piggyback basin development above a thin skinned thrust belt with two detachment levels as a function of interactions between tectonic and superficial mass transfer the case of the subandean zone bolivia abstract the subandean fold and thrust belt of bolivia is characterised by two major detachment levels and large piggyback basins sand box and numerical models have been used to study sedimentation and erosion control on thrust belt evolution and to study the retroactive effects of tectonics on piggyback development in thin skinned thrust belts with two detachment levels analogue models show that surface processes play a dominant role in controlling wedge evolutions erosion promotes fault reactivation and tectonic delamination passive roof duplex while sedimentation promotes forward shifting of the frontal thrust and consequently piggyback basin development numerical models were used to understand the development of the subandean fold and thrust belt of bolivia numerical experiments show that the simultaneity of basement tilting and high sedimentation rates promotes the formation of a stable tectonic wedge outer and inner faults are alternately active during the beginning of deformation a kinematic evolution that favours the development of piggyback basins between the step by step history of the thrust belt predicts that each change in tectonic location is recorded with large unconformities in basins but these unconformities are not well preserved from progressive erosion in the final geometry

effects of topography on the curvature of fold and thrust belts during shortening of a 2 layer model of continental lithosphere abstract we have used analogue experiments to investigate the effects of surface topography on the curvature of fold and thrust belts under conditions of 1 initial relief but no erosion and 2 no initial relief but differential erosion sedimentation and transport in experiments where a 2 layer model lithosphere shortened and thickened in front of an advancing straight piston the geometry of the developing thrust wedge was very sensitive to variations in surface topography in models with an initially flat horizontal surface and in the absence of erosion and sedimentation thrusts were straight propagated forwards and nucleated at buckle folds far in front of an advancing piston around an initial topographic high plateau or cone thrusts tended to be arcuate forming salients towards the foreland initial plateaux and cones tended to behave rigidly while arcuate thrust slices formed around them to accommodate differential slip transfer zones developed on both sides of initial highs fault blocks rotated about vertical axes and thrusts moved in oblique slip within transfer zones in models with initially horizontal surfaces which were subject to differential erosion sedimentation and transport thrusts initially were straight but then progressively rotated around non eroded thickened and stronger areas these worked as indenters in front of which new thrusts nucleated at curved buckle folds these thrusts were also curved their apices being in front of the thickened non eroded areas in nature arcuate structural patterns are to be found around the altiplano of the central andes and around the tromen volcanic ridge in the neuquen basin of northern patagonia we infer that these areas behaved in quasi rigid fashion protected as they were by their high elevations and that differential erosion at the scale of the entire andes may have contributed to oroclinal bending

depleted mantle source for the ulungur river a type granites from north xinjiang china geochemistry and nd sr isotopic evidence and implications for phanerozoic crustal growth abstract the ulungur river granites from north xinjiang china display two petrological trends 1 a peralkaline trend composed of alkali amphibole and alkali pyroxene bearing granites and dykes and 2 an aluminous trend represented by alkali granites monzogranites and aluminous granite dykes within the peralkaline granites rb sr whole rock isochron dating yielded an age of 300 ma for the emplacement of the peralkaline granites and 270 ma for the aluminous granites the ulungur river granites share all the geochemical features common to a type granites of the world the ulungur river granites are post orogenic and emplaced in a post collisional extensional environment the peralkaline and aluminous rocks have indistinguishable nd isotopic compositions they have unusually positive and relatively uniform nd t values ranging from 5 1 to 6 7 for the peralkaline rocks at 300 ma and from 5 5 to 5 9 for the aluminous rocks at 270 ma the initial 87sr 86sr ratios cannot be determined precisely by the whole rock isochron technique mainly because most samples are highly radiogenic and have high rb sr ratios in addition the large variation in sr isotopic compositions can partly be explained by crustal contamination during magma differentiation the nd isotopic data clearly indicate that both the peralkaline and aluminous rocks were derived from a long lived depleted mantle reservoir the formation of the ulungur river a type granites is hypothesized as follows 1 a depleted mantle was first metasomatised then subjected to partial melting leading to the generation of basic magmas now represented by the kalatongke mafic ultramafic complex in the ulungur river area 2 the basic magmas have undergone high degrees of fractional crystallisation with separation of biotite hornblende plagioclase potassium feldspar and other accessory phases such as apatite and ilmenite with the residual magmas forming the peralkaline granites during the magmatic differentiation the liquids were probably contaminated by crustal materials as evidenced by nb depletion and nd sr isotopic systematics on the other hand the formation of aluminous granites involved a replenishment of new mantle derived magmas into the differentiating magma chamber and followed by fractional crystallisation with retention of hydrous phases hornblende and biotite the petrological evolution of the ulungur river granites is thus from peralkaline to calc alkaline and not from calc alkaline to peralkaline as more often observed elsewhere the ulungur river granites in common with the voluminous granitoids occurring in the central asian orogenic belt represent a significant juvenile addition of the continental crust in the phanerozoic

structural characteristic and origin of intra continental fold belt in the eastern sichuan basin south china block abstract the fold and thrust belt in the eastern sichuan basin is represented by a series of subparallel chevron anticlines under the orogenic tectonic setting within the south china block in meso cenozoic period and the influence of the multi layer detachment fault the deformation of the thrust belt exhibits remarkably layered and large scale intracontinental thrusting structural characteristics in this paper we focus on the structural geometry and deformational mechanisms using the latest two dimensional 2d and three dimensional 3d seismic reflection data in combination with well and outcrop data the multi layer detachment faults especially the upper gypsum bearing detachment in the middle triassic jialingjiang formation and lower detachment with gypsum or shale in the lower middle cambrian system directly control the deformational styles of the study area interpretation of seismic sections indicates that the fold and thrust belt has various deformational styles during folding including fault propagation fold fault bend fold and detachment fold with box fold or pop up structural geometry regional location and structural boundaries play significant roles in controlling the deformational styles and distinct differences exist among the different anticlines the huayingshan anticline located at the front of the thrust belt shows intense structural deformation with northwestward thrusting direction and a relatively weak opposite southeastward thrusting in addition the anticlines exhibit structural differences along strike and the fold and thrust belt in the northern segment is influenced by the north china block

effects of lateral friction on the structural evolution of fold and thrust belts insights from sandbox experiments with implications for the origin of landward vergent thrust wedges in cascadia various factors are inferred to influence the structural evolution of fold and thrust belts or thrust wedges but the effects of lateral friction such as that exerted by the opposite block of a strike slip fault in nature or by sidewalls in analogue models have rarely been given sufficient attention and hence are still far from being fully understood up to now seaward vergent and dually vergent thrust wedges have been satisfactorily explained by the classic coulomb wedge theory and can be well reproduced in analogue and numerical models in contrast landward vergent thrust wedges which are uncommon in nature e g those occurring in the cascadia subduction zone have not yet been adequately explained by the classic coulomb wedge theory and can only be reproduced in a few analogue models under particular conditions in order to look closer at the effects of lateral friction on the structural evolution of fold and thrust belts and to explore the origin of landward vergent thrust wedges we conducted a series of sandbox models under different conditions of lateral friction and various ratios of initial average lateral frictional stress to basal shear stress s d results of our models revealed that in the presence of a weak or ductile basal decollement the direction of lateral friction can dictate not only the deformation propagation direction and the surface slope direction but also the structural vergence of fold and thrust belts fold and thrust belts normally show a structural vergence in the same direction as the direction of lateral friction but a deformation propagation direction and surface slope direction opposite to the direction of lateral friction according to the results of models and the relationships between structural vergence and lateral friction direction occurring both in cascadia and the analogue models we propose that an extremely high s d ratio due to an extremely weak basal decollement and landward directed lateral friction exerted by the opposite blocks of basement involved strike slip faults are probably the two key factors responsible for the origin of landward vergent thrust wedges in cascadia this work illustrates that effects of lateral friction should be properly taken into account both in the kinematic analysis and designs of models to simulate fold and thrust belts in the presence of weak or ductile basal decollements

highly evolved juvenile granites with tetrad ree patterns the woduhe and baerzhe granites from the great xing an mountains in ne china abstract in ne china voluminous granitoids were emplaced in late paleozoic and mesozoic times we report here sr nd o isotopic and elemental abundance data for two highly evolved granitic plutons woduhe and baerzhe from the great xing an mountains they show a rather juvenile sr nd isotopic signature and a spectacular tetrad effect in their ree distribution patterns as well as non charac charge and radius controlled trace element behavior the emplacement ages are constrained at 130 4 ma for the woduhe and 122 5 ma for the baerzhe granites by rb sr and sm nd isotope analyses both granites are also characterized by low but imprecise initial 87sr 86sr ratios of about 0 703 the nd sr isotope data argue for their generation by melting of dominantly juvenile mantle component with subordinate recycled ancient crust this is largely compatible with the general scenario for much of the phanerozoic granitoids emplaced in the central asian orogenic belt the parental magmas for both the woduhe and baerzhe granites have undergone extensive magmatic differentiation during which intense interaction of the residual melts with aqueous hydrothermal fluids probably rich in f and cl resulted in the non charac trace element behavior and the tetrad effect of ree distribution both the woduhe and baerzhe granites show the characteristic trace element patterns of rare metal granites but their absolute abundances differ by as much as two orders of magnitude the oxygen isotope compositions of the two granites have been severely disturbed significant 18o depletion in feldspar but not so much in quartz suggests that the hydrothermal alteration took place in a temperature condition of 300 500 c this subsolidus hydrothermal alteration is decoupled from the late stage magma fluid interaction at higher temperatures despite the two distinct and intense events of water rock interaction the rb sr and sm nd geochronological systems seem to have maintained closed hence suggesting that the two events occurred shortly after the plutonic emplacements

sinoprobe deep reflection profile reveals a neo proterozoic subduction zone beneath sichuan basin abstract a new multichannel seismic reflection profile collected across the sichuan basin in southern china by sinoprobe images prominent reflectors that originate within the lower crust and penetrate well into the underlying mantle the geometry of these mantle reflectors is very similar to those observed on other deep reflection profiles that have been interpreted as relicts of ancient subduction considering the geological history of the basement beneath and surrounding sichuan basin and ages of granites encountered in nearby wells we propose that these newly revealed reflectors are the remnants of neo proterozoic subduction that occurred along the nw margin of the yangtze craton this interpretation is consistent with geochemical studies from a gneissic complex at the west margin of the sichuan basin moreover preservation of these reflectors supports the idea that the sichuan lithosphere served as a consolidated tectonic buttress against which the tibetan plateau has impinged to produce the longmenshan orogenic belt

detachment folding fold amplification and diapirism in thrust wedge experiments 1 the relations between detachment folding fold amplification and salt diapirism in contractional settings have been investigated by means of scaled analogue models the viscosity of the silicone layer simulating salt in nature and the shortening rates were combined in order to reproduce weak type 1 models and strong type 2 models decollements deformation patterns in the roof sequence exhibited two contrasting styles 1 outward propagation of detachment folding along the decollement ofp mode and 2 passive roof duplex prd mode in type 2 models detachment folding propagated away from the most external thrust in the floor sequence while in type 1 models long lived detachment folds almost invariably localized amplified above a floor thrust tip as a result of strain localization a silicone wall intruded occasionally into the crestal graben of detachment folds in type 1 and ofp models best fitting of transition models data points indicates nonlinear relations with regression curves close to the equilateral hyperbola equation for both ofp prd and amplified detachment folds box folds transitions a quantitative comparison of model results with nature has been attempted by plotting salt based fold and thrust belts data points on the scaled transition curves obtained from the modeling such a comparison relates shear stress products and ratios to the conditions favoring the amplification of detachment folds and the potential emplacement of ductile diapirs in their core by reducing the roof sequence strength pore fluid pressure b is inferred to shift the equilibrium of fold and thrust belts toward the field of ofp and diapirism

thermal and structural evolution of the external western alps insights from u th sm he thermochronology and rscm thermometry in the aiguilles rouges mont blanc massifs in the western alps the external crystalline massifs ecm are key places to investigate the kinematics and thermal structure of a collisional crustal wedge as their paleo brittle ductile transition is now exhumed at the surface new u th sm he data on zircon and new raman spectroscopy on carbonaceous material rscm data from the aiguilles rouges and the mont blanc massifs coupled to hefty thermal modeling constrain the thermal evolution and exhumation of the massifs in the cover of the aiguilles rouges massif we found that the maximal temperature was about 320 c 25 c close to the maximal temperature reached in the cover of the mont blanc massif 350 c 25 c we show that after a fast heating period the thermal peak lasted 10 15 myrs in the mont blanc massif and probably 5 10 myrs in the aiguilles rouges massif this thermal peak is synchronous with crustal shortening documented in the basement u th sm he data and thermal modeling point toward a coeval cooling of both massifs like other ecm at around 18 ma 1 ma this cooling was related to an exhumation due to the initiation of frontal crustal ramps below the ecm quite synchronously along the western alps arc

late mesozoic cenozoic evolution of the sanjiang basin in ne china and its tectonic implications for the west pacific continental margin abstract this study uses new seismic reflection profiles and exploratory well data to analyze the structural characteristics and evolution of the sanjiang basin in eastern heilongjiang ne china the basin sequence was divided into six stratigraphic units representing discrete middle upper jurassic lower cretaceous upper cretaceous eocene oligocene miocene and quaternary phases of development the sanjiang basin initiated as a passive marginal rift flank to the southern mongol okhotsk ocean during the middle jurassic and primary basin growth was terminated by orogenic deformation related to the mongol okhotsk suture to the north and the accretion of the nadanhada terrane to the east middle upper jurassic strata are controlled by half graben structures active during this phase of basin growth and are limited largely to the west suibin sub basin the wider basin experienced renewed rifting and large scale sag caused by back arc extension along the eurasian continental margin in the early cretaceous terminating during the late cretaceous in a phase of intense compression at the contemporary andean type continental margin this produced a series of thrust folds through the lower and upper cretaceous successions and led to the development of a regional scale erosional unconformity minor subsequent cenozoic extension is attributed to back arc extension along the west pacific continental margin with eocene oligocene miocene and quaternary deposits unconformably overlying the mesozoic sequences in half graben and extensional fault demarcated depocenters most prominently in the east qianjin sub basin

remote sensing of atmospheric and ionospheric signals prior to the mw 8 3 illapel earthquake chile 2015 in the present study a number of atmospheric and some ionospheric anomalies are analyzed which were recorded prior to the mw 8 3 illapel earthquake of september 16 2015 this very large earthquake occurred in central chile close to the coast as the result of thrust faulting on the interface between the nazca plate and south american continent using remotely sensed data extracted from nasa giovanni noaa ncep and noaa ngdc atmospheric and ionospheric anomalies were observed that co registered 35 40 and 25 30 days prior to the main shock respectively with reference to long term time series over the epicentral area significant atmospheric anomalies were recorded for cloud cover geopotential height precipitation rates surface air pressure omega stream function and wind vectors all in the time window of august 5 10 2015 35 40 days prior to the main shock anomalous tec maps were recorded for the same time period satellite images indicate the formation of an unusual cyclone presumably triggered by air turbulences and abnormal atmospheric conditions over the epicentral area including strong vertical winds data from the jicamarca radio observatory in peru more than 2000 km to the north reveal anomalous ionospheric variations on august 15 20 2015 with respect to international reference ionosphere thickness parameters and the altitude of the f layer the observed anomalies are consistent with processes that occur at the ground to air interface due to the stress activation of peroxy defects in the hypocentral volume the flow of positive hole charge carriers to the earth surface expected to have led to massive air ionization generating at first primarily positive airborne ions then negative air ions plus ozone understanding the sequence of processes inside the earth s crust and at the ground to air interface provides information not previously available about the causal and temporal linkages between the various pre earthquake phenomena and the future seismic event

decrease of intensity of elf vlf waves observed in the upper ionosphere close to earthquakes a statistical study 1 we present results of a systematic study of intensity of vlf electromagnetic waves observed by the demeter spacecraft in the upper ionosphere altitude 700 km we focus on the detailed analysis of the previously reported decrease of wave intensity shortly before the main shock during the nighttime using a larger set of data more than 3 5 years of measurements and a newly developed data processing method we confirm the existence of a very small but statistically significant decrease of wave intensity 0 4 hours before the time of the main shock at frequencies of about 1 7 khz it is shown that the decrease does not occur directly above the earthquake epicenter but is shifted about 2 in the westward direction moreover it is demonstrated that the decrease occurs more often close to shallower earthquakes and close to earthquakes with larger magnitudes as it is intuitively expected representing an additional proof of validity of the obtained results finally no dependence has been found on the occurrence of the earthquake below the ocean or below the continents

evidence of electro seismic phenomena abstract ground based observations of electromagnetic precursors to large earthquakes have been reported in japan iran chile greece and the soviet union ionospheric disturbances measured by soviet satellites have been claimed to be seismic precursors in addition observations of very low frequency anomalies measured by geos satellites have been reported by french researchers to confirm reports of electromagnetic precursors to earthquakes a series of low frequency broadband radio frequency receivers were deployed along the san andreas fault system this system of monitors has recorded electromagnetic anomalies occurring just before earthquakes between 1983 and 1986 these anomalies are of two types and are presumably caused by separate effects both of which may be related to stress induced changes in the crust just before fault rupture the first of these types of anomalies appears to be an interruption in the propagation of radio waves radio depressions lasting for many hours before an earthquake the second type is similar to those in previously published reports and consists of short duration broadband radio emissions given the results reported by other researchers and the results from our own experiments we believe that electromagnetic data may be useful as a tool for predicting earthquakes

double evaporitic decollements influence of pinch out overlapping in experimental thrust wedges abstract this article focuses on how deformation and displacements are transferred between two decollements located at different stratigraphic levels by means of analogue modeling using brittle viscous sand silicone systems we present results from ten analogue models in which we varied key parameters such as the amount of horizontal offset or overlap between the pinch outs of the upper and lower decollements the total amount of shortening and the planform geometry of the upper decollement results indicate that i structures root onto the basal and upper decollement defining an inner and an outer domain and ii the offset overlap of the decollements controls the geometry of the transition zone located between the two decollements the propagation of deformation into the foreland both in space and time and the deformation style and kinematics in the different domains of the model when the pinch out of the upper decollement is at an angle with the backstop oblique structures form and the geometry and propagation mode of the structures change progressively along strike we compare our experimental results with other silicone sand analogue models and with the natural examples of the southern pyrenees where upper triassic and eocene oligocene syn tectonic evaporites acted as basal and upper decollements respectively

passive roof thrusting and forelandward fold propagation in scaled brittle ductile physical models of thrust wedges a set of scaled analogue models was performed to investigate the role of a decollement layer in the structural style of fold and thrust belts silicone putty sgm 36 has been employed to represent the ductile decollement while frictional material quartz sand has been used to simulate the brittle behavior of roof and floor sequences situated above and below the decollement respectively in order to explore a wide combination of strength profiles models have been deformed under five distinct rates of compression 0 15 0 3 0 45 0 6 and 1 5 cm h 1 employing four different thicknesses for the silicone layer 0 1 0 2 0 4 and 0 8 cm experimental results indicate that roof sequences exhibit two distinct styles of deformation 1 passive roof duplex prd geometry e g banks and warburton 1986 and 2 outward propagation of folding ofp along the decollement e g davis and engelder 1985 in prd geometry the roof sequence remains relatively stationary being underthrust by a wedge shaped floor duplex while in ofp displacement along the floor thrusts is transferred horizontally along the decollement layer experiments suggest the occurrence of a genetic relationship between shear stresses at the base of the roof sequence b and within the ductile layer d and the development of prd or ofp geometry for a given strain rate the deformation pattern of roof sequences depends upon the b d ratio as well as the absolute b and d values the transition field between ofp and prd styles has been approximated by curvilinear regression of transition style experimental data points with a minimum value of d varying between about 112 and 160 pa to enter the prd field syntectonic sedimentation in the molasse basin is found to inhibit development of folding into the foreland but to promote prd style experiments simulate many of the principal characteristics of fold and thrust belts developed above a basal evaporite decollement as well as the development of passive roof duplexes at mountain fronts shear stress values inferred for many fold and thrust belts correlate well the deformation fields predicted by the present experimental study allowing to propose a simple model describing the mechanical behavior of natural roof sequences underlain by a decollement layer

the interaction of two indenters in analogue experiments and implications for curved fold and thrust belts abstract scaled analogue experiments are used to investigate the indentation of two basement blocks into a sedimentary basin and the formation of a fold and thrust belt the experimental set up has two adjacent indenters moving in parallel with a velocity difference the slow indenter moves with a relative velocity ranging from 40 to 80 of that of the fast one in a first experimental series quartz sand and low friction glass beads represent the sediment stack and its basal detachment respectively silicone oil simulates a viscous detachment in the second series of experiments the surface evolution and the spatio temporal strain distribution are derived from particle image velocimetry piv together with the 3d finite structure derived by cutting the models at the end of each experiment this allows the analysis of the structural evolution of the experimental wedges thrusting wedge development depends crucially on the relative velocity when the slow indenter moves with a velocity of more than 55 of the fast indenter a single curved thrust wedge develops the wedge becomes decoupled along strike slip zone at large velocity differences i e when the slow indenter moves slower than 55 of the faster indenter consequently the thrust front is strongly curved at high 55 60 and smoothly curved at low velocity differences 70 80 in all cases curvature increases during indentation along the most strongly curved portion of the thrust wedge the transfer zone rises particle rotation and material transport oblique to the indentation direction occur directed toward the front of the slow indenter thrusting cycles are timed by the fast indenter and influence thrusting in front of the slow indenter thrusts nucleate in front of the fast indenter wedge and propagate laterally to the slow indenter front this implies distant effects of wedge growth active hundreds of kilometres along strike of orogens silicone oil as a detachment induces a low angle wedge which is less curved than in the glass beads experiments and shows variable thrust vergence with fore and back thrusts we compare our experimental results with the curved fold and thrust belts of the tajik basin in front of the hindu kush and pamir indenters our results are able to explain several first order features

statistical analysis of an ionospheric parameter as a base for earthquake prediction 1 this paper is related to the use of ionospheric density variations to tentatively predict earthquakes the results of this statistical analysis are presented as a function of various parameters the ion density was recorded by the low altitude satellite demeter during more than 6 years and a search for anomalies was automatically conducted with the complete data set in a second time a software checked if each anomaly could correspond to an earthquake the search was conducted at less than 1500 km from the anomaly positions and until 15 days after the anomaly time the earthquakes have been classified depending on their magnitude depth and position below the sea or inland this attempt to predict earthquakes of course generates a lot of false alarms and wrong detections nevertheless it is shown that the number of good detections increases with the magnitude of the earthquakes in average the number of perturbations is higher the day of the earthquake and then smoothly decreases for the days before earthquakes below the sea are better detected there are seismic areas close to the south atlantic magnetic anomaly and at high latitudes where the number of natural perturbations is too important to expect a high number of good detections finally when there are several perturbations corresponding to a single earthquake it is possible to combine their positions to have a better estimation of the location of the future epicenter however uncertainties about the time and the magnitude are large

convergence rate dependent growth of experimental viscous orogenic wedges the effects of convergence rate variations on the evolution of mature orogenic wedges are investigated using temperature dependent variations in the viscosity of paraffin as an analogue for the natural strength distribution in the crust experiments were performed in a thermomechanical shortening apparatus for strain rates ranging between 10 5 and 5 10 5 s 1 experimental wedges accreted at fast convergence rates show steep surface tapers and narrow deformed areas whereas at low strain rates they show lower taper topographies and wider deformed areas during self similar growth a decrease in convergence rate during deformation corresponds to a change from localised to delocalised deformation in concomitance with the outward migration of the deformation front the model results provide insights into deformation partitioning geometry and accretionary mechanisms within orogenic wedges

physical modelling of deformation in the tasman orogenic zone abstract structural vergence within the western subprovince of the lachlan fold belt is towards the hinterland rather than the foreland in contrast to many well known orogenic belts high angle reverse faults and upright folds verge eastwards away from the australian craton towards the inferred centre of orogenic and magmatic activity we designed a series of analogue models to test the anomalous vergence in the western lachlan fold belt particularly the interaction of a stable australian craton with tasman line geometry interacting with weaker oceanic or transitional lithospheric material we found consistently that vergence direction in the models was towards the hinterland not the foreland as in the western lachlan fold belt irrespective of the way the model was deformed strength gradients between the oceanic and cratonic lithosphere control the deformation patterns an important result of the models is that they demonstrate that fold belts with different vergences can be generated without the requirement of subducting oceanic lithosphere

multisatellite observations of an intensified equatorial ionization anomaly in relation to the northern sumatra earthquake of march 2005 here we report multisatellite observations of ionospheric disturbances in relation to the occurrence of the m8 7 northern sumatra earthquake of 28 march 2005 the demeter detection of electro magnetic emissions transmitted from earthquake regions and champ challenging minisatellite payload satellite data were investigated to find possible precursory and postevent phenomena it was found that eia equatorial ionization anomaly strength expressed in the apex height derived from the champ plasma density profile was intensified along the orbits whose longitudes were close to the epicenter within about a week before and after occurrence of the earthquake increases in electron and o density along the orbits close to the epicenter were also observed in the demeter measurements the normalized equatorial plasma density derived from the demeter measurements showed intensification about a week before and after the earthquake reaching maximum the day after the shock and afterward disappearing in addition similar behavior of the eia enhancements related to the m8 0 pisco earthquake of 15 august 2007 was observed surveys of space weather and geomagnetic activities excluded the possibility that these fluctuations were caused by changes in space weather or by a geomagnetic storm statistical analyses of the longitudinal variation revealed that the eia was enhanced in the west of the epicenter and reduced in the east of the epicenter and this fits the increased conductivity model based on these observations we proposed a revised view of seismo ionospheric coupling in the region of the geomagnetic equator to explain the eia features observed in this study

deformation patterns and structural vergence in brittle ductile thrust wedges an additional analogue modelling perspective abstract scaled physical models of brittle ductile thrust wedges investigated the causes leading to the development of the various structural styles observed in fold and thrust belts and accretionary prisms this study focused on some potential controlling factors such as 1 relative strength between the brittle overburden and the viscous decollement layer brittle ductile coupling 2 the effect of very low basal friction and 3 pre shortening rheological stratigraphy including decollement strength type 1 models had a single basal decollement whereas in type 2 models the decollement was embedded in brittle material simulating an upper roof sequence and a lower floor sequence other models investigated the effects produced by an horizon of mechanical weakness at the base of the viscous decollement type 1a and the role of decollement offset type 3 the experiments suggest the occurrence of a genetic relationship between the absolute values of shear stresses and the development of dominating hinterland or foreland verging thrust faults or dually verging thrusts by controlling the orientation of the 1 axis basal friction and decollement offset is found to effectively influence the deformation pattern and structural vergence and could explain the development of dominating backthrusts in cascadian type margins the decoupling of a frontal monocline via the upper decollement type 2 models produced passive roof duplex structures termed composite roof duplex when the frontal monocline coexists with outward fold propagation

ionospheric density variations recorded before the 2010 mw 8 8 earthquake in chile 1 we present a study of plasma density variations observed by the demeter spacecraft in the vicinity of a very powerful earthquake in chile this earthquake of moment magnitude 8 8 occurred on 27 february 2010 with an epicenter located at 35 85 s 72 72 w data recorded 10 20 days before the main shock along orbits close to the future epicenter show increasing plasma densities in a second step a statistical analysis with demeter data has been performed using the first 3 months of the years 2007 2010 to monitor density variations in the vicinity of the epicenter at the same local time and seasonal conditions this study shows that a large increase of the plasma density is very uncommon at this location and at this time and that the increases observed during the days before the main shock could be considered as possible short term precursors of this powerful earthquake

fluid composition and evolution of the langxi ba f deposit yangtze block china new insight from la icp ms study of individual fluid inclusion abstract the langxi vein type ba f deposit located in the southeast of the sichuan basin in the central part of yangtze block south china is hosted by ordovician limestone the paragenesis of the deposit s veins is subdivided into pre syn and post ore stages the syn ore stage includes two fluorite generations with the first fl 1 deposited at 140 to 200 c and the second fl 2 at 140 to 180 c the syn ore barite mineralisation was deposited with the temperature range of 110 160 c and the syn ore calcite records a temperature range of 90 to 140 c these temperature ranges show that the mineralising fluids were low to moderate in temperature and decreased with the initial deposition of fluorite followed by barite and then calcite the types of fluid inclusions in the veins are classified as monophase liquid l type type i biphase liquid vapour l v type type ii and polyphase l v s type type iii brine inclusions the salinity of the mineralising fluid for the three types of inclusions during the deposition of f ba ca is 0 35 21 7 nacl eqv indicating that the ore forming fluid varied greatly during the mineralising process there are no obvious differences in the fluid inclusion density in the different minerals with the average densities being 0 98 g cm3 for fl 1 0 99 g cm3 for fl 2 1 00 g cm3 for barite and 1 01 g cm3 for calcite this shows that the density of the f ba ca mineralising fluid belong to a moderate low density the deposition of the minerals took place with a change from a reducing to an oxidising environment the liquid phase initially included na and cl and evolved containing ca2 so42 k and mg2 la icp ms analyses reveal that the l v type fluid inclusions associated with fl 1 assays 46 600 ppm na 3470 ppm k with a mean na k ratio of 24 28 200 ppm for cl and 1060 ppm br with a mean cl br mass ratio of 27 the second generation fluorite l v type fluid inclusions average around 47 000 ppm na and 12 000 ppm k corresponding to and a na k mass ratio of 7 the halogen content of fl 2 averages 26 200 ppm cl and 950 ppm br corresponding to a cl br mass ratio of 28 these analyses indicate that the mineralising fluid was rich in nacl assuming the fluid inclusions represent samples of the mineralising fluid it is proposed that ba f concentrated in the mineralising fluid were derived from basinal fluids mixed with meteoric water circulating through faults at increased temperature gradients the driving force was late cretaceous tectonic activity related to the subduction of the paleo pacific oceanic plate this model is consistent with the geodynamic setting of other barite fluorite rich districts in the yangtze block of south china

physical experiments of transpressional folding abstract in order to understand the process of folding in obliquely convergent settings we formed folds within a shear box capable of creating homogeneous transpressional deformations folds were created in a single layer of stiff mixed plasticine and silicone that overlay a newtonian silicone for a variety of plate convergence angles as small amplitude folds became visible they were parallel to the long axis of the horizontal finite strain ellipse with increasing deformation the fold hinges rotated parallel with the long axis of the horizontal finite strain ellipse for all angles of convergence this parallelism indicates that fold hinges once formed rotate with the horizontal strain ellipse rather than as material lines the experiments highlight several interesting effects of transpression dynamics the fold hinges initiate parallel to either 1 or 2 and are parallel to either s 1 or s 2 with increasing deformation neither infinitesimal strain stress nor finite strain is resolvable solely from fold geometry further the net amount of contraction determined by folding across the zone was overestimated in all cases except pure contraction this effect is obvious for the case of wrenching where folding implies that the zone contracts if elongation parallel to the fold hinge is not considered therefore attempts to balance cross sections in transpressional zones will tend to overestimate contraction unless the wrench component of deformation is addressed this result is validated by applying the modeling results in folding in central california adjacent to the san andreas fault where cross section balancing indicates higher amounts of contraction than predicted by plate motion

deformation evolution of eastern sichuan xuefeng fold thrust belt in south china insights from analogue modelling abstract the eastern sichuan xuefeng fold thrust belt cxftb located in south china has received wide attention due to its distinctive deformation styles and close relationships with natural gas preservation but its deformation evolution still remains controversial in order to study further this issue we designed three sets of analogue models based on the results of the models we suggest that 1 the deformation in the cxftb may simultaneously initiate along two zones nearby the dayong and qiyueshan faults at 190 ma and then progressively propagate into the interiors of the western hunan hubei and eastern sichuan domains at 140 150 ma and finally reach the front of the huayingshan fault at 120 ma 2 the difference in decollement depth is the main factor determining the patterns of folds in different domains of the cxftb and 3 the eastern sichuan domain may have a basement significantly different from those of the western sichuan and western hunan hubei domains

granites of the southern mongolia carboniferous arc new geochronological and geochemical constraints the crust in southern mongolia is part of the central asian orogenic belt a vast accretionary orogen that records the opening and closure of the palaeo asian ocean in the late proterozoic to palaeozoic the crustal evolution of the region is revealed in basement inliers that also contain intrusion related porphyry ore bodies that are important mineral exploration targets the saykhandulaan inlier in southeast mongolia is a devonian carboniferous segment of island arc crust which is dominantly composed of extrusive and sedimentary lithologies but which also contains the oyut ulaan i type quartz monzonite intrusion a u pb zircon age for the oyut ulaan monzonite indicates emplacement at 330 0 0 5 ma to the east of the saykhandulaan inlier intrusive complexes dominate the neighbouring mandakh inlier new ages are presented for four of these plutons the bronze fox granodiorite 333 6 0 6 ma the narin hudag monzonite 333 2 0 6 ma the shuteen quartz monzonite 325 5 1 0 ma and the north mandakh granite 292 3 0 5 the intrusive bodies of the saykhandulaan and mandakh inliers have two distinct geochronological and geochemical associations 1 mid carboniferous i type monzonites that constitute the most easterly intrusive expression of the southern mongolia carboniferous arc and 2 early permian a type and peralkaline granites that represent a post orogenic phase of voluminous granite emplacement both groups are significantly younger than the nearby oyu tolgoi and tsagaan suvarga cu porphyry ore bodies which have previously been dated as early and late devonian respectively the new data presented here provide constraints on the timing of the transition from island arc magmatism to post collisional extension related magmatism in the region and possible controls on fertile and infertile granitoid intrusions with respect to cu au mineralisation

seismoionospheric gps total electron content anomalies observed before the 12 may 2008 mw7 9 wenchuan earthquake 1 the global ionospheric map gim is used to observe variations in the total electron content tec of the global positioning system gps associated with 35 m 6 0 earthquakes that occurred in china during the 10 year period of 1 may 1998 to 30 april 2008 the statistical result indicates that the gps tec above the epicenter often pronouncedly decreases on day 3 5 before 17 m 6 3 earthquakes the gps tec of the gim and electron density profiles probed by six microsatellites of formosat3 cosmic f3 c are further employed to simultaneously observe seismoionospheric anomalies during an mw7 9 earthquake near wenchuan china on 12 may 2008 it is found that gps tec above the forthcoming epicenter anomalously decreases in the afternoon period of day 6 4 and in the late evening period of day 3 before the earthquake but enhances in the afternoon of day 3 before the earthquake the spatial distributions of the anomalous and extreme reductions and enhancements indicate that the earthquake preparation area is about 1650 km and 2850 km from the epicenter in the latitudinal and longitudinal directions respectively the f3 c results further show that the ionospheric f2 peak electron density nmf2 and height hmf2 significantly decreases approximately 40 and descends about 50 80 km respectively when the gps tec anomalously reduces

ionospheric responses to the october 2003 superstorm longitude local time effects over equatorial low and middle latitudes 1 ionospheric responses to the major magnetic storm disturbances of october 2003 are investigated using database selected in the brazilian and japanese asian longitude sectors data obtained from latitudinally spaced digisondes in the equatorial and low latitude sites in brazil and from the asian and japanese ionosonde network the total electron content data from the extensive japanese gps receiver chain and magnetometer data from the pacific equatorial electrojet stations are analyzed during the period 28 31 october prompt penetrating pp dawn dusk polar cap electric fields produce large f region plasma uplift on the dayside and eveningside while the associated westward electric field on the nightside produces large downdraft of the f region plasma and causes development of westward electrojet current observed for the first time episodes of pp electric field effects appear to be of larger intensity over brazil than over asian longitudes equatorial anomaly development due to undershielding as well as overshielding electric fields was observed in the brazilian and in the asian sectors disturbance dynamo electric field causes large nighttime f layer uplifts that are modulated by strong meridional winds in both sectors the disturbance electric field local time variation patterns are compared with the results of recent global model mtiegcm simulation by richmond et al 2003 and validated in some cases transients of transequatorial winds flipping direction from southward to northward in the widely separated longitude sectors were diagnosed to be present toward the final recovery phase of the storm these results are presented and discussed in this paper

constraints on the depth geometry and kinematics of blind detachment faults provided by fault propagation folds an example from the mesozoic fold belt of south china abstract the mesozoic multi layered thin skinned fault related fold belt in south china is characterized by propagation chevron folding and thrust faulting we examine the geometry and depth of blind detachment faults in this belt using faults and folds that crop out along a well defined cross section a combination of parameters such as backlimb dip angle 2 interlimb angle height of anticline h thickness of the referenced layer h0 width of the anticline ab and thickness change ratio of layering within the forelimb tf t are used to develop new equations to estimate the geometry and depth of the detachment faults in the cross section the huangdushan chevron anticline has parameters revealing a blind fault with a ramp angle of 42 and a flattened segment at a depth of 4 9 km based on existing seismic data we interpret this blind fault as a backthrust developed over an in sequence imbricated duplex of cambrian to ordovician strata a chevron anticline at qiyueshan also reveals a backthrust fault however a broad anticline in lengzhuba and a small cylindrical sinusoidal anticline in yupize reveal a flat ramp flat detachment fault with flat segments at depths of 7 4 and 3 4 km respectively suggesting that the sinian strata were thickened probably by an out of sequence imbricated duplex our results indicate that the flat ramp flat detachment fault along the bottom of the sinian strata produced the out of sequence imbricated duplex and cylindrical sinusoidal folds the in sequence imbricated duplex produced backthrusts and related chevron anticlines we consider that this fault related fold belt was produced by collision between the yangtze block and north china blocks

mesozoic sedimentary evolution of the northwest sichuan basin implication for continued clockwise rotation of the south china block we present new sedimentary data integrated into a regional mesozoic stratigraphic framework to provide a detailed picture of spatio temporal variations in deposition and depocenter migration of the northwest sichuan basin the mesozoic sedimentary evolution is utilized to interpret basin subsidence history and to unravel coeval basin margin tectonics the northwest sichuan basin together with the songpan ganzi terrane behaved as a passive margin south of the qinling paleo tethys from late paleozoic to early middle triassic times and then evolved into a peripheral foreland basin in response to collision of the north and south china blocks since the late middle triassic coeval with strong north south contraction of the songpan ganzi terrane in the late triassic sinistral transpressional deformation of the longmen shan belt led to flexural subsidence of the adjacent western sichuan basin renewed basin margin fold thrust activity triggered recurrence of flexural subsidence of the northwest sichuan basin since the middle jurassic with the depocenter eventually shifting to the northwestern corner of the basin in the early cretaceous sedimentary evolution of the northwest sichuan basin and the basin margin deformation imply that the south china block had been rotating clockwise relative to the north china block throughout the mesozoic with an interim period of early jurassic tectonic quiescence a model is advanced that invokes clockwise rotation of the south china block as a driver for tectonic evolution of both the basin and adjoining structural belts and provides an explanation for several salient features that are otherwise puzzling

differential deformation on two sides of qiyueshan fault along the eastern margin of sichuan basin china and its influence on shale gas preservation abstract structural deformation is one of the main factors controlling shale gas preservation in silurian longmaxi formation in the sichuan basin the exploration practices demonstrate that the shale gas preservation condition in the areas to the west of the qiyueshan fault qysf along the eastern margin of the sichuan basin is better than that to the east in this study we synthesize seismic interpretation apatite fission track aft and triaxial rock mechanics experiment to determine the structural segmentation deformation time and shale fracturability of the qysf belt seismic interpretation shows that the qysf can be divided into three segments among which the central segment is transitional deformation zone the burial depth and deformation structure difference of silurian strata on the two sides of the fault are not variable obviously and shale gas preservation conditions are good aft simulation shows that the initial deformation time of chevron syncline thrust structure to the east of the qysf was 160 120 ma while that of the chevron anticline thrust structure deformation between the qiyueshan and the huayingshan was 100 80 ma and it gradually changes from the central to the north and south rock mechanics test reveals that under the same stress field the difficulty of fracture is influenced the dip angle of the shale bedding plane shale is most likely to produce fracture when the dip angle of bedding plane 34 37 but horizontal formation is difficult to rupture this proves that gentle anticline and syncline are more conducive to shale gas preservation therefore shale gas is mainly enriched in the core of gentle anticline and synclinal combined with the analysis of typical wells we believed that the two sides of the qysf are different in deformation time uplift amplitude and later multi directional stress reworking these cause differences in the direction scale and density of fractures in the strata thus affecting shale gas preservation on two sides of the qysf

fine crustal structure and deformation beneath the great xing an ranges caob revealed by deep seismic reflection profile abstract a crustal seismic reflection profile across the great xing an ranges gxar was recorded in 2011 revealed features of crustal structure and deformation at the eastern margin of the central asian orogenic belt caob the reliability of crust and upper mantle image was improved by rigorous regulations of seismic data acquisition and a series of special procedures for seismic data processing the diversiform seismic reflection fabrics within deep crust to mantle transition zone twt two way time 12 14 s approximately 36 42 km beneath gxar reflects the complicated products of tectonic and magmatic interaction of lower crustal and mantle components during evolution of gxar preliminary processing result shows the contact relationship of the gxar and adjacent basins we can identify lots of curved reflection phases from volcanic rock and opposite moho reflection events this scenario may suggest multi times tectonic transformation from contraction to extension presumably its cause of formation reflects the comprehensive dynamic action of the mongolia okhotsk tectonic system and the circum pacific tectonic system

paleozoic crustal growth and metallogeny of central asia evidence from magmatic hydrothermal ore systems of central kazakhstan abstract the ore deposit spectrum of central kazakhstan reflects a range of lithospheric magmatism controlled by the polycyclic geodynamic evolution of an active continental margin which develops from back arc oceanic settings volcanic hosted massive sulphide cu au ore deposits to subduction controlled calcalkaline magmatism copper porphyries with subsequent stages of crust differentiation of low degree partial melting and extended intramagmatic fractionation molybdenum porphyries on to continental rifting peralkaline ree zr nb rich systems mesothermal gold deposits mark transcrustal shear zone controlled fluid conduits formed during arc slicing and thermal relaxation in a post orogenic setting the ore deposits characterize successive and spatially overlapping stages of crustal growth and consolidation the general subduction setting of this range of ore deposits is reflected by calc alkaline trends in the associated subalkaline high k felsic rocks with a wide range in silica contents the predominant metal spectrum of au cu and mo indicates relatively oxidized magmatic hydrothermal systems in accordance with the metaluminous i type nature of their igneous host rocks i e oxidized igneous precursor material despite of presumably highly variable ratios of mantle crust components in individual magmatic systems gabbros to leucogranites most rocks have very similar positive initial e nd values of 0 to 5 5 and depleted mantle model ages in the range of 500 800 ma the ubiquitous relatively young mantle extraction age is likely to characterize the lower crust of central kazakhstan this basement is interpreted as back arc oceanic crust that formed behind oceanwards drifting continental margin slivers during the initial stages of the active continental margin evolution of the late precambrian angara baltica supercontinent the early back arc oceanic crust was transformed into the present lower crust during the paleozoic orogenic evolution in which the back arc crust was buried by magmatic arc and sedimentary material and recurrently affected by high grade metamorphism basaltic melt injection underplating and granitic melt extraction anorogenic rift related permian peralkaline riebeckite granites with ree zr nb mineralization have very high positive e nd of 5 to 8 which is probably inherited from young subcrustal lithosphere at the mantle crust boundary that was affected by partial remelting due to asthenospheric upwelling during rifting

spacecraft observations of electromagnetic perturbations connected with seismic activity 1 results of a statistical study of intensity of vlf electromagnetic waves observed in the vicinity of earthquakes are presented a unique set of data obtained by the micro satellite demeter altitude of about 700 km nearly sun synchronous orbit and a robust two step data processing has been used in the first step all the measured data are used to construct a map of electromagnetic emissions containing a statistical description of wave intensity at a given point of the satellite orbit under given conditions in the second step the intensity measured close to earthquakes is analyzed using the statistical distribution of background intensity obtained in the first step the changes of wave intensity caused by seismic activity are investigated and their statistical significance is evaluated altogether more than 2 5 years of satellite data have been analyzed and about 9000 earthquakes with magnitudes larger than or equal to 4 8 that occurred all over the world during the analyzed period have been included in the study it is shown that during the night there is a statistically significant decrease by 4 6 db of the measured wave intensity shortly 0 4 hours before an intense surface depth less than or equal to 40 km earthquake

ionospheric density and velocity anomalies before m 6 5 earthquakes observed by demeter satellite abstract the seismo ionospheric density anomalies have been widely studied for last decades based on ground gps and satellite in situ observations in this paper we analyze both ion density and ion velocity observed by the french satellite demeter before 49 earthquakes with m 6 5 in 2010 the results show that both ion density and ion velocity increase anomalously before the earthquakes the differences before and after earthquakes are more significant with larger magnitude and shallower depth the density variations have a positive correlation with the perpendicular velocity which is related to the perpendicular electric field by e v b0 b0 is the background geomagnetic field the slopes of ni ni in units of vs v in units of m s ranges from 0 13 to 0 7 this suggests that the ion density variation is associated with the presence of ion velocity or electric field in the ionosphere the observed peak perpendicular velocity can reach 300 1300 m s before the earthquakes corresponding to a perpendicular electric field e 7 5 32 5 mv m

experimental modelling of orogenic wedges a review abstract experimental modelling applied to the study of orogenic wedge dynamics has been a subject of fruitful research for more than 30 years although the technique dates back as far as the early xix th century on one hand several first order parameters controlling the structural evolution of mountain belts have been intensively investigated using the classic tectonic sandbox models the main parameters are the properties of the basal decollement the deforming material the backstop and fluxes kinematics and surface processes on the other hand the morphological evolution of a mountain relief subjected to changing tectonic or climatic forcing has been addressed using another kind of approach called geomorphic models nowadays the literature is extremely rich particularly for the sandbox technique so that it becomes difficult to have an exhaustive view of the effects of the above parameters on mountain evolution in this article we propose a detailed review of the main results obtained using both tectonic and geomorphic approaches our goal is to provide an almost complete state of the art in the experimental study of relief dynamics to guide present and future researchers in their understanding of mountain belt evolution

the early paleozoic tectonic evolution of the russian altai implications from geochemical and detrital zircon u pb and hf isotopic studies of meta sedimentary complexes in the charysh terekta ulagan sayan suture zone abstract the charysh terekta ulagan sayan suture zone was regarded as a tectonic boundary separating two distinct subduction accretion systems in the central asian orogenic belt caob in the north magmatic arcs such as the gorny altai terrane formed in the southwestern periphery of the siberian continent whereas in the south arc prism systems such as the altai mongolian terrane formed around the so called kazakhstan baikal composite continent with gondwana affinity when did these two systems amalgamate and whether the metamorphic complexes in the suture zone represent precambrian micro continental slivers are critical for our understanding of the accretionary orogenesis and crustal growth rate in the caob a combined geochemical and detrital zircon u pb hf isotopic study was conducted on the meta sedimentary rocks from the ulagan also referred to bashkaus and teletsk complexes in the suture zone the results indicate that the protoliths of these rocks were dominated by immature sediments deposited in a time period between 500 and 420 ma thus precambrian micro continental slivers may not exist in the suture zone and even in the whole altai orogen the meta sedimentary rocks from the ulagan complex yield geochemical compositions between those of common intermediate and felsic igneous rocks implying that these kinds of rocks possibly served as dominant sources detrital zircons from this complex consist of a major population of ca 620 500 ma a subordinate one of ca 931 671 ma and rare grains of ca 2899 1428 ma this age spectrum is compatible with the magmatic records of the western mongolia we propose that the ulagan complex possibly represents part of a subduction accretion complex built upon an active continental margin of the western mongolia in the early paleozoic the remarkable similarities in source nature provenance and depositional setting to the early paleozoic meta sedimentary rocks from the northern altai mongolian terrane imply that the ulagan complex was possibly fragmented from this terrane the meta sedimentary rocks from the teletsk complex show similar detrital zircon populations but contain higher proportions of mafic sediments and have more depleted whole rock nd isotopic compositions our data suggest that the detritus mostly came from the same source as that for the ulagan complex but those from the gorny altai terrane also contributed this implies that the gorny altai and altai mongolian terranes possibly amalgamated prior to the early devonian rather than in the middle devonian to early carboniferous as previously thought thus the widespread devonian to early carboniferous magmatism within these two terranes was possibly generated in a similar tectonic setting moreover the dominant neoproterozoic to early paleozoic detrital zircons from the teletsk complex yield largely varied hf t values of 23 8 to 12 4 indicating that crustal growth and reworking are both important in the accretionary orogenesis

topography as a major factor in the development of arcuate thrust belts insights from sandbox experiments abstract we have used sandbox experiments to investigate and to illustrate the effects of topography upon the development of arcuate thrust belts in experiments where a sand pack shortened and thickened in front of an advancing rectilinear piston the geometry of the developing thrust wedge was highly sensitive to variations in surface topography in the absence of erosion and sedimentation the surface slope tended to become uniform as predicted by the theory of critical taper under these conditions the wedge propagated by sequential accretion of new thrust slices in contrast where erosion or sedimentation caused the topographic profile to become irregular thrusts developed out of sequence for example erosion throughout a hinterland caused underlying thrusts to remain active and inhibited the development of new thrusts in the foreland where initial topography was irregular in plan view accreting thrusts tended to be arcuate they were convex towards the foreland around an initially high area concave towards the foreland around an initially low area initial plateaux tended to behave rigidly while arcuate thrust slices accreted to them thrust motions were radial with respect to each plateau within transfer zones to each side fault blocks rotated about vertical axes and thrust motions were oblique slip at late stages of deformation the surface slope of the thrust wedge tended towards a uniform value initial mountains of conical shape representing volcanoes also escaped deformation except at depth where they detached arcuate thrust slices accreted to front and back where a developing thrust wedge was subject to local incision accreting thrust slices dipped towards surrounding areas of high topography forming vs across valleys arcuate structural patterns are to be found around the three highest plateaux on earth tibet pamirs and altiplano and around the tromen volcanic ridge in the neuquen basin of northern patagonia we infer that these areas behaved in quasi rigid fashion protected as they were by their high topography

experimental insights on the geometry and kinematics of fold and thrust belts above weak viscous evaporitic decollement abstract this paper discusses the differences in mechanical properties and kinematics between fold and thrust belts detaching on evaporitic decollements and those detaching on stronger detachments physical experiments are described that model shortening of a thick brittle cover overlying a weak viscous decollement to gain a better understanding of these differences we tested the influence of 1 the decollement layer thickness and 2 the presence of a deformable backstop on the hinterland side and of a decollement pinch out on the foreland side because of the very low shear strength of the viscous decollement folds and thrusts did not propagate according to a piggy back sequence but by centripetal back and forth propagation additional shortening was accommodated by growth of all existing structures fold symmetry and thrust vergence varied between experiments models confined between two rigid vertical endwalls always deformed by symmetric folding and thrusting in models having a deformable backstop and a foreland decollement pinch out forethrusting initially dominated folds were asymmetric and fault blocks rotated in models having a thick decollement layer folds kept growing asymmetrically diapirism also depended on the initial decollement geometry diapirs formed only in models having a deformable backstop and were restricted to the hanging wall of a fault related fold finally the implications of such kinematics on the thermal history are discussed as well as the likelihood of hydrocarbon maturation and preservation

observations and simulations of seismoionospheric gps total electron content anomalies before the 12 january 2010 m7 haiti earthquake 1 in this paper the total electron content tec of the global ionosphere map gim is used to detect seismoionospheric anomalies associated with the 12 january 2010 m7 haiti earthquake and an ionospheric model is applied to simulate the detected anomalies the gim temporal variation shows that the tec over the epicenter significantly enhances on 11 january 2010 1 day before the earthquake the latitude time tec ltt plots reveal three anomalies 1 the northern crest of equatorial ionization anomaly eia moves poleward 2 the tecs at the epicenter and its conjugate increase and 3 the tecs at two dense bands in the midlatitude ionosphere of 35 n and 60 s further enhance the spatial analysis demonstrates that the tec enhancement anomaly appears specifically and persistently in a small region of the northern epicenter area the simulation well reproduces the three gim tec anomalies which indicate that the dynamoelectric field of the ionospheric plasma fountain might have been perturbed by seismoelectric signals generated around the epicenter during the earthquake preparation period

origin and tectonic significance of a mesozoic multi layer over thrust system within the yangtze block south china abstract in the yangtze block south china a well developed mesozoic thrust system extends through the xuefeng and wuling mountains in the southeast to the sichuan basin in the northwest the system comprises both thin and thick skinned thrust units separated by a boundary detachment fault the dayin fault to the northwest the thin skinned belt is characterized by either chevron anticlines and box synclines to the northwest or chevron synclines to the southeast the former structural style displays narrow exposures for the cores of anticlines and wider exposures for the cores of synclines thrust detachments occur along silurian fs and lower cambrian fc strata and are dominantly associated with the anticlines to the southeast this style of deformation passes gradually into one characterized by chevron synclines with associated principal detachment faults along silurian fs cambrian fc and lower sinian fz strata there are however numerous secondary back thrusts therefore the thin skinned belt is like the valley and ridge province of the north american applachian mountains the thick skinned belt structurally overlies the thin skinned belt and is characterized by a number of klippen including the xuefeng and wuling nappes it is thus comparable to the blue ridge province of appalachia the structural pattern of this thrust system in south china can be explained by a model involving detachment faulting along various stratigraphic layers at different stages of its evolution the system was developed through a northwest stepwise progression of deformation with the earliest delamination along lower sinian strata fz analyses of balanced geological cross sections yield about 18 1 21 total 88 km shortening for the thin skinned unit and at least this amount of shortening for the thick skinned unit the compressional deformation from southeast to northwest during late jurassic to cretaceous time occurred after the westward progressive collision of the yangtze block with the north china block and suggests that the orogenic event was intracontinental in nature

recent progress in ionospheric earthquake precursor study in china a brief review abstract the study of ionospheric anomaly variation before large earthquakes has attracted the attention of geophysicists for many years this is primarily because ionospheric anomaly variation has been considered to constitute one possible method to identify earthquake precursors since china covers several major earthquake zones it is critical for chinese scientists to study possible ionospheric earthquake precursors in this report we provide a brief summary of recent progress in the study of ionospheric earthquake precursors mainly from chinese mainland researchers as well as some other scientists this report focuses on 1 some case studies of ionospheric abnormal behaviors before some great earthquakes around the world e g m7 9 wenchuan earthquake m9 0 tohoku oki earthquake m7 0 haiti earthquake and 2 some statistical characteristics of ionospheric anomalies before earthquakes including their temporal and spatial distributions and the relationship with the forthcoming earthquake the above mentioned studies may provide some new and beneficial insights for the future study of ionospheric earthquake precursors

late paleozoic early mesozoic magmatic history of central inner mongolia china implications for the tectonic evolution of the xingmeng orogenic belt the southeastern segment of the central asian orogenic belt abstract the tectonic setting and location of the southernmost boundary of the central asian orogenic belt caob in the late paleozoic early mesozoic era and the history evolution for the xingmeng orogenic belt xmob are sources of debate within the scientific community this paper presents new geochronological petrological and geochemical data for late paleozoic early mesozoic intrusions from the siziwangqi region in the southeastern caob and discusses the tectonic setting for that area using zircon la mc icpms u pb dating intrusions can be broadly grouped as late carboniferous amphibolite with an age of 323 1 3 4 ma middle late permian granitoids with ages of 271 3 1 5 ma 261 3 3 8 ma 260 6 4 8 ma 259 9 3 5 ma 253 3 4 8 ma and 249 6 4 8 ma early triassic k feldspar granite with an age of 235 0 1 8 ma these studies by interaction of regional geology provide new constraints on the tectonic evolution of the southeastern central asian orogenic belt during the late paleozoic early mesozoic and we predict five stages of tectonic evolution during the late paleozoic early mesozoic 1 the early carboniferous early permian 298 ma which is the active continental margin stage and the exit of the back arc basin during the late carboniferous 2 the early permian middle permian 298 271 ma where there was continued subduction of paleo asian oceanic lithosphere and the solonker ophiolite emplacement at the end of early permian 3 the middle permian 271 261 ma which had continent continent collision between the siberian plate and the north china craton 4 the middle permian middle triassic 261 235 ma which was the collisional orogeny stage with few intermountain basin deposition and the disappearance of marine strata and 5 late triassic

variations of ionospheric total electron content during the chi chi earthquake on 20 september1999 ut 21 septemberin local time lt a large earthquake mw 7 7 struck central taiwan nearthe small town of chi chi the greatest plasma frequency in the ionosphere fof2 observed by the chung li ionosonde 25 0 n 121 2 e reveals three clear precur sors at 1 3 and 4 days prior to the earthquake this paper examines the ionospheric total electron content tec ob served by a network of the global positioning system gps receivers in taiwan area it is found that variations in fof2 and overhead tec recorded at chung li have a similar ten dency combining the data of the network of 13 gps re ceivers time and spatial variations of tec prior to the chi chi earthquake are examined results show that the equa torial anomaly crest moves equatorward and its tec value significantly decreases 1 3 and 4 days before the earth quake a comparison between the disturbed and reference previous 15 day median days confirms that tec decreases significantly around the epicenter in the afternoons of these days finally possible mechanisms are proposed and dis cussed

some statistical results on very low frequency radiowave emissions in the upper ionosphere over earthquake zones abstract an anomalous increase in the intensity of low frequency 0 1 16 khz radiowave emissions was detected using intercosmos 19 data when the satellite was nearly over the epicentre of an earthquake zone ample statistical data are the basis for a determination of the probable spatial temporal dimensions of the region of the upper ionosphere in justify which elf vlf emissions were detected the reliability of the detected phenomenon is 0 8 0 9 the ionospheric regions with the low frequency emissions observed by intercosmos 19 have been found to be formations noise belts extended along 60 of geographic longitude and 2 of geographic latitude the spectral characteristics of elf vlf emissions near seismic areas are specified the earthquake depth and location under a continent or under an ocean has an effect on the results of the satellite observations of earthquakes possible mechanisms of the phenomenon are discussed

giant ionospheric disturbances excited by the m9 3 sumatra earthquake of 26 december 2004 1 an mw 9 3 earthquake originated in the indian ocean off the western coast of northern sumatra at 00 58 53 universal time ut on 26 december 2004 two giant ionospheric disturbances at 01 19 and 04 10 ut are observed by a network of digital doppler sounders in taiwan the first disturbance excited mainly by rayleigh waves which consists of a packet of short period doppler shift variations results in vertical ionospheric fluctuations with a maximum velocity of about 70 m s and displacement of about 200 m the second disturbance in a w shaped pulse propagating at a horizontal speed of 360 70 m s is attributable to coupling of the atmospheric gravity waves agw excited by broad crustal uplift together with the following big tsunami waves around the earthquake source zone the accompanying ionosonde data suggest that the agw in the atmosphere may have caused the ionosphere to move up and down by about 40 km

ionosphere plasma bubbles and density variations induced by pre earthquake rock currents and associated surface charges 1 recent ionospheric observations indicate that the total electron content tec may anomalously decrease or increase up to 5 20 before the occurrence of big earthquakes the ionospheric density variations can be caused by earth surface charges currents produced from electric currents associated with the stressed rock we formulate a coupling model for the stressed rock earth surface charges atmosphere ionosphere system the stressed rock acts as the dynamo to provide the currents for the coupling system the electric fields and currents in the atmosphere and the lower boundary of ionosphere are obtained by solving the current continuity equation j 0 where j is the current density a three dimensional ionosphere simulation code is then used to study the ionospheric dynamics based on the obtained electric fields and currents the simulation results show that a current density jrock 0 2 10 a m2 in an earthquake fault zone is required to cause daytime tec variations of 2 25 the simulation results also show that a current density jrock 0 01 1 a m2 can lead to nighttime tec variations of 1 30 as well as the formation of a nighttime plasma bubble equatorial spread f extending over the whole magnetic flux tube containing the earthquake epicenter we suggest that observations of daytime and nighttime tec variations and a nighttime plasma bubble within the affected region can be used as precursors for earthquake prediction

deformation of brittle ductile thrust wedges in experiments and nature 1 even though the rheology of thrust wedges is mostly frictional a basal ductile decollement is often involved by comparison with purely frictional wedges such brittle ductile wedges generally display anomalous structures such as backward vergence widely spaced thrust units and nonfrontward sequences of thrust development laboratory experiments are used here to study the deformation of brittle ductile thrust wedges results are compared with natural systems in the jura mountains and the northern pakistan salt range and potwar plateau two series of three models are used to illustrate the effects of varying the basal wedge angle and shortening rate v these two parameters directly control variations in relative strength between brittle and ductile layers bd coupling wedges with strong bd coupling low and high v give almost regular frontward sequences with closely spaced thrust units and as such are not significantly different from purely frictional wedges weak bd coupling high and low v gives dominantly backward thrusting sequences intermediate bd coupling produces frontward backward oscillating sequences the spacing of thrust units increases as coupling decreases back thrusts develop in parts of a wedge where bd coupling is weak regardless of the thrust sequence wedges with weak bd coupling need large amounts of bulk shortening more than 30 to attain a state of equilibrium at which stable sliding along the base occurs on this basis we argue that a state of equilibrium has not yet been attained in at least some parts of the jura mountains and eastern salt range and potwar plateau thrust systems

modeling of thrust fronts above ductile and frictional detachments application to structures in the salt range and potwar plateau pakistan series of scaled sandbox models are used to simulate the development of thin skinned simultaneous shortening above adjacent ductile and frictional substrates these models simulate the evolution of the potwar plateau and salt range in pakistan where pale

lithosphere atmosphere ionosphere coupling laic model an unified concept for earthquake precursors validation abstract the paper presents a conception of complex multidisciplinary approach to the problem of clarification the nature of short term earthquake precursors observed in atmosphere atmospheric electricity and in ionosphere and magnetosphere our approach is based on the most fundamental principles of tectonics giving understanding that earthquake is an ultimate result of relative movement of tectonic plates and blocks of different sizes different kind of gases methane helium hydrogen and carbon dioxide leaking from the crust can serve as carrier gases for radon including underwater seismically active faults radon action on atmospheric gases is similar to the cosmic rays effects in upper layers of atmosphere it is the air ionization and formation by ions the nucleus of water condensation condensation of water vapor is accompanied by the latent heat exhalation is the main cause for observing atmospheric thermal anomalies formation of large ion clusters changes the conductivity of boundary layer of atmosphere and parameters of the global electric circuit over the active tectonic faults variations of atmospheric electricity are the main source of ionospheric anomalies over seismically active areas lithosphere atmosphere ionosphere coupling laic model can explain most of these events as a synergy between different ground surface atmosphere and ionosphere processes and anomalous variations which are usually named as short term earthquake precursors a newly developed approach of interdisciplinary space terrestrial framework istf can provide also a verification of these precursory processes in seismically active regions the main outcome of this paper is the unified concept for systematic validation of different types of earthquake precursors united by physical basis in one common theory

decelerating nazca south america and nazca pacific plate motions space geodetic estimates of the rate of nazca south america convergence and nazca pacific spreading averaging over several years show that present day rates are significantly slower than the 3 million year average nuvel 1a model the implied rates of deceleration are consistent with longer term trends extending back to at least 20 ma about the time of initiation of andes growth and may reflect consequences of ongoing subduction and construction of the andes e g increased friction and viscous drag on the subducted slab as the leading edge of south america thickens

magnetic field and electron density anomalies from swarm satellites preceding the major earthquakes of the 2016 2017 amatrice norcia central italy seismic sequence a systematic inspection of the magnetic field and electron density recorded by swarm three satellite constellation over the seismic region hit by the 2016 2017 amatrice norcia central italy seismic sequence has allowed us to identify some possible precursory anomalies when disturbed periods of the geomagnetic conditions are properly taken into account and or avoided this paper aims at studying and interpreting the electromagnetic phenomena occurred before and during the 2016 2017 amatrice norcia central italy seismic sequence in order to look for any possible evidence of precursory anomalies results show magnetic field and electron density anomalies of four tracks that precede the major earthquakes of the seismic sequence after an inspection of the geomagnetic conditions a swarm charlie track acquired on 20 08 2016 that precedes by 3 2 days the beginning of the whole seismic sequence remains unexplainable with the normal geomagnetic disturbance phenomena of the earth s magnetic field furthermore we carry out a blind study of possible relationship between abnormal magnetic field signals detected by swarm satellites during geomagnetic quiet conditions and major seismic events from about 4 months before the start of the seismic sequence until about the first 8 months from the seismic sequence i e a total of one year of analysed data we find a very interesting increase of such anomalies starting about 40 days before the beginning of the seismic sequence it coincides and follows surface and atmospheric alterations resulting in a temporal sequence of anomalies from earth s surface up to ionosphere supporting the possibility of lithosphere atmosphere ionosphere coupling models

suspected seismo ionospheric coupling observed by satellite measurements and gps tec related to the m7 9 wenchuan earthquake of 12 may 2008 anomalous changes in the ionospheric conditions related to the wenchuan earthquake of 12 may 2008 are investigated using electron density ne from detection of electro magnetic emissions transmitted from earthquake regions demeter and champ satellites electric field from demeter and gps total electron content tec maps the normalized ne from the demeter satellite reveal that the previously reported tec increments before the earthquake can be considered as fragments of the gradual equatorial ionization anomaly eia enhancements near the epicenter longitude that began approximately 1 month before the earthquake and reached its maximum with an exceptionally large strength index 8 days prior to the main shock this feature is indirectly confirmed through the champ ne and gps tec data following the eia intensity peak disturbances in the ne and o density were observed in the nightside based on the concurrent electric field and ne changes it is suggested that eia intensification could be triggered by the e field disturbances over the epicenter

late paleozoic post collisional magmatism in the eastern tianshan belt northwest china new insights from geochemistry geochronology and petrology of bimodal volcanic rocks abstract the late carboniferous to permian marks an important phase of terrane amalgamation through accretion collision in the central asian orogenic belt caob the tianshan belt forms part of this sequence where the post collisional event generated an e w trending bimodal volcanic zone that extends for ca 500 km from the southern bogda mt to the easternmost tianshan belt here we report the petrology geochemistry and geochronology of the bimodal volcanic rocks to characterize the post collisional tectonic evolution in late paleozoic the major element chemistry of the basalt and rhyolite samples indicates a bimodal high k calc alkaline affinity the basalts are characterized by high abundance in tio2 th u and pb and depletion in nb ta and p together with slight enrichment in lree contents and low hfse lree ratios the rhyolites show a close affinity to aluminous a type granites with enrichment in k na zr ce y and depletion in p nb ta and ti they also exhibit fractionated ree patterns with prominent negative eu anomalies the petrographic and geochemical data suggest that this bimodal rock series was generated in a post collisional setting the mafic rocks are likely derived from a metasomatized lithospheric mantle assimilation of different crustal components played a minor role in the genesis of these basaltic rocks the la icp ms analysis on zircons from four rhyolites and two basalts yielded similar ages ranging from 295 8 2 8 to 293 3 1 7 ma suggesting an early permian event zircons from the basalts show a wide ehf t range from 0 49 to 13 whereas those from the rhyolites show two groups of ehf t values from 5 to 3 and from 6 to 12 suggesting a mixing of crust mantle material the magmatic zircons from the bimodal volcanic rocks yielded two peaks of tdm2 between 600 820 ma and 1160 1360 ma probably representing two significant episodes of continental crust growth the bimodal volcanic rocks are correlated with the early stage of post collision our results suggest that vertical crustal growth through mantle derived magmas in post collisional setting also played a major role in the construction of the caob

influence of palaeogeography on thrust system geometries an analogue modelling approach for the abruzzi molise italy case history abstract the abruzzi molise sector in the central apennines is a part of a fold and thrust belt that has been deforming since the late cretaceous as a result of collision tectonics between the european and adriatic plates the superposition of different deformational styles highly reworked the originally complex palaeogeography of this portion of the southern tethyan margin analogue modelling has been performed on thrusting mechanisms in the abruzzi molise area in order to 1 reduce the number of admissible hypotheses regarding palaeogeographic setting and 2 define thrusting mechanics both of these goals are crucial for hydrocarbon exploration purposes the sandbox apparatus used to simulate the undeformed passive margin consisted of a thin compartment juxtaposed against a thick one along a linear boundary having variable geometries and mechanical stratigraphy a rigid but mobile backstop was used to deform the stratigraphy in a coulomb thrust wedge results from six experiments show that the geometric relationships between different structural units depend on the distribution of palaeogeographic domains these domains are defined by mechanical and or geometrical parameters such as the orientation between the maximum compression direction and the palaeogeographic boundary the mechanical stratigraphy and the thickness of the successions reproduced in the models the present day tectonic styles and meso cenozoic palaeogeography of the abruzzi molise area are discussed in terms of the mechanisms and structures analysed through the models

intracontinental deformation in a frontier of super convergence a perspective on the tectonic milieu of the south china block abstract since mesozoic the south china region has been located at the center of a triangular area surrounded by westward subduction of the pacific plate northward subduction of the india plate beneath the eurasia plate and collision of the north and south china blocks along the central china orogen this region thus marks the frontier of a super convergent regime within the super convergence domain the compressional structures in the center of the south china block are mainly characterized by shortening thrusting and decollement the block underwent inhomogeneous rejuvenation of the pre existing crust and lithospheric structures through reactivation of late stage activities the surface deformation of the xuefeng intracontinental tectonic system within the south china block is possibly derived from intraplate tectonics particularly the distinct magmatism between the west and east limbs of the xuefeng precambrian uplift is a possible response of the rheological structure of the lithosphere the deep structures as revealed from tomographic studies show marked difference of lithosphere architecture between the eastern and western sub blocks of the south china block these data illustrate the long term mosaic of multi block convergence which led to present day inhomogeneity in the continental lithosphere in south china a comparison of the intensive contraction of the south china block with the distinct features of rifting of the north china block brings out the contrasting structural and tectonic signatures developed in the same frontier of one of the largest super convergent systems on the globe during the mesozoic to cenozoic

neoproterozoic middle paleozoic tectono magmatic evolution of the gorny altai terrane northwest of the central asian orogenic belt constraints from detrital zircon u pb and hf isotope studies abstract the gorny altai terrane ga is a key area in understanding the crustal evolution of the central asian orogenic belt caob this paper reports u pb and hf isotope data for detrital zircons from cambrian to early devonian sedimentary sequences to constrain their provenance as well as the tectono magmatic events and crustal growth in this region nearly all the detrital zircons are characterized by euhedral to subhedral morphology high th u ratios ca 0 1 1 6 and typical oscillatory zoning indicating a magmatic origin the three samples from the gorny altai group middle cambrian to early ordovician yield detrital zircon populations that are composed predominantly of 530 464 ma grains followed by a subordinate group of 641 549 ma old the silurian and devonian samples exhibit similar major zircon populations 555 456 ma and 525 463 ma respectively but a significant amount of additional 2431 772 ma zircons occur in the early devonian sample our results suggest that detritus from the nearby kuznetsk altai intra oceanic island arc served as a unitary source for the cambrian silurian sedimentary sequences but older detritus from other sources added to the early devonian sequence the low abundance of ca 640 540 ma detrital zircons may testify that this island arc was under a primitive stage in this period when mafic volcanic rocks probably dominated in contrast the dominant population of ca 530 470 ma zircons may indicate an increased amount of granitic rocks in the source area suggesting that the kuznetsk altai island arc possibly evolved into a mature one in the cambrian to early ordovician the ca 530 470 ma detrital zircons are almost exclusively featured by positive e hf t values and have two stage hf model ages of ca 1 40 0 45 ga indicating that the precursor magmas were sourced predominantly from heterogeneous juvenile materials we conclude that the late neoproterozoic to early paleozoic magmatism in the kuznetsk altai arc made a significant contribution to the crustal growth in the caob the absence of middle ordovician to early devonian detrital zircons possibly implies that the area changed to a passive margin in the middle ordovician of special significance are the 2431 772 ma zircons in the early devonian sample which are quite comparable to the precambrian detrital zircons from the altai mongolian terrane am but distinct from those from the siberian continent this indicates that the am is a plausible source for the 2431 772 ma zircons our data therefore imply that the ga possibly amalgamated with the am before the early devonian rather than in the late devonian to early carboniferous as previously suggested

strong intracontinental lithospheric deformation in south china implications from seismic observations and geodynamic modeling abstract classical plate tectonics theory predicts concentrated deformation at plate boundaries and weak deformation within plates yet the existence of intracontinental orogens shows that highly deformed regions can occur within continental plates which is geodynamically incompletely understood shear wave splitting measurements in south china show belt parallel i e ne sw fast directions beneath the wulingshan xuefengshan belts while no dominant fast direction is found in the cratonic sichuan basin tomographic studies in the mantle in the same area show that the thickness of lithosphere beneath the intracontinental orogen is larger than that beneath the cratonic sichuan basin in order to better understand these seismic observations we performed numerical experiments of intracontinental lithospheric deformation with the presence of cratonic basin by comparing systematic model results with topography data and constraints on the accumulated amount of shortening in the study region we find that the best fitting result is obtained for models with a strong upper and a wet lower crust and with a weak mantle lithosphere beneath the orogen belt which has an effective viscosity that is 2 orders of magnitude smaller than that of the craton our numerical model successfully explains the belt parallel anisotropy and high velocity anomaly beneath intracontinental orogen and suggests that significant intracontinental lithospheric deformation occurred in south china

vlf emissions associated with earthquakes and observed in the ionosphere and the magnetosphere abstract several electromagnetic phenomena recorded at the time of earthquakes were recorded independently by the geostationary satellite geos 2 above africa longitude 37 e and the polar orbiting satellite aureol 3 apogee 2012 km perigee 408 km inclination 82 5 period 109 5 min the observations were made with magnetic and electric antennae in the frequency range 10 hz 15 khz characteristics of the emissions and differences between low and high altitude observations are presented some geos 2 very low frequency data can be correlated with ionospheric measurements made on ground at the djibouti station latitude 11 n longitude 42 e where increases of the critical frequency f 0 e s of the sporadic e s layer are observed when earthquakes occur nearby time differences between disturbance at ionospheric level and at the height of geos 2 seem to indicate that earthquakes cause two distinct types of electromagnetic disturbance an electromagnetic wave in the ionosphere and a density increase of the e s layer

latitudinal distribution of anomalous ion density as a precursor of a large earthquake 1 data obtained by the u s satellite de 2 are used to investigate possible precursor features in the ionosphere associated with a large earthquake latitude 33 13 longitude 73 07 m 7 5 which occurred during a moderate geomagnetic disturbance atomic oxygen ion and molecular ion distributions show characteristic latitudinal features similar to the well known equatorial ionization anomaly eia feature but centered around the earthquake epicenter we name this the precursor ionization anomaly pia the density minima of both the atomic oxygen and molecular ions are in two latitude zones depending on the distance from the epicenter one of the pia minima aligns with the geomagnetic latitude crossing the epicenter another minimum is found along the geographic latitude of the epicenter these minima are located in an area spanning about 40 in latitude and about 140 in longitude it is noted that the molecular ion minimum is more clearly defined even when the atomic ion density minimum is not indicated clearly the ion density reduction seems to be caused by a superposition of natural quiet time ionospheric eastward electric field and an electric field associated with the earthquake although we studied one single event our careful examination of results suggests that the location and day of occurrence of the pia can be predicted for some large earthquakes even during moderate geomagnetic disturbance if the satellite orbit is properly chosen

oblique closure of the northeastern paleo tethys in central china a branch of the paleo tethys ocean once separated the north china plate from the south china plate however the mode of closure of the northeastern paleo tethys ocean during the late paleozoic to early mesozoic has been debated one reason for this debate is that the collisional suture zone was later buried by large scale thrust faults in the southern qinling dabieshan orogen which made it difficult to reconstruct the amalgamation of the supercontinent in central china new regional geologic mapping provides stratigraphic and structural constraints on the mechanism of this ocean closure our results indicate that dextral transpressional suturing in the southern qinling dabieshan foreland fold thrust belt resulted in the formation of the northern yangtze foreland basin where the stratigraphy precisely shows the time transgressive closure of the ocean and the orogenic sediments shed over 1000 km westward from eastern china to the closing paleo tethys therefore we propose an oblique subduction model to describe the closure of the paleo tethys ocean our findings suggest that prolonged slab pull during the oblique subduction of the oceanic plate continued to drive deep continental subduction thereby forming high and ultrahigh pressure metamorphic rocks and leading to sustained ocean closure

analogue modelling of different angle thrust wrench fault interference in a brittle medium analogue modelling experiments of thrust wrench fault interference in a brittle medium are presented and discussed simultaneous reactivation of confining strike slip and thrust faults bounding a corner zone of interference defined by the angle between the two fault systems is simulated instead of previously reported discrete time and space superposition of alternating thrust and strike slip events the influence of different considered interference angles of 60 90 and 120 is investigated through comparison between the obtained structural configurations in each case it is shown that under these conditions a characteristic morpho structural pattern with a deltoid shape resembling a tie knot consistently forms in the corner zone between the two fault systems the specific structural configuration of a such tie knot structure tks varies significantly as a function of the prescribed fault interference angle which determines the orientation of the displacement vector shear component ds along the main frontal thrust system and critically controls the geometry and kinematics of the tks comparison with three natural examples shows remarkable geometric and kinematic similarity confirming model predictions and suggesting the existence of common underlying dynamic processes governing the specific tks structural configuration of different thrust wrench fault interference corner zones in nature

crustal structures in the area of the 2008 sichuan earthquake from seismologic and gravimetric data abstract the 12 may 2008 the sichuan earthquake was one of the worst natural disasters in china here we present a detailed picture of the epicentral area inferred geophysical data based on the analysis of teleseismic data acquired by a dense seismic network we highlight an abrupt 20 km moho offset between the sichuan basin and the tibetan plateau and a horizontal discontinuity at 15 km depth which may connect with the ruptured zone of the 2008 event we obtain low mean crustal velocity ratios which suggest the absence of a thick and extensive zone of partial melt within the crust beneath the eastern part of the songpan garze terrane all our data support the idea that the longmen shan range mark a zone of active strain localization due to the rigid yangtze craton resisting eastward displacement of the tibetan plateau

ionospheric anomalies possibly associated with m 6 0 earthquakes in the japan area during 1998 2010 case studies and statistical study abstract in this paper we examine pre earthquake ionospheric anomalies in time series and perform a statistical test by using total electron content tec derived from global ionosphere maps gim around the japan area for the first time the normalized gim tec gim tec which is computed based on 15 days backward running mean of gim tec have been investigated for minimizing possible confounding effects of consecutive earthquakes and identify the abnormal signals meanwhile to reduce the effect of strong geomagnetic activities such as geomagnetic storms the criterion for removing the gim tec data have been adapted that is when dst index exceeds 60 nt temporal variations of gim tec for large and destructive earthquakes in japan have been studied which are the 2004 mid niigata prefecture earthquake m6 8 its aftershock m6 1 the 2007 offshore mid niigata earthquake m6 8 and the 2008 iwate miyagi nairiku earthquake m7 2 although there are some positive and negative tec anomalies before and after the four earthquakes there is a tendency that positive tec anomalies appear 1 5 days before all the above earthquakes even during the quiet geomagnetic condition superposed epoch analyses have been performed for the statistical analysis of tec anomalies associated with m 6 0 earthquakes during the 12 year period of may 1998 may 2010 the statistical result indicates the significance of the positive tec anomalies 1 5 days before earthquakes within 1000 km from the epicenter around japan

henry cadell s experimental researches in mountain building their lessons for interpreting thrust systems and fold thrust structures funding the fold thrust research group has been funded by interoil santos oilsearch and nagra the original compilation of cadell s researches was part of an outreach programme funded by bp acknowledgements rwhb is indebted to the late john mendum for arranging access to cadell s notebooks and his field maps that were lodged in the then offices of the british geological survey in murchison house edinburgh this formed part of a collaboration with bgs and the development of the assynt s geology website in the early 2000s many of the images from cadell s notebooks including his experimental results were part of this site regrettably it has not been maintained and is no longer accessible rectifying this loss of resource forms the motivation for this contribution we thank juergen adam and an anonymous referee for construct reviews together with james hammerstein for shepherding the manuscript through the editing process although of course the views expressed in this paper remain the responsibility of the authors alone