commonly associated with all these core complexes result from reverse flow along an orogenic channel channel flow following peak metamorphism beneath a passive roof stretching fault in naxos low angle normal faults associated with regional aegean extension cut earlier formed compressional folds and metamorphic fabrics related to crustal shortening and thickening the fact that low angle normal faults exist in both extensional and compressional tectonic settings and can actively slip at low angles c 60 is needed

structure of the surface wind field from the seasat sar an intensive analysis of the vector wind field of one seasat data set pass 1339 is described wind speed and direction signatures are found in seasat sar synthetic aperture radar images and the resulting estimates are compared with the seasat a scatterometer system sass and simultaneous noaa p 3 aircraft measurements a power law is presented to relate sar measured backscatter to sass estimated wind speed and the sar estimates are shown to agree with the sass estimates to within a standard error of 0 7 m s over a range of wind speeds from 3 m s to 13 m s the surface expressions of atmospheric roll vortices are apparent in several of the sar images and may be responsible for the wind direction signature in these cases wind field estimates averaged over regions of variable sizes are possible because of the high resolution of sar imagery a method for extracting low wave number directionality and its variability from sar spectra is described and sar direction estimates obtained from spectra of 6 4 km square images are shown to have a precision of approximately 10 although a comparison data set that could validate these higher resolution estimates is lacking averages over 40 km square regions are in good agreement with the other wind field information the sar wind direction estimates yield a more complete interpretation in a region with a turning wind field near a front that is ambiguous with only sass observations in this region the flow patterns of the high resolution estimates appear consistent with our knowledge of the overall circulation considering all the observations however in another region the small scale variability is too large and random to represent real wind variability although averages derived from these estimates are still reliable

reappraisal of variscan tectonics in the southern french massif central abstract the comprehensive kinematic analysis of the variscan fold nappes and associated wildflysch in the southeastern montagne noire shows that the nappes were thrust northeastwardly along the cevennes fault as a result of strike slip dominated sinistral transpression between 340 and 323 ma macro and map scale recumbent folding and nappe stacking were achieved by ene directed strike parallel thrust shearing the recumbent folds evolved into sheath folds by interplay of continued strike parallel thrust shearing and strike normal shortening manifested by north verging folds that grew during wildflysch sedimentation these results call for a tectonic reassessment of the southern side of the variscides the foreland basin was decoupled from the hinterland along orogen scale sinistral fault s trending at a high angle to the orogenic trend which interacted with a variety of hinterland ward thrust systems the shift from sinistral transpression to dextral transtension along the cevennes fault after 317 ma accompanied the closure of the iberian armorican syntax by accommodating northeastward escape and gravitational collapse of the northern limb of the syntax these results illustrate the impact of the shift from plate convergence controlled to escape controlled kinematics on shear sense reversal and lower crust exhumation along long lived strike slip fault systems

l band radar backscatter dependence upon surface wind stress a summary of new seasat 1 and aircraft observations radar backscatter from the ocean depends on surface wind stress for a wide range of radar wavelengths here we have reviewed the wind radar relationships for l band radar wavelengths near 25 cm and 20 angle of incidence and hh polarization using a number of aircraft and seasat i sar observations at this wavelength the l band backscatter coefficient from the ocean appears to depend upon surface wind speed u and direction in the following manner k a 1 b cos 2 the wind speed coefficient a is 0 5 0 1 for a wide range of wind speeds the wind direction coefficient b is near zero i e b 0 05 0 05 for lower winds and stable marine boundary layers however one unusual aircraft observation suggests that b 0 20 0 05 for moderate wind speeds and an unstable marine boundary layer we have examined a variety of aircraft and seasat i observations seasat synthetic aperture radar sar observations in conjunction with simultaneous seasat scatterometer measurements provide an excellent measurement of the wind speed coefficient a since a variety of wind speeds can be observed in a few minutes aircraft observations provide an excellent measurement of the wind direction coefficient b since a number of directions can be examined in about 1 hour with special flight patterns designed for multiple look directions thus both aircraft and spacecraft observations were studied in this work we have interpreted these aircraft and spacecraft results in terms of existing theoretical models for radar scattering from the ocean we believe that modulation of echo power by the magnitude of the wind occurs through both large scale slope effects as well as through growth of the short gravity wave height spectrum our data is near an angle of incidence of 20 where a two scale scattering model must be used

probability of earthquake recurrence with nonuniform stress rates and time dependent failure current methods for calculation of long term probabilities for the recurrence of large earthquakes on specific fault segments are based upon models of the faulting process that implicitly assume constant stress rates during the interval separating earthquakes and instantaneous failure at a critical stress threshold however observations indicate that the process of stress recovery following an earthquake involves rate variations at all time scales in addition to stress steps caused by nearby earthquakes additionally the existence of foreshocks aftershocks and possible precursory processes suggest that there may be significant time dependence of the earthquake nucleation process a method for determining the conditional probabilities for earthquake occurrence under conditions of irregular stressing is developed that could be useful at all time scales including those pertinent to short and intermediate term prediction used with models for earthquake occurrence at a stress threshold the addition of variable stressing introduces a simple scaling of the conditional probabilities by stress level and stress rate a model for the time dependent nucleation of earthquake slip has been proposed recently that is based upon laboratory observations of fault strength this failure criterion results in large but relatively short duration changes in the probability of earthquake recurrence particularly following stress steps applied to populations of earthquakes the models predicts a 1 t decay of seismicity following stress steps as observed for aftershocks and for frequency of foreshock mainshock pairs the model suggests that variations of seismicity rates of small earthquakes in the nucleation zone of the expected earthquake directly indicate variations in probability of recurrence of the large earthquake

fluids p t paths and the fates of anatectic melts in the earth s crust this paper presents a model for the longevity and physical behaviour of anatectic melts in the earth s crust it is assumed that a thermal anomaly has caused partial fusion of biotite plagioclase quartz rocks to produce a granitic melt and restitic solids the focus is on the potential chemical and physical outcomes as a function of the various p t fluid conditions rocks undergoing fluid present melting will sustain an increase in bulk density and will become more gravitationally stable diapiric up welling of such material should not occur in fluid absent melting the bulk density will decrease and foster gravitational instability stresses in the surrounding rocks could however lead to fracture and rapid evacuation of the melt with excess fluid and without melt segregation isobaric cooling will cause immediate freezing if t rises above the biotite quartz melting reaction freezing will still occur at the original reaction t diapiric up welling should not occur biotite bearing diatexites might be formed by large degrees of fusion but magma ascent is unlikely in isothermal decompression immediate freezing will ensue and the migmatite should contain orthopyroxene rather than biotite with excess fluid and melt segregation cooling will induce freezing at the fluid saturated granite solidus magma ascent could however occur even for xflh2o 1 in isothermal decompression melt will persist to the granite solidus for the imposed xflh2o limited magma ascent could occur all granites should contain primary igneous biotite for fluid deficient rocks without melt segregation freezing will occur at the t of the original melting if the reaction is overstepped solidification will occur at the original xflh2o magma formation is unlikely migmatites should contain either pyroxene retrogressed to biotite or biotite alone on decompression immediate freezing is likely if t remains at the biotite quartz reaction for higher t melt will survive decompression and freeze at the fluid saturated solidus for some increased xflh2o magma ascent is possible and the melt will freeze very close to the wet granite solidus in fluid deficient rocks with melt segregation cooling and crystallization will cause fluid saturation in situ segregated melt will freeze at the original xflh2o melt ascent will however cause exsolution of a co2 rich fluid with fluid escape melt will freeze close to the wet granite solidus an increase in melt proportion may accompany magma ascent or source up welling any low p granite intrusion should be charnockitic for fluid absent rocks without melt segregation freezing will occur on cooling to the t of the original reaction only transitory migmatites could be formed but melt will survive decompression almost to the h2o saturated granite solidus the rocks will reveal former melt presence only in the existence of veins of coarse retrograde biotite with isothermal decompression further melting may occur forming an orthopyroxene bearing granulite facies migmatite in fluid absent situations with melt segregation magma could be efficiently transported to higher crustal levels if the melt proportion were insufficient for magma formation granulite facies migmatites would result ascending melt would progressively dissolve any entrained restite the granites produced should be charnockitic to aid in interpretation of the modelling results we suggest that it may be slightly more common for the highest grade metamorphic terranes to exhibit isobaric cooling paths that fluid present anatexis is normally limited to the shallower parts of the crust and that fluid absent reactions are more likely at greater depths we conclude that the best models for natural fluid present anatexis are those dealing with essentially pure h2o fluid and that fluid deficient conditions will dominate over fluid excess we also believe that it is common for melts to be physically segregated on scales larger than the diffusion paths of many elements

stochastic slip predictable model for earthquake occurrences recent geophysical studies have indicated that an earthquake recurrence interval and the size of the preceding event are positively correlated this observation is the basis for the deterministic time predictable recurrence model of shimazaki and nakata using the basic assumptions of the time predictable recurrence model we develop a stochastic model of earthquake occurrence that incorporates temporal dependence this paper discusses the formulation of the model and the effect of including temporal dependence hazard estimates for a section of the san andreas fault near parkfield where data has suggested time predictable behavior are obtained for illustrative purposes comparisons are made with the poisson model results indicate that currently used poisson models may give lower estimates of the seismic hazard when there has been a seismic gap of the various sensitivity analyses performed it is observed that slip rate has the largest effect on exceedence probabilites computed from the stochastic time predictable model therefore accurate determinations of slip rates both seismic and aseismic can substantially reduce the uncertainty in seismic hazard estimates

mode of crustal extension determined by rheological layering the results of numerical modelling show that the mechanical stratification of the crust provides the fundamental control on fault spacing and ultimately the mode of extension macroscopic pre existing structures and weaknesses are often thought to govern the behaviour of continental crust under extension and many prior studies have focussed on the effect of heterogeneities in triggering faulting and exhumation of lower crustal material the role played by such features is in fact subordinate to that exerted by the rheological contrast from upper to lower crust in our numerical model the temperature gradient dictates the transition from a strong brittle upper crust to a weaker ductile lower crust we see two distinct extension modes that depend on this vertical rheological contrast the distributed faulting mode and the metamorphic core complex mode the ratio of the integrated strength of the upper to lower crust is an indicator of the resulting mode of extension when this strength ratio is small i e the lower crust is relatively strong the result is distributed densely spaced faulting with limited slip on each fault and no exposure of lower crustal rocks an example could be faulting in the north sea a large strength ratio hence a weak lower crust that flows easily leads to stretching being strongly localised onto relatively few normal fault zones each fault accommodates large displacements eventually dissecting the upper crust and resulting in exhumation of the lower crust this is representative of the metamorphic core complexes of the western u s a and the aegean the actual critical strength ratio for the transition between modes will depend upon secondary factors such as the relative thickness of the lower crust with respect to the upper crust and the degree of fault weakening d 2005 elsevier b v all rights reserved

a time and magnitude predictable model for generation of shallow earthquakes in the aegean area repeat times of strong shallow mainshocks have been determined by the use of instrumental and historical data for 68 seismogenic sources in the aegean and surrounding area 34 n 43 n 18 e 30 e for 49 of these sources at least two interevent times three mainshocks are available for each source by using the repeat times for these 49 sources the following relation has been determined log t t 0 36m min 0 35m p a wheret t is the repeat time measured in years m p the surface wave magnitude of the preceding mainshock mmin the magnitude of the smallest earthquake considered and a parameter which varies from source to source a multilinear correlation coefficient equal to 0 89 was determined for this relation

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

a two state poisson model for seismic hazard estimation abstract most seismic hazard analyses assume that earthquakes have a poisson distribution and that data from recorded earthquakes can be used to predict future seismic activity in a region historic catalogs however may show different earthquake occurrence rates for regions that are geologically similar suggesting on a local scale at least temporal variations in seismicity the simple two state model presented here allows a region to have both seismically active and inactive states in this model earthquakes have a poisson distribution during both states but occur at a higher rate when the region is active the probability of changing from one state to the other at any time is constant the two state model reduces to the usual poisson model if the region is always active or if the rate is the same for both states

alpine deformation on naxos greece a detailed structural study of naxos attic cycladic massif greece reveals two major deformation events the first one is associated with large scale thrusting and high pressure low temperature metamorphism during an early alpine subduction episode the second event occurred during continental extension and the associated development of localized thermal domes where lower crustal rocks were brought into contact with upper crustal units along a major shallow dipping shear zone we agree with a model of naxos as a cordilleran type metamorphic core complex however our observations show that the sense of shear was upper plate moving north during the second event calling for a reinterpretation of existing tectonic models of the cyclades

footprints of storms on the sea a view from spaceborne synthetic aperture radar synthetic aperture radar sar on board seasat observed images of stormlike echoes on the sea in 1978 the core of these images is usually an echo free hole which is attributed to the damping of the short 30 cm radar detectable gravity waves by the intense rain in the storm core although the beating down of waves by rain is consistent with observations by seafarers and with the first scientific explanation of the phenomenon by reynolds 1875 neither theory nor experiment has provided definitive support one experiment appears to provide the key it shows that the kinetic energy of the rain produces sufficient turbulence in a thin fresh water layer to damp 30 cm waves in 10 20 s thus producing the echo free hole a sequence of positive feedbacks then serves to damp the longer waves the angular dependence of the sea surface echo cross sections seen by seasat sar outside the echo free hole indicates winds diverging from the downdraft induced by the intense rain core the wind generated waves and associated echoes extend out to a sharply defined gust front the sea surface footprint thus mimics the features of a storm microburst the variations in surface radar cross section due to a combination of rain and wind effects impacts spaceborne measurements of surface winds by scatterometry and rainfall measurements by radar portions of this synthesis remain speculative but serve as hypotheses for further research

long term earthquake clustering summary we analyse statistically the long term properties of several instrumental earthquake catalogues complete catalogues exhibit both short and long term clustering for earthquakes of all depth ranges after accounting for the effect of short term clustering we find that in residual declustered catalogues long term clustering not periodicity characterizes the occurrence of all earthquakes shallow intermediate and deep the degree of clustering in residual catalogues is the same for earthquakes in different depth ranges circumstantial evidence indicates that the long term v ariation of seismicity is governed by a power law temporal distribution as in short term clustering it is scale invariant the fractal dimension of an earthquake set on the time axis is of the order of 0 8 0 9 therefore mainshock occurrence is closer to a stationary poisson process than standard aftershock sequences of shallow earthquakes

ductile and brittle shortening extension parallel folds and maintenance of crustal thickness in the central aegean cyclades greece in contrast to previous studies that concentrated on the two dimensional crustal strain in the central aegean region cyclades it is shown that nne ssw extension via ductile and brittle stretching and low angle detachments was accompanied and or alternated with horizontal shortening perpendicular to the stretching direction since at least the early miocene roughly e w directed ductile shortening produced large scale overturned and upright folds having axes parallel or slightly oblique to the stretching lineation upright folding and arching of low angle normal faults occurred above the brittle ductile transition and brittle e w compression culminated with vertical axis block rotations strike slip faults and minor thrusts since at least the early miocene the structure of the cycladic massif evolved through alternating and or coeval increments of horizontal shortening and vertical thinning associated with an approximately constant nne ssw stretching exact magnitudes of the vertical and horizontal deformational components are difficult to assess nevertheless we note that extensional tectonics that affected the cyclades during the last 15 20 m y have produced no net crustal thinning we suggest that crustal thickness was maintained by extension parallel folds which represent true contractional structures and that crust was fed into the extended region from its margins

the montagne noire migmatitic dome emplacement french massif central new insights from petrofabric and ams studies in the southern french massif central the montagne noire axial zone is a ne sw elongated granite migmatite dome emplaced within visean south verging recumbent folds and intruded by syn to late migmatization granitoids the tectonic setting of this dome is still disputed thus several models have been proposed in order to better understand the emplacement mechanism of this dome petrofabric and anisotropy of magnetic susceptibility ams studies have been carried out in the granites and migmatites that form the dome core magmatic texture and to a lesser extent weak solid state texture are dominant as a paramagnetic mineral biotite is the main carrier of the magnetic susceptibility on the basis of 135 ams sites the magnetic fabrics appear as independent of the lithology but related to the dome architecture coupling our results with previous structural and geochronological studies allows us to propose a new emplacement model between 340 325 ma the palaeozoic series underwent a compressional deformation represented by nappes and recumbent folds involving the thermal event leading to partial melting until 325 310 ma the dome emplacement was assisted by diapiric processes an extensional event took place at 300 ma after the emplacement of the late to post migmatitic granitic plutons in the northeast side of the dome a brittle normal dextral faulting controlled the opening of the graissessac coal basin

gneiss domes and orogeny many gneiss domes record positive feedback between decompression and partial melting of orogenic middle crust exhumed orogens are riddled with gneiss domes cored by migmatites that underwent dehydration melting during decompression the decreasing buoyancy associated with increasing melt fraction drives further decompression at near isothermal conditions as the partially molten crust rises diapirically this combination of processes may explain the generation and retention of large volumes of crustally derived melt recorded in many deep seated migmatite terranes and inferred for active orogens in exhumed orogens the signature of the rapid ascent of partially molten crust is a gneiss dome cored by migmatite granite the large volume of material involved in the vertical transfer of partially molten crust indicates that the formation of gneiss domes is an efficient mechanism for heat advection during orogenesis

seasat sar cross section modulation by surface winds goasex observations seasat radar observations of the gulf of alaska by the synthetic aperture radar sar and the wind speed scatterometer sass indicate that l band backscatter is modulated by wind speed and possibly by wind direction it is noted that the l band backscatter is approximately proportional to the square root of surface winds and that upwind crosswind differences in backscatter can be as large as 10 in the range of these wind speeds it is suggested that seasat sar images in conjunction with seasat scatterometer data may provide fine scale mapping of ocean winds and directions the need for further seasat sar sass comparisons in order to extend the range of wind speeds is stressed

circum pacific seismic potential 1989 1999 the seismic potential for 96 segments of simple plate boundaries around the circum pacific region is presented in terms of the conditional probability for the occurrence of either large or great interplate earthquakes during the next 5 10 and 20 years i e 1989 1994 1989 1999 and 1989 2009 this study represents the first probabilistic summary of seismic potential on this scale and involves the comparison of plate boundary segments that exhibit varying recurrence times magnitudes and tectonic regimes presenting these data in a probabilistic framework provides a basis for the uniform comparison of seismic hazard between these differing fault segments as well as accounting for individual variations in recurrence time along a specific fault segment and uncertainties in the determination of the average recurrence time

metamorphic core complexes windows into the mechanics and rheology of the crust metamorphic core complexes are products of normal fault displacements sufficient to exhume rocks from below the brittle ductile transition these faults detachments may initiate within the brittle crust at steep angles but they sole into the ductile middle crust and during displacement rotate to gentler dips due to hanging wall extension the exhumed footwall commonly adopts an arched or domed geometry owing to flexural isostatic readjustment and may be overlain by strongly extended upper crustal rocks that slipped on gently dipping low friction shallow segments of the detachment metamorphic rocks exhumed beneath the detachment record progressively increasing flow stress strain localization and strain rate with decreasing temperature providing a window into physical conditions and deformational processes in the mid crust the metamorphic and deformational history of the footwall rocks may reflect tectonic processes that predate formation of the detachment fault in addition to those accompanying exhumation these processes may include diapiric emplacement of gneiss domes or exhumation in a subduction channel and may not be directly related to formation of the core complex factors favouring core complex formation are high gravitational potential energy of the extending crust weak rheology and a change in the tectonic boundary conditions such as a cessation or slowing of plate convergence

test and application of the time and magnitude predictable model to the intermediate and deep focus earthquakes in the subduction zones of the circum pacific belt abstract the test and application of the time and magnitude predictable model in the subduction zones around the circum pacific belt is performed each subduction zone was separated in several seismogenic regions on the basis of tectonic and geometrical features of the subducting lithosphere and for three different depth ranges the data derived from these seismogenic regions were used in order to check the suitability of the regional time and magnitude predictable model as this model was defined for shallow events the results obtained in the present study confirm that this model appropriately describes the behavior of deep seismicity in these regions since a positive c 0 31 0 003 and a negative c 0 13 0 047 dependence were found for the logarithm of the interevent times and the magnitude of following mainshock respectively on the magnitude of the preceding mainshock moreover the slip predictable model was rejected since a negative dependence was found e 0 19 between the interevent times and the magnitudes of the following mainshock probabilities of occurrence of the future strong m 7 0 events in each seismogenic region have been determined for the next decade conditioned on the previous occurrence of such events the magnitudes of the expected events have also been estimated statistical tests for the estimated probabilities exhibit a good correlation with the occurrence rate of such events furthermore the statistical significance of the model has been studied through additional tests the results of this study demonstrate the validity of the regional time and magnitude predictable model in the areas examined

temporary seismic quiescence se turkey summary the border zone that is the contact of the arabian plate with the three plates of turkey eurasia and iran to the north has been remarkably aseismic during this century by extending the period of observation backwards in time by a few centuries it is shown that this seismicity is atypical of the long term behaviour of the zone and due to a quiescent period in the activity of the area during the 20th century in turn this implies that short term data alone do not provide a reliable assessment of earthquake hazard

formation of dome in dome structures results from experimental studies and comparison with natural examples abstract dome in dome structures are frequent in salt provinces and in high grade rocks of orogens their origin is only poorly understood in the present study we have modelled dome in dome structures which result from constrictional radial in plane shortening of a competent layer embedded in a rising less competent matrix both the layer and the matrix consist of non linear viscous plasticine which display a viscosity contrast of 5 the deforming competent layer is characterized by 1 a striking downward drag along the margins 2 a sample scale first order dome and 3 numerous second order domes and basins straddling the first order dome with increasing layer thickness and strain the amplitude a arc length l and wavelength of the second order domes and basins increase however their growth rate is significantly smaller than that of non rising domes and basins which result from a bidirectional flow this restricted growth of rising domes and basins is attributed to the simultaneous growth of the first order dome and explains why hair pin type folds typical for non rising domes and basins are lacking even at higher finite strain similar dome in dome structures like those produced in the present study have been described from deeper levels of salt and gneiss domes or from foliation triple points of interfering diapirs

behavior of the ocean radar cross section at low incidence observed in the vicinity of the gulf stream observational results derived from the airborne c band scatterometer ressac looking at small incidence angles spl les 21 spl deg were acquired in the vicinity of the gulf stream during the surface wave dynamics experiment in february and march 1991 although the instrument was primarily designed to study the directional spectra of long waves it is also possible to process the data to examine the behaviour of the radar cross section spl sigma sup 0 versus incidence spl theta and azimuth spl phi although the classical physical or empirical models of spl sigma sup 0 spl theta spl phi predict that the anisotropy of spl sigma sup 0 versus azimuth increases with wind speed for a given incidence angle spl theta it is found that under some conditions this behaviour does not occur by contrast the anisotropy shows strong minima on certain occasions given the high resolution upper ocean current measurements from airborne expendable current profilers deployed on 5 march 1991 the regions of anisotropic minima could be identified from the three sets of observations march 4 5 and 7 downwind of the core of the gulf stream with a maximum current of 2 m s sup 1 and downwind of the current speed maxima of an anticyclonic rotating warm core ring juxtaposed along the north wall on three other days february 27 march 2 and 6 no clear anisotropic minima of was found because the upper ocean current effects were obscured by variability in surface wind field

timing of formation and exhumation of the montagne noire double dome french massif central new u pb monazite zircon and xenotime ages date the late carboniferous crystallization of the anatectic vialais granite in the montagne noire axial zone and the high temperature deformation and metamorphism of the augen gneiss ordovician granite protolith from which the granite was likely derived the u pb monazite ages obtained from the augen gneiss 308 3 ma late kinematic vialais granite 303 4 ma and post kinematic leucogranite 298 2 ma bracket the high temperature deformation and metamorphism at 310 300 ma clearly postdating regional contraction and nappe emplacement 320 ma the planar linear and locally linear fabrics in the augen gneiss outline a regional scale double dome structure caroux and espinouse sub domes containing smaller km scale upright folds compared to the caroux sub dome the larger migmatitic espinouse sub dome contains abundant leucosome leucogranite bodies and late kinematic intrusions vialais granite the vialais granite displays a weak magmatic foliation that defines the main layering of the espinouse migmatite ellipsoidal quartz sillimanite nodules concentrated above the roof of the granite recorded an increment of strain vertical shortening e ne elongation during granite emplacement and crystallization consistent with the extension event that exhumed the domes these new geochronological and structural data suggest that the montagne noire double dome formed in a pull apart structure within a dextral strike slip system upright folding in the sub domes has been traditionally assigned to a regional contraction event alternatively we propose that local contraction is associated with the convergence of low viscosity crust beneath the upper crust pull apart dynamic models of extension of hot crust indicate that contraction at depth is generated by flow of low viscosity orogenic crust converging and rising to fill the gap created by upper crust extension this interpretation solves the long standing problem of apparent coeval contraction and extension in the montagne noire double dome and establishes migmatite dome emplacement in strike slip corridors as a style of late variscan tectonics

time dependent seismicity in china precise zonation of the territory of china has been performed based on the active known faults type of faulting and seismicity level one hundred and forty seven seismogenic regions were defined forming 10 larger seismic areas and the seismotectonic characteristics in each one of them were investigated in detail after checking for data accuracy and completeness of the shallow earthquakes h 60 km the regional time and magnitude predictable model was applied and the model parameters were estimated based on the model applicability in the studied area probabilities for the occurrence of strong m 6 0 earthquakes during the next 10 years were calculated for each seismogenic region statistical tests have been used proving the superiority of the model in comparison with the time independent one as well as in comparison with the actual earthquake occurrence q 2001 elsevier science ltd all rights reserved

long term earthquake prediction in iran based on the time and magnitude predictable model abstract the region of iran has been divided into 21 seismogenic source areas on the basis of certain seismological and geomorphological criteria in each of these source areas the inter event times between successive main shocks with magnitudes equal to or larger than certain cut off magnitudes were considered these inter event times as well as the magnitudes of the main shocks have been used to determine the following relationships by a multilinear regression technique log t t 0 10m min 0 36m p 0 33 log m 0 6 97 m f 0 66m min 0 29m p 0 61 log m 0 10 69 where tt is the calculated inter event time measured in years mmin is the magnitude of the smallest main shock considered mp and mf are the magnitudes of the preceding and following main shocks and m 0 is the annual seismic moment release in each source area these relationships express the basic idea of the time and magnitude predictable model from which given the time of occurrence and the magnitude of the last main shock in a certain seismogenic source area one can calculate the time of occurrence and the magnitude of the next main shock in that area by using the first and second of the equations respectively however as there is considerable scatter in the observations conditional probabilities for the occurrence of a main shock during the next 10 years 1993 2002 as well as the magnitude of the expected main shock in each seismogenic source area were determined

thrust related diapiric and extensional doming in a frontal orogenic wedge example of the montagne noire southern french hercynian belt abstract the montagne noire which is situated at the toe of the orogenic wedge of the french massif central south european variscides appears to be a well suited area for studying the origin and evolution of middle to upper crustal domes adjacent to foreland basins the data reported in the present paper show that the montagne noire dome is a particular type of basement involved frontal culmination in an orogenic wedge and foreland basin system this frontal culmination is characterized by a syn contractional ht decompression recorded by clockwise ptt paths and widespread strata overturning in thrust and fold structures which controlled the sedimentation in the adjacent foreland basin these unusual characteristics are interpreted to be a result of the succession of thrusting diapirism and extensional collapse antiformal stacking of syn metamorphic thrust sheets controlled the first stages of the foreland basin development diapirism was essentially responsible for the ht decompression and widespread strata overturning extensional doming was a result of late to post metamorphic collapse acting on the pre existing high amplitude dome diapirism and associated isothermal decompression metamorphism which constitute the essential difference between the montagne noire and ordinary frontal ridges in orogenic wedges were probably enhanced by a local partial melting of the upper to middle crust it is suggested that the occurrence of these phenomena in front of an orogenic wedge was related to local over thickening due to the superposition of an upper crustal antiformal stack on top of a lower crustal ramp anticline

strike slip fault geometry in turkey and its influence on earthquake activity the geometry of turkish strike slip faults has been reviewed and described from this data set it appears that fault geometry the distribution of discontinuities such as bends and stepovers along the main fault trace plays an important role in controlling the location of large earthquake rupture segments along the fault zones large earthquake ruptures generally do not propagate past individual stepovers that are wider than 5 km or bends that have angles greater than about 30 more important than the size of each discontinuity however is the total geometric pattern i e the distribution of adjacent bends and stepovers based not only on distance from one another but also on relative discontinuity size certain geometric patterns restraining single or double bends are particularly common and can be viewed as responsible for strain accumulation along portions of the fault zone fault geometry not only plays a role in the extent of earthquake rupture but also in characteristics of earthquake behavior for example large earthquake epicenters often occur near restraining bends or double bends furthermore aftershocks and swarm activity can often be associated with releasing areas areas along the strike slip fault that are undergoing a relatively large amount of extension

flow of partially molten crust and the internal dynamics of a migmatite dome naxos greece 1 migmatite domes are common in metamorphic core complexes dome migmatites deform in the partially molten or magmatic state and commonly record complex form surfaces folds and fabrics while units mantling the dome display a simpler geometry typically formed by transposition during crustal extension we use field observations and magnetic fabrics in the naxos dome greece to quantify the complex flow of anatectic crust beneath an extensional detachment system the internal structure of the naxos dome is characterized by second order domes subdomes pinched synforms and curved lineation trajectories which suggest that buoyancy driven flow participated in dome evolution subdomes broadly occur within two compartments that are separated by a steep n s oriented high strain zone this pattern has been recognized in domes formed by polydiapirism and in models of isostasy dominated flow the preferred model involves a combination of buoyancy and isostasy driven processes the naxos dome may have been generated by regional n s extension that triggered convergent flow of partially molten crust at depth and the upwelling of anatectic migmatites within the dome this pattern is complicated by gravitational instabilities and or overturning of the high melt fraction crust leading to the growth of subdomes as the migmatites within the naxos dome reached a higher structural level they were affected by regional top to the nne kinematics of the detachment system dome formation therefore occurred by a combination of coeval and coupled processes upper crustal extension deep crust contraction during convergent flow of anatectic crust diapirism and or density driven crustal convection forming subdomes and north directed detachment kinematics

the regional time and magnitude predictable model and its application to the alpine himalayan belt abstract the regional time and magnitude predictable model has been introduced and has been shown to be appropriate to describe the behaviour in the occurrence of mainshocks the model implies that the magnitude of the preceding mainshock in a seismogenic region that is the largest earthquake during a seismic excitation governs the time of occurrence and the magnitude of the expected mainshock in this region this model has been applied in 149 seismogenic regions of the alpine himalayan seismic belt the model probability for the occurrence of the next very strong main shock ms 6 5 during the decade 1993 2002 as well as the magnitude of this shock in each of these regions have been calculated furthermore two tests have been performed to check the validity of this model these tests have shown the reliability of the model and its superiority compared to the classical time independent model

viscous collision in channel explains double domes in metamorphic core complexes in hot orogens gneiss domes are a response to upper crustal stretching and lower crustal flow two dimensional thermal mechanical modeling shows that localization of extension in the upper crust triggers in the deep crust oppositely verging horizontal flows that converge beneath the extended region upon viscous collision both flowing regions rotate upward to form two upright domes of foliation double domes separated by a steep median high strain zone in such systems horizontal shortening in the infrastructure develops in an overall extensional setting dome material follows a complex depth dependent strain history from shearing in the deep crustal channel to contraction upon viscous collision in the median high strain zone to extension upon advection into the shallow crust this depth dependent strain history is likely a general feature of dome evolution and is arguably well preserved in double domes such as the montagne noire france and naxos greece gneiss domes

an earthquake doublet in ometepec guerrero mexico on june 7 1982 an earthquake doublet occurred in a gap near ometepec guerrero mexico which had been given a high seismic potential the two earthquakes first event m s 6 9 m b 6 0 16 3 n 98 4 w d 25 km second event m s 7 0 m b 6 3 16 4 n 98 5 w d 8 km of the doublet occurred within five hours of each other we determine the source parameters of these events by inverting surface wave data at a period of 256 s the results are for the first event strike 116 dip 77 slip 88 and seismic moment of 2 8 10 26 dyne cm and for the second event strike 116 dip 78 slip 89 and seismic moment of 2 8 10 26 dyne cm modeling of long period p waves suggests that the first event has a depth of 20 km and is represented by a single trapezoidal source time function with an effective duration of 6 s the second event is best modeled by two sources at depths of 15 and 10 km the combined effective source duration time for the two sources is about 10 s the ratio of the seismic moment obtained from body waves to that from surface waves is 0 5 for the first event and 1 for the second adding the seismic moment of the two events and considering the first week aftershock area 3200 km 2 the stress drop is 4 bars these results suggest that the first event that involved a deeper asperity caused an incremental stress change large enough to trigger the second event if the two events of the doublet broke distinct areas of the subduction zone the coseismic slip is 0 58 m and accounts for about 25 of the total plate motion between the cocos plate and the north america plate accumulated since the last large earthquake in the region other doublets similar to the ometepec doublet have occurred along the middle america trench during the past 70 years a regional distribution of comparable size asperities may be responsible for this relatively frequent occurrence of doublets and for the simplicity of earthquakes in the region the high convergence rate which produces rapid strain accumulation and short recurrence intervals for large earthquakes and the smooth sea floor subducted along the middle america trench may contribute to the homogeneous distribution of comparable size asperities we found a relation log t 1 3 log m 0 t is the average recurrence time and m 0 is the average seismic moment for large earthquakes along the subduction zone in the guerrero oaxaca region where the convergence rate and the properties of the subducted plate are considered relatively uniform a simple asperity model predicts this relation