contemporary crustal deformation in east asia constrained by global positioning system measurements global positioning system gps measurements collected since the early 90 s allow us to derive geodetic velocities at 16 permanent stations in east asia and 68 campaign mode sites in north china the resulting velocity field shows the following 1 contrary to the early inferences that the shanxi rift has accommodated significant right slip motion our results suggest that the rift system at least in its northern part in north china is under ese wnw extension at a rate of 4 2 mm yr the velocity field also suggests that an ese wnw trending left lateral shear zone deforming at a rate of 2 1 mm yr may exist along the north rim of north china at the latitude of 40 n separating actively extending north china in the south from relatively stable mongolia in the north 2 central and east china move at a rate of 8 11 mm yr east southeast with respect to siberia implying that the overall east southeastward motion is the dominant mode of deformation in east china 3 the india plate moves at a rate of 6 1 mm yr slower than the nuvel 1a model prediction relative to the eurasia plate 4 significant eastward motion 20 2 mm yr with respect to siberia occurs in southeastern tibet about half of this eastward motion 11 mm yr is absorbed by structures along the eastern boundary of the tibetan plateau

helium and co2 soil gas emission from santorini greece soil gas investigation is a useful tool to detect active faults the sudden appearance of soil gas anomalies in zones of deep reaching faults represents a promising potential precursor of earthquakes and volcanic eruptions in volcanic areas the development of soil gas monitoring techniques is particularly important as they can represent together with remote sensing techniques the only geochemical methods that can be safely applied during volcanic unrest when it becomes impossible or too dangerous to sample crater fumaroles a soil gas survey was carried out in june 1993 at the main island of thera in the santorini volcanic complex co2 flux and co2 and helium concentrations were measured at 50 cm depth for 76 points covering the entire island with a spacing of 500 m or less several anomalous soil degassing sites have been detected the main anomalies correspond to the kolumbos line and to the kameni line two volcano tectonic fault systems that controlled all the historic volcanic activity of santorini a third anomaly is related to a gas leaking fault cutting the geothermal field of southern thera soil gas data together with geovolcanological and seismological evidence indicate that the kolumbos and kameni lines are the most probable sites for future volcanic or seismic reactivation and provide the basis for the establishment of a new geochemical monitoring technique at thera

interaction between fumarolic gases and thermal groundwaters at vulcano island italy evidences from chemical composition of dissolved gases in waters abstract the chemical composition of some gaseous species dissolved in thermal groundwaters from vulcano island was determined directly in the field the determinations were made using a methodology based on the equilibrium partitioning of gases between a liquid and a gaseous phase the analyses were performed with a portable gas chromatograph using a simple analytical procedure lasting 70 s he and co 2 partial pressures are notably higher than those of waters in equilibrium with the atmosphere confirming an interaction between volcanic gases and groundwaters the highest co 2 values were recorded in wells located in areas of anomalous co 2 and he exhalations related to the active volcano tectonic structures on the island the temporal variations in co 2 concentrations both in the crater fumarolic gases and in the dissolved gases of some wells showed a very similar pattern lastly the lowering of the he contents in the dissolved gases that occurred in 1996 1997 was probably due to a decreased interaction between the main degassing system crater fumaroles and the thermal groundwaters

gas emissions and crustal deformation from the krýsuvik high temperature geothermal system iceland abstract the kr suvik volcanic system is located on the oblique spreading reykjanes peninsula sw iceland since early 2009 the region has been undergoing episodes of localized ground uplift and subsidence from april november 2013 we operated near real time monitoring of gas emissions in kr suvik using a multi component gas analyzer system multi gas collecting data on gas composition from a fumarole h2o co2 so2 h2s the dataset in this study comprises a near continuous gas composition time series the quantification of diffuse co2 gas flux analytical results for direct samples of dry gas seismic records and gps data gas emissions from the kr suvik geothermal system were examined and compared with crustal deformation and seismicity the gas emissions from the kr suvik system are h2o dominated with co2 as the most abundant dry gas species followed by smaller concentrations of h2s the average subsurface equilibrium temperature was calculated as 278 c this is consistent with previous observations made through sporadic spot sampling campaigns in addition the semi continuous multi gas dataset reveals higher variations in gas composition than previously reported by spot sampling the diffuse soil co2 flux is found to be variable between the three studied degassing areas in kr suvik ranging from 10 9 70 9 t day with the highest flux in hveradalir where the multi gas station is located the total flux is estimated as 101 t day comparison between multi gas and geophysical data shows that peaks of h2o rich emissions appears to follow crustal movements coinciding with the h2o rich peaks so2 is detected in minor amounts 0 6 ppmv allowing for calculations of h2o so2 co2 so2 and h2s so2 ratios this is the first time so2 has been detected in the kr suvik area the large variations in h2o co2 and h2o h2s ratios are considered to reflect variable degassing activity in the fumarole the activity of the fumarole appears less intense during intervals of low or no recorded seismic events the h2o co2 and h2o h2s ratios are lower presumably due to h2o condensation affecting the steam jet before reaching the multi gas inlet tube

magmatic gases in well fluids aid the mapping of the flow pattern in a geothermal system abstract gas composition and silica concentrations of well fluids are used in conjunction with pressure temperature and enthalpy data to obtain a model of the drilled part of the krafla geothermal field northeast iceland a magma chamber is located at 3 8 km depth under the field magmatic gases emanate from the chamber and travel via a channel reaching the surface at the hveragil eruptive fissure the composition of the gases is apparently modified on the way in that sulphur which presumably is in the form of sulphur dioxide to begin with is removed on the way and what remains is in the form of hydrogen sulphide at the end it is suggested that the major removal mechanism is the deposition of pyrite and pyrrhotite during the passage of the gases through the hydrothermal system the hydrothermal system is divided into a lower part whose temperature exceeds 300 c and whose fluids are to a varying extent affected by the magmatic gases and an upper part whose temperature is ca 200 c this upper part is a run off from the lower part but the magmatic effects have mostly disappeared there

detection of widespread fluids in the tibetan crust by magnetotelluric studies magnetotelluric exploration has shown that the middle and lower crust is anomalously conductive across most of the north to south width of the tibetan plateau the integrated conductivity conductance of the tibetan crust ranges from 3000 to greater than 20 000 siemens in contrast stable continental regions typically exhibit conductances from 20 to 1000 siemens averaging 100 siemens such pervasively high conductance suggests that partial melt and or aqueous fluids are widespread within the tibetan crust in southern tibet the high conductivity layer is at a depth of 15 to 20 kilometers and is probably due to partial melt and aqueous fluids in the crust in northern tibet the conductive layer is at 30 to 40 kilometers and is due to partial melting zones of fluid may represent weaker areas that could accommodate deformation and lower crustal flow

convergence across the northwest himalaya from gps measurements 1 horizontal velocities of 26 global positioning system gps stations in the northwest himalayan region provide new constraints on the partitioning of india eurasia convergence and elastic strain accumulation about the locked main frontal thrust mft the northwest striking karakorum fault slips at 11 4 mm yr and contributes to east west extension of southern tibet and westward motion of the northwest himalaya towards nanga parbat rather than playing a role in eastward extrusion of tibet crustal shortening across the himalaya occurs within a zone centered about 100 km north of the siwalik foothills and the mft model inversions of the gps data indicate that the mft is locked over a width of 100 km comparison with geologic mft slip rate estimates suggests that this zone is building up a slip deficit at a rate of 14 1 mm yr and will eventually fail in future great earthquakes

history of earthquakes and vertical ground movement in campi flegrei caldera southern italy comparison of precursory events to the a d 1538 eruption of monte nuovo and of activity since 1968 abstract the record of felt earthquakes around naples bay in southern italy is probably complete since the mid 15th century according to this record intense earthquake swarms originating beneath campi flegrei an explosive caldera located along the north coast of naples bay have occurred only twice 1 before the only historical eruption in campi flegrei in 1538 and 2 from mid 1983 to december 1984 earthquake activity during the earlier period which began at least a few years and possibly as many as 30 years before the 1538 eruption damaged many buildings in the city of pozzuoli located near the center of campi flegrei minor seismic activity which consisted of only a few felt earthquakes occurred from 1970 to 1971 the second period of intense earthquake swarms lasted from mid 1983 to 1984 again damaging many buildings in pozzuoli two periods of uplift along the shoreline within campi flegrei have also been noted since the mid 15th century 1 during the few decades before the 1538 eruption and 2 as two distinct episodes since 1968 uplift of a few meters probably occurred a few decades before the 1538 eruption uplift of as much as 3 0 m has occurred in pozzuoli since 1968 these similarities strongly suggest that for the first time in 440 years the same process that caused intense local earthquake swarms and uplift in the early 1500 s and led to an eruption in 1538 has again occurred beneath campi flegrei though no major seismicity or uplift has occurred since december 1984 because of the large amount of extensional strain accumulated during the past two decades if a third episode of seismicity and rapid uplift occurs it may lead to an eruption within several months after the resumption of activity

the present day deformation of the central zagros from gps measurements 1 in 1997 and in 2000 we measured the distances between 14 geodetic benchmarks across the central zagros mountain belt the results show that about 10 mm yr of shortening in the central zagros is distributed across the mountain belt this shortening corresponds to roughly 50 of the total convergence between arabia and eurasia and is consistent in direction the persian gulf does not deform significantly the main zagros reverse fault is not an active kinematic boundary the internal deformation of the folded belt is rather homogeneous at the scale of our survey which does not allow us to detect any individual active blind fault however the strain pattern suggests that n s dextral strike slip faults may accommodate part of the deformation

continuous deformation of the tibetan plateau from global positioning system data global positioning system velocities from 553 control points within the tibetan plateau and on its margins show that the present day tectonics in the plateau is best described as deformation of a continuous medium at least when averaged over distances of 100 km deformation occurs throughout the plateau interior by ese wnw extension and slightly slower nne ssw shortening relative to eurasia material within the plateau interior moves roughly eastward with speeds that increase toward the east and then flows southward around the eastern end of the himalaya crustal thickening on the northeast ern and eastern margins of the plateau occurs over a zone 400 km wide and cannot be the result of elastic strain on a single major thrust fault shortening there accommodates much of india s penetration into eurasia a description in terms of movements of rigid blocks with elastic strain associated with slip on faults between them cannot match the velocity field

oceanic ridge crest processes oceanic ridge crest processes constitute a vigorous frontier of multidisciplinary research with global ramifications in the earth atmospheric and biologic sciences this deep ocean frontier is gradually opening in response to investigations which are elucidating the role of these processes in the lithosphere hydrosphere atmosphere and biosphere and the application of advanced instrumental and interpretive techniques which are increasing the quality and quantity of data these techniques include crustal drilling with borehole logging deep sea drilling project reports high resolution bathymetry sea beam etc side scan sonar seamarc i and ii gloria etc imagery with video and photography multichannel seismics determination of water column properties ctd with rosette sampler etc and submersible applications

present day kinematics of asia derived from geologic fault rates active fault geometry available quaternary rates on major faults and the far field plate motion are used to determine crustal kinematics in the collision zone between india and asia using a finite element formalism to construct a spherical shell model of the asian continent with embedded faults we seek a velocity solution approaching the motion of rigid blocks by minimizing the elastic strain energy in the fault bounded blocks by doing so we test the assumption that long term deformation within continents is mostly localized into major faults in the solution fault motion accounts for more than 80 of the deformation allowing us to describe our velocity model in terms of quasi rigid block rotations on the sphere south china is rotating clockwise about a pole located southwest of borneo implying an e ese velocity vector of 11 mm yr for a point at shanghai in agreement with the velocity vector determined by very long baseline interferometry heki et al 1995 the eastward movement of south china is accommodated by oblique extension along the red river fault at a rate of 10 5 mm yr in the south and by the combination of left lateral strike slip motion on the qinling dabie shan fault and the counterclockwise rotation of the ordos and adjacent blocks in the north the tarim rotates clockwise with respect to dzungaria about a pole located at 44 n 92 e consistent with increasing crustal shortening toward the west throughout the tien shan assuming incompressibility a crustal volume budget over a domain encompassing the tertiary mountain ranges in asia shows that over the last 10 000 years 73 4 of the north south shortening between india and asia has been absorbed by thickening of the lithosphere and 27 has been accommodated by lateral extrusion of continental blocks the present day predominance of thickening in asia results from the relatively slow eastward motion of south china controlled by strike slip faulting in the qinling shan and oblique extension in northeastern china

earthquake potential in and around china estimated from past earthquakes 1 we present an earthquake potential estimate for magnitude 5 4 or larger earthquakes for china the potential is expressed as the rate density or the probability per unit area magnitude and time and it is based on smoothed seismicity we constructed a special earthquake catalog which combines previous catalogs covering different times after deriving regression relationships we estimated moment magnitudes for some events then we used the special catalog for constructing our smoothed seismicity model and testing it retrospectively using maximum likelihood we estimated the completeness threshold the b value and the corner magnitude we adopted a kind of gutenberg richter distribution with modifications at higher magnitude and assumed a uniform b value and upper magnitude limit derived from the special catalog from smoothed seismicity we estimated local a values we have begun a prospective test finding that earthquakes since the beginning of 2000 are quite compatible with the model

contribution of archaeological data to studies of earthquake history in the iranian plateau we use archaeological evidence to identify ancient earthquakes in the vicinity of large 20th century events in the iranian plateau two large earthquakes on the zagros main recent fault were preceded by historical earthquakes in ad 1008 and ad 1107 and by earthquakes in the intervals ad 224 459 and 1650 1600 bc giving return times of 1800 2100 500 800 and 850 950 years the ad 1962 ms 7 2 bo in zahra earthquake on the ipak fault in north central iran was preceded by an earthquake in 2000 1500 bc recorded at the sagzabad mound a return time of 3500 4000 years if there are no missing events the ad 1990 ms 7 3 rudbar tarom earthquake in the western alborz mountains was preceded by an earthquake in 1000 800 bc recorded at the marlik mound a return time of 2800 3000 years the ad 1948 ms 7 2 kopeh dagh earthquake that destroyed ashkabad capital of turkmenistan was preceded by an earthquake in 10 bc ad 10 recorded at mithradatkert nesa mound and by an earthquake in 2000 bc recorded at ak tapeh mound assuming no missing earthquakes this region has an earthquake return time of about 2000 years in khorasan province which was struck by a sequence of large earthquakes from ad 1936 to 1997 a mosque at qa en was destroyed in the mid 11th century ad probably the historical earthquake of ad1066 in the absence of palaeoseismic investigations archaeology offers the promise of recording earthquakes through more than one seismic cycle in different regions of iran q 2001 elsevier science ltd all rights reserved

offset and evolution of the gowk fault s e iran a major intra continental strike slip system abstract we use drainage reconstructions to estimate long term offsets on the gowk fault an oblique right lateral strike slip fault in eastern iran on which there have been a number of recent large earthquakes a 3 km horizontal offset is inferred from well preserved geomorphology we further identify a total cumulative offset of 12 km which produces a simple reconstruction of geomorphology across the fault filling in pull apart basins restoring rivers to linear courses across the fault trace and aligning structural and bed rock features the probable age of the gowk fault and k ar dating of offset basalts north of the study region suggest an overall slip rate of 1 5 2 4 mm year this is small compared with the overall 10 20 mm year of shear expected between central iran and afghanistan and the deficit is likely to have been accommodated on other faults east of the gowk fault drainage displaced by dextral movement leads to the development of a series of basins along the fault and a longitudinal topographic profile that resembles an asymmetric saw tooth the geomorphic evolution of the fault zone at the surface includes both normal and reverse faulting components reflecting a probable ramp and flat structure in cross section this interpretation is consistent with evidence from the analysis of seismological radar and surface rupture data in recent earthquakes

episodic rifting and volcanism at krafla in north iceland radon 222 emission from fumaroles near leirhnjukur from june 1978 until late 1980 radon emission from the leirhnjukur fumaroles was monitored within the krafla caldera of north iceland where episodic volcanism is occurring frequent sampling of the fumaroles shows that no easily identifiable short term radon precursors occur in the days prior to subsidence of the caldera despite an observed increase in microseismicity preceding deflation following the onset of subsidence however the radon emission of the fumaroles gradually increases and reaches a maximum 3 6 days later the radon in the fumaroles is assumed to be transported from depth by steam and noncondensing gases that slowly escape from the geothermal water table the cause of the co episodic increase in radon emission appears to be a temporal rise of the water table driven by fissure closure resulting in an abbreviated transport time for radon to the surface fumaroles furthermore the closing of the fissures appears to cause a transient increase in the velocity of transport making the shape of the anomalies broader and higher than is predicted from a change in the water level alone changes in radon emission also coincide with fluctuations in fumarolic activity and permanent changes in the level of geothermal water that occur during periods of uplift

processes controlling the distribution of boron and chlorine in natural waters in iceland abstract the concentrations of b and cl in natural waters in iceland lie in the range 0 001 10 and 1 20 000 ppm respectively lowest concentrations occur in surface and groundwaters in the central highlands highest cl concentrations are found in high temperature waters on the reykjanes peninsula and highest b concentrations in well waters from high temperature geothermal systems in the axial zones of the active volcanic belts the b and cl contents of icelandic basalts are 0 1 6 6 and 75 750 ppm respectively these large variations are considered to result from variable degassing during consolidation as well as concentration variations in the initial magma tholeftes are lowest in both elements av 1 2 ppm b and 170 ppm ci transitional basalts intermediate av 2 1 ppm b and 240 ppm ci and alkali basalts highest av 3 8 ppm b and 340 ppm cl cl b ratios in tholeiites are most often within 25 50 but somewhat lower in alkali basalts most geothermal waters contain b and cl within 0 05 1 and 10 100 ppm respectively these rather low values are attributed to the low content of b and cl in the basaltic rock the b and cl distribution in the icelandic natural waters indicate that these elements act as essentially incompatible their sources of supply include 1 the atmosphere seawater spray and aerosols 2 the rock with which the water interacts 3 seawater groundwater and 4 magma intrusions in surface water and nonthermal groundwater the dominant source of supply of cl is seawater spray and aerosols but the soil and rock contribute often significantly to the b in these waters their cl b ratio is similar to that of seawater 1330 or somewhat lower boron and cl concentrations generally increase with water temperature warm waters cl b ratios intermediate between those of seawater and basalt with increasing temperature this ratio decreases and gradually approaches that of the rock some high temperature geothermal waters have as low cl b ratios as 1 and b concentrations as high as 10 ppm the cause is either b degassing of the magmatic intrusive heat source or phase separation in the producing aquifer some low temperature waters

slip rates of the karakorum fault ladakh india determined using cosmic ray exposure dating of debris flows and moraines most recent major glacial advance occurred at 90 15 ka this is consistent with the inference of others that alpine glaciers in this region have not necessarily expanded in concert with northern hemisphere continental ice sheets if features including lateral moraines that liu inferred to have been offset 300 350 m by the karakorum fault date from the same period they too imply a slip rate of 3 4 mm yr 1 this slip rate is comparable to rates of extension across grabens within tibet with recent evidence that slip along the altyn tagh fault occurs at 10 mm yr 1 our rate suggests that slip along the boundaries of tibet is not significantly more rapid than extension within the plateau hence plate tectonics in the strictest sense ought not be applied to tibet because tibet does not behave as a rigid plate index terms 1824 hydrology geomorphology 1625 1035 geochemistry geochronology 9320 information related to geographic region asia 8107 tectonophysics continental neotectonics keywords karakorum fault slip rate cosmic ray exposure age beryllium 10

frequency of occurrence of moderate to great earthquakes in intracontinental regions implications for changes in stress earthquake prediction and hazards assessments we investigate the departure of shallow intracontinental earthquakes from the frequency magnitude relationship log n m a bm we consider seven large continental regions but exclude subduction zones in each active and stable areas are differentiated within active areas we separately categorize earthquakes on faults with high slip rates we use data sets from 1978 1994 and 1900 1994 which are complete for moment magnitudes mw 5 3 and 7 0 to calculate changes in b value with mw for all active intracontinental regions combined except asia b changes at 98 confidence from 0 90 to 2 1 at a corner magnitude mc of 6 9 to 7 0 the distribution for stable regions indicates a similar change values of mc are associated with downdip widths of rupture of about 23 to 27 km which are smaller than those for subduction zones in each case mc marks a transition from unbounded to bounded earthquakes in asia events from 1958 to 1994 also delineate a similar change near mc 7 0 earthquakes in asia of 7 0 mw 8 1 from 1900 to 1957 however define a b value of 1 0 and a moment release rate 5 6 times higher than that from 1958 to 1994 those anomalous values indicate that a large region of asia was close to failure i e near a self organized critical state during the earlier period we associate those changes with the giant himalayan earthquake in 1950 of mw 8 6 regional variations in seismic strain release rates correlate with the types of processes at adjacent plate boundaries extrapolating rates of activity of the past 95 years to mw 8 0 indicates that such events should be very rare in stable areas

temporal variations of gas compositions of fumaroles in the tatun volcano group northern taiwan article i nfo he 4 he geochemical monitoring hydrothermal activity is common in the tatun volcano group of northern taiwan helium isotopic compositions of fumarolic samples show that mantle component occupies more than 60 in the previous study along with recent seismic results a magma reservoir is inferred to have existed beneath the area of da you keng where fumarolic venting is the most active in tatun volcano group progressive increases of hcl concentrations and so2 h2s ratio in fumaroles from da you keng have been observed since august 2004 the hcl concentration changed from almost the detection limit to thousands of ppm even up to 30 000 ppm so2 h2s ratios varied from almost 0 to 3 hence so2 became the dominated s species in this area these variations were accompanied by rising temperature of fumaroles in the tatun volcano group especially in the area of da you keng from boiling point to 131 c meanwhile 3

helium isotopes in icelandic geothermal systems ii helium heat relationships abstract a model has been developed that relates the 3he content of the reservoir fluid to the fluid enthalpy in contrast to oceanic hydrothermal systems that display a uniform 3he enthalpy ratio 0 4 14 106 atoms of 3he joule icelandic systems vary by 1000 0 4 400 106 atoms joule a process that preferentially extracts helium relative to heat from a cooling magma produces high 3he enthalpy ratios for young systems e g krafla and low 3he enthalpy ratios for aging magmatic systems e g hveragaerdi using the highest 3he heat ratios measured in the fluid estimates of initial gas concentrations in the basalt are made for 3he 5 10 10 cc g and carbon 1200 ppm low temperature wells near geysir in southwest iceland appear to result from mixing of high temperature fluid 200 c and cold groundwater along a curve of constant 3he enthalpy

shells a thin shell program for modeling neotectonics of regional or global lithosphere with faults the thin plate method of modeling neotectonics uses isostasy and vertical integration of lithospheric strength to reduce three dimensional problems to two dimensions we introduce new thin shell continuum elements and fault elements which satisfy the completeness and compatibility requirements and permit extension of these methods to the lithospheres of spherical planets even a coarse grid of these elements with elastic rheology can reproduce low order toroidal free oscillations in the program shells a realistic frictional dislocation creep rheology is handled by iteration this method converges to solutions which can be numerically tested to confirm that they satisfy both local equilibrium and the balance of torques on whole plates because this code can incorporate both natural plate shapes with internal faults and realistic rheologies it yields models that are readily tested by their predictions of geodetic velocities stresses and fault slip rates

gas changes in the krafla geothermal system iceland abstract a massive influx of gas was encountered in the krafla geothermal system iceland following the start of magmatic activity in the area in 1975 the gas was of magmatic origin but its composition had been modified to predominantly carbon dioxide and a small amount of hydrogen sulphide the gas concentrations of krafla borehole fluids have been monitored since and the pattern has been similar for wells in the affected leirbotnar field i e a maximum in 1977 1978 a secondary maximum in 1980 and a steady decline since the more southerly su urhli ar and hvitholar fields were not affected fumaroles were sampled extensively in 1978 1979 and 1984 1985 a similar decline was observed in the affected area but a geographical trend that had been noticed for the borehole fluids was much clearer in this case the decline is smallest in the northeastern part of the field but more pronounced to the south and west it is suggested that magmatic gas has not entered the geothermal system after 1980 and that the excess gas observed now comes from a supply located in the northeastern part of the field near the explosive crater viti

velocity field in asia inferred from quaternary fault slip rates and global positioning system observations we perform a joint inversion of quaternary strain rates and 238 global positioning system gps velocities in asia for a self consistent velocity field the reference frames for all geodetic velocity observations are determined in our inversion procedure india in moves relative to eurasia eu about a pole of rotation at 29 78 n 7 51 e 0 353 myr 1 which yields a velocity along the himalaya within india that is 73 76 of the magnitude of the in eu nuvel 1a velocity and a vector azimuth that is 8 10 clockwise of nuvel 1a in eu vector azimuth relative to eurasia south china moves at 9 11 mm yr in the direction 110 120 with a pole position 64 84 n 156 74 e 0 12 myr 1 amurian block motion has a pole position in a similar location but at a slower rate 64 61 n 158 23 e 0 077 myr 1 and most of the amurian eurasia motion is accommodated by extension across lake baikal tarim basin moves relative to eurasia about a pole of rotation at 39 24 n 98 2 e 0 539 myr 1 and 16 18 mm yr of shortening is accommodated across the west central tien shan there is distributed e w extension throughout both southern and north central tibet within southern tibet between the longitudes of 77 e to 92 e the deformation field accommodates 16 19 mm yr of e w extension we compare predicted seismic moment rates with those observed in this century in asia total observed seismic moment rates within the entire area of central and east asia 2 2 107 km2 in this century are 2 26 0 7 1020 n m yr 1 as compared with a predicted total rate of 2 03 0 066 1020 n m yr 1 comparisons between observed and predicted moment rates within 42 subregions reflect the generally unstable process of inferring long term seismic moment rates from a catalog of limited duration 94 years an observation period of 10 000 years would be required to reduce uncertainties in observed seismic moment rate to the same size as the uncertainties in model tectonic moment rates inferred from the joint inversion of gps and quaternary rates of strain we show that in general a better correlation with model tectonic moment rate is inferred from the seismicity catalog by considering the numbers of earthquakes above a cutoff magnitude mb 5 0 for the period january 1 1965 to january 1 1999

the chemistry of trace elements in surface geothermal waters and steam iceland abstract the geochemistry of trace elements in surface geothermal fluids in iceland was studied the sampled fluids included hot springs mud pots steam vents and soil solutions with temperatures ranging from 4 to 100 c ph between 2 01 and 9 10 and total dissolved solids between 86 and 4375 ppm the surface geothermal waters may be categorized into three groups based on their chemical composition namely nacl waters steam heated acid sulfate waters and mixed waters nacl waters with ph 8 are considered to represent aquifer geothermal fluids that have undergone boiling in the upflow they contained only low concentrations of most metals

gravity and height variations connected with the current rifting episode in northern iceland abstract following a first gravity survey in 1938 high precision gravity measurements with lacoste romberg gravimeters have been carried out in northern iceland in 1965 1970 1971 and 1975 in order to detect eventual secular gravity variations at that supramarine part of a constructive plate boundary since 1975 when an active rifting episode started there gravity and height variations have been observed in annual intervals these surveys concentrated on the approx 100 km long and 5 km wide fissure zone associated with the krafla central volcano which is the center of the present activity the observations which have been performed at an accuracy level of 0 01 mgal resp 0 03 m give significant information about the long term behaviour of the vertical mass shifts occuring during the rifting process a steep gravity variation gradient observed south of the krafla caldera between 1965 and 1975 may be interpreted as some kind of precursor of the current process since 1975 the rifting event is characterized by shifting activity areas with gravity decrease and elevation at the flanks and gravity increase and subsidence at narrow central parts of the krafla fissure zone the annual variations reaching 0 1 mgal resp 0 5 m and more since 1978 the activity has concentrated on the gjastikki region north of the krafla volcano with decreasing variations in the southern and northern parts of the fissure swarm the average gravity height variation ratio calculated for two profiles south and north of krafla over the observation periods between 1975 and 1979 amounts to 0 2 mgal m but extreme values are found at recently activated areas

secular variations of carbon and helium isotopes at izu oshima volcano japan abstract secular variations in 13c 12c ratios and chemical compositions of gas samples from october 1986 to july 1992 are reported from a 92 95 c steam well located about 3 km north of mt mihara an active volcano on izu oshima island japan the 13c value steeply increased from 2 97 relative to pdb carbonate in december 1986 to 1 15 in march 1988 and then gradually decreased to 1 75 in july 1992 over the same period the co 2 content changed similarly with time even though the experimental error is relatively large these variations are consistent with helium isotope changes initially rapid and then slow enhancements of 3he 4he ratio 13c value and co 2 content are invoked by violent eruptions of izu oshima volcano from 15 november to 18 december 1986 after the eruptive activity depletion of magmatic gas emission and subsequent mixing with crustal fluids in the hydrothermal system may produce the gradual decreases of 3he 4he ratio 13c value and co 2 content taking into account the rates of these decreases we suggest that helium and carbon isotope ratios will return to the situation of before the magmatic eruption within 15 years

chemical variations in fumarolic gases at vulcano island southern italy seasonal and volcanic effects abstract because of increasing in fumarolic activity at vulcano since september 1987 regular sampling and analysis is conducted on the well known f5 crater fumarole t 330 5 c significant chemical variations have been recorded over the period 1987 1989 variations of water vapour in the fumarolic fluid follow seasonal pattern and can be related to both external seasonal and internal volcanic influences suggesting a control by a shallow water aquifer significant variations of h 2 o and of some species in the anhydrous gas phase h 2 so 2 hcl hf n 2 he probably result from chemical or dynamic changes in the feeding system at depth several mechanism are considered for explaining the chemical trends results in relationship to the recent increase in activity a growing input of deep magmatic fluids is not supported by the low co content and the apparent constancy of the 3 he 4 he ratio apparent equilibrium temperatures close to the fumarolic outlet temperature 350 400 c were calculated suggesting isothermal expansion of the gas from a shallow equilibration zone comparison with the fumaroles at sea level porto di levante suggests that these latter may be fed a different hydrothermal systems variable interaction between both systems may account for some of the chemical variations observed at f5 fumarole

reaction path models of magmatic gas scrubbing gas water rock reactions taking place within volcano hosted hydrothermal systems scrub reactive water soluble species sulfur halogens from the magmatic gas phase and as such play a major control on the composition of surface gas manifestations a number of quantitative models of magmatic gas scrubbing have been proposed in the past but no systematic comparison of model results with observations from natural systems has been carried out to date here we present the results of novel numerical simulations in which we initialized models of hydrothermal gas water rock at conditions relevant to icelandic volcanism we focus on iceland as an example of a wet volcanic region where scrubbing is widespread our simulations were performed using the eq3 6 software package at shallow temperature 100 c we find that this range of model gas compositions reproduces well the h2o co2 stot compositional range of reservoir waters and surface gas emissions in iceland from this validation of the model in an extreme end member environment of high scrubbing we conclude that eq3 6 based reaction path simulations offer a realistic representation of gas water rock interaction processes occurring underneath active magmatic hydrothermal systems

large scale crustal deformation of the tibetan plateau the topography velocity and strain fields calculated from a three dimensional newtonian viscous model for large scale crustal deformation are generally in good agreement with results from geological geodetic and earthquake studies in and around the tibetan plateau provided that the model rheology incorporates a weak zone within the deep crust beneath the plateau equivalent to a viscosity of 1012 pa s within a 250 m thick channel or 1018 pa s within a 15 km thick channel model studies and observations show a plateau at 5 km elevation with steep topographic gradients across the southern and northern plateau margins and more gentle gradients across the southeastern and northeastern margins rapid shortening strain is concentrated along the lower portions of the northern and southern plateau margins at rates 20 mm yr model results show north south shortening 10 mm yr in reasonable agreement with gps data 5 8 mm yr of north south shortening across the northern two thirds of the plateau and east west stretching 10 15 mm yr across the eastern half of the high plateau in reasonable agreement with seismic geologic and gps data upper crustal material moves eastward from the plateau proper into a lobe of elevated topography that extends to the south and east clockwise rotation of material around the east himalayan syntaxis at rates up to 10 mm yr occurs partly as a result of dextral shear between indian and asian mantle at depth and partly as a result of gravitational spreading from the high plateau to the south and east there is little difference in model surface deformation for assumptions of moderately weak or extremely weak lower crust except in southern and northern tibet where margin perpendicular extension occurs only for the case of an extremely weak lower crust our results suggest that the tibetan plateau is likely to have gone through a two stage development the first stage produced a long narrow high orogen whose height may have been comparable to the modern plateau the second stage produced a plateau that grew progressively to the north and east east west stretching eastward plateau growth and dextral rotation around the east himalayan syntaxis probably did not begin until well into the second stage of plateau growth perhaps becoming significant after 20 m y of convergence

soil co2 degassing on mt etna sicily during the period 1989 1993 discrimination between climatic and volcanic influences wide variations were measured in the diffuse co2 flux through the soils in three selected areas of mt etna between august 1989 and march 1993 degassing of co2 from the area of zafferana etnea s venerina on the eastern slope of the volcano has been determined to be more strongly influenced by meteorological parameters than the other areas the seasonal component found in the data from this area has been excluded using a filtering algorithm based on the best fitting equation calculated from the correlation between co2 flux values and those of air temperature the filtered data appear to have variations temporally coincident with those from the other areas thus suggesting a common and probably deep source of gas the highest fluxes measured in the two most peripheral areas may correlate well with other geophysical and volcanological anomalous signals that preceded the strong eruption of 1991 1993 and that were interpreted as deep pressure increases anomalous decreases in co2 fluxes accompanied the onset and the evolution of that eruption and have been interpreted as a sign of upward migration of the gas source the variations of co2 flux at the 1989 se fracture have also given interesting information on the timing of the magmatic intrusion that has then fed the 1991 1993 eruption

degassing regime of hekla volcano 2012 2013 hekla is a frequently active volcano with an infamously short pre eruptive warning period our project contributes to the ongoing work on improving hekla s monitoring and early warning systems in 2012 we began monitoring gas release at hekla the dataset comprises semi permanent near real time measurements with a multigas system quantification of diffuse gas flux and direct samples analysed for composition and isotopes 13c d and 18o in addition we used reaction path modelling to derive information on the origin and reaction pathways of the gas emissions hekla s quiescent gas composition was co2 dominated 0 8 mol fraction and the 13c signature was consistent with published values for icelandic magmas the gas is poor in h2o and s compared to hydrothermal manifestations and syn eruptive emissions from other active volcanic systems in iceland the total co2 flux from hekla central volcano diffuse soil emissions is at least 44 t d 1 thereof 14 t d 1 are sourced from a small area at the volcano s summit there was no detectable gas flux at other craters even though some of them had higher ground temperatures and had erupted more recently our measurements are consistent with a magma reservoir at depth coupled with a shallow dike beneath the summit in the current quiescent state the composition of the exsolved gas is substantially modified along its pathway to the surface through cooling and interaction with wall rock and groundwater the modification involves both significant h2o condensation and scrubbing of s bearing species leading to a co2 dominated gas emitted at the summit we conclude that a compositional shift towards more s and h2o rich gas compositions if measured in the future by the permanent multigas station should be viewed as sign of imminent volcanic unrest on hekla

chemistry and isotopic composition of fumarole discharges of furnas caldera abstract two fumarole grounds at lagoa das furnas and furnas village and a fumarole on the bank of ribeira dos tambores are located on a west east tectonic lineament across the topographic low of the furnas caldera the discharge of the fumaroles derives from steam separation from shallow 100 200 m aquifers at temperatures of about 180 c as inferred from nitrogen argon relations and deuterium oxygen isotope relations the hydrothermal fluid is derived from local precipitation after some 10 steam fractionation in the fumarole conduits sulphur isotope ratios of the discharge being close to those of juvenile rock sulphur indicate extensive rock leaching within the aquifers the carbon isotope composition of the fumarole discharge and carbon dioxide saturated waters encountered across the caldera floor suggests that the source of carbon is regional outgassing of mantle derived juvenile carbon dioxide chemistry of the acid gases carbon dioxide and hydrogen sulphide in the discharge indicates a slight fractionation induced by different boiling in the shallow hydrothermal aquifers traces of hydrogen and methane contained in the discharge bear no relation to the low temperature water steam equilibria of the furnas fumaroles assuming a deeper origin of these gases a simple model for binary mixtures of methane and hydrogen indicates that these gases are derived from supercritical conditions presumably equilibrated within hot rocks below the hydrothermal system the remarkably stable ratios of hydrogen and methane also considering their inferred deep origin suggest that these gases might be considered for future chemical monitoring of the fumarole discharge in furnas

changes in frequency size relationship from small to large earthquakes the constant b value observed in frequency magnitude distributions of earthquakes has been taken as an indication of self similarity at all magnitudes hence earthquake properties should scale uniformly in the same way from small to large earthquakes it has often been observed however that the seismic moment released in small earthquakes scales differently with rupture length than it does for large events1 2 where the crossover between small and large events is defined at a rupture dimension equal to the down dip width of the seismogenic zone a possible explanation for this contradiction is that frequency size distributions are biased by small earthquakes small events dominate most global earthquake catalogues because of the short time period covered another source of bias in size distributions is the saturation of earthquake magnitudes for large events here we correct biases in calculations of b values and present evidence for a change in b value in frequency size distributions we find that a break in self similarity from small to large earthquakes occurs at a point where the dimension of the event equals the down dip width of the seismogenic layer

microplate model for the present day deformation of tibet 1 site velocities from 349 global positioning system gps stations are used to construct an 11 element quasi rigid block model of the tibetan plateau and its surroundings rigid rotations of five major blocks are well determined and average translation velocities of six smaller blocks can be constrained where data are well distributed the velocity field can be explained well by rigid block motion and fault slip across block boundaries residual misfits average 1 6 mm yr compared to typical one standard deviation velocity uncertainties of 1 3 mm yr any residual internal straining of the blocks is small and heterogeneous however residual substructure might well represent currently unresolved motions of smaller blocks although any smaller blocks must move at nearly the same rate as the larger blocks within which they lie undetected relative motions between them could be significant particularly where there are gaps in gps coverage predicted relative motions between major blocks agree with the observed sense of slip and along strike partitioning of motion across major faults however predicted slip rates across tibet s major strike slip faults are low only 5 12 mm yr a factor of 2 3 smaller than most rates estimated from fault offset features dated by radiometric methods as 2000 to 100 000 year old previous work has suggested that both gps data and low fault slip rates are incompatible with rigid block motions of tibet the results reported here overcome these objections

pollution from the 2014 15 barðarbunga eruption monitored by snow cores from the vatnajokull glacier iceland abstract the chemical composition of icelandic rain and snow is dominated by marine aerosols however human and volcanic activity can also affect these compositions the six month long 2014 15 bar arbunga volcanic eruption was the largest in iceland for more than 200 years and it released into the atmosphere an average of 60 kt day so2 30 kt day co2 500 t day hcl and 280 t day hf to study the effect of this eruption on the winter precipitation snow cores were collected from the vatnajokull glacier and the highlands northeast of the glacier in addition to 29 bulk snow cores from that precipitated from september 2014 until march 2015 two cores were sampled in 21 and 44 increments to quantify the spatial and time evolution of the chemical composition of the snow the ph and chemical compositions of melted snow samples indicate that snow has been affected by the volcanic gases emitted during the bar arbunga eruption the ph of the melted bulk snow cores ranged from 4 41 to 5 64 with an average value of 5 01 this is four times greater h activity than pure water saturated with the atmospheric co2 the highest concentrations of volatiles in the snow cores were found close to the eruption site as predicted from calpuff so2 gas dispersion quality model the anion concentrations so4 cl and f were higher and the ph was lower compared to equivalent snow samples collected during 1997 2006 from the unpolluted icelandic langjokull glacier higher so4 and cl concentrations in the snow compared with the unpolluted rainwater of marine origin confirm the addition of a non seawater so4 and cl the 34s isotopic composition confirms that the sulphur addition is of volcanic aerosol origin the chemical evolution of the snow with depth reflects changes in the lava effusion and gas emission rates those rates were the highest at the early stage of the eruption snow that fell during that time represented by samples from the deepest part of the snow cores had the lowest ph and highest concentrations of so4 f cl and metals compared with snow that fell later in the winter also the al concentration did exceed world health organisation drinking water standard of 3 7 mol kg in the lower part of the snow core closest to the eruption site collected snow represents the precipitation that fell during the eruption period nevertheless only minor environmental impacts are evident in the snow due to its interaction with the volcanic aerosol gases in addition the microbial communities identified in the snow that fell during the eruption were similar to those found in snow from other parts of the arctic confirming an insignificant impact of this eruption on the snow microecology

crustal thickening versus lateral expulsion in the indian asian continental collision since the beginning of the continental collision between india and asia there has been about 2500 km of convergence and the northward movement of india has been accommodated by major internal deformation of the asian lithosphere the crustal thickening in and around the tibetan plateau is clearly a direct consequence of this collision but there is considerable debate as to whether a large fraction of the indentation has been accommodated by eastward motion of the lithospheric blocks of southeastern asia and southern china numerical experiments described here test this hypothesis for a range of indentation geometries and rheological models of the lithosphere we employ a thin viscous sheet model of the lithosphere with a depth averaged nonlinear viscous rheology described by a stress strain rate exponent n and including gravitational buoyancy forces scaled by the dimensionless argand number ar the eastern boundary for the collision region is described as a lithostatic boundary the precollision normal stress is determined by static balance and that constant stress is applied throughout the collision the experiments show that during collision the eastern boundary is smoothly displaced to the east at a rate about 1 4 of the indentation rate with only minor variation due to geometry or rheology crustal thickening rates in the region of the plateau are reduced by between 10 and 25 of the corresponding rates determined for similar experiments with a rigid eastern boundary to generalize from the results of these experiments the total north south shortening strain produced by the collision is partitioned between crustal thickening and eastward displacement in the ratio of at least 3 1 and more probably 4 1

the fluid geochemistry of icelandic high temperature geothermal areas abstract icelandic high temperature geothermal systems are considered to number thirty three thereof three are submarine and seven subglacial all are briefly described but the chemistry of fluids from twenty four of them is considered the fluid in the three submarine areas and those four on land that are closest to the sea are relatively saline but to a differing extent mixed with groundwater the rest contain dilute fluids the fluids of the central highland systems are mostly locally derived but may in some instances be quite old whereas those in the northerly krafla area which is inland and the oxarfjor ur area which is close to the sea appear to be a mixture of local and central highland water but those in the inland hengill geysir namafjall and theistareykir areas appear to have travelled relatively long distances from the central highlands the gas observed is magmatic except in the northerly oxarfjordur area close to the sea where it is apparently derived from organic sediments

earthquakes in a model of seismic zone with embedded pre existing faults we construct a simple quasi static model of seismic zone with embedded pre existing faults and present a self consistent method for incorporating both the stick slip behavior at the fault surfaces and the long ranged stress redistribution following a rupture or a slip event driven by a slow tectonic plate relative motion the model evolves to a critical state exhibiting gutenberg richter power law for the frequency size distributions results on spatial and statistical features of earthquakes in the model are also presented

a deforming block model for the present day tectonics of tibet 1 we use gps data from 45 sites across the tibetan plateau surveyed between 1991 and 2001 to study the distribution of strain in that part of the india eurasia collision zone the plateau is cut by a few major rapidly slipping strike slip fault zones with broadly distributed strain between those zones the gps velocities can be fit well by a simple deforming block model that combines uniform strain with the motion of blocks separated by the major known fault zones within the plateau the boundaries of the four blocks in this model correspond to the major rapidly slipping faults a rigid block model with a smaller number of blocks fits the data poorly and can be rejected we estimate that 5 9 0 7 mm yr of extension in the n69 w direction occurs on the yadong gulu rift south of the plateau localized extension may extend as far north as the nyainqentanglha range we find 7 4 0 7 mm yr of right lateral slip on the karakorum jiali fault zone significantly slower than that previously estimated from offset geologic features our deforming block model and a two dimensional single fault screw dislocation model give lower and upper bounds of 4 4 1 1 and 10 3 0 4 mm yr on the slip rate on the kunlun fault respectively comparable in its highest to the long term slip rate observed geologically the distributed deformation is surprisingly uniform over the tibetan plateau qaidam basin and qilian shan and approximates a combination of pure shear and uniaxial contraction with the same axes of maximum contraction n32 e this strain field is a combination of shortening and extension that produces little net dilatation 1 area loss per million years at present the broadly distributed strain most likely represents slip on many faults each with a relatively low slip rate distributed conjugate strike slip faulting is the most plausible mechanism to produce the observed strains as supported by the record of medium to large earthquakes within the plateau the distributed deformation is just as important in the accommodation of the total india eurasia convergence as is slip on the major faults the eastward motion of central tibet is as large as 50 of the convergence rate between india and eurasia however this eastward motion is not motion of a relatively undeforming block bounded by rapidly moving strike slip faults as suggested by past extrusion models instead much of this eastward extrusion is driven by the internal extension of the plateau our inference is in agreement with the model of f shen et al 2001 that suggested east west extension north south contraction and eastward plateau growth dominate the present tectonics of the tibetan plateau

constraining the extent of crust mantle coupling in central asia using gps geologic and shear wave splitting data abstract we have obtained constraints on mechanical crust mantle coupling for tibet and yunnan indo china by comparing the observed surface deformation field inferred from gps and quaternary fault slip rate data with the mantle deformation field inferred from several sks shear wave splitting data sets we first determined whether the anisotropy is dominantly asthenospheric or lithospheric by testing simple models of both types against the observed values of the fast polarization direction which is assumed to be parallel to the horizontal projection of the direction of maximum shear for asthenospheric flow we solved for a best fitting uniform sub asthenospheric velocity model for eurasia the fit however was not satisfactory rms misfit 20 solving for separate uniform flow fields in each region improves the fit 15 for tibet 11 for yunnan although the resulting flow fields are inconsistent with several geophysical and geological constraints and thus considered unlikely we then considered lithospheric models for tibet vertically coherent deformation i e maximum shear direction from surface deformation is parallel to yields an improved match 11 for left lateral shear both the goodness of fit and the dominance of left lateral surface faulting in tibet argue for a lithospheric source of anisotropy the misfit for yunnan is large for either right 53 or left lateral 49 shear which argues for complete crust mantle decoupling in yunnan we show that the fast polarization directions throughout both the tibet and yunnan region can be fit by a single lithospheric dynamic model in which there is strong coupling between crust and mantle beneath tibet but a complete decoupling between crust and mantle beneath yunnan crust this dynamic model predicts left lateral maximum shear directions within the mantle that align with fast polarization directions in both regions 9 these maximum shear directions within the mantle align with the left lateral maximum shear directions in the crustal deformation field in tibet but are not in yunnan our results have the following implications first the coherence between crust and mantle deformation in tibet implies strong crust mantle mechanical coupling since this is the only way that crustal buoyancy forces required to account for the surface deformation field can be transmitted into the mantle this behavior is consistent with a uniform strength lithosphere or strong crust but not with a substantially weaker crust for example it is inconsistent with the popular jelly sandwich rheology and thus precludes behavior such as large scale lower crustal flow in tibet the crust mantle coherence is also incompatible with mantle delamination second crust mantle decoupling within the yunnan lithosphere argues that mantle deformation there is controlled only by boundary conditions crustal buoyancy forces are not transmitted into the mantle beneath yunnan moreover the dynamic model for the mantle shows that the yunnan crust is moving south with respect to the mantle at rates as high as 30 mm yr third there is a fundamental rheological lithospheric transition between tibet and yunnan that may provide a key to understanding this significant orogen

modeling mountain building and the seismic cycle in the himalaya of nepal a host of information is now available regarding the geological and thermal structure as well as deformation rate across the himalaya of central nepal these data are reconciled in a two dimensional mechanical model that incorporates the rheological layering of the crust which depends on the local temperature and surface processes over geological timescale 5 ma the 20 mm yr estimated shortening rate across the range is accommodated by localized thrust faulting along the main himalayan thrust fault mht the mht reaches the surface along the foothills where it is called the main frontal thrust fault mft the mht flattens beneath the lesser himalaya and forms a midcrustal ramp at the front of the higher himalaya consistent with the river incision and the anticlinal structure of the lesser himalaya farther northward the mht roots into a subhorizontal shear zone that coincides with a midcrustal seismic reflector aseismic slip along this shear zone is accommodated in the interseismic period by elastic straining of the upper crust increasing the coulomb stress beneath the front of the higher himalaya where most of the microseismic activity clusters negligible deformation of the hanging wall requires a low apparent friction coefficient less than 0 3 on the flat portion of the mht on the ramp might be as high as 0 6 sensitivity tests show that a rather compliant quartz rich rheology and a high radioactive heat production in the upper crust of 2 5 w m 3 is required erosion affects the thermal structure and interplays with crustal deformation a dynamic equilibrium is obtained in which erosion balances tectonic uplift maintaining steady state thermal structure topography and deformation field using a linear diffusion model of erosion we constrain the value of the mass diffusivity coefficient to 0 5 1 6 l0 4 m 2 yr this study demonstrates that the data are internally consistent and compatible with current understanding of the mechanics of crustal deformation and highlight the role of viscous flow in the lower crust and of surface erosion in orogeny processes on the long term as well as during interseismic period

a no net rotation model of present day surface motions a significant portion of the earth s surface consists of zones of diffuse deformation the interior regions of these diffuse zones of deformation move at distinctly different velocities from that of adjacent plates and because of their complexities have been ignored in previous no net rotation nnr models we have calculated a new nnr model from a continuous velocity field that incorporates both rigid plate motion and velocity gradients within plate boundary zones when compared with earlier nnr models we find significantly different angular velocities for many plates differences between the nnr model presented here and earlier nnr models can be attributed to the effect of including velocity gradients in diffuse plate boundary zones as well as to the actual differences between geodetically derived surface motions and geologic estimates

late quaternary to decadal velocity fields in asia 1 fields of crustal velocity and strain rate within asia averaged over horizontal distances of 300 km are calculated from estimates of quaternary slip rates on faults and rates of change of lengths of baselines between gps sites the calculated fields fit strain rate components estimated from quaternary slip rates within 95 confidence limits and fit the gps data with an rms residual of 2 5 mm yr 1 the strain rate field constrained only by quaternary slip rates of faults differs from the combined solution at the level of 20 nstrain yr 1 and the differences are explicable by the limited accuracy of geological estimates of slip rate therefore the strain rate fields determined by geodetic measurements taken on the 10 year timescale are consistent with geological observations on the 104 year timescale the combined solution for velocities shows plate or block like motion within deforming asia only in tarim south china and the amurian region elsewhere the kinematics of rigid blocks does not provide a useful description of the motion in particular velocities relative to eurasia point at high angles to contours of their magnitudes not parallel to them as they would if large regions moved as rigid blocks the axes of principal horizontal compressional strain align with topographic gradients in agreement with previous suggestions that asia deforms as a continuum under the influence of gravity

present day kinematics at the india asia collision zone the collision of the indian subcontinent with asia drives the growth and evolution of the greater tibetan plateau region fault slip rates resulting from the relative motion between crustal blocks can provide a kinematic description of the distribution of presentday deformation i construct a three dimensional regional scale elastic block model of the india asia collision zone that is consistent with geodetic observations of interseismic deforma tion mapped fault system geometry historical seismicity and the mechanics of the earthquake cycle this mechanical model of the elastic upper crust yields a set of kinematically consistent fault slip rates and block motions that may serve to constrain dynamic models of continental crustal dynamics

plate convergence measured by gps across the sundaland philippine sea plate deformed boundary the philippines and eastern indonesia summary the western boundary of the philippine sea ph plate in the philippines and eastern indonesia corresponds to a wide deformation zone that includes the stretched continental margin of sundaland the philippine mobile belt pmb extending from luzon to the molucca sea and a mosaic of continental blocks around the ph australia sunda triple junction the gps geodyssea data are used to decipher the present kinematics of this complex area in the philippines the overall scheme is quite simple two opposing rotations on either side of the left lateral philippine fault clockwise to the southwest and counterclockwise to the northeast transfer 55 per cent of the ph sundaland convergence from the manila trench to the northwest to the philippine trench to the southeast further south 80 per cent of the ph sunda convergence is absorbed in the double subduction system of the molucca sea and less than 20 per cent along both continental margins of northern borneo finally within the triple junction area between the sundaland ph and australia plates from sulawesi to irian jaya preferential subduction of the celebes sea induces clockwise rotation of the sulu block which is escaping toward the diminishing celebes sea oceanic space from the eastwardadvancing ph plate to the south we identify an undeformed banda block that rotates counterclockwise with respect to australia and clockwise with respect to sundaland the kinematics of this block can be defined and enable us to compute the rates of southward subduction of the banda block within the flores trench and of eastward convergence of the makassar straits with the banda block the analysis made in this paper confirms that this deformation is compatible with the eastward motion of sundaland with respect to eurasia determined by the geodyssea programme but is not compatible with the assumption that sundaland belongs to eurasia as was often assumed prior to this study

opaque minerals in geothermal well no 7 krafla northern iceland abstract study of the opaque minerals from well no 7 krafla indicates two mineral assemblages 1 hydrothermally altered igneous minerals and 2 secondary minerals that have precipitated from the geothermal fluid at depths down to 2140 m and at temperatures up to more than 340 c chief amongst the chemically precipitated minerals are pyrite pyrrhotite and goethite which is described here for the first time in an icelandic geothermal drill hole the geothermal system at krafla has been periodically disturbed by the influx of volcanic emanations this article attempts to interpret by use of thermochemical calculations the processes affecting the precipitated mineral assemblage

review of the evolution of geochemical monitoring networks and methodologies applied to the volcanoes of the aeolian arc italy abstract fluids discharged from volcanic systems are the direct surface manifestation of magma degassing at depth and provide primary insights for evaluating the state of volcanic activity we review the geochemical best practice in volcanic surveillance based to a huge amount of monitoring data collected at different active volcanoes using both continuous and discontinuous approaches the targeted volcanoes belong to the aeolian arc located in the tyrrhenian sea italy and they have exhibited different activity states during the monitoring activities reported here la fossa cone on vulcano island has been in an uninterrupted quiescent stage characterized by variable solfataric activity in contrast stromboli island has shown a persistent mild explosive activity episodically interrupted by effusive eruptions in 1985 2002 2007 and 2014 panarea island which is the summit of a seamount rising from the seafloor of the southern tyrrhenian sea showed only undersea fluid release the only observable clues of active volcanism at panarea island have been impulsive changes in the undersea fluid release with the last submarine gas burst event being observed in november 2002 the geochemical monitoring and observations at each of these volcanoes has directly involved the volcanic plume and or the fumarole vents thermal waters and diffuse soil degassing depending on the type of manifestations and the level of activity encountered through direct access to the magmatic samples when possible and the collection of as much observable data related to the fluid release as possible the aim has been i to verify the thermodynamic equilibrium condition ii to discern among the possible hydrothermal magmatic marine and meteoric sources in the fluid mixtures iii to develop models of the fluid circulation supported by data iv to follow the evolution of these natural systems by long term monitoring and v to support surveillance actions related to defining the volcanic risk and the evaluation and possible mitigation of related hazards the examples provided in this review article show the close relationships among data analysis interpretation and modeling we particularly focus on describing the fieldwork procedures since any theoretical approach must always be verified and supported by field data rather than just by experiments controlled in laboratory indeed the natural systems involve many variables producing effects that cannot be neglected the monitored volcanic systems have been regarded as natural laboratories and all of the activities have focused on both volcanological research and surveillance purposes in order to ensure that these two goals have overlapped an appendix is also included that explains the scientific approach to the systematic activities regarding geochemical monitoring of volcanic activity

changes in heat released by hydrothermal circulation monitored during an eruptive cycle at mt etna italy the shallow vertical temperature profile has been measured in the proximity of an eruptive fissure far about 4 km north northeast from mt etna central craters the monitoring site was a steam heated soil lying between a group of flank fractures on the upper northeast flank of mt etna italy i e on the northeast rift we chose this area because it was close to an eruptive fissure that opened in 2002 and extended from about 2500 to about 1500 m a s l with our aim being to determine a connection between this fracture system and the ongoing volcanic activity heat flux anomalies from the ground from september 2009 to september 2012 were evaluated changes in the hydrothermal release which can be related to variations in volcanic activity are discussed and compared to the published geophysical data the heat flux ranges varied during the pre eruptive from about 7 to 38 w m 2 syn eruptive from about 3 to 49 w m 2 and post eruptive phases with the heat released being lowest at the latter phase from about 1 to 20 w m 2 moreover the heat flux time variation was strongly correlated with the eruption rate from the new southeast crater between january 2011 and april 2012 the migration of magma through active conduits acts as a changing heating source for steam heated soils located above the active fractures our findings suggest that tracking the heat flux above active fractures constitutes a useful investigation field for low cost thermal monitoring of volcanic activity time variations in their emissions could highlight the relationship between a hydrothermal circuit and the local network of fractures possibly indicating variation in the structural weakness of a volcanic edifice continuous monitoring of heat flux combined with a realistic model would contribute to multidisciplinary investigations aimed at evaluating changes in volcano dynamics

crust and upper mantle shear velocity structure beneath the tibetan plateau and surrounding regions from interevent surface wave phase velocity inversion average a priori shear velocity models are constructed for the tien shan tarim basin pamir hindu kush himalaya and ne india these models are shown to account for most of the lateral velocity heterogeneity at wavelengths 1000 km interevent fundamental mode rayleigh and love wave phase velocities were measured in the period range 32 200 s and were inverted for path averaged shear velocity structures these in turn were regionalized to estimate average isotropic structures beneath the six regions listed above low upper mantle velocities are observed beneath the western and eastern tien shan the tarim basin structure is poorly constrained but exhibits very low upper crustal velocities probably due to deep sedimentary accumulation and either very high upper mantle velocities exist 4 8 km s in a layer 70 km thick or the lithosphere is very thick 180 km low upper mantle velocities are observed beneath the chang thang region the central and the northeast plateau but not beneath the southern or southeastern plateau the crustal velocity gradient with depth is zero in the east central plateau consistent with lower crustal basaltic intrusions there but is positive to the west and southeast of this zone upper mantle structures show that the indian lithosphere could have subducted beneath the entire plateau only if either 1 mantle in the depth range 115 185 km has been altered or removed to reduce its average velocity or 2 the indian lithosphere is only 85 km thick

cluster analysis of soil co2 data from mt etna italy reveals volcanic influences on temporal and spatial patterns of degassing soil co2 concentration data were collected periodically from july 2001 to june 2005 from sampling site grids in two areas located on the lower flanks of mt etna volcano paterno and zafferana etnea santa venerina cluster analysis was performed on the acquired data in order to identify possible groups of sites where soil degassing could be fed by different sources in both areas three clusters were recognised whose average co2 concentration values throughout the whole study period remained significantly different from one another the clusters with the lowest co2 concentrations showed time averaged values ranging from 980 to 1 170 ppm vol whereas those with intermediate co2 concentrations showed time averaged values ranging from 1 400 to 2 320 ppm vol and those with the highest concentrations showed time averaged values between 1 960 and 55 430 ppm vol we attribute the lowest co2 concentrations largely to a biogenic source of co2 conversely the highest co2 concentrations are attributed to a magmatic source whereas the intermediate values are due to a variable mixing of the two sources described above the spatial distribution of the co2 values related to the magmatic source define a clear direction of anomalous degassing in the zafferana etnea santa venerina area which we attribute to the presence of a hidden fault whereas in the paterno area no such oriented anomalies were observed probably because of the lower permeability of local soil time series analysis shows that most of the variations observed in the soil co2 data from both areas were related to changes in the volcanic activity of mt etna seasonal influences were only observed in the time patterns of the clusters characterised by low co2 concentrations and no significant interdependence was found between soil co2 concentrations and meteorological parameters the largest observed temporal anomalies are interpreted as release of co2 from magma batches that migrated from deeper to shallower portions of etna s feeder system the pattern of occurrence of such episodes of anomalous gas release during the observation period was quite different between the two studied areas this pattern highlighted an evident change in the mechanism of magma transport and storage within the volcano s feeder system after june 2003 interpreted as magma accumulation into a shallow 8 km depth reservoir

a simplified spring block model of earthquakes the time interval between earthquakes is much larger than the actual time involved during slip in an individual event the authors have used this fact to construct a cellular automaton model of earthquakes this model describes the time evolution of a 2 d system of coupled masses and springs sliding on a frictional surface the model exhibits power law frequency size relations and can exhibit large earthquakes with the same scatter in the recurrence time observed for actual earthquakes

application of an inhomogeneous stress patch model to complex subduction zone earthquakes a discrete interaction matrix approach in recent years it has been recognized that the level of shear and normal stress along a fault can vary thus the stress is spatially and temporally inhomogeneous moreover it has also been suspected that faults might interact in some way with the result that a variety of earthquake magnitudes might be produced along a given length of fault at varying times in order to explore these ideas we have developed a quantitative formalism which we call the interaction matrix method to express the influence of one fault upon another this matrix is calculated by use of the energy change for a system of interacting cracks or faults and therefore gives energy consistent results specifically the interaction matrix relates the area averaged stress on the fault segment to the area averaged slip state on all the other fault segments in the system since any fault can be subdivided into an arbitrary number of fault segments the interaction matrix can have arbitrary dimension in fact the continuum limit is recovered as the dimension of the matrix approaches infinity we combine this matrix method with a segmentation or patch model for earthquakes in which each discrete segment of a fault has the same coseismic stress change defined as the difference between the driving stress at which healing occurs minus the driving stress at which sliding starts each time it slips we show that slip on a patch during an earthquake can vary substantially depending on how it interacts with other nearby patches in this model it is quite possible for the spatial distribution of stress on the fault following an event to be again in a spatially inhomogeneous state rather than in a uniform state as is often assumed hence the seismic moment produced by an earthquake on a given set of patches can vary substantially depending on the sequence of sliding and healing on the different patches to apply these ideas we devised a means to calculate the interaction matrix elements and used them to quantitatively examine earthquake sequences off the colombia ecuador coast and in the nankai trough near japan

earthquake failure sequences along a cellular fault zone in a three dimensional elastic solid containing asperity and nonasperity regions numerical simulations of earthquake failure sequences along a discrete cellular fault zone are performed for a three dimensional 3 d model representing approximately the central san andreas fault the model consists of an upper crust overlying a lower crust and mantle region together defining an elastic half space with a vertical half plane fault the fault contains a region where slip is calculated on a uniform grid of cells governed by a static kinetic friction law and regions where slip is prescribed so as to represent tectonic loading aseismic fault creep and adjacent great earthquakes the computational region models a 70 km long and 17 5 km deep section of the san andreas fault to the nw of the great 1857 rupture zone different distributions of stress drops on failing computational cells are used to model asperity parkfield asperity and nonasperity fault regions the model is inherently discrete and corresponds to a situation in which a characteristic size of geometric disorder within the fault i e cell size here a few hundreds of meters is much larger than the nucleation size of the order of tens of centimeters to tens of meters based on slip weakening or state evolution slip distances the computational grid is loaded by a constant plate motion imposed at the lower crust upper mantle and creeping fault regions and by a staircase slip history imposed at the 1857 and 1906 rupture zones stress transfer along and outside the fault due to the imposed loadings and failure episodes along the computational grid is calculated using 3 d elastic dislocation theory the resulting displacement field in the computational region is compatible with geodetic and seismological observations only when the asperity and nonasperity regions are characterized by significantly different average stress drops the frequency magnitude statistics of the simulated failure episodes are approximately self similar for small events with b 1 2 the b value of statistics based on rupture area ba is about 1 but are strongly enhanced with respect to self similarity for events larger than a critical size this is interpreted as a direct manifestation of our 3 d elastic stress transfer calculations beyond certain rupture area and potency seismic moment divided by rigidity release values the event is usually unstoppable and it continues to grow to a size limited by a characteristic model dimension this effect is not accounted for by cellular automata and block spring models in which the adopted simplified stress transfer laws fail to scale properly with increasing rupture size the simulations suggest that local maxima in observed frequency magnitude statistics correspond to dimensions of coherent brittle zones such as the width of the seismogenic layer or the length of a fault segment bounded by barriers the analysis indicates that a single cell size representing approximately a single scale of geometric disorder cannot induce self similarity in a 3 d elastic model over a broad range of magnitudes a representation of geometric disorder covering a range of scales may thus be required to generate a wide domain of self similar gutenberg richter statistics our simulations show a great diversity in the mode of failure of the parkfield asperity the earthquakes themselves define an irregular sequence of events the modeling like many other discrete fault models suggests that expectations for periodic parkfield earthquakes and or simple precursory patterns repeating from one event to the other are unrealistic

revel a model for recent plate velocities from space geodesy 1 we present a new global model for recent plate velocities revel describing the relative velocities of 19 plates and continental blocks the model is derived from publicly available space geodetic primarily gps data for the period 1993 2000 we include an independent and rigorous estimate for gps velocity uncertainties to assess plate rigidity and propagate these uncertainties to the velocity estimates the velocity fields for north america eurasia and antarctica clearly show the effects of glacial isostatic adjustment and australia appears to depart from rigid plate behavior in a manner consistent with the mapped intraplate stress field two thirds of tested plate pairs agree with the nuvel 1a geologic 3 myr average velocities within uncertainties three plate pairs caribbean north america caribbean south america and north america pacific exhibit significant differences between the geodetic and geologic model that may reflect systematic errors in nuvel 1a due to the use of seafloor magnetic rate data that do not reflect the full plate rate because of tectonic complexities most other differences probably reflect real velocity changes over the last few million years several plate pairs arabia eurasia arabia nubia eurasia india move more slowly than the 3 myr nuvel 1a average perhaps reflecting long term deceleration associated with continental collision several other plate pairs including nazca pacific nazca south america and nubia south america are experiencing slowing that began 25 ma the beginning of the current phase of andean crustal shortening

monitoring of fumarole discharge during the 1975 1982 rifting in krafla volcanic center north iceland abstract fumarole discharge chemistry in the krafla geothermal field changed regionally during the 1975 1982 rifting activity the discharge chemistry previously encountered in the krafla fumarole grounds was masked by a carbon dioxide rich gas during the first weeks of rifting the new discharge composition remained unchanged until 1983 when the first signs of recovery of the previous equilibrium composition appeared at the margins of the area the outgassing carbon dioxide is released from the deep aquifers beneath the area by the interaction of magmatic gas with the hydrothermal system in addition to juvenile magmatic carbon the outgassing contains carbon released from the hydrothermal systed upon reaction with acid magmatic gases increased boiling of the hydrothermal fumaroles was induced by the lowering of the partial pressure of steam due to increased gas content in the fumarole conduits at the center of rifting activity above the magma chamber the fumarole discharge was temporarily mixed with magmatic gases during local effusive activity hydrogen was the dominating magmatic gas in that discharge due to the preferred degassing of hydrogen from magma at shallow levels these hydrogen pulses increased in magnitude and duration towards the end of rifting in 1982 the discharge chemistry correlates with the expansion of the magma reservoir of the volcano regional change of long duration and local volcanism short lived change hydrogen pulses the chemical monitoring of fumaroles in krafla shows that the chemical surveillance of volcanos needs rapid methods for sampling and complete chemical analysis which can be interpreted in terms of reactions and magmatic processes

three dimensional velocity images of the crust and upper mantle beneath the north south zone in china we have determined the three dimensional p wave velocity structure beneath the north south tectonic belt between tibet and eastern china by simulta neously inverting local regional and teleseismic data our data set is composed of 45 028 p wave arrival times from 602 local and regional earthquakes and 985 travel times from 102 teleseismic events with the lsqr sparse linear equations and least squares algorithm the p wave velocity perturbations were estimated by the simul taneous inversion of hypocenters and medium parameters from the surface to a depth of 200 km we tested the stability and the resolution of our inverted results with a checkerboard test and found that the models are well resolved up to a depth of about 50 km for most parts of the studied region results show that the north south tectonic belt is characterized by a significant lateral heterogeneity in velocity both in the crust and in the upper mantle correlating these velocity images with the main tectonic features we find that 1 the shallow velocity distribution above 3 km is consistent with the topographic features and the basin distribution 2 the middle lower crustal velocities from 20 km to 50 km characterize a mechanically weak north south tec tonic belt because it bears a relatively lower velocity perturbation over a large re gion 3 the upper mantle velocities from 85 km to 120 km delineate the eastern tibetan boundary but changes in some subzones may reflect the effects of several tectonic events including paleorifting the cenozoic convergence between tibet and southeastern china and other tectonic episodes

fertilizing potential of volcanic ash in ocean surface water the fertilization potential of newly erupted and well preserved ash from the 2000 hekla eruption in iceland was measured for the first time by flow through experiments as previously shown 1 the north atlantic ocean including the subarctic seas surrounding iceland is the largest net sink of the world s oceans for atmospheric co 2 owing to biological drawdown during summer 2 almost complete consumption of phosphate in chlorophyll rich areas of the north atlantic ocean might limit primary production and 3 in the southern pacific ocean and parts of the equatorial pacific ocean iron might limit primary production we found through laboratory experiments that volcanic ash exposed to seawater initially releases large amounts of adsorbed phosphate 1 7 mmol g 21 h 21 iron 37 0 mmol g 21 h 21 silica 49 5 mmol g 21 h 21 and manganese 1 7 mmol g 21 h 21 dissolution of acid aerosols adsorbed to the surface of the ash caused the high initial release of major and trace elements because of the instantaneous dissolution of adsorbed components when newly erupted volcanic ash comes in contact with the ocean surface water macronutrients and bioactive trace metals are released fast enough to become available to support primary production

block model of earthquake sequence abstract a model of interaction of lithospheric blocks is suggested dynamics of the lithosphere is described as an alternation of slow deformations and ruptures earthquakes the model is used to produce an artificial catalog of seismicity and the properties of this catalog are compared with and contrasted to the properties of real seismicity catalogs by this means it is possible to determine which properties of earthquake sequences can be derived from simple assumptions about the processes that occur in the lithosphere we consider both the instability of the process and possibility that large earthquakes might be predicted

contemporary crustal deformation around the southeast borderland of the tibetan plateau 1 we derive a detailed horizontal velocity field for the southeast borderland of the tibetan plateau using gps data collected from the crustal motion observation network of china between 1998 and 2004 our results reveal a complex deformation field that indicates that the crust is fragmented into tectonic blocks of various sizes separated by strike slip and transtensional faults most notably the regional deformation includes 10 11 mm yr left slip across the xianshuihe fault 7 mm yr left slip across the anninghe zemuhe xiaojiang fault zone 2 mm yr right slip across a shear zone trending northwest near the southern segment of the lancang river fault and 3 mm yr left slip across the lijiang fault deformation along the southern segment of the red river fault appears not significant at present time the region south and west of the xianshuihexiaojiang fault system whose eastward motion is resisted by the stable south china block to the east turns from eastward to southward motion with respect to south china resulting in clockwise rotation of its internal subblocks active deformation is detected across two previously unknown deformation zones one is located 150 km northwest of and in parallel with the longmenshan fault with 4 6 mm yr right slip and another is continued south southwestward from the xiaojiang fault abutting the red river fault with 7 mm yr left slip while both of these zones are seismically active the exact locations of faults responsible for such deformation are yet to be mapped by field geology comparing our gps results with predictions of various models proposed for tibetan plateau deformation we find that the relatively small sizes of the inferred microblocks and their rotation pattern lend support to a model with a mechanically weak lower crust experiencing distributed deformation underlying a stronger highly fragmented upper crust

morphology displacement and slip rates along the north anatolian fault turkey 1 geological and geomorphological offsets at different scales are used to constrain the localization of deformation total displacement and slip rates over various timescales along the central and eastern north anatolian fault naf in turkey the naf total displacement is reevaluated using large rivers valleys 80 15 km and structural markers pontide suture 85 25 km tosya vezirkopru basins 80 10 km these suggest a neogene slip rate of 6 5 mm yr over 13 myr the river network morphology shows offsets at a range of scales 20 m to 14 km across the main fault trace and is also used to estimate the degree to which deformation is localized at a smaller scale the morphology associated with small rivers is offset by 200 m along the naf the age of these features can be correlated with the holocene deglaciation and a slip rate of 18 3 5 mm yr is determined this is consistent with a rate of 18 5 mm yr deduced independently from the 14c dating of stream terrace offsets over the short term gps data gives a similar rate of 22 3 mm yr all our results tend to show that most of the deformation between the anatolian and eurasian lithospheric plates has been accommodated along or very close to the active trace of the naf the difference between the neogene and the holocene slip rate may be due to the recent establishment of the current plate geometry after the creation of the naf

continuous monitoring of distal gas emanations at vulcano southern italy the increasing activity of vulcano island italy since 1985 led to the initiation of continuous geochemical monitoring of the lateral soil gas emissions on the basis both of their relative geochemical characteristics and of local considerations three gaseous components were selected for monitoring namely co2 he and 222rn monitoring has been performed by means of specific analysers gases extracted from a water well located at the foot of the active cone were selected for monitoring on the basis of their geochemical and isotopic characters that indicate their genetic link with central high temperature fumarolic gases emitted at the crater very strong variations of gas composition can be observed within one day from 1 to about 94 for co2 some variations display a daily character and can be correlated with that of atmospheric pressure the three monitored gases are highly correlated suggesting very high kinetics of gas transfer in the system because of these considerable variations of chemical composition bulk concentrations obviously are not suitable for monitoring at vulcano however the evolution with time of ratios such as 222rn co2 and he co2 the latter being corrected for atmospheric contamination supplies numerical parameters that the expected to characterize the intensity of the degassing process a new input of magmatic gases that would lead to an increase in the 222rn co2 and he co2 ratios should therefore be detected by such a monitoring station

geodetic evidence for a low slip rate in the altyn tagh fault system the collision between india and asia has been simulated with a variety of computational models that describe or predict the motions of the main faults of east asia geological slip rate estimates of 20 30 mm yr 1 suggest that the largest of these faults the 2 000 km long altyn tagh fault system on the northern edge of the tibetan plateau absorbs as much of the indo asian convergence signal as do the himalayas partly by oblique slip and partly by contraction and mountain growth however the predictions of dynamic models for asian deformation and the lower bounds of some geological slip rates estimates 3 9 mm yr 1 refs 7 8 suggest that the altyn tagh system is less active here we report geodetic data from 89 91 degrees e that indicate left lateral shear of 9 5 mm yr 1 and contraction of 3 1 mm yr 1 across the altyn tagh system this result combined with our finding that at 90 degrees e tibet contracts north south at 9 1 mm yr 1 supports the predictions of dynamic models of asian deformation

experimental monitoring of carbon dioxide by low power ir sensors soil degassing in the furnas volcanic centre azores abstract in october 1993 two experimental carbon dioxide sensors were installed at the furnas volcanic centre sao miguel the monitoring sites are tilt meter stations in furnas village and at castelo branco on the sw caldera rim the selection of these observation sites is meant to record changes in carbon dioxide outgassing close to an active fumarole ground furnas village 3 m deep well and at an outer caldera wall castelo branco 6 m deep well where geothermal processes are definitely absent recording of carbon dioxide was made for one year by hourly readings from october 1993 to october 1994 the experiment revealed carbon dioxide pulses characterised by short rise times hours and fading on the time scale of days interpretation of the data in relation to meteorological conditions is preliminary and suggestive an overall covariation of carbon dioxide outgassing and changes in atmospheric pressure and or precipitation is observed at the calderas fumarole grounds of the furnas village a favoured degassing mechanism is based on increased out diffusion of carbon dioxide from the soil layer at the onset of low pressure intervals due to increased boiling and carbon dioxide release from the shallow local hydrothermal aquifers increased soil degassing after heavy rain is attributed to closure of the porous surface layer resulting in an increased partial pressure of carbon dioxide at the base of the instrument well at the castelo branco station which is located on a narrow ridge some 20 m above the surroundings the opposite effect of barometric pressure is observed on the very low carbon dioxide flux this still unexplained covariation may be related to chemical conditions within the soil during high pressure dry soil and low pressure wet soil periods after every impulsive increase in carbon dioxide flux the normal baseline is slowly reached a periodic effect on soil degassing to a first approximation of tidal origin cannot be excluded at castelo branco it is concluded that the experimental sensors are adequate for detailed long standing evaluation of monitoring sites which needed prior to permanent monitoring of soil degassing

soil and fumarole gases of mount etna geochemistry and relations with volcanic activity abstract between 1993 and 1996 gas samples were collected on mt etna volcano from both high and low temperature fumaroles and from soils in areas of anomalous degassing located on the flanks of the volcanic edifice the chemical composition of all the emitted gases is consistent with their magmatic origin during their transport to the surface they would undergo shallow mixing processes mostly with air locally as in the case of a point in the lower southwestern flank of the volcano p39 very high contents of he and ch4 indicate that deep gases mainly interact with ground waters and also with a hydrocarbon reservoir the isotopic composition of carbon in co2 from these gases also suggests its primary magmatic origin with inferred 13 c values of magmatic co2 in the range 2 to 1 vs pdb such values significantly more positive than those measured in morbs are in the typical range measured at the other mediterranean volcanoes 5 to 0 more negative values can be explained by shallow interactions between magmatic and organic co2 and or between the former and cold t 120 c ground waters both chemical and isotopic gas geothermometers agree in indicating calculated temperatures ranging from 180 to 270 c for the soil gases collected from low temperature fumaroles near the summit and temperatures around 150 c for the cold gases from p39 thus confirming the presence of a hydrothermal aquifer beneath this point a chemical geothermometer applied on the gases collected from the high temperature fumaroles near the summit craters shows equilibrium temperatures ranging from 385 to 690 c lastly many of the studied parameters showed anomalous variations in time during the studied period the most important of these concerned the flux of co2 through the soil and the concentration of soil h2 which were closely correlated with strong increases in the volcanic activity of etna

patterns of seismic activity preceding large earthquakes we analyze the patterns of seismic activity which precede large events in a mechanical model of a fault the model generates a statistical distribution of events similar to that observed for a single fault with a scaling region consistent with the gutenberg richter law at small and moderate magnitudes and an excess of events at large magnitudes we find only slight variation in the scaling behavior during a loading cycle however we do observe systematic variations in space and time of the overall rate of activity in the model the activity accelerates dramatically preceding a large event and is usually a maximum hi the neighborhood of the future epicenter these results are compared to california seismicity data where we find that activity patterns vary regionally looking at patterns of activity in the san francisco bay area since 1948 we find an increase of activity on the calaveras fault near san jose beginning in the 1980s which if our model is relevant would forecast a large earthquake in that region the 1989 loma prieta earthquake occurred on the san andreas fault within 30 km of the section of the calaveras fault showing increased activity

chemistry of gases associated with geothermal activity and volcanism in iceland a review the concentrations of co2 h2s and h2 in geothermal reservoir fluids in iceland are fixed by equilibria with alteration minerals ch4 concentrations are typically very low and gas gas equilibria involving co2 h2 and ch4 are generally not closely approached in some geothermal systems the n2 is atmospheric only but a magmatic n2 contribution is significant in others n2 ar ratios lie mostly between that of the atmosphere 85 and the n2 ar ratio in cold water in contact with the atmosphere 37 fluids with a strong magmatic n2 contribution have n2 ar ratios of 40 60 during several volcanic eruptions in iceland magmatic gases have emerged at the surface beyond the eruptive vents and mixed with surrounding groundwaters co and h2 can be detected closest to the vent but only co2 is detected at greater distances during the present volcanic episode at krafla fugitive constituents have been transported into the geothermal reservoir from the underlying magma chamber probably most of the carbon and sulphur in altered rocks of high temperature geothermal systems have been derived from degassing magma bodies

equivalent strike slip earthquake cycles in half space and lithosphere asthenosphere earth models by virtue of the images used in the dislocation solution the deformation at the free surface produced throughout the earthquake cycle by slippage on a long strike slip fault in an earth model consisting of an elastic plate lithosphere overlying a viscoelastic half space asthenosphere can be duplicated by prescribed slip on a vertical fault embedded in an elastic half space for the case in which each earthquake ruptures the entire lithosphere thickness h the half space equivalent slip rate is as follows depth interval 0 h slip identical to that in lithosphere asthenosphere model i e abrupt coseismic slip and no subsequent slip depth interval 2n 1 h to 2n 1 h n 1 2 slip rate uniform in space and dependent upon time as fn t exp t a where fn is a n 1 degree polynomial in t a is twice the asthenosphere relaxation time and t is measured from the instant after the preceding earthquake the slip rate averaged over the seismic cycle in each depth interval equals the secular rate of relative plate motion for reasonable values of a slip rates below 5h do not vary much from that mean value and can be treated as constant thus the surface deformation due to the earthquake cycle in the lithosphere asthenosphere model can be calculated very simply from the half space model with time dependent slip in the two depth intervals h 3h and 3h 5h and uniform slip at a rate equal to the secular relative plate velocity below depth 5h inversion of 1973 1988 geodetic measurements of deformation across the segment of the san andreas fault in the transverse ranges north of los angeles for the half space equivalent slip distribution suggests no significant slip on the fault above 30 km and a uniform slip rate of 36 mm yr below 30 km one equivalent lithosphere asthenosphere model would have a 30 km thick lithosphere and an asthenosphere relaxation time greater than 33 years but other models are possible

continuous monitoring of hydrogen and carbon dioxide at mt etna article i nfo this study assessed the use of an h2 fuel cell as an h2 selective sensor for volcano monitoring the resolution repeatability and cross sensitivity of the sensor were investigated and evaluated under known laboratory conditions a tailor made device was developed and used for continuously monitoring h2 and co2 at mt etna throughout 2009 and 2010 the temporal variations of both parameters were strongly correlated with the evolution of the volcanic activity during the monitoring period in particular the co2 flux exhibited long term variations while h2 exhibited pulses immediately before the explosive activity that occurred at mt etna during 2010

kinematic modelling of neotectonics in the persia tibet burma orogen summary we apply a new kinematic modelling technique program neokinema to estimate neotectonic flow in the persia tibet burma orogen the models fit geodetic benchmark velocities geological fault slip rates and stress directions seismic moment tensor orientations using a weightedleast squares method models predict long term velocities anelastic strain rates and preferred fault slip rates averaged over timescales of 10 4 10 6 yr while we find a few regions of low anelastic strain rate the mean continuum strain rate in the preferred model is 2 2 10 16 s 1 0 7 per cent ma 1 so the india eurasia collision should not be modelled as an interaction between rigid microplates for most faults preferred fault slip rates agree with geological slip rates within their uncertainty bounds this suggests that deformation imaged by geodesy over tens of years is consistent with deformation over 10 4 10 6 yr given appropriate elastic corrections we also calculate maps of long term average seismicity rate based on model fault slip rates and anelastic strain rates in the continuum using the seismicity parameters of most comparable type of plate boundary the pattern is generally in agreement with actual m 5 67 earthquakes in the cmt catalogue 1977 2002 except that the himalayan front high zagros and altyn tagh zones have been quieter than predicted the spatial integral of our forecast over the orogen is 371 m 5 67 earthquakes 25 75 yr versus 238 which actually occurred if this discrepancy has high significance it means that some step s in our forecast method are faulty such as the assumption of equal coupled seismogenic thickness in all continental convergent boundaries if it is only an artefact of stochastic time dependence then this may have occurred in the orogen in the external calibration region or in both independent evidence suggests that large earthquakes with many aftershocks will occur along the himalayan front in the future possibly reducing this discrepancy

paleoseismic evidence of great surface rupture earthquakes along the indian himalaya 1 toward understanding the relationship between strain accumulation and strain release in the context of the mechanics of the earthquake and mountain building process and quantifying the seismic hazard associated with the globes largest continental thrust system we describe the late quaternary expression and paleoseismic evidence for great surface rupture earthquakes at six sites along the himalayan frontal thrust hft system of india our observations span a distance of 250 km along strike of the hft uplifted and truncated fluvial terrace deposits resulting from the holocene displacements on the hft are preserved along canyons of the ghaggar markanda shajahanpur and kosi rivers dividing the elevation of the bedrock straths at each site by their ages yields estimates of the vertical uplift rate of 4 6 mm yr which when assumed to be the result of slip on an underlying thrust dipping at 20 45 are equivalent to fault slip rates of 6 18 mm yr or shortening rates of 4 16 mm yr trench exposures reveal the hft to fold and break late holocene surface sediments near the cities and villages of chandigarh kala amb rampur ganda lal dhang and ramnagar radiocarbon ages of samples obtained from the displaced sediments indicate surface rupture at each site took place after a d 1200 and before a d 1700 uncertainties attendant to the radiocarbon dating currently do not allow an unambiguous definition of the capping bound on the age of the displacement at each site and hence whether or not the displacements at all sites were contemporaneous trench exposures and vertical separations measured across scarps at rampur ganda lal dhang and ramnagar are interpreted to indicate single event displacements of 11 38 m dividing the observed single event vertical components of displacement by the estimated longer term uplift rates indicates 1330 3250 or more years should be required to accumulate the slip sufficient to produce similar sized displacements surface rupture appears to not have occurred during the historical 1905 kangra mw 7 7 1934 bihar nepal mw 8 1 and 1950 assam mw 8 4 earthquakes which also occurred along the himalayan front yet we observe clear evidence of fault scarps and displacements in young alluvium and progressive and continued offset of fluvial terrace deposits along the hft we suggest on this basis and the size and possible synchroneity of displacements recorded in the trenches that there exists the potential for earthquakes larger than recorded in the historical record and with the potential to rupture lengths of the hft greater than the 250 km we have studied

deformation kinematics in the western united states determined from quaternary fault slip rates and recent geodetic data we estimate the horizontal velocity gradient tensor field from quaternary fault slip rates and recent global positioning system gps and very long baseline interferometry vlbi velocity solutions in the western united states transform plate boundary zone the total velocity obtained from the quaternary fault slip rate data across the entire plate boundary is within 1 mm yr of the nuvel 1a predicted pacific pa north american na plate motion velocity but directions are 5 6 anticlockwise of directions given by nuvel 1a the total velocity obtained from inversion of recent geodetic data is 2 3 anticlockwise from the nuvel 1a na pa velocity but the difference between the two is not significant at the 95 confidence level the discrepancy between the total pa na motion obtained from the geological data and nuvel 1a indicates that a marginally significant amount of ne sw shortening possibly as much as 5 mm yr is missing overall in the geologic data shortening may occur in the long term in the offshore and coastal areas of california where such shortening is required in the shorter term geodetic solution the seismic moment released in the last 148 years is 59 of the total moment release rate expected from long term strain rate field including both seismic and aseismic deformation derived from the inversion of geological data with nuvel 1a far field pa na motion constraints the accumulated strain in the areas containing the southern san andreas fault san jacinto fault the san francisco bay area and the area containing the ventura basin in the western transverse ranges in the last 148 years is the equivalent to that which could be released by an mw 7 0 earthquake in each 50 100 15 km3 crustal volume if strain is to be released seismically in these areas

late cenozoic right lateral strike slip faulting in southern tibet field observations collected during the sino french himalaya tibet cooperation project 1980 1982 show that right lateral faulting between southern and northern tibet roughly along the chord joining the eastern and western syntaxes of the himalayan arc is a major component of the active tectonics north of the himalayas just north of the well developed rifts of southern tibet we studied three right lateral 100 200 km long strike slip faults forming an en echelon array along that chord evidence for earthquake surface breaks was found on each of these faults for the m 8 beng co or damxung strike slip earthquake of november 18 1951 rupture parameters could be constrained to be 8 2 m and l 90 km offset glacial and postglacial morphological markers 105 years and 104 years b p imply displacement rates of the order of 1 2 cm yr on the three faults the en echelon fault zone appears to extend westward 2000 km across the plateau to the karakorum fault and is thus referred to as the karakorum jiali fault zone kjfz fast rates of slip on it and on faults along the northern rim of tibet appear to contrast with the slower rates of deformations in the interior of the plateau our estimates of slip rates on the strike slip and normal faults of southeastern tibet suggest that eastward extrusion of north tibet between the right lateral kjfz and the left lateral altyn tagh and kun lun faults absorbs at least 30 of the present convergence between india and asia we propose an instantaneous velocity model of the active tectonics of asia compatible with such faulting rates and geometries evidence for tertiary right lateral strike slip movements in southern tibet and around the eastern syntaxis of the himalayas is also found in the structural record offsets of various large scale geological features imply that these movements have been large

stable isotopic aspects of fluid flow in the krafla namafjall and theistareykir geothermal systems of northeast iceland abstract water and steam condensates from the krafla namafjall and theistareykir geothermal systems have been studied using hydrogen and oxygen stable isotope ratios to gain more information on thermal fluid flow the effect of rifting on individual fields and the provenance of recharge to these fields at krafla there are minor differences between individual wellfields but recharge is essentially local only one well shows signs of a change in composition over a 6 year production period but a local volcanic eruption in 1984 affected fumarole steam compositions the nearby namafjall field has isotopic compositions suggesting that recharge is ultimately derived from a long distance to the south perhaps by a combination of surface and groundwater flow some local spring and shallow well compositions have been affected by the post 1975 rifting episode the undrilled theistareykir field has an inflow estimated to be of similar isotopic composition to namafjall some fumaroles have an anomalously depleted 18o composition and rayleigh condensation is postulated to explain them

the chemical composition of rivers and snow affected by the 2014 2015 barðarbunga eruption iceland abstract the 2014 15 bar arbunga volcanic eruption was the largest in iceland for more than 200 years this eruption released into the atmosphere on average 60 000 tonnes day of so2 30 000 tonnes day of co2 and 500 tonnes day of hcl affecting the chemical composition of rain snow and surface water the interaction of these volcanic gases with natural waters decreases fluid ph and accelerates rock dissolution this leads to the enhanced release of elements including toxic metals such as aluminium to these waters river monitoring including spot and continuous osmotic sampling shows that although the water conductivity was relatively stable during the volcanic unrest the dissolution of volcanic gases increased the so4 f and cl concentrations of local surface waters by up to two orders of magnitude decreasing the carbon alkalinity in addition the concentration of sio2 ca mg na and trace metals rose considerably due to the water molten lava and hot solid lava interaction the presence of pristine lava and acidic gases increased the average chemical denudation rate calculated based on na flux within jokulsa a fjollum catchment by a factor of two compared to the background flux melted snow samples collected at the eruption site were characterised by a strong dependence of the ph on so4 f and cl and metal concentrations indicating that volcanic gases and aerosols acidified the snow protons balanced about half of the negatively charged anions the rest was balanced by water soluble salts and aerosols containing a variety of metals including al fe na ca and mg the concentrations of f al fe mn cd cu and pb in the snowmelt water surpassed drinking and surface water standards snowmelt river water mixing calculations indicate that low alkalinity surface waters such as numerous salmon rivers in east iceland will be more affected by polluted snowmelt waters than high alkalinity spring and glacier fed rivers

effects of volcanic eruptions on the co2 content of the atmosphere and the oceans the 1996 eruption and flood within the vatnajokull glacier iceland abstract the october 1996 eruption within the vatnajokull glacier iceland provides a unique opportunity to study the net effect of volcanic eruptions on atmospheric and oceanic co2 volatile elements dissolved in the meltwater that enclosed the eruption site were eventually discharged into the ocean in a dramatic flood 35 days after the beginning of the eruption enabling measurement of 50 dissolved element fluxes the minimum concentration of exsolved co2 in the 1 1012 kg of erupted magma was 516 mg kg s was 98 mg kg cl was 14 mg kg and f was 2 mg kg the ph of the meltwater at the eruption site ranged from about 3 to 8 volatile and dissolved element release to the meltwater in less than 35 days amounted to more than one million tonnes equal to 0 1 of the mass of erupted magma the total dissolved solid concentration in the floodwater was close to 500 mg kg ph ranged from 6 88 to 7 95 and suspended solid concentration ranged from 1 to 10 according to h o c and s isotopes most of the water was meteoric whereas the c and s were of magmatic origin both c and s went through isotopic fractionation due to precipitation at the eruption site creating short cuts in their global cycles the dissolved fluxes of c ca na si s and mg were greatest ranging from 1 4 1010 to 1 4 109 mol the dissolved c flux equaled 0 6 million tonnes of co2 the heavy metals ni mn cu pb and zn were relatively mobile during condensation and water rock interactions at the eruption site about half of the measured total carbon flood flux from the 1996 vatnajokull eruption will be added to the long term co2 budget of the oceans and the atmosphere the other half will eventually precipitate with the ca and mg released thus for eruptions on the ocean floor one can expect a net long term c release to the ocean of less than half that of the exsolved gas this is a considerably higher net c release than suggested for the oceanic crust by staudigel et al geochim cosmochim acta 53 1989 3091 in fact they suggested a net loss of c therefore magma degassed at the ocean floor contributes more c to the oceans and the atmosphere than magma degassed deep in the oceanic crust the results of this study show that subglacial eruptions affecting the surface layer of the ocean where either mn fe si or cu are rate determining for the growth of oceanic biomass have a potential for a transient net co2 removal from the ocean and the atmosphere for eruptions at high latitudes timing is crucial for the effect of oceanic biota eruptions occurring in the wintertime when light is rate determining for the growth of biota have much less potential for bringing about a transient net negative co2 flux from the ocean atmosphere reservoir

global positioning system constraints on plate kinematics and dynamics in the eastern mediterranean and caucasus we present and interpret global positioning system gps measurements of crustal motions for the period 1988 1997 at 189 sites extending east west from the caucasus mountains to the adriatic sea and north south from the southern edge of the eurasian plate to the northern edge of the african plate sites on the northern arabian platform move 18 2 mm yr at n25 5 w relative to eurasia less than the nuvel 1a circuit closure rate 25 1 mm yr at n21 7 w preliminary motion estimates 1994 1997 for stations located in egypt on the northeastern part of africa show northward motion at 5 6 2 mm yr also slower than nuvel ia estimates 10 1 mm yr at n2 4 e eastern turkey is characterized by distributed deformation while central turkey is characterized by coherent plate motion internal deformation of 2 mm yr involving westward displacement and counterclockwise rotation of the anatolian plate the anatolian plate is de coupled from eurasia along the right lateral strike slip north anatolian fault naf we derive a best fitting euler vector for anatolia eurasia motion of 30 7 0 8 n 32 6 0 4 e 1 2 0 1 myr the euler vector gives an upper bound for naf slip rate of 24 1 mm yr we determine a preliminary gps arabia anatolia euler vector of 32 9 1 2 n 40 3 1 1 e 0 8 0 2 myr and an upper bound on left lateral slip on the east anatolian fault eaf of 9 1 mm yr the central and southern aegean is characterized by coherent motion internal deformation of 2 mm yr toward the sw at 30 1 mm yr relative to eurasia stations in the se aegean deviate significantly from the overall motion of the southern aegean showing increasing velocities toward the trench and reaching 10 1 mm yr relative to the southern aegean as a whole

insar observations of low slip rates on the major faults of western tibet two contrasting views of the active deformation of asia dominate the debate about how continents deform i the deformation is primarily localized on major faults separating crustal blocks or ii deformation is distributed throughout the continental lithosphere in the first model western tibet is being extruded eastward between the major faults bounding the region surface displacement measurements across the western tibetan plateau using satellite radar interferometry insar indicate that slip rates on the karakoram and altyn tagh faults are lower than would be expected for the extrusion model and suggest a significant amount of internal deformation in tibet