groundwater electrical conductivity and soil radon gas monitoring for earthquake precursory studies in koyna india abstract hourly monitoring of electrical conductivity ec of groundwater along with groundwater levels in the 210 m deep boreholes specially drilled for pore pressure earthquake studies and soil rn gas at 60 cm below ground level in real time in the koyna warna region characterized by basaltic rocks 1500 m thick and dotted with several sets of fault systems western india provided strong precursory signatures in response to two earthquakes m 4 7 on 14 11 09 and m 5 1 on 12 12 09 that occurred in the study region the ec measured in govare well water showed precursory perturbations about 40 h prior to the m 5 1 earthquake and continued further for about 20 h after the earthquake in response to the m 4 7 earthquake there were ec perturbations 8 days after the earthquake in another well koyna which is located 4 km north of govare well no precursory signatures were found for the m 4 7 earthquake while for m 5 1 earthquake post seismic precursors were found 18 days after the earthquake increased porosity and reduced pressure head accompanied by mixing of a freshwater component from the top zone due to earthquakes are the suggested mechanisms responsible for the observed anomalies in ec another parameter soil rn gas showed relatively proportional strength signals corresponding to these two earthquakes in both the cases the pre seismic increase in rn concentration started about 20 days in advance the co seismic drop in rn levels was less by 30 from its peak value for the m 4 7 earthquake and 50 for the m 5 1 earthquake the rn anomalies are attributed to the opening and closing of micro fractures before and during the earthquake on line monitoring of these two parameters may be useful to check the entire chemistry change due to earthquake which may help to forecast impending earthquakes

upper mantle tomography beneath the pacific northwest interior abstract the pacific northwest has undergone extensive tectonic and magmatic construction in the cenozoic and many clues to its history are in a well resolved upper mantle structure we present new p s and v p v s models that benefit from improved algorithms and additional data from recently deployed flexible array experiments in the region of the columbia river basalts western snake river plain and idaho batholith we refine the geometries of previously imaged structures and identify new anomalies beneath the pacific northwest a clear separation is resolved between the wallowa and idaho structures that extends from the base of the crust to the depth extent of these structures the separation follows the precambrian margin of north america possibly indicating separate tectonic histories for the two structures a shallow fast anomaly beneath idaho batholith may be responsible for the observed curvature of the yellowstone track around this batholith and a strong and unusually deep 180 250 km slow anomaly is present east of the apparent juan de fuca slab gap resolving these structures well is important in understanding the origin of the lithospheric fragments in the mantle and key to any reconstruction of the evolution of the pacific northwest farallon kula juan de fuca tectonic system of most relevance understanding the origin of the imaged high velocity mantle structures provides strong constraint on their density that otherwise would be largely unknown which controls the evolution of vertical and horizontal stresses acting at the base of the lithosphere and hence the evolution of topography also resolving the volumes of partially molten upper mantle shapes our understanding on the origin of the abundant volcanism in the pacific northwest interior

new standards for reducing gravity data the north american gravity database the north american gravity database as well as data bases from canada mexico and the united states are being revised to improve their coverage versatility and accuracy an important part of this effort is revising pro cedures for calculating gravity anomalies taking into ac count our enhanced computational power improved ter rain databases and datums and increased interest in more accurately defining long wavelength anomaly components users of the databases may note minor differences be tween previous and revised database values as a result of these procedures generally the differences do not impact the interpretation of local anomalies but do improve re gional anomaly studies the most striking revision is the use of the internationally accepted terrestrial ellipsoid for the height datum of gravity stations rather than the conven tionally used geoid or sea level principal facts of gravity observations and anomalies based on both revised and pre vious procedures together with germane metadata will be available on an interactive web based data system as well as from national agencies and data centers the use of the revised procedures is encouraged for gravity data reduc tion because of the widespread use of the global position ing system in gravity fieldwork and the need for increased accuracy and precision of anomalies and consistency with north american and national databases anomalies based on the revised standards should be preceded by the adjec tive ellipsoidal to differentiate anomalies calculated us ing heights with respect to the ellipsoid from those based on conventional elevations referenced to the geoid

crust and upper mantle structure beneath the pacific northwest from joint inversions of ambient noise and earthquake data 1 we perform a joint inversion of phase velocities from both earthquake and ambient noise induced rayleigh waves to determine shear wave velocity structure in the crust and upper mantle beneath the pacific northwest we focus particularly on the areas affected by mid miocene to present volcanic activity the joint inversion combined with the high density seismic network of the high lava plains seismic experiment and data from the earthscope transportable array provides outstanding resolution for this area in oregon we find that the pattern of low velocities in the crust and uppermost mantle varies between the high lava plains physiographic province and the adjacent northwestern basin and range these patterns may be due to the presence of the brothers fault zone which separates the clockwise rotating northwest basin and range from the relatively undeformed areas further north further to the east the owyhee plateau snake river plain srp and northeastern basin and range are characterized by high crustal velocities though the depth extent of these fast wave speeds varies by province of particular interest is the mid crustal high velocity sill previously only identified within the srp we show this anomaly extends significantly further south into utah and nevada we suggest that one possible explanation is lateral crustal extrusion due to the emplacement of the high density mafic mid crustal sill structures within the srp

crustal structure of the northwestern basin and range province and its transition to unextended volcanic plateaus 1 the northwestern margin of the basin and range province is characterized by a transition from low magnitude 20 extension in northwestern nevada to relatively unextended volcanic plateaus in northeastern california seismic velocity and potential field modeling provides new control on the mesozoic to present tectonic evolution of this poorly understood portion of the u s cordillera we document 20 crustal thinning associated with basin and range extension from a crustal thickness of 37 km under northeastern california to 31 km under northwestern nevada that is consistent with the amount of extension recorded in the upper crust in northwestern nevada suggesting the crustal response to extension was relatively homogeneous over the entire crustal column our modeling also shows a well defined 80 km wide zone of unusually low upper crustal velocities 5 9 6 1 km s that coincide with the surface location of sparse cretaceous granites locating the elusive northern extension of the sierra nevada batholith through northwestern nevada for the first time in the subsurface combining geological and geophysical data we reconstruct the late cretaceous to present crustal evolution of this region documenting an interplay between magmatic addition to the crust erosional exhumation sedimentation and extension that has reversed the direction of crustal thinning from a west facing continental margin to an east facing interior basin margin over this time interval finally we find no evidence in northwestern nevada for unusually thick crust 40 km prior to basin and range extension

five decades of triggered earthquakes in koyna warna region western india a review abstract we review reservoir triggered seismicity rts in the koyna warna region of india since the impoundment of the koyna reservoir in 1962 until the year 2015 we include seismicity that occurred farther south in response to the impoundment of warna reservoir in 1993 about 35 km to the south of koyna reservoir the on going earthquake activity for more than five decades in a small seismic volume of about 30 20 10 km3 has characterized the koyna warna region as globally unique and significant to date 22 earthquakes of m 5 about 200 earthquakes of m 4 and several thousand smaller earthquakes have been recorded by a dense network of stations in the region various seismological geophysical and hydrological studies have been carried out to understand the phenomenon of triggered seismicity including source mechanism fault geometry crustal structure earthquake processes causal relationship with reservoir water level changes and anomalous water level fluctuations in cased bore wells the present review takes stock of all such studies undertaken so far to summarise the understanding on various geo scientific issues and milestone achievements with regard to mechanism of triggered seismicity and source processes fault plane solutions commensurate with geometry of faulting source parameters seismogenic depth crustal structure and the role of reservoir water level two stage increase in seismic energy release coinciding with peaks of annual filling and draining cycle of reservoir with one month delay vis a vis spurt of moderate earthquakes m 5 due to i rapid rise in reservoir level 12 m week ii reservoir water level exceeding the previous maxima and iii duration for which high reservoir level is retained are characteristic features numerical models simulating diffusion of pore fluid pressure fronts during the filling stage of reservoir suggest stress perturbations of the order of 0 75 2 25 bar at hypocentral depth triggering earthquakes on critically stressed pre existing faults in the year 2005 a 13 station digital seismometers network became functional that characterized the distribution of epicentres in the area with increased accuracy and suggested four major seismic zones with well defined clusters scientific drilling carried out recently provide several new information regarding the subsurface geology and structure in the koyna region such as i thickness of deccan traps 933 in the koyna area and 1185 m in the warna area ii presence of granite gneiss basement directly underlying the deccan traps iii absence of infratrappean sediments and iv temperature not exceeding 150 c at hypocentral depth it is planned to establish a deep borehole observatory close to the seismic source zone for direct measurements of physical and mechanical properties of rocks pore fluid pressure hydrology thermal condition and other parameters of an intra plate active fault zone in the near field of earthquakes before during and after their occurrence results from such experiment and long term in situ monitoring of critical parameters would enhance our understanding on the mechanism of triggered earthquakes and the role of reservoir water level fluctuations

crustal structure beneath the high lava plains of eastern oregon and surrounding regions from receiver function analysis 1 we analyze teleseismic p to s receiver functions to image crustal structure beneath the high lava plains hlp of eastern oregon and surrounding regions coverage from 206 broadband seismic stations provides the first opportunity to resolve variations in crustal composition thickness and heterogeneity on scales of a few km in depth and tens of km laterally across the hlp region we utilize both h stacking and a new gaussian weighted common conversion point stacking technique we find crust that is 40 km thick beneath the cascades idaho batholith and owyhee plateau and thinner 31 km crust beneath the hlp and northern great basin low poisson s ratios of 0 240 characterize the granitic crust beneath the idaho batholith while the owyhee plateau exhibits values of 0 270 typical of average continental crust the owyhee plateau is a thick simple crustal block with distinct edges at depth the western hlp exhibits high average values of 0 304 typical for regions of widespread basaltic volcanism combined with other geological and geophysical observations the areas of abnormally high poisson s ratios 0 320 and low velocity zones in the crust beneath north central and southern oregon are consistent with the presence of partial melt on either side of the hlp trend suggesting a central zone where crustal melts have drained to the surface perhaps enabled by the brothers fault zone thicker crust and an anomalous n s band of low poisson s ratios 0 252 skirting the steens mountain escarpment is consistent with residuum from a midcrustal magma source of the massive flood basalts supporting the view of extensive mafic underplating and intraplating of the crust from cenozoic volcanism

anomalous fluid emission of a deep borehole in a seismically active area of northern apennines italy abstract the miano borehole 1047 m deep is located close to the river parma in the northern apennines italy a measuring station has been installed to observe the discharge of fluids continuously since november 2004 the upwelling fluid of this artesian well is a mixture of thermal water and ch4 as main components in non seismogenic areas a relatively constant fluid emission would be expected perhaps overlaid with long term variations from that kind of deep reservoir over time however the continuous record of the fluid emission in particular the water discharge the gas flow rate and the water temperature show periods of stable values interrupted by anomalous periods of fluctuations in the recorded parameters the anomalous variations of these parameters are of low amplitude in comparison to the total values but significant in their long term trend meteorological effects due to rain and barometric pressure were not detected in recorded data probably due to reservoir depth and relatively high reservoir overpressure influences due to the ambient temperature after the discharge were evaluated by statistical analysis our results suggest that recorded changes in fluid emission parameters can be interpreted as a mixing process of different fluid components at depth by variations in pore pressure as a result of seismogenic stress variation local seismicity was analyzed in comparison to the fluid physico chemical data the analysis supports the idea that an influence on fluid transport conditions due to geodynamic processes exists water temperature data show frequent anomalies probably connected with possible precursory phenomena of local seismic events

three dimensional seismic velocity structure of the northwestern united states 1 we present a high resolution three dimensional p wave tomography model for the northwestern united states major features of the model include clear well resolved images of the juan de fuca gorda slab to depths of at least 500 km reduced velocities beneath newberry volcano and north central oregon increased velocities beneath the idaho batholith and a deep slab like eastward dipping feature of increased velocities beneath nevada we find no evidence for a mantle plume in this region and demonstrate that suggested disruption of the juan de fuca slab beneath oregon in the vicinity of newberry volcano is an inversion artifact we interpret the primary features of this new model within the framework of post laramide tectonomagmatism and the continuing tectonic evolution of the cascadia subduction zone a model explaining the regional tectonomagmatic history consistent with the imaged seismic velocity structure is one driven by mantle flow responding to the evolving subduction system

geochemical precursors to seismic activity studies of earthquake precursory phenomena during the last several decades have found that significant geophysical and geochemical changes can occur prior to intermediate and large earthquakes among the more intensely investigated geochemical phenomena have been 1 changes in the concentrations of dissolved ions and gases in groundwaters and 2 variations in the concentrations of crustal and mantle volatiles in ground gases the concentration changes have typically showed no conanomalies trend either increasing or decreasing and the spatial and temporal distribution of the observed anomalies have been highly variable as a result there is little agreement on the physical or chemical processes responsible for the observed anomalies mechanisms proposed to account for precursory groundwater anomalies include ultrasonic vibration pressure sensitive solubility pore volume collapse fracture induced increases in reactive surfaces and aquifer breaching fluid mixing precursory changes in soil gas composition have been suggested to result from pore volume collapse micro fracture induced exposure of fresh reactive silicate surfaces and breaching of buried gas rich horizons an analysis of the available field and laboratory data suggests that the aquifer breaching fluid mixing ab fm model can best account for many of the reported changes in temperature dissolved ion and dissolved gas concentrations in groundwater ultrasonic vibration and pressure sensitive solubility models cannot reasonably account for the geochemical variations observed and although the pore collapse model could explain some of the observed chemical changes in groundwater and ground gas uncertainties remain regarding its ability to generate anomalies of the magnitude observed other geochemical anomalies in particular those associated with hydrogen and radon seem best accounted for by increases in reactive surface areas irsa model that may accompany precursory deformation around the epicenter of an impending earthquake analysis of the probable response of these models to the earthquake preparation process as well as to other environmental factors suggests that geochemical monitoring programs can provide information that may be valuable in forecasting the probability of an earthquake however because of the complexity of the earthquake preparation process the absolute prediction of seismic events using geochemical methods alone does not presently appear to be feasible

distribution and geochronology of oregon plateau u s a flood basalt volcanism the steens basalt revisited the timing and petrogenesis of mid miocene flood basalt volcanism in the northwest united states has been extensively addressed yet the chemical characteristics and temporal details of the steens basalt exposed on the oregon plateau are poorly defined steens basalt volcanism has generally been accepted to have occurred at 16 6 ma coeval and or just prior to the onset of columbia river basalt group volcanism to the north new major and trace element analyses and nine 40 ar 39 ar ages ranging from 15 51 0 28 to 16 58 0 18 ma were obtained on oregon plateau flood basalt lava flows from stratigraphic sections in close proximity to steens mountain additionally new 40 ar 39 ar ages were obtained on the uppermost and thirty first lava flow down from the top of the 1 km section of steens basalt exposed at steens mountain and yield eruption ages of 16 59 0 10 and 16 55 0 10 ma respectively field relations between these basalt sections suggest that multiple eruptive centers were present in the vicinity of steens mountain the chemical and chronologic data presented in this study illustrate that flood basalts with the steens basalt chemical signature erupted across the southern oregon plateau over a much greater timespan than what is typically quoted for the steens mountain type section these data suggest that the main volume of steens basalt volcanism erupted over at least an 1 m y duration from eruptive loci in the vicinity of steens mountain while likely much less voluminous volcanism and lithospheric input of mafic magma appears to have occurred for n2 ma across the oregon plateau these new geochemical and geochronological constraints verify a common temporal link between steens malheur gorge region and columbia river basalt group crbg volcanism this direct temporal link requires that petrogenetic and tectonic models of mid miocene northwestern u s flood basalt volcanism recognize that the northern columbia plateau and southern oregon plateau portions of this mid miocene basalt province were erupting simultaneously during portions of the regional event 2007 elsevier b v all rights reserved

perturbation analysis of convective instability of oceanic lithosphere and initiation of subduction zones a linear perturbation analysis is made on convective instability of the oceanic lithosphere to understand the occurrence of subduction on the earth the oceanic lithosphere is modeled by the upper part of top thermal boundary layer in a convecting newtonian temperature dependent viscosity fluid thickening of oceanic lithosphere with its age due to cooling at the surface is modeled by thickening of the thermal boundary layer with time its thickening rate l is a measure of the rate with which temperature in the thermal boundary layer decreases with time and hence is a measure of the rate with which viscosity in the thermal boundary layer increases with time the linear perturbation analysis shows the possible excitation of plural eigenmodes to give rise to an instability in the thermal boundary layer depending on a threshold value rc of the local rayleigh number r of the thermal boundary layer further rc is shown to be a linearly increasing function of l which is treated as a free parameter from estimates of r and l appropriate for the major oceanic lithosphere denoted as robs and l obs respectively i find that rc l 0 robs rc l l obs the flow pattern of mantle convection depends strongly on which eigenmodes are excited by the convective instability in thermal boundary layer 1 when r is lower thanrc only the fundamental and the first higher modes at most are excited the resulting mantle convection manifests itself as the secondary convection 2 when r is higher than rc the modes higher than the first higher mode are also excited the resulting mantle convection involves lithospheric instability leading to large local deformation in the oceanic lithosphere and finally to subduction of the oceanic lithosphere this result implies that 1 subduction does not begin newly in the major oceanic lithosphere at present since lithospheric instability is suppressed by thickening of the major oceanic lithosphere neither by its high viscosity nor by its buoyancy 2 subduction will newly begin in the major oceanic lithosphere due to lithospheric instability in future when the oceanic lithosphere becomes so old that its thickening rate l decreases to sufficiently small value the latter result suggests that lithospheric instability is an important agent that maintains multiplate tectonics on the earth

geochemical challenge to earthquake prediction the current status of geochemical and groundwater observations for earthquake prediction in japan is described the development of the observations is discussed in relation to the progress of the earthquake prediction program in japan three major findings obtained from our recent studies are outlined i long term radon observation data over 18 years at the ske suikoen well indicate that the anomalous radon change before the 1978 izu oshima kinkai earthquake can with high probability be attributed to precursory changes ii it is proposed that certain sensitive wells exist which have the potential to detect precursory changes iii the appearance and nonappearance of coseismic radon drops at the ksm kashima well reflect changes in the regional stress state of an observation area in addition some preliminary results of chemical changes of groundwater prior to the 1995 kobe hyogo ken nanbu earthquake are presented

the yellowstone snake river plain seismic profiling experiment crustal structure of the eastern snake river plain seismic refraction profiles recorded along the eastern snake river plain esrp in southeastern idaho during the 1978 yellowstone snake river plain cooperative seismic profiling experiment are interpreted to infer the crustal velocity and attenuation q 1 structure of the esrp travel time and synthetic seismogram modeling of a 250 km reversed refraction profile as well as a 100 km detailed profile indicate that the crust of the esrp is highly anomalous approximately 3 to 6 km of volcanic rocks with some interbedded sediments overlie an upper crustal layer compressional velocity approx 6 1 km s which thins southwestward along the esrp from a thickness of 10 km near island park caldera to 2 to 3 km beneath the central and southwestern portions of the esrp an intermediate velocity approx 6 5 km s layer extends from approx 10 to approx 20 km depth a thick approx 22 km lower crust of compressional velocity 6 8 km s a total crustall thickness of approx 42 km and a p sub n velocity of approx 7 9 km s is observed in the esrp similar to the western snake river plain and the rocky mountains provinces high attenuation is evident on the amplitude corrected seismic data due to low q values in the volcanic rocks q sub p more 20 to 200 and throughout the crust q sub p 160 to 300 based on these characteristics of the crustal structure and volcanic age progression data it is suggested that the esrp has resulted from an intensitive period of intrusion of mantle derived basaltic magma into the upper crust generating explosive silicic volcanism and associated regional uplift and caldera collapse this activity began about 15 m y ago in southwestern idaho and has migrated northeast to its present position at yellowstone subsequent cooling of the intruded upper crust results in the 6 5 km s velocity intermediate layer crustal subsidence and periodic basaltic volcanism as represented by the esrp complete the sequence of crustal evolution less

earthquake m 5 1 induced hydrogeochemical and δ18o changes validation of aquifer breaching mixing model in koyna india summary hydrochemical parameters and oxygen 18 18o were measured in groundwater from wells and spring waters from the active seismic area around koyna warna reservoirs over a period of three years 2005 2007 to explore their relationship with seismicity in comparison to average values observed later hydrochemical data of one of the wells revealed increased concentrations of chloride 100 per cent sulphate 300 per cent and fluoride 700 per cent while the 18o value decreased contemporarily to the occurrence of an earthquake of magnitude 5 1 on 2005 march 14 based on the hydrochemical and isotopic characteristics of different well waters in this area we conceptualize a model of aquifer breaching and mixing of deep aquifer water with shallow aquifer water due to the earthquake we estimated the fractions of two components of different aquifer waters mixed using two conservative tracers chloride and 18o the necessary mixing proportions of 50 per cent are unprecedented and call for further work to understand the earthquake related processes causing the observed hydrogeochemical and isotopic anomalies in the koyna warna region

long term seismotectonic influence on the hydrochemical composition of a spring located at koryaksky volcano kamchatka deduced from aggregated earthquake information the analysis of earthquake related signals in hydrochemical time series is still a challenging task mostly it is unclear how the geometrical and energetic distribution of earthquakes is influencing variation in the hydrochemical composition of monitoring sites e g located close to volcanoes past research showed that linear stress release models alone are not capable to explain sufficiently observed variation in hydrochemical time series due to earthquake activity a spring located at the base of koryaksky volcano which has shown hydrochemical variation close to 5 major earthquakes was chosen to analyse relation patterns between hydrochemical variation and seismicity a possible mechanism explaining observed hydrochemical variation that seismic waves trigger an underground water pumping caused by nucleation of gas bubbles in magma was proposed consequences are an increase of discharge gas content in water and changes in the mixing ratios of waters of different genesis based on functions of aggregated earthquake information e it is herein shown that seismotectonic triggered processes have a significant influence on the variation of the hydrochemistry of the spring lasting longer than two decades at least seven categories of relation patterns between hydrochemical variation and seismotectonic activity e can be identified a conducted spectral analysis shows that earthquake activity and hydrochemistry share spikes in frequencies results prove that the use of functions of transformed aggregated seismic observations is useful to represent the seismotectonic activity for analysing earthquake related signals in hydrochemical time series

earthquake impact on iron isotope signatures recorded in mineral spring water we investigated the iron isotope signatures of dissolved fe in the water of the wettinquelle mineral spring bad brambach germany by time series sampling covering seismically active periods related to tectonic activity near the eger rift system in central europe our objective was to test whether fe isotopes trace earthquake induced abiotic and biotic changes in the fluid rock interaction of the deep fissured granitic aquifer we found that the dissolved fe isotope signatures in spring water are distinct from the granitic source signature 56fe 0 09 particularly we discovered that water 56fe values are remarkably stable 0 01 0 11 2sd n 4 before and during a strong seismic swarm period in 2000 local magnitudes ml 3 while o2 and h2 concentrations in water decrease and dissolved fe content increases later recurring events of lower 56fe values down to 0 3 are observed in the period from 2001 to 2003 with intermittent seismic events 1 ml 2 6 the observations indicate a time lag between tectonic forcing and fe isotope response the role of abiotic fluid rock interaction and fe utilizing bacteria identified in the mineral spring water on fe isotope fractionation is discussed we explain recurring changes towards isotopically lighter values by a combination of fe dissolution from deep granite and admixture of isotopically light fe generated by a complex combination of abiotic and biotic processes operating in the aquifer when disturbed by swarm earthquakes events we propose a conceptual model scenario of earthquake triggered changes in biogeochemical processes

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

tectonic controls on magma genesis and evolution in the northwestern united states abstract field chronologic chemical and isotopic data for late cenozoic basaltic rocks from the northwestern united states illustrate the relationship between crustal structure and tectonic forces in controlling the genesis and evolution of continental volcanism in the northwestern u s the first major episode of basaltic volcanism was triggered by crustal rifting in a back arc environment east of the westward migrating volcanic arc created by the subduction of the juan de fuca plate beneath the north american plate rifting and volcanism were concentrated by pre existing zones of crustal weakness associated with boundaries between the old archean core of the continent and newly accreted terranes basalts erupted during this time columbia river steens mountain show evidence of significant fractionation histories including contamination by crust of varying age depending on the crustal structure at the eruption site presumably this reflects ponding and stagnation of primary magmas in the crust or at the crust mantle interface due to their encounter with thick crust not yet extended and still containing its low density easily fusible component continued rifting of this crust and modification of its composition through extraction of rhyolitic partial melts and deposition of the fractionation products from primary basaltic melts coupled with a shift in stress orientation roughly 10 5 ma ago allowed relatively unfractionated and uncontaminated magmas to begin reaching the surface in the western part of the region oregon plateau these magmas tapped a mantle source similar to that which produced most of the ocean island basalts of the northern hemisphere to the east snake river plain however the mantle sampled by basaltic volcanism has isotopic characteristics suggesting it has preserved a record of incompatible element enrichment processes associated with the formation of the overlying archean crustal section some 2 6 ga ago

crustal structure of the eastern snake river plain determined from ray trace modeling of seismic refraction data ray trace travel time modeling of the seismic refraction record sections for a profile from near soda springs idaho to near mckay idaho was used to derive a crustal model across the eastern snake river plain esrp the derived crustal model is consistent with the velocity structure interpreted from a profile along the axis of the esrp the interpretation also indicates that significant lateral inhomogeneities exist in the upper crust beneath the esrp when compared with the upper crust beneath the adjoining northern rocky mountain and basin and range provinces the most prominent features of the crustal structure inferred by the ray trace modeling are as follows 1 the northwest margin of the esrp was modeled as a fault structure downthrown on the srp side se with an offset of greater than 4 km the southeast margin conversely appears to be downwarped with possible minor faulting paleozoic sedimentary rocks are present beneath the cenozoic volcanics of the esrp possibly to and beyond 40 km from the southeastern margin of the esrp near blackfoot idaho 2 the modeling indicates no abrupt variation in the depth to the top of the lower crustal layer near the margins of the esrp 3 an intermediate 6 5 km s layer occurring beneath the esrp interpreted from a refraction profile located along the axis of the esrp was found to be localized within the esrp margins this layer is interpreted as a pervasive intrusion of higher velocity material from the upper mantle into the highly fractured upper crustal layer in this region 4 a density model of the crust across the esrp was prepared with the densities selected using the interpreted seismic velocities as a constraint the gravity field calculated from this model resulted in a good match to observed gravity data over the eastern snake river plain

earthquake induced chemical changes in the thermal waters of the umbria region during the 1997 1998 seismic swarm the compositional data collected at three thermal springs in the umbria region over a sampling period lasting two and a half hydrological years included the entire seismic sequence striking the central apennines italy in 1997 1998 wide temporal variations in the chemical composition and temperature of thermal waters were observed at all the sampling sites the widest were recorded at the triponzo sampling site where a temperature drop of 2 c and 20 c preceded by 4 days and 2 days respectively the occurrence of the event characterized by the deepest hypocentre of the entire seismic sequence despite such a macroscopic preseismic anomaly the recorded variations were not related to single seismic events or to the release rate of the seismic energy they actually seem to have been induced by permeability variations related to crustal deformation in the absence of elastic energy release and were thus linked to the whole seismogenic process

short term earthquake forecasting may be feasible at koyna india abstract reservoir triggered earthquakes have been occurring since the impoundment of shivaji sagar lake created by koyna dam in 1962 near the west coast of india over the past 38 years 15 earthquakes of magnitude 5 including the biggest reservoir triggered earthquake of m 6 3 on december 10 1967 and several hundred thousand smaller earthquakes have occurred we believe it is an ideal site for monitoring earthquake precursors which may lead to forecasts of m 5 earthquakes with adequate accuracy this optimism is based on the fact that here earthquakes occur in a small area of 30 km by 15 km and there are no other seismically active regions in the near vicinity the epicentral region is accessible for all kinds of experiments and observations and certain characters of koyna seismicity are quite well understood

rocky mountain evolution tying continental dynamics of the rocky mountains and deep probe seismic experiments with receiver functions 1 in this study we have determined the crustal structure using three different receiver function methods using data collected from the northern transect of the continental dynamics of the rocky mountains cd rom experiment the resulting migrated image and crustal thickness determinations confirm and refine prior crustal thickness measurements based on the cd rom and deep probe experiment data sets the new results show a very distinct and thick lower crustal layer beneath the archean wyoming province in addition we are able to show its termination at 42n latitude which provides a seismic tie between the cd rom and deep probe seismic experiments and thus completes a continuous north south transect extending from new mexico into alberta canada this new tie is particularly important because it occurs close to a major tectonic boundary the cheyenne belt between an archean craton and a proterozoic terrane we used two different stacking techniques based on a similar concept but using two different ways to estimate uncertainties furthermore we used receiver function migration and common conversion point ccp stacking techniques the combined interpretation of all our results shows 1 crustal thinning in southern wyoming 2 strong northward crustal thickening beginning in central wyoming 3 the presence of an unusually thick and high velocity lower crust beneath the wyoming province and 4 the abrupt termination of this lower crustal layer north of the cheyenne belt at 42n latitude

springwater chloride ion anomaly prior to a ml 5 2 pyrenean earthquake abstract we performed over a 598 day sampling period chemical analyses of commercially bottled spring water namely alet water rising in the vicinity of saint paul de fenouillet french eastern pyrenees where a ml 5 2 earthquake occurred these data display a chloride ion anomaly starting 5 days prior to the quake and lasting 10 13 days the anomaly is characterized by cl concentrations 36 above background values this precursory chemical change is attributed to a pre seismic strain change which induced mixing of geochemically different aquifers chloride rich groundwaters are known to rise close 10 km to the alet spring and mixing calculations suggest that a limited inflow of similar waters within the alet hydrologic system is a viable explanation for the chloride ion anomaly this result confirms that mineral springs are promising sites for the search of earthquake geochemical precursors

middle precambrian provenance of jurassic sandstone in the mino terrane central japan th u total pb evidence from an electron microprobe monazite study precise electron microprobe analyses have been made on detrital monazites in jurassic sandstones of the mino terrane central japan and their th u pb relations are examined in terms of pbo and tho2 tho2 tho2 plus the equivalent of uo2 the pbo tho2 ratios of most detrital monazites 403 of 581 grains cluster in the range from 0 0763 to 0 0618 other grains show the ratio of about 0 0541 46 grains 0 0364 29 grains 0 0170 24 grains and 0 0116 79 grains the pbo tho2 ratio of 0 0763 0 0618 is nearly identical with that of monazites in a middle precambrian 1740 ma gneiss clast from the kamiaso conglomerate of the mino terrane this strongly suggests that the detrital monazites were derived from gneisses and or granitoids of middle precambrian age the ratio of 0 0116 is nearly the same as that of monazites in a permian 274 ma paragneiss of the hida terrane north to the mino terrane the pbo tho2 monazite data coupled with palaeocurrent analyses and petrological characteristics of sandstones show that middle precambrian high grade metamorphic rocks and granitoids were widespread both in the northern and southern source regions of the e w trending jurassic basin of the mino terrane the pbo tho2 ratio of detrial monazites is a useful new measure for the provenance analysis of clastic rocks

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

chemical and isotopic seismic precursory signatures in deep groundwater cause and effect abstract exploratory hydrochemical studies were initiated in koyna india to examine the chemical changes in the deep groundwater due to seismic activity 2 months before the occurrence of a m 5 1 earthquake on 14th march 2005 a few deep wells 100 250 m out of a dozen recorded hydrochemical anomalies induced by this earthquake and the anomalies continued for the next 3 months periodical hydrochemical data of one of the wells indicated a linear increase in cl so 4 2 f and depleted 18 o from august 2006 to march 2009 though there is no long term change in groundwater level except short duration seasonal change the observed linear change is hypothesised as an effect of aquifer response to seismic stress related to an impending earthquake of m 5 the observed temporal change in different chemical concentrations projected linearly to the levels of march 2005 and estimated the time of the impending earthquake the same as that of march 2005 event as 2011 12 further the time projection also made based on exponential increase in hydrochemistry after 3 2009 advanced the possible time window to 2010 11 this hypothesis was realized on 12 december 2009 with an earthquake of m 5 1 even the simple arithmetic mean of the 45 a earthquake m 5 history of koyna indicates a recurrence time of 5 4 a to account for the observed temporal hydrochemical changes a model based on mixing of two aquifer waters caused by seismic stress was proposed hourly monitoring of electrical conductivity ec of groundwater also recorded conductivity changes induced by the m 5 1 earthquake on 12th december 2009 a very important observation that emerges from this study is that the cyclic change in subsurface stress leads to earthquakes continuous monitoring of ec may be helpful in visualizing the effect of tectonic forces on groundwater chemistry

moderate rates of late quaternary slip along the northwestern margin of the basin and range province surprise valley fault northeastern california 1 the 86 km long surprise valley normal fault forms part of the active northwestern margin of the basin and range province in northeastern california we use trench mapping and radiocarbon luminescence and tephra dating to estimate displacements and timing of the past five surface rupturing earthquakes on the central part of the fault near cedarville a bayesian oxcal analysis of timing constraints indicates earthquake times of 18 2 2 6 10 9 3 2 8 5 0 5 5 8 1 5 and 1 2 0 1 ka these data yield recurrence intervals of 7 3 4 1 2 5 3 2 2 7 1 6 and 4 5 1 5 ka and an elapsed time of 1 2 0 1 ka since the latest surface rupturing earthquake our best estimate of latest quaternary vertical slip rate is 0 6 0 1 mm a this late quaternary rate is remarkably similar to long term 8 14 ma minimum vertical slip rates 0 4 0 5 0 3 mm a calculated from recently acquired seismic reflection and chronologic and structural data in surprise valley and the adjacent warner mountains however our slip rate yields estimates of extension that are lower than recent campaign gps determinations by factors of 1 5 4 unless the fault has an unusually shallow 30 35 dip as suggested by recently acquired seismic reflection data coseismic displacements of 2 4 5 1 m documented in the trench and probable rupture lengths of 53 65 km indicate a history of latest quaternary earthquakes of m 6 8 7 3 on the central part of the surprise valley fault

detailed three dimensional shear wave velocity structure of the northwestern united states from rayleigh wave tomography abstract since the mid miocene the northwestern united states has experienced extensive flood basalt volcanism followed by the formation of two time progressive tracks of silicic volcanism the yellowstone snake river plains ysrp and the high lava plains hlp the ysrp track progresses towards the northeast parallel to north american plate motion and has therefore often been attributed to a deep mantle plume source however the hlp track progresses to the northwest over the same time frame in a direction not consistent with any regional plate motion the causes of the mid miocene flood basalts and the tracks of the ysrp and hlp are a matter of ongoing debate we present results of rayleigh wave phase velocity inversions and inversions for 3 d shear wave velocity structure of the northwestern united states using data collected from the high lava plains seismic experiment and the earthscope usarray transportable array ta the large number of stations used in these inversions allows us to show an unprecedented level of detail in the seismic velocity structures of this tectonically complex area our velocity images indicate that low s wave velocities in the uppermost mantle do not well match the track of hlp volcanism while at the surface the newberry caldera appears to anchor the nw end of the hlp hotspot track the seismic results show that it lies in a separate north south trending low velocity band just east of the cascades that is distinct from the main hlp trace the ultra low s wave velocities beneath the ysrp track extend locally to at least 175 km depth and are by far the most prominent seismic anomalies in the region along axis the ysrp hotspot track is characterized by a discrete low velocity channel in the upper mantle that shallows narrows and intensifies to the northeast but then deepens rapidly to the north beneath yellowstone the shallowing of the low velocity anomaly to the northeast is consistent with a stationary heat source beneath a moving plate coupled with basin and range extension and heating

geochronology of age progressive volcanism of the oregon high lava plains implications for the plume interpretation of yellowstone 1 the high lava plains province hlp is a late cenozoic bimodal volcanic field at the northern margin of the basin and range province in southeastern oregon that hosts a westward younging trend of silicic volcanism that crudely mirrors northeastward migration of silicic volcanism along the yellowstone snake river plain ysrp trend we present 40ar 39ar ages for 19 rhyolite domes 5 rhyolite ash flow tuffs and 34 basaltic lavas from the hlp the previously identified trend of westward migration of hlp rhyolites is confirmed the rate of propagation is 33 km m y from 10 to 5 ma slowing to 13 km m y after 5 ma the duration of silicic volcanism at any locus is 2 m y three older hlp dacite domes yielded ages of 15 5 ma basalts are not age progressive we identify several episodes of increased basaltic activity at 7 5 7 8 5 3 5 9 and 2 3 ma with the younger episode likely continuing into the recent the hlp and ysrp trends emerged from the axis of middle miocene basaltic volcanism of the columbia river and steens basalts we propose a model in which 1 miocene flood basalts and widespread silicic rocks are the result of emplacement of a plume head near the craton margin enhanced by flow up a topographic gradient along the base of the lithosphere at the craton margin 2 the hlp trend is the result of westward flow originating at the craton margin and 3 the ysrp trend is the trace of the motion of the north american plate over the tail of the plume

age constraints on late paleozoic evolution of continental crust from electron microprobe dating of monazite in the peloritani mountains southern italy another example of resetting of monazite ages in high grade rocks in situ monazite microprobe dating has been performed for the first time on trondhjemite and amphibolite facies metasediments from the peloritani mountains in order to obtain information about the age of metamorphism and intrusive magmatism within this still poorly known sector of the hercynian belt all samples show single stage monazite growth of hercynian age one migmatite and one biotitic paragneiss yielded monazite ages of 311 4 and 298 6 ma respectively these ages fit with previous age determinations in similar rocks from southern calabria indicating a thermal metamorphic peak at about 300 ma at the same time as widespread granitoid magmatism the older of the two ages might represent a slightly earlier event possibly associated with the emplacement of an adjacent trondhjemite pluton previously dated by shrimp at 314 ma no evidence for pre hercynian events and only a little indication for some monazite crystallization starting from ca 360 ma were obtained from monazite dating of the metasediments suggesting either a single stage metamorphic evolution or a significant resetting of the monazite isotope system during the main hercynian event ca 300 ma rare monazite from a trondhjemite sample yields evidence for a late hercynian age of about 275 ma this age is interpreted as representing a post magmatic stage of metasomatic monazite crystallization which significantly postdates the emplacement of the original magmatic body

crustal genesis on the oregon plateau the areal and temporal distribution and the chemical and isotopic characteristics of cenozoic volcanic rocks from the oregon plateau reflect the changing tectonic conditions affecting this area over the last 20 m y following subduction zone related calc alkaline volcanism flood basalt eruptions occurred in the time interval 18 14 ma this primarily basaltic volcanism is interpreted to be the result of a major shift in spreading orientation of the juan de fuca ridge that resulted in changes in the geometry of subduction against the pacific northwest the compositions of the mid miocene flood basalts show signs of extensive crystal fractionation in some cases accompanied by crustal contamination roughly 11 m y ago basalt eruptions showed an increasing tendency toward smaller volumes and less evolved compositions this implies that as extension in the oregon plateau proceeded the crust became less of an impediment to the passage of relatively unfractionated mantle melts initial sr nd and pb isotopic compositions of all the basalts show more correlation with the geographic position of eruption than with the composition of the lava primary control over the isotope systematics appears to be due to changes in the age and chemical characteristics of the crust and mantle throughout this area these observations suggest that an area of some 130 000 km2 of crust and basalt depleted subcontinental mantle has been added to northwestern north america over the last 20 m y the intensity of basalt volcanism as manifest in the columbia river group and in the oregon plateau does not appear to reflect the presence of a hot spot beneath the area both the areal and temporal distribution of the lavas and their geochemical characteristics are more easily reconciled with the suggestion that this crustal section grew by back arc spreading in a manner analogous to the formation of the marginal basins of the western pacific this spreading initiated along the western border of the archean wyoming craton with the location of mantle ascent melt production and extraction controlled by the changing geometry of subduction the existence of a zone of lithospheric weakness and the presence of a thick low density subcontinental mantle keel existing beneath the archean craton in this area

a controlled source seismic and gravity study of the high lava plains hlp of eastern oregon 1 this study employs data collected during the high lava plains hlp controlled source seismic experiment conducted in september 2008 in this experiment 2612 short period seismic recorders and 120 3 component recorders were deployed across eastern oregon and adjacent parts of nevada and idaho to record 15 seismic sources seismic and gravity data were integrated to create 2 d crustal scale p wave velocity and density models for the 400 km long nw se and n s profiles to provide a better understanding of the crustal and upper mantle structure and ultimately the magmatic and tectonic evolution of the region these models are the first high resolution images beneath the path of migratory bi modal volcanism that dotted the high lava plains beginning at 16 ma our models show that the crustal structure across the hlp region is similar to that of the northern basin and range which has experienced extension since 35 ma but with moderate magmatic modification of the crust a thick layer 5 7 km of sediments and volcanics extends over most of the area and is thickest in the harney basin area we interpret denser faster material in the lower to middle crust under the southern harney basin area to be mafic intraplating we have also identified a region of denser faster material in the upper crust in the vicinity of oregon idaho border the crust thickens from 34 to 37 km and the lower crust increases in density 2 8 2 85 g cm3 from west to east across eastern oregon in close proximity to the interpreted position of the 0 706 sr isotope line suggesting a decrease in extension in the lowermost crust below the southeastern hlp there is relatively high velocity 7 2 7 4 km s and density 2 95 g cm3 that suggests the presence of underplating the hlp region has undergone moderate extension and the average crustal velocity is somewhat higher than in the adjacent basin and range suggesting some magmatic modification in the lower crust but not as much as might be expected given the voluminous surface volcanism

search for earthquake precursors in well water levels in a localized seismically active area of reservoir triggered earthquakes in india 1 four cases of coseismic changes are observed in water levels recorded at a close network of wells around seismically active koyna warna region in western india during 1997 2000 while coseismic increase of 2 7 cm in water levels is observed for earthquakes of m 4 3 4 7 in three cases a trough like decrease of 0 4 8 cm is observed at 7 wells for an m 5 2 earthquake all these earthquakes occurred within the network of wells drilled for the study our results suggest that decrease in water levels prior to these earthquakes may be premonitory in nature we show that magnitude of the earthquake and epicentral distance are two vital parameters to record anomalous changes in our study local earthquakes of m 4 3 are recorded at a maximum distance of about 24 km our studies provide first observations from a unique experiment in india which will have implications in developing earthquake prediction models

nature of the crust beneath northwest basin and range province from teleseismic receiver function data received 30 july 2007 revised 12 april 2008 accepted 2 july 2008 published 14 october 2008 1 we utilized teleseismic receiver function techniques complemented by active source refraction seismology to study the crustal structure and continental rift processes responsible for the development of the northwest corner of the basin and range province in northwest nevada our passive seismic array of 28 short period stations spanning 70 km west to east and 5 broadband usarray transportable array stations that extended our aperture to 230 km provided data on crustal properties independent of the results of our active source refraction experiment combining data from the two experiments provides better constraints on moho depth vp vs ratio and the structure and composition of the crust beneath the northwestern basin and range province than possible from either experiment alone our new data indicate moho depths that vary from 29 5 on the east to 36 5 km in the west along the passive source array and vp vs ratios that systematically span a wide range from 1 68 to 1 83 velocity modeling of data collected from the 300 km wide angle refraction reflection survey provides comparable moho depths of 32 37 km under the same region decreasing vp vs is correlated with decreasing crustal thickness with vp vs ratio 1 80 in northeast california and vp vs 1 74 in the thinner crust of the basin and range province we associate the high vp vs of northeast california with mafic additions to the crust during formation of the modoc plateau in a region of accreted paleozoic island arc terrans similar to those exposed in the eastern klamaths and northwestern sierra nevada unusually low vp vs in conjunction with low absolute vp and vs is observed beneath the central part of our array and may be due to the roots of the sierra nevada batholith now dismembered by basin and range faults back azimuthal stacking of our receiver function data suggests a northwest oriented crustal anisotropy fast direction beneath this region parallel to the northwest to southeast oriented cenozoic extension experienced by the basin and range province and suggestive of a similar flow direction in the middle to lower crust

coupling between mineral reactions chemical changes in groundwater and earthquakes in iceland chemical analysis of groundwater samples collected from a borehole at hafralaekur northern iceland from october 2008 to june 2015 revealed 1 a long term decrease in concentration of si and na and 2 an abrupt increase in concentration of na before each of two consecutive m 5 earthquakes which occurred in 2012 and 2013 both 76 km from hafralaekur based on a geochemical major elements and stable isotopes petrological and mineralogical study of drill cuttings taken from an adjacent borehole we are able to show that 1 the long term decrease in concentration of si and na was caused by constant volume replacement of labradorite by analcime coupled with precipitation of zeolites in vesicles and along fractures and 2 the abrupt increase of na concentration before the first earthquake records a switchover to nonstoichiometric dissolution of analcime with preferential release of na into groundwater we attribute decay of the na peaks which followed and coincided with each earthquake to uptake of na along fractured or porous boundaries between labradorite and analcime crystals possible causes of these na peaks are an increase of reactive surface area caused by fracturing or a shift from chemical equilibrium caused by mixing between groundwater components both could have been triggered by preseismic dilation which was also inferred in a previous study by skelton et al 2014 the mechanism behind preseismic dilation so far from the focus of an earthquake remains unknown

upper crustal structure of newberry volcano from p wave tomography and finite difference waveform modeling 1 seismic tomography combined with waveform modeling constrains the dimensions and melt content of a magma body in the upper crust at newberry volcano we obtain a p wave tomographic image by combining travel time data collected in 2008 on a line of densely spaced seismometers with active source data collected in the 1980s the tomographic analysis resolves a high velocity intrusive ring complex surrounding a low velocity caldera fill zone at depths above 3 km and a broader high velocity intrusive complex surrounding a central low velocity anomaly at greater depths 3 6 km this second upper crustal low velocity anomaly is poorly resolved and resolution tests indicate that an unrealistically large low velocity body representing 60 km3of melt could be consistent with the available travel times the 2008 data exhibit low amplitude first arrivals and an anomalous secondary p wave phase originating beneath the caldera two dimensional finite difference waveform modeling through the tomographic velocity model does not reproduce these observations to reproduce these phases we predict waveforms for models that include synthetic low velocity bodies and test possible magma chamber geometries and properties three classes of models produce a transmittedp phase consistent with the travel time and amplitude of the observed secondary phase and also match the observed lower amplitude first arrivals these models represent a graded mush region a crystal suspension region and a melt sill above a thin mush region the three possible magma chamber models comprise a much narrower range of melt volumes 1 6 8 0 km3 than could be constrained by travel time tomography alone

radon recording of uttarkashi earthquake spatial and temporal distribution of radon is recorded in both soil gas and groundwater using two different techniques viz track etch method and emanometry radon recording stations have been set up at one site in amritsar and four sites in the kangra valley himachal pradesh under the himalayan seismicity project the track etch method gives integrated measurement of radon over a week or a fortnight whereas emanometry is used for daily recording of radon activity in soil gas and groundwater the uttarkashi earthquake mb 6 5 ms 7 0 occurred on october 20 1991 oct 19 u t in the garhwal himalayas 30 78 n 78 77 e about 330 km from our recording stations in the kangra valley and about 450 km from amritsar respectively radon anomalies were recorded at all sites in kangra valley and amritsar about a week before the uttarkashi earthquake which clearly establishes that radon changes can be effective for forecasting some earthquakes

faulting in a propagating continental rift insight from the late miocene structural development of the abert rim fault southern oregon usa abstract new geological mapping and 40ar 39ar ages reveal a temporal progression of faulting along a major extensional fault the abert rim fault at the active margin of the basin and range province in the western u s the onset of extensional deformation near lake abert coincided with widespread basaltic volcanism fault cross cutting relationships and tilt of volcanic layers demonstrate that nw striking faults formed between 8 9 and 7 5 ma and were subsequently cut by the nne striking abert rim fault sequential restoration of cross sections indicate that the abert rim fault south of 42 40 n latitude had 250 m of stratigraphic separation prior to deposition of the rattlesnake tuff at 7 ma low values of net extension 4 and long term rates of geologic deformation 1 mm yr suggest that regional extension since 10 ma has occurred primarily by diking we model province wide along and across strike expansion within the margin of the basin and range province as regional dilation accompanying northward propagation of the walker lane transform the growth of this extensional province is superimposed on a previously unrecognized early miocene volcanic landscape marked by volcanism between 21 4 and 22 3 ma dike orientations within one of these early miocene volcanoes and evidence for the existence of as much as 500 m of paleo topography prior to widespread deposition of the steens basalts at 16 ma suggests that late miocene faults near lake abert may reactivate an older structural fabric

stratigraphic and structural evolution of the middle miocene synvolcanic oregon idaho graben the oregon idaho graben is a newly identified north south trending synvolcanic graben in southeastern oregon and southwestern idaho within the middle miocene backarc rift system that extends 1100 km from southern nevada to southeastern washington the graben formed along the western margin of the north american craton shortly after the largest volumes of tholeiitic flood basalt erupted columbia river basalt group steens pueblo basalt basalt of malheur gorge basalt and latite unit of ekren et al 1981 1 rhyolite flows and ash flow tuffs 16 1 14 0 ma erupted from northeastern oregon dooley volcanics to northern nevada mcdermitt volcanic field shortly after the flood basalt was emplaced subsidence of the oregon idaho graben 15 5 15 3 ma coincides with eruption of rhyolite flows and caldera related ash flow tuffs from vents along the margins and within the graben mafic and silicic intragraben volcanism accompanied sedimentation from about 15 3 to 10 5 ma sedimentary and volcanic rocks from extrabasinal sources especially southwestern idaho were introduced periodically after initial subsidence the evolution of the oregon idaho graben is divided into three stages stage 1 15 3 14 3 ma followed intragraben caldera collapse and was marked by deposition of fluvial and lacustrine sediment across the graben stage 2 14 3 12 6 ma movement on intragraben fault zones divided the graben into distinct subbasins and marked the onset of calc alkalic volcanism fine grained tuffaceous sediment derived from glassy rhyolite and pyroclastic deposits and basalt tuff cones interbedded with rhyolite ash and lapilli fall deposits and locally erupted basalt hydrovolcanic deposits predominated during synvolcanic subsidence synsedimentary hot spring alteration and precious metals mineralization of graben fill were controlled by the same intragraben fault zones that served as magmatic conduits during stage 3 12 6 10 5 ma the subbasins were filled and graben wide fluviatile and lacustrine sedimentation resumed at about the same time renewed rhyolitic volcanism occurred on both flanks and tholeiitic volcanism resumed within the oregon idaho graben subsidence in the oregon idaho graben ceased as west northwest striking faults related to the formation of the western snake river plain became active 1 ref 28

gigantic seismogenic landslides of summer lake basin south central oregon subsidence of summer lake basin situated in the northwestern basin and range province in south central oregon has exposed a kilometer thick neogene sequence of dense volcanic flow rocks overlying very weak tuffaceous sedimentary rocks in the bounding winter ridge slide mountain escarpment subsidence occurs along the active 40 km long winter ridge slide mountain fault which is capable of producing mw 7 earthquakes with near field maximum horizontal acceleration approaching 1 g gigantic landslides cubic kilometers in volume scallop the southwestern part of the escarpment and the deposits run out several kilometers characteristic of rock avalanches geotechnical rock mass characterization and slope stability analyses confirm observations that these landslides were initiated within the weak tuffaceous sedimentary rocks along shallow east dipping planar failure surfaces are insensitive to groundwater fluctuations and are stable under static conditions pseudostatic analyses reveal that strong shaking is required to trigger landsliding the bennett flat landslide failed as a single event between 900 270 ka and 16 8 ka the landslide has a depletion zone volume of 1 1 km3 but only 0 3 km3 of debris is discernible in the accumulation zone the foster creek landslide also appears to have failed as a single event between 180 and 16 8 ka the landslide has a depletion zone volume of 2 9 km3 but only 0 3 km3 of debris is discernible in the accumulation zone the punchbowl landslide evidences multiple events the most recent of which failed in the holocene and had a volume of 0 4 km3 0 5 km3 of debris is found in the accumulation zone

receiver function imaging of upper mantle complexity beneath the pacific northwest united states abstract small scale topographic variations on the upper mantle seismic discontinuities provide important constraints on the thermal influences of upwellings and downwellings in geodynamically complex regions subduction of the juan de fuca plate and other tectonic processes dominating the pacific northwest united states in the cenozoic involve massive thermal flux that likely result in an upper mantle that has strong 3 d temperature variations we address the interaction of such processes in the region using receiver functions to image the upper mantle seismic discontinuities at 410 and 660 km we utilized over 15 000 high quality receiver functions gathered from 294 teleseismic earthquakes recorded at 277 regional broadband seismic stations primarily those of the earthscope usarray transportable array we find the average depths of the discontinuities to be 412 km and 658 km respectively with no obvious 520 km discontinuity detected the peak to peak range is greater on the 410 than the 660 suggesting the possibility of more significant regional dynamic processes at upper mantle depths our results are not consistent with a mantle plume below central oregon in the high lava plains region our observation of a thinner transition zone beneath the western snake river plain region however is consistent with a regional increase in mantle temperatures perhaps due to either asthenospheric flow from beneath and around the southern edge of the juan de fuca plate or to vertical flow in the form of regional mantle upwelling related to the snake river plain yellowstone hotspot track further our results are not consistent with a simple subducting juan de fuca slab morphology but rather suggest similar levels of significant complexity in slab structure found by recent regional tomographic studies we find evidence for a thickened and therefore cooler mantle transition zone beneath the wallowa idaho batholith region consistent with tomographic models which suggest broad scale increased seismic velocities to transition zone depths we speculate that this region may be the location of mantle downwelling at larger scales than previously proposed