boron geochemistry from some typical tibetan hydrothermal systems origin and isotopic fractionation the tibetan plateau is characterized by intense hydrothermal activity and abnormal enrichment of trace elements in geothermal waters hydrochemistry and b isotope samples from geothermal waters in tibet were systematically measured to describe the fractionation mechanisms and provide constraints on potential b reservoirs b concentrations range from 0 35 to 171 90 mg l and isotopic values vary between 16 57 and 0 52 geothermal fields along the indus yarlung zangbo suture zone and n s rifts are observed with high b concentrations and temperatures the similar hydrochemical compositions of high b geothermal waters with magmatic fluid and consistent modeling of b isotopic compositions with present 11b values imply that the b in high b geothermal waters is mainly contributed by magmatic sources probably through magma degassing in contrast geothermal fields in other regions of the lhasa block have relatively low b concentrations and temperatures after considering the small fractionation factor and representative indicators of na ca cl hco3 na k and si the conformity between modeling results and the isotopic compositions of host rocks suggests that the b in low temperature geothermal fields is mainly sourced from host rocks according to simulated results the b in some shallow geothermal waters not only originated from mixing of cold groundwater with deep thermal waters but it was also contributed by equilibration with marine sedimentary rocks with an estimated proportion of 10 it was anticipated that this study would provide useful insight into the sources and fractionation of b as well as further understanding of the relationships between b rich salt lakes and geothermal activities in the tibetan plateau

the 1976 friuli ne italy thrust faulting earthquake a reappraisal 23 years later we revisit the 1976 friuli earthquake sequence by combining hypocenters relocation long period surface wave inversion field geology and strong motion modelling we show that fault related folding is the main active deformation by which the seismic energy was released during the main shock ms 6 5 and that some of the surface effects reported in 1976 correspond to widespread bedding planes displacements induced by flexural slip folding the fault evolved from blind to semi blind along strike showing the control of the inherited structural geology on the fault surface break and rupture arrest our fault model produces waveforms that fit the accelerograms recorded in the area

magmatism and metamorphism in the lhasa block tibet a geochronological study u pb systematics in small fractions of zircon monazite and sphene 5 to 20 grains each have been analyzed in order to decipher the age and origin of magmatism in the lhasa block and to date the tectono metamorphic events additionally we analyzed a few minerals for rb sr the results show that the granites and an ignimbrite were formed essentially through anatexis of continental crust the magma source regions of which consisted of palaeozoic to precambrian materials up to 2 b y in age the following episodes can be distinguished 1 an early tertiary plutonism volcanism in the southern lhasa block yangbajing region strongly related to intracontinental tectono metamorphism 2 a late jurassic to early cretaceous plutonism in the central and northern lhasa block and 3 a middle jurassic low grade metamorphism affecting the basement at the northern margin 171 6 m y ago the early tertiary magmatism and metamorphism in the south are probably a direct result of tethys subduction indian plate

helium and carbon isotopic signatures of thermal spring gases in southeast yunnan china abstract late palaeozoic and cenozoic magmatism including pingbian quaternary basaltic volcanoes occurs in southeast yunnan china where seismic tomography evidence indicates magma activity in the uppermost mantle however the characteristics of mantle fluid release remain poorly understood here we report the chemical compositions of hot spring gases in se yunnan and measure the 3he 4he ratios 4he 20ne ratios and 13c values co2 ch4 to determine their origins and the factors influencing their migration except for five samples contaminated by the atmosphere 4he 20ne ratios 0 39 2 39 the rc ra ratios rc is the air corrected 3he 4he ratio ra is the air ratio with 1 4 10 6 range from 0 042 ra to 0 470 ra indicating that the helium is mostly of crustal origin with minor addition of mantle derived helium the calculated maximum proportion of mantle helium was 5 of total helium indicating that mantle 3he leakage correlates with the ductile lower crust the hot spring gases are fractionated by the partial dissolution of co2 in groundwater and the initial 13cco2 values are modelled by rayleigh fractionation within a range of 26 5 to 6 14 the modelled co2 in samples estimated by the he c isotope coupling model originates from the mixing of limestone and organic sediment end members the isotopic signature of ch4 69 2 to 35 9 suggests a thermogenic source and microbial oxidation in some samples furthermore the apparent isotopic temperatures are estimated using fractionation factors for ch4 and co2 suggesting a lack of magmatism in the crust beneath the red river fault zone 188 318 c but partial melting under the bozhushan granitoid plutons 572 688 c the low emission of mantle derived helium is attributed to the low fault permeability and minor active crustal deformation in present day se yunnan which restrain the upward migration of mantle fluids

a seismic source zone model for the seismic hazard assessment of the italian territory abstract we designed a new seismic source model for italy to be used as an input for country wide probabilistic seismic hazard assessment psha in the frame of the compilation of a new national reference map we started off by reviewing existing models available for italy and for other european countries then discussed the main open issues in the current practice of seismogenic zoning the new model termed zs9 is largely based on data collected in the past 10 years including historical earthquakes and instrumental seismicity active faults and their seismogenic potential and seismotectonic evidence from recent earthquakes this information allowed us to propose new interpretations for poorly understood areas where the new data are in conflict with assumptions made in designing the previous and widely used model zs4 zs9 is made out of 36 zones where earthquakes with m w 5 are expected it also assumes that earthquakes with m w up to 5 may occur anywhere outside the seismogenic zones although the associated probability is rather low special care was taken to ensure that each zone sampled a large enough number of earthquakes so that we could compute reliable earthquake production rates although it was drawn following criteria that are standard practice in psha zs9 is also innovative in that every zone is characterised also by its mean seismogenic depth the depth of the crustal volume that will presumably release future earthquakes and predominant focal mechanism their most likely rupture mechanism these properties were determined using instrumental data and only in a limited number of cases we resorted to geologic constraints and expert judgment to cope with lack of data or conflicting indications these attributes allow zs9 to be used with more accurate regionalized depth dependent attenuation relations and are ultimately expected to increase significantly the reliability of seismic hazard estimates

helium isotopes tectonics and heat flow in the northern caucasus abstract 109 new measurements of 3he 4he r in subsurface fluids of the northern caucasus coupled with the data obtained previously allow regional regularities in the distribution of helium isotopic composition to be examined cis caucasian foredeeps show the lowest radiogenic r values the average rav value is slightly higher in gases of the scythian plate beyond the stavropol arch within the arch elevated r 1 6 4 5 10 7 indicates an input of mantle derived helium this input is even more evident to the south of starvropol arch in the caucasian mineral water area where the 8 ma old laccolithes occur and r values approach 5 11 10 7 the highest r values up to 0 7 0 9 10 5 are observed further to the south in the central segment of the greater caucasus where recent volcanism is manifested enhanced r values do not correlate with the crustal thickness but reflect degassing of magmatic reservoirs including those yet unknown according to the recent sr nd o data the young volcanic rocks are of mantle affinity but they are contaminated by a crustal component the average rav values in fluids and 87sr 86sr ratios in host magmatic rocks show an inverse correlation suggesting mixing of crustal and mantle materials r values vary inversely with apatite fission track ages of crystalline basement rocks the ages increase westward of the elbrus volcano most likely recording the thermal degradation of the greater caucasus since the pre cainozoic magmatic activity a direct correlation between rav values and background conductive heat flow densities implies that discharge of the mantle melts into the crust is the common cause of the geochemical geochronological and geothermal regularities observed elevated r values are generally observed in co2 bearing fluids low values are typical of ch4 gases a few n2 rich gases display highly variable r relationships between the major gas constituents and noble gas isotopes are discussed fractionation loss and gain of these species are considered as the processes controlling the compositions of underground fluids

active intraplate deformation within adria examples from the adriatic region abstract recent seismicity recorded in the adriatic region suggests that active deformation occurs within the adria plate earthquakes are common in the adjoining chains and in particular along the northern apennines in the southern alps and along the dinaric albanian hellenic thrust fronts in addition medium to low grade seismicity also affects the foreland and is clustered along two main transects through the centre of the adriatic region the two zones of active deformation correspond to the mid adriatic ridge and the gargano region and approximately trend nw se and e w respectively several interpretations have been proposed to explain the deformation observed within the adriatic foreland including a variety of contrasting kinematic and geodynamic models we attempted to unravel the complicated structural evolution of the central adriatic region by interpreting industrial and ministerial shallow and deep seismic profiles and the recent seismicity recorded in the adriatic the subsurface study allowed us to better understand the structural style timing and rates of deformation affecting the mid adriatic ridge and the gargano region and to unravel the relationships of active deformation with respect to the adjacent chains the results of our study indicate that the structural setting and type of seismicity of the central adriatic can be explained in terms of active intraplate deformation with the reactivation of inherited discontinuities

calculated temperatures in overthrust terrains and possible combinations of heat sources responsible for the tertiary granites in the greater himalaya there are three obvious sources of heat that affect the temperature in a region of thrust faulting heat supplied from below the lower thrust plate radiogenic heating within the crusts of both the upper and especially the lower plates and frictional heating along the fault we assume that heat is conducted primarily in the vertical direction and that solutions to the one dimensional time dependent heat conduction equation can be used to describe the temperature field in overthrust zones the effects of these three sources of heating can be isolated from one another treated separately and then combined in ratios proportional to various assumed rates of heating provided by each we then use calculations for a range of possible combinations of heat sources that may have caused two media granites of late tertiary age in the greater himalaya because of the uncertainties in the age of the granites in the depth at which they formed in the amounts of heat flux supplied to the base of the lithosphere and of radiogenic heat production in the crust inb the value of the coefficient of thermal conductivity and in other parameters a broad range of possible combinations of parameters is possible temperature can reach themore solidus for granite melts with various plausible combinations of parameters both that include no shear heating and that require frictional stresses of 100 s of mpa on the main central thrust for instance if the initial steady state geotherm in the crust now comprising the himalaya were that of a typical shield then frictional heating with a stress in excess of 100 mpa 1 kbar would be necessary to raise the temperature of material near a thrust fault at 20 or 30 km depth to 650 sup 0 c less

determining the present day kinematics of the idrija fault slovenia from airborne lidar topography abstract located in central europe at the junction of the southern alps and the dinarides the 100 km long idrija fault striking n310 and dipping 80 ne is often considered as the potential source of the historical 1511 earthquake estimated macroseismic magnitude mm 6 8 using 1 25 000 to 1 5000 topographical maps satellite images spot5 12 5 m illuminated dem and airborne lidar data derived 1 m dem we examined in detail the idrija fault trace along a 20 km long swath in the central portion of the fault combining topographic and remote sensing data allows characterizing the recent activity along the idrija fault and estimating its cumulative displacement along strike between tolmin and godovic the fault trace is mostly linear but appears divided into three disconnected segments of 11 20 km long morphological evidences such as offset streams and ridges and major drainage abandonments suggest ongoing movement at three sites field observations and lidar dem analysis allow measuring cumulative dextral offsets comprised between 35 and 65 m we found two larger offsets of 140 m and 360 m at the southeasternmost site the vertical component is significant and revealed by a rake ranging from 0 to 33 the derived n303 n310 striking slip vector is in agreement with the motion along this fault as suggested by the geodesy assuming that the smallest measured offsets have been recorded after the last glacial maximum lgm about 20 ka ago the minimum slip rate for the idrija fault is about 1 5 mm yr over this period of time

new empirical relationships among magnitude rupture length rupture width rupture area and surface displacement source parameters for historical earthquakes worldwide are compiled to develop a series of empirical relationships among moment magnitude m surface rupture length subsurface rupture length downdip rupture width rupture area and maximum and average displacement per event the resulting data base is a significant update of previous compilations and includes the additional source parameters of seismic moment moment magnitude subsurface rupture length downdip rupture width and average surface displacement each source parameter is classified as reliable or unreliable based on our evaluation of the accuracy of individual values only the reliable source parameters are used in the final analyses in comparing source parameters we note the following trends 1 generally the length of rupture at the surface is equal to 75 of the subsurface rupture length however the ratio of surface rupture length to subsurface rupture length increases with magnitude 2 the average surface displacement per event is about one half the maximum surface displacement per event and 3 the average subsurface displacement on the fault plane is less than the maximum surface displacement but more than the average surface displacement thus for most earthquakes in this data base slip on the fault plane at seismogenic depths is manifested by similar displacements at the surface log linear regressions between earthquake magnitude and surface rupture length subsurface rupture length and rupture area are especially well correlated showing standard deviations of 0 25 to 0 35 magnitude units most relationships are not statistically different at a 95 significance level as a function of the style of faulting thus we consider the regressions for all slip types to be appropriate for most applications regressions between magnitude and displacement magnitude and rupture width and between displacement and rupture length are less well correlated and have larger standard deviation than regressions between magnitude and length or area the large number of data points in most of these regressions and their statistical stability suggest that they are unlikely to change significantly in response to additional data separating the data according to extensional and compressional tectonic environments neither provides statistically different results nor improves the statistical significance of the regressions regressions for cases in which earthquake magnitude is either the independent or the dependent parameter can be used to estimate maximum earthquake magnitudes both for surface faults and for subsurface seismic sources such as blind faults and to estimate the expected surface displacement along a fault for a given size earthquake

river gradient anomalies reveal recent tectonic movements when assuming an exponential gradient decrease along a river course abstract high resolution digital models combined with gis or other terrain modelling software allow many new possibilities in geoscience in this paper we develop describe and test a novel method the gla method to detect active tectonic uplift or subsidence along river courses it is a modification of hack s sl index method in order to overcome the disadvantages of the latter the core assumption of the gla method is that over geological time river profiles quickly adjust to follow an exponential decrease in elevation along the river course any large deviation can be attributed to active tectonic movement or to disturbances in erosion sedimentation processes caused by an anthropogenic structure e g artificial dam during the testing phase the locations of identified deviations were compared to the locations of faults identified on a 1 100 000 geological map results show that higher magnitude deviations are found within a maximum radius of 200 m from the fault and the majority of detected deviations within a maximum radius of 600 m from faults or thrusts however these results are not the best that could be obtained because the geological map that was used and the only one available for the area is not of the appropriate scale and was therefore not precise enough comparison of deviation magnitudes against psinsar measurements of vertical displacements in the vicinity revealed that in spite of the very few suitable points available a good correlation between both independent methods was obtained r 2 0 68 for the e research area and r 2 0 69 for the w research area the gla method was applied to the three test sites where previous studies have shown active tectonic movements it shows that deviations occur at the intersections between active faults and river courses as well as also correctly detected active uplift attributed to the increased sedimentation rate above an artificial hydropower dam and an increased erosion rate below the method gives promising results and it is acknowledged that the gla method needs to be tested in other locations around the world

structure and evolution of the himalaya tibet orogenic belt the 1981 french chinese expedition to tibet focused on the lhasa block extending earlier coverage 400 km north of the tsangpo suture the lhasa block stood between 10 and 15 n latitude over most of the upper cretaceous and eocene and if gondwanian in origin had detached from gondwana by early permian seismic profiles reveal a complex moho topography resulting both from multiple continental thrusting and large scale strike slip faulting subduction related granitoids representing mixtures of mantle and crustal components and anatectic granitoids have been analysed and dated this study emphasizes the role of smaller blocks in the accretion of the continental mosaic

the dinaric fault system large scale structure rates of slip and plio pleistocene evolution of the transpressive northeastern boundary of the adria microplate located at the northeastern corner of the adria microplate the alps dinarides junction represents a key region for understanding how the adria microplate interacts with stable europe however little is known on how the present day deformation imposed by the rotation of the adria microplate is absorbed across the dinarides using morphotectonic analysis based on satellite and aerial images accurate topographical maps and digital elevation models combined with field investigations we mapped in detail the three main active faults of the northern dinarides geomorphic and geological cumulative displacements ranging from a few meters to several kilometers have been identified on those faults and dated for the most recent ones using 36 cl exposure dating those results yielded a total right lateral motion of 3 8 0 7 mm yr oriented n317 comparing our results with the motion expected from adria rotation models suggests that the northern dinarides absorbs most of the predicted adria eurasia motion thus representing the eastern boundary of the microplate however a significant e w component is lacking suggesting that part of the stress imposed by the microplate rotation is transferred farther to the east finally bounds placed on the plio pleistocene kinematics confirm that faulting onset occurred during the early pliocene and evidence a significant kinematic change at the early middle pleistocene boundary

partial melting zones in the crust in southern tibet from magnetotelluric results magnetotelluric studies in southern tibet along a north south traverse 200 km long crossing the yarlung zangbo suture zone near lhasa have enabled us to construct a two dimensional model in which layers of anomalously high conductivity exist at depths shallower than 33 km the electrical properties of these layers are different on the two sides of the suture zone we show here that the most plausible explanation of the high conductivity is the existence of partial melting zones in the upper part rather than the lower part of a crust 70 km thick this represents a powerful constraint for thermo mechanical models of continental collisions

enhanced carbon export to the abyssal depths driven by atmosphere dynamics long term biogeochemical observations are critical to understand the natural ability of the oceans to fix co2 into organic carbon and export it to the deep as sinking particles here we present results from a 3 year 2010 2013 sediment trap deployment that allowed detecting interannual variations of carbon fluxes beyond 4000 m depth in the eastern mediterranean sea anomalous atmospheric conditions triggering strong heat losses in winter spring 2012 resulted in convective mixing nutrient uplifting and a diatom dominated bloom southeast of crete phytoplankton growth reinforced by the arrival of nutrients from airborne etna volcano ash was the highest in the last decade satellite derived chl a concentrations up to 1 9 mg m 3 this situation caused carbon export to increase by 2 orders of magnitude 12 2 mg m 2 d 1 with respect to typical values which demonstrates how pulses of sinking fresh phytodetritus linked to rare atmospheric processes can episodically impact one of the most oligotrophic environments in the world ocean

helium and carbon isotope variations in liaodong peninsula ne china chemical and c he isotopic compositions have been measured for n2 rich hydrothermal gases from the liaodong abbreviation of east liaoning province peninsula from which the oldest crustal rocks in china with 3 8 ga outcrop with the exception of one sample containing tritogenic 3he and atmospheric 4he in liaoyang the observed 3he 4he ratios from 0 1 ra to 0 7 ra indicate 1 8 helium from mantle 92 98 from crust and 0 1 0 8 from atmosphere despite the lack of quaternary volcanism such 3he 4he ratios suggest together with geophysical evidences the existence of intrusive magmas that contain mantle helium and heat within the liaodong middle lower crust the 3he 4he ratios are high along the ne trending jinzhou faults and gradually decrease with the increase of distance from the faults such a spatial distribution suggests that the mantle helium exsolves from magmatic reservoir in the middle lower crust becomes focused into the root zones of jinzhou faults and subsequently traverses the crust via permeable fault zones when transversely migrated by groundwater circulation in near surface mantle helium with high 3he 4he ratio may have been further diluted to the observed values by addition of radiogenic helium produced in the crust this pattern shows strong evidence that the major faults played an important role on mantle derived components transport from mantle upwards

field evidence for active normal faulting in tibet crustal thickening does not now occur in southern tibet field observations made during the chinese french expedition of 1980 support an earlier hypothesis based on a combined analysis of satellite images and fault plane solutions of earthquakes immediately north of the highest peaks of the himalayas the tectonic regime is dominated by east west extension we have mapped a large number of north south normal faults which sharply cut the glacial and post glacial morphology and followed several recent earthquake breaks along faults detected on satellite and aerial photographs microtectonic measurements in the quaternary suggest that the maximum principal stress is vertical

shape analysis of isoseismals based on empirical and synthetic data we present an attempt to compare modeled ground motion acceleration fields with macroseismic observations two techniques for the representation of the observed intensities by isoseismals a smoothing technique and one which visualizes the local uncertainty of an isoseismal are tested with synthetic and observed data we show how noise in the data and irregularities in the distribution of observation sites affect the resolution of the isoseismal s shape in addition to standard elongated shapes we identify cross like patterns in the macroseismic observations for two italian earthquakes of strike slip type similar patterns are displayed by the theoretical peak acceleration fields calculated assuming the point source models given in the literature

interseismic coupling seismic potential and earthquake recurrence on the southern front of the eastern alps ne italy here we use continuous gps observations to document the geodetic strain accumulation across the south eastern alps ne italy we estimate the interseismic coupling on the intracontinental collision thrust fault and discuss the seismic potential and earthquake recurrence we invert the gps velocities using the back slip approach to simultaneously estimate the relative angular velocity and the degree of interseismic coupling on the thrust fault that separates the eastern alps and the venetian friulian plain comparison between the rigid rotation predicted motion and the shortening observed across the area indicates that the south eastern alpine thrust front absorbs about 70 of the total convergence between the adria and eurasia plates the coupling is computed on a north dipping fault following the continuous external seismogenic thrust front of the south eastern alps the modeled thrust fault is currently locked from the surface to a depth of 10 km the transition zone between locked and creeping portions of the fault roughly corresponds with the belt of microseismicity parallel and to the north of the mountain front the estimated moment deficit rate is 1 3 0 4 1017 nm yr the comparison between the estimated moment deficit and that released historically by the earthquakes suggests that to account for the moment deficit the following two factors or their combination should be considered 1 a significant part of the observed interseismic coupling is released aseismically and 2 infrequent large events with long return period 1000 years and with magnitudes larger than the value assigned to the largest historical events mw 6 7

helium and carbon isotopic compositions of hot spring gases in the tibetan plateau abstract the tibetan plateau is one of the most active geothermal areas in the himalayan geothermal belt however the heat source of the geothermal manifestation is unknown because of a lack of quaternary volcanoes in this area except in western yunnan and northern tibet in order to unravel the heat source and the origin of volatile components in hot spring gases in the southern tibetan plateau we have measured helium and carbon isotope ratios of hot spring gases from yangbajain district and some northern sites the observed helium compositions in the hot spring gases are explained by the mixing of an air component and underground components whose mean end member 3 he 4 he ratio is 0 12 ratm for yangbajain and 0 22 ratm for the northern sites respectively despite the lack of quaternary volcanism such 3 he 4 he ratios are an order of magnitude higher than that of stable continental crust 0 02 ratm these results may imply the existence of intrusive magmas that contain mantle helium in the thick tibetan crust the mantle helium with high 3 he 4 he ratio may have been diluted to the observed values by radiogenic helium produced in the crust the observed high co2 3 he ratios of the samples 1010 1012 relative to that of morb 2 109 indicate that most carbon dioxide in the samples is derived from crustal materials such as organic matter and marine carbonate minerals regional differences are observed not only in the mean end member 3 he 4 he ratios of the underground components but also in the 13c co2 values of the hot spring gases between yangbajain 9 1 to 6 3 and the northern sites 4 3 to 1 0 these features suggest heterogeneity among basement rocks the lower 3 he 4 he ratio in yangbajain may be due to a larger addition of radiogenic 4 he from basement rocks that are enriched with uranium and thorium the higher 13 c co2 value of the hot spring gases from the northern sites may be due to the addition of carbon dioxide from underlying sedimentary rocks containing more marine carbonate minerals

helium isotope compositions in sedimentary basins in china abstract the abundance and isotopic composition of he have been determined for a variety of natural gases oil field gases in sedimentary basins in the continent of china the 3 he 4 he and 4 he 20 ne ratios range from 0 004 to 4 99 ra where ra denotes atmospheric 3 he 4 he ratio 1 4 10 6 and from 100 39 000 respectively helium in the gas sample is composed of mantle derived he and crustal radiogenic he the high 3 he 4 he ratios were observed in the sedimentary basins which underwent cenozoic extension in the eastern domain such as the songliao liaohe north china subei sanshui and south china sea basins the basins where mantle derived he is recognized are characterized by the presence of surface and subsurface volcanic rocks high terrestrial heat flow deep faults and thinned crust on the other hand regions which underwent pre tertiary extension such as the jungar tarim tuba caidam and yumen basins in the nw and tectonic loading such as the ordos and sichuan basins in the central domain are marked by almost pure radiogenic 4 he of crustal origin and thus by an apparent absence of mantle derived he which coincides with complete lack of cenozoic volcanics low terrestrial heat flow and thickened crust such a 3 he 4 he distribution pattern clearly indicates that tectonic environment control the distribution of he isotopes in the continent of china

heat focussing granite genesis and inverted metamorphic gradients in continental collision zones abstract the thermal conductivity of sedimentary rocks is usually much lower than that of crystalline rocks gneisses and granites continental collision zones are characterized by large scale thrusts which superpose crystalline basement and sedimentary layers this leads to heat refraction effects of significant magnitude sedimentary layers act as a barrier to the transport of heat we show that the peculiar geometry of a gently sloping sedimentary layer thrust into more conductive rocks is very efficient in diverting the vertical flux of heat temperatures can vary by more than 50 along the horizontal and reach a marked maximum at the top of crystalline layers these results are in general agreement with the main features of orogenic belts as exemplified by the himalayas they explain why the young leucogranites of the main central thrust mct are confined to a narrow belt at the top of the basement slab they also account for the inverted metamorphic gradient observed there in a crustal accretionary wedge folding and thrusting modify the structure of the upper crust by thickening the sedimentary cover and by introducing sedimentary rocks at depth this leads to high temperatures at shallow depths in specific places les zones de collision continentale se caracterisent par de grands chevauchementsafaible pendage qui empilent les unes sur les autres des couches de socle cristallin et des couches sedimentaires cette structure particuliere engendre d importants effets de refraction thermique en effet leur conductibilitethermiqueetant normalement bien plus faible que celle des roches cristallines les formations sedimentaires font office de barrieres pour le transfert thermique le flux de chaleur se trouve fortement devie dans un plan horizontal la temperature peut varier de plus de 50 les maximaetant situesal interface superieur des dalles cristallines en ces endroits precis les isothermes profonds remontent tres significativement ces resultats rendent bien compte de plusieurs faits essentiels observes dans l himalaya zoneographie inverse du metamorphisme localisation des leucogranites le long d une bandeetroite situee au sommet de la dalle du tibet

quaternary extension in southern tibet field observations and tectonic implications we summarize evidence for quaternary and active faulting collected in the field during three sino french expeditions to southeastern tibet 1980 1982 detailed mapping of quaternary and active faults as well as microtectonic measurements indicate that normal faulting has been the dominant tectonic regime north of the himalayas in the last 2 0 5 m y the maximum horizontal principal stress in south tibet appears to be only the intermediate principal stress 2 1 being vertical south of the chord joining the eastern and western syntaxes of the himalayan arc extensional strains are principally localized within seven regularly spaced rift zones three of which have been studied in some detail the extension direction is determined to be n96 e 7 mainly from statistical averaging of strikes of newly formed normal faults throw rates on normal faults are evaluated for different time spans 2 0 5 m y 60 40 kyr and 10 2 kyr b p using structural and topographic reliefs as well as synglacial and postglacial vertical offsets the rate of quaternary extension is about 1 m y 1 along an 1100 km long ese traverse across south tibet this corresponds to a spreading rate of 1 0 6 cm yr this rate and the divergent horizontal projections of slip vectors of earthquakes along the himalayan front constrain the rate at which rigid india underthrusts southern tibet to be 2 1 cm yr although most of the normal faults appear to be independent of and nearly orthogonal to the e w mesozoic tertiary tectonic fabric the yadong gulu rift appears to be guided for over 130 km by the older oblique ne sw nyainqentanglha range and fault zones along it this reactivated zone is the most prominent left lateral strike slip fault system in se tibet excepting this zone and the vicinity of the se extremity of the karakorum fault quaternary strike slip faulting is rare in south tibet i e south of the chord between the syntaxes of the himalayan arc north of the chord the tectonic style is different there minor conjugate strike slip faulting is widespread and appears to control quaternary normal faulting which is more diffuse and subdued than in south tibet along the chord the presence of a major zone of active right lateral en echelon strike slip faults karakorum jiali fault zone probably reflects the greater facility of eastward extrusion in north central tibet in response to the northward push of india the eastern himalayan syntaxis may be an obstacle to such extrusion movements south of the chord

source geometry of historical events retrieved by synthetic isoseismals abstract the possibility of computing complete synthetic signals for laterally homogeneous structural models in an exact efficient and computationally rapid way allows an investigation of the effects of given source and structural models on the macroseismic field synthetic isoseismals are computed by first adding vectorially in the horizontal plane the sh wave and p sv wave displacement fields the maximum zero to peak value of displacement is then calculated at points distributed in space in such a way that it is easy to contour the isolines automatically this methodology developed mainly in the point source approximation and used to investigate the macroseismic field of some instrumentally recorded earthquakes can also be applied to historical events

origin of carbon in fumarolic gas from island arcs abstract we have measured 3 he 4 he ratios 13c values and co 2 3 he ratios of fumaroles and hot spring gases in three volcanic areas in japan the 3 he 4 he ratios 13c values and co 2 3 he ratios vary from 02 05 ratm 9 7 to 2 7 and from 7 74 109 to 1 18 1011 respectively based on these data and those in the literature we present the first quantitative estimates of the upper mantle sediment and limestone including slab components in co2 of volcanic and hydrothermal fluids from subduction zones taking compiled c isotopic data of limestone and organic sediment assuming that the co 2 3 he ratio and 13c value of mid ocean ridge basalt morb are representative of the upper mantle component and that later isotopic and elemental fractionations are minimal it is possible to deconvole each fraction of c on the basis of simple mixing equations up to 20 of the carbon in high temperature volcanic gases in subduction zones is derived from a morb type source while the major fraction of the gases is attributable to co2 produced by decarbonation of subducted marine limestone and slab carbonate

6600 years of earthquake record in the julian alps lake bohinj slovenia sequences of lake sediments often form long and continuous records that may be sensitive recorders of seismic shaking a multi proxy analysis of lake bohinj sediments associated with a wellconstrained chronology was conducted to reconstruct holocene seismic activity in the julian alps slovenia a seismic reflection survey and sedimentological analyses identified 29 homogenite type deposits related to mass wasting deposits the most recent homogenites can be linked to historical regional earthquakes i e 1348 ad 1511 ad and 1690 ad with strong epicentral intensity greater than damaging viii on the medvedev sponheuer karnik scale the correlation between the historic earthquake dataset and the homogenites identified in a core isolated from local stream inputs allows interpretation of all similar deposits as earthquake related this work extends the earthquake chronicle of the last 6600 years in this area with a total of 29 events recorded the early holocene sedimentary record is disturbed by a seismic event 6617 94 yr cal bp that reworked previously deposited sediment and led to a thick sediment deposit identified in the seismic survey the period between 3500 to 2000 yr cal bp is characterized by a major destabilization in the watershed by human activities that led to increases in erosion and sedimentation rates this change increased the lake s sensitivity to recording an earthquake earthquake sensitivity threshold index with the occurrence of 72 turbidite type deposits over this period the high turbidite frequency identified could be the consequence of this change in lake earthquake sensitivity and thus these turbidites could be triggered by earthquake shaking as other origins are discarded this study illustrates why it is not acceptable to propose a return period for seismic activity recorded in lake sediment if the sedimentation rate varies significantly

microtremor hvsr study for assessing site effects in the bovec basin nw slovenia related to 1998 mw5 6 and 2004 mw5 2 earthquakes abstract the bovec basin which is filled with glacial and fluvial sediments has recently been struck by two strong earthquakes 1998 and 2004 which caused extensive damage vii viii ems 98 strong site effects resulted in large variations in damage to buildings in the area which could not be explained by the surface variations in quaternary sediments the microtremor horizontal to vertical spectral ratio hvrs method was therefore applied to a 200 m dense grid of free field measurements to assess the fundamental frequency of the sediments large variations in the sediment frequency 3 22 hz were obtained with most of the observed values in the range 6 12 hz the observed frequencies cannot be related to the total thickness of quaternary sediments sand gravel but can be explained by the presence of conglomerate or lithified moraine at shallow depths the results were compared also with the velocity structure derived from seismic refraction data microtremor measurements performed in several two and some three and four storey houses masonry with rc floors which prevail in the bovec basin have shown that the main building frequencies in the area are in the range 7 11 hz this indicates that damage to houses in both earthquakes in some parts of the basin was enhanced by site amplification and soil structure resonance areas of possible soil structure resonance were identified in the settlements bovec brdo bovec mala vas cezsoca and kal koritnica considerable changes in fundamental frequencies within short distances were established in the town of bovec their values are as high as 22 hz in the central part of the town but diminish to 6 11 hz in the adjacent brdo and mala vas districts this is in agreement with the distribution of damage in both earthquakes which was considerably higher in brdo and mala vas although the houses in the central part of the town are older microtremor investigations have proved an effective tool for assessment of site effects in cases of complex geological structure commonly encountered in young alpine basins filled with glaciofluvial sediments which are partly cemented lithified layers can considerably change the fundamental frequency and consequently the site effects by taking additional measurements in buildings possible soil structure resonance can be identified

reassessment of the source of the 1976 friuli ne italy earthquake sequence from the joint inversion of high precision levelling and triangulation data summary in this study we revisit the mechanism of the 1976 friuli ne italy earthquake sequence main shocks mw 6 4 5 9 and 6 0 we present a new source model that simultaneously fits all the available geodetic measurements of the observed deformation we integrate triangulation measurements which have never been previously used in the source modelling of this sequence with high precision levelling that covers the epicentral area we adopt a mixed linear non linear optimization scheme in which we iteratively search for the best fitting solution by performing several linear slip inversions while varying fault location using a grid search method our preferred solution consists of a shallow north dipping fault plane with assumed azimuth of 282 and accommodating a reverse dextral slip of about 1 m the estimated geodetic moment is 6 6 1018 nm mw 6 5 in agreement with seismological estimates yet our preferred model shows that the geodetic solution is consistent with the activation of a single fault system during the entire sequence the surface expression of which could be associated with the buia blind thrust supporting the hypothesis that the main activity of the eastern alps occurs close to the relief margin as observed in other mountain belts the retrieved slip pattern consists of a main coseismic patch located 3 5 km depth in good agreement with the distribution of the main shocks additional slip is required in the shallower portions of the fault to reproduce the local uplift observed in the region characterized by quaternary active folding we tentatively interpret this patch as postseismic deformation afterslip occurring at the edge of the main coseismic patch finally our rupture plane spatially correlates with the area of the locked fault determined from interseismic measurements supporting the hypothesis that interseismic slip on the creeping dislocation causes strain to accumulate on the shallow above 10 km depth locked section assuming that all the long term accommodation between adria and eurasia is seismically released a time span of 500 700 years of strain accumulating plate motion would result in a 1976 like earthquake

aqueous and isotope geochemistry of mineral springs along the southern margin of the tibetan plateau implications for fluid sources and regional degassing of co2 springs issuing from different faults and shear zones along the crest of the himalayas tap three different levels of crust beneath the tibetan plateau from structurally highest to lowest these are the tingri graben the south tibetan detachment system stds and the ama drime massif adm the aqueous chemistry reflects water rock interactions along faults and is consistent with mapped rock types major ion chemistry and calculated temperatures indicate that spring waters have circulated to greater depths along the n s trending faults that bound the tingri graben and ama drime detachment add compared to the stds suggesting that these structures penetrate to greater depths springs have excess co2 n2 he and ch4 compared to meteoric water values implying addition from crustal sources the 3he 4he ratios range from 0 018 to 0 063 ra and are consistent with a crustal source for he the 13c values of dissolved inorganic carbon dic and co2 gas range from 5 5 to 3 8 and 13 1 to 0 3 versus peedee belemnite respectively sources of carbon are evaluated by calculating isotopic trajectories associated with near surface effervescence of co2 positive 13c values of the tingri graben and stds springs are consistent with decarbonation of marine carbonates as the source of co2 negative values for the add springs overlap with mantle values but are best explained by metamorphic devolatilization of reduced sedimentary carbon the 15n values of n2 range from 2 2 to 2 1 versus air and are explained by mixtures of air derived nitrogen metamorphic devolatilization of sedimentary nitrogen and nitrogen from near surface biogenic processes co2 flux is estimated by scaling from individual springs 105 mol a 1 per spring to extensional structures across the southern limit of the tibetan plateau and likely contributes between 108 and 1011 mol a 1 up to 10 to the global carbon budget

magmatic fluid input explaining the geochemical anomaly of very high arsenic in some southern tibetan geothermal waters abstract tibet is characterized by extremely high terrestrial heat flow and widely distributed hydrothermal systems among which many are discharging geothermal waters with extremely high arsenic concentrations from over 10 mg l to up to 126 mg l the distribution of these high arsenic waters is basically in accordance with the location of the indian continental subduction zone a detailed analysis indicates that host rock leaching alone cannot explain the observed arsenic anomaly instead substantial contribution of arsenic from the underlying magma chambers is postulated which are likely mantle derived intrusions that have been severely contaminated by the very thick crustal material below southern tibet possibly including deep seated arsenic rich sedimentary rocks alternatively the partial melts at crustal depths reflected by the detected low velocity and or high conductivity anomalies in southern tibet serving as the magmatic heat source of the high arsenic hydrothermal systems may also form indirectly under the high temperature conditions generated by mantle upwelling or due to crustal thickening low sulfide concentrations further promote high dissolved arsenic concentrations with little formation of thioarsenates and no precipitation of limiting arsenic sulfide phases in contrast mantle magmas less affected by crustal contamination serving as the heat source of many hydrothermal systems in rift zones and hot spots worldwide where the crust is thinner are releasing magmatic fluids lower in arsenic and higher in mantle sulfur species overall the existence of a magmatic heat source alone does not ensure the formation of geothermal waters with very high arsenic concentrations and geothermal waters from sedimentary rock hosted systems are neither necessarily arsenic rich the most critical factor controlling the arsenic concentration of geothermal water discharging from a magmatic hydrothermal system is the geological genesis of the magma fluid and its chemical composition

gps monitoring and earthquake prediction a success story towards a useful integration abstract we describe a success story at the junction between south eastern alps and external dinarides that has led to an early deployment of gps stations prior to the predicted july 12th 2004 moderate size slovenia krn mountain earthquake the success story consisted in a straightforward integration between a long lasting lithosphere scale rock mechanics experiment along with gps monitoring leading to a physical model of stress evolution and tested earthquake prediction experiment using m8s cn and rtp algorithms to point out the area of the impending earthquake within the alarmed area by the prediction algorithms the lithosphere scale rock mechanics experiment revealed that the location of the 2004 event falls within an area of stress shadow due to the recent 1998 bovec earthquake but is also very close to an area of increased stress due to the long lasting effect of the 1511 event the pre and post 2004 earthquake gps data provided the following results 1 the krn mountain earthquake magnitude has to be increased from mw 5 2 to 5 5 therefore doubling the fault slip in order to provide a better fit to the near field displacements accordingly the rtp 2004 alarm in northern dinarides can be considered a successful prediction now that the magnitude is inside the prediction range 2 the existence of an important amount of aseismic deformation related to such a moderate size earthquake and the feasibility of monitoring these transients 3 the evidence of a resolved acceleration of the strain rates one year prior to the earthquake 4 the robustness of the bayesian approach in detecting discontinuities in the times series their magnitude and statistical significance the discontinuities or jumps in the time series can correspond to coseismic deformation or time dependent deformation such as creeping slow motion strain acceleration and transients in general 5 when integrated with tested earthquake prediction algorithms the capability to forecast earthquakes can be extended to the scale of the active fault systems

geothermal fields of china abstract there are over 2500 known occurrences of geothermal phenomena in china these lie mainly in four major geothermal zones xizang tibet yunnan taiwan east coast and north south hot water has also been found in boreholes in major mesozoic cenozoic sedimentary basins this paper presents a summary of present knowledge of these geothermal zones the geological settings of geothermal occurrences are associated mainly with magmatic activity fault uplift and depressional basins and these are described by examples of each type increased multipurpose utilisation of geothermal resources is planned and examples are given of current usages

seismic zoning of slovenia based on deterministic hazard computations seismic hazard of the territory of slovenia is estimated using a deterministic approach based on the computation of complete synthetic seismograms the input data are the catalogues of earthquakes and fault plane solutions for slovenia and surrounding regions structural models are defined based on available seismological and geophysical information but are mainly constrained by surface wave dispersion and 3 d tomographic modelling of the upper crust seismogenic zones are delineated considering geotectonic characteristics fault plane solutions and distribution of earthquake hypocentres outside slovenia seismogenic zones are extended up to distances from which they can considerably influence seismic hazard estimates synthetic seismograms are computed using the receiver structure along the entire path by normal mode summation up to 1 hz for receiver sites on a 0 2 0 2 degrees grid and scaled to the magnitude of the earthquake allowing for spectral falloff at each site the maximum value of horizontal velocity horizontal displacement and design ground acceleration are considered as hazard parameter the highest values are obtained for western slovenia where the hazard is controlled by the strongest earthquake in the catalogue the idrija event of march 26 1511

constraints on the location and mechanism of the 1511 western slovenia earthquake from active tectonics and modeling of macroseismic data abstract the 1511 western slovenia earthquake m 6 9 is the largest event occurred so far in the region of the alps dinarides junction though it strongly influences the regional seismic hazard assessment the epicenter and mechanism are still under debate the complexity of the active tectonics of the alps dinarides junction is reflected by the presence of both compressional and transpressional deformations this complexity is witnessed by the recent occurrence of three main earthquake sequences the 1976 friuli thrust faulting events the 1998 bovec krn mountain and the 2004 kobarid strike slip events the epicenters of the 1998 and 2004 strike slip earthquakes ms 5 7 and ms 4 9 respectively lie only 50 km far from the 1976 thrust earthquake ms 6 5 we use the available macroseismic data and recent active tectonics studies to assess a possible epicenter and mechanism for the 1511 earthquake and causative fault according with previous works reported in the literature we analyze both a two and a single event case defining several input fault models we compute synthetic seismograms up to 1 hz in an extended source approximation testing different rupture propagations and applying a uniform seismic moment distribution on the fault segments we extract the maximum horizontal velocities from the synthetics and we convert them into intensities by means of an empirical relation a rounded to integer misfit between observed and computed intensities is performed considering both a minimized and a maximized databases built to avoid the use of half degree macroseismic intensity data points our results are consistent with a 6 9 magnitude single event rupturing 50 km of the idrija right lateral strike slip fault with bilateral rupture propagation

subduction related hot spring type gold mineralization in the central tengchong block southwestern china abstract numerous present day hot springs and associated ancient lianghe gold deposit occur in the central tengchong block sw china associated with oceanic crust subduction from the center outwards the alteration zones in the hot spring of the rehai consist of alunite and silica in a breccia zone a kaolinite and illite zone and a chlorite illite kaolinite zone the gas phase in the hot spring is dominated by co 2 with 13 c ranging from 4 5 to 7 2 these features indicate a major magmatic origin of the hot spring gas the 3 he 4 he ratios in the gas from central tengchong vary from 1 56 to 5 88 approaching to those of the morb this is probably related to the ongoing subduction of the indian plate beneath the tengchong block the hot spring waters in the central tengchong block have much higher content of au and other elements e g ag as sb and tl than other typical hot springs such as hasbrouck sulfer etc in the world the hot springs with more mantle gas contribution and higher water temperature show more elevated au contents which implies that the metal in the hot spring was most likely contributed from the magmatic gas the compiled d o isotopes of the hot spring waters from previous studies suggest that they are primarily derived from meteoric water a genetic model for the hot spring system in the central of tengchong has been tentatively established the gold charged hot spring is genetically connected to an active magma chamber which was produced by subduction of oceanic crust the chamber is driving long term surface meteoric circulation and constantly releasing magmatic volatiles enriched with metals as hot spring water mixed with magmatic volatiles causing decompression boiling and forming hydraulic fractures to penetrate the roof of siliceous sinter which induced the continuing metal deposition and formed the lianghe hot spring

geochemical features of the geothermal fluids from the mapamyum non volcanic geothermal system western tibet china abstract mapamyum geothermal field mgf in western tibet is one of largest geothermal areas characterized by the occurrence of hydrothermal explosions on the tibetan plateau the geochemical properties of hydrothermal water in the mgf system were investigated to trace the origin of the solutes and to determine the equilibrium temperatures of the feeding reservoir the study results show that the geochemistry of hydrothermal waters in the mgf system is mainly of the na hco 3 type the chemical components of hydrothermal waters are mainly derived from the minerals in the host rocks e g k feldspar albite ca montmorillonite and mg montmorillonite the hydrothermal waters are slightly supersaturated or undersaturated with respect to aragonite calcite dolomite chalcedony and quartz saturation indices close to 0 but are highly undersaturated with respect to gypsum and anhydrite saturation indices d and 18 o data confirm that the meteoric water acts as the water source of the geothermal waters an 220 c equilibrated reservoir temperature of hydrothermal spring waters was calculated via both the na k mg ternary diagrams and the cationic chemical geothermometers the log p co 2 of hydrothermal waters in the mgf system ranges from 2 59 to 0 57 and 13 c of the total dissolved inorganic carbon ranges from 5 53 to 0 94 suggesting that the carrier co 2 in hydrothermal water are mainly of a magmatic or metamorphic co 2 origin

the database of individual seismogenic sources diss version 3 summarizing 20 years of research on italy s earthquake geology abstract this paper describes the main characteristics the evolution and the structure of the database of individual seismogenic sources diss and particularly of its release of early 2007 the database contains the results of the investigations of the active tectonics in italy during the past 20 years the first two sections of this paper document the recent evolution in mapping and archiving italian active fault data in relation to important achievements in the understanding of italian tectonics some of which were spurred by significant earthquakes the central sections describe the current structure of the database the reasons for its assumptions and data categories its current contents its evolution through several years of improvements the last section describes how the current contents of the database correspond with the existing strain and stress data available from focal mechanism borehole breakout and gps data for the whole of italy the database supplies a fresh and unified view of active and seismogenic processes in italy by building on basic physical constraints concerning rates of crustal deformation on the continuity of deformation belts and on the spatial relationships between adjacent faults both at the surface and at depth

hydrogeochemistry of high temperature geothermal systems in china a review as an important part of the mediterranean himalayas geothermal belt southern tibet and western yunnan are the regions of china where high temperature hydrothermal systems are intensively distributed of which rehai yangbajing and yangyi have been investigated systematically during the past several decades although much work has been undertaken at rehai yangbajing and yangyi to study the regional geology hydrogeology geothermal geology and geophysics the emphasis of this review is on hydrogeochemical studies carried out in these geothermal fields understanding the geochemistry of geothermal fluids and their environmental impact is critical for sustainable exploitation of high temperature hydrothermal resources in china for comparison the hydrogeochemistry of several similar high temperature hydrothermal systems in other parts of the world are also included in this review it has been confirmed by studies on cl and stable isotope geochemistry that magma degassing makes an important contribution to the geothermal fluids from rehai yangbajing and yangyi though meteoric water is still the major source of recharge for these hydrothermal systems however the mechanisms of magma heat sources appear to be quite different in the three systems as recorded by the 3he 4he ratios of escaping geothermal gases a mantle derived magma intrusion to shallow crust is present below rehai although the intruding magma has been heavily hybridized by crustal material by contrast the heat sources below yangbajing and yangyi are inferred to be remelted continental crust besides original sources the geochemistry of characteristic constituents in the geothermal fluids have also been affected by temperature dependent fluid rock interactions boiling and redox condition changes occurring in the upper part of hydrothermal systems and mixing with cold near surface waters the geothermal fluids from rehai yangbajing and yangyi contain very high concentrations of some toxic elements since local drinking water sources may be mixed with geothermal water and irrigation with water containing geothermally derived harmful elements possibly leading to accumulation in crops consumed by human beings the natural geothermal spring discharge or anthropogenic geothermal wastewater drainage of these fields poses a threat to the environment and human health future research work should focus on estimation of stable o and h isotope compositions of magmatic water related to high temperature hydrothermal systems in china which is of significance for the quantitative source study of geothermal fluid recharged by degassed magmatic waters attention should also be paid to some constituent species in geothermal fluid of strong environmental significance such as thioarsenate that is crucial for the fate of as discharged from geothermal springs especially sulfidic hot springs

seismogenic sources in the adriatic domain abstract we present an overview of the seismogenic source model of the adriatic domain included in the latest version of the diss database http diss rm ingv it diss and in the european share database http diss rm ingv it share the model consists of composite and individual seismogenic sources located inside and along the margins of the adria plate in order to locate and parameterize the sources we integrated a wide set of geological geophysical seismological and geodynamic data either available from published literature or resulting from our own field work seismic profile interpretations and numerical modelling studies we grouped the sources into five regions based on geometrical and kinematic homogeneity criteria seismogenic sources of the central western adriatic north eastern adriatic eastern adriatic and central adriatic regions belong to the northern apennines external dinarides and offshore domains respectively they are characterized by nw se strike reverse to oblique kinematics and shallow crustal seismogenic depth seismogenic sources of the southern western adriatic region instead are e w striking dextral strike slip faults cutting both the upper and lower crust the fastest moving seismogenic sources are the most southern thrusts of the eastern adriatic and the strike slip sources of the southern western adriatic while the seismogenic sources of the central adriatic exhibit the lowest slip rates estimates of maximum magnitude are generally in good agreement with the historical and instrumental earthquake records except for the north eastern adriatic region where seismogenic sources exhibit a potential for large earthquakes even though no strong events have been reported or registered all sources included in the database are fully geometrically and kinematically parameterized and can be incorportaed in seismic hazard calculations and earthquake or tsunami scenario simulations

travertine deposits from along the south tibetan fault system near nyalam tibet a newly investigated travertine deposit in southern tibet provides a window into holocene hydrological geomorphic and climatic processes near the boundary of the tibetan plateau and high himalaya travertine deposited as a result of the degassing of co 2 rich groundwater as it emerges on the earth s surface is in many cases formed along the trace of major crustal scale faults in primarily extensional tectonic regimes a travertine platform measuring roughly 1 km by 0 5 km exists near the town of nyalam in southern tibet along a major himalayan down to the n normal fault the south tibetan fault system a wide variety of travertine depositional textures and features are recorded in the platform on a series of terraces active travertine deposition was observed from spring mounds and seeps along the base of the platform at the modern river level palaeotemperatures of spring water calculated from 18 o of the travertine range from 9 to 25 c which closely matches the temperatures recorded from modern springs in the area a complex geomorphological landscape records interaction between growing alluvial fans travertine accumulation and a rapidly down cutting river with associated fluvial terraces river incision was contemporaneous with travertine deposition as indicated by cemented fluvial river gravel layers interbedded with travertine high 87 sr 86 sr ratios in the travertine mean of 0 7168 indicate subsurface fluid interaction with radiogenic crystalline rocks of the underlying greater himalaya uranium series ages of the travertine platform range from 5400 a 950 a to 11 600 a 1000 a and indicate a younging progression from higher terraces near the valley wall to lower terraces at present day river level travertine that overlies a river gravel terrace 18 m above river level formed at 11 600 a this date yields a local incision rate of 1 6 mm a 1 consistent with estimated fluvial incision rates in the high himalaya the range of our u series ages coincides with an interval of higher precipitation associated with greater intensity of the indian monsoon which led to elevated spring discharge and carbonate precipitation in this part of the high himalayas

fault plane structure of the antofagasta chile earthquake of 1995 from a large dataset of aftershocks in the rupture area of the mw 8 0 1995 antofagasta earthquake we derived the spatial distribution of hypocenters and a b value map along the fault plane we further examined various focal mechanisms of the aftershock sequence the b value distribution on the fault plane clearly indicates the heterogeneity of the rupture area we found a positive correlation between the b value variations and the main shock source time function determined by delouis 1996 where zones of high b value are related to high slip with these results we propose to have found evidence for the segmentation of the fault plane and suggest that the mapped inhomogeneities could have played the role of asperities prior to the main shock rupture

delineation of the geometry of nodes in the alps dinarides hinge zone and recognition of seismogenic nodes m 6 we introduce a new method based on the analysis of the topographical alignments and used to delineate the structural boundaries of the nodes which permits the definition of relatively narrow earthquake prone areas by the pattern recognition approach the structurally bounded nodes capable of earthquakes with m 6 0 identified with pattern recognition in fact cover a significantly smaller area of the study region as compared with that defined by gorshkov et al 2004 who used conventional circles the proposed method thus improves the precision in the location of potential large earthquakes

neo alpine structural evolution and present day tectonic activity of the eastern southern alps the case of the ravne fault nw slovenia abstract the ravne fault is an actively propagating nw se trending dextral strike slip fault in the julian alps of nw slovenia which has been responsible for two moderate sized earthquakes in the last decade strike slip displacements on moderate steep fault planes are responsible for the recent seismic activity that is confined to shallow crustal levels the fault is growing by interaction of individual right stepping fault segments and breaching of local transtensional step over zones the fault geometry is controlled by the original geometry of the nw se trending thrust zone modified by successive faulting within the fault zone in the modern n directed maximum horizontal stress regime the segmented fault is lengthening by active growth at the fault s nw end the spatial distribution of earthquake clusters shows that activity on strike slip segments and thrust faults is contemporaneous detailed analysis of the spatial pattern of earthquake events and surface fault geometries suggests that for earthquakes of similar magnitudes and similar fault kinematics the deciding factor for whether an earthquake rupture will breach a step over zone is the relationship between the lengths of individual neighbouring fault segments and fault separation distances in the step over zones the ravne fault represents an example of a tectonic structure that lies in an area subjected to multiple tectonic events under different regional stress conditions at epicentral depths the fault system is accommodating recent strain along newly formed fault planes whereas in upper parts of the crust the activity is distributed over a wider deformation zone that includes reactivated brittle thrust faults

environmental impacts of geothermal waters with extremely high boron concentrations insight from a case study in tibet china abstract boron is a potentially toxic element in the environment and commonly enriched in high temperature geothermal waters in this study seven typical boron rich geothermal areas in tibet china were selected as the study areas for comprehensively investigating the geochemistry of geothermal boron and its environmental impact the geothermal waters were classified into four types acid low boron waters acid high boron waters neutral alkaline low boron waters and neutral alkaline high boron waters the enrichment of boron in the neutral alkaline high boron geothermal waters is attributed to the input of magmatic fluids whereas the host rock leaching is the primary boron source for the neutral alkaline low boron geothermal waters the acid low boron waters are essentially locally perched groundwaters heated by geothermal vapors separated from flashed deep geothermal fluids and thereby their boron comes mainly from the limited leaching of the host rocks of the shallow aquifers as for the acid high boron waters they could be formed via a mixing between acid low boron waters and neutral alkaline geothermal waters with the latter as the primary boron source the boron species in these geothermal waters comprise mainly h3bo3 b oh 4 polyborate ions and fluoroborate complexes all of which are affected by the ph temperature and f and b concentrations of the waters when the geothermal waters flow out of the hot spring vents the rapid changes in unstable parameters like ph and water temperature will lead to the conversion of b oh 4 and polyborate ions to h3bo3 the discharge of the boron rich geothermal waters has contaminated the surface waters and sediments in and around the investigated geothermal areas in turn the boron sorbed onto into the hot spring sediments is liable to be released either in short term if it is originally exchangeable boron or in long term if carbonates fe mn oxides or organic matters sulfides combined boron this study enhances the understanding of geothermal boron speciation and its environmental impact and provides insights for rational exploitation of hydrothermal resource without inducing geothermal boron pollution

impact of additional dead carbon on the circulation estimation of thermal springs exposed from deep seated faults in the dongguan basin southern china abstract in hydrothermal systems the dissolved carbon of thermal groundwater may contain components derived from mineral alterations under high temperatures metamorphic source and or from magmatic gases additionally from carbonate dissolution most common these components are known as additional dead carbon which dilutes the modern carbon used for dating leading to the overestimation of 14c ages four typical geothermal springs hosted by deep seated faults and eighteen non thermal springs and wells from the dongguan basin of southern china were investigated to assess the circulation times of the hydrothermal system based on their radiocarbon contents for the thermal springs the circulation depth approximately 3648 m the apparent 14c ages 20 15 to 12 97 ka and the 13c calibrated 14c ages 16 02 to 8 55 ka were estimated the circulation speed of the thermal groundwater was as low as 0 46 m a which was too slow for a fracture hydrothermal system hosted by deep faults the analysis of the helium and carbon isotopes in the thermal groundwater revealed the existence of mantle derived carbon and thermally altered carbon from limestones a 13c 3he 4he illustration was proposed to correct for the additional dead carbon content according to the reassessed 14c ages the groundwater circulation time was overestimated and the circulation speed of the thermal groundwater was underestimated in hydrothermal system the reassessed 14c ages can provide a more reasonable result than the initial slow estimate in the context of a fracture hydrothermal system hosted by deep faults we conclude that measured 14c contents should be reassessed during the use of radiocarbon dating for thermal groundwater if additional dead carbon exists in the water

ge si ratios indicating hydrothermal and sulfide weathering input to rivers of the eastern tibetan plateau and mt baekdu abstract concentrations of dissolved silicon in river waters reflect a complex interplay among chemical weathering of primary silicate minerals formation and weathering of secondary clay minerals hydrothermal input and biological cycling formation and dissolution of opal phytoliths and growth of diatoms we applied the ge si ratio to assess the different sources of dissolved si in rivers hailing from the eastern tibetan plateau the salween mekong chang jiang yangtze hong red and huang he yellow and from mt baekdu the duman elevated riverine ge si ratios were observed in arid regions with high geothermal activity in the salween chang jiang and mt baekdu streams in the huang he and hong river basins geothermal influence was not as pronounced but weathering of sulfide and coal bearing minerals may be responsible for the high ge si ratios in rivers where inputs from hydrothermal and sulfide weathering are minimal our data mostly fall in the weathering limited regime of high riverine si concentrations and low ge si ratios

the 1998 bovec krn mountain slovenia earthquake sequence we study the 1998 bovec krn mountain slovenia earthquake sequence by combining hypocenters relocation strong motion inversion digital elevation modelling and field geology the main shock ms 5 7 a 12 km right lateral strike slip event on the dinaric fault system occurred on a sub vertical fault plane the rupture confined between 3 and 9 km depth with no evidence of surface faulting propagated bilaterally within two structural barriers the northwestern barrier is at the junction between dinaric and alpine structures where there is a sharp change in the geometry of faulting the southeastern barrier is within the dinaric system and its surface expression corresponds to the tolminka spring perched basin a 1 km restraining step over at this site the bovec krn earthquake fault overlaps with a 30 km strike slip fault segment that is free of aftershocks and could be undergoing an increase of stress this fault system represents the northern branch of the idrija right lateral fault

application of airborne lidar to mapping seismogenic faults in forested mountainous terrain southeastern alps slovenia results are presented of the first airborne lidar survey ever flown in europe for the purpose of mapping the surface expression of earthquake prone faults detailed topographic images derived from lidar data of the idrija and ravne strike slip faults in nw slovenia reveal geomorphological and structural features that shed light on the overall architecture and kinematic history of both fault systems the 1998 mw 5 6 and 2004 mw 5 2 ravne fault earthquakes and the historically devastating 1511 m 6 8 idrija earthquake indicate that both systems pose a serious seismic hazard in the region because both fault systems occur within forested terrain a tree removal algorithm was applied to the data the resulting images reveal surface scarps and tectonic landforms in unprecedented detail importantly two sites were discovered to be potentially suitable for fault trenching and palaeo seismological analysis this study highlights the potential contribution of lidar surveying in both low relief valley terrain and high relief mountainous terrain to a regional seismic hazard assessment programme geoscientists working in other tectonically active regions of the world where earthquake prone faults are obscured by forest cover would also benefit from lidar maps that have been processed to remove the canopy return and reveal the forest floor topography

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

the seismotectonic characteristics of slovenia slovenia with its neighbouring areas lies at the junction of the alps the dinarides and the pannonian basin these belong to the three plates europe adria and tisza on the slovenian territory itself converge the external dinarides nw se oriented right lateral strike slip faults the transdanubian range ne sw oriented left lateral strike slip faults and the southern alps e w oriented thrusts the direction of the principal stress 1 azimuth 6 dip 8 is determined under the assumption of uniform stress throughout the region dip of the least principal stress 3 of 5 is consistent with the regional strike slip regime listed structures form a pure shear structural mechanism on a regional scale

on the inverse problem for earthquake rupture the haskell type source model in order to gain insight into how to invert seismograms correctly to estimate the details of the earthquake rupturing process we perform numerical experiments using artificial data generated for an idealized faulting model with a very simple rupture and moment release history and solve the inverse problem using standard widely used inversion methods we construct synthetic accelerograms in the vicinity of an earthquake for a discrete analog of the haskell type rupture model with a prescribed rupture velocity in a layered medium a constant level of moment is released as the rupture front passes by we show that using physically based constraints such as not permitting back slip on the fault allows us to reproduce many aspects of the solution correctly whereas the minimum norm solution or the solution with the smallest first differences of moment rates in space and time do not reproduce many aspects for the cases studied here with the positivity of moment rate constraint as long as the rupturing area is allowed to be larger than that in the forward problem it is correctly found for the simple faulting model considered in this paper provided that the rupture velocity and the earth structure are known if however the rupture front is constrained either to propagate more slowly or the rupturing area is taken smaller than that in the forward problem we find that we are unable even to fit the accelerograms well use of incorrect crustal structure in the source region also leads to poor fitting of the data in this case the proper rupture front is not obtained but instead a ghost front is found behind the correct rupture front and demonstrates how the incorrect crustal structure is transformed into an artifact in the solution the positions of the centroids of the moment release in time and space are generally correctly obtained

mantle fluids in the karakoram fault helium isotope evidence abstract the karakoram fault kkf is the 1000 km long strike slip fault separating the western himalaya from the tibetan plateau from geologic and geodetic data the kkf is argued either to be a lithospheric scale fault with hundreds of km of offset at several cm a or to be almost inactive with cumulative offset of only a few tens of kilometers and to be just the upper crustal localization of distributed deformation at depth here we show 3he 4he ratios in geothermal springs along a 500 km segment of the kkf are 3 100 times the normal ratio in continental crust providing unequivocal evidence that a component of these hydrologic systems is derived from tectonically active mantle mantle enrichment is absent along the indus yarlung suture zone isz just 35 km southwest of the kkf suggesting that the mantle fluids flow only within the kkf within the last few ma the kkf must have accessed tectonically active tibetan mantle northeast of the mantle suture which we therefore locate vertically beneath the kkf very close to the surface trace of the isz hence in southwestern tibet indian crust may not now be underthrusting substantially north of the isz even though miocene underthrusting may have placed indian crust north of the isz in the lower half of the tibetan plateau crust this is in significant contrast to central and eastern tibet where underthrust indian material not only forms the lower half of the tibetan crust but is also currently underthrusting for 200 km north of the isz our new constraint on kkf penetration to the mantle allows an improved description of the continuously evolving karakoram fault as a tectonically significant yet perhaps geologically ephemeral lithospheric structure

southern limit of mantle derived geothermal helium emissions in tibet implications for lithospheric structure the isotopic composition of helium emitted from geothermal springs in the southern tibetan plateau reported as rc ra rc air corrected sample 3 he 4 he ra air 3 he 4 he ranges from 0 013 to 0 38 and defines two principal domains in southernmost central tibet helium isotope ratios are typical of radiogenic helium production in the crust rc ra 6 0 05 crustal helium domain further north there is a resolvable 3 he anomaly consistent with a mantle contribution r ra s 0 1 mantle helium domain the highest values of 0 27 0 38 ra occur at the southern end of the karakoram fault the boundary between the two domains lies 50 100 km north of the indus zangpo suture zone there seems to be no association between the 3 he anomaly and zones of active normal faulting and litho tectonic crustal units such as the ultramafic rocks of the indus zangpo suture zone and the gangdese intrusive belt although scavenging of mantle derived helium stored in large ultrabasic and basic intrusions in the crust cannot be ruled out entirely we argue that the 3 he anomaly most plausibly reflects degassing of volatiles from young quaternary mantlederived melts intruded into the crust as such it defines the southern limit of recent mantle melting and mantle melt extraction beneath the tibetan plateau the southern limit of the 3 he anomaly coincides with the junction between the indian and asian plates in the region where the indian lithospheric slab steepens and is subducted beneath tibet as suggested by seismic studies recent mantle melting and melt extraction is confined to the asian mantle but the southern limit of the melt zone may have migrated northwards during the last 10 ma as the indian lithosphere has progressively underthrust the himalayas and tibet fl 2000 elsevier science b v all rights reserved