experimental seismic event screening criteria at the prototype international data center experimental seismic event screening capabilities are described based on the difference of body and surface wave magnitudes denoted as m s m b and event depth these capabilities have been implemented and tested at the prototype international data center pidc based on recommendations by the idc technical experts on event screening in june 1998 screening scores are presented that indicate numerically the degree to which an event meets or does not meet the m s m b and depth screening criteria seismic events are also categorized as onshore offshore or mixed based on their 90 location error ellipses and an onshore offshore grid with five minute resolution although this analysis is not used at this time to screen out events

from oblique arc continent collision to orthogonal plate subduction in the southeastern central asia orogenic belt during paleozoic evidence from superimposed folds at the northern margin of the north china craton abstract accretionary kinematic history of the central asia orogenic belt caob remains unclear in previous geological studies based on detailed structural analysis of newly identified folds on the northern margin of the north china craton ncc we propose a tectonic model suggesting that paleozoic accretion of the orogenic belt includes two phases of deformation the first phase of deformation is oblique collision of the bainaimiao arc and the ncc which was followed by orthogonal subduction of the paleo asian ocean in the second phase of deformation the change of plate kinematics is supported by two generations of folding namely d1 db and d2 da both d1 db and d2 da folds developed in the bayan obo group bog a meso and neoproterozoic rift sequence deposited on the passive continental margin of the ncc d1 db folds were superimposed by the east west trending d2 da folds the d1 db folds developed as a result of oblique collision of the bainaimiao arc and the ncc the d2 da folds developed in response to the southward orthogonal subduction of the paleo asian ocean plate they formed between latest silurian and early permian coeval with the two accretion events at the northern edge of the ncc our study suggests that multiphase deformation of sedimentary layers on the subducting plates provide important constraints for kinematic evolution of plate tectonics

the physical basis of mb ms and variable frequency magnitude methods for earthquake explosion discrimination we use recent results from deterministic numerical modeling of earthquakes and explosions to develop an improved physical basis for earthquake explosion discrimination we use six three dimensional finite difference simulations of earthquakes for the earthquake source models and four empirical and four numerical models for explosions in different materials four factors contribute to the success of the mb ms discriminant source spectra focal mechanism near source elastic properties and interference of p spectral differences contribute about 0 5 magnitude unit to the separation between earthquake and explosion populations for large events but this difference vanishes for events with mb 4 0 using a frequency band of 0 5 3 0 hz for small events the vfm discriminant is complementary to mb ms in several ways vfm is improved by p interference while mb ms is degraded vfm is more effective for hard rock explosions while mb ms will preferentially discriminate explosions in low velocity materials and vfm is insensitive to fault orientation vfm is more sensitive to noise and regional attenuation differences than mb ms simultaneous use of both methods should allow improved discrimination of small events

occurrence stratigraphy and geochemistry of late quaternary tephra layers in the aegean sea and the marmara sea abstract several discrete tephra layers occur in 2 5 10 3 m long cores from the aegean sea whereas a single tephra is identified in 3 5 9 7 m long cores from the marmara sea major and trace element data on these tephras delineate eight distinct groups the geochemical data and multivariate statistics allow the correlation of the tephra layers with six previously described marine tephras from the eastern mediterranean sea potential terrestrial sources are suggested for the others the chronostratigraphy of the tephra layers was established using several radiocarbon dates and the oxygen isotope stratigraphy from two long piston cores four widespread tephra layers occur within the upper quaternary sediments of the aegean sea the two youngest widespread tephra layers were derived from the santorini volcano of south central aegean sea z2 the minoan eruption ca 3 6 ka and y2 the cape riva eruption ca 21 7 ka the y2 tephra is also identified in three piston cores from the marmara sea the two older widespread tephra layers originated from the eruptions which emplaced the campanian ignimbrite of the italian volcanic provinces i e the y5 tephra ca 39 3 ka and from the nisyros volcano of the southeastern aegean sea the consistent occurrence of the nisyros tephra below the y5 tephra confirms similar findings in a lake core on the island of lesbos linear extrapolations using the oxygen isotope stratigraphy suggest an age of 42 44 ka for the nisyros eruption three additional tephra layers with a limited regional distribution are identified in the aegean sea cores two of these tephras originated from the yali volcano of the southeastern aegean sea and from the aeolian islands i e x1 tephra a series of six mugearite tephra beds in the south skiros basin is interpreted as a set of redeposited turbidites

advancing santorini s tephrostratigraphy new glass geochemical data and improved marine terrestrial tephra correlations for the past 360 kyrs abstract the island of santorini in the aegean sea is one of the world s most violent active volcanoes santorini has produced numerous highly explosive eruptions over at least the past 360 kyrs that are documented by the island s unique proximal tephra record however the lack of precise eruption ages and comprehensive glass geochemical datasets for proximal tephras has long hindered the development of a detailed distal tephrostratigraphy for santorini eruptions in light of these requirements this study develops a distal tephrostratigraphy for santorini covering the past 360 kyrs which represents a major step forward towards the establishment of a tephrostratigraphic framework for the eastern mediterranean region we present new epma glass geochemical data of proximal tephra deposits from twelve plinian and numerous inter plinian santorini eruptions and use this dataset to establish assignments of 28 distal marine tephras from three aegean sea cores kl49 kl51 and lc21 to specific volcanic events based on interpolation of sapropel core chronologies we provide new eruption age estimates for correlated santorini tephras including dates for major plinian eruptions upper scoriae 1 80 8 2 9 ka vourvoulos 126 5 2 9 ka middle pumice 141 0 2 6 ka cape thera 156 9 2 3 ka lower pumice 2 176 7 0 6 ka lower pumice 1 185 7 0 7 ka and cape therma 3 200 2 0 9 ka but also for 17 inter plinian events older plinian and inter plinian activity between 310 ka and 370 ka documented in the distal terrestrial setting of tenaghi philippon ne greece is independently dated by palynostratigraphy and complements the distal santorini tephrostratigraphic record

spatial variations of ductile strain in fold and thrust belts from model to nature abstract fold and thrust belts ftbs accommodate tectonic convergence through folding and faulting of crustal rocks during a collisional event between two continental plates although evidence of distributed deformation is common in ftbs that usually leads to continuous foliations and regionally occurring ductile structures of multiple orders it has rarely been given much attention assuming that zones of localized deformation like shear zones and brittle faults accommodate the entire amount of tectonic convergence this study presents 3d laboratory scale models using viscous thin sheet as crustal layers to understand the evolution of ductile strain in a tectonic wedge we varied the degree of mechanical coupling at the basal decollement i e weak versus strong to investigate this issue at constant convergence velocity in all experiments to avoid the influence of rate dependence on viscous rheology our results reveal that the strength of basal decollement controls the mode of wedge growth and hence the strain pattern particularly towards the hinterland the weak decollement models yield a zone of constriction towards the central part of hinterland explaining the occurrence of isolated patches of l tectonites and cross folds in ftbs while the strong decollement condition allows gravity driven flow to be active in the hinterland leading to orogen parallel recumbent folds in contrast both weak and strong decollement models produce deformation that characterises the commonness of pervasive hinterland dipping ductile fabrics towards the mountain front we correlate our findings to show that spatio temporal variations in basal coupling are responsible for varying occurrence of ductile structures in ftbs

benthic foraminiferal response to changes in bottom water oxygenation and organic carbon flux in the eastern mediterranean during lgm to recent times abstract we present a high resolution study of benthic foraminiferal abundances in 4 cores from the central aegean and ne levantine seas spanning the interval from 30 ka bp to the present the benthic foraminiferal faunas indicate that during lgm times bottom waters were well ventilated while organic flux to the sea floor was significantly higher than today from 30 to 10 2 ka bp faunal density and composition suggest a gradual decrease in organic flux to the sea floor this trend is interrupted by a short return to higher organic flux levels during the younger dryas 12 8 11 5 ka bp the faunas immediately preceding the early to middle holocene organic rich layer sapropel s1 are very similar to late holocene faunas indicating oligotrophic conditions the transition from well ventilated bottom waters to anoxic levantine basin or strongly dysoxic aegean sea bottom waters appears to take place within a time span of only 600 years from 10 8 to 10 2 ka bp sapropel s1 10 2 6 4 ka bp is characterized by extended periods of bottom water anoxia in the levantine basin and by strongly dysoxic conditions punctuated by episodic re ventilation events in the aegean sea re establishment of fully oxygenated bottom water conditions after sapropel s1 was extremely rapid the ensuing late holocene faunas are very similar to recent faunas found in the aegean sea suggesting much lower fluxes of organic matter to the sea floor than during glacial times

the late mis 5 mediterranean tephra markers a reappraisal from peninsular italy terrestrial records abstract we present new tephrostratigraphic records from the late mis 5 ca 110 80 ka terrestrial sediments from southern and central italy on the one hand the central italy record consists of an outcropping lacustrine sequence from the sulmona intermountain basin that contains four trachytic phonolitic tephra layers pop3 pop2a pop2b pop1 all of which show a k alkaline affinity that is typical for the roman co magmatic province the pop3 and pop1 layers were dated by 40 ar 39 ar method at 106 2 1 3 ka 2 and 92 4 4 6 ka 2 respectively the sequence in southern italy on the other hand is represented by post tyrrhenian coastal deposits of the cilento area campania which contain two trachytic layers cil2 cil1 that show the same k alkaline affinity based on their chemical compositions and radiometric ages pop3 and pop1 are firmly correlated with the marine tephra layers x 5 105 2 ka and c 22 ca 90 ka which in turn match tephras tm 25 and tm 23 11 respectively in the lacustrine sequence of lago grande di monticchio southern italy of note the pop1 layer also matches the adriatic sea tephra prad 2517 that was previously correlated with the older x 5 layer the tephra couplet pop2a and pop2b ca 103 and 103 5 ka extrapolated ages are compatible with the tm 24b and tm 24 3 tephras in monticchio which match both the stratigraphic positions and the chemical compositions in the cilento area as well as the already described x 6 layer ca 108 ka cil2 we recognise a new stratigraphic superimposed layer cil1 that matches the pop3 tm 25 c 27 x 5 mediterranean marker s in summary the data presented here provide new chemical and 40 ar 39 ar chronological constraints towards a robust late mis 5 tephrostratigraphy of the central mediterranean although at the same time they also reveal how the tephrostratigraphy itself might be flawed when dealing with tephra markers that are not adequately constrained and characterised

treatment of correlation for clustered reference data in kriging regional seismic discriminants abstract substantial improvements to the performance of discriminating explosions from earthquakes have been demonstrated by correcting regional seismic phase amplitudes or their ratios e g pn sn and pn lg for variations in propagation path and station effects one of the most promising methods for estimating the corrections and their uncertainties is a form of bayesian kriging however there are valid concerns regarding the robustness of the kriged amplitude corrections to aberrant calibration data that is that regional phase amplitudes from earthquakes with anomalous mechanisms depths and or paths could significantly bias the amplitude correction grids the methodology of bottone et al 2002 will properly account for such situations unless the residual variance is correlated to first demonstrate the problem the approach of bottone et al 2002 is applied to explosions and clusters of earthquakes with distinct focal mechanisms at the nevada test site nts the results indicate that serious discrimination errors i e miscategorizations of explosions as earthquakes can occur in the case of highly correlated clusters the localized reference data are weighted too high in estimating the corrections and the posterior calibration uncertainties become too small to address this issue an extension of the kriging methodology incorporating an additional correlation length to treat correlated focal mechanisms is presented and tested on the nts data sets and on large samples of explosions and earthquakes worldwide application to the worldwide data sets indicates that the power of the hypothesis test to reject earthquakes as explosions is marginally reduced without miscategorizing any known explosions and providing a robust treatment of clustered data

pumice deposits of the santorini lower pumice 2 eruption on anafi island greece indications for a plinian event of exceptional magnitude abstract isolated patches of santorini pumice deposits are analysed from the non volcanic island of anafi at a distance of 31 38 km east from the centre of the santorini caldera the deposits are plinian fall profiles with a primary thickness at this distance of 1 2 1 5 m and mp maximum pumice and ml maximum lithic diameters of 5 and 4 cm respectively the characteristic profile sequence of the analysed anafi deposits corresponds perfectly with the plinian sequence of the lower pumice 2 lp2 profiles on thera the main island of the santorini group with the sub divisions into lp2 a2 1 lp2 a2 2 and lp2 a3 pumice glass chemistry phenocryst assemblage and the significant content of grey cauliform scoriae make the compositional correlation with the plinian lp2 eruption of santorini unambiguous with the new identification of lp2 deposits on anafi together with an 4 5 times greater thickness in the main axis of dispersal of the proximal plinian lp2 deposits compared to the minoan fallout on thera the plinian opening phase of the 172 ka lp2 eruption lp2 a is regarded by far as the most voluminous of all plinian eruptive phases on santorini

refolding by flexural flow the existing method of derivation of the magnitude of simple shear in flexural slip and flexural flow folds has been extended to the general case of folds in which the radius of curvature varies continuously over a fold arc of any shape in agreement with earlier conclusions the present analysis shows that is equal to the dip angle measured in radians this result is applied to the situation in which an early fold f1 on a passively behaving layer is refolded by flexural flow on the axial planar cleavage of f1 both the theory and the folding experiments with paper stacks show that the f2 folds on the passively behaving layers show an unusual pattern of thickness variation with the orthogonal thickness continuously increasing or continuously decreasing from one limb to the other without a maximum or a minimum at the hinge flexural slip or flexural flow folds may be identified from this characteristic pattern of thickness variation the asymmetry of the smaller f1 folds on the layering is strongly modified by later folding on the axial planar cleavage

the typical large scale superposed folds in the central south china implications for mesozoic intracontinental deformation of the south china block abstract the south china block has experienced polyphase intensive intracontinental deformation in the mesozoic time large scale superposed folds in central south china document the mesozoic tectonic events within the south china block here we present new structural data related to synfolding deformation coupling with chronological data to reconstruct the deformation sequence and tectonic regime during crustal shortening these data indicate that the superposed folds dominated by a two stage tectonic compressive regime experienced two phases of superposed buckle folding leading to the orthogonal superposition of ne sw trending folds onto wnw ese trending folds between the late middle jurassic and the earliest early cretaceous our structural analysis together with geochronological data for this area suggests that the south china block predominately underwent two phases of intracontinental deformation during the mesozoic the early phase of tectonism d1 is characterized by a late middle triassic to earliest early jurassic ne sw compression causing the occurrence of an orogeny perpendicular shortening accompanying with evident magmatism this tectonic event was most likely associated with progressive clockwise collision of the south china block toward the north in the indosinian event subsequent tectonic activity d2 between the late middle jurassic and the earliest early cretaceous contributed to a phase of nw se contraction that overprinted the early ne sw shortening in the interior of the south china block generating a large scale nw convex fold belt and the typical large scale superposed folds within the central south china block the later tectonism was probably driven by the nw directed subduction of the paleo pacific plate beneath the eastern part of the asian continent

mega fold interference patterns in the beishan orogen nw china created by change in plate configuration during permo triassic termination of the altaids abstract kilometer size fold interference patterns in the beishan orogenic collage boc in the southernmost altaids formed by fold superimposition in fossiliferous permian sedimentary rocks first phase f 1 upright and almost north trending folds were refolded by e to ene trending f 2 folds whose axial planes and axes are vertical or subvertical from east to west there is a regional change in style of interference patterns from lobate cuspate to crescent to mushroom shape this variation is accompanied by a westward decrease in the f 2 interlimb angle and related to a higher percentage of coarse grained clastic rocks suggesting a dependence of the f 2 deformation on lithology axial planar slaty cleavages are well developed in f 1 and poorly developed in f 2 folds the superposed folds mainly underwent flexural slip and flexural flow folding to give rise to the lobate cuspate pattern and to the crescent pattern caused by flattening and flexural flow folding where the sediments were unconsolidated and enriched in fluids the two folding events are interpreted to result from a major change in plate configuration that caused the inversion of an inter arc basin during the final amalgamation of the boc in the latest permian to early to mid triassic the two folding events bracketed between a maximum detrital zircon age of

coeval folding and boudinage under plane strain with the axis of no change perpendicular to the layer plane strain coaxial deformation of a competent plasticine layer embedded in an incompetent plasticine matrix was carried out to improve our understanding about the evolution of folds and boudins if the layer is oriented perpendicular to the y axis of the finite strain ellipsoid the rock analogues used were beck s green plasticine matrix and beck s black plasticine competent layer both of which are strain rate softening modelling materials with a stress exponent n ca 8 the effective viscosity of the matrix plasticine was changed by adding different amounts of oil to the original plasticine at a strain rate dot e of 10 3 s 1 and a finite strain e of 10 the effective viscosity of the matrix ranges from 1 2 106 to 7 2 106 pa s the effective viscosity of the competent layer has been determined as 4 2 107 pa s if the viscosity ratio is large ca 20 and the initial thickness of the competent layer is small both folds and boudins develop simultaneously although the growth rate of the folds seems to be higher than the growth rate of the boudins the wavelength of both structures is approximately the same as is suggested by analytical solutions a further unexpected but characteristic aspect of the deformed competent layer is a significant increase in thickness which can be used to distinguish plane strain folds and boudins from constrictional folds and boudins

the 9 september 2016 north korean underground nuclear test we characterize the seismic events that occurred in north korea on 9 september 2016 and south korea on 12 september 2016 the 9 september 2016 event was identified as an explosion and the two 12 september 2016 events were identified as natural earthquakes using the p s p and s wave spectral ratios pg lg pn lg and pn sn as discriminants the explosive event was relocated within the north korean nuclear test site using a relative location method and the 2006 north korea underground nuclear test as the master event and the epicenter was identified at 41 2976 degrees n latitude and 129 0804 degrees e longitude from the regional lg and rayleigh waves the body and surface wave magnitudes for the 9 september 2016 event were calculated as m b lg 4 8 0 2 and m s 4 2 0 1 by adopting an empirical magnitude yield relation for the body wave magnitude and assuming that the explosion was fully coupled and detonated at a normally scaled depth we estimated that the seismic yield was similar to 6 kt and the uncertainty range was between 3 and 11 kt if an overburied depth range between 780 and 1200 m was applied then the yield would be increased to 16 22 kt

superimposed folding and thrusting by two phases of mutually orthogonal or oblique shortening in analogue models abstract orogens may suffer more than one phase shortening resulting in superposition of structures of different generations superimposition of orthogonal or oblique shortening is studied using sandbox and centrifuge modelling results of sand models show that in orthogonal superimposition the two resulting structural trends are approximately orthogonal to each other in oblique superimposition structures trend obliquely to each other in the relatively thin areas of the model foreland and mutually orthogonal in areas where the model is thickened during the first phase of shortening i e the hinterland thrusts formed during the first shortening phase may be reactivated during the later shortening phase spacing of the later phase structures is not as wide as expected considering they across the pre existing thickened wedge superposition of structures results in formation of type 1 fold interference pattern bedding is curved outwards both in the dome and basin structures folded layers are dipping and plunging outwards in a dome while they are dipping and plunging inwards in a basin in the areas between two adjacent domes or basins i e where an anticline is superimposed by a syncline or a syncline is superimposed by an anticline bedding is curved inwards and the anticlines plunge inwards and the synclines outwards the latter feature could be helpful to determine the age relationship for type 2 fold interference pattern in tectonic regions where multiple phases of shortening have occurred the orogenic scale dome and basin and arrowhead shaped interference patterns are commonly formed as in the models however in some areas the fold interference pattern might be modified by a later phase of thrusting similar to models results superimposition of two and or even more deformation phases may not be recorded by structures all over the tectonic area

superposed deformations and their hybrid effects the rhoscolyn anticline unravelled this study of the controversial structures of the rhoscolyn anticline suggests a different result of two phase coaxial deformation from ramsay9s type 3 interference fold patterns from detailed field observations of the sequence of bedded quartzites psammites pelites and oblique quartz veins with their strong competence contrasts we conclude that the rhoscolyn anticline was an original tight upright f 1 anticline that has undergone modification and distortion in a second deformation d 2 this second deformation is an oblique but near vertical pure shear with a quantifiable strain ratio r 3 that altered the rhoscolyn anticline and its minor structures into a more open se overturned antiform with c 260 m hinge migration refolded folds are rare but hybrid f 1 f 2 minor folds and their fabrics especially in the region between old and new hinges provide clues to the two stage history oblique distortion of originally nw verging f 1 minor folds has resulted in their apparent neutral vergence in the present day hinge of the rhoscolyn anticline we regard the structures and fabrics in quartzites and psammites as more reliable indicators of the region9s deformation history than those in pelites or quartz veins and this may prove true for other regions of polyphase deformation

hinge migration and hinge replacement abstract the axial migration angle is defined as the angle between the current hinge line and a marker line which was parallel to the initial hinge line it is generally assumed that the marker line is deformed in an entirely passive manner whereas the fold axis traces out the orientations of the long axis of the sectional strain ellipse this concept is modified when the competence contrast between a layer and its embedding medium is taken into consideration large values of may be obtained in constrictional deformations however because of strong hinge line arcuations of the nonplane noncylindrical folds the concept of hinge migration will not be meaningful hinge migration is greatly influenced by the competence of layers in inextensible layers the magnitude of hinge migration may become very large even in flattening and plane strain on the other hand hinge migration will be very small or negligible if buckle folding is associated with large layer parallel homogeneous strain the concept of hinge migration and hinge replacement have been critically analysed for development of types 0 1 and 2 fold interference patterns

interfering folds in constrictional deformation abstract experiments on buckle folding indicate that in pure constriction 2 3 2 3 there is an association of domes and basins with nonplane noncylindrical folds the areas of domes and basins are reduced with increasing deformation there is a dominant fold trend perpendicular to 3 with a less dominant trend perpendicular to 3 folds at an angle to these two sets may also occur the divergent folds link up in smooth arcs or join up at a dome or a basin over a relatively large domain the interference pattern produced by general constriction can be recognized by the association of domes and basins with nonplane noncylindrical folds by occurrence of hair pin bends of hinge lines of open folds by occurrence of amoeboid outcrop patterns and by absence of a consistent overprinting relation among different sets of folds layers subparallel to the 3 axis of general constriction may give rise to two or more sets of coaxial cylindrical folds with orthogonal axial surfaces

superimposed folding and oblique structures in the palaeomargin derived units of the central betics sw spain the subbetic units consist of a deformed wedge of sedimentary rocks deriving from the south iberian palaeomargin in the westernmost segment of the alpine mediterranean orogenic belt in the central betics shortening produced folding thrusting and nappe stacking the structural trend is ne sw to ene wsw and the internal structure of the thrust sheets which shows no preferred vergence is strongly controlled by the rheology of the decollement level a viscous layer of triassic evaporites and of the overlying carbonate rock sequence the relationships of piggyback basin miocene sediments with the main structures show that the latter developed during the aquitanian burdigalian transition superimposed folding is described for the first time in the study area the origin of the interference cannot be determined at present but may be related to initially oblique structures refolded during progressive deformation a revision of previously published palaeomagnetic data in the light of the data presented in this paper in conjunction with a model of the structural evolution of the subbetic units of the western betics permits us to establish milestones of the tectonic evolution of the external zones in the northern branch of the gibraltar arc

analysis of kilometric scale superposed folding in the central coal basin cantabrian zone nw spain abstract the carboniferous paralic sequence of the central coal basin cantabrian zone hercynian nw spain contains an outstanding example of kilometric scale superposed folding that allows comparison with previous experimental models first generation folds have a n s trend and mainly constitute a fold train of fault propagation folds in which an increase of interlimb angle and an increase in the dip of the axial plane is observed from west to east a second folding phase gave rise to two types of upright roughly e w oriented superposed folds the superposed folds generated in general by buckling but their trend and situation are controlled by lateral ramps of the previous thrusts in many cases superposed folds of the first type are the most common and have developed on the limbs of previous folds without folding their axial surfaces they occur in zones and usually have kilometre scale hinge lines with syngenetic curved traces these folds present wavelengths distinctly smaller than those of the previous folds the second type of superposed folds affect both the limbs and axial planes of the previous folds these second type folds are in some cases smaller than previous folds and have developed on closed early folds but in other cases they are large wavelength folds related to the tightening of lateral ramps of the thrusts

aegean sea as driver of hydrographic and ecological changes in the eastern mediterranean the eastern mediterranean is undergoing a long term increase in net evaporation which may have preconditioned the profound changes that occurred in its deep sea ventilation over the past two decades we test the sensitivity of aegean convective deep water formation to forcing in the opposite sense based on a last interglacial episode of enhanced freshwater injection into the eastern mediterranean we find that aegean subsurface ventilation collapsed completely within 40 20 yr promoting euxinic conditions hostile to aerobic life that expanded toward the photic layer within 650 250 yr similar conditions extended throughout the eastern mediterranean 300 120 yr later these findings emphasize the exceptional sensitivity of aegean deep water formation to climate forcing driving large scale hydrographic adjustments throughout the eastern mediterranean and beyond

patterns of fold interference influence of early fold shapes abstract model experiments were specifically designed to test the effect of different profile shapes of early folds on refolding patterns comparison of natural examples with experimental results and analogy with engineering information on buckling of fold shapes suggest that when layers are mechanically active during refolding the profile shape of the early folds markedly affects the patterns of fold interference open rounded folds tend to refold to form dome and basin patterns of interference whereas isoclinal folds tend to refold by folding their axial plane forming type 2 patterns of interference hence the dimensions and shape of the profile of the early folds control the preferred buckling mode during refolding

teleseismic location techniques and their application to earthquake clusters in the south central pacific abstract improved methods for single and multiple event hypocenter determinations are developed and applied to the problem of locating earthquake clusters in the south central pacific ocean bayesian statistical methods are used to incorporate a priori information about arrival time variance into the derivation of hypocenter confidence ellipsoids permitting a more realistic calculation of critical parameters in the case where the number of stations is small the diagonal elements of certain projection operators called data importances by minster et al 1974 are used to evaluate network balance the hypocentroid of an event cluster is defined to be the average location of events within the cluster and the deviations of individual hypocenters from the hypocentroid are called cluster vectors the problem of estimating the cluster vectors can be decoupled from the problem of estimating the hypocentroid by a simple but fundamental mathematical result here termed the hypocentroidal decomposition theorem the algorithm based on this analysis appears to have many advantages over other published methods for multiple event location both in its efficient use of available information and its computational speed the application of this method to three clusters of shallow intraplate seismicity in the south central pacific designated regions a b and c demonstrates that the seismicity within each cluster is very localized the rms lengths of the cluster vectors for each group of epicenters are estimated to be only 9 6 and 12 km respectively estimates of the epicentroids are

teleseismic slowness azimuth station corrections for the international monitoring system seismic network abstract the prototype international data center pidc in arlington virginia has been developing and testing software and procedures for use in the verification of the comprehensive test ban treaty after three years of operation with a global network of array and three component stations it has been possible to characterize various systematic biases of those stations that are designated in the treaty as part of the international monitoring system ims these biases include deviations of azimuth and slowness measurements from predicted values caused largely by lateral heterogeneity for events recorded by few stations azimuth and slowness are used in addition to arrival time data for location by the pidc corrections to teleseismic azimuth and slowness observations have been empirically determined for most ims stations providing data to the pidc application of these corrections is shown to improve signal association and event location at some stations an overall systematic bias can be ascribed to local crustal structure or to unreported instrumental problems the corrections have been applied in routine operation of the pidc since february 1998

superposed deformation fabrics in the precambrian metabasic rocks of the iron ore group singhbhum craton eastern india evidences from anisotropy of magnetic susceptibility studies abstract anisotropy of magnetic susceptibility ams data have been utilized to build up the multiple deformation sequences and strain variation from an apparently undeformed metabasic lava sequence of the basal part of the paleo mesoarchean greenstone succession of the iron ore group rocks in the western iron ore basin singhbhum craton eastern india the basal lava crops out bordering the regional horseshoe shaped outcrop the horseshoe synclinorium structure of the overlying bif rocks ams data of 892 cylindrical specimens drilled from 83 samples collected from different structural domains within the synclinorium structure are presented in the analysis ams orientation data have been analyzed in the light of superposed fold type 1 interference fabrics developed within bif as a result of successive deformation episodes d1 and d2 it is found that the lava samples ubiquitously present two consistent magnetic fabrics homogeneous over smaller sub areas which have been successfully correlated with the d1 and d2 deformation fabrics from the bif rocks moreover a regional scale variation in intensity and nature of strain is noticed from the ams data which have been utilized to decipher folding mechanism as well as the changing deformation pattern during successive folding events

kilometer scale refolded folds caused by strike slip reversal and intraplate shortening in the beishan region china 1 spectacular refolded folds clearly visible from space deform permian turbidite successions in a 180 km2 fault bounded compartment within the beishan region of northwestern china the folds formed after final terrane amalgamation of the central asian orogenic belt and record an important sequence of intraplate deformation events in central asia during the late permian jurassic the fold interference patterns are dominantly type 2 refolds with kilometer scale wavelengths they are bounded to the north and south by regional e w faults with multiple displacement histories as revealed by crosscutting ductile and brittle fabrics and kinematic indicators indicating opposing senses of motion the proximity of the refolded folds to the main bounding faults strongly suggests that the fold interference structures were caused by strike slip fault reactivation and shear related bending of f1 folds combined with components of n s compression across the compartment faulting within the folded compartment is limited to an array of right lateral strike slip faults which appear to have helped accommodate room problems during the refolding event the driving force for the deformation was likely to be distant including regional block collision to the south large scale rotations between the siberian and north china cratons and plate boundary convergence along the eastern chinese margin our study demonstrates that continental interior regions characterized by terrane collages are susceptible to reactivation by distant plate margin effects and that polyphase reactivation of major strike slip and oblique slip faults can generate refolding within upper crustal basinal compartments in addition the fault bounded basin containing the refolded folds in the beishan region is surrounded by older more complexly deformed crystalline basement therefore the deformed basin sequence represents a unique compartmental archive of the permian triassic history of intraplate deformation north of tibet

recognition of the minoan tephra in the acigol basin western turkey implications for inter archive correlations and fine ash dispersal here we report the recognition of the minoan tephra layer in the acigol basin western turkey which represents the most eastward occurrence of this tephra on land and the first in continental deposits out of lacustrine sediments in mainland turkey the correlation is supported by glass and mineral geochemistry which includes solution and laser ablation icp ms data for trace and rare earth elements thickness and grain size data allow the extension of already described occurrences to an area of about 359 000 km 2 from the eastern mediterranean to black sea throughout central western turkey coupling dispersal area and grain size data suggests the joint influence of high and low atmosphere dynamics in dispersal of fine ash during volcanic eruptions the thickness and lateral continuity of the minoan tephra in the acigol basin testifies to the widespread impact on the late bronze age environment of mainland turkey of this important ash deposit copyright 2013 john wiley sons ltd

mesozoic and cenozoic multiple deformations in the helanshan tectonic belt northern china abstract the helanshan tectonic belt htb is located in the tectonic boundary between the alxa massif and the ordos basin and witnessed the tectonic processes between the alxa massif and the ordos basin the deformation structures in the phanerozoic successions are keys to understanding the multiple phases of deformation along the htb together with regional geology our new geological mapping and structural analysis reveal that htb has been formed at least by four phases of deformation during the mesozoic and cenozoic times first phase of deformation d1 is represented by the wnw trending open folds of the paleozoic and triassic strata and formed by nne ssw contraction the angular unconformity between the deformed paleozoic triassic strata and overlying middle jurassic strata constrains that d1 occurred in the early jurassic second phase of deformation d2 is indicated by the ne striking tight folds of the triassic and jurassic strata and the superimposed deformation on d1 structures geometrical and kinematic analysis suggests that d2 was constructed by a phase of nw se contraction the angular unconformity between the middle jurassic and the lower cretaceous strata suggests that d2 was formed during the late jurassic third phase of deformation d3 is characterized by nne striking normal faults on both sides of the htb which separate the htb from the bayanhote basin to the west and yinchuan graben to the east d3 is consistent with the regional ne trending horst graben structural system and correlates to a regional extension in wnw direction according to the contact correlation of the lower cretaceous deposits and these normal faults they are indicated as syndepositional faults during the early cretaceous the fourth phase of deformation d4 was characterized by nw striking open folds and the ne trending strike slip faults in the eocene strata as well as the older strata together with the youngest strata involved into d4 deformation is the oligocene the previous age of 13 4 ma for the reactivation of the zongbieli zhengyiguan fault constrains the deformation time of d4 in the late miocene

response of basement and cover rocks to multiple deformations a study from the precambrian of rajasthan western india abstract metasedimentary rocks of the aravalli group of early proterozoic age 2000 2500 ma are underlain by migmatitic gneisses forming the banded gneissic complex bgc with radiometric ages varying widely from 3500 ma to much younger both the basement and the cover rocks are however involved in superposed folding of identical style and sequence in the metasedimentary cover rocks isoclinal folds of the first set f 1 with an axial planar cleavage have been affected by coaxial folds f 14 in some places and have been overprinted by a set of open upright folds f 2 with n s striking axial planes these structures are affected by small scale conjugate folds and kink bands f 3 with subhorizontal axial planes caused by a vertical compression and by upright kinks and conjugate folds f 4 developed by longitudinal shortening the f 1 f 1a and f 2 structures match in their entirety with those in the migmatites forming the basement gneisses the migmatization being synkinematic with the first folding this suggests that the bgc in its present state represents a largely mobilized basement

sedimentology and geochemistry of an exceptionally preserved last interglacial sapropel s5 in the levantine basin mediterranean sea abstract a combined study of lithological geochemical and physical sediment properties is reported from a completely laminated s5 sapropel recovered in three gravity cores m40 4 sl67 m51 3 sl103 m51 3 sl104 from the pliny trench region of the eastern mediterranean the thickness of the studied sapropel s5 varies between 85 and 91 cm and tops most s5 sapropels in the mediterranean based on optical features like color and thickness of laminae the sapropels were subdivided into thirteen distinct lithostratigraphic zones these zones as well as the finer layering pattern within them could be followed exactly among the three cores indicating that the processes responsible for this variation acted at least on a regional scale the sapropel sediment is characterized by exceptionally high porosity which is strongly correlated with si ca this relationship implies that the sapropel is in essence an organic matter rich diatomite and its exceptional thickness can be explained by preservation of diatoms forming a loosely packed sediment fabric compared to other s5 sapropels the preservation of diatoms has apparently led to a twofold increase in the thickness of the sapropel layer relative abundances of 10 elements were determined at ultra high resolution 0 2 mm by xrf scanner over the complete length of each sapropel including several cm of enclosing marl an analysis of the chemical data indicates that the lowermost 13 cm of the sapropel is chemically more similar to the underlying marl and that the sediment chemistry shows different signals at different scales the strongest pattern is the contrast between the sapropel and the surrounding marl which is accentuated in elements indicative for redox conditions as well as terrigenous sediment input and productivity within the sapropel a mm to cm scale layering is observed the abundances of many elements are systematically linked to the pattern of these layers indicating a common origin related to productivity and or terrigenous sediment and or redox conditions this pattern indicates a link to a regional climatic process making the s5 sapropel horizon in m40 4 sl67 m51 3 sl103 and m51 3 sl104 a potential high resolution archive of climatic variability during the last interglacial in the mediterranean sea and its adjacent landmasses

conical folding in the core of an orocline a geometric analysis from the cantabrian arc variscan belt of nw iberia abstract the cantabrian arc of the variscan belt has been recently defined as a true orocline constraining kinematics and deformation timing this curved sector of the orogenic belt is characterized by two different fold sets 1 one runs parallel to the outcrops of the main thrusts and describes a horseshoe shape concave towards the east and 2 another is radial to the arc a detailed geometric study of the fold interference patterns in the cantabrian arc revealed the conical nature of the folds belonging to the radial set these conical folds developed with different geometrical characteristics semi apical angles and axis attitudes depending on the initial orientation and geometry of the folded surfaces they are interpreted to result from a vertical axis rotation during oroclinal buckling of the variscan belt in nw iberia this study of conical folds in the cantabrian arc highlights that conical folds in curved orogenic arcs are a powerful tool for establishing the sequence of tectonic events because interference patterns due to vertical axis secondary differential rotations provide unique geometrical characteristics observed in the cantabrian arc that can be extrapolated to other oroclines

orogen transverse tectonic window in the eastern himalayan fold belt a superposed buckling model abstract the eastern lesser himalayan fold thrust belt is punctuated by a row of orogen transverse domal tectonic windows to evaluate their origin a variety of thrust stack models have been proposed assuming that the crustal shortening occurred dominantly by brittle deformations however the rangit window rw in the darjeeling sikkim himalaya dsh shows unequivocal structural imprints of ductile deformations of multiple episodes based on new structural maps coupled with outcrop scale field observations we recognize at least four major episodes of folding in the litho tectonic units of dsh the last episode has produced regionally orogen transverse upright folds f 4 the interference of which with the third generation f 3 orogen parallel folds has shaped the large scale structural patterns in dsh we propose a new genetic model for the rw invoking the mechanics of superposed buckling in the mechanically stratified litho tectonic systems we substantiate this superposed buckling model with results obtained from analogue experiments the model explains contrasting f 3 f 4 interferences in the lesser himalayan sequence lhs the lower order terrain scale folds have undergone superposed buckling in mode 1 producing large scale domes and basins whereas the rw occurs as a relatively higher order dome nested in the first order tista dome the gondwana and the proterozoic rocks within the rw underwent superposed buckling in modes 3 and 4 leading to type 2 fold interferences as evident from their structural patterns

reappraisal of the structure of the western iron ore group singhbhum craton eastern india implications for the exploration of bif hosted iron ore deposits abstract the middle to late archean iron ore group rocks occurring along the western margin the western iron ore basin of the singhbhum granite massif in the singhbhum craton were deformed during iron ore orogeny and are disposed in a horseshoe shaped synclinal structure in the eastern part of the indian shield the western iron ore basin hosts almost all the major high grade iron ore deposits of eastern india contrary to the established view present analysis emphasizes that the horseshoe fold in reality is a synclinorium consisting of a syncline anticline fold pair which were later cross folded along an east west axis structural analysis in the eastern anticline of the horseshoe synclinorium suggests that the bif hosting the high grade iron ore bodies are disposed in three linear nne ssw trending belts each showing an open synclinal geometry later cross folding produced development of widespread dome and basin pattern at the sub horizontal hinge zones of these synclinal fold belts the major iron ore deposits in the eastern anticline at the present level of erosion are preferentially localized within shallow elongated basinal structures only the axis of the adjoining western syncline was similarly uplifted as partial culminations where cross folded against e w anticlinal axes but here the bif iron ore bodies are preferentially localized within elongated domal structures in contrast to the basinal sites in the adjacent eastern anticline such an inference based on structural analysis could probably be utilized as a potential tool for all future explorations reserve estimation and recovery of the iron ore deposits in the terrain

advanced seismic analyses of the source characteristics of the 2006 and 2009 north korean nuclear tests in 2006 and 2009 north korea conducted underground nuclear tests at a remote mountainous site in the northeastern part of the country both events were small leading to uncertainties for location yield estimation and discrimination based on seismic observations the objectives of the studies described in this paper have been to more fully exploit data from the international monitoring system ims network and other unclassified sources e g incorporated research institutions for seismology iris japanese national research institute for earth science and disaster prevention nied to analyze these nuclear tests we have used differential waveform interferometry dwif to refine relative locations for the tests and extended the methodology using observations from regional stations to estimate relative emplacement depths which are consistent with explosion source model predictions for broadband regional p wave spectral ratios topographic data from the test site were analyzed to constrain relative locations and depths needed for containment of the two tests based on normal testing practice network averaged teleseismic p wave spectra were inverted using a model based approach and provide explosion yield estimates in the range 0 6 1 0 kt for the 2006 test and 2 0 4 8 kt for the 2009 test depending on assumed emplacement depth detailed spectral analysis of broadband regional p observations are most consistent with theoretical explosion models with yields of 0 9 and 4 6 kt for the 2006 and 2009 tests respectively with associated source depths of 200 and 550 m consistent with previous studies the surface wave m s magnitudes for the 2006 and 2009 tests provide anomalously large m s yield estimates and problematic m s m b identification characteristics finite difference simulations of long period surface wave signals incorporating tensile prestress consistent with the regional tectonics lead to predicted m s values that agree much better with the observed values

superposed buckle folding in the eastern iberian chain spain abstract the aliaga area eastern iberian chain shows large scale examples of buckle superposition developed during tertiary folding in most cases ene trending folds overprint earlier nnw sse trending ones the resulting structures are mapped analysed and genetically classified by comparison with analogue models described by several authors the following types are found standard type 1 1a dome and basin structure 1b unequal wavelength overprinted folds modified type 1 1c t shaped joined folds 1d t shaped abutting folds 1e l shaped folds 1f snake like folds standard type 2 2a non cylindrical buckling of earlier axial surfaces involving hinge replacement different superposed sets of flexural slip striations record successive folding episodes in snake like folds and hinge replacement in the case of type 2a superpositions types 1 and 2 apparently develop where the earlier folds have interlimb angles over and below 90 respectively which fits the results of analogue modelling and theoretical analysis by previous authors types 1b and 1d are associated with higher w1 w2 wavelength ratios than types 1a and 1c other controlling factors are viscosity contrast and erosion processes specifically erosion of competent limestone beds in the hinge zone of a nnw sse trending anticline allowed the near vertical eastern limb to be refolded into snake like folds

rapid coupling between ice volume and polar temperature over the past 150 000 years a new approach to dating a continuous sea level record using speleothem u th ages shows that past variations in global ice volume occurred within centuries of polar climate change with rates of sea level rise reaching at least 1 metre per century

tracing the laacher see tephra in the varved sediment record of the trzechowskie palaeolake in central northern poland abstract tephrochronological studies of partly varved sediments of trzechowskie palaeolake in central northern poland led to the finding of the late allerod laacher see tephra lst from the eifel volcanic field for the first time in a very distal site ca 840 km ene from its volcanic source the detection of glass shards of the lst involved a comprehensive combination of techniques i e biostratigraphical constrains high resolution xrf core scanning and areal xrf mapping of impregnated sediment slabs as well as detailed visual inspection of sediments the major element chemistry of volcanic glass confirmed the laacher see tephra composition in trzechowskie palaeolake sediments suggesting a deposition from the middle laacher see tephra mlst c or upper laacher see tephra ulst dispersal fans the finding of the lst in this palaeolake enables direct synchronisation with other high resolution archives in north central europe i e lake meerfelder maar rehwiese palaeolake to investigate regional variations of environmental responses at the onset of the younger dryas along a west east transect through north central europe

comment on q for short period p waves is it frequency dependent by a douglas summary douglas 1992 has presented evidence based on deconvolution analyses of british array data recorded from explosions at the shagan river test site sts ussr and the nevada test site nts usa from which he has concluded that the source time dependence characteristics of explosions at these test sites is significantly different from that associated with the mueller murphy m m seismic source model the objective of this note is to demonstrate that the m m model is in fact consistent with a very large variety of short period p wave observations from explosions and to argue that the alternate source time function proposed by douglas 1992 is inconsistent with both theoretical and observational constraints on the explosion source process more specifically network averaged teleseismic p wave spectra corresponding to nts french sahara and sts explosions in granite are used to illustrate the fact that the m m source model can provide remarkably good descriptions of the observed amplitude levels and spectral shapes over the short period band extending from at least 0 5 to 2 5 hz as well as seismic estimates of explosion yield which agree very closely with corresponding yield estimates obtained from other independent sources

geoarchaeological tsunami deposits at palaikastro crete and the late minoan ia eruption of santorini abstract the explosive eruption at santorini in the aegean sea during the second millennium bce was the largest holocene volcanic upheaval in the eastern mediterranean region the eruption was disastrous for the minoan settlements at santorini but the effect on human society in the neighbouring islands and regions is still clouded in uncertainty tsunami generation was suggested but comparatively little evidence was found the lack of firm tsunami traces is particularly puzzling in crete with its coastal settlements of the late minoan ia period during which the santorini eruption occurred here we report the discovery of extensive geoarchaeological tsunami deposits at palaikastro in north eastern crete these deposits are characterized by a mixture of geological materials including volcanic santorini ash and archaeological settlement debris various tsunami signatures were identified 1 erosional contact with the underlying strata 2 volcanic ash intraclasts in the lower part of the deposit 3 reworked building stone material in the lower part of the deposit 4 individual marine shells 5 marine micro fauna 6 imbrication of rounded beach pebbles settlement debris ceramic sherds and even bones 7 multi modal chaotic composition late minoan human settlement activities at palaikastro provided architectural and stratigraphic frameworks in space and time that recorded and preserved tsunami evidence as geoarchaeological deposits such stratigraphic resolution and preservation may not occur in the natural landscape volcanic ash transported by wind from santorini south east to crete preceded the tsunami geological archaeological and radiocarbon dating criteria all converge indicating that the tsunami deposits are coeval with the minoan santorini eruption field evidence suggests that tsunami waves at palaikastro were at least 9 m high inverse tsunami modeling was attempted based on these newly discovered tsunamigenic deposits the initial wave in the generation region at santorini that best fits the stratigraphic data is a wave with 35 to 15 m initial amplitude and a crest length of about 15 km

physical models of regional fold superposition the role of competence contrast abstract physical models of superposed folds demonstrate that rheologic contrast strongly controls the style of fold interference rheologic contrast affects strain partitioning between layer parallel shortening and buckling and affects the development of structural anisotropies parallel to first generation folds laminates with insignificant competence contrast are characterized by circular to elliptical domes and basins type 1 interference in addition to folding the layers accommodate shortening by layer parallel thickening preferentially in the fold culminations laminates with significant competence contrast are characterized by buckled fold hingelines and axial surfaces type 2 interference the less competent layers thicken in the hinges the more competent layers maintain their initial thickness in plan view the f 1 hingelines are refolded in a lobate cuspate to box style whose axial traces form conjugate pairs the models are dynamically scaled to represent folds with km scale wavelengths the evolution of surface structures map patterns at different depths and equal area projections synthesized from structure contour maps were used for analysis comparable to regional analysis common to field studies gravitational body forces effectively damp the vertical amplitudes of both the first and second generation folds thereby enhancing the formation of type 2 interference

information from folds a review abstract folds are spectacular geological structures that are seen in layered rock on many different scales to mark 30 years of the journal of structural geology we review the information that can be gained from studies of folds in theory experiment and nature we first review theoretical considerations and modeling from classical approaches to current developments the subject is dominated by single layer fold theory with the assumption of perfect layer parallel shortening but we also review multilayer fold theory and modeling and folding of layers that are oblique to principal stresses and strains this work demonstrates that viscosity ratio degree of non linearity of the flow law anisotropy and the thickness and spacing distribution of layers of different competence are all important in determining the nature and strength of the folding instability theory and modeling provide the basis for obtaining rheological information from natural folds through analysis of wavelength thickness ratios of single layer folds and fold shapes they also provide a basis for estimating the bulk strain from folded layers information about folding mechanisms can be obtained by analysis of cleavage and fabric patterns in folded rocks and the history of deformation can be revealed by understanding how asymmetry can develop in folds by how folds develop in shear zones and how folds develop in more complex three dimensional deformations

source specific station corrections for regional phases at fennoscandian stations the iaspei91 global travel time curves are used as the default for event location at the prototype international data center pidc in order to improve event location a 1 d baltic travel time model was implemented at the pidc in 1997 for locating events using regional phases from fennoscandian stations where a single model is insufficient for characterizing the regional geology path dependent corrections or source specific station corrections ssscs are more appropriate for event locations we have developed ssscs for regional phases at the fennoscandian stations by interpolating travel times through different 1 d models ssscs for stations nris and spits are also derived given the fact that paths from both stations to high latitude events are within the fennoscandia regionalization as baltic

triassic deformation of permian early triassic arc related sediments in the beishan nw china last pulse of the accretionary orogenesis in the southernmost altaids abstract the beishan orogenic collage boc in the southernmost altaids provides evidence of the final stage of evolution of the paleo asian ocean however the closure time of the paleo asian ocean in the boc is controversial from field mapping and structural analysis of mesoscale superposed folds in early triassic sediments in the hongyanjing basin in the central boc we define at least two phases of deformation which we can bracket in age as end permian to early late triassic the sandstones in the basin are poorly sorted with angular clasts which indicates immaturity characteristic of proximal and rapid deposition geochemical data indicate that the hongyanjing basin probably developed in an arc related setting near an active continental margin or mature island arc combined with published regional geological data we interpret the hongyanjing basin as a permian early triassic inter arc basin between the carboniferous mazongshan arc to the north and the ordovician to permian huaniushan dundunshan arc to the south in addition the age distribution of our sediments shows that the active continental margin or continental arc on which the hongyanjing arc related basin sat was somehow independently distributed in the paleo asian ocean without any major contribution of provenance from the tarim craton and dunhuang block to the south and southern mongolia accretionary system to the north deformation of the superposed folds began in the end permian continued in the early triassic and ended before the middle late triassic 219 ma therefore the accretionary orogenesis in the beishan part of the southernmost altaids was still ongoing in the early to middle triassic and it finished in the late triassic which might have been the last pulse of the accretionary orogenesis in the southernmost altaids we correlate this terminal event with tectonic developments in the kunlun and qinling orogens in the tethyan domain

tectonic evolution of the yaounde segment of the neoproterozoic central african orogenic belt in southern cameroon the deformation history of the neoproterozoic central african orogenic belt in southern cameroon is well recorded in the low to high grade rocks outcropping in the area around yaounde the fabrics in these rocks are con sistent with two main ductile deformation events d1 and d2 d 1 predated emplacement of calc alkaline dioritic bodies and caused the formation of nappes that resulted in high pressure granulite metamorphism of soft sediments a strong overprinting of these nappes during d2 symmetric extension probably associated with large scale foliation boudinage and or gneissic doming and intense magmatic underplating gave rise to regional flat lying fabrics the latter were further buckled by d3 and d4 folding phases defining a vertical constriction occurring with a major east west to nw se shortening direction the corresponding f3 and f4 folds trend north south to ne sw and east west to nw se respectively and represent the main regional strain patterns based on the east west to nw se maximum shortening orientation indicated by f3 folds it is proposed that the nappe stacking phase d 1 occurred in the same direction the deformation history in the area can thus be described as corresponding principally to alternating east west to nw se contractions and north south to ne sw orogenic parallel extensions at the regional scale this could be due to the transaharan east west collisional system

inverted fold hinge an end member of hinge rotation by superposed buckle folding in the precambrian terrain of western india abstract plunge reversal by hinge rotation due to superposed buckle folding ends when one of the hinge segments rotates to a reclined sensu stricto geometry rotation beyond this limit called the critical stage of hinge rotation inverts the rotating hinge segment from an antiform to a synform or vice versa in the sawar bajta area in the precambrian terrain of western india a segment of a synformal early fold has been inverted to an antiform producing an antiform synform fold pair with a common hinge and a common axial surface later compression folded the limbs and axial surface of the early synform and rotated its two adjacent hinge segments in opposite directions unequal rotation inverted one of the segments and bowed the common hinge upward to produce a mega sheath fold with 46 hinge angle the sheath folded basement cover rock contact delineates an eye fold with more than 30 km long perimeter on map profile the inverted segment rotated more than 17 beyond the critical position to what is probably the end member of hinge rotation the interlimb angle of the inverted segment increased indicating progressive opening up of the fold which inhibits further rotation beyond the limit set by the end member

evidences for a noachian hesperian orogeny in mars a number of tectonic structures have been located at the thaumasia plateau daedalia planum and aonia terra mars they include isolated folds with axial traces up to 200 km long trains of tightly folded structures tens of km long and thrusts their size and geometry are similar to those on earth and the direction of compression seems to have varied amply with time suggesting a complex tectonic evolution crater counts on the deformed terrain point to noachian to early hesperian ages on the basis of the geometry and geological relations of these structures we propose that they form part of an old martian orogen the thaumasia aonia orogen which embraced not only the thaumasia plateau but areas of daedalia planum aonia terra and nereidum montes as well a regional coherent layering is previous to the deformation and could represent the trace of even older stresses on the martian lithosphere

modes of superposed buckling in single layers controlled by initial tightness of early folds in a series of experiments with soft test models superposed buckling folds were produced in a competent layer resting on a slab of incompetent painter s putty the angle between the hinge lines of the first set of cylindrical folds f1 and the direction of the second compression p2 was varied in the different experiments the experiments showed that with an increase in the initial tightness of f1 there was a transition from one mode of superposed buckling to another when the interlimb angle of f1 was very large the superposed deformation gave rise to a dome and basin pattern the first mode of superposed buckling the second mode with small f2 folds riding over larger f1 folds developed when the initial interlimb angle ranged roughly between 135 and 90 the third mode was observed when the f1 interlimb angle was less than about 90 but the fold was not very tight in the third mode a set of non plane non cylindrical folds developed however the sinuous hinge line of the non cylindrical structure was newly created by replacing the old f1 hinge when f1 was very tight or isoclinal the fourth mode of superposed buckling led to the development of non plane non cylindrical folds without concomitant hinge replacement

mega arrowhead interference patterns in the central part of the yanshan orogenic belt north china abstract the chengde pingquan region is located in the central part of the yanshan orogenic belt yob at daheishan and pingquan in the central yob thrusts and folds of variable trends are displayed in 2 km scale fold interference patterns detailed field mapping was conducted to decipher the geometry of these two superimposed structures map view geometry and stereonet plots for outcrop scale folds indicate that the superimposed structures form arrowhead interference pattern where nw se trending f 1 folds are refolded by later ene wsw f 2 folding after remove the effects of later faulting restored map views of the superimposed structures show that when the f 1 folds have inclined axial surfaces but with no an overturned limb an arrowhead interference pattern here called modified type 2 pattern can form our field data and reinterpretation of the findings of previous studies suggest that five major shortening phases have occurred in the chengde pingquan region the first two phases which formed the superimposed folds occurred earlier than the late triassic d1 and during the late triassic to early jurassic d2 these two phases were followed by three deformation phases that are mainly characterized by thrusting and strike slip faulting which strongly modified the large scale fold interference patterns

the discovery of santorini minoan tephra in western turkey dispersal of volcanic ash from the violent bronze age minoan eruption of the santorini volcano in the southern aegean has been the subject of much research1 6 a sediment core taken from a small mountain lake in western turkey contains a layer of tephra from the minoan eruption the santorini origin is established by refractive index major glass chemistry and stratigraphic position the lake is located north of the recognized dispersal area for the tephra this deposit provides evidence for dispersal of the minoan tephra well to the northeast of santorini and implies that the west coast of asia minor must have experienced heavy tephra fallout from the bronze age eruption the minoan tephra has not previously been identified from sites in turkey

delayed hydrological response to greenland cooling at the onset of the younger dryas in western europe during the younger dryas cold event about 12 800 years ago environmental change in western europe seems to occur 170 years after cooling over greenland lake sediment analyses confirm this delay and suggest european hydrological and vegetation change occurred only after the build up of sea ice in the north atlantic pushed the westerly wind system south

path dependent regional phase travel time corrections for the international monitoring system in north america the software developed for the comprehensive nuclear test ban treaty ctbt international data centre idc in vienna austria uses the iaspei91 seismic travel time tables as default however in reality travel times as a function of source location are different for each station especially at regional distances this is not modeled by a global one dimensional model such as iaspei91 the software therefore allows the application of a suite of travel time corrections for improved travel time prediction and consequently more accurate hypocentral locations to account for path dependency we have developed gridded source specific station corrections ssscs for pn sn pg and lg phases for 22 international monitoring system ims stations in north america in deriving the ssscs and associated modeling errors we used a methodology that had been successfully applied previously for fennoscandia we first compiled regionalized one dimensional travel times for north america then we assigned travel times as weighted sums of the travel times in each region to calculate ssscs validation testing of the ssscs was conducted using two separate sets of north american ground truth gt events with location accuracies within 10 km gt0 gt10 these events were recorded at ims stations between 1995 and 1999 and distributed throughout north america test event location results with ssscs applied show reductions in both mislocations and error ellipses for gt events with location accuracies better than 2 km the median change in location was a 5 km improvement and the median area of the 90th percentile error ellipses was reduced from 2550 km 2 to 910 km 2 using ssscs for both data sets the median improvement is less than 5 km the testing emphasized that gt events with accuracies 5 km or better are crucial for validating ssscs using ssscs for all 51 gt0 gt10 events used in the validation testing the median area of the error ellipses was reduced to less than 1000 km 2 and the error ellipse reductions were achieved without significant degradation of coverage the modeling errors used in this study may be somewhat underestimated however leaving the target goal of error ellipses less than 1000 km 2 still somewhat in question we expect the ssscs event locations and uncertainties can be improved by future refinement of travel times and modeling errors these corrections were implemented in the operational prototype idc system located in arlington virginia in march 2000 and have been delivered to the vienna idc in january 2001

tubular folds and sheath folds definitions and conceptual models for their development with examples from the grapesvare area northern sweden abstract two parameters are used in the classification of highly non cylindrical folds the hinge line angle and the ratio of the length of the cone axis to that of the long axis of the cross section of the structure at the position where the hinge angle was measured if in a non cylindrical fold a cross section can be selected so that the hinge angle w measured where the cross section cuts the cone is less than 90 and the length of the cone axis x is more than a quarter of the length of the long axis y of the cross section the fold is a sheath fold a tight sheath fold with w x y 1 can be termed a tubular fold a tubular fold is thus an extreme type of sheath fold while sheath folds with w 20 but x y 0 25 but tubular folds from the grapesvare area comply to the definition given above and they occur in a structural setting that is consistent with the models described

erosion controlled geometry of buckle fold interference refolding structures in the aliaga area iberian chain spain show how erosion can exert a control on the geometry of buckle fold interference early miocene ene trending buckle folds are superposed on a large nnw sse anticline eocene oligocene north of aliaga the earlier hinge zone in the competent limestone unit controlling buckling urgon facies lower cretaceous constitutes a mechanical obstacle to refolding which induces development of essentially conical type 2 interference to the south erosional removal of the hinge zone at that competent unit allowed the near vertical eastern limb to behave as independent layers being refolded into cylindrical near vertical axis folds showing a snake like map pattern lower miocene conglomerates containing pebbles of jurassic origin whose source area was the core of the earlier nnw sse trending anticline indicate that this jurassic core had been effectively exhumed before refolding occurred in this way snake like folds constitute a new case of erosion controlled tectonic structure

the influence of initial fold geometry on type 1 and type 2 interference patterns an experimental approach abstract experiments on superposed folding were performed in a plane strain pure shear rig using paraffin wax as an analogue for rocks a series of pre formed cylindrical folds were refolded with the compression direction acting parallel to the initial fold hinge direction the intermediate axis perpendicular to the first fold axial plane and the extension direction parallel to the first fold axial plane and perpendicular to its axis type 1 interference geometry roundness tightness and amplitude were varied to investigate the influence of first fold geometry on the interference patterns experimental folding of an initially planar layer oriented parallel to the first fold envelope provides a reference geometry for comparison the results suggest that hinge roundness has less influence on the interference pattern than other factors close initial folds refold into type 2 interference patterns which become even more pronounced as the tightness increases open folds produce type 1 interference patterns folds with the same interlimb angle and the same roundness produce different interference patterns depending on relative amplitude folds with relatively large amplitude are refolded into type 2 patterns whereas folds with small amplitude give clear dome and basin structures in a second set of experiments the compression direction also acted parallel to the first fold hinge but the orientations of the intermediate and extension axes were interchanged the interference patterns obtained are very similar to those in type 1 interference geometry suggesting that the major factor in determining whether type 1 or type 2 interference patterns develop is the initial fold geometry and not the kinematics of the second deformation

polyphase structural deformation of low to medium grade metamorphic rocks of the liaohe group in the jiao liao ji orogenic belt north china craton correlations with tectonic evolution abstract the paleoproterozoic jiao liao ji orogenic belt in the eastern north china craton provides evidence of the evolution from the early rifting and ocean opening to the final collision of the longgang and nangrim blocks however it is still open to debate and thus controversial as to whether the jiao liao ji orogenic belt formed by closure of a rift without subduction or from an ocean with subduction based on detailed field mapping and structural analysis on a micro meso scale of the liaohe group in the center of the orogenic belt we define at least four phases of deformation and metamorphism s 0 is bedding formed during deposition of the lower liaohe sediments in the liaohe back arc basin during d 1 deformation an early greenschist facies event m 1 was associated with a bedding parallel s 1 metamorphic foliation penetrative axial planar foliation micro to meso scale folds f 1 and an l 1 lineation all formed during accretion probably in a trench subduction setting an m 2 metamorphism took place during medium pressure barrovian type amphibolite facies conditions and associated d 2 deformation that gave rise to major thrusts open isoclinal folds and a well developed crenulation cleavage during exhumation of high pressure and high temperature rocks and collision of the longgang and nangrim blocks m 3 metamorphism at sillimanite m 3 1 and cordierite m 3 2 grade was associated with d 3 deformation that produced regional gentle re folds related to post collisional exhumation of the orogenic belt an m 4 retrograde metamorphism and d 4 deformation gave rise to a weak foliation that can be correlated with late cretaceous extension that affected the whole eastern north china craton we present new isotopic ages la icpms u pb zircon of a granitic vein 2162 ma a pegmatite 1840 ma and a very late granite 114 ma that are integrated with relevant published data accordingly the formation age of deformation and metamorphism was set up and at last a modified tectonic model was presented

opening and closing of folds in superposed deformations abstract during superposed deformation an early fold f1 may either tighten or open out opening out is possible if during the second deformation there is a bulk extension across the f1 axial plane the theoretical model indicates that the rate of opening out is largely controlled by the initial tightness of the fold the results of the numerical model are in agreement with analog experiments of superposed buckling and show that if there is a relatively small range of variation of initial tightness of f1 folds the range of fold tightness becomes much larger after the opening out of the folds in the second deformation consequently the refolded structure may show a close association of different modes of superposed buckling in a type 2 fold interference the continued opening out of f1 invariably causes a replacement of the initial f1 hinge line by a new and more sinuous hinge line when the shortening direction p2 of the second deformation was at an acute angle to the f1 axis depending upon their local orientation with respect to p2 the f1 folds were tightened in some places and were opened out elsewhere when the enveloping surface is inclined in the direction of maximum stretching of second deformation segments of f1 and f2 hinge lines may both rotate to lie in the extension field and both f1 and f2 may open out with progressive deformation if f1 has a low pitch and p2 is parallel to the f1 axis the two sets of hinge lines may become subparallel at an advanced stage of deformation the resulting structure is morphologically similar to non planar sheath folds

multiple phases of deformation in the southern helanshan tectonic belt northern china abstract the southern helanshan tectonic belt shtb is surrounded by the alxa massif the ordos basin and the tibetan plateau and its phanerozoic structures records crucial phanerozoic deformation characteristics for studying the multi phased intracontinental deformation processes among these neighboring units combined with regional geology our structural analysis reveals that the shtb has experienced five phases of shortening deformation during the phanerozoic the first phase d1 is represented by e w trending overturned folds in the cambrian and ordovician strata these folds resulted from two episodes of n s shortening during the late cambrian early ordovician and late ordovician early devonian respectively which were attributed to the closure of the qilian ocean the second phase d2 is characterized by e w trending open folds involving the upper devonian strata which was the products of n s shortening caused by the assembly of the qilian ocean and the north china craton ncc at the end of devonian the third phase d3 is indicated by some wnw trending jura type folds in the carboniferous strata formed by nne ssw shortening during the late triassic early jurassic related to the collision between the ncc and the south china block the fourth phase d4 is inferred by nne trending shortening structures in the jurassic and its underlying strata generated by wnw ese shortening in the late jurassic echoing the paleo pacific subduction the fifth stage d5 is characterized by the ne sw shortening in the late miocene leading to the formation of many nw se striking thrust faults in the miocene and its underlying strata because the outward expansion of the tibetan plateau

folds and the strain ellipsoid a general model abstract a new general model is proposed to account for non orthogonal relationships of fold axes and axial surfaces to the axes of the finite strain ellipsoid descriptions in the literature of such relationships e g plunge variations and transecting cleavage are reviewed and the development of the model is outlined the model is described in which plane strain k 1 or slight flattening strain k 0 71 or slight constrictional strain k 1 85 are imposed on a suite of layers with oblique orientations to the bulk strain axes x y z folds will initiate perpendicular to the direction of shortening in the layer and develop as non material lines moving through the layer by angular migration at geologically realistic finite strains the folds will be transected by xy cleavage in slight flattening strain folds are likely to be cylindroidal with axes not measurably oblique to xy in slight constrictional strain en echelon periclines are predicted with marked transection by cleavage in some examples the interference of two directions of folding will give rise to severe plunge variations and even downward facing although strain markers frequently indicate finite strains in the flattening field this may result from the superimposition of slightly constrictional tectonic strain on compactional flattening

synchronous development of type 2 and type 3 fold interference patterns evidence for recumbent sheath folds in the allendale area broken hill nsw australia abstract synchronous development of type 2 and type 3 fold interference patterns occur in the poly deformed broken hill inlier the interference patterns have resulted from the superposition of recumbent f2 folds and n s oriented upright f3 folds the synchronous development of type 2 and type 3 fold interference patterns is attributed to variation in the hinge of f2 folds by as much as 90 suggesting the development of a regional scale sheath like fold geometry during d2 overprinting relationships along the eastern limb of the pap synform suggests that it formed part of a recumbent fold hinge that was flattened during horizontal crustal shortening this has resulted in the development of a modified type 3 fold interference pattern the results of this study show that the type 2 and type 3 fold interference patterns can develop during the same deformation event in an evolving orogen

the detailed tephrostratigraphy of a core from the south east black sea spanning the last 60 ka one visible volcanic ash layer and 21 non visible cryptotephra horizons have been identified in the m72 5 25 gc1 core from the south east black sea that spans the last 60 ka glass chemistry suggests that the tephras derive from italian hellenic and turkish sources the visible tephra layer is trachytic in composition and has been correlated to the 39 ka campanian ignimbrite super eruption from campi flegrei caldera italy two cryptotephra layers are associated with eruptions from acigol volcano turkey around the last glacial maximum another is linked to activity at erciyes dagi in the early holocene perikartini or karagullu and a cryptotephra layer near the top of the core correlates to the 3 6k cal a bp minoan marine z2 tephra from santorini thera greece this extends the known dispersal area for all these volcanic ash units many other calc alkaline rhyolite layers preserved in the core are likely to be from central anatolian sources but the lack of detailed proximal data for many of the volcanoes in the region prohibits further correlations the tephrostratigraphy and glass compositional data presented here allow the tephra layers to be used to correlate sedimentary archives across the region and help to extend the mediterranean tephrochronology framework towards the east