most and least likely locations of large to great earthquakes along the pacific coast of mexico estimated from local recurrence times based on b values we mapped t l and p l local recurrence time and local probability density respectively for m max 7 2 earthquakes along the plate margin of the pacific coast of mexico in order to test two hypotheses the first is that the minima in t l or maxima in p l extracted probabilistically from the frequency magnitude distribution map asperities the second hypothesis is that recurrence times for characteristic events are estimated more correctly by local recurrence times than by the overall recurrence times of the zone comparing these results to the observed recurrence times for events of m 7 0 we find good agreement the coast of guerrero between longitude west 100 5 and 101 5 and the segment off the coast of southern chiapas show the shortest t l estimated as about 20 yr the location at longitude 98 5 near the boundary of guerrero with oaxaca the ometepec segment follows with estimates of about 30 yr as the next shortest t l along the coast of guerrero between 99 and 100 5 longitude t l is estimated as about 40 yr and finally in the segments off the oaxacan coast near 95 7 and 97 7 longitude t l ranges from 40 to 60 yr these volumes we define as asperities long local recurrence times are observed for the areas offshore from the isthmus of tehuantepec on the pacific plate off the coast of guerrero on land along the coast of most of oaxaca and along the northernmost 40 km of the guerrero coast if our ideas are correct then major moment release should emanate from the volumes we defined as asperities and relatively minor moment release should emanate from the volumes identified by the relatively long local recurrence times

attenuation relationships of peak ground acceleration and velocity for crustal earthquakes in taiwan strong seismic ground motion data obtained by the taiwan strong motion instrumentation program tsmip and central mountain strong motion array cmsma are used to derive new attenuation relationships for the vertical and horizontal peak ground acceleration pga and peak ground velocity pgv for crustal earthquakes in taiwan more than 7900 three component accelerograms recorded from 51 crustal earthquakes in taiwan with m w magnitudes ranging from 4 0 to 7 1 have been analyzed to study the dependence of peak ground motion parameters on magnitude distance regional and local site effects through attenuation relationships we first found that for both pga and pgv the attenuation relationships decay faster with distance for the vertical component than for the horizontal component also the attenuation relationships decay faster with distance for the vertical pga than for the vertical pgv we further compared the attenuation relationships for three subregions chy iwa and nto and the whole taiwan region twn it is found that the chy area has higher ground motion either in pga or pgv than the other areas especially at near source distances this is because the chy area is located on a thick recent alluvial plain comparison of our new attenuation relationships with strong motion data from the 1999 chi chi earthquake m w 7 7 and the 2003 cheng kung earthquake m w 6 8 shows that the attenuation relationships developed for m w 7 can be extrapolated to make reasonable estimates of strong motion from larger m w 7 earthquakes finally we analyzed the residuals to investigate variations of pga and pgv with respect to site conditions the results show that 1 the residual contour maps especially for the pgv have high consistency with the regional geology and topography of taiwan 2 the pgv residual contours reveal that taipei basin changhua plain chianan plain pingtung valley ilan plain and taitung longitudinal valley have high residual values note that most major metropolitan areas all fall in high residual areas 3 the site classification based on geologic criteria by lee et al 2001 can be simplified into three classes that is class e for soft soils a combination of classes c and d for dense and stiff soils and class b for rocks these three site classes are mostly distributed respectively in the alluvial plains at an elevation less than 50 m in terraces and hills at an elevation less than 1000 m and in high mountainous areas

stress changes modelled for the sequence of strong earthquakes in the south iceland seismic zone since 1706 the south iceland seismic zone is roughly speaking situated between two sections of the mid atlantic ridge i e the reykjanes ridge southwest of iceland and the eastern volcanic zone on the island it is a transform zone where earthquakes are expected to occur on e w trending left lateral shear faults equivalent to conjugate n s oriented right lateral rupture planes in fact earthquakes take place on en echelon n s oriented faults which is indicated by the distribution of main shock intensities aftershocks as well as by surface fault traces the stress field continuously generated in the fault zone by opening of the adjacent ridges is computed and superimposed on the stress field changes induced by a series of 13 earthquakes m 6 between 1706 and 2000 the level of the pre seismic stress field is analysed as well as the size of the area under high stress finally the post seismic stress field of june 2000 is analysed to see where high stresses might have accumulated the modelling indicates that the rupture planes located on separated parallel n s striking zones are dense enough to lead to an area wide stress release by the series of events the obtained pre seismic stress level for most events is high and stable with the exception of situations when several strong shocks occur over a time span of several days i e display typical main shock aftershock patterns the size of areas under high stress aside from of the rupture plane i e where no event occurs at the specific time is of medium to small size

probability for simulating future earthquakes with mw 6 0 in taiwan for seismic hazard for the earthquake catalog from 1900 to 2008 in this study we use extreme value theory based on gumbel equation derivations to estimate the gutenberg richter a and b parameters for taiwan data are from the augmented homogenized in terms of moment magnitude historic catalog for taiwan the island is divided into grids of 0 2 latitude by 0 2 longitude and gumbel type 1 statistical analysis is applied the values of a and b are then used to determine the probability of large earthquakes m w 6 0 occurring at each grid the results show two relatively high probability paths for large earthquakes one extending from hsinchu southward to taichung chiayi and tainan in western taiwan and the other from ilan southward to hualian and taitung in eastern taiwan both of which are characterized by low b values it indicates that future earthquakes can be expected along these paths characterized by low b values additionally maximum peak ground acceleration and maximum peak ground velocity determined from respective attenuation laws and a gridding regimen of 0 1 latitude by 0 1 longitude for taiwan follow similar paths to that of the low b values

locked and creeping patches along the hayward fault california the results of mapping locked and unlocked patches on the hayward fault using the local recurrence time method are compared with models derived from surface creep and geodetic measurements the data used were the m 1 0 earthquakes in the usgs catalog since 1981 0 located within 5 km of the fault trace along the central and southern segments agreement with the other methods is satisfactory the 1868 rupture except for its two ends is classified as a locked segment by our method in the northern part of the hayward fault the data are poor and the results of the three methods differ short local recurrence times in the northern part suggest that an asperity exists there which is capable of an m6 5 class event

grain boundary migration of water and carbon dioxide during uplift of garnet zone alpine schist new zealand deformed quartz veins in garnet zone schist adjacent to the active alpine fault new zealand have fluid inclusions trapped along quartz grain boundaries textures suggest that the inclusions formed in their present shapes during annealing of the deformed veins many of the inclusions are empty but some contain carbon dioxide with densities that range from 0 16 to 0 80 g cm 3 no water nitrogen or methane was detected the inclusions are considerably more co2 rich than either the primary metamorphic fluid 5 co2 or fluids trapped in fracture related situations in the same or related rocks 50 co2 enrichment of co2 is inferred to have resulted from selective migration wicking of saline water from the inclusions along water wet grain boundaries after cooling induced immiscibility of a water co2 mixture inclusion volumes changed after loss of water non wetting co2 remained trapped in the inclusions until further percolation progressively removed co2 in solution this mechanism of fluid migration dominated in ductile quartz rich rocks near but below the brittle ductile transition at deeper levels hydraulic fracturing is also an important mechanism for fluid migration whereas at shallower levels advection through open fractures dominates the fluid flow regime

test of seismic hazard map from 500 years of recorded intensity data in japan abstract maximum seismic intensity maps for japan are constructed using the recorded intensity data from 1498 to 2007 and are used to test the probabilistic seismic hazard map pshm by the headquarters for earthquake research promotion japan the historical intensity maps are compared with the hazard maps of probable maximum seismic intensity for a 475 yr return period assuming a poisson distribution 10 in 50 yrs we look at cases that include all events only subduction zone earthquakes and all events excluding subduction zone earthquakes the megathrust earthquakes in the subduction zones produce large bands of high intensities along the pacific coast side while onshore crustal earthquakes create a patchy distribution of large intensities over all of japan the maximum recorded intensity map for the past 500 yrs and the maximum predicted intensity map for the return period from the pshm are very similar for the cases including all events and the subduction zone earthquakes while there is poor correlation for the third category that includes mostly onshore crustal earthquakes if we consider only the amount of area not the specific locations the recorded intensity map and the pshm using the maximum case have a high degree of correlation for japanese meteorological agency jma intensity higher than 4 for all of the cases statistically the present hazard maps for japan seem to agree with the past intensity distributions and can be regarded as appropriate hazard maps even though there may be strong dependencies on uncertain model parameters for the pshms

fluids in coesite bearing rocks of the tso morari complex nw himalaya evidence for entrapment during peak metamorphism and subsequent uplift fluid inclusions trapped in coesite bearing rocks provide important information on the fluid phases present during ultrahigh pressure metamorphism the subduction related coesite bearing eclogites of the tso morari complex himalaya contain five major types of fluids identified by microthermometry and raman spectroscopy these are 1 high salinity brine 2 n 2 3 ch 4 4 co 2 and 5 low salinity aqueous fluids these fluids were trapped during both deep subduction and exhumation processes the coesite bearing rocks are inferred to have been buried to a depth of 120 km where they experienced ultrahigh pressure metamorphism the fluid rock interaction provides direct evidence for fluid derivation during a deep subduction process as demonstrated by silica carbonate assemblages in eclogite high salinity brine n 2 and ch 4 inclusions are remnants of prograde and peak metamorphic fluids whereas co 2 and low salinity aqueous fluids appear to have been trapped late during uplift the high salinity brine was possibly derived from subducted ancient metasedimentary rocks whereas the n 2 and ch 4 fluids were likely generated through chemical breakdown of nh 3 bearing k minerals and graphite alternatively ch 4 might have been formed by a mixed fluid that was released from calcareous sediments during subduction or supplied through subducted oceanic metabasic rocks high density co 2 is associated with matrix minerals formed during granulite facies overprinting of the ultrahigh pressure eclogite during retrogression to amphibolite facies conditions low salinity fluids were introduced from external sources probably the enclosing gneisses this source enhances salinity differences as compared to primary saline inclusions the subducting indian lithosphere produced brines prior to achieving maximal depths of 120 km where fluids were instead dominated by gaseous phases subsequently the indian lithosphere released co 2 rich fluids during fast exhumation and was then infiltrated by the low salinity aqueous fluids near the surface through external sources elemental modelling may improve quantitative understanding of the complexity of fluids and their reactions

evolution of the mo rich scheelite skarn mineralization at kozbudaklar western anatolia turkey evidence from mineral chemistry and fluid inclusions abstract the kozbudaklar scheelite skarn deposit in the tavsanli zone located approximately 22 km southeast of bursa is hosted by the triassic calcic inonu marble and eocene topuk pluton at least four stages have been recognized through skarn evolution scheelite skarn distributed close to the topuk pluton occurred during the early stage 1 and late stage 2 prograde substages the early prograde endo and exoskarn are composed of hedenbergite hd 96 joh 4 plagioclase an 55 64 and hedenbergite hd 61 94 joh 4 7 accompanied by calcic garnet grs 38 94 sps 1 5 alm 0 and scheelite pow 1 6 the second stage represents a relatively oxidized mineralogy dominated by diopside hd 16 48 joh 0 9 subcalcic garnet grs 24 92 sps 0 11 alm 0 31 and scheelite pow 7 32 the stage 3 and 4 mineral assemblages are characterized by few hydrous minerals in the retrograde stage and intense fracturing fluid inclusions from skarn rocks are indicative of multiple fluid events 1 low moderate salinity 5 16 wt nacl equiv inclusions homogenized dominantly by a high temperature 308 c to 600 c liquid phase in stage 1 fluid inclusions in an early garnet homogenized over a similar temperature range 440 c and 459 c into both liquid and vapor phases eutectic temperatures ranging from 61 7 c to 35 0 c that indicate the presence of h 2 o nacl mgcl 2 cacl 2 co 2 solutions 2 coexisting daughter mineral bearing high salinity 29 5 70 wt nacl equiv and vapor rich moderate salinity 11 5 16 7 wt nacl equiv inclusions that homogenized in the liquid phase by the disappearance of the vapor phase at a similar temperature range 308 c to 600 c in stage 2 eutectic temperatures range from 67 9 c to 51 8 c that shows the presence of h 2 o nacl co 2 ch 4 n 2 solutions 3 low moderate salinity 12 5 7 6 wt nacl equiv and temperature 320 c to 215 c inclusions homogenized by the liquid phase in stage 3 eutectic temperatures range from 59 5 c to 44 2 c indicating the presence of h 2 o nacl mgcl 2 cacl 2 co 2 solutions 4 inclusions of low salinity 9 9 0 9 wt nacl equiv and homogenization temperature 183 c to 101 c in stage 4 these data show that the kozbudaklar skarn deposit was formed in a magmatic hydrothermal system in this model carbonaceous fluids may have been exsolved from the plutonic rock during its emplacement and crystallization fluid inclusion data indicate that fluid boiling and immiscibility occurred at temperatures between 440 c and 459 c and pressures ranging from 50 mpa to 60 mpa based on hydrostatic considerations early scheelite was precipitated with relatively reduced mineral compositions as a result of depressurization mo rich scheelite with oxidized minerals formed via high salinity and vapor rich inclusions the second scheelite mineralization occurred in a normal hydrothermal system by an infiltration mechanism at pressures between approximately 40 and 1 5 mpa at shallow depths

estimated seismic intensity distributions for earthquakes in taiwan from 1900 to 2008 in this study we recreated peak ground accelerations pga and peak ground velocity pgv distributions for taiwan by applying the attenuation relations of liu and tsai 2005 to calculate the pga and pgv values for 1989 mw 5 0 earthquakes in a catalog of earthquakes from 1900 to 2008 with homogenized magnitude mw chen and tsai 2008 we further combined the pga and pgv values to obtain corresponding modified mercalli intensity mmi values wald quitoriano heaton kanamori et al 1999 and their spatial distributions and recurrence intervals we adopted a logarithmic functional form analogous to the gutenberg richter relation for seismicity to represent the annual frequency of seismic intensity parameters log10n a blog10pga log10n a blog10pgv and log10n a bi the regions with high pga and pgv values are often associated with low b values in these equations as it is well known that the mw 7 45 chi chi earthquake of 21 september 1999 had produced high pga values in excess of 0 9g and pgv values in excess of 300 cm s we used these relations to estimate the poisson probability distributions in taiwan for mmi viii i e pga 485g for recurrence intervals of 30 50 and 100 years the results show a wide range of differences in the poisson probability of mmi viii among different areas of taiwan for example for a 50 year interval this probability at 10 major cities in taiwan is as follows taipei 0 67 hsinchu 2 15 taichung 5 24 chiayi 24 35 tainan 1 61 kaohsiung 0 04 hengchun 4 94 ilan 17 67 hualien 37 04 and taitung 9 82 these esti mates should be of interest to city planners especially for earthquake preparedness planning

synthetic h2oco2 fluid inclusions in spontaneously nucleated forsterite enstatite and diopside hosts the method and applications abstract synthetic h2o co2 fluid inclusions have been produced in forsterite diopside and enstatite hosts during the spontaneous nucleation and growth of these phases at t 800 980 c and p 6100 7800 bars via the reactions 2 trem 18h 2 o 4 diopside 3 forsterite 5si oh 4 2h 2 o 1 trem 3h 2 o 2 diopside 3 enstatite si oh 4 2h 2 o 2 the inclusions are large 10 40 m abundant and commonly of regular shape making them ideal as standards for microthermometric and spectroscopic analyses the technique provides the opportunity to study fluid inclusion trapping mechanisms and their potential effect on inclusion chemistry the fluid inclusions exhibit a small degree of compositional scatter about the ambient composition deviations between the ambient and inclusion composition increase for experiments performed in the presence of low 3 8 c thermal gradients along the capsule length this observation suggests that compositional heterogeneities may develop in the absence of fluid convection in the capsule the effect on the inclusion composition however does not exceed 3 mol in xco2 for all inclusions studied the advantages of this technique are 1 it provides a means of producing fluid inclusions of known compositions in hosts other than quartz and 2 inclusion formation is relatively slow allowing ample time for the p t x fluid conditions of the run to equilibrate the disadvantages are that the small grains produced can be difficult to work with and the host producing reactions are viable over a relatively narrow range of p t x fluid conditions

inferring transport characteristics in a fractured rock aquifer by combining single hole ground penetrating radar reflection monitoring and tracer test data 1 investigations of solute transport in fractured rock aquifers often rely on tracer test data acquired at a limited number of observation points such data do not by themselves allow detailed assessments of the spreading of the injected tracer plume to better understand the transport behavior in a granitic aquifer we combine tracer test data with single hole ground penetrating radar gpr reflection monitoring data five successful tracer tests were performed under various experimental conditions between two boreholes 6 m apart for each experiment saline tracer was injected into a previously identified packed off transmissive fracture while repeatedly acquiring single hole gpr reflection profiles together with electrical conductivity logs in the pumping borehole by analyzing depth migrated gpr difference images together with tracer breakthrough curves and associated simplified flow and transport modeling we estimate 1 the number the connectivity and the geometry of fractures that contribute to tracer transport 2 the velocity and the mass of tracer that was carried along each flow path and 3 the effective transport parameters of the identified flow paths we find a qualitative agreement when comparing the time evolution of gpr reflectivity strengths at strategic locations in the formation with those arising from simulated transport the discrepancies are on the same order as those between observed and simulated breakthrough curves at the outflow locations the rather subtle and repeatable gpr signals provide useful and complementary information to tracer test data acquired at the outflow locations and may help us to characterize transport phenomena in fractured rock aquifers

power law breakthrough curve tailing in a fracture the role of advection summary we offer an explanation of the strongly tailed solute breakthrough curve typically observed when a tracer test is conducted in fractured bedrock in this example we limit the model to a single planar fracture of varying aperture flow heterogeneity derives from variable fracture aperture which implies variable transmissivity t the analysis employs a physically based model well suited to strong heterogeneity and relies only upon advective transport the purely advective model is able to explain a power law trend of magnitude 2t o 3 in the breakthrough curve tail a range that has been found in field tracer experiments the principle cause of this trend is the comparatively slow transport in zones of small transmissivity tight aperture slow advection occurs when either heterogeneity variance of ln t i s strong or when the assumed heterogeneity distribution is non gaussian thus we link breakthrough tailing to the statistical parameters for the transmissivity field

production of carbonic fluids during metamorphism of graphitic pelites in a collisional orogen an assessment from fluid inclusions abstract fluid inclusions in quartz veins within proterozoic metamorphic rocks in the black hills south dakota were examined by microthermometry and raman spectroscopy to assess the evolution of fluid compositions during regional metamorphism of organic rich shales and late orogenic magmatism both of which were related to the collision of the wyoming and superior crustal blocks fluid inclusions occur in veins that began to be generated before or during regional compression and metamorphism that reached at least garnet grade conditions and in veins within the aureole of the harney peak granite hpg where temperatures reached second sillimanite grade conditions early veins in the schists have undergone recrystallization during heating and deformation that modified the composition of early ch4 or co2 and n2 dominated inclusions these fluids were apparently trapped under conditions of immiscibility with a saline aqueous fluid phase they are interpreted to represent components generated during maturation of organic matter and dehydration of phyllosilicates during incipient metamorphism at reducing fo2 conditions most inclusions in the quartz veins are however secondary co2 bearing they imply a transition to higher fo2 conditions with increasing temperature of regional metamorphism the fo2 conditions may have been controlled by the mineral assemblage in the host metapelites the prevalence of bimodal distributions of trapped co2 n2 and aqueous endmembers in the biotite and garnet zones also suggests that two immiscible fluid phases existed during the regional metamorphism in the aureole of the hpg graphite was evidently consumed by influx of magmatic fluids co2 h2o fluid inclusions dominate but they have significantly less n2 than inclusions at lower metamorphic grades all inclusions define secondary trails in mostly unstrained quartz the bimodality of inclusion compositions is not as well defined as at lower grades with many inclusions containing intermediate co2 h2o compositions this suggests that a single fluid phase existed at the high temperatures in the granite aureole but then unmixed during cooling a set of late quartz veins with graphitized and tourmalinized selvages in the granite aureole contains ch4 bearing inclusions with little n2 the existence of ch4 in these inclusions is attributed to complexing of magmatic b with hydroxyl anions taken from the co2 h2o fluid phase effectively causing reduction in fo2 and promoting precipitation of graphite

mapping the b value anomaly at 100 km depth in the alaska and new zealand subduction zones a positive anomaly in the frequency magnitude distribution b value is detected at approximately 90 100 km depth in two subduction zones the b value in this anomalous zone is 40 higher than in adjacent volumes we use regional catalogs with a magnitude of completeness of 2 6 central alaska and cook inlet 2 0 shumagin islands and 3 5 new zealand to resolve the b value as a function of space in more detail we project all earthquakes onto planes perpendicular to the strike of the slab these cross section views of the b value distribution locate the high b value anomalies at a depth of 90 100 km on the upper surface of the wadati benioff zone at these depths slab dehydration may increase pore pressure thus lowering the effective stress and increasing the b value increased pore pressure would also lower the liquidus in the overlying asthenosphere giving rise to the volcanism that occurs directly above this zone

mineralogy fluid inclusions and carbon isotopes of the kaman iron deposits central anatolia turkey implication for ore genesis and hydrothermal evolution abstract the kaman iron deposits are located in central anatolia and are hosted by the triassic bolcadag marble and upper cretaceous celebi granitoid magnetite mineralization manifests as rhythmic banded and irregular lenses which can be massive or disseminated within calcic marble and skarn zones six main paragenetic stages of skarn formation and ore deposition have been identified 1 na ca alterations composed of plagioclase an4 31 and actinolite 2 a prograde stage representing oxidized mineralogy dominated by diopside di62 98joh0 4 grossular andradite grs15 84alm4 8sps1 4 and magnetite 3 a retrograde stage consisting of epidote ep51 62cli38 49 magnetite calcite quartz and less abundant sulfides and chlorite 4 a quartz calcite pyrite stage containing pyrite quartz calcite and chlorite and 5 6 quartz carbonate and supergene stages characterized by quartz calcite hematite and chalcedony goethite fluid inclusion and carbon isotope studies have shown that the prograde stage formed from moderate high salinity 7 1 to 70 wt nacl eq and high temperature 339 to 600 c fluids liquid and vapor rich inclusions in an early garnet were homogenized in the liquid and vapor phases in a similar temperature range 513 and 529 c the 18o and 13c of calcites that accompany rhythmic banded magnetite ranged from 22 82 to 23 50 and 4 68 to 5 31 respectively the retrograde stage was formed from low high salinity 2 9 to 45 4 wt nacl eq and low high temperature 167 to 459 c fluids the 18o and 13c of skarn calcites ranged from 4 34 to 15 86 and 3 57 to 0 23 respectively the quartz calcite pyrite stage was formed from low salinity 3 1 7 5 wt nacl eq and temperature 171 392 c fluids the 18o and 13c values were 2 38 and 2 43 respectively the quartz carbonate stage formed from low salinity 3 6 to 5 7 wt nacl eq and temperature 129 to 169 c in all phases the eutectic and clathrate melting temperatures ranged from 59 5 to 52 2 c and 4 4 to 12 0 c respectively this indicates that the solutions contain h2o nacl cacl2 mgcl2 co2 these fluid inclusion data suggest that fluid boiling occurred under pressures between 60 and 70 mpa based on hydrostatic consideration during the prograde stage the main magnetite deposition occurred following boiling with rising salinity and temperature magmatic hydrothermal fluids and in the pressure range of 15 to 50 mpa depletion in 13c was attributed to high temperature fluid infiltration and indicates an open system volatilization process it is suggested that the retrograde stage had developed in two episodes with the carbofracturing effect triggered by co2 the carbon isotope data of calcites indicate the mixing of low temperature metasomatic and meteoric water in later stages the mineralogy microthermometry and carbon isotope results reveal that kaman iron deposits were developed by a combination of processes such as contact infiltration metasomatism fluid rock interaction cooling and fluid mixing as a result of decreasing pressure

ground penetrating radar response to fracture fluid salinity why lower frequencies are favorable for resolving salinity changes time lapse ground penetrating radar gpr surveys exploit signal amplitude changes to monitor saline tracers in fractures and to identify groundwater flow paths however the relationships between gpr signal amplitude phase and frequency with fracture aperture and fluid electrical conductivity are not well understood we used analytical modeling numerical simulations and field experiments of multifrequency gpr to investigate these relationships for a millimeter scale aperturefracturesaturatedwithwaterofvaryingsalinity we found that the response of lower frequency radar signals detects changes in fluid salinity better than the response of higher frequency signals increasing fluid electrical conductivity decreases low frequency gpr signal wavelength which improves its thin layer resolution capability we concluded that lower signal frequencies such as 50 mhz and saline tracers of up to 1 s m conductivity are preferablewhenusinggprtomonitorflowinfracturedrock furthermore we found that gpr amplitude and phase responsesaredetectableinthefieldandpredictablebyemtheory and modeling therefore they can be related to fracture aperture and fluid salinity for hydrologic investigations of fractured rockflowandtransportproperties

temporal and three dimensional spatial analyses of the frequency magnitude distribution near long valley caldera california summary the 3 d distribution of the b value of the frequency magnitude distribution is analysed in the seismically active parts of the crust near long valley caldera california the seismicity is sampled in spherical volumes containing n 150 earthquakes and centred at nodes of a grid separated by 0 3 km significant variations in the b value are detected with b ranging from b 0 6 to b 2 0 high b value volumes are located near the resurgent dome and at depths below 5 km at mammoth mountain b values are found to be much lower south of the long valley caldera we interpret this to indicate that an active magma body has advanced from depths below 8 km to depths of 4 to 5 km beneath mammoth mountain in 1989 and that anomalous crust either highly fractured or containing unusually high pore pressure such as is the case in the vicinity of active magma bodies exists north of the seismically active area beneath the resurgent dome at all depths we also investigate the spatial distribution of temporal variations of the frequency magnitude distribution by introducing diverential b value maps b values increased from b 0 8 to b 1 5 underneath mammoth mountain at the onset of the 1989 earthquake swarm and remained high thereafter this suggests that an intrusion permanently altered the average distribution of cracks at 5 10 km depth or that the pore pressure permanently increased we propose that high b values are a necessary but not suycient condition near a magmatic body and therefore spatial b value mapping can be used to aid in the identification of active magma bodies

variations in the frequency magnitude distribution with depth in two volcanic areas mount st helens washington and mt spurr alaska the frequency magnitude distribution of earthquakes characterized using the b value is examined as a function of space beneath mount st helens 1988 1996 and mt spurr 1991 1995 at mount st helens two volumes of anomalously high b b 1 3 can be observed at depths of 2 6 3 6 km below the crater floor and below 6 4 km these anomalies coincide with 1 the depth of vesiculation of ascending magma and 2 the suggested location of a magma chamber at mount st helens study of mt spurr reveals an area of high b value b 1 3 at a depth of about 2 3 4 5 km below the crater floor of the active vent crater peak we propose that the higher material heterogeneity in the vicinity of a magma chamber or conduit due to vesiculation of the ascending magma is the main cause of the increased b value at shallow depths alternatively interaction of magma with groundwater may have increased pore pressure and lowered the effective stress the deeper anomaly at mount st helens is likely caused by high thermal stress gradients in the vicinity of the magma chamber our results indicate that detailed mapping of the frequency magnitude distribution can be used as a tool to trace vesiculation and locate active magma chambers

geochemical and geochronological constraints on the formation of shear zone hosted cu au bi te mineralization in the stanos area chalkidiki northern greece abstract copper gold bismuth tellurium mineralization in the stanos area chalkidiki peninsula greece occurs in the proterozoic to silurian aged serbomacedonian massif which tectonically borders the mesozoic circum rhodope metamorphic belt to the west and crystalline rocks of the rhodope massif to the east this area contains the paliomylos chalkoma and karambogia prospects which are spatially related to regional nw se trending shear zones and hosted by marble amphibolite gneiss metagabbro and various muscovite biotite chlorite actinolite feldspar quartz schists of the silurian vertiskos unit metallic minerals occur as disseminated to massive aggregates along foliation planes and in boudinaged quartz veins iron bearing sulfides pyrite arsenopyrite and pyrrhotite formed prior to a copper bearing stage that contains chalcopyrite along with galena sphalerite molybdenite and various minerals in the system bi cu pb au ag te fluid inclusion homogenization temperatures of primary aqueous liquid vapor inclusions in stage i quartz veins range from 170 1 c to 349 6 c peak at 230 c with salinities of 4 5 to 13 1 wt nacl equiv calculated isochores intersect p t conditions associated with the upper greenschist facies caused by local overpressures during late stage tectonic movement along the shear zone in the eocene which produced stretching and unroofing of rocks in the region values of 34 s for sulfides in the stanos shear zone range from 2 42 to 10 19 and suggest a magmatic sulfur source with a partially reduced seawater contribution for fluids in equilibrium with quartz 18 o at 480 c varies from 5 76 to 9 21 but does not allow for a distinction between a metamorphic and a magmatic fluid a 187 re 187 os isochron of 19 2 2 1 ma for pyrite in the paliomylos prospect overlaps ages obtained previously from intrusive rocks spatially related to the skouries porphyry cu au the asimotrypes au and the intrusion related palea kavala bi te pb sb au deposits in northern greece as well as alteration minerals in the carbonate replacement madem lakkos pb zn deposit ore forming components of deposits in the stanos area were likely derived from magmatic rocks at shallow depth that intruded an extensional shear environment at 19 ma

multiple stage tungsten mineralization in the silurian jiepai w skarn deposit south china insights from cathodoluminescence images trace elements and fluid inclusions of scheelite abstract the jiepai deposit located in the northeastern part of the miao ershan yuechengling batholith south china is characterized by predominant skarn mineralization that formed near the contact between the silurian biotite granites and the upper cambrian carbonate rocks jiepai scheelites are recognized as two main generations based on their occurrences cathodoluminescence cl signatures and ree systematics prograde skarn hosted scheelite i has uniformly dark cl characteristics and lree enriched patterns retrograde skarn hosted scheelite iia is homogeneously dark under cl and has a slightly mree enriched pattern whereas quartz vein hosted scheelite iib is delineated by fine oscillatory cl zones and a relatively flat ree pattern additionally the cl images reveal that both scheelite i and ii were modified by later stage hydrothermal overprints which occur as ubiquitous overgrowth rims and cutting veins with bright cl signatures low ree but similar ree patterns to their precursors the compositional variations and fluid inclusions in jiepai scheelites identify episodic pulses of hydrothermal fluids with different properties the ore forming fluids with high nb ta but low nb ta and rey in the early retrograde stage are featured by moderate to high temperature and low to moderate salinity under relatively oxidizing conditions they interacted with the host rock and underwent boiling to precipitate scheelite i by contrast the fluids with higher nb ta and rey but lower nb ta in the late retrograde stage have slightly lower temperature and higher salinity we therefore speculate that scheelite ii may deposit from later magmatic fluids that have experienced continued boiling in more reducing environment

interpreting tracer breakthrough tailing from different forced gradient tracer experiment configurations in fractured bedrock 1 conceptual and mathematical models are presented that explain tracer breakthrough tailing in the absence of significant matrix diffusion model predictions are compared to field results from radially convergent weak dipole and push pull tracer experiments conducted in a saturated crystalline bedrock the models are based upon the assumption that flow is highly channelized that the mass of tracer in a channel is proportional to the cube of the mean channel aperture and the mean transport time in the channel is related to the square of the mean channel aperture these models predict the consistent 2 straight line power law slope observed in breakthrough from radially convergent and weak dipole tracer experiments and the variable straight line power law slope observed in push pull tracer experiments with varying injection volumes the power law breakthrough slope is predicted in the absence of matrix diffusion a comparison of tracer experiments in which the flow field was reversed to those in which it was not indicates that the apparent dispersion in the breakthrough curve is partially reversible we hypothesize that the observed breakthrough tailing is due to a combination of local hydrodynamic dispersion which always increases in the direction of fluid velocity and heterogeneous advection which is partially reversed when the flow field is reversed in spite of our attempt to account for heterogeneous advection using a multipath approach a much smaller estimate of hydrodynamic dispersivity was obtained from push pull experiments than from radially convergent or weak dipole experiments these results suggest that although we can explain breakthrough tailing as an advective phenomenon we cannot ignore the relationship between hydrodynamic dispersion and flow field geometry at this site the design of the tracer experiment can severely impact the estimation of hydrodynamic dispersion and matrix diffusion in highly heterogeneous geologic media

man made changes of seismicity rates seismicity catalogs contain important information about processes which occur in seismically active regions of the earth many authors have examined these catalogs for patterns and variations in patterns which might reflect changes in these processes we have found that these catalogs include a complex mixture of real and man made changes one must identify and account for the man made changes before the real ones can be identified and understood many man made changes in seismicity catalogs are manifested as changes in seismicity rates and can therefore be identified through careful examination of these rates obvious effects include increases or decreases in the detection and reporting of smaller events which accompany the installation or closure of seismic stations these types of changes can be recognized by examining the distribution of seismicity rate changes in the magnitude domain they are characterized by increases or decreases in the number of small events in the catalog at times when the number of larger events remains constant systematic changes in the magnitudes assigned to events can also be identified by examining seismicity rates because they cause apparent changes in rates of data sets with magnitude cutoffs the sign of the apparent rate change depends on the sign of the magnitude change and the type of cutoff used the effects of detection changes can be easily remedied by using a magnitude cutoff which eliminates the smaller events from consideration the techniques we have developed allow one to determine the optimum cutoff magnitude corrections are necessary for remedying the effects of systematic changes in magnitude estimates these corrections can be determined through modeling of observed rate changes caused by these shifts man made changes are present in all seismicity catalogs whether local regional or teleseismic they must be accounted for if these catalogs are to provide meaningful information on real process changes in the earth

fluids in the crust during regional metamorphism forty years in the waterville limestone figure 1 research over the last four decades on carbonate rocks of the waterville limestone maine u s a has contributed to the development of both concepts and methodologies for understanding fluid rock interaction during regional metamorphism including 1 buffering of fluid composition by mineral reactions 2 infiltration of carbonate rocks by aqueous fluids 3 petrologic fluid rock ratios 4 infiltration driven metamorphism 5 one and two dimensional continuum models for coupled fluid flow and mineral reaction 6 time integrated fluid fluxes and 7 channelized horizontal fluid flow in the direction of increasing temperature within chemically isolated layers disagreement between the last concept and both hydrodynamic models for metamorphic fluid flow and empirical evidence for homogenization of fluid composition at a scale much larger than layer thickness motivated development of the latest models for coupled fluid flow and mineral reaction in the waterville limestone the new models consider a flow medium composed of layers that differ in the initial amounts and compositions of minerals both horizontal flow in the direction of increasing temperature and vertical flow in the direction of decreasing pressure and temperature significant but imperfect homogenization of fluid composition across layering by co2 h2o interdiffusion and infiltration by fluids that are spatially variable in composition on the kilometer scale with co2 content increasing with increasing grade of metamorphism the new models reproduce measured progress of the biotite forming reaction in the waterville limestone over a range of spatial scales spanning six orders of magnitude from differences in reaction progress of up to a factor of 100 between adjacent centimeter thick layers to the coexistence of mineral reactants and products over a distance of 13 km parallel to the metamorphic field gradient results imply that the present spatial distributions of reaction progress represent a steady state achieved when rocks closely approached equilibrium with the infiltrating fluid during metamorphism the new models resolve what for many years appeared to be fundamental discrepancies among petrologic data for regionally metamorphosed carbonate rocks hydrodynamic models of regional metamorphism and the length scales of mass transport of volatiles across layering by diffusion 1 pending yes

apparent apertures from ground penetrating radar data and their relation to heterogeneous aperture fields considering fractures with heterogeneous aperture distributions we explore the reliability of constant aperture estimates derived from ground penetrating radar gpr reflection data we generate geostatistical fracture aperture realizations that are characterized by the same mean aperture and variance but different hurst exponents and cut off lengths for each of the 16 classes of heterogeneity considered we generate 1000 fracture realizations from which we compute gpr reflection data using our recent effective dipole forward model we then use each noise contaminated data set individually to invert for a single apparent aperture that is we assume that the fracture aperture is homogeneous we find that the inferred apparent apertures are only reliable when fracture heterogeneity is non fractal the hurst exponent is close to 1 and the scale of the dominant aperture heterogeneities is larger than the first fresnel zone these results are a direct consequence of the nonlinear character of the thin bed reflection coefficients as fracture heterogeneity is ubiquitous and often fractal our results suggest that robust field based inference of fracture aperture can only be achieved by accounting for the nonlinear response of fracture heterogeneity on gpr data

applying avo analysis to gpr data for reflected wave phenomena in both seismology and ground penetrating radar gpr the amplitudes of the reflected waves depend on the incidence angles and the physical properties of the media above and below an interface amplitude variation with offset avo analysis employs knowledge of reflected wave phenomena to constrain the physical properties of two media at an interface ostrander 1984 demonstrated that avo analysis can be used on seismic reflection data in certain instances to obtain information about the subsurface not revealed by traveltime offset relationships i e traditional seismic cross sections quantifiable information about the physical properties of the subsurface may then be extracted avo analysis proven for a decade to work well in reflection seismology may be useful in near surface hydrogeological situations when applied carefully to gpr data to better constrain the presence or absence of nonaqueous phase liquid contaminants napls in the subsurface

coupling ground penetrating radar and fluid flow modeling for oilfield monitoring applications the recent introduction of smart well technology allows for new geophysical monitoring opportunities smart wells which allow zonal production control combined with monitoring techniques capable of capturing the arrival of undesired fluids have the potential to significantly increase the oil recovery we consider borehole radar as a valuable technology for monitoring of the near well region by coupling a drainage process of a bottom water drive reservoir with electromagnetic simulations we find that radar sensors located in the production well can successfully map the fluid saturation evolution in low conductivity reservoirs 0 02 s m a system performance above 80 db is necessary to record reflections in the range of 10 m higher conductivity values strongly reduce the radar investigation depth despite the technical challenges to implement a permanent down hole radar system the potential semi continuous acquisition would make 4d ground penetrating radar a promising technology in capturing the near well fluid dynamics suitable environments are bottom water drive reservoirs with thin oil layer and heavy oil reservoirs exploited by steam assisted gravity drainage processes

discrete dual porosity model for electric current flow in fractured rock the identification of fractures and the characterization of their properties are of critical importance in a wide variety of research fields and applications to this end geophysical methods are of significant interest as they can provide information regarding the spatial distribution of a number of subsurface physical properties in a rapid and noninvasive manner electrical resistivity surveying in particular has been shown in several previous investigations to exhibit sensitivity to the presence of fractures suggesting that geoelectrical experiments may contain important information regarding how fractures are distributed and connected in the subsurface however a lack of suitable numerical modeling tools for electric current flow in fractured media has prevented a detailed and systematic exploration of this concept to address this issue we present a novel discrete dual porosity modeling approach that is specifically tailored to the electrical resistivity problem with our approach an analytical formulation for fracture matrix current flow exchange at the fracture scale is integrated into a discrete fracture network model which is then combined with a block scale finite volume representation of the rock matrix our methodology allows for low cost and accurate simulation of electric current flow through both the fractures and matrix and is readily applicable to complex fracture networks at relatively large scales although formulated here in two dimensions this work represents an important first step toward investigating the effect of fracture network characteristics on bulk electrical properties as well as toward the simulation of geoelectrical survey data in realistic fractured rock environments

nucleation points of recent mainshocks in southern iceland mapped by b values the earthquake catalog in southern iceland between 20 25 w and 21 3 w is complete down to approximately mw 0 and shows no evidence for mag nitude shifts as a function of time since 1991 this means that 6902 earthquakes m 0 1 depth 20 km are available for studies of seismicity patterns preceding the two ms 6 6 mainshocks in 2000 in their source volumes and vicinity 20 25 w and 20 9 w the power law of the frequency magnitude relationship holds down to m0 detailed mapping including 3d mapping of the b value of the frequency magnitude distribution shows that variations from b 0 6 to 1 4 exist over distances of about 2 km this suggests that the tectonic fabric in southern iceland is hetero geneous on a small scale the hypocenters of the two ms 6 6 mainshocks and one additional m 4 5 mainshock are associated with low b values 0 6 0 8 statistically significantly different from volumes in their vicinity therefore one can expect future mainshocks in southern iceland to also emanate from volumes characterized by low b values however the small dimensions of these asperities may render it difficult to identify them before the mainshocks occur low values of estimated local recur rence times 500 2000 years map the two fault zones that ruptured in 2000 against a background of local recurrence times longer than 5000 years the first of the two m 6 6 mainshocks emanated from a volume of short estimated local recurrence time this supports the hypothesis that asperities with short local recurrence times control locations of major ruptures mapping of b values in cross sections shows anomalies of high b at the bottom of the seismogenic crust correlating with the change of its thickness in the middle of the study area these high b value anomalies and other pockets of such anomalies at shallower depths are best interpreted as caused by high pore pressure because evidence of fluids under high pressure is ubiquitous in this area

enrichment of co2 in fluid inclusions in quartz by removal of h2o during crystal plastic deformation abstract ductile strain induced leakage of h 2 o from mixed co 2 h 2 o fluid inclusions in quartz is proposed as a mechanism for producing occurrences of pure co 2 fluid inclusions in metamorphic rocks the h 2 o needed for hydrolytic weakening of quartz under stress may be provided by the h 2 o in fluid inclusions with dislocation creep as dislocations nucleate on the walls of fluid inclusions or intersect them h 2 o can be transported with the dislocations from the inclusion to the grain boundaries the process should continue so long as there is stress on the host quartz and the inclusion contains h 2 o the h 2 o taken to the grain boundaries would due to its wetting properties be wicked out along the grain boundaries if the h 2 o is totally removed from an inclusion by a flux of dislocations through the quartz during the crystal plastic flow then a residual inclusion bearing components other than water should remain a mixed co 2 h 2 o inclusion would as a consequence of the process become a pure co 2 fluid inclusion during dynamic recrystallization the co 2 would collect at grain boundary triple junctions and following grain boundary migration would become incorporated into the recrystallized quartz as fluid inclusions this mechanism of generating pure co 2 inclusions could result in co 2 fluid inclusions having densities appropriate for the pressure temperature conditions during deformation using estimates of temperature of deformation the total confining pressure during deformation could be determined from the density of the co 2 fluid in these inclusions

a catalog of taiwan earthquakes 1900 2006 with homogenized mw magnitudes taiwan has a relatively complete catalog of earthquakes since the first seismograph was installed in 1897 however due to changes in seismographic characteristics network coverage and observational practice the definition and procedure for magnitude determination were different during different time periods recognizing a complete catalog of earthquakes with consistent magnitudes is essential for delineating seismicity patterns and assessing seismic hazards for taiwan efforts have been made to convert the original magnitudes of earthquakes in taiwan based on various magnitude scales to a common m l or m s magnitude scale unfortunately the m l or m s magnitude scales chosen for previous studies all are subject to a fundamental limitation of saturation toward large earthquakes besides these studies are nearly two decades old in order to avoid this limitation and to follow the current trend we have chosen in this study to convert original magnitudes of various scales to a common m w scale in this study we used two independent methods for magnitude conversion in the first method we converted the original magnitudes to m w through empirical relations between these magnitudes and m w this magnitude is called the old m w in the second method we used the best fitting a and b values to convert the original magnitudes to m w this magnitude is called the new m w the converted m w magnitudes from both methods have resulted in significant improvements over the original magnitudes and are in good agreement with each other nevertheless by examining the log10 n versus m w plots we found better linearity and tighter overlap among different time periods for the new m w than for the old m w thus we chose the new m w as the unified magnitude for the catalog of taiwan earthquakes finally a list of 899 earthquakes from 1900 to 2006 with m w 5 5 is presented graphic 1 see the earthquake lists available in the electronic supplement to this article the list is considered complete for the whole period from 1900 to 2006 1 embed inline graphic 1 gif

comparing flux averaged and resident concentration in a fractured bedrock using ground penetrating radar this is the published version copyright 2010 by the american geophysical union all rights reserved

strain release and strain build up in the south iceland seismic zone abstract the south iceland seismic zone is a 70 km long and 10 20 km broad area of land in southern iceland where historically the most destructive earthquakes in iceland have occurred the zone is part of the e w bridge between the mid atlantic ridge and the neovolcanic zone which is an eastward offset of the ridge through iceland the basis for the present study is a historical and an instrumental earthquake catalogue the nature of strain release in earthquakes and as it is revealed in earthquake cracks and observations of aseismic strain release and source propagation the strain build up is modelled as an interplay between the general e w drift across the mid atlantic ridge and stresses caused by the horizontal outflow of upwelling mantle material a complex model of strain release is outlined including seismic as well as aseismic components while seismic strain release plays the dominant role in the eastern and central part of the zone to a depth even below 15 km aseismic slip takes up most of the motion in the western part of the zone and in its continuation in the reykjanes peninsula towards the reykjanes rid e

measuring well hydraulic connectivity in fractured bedrock using periodic slug tests summary periodic hydraulic experiments were conducted in a five spot well cluster completed in a single bedding plane fracture tests were performed by using a winch operated slug submerged solid cylinder to create a periodic head disturbance in one well and observing the phase shift and attenuation of the head response in the remaining wells transmissivity t and storativity s were inverted independently from head response inverted t decreased and s increased with oscillation period estimated s was more variable among well pairs than t suggesting s may be a better estimator of hydraulic connectivity among closely spaced wells these estimates highlighted a zone of poor hydraulic connection that was not identified by a constant rate test conducted in the same wells periodic slug tests appear to be a practical and effective technique for establishing local scale spatial variability in hydraulic parameters

single hole gpr reflection imaging of solute transport in a granitic aquifer 1 identifying transport pathways in fractured rock is extremely challenging as flow is often organized in a few fractures that occupy a very small portion of the rock volume we demonstrate that saline tracer experiments combined with single hole ground penetrating radar gpr reflection imaging can be used to monitor saline tracer movement within mm aperture fractures a dipole tracer test was performed in a granitic aquifer by injecting a saline solution in a known fracture while repeatedly acquiring single hole gpr sections in the pumping borehole located 6 m away the final depth migrated difference sections make it possible to identify consistent temporal changes over a 30 m depth interval at locations corresponding to fractures previously imaged in gpr sections acquired under natural flow and tracer free conditions the experiment allows determining the dominant flow paths of the injected tracer and the velocity 0 4 0 7 m min of the tracer front

equilibrium dihedral angles in the system h2o co2 nacl calcite and implications for fluid flow during metamorphism fluid calcite calcite dihedral angles have been measured for fluids in the system h2o co2 nacl between 1 and 2 kbar and 550 750 c it is found that the calcite calcite h2o dihedral angle decreases steadily with addition of nacl from a value of about 80 pure water to 44 60 wt nacl the co2 h2o system displays a well defined minimum at x co 2 0 5 with a dihedral angle of 50 in contrast to those of pure co2 and h2o which are 90 and 80 respectively experiments containing fluids which are immiscible at run conditions showed a bimodal distribution of dihedral angles in the co2 h2o nacl system which can be approximately correlated with the compositions of the two fluid phases such bimodality was only observed for immiscible fluids in the h2o nacl system if the quench rate exceeded about 200 c per min this is probably due to the extremely rapid establishment of the single phase dihedral angle on quenching the fluid phase topology in devolatilising marbles will only be a connected network for very saline brines and fluids with x co 2 close to 0 5 fluids trapped in fluid inclusions in calcite grains in marbles may be predominantly h2o rich or co2 rich and of low salinity all other fluid compositions in the h2o co2 nacl calcite system will occupy isolated pores the largest of which will grow at the expense of the smallest escape of fluid produced during devolatilisation reactions under such conditions will occur by fluid overpressuring and hydrofracture in contrast previous experimental studies of quartz fluid dihedral angles between 950 and 1100 c watson and brenan 1987 predict that quartz dominated lithologies will permit pervasive flow of h2o nacl fluids but not of h2o co2 fluids documented geological examples of differences in permeability and fluid flow mechanism between metamorphic argillites psammites and limestones which support the results of the experimental studies are discussed

earthquake statistics at parkfield 1 stationarity of b values 1 in this paper paper 1 we quantitatively show that the heterogeneous pattern of b values of the gutenberg richter relation in the parkfield segment of the san andreas fault is to a high degree stationary for the past 35 years this prepares the grounds for paper 2 where we test the hypothesis that our model of spatially varying b values forecasts future seismicity more accurately than the approach in which one assumes a constant b value equal to the average regional value the method we develop to measure stationarity in the presence of spatial heterogeneity consists of the following steps 1 determine the optimal dimensions of the sampling volume by mapping b values with a wide range of radii and selecting the largest radius that gives the most detailed resolution of the b value heterogeneity along the selected fault segment the high data density permits the definition of the dominant dimensions of the seismotectonic fabric which is about 8 10 km 2 map the difference in b value between two periods selecting numerous possible catalog divisions 3 identify significant changes of b values by the utsu test utsu 1992 along the studied fault segment of 110 km length only one patch of radius 5 km showed a significant increase in b from below average to above as a function of time this change in b initiates around 1993 and thus correlates in space and time with a well documented episode of creep at depth using the derived spatial variable b value distributions we find that the highest probability for earthquakes with magnitude m 6 is in the middle mountain asperity where the 1966 parkfield earthquake nucleated and where all m 4 5 events in the data set occurred in contrast if only the regional average b value of 0 92 is used to predict future seismicity the creeping segment north of parkfield should produce major earthquakes most frequently a conclusion that contradicts the observations

estimates of large magnitude late cambrian earthquakes from seismogenic soft sediment deformation structures central rocky mountains a variety of unusual early post depositional deformation structures exist in grainstone and flat pebble conglomerate beds of upper cambrian strata western colorado including slide scarps thrusted beds irregular blocks and internally deformed beds thrusted beds up to tens of centimetres thick record thrust movement of a part of a bed onto itself along a moderate to steeply inclined 15 to 40 ramp locally producing hanging wall lenses with fault bend geometries thrust plane orientations are widely distributed and in some cases nearly oppositely oriented in close proximity indicating that they did not form as failures acted upon by gravity forces irregular bedded to internally deformed blocks are isolated on generally flat upper bedding surfaces these features represent parts of beds that detached moved up onto and some distances across the laterally adjacent undisturbed bed surfaces deformation of thin intervals of mud on the ocean floor by moving blocks rules out the possibility of storm induced deformation because the mud was not eroded by high shear stresses that would accompany the extremely large forces required to produce and move the blocks finally internally deformed beds are characterized by large blocks fitted fabrics of highly irregular fragments and contorted lamination which represent heterogeneous deformation such as brecciation and liquefaction the deformation structures were produced by earthquakes linked to the reactivation of mesoproterozoic crustal scale shear zones in the central rockies during the late cambrian analysis of the deformation structures indicates very large body forces and calculated earthquake generated ground motion velocities of ca 1 6 m sec 1 these correspond to moment magnitudes of ca 7 0 or more and a mercalli intensity of x these are the only known magnitude estimates of phanerozoic other than quaternary large intensity earthquakes for the rocky mountain region and they are as large as or larger than previous estimates of proterozoic earthquakes along these major shear zones of the central rockies

time lapse imaging of saline tracer transport in fractured rock using difference attenuation radar tomography 1 accurate characterization of fractured rock aquifer heterogeneity remains one of the most challenging and important problems in groundwater hydrology we demonstrate a promising strategy to identify preferential flow paths in fractured rock using a combination of geophysical monitoring and conventional hydrogeologic tests cross well differenceattenuation ground penetrating radar was used to monitor saline tracer migration in an experiment at the u s geological survey fractured rock hydrology research site in grafton county new hampshire radar data sets were collected every 10 min in three adjoining planes for 5 hours during each of 12 tracer tests an innovative inversion method accounts for data acquisition times and temporal changes in attenuation during data collection the inverse algorithm minimizes a combination of two functions the first is the sum of weighted squared data residuals second is a measure of solution complexity based on an a priori space time covariance function subject to constraints that limit radarattenuation changes to regions of the tomograms traversed by high difference attenuation ray paths the time series of tomograms indicate relative tracer concentrations and tracer arrival times in the image planes from these we infer the presence and location of a preferential flow path within a previously identified zone of transmissive fractures these results provide new insights into solute channeling and the nature of aquifer heterogeneity at the site index terms 0910 exploration geophysics data processing 0915 exploration geophysics downhole methods 1829 hydrology groundwater hydrology 1832 hydrology groundwater transport 1894 hydrology instruments and techniques keywords radar tomography fractured rock ground penetrating radar geophysics hydrogeophysics

four dimensional mapping of tracer channelization in subhorizontal bedrock fractures using surface ground penetrating radar 1 to observe flow channeling in situ surface ground penetrating radar gpr was used to detect a saline tracer moving through a sub horizontal bedrock fracture the tracer is mapped using amplitude variations resulting from the significant difference in electromagnetic properties between the tracer and natural ground water within the fracture results show that hydrogeophysical investigations using gpr can successfully image tracer movement in a variety of flow configurations in three spatial dimensions through time hence 4d observed tracer travel paths demonstrated meter scale spatial variability that may be attributed to heterogeneity in fracture aperture

estimating seismic hazards from the catalog of taiwan earthquakes from 1900 to 2014 in terms of maximum magnitude maximum expected earthquake magnitude is an important parameter when designing mitigation measures for seismic hazards this study calculated the maximum magnitude of potential earthquakes for each cell in a 0 1 0 1 grid of taiwan two zones vulnerable to maximum magnitudes of m w 6 0 which will cause extensive building damage were identified one extends from hsinchu southward to taichung nantou chiayi and tainan in western taiwan the other extends from ilan southward to hualian and taitung in eastern taiwan these zones are also characterized by low b values which are consistent with high peak ground shaking we also employed an innovative method to calculate at intervals of m w 0 5 the bounds and median of recurrence time for earthquakes of magnitude m w 6 0 8 0 in taiwan

aseismic slip in earthquake nucleation and self similarity evidence from parkfield california aseismic slip microearthquakes and moderate earthquakes all take place along the san andreas fault at parkfield california in this letter we discuss the relationship of these slip mechanisms by establishing and modelling the local microearthquake size frequency distribution by examining the effect of background noise on earthquake event detection we show that the distribution is complete for m 0 3 unlike the gutenberg richter law the distribution begins with a relatively small number of very small events further the scaling relation of the distribution changes continuously with event size noting that many parkfield aseismic slip or creep events have moments equivalent to the smaller microearthquakes we show that the nucleation of microearthquakes by this type of slip can account for the size frequency distribution such a model does not require a lower limit to either earthquake or creep event size rather it suggests that at parkfield a transition from creep dominated slip to earthquake dominated slip takes place in the range of moments equivalent to magnitudes close to m 0 9 this is well above the m 0 3 detection limit of the seismic network but right at the limit of current near surface strain instruments

source and path of magma for volcanoes in the subduction zone of northeastern japan the assumption that the source of magma for volcanoes in subduction zones is located in the mantle immediately above the top of the subducting slab at approximately 100 km depth and straight beneath the volcanoes is incorrect in northeastern japan the combination of evidence from velocity tomography in the mantle wedge above the slab and mapping of earthquake size distribution within it strongly points to a source of fluids at the top of the slab at 140 to 150 km depth from where material rises along an inclined path to the volcanoes

fluid immiscibility in metamorphic rocks evidence of fluid immiscibility in metamorphic rocks comes in the best of all worlds from fluid inclusion observations in fact fluid immiscibility should be anticipated over the full range of metamorphic conditions provided that appropriate bulk fluid compositions are present in a review paper entitled metamorphic fluids the evidence from fluid inclusions crawford and hollister 1986 summarized the role of fluid immiscibility in metamorphism was only recognized after serious study of fluid inclusions in metamorphic rocks was underway in the late 1970s and has yet to attract the attention of more than a handful of petrologists studying metamorphic rocks since then tremendous progress has been made a huge amount of fluid inclusion studies have convincingly shown that immiscible fluids can be present in rocks of all bulk compositions and at all p t conditions thermodynamic databases of minerals solid solutions and fluid mixtures along with the development of gibbs free energy minimization programs now allow for detailed prediction of the evolution of phase assemblages and mineral compositions in p t space significant progress has also been made in understanding reaction kinetics diffusional and convective mass transport and the interpretation of fluid rock interaction during metamorphism given the vast fluid inclusion evidence of immiscibility it would appear however that phase petrology and mass transport in any specific rock where fluids are involved are not correctly interpreted if possible or proven immiscibility is not considered relatively few studies directly link mineral reactions with immiscible fluids therefore this review aims at working out the effects of fluid immiscibility on the progress of metamorphic reactions and fluid transport over a wide range of conditions questions arise directly from the fluid inclusion record in metamorphic rocks this chapter however is organized the other way round at first it summarizes phase relations of fluid systems pertinent to

mapping the frequency magnitude distribution in asperities an improved technique to calculate recurrence times we hypothesize that highly stressed asperities may be defined by mapping anomalously low b values along the san andreas fault near parkfield the asperity under middle mountain with its b 0 46 can be distinguished from all other parts of the fault surface likewise along the calaveras fault the northern asperity of the morgan hill 1984 m6 2 rupture can be identified by its low b of 0 5 as a high stress patch along the fault we add further evidence to the observations that the b value of the frequency magnitude relationship of earthquakes is inversely proportional to stress by showing that it decreases with depth in the parkfield segment of the san andreas and along the calaveras fault in both of these areas b values above and below 5 km depth are 1 2 and 0 8 respectively we propose that probabilistic recurrence times tr based on the seismicity parameters a and b should be calculated from their values within asperities only instead of from the values of the entire rupture area of the maximum expected earthquake the strong patches on faults control the time of rupture because they are capable of accumulating larger stresses than the rest of the fault zone which slips along passively when an asperity breaks therefore no information on tr is contained in the passive fault segments only in the asperities at parkfield the probabilistic estimates of tr derived from the data in the whole rupture and in the asperity only are 72 18 24 and 23 12 18 years respectively compared to the historically observed repeat time of 22 years at morgan hill the tr estimates are 122 46 76 and 78 47 110 years respectively compared to the observed repeat time of 72 years

a systematic test of the hypothesis that the b value varies with depth in california we spatially map the shallow to deep b value ratio in the crust in california previous studies of the frequency magnitude distribution as a function of depth for selected crustal regions indicated that b decreases from b 1 1 in the 0 5 km depth range to b 0 8 in the depth range 7 15 km our detailed mapping confirms that this pattern can be established at the 99 significance level for about 32 of the entire seismically active crust about 2 of the crust displays the opposite b gradient one such area is the san francisco bay area we speculate that differences in stress levels are the main factor controlling the depth dependency of b these results confirm that the b value should not always be considered a constant in studies such as seismic hazard estimations

3d polarimetric gpr coherency attributes and full waveform inversion of transmission data for characterizing fractured rock ground penetrating radar gpr can detect and describe fractures to help us characterize fractured rock formations a fracture alters the incident waveform or wave shape of a gpr signal through constructive and destructive interference depending on the aperture fill and orientation of the fracture because the electromagnetic em waves of gpr are vectorial features exhibiting strong directionality can change the state of polarization of the incident field gpr methods that focus on changes in waveform or polarization can improve detection and discrimination of fractures within rock bodies an algorithm based on coherency a seismic attribute that delineates discontinuities in wavelet shape is developed for polarimetric gpr it uses the largest eigenvalue of the time domain scattering matrix when calculating coherence this algorithm is sensitive to wave shape and is unbiased by the polarization of gpr antennas polarimetric coherency works better than scalar coherency in removing the effects of polarization on field data collected from a fractured limestone plot used for hydrologic experimentation another method for time domain full waveform inversion of transmission data quantitatively determines fracture aperture and em properties of fill based on a thin layer model inversion results from field data show consistency with the location of fractures from reflection data these two methods offer better fracture detection capability and quantitative information on fracture aperture dielectric permittivity and electrical conductivity of the fill than traditional gpr imaging and scalar coherency attributes

comparison of the historical record of earthquake hazard with seismic hazard models for new zealand and the continental united states we compare the historical record of earthquake hazard experienced at 78 towns and cities sites distributed across new zealand and the continental united states with the hazard estimated from the national probabilistic seismic hazard psh models for the two countries the two psh models are constructed with similar methodologies and data our comparisons show a tendency for the psh models to slightly exceed the historical hazard in new zealand and westernmost continental united states interplate regions but show lower hazard than that of the historical record in the continental united states intraplate region factors such as non poissonian behavior parameterization of active fault data in the psh calculations and uncertainties in estimation of ground motion levels from historical felt intensity data for the interplate regions may have led to the higher than historical levels of hazard at the interplate sites in contrast the less than historical hazard for the remaining continental united states intraplate sites may be largely due to site conditions not having been considered at the intraplate sites and uncertainties in correlating ground motion levels to historical felt intensities the study also highlights the importance of evaluating psh models at more than one region because the conclusions reached on the basis of a solely interplate or intraplate study would be very different

investigating multi polarization gpr wave transmission through thin layers implications for vertical fracture characterization this is the published version copyright 2006 american geophysical union all rights reserved

high density co2 n2 inclusions in eclogite facies metasediments of the munchberg gneiss complex se germany the eclogite facies metasedimentary rocks in the munchberg gneiss complex t 630 30 c p 17 24 kbar locally contain co2 n2 rich fluid inclusions of extremely low molar volumes 32 cm3 mol in quartz these fluid compositions are mainly found in rocks intercalated with calcsilicate bands densities were determined from low temperature phase transitions like stable or metastable homogenization l v l partial homogenization s l v s l and the transition s l l l liquid v vapour s solid the high fluid densities are in agreement with eclogite facies pressure and temperature and subsequent amphibolite facies co2 n2 inclusions were not observed in adjacent eclogites nor in non calcareous metasediments these rock types contain predominantly h2o rich inclusions correlating with amphibolite facies conditions the variation of fluid composition with lithological differences indicates local fluid gradients and speaks against a pervasive fluid flow during eclogite facies metamorphism

most likely locations of large earthquakes in the kanto and tokai areas japan based on the local recurrence times abstract we examined the hypothesis that minima in local recurrence time tl or equivalently maxima in local probability pl may map asperities in the kanto and tokai areas of japan where the earthquake catalog of the national research institute for earth science and disaster prevention nied is complete at the m 1 5 m1 5 level we mapped tl pl based on the a and b values of the nearest earthquakes within 20 km of every node of a grid spaced 0 01 for m7 target events only earthquakes within the top 33 km were used the b values increase strongly with depth in several areas therefore some of the tl pl anomalies are not revealed if data from the entire crustal seismogenic zone are mixed thus we mapped tl pl separately for the top 15 km and the rest of the depth range as well as for the entire seismogenic crust the resulting tl and pl maps show that approximately 12 of the total area shows anomalously short recurrence times out of six shallow target events with m 6 5 and which occurred since 1890 five are located within the anomalous areas with tl

a comparative fluid inclusion study of the waterville and sangerville vassalboro formations south central maine petrologic and oxygen isotope data indicate that water rich fluids infiltrated metasedimentary rocks of the waterville and sangerville formally vassalboro formations south central maine during peak metamorphism and depleted sangerville rocks in alkalis but not equivalent waterville rocks fluid inclusion data from two outcrops 1 km apart one of the waterville and the other of the sangerville formations suggest a cause for the geochemical difference between the two units postulated peak metamorphic inclusions the texturally earliest of aqueous inclusions in the metasediments approximate the water rich compositions of peak fluids predicted by mineral fluid equilibria and have average salinity in the sangerville formation three times that of equivalent waterville inclusions the higher salinity in the sangerville fluids could explain the greater alkali depletion in these rocks probable pre peak or prograde inclusions are preserved in metasediments as the texturally earliest carbonic inclusions which contain co2 ch4 n2 h2o as determined by microthermometry and raman spectrometry they may have formed by breakdown of organic matter probable retrograde inclusions occur as texturally late aqucous inclusions in healed fractures with salinity ranges indistinguishable between the two formations synmetamorphic granitic dikes present in the two outcrops were ruled out as a source for fluids in metasediments because composition and density ranges of inclusions in dikes and metasediments are fundamentally different and because there is no correlation between the abundance or composition of inclusions in a sample and proximity to dikes isochores for many of the inclusions in both metasediments and dikes are not consistent with the inferred p t conditions of their trapping but intersect at 300 to 400 c and 1 to 2 kbar the intersections probably resulted because inclusion densities continued to equilibrate during uplift and cooling until quartz became rigid the present densities are those at the last equilibration not the time of trapping in contrast the clear distinctions in inclusion compositions between dikes and between dike and country rock show that the original compositional differences generally have been preserved

temporal and spatial scaling of hydraulic response to recharge in fractured aquifers insights from a frequency domain analysis quantification of the recharge in fractured aquifers is particularly challenging because of the multiscale heterogeneity and the range of temporal scales involved here we investigate the hydraulic response to recharge of a fractured aquifer using a frequency domain approach transfer functions are calculated in a range of temporal scales from 1 day up to a few years for a fractured crystalline rock aquifer located in ploemeur s brittany france using recharge and groundwater level fluctuations as input and output respectively the spatial variability of the response to recharge characteristic response time amplitude temporal scaling is analyzed for 10 wells sampling the different compartments of the aquifer some of the transfer functions follow the linear reservoir model behavior on the contrary others display a temporal scaling at high frequency that cannot be represented by classic models large scale hydraulic parameters estimated from the low frequency response are compared with those estimated from hydraulic tests at different scales the variability of transmissivity and storage coefficient tends to decrease with scale and the average estimates converge toward the highest values at large scale the small scale variability of diffusivities which implies the existence of a range of characteristic temporal scales associated with different pathways is suggested to be at the origin of the unconventional temporal scaling of the hydraulic response to recharge at high frequency

mapping asperities by minima of local recurrence time san jacinto elsinore fault zones minima of the local recurrence time tl m are correlated with the locations of historical main shocks in the san jacinto sj elsinore e fault zones of southern california we define tl m as the recurrence time calculated from the local b and a values of the frequency magnitude distribution earthquakes within 6 and 10 km from each point in the sj and e fault zones respectively we propose that anomalously low tl m values map asperities out of six historic main shocks 1899 1968 five ruptured substantial parts of four asperities mapped by our method which uses solely the modern earthquake catalog m 1 2 1981 0 1998 8 we estimate the probability for this correlation to occur at random as 10 2 to 10 3 depending on the scenario chosen it appears that the minima in tl m are tied to minima in b values more than to maxima in a values thus locations of low b values can also be used as an indication where asperities may be located and where main shocks are most likely the anza gap a segment of the san jacinto fault with low a values is mapped as an asperity by our method the heterogeneity in b values is strong throughout the study area the b values range from 0 5 to 1 8 over distances of 10 km volumes with approximately constant b values have radii of r 8 6 km our results suggest that detailed mapping of b values and local recurrence times in volumes with a few kilometers radius reveals important information about the local seismic hazard hitherto untapped by conventional seismicity analyses