self driven mode switching of earthquake activity on a fault system theoretical results based on two different modeling approaches indicate that the seismic response of a fault system to steady tectonic loading can exhibit persisting fluctuations in the form of self driven switching of the response back and forth between two distinct modes of activity the first mode is associated with clusters of intense seismic activity including the largest possible earthquakes in the system and frequency size event statistics compatible with the characteristic earthquake distribution the second mode is characterized by relatively low moment release consisting only of small and intermediate size earthquakes and frequency size event statistics following a truncated power law the average duration of each activity mode scales with the time interval of a large earthquake cycle in the system the results are compatible with various long geologic paleoseismic and historical records the mode switching phenomenon may also exist in responses of other systems with many degrees of freedom and nonlinear dynamics 1999 elsevier science b v all rights reserved

extension of continental crust by anelastic deformation during the 2011 tohoku oki earthquake the role of extensional faulting in the generation of a great tsunami abstract observations of seafloor morphologies and environments made before and after the 2011 tohoku oki earthquake reveal open fissures generated during the earthquake where the fault trace is interpreted on seismic profiles to intersect the seafloor anomalously high heat flow was observed at a landward dipping normal fault in august 2011 five months after the earthquake but by august 2012 heat flow measured at the same station had decreased to close to the background value which suggests that the normal fault ruptured during the 2011 earthquake these seafloor observations and measurements demonstrate deformation that was both extensional and anelastic within the overriding continental plate during the 2011 earthquake seismic profiles as well as seafloor bathymetry data in the tsunami source area further demonstrate that landward dipping normal faults extensional faults collapse the continental framework and detach the seaward frontal crust from the landward crust at far landward from the trench the extensional and anelastic deformation i e normal faulting observed in both seafloor observations and seismic profiles allows the smooth seaward movement of the continental crust seaward extension of the continental crust close to the trench axis in response to normal faulting is a characteristic structure of tsunami source areas as similar landward dipping normal faults have been observed at other convergent plate margins where tsunamigenic earthquakes have occurred we propose that the existence of a normal fault that moves the continental crust close to the trench can be considered one indicator of a source area for a huge tsunami

geothermal evidence for fluid flow through the gas hydrate stability field off central chile transient flow related to large subduction zone earthquakes fluids are suspected to play a major role in the nucleation and rupture propagation of earthquakes in chile seismological data were previously interpreted to indicate that fluids captured in the fault zone are released periodically during large underthrust earthquakes leading to post seismic fluid flow in central chile heat flow derived from the presence of a bottom simulating reflector bsr show a smooth trend across the margin bsr derived data are in excellent agreement with thermal subduction zone models over the young accretionary prism both bsr derived and measured surface heat flow support a common trend landwards of the backstop however measured heat flow triples over a distance of 20 30 km producing a profound discrepancy to the bsr derived data we suggest that this disparity is related to transient flow of warm fluids through the gas hydrate stability zone possibly caused by fluids released after large underthrust earthquakes such flow events may inherently affect the distribution of solid gas hydrates between the seafloor and the bsr

reflection seismic images and amplitude ratio modelling of the chilean subduction zone at 38 25 s abstract active source near vertical reflection nvr data from the interdisciplinary project tipteq were used to image and identify structural and petrophysical properties within the chilean subduction zone at 38 25 s where in 1960 the largest earthquake ever recorded mw 9 5 occurred reflection seismic images of the subduction zone were obtained using the post stack depth migration technique to process the three components of the nvr data allowing to present p and s stacked time sections and depth migrated seismic reflection images next the reflectivity method allowed to model traveltimes and amplitude ratios of pairs of reflections for two 1d profiles along the studied transect the 1d seismic velocities that produced the synthetic seismograms with amplitudes and traveltimes that fit the observed ones were used to infer the rock composition of the different layers in each 1d profile finally an image of the subduction zone is given the chilean subduction zone at 38 25 s underlies a continental crust with highly reflective horizontal as well as dipping events among them the lanalhue fault zone lfz interpreted to be east dipping is imaged to very shallow depths for the first time in terms of seismic velocities the inferred composition of the continental crust is in agreement with field geology observations at the surface along the profile furthermore no measurable amounts of fluids above the plate interface in the continental crust in this part of the chilean subduction zone are necessary to explain the results a large scale anisotropy in the continental crust and upper mantle is qualitatively proposed however quantitative studies on this topic in the continental crust of the chilean subduction zone at 38 25 s do not exist to date

exploring the relationship between soil degassing and seismic activity by continuous radon monitoring in the longitudinal valley of eastern taiwan abstract donghua dh continuous soil gas monitoring station is located on the suture zone in eastern taiwan the variations in radon concentration are synchronized to variations in carbon dioxide co 2 which is considered as the companion gas for radon rn results reveal that semi diurnal variation of soil gas probably generated by the solar tide effect achieve values of 500 bq m 3 for rn and 0 4 for co 2 the variations exceeding the threshold by statistical analysis can be used to identify events associated with geodynamic processes such as earthquakes a significant increase in soil gas concentrations was recorded 2 months before the rueisuei earthquake m l 6 4 october 31 2013 and recurrent anomalies were observed 3 weeks before the fanglin earthquake m l 5 9 may 21 2014 both earthquakes occurred in the longitudinal valley area of eastern taiwan this study suggests that longer periods of soil gas anomalies are positively correlated with impending earthquake of larger magnitude from the high precision gps data showed an appreciable decrease in extension rate was also observed approximately 4 months before the rueisuei earthquake it is worthy to have a continuous monitoring on multiple parameters soil radon carbon dioxide atmospheric pressure humidity temperature and precipitation at dh station

helium isotopes in dead sea transform waters abstract the concentrations and isotopic compositions of helium and relative abundances of co2 were studied in brines and freshwater springs groundwater wells and gas bubbles in and around the dead sea transform dst fault system the latter forms part of the plate boundary between the african and arabian plates along which intensive tectonic and volcanic activity occurred and where a range of freshwater to hypersaline water bodies percolate the atmosphere normalized 3he 4he ratios r ra show a distinct geographic gradient whereby fluids in the north part of the dst near lake kinneret are characterized by r ra 2 these values decrease gradually southward until the arava valley where they are approximately 0 15 reflecting a corresponding decrease in the mantle derived he fraction from about 30 in the north to a few percent in the south freshwater springs outside the dst in the galilee and judea mountains are characterized by r ra ratios close to unity reflecting the dominance of atmosphere derived helium although they still contain a few percent of a mantle component the spatial pattern of change in r ra ratios is independent of regional tectonic activity rifting which is similar around the lake kinneret basin and the dead sea and a correlation does not exist between such activity and he concentrations and co2 3he ratios in contrast helium concentrations and to a lesser extent co2 he ratios correlate with temperatures of the sampled fluids reflecting a dilution process of a deep hot mantle component as it percolates upwards toward the surface the preferential injection of a mantle he toward the surface in the north dst is facilitated by deep faults and a shallower moho boundary which are also associated with enhanced volcanism in the north dst and is superimposed over a regionally scaled mantle background value regionally the observations reflect a transition from a domination of a dilute mantle end member in the north which itself is the product of a mixture between mantle and crustal helium to a dominant crustal radiogenic end member in the south the r ra ratio in basaltic olivines and diopside from the golan is on average 6 6 0 7 lower than typical mantle values 8 but corresponding to comparable sub continental mantle compositions

episodic development of a convergent margin inferred from structures and processes along the southern chile margin seismic reflection data acquired in the vicinity of isla mocha across the southern coast of chile image structures formed along the continental margin and reveal an episodic history of accretion nonaccretion and possibly erosion structures formed at the toe of the continental slope suggest frontal accretion of to 1 km of trench fill seismic images also reveal that a small accretionary wedge 20 30 km wide abuts the truncated continental metamorphic basement that extends seaward from beneath the shelf the small size of the accretionary wedge on three profiles examined here is not consistent with a long history of accretion with the current deformational style as current rates of frontal accretion could have accumulated all of the existing accretionary wedge in less than 1 2 m y this is a small fraction of convergence history along this margin and the current accretionary mode has not been consistently maintained in the past the isla mocha region is located between the temperate climate of central chile and the glacial climate of southern chile and climatic conditions in this region have likely fluctuated sufficiently to cause significant variation in trench sediment supply accretionary and nonaccretionary or erosional episodes are probably linked to temporal variations in trench sediment thickness as suggested by observations along the chile margin currently thick trench sediment correlates with accretion along the southern chile margin and thin trench sediment correlates with nonaccretion tectonic erosion as near the chile ridge and from the juan fernandez ridge to northern chile the isla mocha region also lies 900 1000 km north of the chile triple junction and the chile ridge lies approximately 2000 km to the west and has not yet collided and affected the margin near isla mocha this part of the precollision zone provides an excellent reference to examine the effects of chile ridge collision in the development of the chile margin the most apparent effect of subduction of the buoyant young crust of the chile ridge is a shallow trench that is nearly devoid of sediment consequently the triple junction is undergoing nonaccretion or erosion and the accretionary complex near the triple junction remains smaller than to the north or south because the current phase of rapid accretion elsewhere in the trench has bypassed the triple junction region the interplay of subduction zone processes such as trench sedimentation and ridge collision has resulted in an episodic development of the margin and produced a discontinuous record of convergence history within the accretionary wedge

fluid accumulation along the costa rica subduction thrust and development of the seismogenic zone in 2011 we acquired an 11 55 km 3 d seismic reflection volume across the costa rica margin nw of the osa peninsula to accurately image the subduction thrust in 3 d to examine fault zone properties and to infer the hydrogeology that controls fluid accumulation along the thrust following processing to remove water column multiples noise and acquisition artifacts we constructed a 3 d seismic velocity model for kirchhoff prestack depth migration imaging images of the plate boundary thrust show high reflection amplitudes underneath the middle to lower slope that we attribute to fluid rich poorly drained portions of the subduction thrust at 5 km subseafloor beneath the upper slope the plate interface abruptly becomes weakly reflective which we interpret as a transition to a well drained subduction thrust mineral dehydration during diagenesis may also diminish at 5 km subseafloor to reduce fluid production and contribute to the downdip change from high to low amplitude there is also a layered fabric and systems of both thrust and normal faults within the overriding plate that form a plumbing system faults commonly have fault plane reflections and are presumably fluid charged the faults and layered fabric form three compartmentalized hydrogeologic zones 1 a shallow ne dipping zone beneath the slope 2 a steeply sw dipping zone beneath the shelf slope break and 3 a ne dipping zone beneath the shelf the more direct pathway in the middle zone drains the subduction thrust more efficiently and contributes to reduced fluid pressure elevates effective stress and creates greater potential for unstable coseismic slip

control of sulfate pore water profiles by sedimentary events and the significance of anaerobic oxidation of methane for the burial of sulfur in marine sediments abstract gravity driven mass flow deposits proven by sedimentary and digital echosounder data are indicative for prevailing dynamic sedimentary conditions along the continental margin of the western argentine basin in this study we present geochemical data from a total of 23 gravity cores pore water so 4 is generally depleted within a few meters below the sediment surface by anaerobic oxidation of methane aom the different shapes of so 4 profiles concave kink and s type can be consistently explained by sedimentary slides possibly in combination with changes in the ch 4 flux from below thus mostly representing transient pore water conditions since slides may keep their original sedimentary signature a combined analysis and numerical modeling of geochemical physical properties and hydro acoustic data could be applied in order to reconstruct the sedimentary history we present first order estimates of the dating of sedimentary events for an area where conventional stratigraphic methods failed to this day the results of the investigated sites suggest that present day conditions are the result of events that occurred decades to thousands of years ago and promote a persisting mass transport from the shelf into the deep sea depositing high amounts of reactive compounds the high abundance of reactive iron phases in this region maintains low hydrogen sulfide levels in the sediments by a nearly quantitative precipitation of all reduced sulfate by aom for the total region we estimate a so 4 or ch 4 flux of 6 6 10 10 moles per year into the zone of aom projected to the global continental slope and rise area this may sum up to about 2 6 10 12 moles per year provided that the sulfur is completely fixed in the sediments it is about twice the global value of the recent global sulfur burial in marine sediments of 1 2 10 12 moles per year as previously estimated thus aom obviously contributes very significantly to the regulation of global sulfur reservoirs which is hitherto not sufficiently recognized this finding may have implications for global geochemical models as sulfur burial is an important control factor in the development of atmospheric oxygen levels over time

fault zone controlled seafloor methane seepage in the rupture area of the 2010 maule earthquake central chile seafloor seepage of hydrocarbon bearing fluids has been identified in a number of marine forearcs however temporal variations in seep activity and the structural and tectonic parameters that control the seepage often remain poorly constrained subduction zone earthquakes for example are often discussed to trigger seafloor seepage but causal links that go beyond theoretical considerations have not yet been fully established this is mainly due to the inaccessibility of offshore epicentral areas the infrequent occurrence of large earthquakes and challenges associated with offshore monitoring of seepage over large areas and sufficient time periods here we report visual geochemical geophysical and modelling results and observations from the concepcion methane seep area offshore central chile located in the rupture area of the 2010 mw 8 8 maule earthquake high methane concentrations in the oceanic water column and a shallow sub bottom depth of sulfate penetration indicate active methane seepage the stable carbon isotope signature of the methane and hydrocarbon composition of the released gas indicate a mixture of shallow sourced biogenic gas and a deeper sourced thermogenic component pristine fissures and fractures observed at the seafloor together with seismically imaged large faults in the marine forearc may represent effective pathways for methane migration upper plate fault activity with hydraulic fracturing and dilation is in line with increased normal coulomb stress during large plate boundary earthquakes as exemplarily modelled for the 2010 earthquake on a global perspective our results point out the possible role of recurring large subduction zone earthquakes in driving hydrocarbon seepage from marine forearcs over long timescales

assesment of the response of the meteorological hydrological parameters on the soil gas radon emission at hsinchu northern taiwan a prerequisite to identify earthquake precursors abstract the present study is an attempt to assess and quantify the influence of the meteorological atmospheric temperature and pressure and hydrological rainfall and ground water head gwh parameters on the soil gas radon emission at hsinchu northern taiwan the quasi periodic variations corresponding to diurnal and semi diurnal periods were estimated and eliminated by decomposing the time series for the period of september 16 2009 to march 5 2010 to singular spectrum analysis the reconstructed non periodic variations which reproduce the salient feature of recorded time series were searched for meteorological hydrological influences in radon emission the combined response of barometric pressure and atmosphere temperature are found to be small when compared to the total variability in radon the influence of rainfall on radon is found to be strongest at the onset of rainfall radon shows a step jump that attains peak with a time lag of 12 15 h this enhancement is attributed to entrapment of soil gas in the top soil cover as increased soil moisture prevents escape of radon into the atmosphere capping effect the decay of radon after the recession of rainfall is approximated by double exponential decay terms one corresponding to the natural decay of radon with half life of 3 84 days and second representing slow weakening of capping effect the third effect related to internal loading due to rise and fall of groundwater modulates the propagation of radon in overlying strata accounting for the long term variations in radon the rainfall inflicted changes in radon look strikingly similar to earthquake related precursory or co seismic perturbations inferred by long term synotopic observations it is surmised that unless radon variations are corrected for meteorological hydrological contamination some precursory signals are masked on one hand while on the other hand some anomalies are falsely viewed as earthquake precursors

marine pore water sulfate profiles indicate in situ methane flux from underlying gas hydrate marine pore water sulfate profiles measured in piston cores are used to estimate methane flux toward the sea floor and to detect anomalous methane gradients within sediments overlying a major gas hydrate deposit at the carolina rise and blake ridge u s atlantic continental margin here sulfate gradients are linear implying that sulfate depletion is driven by methane flux from below rather than by the flux of sedimentary organic matter from above thus these linear sulfate gradients can be used to quantify and assess in situ methane flux which is a function of the methane inventory below

southeast pacific tectonic evolution from early oligocene to present plate tectonic reconstructions of the nazca antarctic and pacific plates are presented from late oligocene to present these reconstructions document major plate boundary reorganizations in the southeast pacific at dirons 6c 24 ma 6 o 20 ma and 5a 12 ma and a smaller reorganization at chron 3 o 5 ma during the chron 6 o reorganization it appears that a ridge propagated into crust north of the northernmost pacific antarctic ridge between the chiloe fracture zone fz of the chile ridge and agassiz fz of the pacific nazca ridge which resulted in a northward jump of the pacific antarctic nazca pac ant naz mid ocean triple junction during the chron 5a reorganization the chile ridge propagated northward from the valdivia fz system to the challenger fz through lithosphere formed roughly 5 myr earlier at the pacific nazca ridge during this reorganization a short lived microplate the friday microplate existed at the pac ant naz triple junction the pac ant naz triple junction jumped northward 500 km as a result of this reorganization from a location along the valdivia fz to a location along the challenger fz the chron 5a reorganization also included a change in spreading direction of the chile and pacific antarctic ridges the reorganization at chron 3 o initiated the formation of the juan fernandez and easter microplates along the east pacific rise the manner of plate boundary reorganization at chron 6 o and chron 5a and possibly today at the juan fernandez microplate included a sequence of rift propagation transfer of lithosphere from one plate to another microplate formation and microplate abandonment and resulted in northward migration of the pac ant naz triple junction the associated microplate differs from previously studied microplates in that there is no failed ridge

sedimentary fill of the chile trench 32 46 s volumetric distribution and causal factors the chile trench of the convergent continental margin of central chile is a sediment filled basin that stretches over 1500 km in a north south direction the sediment fill reflects latitudinal variations in climate as well as in the morphology and geology of chile but also of sediment transport processes to the trench and within the trench we try to untangle these signals by calculating the total volume and the latitudinal volume distribution of trench sediments and by relating this distribution to a number of factors that affect this pattern the volume calculation is based on a model geometry of the top of the subducting oceanic plate that is buried beneath trench sediments and the sea floor as measured by swath bathymetry we obtain the model geometry of the subducting plate by interpolating between depth converted seismic reflection profiles that cross the trench the total volume of the trench fill between 32 and 46 s is calculated to be 46000 500 km 3 the resulting latitudinal volume distribution is best explained by a sedimentation model that alternates between 1 glacial phases of high sediment flux from southern chile combined with active latitudinal sediment transport within the trench and 2 interglacial phases over which sediment input is dominated by local factors supplementary material top of the oceanic basement tob grid is available as ascii raw data files xyz at www geolsoc org uk sup18664

anomalous non isotropic temporal variation of gamma radiation from radon progeny within air in confined conditions summary new experimental results add information on the space time variation pattern of nuclear radiation from radon in air at confined conditions using five gamma sensors placed around a canister containing radon in gas demonstrated temporal variation consisting of a long term variation which may be related to an annual variation multiday md signals and periodic daily radon dr signals separate processes drive the md and dr signals both md and dr signals exhibit inverse temporal variation patterns in the east west and north south directions the md and dr signal patterns along the vertical axis are associated with the north south directed radiation pattern suggesting that the up down axis of the system is actually inclined relative to the vertical axis of the canister i e related to the latitude of the experiment the relations of the time space variations including the apparent tilt relative to a principal geographic direction imply a connection to global orientation these results are in line with the proposition of an influence of a component of solar irradiation on variation patterns of nuclear radiation from radon

active tectonics of the south chilean marine fore arc 35 s 40 s the south chilean marine fore arc 35 s 40 s is separated into four tectonic segments concepcion north concepcion south nahuelbuta and tolten from north to south these are each characterized by their individual tectonic geomorphology and reflect different ways of mechanical and kinematic interaction of the convergent nazca and south american plates splay faults that cut through continental framework rock are seismically imaged in both concepcion segments and the tolten segment additionally the concepcion south segment exhibits prominent upper plate normal faults normal faults apparently relate to uplift caused by sediment underthrusting at depth this has led to oversteepening and gravitational collapse of the marine fore arc there is also evidence for sediment underthrusting and basal accretion to the overriding plate in the tolten segment there uplift of the continental slope has created a landward inclined seafloor over a latitudinal distance of 50 km in the nahuelbuta segment transpressive upper plate faults aligned oblique to the direction of plate motion control the seafloor morphology based on a unique acoustic data set including 90 of bathymetric coverage of the continental slope we are able to reveal an along strike heterogeneity of a complexly deformed marine fore arc which had escaped attention in previous studies that only considered the structure along transects normal to the plate margin

tectonic control on sediment accretion and subduction off south central chile implications for coseismic rupture processes of the 1960 and 2010 megathrust earthquakes based on a compilation of published and new seismic refraction and multichannel seismic reflection data along the south central chile margin 33 46 s we study the processes of sediment accretion and subduction and their implications on megathrust seismicity in terms of the frontal accretionary prism fap size the marine south central chile fore arc can be divided in two main segments 1 the maule segment south of the juan fernandez ridge and north of the mocha block characterized by a relative large fap 20 40 km wide and 2 the chiloe segment south of the mocha block and north of the nazca antarctic south america plates junction characterized by a small fap 10 km wide in addition the maule and chiloe segments correlate with a thin 1 km thick and thick 1 5 km thick subduction channel respectively the mocha block lies between 37 5 and 40 s and is configured by the chile trench mocha and valdivia fracture zones this region separates young 0 25 ma oceanic lithosphere in the south from old 30 35 ma oceanic lithosphere in the north and it represents a fundamental tectonic boundary separating two different styles of sediment accretion and subduction respectively a process responsible for this segmentation could be related to differences in initial angles of subduction which in turn depend on the amplitude of the down deflected oceanic lithosphere under trench sediment loading on the other hand a small fap along the chiloe segment is coincident with the rupture area of the trans pacific tsunamigenic 1960 earthquake mw 9 5 while a relatively large fap along the maule segment is coincident with the rupture area of the 2010 earthquake mw 8 8 differences in earthquake and tsunami magnitudes between these events can be explained in terms of the fap size along the chiloe and maule segments that control the location of the updip limit of the seismogenic zone the rupture area of the 1960 event also correlates with a thick subduction channel chiloe segment that may provide enough smoothness at the subduction interface allowing long lateral earthquake rupture propagation

fluid accumulation and channeling along the northern barbados ridge decollement thrust a volume of three dimensional seismic reflection data acquired in 1992 imaged the decollement beneath the northern barbados ridge accretionary prism revealing reflection amplitude and waveform variations attributed to fluid accumulations along the plate boundary fault we model the seismic reflection by inversion for seismic impedance the product of velocity and density throughout the 5 x 25 km survey area and thus map physical property variations in 1997 ocean drilling program leg 171a penetrated the protodecollement and decollement at five sites with a logging while drilling lwd tool to log density and other physical properties of the decollement we construct a regional map of density and inferred porosity within the decollement from seismic models calibrated with lwd density data in the sediments out in front of the trench the protodecollement forms in a radiolarian rich miocene mudstone with an anomalously high porosity 70 75 that appears as a pervasive inherent characteristic of this interval seaward of the deformation front in the decollement beneath the wedge a consolidation trend of decreasing porosity runs perpendicular to the deformation front with porosity decreasing from 70 at the wedge toe to 50 4 km from the wedge toe a second distinct trend also forms along a 10 km long 1 to 2 km wide ne sw zone in which porosity is 70 as high as it is in the protodecollement this zone can be explained as an area of the decollement where fluid accumulations develop by maintaining high fluid content we postulate that high fluid content is maintained by continuous recharge flowing into and along this channel this porosity distribution within the decollement also strongly influences fluid migration into the overlying accretionary wedge and is directly associated with fluid charging of ramps and out of sequence thrusts above the decollement

methane sources distributions and fluxes from cold vent sites at hydrate ridge cascadia margin to constrain the fluxes of methane ch4 in the water column above the accretionary wedge along the cascadia continental margin we measured methane and its stable carbon isotope signature 13c ch4 the studies focused on hydrate ridge hr where venting occurs in the presence of gas hydrate bearing sediments the vent ch4 has a light 13c ch4 biogenic signature 63 to 66 pdb and forms thin zones of elevated methane concentrations several tens of meters above the ocean floor in the overlying water column these concentrations ranging up to 4400 nmol l 1 vary by 3 orders of magnitude over periods of only a few hours the poleward undercurrent of the california current system rapidly dilutes the vent methane and distributes it widely within the gas hydrate stability zone ghsz above 480 m water depth the methane budget is dominated by isotopically heavier ch4 from the shelf and upper slope where mixtures of various local biogenic and thermogenic methane sources were detected 56 to 28 pdb the distribution of dissolved methane in the working area can be represented by mixtures of methane from the two primary source regions with an isotopically heavy background component 25 to 6 pdb methane oxidation rates of 0 09 to 4 1 per day are small in comparison to the timescales of advection this highly variable physical regime precludes a simple characterization and tracing of downcurrent plumes however methane inventories and current measurements suggest a methane flux of approximately 3 104 mol h 1 for the working area 1230 km2 and this is dominated by the shallower sources we estimate that the combined vent sites on hr produce 0 6 104 mol h 1 and this is primarily released in the gas phase rather than dissolved within fluid seeps there is no evidence that significant amounts of this methane are released to the atmosphere locally

radium precipitation and extreme 238u series disequilibrium along the dead sea coast israel abstract very intense gamma ray emissions produced by nuclides in the 238 u decay series were measured in active and relict spring deposits along the dead sea coast precipitates of ra near sites of modern springs provide a local source of rn to coexisting waters relict spring deposits representing prior dead sea levels contain high concentrations of ra the ra in both cases has been derived from the dead sea waters or from the dead sea in combination with a ra component from the primary spring water and coprecipitated with hydrous oxides of mn and fe the metal oxides precipitated in response to the mixing of the fresher spring waters with the dead sea brine

seismicity of the eastern mediterranean region perspective from the sinai subplate we conducted a comprehensive study of the seismicity of the eastern mediterranean and examined its relation to the regional plate tectonics based on various published catalogs we have constructed a new list of ml 4 earthquakes which were recorded during the years 1900 1991 and represents most of the seismic moment released in the area over this period b values are 1 02 1 0 and 1 07 for the whole sinai subplate the dead sea transform and the cypriot arc respectively seismic efficiency of the dead sea transform is very low about 7 stressing the role of aseismic deformation in that plate border most of the major and moderate events ml 5 occur in belts associated with the geologically documented borders of the sinai subplate the cypriot convergent arc in the north the dead sea transform in the east and the rift of suez in the southwest the latter like the gulf of eilat aqaba was considered aseismic during the first half of the century the northwestern border however could not be delineated low level activity appears within the subplate especially north of latitude 32 n reflecting the breakdown of this part of sinai as it approaches the cypriot convergence zone though most of the seismic moments tend to concentrate along the subplate borders some moderate activity spreads out in wide belts which reflect the complexity of deformation accompanying motion along the subplate borders

radon in soil gas how to identify anomalies caused by earthquakes anomalies have been observed in rn content in soil gas from 3 boreholes at the orlica fault in the krsko basin slovenia to distinguish the anomalies caused by environmental parameters air and soil temperature barometric pressure rainfall from those resulting solely from seismic activity the following approaches have been used i deviation of rn concentration from the seasonal average ii correlation between time gradients of rn concentration and barometric pressure and iii regression trees within a machine learning program approach i is much less successful in predicting anomalies caused by seismic events than approaches ii and iii if 2 criterion is used and is equally successful if 1 is used approaches ii and iii did not fail to observe an anomaly preceding an earthquake but show false seismic anomalies the number of which is much lower with iii than with ii model trees are shown to outperform other approaches a model has been built which in the seismically non active periods when rn is presumably influenced only by environmental parameters predicts the concentration with a correlation of 0 8 this correlation is reduced significantly in the seismically active periods

conditions for hydrofracture and the fluid permeability of accretionary wedges abstract the dewatering of fine grained sediment piles in accretionary wedges is controlled by zones of active deformation episodic hydrofracture in these zones enhances permeability enabling fluid flow to be faster than the speed of underthrusting here i investigate the mechanics of simultaneous shear failure and hydrofracture in muddy rocks as a function of the faulting mode the physical properties of model rock types are chosen to represent uncemented mud or cherty marly mudstones that have undergone significant diagenesis during thrust faulting hydrofracture always requires pore fluid pressures in excess of the lithostatic load whereas shallow level wrenching or normal faulting permits hydrofracture at hydrostatic pressures significantly lower than lithostatic load all three faulting modes are expected to occur in an accretionary wedge attempting to dynamically maintain its critical taper the model computations indicate that in the upper 80 120 m of a section of soft mudstone hydrofracture inevitably accompanies wrench or normal faulting hard mudstones inevitably hydrofracture to depths of up to 1400 m during normal faulting these differences in mechanical behaviour have profound consequences for fluid venting capabilities of accretionary wedges they influence hydrocarbon trapping and play a role in the localisation of mud diapirs and mud volcanism

toward understanding tectonic control on the mw 8 8 2010 maule chile earthquake the maule earthquake of 27th february 2010 m w 8 8 affected similar to 500 km of the nazca south america plate boundary in south central chile producing spectacular crustal deformation here we present a detailed estimate of static coseismic surface offsets as measured by survey and continuous gps both in near and far field regions earthquake slip along the megathrust has been inferred from a joint inversion of our new data together with published gps insar and land level changes data using green s functions generated by a spherical finite element model with realistic subduction zone geometry the combination of the data sets provided a good resolution indicating that most of the slip was well resolved coseismic slip was concentrated north of the epicenter with up to 16 m of slip whereas to the south it reached over 10 m within two minor patches a comparison of coseismic slip with the slip deficit accumulated since the last great earthquake in 1835 suggests that the 2010 event closed a mature seismic gap slip deficit distribution shows an apparent local overshoot that highlight cycle to cycle variability which has to be taken into account when anticipating future events from interseismic observations rupture propagation was obviously not affected by bathymetric features of the incoming plate instead splay faults in the upper plate seem to have limited rupture propagation in the updip and along strike directions additionally we found that along strike gradients in slip are spatially correlated with geometrical inflections of the megathrust our study suggests that persistent tectonic features may control strain accumulation and release along subduction megathrusts c 2012 elsevier b v all rights reserved

aftershock seismicity of the 27 february 2010 mw 8 8 maule earthquake rupture zone on 27 february 2010 the mw 8 8 maule earthquake in central chile ruptured a seismic gap where significant strain had accumulated since 1835 shortly after the mainshock a dense network of temporary seismic stations was installed along the whole rupture zone in order to capture the aftershock activity here we present the aftershock distribution and first motion polarity focal mechanisms based on automatic detection algorithms and picking engines by processing the seismic data between 15 march and 30 september 2010 from stations from iris ipgp gfz and university of liverpool we determined 20 205 hypocentres with magnitudes mw between 1 and 5 5 seismic activity occurs in six groups 1 normal faulting outer rise events 2 a shallow group of plate interface seismicity apparent at 25 35 km depth and 50 120 km distance to the trench with some variations between profiles along strike the aftershocks occur largely within the zone of coseismic slip but extend 50 km further north and with predominantly shallowly dipping thrust mechanisms along dip the events are either within the zone of coseismic slip or downdip from it depending on the coseismic slip model used 3 a third band of seismicity is observed further downdip at 40 50 km depth and further inland at 150 160 km trench perpendicular distance with mostly shallow dipping 28 thrust focal mechanisms indicating rupture of the plate interface significantly downdip of the coseismic rupture and presumably above the intersection of the continental moho with the plate interface 4 a deep group of intermediate depth events between 80 and 120 km depth is present north of 36 s within the maule segment a large portion of events during the inter seismic phase originated from this depth range 5 the magmatic arc exhibits a small amount of crustal seismicity but does not appear to show significantly enhanced activity after the mw 8 8 maule 2010 earthquake 6 pronounced crustal aftershock activity with mainly normal faulting mechanisms is found in the region of pichilemu 34 5 s these crustal events occur in a 30 km wide region with sharp inclined boundaries and oriented oblique to the trench the best located events describe a plane dipping to the southwest consistent with one of the focal planes of the large normal faulting aftershock mw 6 9 on 11 march 2010

submarine weathering of silicate minerals and the extent of pore water freshening at active continental margins in order to investigate how submarine weathering processes may affect the water balance of sediments at convergent plate margins six sediment cores were retrieved off central chile at water depth between 800 and 4000 m the sediment solid phase was analyzed for its major element composition and the pore fluids were analyzed for dissolved sulfate sulfide total alkalinity major cations chloride bromide iodide hydrocarbons as well as the carbon isotopic composition of methane because of negligible weathering on land surface sediments off central chile are rich in reactive silicate minerals and have a bulk composition similar to volcanic rocks in the adjacent andes deep sourced fluxes of alkalinity cations and chloride indicate that silicate minerals are subject to weathering in the forearc during burial comparison of deep sourced signals with data from nearby ocean drilling program sites reveals two different types of weathering processes in shallow tens of meters methanic sediments of slope basins with high organic carbon burial rates reactive silicate minerals undergo incongruent dissolution through reaction with co2 from methanogenesis at greater burial depth hundreds of meters silicate weathering is dominated by authigenic smectite formation this process is accompanied by uptake of water into the clay interlayers thus leading to elevated salinities in the surrounding pore water deep seated smectite formation is more widespread than shallow silicate dissolution as it is independent from the availability of co2 from methanogenesis although solute transport is not focused enough to form cold seeps in the proper sense tectonically induced diffuse fluid flow transfers the deep seated signal of smectite formation into the shallow sediments the temperature controlled conversion of smectite to illite is considered the most important dehydration process in marine forearc environments depth of kilometers however in agreement with other studies at active margins e g aleutians cascadia nankai trough and despite ubiquitous evidence for smectite formation little evidence for seafloor seepage of dehydration fluids could be found off central chile we argue that the circular process of pore water uptake during smectite formation and release upon illitization implies a balanced freshwater budget and therefore a rather limited potential for net pore water freshening on a margin wide scale according to this rationale pore water freshening at seafloor seeps preferentially occurs at lower latitudes central america barbados mediterranean ridge where terrestrial weathering is more intense thus leading to external i e detrital smectite and thus freshwater inputs to the subduction system

crustal extensional faulting triggered by the 2010 chilean earthquake the pichilemu seismic sequence 1 we report a sequence of crustal quakes that began after the mw 8 8 thrust subduction maule earthquake that affected the central chile margin on 27 february 2010 this activity lasted by several months having the most important events on 11 march 2010 mw 6 9 and mw 7 0 with normal focal mechanisms seismicity shows a rupture oriented along a nw striking and sw dipping normal fault from the surface down to the interplate contact seismicity can be correlated with neotectonics extensional structures similarly oriented in the region which have coexisted with nne ssw reverse faults since the late pliocene even though both have older periods of activity since the paleozoic this crustal rupture would have been triggered by the high coulomb stress change produced by the maule earthquake enhanced by likely fluid presence along weakened zones of the forearc crust as evidenced by high vp vs ratio the occurrence of relevant neotectonic activity in coincidence with short term deformation suggests a relationship with long term tectonic features of this region which would have been acting as a barrier during the interseismic period increasing the strain accumulation and triggering contractional faulting in the crust as well as producing high slip patches during great subduction ruptures favoring triggering of crustal extensional faulting crustal faulting in pichilemu suggests that this kind of events should be considered in seismic hazard analysis despite the absence of historical crustal seismic activity before the maule earthquake

geochemical signals related to the 2011 2012 el hierro submarine eruption abstract on 10 october 2011 a submarine volcanic eruption began 2 km south of the island of el hierro canary islands spain it was the first eruption after 40 years of quiescence in the canarian archipelago since mid july 2011 a multiparametric network has been deployed by the instituto geografico nacional hereinafter ign to monitor volcanic processes the data recorded by five stations measuring the air and soil temperature co2 and radon concentration in the air inside four galleries and one well are the focus of the present paper two important anomalies were found that improve comprehension of the volcanic process first a clear increase in co2 concentration in one gallery from 825 19 to 2305 35 ppm which seems to be mainly controlled by ground deformation measured during the unrest period preceding the eruption second a relationship between radon concentration in air in a well located in the northern side of the island with seismic energy release several peaks with up to 115 increase and ground deformation 50 growth in background level also before the eruption onset lastly changes in radon concentration during eruptive period seem to be modulated by seismic activity increases up to 233 which in turn is likely related to variations in magma rheology

gas geochemistry and seismotectonics a review abstract publications on soil and spring gases have been examined regarding their relationships with both tectonic and seismic activities the main sources behaviours and uses of species detected in soils and springs are displayed and their mode of sampling and analysing briefly described the main patterns of degassing in soils are described and we outline the wide range of geochemical signatures as the result of both permeability and mineralogical contrasts because thermomineral waters have been in contact with great volumes of crustal rocks at various depths spring gases might be more representative of the local environment than soil gases moreover gas signature comparisons show that spring gases are much more enriched with deep gases and slightly contaminated by atmospheric gases therefore they can be considered as better samples for identifying precursors of earthquakes environmental perturbations are examined and it is shown from divergent cases that pressure temperature soil moisture or earth tides may generate very high perturbations of the degassing process such effects demonstrate that no systematic correction law can be proposed and that removing external contributions from gas concentrations must be performed case by case this demonstrates therefore the need for the simultaneous measurement of external parameters during gas monitoring a qualitative examination of about 150 claimed precursors proposed in the literature has been reviewed as noted by previous authors anomalies appear at distances sometimes much greater than typical source dimensions and occur in the field of strain higher than 10 9 most of them being in the field of strain higher than 10 8 taking into account the very high heterogeneity of such a set of data we can suggest that amplitudes of gas anomalies are independent of both magnitudes and epicentral distances of related earthquakes suggesting local conditions to control amplitudes on the contrary precursory time and duration of anomalies seem to increase both with magnitudes and epicentral distances abundant evidence demonstrates the major role of crustal fluids in the earthquake cycle many works have outlined the fact that crustal instabilities can appear as the result of low stress strain perturbations during loading it has been suggested that motion of fluids may occur at various scales from microcrack fluid transfer up to changes of hydraulic levels of water tables the study of subsequent anomalies is expected to supply a tool for earthquake prediction following previous authors we outline the need for further methodological improvements including the setting up of multiparameter station networks and the simultaneous recording of the main external parameters atmospheric pressure water and air temperature soil moisture for signal processing

consolidation patterns during initiation and evolution of a plate boundary decollement zone northern barbados accretionary prism borehole logs from the northern barbados accretionary prism show that the plate boundary decollement initiates in a low density radiolarian claystone with continued thrusting the decollement zone consolidates but in a patchy manner the logs calibrate a three dimensional seismic reflection image of the decollement zone and indicate which portions are of low density and enriched in fluid and which portions have consolidated the seismic image demonstrates that an underconsolidated patch of the decollement zone connects to a fluid rich conduit extending down the decollement surface fluid migration up this conduit probably supports the open pore structure in the underconsolidated patch

hydrogeology and mechanics of subduction zone forearcs fluid flow and pore pressure at subduction zones fluid flow pore pressure and tectonic processes are tightly interconnected excess pore pressure is driven by tectonic loading and fluids released by mineral dehydration and it has profound effects on fault and earthquake mechanics through its control on effective stress the egress of these overpressured fluids which is in part governed by the presence of permeable fault zones is a primary mechanism of volatile and solute transport to the oceans recent field measurements new constraints gained from laboratory studies and numerical modeling efforts have led to a greatly improved understanding of these coupled processes here we summarize the current state of knowledge of fluid flow and pore pressure in subduction forearcs and focus on recent advances that have quantified permeability architecture fluxes the nature and timing of transience and pressure distribution thus providing new insights into the connections between fluid metamorphic mechanical and fault slip proc

flux and dispersion of gases from the drachenschlund hydrothermal vent at 8 18 s 13 30 w on the mid atlantic ridge hydrothermal emission of mantle helium appears to be directly related to magma production rate but other processes can generate methane and hydrogen on mid ocean ridges in an on going effort to characterize these processes in the south atlantic the flux and distribution of these gases were investigated in the vicinity of a powerful black smoker recently discovered at 8 17 9 s 13 30 4 w the vent lies on the shoulder of an oblique offset in the mid atlantic ridge and discharges high concentrations of methane and hydrogen measurements during expeditions in 2004 and 2006 show that the ratio of ch4 to 3he in the neutrally buoyant plume is quite high 4 108 the ctd stations were accompanied by velocity measurements with lowered acoustic doppler current profilers ladcp and from these data we estimate the methane transport to have been 0 5 mol s 1 in a wsw trending plume that seems to develop during the ebb tidal phase this transport is an order of magnitude greater than the source of ch4 calculated from its concentration in the vent fluid and the rise height of the plume from this range of methane fluxes the source of 3he is estimated to be between 0 14 and 1 2 nmol s 1 in either case the 3he source is significantly lower than expected from the spreading rate of the mid atlantic ridge from the inventory of methane in the rift valley adjacent to the vent it appears that the average specific rate of oxidation is 2 6 to 23 yr 1 corresponding to a turnover time between 140 and 16 days vertical profiles of methane in the surrounding region often exhibited gaussian like distributions and the variances appear to increase with distance from the vent using a gaussian plume model we obtained a range of vertical eddy diffusivities between 0 009 and 0 08 m2m2 s 1 these high values may be due to tidally driven internal waves across the promontory on which the vent is located

statistically significant relation between radon flux and weak earthquakes in the dead sea rift valley detailed monitoring of radon rn flux in gravel was carried out for a period of eight years near the active dead sea rift fault the temporal relationship between hundreds of weak earthquakes 4 6 ml 0 and rn flux signals was tested for time intervals related to the start time of 110 rn flux signals earthquakes located within three pull apart grabens of the dead sea rift valley were found to occur preferentially within the time interval of the first 3 days after the start time of 110 rn anomalies and the excess of earthquakes 82 relative to the expected value is highly significant p 003 however a similar relationship is not found in the two weeks preceding or following the start time of the rn anomalies for earthquakes occurring within the dead sea rift in structurally higher segments or out of the dead sea rift

geochemical surface exploration for hydrocarbons in north sea approximately 350 sediment samples were taken in the central part of the north sea and hydrocarbon composition methane c1 and ethane c2 yields and carbon isotope composition of the methane dgr13c1 adsorbed in the sediment were determined methane generation or oxidation by bacterial activity can not be deduced from the analytical data this fact is explained by the assumption of a threshold of methane concentration in sediments below which methane oxidizing bacteria are inactive and that this threshold was not reached in the area investigated background gases in the surface sediments characterized by low c1 yields and dgr13c1 37 ppt can be distinguished from thermal sediment g ses which are obviously derived from a hydrocarbon generating source rock in the subsurface source rock data obtained from several wells situated on a cross section through the investigated area were compared to the geochemical patterns of the sediment gases and used to define profile sections with good dgr13c1 approx 40 ppt yield c1 approx 217 ppb and poor source rock properties dgr13c1 approx 33 ppt yield c1 approx 24 ppb an assessment of the source rock potential of the whole area under investigation has been carried out using the geochemical data of the surface sediment gases and taking into account that the c1 and c2 yields are generally higher in clay sediments than in sand samples the number of producing wells was related to the number of all wells 271 in the areas characterized by surface geochemistry as good or poor source rock areas the comparison showed that the relative number of producing wells is higher in areas geochemically characterized as good hydrocarbons in surface sediments of good north sea areas are not generated by bacteria at shallow depth they are formed thermally from the organic carbon of deep source rocks and migrate to the surface therefore they are indicative of thermal hydrocarbon generation in the subsurface

does permanent extensional deformation in lower forearc slopes indicate shallow plate boundary rupture abstract seismic rupture of the shallow plate boundary can result in large tsunamis with tragic socio economic consequences as exemplified by the 2011 tohoku oki earthquake to better understand the processes involved in shallow earthquake rupture in seismic gaps where megathrust earthquakes are expected and investigate the tsunami hazard it is important to assess whether the region experienced shallow earthquake rupture in the past however there are currently no established methods to elucidate whether a margin segment has repeatedly experienced shallow earthquake rupture with the exception of mechanical studies on subducted fault rocks here we combine new swath bathymetric data unpublished seismic reflection images and inter seismic seismicity to evaluate if the pattern of permanent deformation in the marine forearc of the northern chile seismic gap allows inferences on past earthquake behavior while the tectonic configuration of the middle and upper slope remains similar over hundreds of kilometers along the north chilean margin we document permanent extensional deformation of the lower slope localized to the region 20 8 s 22 s critical taper analyses the comparison of permanent deformation to inter seismic seismicity and plate coupling models as well as recent observations from other subduction zones including the area that ruptured during the 2011 tohoku oki earthquake suggest that the normal faults at the lower slope may have resulted from shallow possibly near trench breaking earthquake ruptures in the past in the adjacent margin segments the 1995 antofagasta 2007 tocopilla and 2014 iquique earthquakes were limited to the middle and upper slope and the terrestrial forearc and so are upper plate normal faults our findings suggest a seismo tectonic segmentation of the north chilean margin that seems to be stable over multiple earthquake cycles if our interpretations are correct they indicate a high tsunami hazard posed by the yet un ruptured southern segment of the seismic gap

deep sulfate reduction completely mediated by anaerobic methane oxidation in sediments of the upwelling area off namibia abstract porewater concentrations of sulfate methane and other relevant constituents were determined on four sediment cores from the high productivity upwelling area off namibia which were recovered from the continental slope at water depths of 1300 and 2000 m at all four stations a distinct sulfate methane transition zone was observed several meters below the seafloor in which both sulfate and methane are consumed nutrient porewater concentration profiles do not show gradient slope changes at the depths of the transition zones flux calculations carried out on the basis of the determined porewater profiles revealed that anaerobic methane oxidation accounts for 100 of deep sulfate reduction within the sulfate methane transition zone and consumes the total net diffusive sulfate flux a significant contribution of organic carbon oxidation to the reduction of sulfate at these depths could therefore be excluded we state that porewater profiles of sulfate with constant gradients above the transition zones are indicative for anaerobic methane oxidation controlling sulfate reduction

permanent fore arc extension and seismic segmentation insights from the 2010 maule earthquake chile 1 geologists have long known that young normal faults are an important structural element of the andean coastal cordillera but their relationship to the subduction seismic cycle is still unclear some of the largest aftershocks of the 2010 mw 8 8 maule earthquake in central chile were nucleated on upper plate normal faults including the mw 6 9 and 7 0 events of the pichilemu earthquake sequence we use the available coseismic gps displacements moment tensor sums and slip distribution models for the maule earthquake to compute the static strain and stress fields imposed on the upper plate by slip on the subduction interface the extensional strains calculated from coseismic gps and from a moment tensor sum of the pichilemu events have similar orientations and orders of magnitude the normal coulomb stress increment csi on the pichilemu fault has maximum positive stresses as high as 4 9 mpa regionally the maule event produced a semi elliptical radial pattern of static extension and deviatoric tension csi 1 5 mpa along the coastal cordillera enclosing the rupture area this elliptical pattern mimics the trends of the major upper crustal structures the static deformation field produced by a great subduction earthquake is an effective mechanism for generating permanent extension above the seismogenic zone reactivating suitably oriented long lived normal faults we suggest that the semi elliptical outline of the first order structures along the coastal cordillera may define the location of a characteristic long lived megathrust segment this observation implies a persistence at least over the quaternary of great subduction ruptures along the maule segment

evolution of the nankai trough decollement from the trench into the seismogenic zone inferences from three dimensional seismic reflection imaging we mapped the amplitude of the nankai trough subduction thrust seismic reflection from the trench into the seismogenic zone with three dimensional seismic reflection data the decollement thrust forms within the lithologically homogeneous lower shikoku basin facies along an initially nonreflective interface the reflection develops from a porosity contrast between accreted and underthrust sedimentary material because of accretionary wedge consolidation and rapid loading and delayed consolidation of the underthrust section a decollement amplitude map shows a significant decline from high amplitudes at the trench to barely detectable levels 25 30 km landward three other observations coincide with the amplitude decline 1 the decollement initially steps down to deeper stratigraphic levels 2 the wedge taper increases dramatically and 3 the thrust becomes seismogenic the amplitude decline and the coincident decollement and accretionary wedge tectonic and seismogenic behavior are attributed to the loss of fluids and potentially loss of excess fluid pressures downdip along the subduction thrust

increase in radon emission due to rock failure an experimental study 1 radon anomalies are commonly observed prior to dynamic failure in the crust and are interpreted as cracking of the medium thus attracting considerable attention in understanding the precursory phenomena of earthquakes and volcanic activity in this study we have compared the starting radon emissions from low porosity crystalline lava phonolite samples with those from damaged and failed samples the damaged sample was loaded up to just beyond the end of the linear elastic phase as evidenced by the output of ae energy the increase in total porosity and a decrease in p wave and s wave velocity relative to the intact sample whereas the failed sample showed deformation behaviour characteristically brittle with increasing values of ae output and porosity as the sample approached macroscopic failure radon measurements have evidenced that dilatational microcracking of deformed sample produced no significant variation in radon emanation with respect to the intact sample in contrast after macroscopic failure radon emanation drastically increased therefore major finding from this study is that in the case of low porosity and relatively high strength crystalline lavas the development of a macroscopic fracture provides new large exhaling surface resulting in a substantial increase in radon emission rate

the 2010 mw 8 8 maule megathrust earthquake of central chile monitored by gps large earthquakes produce crustal deformation that can be quantified by geodetic measurements allowing for the determination of the slip distribution on the fault we used data from global positioning system gps networks in central chile to infer the static deformation and the kinematics of the 2010 moment magnitude m w 8 8 maule megathrust earthquake from elastic modeling we found a total rupture length of 500 kilometers where slip up to 15 meters concentrated on two main asperities situated on both sides of the epicenter we found that rupture reached shallow depths probably extending up to the trench resolvable afterslip occurred in regions of low coseismic slip the low frequency hypocenter is relocated 40 kilometers southwest of initial estimates rupture propagated bilaterally at about 3 1 kilometers per second with possible but not fully resolved velocity variations

gps derived deformation of the central andes including the 1995 antofagasta mw 8 0 earthquake in order to study both the interplate seismic loading cycle and the distribution of intraplate deformation of the andes a 215 site gps network covering chile and the western part of argentina was selected monumented and observed in 1993 and 1994 a dense part of the network in northern chile and northwest argentina comprising some 70 sites was re observed after two years in october november 1995 the m w 8 0 antofagasta north chile earthquake of 30th july 1995 took place between the two observations the city of antofagasta shifted 80 cm westwards by this event and the displacement still reached 10 cm at locations 300 km from the trench three different deformation processes have been considered for modeling the measured displacements 1 interseismic accumulation of elastic strain due to subduction coupling 2 coseismic strain release during the antofagasta earthquake and 3 crustal shortening in the sub andes eastward displacement of the sites to the north and to the south of the area affected by the earthquake is due to the interseismic accumulation of elastic deformation assuming a uniform slip model of interseismic coupling the observed displacements at the coast require a fully locked subduction interface and a depth of seismic coupling of 50 km the geodetically derived fault plane parameters of the antofagasta earthquake are consistent with results derived from wave form modeling of seismolog ical data the coseismic slip predicted by the variable slip model reaches values of 3 2 m in the dip slip and 1 4 m in the strike slip directions the derived rake is 66 our geodetic results suggest that the oblique nazca south american plate convergence is accommodated by oblique earthquake slip with no slip partitioning the observed displacements in the back arc indicate a present day crustal shortening rate of 3 4 mm year which is significantly slower than the average of 10 mm year experienced during the evolution of the andean plateau

ground water radon anomaly before the kobe earthquake in japan radon concentration in ground water increased for several months before the 1995 southern hyogo prefecture kobe earthquake on 17 january 1995 from late october 1994 the beginning of the observation to the end of december 1994 radon concentration increased about fourfold on 8 january 9 days before the earthquake the radon concentration reached a peak of more than 10 times that at the beginning of the observation before starting to decrease these radon changes are likely to be precursory phenomena of the disastrous earthquake

a clear case of radon anomaly associated with a micro earthquake event in a stable continental region 1 though many worldwide attempts to establish radon anomalies in soil and groundwater as precursors for major earthquakes are made yet practically no such work has been reported for micro earthquakes in a stable continental region scr from the continuous radon measurements for five months at a depth of 1 m in fractured granitic area we report for the first time that enhanced radon concentration preceded seventeen hours the occurrence of micro earthquake the peak radon level twice the normal concentration was reached thirteen hours before the occurrence of the event and decayed exponentially during the next 5 days to come to normal level this radon precursor pertains to a dry period unaffected by meteorological factors thus exemplifies clearly its association with micro earthquake

radon signals in the gavnunim intrusion makhtesh ramon israel summary high time resolution monitoring of radon using alpha detectors is carried out in a massive and jointed syenite located in arid southern israel monitoring at a resolution of 15 min is conducted in two boreholes at depths of 1 2 and 85 90 m resulting in more then 10 yr long time series systematic temporal variation patterns manifesting large relative signals are composed primarily of annual ar multiday md daily dr and subdaily sdr radon signals prominent periodic diurnal variation underlies the dr and probably also the sdr signals diurnal s1 24 hr and semidiurnal s2 12 hr constituents characterize the dr signal at 1 2 m while diurnal constituents typical for gravity related periodicities m2 o1 are absent the amplitudes of the s1 and s2 constituents calculated for consecutive 512 hr long time intervals exhibit a similar covarying annual pattern the periodic dr signal is absent at 85 m depth the peak time of sdr signals occurring at this depth in some days exhibits a 24 and 12 hr periodicity time offsets of hours are observed between time series of the measured signal from the two levels the lag investigated for the decomposed md signal using consecutive 20 d long time intervals shows that the signal at depth systematically lags by around 9 hr the signal at the shallow level discrepancy of the patterns of the temporal variation in the time domain and also in the frequency and time frequency domains of the diurnal periodic components indicates that atmospheric influence on the radon signal is insignificant even at a depth of 1 2 m combining this conclusion with the compound interrelations occurring among the different radon signals suggests that other geophysical processes are driving the radon variation in the subsurface geogas it is suggested that the significant s1 and s2 signatures and their modulations are imposed on the radon system by means of a direct link with solar radiation tide

tropical forcing of north pacific intermediate water distribution during late quaternary rapid climate change abstract evidence is presented demonstrating intermediate water 500 m temperature variability at odp hole 893a in santa barbara basin during submillennial climate change 11 60 ka benthic 18 o oscillations are considered to result primarily from shifts in intermediate water temperature at the site detailed comparison of both benthic and planktonic records from the basin provide crucial evidence for differing surface and intermediate water mass temporal responses to rapid climate change gradual warming of intermediate water compared to abrupt cooling suggests mechanistic differences between processes controlling north pacific intermediate water expansion and contraction relative to southern component intermediate waters comparisons suggest intermediate water warming preceded by 60 200 years the most rapid interval of surface warming inferred to be associated with north pacific atmospheric reorganization tropical forcing of sea level anomalies in the eastern pacific via trade wind strength may control california undercurrent flow 300 500 m and be the cause of early intermediate water warming in santa barbara basin

inversion of forearc basins in south central chile caused by rapid glacial age trench fill this study examines the response of a forearc to the increase in sediment flux to the trench caused by the onset of glacial denudation in the patagonian andes we investigated shelf coastal basins in south central chile which generally comprise eocene early miocene nearshore facies overlain by late miocene early pliocene deep water siltstones and by late pliocene quaternary nearshore deposits seismic profiles and coastal exposures reveal eocene early pliocene extension followed by ongoing late pliocene compression evidenced from growth strata adjacent to seismically active reverse faults the onset of major global cooling ca 6 ma triggered glacial denudation in the uplifted high andes exhumed material transported along the steep and humid andean western slope increased trench sedimentation rates and caused continuous accretion and subduction of terrigenous material we interpret forearc basin inversion as a response to a decrease in slope and basal friction of the wedge caused by frontal accretion and subduction of water rich material respectively in order to reach a critical taper this process lifted the shelf 1 5 km during the middle pliocene the juan fernandez ridge and chile rise confined 2 km trench fill between 45 and 34 s limiting accretion and basin inversion glacial age trench fill and the steady decrease in plate convergence rate shifted this segment of the margin from erosive to accretionary during the pliocene

why is earthquake prediction research not progressing faster abstract as a physical phenomenon earthquakes must be predictable to a certain degree however the problem is difficult because the source volume inside the earth is inaccessible to direct observation and because the most important parameter the stress level cannot be measured directly also seismology is such a young science that the cause of earthquakes was discovered in the 1960s only advanced seismograph networks as well as modern techniques to measure crustal deformations such as the global positioning system gps and the synthetic aperture radar interferometry technique insar have come on line only recently and only in japan are they deployed with the densities necessary for significant advances in the understanding of the rupture initiation process in addition no real program for earthquake prediction research exists in the united states largely because funding agencies and peer reviewers shy away from a field in which unprofessional but motivated individuals are active although claims of successful predictions are often not justified a few correct predictions have been made most of these had time windows of years but some were accurate to days and allowed preparatory actions to make significant progress we must learn how to conduct rigorous science in a field where amateurs cannot be discouraged to venture leadership is necessary to raise the funding to an adequate level and to involve the best minds in this promising potentially extremely rewarding but controversial research topic

coseismic and postseismic stress rotations due to great subduction zone earthquakes 1 the three largest recent great subduction zone earthquakes 2011 m9 0 tohoku japan 2010 m8 8 maule chile and 2004 m9 2 sumatra andaman exhibit similar coseismic rotations of the principal stress axes prior to each mainshock the maximum compressive stress axis was shallowly plunging while immediately after the mainshock both the maximum and minimum compressive stress axes plunge at 45 dipping faults can be oriented for either reverse or normal faulting in this post mainshock stress field depending on their dip explaining the observed normal faulting aftershocks without requiring a complete reversal of the stress field the significant stress rotations imply near complete stress drop in the mainshocks with 80 of the pre mainshock stress relieved in the tohoku and maule earthquakes and in the northern part of the sumatra andaman rupture the southern part of the sumatra andaman rupture relieved 60 of the pre mainshock stress the stress axes rotated back rapidly in the months following the tohoku and maule mainshocks and similarly in the southern part of the sumatra andaman rupture a rapid postseismic rotation is possible because the near complete stress drop leaves very little background stress at the beginning of the postseismic reloading in contrast there has been little or no postseismic rotation in the northern part of the sumatra andaman rupture over the 7 years since the mainshock all m 8 0 subduction earthquakes since 1990 with an adequate number of pre and post mainshock events were evaluated and not all show similar coseismic stress rotations deeper earthquakes exhibit smaller coseismic stress rotations likely due to increasing deviatoric stress with depth

subduction zone earthquake as potential trigger of submarine hydrocarbon seepage methane is abundant in marine sediments analysis of sediment cores and seismic images of marine sediments obtained off the coast of pakistan show fracturing of gas hydrates and an increase in upward methane flux in the decades following a large earthquake in the arabian sea in 1945 suggesting that quakes can trigger hydrocarbon seepage

radon daily signals in the elat granite southern arava israel 1 high time resolution monitoring of radon 222rn in three boreholes 4 10 and 53 m deep along a 0 6 km transect is carried out in massive granite in southern israel three components of variation occur in the measured signal ms seasonal radon sr periodic multiday md and daily radon dr periodic temporal variation of the components suggests an association between the overall level of the long term variation and the amplitude of the daily variation the daily mean level of radon and the daily standard deviation vary periodically throughout the year time offsets occur among time series of the ms and were investigated also for the md and dr components using consecutive 20 day intervals spanning 900 days the resulting time series show that systematic time offsets occur whereby the radon signal always occurs first at the easternmost site the md shows a gradually varying lag of 0 12 h and the dr a stable 1 3 h lag spectral analysis shows that diurnal 24 h and semidiurnal 12 h periodic components characterize the dr the amplitudes of these components exhibit regular temporal variation having a seasonal pattern the ratios of co occurring amplitudes of these components define a linear pattern indicating a fundamental statistical property in the frequency domain of the radon time series the results indicate that unrecognized dynamic processes are driving the radon signal in the subsurface regime of the pluton suggesting new prospects for radon behavior in the frame of interacting geodynamic tectonic and earth sun system related processes

structure inferred mechanical properties and implications for fluid transport in the decollement zone costa rica convergent margin faults in a variety of tectonic settings can act as both conduits for and barriers to fluid flow sometimes simultaneously documenting the interaction between hydrologic and tectonic processes in active faults in situ is the key to understanding their mechanical behavior and large scale fluid transport properties we present observations of the plate boundary decollement zone at the middle america trench off costa rica showing that it is structurally divisible into an upper brittle fracture dominated domain overlying a lower ductile domain pore water geochemical evidence shows that along fault flow is occurring specifically in the upper brittle domain but is hydrologically isolated from fluids in the underlying footwall sediments we propose a model for the mechanics of these contrasting domains in which differing stress paths coexist in the upper and lower parts of the decollement zone the data suggest a mechanically controlled permeability anisotropy at a scale of several meters to 10 m across the decollement zone this documentation of separate yet simultaneously active mechanical and hydrologic subregimes within a decollement provides a relatively simple explanation for enhanced along fault permeability coexisting with reduced cross fault permeability without requiring matrix scale permeability anisotropy

application of artificial neural networks in simulating radon levels in soil gas abstract anomalies have been observed in radon content in soil gas from three boreholes at the orlica fault in the krsko basin slovenia to distinguish the anomalies caused by environmental parameters air and soil temperature barometric and soil air pressure rainfall from those resulting solely from seismic activity the following approaches have been used first the seismic activity data were eliminated from the dataset and then an artificial neural network ann with 5 inputs for environmental parameters and a single output radon concentration was trained with the standard backpropagation learning rule then the predictions of rn concentrations cp generated with this ann for the whole dataset were compared to measurements cm and three types of anomalies ca correct anomaly fa false anomaly and na no anomaly have been detected in the signal cm cp 1 by varying five parameters describing an anomaly within predefined intervals an exhaustive search among results was made to find the best ones and thus identifying the best set of parameters finally an attempt was made to shorten the search procedure by training another ann with numbers of anomalies of each type in the input and five anomaly detection parameters in the output with these procedures we were able to correctly predict 10 seismic events out of 13 within the 2 year period

physical properties and gas hydrate at a near seafloor thrust fault hikurangi margin new zealand the p paku fault zone drilled at iodp site u1518 is an active splay fault in the frontal accretionary wedge of the hikurangi margin in logging while drilling data the 33 m thick fault zone exhi